HomeMy WebLinkAbout08-07-2012 ss2 hydro modification &coderevisionscounci lac enOa I epo t
Meeting Date
8/7/1 2
Item Numbe r
SS 2
C I T Y O F S A N L U I S O B I S P O
FROM :
Carrie Mattingly, Interim Director of Public Work s
Prepared By :Barbara Lynch, Deputy Director of Public Works
SUBJECT : REVIEW OF DRAFT CRITERIA FOR APPLICATION O F
HYDROMODIFICATION MANAGEMENT STANDARDS FO R
DEVELOPMEN T
RECOMMENDATION
Participate in a study session to provide comments on proposed hydromodification managemen t
draft criteria, including thresholds for applying the criteria to new development, performanc e
requirements, and impacts associated with implementing current Central Coast Regional Wate r
Quality Control Board recommendations .
REPORT-IN-BRIE F
Central Coast Regional Water Quality Control Board (CCWB) staff has completed draft
requirements for development, related to stormwater quality and quantity. The City will be require d
to adopt and enforce the regulations once they are adopted by the CCWB . As drafted, thes e
regulations will effect private development and some City project work.
The proposed requirements are tied to the square footage of impervious surface created by a project .
Requirements are additive, increasing as impervious surface increases . Theregulations also includ e
options for project impacts to be mitigated at alternate sites .
When the draft requirements are adopted by the CCWB, revisions to City codes, plans, standards ,
and guidelines will be needed . Examples of potential code changes are included in this report an d
will need to be adopted prior to implementation, currently expected in March 2013 .
A definitions page is included as Attachment 3 .
DISCUSSIO N
Backgroun d
In June of 2009, the City was enrolled in the State Genera l
Permit National Pollutant Discharge Elimination Syste m
permit program governing stormwater . This program i s
overseen by the CCWB acting on behalf of the Stat e
Water Resources Control Board which receives it s
authority from the Federal Environmental Protection
Agency . The permit contains a Stormwater Management
Plan the City must follow, covering more than 30 0
activities, including a requirement to develop and
Hydromodification :
The changing effect of
water moving acros s
the landscape
Hydromodification Management Draft Criteria Page 2
implement a hydromodification management plan .
What is Hydromodification ?
Hydromodification is a term used to describe the changing effect of water moving across th e
landscape . In urban areas where development occurs, changes are triggered by development throug h
compaction of soils, changing of vegetative cover, construction of impervious surfaces, an d
rerouting of traditional drainage channels . These changes can result in creek incising, reduce d
groundwater recharge, and altered habitat . Management of hydromodification can reduce ongoin g
deterioration of natural channels resulting from increasing flood flows, minimize the need for ban k
protection, increase infiltration, and protect habitat from deterioration .
Local Hydromodification Management Planning Effort s
When the CCWB mandate for hydromodification management was first put forward, agencie s
throughout the County protested due to the significant cost (estimated at $400,000) and work effor t
associated with development of a plan. Concerns were also expressed about the propose d
prescriptive language and potential impact to development . In response, the CCWB established a
program called the "Joint Effort ." Through the Joint Effort, it was envisioned the CCWB woul d
work with a consulting team and stakeholders to develop a regional plan . On January 19, 2010 ,
Council supported the City's participation in the Joint Effort (Attachment 1).
The Joint Effor t
As originally proposed by the CCWB, the Joint Effort was to be a two phase process ; phase one,a
technical review of the land conditions of the Central Coast, and phase two, a pairing up o f
conditions with requirements for development .
In the first phase, consultants hired by the CCWB collected physical land condition informatio n
from participating agencies and performed analyses to determine areas of commonality .For
example, if an area in San Luis Obispo had similar land characteristics of soil type, slopes ,
propensity to produce run-off, ground water basins, and drainage ways, it was identified as the sam e
type of watershed "zone" as an area of Santa Barbara or Monterey of similar characteristics . Th e
analysis yielded ten separate watershed types, each designated by a zone number . The City is
largely covered under Zone 1, with some smaller areas in other zones .
The result of the second phase was a document identified as the Post-Construction Stormwate r
Management Requirements for Development Projects in the Central Coast Region,also known a s
"Criteria" (Attachment 2). This document aligns the watershed zones with specific criteria that mus t
be met by development, generally in the area of retention and infiltration of runoff . In addition t o
the Criteria information, the CCWB produced a companion technical support document to explai n
the Criteria and the relationship between the watershed management zones developed in Phase 1 ,
and the criteria established in Phase 2 (Attachment 2).
While the CCWB initially anticipated agencies would complete the second phase, the CCW B
completed the entire scope of work for adoption by agencies . It is this second phase work product,
the Criteria, that is the focus of this study session . Phase 2 work will be reviewed by the CCWB in
September for adoption . If adopted in September, each agency will be required under the condition s
of its enrollment under the General Permit and the Joint Effort to adopt the requirements and appl y
them to all regulated projects by March 13, 2013 .
SS2-2
Hydromodification Management Draft Criteria Page 3
The Criteri a
The Criteria establishes categories of projects, based on size, to which it applies and various level s
of performance requirements . The Criteria uses impervious area as the indicator for determining th e
level of regulation . The Criteria relies on two main strategies to reduce watershed impacts ; 1 )
maximize use of Low Impact Development concepts, including verification that applicants hav e
looked seriously at all options ; and 2) maximize retention of stormwater on site, along with hig h
flow management .
Performance Requirements
After determining if a project is regulated or not, the Criteria prescribes five levels of Performanc e
Requirements . Each level is additive to the previous level, with the complexity of requirements tie d
to increasing project size . For example, if the development includes 16,000 ft 2 of impervious
surface, the project will be required to complete site design, water quality treatment, and retention .
An example of this size of project is discussed below .
L Lev el Performance Requiremen t
Site Design
S Tyre hect (ft-) ! rimery ious Surfac e
> 2,500 ft2 impervious (including detached single 1 umly)1
2 Water Quality Treatment > 5,000 ft2 net impervious - development / redevelopment
> 15,000 ft2 impervious - detached single family
3 Retention > 15,000 ft2 impervious - development / redevelopmen t
> 15,000 ft2 impervious - detached single famil y
4 Peak Management > 22,500 ft2
2
impervious - development/ redevelopmen t
> 22,500 ft impervious - detached single family
5 Special Circumstances Performance requirements 3 and 4 may be waived
Concerns regarding Performance Level 3 - Retentio n
Retention of stormwater is the most difficult objective to attain and the most concerning fo r
agencies because of its potential to interfere with infill development and compact urban form b y
increasing the difficulty of compliance for projects with limited space . The level of retention th e
SS2-3
Hydromodification Management Draft Criteria Page 4
CCWB is requiring is also concerning as it would approximately double the volume of water a sit e
is required to retain when compared to the requirements currently in use in other jurisdictions .
Based on feedback from the development community, compliance for new development o n
previously undisturbed areas will be less difficult than meeting the requirements with infill projects .
Alternative Complianc e
As proposed, the Alternative Compliance section of the Criteria requires development to meet th e
performance requirements elsewhere in the watershed if they cannot be met on the develope d
property . The CCWB has listed two methodologies to accomplish this : in-lieu fees or regional
facilities .
In-lieu fee .In-lieu fee programs require nexus to development . Under this program, the Cit y
would be responsible for having approved projects on the shelf for which the in-lieu fee s
would be collected and, eventually, applied to the approved project . Approved project s
would need to be within the development's watershed to reasonably apply nexus . A number
of developments would need to come forward for the City to accumulate a reasonabl e
amount of money to implement an in-lieu project due to the limited timeframe the CCW B
allows for project implementation .
Regional facilities .Regional projects would be of a similar nature to the in-lieu fe e
program, in-lieu collected by the City, or a project built by the City or a development, an d
costs recouped through subsequent development .
The CCWB is open to assessing other options aside from in-lieu fees or regional facilities . On e
option under consideration is an exchange program . Developer A could work with Property Owne r
B to improve retention on Property Owner B's site in the amount "owed" for the development o f
Developer A's property. There are myriad complexities associated with this option includin g
maintenance of the retention facility in perpetuity and impacts to future development potential .
Application of CCWB's Proposed Regulation s
Staff looked at some projects including private projects, representative of the smaller infill type o f
development occurring in the City to assist the Council in understanding how the draft regulatio n
might affect projects, and some public projects .
Project 1– Small In-Fill Housing Project Over 2,500 square feet impervious surfac e
The first project was a two lot, single family small residential development . The homes were each
under 1,500 ft2 and, with driveways and porches, totaled approximately 2,650 ft 2 in new imperviou s
surface . Given the proximity to the lowest threshold for regulation of 2,500 ft 2, it is likely som e
simple efforts to reduce impervious surfaces could be made to remove the project completely from
regulation . The project could complete some simple pervious surface work on the patios o r
driveways, or use narrow strips for the driveway, a "Hollywood" type driveway, in-lieu of ful l
width impervious paving . These approaches are accepted under the City's current design standards .
Project 2 Medium In-Fill Mixed Use Project Over 15,000 square feet impervious surfac e
The second project reviewed was a single lot redevelopment to mixed use . There is a single buildin g
footprint of approximately 3,600 ft 2 ; however, the remainder of the lot is largely paved to provid e
parking for both the commercial and residential uses, and includes a small parking structure . In
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Hydromodification Management Draft Criteria Page 5
total, this project results in 21,000 ft2 of new or replaced impervious surfaces . This development
would fall under the requirements to do runoff retention (impervious surface creation over 15,00 0
ft2 ) in addition to site design and water quality treatment .
Given the small footprint of the structures, the developer may have been able to eliminate th e
retention requirement through pervious pavement in the areas of the parking lot outside of th e
structure . However, given the limited size of the site, infiltration of water would have to occu r
immediately adjacent to the structures . This is generally not an acceptable practice, so for purpose s
of this example, the assumption is that this is not feasible and the project must consider othe r
alternatives .
The requirements allow redevelopment to reduce by half the portion of the surface area that must b e
used for calculation of runoff volumes for retention . In this example, this reduced volume of wate r
will take approximately one City lot, 100' x 50' x 3' deep to treat and infiltrate the volume . Give n
that the development is unable to complete that work on site under the current developmen t
scenario, there are two options . The development can be scaled back until it is small enough to
balance impervious areas with infiltration areas, or it can move into alternative compliance ,
discussed above . Scaling the project back would entail reducing the footprint of the building and/o r
parking areas by about 5,600 ft2 and increasing the infiltration area by the same amount . This
effectively takes the project below the threshold requiring retention of stormwater on site .
These two examples illustrate that some developments will hardly feel a ripple, while others will b e
significantly challenged to proceed . Of greatest concern to staff are the smaller infill commercial o r
mixed use projects that require parking . The infill lots are relatively small dictating that infiltratio n
will be needed in close proximity to structures .
Project 3 — City Project - Road Widenin g
The City currently has a short section of South Higuera Street below Elks Lane that needs to b e
widened to complete the four lanes . The stretch is about 225 feet long . To add a 12 foot lane woul d
result in 2,700 ft 2 of additional roadway . This project would not be exempt . The requirements for
projects below the water quality treatment level of 15,000 ft2 are clearly geared toward developmen t
not roadways based on wording in the Criteria : "minimize impervious surfaces by concentratin g
improvements on the least sensitive portion of the site," "direct roof runoff into cistern,""direct
runoff from driveway". How these requirements are to be applied to minor road widenings i s
uncertain .
The Criteria is not clear if the 2,500 ft 2 limit applies to roadway expansion projects . A recent
addition of a right turn pocket at California and Foothill resulted in about 500 ft 2 of new pavement .
If the 2,500 limit applies to roadwork, a small safety project such as this would be exempt .
Project 4 — Downtown Project Limited to Alternative Complianc e
A project in the downtown where buildings cover the entire property and are immediately adjacen t
to other buildings and City infrastructure in the right-of-way, will have few opportunities to perfor m
hydromodification management onsite . This would apply to both private development and the
City's construction of public facilities, for example a new parking garage . These development s
would be required to use Alternative Compliance presently described by the CCWB to be an in-lie u
fee option or regional project .
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Hydromodification Management Draft Criteria Page 6
Impacts to City Codes and Guidance Document Revision s
As a condition of enrollment in the Joint Effort, agencies were required to complete tasks related t o
preparing the way for hydromodification management . City staff reviewed 26 City polic y
documents that are related to the proposed regulation .
Preliminary findings demonstrate the City has a long history of resource protection . Despite thi s
commitment, if the regulations are adopted as written, some significant policy changes have bee n
identified :
1.Elimination of specific pavement width requirements except for Fire acces s
2.Elimination of specific on-street parking requirement s
3.Changed emphasis from integral sidewalk (no parkway) to detached sidewal k
4.Elimination of mandatory vertical curb s
5.References to the need for consideration and inclusion of Low Impact Development an d
Hydromodification Management control s
Minor language revisions are being pursued as part of the upcoming Subdivision Code revision an d
the Open Space Management plan . Other language changes are proposed that simply aler t
developers to the need to apply modern design principles to reduce the impact of development o n
the land . Minor revisions to the Community Design Guidelines are scheduled for Architectura l
Review Commission discussion in late August . Proposed minor changes to the Subdivisio n
Ordinance will be incorporated into the next update . Work will be starting on that effort before th e
end of the year and should be complete in 12 to 18 months .
Conflicts with Other Legislative Directio n
The Criteria proposed appear to conflict with other legislative direction from the State . Senate Bil l
375 was passed in 2008 . This bill requires regional transportation agencies such as the San Lui s
Obispo Council of Governments (SLOCOG) to adopt a Sustainable Communities Strategy as part o f
its regional transportation plan . The intent of these strategies is to reduce emissions from ligh t
trucks and automobiles within the region . The primary method of achieving emissions reductions i s
to provide infill opportunities so that trip lengths are decreased as housing, employment, an d
services are provided in closer proximity to one another .
The Regional Housing Needs Allocation, or RHNA, assigned by the State office of Housing and
Community Development is also tied to the Sustainable Communities Strategy . With the allocatio n
of affordable housing requirement distributed to the region, each jurisdiction within the County i s
required to demonstrate its ability to accommodate the number of housing units assigned to it . For
the City of San Luis Obispo, some of this will be through infill opportunities and some through th e
planned expansion areas . At some point, however, the Criteria being proposed could mak e
compliance with the RHNA allocation very difficult. Non-compliance with the Sustainabl e
Communities Strategy and/or inability to show accommodation of the City's required housin g
allocation could result in lost transportation funding for infrastructure projects .
Community Involvemen t
Three years ago, in response to the CCWB requirement to implement hydromodification
management principles in the region, a countywide Hydromodification Technical Advisor y
Committee (TAC) was formed . The TAC is a mix of agency engineering and planning staff, privat e
engineering consultants, environmental community representatives, and the Home Builder s
SS2-6
Hydromodification Management Draft Criteria Page 7
Association . Although no longer active, the Chamber of Commerce also had a member on the TAC .
The TAC does not include a member of the CCWB, although work products of the TAC are
provided to the CCWB . The TAC has been a forum for discussion of the work products of th e
CCWB consultants, development of interim Low Impact Development requirements for sharing an d
countywide consistency, sharing of code review checklists and training materials, and preparatio n
of recommended definitions and criteria for CCWB consideration .
The CCWB established a small group to review the work product of its consultants ; primaril y
engineering, planning, and geotechnical experts . It conducted public presentations of the phase 1
and phase 2 findings in both the northern and southern areas of the region . City staff assisted with
public outreach by notifying the City's interested parties list on the most recent presentations on th e
Criteria to raise awareness . Both the development community and local agencies have commente d
on the draft criteria language . The CCWB is scheduled to hold a public meeting on the draft criteri a
language on September 6, 2012 . City staff will be in attendance .
The California Stormwater Quality Association (CASQA), of which the City is a member ,
submitted a letter in strong opposition to the proposed criteria (Attachment 4). The primary thrust o f
the letter is that individual Regional Boards are "ratcheting up" requirements for new developmen t
with each agency permit before prior requirements have been assessed for effectiveness .
Additionally, this regulation is coming at the same time as the new State General Permit, which als o
contains hydromodification management language . The language in the State General Permit is les s
stringent and will provide more uniform regulation across the State . CASQA argues the Stat e
General Permit should be applied to the Central Coast Region, rather than having the region single d
out and treated differently .
Next Step s
The City is under obligation, through its regulation under the stormwater permitting program an d
the regional requirements, to adopt hydromodification . Staff will be attending and speaking to loca l
concerns at the CCWB meeting in September as will other agency representatives from the region .
The TAC will be meeting a few days in advance to discuss comments for the meeting . The Council
may wish to provide staff with specific concerns or provide testimony at the CCWB hearing . There
is some activity, demonstrated by the CASQA letter, to shift this region into the requirements of th e
new State General Permit .
CONCURRENCE S
Public Works has been collaborating with Community Development to provide comments on th e
draft hydromodification criteria and to modify City codes and guidance documents in preparatio n
for implementation of the proposed regulations .
FISCAL IMPAC T
Fiscal impacts from the proposed regulation have not been quantified at this time . It will require
additional resources and a complicated analysis to quantify these impacts based on the adopte d
regulation (which is still subject to change prior to adoption by the CCWB). It is anticipated impact s
to the City will range from minor to significant .
SS2-7
Hydromodification Management Draft Criteria Page 8
The following are some of the impacts anticipated as a result of hydromodification regulation (th e
list is not exhaustive):
1.Additional layer of development review for each projec t
2.Annual reporting of hydromodification management effort s
3.Ongoing monitoring of maintenance and post-construction facility performanc e
4.Update of City of SLO Drainage Design Manual to incorporate new hydromodificatio n
requirements and to ensure hydromodification and flood management are addressed in a
compatible wa y
5.Road expansion projects will trigger performance requirements ; to what extent remain s
unclear at this tim e
6.Installation and long-term maintenance of vegetative filtering installed as a result o f
performance requirements for larger project s
7.Based on development community feedback, the Criteria creates barriers to developin g
urban infill project s
ALTERNATIVE S
Hydromodification Management Plans have been in place in larger urbanized areas for several year s
and are requirements in the Draft General Stormwater Management NPDES Permit under which th e
City will be regulated. Upon adoption of the Criteria by the CCWB, the City must either full y
implement the requirements or mount a successful legal challenge to the new regulation .
Public and private efforts regarding the Criteria are focused on reasonable regulation .
ATTACHMENT S
1.January 19, 2010 Council Agenda Repor t
2.Draft Resolution Approving Post-Construction Stormwater Management Requirements fo r
Development Projects in the Central Coast Regio n
Draft Post-Construction Stormwater Management Requirements (Attachment 1 to Draf t
Resolution)
Draft Technical Support Document (Attachment 2 to Draft Resolution )
3.Definition s
4.CASQA Comment Lette r
t:\coundlagenda reports\ 201212012-08-071hydromcdillwLuu&~_~ i_.i_i_:.~
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SS2-8
ATTACHMENT 1-1
counci lA acEnOa aEpoM
Mceting Data 1-19-1 0
item Number
C I T Y O F S A N L U I S O B I S P O
FROM :
Jay Walter, Director of Public Work s
Prepared By :Barbara Lynch, City Engineer
SUBJECT : HYDROMODIFICATION PLAN, JOINT EFFORT PARTICIPATIO N
RECOMMENDATION
Authorize staff to proceed with the development of a Hydromodification Management Pla n
under the conditions of the Central Coast Regional Water Quality Control Board's joint effor t
proposal .
DISCUSSIO N
Backgroun d
The City is mandated under federal regulations relating to clean water to have and enforce a
Stormwater Management Plan . The City is enrolled under the state's General Stormwater Permit
via the approval of the Stormwater Management Plan by the Regional Water Quality Contro l
Board, the regional arm of the State Water Board . The State Water Board is tasked with th e
enforcement of the Clean Water Act by the federal Environmental Protection Agency .
Under the approved Stormwater Management Plan, the City has an obligation to produce a
Hydromodification Management Plan over the course of five years . In addition, an interim
hydromodification plan must be adopted by June of this year.
The Regional Board is now proposing an alternative path for agencies to achiev e
hydromodification regulation to be done as a "joint effort"through the Regional Board . If th e
City participates in the joint effort, the final plan is anticipated to be complete in two years .
Although this is sooner than under the City's existing permit, the City would not have to adopt an
interim plan by June 2010 . The City will be expected to encourage Low Impact Developmen t
(LID) techniques in new projects and provide resources to developers on LID . LID methods ar e
intended to minimize impacts to the landscape and methods are available from multiple source s
for developers to consider in designing their projects .
What is Hydromodification and why should the City be concerned ?
The term hydromodification is used to describe the alteration of the natural flow of water throug h
landscape . When changes to the land take place, such as those that occur with development -
compacting soils, changing vegetative cover, adding impervious surfaces, altering drainag e
patterns — natural hydrologic processes of absorption, infiltration and run off, are altered . Thes e
changes can result in increased creek channel instability, degraded water quality, reduced groun d
water recharge, and changes in riparian and aquatic habitats .
Hydromodification has been under study for a number of years, but until more recently, was no t
regulated . In early 2003, agencies in the San Francisco Bay Area were directed to begi n
SS2-9
ATTACHMENT 1 -2
Hydromodification Joint Effort Participation Page 2
development and implementation of hydromodification requirements . As part of the July 200 9
approval of the City's Stormwater Management Plan, the City is now under obligation to produc e
and enforce requirements regarding hydromodification that occurs as a result of development an d
redevelopment . The Environmental Protection Agency is also looking at new regulations t o
require these types of plans .
The local Regional Water Quality Control Board (Regional Board) recently established throug h
its goal setting process a goal of "Healthy Watersheds ." They have defined that as :
1.Rainfall surface run off is at pre-development level s
2.Watershed storage of run off, through infiltration, recharge, baseflow, and interflow, is a t
pre-development level s
3.Stream banks are stable, within a natural rang e
4.Sediment supply and transportation occur within a natural rang e
5.Riparian and aquatic habitats are optimal, including stream flow and biotic condition s
The Regional Board has determined that to achieve healthy watersheds, hydromodificatio n
regulation for development and redevelopment is needed . That has translated into th e
requirements for a Hydromodification Management Plan within the City and all other regiona l
agencies .
The Joint Effor t
When the requirement for hydromodification first appeared in a letter to local agencies, loca l
agencies and private organizations were extremely concerned . That concern was voiced o n
numerous occasions and some softening of the original requirements was made . Municipalitie s
expressed concerns with the scope of the work involved to develop these plans for which the y
have neither the staff expertise nor the resources to hire consultants . Plans, such as these, ca n
cost on the order of $400,000 for an agency of the City's size . At the urging of, and with the hel p
of the Low Impact Development Center (LIDC), the Regional Board developed a program title d
the "Joint Effort ." The Regional Board secured a $600,000 grant to develop regiona l
hydromodification control methodology . The Regional Board is providing the grant to the LIDC
who will hire experts to develop the methodology . The Regional Board has extended a n
invitation to all agencies in the region to participate in this effort . The region roughl y
encompasses Monterey, San Luis Obispo, and Santa Barbara counties .
The Joint Effort is just what it sounds like . It is a unified approach, including any agency wishin g
to participate, guided by the Regional Board and using the expertise of the LIDC to develop a
regional plan . Water Board staff believes that a joint effort could provide numerou s
environmental and other benefits by developing scientifically valid criteria, improving regiona l
consistency in control implementation, leveraging limited municipal resources and fosterin g
community buy-in essential for long lasting changes in stormwater management . Ultimately, th e
City will have a set of performance based requirements that can be implemented by new an d
redevelopment, and guidelines for when the requirements are not appropriate .
The Regional Board has listed the following items and advantages of participation :
1 . Focuses on reasonable scientifically based techniques with clear outcomes
SS2-10
ATTACHMENT 1 -3
Hydromodification Joint Effort Participation Page 3
Provides State funding for the first phase of the technical wor k
Saves staff time and agency costs as a result of working with others under the sam e
schedule and receiving implementation assistance from the LID C
4.Dispenses with interim criteria, due in one year, and focuses on final criteri a
5.Ensures better consistency in the outcomes for Phase II communities (lower populatio n
cities and counties), both technical and regulator y
6.Provides greater certainty for the development community of what is required and the basi s
for those requirement s
7.Addresses the unique conditions of each community ; one methodology - differing criteri a
8.Allows municipalities to focus on their strengths (process and implementation), an d
delegates the highly technical, scientific work to subject area experts .
Changing requirements twice in a few years (as currently required in the City's Stormwate r
Management Plan) will introduce complications for project applicants requiring additiona l
time for project review and approval .
10.Adoption of interim criteria (currently required), that may not fully reflect local hydrologi c
conditions may introduce unnecessary costs for developers and municipalities .
11.Participants will have input in the determination of the Maximum Extent Practicabl e
standard determination
12.Participants will likely undergo a streamlined review process of their implementatio n
measures and hydromodification criteria since measures and criteria will be develope d
through collective municipality involvement and Regional Board staff participatio n
13.Municipalities not participating may incur additional costs while undergoing Regional Boar d
staff review due to the need to individually demonstrate equivalent effort and effectivenes s
of their implementation measures and hydromodification criteri a
Joint Effort Scop e
Phase 1 of the work will include preliminary engineering and geomorphologic analysis, and th e
development of a methodology that the City can use to determine its landscape specifi c
hydromodification control criteria . During Phase 2 of the work, the methodology will be applie d
to the City specifically to determine land specific control criteria .
The LDIC is working with the State Water Board to use the methodology developed under thi s
effort on a Statewide basis, to create a consistent approach to this type of regulation . The scope
of work for the LIDC is :
1.Assist municipalities in obtaining funding and resources to conduct analysis and revision t o
municipal codes, including implementation of a small grant program, and training fo r
municipalities on how to integrate LID into code s
2.Provide sample LID ordinances the City can incorporate into its local regulatory framewor k
3.Provide LID Technical optimization guidance - assist new and redevelopment projec t
stakeholders in determining whether they have made adequate effort to incorporate LI D
Into their site designs
4.Provide an education tool that municipal stormwater program staff can use to understan d
and communicate what is involved in the development of applicability threshold s
5.Work with the Regional Board staff and municipalities to identify acceptable LID Bes t
Management Practices manuals that can be used for design and hydrologic analysis
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ATTACHMENT 1 -4
Hydromodification Joint Effort Participation Page 4
6 . Launch the virtual LIDC website in partnership with the California Stormwater Qualit y
Association to provide information on LID and its implementatio n
Term s
Participating agencies are required to provide labor in support of the effort through information /
data provision specific to the jurisdiction, and meet specific milestones on items such a s
municipal code review and revision, training, and implementation of LID . The City will need t o
dedicate staff resources to meet these milestones in a timely manner . This work would b e
required whether the City participated or not . Participation merely dictates an earlier timeframe .
The City's permit language will need to be revised and approved by February 2010 . Staff wil l
need to be available to provide comments on work products as the Regional Board makes draf t
work available . The City will also be responsible for completing Phase II work if additional gran t
funding is not found to fund continued work by the LIDC .
Staff has submitted the declaration of intent to participate included in the Attachment ; however ,
that declaration is not binding until such time as the revisions to the Stormwater Managemen t
Plan are submitted and approved, which will follow Council action on this item.
Deny Participatio n
The City would then shoulder the whole cost for its plan and possibly have a plan that is no t
consistent with other agencies, making it more difficult for the development community t o
comply with applicable standards . The City will also likely face more in depth review of its pla n
by the Regional Board because the Regional Board staff will not be as closely involved in th e
scoping and preparation .
CONCURRENCE S
City staff is currently active in a County Technical Advisory Committee (an affiliation o f
municipalities, consultants and developers) formed to work together on implementation of th e
hydromodification requirements . At the most recent committee meeting, it was reported that 3 0
of the 38 Phase II communities (small agencies) are intending to participate in the Joint Effort .
FISCAL IMPACT
The total cost to complete a joint effort for all Central Coast Phase communities is estimated t o
be between $1 .5 and $2 million. The State Water Board Cleanup and Abatement Account i s
funding $600,000 of the total amount . The Central Coast Water Board is actively seekin g
additional funding including Central Coast Water Board Settlement Funds, and America n
Recovery and Reinvestment Act dollars, and will support agency applications for Proposition 8 4
funds should they become available .
If the Regional Board is unable to obtain additional funds, agencies will either need to continu e
to band together to complete the work, or they will have the results from the first portion of th e
work, completed with the available $600,000, to move forward on their own to complete the
work . The one down side of participation is that funding for completion may be needed soone r
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Hydromodification Joint Effort Participation Page 5
rather than later to complete the work . Staff currently shows a $200,000 projected commitmen t
for 2011-12 in the 2009-11 Financial Plan .
Through the local Hydromodification Technical Advisory Committee (TAC), a draf t
Memorandum of understanding is under discussion for local communities to continue the join t
effort with the LIDC in the event the additional funds are not forthcoming from other sources .
Agencies represented at the local Technical Advisory Committee believed there would b e
support from their political bodies for such an effort . Staff believes this type of continued joint
effort would keep the cost to a minimum . The committee will be working on language for a
Memorandum of Understanding between agencies in the event it is needed . That Memorandum
would be brought to each political body for authorization .
Staff agrees with the Regional Board that a joint effort is a cost effective way to generate thes e
new requirements for development and re-development, and will provide a much more consisten t
set of requirements across the region for implementation by the development community .
ALTERNATIV E
The Council may decide not to participate .This alternative is not recommended since the Cit y
will still be required to produce these work products at some point, and not participating wil l
result m higher costs, additional staff work effort, and a more challenging approval process wit h
the Regional Board.
ATTACHMEN T
Central Coast Regional Water Quality Control Board Joint Effort Participation Lette r
t :\council agenda reports\public works car\2010\admin\hydromodificationyt effort rpt .doc
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ATTAC HCaliforniaRegional Water Quality Control Boar d
Central Coast Regio n
Internet Address : http ://www .waterboards .ca .gov/centralcoas t
895 Aerovista Place, Suite 101, San Luis Obispo, California 93401-790 6
Phone (805) 549-3147 FAX (805) 543-039 7
<<First_Name>>
<<AgencyNam e
<<AgencyMailingAddres s
<<AgencyCity», CA <<AgencyZip>>
Dear « FirstName»:
NOTIFICATION TO TRADITIONAL, SMALL MS4 DISCHARGERS REGARDIN G
OPPORTUNITY TO PARTICIPATE IN THE JOINT EFFORT FOR DEVELOPIN G
HYDROMODIFICATION CONTROL CRITERIA IN COMPLIANCE WITH THE MUNICIPA L
STORMWATER PERMI T
This letter provides Phase II municipal stormwater dischargers with the opportunity to participat e
in a Joint Effort to develop hydromodification control criteria as an alternative to the curren t
requirements for developing interim criteria found in municipalities' Storm Water Managemen t
Plans (SWMPs). Water Board staff is providing this opportunity in response to concerns ,
expressed by municipalities, about achieving compliance with current requirements fo r
developing interim hydromodification control criteria and enforceable mechanisms by the end o f
Year 1 of SWMP implementation . This letter provides some background and outlines th e
process by which Water Board staff will work with those municipalities choosing to participate i ntheJoint Effort . The process described below includes the following :
The terms and declaration of participation in the Joint Effort ;
The steps and schedule for amending SWMPs ; and
The new best management practices that will be amended to SWMPs .
Additionally, this letter includes a discussion of factors to consider in deciding whether t o
participate in the joint effort .
BACKGROUN D
The Joint Effort for Hydromodification Control is an effort to create a methodology for developin g
hydromodification control criteria ; derive criteria by applying that methodology ; and suppor t
implementation of the resulting criteria for new and redevelopment projects . The effort include s
oversight and funding by the Water Board for a team of subject area experts to develop th e
methodology . The Joint Effort is expected to span a period of two years, commencing with th e
start date for consulting contracts with subject area experts, anticipated to be the first week o f
November, 2009 . Water Board staff will replace the current requirements for developing interi m
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Linda S. Adams
Agency . Secretary
October 20, 2009
Arnold Schwarzenegge r
Governor
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October 20, 200 9
and long-term hydromodification control criteria with new requirements for municipalitie s
participating in the Joint Effort .
The Water Board has secured $600,000 for the Joint Effort from the State Water Board's
Cleanup and Abatement Account . These funds have been allocated to the Central Coast Lo w
Impact Development (LID) Center for securing contracts with subject area experts and fo r
providing contract management and technical oversight of these consultants . The scope o f
work for these funds will include the development of a methodology that municipalities can us e
to determine their landscape-specific hydromodification control criteria . The scope of work wil l
also include preparation of the preliminary engineering and geomorphologic analyses require d
to determine the hydromodification control criteria . Water Board and LID Center staff wil l
provide more detailed information regarding the scope of work for this first phase of the Join t
Effort to participating municipalities via meetings in early November . During the second year o f
the Joint Effort, each municipality will apply the methodology to determine its landscape-specifi c
hydromodification control criteria .
Most critically, the Joint Effort includes an implementation strategy to ensure successful use o f
LID and effective controls on hydromodification . Water Board staff has designed th e
requirements of the implementation strategy to be consistent with municipalities' existing SWM P
requirements . For example, as with current requirements for interim criteria, municipalitie s
participating in the Joint Effort must develop applicability thresholds to determine to whic h
projects the new criteria will apply . Also similar to current requirements, the Joint Effort require s
municipalities to develop enforceable mechanisms for implementing hydromodification control s
in new and redevelopment projects . The Joint Effort also requires guidance and training fo r
those enforcing, and those subject to, requirements for hydromodification control and LID .
The Joint Effort implementation strategy can also serve to initiate municipalities' complianc e
with SWMP requirements for long-term watershed protection, since the implementation strateg y
and long-term watershed protection are both based on a foundation of enforceabl e
mechanisms, quantifiable measures, and adequate guidance and training for those enforcing ,
and those subject to requirements .
The necessary steps to implement LID and effective hydromodification were the focus of a
series of charettes conducted this fall by Water Board staff and attended by 115 municipa l
stormwater stakeholders . The outcomes of these charettes include specific milestones tha t
Water Board staff will establish as requirements for the participating municipalities to complet e
throughout the two-year Joint Effort to prepare for successful implementation . (See Attachmen t
1 :Best Management Practices for Joint Effort Participants). The language of the milestone s
provides municipalities with flexibility to implement their programs in a manner that works for
them, while also helping to provide assurance that municipalities will implement effectiv e
programs .
PROCESS FOR THE JOINT EFFOR T
Terms of Participation Summary
This letter is intended to solicit participation in the Joint Effort and to make clear the terms o f
participation . The terms of participation include a municipality agreeing to : 1) work with a
consultant team to ensure that accurate information about local hydrologic conditions is used i n
developing the methodology during the first phase of the project, and 2) develop fina l
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hydromodification control criteria, and 3) execute a strategy to implement hydromodificatio n
controls and LID . Municipalities will "participate" in the Joint Effort by taking specific actions tha t
will be codified in changes to SWMPs .
For those choosing to participate, the Water Board staff requires a written declaration of th e
municipality's intent to meet the terms of participation . A template Declaration Form is attache d
to facilitate a municipality's agreeing to the terms and notifying the Water Board (Enclosure).
To allow the consultants to efficiently schedule their work, Water Board staff requires that eac h
municipality choosing to participate indicate its intentions by sending a completed Declaratio n
Form to the Water Board by November 30, 2009 .
Process and Schedule for Amending SWMP s
Each municipality participating in the Joint Effort must amend their SWMPs to include the Bes t
Management Practices (BMPs) in Attachment 1, and remove and/or revise existing SWM P
language that duplicates or conflicts with the language in the new BMPs . For example, existin g
BMPs for developing interim hydromodification control criteria in one year would be remove d
and replaced with the BMP to develop criteria in two years . The process and schedule fo r
amending the SWMPs is as follows :
January 4-21, 2010
Water Board staff will assist municipalities in amending thei r
SWMPs .Prior to the month of January, Water Board staff will
contact municipality representatives to schedule meetings .
January 29, 2010 Municipalities must submit a copy of amended SWMP pages (i n
track changes) to the Water Board .
February 1-9, 2010
Water Board staff will review the revised SWMP pages to verify tha t
the revisions have been correctly incorporated and will notify th e
municipality of any additional necessary revisions .
February 19, 2010 Municipalities must re-submit a final version of their SWMPs in wor d
format and portable document format (pdf).
February 22-26, 2010 Water Board Executive Officer sends letters to municipalitie s
approving SWMP revisions .
The cities of Santa Maria, Lompoc, and Santa Barbara have existing BMPs requiring them t o
submit interim hydromodification control criteria before January 29, 2010 . Should these citie s
choose to participate in the Joint Effort, they must amend their SWMPs to incorporate the Join t
Effort BMPs and submit their amended SWMPs by their Year 1 Annual Report submittal date, o r
January 29, 2010, whichever date comes sooner . The time periods for review, revision, an d
approval of the updated SWMPs for these cities will match the time periods described abov e
(one week for Water Board staff review, one week for municipality revision and re-submittal, an d
one week for Water Board Executive Officer approval). Water Board staff will identify specifi c
dates for each of these cities following receipt of their Declaration Form .
Best Management Practice s
Participants in the Joint Effort will develop the capacity to implement hydromodification contro l
and LID based on a foundation of enforceable mechanisms, numeric performance standard s
and applicability criteria, and adequate guidance and training for those enforcing, and thos e
subject to requirements . As participants build this foundation, they will also promote LID i n
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projects subject to their approval . The BMPs included in Attachment 1 codify the steps t o
building this foundation, and municipalities participating in the Joint Effort will amend thei r
SWMPs to incorporate these BMPs . Attachment 1 also provides context for the BMPs an d
reflects the input of municipal stormwater stakeholders in the Central Coast Region .
Schedule for Completing BMPs and Measurable Goal s
Several of the Measurable Goals are dependent on the completion of earlier milestones . Th e
schedule for completing the Measurable Goals is therefore based on the presumption that thes e
milestones stay on track, e .g ., methodology is developed in the first year ; Water Board staff vet s
and recommends LID guidance manuals for use by municipalities in the second quarter ; th e
Central Coast LID Center provides assistance on municipal code revisions in the secon d
quarter . As the Joint Effort progresses, Water Board staff will evaluate scheduling conflict s
resulting from circumstances beyond the control of participating municipalities and mak e
necessary adjustments .
FACTORS TO CONSIDER IN DECIDING WHETHER TO PARTICIPATE IN THE JOINT
EFFOR T
The Phase II Municipal General Permit's Minimum Control Measure for Post-Constructio n
Stormwater Management "requires long-term post-construction BMPs that protect water qualit y
and control runoff flow, to be incorporated into development and significant redevelopmen t
projects ." The Joint Effort represents the Water Board staff's responsiveness to the challenge s
faced by municipalities in achieving compliance with this requirement, and it is a strategy tha t
improves the likelihood of success in establishing effective post-construction stormwate r
controls . In deciding whether to participate in the Joint Effort, municipalities must conside r
whether compliance with this Permit requirement is more achievable and effective throug h
participation in the Joint Effort, or through implementation of the existing BMPs in their SWMPs .
Advantages of Participatio n
Specific advantages of participation to consider are that the Joint Effort :
•Focuses on reasonable scientifically based techniques with clear outcome s
•Provides State funding for the initial part of the technical work ($600K )
•Dispenses with Interim Criteria, due in one-year, and focuses on more robust, final criteri a
•Ensures better consistency in the outcomes for Phase II communities, both technical an d
regulatory
•Provides greater certainty for the development community of what is required and the basi s
for those requirement s
•Addresses the unique conditions of each community ; one methodology – differing criteri a
•Provides multiple benefits of working with others on the same schedule (saves costs an d
time )
•Allows municipalities to focus on their strengths (process and implementation), an d
delegates the highly technical, scientific work to subject area expert s
Cost Factor s
The cost of compliance with the SWMP post-construction stormwater requirements will var y
depending on each municipalities' unique conditions, including size, growth rate, and curren t
capacity to implement BMPs . In deciding whether to participate in the Joint Effort, the relevan t
question with respect to costs is whether compliance with post-construction requirements coul d
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be achieved more affordably through the Joint Effort or through existing SWMP requirements .
The cost factors to consider in evaluating that question are both direct cost factors, and ris k
related cost factors . For example :
Development of Criteria, Applicability Thresholds, and Enforceable Mechanism s
Direct Cost Factors
•Direct cost savings of Joint Effort : The Joint Effort provides State funding for developing a
methodology and for compiling the information for derivation of criteria ($600K).
Risk Related Cost Factors
•Establishment of long-term criteria necessitates at least the same level of effort as th e
Joint Effort (possibly more because individual municipalities will have to contract ,
coordinate, review and integrate products on their own). In addition to the cost of lon g
term criteria, each municipality must also pay for establishment and use of interim criteria .
•A Joint Effort to develop a single set of hydromodification control criteria, enforceabl e
mechanisms, and applicability thresholds in a period of two years, should be more cos t
effective than developing Interim Criteria, enforceable mechanisms, and applicabilit y
thresholds in one year, then Long-Term Criteria in two to four years (existin g
requirements) for the following reasons :
- Municipalities will likely incur additional costs to develop and then replace Interi m
Criteria with Long-Term Criteria ; these costs may accrue when making change s
to enforceable mechanisms as well as guidance and training to implement th e
Long-Term Criteria .
Changing requirements twice in a few years will introduce complications fo r
project applicants requiring additional resources by municipal staff for projec t
review and approval .
Adopting Interim Criteria that do not fully reflect local hydrologic conditions ma y
introduce unnecessary costs for developers and municipalities . This has bee n
the case in some jurisdictions that applied controls developed for other region s
only to repeal the requirements once they were determined to be unnecessary .
•At this time costs to an individual municipality for development of acceptable Long-Ter m
Criteria under existing requirements can not be estimated with any more certainty tha n
costs of deriving criteria from the methodology developed through the Joint Effort .
Implementation Strateg y
Direct Cost Factors :
•Direct cost savings of Joint Effort : Potential savings in time and money should b e
realized for Joint Effort participants due to the multiple benefits of working with others o n
the same schedule and receiving implementation assistance from the Central Coast LI D
Center .
•Through the Joint Effort, municipalities will be able to focus their resources on th e
implementation strategy, and delegate the highly technical, scientific work to subjec t
area experts funded by the State .
Risk Related Cost Factors
•The Water Board evaluates compliance with General Permit post-constructio n
stormwater requirements based on the Maximum Extent Practicable standard .
Participants in the Joint Effort could be at a potential advantage by helping determin e
how the Water Board defines this dynamic standard . For example, participants in th e
Joint Effort will likely undergo a streamlined review process of their implementatio n
measures and hydromodification criteria, since the measures and criteria will b e
developed through collective municipality involvement and close Water Board staff
participation . Municipalities not participating in the Joint Effort, on the other hand, ma y
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incur additional costs while undergoing the Water Board staff review process when the y
must individually demonstrate equivalent effort and effectiveness of their implementatio n
measures and hydromodification criteria .
Municipalities' Role in Developing Methodology for Hydromodification Control Criteri a
Municipalities will have the opportunity to review the draft methodology and provide comment s
to Water Board staff before Water Board staff approves a final methodology for application i n
municipalities throughout the Central Coast Region . Municipal staff will also work directly wit h
the project consultants to ensure that accurate information about local hydrologic conditions i s
used in developing the methodology during the first phase of the project . Water Board staff will
also provide stakeholders with status reports on the progress of the Joint Effort throughout th e
Region via websites and other methods of communication .
Project consultants will provide more detailed information regarding the scope of work fo r
developing the methodology in a series of meetings in the northern, central, and souther n
portions of the Central Coast Region . These meetings will communicate the purpose, scope ,
goals and objectives of the tasks for developing the methodology to municipalities, th e
engineering/development community, and/or other stakeholders . The meetings will also initiat e
interaction between municipalities and the consultant team who will be working together (alon g
with Water Board staff) to ensure success on this project . The presentations are currentl y
anticipated for the week of November 16 th , prior to the due date for submittal of the Declaratio n
Form . Water Board staff will send notices with meeting locations and times to participatin g
municipalities and interested stakeholders when they become available .
Implementation Assistance Availabl e
The Water Board established a Low Impact Development Endowment Fund (LID Fund) in 200 8
to fund the services of the Central Coast LID Center . The Central Coast LID Center 2009-201 0
Work Plan includes tasks for providing assistance that directly supports municipalities '
implementation of Joint Effort BMPs . These tasks include :
•Assist municipalities in obtaining funding and resources to conduct analysis and revisions t o
municipal code . This includes implementation of a small grant program, and training fo r
municipalities on how to integrate LID into codes . Funds for the small grant program wil l
come from the LID Fund .
•Provide sample LID ordinances that MS4s can incorporate into their local regulatory
framework.
•Provide LID Technical Optimization Guidance : Assist new and redevelopment projec t
stakeholders in determining whether they have made adequate effort to incorporate LID int o
their site designs .
•Provide an education tool that municipal stormwater program staff can use to understan d
and communicate what is involved in the development of Applicability Thresholds .
•Work with the Water Board staff and municipalities to identify acceptable LID BMP manual s
that can be used for BMP design and hydrologic analysis .
•Launch the Virtual LID Center website, in partnership with the California Stormwater Qualit y
Association, to provide information on LID and its implementation .
Water Board staff anticipates the Central Coast LID Center work plan for 2010-2011 will includ e
additional tasks to support municipalities in the second year of the Joint Effort toward successfu l
implementation of LID and hydromodification controls .
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Opportunity to Address the Central Coast Water Boar d
At any time, participants in the Joint Effort may elect to bring issues and concerns directly to th e
Central Coast Water Board . The first such opportunity will be the October 23, 2009 Wate r
Board meeting in the City of Santa Barbara . A discussion of the status of the Joint Effort i s
included in the Executive Officer's Report for this meeting . See Item 21 on the meeting agend a
at : http ://www .waterboards .ca .gov/centralcoast/board_info /
NOTIFICATION OF DECLARATION TO PARTICIPATE IN THE JOINT EFFOR T
Please return the attached Declaration Form to indicate your intention to participate in the Join t
Effort by November 30, 2009 . If you have any questions regarding this letter, please contac t
Dominic Roques,at droques@waterboards .ca.gov or at (805) 542-4780,or Phillip Hamme r
at phammer@waterboards .ca .qov or at (805) 549-3882 .Also, please visit our website fo r
helpful documents about the Joint Effort under the banner, "Announcements" see at :
http ://www .waterboards .ca .gov/centralcoast /
Sincerely ,
Roger W . Brigg s
Executive Office r
cc :
Interested Parties Lis t
Attachment 1 : Best Management Practices for Joint Effort Participant s
Enclosure :Declaration For m
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Attachment 1
Attachment 1 : Best Management Practices for Joint Effort Participant s
Joint Effort participants must amend their SWMPs to include the BMPs in Table 1, and remov e
and/or revise existing SWMP language that duplicates or conflicts with the language in the ne w
BMPs . The following provides a description of the schedule, intent, and scope of the BMPs i n
Table 1
Enforceable Mechanisms :Municipal Code s
Municipalities shape land use development through planning that in turn relies on codes ,
regulations, standards and other enforceable mechanisms applied to projects throughout th e
review and approval process . To effectively implement hydromodification controls and LID ,
municipalities will need to develop and/or modify these enforceable mechanisms . T o
accomplish this, the first step is to analyze all applicable codes, regulations, standards, and/o r
specifications to identify changes needed to implement hydromodification controls and LID .
Once identified, making the necessary changes requires direct involvement by the variou s
municipal officials responsible for enforcing different parts of the municipal codes . For thes e
officials, outreach and education about the stormwatermanagement objectives of code change s
will be essential to establish effective code to implement LID and hydromodification controls .
Finally, municipalities must follow their approval process for code revisions . Therefore,Join t
Effort participants have two full years to approve new and/or modified codes and regulations .
Though final hydromodification control criteria may not be available until the end of the two-yea r
period, municipalities can work toward adoption of ordinances prior to their availability . Severa l
Central Coast stormwater entities have adopted stormwater ordinances in advance of havin g
specific post-construction criteria by incorporating by reference a companion document that will ,
at a future date, include such criteria . Water Board staff will re-evaluate the timing of ordinanc e
adoption after the first year of the Joint Effort.
Hydromodification Control Criteri a
Participating municipalities will have two years and technical assistance in developin g
hydromodification control criteria . In the first year, the Water Board will pay consultants t o
develop a methodology and compile information necessary to derive criteria . Municipalities wil l
need to coordinate with the consultant team as it develops the methodology to ensure that th e
resulting methodology addresses local hydrologic conditions .
Municipalities will have the opportunity to review the methodology and provide comments to th e
Water Board before it adopts the methodology for application in the Central Coast Region . I n
the second year of the Joint Effort, municipalities will apply the methodology to derive criteri a
suited to their hydrologic and watershed conditions . Measurable Goals for this BMP includ e
producing hydromodification control criteria by the end of the two-year Joint Effort, an d
application of the criteria by the end of the following quarter .
Applicability Threshold s
Applicability Thresholds are the specific conditions that determine whether a developmen t
project is subject to hydromodification controls . As with current SWMP requirements fo r
preparing Applicability Thresholds (or Criteria), municipalities participating in the Joint Effort
must compile and analyze information on the scale, type and potential for new an d
redevelopment . Then, once hydromodification control criteria become available, municipalitie s
can evaluate the criteria relative to their development patterns and potential, and deriv e
appropriate Applicability Thresholds that will be consistent with long-term watershed protectio n
goals . They must be complete by the end of the two-year Joint Effort period – a schedule tha t
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allows for the simultaneous development of hydromodification control criteria and Applicabilit y
Thresholds with optimal cross communication to ensure a cohesive product .
The Central Coast LID Center will provide education and assistance to municipalities fo r
developing Applicability Thresholds as part of the Joint Effort . Charette participants also gav e
examples of some specific steps and possible schedules (quarters, `Q,' when completed) fo r
completing the Applicability Threshold BMP . These include :
•Research existing criteria from other guidance manuals to determine if it can be used (Q1 )
•Identify historical project scale data (i .e ., square footage areas of green space an d
impervious cover)to determine municipal growth, development, and redevelopment pattern s
•Complete an existing parcel inventory and review General Plan for planned growth t o
determine what types of projects are coming (Q1 to 0-4 )
•Compile, review, summarize statistics of current development trends and futur e
development sites (Q1 to Q-4 )
•Match hydromodification control criteria against future projects to establish thresholds (Q5 -
Q8 )
Implementation Strategy for LID and Hydromodification Contro l
This BMP requires the municipality to develop and enact a strategy for implementing LID an d
hydromodification control for new and redevelopment projects . The strategy will provid e
appropriate education and outreach for all applicable target audiences, and will include specifi c
guidance for LID BMP design and for complying with hydromodification control criteria . Th e
strategy will also apply LID principles and features to new and redevelopment projects during th e
two-year period preceding adoption of hydromodification control criteria . The followin g
Measurable Goals are specific milestones for completing this BMP .
Guidance
LID BMP Design Guidance
This Measurable Goal requires the municipality to develop, advertise and make available LI D
BMP Design Guidance suitable for all stakeholders by the end of the first year of the Joint Effort .
To assist municipalities in ,completing this BMP, the Central Coast LID Center will recommen d
existing BMP manuals that provide appropriate guidance for municipal staff and projec t
applicants . Municipalities will need to tailor the guidance for their local circumstances, possibl y
emphasizing different BMPs based on local conditions and development patterns . However ,
early identification of appropriate LID guidance will support the related Measurable Goal o f
interim LID implementation (see below).
Hydrologic Analysis Guidance
This Measurable Goal requires the municipality to develop specific guidance on how to mee t
and demonstrate compliance with new hydromodification control criteria and LID requirements ;
and to make the guidance available to new and redevelopment project applicants by the end o f
the Joint Effort. Water Board staff supports developing hydrologic analysis guidance whic h
provide developers a simple and clear path to use to comply with hydromodification contro l
criteria . We also recognize that guidance cannot be finalized until the specific hydromodificatio n
control criteria are known ; therefore the guidance is not required to be complete until the end o f
the Joint Effort .
Water Board staff recognizes municipalities will need to be strategic in integratin g
hydromodification control criteria, applicability thresholds, and hydrologic analysis guidanc e
during the second year of the Joint Effort . Staff finds that the schedule for completion of thes e
Measurable Goals by the end of the two-year period will promote the necessary integration an d
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is an appropriate target . Central Coast LID Center assistance for implementation will also b e
provided throughout the Joint Effort .
Examples of helpful guidance were provided by charette participants, and include :
•Checklists for BMP applicabilit y
•Guidelines, standard conditions of approval, required documentatio n
•Decision-making process, checklists, decision tree for development proces s
•Site specific options for developer s
•Identify what BMPs/LID techniques are applicabl e
•Example calculations using hydromodification control criteri a
•BMP sizing factors for achieving hydromodification criteri a
•Client Assistance Memos for specific designs, e .g ., parking lot s
•Standards and stock conditions of approval for plan s
•Pre-construction field meetings and pamphlets ; training for maintenance ; train people o n
requirements (updates to codes and standards )
EducationandOutreac h
Municipalities participating in the Joint Effort have considerable flexibility in designing an d
conducting education and outreach to support implementation of LID and hydromodificatio n
requirements . However, this Measurable Goal requires them to document goals, schedules ,
and target audiences for education and outreach for the following strategic objectives :
enforceable mechanisms, hydromodification control criteria, applicability thresholds, LID BM P
design, and compliance with LID and hydromodification control criteria . Documentation will b e
through a Tracking Report indicating the municipality's accomplishments in education an d
outreach supporting these objectives .
The Central Coast LID Center will provide education and outreach assistance for the followin g
objectives : municipal code analysis and revision, Applicability Thresholds, and LID BMP desig n
guidance . This assistance may include training modules that can be used by municipalities i n
their education and outreach effort . Additionally, charette participants suggested a variety o f
goals for education and outreach, including :
•Plan and establish training program ; create credential program s
•Conduct outreach to internal stakeholders for municipal code revision s
•Conduct outreach and education on hydromodification control criteri a
•Attend training, if available, on fundamentals of developing Applicability Threshold s
•Conduct outreach for Establishing Applicability Threshold s
- Hold a workshop with development community for input on what implementations ar e
cost-effective and feasibl e
•Conduct outreach for Interim LID Implementation to development community, plannin g
commission, city council, and staf f
•Implement LID Capital Improvement Pilot Projects and demonstration s
Interim Implementatio n
While several municipalities in the Central Coast Region have successfully integrated LID int o
development projects, it remains challenging to do so for most projects in most municipalities ,
since the municipalities typically lack a clear process and adequate guidance for their staff an d
the development community . The measurable goal for Interim LID Implementation require s
municipalities to identify applicable projects and apply LID principles and features during th e
two-year period that precedes the availability of enforceable mechanisms for LID . Municipalitie s
will have flexibility in defining applicable projects, but they will also be required to track an d
report on their effectiveness in requiring implementation of LID during this interim period .
California Environmental Protection Agenc y
Recycled Paper
SS2-23
ATTACHMENT 1 - 1 6
4 Attachment 1
A significant challenge for municipalities currently is the fragmented development review an d
permitting process . One possible measure to address this challenge is to select an d
disseminate LID guidance among the multiple units within municipal government to ensure mor e
awareness among staff in these units and consistency in the specific requirements they impos e
on development projects . The Central Coast LID Center will recommend LID manuals in th e
second quarter of the Joint Effort that could serve as appropriate guidance for interim LI D
implementation . Municipalities' experience with requiring LID over the two-year period wil l
facilitate a smooth transition toward the enforceable requirements that come at the end of th e
Joint Effort .
Table 1 : Best Mana g ement Practices and Measurable Goals for Joint Effort Participant s
BMP Measurable Goals Schedul e
(Quarters))
Enforceable Mechanism s
Develop and/or modify enforceabl e
mechanisms that will effectivel y
implement hydromodification control s
and LID . Enforceable mechanism s
may include municipal codes ,
regulations, standards, an d
specifications .
An analysis of all applicable codes ,
regulations, standards, and/o r
specifications that identifie s
modifications and/or addition s
necessary to effectively implemen t
hydromodification controls and LI D
Approved new and/or modifie d
enforceable mechanisms tha t
effectively resolve regulatory conflict s
and implement hydromodificatio n
controls and LID in new an d
redevelopment project s
Apply new and/or modified enforceabl e
mechanisms to all applicable new an d
redevelopment projects
Q 2
Q 8
Q 9
Hydromodification Control Criteri a
Derive municipality-specific criteria fo r
controlling hydromodification in ne w
and redevelopment projects usin g
Water Board-approved methodolog y
developed through the Joint Effort .
Hydromodification Control Criteria Q 8
Applicability Threshold s
Select Applicability Thresholds fo r
applying Hydromodification Contro l
Criteria to new and redevelopmen t
projects . Applicability thresholds will b e
consistent with long-term watershe d
protection .
Applicability Thresholds Q8
California Environmental Protection Agenc y
L'
Recycled Paper
SS2-2 4
ATTACHMENT 1 - 1 7
Attachment 1
Q 4
Q8
Q 2
Q 8
Q2—8
Q 9
Guidance
1.Develop, advertise and mak e
available LID BMP Design Guidanc e
suitable for all stakeholder s
2.Specific guidance on how to achiev e
and demonstrate compliance wit h
the hydromodification control criteri a
and LID requirements mad e
available to new and redevelopmen t
project applicant s
Education and Outreac h
1.Documentation of goals, schedules ,
and target audiences for educatio n
and outreach the municipality wil l
conduct in support of the followin g
strategic objectives : enforceable
mechanisms, hydromodificatio n
control criteria, applicabilit y
thresholds, LID BMP design, an d
compliance with LID an d
hydromodification control criteri a
2.Tracking Report indicatin g
municipality's accomplishments i n
education and outreach supportin g
implementation of LID an d
hydromodification control for new
and redevelopment projects
Interim LID Implementation
1.Apply LID principles and features t o
all applicable new an d
redevelopment projects .
2.Tracking Report, for the period Q2 t o
Q8, identifying LID design principle s
and features incorporated into eac h
applicable new and redevelopmen t
project
Implementation Strategy for LID an d
Hydromodification Contro l
Develop and enact a strategy fo r
implementing LID an d
hydromodification control for new an d
redevelopment projects . The strateg ywillprovide appropriate education an d
outreach for all applicable targe t
audiences, and will include specifi c
guidance for LID BMP design and fo r
complying with hydromodificatio n
control criteria . The strategy will als o
apply LID principles and features t o
new and redevelopment projects durin g
the two-year period preceding adoptio n
of hydromodification control criteria .
*The schedule refers to the eight quarters of the two-year Joint Effort and the first quarte r
following . Quarter 1 will begin November 1, 2009 with commencement of the Joint Effort .
YEAR 1
Q1 = Nov 1, 2009 - Jan 31, 201 0
Q2 = Feb 1, 2010 - April 30, 201 0
Q3= May 1, 2010-July 31, 201 0
Q4=Aug 1, 2010-Oct30, 201 0
YEAR 2
Q5= Nov 1, 2010-Jan 31, 201 1
Q6 = Feb 1, 2011 - April 30, 201 1
California Environmental Protection Agenc y
Recycled Paper
YEAR 3
Q9= Nov 1,2011 - Jan 31, 201 2
Based on this schedule, Measurable Goals for a municipality participating in the Joint Effor t
must be completed by : April 30, 2010, October 30, 2010, October 30, 2011, and January 31 ,
2012 . This last date is the date by which the municipality needs to be implementing their post -
construction controls on all applicable new and redevelopment projects. Reporting o n
completion of all BMPs will be included in the municipalities' Annual Reports .
ATTACHMENT 1 - 1 8
Attachment 1
Q7 = May 1 2011 July 31, 201 1
Q8 = Aug 1 2011 - Oct 30, 201 1
California Environmental Protection Agency
Recycled Paper
SS2-26
ATTACHMENT 1 - 1 9
DECLARATION FOR M
DATE :
TO :Central Coast Water Quality Control Boar d
895 Aerovista Place,Suite 10 1
San Luis Obispo, CA 9340 1
ATTENTION : Dominic Roques
DECLARATION TO PARTICIPATE IN THE JOINT EFFORT FO R
DEVELOPING HYDROMODIFICATION CONTROL CRITERIA I N
COMPLIANCE WITH THE MUNICIPAL STORMWATER PERMI T
Municipality/Permittee Name :
I understand the terms of participating in the Central Coast Joint Effort fo r
Developing Hydromodification as explained in -the Central Coast Wate r
Quality Control Board's October 20, 2009 letter . This correspondenc e
serves as a declaration of the intention of the municipality listed above t o
participate in the Joint Effort .
Print Nam e
Signature
SS2-27
CITY STAFF REPORT - ATTACHMENT 2 -1
CALIFORNIA REGIONAL WATER QUALITY CONTROL BOAR D
CENTRAL COAST REGIO N
895 Aerovista Place, Suite 10 1
San Luis Obispo, Californi a
DRAFT RESOLUTION NO . R3-2012-002 5
APPROVING POST-CONSTRUCTION STORMWATER MANAGEMENT REQUIREMENT S
FOR DEVELOPMENT PROJECTS IN THE CENTRAL COAST REGIO N
The Central Coast Regional Water Quality Control Board (Central Coast Water Board) find s
that :
Backqroun d
On December 8, 1999, USEPA promulgated regulations, known as Phase II, requirin g
permits for stormwater discharges from small MS4s and from construction sites disturbin g
one and five acres of land . On April 30, 2003, the State Water Resources Control Boar d
adopted the National Pollutant Discharge Elimination System (NPDES) General Permit fo r
the Discharge of Storm Water from Small Municipal Separate Storm Sewer Systems, Orde r
No . 2003-0005-DWQ (Phase II Municipal General Permit). Regulated small MS4s ar e
required to apply to obtain coverage under the Phase II Municipal General Permit an d
complete a Storm Water Management Plan (SWMP). The Central Coast Water Boar d
implements the Phase II Municipal General Permit to be consistent with its Water Qualit y
Control Plan, Central Coast Region (Basin Plan) to ensure protection of water quality ,
beneficial uses, and the biological and physical integrity of watersheds in the Central Coas t
region . The Central Coast Water Board Executive Officer requires specific conditions fo r
MS4s' SWMPs pursuant to the federal Clean Water Act, the Basin Plan, and the Phase I I
Municipal General Permit .
2.The Phase II Municipal General Permit requires regulated small MS4s to develop an d
implement a SWMP that includes BMPs, measurable goals, and timetables fo r
implementation, designed to reduce the discharge of pollutants to the maximum exten t
practicable (MEP) and to protect water quality . The Phase II Municipal General Permi t
requires regulated small MS4s to address stormwater runoff from development an d
redevelopment projects through post-construction stormwater management requirements .
Phase II Municipal General Permit section D, requires the Permittee to incorporate change s
required by or acceptable to the Central Coast Water Board Executive Officer into th e
Permittee's SWMP and adhere to its implementation .
3.On February 15, 2008, the Central Coast Water Board Executive Officer notified un-enrolle d
traditional, small MS4 stormwater dischargers and two un-enrolled non-traditional, smal l
MS4 stormwater dischargers (University of California at Santa Barbara and Santa Cruz) o f
the process the Central Coast Water Board would follow for enrolling the MS4s under th e
Phase II Municipal General Permit . In the February 15, 2008 correspondence, the Centra l
Coast Water Board Executive Officer stated his intent to require MS4s to include in thei r
SWMPs a schedule for development and adoption of hydromodification control standards .
Subsequently, the Executive Officer required the MS4s' SWMPs to include provisions fo r
SS2-28
-2 -Draft Resolution No . R3-2012-0025
CITY STAFF REPORT - ATTACHMENT 2 -2
September 6, 201 2
development and implementation of hydromodification control criteria . For MS4s previousl y
enrolled, the Central Coast Water Board Executive Officer generally required those MS4s '
SWMPs to be updated with hydromodification control provisions .
4.On August 4, 2009 and October 20, 2009, the Central Coast Water Board Executive Office r
notified the MS4s of the option to participate in the Central Coast Joint Effort for developin g
hydromodification control criteria (Joint Effort) as a means to meet the hydromodificatio n
control criteria development, adoption, and implementation commitments in the MS4s '
SWMPs . MS4s agreeing to participate in the Joint Effort (Joint Effort MS4s) submitted a
written declaration of their intent to meet the terms of participation .
5.Between January and August 2010, Central Coast Joint Effort MS4s amended their SWMP s
to include Best Management Practices (BMPs) to codify steps the Central Coast Wate r
Board Executive Officer required of them to participate in the Joint Effort . These BMP s
include development and implementation of hydromodification control criteria and selectio n
of applicability thresholds pursuant to the Joint Effort .
6.On September 28, 2010, the Central Coast Central Coast Water Board Executive Office r
notified the Joint Effort MS4s of the commencement of the Joint Effort .
7.On December 2, 2009, the City of Salinas requested to participate in the Joint Effort . O n
May 17, 2011, Central Coast Water Board Executive Officer outlined to the City of Salina s
the steps they needed to take to formalize participation in the Joint Effort . On August 16 ,
2011, the City of Salinas modified its SWMP to include these steps . On May 3, 2012, th e
Central Coast Water Board approved Order No . R3-2012-0005, NPDES Permit No .
CA0049981, Waste Discharge Requirements for City of Salinas Municipal Stormwate r
Discharges . Order No . R3-2012-0005, Provision J requires the City of Salinas to revise it s
Stormwater Development Standards to incorporate the Post-Construction Requirements ,
developed by the Joint Effort .
Stormwater Management to Protect Beneficial Use s
8.Prior to the Joint Effort, information on the local characteristics of Central Coast watershed s
was inadequate for MS4s to develop Post-Construction Requirements that protec t
watershed processes so that beneficial uses of receiving waters are maintained and, wher e
applicable, restored . The Central Coast Water Board secured funds from the State Wate r
Quality Control Board's Cleanup and Abatement Account to support acquisition an d
assessment of information to inform the development of hydromodification control criteri a
and related Post-Construction Requirements . These funds were used to establish an exper t
team of scientists that would characterize the Central Coast region's watersheds and hel p
create a methodology for developing Post-Construction Requirements based on tha t
characterization . The Post-Construction Requirements included in this Resolutio n
(Attachment 1) are based on the methodology, which has been summarized in the Draf t
Technical Support Document for Post-Construction Stormwater Management Requirement s
for Development Projects in the Central Coast Region (Technical Support Document )
(Attachment 2).
9.The Draft Technical Support Document (Attachment B) contains rationale, justification, an d
explanation for the Post-Construction Requirements . This information is hereb y
incorporated by reference .
SS2-29
CITY STAFF REPORT - ATTACHMENT 2 -3
Draft Resolution No . R3-2012-0025 -3 -
September 6, 201 2
10.Urban runoff is a leading cause of pollution throughout the Central Coast region .
Development and urbanization increase pollutant loading and volume, velocity, frequency ,
and discharge duration of stormwater runoff . First, natural vegetated pervious ground cove r
is converted to impervious surfaces such as highways, streets, rooftops and parking lots .
While natural vegetated soil can both absorb rainwater and remove pollutants providing a n
effective natural purification process, in contrast, impervious surfaces can neither absor b
water nor remove pollutants, and thus the natural purification characteristics are lost .
Second, urban development creates new pollution sources as the increased density o f
human population brings proportionately higher levels of vehicle emissions, vehicl e
maintenance wastes, pesticides, household hazardous wastes, pet wastes, trash, and othe r
anthropogenic pollutants, which can either be washed or directly dumped into the MS4 . As
a result, the runoff leaving the developed urban area is significantly greater in pollutant loa d
than the pre-development runoff from the same area . These increased pollutant loads must
be controlled to protect downstream receiving water quality .
11.A higher percentage of impervious area correlates to a greater pollutant loading, resulting i n
turbid water, nutrient enrichment, bacterial contamination, organic matter loads, toxi c
compounds, temperature increases, and increases of trash or debris .
12.The discharge of pollutants and/or increased flows from MS4s can cause or threaten t o
cause exceedances of applicable receiving water quality objectives, impair or threaten t o
impair designated beneficial uses, and result in a condition of pollution (i .e ., unreasonabl e
impairment of water quality for designated beneficial uses), contamination, hazard, o r
nuisance .
13.Maintenance and restoration of watershed processes impacted by stormwater managemen t
is necessary to protect water quality and beneficial uses . Watershed processes affected b y
stormwater, by actions to manage stormwater, and/or by land uses that alter stormwate r
runoff patterns include the following : 1) overland flow, 2) groundwater recharge, 3) interflow ,
4) evapotranspiration, 5) delivery of sediment and organic matter to receiving waters, and 6 )
chemical and biological transformations . These watershed processes must be maintaine d
and protected in order to support beneficial uses throughout the Central Coast region's
watersheds . Restoration of degraded watershed processes, impacted by stormwate r
management, is necessary to protect water quality and re-establish impacted beneficia l
uses . New development, redevelopment, and existing land use activities create alteration s
to stormwater runoff conditions which in turn result in changes to watershed processes tha t
can cause or contribute to impairment of beneficial uses and violations of water qualit y
standards . Future growth planned within the Central Coast region will degrade watershe d
processes if not managed properly .
14.Low Impact Development (LID) is an effective approach to managing stormwater to minimiz e
the adverse effects of urbanization and development on watershed processes and beneficia l
uses resulting from changes in stormwater runoff conditions . LID strategies can achiev e
significant reductions in pollutant loading and runoff volumes as well as greatly enhance d
groundwater recharge rates . The proper implementation of LID techniques results in greate r
benefits than single purpose stormwater and flood control infrastructure .
15.Controlling urban runoff pollution by using a combination of onsite source control and LI D
BMPs augmented with treatment control BMPs before the runoff enters the MS4 is importan t
for the following reasons : 1) many end-of-pipe BMPs (such as diversion to the sanitar y
sewer) are typically ineffective during significant storm events, but onsite source contro l
SS2-30
CITY STAFF REPORT - ATTACHMENT 2 -4
Draft Resolution No . R3-2012-0025
September 6, 201 2
BMPs can be applied during all runoff conditions ; 2) end-of-pipe BMPs are often incapabl e
of capturing and treating the wide range of pollutants which can be generated on a sub -
watershed scale ; 3) end-of-pipe BMPs are more effective when used as polishing BMPs ,
rather than the sole BMP to be implemented ; 4) end-of-pipe BMPs do not protect the qualit y
or beneficial uses of receiving waters between the source and the BMP ; and 5) offsite end-
of-pipe BMPs do not aid in the effort to educate the public regarding sources of pollution an d
their prevention .
16.The risks associated with infiltration can be properly managed by many techniques ,
including : 1) designing landscape drainage features that promote infiltration of runoff, but d o
not "inject" runoff (injection bypasses the natural processes of filtering and transformatio n
that occur in the soil),2) taking reasonable steps to prevent the illegal disposal of wastes, 3 )
protecting footings and foundations, and 4) ensuring that each drainage feature i s
adequately maintained in perpetuity . However, in some circumstances, site conditions (e .g .,
historical soil contamination) and the type of development (i .e., urban infill) can limit th e
feasibility of retaining, infiltrating, and reusing stormwater at sites .
17.Redevelopment projects involve work on sites with existing impervious surfaces and othe r
disturbances that contribute pollutants to receiving waters and potentially impact watershe d
processes such as infiltration . Though implementation of infiltration based LID measure s
may be constrained by these conditions, post-construction stormwater management applie d
to redevelopment projects still holds the potential to partially mitigate these existing impact s
as well as the impacts associated with the new or expanded portions of the project .
18.Providing long-term operation and maintenance of structural flow/volume control an d
treatment BMPs is necessary so that the BMPs maintain their intended effectiveness a t
managing runoff flow/volume and removing pollutants . If BMPs are not properly maintained ,
new development and redevelopment will cause degradation of watershed processes .
19.When water quality impacts are considered during the planning stages of a project, ne w
development and many redevelopment projects can more efficiently incorporate measure s
to protect water quality and beneficial uses . Planning decisions should account for potentia l
stormwater impacts to reduce pollutant loading and manage flows in order to maintain an d
restore watershed processes as necessary to protect water quality and beneficial uses .
20.Infiltration and subsurface flow are the dominant hydrologic processes across all intact
watersheds of the Central Coast region . Different physical landscapes, defined by thei r
surface geology and slope, respond differently to the changes in watershed processe s
imposed by urbanization, but the shift from infiltration to surface flow is ubiquitous .
21.The Post-Construction Requirements' emphasis on protecting and, where degraded ,
restoring key watershed processes is necessary to create and sustain linkages betwee n
hydrology, channel geomorphology, and biological health necessary for healthy watersheds .
These linkages cannot be created by fine-tuning any particular flow attribute (e .g ., peak ,
duration) or reconstructing a desired geomorphic feature alone .Instead, these critica l
linkages only occur where key watershed processes are intact .
22.Section 402 (p) of the Clean Water Act requires the Administrator of the United States
Environmental Protection Agency (USEPA) or her designated agent, in this instance, th e
Central Coast Water Board, to require as part of the stormwater program "controls to reduce
SS2-31-
CITY STAFF REPORT - ATTACHMENT 2 -5
Draft Resolution No. R3-2012-0025 -5 September 6, 201 2
the discharge of pollutants to the maximum extent practicable, including managemen t
practices, control techniques and system, design and engineering methods, and such othe r
provisions as the Administrator or the State determines appropriate for the control of suc h
pollutants ." [USC Section 1342 (p)(3)(B)]. The maximum extent practicable (MEP) standar d
is an ever-evolving, flexible, and advancing concept, which considers technical an d
economic feasibility . As knowledge about controlling urban runoff continues to evolve, s o
does that which constitutes MEP . Reducing the discharge of stormwater pollutants to th e
MEP in order to protect beneficial uses requires review and improvement, which include s
seeking new opportunities, such as establishing these Post-Construction Requirements .
Establishinq Post-Construction Requirements
23.This Resolution enacts Post-Construction Requirements which fulfill the Joint Effort BMPs i n
the Joint Effort MS4s' SWMPs requiring development of hydromodification control criteri a
and applicability thresholds .
24.The Post-Construction Requirements enacted by this Resolution protect the beneficial use s
of Waters of the United States . The intent of the Post-Construction Requirements enacte d
by this Resolution is to focus on those discharges that threaten beneficial uses, and t o
require implementation of BMPs to reduce stormwater pollutant discharges to the MEP and
protect water quality and beneficial uses . The Post-Construction Requirements enacted b y
this Resolution are consistent with the evolving MEP standard .
25.This action to adopt this Resolution is exempt from the provisions of the Californi a
Environmental Quality Act (Public Resources Code §21100, et seq .) in accordance wit h
section 13389 of the Porter-Cologne Water Quality Control Act (Porter-Cologne, Division 7
of the California Water Code).
26.The Post-Construction Requirements, developed by the Joint Effort, will become effectiv e
upon approval of this Resolution by the Central Coast Water Board .
Stakeholder Involvement
26 . On August 27, 2009, September 3, 2009, and September 8, 2009, Central Coast Wate r
Board staff held stakeholder workshops around the Central Coast region to provide a n
opportunity for stakeholders to help select project milestones for the two-year Joint Effor t
process . At the October 23, 2009, December 9, 2010, December 11, 2011, and March 15 ,
2012 Central Coast Water Board Meetings, staff provided updates on the Joint Effort to th e
public and Board Members . Central Coast Water Board staff established the Joint Effor t
Review Team (JERT), consisting of stakeholders representing the regulated governmenta l
agencies, environmental management agencies, developers, and technical consultants, t o
provide review of Joint Effort project deliverables . The JERT met for the first time Decembe r
15, 2010, and held its seventh meeting March 28, 2012 . On February 9 and October 31 ,
2011, Central Coast Water Board staff distributed to stakeholders Joint Effort updates an d
status reports . In December 2011 and January 2012, Central Coast Water Board staf f
conducted outreach to Joint Effort MS4s on the status of the Joint Effort . On February 1 5
and 16, 2012, Central Coast Water Board staff conducted workshops to provide updates o n
the Joint Effort .
27.Central Coast Water Board staff implemented a process to inform interested persons an d
the public and solicit comment on the Post-Construction Requirements developed throug h
SS2-32
CITY STAFF REPORT - ATTACHMENT 2 -6
Draft Resolution No . R3-2012-0025 -6-September 6, 2012
the Joint Effort . On June 5th and 6 th ,2012, Central Coast Water Board staff conducte d
workshops on the Post-Construction Requirements . On May 14, 2012, staff issued a publi c
notice indicating that the Central Coast Water Board would consider adoption of the Post
Construction Requirements . The public notice provided the public a 53-day public commen t
period preceding the Central Coast Water Board hearing . Central Coast Water Board staf f
responded to oral and written comments received from the public . All public comments wer e
considered . Public notice of the public hearing was given by electronic mail on XXX 201 2
Relevant documents and notices were also made available on the Central Coast Wate r
Board website .
28 . On September 6, 2012, in San Luis Obispo California, the Central Coast Water Board held a
public hearing and heard and considered all public comments and evidence in the record .
THEREFORE, be it resolved that :
1.The Post-Construction Requirements, as defined in Attachment 1 are appropriate an d
effective requirements for small MS4s subject to the post-construction requirements of th e
current and subsequent Phase II municipal General Permits to apply to developmen t
projects, in order to protect watershed processes so that beneficial uses of receiving water s
affected by stormwater management are maintained and, where applicable, restored .
2.The Central Coast Water Board adopts the Post-Construction Requirements, as defined i n
Attachment 1, as the minimum post-construction criteria that Central Coast Joint Effort MS4 s
must apply to applicable new development and redevelopment projects in order to protect
water quality and comply with the MEP standard and Phase II Municipal General Permi t
section D, which requires implementation of the SWMP and its incorporated BMPs .
3.As minimum criteria, MS4s may establish criteria more stringent than the Post-Constructio n
Requirements as defined in Attachment 1 . The MS4 may determine the need for greate r
stringency based on specific factors and conditions affecting implementation of the Post -
Construction Requirements . Greater stringency may be achieved by lower applicabilit y
thresholds where practical ; additional site design and runoff reduction requirements ; an dmorerigorous flow control (peak management) criteria than indicated in the Pos t
Construction Requirements as defined in Attachment 1 .
4.Central Coast Joint Effort MS4s shall amend or attach the Post-Construction Requirements ,as defined in Attachment 1, to their SWMP, so that the Post-Construction Requirements ar e
a part of the SWMPs . The Central Coast Water Board Executive Officer, through th e
certification of this Resolution, hereby approves these modifications to the SWMPs .
5.By March 13, 2013, the Central Coast Joint Effort MS4s shall apply the Post-Constructio n
Requirements to all regulated projects as defined in Attachment 1 . Central Coast Join t
Effort MS4s shall continue to apply the Post-Construction Requirements to all regulate d
projects as defined in Attachment 1, pursuant to subsequent Phase II Municipal Genera l
Permits, unless the Central Coast Water Board Executive Officer requires otherwise .
6.The Central Coast Water Board adopts the Post-Construction Requirements, as defined i n
Attachment 1, as the minimum post-construction criteria that the City of Salinas must appl y
to applicable new development and redevelopment projects in order to protect water qualit y
and comply with the MEP standard and Order No . R3-2012-0005, NPDES Permit No .
SS2-33
CITY STAFF REPORT - ATTACHMENT 2 -7
Draft Resolution No . R3-2012-0025 -7 -September 6, 201 2
CA0049981, Waste Discharge Requirements for City of Salinas Municipal Stormwate r
Discharges .
I, Roger W . Briggs, Executive Officer, do hereby certify the foregoing is a full, true, and correc t
copy of the resolution adopted by the California Regional Water Quality Control Board, Centra l
Coastal Region on September 6, 2012 .
Roger W . Brigg s
Executive Office r
ATTACHMENT 1 : Draft Post-Construction Stormwater Management Requirements fo r
Development Projects in the Central Coast Region
ATTACHMENT 2:Draft Technical Support Document for Post-Construction Stormwate r
management Requirements for Development Projects in the Central Coast Region
SS2-34
CITY STAFF REPORT - ATTACHMENT 2
3an Lu ;c Obi=p.~o
17 .1
D■t soul ce s
Watershed management zones : Stillwater Seen , 0 2
Base data ESRI 2010
Stillwater Science s
wwwstiliwate!sci .com
CITY STAFF REPORT - ATTACHMENT 2 -9
ATTACHMENT 1
DRAFT POST-CONSTRUCTION STORMWATER MANAGEMENT REQUIREMENT S
FOR DEVELOPMENT PROJECTS IN THE CENTRAL COAST REGIO N
TABLE of CONTENT S
A .Watershed Management Zones (WMZs)1B. Post-Construction Requirements 11)Regulated Projects 12)Performance Requirement No . 1 : Site Design and Runoff Reduction 33)Performance Requirement No . 2 : Water Quality Treatment 44)Performance Requirement No . 3 : Runoff Retention 65)Performance Requirement No . 4 : Peak Management 1 06)Performance Requirement No . 5 : Special Circumstances 1 2
7)Required Hydrologic Analysis 1 4C. Alternative Compliance (Off-Site Compliance)1 41)Technical Infeasibility 1 42)Approved Watershed or Regional Plan 1 43)Approved Urban Sustainability Area 1 5D. Field Verifications of Post-Construction Stormwater Control Measures 1 6E. Operation and Maintenance for Structural SCMs 1 7
1)O&M Plan 1 72)Maintenance Agreement and Transfer of Responsibility for SCMs 1 73)Structural Stormwater Control Measure O&M Database 1 8F. Permittee Reporting Requirements 1 8ATTACHMENT A : Watershed Management Zones 20ATTACHMENT B : Designated Groundwater Basins 2 1ATTACHMENT C : Definitions Related to Post-Construction Requirements 24
SS2-36
CITY STAFF REPORT - ATTACHMENT 2 - 1 0ATTACHMENT1
A. Watershed Management Zones (WMZs )
The urbanized portions of the Central Coast Region are categorized into 10 Watershe d
Management Zones (WMZs), based on common key watershed processes an d
receiving water type (creek, marine nearshore waters, lake, etc). Maps in Attachment A
illustrate the WMZs for the Central Coast Region's urbanized areas . Designate d
Groundwater Basins of the Central Coast Region (Attachment B) underlie some but no t
all WMZs in urbanized portions of the Central Coast Region . The map and table i n
Attachment B illustrates the Groundwater Basins of the Central Coast Region . Eac h
WMZ and, where present, Groundwater Basin, is aligned with specific Post -
Construction Stormwater Management Requirements to address the impacts o f
development on those watershed processes and beneficial uses .
1)The Permittee shall maintain the ability to identify the WMZs and their boundaries ,
and to determine the WMZ in which development projects are proposed, throughou t
the urbanized portions of their jurisdiction corresponding with the Phase II Municipa l
Stormwater Permit boundary .
2)The Permittee shall maintain the ability to determine whether development project s
are proposed in areas overlying designated Groundwater Basins, throughout th e
urbanized portions of their jurisdiction subject to the Phase II Municipal Stormwate r
Permit .
B . Post-Construction Requirement s
The primary objective of these Post-Construction Stormwater Managemen t
Requirements (hereinafter, Post-Construction Requirements) is to ensure that th e
Permittee is reducing pollutant discharges to the Maximum Extent Practicable an d
preventing stormwater discharges from causing or contributing to a violation of receivin g
water quality standards in all applicable development projects that require approval s
and/or permits issued under the Permittee's planning, building, or other comparabl e
authority . The Post-Construction Requirements emphasize protecting and, wher e
degraded, restoring key watershed processes to create and sustain linkages betwee n
hydrology, channel geomorphology, and biological health necessary for health y
watersheds . Maintenance and restoration of watershed processes impacted b y
stormwater management is necessary to protect water quality and beneficial uses .
1) Regulated Project s
Regulated Projects include all New Development or Redevelopment projects tha t
create and/or replace >2,500 square feet of impervious surface (collectively over th e
entire project site), including the following road projects/practices :
a)Removing and replacing a paved surface resulting in alteration of the original lin e
and grade, hydraulic capacity or overall footprint of the roa d
b)Extending the pavement edge without increasing the size of the road prism, o r
paving graveled shoulders
c)Resurfacing by upgrading from dirt to asphalt, or concrete ; upgrading from grave l
to asphalt, or concrete ; or upgrading from a bituminous surface treatment ("chi p
seal") to asphalt or concrete
d)Regulated Projects do not include :
i) Road maintenance :
SS2-37
CITY STAFF REPORT - ATTACHMENT 2 - 1 1ATTACHMENT1
Draft Resolution No . R3-2012-0025 -2-September 6, 201 2
(1)Pothole and square cut patchin g
(2)Overlaying existing asphalt or concrete pavement with asphalt or concret e
without expanding the area of coverag e
(3)Shoulder gradin g
(4)Reshaping/regrading drainage system s
(5)Crack sealing
(6)Resurfacing with in-kind material without expanding the road pris m
(7)Practices to maintain original line and grade, hydraulic capacity, an d
overall footprint of the roa d
ii)Sidewalk and bicycle path projects, where no other impervious surfaces ar e
created or replaced, built to direct stormwater runoff to adjacent vegetate d
area s
iii)Trails and pathways, where no other impervious surfaces are replaced o r
created, and built to direct stormwater runoff to adjacent vegetated area s
iv)Underground utility projects that replace the ground surface with in-kin d
material or materials with similar runoff characteristic s
v)Curb and gutter improvement or replacement projects that are not part of an y
additional creation or replacement of impervious surface area (e .g .,
sidewalks, roadway )
vi)Second-story additions that do not increase the building footprin t
vii)Raised (not built directly on the ground) decks, stairs, or walkways designe d
with spaces to allow for water drainag e
viii)Photovoltaic systems installed on/over existing roof or other imperviou s
surfaces
ix)Temporary structures (in place for less than six months )
x)Electrical and utility vaults, sewer and water lift stations, backflows and othe r
utility device s
xi)Above-ground fuel storage tanks and fuel farms with spill containment syste m
e) For all New Development Regulated Projects :
i)Site Design Measures shall be applied throughout the Regulated Project sit e
ii)Water Quality Treatment, Runoff Retention, and Peak Managemen t
Performance Requirements, as applicable to the Regulated Project, shal l
apply to the entire site .
f) For Redevelopment Regulated Projects :
i)Site Design Measures shall be applied throughout the Regulated Project sit e
ii)Water Quality Treatment and Runoff Retention Performance Requirement s
shall apply to runoff generated from new and replaced impervious surfaces o n
the Regulated Project sit e
iii)Peak Management Performance Requirements shall apply only to th e
additional runoff generated by increased impervious surfaces on th e
Regulated Project sit e
iv)Water Quality Treatment Performance Requirements shall apply to the runof f
from existing, new, and replaced impervious surfaces on sites where runoff
from existing impervious surfaces cannot be separated from runoff from ne w
and replaced impervious surfaces
SS2-38
CITY STAFF REPORT ATTACHMENT 2 - 1 2
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -3-September 6, 201 2
The Permittee shall apply the Post-Construction Requirements to all applicabl e
Regulated Projects that require approvals and/or permits issued under th e
Permittee's planning, building, or other comparable authority, within 180 days o f
Central Coast Water Board approval of the Post-Construction Requirements .
Applicable projects include both private development requiring permits, an d
public projects :
i) Private Development Project s
(1)Discretionary Projects If the project is subject to a vesting tentative ma p
or development agreement, the Permittee shall apply the Post -
Construction Requirements to those projects that have not received a
vested tentative map or development agreement within 180 days o f
Central Coast Water Board approval of the Post-Constructio n
Requirements .For all applicable development projects requirin g
discretionary approvals that are not subject to a vesting tentative map o r
development agreement, or which have an expired vesting tentative ma p
or development agreement, the Permittee shall apply the Post -
Construction Requirements within 180 days of Central Coast Water Boar d
approval of the Post-Construction Requirements . Discretionary approval s
include, but are not limited to the following : general plan amendment, trac t
or parcel map, subdivision map, zoning change or rezoning, tentativ e
map,conditional use permit, or other development approval .
(2)Ministerial Projects – If a project is subject to ministerial approval, th e
Permittee shall apply the Post-Construction Requirements within 180 day s
of Central Coast Water Board approval of the Post-Constructio n
Requirements . If the applicable project receives multiple ministeria l
approvals, the Permittee shall apply the Post-Construction Requirement s
to the first ministerial approval within 180 days of Central Coast Wate r
Board approval of the Post-Construction Requirements . Ministerial
approvals include, but are not limited to, building permits, site engineerin g
improvements, and grading permits .
ii) Public Development Project s
(1) The Permittee shall develop and implement an equivalent approach, to th e
approach used for private development projects, to apply the Pos t
Construction Requirements to applicable public development projects ,
including projects of the University of California at Santa Cruz and Sant a
Barbara .
2) Performance Requirement No . 1 : Site Design and Runoff Reductio n
a) The Permittee shall require all Regulated Projects that create and/or replace >
2,500 square feet of impervious surface, including detached single-family hom e
projects, to utilize the following site design and runoff reduction measures, wher e
feasible :
i)Prevent disturbance of creeks and natural drainage feature s
ii)Minimize compaction of native soil s
iii)Limit clearing and grading of native vegetation at the site to the minimum are a
needed to build the project, allow access, and provide fire protection
SS2-3 9
g )
CITY STAFF REPORT - ATTACHMENT 2 - 1 3
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -4-September 6, 201 2
iv)Minimize impervious surfaces by concentrating improvements on the least -
sensitive portions of the site, while leaving the remaining land in a natura l
undisturbed state
v)Direct roof runoff into cisterns or rain barrels for reus e
vi)Direct roof runoff onto vegetated area s
vii)Direct runoff from sidewalks, walkways, and/or patios onto vegetated area s
viii)Direct runoff from driveways and/or uncovered parking lots onto vegetate d
area s
ix) Construct bike lanes, driveways, uncovered parking lots, sidewalks ,
walkways, and patios with permeable surface s
b) The Permittee shall confirm that projects comply with Site Design and Runof f
Reduction Performance Requirements by means of appropriate documentatio n
(e .g ., check lists) accompanying applications for project approval .
3) Performance Requirement No . 2 : Water Quality Treatmen t
a)The Permittee shall require Regulated Projects that create and/or replace >
5,000 square feet of net impervious surface area, and detached single-famil y
homes that create and/or replace >15,000 square feet of impervious surface, t o
treat stormwater runoff as required in the Water Quality Treatment Performanc e
Requirements in Section (3 .b .) to reduce pollutant loads and concentration s
using physical, biological, and chemical removal .
i) Net impervious surface area is the sum of new and reconstructed imperviou s
areas, minus any new pervious area created by elimination or demolition o f
existing on-site impervious surfaces : Net Impervious Area = (New an d
Replaced Impervious Area) – (New Pervious Area)
b)The Permittee shall require each Regulated Project subject to Water Qualit y
Treatment Performance Requirements to treat runoff using the onsite measure s
below, listed in the order of preference (highest to lowest):
i)Low Impact Development (LID) Treatment Systems – Implement harvestin g
and re-use, infiltration, and evapotranspiration Stormwater Control Measure s
that collectively achieve the following hydraulic sizing criteria for LID systems :
(1) Hydraulic Sizing Criteria for LID Treatment Systems - LID systems shal l
be designed to retain stormwater runoff equal to the volume of runof f
generated by the 85th percentile 24-hour storm event, based on loca l
rainfall data .
ii)Biofiltration Treatment Systems – Implement biofiltration treatment system s
using facilities that must be demonstrated to be at least as effective as a
biofiltration treatment system with the following design parameters :
(1) Maximum surface loading rate appropriate to prevent erosion, scour an d
channeling within the biofiltration treatment system itself and equal to 5
inches per hour, based on the flow of runoff produced from a rain even t
equal to or at least :
(a)0 .2 inches per hour intensity ; o r
(b)Two times the 85th percentile hourly rainfall intensity for the applicabl e
area, based on historical records of hourly rainfall depth
(2) Minimum surface reservoir volume equal to surface area times a depth o f
6 inches
SS2-40
CITY STAFF REPORT - ATTACHMENT 2 - 1 4
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -5-September 6, 201 2
(3)Minimum planting medium depth of 24 inches . The planting medium mus t
sustain a minimum infiltration rate of 5 inches per hour throughout the lif e
of the project and must maximize runoff retention and pollutant removal .
A mixture of sand (60%-70%) meeting the specifications of America n
Society for Testing and Materials (ASTM) C33 and compost (30%-40%)
may be used .
(4)Proper plant selectio n
(5)Subsurface drainage/storage (gravel) layer with an area equal to th e
surface area and having a minimum depth of 12 inche s
(6)Underdrain with discharge elevation at top of gravel laye r
(7)No compaction of soils beneath the facility (ripping/loosening of soil s
required if compacted )
(8)No liners or other barriers interfering with infiltratio n
iii) Non-Retention Based Treatment Systems Implement Stormwater Contro l
Measures that collectively achieve at least one of the following hydrauli c
sizing criteria for non-retention based treatment systems :
(1) Hydraulic Sizing Criteria for Non-Retention Based Treatment Systems :
(a) Volume Hydraulic Design Basis – Treatment systems whose primar y
mode of action depends on volume capacity shall be designed to trea t
stormwater runoff equal to the volume of runoff generated by the 85t h
percentile 24-hour storm event, based on local rainfall data .
'(b) Flow Hydraulic Design Basis – Treatment systems whose primar y
mode of action depends on flow capacity shall be sized to treat :
(i)The flow of runoff produced by a rain event equal to at least tw o
times the 85th percentile hourly rainfall intensity for the applicabl e
area, based on historical records of hourly rainfall depths ; o r
(ii)The flow of runoff resulting from a rain event equal to at least 0 .2
inches per hour intensity .
c) Stormwater Control Plan Requirements – For each Regulated Project subject t o
the Water Quality Treatment Performance Requirement, the Permittee shal l
require the Project Applicant to provide the below information in a Stormwate r
Control Plan . The Permittee shall not grant final project approval, until th e
Stormwater Control Plan for the Regulated Project sufficiently demonstrates th e
Regulated Project design meets the Water Quality Treatment Performanc e
Requirements .
i)Water Quality Treatment Reporting Requirement s
ii)Project name, application number, location including address an d
assessor's parcel numbe r
iii)Name of Applican t
iv)Project Phase number (if project is being constructed in phases )
v)Project Type (e .g ., commercial, industrial, multi-unit residential, mixed-use ,
public), and descriptio n
vi)Total project site are a
vii)Total new impervious surface area, total replaced impervious surface area ,
total new pervious area, and calculation of Net Impervious Area
SS2-41
CITY STAFF REPORT - ATTACHMENT 2 - 1 5
ATTACHMENT 1Draft Resolution No . R3-2012-0025 -6-September 6, 201 2
viii)Statement of Water Quality Treatment Performance Requirements tha tapply to the Projec t
ix)Summary of Site Design and Runoff Reduction Performance Requiremen tmeasures selected for the projec t
x)Description of all post-construction structural Stormwater Control Measure sxi)Supporting calculations used to comply with the applicable Water Qualit yTreatment Performance Requirement s
xii)Documentation certifying that the selection, sizing, and design of th e
Stormwater Control Measures meet the full or partial Water Qualit yTreatment Performance Requiremen t
xiii)Water quality treatment calculations used to comply with Water Qualit y
Treatment Performance Requirement and any analysis to suppor t
infeasibility determinatio n
xiv)Statement of Compliance :
(1) Statement that Water Quality Treatment Performance Requirement ha sbeen met on-site, or, if not achievable :
(a)Documentation of the volume of runoff for which compliance cannot b e
achieved on-site and the associated off-site compliance requirements .(b)Statement of intent to comply with Water Quality Treatmen t
Performance Requirement through Alternative Complianc e
4) Performance Requirement No . 3 : Runoff Retentio n
a)The Permittee shall require Regulated Projects that create and/or replac e
>15,000 square feet of impervious surface in WMZs 1, 2, 5, 6, 8 and 9, and thos e
portions of WMZs 4, 7, and 10 that overlie designated Groundwater Basin s
(Attachment B) to meet the Runoff Retention Performance Requirements i nSections 4 .b-c) using the LID Development Standards in Section 4 .e . for optima l
management of watershed processes .
b)Adjustments to these Runoff Retention Performance Requirements are possibl e
for Redevelopment Projects (Section 4 .d .) and Special Circumstances (Sectio n6).
c)The Permittee shall require Regulated Projects, subject to the Runoff Retentio n
Performance Requirements, to meet the following Performance Requirements :
i) Watershed Management Zone 1 and portions of Watershed Managemen t
Zones 4, 7 and 10 which overlie designated Groundwater Basins :(1)Retain 95th Percentile Rainfall Event – Prevent offsite discharge fro m
events up to the 95 th percentile 24-hour rainfall event as determined fro mlocal rainfall data .
(2)Compliance must be achieved via infiltratio n
ii) Watershed Management Zone 2 :
(1)Retain 95th Percentile Rainfall Event – Prevent offsite discharge fro m
events up to the 95 th percentile 24-hour rainfall event as determined fro m
local rainfall data .
(2)Compliance must be achieved via storage, rainwater harvesting ,
infiltration, and/or evapotranspiration .
iii) Watershed Management Zones 5 and 8 :
SS2-42
CITY STAFF REPORT - ATTACHMENT 2- 1 6
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -7-September 6, 201 2
(1)Retain 85th Percentile Rainfall Event – Prevent offsite discharge fro m
events up to the 85 t h percentile 24-hour rainfall event as determined fro m
local rainfall data .
(2)Compliance must be achieved via infiltration .
iv) Watershed Management Zones 6 and 9 :
(1)Retain 85th Percentile Rainfall Event – Prevent offsite discharge fro m
events up to the 85 th percentile 24-hour rainfall event as determined fro m
local rainfall data .
(2)Compliance must be achieved via storage, rainwater harvesting ,
infiltration, and/or evapotranspiration .
d) Adjustments to the Runoff Retention Performance Requirements fo r
Redevelopment – Where the Regulated Project includes replaced impervious
surface, the following adjustments apply :
i)Redevelopment Projects outside an approved Urban Sustainability Area, a s
described in Section C .3 . – The total amount of replaced impervious surface ,
subject to Runoff Retention Performance Requirements, shall be multiplied by
0 .5 when calculating the volume of runoff to be retained .
ii)Redevelopment Projects located within an approved Urban Sustainabilit y
Area (Section C .3 .) - The total amount of new and replaced imperviou s
surface, subject to Runoff Retention Performance Requirements, shall b e
multiplied by 0 .5 when calculating the volume of runoff to be retained .
e) LID Standards – The Permittee shall require Regulated Projects, subject t o
Runoff Retention Performance Requirements, to meet Runoff Retentio n
Performance Requirements (Section 4 .c .i .-iv .) using the following LI D
Development Standards :
i) Site Assessment Measures – Permittees shall require the applicant for eac h
Regulated Project to identify opportunities and constraints to implement LI D
Stormwater Control Measures . Permittees shall require the applicant t o
document the following, as appropriate to the development site :
•Site topograph y
•Hydrologic features including contiguous natural areas, wetlands ,
watercourses, seeps,or spring s
• Depth to seasonal high groundwate r
•Locations of groundwater wells used for drinking wate r
•Depth to an impervious layer such as bedroc k
•Presence of unique geology (e .g ., karst)
• Geotechnical hazard s
• Documented soil and/or groundwater contaminatio n
•Soil types and hydrologic soil groups
•Vegetative cover/tree s
•Run-on characteristics (source and estimated runoff from offsite whic h
discharges to the project area )
•Existing drainage infrastructure for the site and nearby areas including th e
location of municipal storm drain s
+Structures including retaining walls
SS2-43
Draft Resolution No . R3-2012-0025
CITY STAFF REPORT - ATTACHMENT 2 - 1 7
ATTACHMENT 1
September 6, 201 2
•Utilitie s
•Easements
•Covenant s
Zoning/Land Us e
•Setbacks
• Open space requirement s
Other pertinent overlay(s )
ii) Site Design Measures – Permittees shall require the applicant for eac h
Regulated Project to optimize the use of LID site design measures, a s
feasible and appropriate at the project site :
•Define the development envelope and protected areas, identifying area s
that are most suitable for development and areas to be left undisturbe d
• Conserve natural areas, including existing trees, other vegetation, and soil s
Concentrate development on portions of the site with less permeable soil s
and preserve areas that can promote infiltratio n
•Limit the overall impervious footprint of the projec t
•Construct streets, sidewalks, or parking lot aisles to the minimum width s
necessary, provided that public safety or mobility uses are no t
compromise d
• Set back development from creeks, wetlands, and riparian habitat s
▪Conform the site layout along natural landform s
•Avoid excessive grading and disturbance of vegetation and soil s
•Minimize disturbance to the site's natural drainages (e .g ., natural swales ,
topographic depressions, etc .)
iii) Delineation of discrete Drainage Management Areas (DMAs) – The Permitte e
shall require each Regulated Project to delineate DMAs to support a
decentralized approach to stormwater management .
(1)The Permittee shall require the applicant for each Regulated Project t o
provide a map or diagram dividing the entire project site into discret e
DMA s
(2)The Permittee shall require the applicant for each Regulated Project t o
account for the drainage from each DMA using measures identified i n
Sections 4 .d .iv . and 4 .d .v ., below .4 .e ?
iv) Site Runoff Reduction Measures - Permitees shall require each Regulate d
Project to implement Site Runoff Reduction Measures, where feasible, t o
reduce the amount of runoff for which retention and treatment is required .
Any remaining volume subject to the Runoff Retention Performanc e
Requirement must be addressed using structural Stormwater Contro l
Measures (Section 4 ..v .). Site Runoff Reduction Measures include th e
following :
SS2-44
CITY STAFF REPORT - ATTACHMENT 2 - 1 8
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -9-September 6, 201 2
(1)Undisturbed or areas planted with native vegetation that do not receiv e
runoff from other areas may be considered self-treating and no additiona l
stormwater management is required .
(2)Runoff from impervious surfaces may be directed to undisturbed or natura l
landscaped areas when the applicant can demonstrate the runoff from th e
impervious surfaces will be infiltrated and will not produce runoff to th e
storm drain system, or a surface receiving waterbody, or create nuisance
ponding that may affect vegetation health or contribute to vector issues .
v) Structural Stormwater Control Measures - Permittees shall require that runoff
from the Regulated Project that cannot be managed using Site Desig n
(Section 4 .e .ii .)or Runoff Reduction measures (Section 4 .e .iv .) bedirected t o
one or more Structural Stormwater Control Measures .
(1) Structural Stormwater Control Measures that optimize protection an d
restoration of watershed processes, such as those associated with small -
scale, decentralized, LID measures, shall be prioritized . Structura l
Stormwater Control Measures consistent with LID principles of retentio n
and/or treatment via infiltration, evapotranspiration, filtration, or capture
and reuse, include :
(a)Bioretention (infiltration design )
(b)Rainwater harvesting and reuse (e .g ., cisterns)
(c)Pervious Pavement (infiltration design )
(d)Vegetated Roof s
(e)Soil Amendment s
(2) LID Stormwater Control Measure/Best Management Practice (BMP )
Selection and Design Guidance – Guidance is available from the followin g
resources :
(a)The Southern California LID BMP Manua l
(b)The Contra Costa C .3 Manua l
(c)The City of Santa Barbara LID BMP Manua l
Where LID Stormwater Control Measures and/or BMPs are not feasible, the
Permittee may allow Regulated Projects to use conventional designs to meet th e
Runoff Retention Performance Requirement (Section 4 .c .) including :
i)Infiltration (Retention) Basin s
ii)Infiltration Trenche s
iii)Dry Well s
iv)Constructed Wetland s
v)Wet Pond s
Reporting Requirements - For each Regulated Project subject to the Runof f
Retention Performance Requirement, the Permittee shall require the Projec t
Applicant to provide the below information in a Stormwater Control Plan . Th e
Permittee shall not grant final project approval, until the Stormwater Control Pla n
for the Regulated Project sufficiently demonstrates the Regulated Project desig n
SS2-4 5
)
g )
CITY STAFF REPORT - ATTACHMENT 2 - 1 9
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -10-September 6, 201 2
meets the Water Quality Treatment and Runoff Retention Performanc e
Requirements .
i)Project Name, application number, and location including address an d
assessor's parcel numbe r
ii)Name of Applican t
iii) Project Phase number (if project is being constructed in phases )
iv) Project Type (e .g ., commercial, industrial, multiunit residential, mixed-use ,
public), and descriptio n
v)Total project site are a
vi) Total new and/or replaced impervious surface are a
vii) Statement of Water Quality Treatment and Runoff Retention Performanc e
Requirements that apply to the Projec t
viii) Adjusted Requirements based on the local jurisdiction's approval, that th e
Project is allowed a Special Circumstance, Watershed or Regional Plan, o r
Urban Sustainability Area designatio n
ix) Site assessment summar y
x)LID Measures used :
(1)Site design measure s
(2)Runoff Reduction Measure s
(3)Post-construction structural Stormwater Control Measure s
xi) Summary of Runoff Reduction Measures and Structural Stormwater Contro l
Measures, by Drainage Management Area, as well as for the entire sit e
xii) Supporting calculations used to comply with the applicable Water Qualit y
Treatment and Runoff Retention Performance Requirement s
xiii) Documentation demonstrating infeasibility where on-site compliance canno t
be achieve d
xiv) Documentation of certification that the selection, sizing, and design of th e
Stormwater Control Measures meets the applicable Water Qualit y
Treatment and Runoff Retention Performance Requiremen t
xv) O&M Plan for all structural Stormwater Control Measures to ensure long -
term performanc e
xvi) Owner of facilitie s
xvii) Statement of Compliance :
(1) Statement that the Water Quality Treatment and Runoff Retentio n
Performance Requirements have been met on-site, or, if not achievable :
(a)Documentation of the volume of runoff for which compliance cannot b e
achieved on-site and the associated off-site compliance requirements .
(b)Statement of intent to comply with Water Quality Treatment and Runof f
Retention Performance Requirements through an Alternativ e
Compliance agreement .
5) Performance Requirement No . 4 : Peak Managemen t
The Permittee shall require all Regulated Projects that create and/or replac e
>22,500 square feet of impervious surface in Watershed Management Zones 1, 2, 3 ,
6, and 9 to manage peak stormwater runoff as required below (5 .a .i .), and to mee t
Water Quality Treatment and Runoff Retention Performance Requirements .
SS2-46
CITY STAFF REPORT - ATTACHMENT 2 - 2 0
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -11-September 6, 201 2
a)The Permittee shall apply the following Peak Management Performanc e
Requirements :
i) Post-development peak flows, discharged from the site, shall not exceed pre -
project peak flows for the 2- through 100-year storm events .
b)Reporting Requirements For each Regulated Project subject to the Pea k
Management Performance Requirement, the Permittee shall require the Projec t
Applicant to provide the below information in a Stormwater Control Plan . Th e
Permittee shall not grant final project approval, until the Stormwater Control Pla n
for the Regulated Project sufficiently demonstrates the Regulated Project desig n
meets the Water Quality Treatment, Runoff Retention, and Peak Managemen t
Requirements .
i)Project Name, application number, and location including address an d
assessor's parcel numbe r
ii)Name of Applicant
iii) Project Phase number (if project is being constructed in phases )
iv) Project Type (e .g ., commercial, industrial, multiunit residential, mixed-use ,
public), and descriptio n
v)Total project site are a
vi) Total new and/or replaced impervious surface are a
vii) Statement of Water Quality Treatment, Runoff Retention, and Pea k
Management Performance Requirements that apply to the Projec t
viii) Adjusted Requirements based on the local jurisdiction's approval, that th e
Project is allowed a Special Circumstance, Watershed or Regional Plan, o r
Urban Sustainability Area designatio n
ix) Site assessment summar y
x) LID Measures used :
(1)Site design measure s
(2)Runoff Reduction Measure s
(3)Post-construction structural Stormwater Control Measure s
xi) Summary of Runoff Reduction Measures and Structural Stormwater Contro l
Measures, by Drainage Management Area, as well as for the entire sit e
xii) Supporting calculations used to comply with the applicable Water Qualit y
Treatment, Runoff Retention, and Peak Management Performanc e
Requirement s
xiii) Documentation demonstrating infeasibility where on-site compliance canno t
be achieve d
xiv) Documentation of certification that the selection, sizing, and design of th e
Stormwater Control Measures meets the applicable Water Qualit y
Treatment, Runoff Retention, and Peak Management Performanc e
Requirement s
xv) O&M Plan for all structural SCMs to ensure long-term performanc e
xvi) Owner of facilitie s
xvii) Statement of Compliance :
(1) Statement that the Water Quality Treatment, Runoff Retention, and Pea k
Management Performance Requirements have been met on-site, or, i f
not achievable :
SS2-47
CITY STAFF REPORT - ATTACHMENT 2 - 2 1
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -12-September 6, 201 2
(a)Documentation of the volume of runoff for which compliance cannot b e
achieved on-site and the associated off-site compliance requirements .
(b)Statement of intent to comply with Water Quality Treatment, Runof f
Retention, and Peak Management Performance Requirements throug h
an Alternative Compliance agreement .
6) Performance Requirement No . 5 : Special Circumstance s
The Permittee may designate Regulated Projects as subject to Specia l
Circumstances based on certain site and/or receiving water conditions . The Specia l
Circumstances designation exempts a Regulated Project from Runoff Retentio n
and/or Peak Management Performance Requirements where those Performanc e
Requirements would be ineffective to maintain or restore beneficial uses of receivin g
waters . The Regulated Project subject to Special Circumstances must still compl y
with the Water Quality Treatment Performance Requirements .
a) Special Circumstances include :
i) Highly Altered Channel Special Circumstance :
The Permittee may designate Regulated Projects as subject to Specia l
Circumstances for Highly Altered Channels for the following conditions :
(1)Project runoff discharges into stream channels that are concrete-lined o r
otherwise continuously armored from the discharge point to the channel's
confluence with a lake, large river (>200-square mile drainage area).
(2)Project runoff discharges to a continuous underground storm drain syste m
that discharges directly to a lake, large river (>200-square mile drainag e
area), or marine nearshore waters
(3)Under no circumstance described in 6 .a .i . can runoff from the Regulate d
Project result in adverse impacts to downstream receiving water s
ii) Intermediate Flow Control Facility Special Circumstance :
(1)The Permittee may designate Regulated Projects as subject to Specia l
Circumstances for Intermediate Flow Control Facilities if the project runof f
discharges to an existing flow control facility that regulates flow volume s
and durations to levels that have been demonstrated to be protective o f
beneficial uses of the receiving water downstream of the facility .
(2)The flow control facility must have the capacity to accept the Regulate d
Project's runoff .
(3)Demonstration of facility capacity to accept runoff and to regulate flo w
volumes and durations must include quantitative analysis based o n
numeric, hydraulic modeling of facility performance .
(4)Under no circumstance described in 6 .a .ii . can runoff from the Regulate d
Project result in adverse impacts to downstream receiving waters .
iii) Historic Lake and Wetland Special Circumstance :
(1) The Permittee may designate Regulated Projects as subject to Specia l
Circumstances for Historic Lakes and Wetlands for the followin g
conditions :
(a) Project is located where there was once a historic lake or wetlan d
where pre-development hydrologic processes included filtration an d
SS2-48
CITY STAFF REPORT - ATTACHMENT 2 - 2 2
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -13-September 6, 201 2
storage but no significant infiltration to support downstream receivin g
water.
(b) The Special Circumstance has been established based on a
delineation of the historic lake or wetland approved by the Centra l
Coast Water Board Executive Office r
b) Performance Requirements for Highly Altered Channel and/or Intermediate Flow
Control Facility Special Circumstance s
i) For Regulated Projects that : 1) create and/or replace >22,500 square feet o f
impervious surface ;2)are located in WMZs 1, 2 5, and 8, and those portion s
of WMZs 4, 7, and 10 that overlie a designated Groundwater Basi n
(1)Water Quality Treatment (Performance Requirement No . 2 )
(2)Runoff Retention (Performance Requirement No . 3 )
ii) For Regulated Projects that :1)create and/or replace >22,500 square feet o f
impervious surface ;and 2) are located in WMZs 3, 6, and 9, and thos e
portions of WMZs 4, 7, and 10 that do not overlie a designated Groundwate r
Basin :
(1) Water Quality Treatment (Performance Requirement No . 2 )
c) Performance Requirements for Historic Lake and Wetland Specia l
Circumstances
i) For Regulated Projects that create and/or replace >15,000 and < 22,50 0
square feet of impervious surface and meet the Historic Lake and Wetlan d
Special Circumstance :
(1)Water Quality Treatmen t
(2)Detention : Detain runoff such that the post-project peak discharge rat e
does not exceed the pre-project rate for all runoff up to the 95 th percentil e
24-hr rainfall event, or a more protective rate consistent with th e
Permittee's own development requirement s
ii) For Regulated Projects that create and/or replace >22,500 square feet o f
impervious surface and meet the Historic Lake and Wetland Specia l
Circumstance :
(1)Water Quality Treatmen t
(2)Peak Management : Detain runoff such that the post-project pea k
discharge rate does not exceed the pre-project rate for the 95t h percentil e
24-hr rainfall event and the 2- through 100-yr storm events or a mor e
protective rate consistent with the Permittee's own developmen t
requirements .
d) Documentation and Approval of Special Circumstances – The Permittee shal l
provide reasonable documentation to justify that a Regulated Project is mor e
appropriately categorized under the Special Circumstances category .
i) Historic Lake and Wetland Special Circumstance - Prior to granting a
Regulated Project Special Circumstances, the Permittee shall submit a
proposal to the Central Coast Water Board Executive Officer for review an d
approval . The proposal shall include, at a minimum :
(1) Delineation of historic lakes and wetlands and any supporting technica l
information to substantiate the requested Special Circumstance s
designation ; and
SS2-49
CITY STAFF REPORT - ATTACHMENT 2 - 2 3
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -14-September 6, 201 2
(2) Documentation that the proposal was completed by a registere d
professional engineer, geologist, architect, and/or landscape architect .
7) Required Hydrologic Analysi s
The hydrologic analysis requirements for post-construction new development an d
redevelopment are as follows :
a)For Regulated Projects between 5,000 square feet and 22,500 square feet ,
single-event based analyses may be use d
b)For Regulated Projects >22,500 square feet a calibrated continuous simulatio n
hydrologic model to select stormwater control measures must be use d
C . Alternative Compliance (Off-Site Compliance )
Alternative Compliance refers to Water Quality Treatment, Runoff Retention and Pea k
Management Performance Requirements that are achieved off-site throug h
mechanisms such as developer fee-in-lieu arrangements and/or use of regiona l
facilities . Alternative Compliance may be allowed under the following circumstances :
1) Technical Infeasibilit y
Off-site compliance with Water Quality Treatment, Runoff Retention, or Pea k
Management Performance Requirements may be allowed when technica l
infeasibility limits or prevents use of structural Stormwater Control Measures .
a)To pursue Alternative Compliance based on technical infeasibility, the Regulate d
Project applicant must submit a site-specific hydrologic and/or design analysi s
conducted and endorsed by a registered professional engineer, geologist ,
architect, and/or landscape architect, demonstrating that compliance with th e
applicable numeric Post-Construction Stormwater Management Requirements i s
technically infeasible .
b)Technical infeasibility may be caused by site conditions, including :
i)Depth to seasonal high groundwater limits infiltration and/or prevent s
construction of subgrade stormwater control measure s
ii)Depth to an impervious layer such as bedrock limits infiltratio n
iii)Sites where soil types significantly limit infiltratio n
iv)Sites where pollutant mobilization in the soil or groundwater is a documente d
concer n
v)Space constraints (e .g ., infill projects, some redevelopment projects, hig h
density development)
vi)Geotechnical hazard s
vii)Stormwater control measures located within 100 feet of a groundwater wel l
used for drinking wate r
viii)Incompatibility with surrounding drainage system (e .g ., project drains to a n
existing stormwater collection system whose elevation or location preclude s
connection to a properly functioning treatment or flow control facility )
2) Approved Watershed or Regional Pla n
An approved Watershed or Regional Plan as described below (C .2 .a .), may be use d
to justify Alternative Compliance for a Regulated Project's numeric Runoff Retentio n
and Peak Management Performance Requirements without demonstrating technica l
infeasibility .
SS2-50
CITY STAFF REPORT - ATTACHMENT 2 - 2 4
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -15-September 6, 201 2
a) The Permittee must submit the proposed Watershed or Regional Plan to th e
Central Coast Water Board Executive Officer for approval.Watershed an d
Regional Plans must take into consideration the long-term cumulative impacts o f
urbanization including existing and future development and include, at minimum :
i)A description of the project(s) that will provide off-site mitigation . Th e
proposed off-site projects may be existing facilities and/or prospectiv e
projects .
ii)The location of the proposed off-site project(s), which must be within th e
same WMZ, and if possible within the same subwatershed, as the Regulate d
Project .
iii)Demonstration that implementation of projects per the Watershed or Regiona l
Plan will be as effective in maintaining watershed processes a s
implementation of the applicable Post-Construction Stormwater Requirement s
on-site . The proposal must include quantitative analysis (e .g ., calculation s
and modeling) used to evaluate off-site compliance .
iv)A schedule for completion of offsite mitigation project(s), where the off-sit e
mitigation project(s) has not been constructed .
b) The Permittee may use projects identified per the Watershed or Regional Plan to
meet Water Quality Treatment Performance Requirements off-site only when :
i)The Regulated Project applicant has demonstrated that on-site water qualit y
treatment is infeasible as described in Section C .1 .b ., an d
ii)The proposed off-site project(s) has been demonstrated to comply with th e
Water Quality Treatment Performance Requirements for the Regulate d
Project .
3) Approved Urban Sustainability Are a
The Permittee may allow Regulated Projects located within an approved Urba n
Sustainability Area to pursue Alternative Compliance for numeric Runoff Retentio n
and Peak Management Performance Requirements without demonstrating technica l
infeasibility .
a) The Urban Sustainability Area may only encompass redevelopment, hig h
density, and transit-oriented development projects that are intended to promote
infill of existing urban areas and reduce urban sprawl The Permittee mus t
submit a proposal to the Central Coast Water Board Executive Officer fo r
approval of an Urban Sustainability Area . The USA proposal must include, a t
minimum :
i) A definition and delineation of the USA for high-density infill an d
redevelopment for which area-wide approval for Alternative Compliance i s
sought .
Information and analysis that supports the Permittee's intention to balanc e
water quality protection with the needs for adequate housing, populatio n
growth, public transportation and management, land recycling, and urba n
revitalization .
iii)Demonstration that implementation of Alternative Compliance for Regulate d
Projects in the USA will meet or exceed the on-site requirements for Runof f
Retention and Peak Management . The proposal must include quantitative
SS2-51
CITY STAFF REPORT - ATTACHMENT 2 - 2 5
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -16-September 6, 201 2
analysis (e .g ., calculations and modeling) used to evaluate off-sit e
compliance .
b) The Permittee may allow Regulated Projects in a USA to meet Water Qualit y
Treatment Performance Requirements off-site only when :
i)The Regulated Project applicant has demonstrated that on-site water qualit y
treatment is infeasible as described in C .1 .a .b ., an d
ii)The proposed off-site project(s) have been demonstrated to comply with th e
Water Quality Treatment Performance Requirements .
4)Other situations as approved by the Central Coast Water Board Executive Office r
5)Location of Alternative Compliance Project(s) – Offsite mitigation projects must b e
located in the same Watershed Management Zone as the Regulated Projec t
6)Timing and Funding Requirements for Alternative Compliance Projects – Th e
Permittee shall develop a schedule for the completion of off-site mitigation projects ,
including milestone dates to identify funding, design, and construction of the off-sit e
projects .
a)Off-site mitigation projects shall be completed as soon as possible, and at th e
latest, within 4 years of the certificate of occupancy for the first project tha t
contributed funds toward the construction of the off-site mitigation project, unles s
a longer period is otherwise authorized by the Central Coast Water Boar d
Executive Officer .
b)Funding sufficient to address the off-site mitigation volume must be transferred t o
the Permittee (for public off-site mitigation projects) or to an escrow account (fo r
private off-site mitigation projects) within one year of the initiation of construction .
c)The timeline for completion of the off-site mitigation project may be extended, u p
to five years after the completion of the Regulated Project, with prior Centra l
Coast Water Board Executive Officer approval . Central Coast Water Boar d
Executive Officer approval will be granted contingent upon a demonstration o f
good faith efforts to implement an Alternative Compliance project, such as havin g
funds encumbered and applying for the appropriate regulatory permits .
D . Field Verifications of Post-Construction Stormwater Control Measure s
1)The Permittee shall establish and implement a mechanism (a checklist or othe r
tools) to verify 'that structural Water Quality Treatment, Runoff Retention, and/o r
Peak Management controls are designed and constructed in accordance with thes e
Post-Construction Stormwater Management Requirement s
2)Prior to occupancy of each Regulated Project, the Permittee shall field verify that th e
Site Design, Water Quality Treatment, Runoff Retention, and/or Peak Managemen t
controls have been implemented in accordance with these Post-Constructio n
Requirement s
'A series of checklists that can be used by both inspectors and maintenance personnel is available i n
the City of Santa Barbara Storm Water BMP Guidance Manual, Appendix H : Facility Inspection an d
Maintenance Checklists . GeoSyntec Consultants, July 2008 .
http ://www .santabarbaraca .gov/Resident/Communitv/Creeks/Low Impact Development .htm
SS2-52
CITY STAFF REPORT - ATTACHMENT 2 - 2 6
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -17-September 6, 201 2
a)The Permittee may accept third-party verification of SCMs conducted an d
endorsed by a registered professional engineer, geologist, architect, and/o r
landscape architec t
b)The Permittee shall ensure, through conditions of approval or other legall y
enforceable agreements or mechanisms, that site access is granted to al l
representatives of the Permittee, local mosquito and vector control agency staff ,
and Central Coast Water Board staff, for the sole purpose of performin g
operation and maintenance (O&M)inspections of the installed Stormwate r
Control Measure s
E . Operation and Maintenance for Structural SCM s
The Permittee shall require O&M Plans and Maintenance Agreements that clearl y
establish responsibility for all structural Water Quality Treatment, Runoff Retention ,
and/or Peak Management controls on private and public Regulated Projects . Th e
Permittee shall also maintain a structural SCM tracking database to support long-ter m
performance of structural SCMs .
1) O&M Pla n
The Regulated Project applicant shall develop and implement a written O&M Pla n
that, at a minimum, includes each component listed below . The Permittee may allo w
the Regulated Project applicant to include the O&M Plan components in th e
Stormwater Control Plan in place of developing a separate document . The
Permittee shall approve the O&M Plan prior to final approval/occupancy . The O&M
Plan must include, at minimum :
a)A site map identifying all structural Stormwater Control Measures requiring O&M
practices to function as designe d
b)O&M procedures for each structural stormwater control measure including, bu t
not limited to, LID facilities, retention/detention basins, and proprietorship
devices .
c)The O&M Plan will include short-and long-term maintenance requirements ,
recommended frequency of maintenance, and estimated cost for maintenance .
2) Maintenance Agreement and Transfer of Responsibility for SCM s
Prior to issuing approval for final occupancy each Permittee shall require tha t
Regulated Projects subject to these Post-Construction Requirements provid e
verification of ongoing maintenance provisions for Structural Stormwater Contro l
Measures, including but not limited to legal agreements, covenants, CEQ A
mitigation requirements, and or conditional use permits . Verification shall include, a t
a minimum :
a) The project owner's signed statement accepting responsibility for the O&M of th e
installed onsite and/or offsite structural treatment and flow control SCMs unti l
such responsibility is legally transferred to another entity ; and eithe r
i)A signed statement from the public entity assuming responsibility fo r
structural treatment and flow control SCM maintenance and stating that th e
SCM meets all local agency design standards ; o r
ii)Written conditions in the sales or lease agreements or deed for the projec t
that require the buyer or lessee to assume responsibility for the O&M of th e
SS2-53
CITY STAFF REPORT - ATTACHMENT 2 - 2 7
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -18-September 6, 201 2
onsite and/or offsite structural treatment and flow control SCM until suc h
responsibility is legally transferred to another entity ; o r
iii)Written text in project deeds, or conditions, covenants and restrictions fo r
multi-unit residential projects that require the homeowners association or, i f
there is no association, each individual owner to assume responsibility for th e
O&M of the onsite and/or offsite structural treatment and flow control SC M
until such responsibility is legally transferred to another entity ; o r
iv)Any other legally enforceable agreement or mechanism, such as recordatio n
in the property deed, that assigns responsibility for the O&M of the onsite
and/or offsite structural treatment and flow control SCM to the projec t
owner(s) or the Permitte e
3) Structural Stormwater Control Measure O&M Databas e
The Permittee shall develop a database with information regarding each structura l
Stormwater Control Measure installed per these Post-Construction Stormwate r
Management Requirements . The Database shall contain, at a minimum, fields for :
a) SCM identification number and location/addres s
b) Type of SC M
c) Completion date of the following project stages, where applicable :
i)Constructio n
ii)Field verification of SC M
iii)Final Project approval/occupanc y
iv)O&M plan approval by Permitte e
d) Location (physical and/or electronic) where the O&M Plan is available to vie w
e) Party responsible for O&M
f) Source of funding for O&M
g) Verification that responsible party has maintained the SCM as outlined in th e
O&M Plan, or, indication that a self-inspection program is in place to verify tha t
the SCM continues to function as designed and to repair and/or replace the SC M
if it is not functioning as designe d
h) Any problems identified during inspections including any vector or nuisanc e
problems .
F . Permittee Reporting Requirement s
1) The Permittee shall submit as part of Stormwater Program Annual Reporting ,
documentation (e .g ., permit applications including checklists of Stormwater Contro l
Measures) used in project review and approval that demonstrates the Site Desig n
and Runoff Reduction Performance Requirement (No . 1) is applied to all applicabl e
projects .
2) The Permittee shall report the following for all Regulated Projects subject to numeri c
Performance Requirements (Nos . 2, 3, 4, and 5) in Stormwater Program Annua l
Reporting :
a)The total number of completed Regulated Project s
b)The total number of Regulated Projects within each of the following categories o f
new and/or replaced impervious surface :
i) > 5,000 and <15,000 (based on Net Impervious Area)
SS2-54
CITY STAFF REPORT - ATTACHMENT 2 - 2 8
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -19-September 6, 201 2
ii) > 15,000 and < 22,50 0
Hi)>25,00 0
b) The total number of Regulated Projects granted any of the following :
i)Special Circumstances – Highly Altered Channe l
ii)Special Circumstances – Intermediate Flow Control Facilit y
iii)Special Circumstances – Historic Lake or Wetland
iv)Alternative Compliance – Technical Infeasibilit y
v)Alternative Compliance – Watershed or Regional Pla n
vi)Alternative Compliance – Urban Sustainability Are a
c) A list of mitigationprojects constructed for Alternative Compliance and th e
following project information :
i)A summary description of pollutant and flow reduction analyses (compile d
from design specifications submitted by project applicants and approved b y
the Permittee) comparing the expected aggregate results of Alternativ e
Compliance projects to the results that would otherwise have been achieve d
by meeting the numeric Performance Requirements on-sit e
ii)For public offsite mitigation projects, a summation of total offsite mitigatio n
funds raised to date and a description (including location, general desig n
concept, volume of water expected to be retained, and total estimate d
budget) of all pending public offsite mitigation project s
d) Number of Regulated Projects where Field Verification of Post-Constructio n
Stormwater Management Measures was required and was NOT complete d
e) Number of Regulated Projects where the required O&M Plan was NO T
submitted/complete d
f) Number of Regulated Projects where Ownership and Responsibility of structura l
Stormwater Control Measures was not complete d
g) Structural Stormwater Control Measure O&M Database, including element s
identified in Section E .3 .
i) The Permittee shall provide Central Coast Water Board staff electroni c
access to the database .
S'S2-55
CITY STAFF REPORT - ATTACHMENT 2 - 2 9
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -20-September 6, 201 2
ATTACHMENT A : Watershed Management Zone s
Available electronically at:
http ://www.waterboards .ca.gov/centralcoast/water issues/programs/stormwater/d
ocs/lid/lid hvdromod charette index .shtml
SS2-56-
CITY STAFF REPORT - ATTACHMENT 2 - 3 0
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -21-September 6, 201 2
ATTACHMENT B : Designated Groundwater Basin s
Groundwater basin areas are defined by the California Department of Water Resource s
(CDWR)2 and used in the Central Coast Water Board Joint Effort for Hydromodificatio n
Control to identify groundwater receiving-water issues and areas where recharge is a
key watershed process . CDWR based identification of the groundwater basins on th e
presence and areal extent of unconsolidated alluvial soils identified on a 1 :250,00 0
scale from geologic maps provided by the California Department of Conservation ,
Division of Mines and Geology . CDWR then further evaluated identified groundwate r
basin areas through review of relevant geologic and hydrogeologic reports,wel l
completion reports, court-determined adjudicated basin boundaries, and contact wit h
local agencies to refine the basin boundaries .
Designated Groundwater Basins include those identified in the CDWR Groundwate r
Basins Map . Numbers correspond to Groundwater Basins in Table 1 .
2 California Department of Water Resources . 2004 . Groundwater basin map.
<http ://www .water .ca .gov/groundwater/bulletin118/gwbasin_maps_descriptions .cfm>. Accesse d
September 15, 2006 .
Draft Resolution No . R3-2012-0025 -22 -
CITY STAFF REPORT - ATTACHMENT 2 - 3 1
ATTACHMENT 1
September 6,201 2
Central Coast Hydromadification Projec t
CDWR Grr_,t,,ndwater Basins 1 qtr ,r{.
so
?.911c;
SS2-58
CITY STAFF REPORT - ATTACHMENT 2 - 3 2
ATTACHMENT 1
Draft Resolution No .R3-2012-0025 -23-September 6, 201 2
Table 1 :Groundwater Basins in the Central Coast Region by GIS Basin Number (Se e
M a
GIS BASIN GROUNDWATER BASIN NAM E
NUMBER
Carpinteri a
2 Santa Barbar a
Montecit o
Los Osos valle y
Rinconada valley
Pozo valle y
Chorro valley 5 4
21 Morro valley 5 5
22 ' Toro valle y
23 I Carrizo Plai n
Cayucos valle y
Old valle y
Villa valle y
27 ! Santa Rosa valle y
San Simeon valle y
Arroyo de la Cruz valle y
San Carpoforo Valle y
Cholame valle y
Salinas valle y
33 Lockwood valle y
34 Salinas valle y
Big Spring are a
Rafael valley
San Luis Obispo valle y
Santa Ynez River valle y
Santa Ynez River valle y
Lockwood valle y
Mil Potrero are a
San Antonio Creek valle y
Huasna valle y
Santa Mari a
Cuyama valley
GIS BASIN GROUNDWATER BASI N
NUMBER NAM E
1 35 Peach Tree valle y
36 Hernandez valle y
37 , Salinas valle y
j 38 Bitter Water valle y
Dry Lake valle y
40 Carmel valle y
41 Salinas valle y
San Benito river valle y
43 Salinas valle y
44 Tres Pinos valle y
45 Salinas valle y
46 Upper Santa Ana valle y
Salinas valle y
Salinas valle y
Santa Ana valle y
Quien Sabe valle y
Gilroy-Hollister valle y
1 8
1 9
2 0
32
Felton are a
64 1 Santa Cruz Purisima formatio n
65 Ano Nuevo are a
6 6
56 w
57
..,
West Santa Cruz terrac e
Majors cree k
Soquel valle y
West Santa Cruz terrac e
West Santa Cruz terrac e
Gilroy Hollister valle y
Pajaro valle y
Scotts valle y
Needle Rock poin t
Gilroy-Hollister valle y
West Santa Cruz terrac e
Pescadero valle y
Santa Clara valley
SS2-59
CITY STAFF REPORT - ATTACHMENT 2 - 3 3
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -24-September 6, 201 2
ATTACHMENT C : Definitions Related to Post-Construction Requirement s
Bioretention –A Stormwater Control Measure designed to retain stormwater runof f
using vegetated depressions and soils engineered to collect, store, treat, and infiltrat e
runoff . Bioretention designs do not include underdrains .
Biotreatment or Biofiltration Treatment –A Stormwater Control Measure designed t o
detain stormwater runoff, filter stormwater through soil media and plant roots, an d
release the treated stormwater runoff to the storm drain system . Biotreatment system s
include an underdrain .
Discretionary Approval –A project approval which requires the exercise of judgmen t
or deliberation when the MS4 decides to approve or disapprove a particular activity ,
as distinguished from situations where the MS4 merely has to determine whethe r
there has been conformity with applicable statutes, ordinances, or regulations .
Dispersion –The practice of routing stormwater runoff from impervious areas, such a s
rooftops, walkways, and patios, onto the surface of adjacent pervious areas .
Stormwater runoff is dispersed via splash block, dispersion trench, or sheet flow an d
soaks into the ground as it moves slowly across the surface of the pervious area .
Drainage Management Area (DMAs) –Following the low impact development principl e
of managing stormwater through small-scale, decentralized measures, DMAs ar e
designated individual drainage areas within a Regulated Project that typically follow
grade breaks and roof ridge lines and account for each surface type (e .g ., landscaping ,
pervious paving, or roofs). Stormwater Control Measures for runoff reduction an d
structural facilities are designed for each DMA .
Evapotranspiration (ET) –The loss of water to the atmosphere by the combine d
processes of evaporation (from soil and plant surfaces) and transpiration (from plan t
tissues).
Flow-Through Water Quality Treatment Systems –Stormwater Control Measure s
that are designed to treat stormwater through filtration and/or settling . Flow-throug h
systems do not provide significant retention or detention benefits for stormwater volum e
control .
Groundwater Basins -Groundwater basin areas defined by the California Departmen t
of Water Resources (DWR) and used in the Central Coast Water Board Joint Effort fo r
Hydromodification Control to identify groundwater receiving-water issues and area s
where recharge is a key watershed process . DWR based identification of th e
groundwater basins on the presence and areal extent of unconsolidated alluvial soil s
identified on a 1 :250,000 scale from geologic maps provided by the Californi a
Department of Conservation, Division of Mines and Geology . DWR then furthe r
evaluated identified groundwater basin areas through review of relevant geologic an d
SS2-60
CITY STAFF REPORT -ATTACHMENT 2 - 3 4
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -25-September 6, 201 2
hydrogeologic reports, well completion reports, court-determined adjudicated basi n
boundaries, and contact with local agencies to refine the basin boundaries .
Rainwater Harvest –Capture and storage of rainwater or stormwater runoff for late r
use, such as irrigation (without runoff), domestic use (e .g . toilets), or storage for fire
suppr e ssion .
Impervious Surface –A hard, non-vegetated surface area that prevents or significantl y
limits the entry of water into the soil mantle, as would occur under natural condition s
prior to development . Common impervious surfaces include, but are not limited to, roo f
tops, walkways, patios, driveways, parking lots or storage areas, concrete or asphal t
paving, oiled, macadam or other surfaces which similarly impede the natural infiltratio n
of stormwater . Open, uncovered retention/detention facilities shall not be considered a s
impervious surfaces for purposes of determining whether the thresholds for applicatio n
of Performance Requirements are exceeded . However, for modeling purposes, open ,
uncovered facilities that retain/detain water (e .g .,retention ponds, pools) shall b e
considered impervious surfaces .
Land recycling –The reuse of abandoned, vacant, or underused properties fo r
redevelopment or repurposin g
Landscaped Areas –Areas of soil and vegetation not including any imperviou s
surfaces of ancillary features such as impervious patios, BBQ areas, and pools .
Large River –A river draining 200 square miles or more .
Low Impact Development (LID) – A stormwater and land use management strategy
that strives to mimic pre-disturbance hydrologic processes of infiltration, filtration ,
storage, evaporation, and transpiration by emphasizing conservation, use of on-sit e
natural features, site planning, and distributed stormwater management practices tha t
are integrated into a project design .
Ministerial Approval A project approval which involves little or no persona l
judgment by the MS4 as to the wisdom or manner of carrying out the project and onl y
involves the use of fixed standards or objective measurements .
Native Vegetation Vegetation comprised of plant species indigenous to the Centra l
Coast Region and which reasonably could have been expected to naturally occur on th e
site .
Net impervious area=The sum of new and replaced impervious areas, minus any ne w
pervious area created by elimination or demolition of existing on-site imperviou s
surfaces :Net Impervious Area =(New and Replaced Impervious Area) - (New Perviou s
Area)
CITY STAFF REPORT - ATTACHMENT 2 - 3 5
ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -26-September 6, 201 2
New Development Land disturbing activities that include the construction o r
installation of buildings, roads, driveways and other impervious surfaces . Development
projects with pre-existing impervious surfaces are not considered New Development .
Percentile Rainfall Event (e .g .,85th and 95th) – A percentile rainfall event represent s
a rainfall amount which a certain percent of all rainfall events for the period of record d o
not exceed . For example, the 95th percentile rainfall event is defined as the measure d
rainfall depth accumulated over a 24-hour period, for the period of record, which rank s
as the 95th percentile rainfall depth based on the range of all daily event occurrence s
during this period .
Permeable or Pervious Surface –A surface that allows varying amounts of
stormwater to infiltrate into the ground . Examples include pasture, native vegetatio n
areas, landscape areas, and permeable pavements designed to infiltrate .
Project Site –The area defined by the legal boundaries of a parcel or parcels of lan d
within which the new development or redevelopment takes place and is subject to thes e
Post-Construction Stormwater Management Requirements .
Receiving Waters -Bodies of water, surface water systems or groundwater tha t
receive surface water runoff through a point source, sheet flow or infiltration .
Redevelopment –On a site that has already been developed, construction o r
installation of a building or other structure subject to the Permittee's planning an d
building authority including : 1) the creation or addition of impervious surfaces ; 2) th e
expansion of a building footprint or addition or replacement of a structure ; or 3 )
structural development including construction, installation or expansion of a building o r
other structure . It does not include routine road maintenance, nor does it includ e
emergency construction activities required to immediately protect public health an d
safety .
Replaced Impervious Surface –The removal of existing impervious surfaces down t o
bare soil or base course, and replacement with new impervious surface . Replacemen t
of impervious surfaces that are part of routine road maintenance activities are no t
considered replaced impervious surfaces .
Self-Retaining Areas (also called "zero discharge" areas), are designed to retai n
some amount of rainfall (by ponding and infiltration and/or evapotranspiration) withou t
producing stormwater runoff . Self-Retaining Areas may include graded depressions wit h
landscaping or pervious pavement .
Self-Treating Areas are a portion of a Regulated Project in which infiltration ,
evapotranspiration and other natural processes remove pollutants from stormwater . Th e
self-treating areas may include conserved natural open areas and areas of nativ e
landscaping . The self-treating area only treats the rain falling on itself and does no t
receive stormwater runoff from other areas .
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ATTACHMENT 1
Draft Resolution No . R3-2012-0025 -27-September 6, 201 2
Routine Road Maintenance –includes pothole and square cut patching ; overlayin g
existing asphalt or concrete pavement with asphalt or concrete without expanding th e
area of coverage ; shoulder grading ; reshaping/regrading drainage systems ; crack
sealing ; resurfacing with in-kind material without expanding the road prism or alterin g
the original line and grade and/or hydraulic capacity of the road .
Single-Family Residence –The building of one single new house or the additio n
and/or replacement of impervious surface associated with one single existing house ,
which is not part of a larger plan of development .
Stormwater Control Measures –Stormwater management measures integrated int o
project designs that emphasize protection of watershed processes through replication o f
pre-development runoff patterns (rate, volume, duration). Physical control measure s
include, but are not limited to, bioretention/rain gardens, permeable pavements, roo f
downspout controls, dispersion, soil quality and depth, minimal excavation foundations ,
vegetated roofs, and water re-use : Design control measures include but are not limite d
to conserving and protecting the function of existing natural areas, maintaining o r
creating riparian buffers, using onsite natural drainage features, directing runoff fro m
impervious surfaces toward pervious areas, and distributing physical control measure s
to maximize infiltration, filtration, storage, evaporation, and transpiration of stormwate r
before it becomes runoff .
Stormwater Control Plan –A plan, developed by the Regulated Project applicant ,
detailing how the project will achieve the applicable Post-Construction Stormwate r
Management Requirements (for both onsite and offsite systems).
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CITY STAFF REPORT - ATTACHMENT 2 - 3 7
Post-Constructio n
Stormwater Management Requirement s
For Development Projects in th e
Central Coast Region, Californi a
Draft Technical Support Documen t
For the September 6, 201 2
Central Coast Water Board Meetin g
Prepared May 14, 201 2
CALIFORNIA REGIONAL WATER QUALITY CONTROL BOAR D
CENTRAL COAST REGIO N
895 Aerovista Place, Suite 101, San Luis Obispo, California 9340 1
Phone • (805) 549-314 7
http ://www .waterboards .ca .gov/centralcoast/
To request copies of this report please contac t
Dominic Roques at (805) 542-4780, or by email at :
d roques(a,waterboa rds .ca .go v
Documents also are available at :
http ://www .waterboards .ca .gov/centralcoast/water_issues/programs/stormwater/docs/lid/lid_hy d
romod charette index .shtml
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ATTACHMENT 2
I .Introduction 1
Contents of this Technical Support Document 1
I I . Regulatory Context 2
Ill . Watershed Management Zones 3
1)Watershed Processes 3
Watershed Processes Identified in the Central Coast Region :4
2)Landscape Assessment as Basis of Watershed Management Zones 5
Physical Landscape Zones 5
Receiving Waters 7
Watershed Management Zones 8
Summary Characteristics of the Watershed Management Zones 1 3
IV . Management Strategies for Watershed Management Zones 1 5
1)Flow Control 1 6
2)Water Quality Treatment
3)Preserve Delivery of Sediment and Organics 1 6
4)Maintain Soil and Vegetation Regime 1 6
5)Land Preservation 1 6
V . Post-Construction Performance Requirements 1 7
1)Regulated Projects 1 7
2)Performance Requirement No . 1 : Site Design and Runoff Reduction :1 7
3)Performance Requirement No . 2 : Water Quality Treatment 1 8
4)Performance Requirement No . 3 : Runoff Retention 2 0
The Basis for Requiring Runoff Retention 2 1
Retention Requirements Keyed to WMZs :2 2
Feasibility of Achieving Retention 2 3
Adjustments to the Runoff Retention Performance Requirements for Redevelopment 2 5
5)Performance Requirement No . 4 : Peak Management 2 5
6)Performance Requirement No . 5 : Special Circumstances 2 7
Historic Lake and Wetland Special Circumstance `2 7
Highly Altered Channel Special Circumstance 2 8
Intermediate Flow Control Facility Special Circumstance 2 8
7)Required Hydrologic Analysis 2 8
VI . Alternative Compliance (Off-site Compliance)2 9
Requirements for Projects Covered by a Watershed or Regional Plan 3 0
Requirements for Projects Covered by an Urban Sustainability Area 3 0
VI I . Reporting 3 1
1)Project Applicant Reporting to Permittee 3 1
2)Permittee Reporting to the Central Coast Water Board 32
VIII . References 3 2
ATTACHMENT A 34
ATTACHMENT B 3 5
ATTACHMENT C 38
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CITY STAFF REPORT - ATTACHMENT 2 - 3 9
I .Introductio n
The management of stormwater runoff from sites after the construction phase is vital t o
controlling the impacts of development on water quality . The increase in impervious surface s
such as rooftops, roads, parking lots, and sidewalks due to land development can have a
detrimental effect on aquatic systems post construction . Runoff from impervious areas ca n
contain a variety of pollutants that are detrimental to water quality, including sediment, nutrients ,
heavy metals, pathogenic bacteria, and petroleum hydrocarbons . High levels of imperviou s
cover can result in stream warming and loss of aquatic biodiversity in urban areas .
Imperviousness limits both shallow groundwater movement and recharge of underlyin g
groundwater basins . Impervious surfaces also reduce the supply of natural, beneficial sedimen t
and organic matter to receiving waters .
The main goal of post-construction stormwater management is to prevent or limit these effects .
This goal is best pursued by setting performance standards for new and redevelopment projects
to ensure the projects integrate measures into their design and construction that protect, or t o
the extent feasible restore, the natural processes that support healthy aquatic systems . Ove r
time, parcel-based requirements reduce the cumulative impacts of development at th e
watershed scale .
These Post-Construction Stormwater Management Requirements for Development Projects i n
the Central Coast Region (Post-Construction Requirements) establish the specific performanc e
criteria and related implementation measures that municipalities will use to implement post -
construction stormwater management actions . As with many other aspects of urban stormwate r
management (e .g ., illicit discharge detection and elimination, construction management, publi c
education and outreach), municipalities possess the authority to implement post-constructio n
stormwater management actions to prevent impacts from urban runoff . Through implementatio n
of these Post-Construction Requirements, municipalities will ensure that the new an d
redevelopment projects they approve integrate measures into their design and construction t o
protect, or to the extent feasible restore, the processes supporting healthy aquatic system s
throughout the life of the project .
Contents of this Technical Support Documen t
This Technical Support Document is intended to provide background, explanation an d
justification for the Post-Construction Requirements . The background discussion includes th e
regulatory context in which the Post-Construction Requirements were developed . It continue s
with a presentation of the analytical basis for developing the Watershed Management Zone s
that determine which Post-Construction Requirements are applied on a given development sit e
in the Central Coast Region .
Management Strategies are then discussed as the foundation of the specific Performance
Requirements . In Section V ., each Performance Requirement is discussed in detail as are ke y
aspects of applicability, including exempt projects . The Technical Support Document the n
describes Alternative Compliance approaches that allow for off-site compliance wit h
Performance Requirements . Additional details are also provided on reporting, including a
discussion of the Stormwater Control Plan and the central role it is expected to play in achievin g
1
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ATTACHMENT 2
implementation of Low Impact Development (LID). For each of these items, the Technica l
Support Document includes explanation and justification as necessary .
II .Regulatory Context
On April 30, 2003, the State Water Resources Control Board adopted the National Pollutan t
Discharge Elimination System (NPDES) General Permit for the Discharge of Storm Water fro m
Small Municipal Separate Storm Sewer Systems (MS4s), Order No . 2003-0005-DWQ'(Phase I I
Municipal General Permit). On February 15, 2008, the Central Coast Water Board Executiv e
Officer notified un-enrolled traditional, small MS4 stormwater dischargers and two un-enrolle d
non-traditional, small MS4 stormwater dischargers (University of California at Santa Barbar a
and Santa Cruz) of the process the Central Coast Water Board would follow for enrolling th e
MS4s under the Phase II Municipal General Permit . The Executive Officer also included in thi s
notification interim hydromodification control criteria and the expectation that dischargers '
Stormwater Management Programs (SWMPs) present a schedule for development and
adoption of long-term hydromodification control standards .
On August 4, 2009 and October 20, 2009, the Central Coast Water Board Executive Office r
notified dischargers of the option to pursue and participate in a "Joint Effort" for developin g
hydromodification control criteria, in compliance with the Phase II Municipal General Permit . Al l
traditional, small MS4 stormwater dischargers in the Central Coast agreed to participate in th e
Joint Effort by submitting a written declaration of their intent to meet the terms of participation .
Each discharger also amended their SWMP to include Best Management Practices (BMPs) t o
codify the steps of participation in the Joint Effort .
On September 2, 2010 the Central Coast Water Board hired contractors to assist in th e
development of hydromodification control criteria and on September 28, 2010, Central Coas t
Water Board staff notified traditional, small MS4 stormwater dischargers of the commencemen t
of the Joint Effort .
The Phase II Municipal General Permit requires small MS4s to develop and implement a SWM P
that describes BMPs, measurable goals, and timetables for implementation, designed to reduce
the discharge of pollutants to the maximum extent practicable (MEP) and to protect wate r
quality .The General Permit requires regulated small MS4s to require long-term post -
construction BMPs that protect water quality and control runoff flow, to be incorporated int o
development and redevelopment projects . The General Permit further requires the Permitte e
to incorporate changes required by or acceptable to the Water Board Executive Officer into th e
Permittee's SWMP and to adhere to its implementation .
These Post-Construction Requirements fulfill the Joint Effort BMPs and are the minimum post
construction criteria that Central Coast traditional, small MS4 stormwater dischargers must
apply to applicable new development and redevelopment projects in order to comply with th e
MEP standard .
Central Coast Water Board staff included specific language on what is required and how t o
demonstrate implementation of the Post-Construction Requirements . This specific languag e
describing what to do and what to report will greatly assist Water Board staff in determinin g
compliance with the Post-Construction Requirements and attainment of the MEP standard .
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III . Watershed Management Zone s
The urbanized portions of the Central Coast Region are categorized into 10 Watershe d
Management Zones (WMZs), based on common key watershed processes and receiving wate r
type (creek, ocean, lake, etc). Maps in Attachment A illustrate the WMZs for the Central Coas t
Region's urbanized areas . Designated Groundwater Basins of the Central Coast Regio n
(Attachment B) underlie some but not all WMZs in urbanized portions of the Central Coas t
Region . Each WMZ and, where present, Groundwater Basin, is aligned with specific Post -
Construction Stormwater Management Requirements (Post-Construction Requirements) t o
address the impacts of development on watershed processes and beneficial uses .
These Post-Construction Requirements require the Permittee to have the ability to determin e
the WMZ in which development projects are proposed, throughout the urbanized portions o f
their jurisdiction corresponding with the Phase II Municipal Stormwater Permit boundary . Th e
Permittee must also have the ability to determine whether development projects are proposed i n
areas overlying designated Groundwater Basins .
The maps in Attachment A illustrate the WMZs in all the urbanized areas of the Central Coast .
However, to implement these Post-Construction Requirements, Permittees may require acces s
to spatial data files of WMZs and Groundwater Basins which they can download for their ow n
use . These files are available for download at the following website :
http ://www .waterboards .ca .gov/centralcoast/water issues/programs/stormwater/docs/lid/lid hy d
romod charette index .shtm l
Permittees may also elect to identify WMZs for areas within their jurisdiction, but not depicted a s
urbanized areas on the maps in Attachment A . The spatial data available at the above websit e
provide the necessary information to designate WMZs in these areas .
The Watershed Management Zones are the basis for post-construction requirement s
appropriate to the physical context in which development occurs . A key principle underpinnin g
the WMZs is that every location on the landscape does not require the same set of stormwate r
mitigation measures, because of intrinsic differences in the key watershed processes at eac h
location and the sensitivity to those processes of the downstream receiving water(s). The Join t
Effort contractors completed technical tasks to develop and implement a methodology to identif y
Post-Construction Requirements consistent with this principle .''2'3'4'5'6'7
The following describes two critical steps conducted by the Joint Effort contractors to suppor t
the development of Post-Construction Requirements : (1) identify watershed processes that ar e
integral to receiving water health in the Central Coast Region, and (2) conduct a landscap e
assessment to identify the basis for defining Watershed Management Zones .
1) Watershed Processe s
Helmle & Booth, 2011a .
2 Helmle & Booth, 2011b .
3 Helmle & Booth, 2011c .4 Booth, et al, 2011a .
5 Booth, et al, 2011 b .
6 Booth, et al, 2012 .
Helmle, C ., 2012 .
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Watershed processes of interest in the context of stormwater management are those that hav e
their ultimate expression in receiving waters, including groundwater . Watershed processe s
across the landscape of the Central Coast Region are similar to those found in temperat e
latitudes throughout the world . Field observations, conducted across the entire geographi c
extent of the Central Coast, confirmed that conditions and processes in the intact watersheds o f
the Central Coast were overall consistent with prior assessments of watershed processes .' Th e
focus on intact watersheds provided a basis for describing what are effectively predevelopmen t
conditions . Only a few systematic and readily recognized differences distinguished differen t
suites of processes in different areas .
Broadly, all but the steepest mountain ridges and the driest hillslopes are well-vegetated ,
whether by chaparral, coastal scrub, grasslands, oak woodlands, or evergreen forest . Mos t
hillslopes are relatively ungullied, expressing a predominance of the hydrologic processes o f
infiltration and subsurface movement of water after precipitation first falls on the ground surface .
These hydrologic processes, in turn, largely control the movement of sediment and plant detrita l
material . Sediment movement is driven by gravity and so is negligible on flat ground regardles s
of the geologic material . On slopes, surface erosion (rilling, gullying) occurs only in th e
presence of surface flow, and its expression is rare (in undisturbed areas) except in a few ver y
weak rock types . Landslides (and other forms of mass wasting) are more dependent on roc k
strength, for which the Central Coast has excellent examples at both the weak (Francisca n
melange) and strong (crystalline rocks) ends of the spectrum .
In addition to the watershed processes of infiltration and subsurface movement of water, whos e
activity and influence were observed or inferred from observation, four other processes lon g
recognized from prior watershed studies were included in the subsequent application of thi s
analysis to determine effective stormwater management strategies and support these Post -
Construction Requirements . They include evapotranspiration, delivery of sediment and Organi c
matter to receiving waters, and chemical and biological transformations .
Watershed Processes Identified in the Central Coast Region :9
Overland Flow :Precipitation reaching the ground surface that does not immediately soak i n
must run over the land surface (thus, "overland" flow). Most un-compacted, vegetated soil s
have infiltration capacities of one to several inches per hour at the ground surface, whic h
exceeds the rainfall intensity of even unusually intense storms of the Central Coast and s o
confirms the field observations of little to no overland flow in undisturbed watersheds . I n
contrast, pavement and hard surfaces reduce the effective infiltration capacity of the groun d
surface to zero, ensuring overland flow regardless of the meteorological attributes of a storm ,
together with a much faster rate of runoff relative to vegetated surfaces .
Groundwater Recharge and Infiltration :These closely linked hydrologic processes ar e
dominant across most intact landscapes of the Central Coast Region . They can be thought of a s
the inverse of overland flow ; precipitation that reaches the ground surface and does no t
immediately run off has most likely infiltrated . Their widespread occurrence is expressed by th e
common absence of surface-water channels on even steep (undisturbed) hillslopes . Thus, o n
virtually any geologic material on all but the steepest slopes (or bare rock), infiltration of rainfal l
into the soil is inferred to be widespread, if not ubiquitous . With urbanization, changes to th e
8 Helmle &Booth, 2011 b . p . 3 .
Booth,et al, 2011b . p . 31 .
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process of infiltration are also quite simple to characterize : some (typically large) fraction of tha t
once-infiltrating water is now converted to overland flow .
Interflow ;Interflow takes place following storm events as shallow subsurface flow (usuall y
within 3 to 6 feet of the surface) occurring in a more permeable soil layer above a les s
permeable substrate . In the storm response of a stream, interflow provides a transition betwee n
the rapid response from surface runoff and much slower stream discharge from deepe r
groundwater . In some geologic settings, the distinction between "interflow" and "dee p
groundwater" is artificial and largely meaningless ; in others, however, there is a strong physica l
discrimination between "shallow" and "deep" groundwater movement . Development reduce s
infiltration and thus interflow as discussed previously, as well as reducing the footprint of th e
area supporting interflow volume .
Evapotranspiration :In undisturbed humid-region watersheds, the process of returning water t o
the atmosphere by direct evaporation from soil and vegetation surfaces, and by the activ e
transpiration by plants, can account for nearly one-half of the total annual water balance ; i n
more arid regions, this fraction can be even higher . Development covers soils with imperviou s
surfaces and usually results in the compaction of soils when grading occurs . Native plants ar e
often replaced with turf, which typically has lower rates of evapotranspiration unless irrigate d
throughout the summer months .
Delivery of Sediment to Receiving Waters :Sediment delivery into the channel network is a
critical process for the maintenance of various habitat features in fluvial systems (althoug h
excessive sediment loading from watershed disturbance can instead be a significant source o f
degradation). Quantifying this rate can be difficult and discriminating the relative contributio n
from different geologic materials even more so ; however, the overriding determinism of hillslop e
gradient is widely documented . In the post-construction period, maintenance of sedimen t
delivery is essential to the health of certain receiving-water types (as is organic matter delivery),
and it is this (long-term) process that is being addressed here . Development commonly cover s
surfaces, and non-native vegetation may also prevent the natural supply of sediment fro m
reaching the stream .
Delivery of Organic Matter to Receiving Waters :The delivery of organic matter is critical t o
receiving water health as it forms the basis for the aquatic food web . Delivery of organic matte r
follows similar pathways as inorganic matter (e .g ., sediment). However, the dominant amoun t
and timing of delivery is often associated with the presence, width, and composition of th e
vegetative riparian zone .
Chemical and Biological Transformations :This encompasses the suite of watershed processe s
that alter the chemical composition of water as it passes through the soil column on its path t o
(and after entry into) a receiving water . The conversion of subsurface flow to overland flow in a
developed landscape eliminates much of the opportunity for attenuation and transformation s
within the soil column, and this is commonly expressed through degraded water quality . Th e
dependency of these processes on watershed conditions is complex in detail, but in general a
greater residence time in the soil should be correlated with greater activity for this group o f
processes . Since residence time is inversely proportional to the rate of movement, the relativ e
importance of this process is anticipated to be inversely proportional to slope .
2) Landscape Assessment as Basis of Watershed Management Zone s
Physical Landscape Zones
5
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Determinants of the primary watershed processes have been cataloged by many prior studies .
Commonly recognized attributes include the material being eroded (i .e ., geologic material),a
measure of topographic gradient (hillslopes, basin slope), climate (mean annual temperature ,
mean annual precipitation, climate zone, latitude), land cover (vegetation, constructed cover an d
imperviousness), and episodic disturbance (e .g ., fire, large storms). Reid and Dunne (1996 )
noted that every study area requires simplification and stratification, with topography an d
geology as the primary determinants with land cover as a "treatment" variable within eac htopography—geology class . This perspective is consistent with the underlying purpose fo r
defining Physical Landscape Zones, namely to identify and stratify watershed conditions an d
processes across the undisturbed landscape of the Central Coast . Thus, geologic material an d
hillslope gradient were the two landscape attributes judged to be the major determinants o f
watershed processes and characterized for this step .1 0
Thus, 15 Physical Landscape Zones can be identified across the Central Coast Region, eac h
with a set of properties that are well-correlated with their key watershed processes in a nundisturbed landscape . Other factors of potential relevance, particularly the spatial variability o f
precipitation and the influence of different vegetation types in undisturbed watersheds (e .g .,trees vs .shrubs vs . grasslands) were explored but were found to have at most a secondar y
influence on the dominance of particular watershed processes across the Central Coast as awhole.1 1
The fifteen final landscape categories (plus "open water") of the Central Coast Region ar e
identified in Table 1, and consist of five geologic material types each divided into three hillslop egradient categories :
1.Franciscan melange : a heterogeneous collection of resistant rocks within a matrix o f
weaker material that has filled the spaces between the resistant clasts (exposed ove r
8% of the land area of the Central Coast).
2.Pre—Quaternary crystalline rocks : a group of geologically old and generally quit eresistant rocks (23% of the Central Coast).
3.Early to Mid—Tertiary sedimentary rocks : primarily resistant sandstones but also som eweaker shales and siltstones (30% of the Central Coast).
4.Late Tertiary sediments : weakly cemented sedimentary rocks of relatively youn g
geologic age (6% of the Central Coast).
5.Quaternary sedimentary deposits : weakly cemented or entirely uncemented silt, sand ,
and gravel that has been deposited in geologically recent time (i .e ., the last 2 .5 millio nyears; 33% of the Central Coast).
10 Booth, et al, 2011b . p . ii .11 Ibid . p . 4 .
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Table 1 .Physical Landscape Zone areas as a proportion of the Central Coast Region .
Physical Landscape Zon e
(geologic material and hillslope gradient C%slope %of total are a
Franciscan melange ;0 — 10 %
Franciscan melang10 40%
Franciscan melange ; >40%2 %°
Pre—Quaternarycrystalline rocks ;0 10%1 %
Pre—Quaternary crystalline rocks ; 10 —40%° 11 %
Pre-Quaternary crystalline rocks ; >40%11 %
Early to Mid—Tertiary sedimentary ; 0 — 10%2%
CITY STAFF REPORT - ATTACHMENT 2 - 4 5
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Early to Mid—Tertiary sedimentary ; 10 — 40%16 %
Early to Mid—Tertiary sedimentary ; >40%12 %
Late Tertiary sediments ; 0 — 10%1 %
Late Tertia sediments ; 10 — 40%4 %
Late Tertiar sediments ;>40%2 %
Quaternary sedimental deposits ;0 10%18 %M
Quaternary sedimentary deposits ; 10 40%14 %
Quaternary sedimentary deposits ;>40%1 %
0 .4 %
Receivinq Water s
Receiving waters of the Central Coast are diverse, comprising streams, rivers, lakes, wetlands ,
marine nearshore, and groundwater basins . The management of stormwater at particula r
locations on the landscape will depend not only on the key watershed processes associate d
with the Physical Landscape Zone but also on the nature of the receiving water . Not every
watershed process is critical, or even necessarily relevant, to the long-term health of every typ e
of receiving water . The associations shown in Table 2 are based on a general scientifi c
understanding of the interaction of runoff and detrital material with receiving waters, and ar e
recognized in the Joint Effort .
Table 2 .The association of watershed processes with receiving-water types . Cells with "X "
indicate those watershed processes that may be affected by urban development, with potentiall y
snificant consequences for the indicated receiving water .nry,_
Watershed Processe s
Open wate r
Source : Booth, et al, 2011b . p .4 .
Marine Nearshor e
Groundwater Basin s
a . Defined as having a drainage area >200-square mil e
Source : Booth, et al, 2012 . p .3 .
7
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A few patterns are evident in the association of receiving water type and watershe dprocesses:1 2
Streams are commonly affected by alterations to any of the watershed processes an d
are well-recognized to respond to disturbances in their contributing watersheds, and the y
are particularly efficient at passing the effects of disturbance farther downstream . Fo r
these reasons, they are a useful surrogate for the full range of receiving waters, but thei r
sensitivity to changes in the delivery of water, sediment, and organics is not fully share dbyevery other receiving-water type .
2.Natural rates of sediment delivery are presumed important (and beneficial) for streams ,
large rivers, and the marine nearshore environment, because they sustain in-strea mhabitat and maintain beaches . Conversely, sediment delivery is not a beneficial proces s
to maintain for lakes and wetlands (indeed, processes that indirectly increase rates o f
sediment delivery, particularly overland flow, are detrimental) and is irrelevant fo r
groundwater recharge .
3.All receiving waters are influenced by changes to Chemical and Biologica l
Transformations (i .e ., all are water-quality sensitive).
4.The interrelated processes of overland flow, interflow, infiltration, and evapotranspiration ,which in combination determine surface water flow rates and volumes, are only o f
concern for streams and wetlands - lakes and large rivers are defined on the basis o f
their anticipated insensitivity to typical urban-induced changes in these discharg e
parameters (and thus management strategies do not target these processes for thes e
receiving waters).
5.Groundwater aquifers depend on infiltration, but management for infiltration to aquifer s
will have different criteria (and perhaps different strategies as well) than management o f
infiltration as it relates to groundwater discharge to streams or reducing overland flo w(i .e ., runoff volume).
Where discharge passes from one receiving-water type to another (for example, discharge to a
stream then enters a lake), in nearly all cases the "direct" receiving water (i .e ., where the runoff
first arrives) will determine the necessary management strategies rather than the "terminal "
receiving water (the ocean, in all cases ; but with potentially an intermediate wetland, lake, o rlargeriver).This is because downstream waterbodies are, in general, less sensitive to impact s
by virtue of increasing drainage area, and because the most common direct receiving wate r
(streams) already has the greatest sensitivity and therefore will be subject to the most restrictiv emitigation. The only exceptions to this rule are (1) drainage into a lake and then to a stream,fo r
which the standing water is presumed to have always functioned to eliminate downstrea m
sediment discharge, and so protection of this process is not necessary ; and (2) drainage tha t
includes a lake or wetland as either a terminal or intermediate receiving water,for whic h
targeted control of nutrients or other water quality constituents may be necessary to avoi dexcessive loading .1 3
Watershed Management Zone s
Ten Watershed Management Zones (WMZs) were identified for the Central Coast region . Th e
following discusses the process that lead to these ten WMZs . In the terminology of the Join t
Effort, every location on the landscape has two attributes : its Physical Landscape Zone ,
determined by the underlying geology and the local hillslope gradient ; and its direct receiving
1 2 Booth, et al, 2012 . pp . 3, 4 .13 !bid, p . 4 .
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CITY STAFF REPORT - ATTACHMENT 2 - 4 7
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water type. These combine to define the "Watershed Management Zones," of which there ar e
90 unique combinations (reflecting 15 Physical Landscape Zones and 6 receiving water types).
For simplicity, however, Physical Landscape Zones with equivalent sets of key watershe d
processes combine into single Physical Landscape Zone groups, reducing their number to 9
and thus the total number of unique combinations (9 Physical Landscape Zones x 6 receivin g
water types) to 54 .
The important watershed processes associated with each of these 54 Physical Landscape Zon e
-Receiving Water combinations are displayed in Table 3 (using the watershed proces s
abbreviations shown at the bottom of the table). Processes listed before the "/" were judged t o
be of primary concern because they are major factors undergoing large potential change wit h
urbanization ; those after the "/" do not typically show such a high magnitude of potentia l
change .1 4
Table 3 .Key watershed processes associated with each unique Physical Landscape Zone –
Receiving Water combination . (Abbreviations defined below table )
PHYSICAL
LANDSCAP E
ZON E
GGeology and Percent Slope
WATERSHED PROCESSES B Y
DIRECT RECEIVING WATER TYP E
Stream Wetland Lake Larg e
River
Marin e
Nearshore
Ground -
Wate r
Basi n
Franciscan melange 0-10 %
Pre-Quaternary crystalline 0-10%
CBT /OF ET ,
o0
CBT / OF ,ET, DO CBT /DO CBT /CBT / DO CBT /
Early to Mid-Tertiary sed . 0-10%
OF, CBT ,GW / IF ,
ET, DO
OF, CBT ,GW / IF ,ET, DO CDO /CBT /CBT / DO CBT/G W
Late Tertiary sediments 0-10 %
Quaternary deposits 0-10 %Y
OF, CBT ,GW / IF ,ET, DO
OF, CBT ,GW / IF ,ET, DO
CBT /DO CBT /CBT / DO CBT G W~
Franciscan melange 10-40 %
Pre-Quaternary crystalline 10-40%
/ OF, ET ,
Do, CBT
/ OF, ET ,
DO, CBT
/ DO ,
CBT /CBT ! DO, CBT /CBT
Early to Mid-Tertiary sec'. 10-40%
OF / GW,IF ET ,
DS, DO ,CBT
OF / GW,
IF, ET ,
DO, CBT
/ DO ,
CBT
/ DS ,
CBT
/ DS, DO ,
CBT
/
GW,CBT
Late Tertiary sediments 10-40 %
Quaternary deposits 10-40%
OF, GW /
IF, ET ,DS, DO ,CBT
OF, GW IIF E TDo,CBT
/ DO ,CBT / DS ,CBT / DS, DO,CBT GW /CBT
Franciscan melange >40 %
Pre-Quaternary crystalline >40%
DS / OF ,ET, DO / OF, ET ,DO / DO DS/DS/DO /
Early to Mid-Tertiary sed . >40%
DS / OF ,GW, IF ,ET ; DO
/ OF GWIF, ET, DO / DO DS /DS / DO / GW
Late Tertiary sediments >40 %
Quaternary deposits >40%
DSF / GW ,
DO
/ GW, IF ,ET, DO / DO DS /DS/DO / GW
Source : Booth, et al, 2012 . pp . 5, 6 .
14 Booth, et al, 2012 . p . 5 .
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9
CITY STAFF REPORT - ATTACHMENT 2 - 4 8
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Watershed Process Abbreviations :
OF = OVERLAND FLO W
GW = GROUNDWATER RECHARG E
IF = I NTERFLOW
ET = EVAPOTRANSPIRATIO N
CBT = CHEMICAL AND BIOLOGICAL TRANSFORMATION S
DS = DELIVERY OF SEDIMEN T
DO DELIVERY OF ORGANIC S
The watershed processes identified in each cell of Table 3 form the basis for determining th e
necessary elements of stormwater mitigation for each WMZ . Stormwater mitigation i s
presumed to always include the following additional treatments :
•All stormwater mitigation includes receiving water buffers or waterbody set-backs wher e
applicable, resulting in mitigation of "DO" and "DS" at a low level of change (e .g .,
combinations "CBT/DO" and "CBT/DS" can be truncated to "CBT/").
•All stormwater mitigation includes some basic level of water quality treatment, and thu s
"CBT" at a low level of change will always be mitigated (e .g ., combinations "/DO, CBT "can be expressed simply as "/DO").
•If a high level of GW change/concern is indicated, a high level of CBT mitigation wil l
occur because of the infiltration required for recharge of groundwater aquifers (e .g ., th e
combination "GW, CBT/" becomes "GW/").
These conditions and principles result in a simplified presentation (Table 4),whose colors are
keyed to geographic locations on the associated map of Watershed Management Zones (Figure1). The presence or absence of an underlying groundwater basin is similarly determined fro m
the mapping available to Permittees (see Section III).
Table 4 .A reorganized and simplified presentation of Table 3 . Numbers specify which WMZ i s
represented by the Physical Landscape Zone — Receiving Water combination expressed by th ecell. Those marked with an asterisk will require protection of groundwater recharge if underlai nbya mapped groundwater basin .
DIRECT RECEIVING WATE R
Lake ,
w/G W
Basi n
PHYSICAL LANDSCAPE ZON E
Geology and Percent Slope
Lg . Rivers &
Marine ,
w/GW Basi n
Franciscan melange 0-10 %
Franciscan melange 10-40 %
Franciscan melange >40 %
Pre-Quaternary crystalline 0-10 %
Pre-Quaternary crystalline 10-40 %
Pre-Quaternary crystalline >40 %
Quaternary deposits 0-10 %
Quaternary deposits 10-40%
10
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CITY STAFF REPORT - ATTACHMENT 2 - 4 9
ATTACHMENT 2
Key for Table 4 .
Watershed Processes
(Processes before the "I"are of primary concern ; those after the "I"do not
show as high a magnitude of potential change)
Watershe d
Managemen t
Zon e
Overland Flow, Groundwater Recharge / Interflow, Evapotranspiratio n
Overland Flow / Groundwater Recharge, Interflow, Evapotranspiratio n
Chemical and Biological Transformations / Overland Flow, Evapotranspirationi t 3 ;
Chemical and Biological Transformations (*)/
Delivery of Sediment / Groundwater Recharge, Interflow, Evapotranspiratio n
Delivery of Sediment / Overland Flow, Evapotranspiratio n
Delivery of Sediment / (*)7
/Groundwater Recharge, Interflow, Evapotranspiration 8
/Overland Flow, Evapotranspiration 9
/(*)10
*Groundwater Recharge, if underlain by Groundwater Basi n
Quaternary deposits >40%,£8 1 0
Late Tertiary sediments 0-10 %
Late Tertiary sediments 10-40 %
Late Tertiary sediments >40%5' ,5 1 0
Early to Mid-Tertiary sed . 0-10 %
Early to Mid-Tertiary sed . 10-40 %
Early to Mid-Tertiary sed . >40 %
Source : Booth, et al, 2011 a .
11
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CITY STAFF REPORT - ATTACHMENT 2 - 5 0
ATTACHMENT 2
12
SS2-7 7
Waters?ied management zones
Figure 1 .Watershed Management Zones .
spatial data coverages available separately .)
Source : Booth, et al, 2012 .
~hl}tl'ut y ~i lt`11Ct'rstillv;et'rscicorn ;
Areas defined in Table 4 . (High resolutio n
ROMODIP1cAn
D.thl
rr :;
>s :r rt 20)0
H41si,ad- tnC ^l~e~ralEarth 2010
CITY STAFF REPORT - ATTACHMENT 2 - 5 1
ATTACHMENT 2
Summary Characteristics of the Watershed Management Zones 1 5
The following summarizes each WMZ's characteristics and the management approache s
needed to protect the key watershed processes for that WMZ . Table 5 indicates the distributio n
of the WMZs within the Central Coast Region's urban areas . Attachment A includes maps o f
the WMZs in the Central Coast Region's urban areas . Spatial data files are availabl e
electronically (See Section III .).
WMZ 1 :Characteristics :Drains to stream or to wetland . Underlain by : Quaternary and Late
Tertiary deposits, 0-40%; Early to Mid-Tertiary sediments, 0-10%.Attributes an d
Management Approach :This single WMZ includes almost two-thirds of the urba n
area of the Central Coast Region (Table 5); it is defined by low-gradient deposit s
(Quaternary and Tertiary in age) together with the moderately sloped areas of thes e
younger deposits that drain to a stream or wetland . The dominant watershe d
processes in this setting are infiltration into shallow and deeper soil layers ;
conversely, overland flow is localized and rare . Management strategies shoul d
minimize overland flow and promote infiltration, particularly into deeper aquifers i f
overlying a groundwater basin in its recharge area .
WMZ 2 :Characteristics :Drains to stream or to wetland . Underlain by Early to Mid-Tertiar y
sediments, 10-40%.Attributes and Management Approach :This WMZ is similar t o
WMZ 1 in both materials and watershed processes, but groundwater recharge i s
anticipated to be a less critical watershed process in most areas . While almost 9 %
of the urban areas of the Central Coast Region are in this WMZ (Table 5), only 1 %
overlies a groundwater basin ; thus, whereas management strategies need to
minimize overland flow as with WMZ 1, they need not emphasize groundwate r
recharge as the chosen approach to the same degree .
WMZ 3 :Characteristics :Drains to stream or to wetland . Underlain by Franciscan melang e
and Pre-Quaternary crystalline, 0-10%.Attributes and Management Approach :Thi s
WMZ includes those few flat areas of the Central Coast Region underlain by old ,
generally impervious rocks with minimal deep infiltration (and intersecting with n o
mapped groundwater basins). Overland flow is still uncommon over the surfac e
soil ; and chemical and biological remediation of runoff, reflecting the slo w
movement of infiltrated water within the flat soil layer, are the dominant watershe d
processes . Management strategies should promote treatment of runoff throug h
infiltration, filtration, and by minimizing overland flow .
WMZ 4 :Characteristics :Drains to lake, large river, or marine nearshore . Underlain by al l
geologic types, 0-10%, and Quaternary and Late Tertiary deposits, 10-40%.
Attributes and Management Approach :This WMZ covers those areas geologicall y
equivalent to WMZ's 1 and 3, but draining to one of the receiving water types tha t
are not sensitive to changes in flow rates . The dominant watershed processes i n
this low-gradient terrain are those providing chemical and biological remediation o f
runoff, but a specific focus on infiltration management strategies is only necessary
for those parts of this WMZ that overlie a groundwater basin . This WMZ cover s
13 .6% of Central Coast Region's urban areas (Table 5); almost 11% of the region's
urban areas are in this WMZ and overlie a groundwater basin .
15 Booth, et al, pp . 13, 14 .
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CITY STAFF REPORT - ATTACHMENT 2 - 5 2
ATTACHMENT 2
WMZ 5 :Characteristics :Drains to stream . Underlain by Quaternary deposits, Late Tertiar y
deposits, and Early to Mid-Tertiary sediments, >40%.Attributes and Managemen t
Approach :These steep, geologically young, and generally infiltrative deposits ar e
critical to the natural delivery of sediment into the drainage system, managemen t
strategies should also maintain the relatively high degree of shallow (and locall y
deeper) infiltration that reflects the relatively permeable nature of these deposits .
Because this WMZ only covers steeply sloping areas, however, it is relatively
uncommon in urban areas (<3%).
WMZ 6 :Characteristics :Drains to stream . Underlain by Franciscan melange and Pre -
Quaternary crystalline, >40%.Attributes and Management Approach :The steepl y
sloping geologic deposits not in WMZ 5 are included here ; they are similarl y
important to the natural delivery of sediment into the drainage system but have littl e
opportunity for deep infiltration, owing to the physical properties of the underlyin g
rock . Management strategies should maintain natural rates of sediment deliver y
into natural watercourses but avoid any increase in overland flow beyond natura l
rates, which are low where undisturbed even in this steep terrain .
WMZ 7 :Characteristics :Drains to large river or marine nearshore . Underlain by all geologi c
types, >40%.Attributes and Management Approach ;This WMZ is very rare in th e
urban parts of the Central Coast Region (0 .1% total) because such terrain provides
little space or opportunity for urban development . The receiving waters tha t
characterize this WMZ are insensitive to changes in runoff rates but still depend o n
natural sediment delivery processes for their continued health ; thus, managemen t
strategies need to focus on maintaining the delivery of sediment in the few area sthat the WMZ is found .
WMZ 8 :Characteristics :Drains to wetland . Underlain by Quaternary deposits, Late Tertiar y
deposits, and Early to Mid-Tertiary sediments >40%.Attributes and Managemen tApproach:Equivalent to WMZ 5 but with a different receiving-water type, thes e
steep and generally infiltrative deposits should be managed to maintain th e
relatively high degree of shallow (and locally deeper) infiltration that reflects th e
relatively permeable nature of these deposits . Delivery of sediment, however, i s
unlikely to be important to downstream receiving water (i .e ., wetland) health . Eve n
more so than with the other steep WMZs, this type is extremely uncommon in th e
Central Coast Region's urban areas (0 .1%).
WMZ 9 :Characteristics :Drains to wetland . Underlain by Franciscan melange and Pre -Quaternary crystalline, >10%; or drains to stream or wetland, and underlain b y
Franciscan melange and Pre-Quaternary crystalline, 10-40%.Attributes an dManagement Approach :These moderately sloping, older rocks that drain to either astream or wetland are neither extremely sensitive to changes in infiltrativ e
processes (because the underlying rock types are typically impervious), nor ke y
sources of sediment delivery (because slopes are only moderate in gradient).
Overland flow is still uncommon over the surface soil, and so managemen t
strategies should apply reasonable care to avoid gross changes in the distribution o frunoff between surface and subsurface flow paths . About 6% of the urban parts o fthe Central Coast Region are found on this WMZ (Table 5); none include a n
underlying groundwater basin, emphasizing the relative unimportance o fmaintaining deep infiltration .
14
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CITY STAFF REPORT - ATTACHMENT 2 - 5 3
ATTACHMENT 2
WMZ 1O :Characteristics :Drains to lake, large river, or marine nearshore . Underlain b y
Franciscan melange, Pre-Quaternary crystalline, Early to Mid-Tertiary sediments ,
10-40%; or, drains to lake and underlain by all geologic types >40%.Attributes an d
Management Approach :Covering less than 1% of the urban areas of the Region ,
this WMZ drains into those receiving waters insensitive to changes in runoff rates .
It includes the moderately sloped areas that are anticipated not to be key sediment -
delivery sources (by virtue of hillslope gradient) or that drain into lakes (whic h
generally do not require natural rates of sediment delivery for their continue d
health). Across the entire urbanized part of the Central Coast Region, less than 1
square kilometer of this WMZ also overlies a mapped groundwater basin ,
suggesting that a broad management focus on deep infiltration is unwarranted .
IV . Management Strategies for Watershed Management Zones 1 6
These Post-Construction Requirements shift from the historic, symptomatic approach t o
stormwater management and hydromodification control to an approach focusing on th e
protection of key watershed processes . Instead of identifying a problematic outcome of urba n
development (e .g ., "eroding stream channels") and requiring a targeted 'fix' to the 'problem '
(e .g ., "armor the bank"), these Post-Construction Requirements target the root causes o f
changes to receiving waters—namely, aspects of development projects that disrupt th e
watershed processes that sustain the health and function of these waterbodies . Furthermore ,
these Post-Construction Requirements reflect the geographic diversity of the Central Coast b y
stratifying the region into Watershed Management Zones allowing management to focus o n
watershed processes where they are known to occur . Management strategies, therefore, mus t
focus on the key watershed processes of each Watershed Management Zone . The result is a
process-based stormwater management approach .
To support process-based stormwater management, broad sets of management strategies ca n
be assigned that target the protection of watershed processes in various settings, and for whic h
'6 Booth, et al, 2012 . pp . 15, 16 .
SS2-8 0
Table 5 .Percentae of Central Coast Urban Areas by WM Zwhiz.1 Percent Urban Are a
62 .6
8 .8
2 .5
13 .6
2 .6
2 .2
100 %
Source : GIS analysis by Stillwater Sciences, 201 2
15
CITY STAFF REPORT ATTACHMENT 2 - 5 4
ATTACHMENT 2
numeric performance requirements are provided . Although there is no formally accepted "list" o f
such strategies, the following set offers a useful organizational framework :
1)Flow Contro l
Flow Control encompasses a broad range of stormwater criteria for addressing hydraulic an d
hydrologic goals . This includes regulations that typically mandate that (1) post-developmen t
peak flows are less than or equal to pre-development peak flows for a series of intermediat e
and/or large design storm events (i .e .,"storm event peak flow control); (2) runoff from flow s
with the highest risk potential for channel erosion, and by extension damage to aquatic habitat ,
are not increased in duration ("flow-duration control"); and (3) runoff is infiltrated or retaine d
onsite, without specific reference to the range of stream-channel flows that are affected, t o
maintain groundwater flow or reduce overall runoff volume ("retain volume").
2)Water Quality Treatmen t
Water Quality Treatment includes a suite of Stormwater Control Measures (SCMs) that addres s
the major link between urbanization and water quality impairment, which is caused by th e
increased runoff from impervious surfaces and soil compaction of pervious areas,and th e
delivery of urban sources of pollutants such as nutrients from fertilizer, metals from brake pads ,
and sediment from exposed soil surfaces .
3)Preserve Delivery of Sediment and Organic s
Preserve Delivery of Sediment and Organics into the channel network is critical for th e
maintenance of various habitat features and aquatic ecosystems in the fluvial setting . Whil e
preservation of these functions is not a goal found in most stormwater regulations, it is ofte n
discussed qualitatively as a goal in establishing or justifying riparian buffer requirements .
4)Maintain Soil and Vegetation Regim e
Maintain Soil and Vegetation Regime is a valuable and highly effective alternative to water -
quality treatment, because much impairment is due to the isolation of soil and vegetation fro m
the path of urban stormwater runoff, which in turn eliminates the processes of filtration ,
adsorption, biological uptake, oxidation, and microbial breakdown (collectively termed th e
watershed process of "Chemical and Biological Transformations" by the Joint Effort). Note tha t
this management strategy overlaps with several others : not only can it accomplish water-qualit y
treatment, but also it can constitute stormwater volume-based flow control and preserve th e
delivery of sediment and organics to waterbodies if located adjacent to waterbodies . Moreover ,
it is a (typically intentional) byproduct of any application of land-preservation strategies as well .
5)Land Preservatio n
Land Preservation includes open space requirements and minimization of effective imperviou s
area . Both have the goal of avoiding or directing runoff from impervious surfaces to perviou s
areas, rather than routing it directly to the storm drainage system .
Within each broad category of management strategies, multiple SCMs are available for direc t
application to meet performance criteria . Similarly, a single SCM may reflect multipl e
management strategies and address more than one watershed process, which provides th e
reminder that well-chosen SCMs can accomplish multiple objectives within a relatively simpl e
mitigation approach . In addition, some SCMs are traditional facilities ('structural' SCMs),
whereas others may affect overall site design, choice of construction materials and approaches ,
or may invoke programmatic strategies administered over a larger area (e .g ., rain barre l
incentive program). This great variety of available measures means the designer will likely nee d
to make use of a suite of SCMs that, in combination, can meet the performance requirements
16
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CITY STAFF REPORT - ATTACHMENT 2 - 5 5
ATTACHMENT 2
required for the protection of watershed processes at the site . The designer's task is to optimiz e
the choice of SCMs to achieve the desired net benefits with a desired level of simplicity an d
necessary degree of reliability .
V . Post-Construction Performance Requirement s
The core of these Post-Construction Requirements is a group of Performance Requirements fo r
new and redevelopment projects that invoke the management strategies discussed above . Th e
following discusses each Performance Requirement and related implementation requirements ,
including the types of projects subject to the Performance Requirements and the necessar y
analytical methods required to meet compliance .Flow charts to assist in determining whic h
Performance Requirements apply are provided in Attachment C .
The Performance Requirements rely on four important strategies that are critical to recognize fo r
a full understanding of how the requirements, taken together, will result in protection o f
watershed processes and the beneficial uses they support : 1) a reliance on LID to the exten t
feasible to achieve protection of the broadest suite of watershed processes not effectivel y
targeted by structural controls ; 2) the use of Stormwater Control Plans to ensure projec tapplicantshave followed due diligence in selecting SCMs and have optimized LID ; 3) th e
combination of retention and peak management requirements on larger sites to achieve a broa d
spectrum of watershed process protection while also protecting stream channels fro m
hydromodification impacts ; and 4) the additive application of Performance Requirements a s
projects trigger each size threshold (e .g ., the largest sites must meet Performanc e
Requirements applying to smaller sites). Elements of these strategies are integrated into th e
Performance Requirements to support successful implementation .
1)Regulated Project s
Development projects subject to these requirements are a subset of the diverse spectrum o f
development projects Permittees approve . The Post-Construction Requirements specify
several exemptions, including, for example, road maintenance projects and trail projects (whe n
not part of a project creating additional impervious surfaces) that direct runoff to adjacen t
vegetated areas .
Following a convention used throughout the United States, these Post-Constructio n
Requirements use the amount of impervious surface as the parameter of interest in determinin g
applicability . Thus, only projects that create and/or replace impervious surface are potentiall y
eligible for regulation of post-construction requirements . Water Board staff recognizes that a
development project's impervious surface is an imperfect proxy for all potential post -
construction impacts of the project . For example, land disturbance that does not lead to th e
placement of impervious surfaces (e .g ., construction of a gravel road) may still result in impact s
to watershed processes by potentially compacting infiltrative soils, removing vegetation, o r
permanently altering drainage patterns .
These Post-Construction Requirements compensate for this imperfection by applyin g
Performance Requirements, in some cases, to the entire site area, not just the imperviou s
surface area .For example, Performance Requirement No .s 1-4 are applied throughout th e
entire site of all New Development projects . For Redevelopment Projects with existin g
impervious surfaces, Performance Requirement No . 1 applies to the entire site area, whil e
Performance Requirement No .s 2-4 apply only to the new and/or replaced impervious surfaces .
2) Performance Requirement No . 1 : Site Design and Runoff Reductio n
17
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CITY STAFF REPORT ATTACHMENT 2 - 5 6
ATTACHMENT 2
This requirement applies to projects that create and/or replace >2,500 square feet o f
impervious surface and requires projects to utilize site design and runoff reduction measures ,
where feasible . The site design measures are the first and best opportunity to invok e
management strategies for land preservation, and maintenance of soil and vegetation regime ,
which in turn support other strategies for flow control, water quality treatment, and preservin g
delivery sediment and organic matter to receiving waters . For example, minimizing imperviou s
surfaces and minimizing compaction of native soils in site design preserves land area availabl e
to support these watershed processes, and retains the soils' capacity to infiltrate water, reducin g
runoff that requires treatment and flow controls . Performance Requirement No .1 invokes th e
LID design concept of mimicking predevelopment hydrology to the extent feasible .
Projects creating and/or replacing 2,500 square feet of impervious surface are too small t o
justify numeric requirements that would require hydrologic or engineering analysis . However ,
they are large enough to generate impacts to watershed processes, both individually an d
cumulatively, over time in a watershed . Permittees must apply this requirement by informin g
project applicants that the nine specific measures must be pursued on the project site wher e
feasible, and requiring the applicant, through application/approval documents, to indicate whic h
measures are being implemented on their project . Performance Requirement No .1 is require d
on all Regulated Projects in all WMZs, however, Regulated Projects > 15,000 square feet wil l
achieve compliance with Performance Requirement No . 1 by complying with the LID Standard s
required in Performance Requirement No . 3 .
3) Performance Requirement No . 2 : Water Quality Treatmen t
The Water Quality Treatment Performance Requirement in these Post-Constructio n
Requirements applies to Regulated Projects that create and/or replace > 5,000 square feet o f
Net impervious surface area, and to detached single-family residences that create and/o r
replace > 15,000 square feet of impervious surface . Net impervious surface area, or, the su m
of new and reconstructed impervious areas, minus any new pervious area created b y
eliminating existing impervious surfaces on-site, is used to determine applicability for non -
single-family residences . The Net calculation is intended to provide a possible exemption fo r
projects that would be subject to Water Quality Treatment Performance Requirements whe n
their new and replaced impervious surfaces exceed 5,000 square feet, even when the projec t
removes impervious surfaces and achieves a lower total imperviousness . While expected t o
occur in a limited number of cases, the Net calculation may provide applicantsan incentive t o
reduce the total amount of imperviousness as part of some of the smaller Regulated Projects .
Performance Requirement No . 1 applies to all projects in all Watershed Management Zone s
and is applied `cumulatively' (i .e ., it applies to all projects larger than 15,000 square feet).
A National Urban Runoff Program (NURP) study showed that heavy metals, organics, colifor m
bacteria, nutrients, oxygen demanding substances (e .g ., decaying vegetation), and tota l
suspended solids are found at relatively high levels in stormwater and non-stormwate r
discharges ." It also found that MS4 discharges draining residential, commercial, and ligh t
industrial areas contain significant loadings of total suspended solids and other pollutants . I n
addition, the State Water Board Urban Runoff Technical Advisory Committee (TAC) finds tha t
urban runoff pollutants include sediments, nutrients, oxygen-demanding substances, heav y
17 State Water Resources Control Board .Order WQ 2001-15, In the Matter of Petitions of Buildin g
Industry Association of San Diego County and Western States Petroleum Association,15 Novembe r2001. Web . 11 August 2011 .
18
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CITY STAFF REPORT - ATTACHMENT 2 - 5 7ATTACHMENT2
metals, petroleum hydrocarbons, pathogenic bacteria, viruses, and pesticides .18 Runoff tha t
flows over streets, parking lots, construction sites, and industrial, commercial, residential, an d
municipal areas carries these untreated pollutants through MS4s directly to receiving waters .
The Natural Resources Defense Council (NRDC) 1999 Report,"Stormwater Strategies ,
Community Responses to Runoff Pollution"identifies concentration of pollutants in runoff to b e
one of the main causes of the stormwater pollution problem in developed areas . The repor t
states that certain industrial, commercial, residential and construction activities are larg e
contributors of pollutant concentrations in stormwater runoff. As human population densit y
increases, it brings with it proportionately higher levels of car emissions, car maintenanc e
wastes, municipal sewage, pesticides, household hazardous wastes, pet wastes, and trash .
Studies show that the level of imperviousness in an area strongly correlates with the quality o f
nearby receiving waters .19 One comprehensive study, which looked at numerous areas ,
variables, and methods, revealed that stream degradation occurs at levels of imperviousness a s
low as 10 – 20 percent.20 Stream degradation is a decline in the biological integrity and physica l
habitat conditions that are necessary to support natural biological diversity . For instance, fe w
urban streams can support diverse benthic communities with imperviousness greater than o r
equal to 25 percent .21 To provide some perspective, a medium density, single-family residentia l
area can be from 25 percent to 60 percent impervious (variation due to street and parkin g
design).22 More recently, a report on the effects of imperviousness in southern Californi a
streams found that local ephemeral and intermittent streams are more sensitive to such effects
than streams in other parts of the country . This study, by the Southern California Coastal Wate r
Research Program, estimated a thresholdl of response at a two to three percent change i n
percent of impervious cover in a watershed .23'2 4
According to the Center for Watershed Protection, urbanization strongly shapes the quality o f
both surface and groundwater in arid and semi-arid regions of the southwest . Since rain event s
are so rare, pollutants have more time to build up on impervious surfaces compared to humi d
regions . Therefore, pollutant concentrations in stormwater runoff from arid watersheds tend t o
be higher than that of humid watersheds .25 The effect of antecedent rainfall events i s
demonstrated in a recent report from the California Department of Transportation (Caltrans) tha t
found the concept of a seasonal first flush is applicable to the southern California climate .26
The Water Quality Treatment Performance ;Requirement addresses post-construction pollutan t
loading through treatment measures that eriiphasize LID (harvesting and re-use, infiltration, an d
evapotranspiration) and biofiltration overt ,conventional non-retention based or flow-base d
treatment approaches . All SCMs are to! be designed for 85 th percentile rainfall events a s
specified .
18 State Water Resources Control Board . Nonpc int Source Pollution Control Program .Urban Runoff
Technical Advisory Committee Report,November 1994 . Web . 11 August 2011 .
19 Federal Register, 1999 .
20 Ibid .21 Ibid .22 Schueler, et al, 2000a .
23 Coleman, et al, 2011 . p . iv .
24 Helmle and Booth, 2011a, p . 10 .25 Schueler, et al, 2000b .
26 Stenstrom, et al, 2011 .
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CITY STAFF REPORT ATTACHMENT 2 - 5 8
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Flow-through treatment methods are generally recognized as achieving less than 100 percent
pollutant removal from runoff leaving the site . By comparison, retention would result in 10 0
percent removal by virtue of preventing the discharge of runoff from the specified design storm .
However, in these Post-Construction Requirements the allowance of flow-based treatment for
projects up to 15,000 square feet is provided in recognition of several factors: 1) total pollutan t
generation and associated water quality impacts from smaller projects are anticipated to be les s
than those of larger (>15,000 square feet) projects ; 2) greater technical challenges due to space
constraints of achieving retention on smaller sites relative to larger sites ; and 3) higher costs ,
relative to total project value, for smaller projects to achieve retention . Furthermore, th e
retention requirement imposed for projects larger than 15,000 square feet places an upper limi t
on the use of flow-based treatment .
While the option of flow-through treatment is available for projects <15,000, the project applican t
must submit a Stormwater Control Plan demonstrating why LID and biofiltration treatmen t
systems could not be implemented . Permittees are required to review the Stormwater Contro l
Plan and confirm that the feasibility of LID and biofiltration treatment system implementation ha s
been exhausted before approving non-retention based treatment systems .
Water Board staff places biofiltration treatment before non-retention based treatment systems i n
the order of preference because of the potential for the biofiltration system to achiev e
infiltration/retention and to replicate watershed processes (evapotranspiration, chemical and
biological transformations) to a greater degree than other flow-through (non-retention )
measures . The biofiltration treatment system can provide infiltration to the extent site soils allow
it (e .g .,in sites with highly infiltrative soils, the system would be expected to infiltrate, thus ,
retain a greater proportion of runoff directed to it, whereas a site with lower permeable soil s
would release more treated runoff to the storm drain system or receiving water.) Whil e
additional information is needed to ascertain more precise understanding of the pollutant
removal efficiency of these systems, Water Board staff supports their use because of th e
multiple benefits they offer over non-retention based treatment systems .
The option of providing treatment with biofiltration treatment systems is stipulated by th e
requirement that the system used be as effective as a biofiltration treatment system with th e
design parameters specified in the Post-Construction Requirements . Water Board staf f
recommends that the minimum specifications for biofiltration systems in the Post-Constructio n
Requirements be used in conjunction with additional guidance and specifications to ensur e
proper functioning of biofiltration systems . Water Board staff modified the specification o f
minimum planting depth in biofiltration systems from that specified in designs used commonly i n
parts of the San Francisco Bay Area . A 24-inch minimum planting medium depth, as oppose d
to the 18-inch minimum depth indicated in the Bay Area specifications, is required because o f
current uncertainty of performance for bioretention systems with under-drains .27 Question s
remain about the functional roles of plants and specified soils mixes in California's arid climate ,
and providing greater soil media depth can provide improved performance in the interim period ,
as California research is carried out and regional guidelines are developed . Technical guidance
for designing bioretention facilities is available from the Central Coast LID Initiative . Th e
guidance includes specification and plant lists selected for the Central Coast climate .
(http ://www .centralcoastlidi .org/Central_Coast' LIDI/LID_Structural_BMPs .html )
4) Performance Requirement No . 3 : Runoff Retentio n
2 7 Hunt, et al, 2012 . pp . 6, 8, 10 .
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CITY STAFF REPORT - ATTACHMENT 2 - 5 9
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All Regulated Projects that create and/or replace >15,000 square feet of impervious surface i n
all WMZs except WMZ 3, which is underlain by generally impervious rocks, must retai n
stormwater runoff to protect watershed processes so that beneficial uses of receiving waters ar e
maintained and, where applicable, restored . Where technically feasible, the goal of th e
retention requirement is that 100 percent of the volume of water from storms less than or equa l
to the indicated percentile event (85 th or 95 0 ), over the footprint of the project, will not discharg e
to surface waters . This Performance Requirement indicates compliance can be achieve d
through infiltration in some WMZs, and through non-infiltrative (storage, use, etc .) methods i n
others .
TheBasisfor Requiring Runoff Retentio n
For the purposes of these Post-Construction Requirements, retaining runoff from all rain storm s
up to and including the 85 th or 95 th percentile storm is analogous to maintaining or restoring th e
pre-development hydrology with respect to I .the volume, flow rate, duration and temperature o f
the runoff for most sites . Retention of runoff up to these percentile storms is indicated becaus e
this storm size represents the volume that appears to best represent the volume that is full y
infiltrated in a natural condition and thus should be managed onsite to maintain this pre -
development hydrology for duration, rate and volume of stormwater flows . Maintaining pre -
development runoff duration, rate, and volume provides broad support to watershed processes ,
including, reduced overland flow, infiltration,'interflow, and groundwater recharge, and achieve s
reductions in urban pollutant loading of receiving waters that are non-existent under natura l
conditions .
In general, only large storms generate significant runoff under pre-development conditions . Th e
Joint Effort landscape analysis confirmed that this holds true for most of the Central Coas t
Region and the designated WMZs reflect this .28 The relative rarity of overland flow i n
undisturbed conditions is not unique to the Central Coast however . It is in fact the basis fo r
federal stormwater control standards promulgated by the Energy Independence and Securit y
Act of 2007 29 (EISA) and applied throughout the United States . The EISA standard includes a
95 th percentile retention requirement for federal facilities creating or replacing > 5,000 squar e
feet. Rain storms smaller than the 95 th percentile storm are considered small storms . The
EISA Technical Guidance states :
"The runoff produced by these small storms and the initial portion of large r
storms has a strong negative cumulative impact on receiving water hydrolog y
and water quality . In areas that have been developed, runoff is generated fro m
almost all storms, both small and large, due to the impervious 'surfaces
associated with development and the loss of soils and vegetation . In contrast,
natural or undeveloped areas discharge little or no runoff from small storms
because the rain is absorbed by the landscape and vegetation . Studies hav e
shown that increases in runoff event frequency, volume and rate can b e
diminished or eliminated through the use of Green Infrastructure/LID designs an d
practices, which infiltrate, evapotranspire, and capture and use stormwater ."30
Retaining 100 percent of all rainfall events equal to or less than the 95 th percentile rainfall even t
approach was selected because "it employ$ natural treatment and flow attenuation methods tha t
are presumed to have existed on the site before construction of infrastructure (e .g ., building ,
28 Booth, et al, 2011b .p .vi .
29 USEPA, 2010 . http ://www .epa .gov/owow/NRS/lid/section438/pdf/final_sec438_eisa .pd f
30 Ibid . p . 13 .
21
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roads, parking lots, driveways,) and is intended to infiltrate or evapotranspirate the full volume o f
the 95th percentile storm ."3 1
The United States Environmental Protection Agency's 2010 MS4 Permit Improvement Guid e
provides the 95 th percentile criterion as an example for communities to adopt . In that guidance
document, one of the examples of site performance standards states,`Design,construct,an d
maintain stormwater management practices that manage rainfall onsite, and prevent the offsit e
discharge of the precipitation from all rainfall events less than or equal to [insert standards, suc h
as `the 95th percentile rainfall event']."32
Runoff retention requirements achieve water quality treatment objectives as well . For th e
purposes of these Post-Construction Requirements, achieving compliance with Performanc e
Requirement No . 3 equates with compliance with Performance Requirement No .2,Wate r
Quality Treatment, since runoff retention effectively eliminates pollutant loading of receivin g
waters from rain events up to the 85 th or 95 th Percentile event .
Retention Requirements Keved to WMZ s
In WMZ 1 and, where overlying Groundwater Basins, in WMZs 4, 7 and 10, Performanc e
Requirement No . 3 is to retain the 95th Percentile via infiltration . The conclusion of the Joint
Effort landscape analysis 33 is that the dominant watershed process throughout these WMZs i s
infiltration into shallow and deeper soil layers and that overland flow is localized and rare (se e
Table 4 Key). The imperative for infiltration to support recharge of known groundwater basins i s
self-evident in a region as heavily reliant on groundwater as the Central Coast .
In WMZ 2 Performance Requirement No . 3 is to retain the 95th Percentile event via storage ,
rainwater harvesting, infiltration, and/or evapotranspiration . Infiltration is not essential in thi s
WMZ (only 1% of the Central Coast Region's urban area in this WMZ overlies a groundwate r
basin). Nevertheless, overland flow is still rare due to subsurface flow,so the retentio n
requirement prevents discharges below a threshold presumed to replicate pre-developmen t
hydrology. Where non-infiltrative methods are allowed, runoff can be harvested and used an d
ultimately may be discharged via a sanitary treatment system . For example, if runoff is capture d
for non-potable uses such as toilet flushing or other uses that are not irrigation related, thes e
waters potentially could be discharged into the sanitary sewer system .
Performance Requirement No .3 for WMZs 5, 6, 8, and 9 is to retain the 85th Percentile Rainfal l
Event . The dominant watershed processes in these WMZs, as determined by receiving wate r
type, geologic material and slope, indicate a threshold for retention lower than the 95 t h
percentile required for WMZs 1 and 2, and WMZs 4, 7, and 10 where they overly groundwate r
basins . Watershed processes in WMZs 5, 6, 8, and 9 also include groundwater recharge ,
interflow, and overland flow (see Table 4 Key), and these processes are effectively managed b y
retention of small storms on site . However, the processes are less critical or less responsive t o
disturbance than in the WMZs where 95 th percentile retention is required .
In WMZs 5 and 8, compliance must be achieved via infiltration . These steep, geologicall y
young, and generally infiltrative deposits require management strategies to maintain th e
relatively high degree of shallow (and locally deeper) infiltration that reflects the relativel y
31 Ibid, pp . 12, 13 .
32 Ibid,p . 52 .
33 Booth,et al, 2011b . p . vi .
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CITY STAFF REPORT - ATTACHMENT 2 - 6 1
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permeable nature of these deposits . However slopes greater than 40% indicate a low potentia l
for overland flow under undisturbed conditions .
WMZs 6 and 9 allow retention of the 85th Percentile Rainfall event through storage, rainwate r
harvesting, infiltration, and/or evapotranspiration, where feasible . WMZ 6 includes steepl y
sloping areas that provide little opportunity for deep infiltration, owing to the physical propertie s
of the underlying rock . Management strategies should avoid any increase in overland flo w
beyond natural rates, which are low where undisturbed even in this steep terrain . WMZ 9
includes moderately sloped, older rocks that drain to either a stream or wetland that are no t
extremely sensitive to changes in infiltrative processes (because the underlying rock types ar e
typically impervious). Overland flow is still uncommon over the surface soil, however retentio n
is required to avoid gross changes in the distribution of runoff between surface and subsurfac e
flow paths . Deep infiltration is unnecessary in the absence of an underlying groundwater basin .
Feasibility of Achieving Retentio n
These Post-Construction Requirements require all applicable Regulated Projects to meet th e
Runoff Retention Performance Requirements using LID Development Standards, which include :
site assessment measures ; site design measures ; site runoff reduction measures ; and structura l
SCMs that optimize protection and restoration of watershed processes, such as bioretentio n
and other small-scale, decentralized, LID measures . The applicant must demonstrate throug h
submittal of the Stormwater Control Plan that each of these elements has been achieved to th e
extent feasible before selecting more conventional structural SCMs . Where LID SCMs and/o r
BMPs are not feasible, the Permittee may allow Regulated Projects to use conventional design s
(wet ponds, dry wells, infiltration basins) to meet the Runoff Retention Performanc e
Requirement .
The site assessment and site design measures are the first and best opportunity to invoke th e
entire suite of management strategies that protect watershed processes, including : land
preservation, maintenance of soil and vegetation regime, flow control, water quality, and th e
delivery sediment and organic matter to receiving waters . The runoff reduction measures ar e
intended to further reduce the total volumes of runoff that must be retained through structura l
measures by directing runoff to undisturbed or natural landscaped areas that the applicant ca n
demonstrate infiltrate runoff . The applicant should quantify the portion of the total Performanc e
Requirement retention volume addressed through these measures and then address any
remaining volume using structural SCMs . Structural SCMs consistent with LID principles o f
retention and/or treatment via infiltration, evapotranspiration, filtration, or capture and reuse ar e
to be prioritized in addressing the remaining volume .
The LID Development Standard ensures that the project applicants avail themselves of th e
great variety of available measures that, in combination, can meet the performance
requirements required for the protection of watershed processes at the site . The applicant's
task is to optimize the choice of SCMs to achieve the desired net benefits with a desired level o f
simplicity and necessary degree of reliability . LID Stormwater Control Measure/Bes t
Management Practice selection and design guidance is available from the following resources :
1) Southern California LID BMP Manual,34 2) Contra Costa C .3 Manual,3 5 and 3) City of Sant a
sa LID Manual for Southern California : Technical Guidance and Site Planning Strategies .
(http ://www .casqa .org/LID/tabid/240/Default .aspx)
35 Contra Costa Glean Water Program, C .3 Guidebook (http ://www.cccleanwater .org/c3-guidebook .html )
23
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Barbara LID BMP Manual .36 Guidance specific to LID structural BMPs is also available throug hthe Central Coast LID Initiative .3 7
Studies Evaluating Feasibility of Retaining the 95 th Percentile Rain Even t
While there is substantial information available offering broad justification for retentio n
requirements, there is an increasing number of studies evaluating the feasibility of actuall yachieving retention requirements in development projects . Two studies are discussed here :
Horner and Gretz, 2011 :This study investigated the degree to which low-impact developmen tmethods or green infrastructure, can meet retention standards .38 The study assessed fiv e
urban land use scenarios (three residential, one retail commercial, and one infil l
redevelopment), each placed in four climate regions in the continental United States o n
regionally common soil types (Hydrologic Soil Group (HSG) B, C, D).
For the 95th percentile retention standard, the investigators found that infiltration/bioretentio n
methods could retain all post-development runoff and pre-existing groundwater recharge, a s
well as attenuate all pollutant transport, in three residential land use development types on HS G
B soils, in all cases, in all regions, taking a fraction of the available pervious area to do so . Fo r
the more highly impervious commercial retail and redevelopment cases, bioretention woul d
retain about 45 percent of the runoff and pollutants generated and save about 40 percent of th epre-development recharge . Applying roof runoff management measures in these case s
approximately doubled retention and pollutant reduction for the retail commercial land use an d
raised it to 100 percent for the redevelopment scenario . These measures include harvesting ,
temporarily storing, and applying roof runoff to use in the building or, efficiently directing roo f
runoff into the soil through downspout dispersion systems .
Results were generally similar with HSG C soils, although more of the pervious portion of site s
was required to equal the retention seen on B soils . For development on the D soils in al l
climate regions, use of roof runoff management techniques was estimated to increase runof f
retention and pollutant reduction from zero to approximately one-third to two-thirds of the post -development runoff generated, depending on the land use case .3 9
Using the LID methods considered, projects on HSG B and C soils were projected to meet th e95thpercentile retention standard in all but 12 of 125 evaluations . On HSG D soils, al l
hypothetical projects were able to retain greater than 50 percent of the runoff volume associated "with the 85th percentile, 24-hour precipitation event and the authors noted that opportunities t o
use practices or site design principles not modeled in their analysis could potentially furthe rincrease the runoff retention volume .40
The distribution of soil types within the urban areas of the Central Coast indicate tha t
approximately half of the region has high to moderately infiltrative soils, A and B, and half ha sslow to very slow infiltrative soils, C and D (Table 6). The soil groups, based on estimates o f
runoff potential are mapped over broad areas that do not capture variations in the infiltrativ e
36 City of Santa Barbara Storm Water Best Management Practices (BMP) Guidance Manua l(http ://www .santabarbaraca .gov/Resident/Community/Creeks/Storm Water Management_Program .htm)
37 LIDI Structural BMPs . http ://www .centralcoastlidi .org/Central_Coast LIDI/LID Structural BMPs .htm l38Horner and Gretz, 2011 .sa Ibid, p .i .
4o Ibid, p . 42 .
24
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CITY STAFF REPORT - ATTACHMENT 2 - 6 3
ATTACHMENT 2
capacity of soils . Consequently, sites mapped as a particular HSG Group, will likely exhibi t
variation in infiltration capacities .
Table 6.Soil Types within Urban Areas of the Central Coas t
Hydrologic Soil Group . Percentage in Urban Area s
A 13 %
37 %
27 %
Source : Stillwater Sciences, GIS analysi s
Technical Guidance for the Federal EISA:The EISA Technical Guidance includes nine cas e
studies of projects designed to retain the 95 th percentile rain event . The case studies ar e
intended to be representative of the range of projects subject to the EISA requirements an d
include differing geographic locations, site conditions, and project sizes and types ; all fo r
projects with a footprint greater than 5,000 square feet . Assumptions were used to keep a
"somewhat conservative cap" on the scenarios in order to demonstrate the feasibility of th e
approach .'
Although sites varied in terms of climate and soil conditions, in most of the scenarios selected ,
the 95th percentile storm event could be managed onsite with LID and green infrastructur e
systems .42 The case studies include eight sites where it was technically feasible to design th e
stormwater management system to retain the 95th percentile storm onsite . On a ninth site, sit e
constraints allowed the designers to retain only 75% of the 95th percentile storm .4 3
Adjustments to the Runoff Retention Performance Requirements for Redevelopmen t
In acknowledgement of the technical challenges of meeting retention requirements i n
redevelopment contexts, and consistent with a presumed water quality benefit of infill an d
redevelopment, relative to new development, these Post-Construction Requirements includ e
adjustments to the Runoff Retention Performance Requirement for redevelopment . There i s
precedent for such adjustments in other California municipal stormwater permits as well . I n
these Post-Construction Requirements the adjustment is applied to the total amount o f
impervious surface that must meet the Performance Requirement . The adjustments result i n
less of the impervious surface being subject to the retention requirement . In all Regulate d
Projects, one-half (50%) of replaced impervious surface is subject to the Retentio n
Requirements . The entire area (100%) of new impervious surface remains subject to th e
Retention Requirements, unless the project is within an Urban Sustainability Area and eligibl e
for Alternative Compliance . In that instance, one-half (50%) of new imperious surface is subjec t
to the Retention Requirements . The Urban Sustainability Area is discussed in greater detai l
below (Alternative Compliance).
5) Performance Requirement No . 4 : Peak Managemen t
The Peak Management Performance Requirement is applied to projects that create and/o r
replace >22,500 square feet of impervious surface . The criterion itself (post-development pea k
flows shall not exceed pre-project peak flows for the 2- through 100-yr storm events) ha s
precedent in the Central Coast Region as the Santa Barbara County flood control requirement .
Peak management is required only in Watershed Management Zones where receiving water s
41 USEPA, 2009 . p . 26 .42 Ibid, p . 54 .
43 !bid, p . 25 .
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CITY STAFF REPORT- ATTACHMENT .2 -.64
.ATTACHMENT 2 :
(streams) are potentially impacted by hydromodification effects resulting from alterations t o
runoff duration, rate, and volume . These include WMZs 1, 2, 3, 6, and 9 .
Water Board staff recognizes that peak management alone is not sufficient to protec t
downstream receiving waters due to the extended flow durations that can still cause advers e
impacts . However, Water Board staff anticipates that the Peak Management criterion,whe n
used in combination with the Runoff Retention requirement, will achieve a broad spectrum o f
watershed process protection while also protecting stream channels from hydromodificatio nimpacts. Water Board staff's judgment is based on the fact that the retention requirement i s
expected to avoid gross changes in the distribution of runoff between surface and subsurface
flow paths for smaller events, and that peak management is expected to provide critical strea m
protection from the larger events, starting conservatively at the 2-year storm event .
Relationship of Retention/Peak Management to Flow Duration Manaqemen t
Retaining both the runoff produced by small storms and the first part of larger storms ca n
reduce the cumulative impacts of altered flow regimes on receiving water hydrology, includin g
channel degradation and diminished baseflow . For example, the EISA Technical Guidanc e
states, for the purposes of this guidance, retaining all storms up to and including the 95t h
percentile storm event is analogous to maintaining or restoring the pre-development hydrolog y
with respect to the volume,flow rate, duration and temperature of the runoff for most sites .144
Using retention to maintain flow duration in particular addresses a well-recognized cause o f
impacts to stream stability . Many current municipal stormwater permits require flow duratio n
control to protect streams from the effects of flow regimes altered by urban development . Th e
use of flow-duration matching in pre- and post-development conditions to maintain channe l
stability was first suggested in 1989 in watershed plans being developed for the greater Seattl earea. The range of urban-influenced flows requiring control was initially established as one-hal fof the two-year recurrence (0 .5Q2) through the 100-year flow (Qioo).4 5 Flow-duratio n
management typically relies on structural solutions including detention systems with orific e
sizing to maintain release rates below the specified critical flow (e .g ., 0 .5Q2).
The current stormwater control manual for western Washington State regulations includes th e
requirement for flow-duration control from one-half of the two-year recurrence (0 .5Q2) throug h
the 50-year flow (Q5o) and includes an exemption for channels draining long-urbanize d
watersheds (and thus presumably re-stabilized). At the same time, the manual explicitl yrecognizes the fundamental limitation of flow control : "The engineered stormwater conveyance ,
treatment, and detention systems advocated by this and other stormwater manuals can reduce
the impacts of development to water quality and hydrology . But they cannot replicate th enatural hydrologic functions of the natural watershed that existed before development, nor ca n
they remove sufficient pollutants to replicate the water quality of pre-development conditions ."46
While the western Washington State flow-duration requirements remain in place, a recent rulin g
by the Washington State Pollution Control Hearings Board overturned the narrow regulator yfocus on flow-duration standards . The ruling "require[s] non-structural preventive actions an dsource reduction approaches, including Low Impact Development Techniques (LID), to minimiz ethe creation of impervious surfaces, and measures to minimize the disturbance of soils an d
SS2-9 1
44 USEPA, 2009 .45 Helmle and .Booth, 2011a . p . 4 .46 Ibid, p . 4 .
CITY STAFF REPORT - ATTACHMENT 2 - 6 5
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vegetation where feasible ."47 The ruling represents an acknowledgement that flow-duratio n
standards alone are not sufficient to protect or restore receiving waters and that requirement s
associated with on-site retention such as those represented by LID principles, in combinatio n
with flow-duration management of larger storms are more protective .
In California, hydromodification control standards for post-construction new and redevelopmen t
established in the Bay Area municipal permits generally require that post-project runoff shall no t
exceed pre-project rates or durations over a range of storm event sizes from one-tenth of the 2 -
year recurrence flow (0 .1 Q2)up to the 10-year flow (Q1o).48 Meanwhile, in Southern California ,
authors citing several studies that relate storm event discharge to sediment transport, noted tha t
any attempt to match pre-development flow duration across the entire spectrum of discharge s
would be problematic, since development leads to an increase in the total runoff volume and s o
some flows must increase in their total duration to account for the extra total discharge .49
An evaluation of candidate numeric criteria to protect watershed processes conducted for th e
Joint Effort found that overall ; while providing stream channel stability, flow duratio n
management narrowly targets the full spectrum of watershed processes .50 Recognizing the flo w
duration control inherent in the Runoff Retention Performance Requirement as well as th e
limitation of flow duration matching requirements found in other California stormwater permits ,
Water Board staff selected not to include specific criteria for matching flow duration in thes e
Post-Construction Requirements .
6) Performance Requirement No . 5 : Special Circumstance s
The Joint Effort landscape analysis supporting the designation of WMZs was completed at a
scale appropriate to a regional scope and scale of the overall Joint Effort . In any broad-scal e
characterization of a landscape, general patterns will tend to overwhelm minor variations withi n
broad categories, and ignore uncommon exceptions or outright contradictions . The applicatio n
of regional-scale data to specific localities always includes potential errors, either with imprecis e
geographic placement or the loss of detail that may be "insignificant" at a regional scale bu t
quite relevant on a particular location of interest .51 These Post-Construction Requirements
allow the Permittee to designate Regulated Projects as subject to `Special Circumstances '
based on certain site and/or receiving water conditions that were not captured at the regiona l
scale of analysis . The Special Circumstances designations effectively exempt Regulate d
Projects from Retention and/or Peak Management Performance Requirements where those
Performance Requirements would be ineffective or inappropriate to maintaining or restorin g
beneficial uses of receiving waters . Water Quality Treatment Performance Requirements ar e
not affected by Special Circumstance designations (i .e ., no exemptions are available fo r
Performance Requirement 2).
Historic Lake and Wetland Special Circumstanc e
Over time, California has lost many receiving waters such as lakes, and wetlands, to huma n
land use activities (e .g . reclamation, fill, rerouting of water, etc .). These historic environments
had intrinsic value and also provided water quality and hydrologic benefit to downstrea m
waterbodies (e .g ., streams). The Joint Effort analysis was conducted at a scale that did no t
account for these historic hydrologic features and the resulting WMZs do not address th e
47 !bid, p .4
48 Ibid, p . 1 3
49 Ibid, p .7
5o Helmle .C ., 2012 .
51 Booth, et al,2011b . p . 23 .
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CITY STAFF REPORT - ATTACHMENT 2 - 6 6
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special circumstance of their occurrence . Consequently, the infiltration requirements indicate d
for the WMZs may not be appropriate for a development project located where there was once a
historic hydrologic feature such as a lake or wetland . In these situations, pre-developmen t
hydrologic processes did not include significant infiltration of rainwater but did include filtration ,storage, and ponding ; resulting in the feature functioning as a detention facility . When the
largest rainfall events filled these features, their overflow and release of runoff into downstrea m
receiving waters was attenuated by their storage capacity .
Where the Permittee can provide reasonable documentation of the occurrence and location o f
historic lakes and wetlands, it may designate projects within such areas as a Specia l
Circumstance for Historic Lake and Wetland . Such projects are then subject to detention and/o r
peak management Performance Requirements more suited to the historic conditions an d
sensitivity to downstream receiving waters .
The Permittee may select to undertake the analysis to support the designation of the Specia l
Circumstance for Historic Lake and Wetland on a case-by-case basis as projects are propose d
in areas potentially qualifying for the designation . Alternately, the Permittee may pursue a n
area-wide assessment that supports subsequent project designations . In either case, th e
Permittee shall submit a proposal to the Water Board Executive Officer for review and shall not
grant the Special Circumstance designation until the Water Board Executive Officer has grante d
approval .
Hiqhly Altered Channel Special Circumstance
The Permittee may designate Regulated Projects as subject to Special Circumstances fo r
Highly Altered Channels when project runoff discharges into concrete-lined or otherwis e
continuously armored stream channels, or are contained by a continuous underground stor m
drain system, from the discharge point to the channel's confluence with a lake, large rive r
(>200-squaremile drainage area), or ocean .
Intermediate Flow Control Facility Special Circumstanc e
The Permittee may designate Regulated Projects as subject to this Special Circumstance where
Project runoff discharges to an existing flow control facility that regulates flow volumes an d
durations to levels that have been demonstrated to be protective of beneficial uses of th e
receiving water downstream of the facility . The flow control facility must have the capacity t oaccept the Regulated Project's runoff .
Projects in the Highly Altered Channel and Intermediate Flow Control Facility Specia l
Circumstances are considered to present no risk of hydromodification to the streams they drai nto.Consequently, the peak management requirements that would otherwise apply are waived .
However, depending on the WMZ and identified watershed processes, runoff retention may stil l
be required, and in all WMZs, Water Quality Treatment Requirements still apply .
7)Required Hydrologic Analysi s
The computational methods needed to evaluate the runoff from a developed area after applyin g
the Runoff Retention and Peak Management Performance Requirements depend on th edrainage characteristics and the size of the developed area .Use of a continuous simulatio n
model is generally preferred to most accurately estimate changes in runoff due to development.Single event models tend to overestimate peak flow rates from pervious areas because the ycannot adequately model subsurface flow . Additionally, peak flow rates tend to b e
overestimated as the actual time of concentration is typically greater than what is assumed .
28
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Water Board staff recognizes that the use of continuous simulation models, such as thos e
based on the EPA's HSPF (Hydrologic Simulation Program-Fortran), present challenges i n
evaluating flow control options, primarily due to lack of local calibration and adequat e
representation of emerging BMPs, particularly those associated with LID . Water Board staff
also recognizes that failure to achieve high precision in hydrologic analyses in larger project s
presents greater potential risks to water quality than smaller projects . Consequently, th e
hydrologic analysis requirements are tied to project size . For projects between 5,000 an d
22,500 square feet, applicants can use single-event based analyses . For projects >22,500 ft 2
applicants must use a calibrated continuous simulation hydrologic model to calculate runoff ,
retention, infiltration, and water quality treatment performance .
The Water Board strongly encourages that applicants gain an understanding of limitations an d
ways to better estimate conditions when using single-event based hydrologic analysis . The LI D
Manual for Southern California includes a comparison and discussion of commonly used single -
event and continuous simulation models used to evaluate SCMs .
VI . Alternative Compliance (Off-site Compliance )
Alternative Compliance refers to achieving Performance Requirements off-site throug h
mechanisms such as developer fee-in-lieu arrangements and/or use of regional facilities .
Alternative Compliance is allowed for several circumstances including technical infeasibility, a n
approved Watershed or Regional Plan, or an approved Urban Sustainability Area . The Wate r
Board Executive Officer may also approve Alternative Compliance in situations other tha n
these.
Technical infeasibility constrains what can be done on some sites to manage stormwater and a n
alternative is necessary to allow for compliance to be achieved off-site . The site conditions tha t
generally cause or contribute to technical infeasibility in these Post-Construction Requirement s
are consistent with those indicated municipal stormwater permits throughout California . Fo r
Alternative Compliance options to be allowed solely for technical infeasibility, project applicant s
must submit information demonstrating that meeting the Performance Requirements i s
technically infeasible . However, projects allowed Alternative Compliance under Watershed o r
Regional Plans and Urban Sustainability Areas are not required to demonstrate technica l
infeasibility for Runoff Retention and Peak Management, thus affording these projects a n
advantage over projects not covered by those overarching assessments .
The Watershed or Regional Plans and Urban Sustainability Areas are programmati c
approaches that may be undertaken by Permittees to increase their flexibility in th e
implementation of Post-Construction Requirements . Water Board staff recognizes the multipl e
priorities confronting municipalities as they manage the growth occurring within thei r
boundaries. These programmatic approaches require planning and assessment work on th e
part of the Permittee that can balance water quality protection goals with the needs for adequat e
housing, population growth, public transportation and management, land recycling, and urba n
revitalization .
"Stormwater cannot be adequately managed on a piecemeal basis due to the complexity of bot h
the hydrologic and pollutant processes and their effect on habitat and stream quality ."'
52 National Research Council, National Academies Press, 2008 . p . 8 .
29
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CITY STAFF REPORT - ATTACHMENT 2 - 68
ATTACHMENT 2
With this statement and many that follow, a recent report on managing stormwater in the Unite d
States prepared by the National Research Council (NRC) for the United States Environmenta l
Protection Agency (USEPA), argues for a comprehensive strategy to address stormwate r
impacts at a variety of scales and to curb the development patterns that create exces s
imperviousness and other anthropogenic disturbances to watershed processes . Beyond th e
site-level, stormwater impacts are linked to the overall pattern of development in a watershed ,
including its location and form . The NRC report promotes a watershed-based approach t o
stormwater management to move beyond the piecemeal approach and address both site and
watershed scales .
In an effort to invoke such an approach, these Post-Construction Requirements provid e
Permittees with the option of developing Watershed or Regional Plans . This Alternative
Compliance provision is intended to provide Permittees with an opportunity to identify off-sit e
mitigation projects that address the full suite of watershed processes more effectively than coul dbe done on-site . The Plans would identify off-site SCMs that, when implemented, would be a t
least as effective in maintaining watershed processes as on-site implementation of th e
applicable Post-Construction Stormwater Requirements . Watershed and Regional Plans
developed per these Post-Construction Requirements will take into consideration the long-ter m
cumulative impacts of urbanization including existing and future development and include .
Requirements for Projects Covered by a Watershed or Regional Pla n
No adjustments are made to the Performance Requirements for projects in a Watershed Plan o rRegional Plan (i .e ., off-site compliance must meet the same requirements as if met on-site).
The primary relief for the project applicant provided by this Alternative Compliance is th e
permission to go off-site, and the waiving of the requirement to demonstrate technica l
infeasibility of achieving the Performance Requirements on-site .
Requirements for Projects Covered by an Urban Sustainabilitv Are a
The adjustment to Performance Requirements for projects located within an approved Urba n
Sustainability Area is a reduction in the amount impervious surface subject to the RunoffRetention Performance Requirement . Qualifying projects can multiply their total new andreplaced impervious surface by 0 .5 when calculating the volume of runoff to be retained on-site ,or off-site .
The Urban Sustainability Area developed per these Post-Construction Requirements shoul dencompass redevelopment, high density, and transit-oriented development projects that ar eintended to promote infill of existing urban areas and reduce urban sprawl . The Urba n
Sustainability Areas are intended to support the Permittee's efforts to balance water qualit y
protection with the needs for adequate housing, population growth, public transportation an dmanagement, land recycling, and urban revitalization .
Central Coast Water Board staff acknowledges multiple environmental benefits of infill an dredevelopment as compared to greenfield development . While these benefits surely includ ewater quality benefits, they are challenging to quantify in any meaningful sense . Nevertheless ,we can presume a nexus to water quality and watershed health from focusing development i nthe urban core . This `infill' development typically requires less supporting infrastructure (e .g .,roads, utilities) and occurs in areas that are already disturbed, as compared to greenfiel ddevelopment, which creates new impacts and expands the urban footprint .
In recognition of the presumed water quality benefit of infill and redevelopment, and to b econsistent with post-development requirements in other current municipal stormwater permits i n
30
SS2-95
CITY STAFF REPORT - ATTACHMENT 2 - 6 9
ATTACHMENT 2
California, Central Coast Water Board staff includes in these Post-Construction Requirement s
adjustments to Performance Requirements for all redevelopment sites and further adjustment s
for Alternative Compliance projects in an approved Urban Sustainability Area . (See Sectio n
V.4 .)
Central Coast Water Board staff is not basing these adjustments to the Performanc e
Requirements on any assumption that equivalent requirements for infill and greenfield project s
results in fewer infill projects being pursued . Water Board staff cannot predict whether th e
adjustments, which result in less stringent requirements for redevelopment projects, will addres s
any perceived or real aversion to such projects by the development community . Water Boar d
staff has no information beyond anecdotal information to support any assumption abou t
greenfield projects being preferred to infill or redevelopment projects because of the challenge s
of meeting stormwater requirements in infill or redevelopment sites .
The limited information Water Board staff has reviewed does not support the contention tha t
stormwater regulations are a critical factor in determining the location of development . Th e
Smart Growth Association, American Rivers, Center for Neighborhood Technology, Rive r
Network, and the National Resources Defense Council, asked ECONorthwest to investigat e
whether stormwater regulations that require or encourage LID, applied uniformly to greenfiel d
development and redevelopment, would impact developers' decisions about where and how t o
build . The study, based on case studies of multiple municipalities, indicated that implementin g
LID in redevelopment situations tended to be more challenging than on greenfiel d
developments, because LID techniques are usually more site-specific and custom . However ,
developers were not choosing to invest in greenfield developments over redevelopmen t
because of LID standards . The study indicated that developers' decision-making process fo r
projects incorporates a wide range of economic factors, including various construction costs ,
current and future market conditions, regulatory incentives and disincentives, and uncertainty
and risk . Many developers interviewed for the study described the cost of implementin g
stormwater controls as minor compared to other economic factors they considered in decidin g
whether or not to pursue a project, especially in the context of complex redevelopment project s
and green building infill projects . The study points out that the demand for green buildings an d
sustainable stormwater practices has been increasing in response to the rapid growth in th e
global green building industry, which will likely play an important role in developers' decisions fo r
how and where to build .53
VII .Reportin g
1) Project Applicant Reporting to Permitte e
The Post-Construction Requirements require all applicants for projects > 5,000 square feet t o
submit a Stormwater Control Plan . As additional Performance Requirements apply wit h
increasing project size, the information required to be included in the Stormwater Control Pla n
also adjusts accordingly . The Post-Construction Requirements identify specific content s
associated with each Performance Requirement .
Stormwater Control Plans provide the Permittee information to support review of project SCM s
and are often required in California municipal stormwater permits to improve implementation o f
post-construction requirements . They address a common difficulty encountered when projec t
applicants and municipal staff evaluating projects lack experience with identification an d
implementation of LID stormwater management strategies . This can lead to a reliance o n
53 ECONorthwest, 2011
SS2-9 6
31
CITY STAFF REPORT -ATTACHMENT 2 7 0
ATTACHMENT 2
conventional stormwater management strategies when alternatives that provide greate r
protection of watershed processes are available and feasible . Stormwater Control Plans serv e
to focus project review on key steps of the LID design process that are inherently difficult t o
evaluate, including : site assessment, site design, and runoff reduction measures . They als o
provide the framework for the applicant to submit the necessary technical information to indicat e
the infeasibility of meeting Performance Requirements on-site .
2) Permittee Reporting to the Central Coast Water Boar d
The reporting requirements include items that the Permittee must submit to the Water Boar d
throughStormwater Program Annual Reporting . The information is necessary for the Wate r
Board to evaluate compliance with these Post-Construction Requirements . The requirements
are scalable to the size of the municipality in that smaller municipalities with less developmen t
activity will have less to report than larger municipalities with more development activity .
VIII . Reference s
Booth, Derek B ., E .A . Gilliam, S . Araya, C . Helmle ; and J . Riverson .2011a .Watershe d
Characterization Part 2 : Watershed Management Zones and Receiving-Water Conditions .
Report by Stillwater Sciences and TetraTech, Santa Barbara, CA,for Central Coast Regiona l
Water Quality Control Board Joint Effort for Hydromodification Control and LID, 52 pp .
Booth, Derek B ., E .A. Gilliam, S . Araya, and C . Helmle . 2011b .The Linkage Analysis :
Landscape Characterization, Receiving-Water Conditions, Watershed Processes, and Huma n
Disturbance .Report by Stillwater Sciences and TetraTech, Santa Barbara, CA, for Centra l
Coast Regional Water Quality Control Board Joint Effort for Hydromodification Control and LID ,62 p p
Booth, Derek . B ., S . Araya, C . Helmle, and E .A . Gilliam, 2012 .Methodology Report .Report b y
Stillwater Sciences and TetraTech, Santa Barbara, CA, for Central Coast Regional Wate r
Quality Control Board Joint Effort for Hydromodification Control and LID .
Coleman, Derrick, Craig MacRae, and Eric D . Stein, 2011 .Effect of Increases in Peak Flow sand Imperviousness on the Morphology of Southern California Streams . Technical Report No .450. Southern California Coastal Water Research Project, April 2005 .
ECONorthwest, 2011 .Managing Stormwater in Redevelopment and Greenfield Developmen tProjects Using Green Infrastructure : Economic Factors that Influence Developers' Decision .June .
Federal Register 64, 8 December 1999 :National Pollutant Discharge Elimination System –
Regulations for Revision of the Water Pollution Control Program Addressing Storm Wate rDischarges, Final Rule .Web accessed August 10, 2011 .
Helmle, C ., D .B . Booth, 2011a .Development and Implementation of HydromodificationContro lMethodology: Literature Review.Report by TetraTech and Stillwater Sciences, Santa Barbara ,CA,for Central Coast Regional Water Quality Control Board Joint Effort for Hydromodificatio nControl and LID . January .
Helmle, C ., D .B . Booth, 2011b .Development and Implementation of Hydromodification Contro lMethodology: Review of Existing Data .Report by TetraTech and Stillwater Sciences, Sant a
32
SS2-97
CITY STAFF REPORT - ATTACHMENT 2 - 7 1
ATTACHMENT 2
Barbara, CA, for Central Coast Regional Water Quality Control Board Joint Effort fo r
Hydromodification Control and LID . May .
Helmle, C ., D .B . Booth, 2011c .Watershed Characterization Part 1 : Precipitation an d
Landscape .Draft Report by TetraTech and Stillwater Sciences, Santa Barbara, CA, for Centra l
Coast Regional Water Quality Control Board Joint Effort for Hydromodification Control and LID .
July 7, 2011 .
Helmle, C ., 2012 .Summary of Candidate Numeric Criteria Effectiveness .Report by TetraTech ,
Santa Barbara, CA, for Central Coast Regional Water Quality Control Board Joint Effort fo r
Hydromodification Control and LID . March .
Horner, R . R ., J . Gretz, 2011 .Investigation of the Feasibility and Benefits of Low-Impact Sit e
Design Practices Applied to Meet Various Potential Stormwater Runoff Regulatory Standards .
Report to U .S . Environmental Protection Agency from Natural Resources Defense Council .
December.
Hunt, William F ., A . Davis, and R . Traver .Meeting Hydrologic and Water Quality Goals throug h
Targeted Bioretention Design .Journal of Environmental Engineering, Submitted March 7, 2011 ;
accepted October 6, 2011 ; posted ahead of print October 8, 2011 . Copyright 2011 by th e
American Society of Civil Engineers, 15 pp .
National Research Council, National Academies Press, 2008 .Urban Stormwater Management
in the United States.Washington, D .C .: Web . 16 August 2011 .
<www .epa .gov/npdes/pu bs/n rc_stormwaterrepo rt . pdf>.
Reid, L . M ., Thomas Dunne, 1996 .Rapid Evaluation of Sediment Budgets .Catena Verla g
GmbH, Germany, 164 pp . (Secondary reference quoted by Booth, et al, 2011b .)
Schueler, T.R., and Heather K . Holland, eds . , 2000a .The Importance of Imperviousnes s
(Article 1)." Watershed Protection Techniques .Ellicott City, MD : Center for Watershe d
Protection .
Schueler, T .R ., and Heather K . Holland, eds ., 2000b .Storm Water Strategies for Arid and Semi -
Arid Watersheds (Article 66)." Watershed Protection Techniques.Ellicott City, MD : Center fo r
Watershed Protection .
Stenstrom, Michael K . and Masoud Kayhanian, 2011 .First Flush Phenomeno n
Characterization, Report No . CTSW-RT-05-073-02 .6.California Department of Transportation ,
August 2005 Web . 11 August . <http ://www .dot .ca .gov/hq/env/stormwater/special/newsetup/>.
USEPA, 2009 . Technical Guidance on Implementing the Stormwater Runoff Requirements fo r
Federal Projects under Section 438 of the Energy Independence and Security Act . December .
EPA 841-B-09-001 .
2010 . MS4 Permit Improvement Guide . April . EPA 833-R-10-001 .
33
SS2-98
CITY STAFF REPORT - ATTACHMENT 2 - 7 2
ATTACHMENT 2
ATTACHMENT A
Watershed Management Zone s
Available electronically at :
http ://www.waterboards .ca .gov/centralcoast/water issues/programs/stormwater/d
ocs/lid/lid hvdromod charette index .shtml
34
SS2-99
CITY STAFF REPORT - ATTACHMENT 2 - 7 3
ATTACHMENT 2
ATTACHMENT B
Designated Groundwater Basin s
Groundwater basin areas are defined by the California Department of Water Resource s
(CDWR)5 4 and used in the Central Coast Water Board Joint Effort for Hydromodificatio n
Control to identify groundwater receiving-water issues and areas where recharge is a
key watershed process . CDWR based identification of the groundwater basins on th e
presence and areal extent of unconsolidated alluvial soils identified on a 1 :250,00 0
scale from geologic maps provided by the California Department of Conservation ,
Division of Mines and Geology . CDWR then further evaluated identified groundwate r
basin areas through review of relevant geologic and hydrogeologic reports, wel l
completion reports, court-determined adjudicated basin boundaries, and contact wit h
local agencies to refine the basin boundaries .
Designated Groundwater Basins include those identified in the CDWR Groundwate r
Basins Map . Numbers correspond to Groundwater Basins in Table 1 .
5 'California Department of Water Resources . 2004 . Groundwater basin map .
<http ://www .water .ca .gov/groundwater/bulletin118/gwbasin_maps_descriptions .cfm >. Accessed
September 15, 2006 .
35
SS2-100
CITY STAFF REPORT - ATTACHMENT 2 - 7 4
ATTACHMENT 2
Coast Hydromodii cation Projec t
CDWR Groundwater Basin s
t i(7 i :;_Pa wr,I,:for hers1cxtd{x, ',,16
tr 13 2 to
1.1i1~;1
Central /.A Ili:,
arc
36
SS2-101
CITY STAFF REPORT - ATTACHMENT 2 - 7 5
ATTACHMENT 2
Table 1 :...,....Groundwater Basins in the Central Coast Region by GIS Basin Numbe r
Chorro valle y
Morro valle y
GIS BASIN GROUNDWATER BASIN NAM E
NUMBE R
1 Carpinteria
Santa Barbara
Montecit o
Foothil l
i 24 Cayucos valle y
Old valle y
26 Villa valle y
27 Santa Rosa valle y
28 an Simeon valle y
( 29 Arroyo de la Cruz valle y
30 San Carpoforo valle y
3 132
33 ,.,.
4
GIS BASIN GROUNDWATER BASI N
NUMBER NAM E
35 Peach Tree valle y
36 Hernandez valle y
37 Salinas valle y
38 Bitter Water valle y
Dry Lake valle y
Carmel valley
Salinas valle y
San Benito river valle y
Gilroy Hollister valle y
1 Pajaro valle y
Scotts valle y
63 Felton are a
64 Santa Cruz Purisima formatio n
65 Ano Nuevo are
a 66Gilroy-Hollister valle y
Pescadero valle y
Santa Clara valle y
8
9
i 7
Golet a
Santa Ynez River valle y
Santa Ynez River valle y
Lockwood valle y
Mil Potrero are a
San Antonio Creek valle y
11 1 Huasna valle y
Santa Mari a
Cuyama valley
Big Spring are a
Rafael valley
San Luis Obispo valley
Los Osos valley
Rinconada valle y
Pozo valle y
Toro valle y
Carrizo Plai n
Cholame valle y
Salinas valle y
Lockwood valle y
Salinas valley
Salinas valle y
Tres Pinos valle y
Salinas valle y
Upper Santa Ana valle y
Salinas valle y
Salinas valley
Santa Ana valle y
Quien Saba valle y
Gilroy-Hollister valle y
Soquel valley __.__._..
West Santa Cruz terrace
West Santa Cruz terrace
Needle Rock poin t
Gilroy Hollister valle y
West Santa Cruz terrac e
West Santa Cruz terrace
37
SS2-102
CITY STAFF REPORT - ATTACHMENT 2 - 7 6
Flow Chart to Determine Performance Requirement s
Start Her e
Is the project
Exempt or does no t
discharge to MS4 ?
YES NO
Project is < 2,500 ft 2
of new and replace d
impervious surfac e
YES NO
Project is a
detached singl e
family residence ?
YES N O
y
SFR > 2,500 ft2
See Figure 1 d
EXEMPT
No Stormwate r
Requirements
All Others
See Figure l b
Figure la .Initial Screening for All Development Projects
SS2-103
CITY STAFF REPORT - ATTACHMENT 2 - 7 7
Projects > 2,500 ft 2
Project is > 2,50 0
but < 5,000 ft 2 o f
new and replace d
impervious surfac e
Performance Requirement #1
(Site Design)
Project is > 5,00 0
but < 15,000 ft 2 o f
NET imperviou s
surfac e
Performanc e
Requirements #1
(Site Design) and #2
(WQ Treatment)
Project is >15,000 ft 2
of new and replace d
impervious surfac e
See Figure 1 c
Figure lb .Requirements for Small to Moderate Development Projects
SS2-104
CITY STAFF REPORT - ATTACHMENT 2- 78
Projects >15,000 ft 2 new and replaced impervious are a
Ye sDoestheproject fall under th e
Special Circumstance s
designation?
See Specia l
Circumstance s
(Performance
Requirement #5 )
No
Determine WMZ and appl y
Performance Requirement #3
(Runoff Retention )
Watershed Management Zon e
1 2 3 4 5 6 7 8 9 1 0
1.Retain 95 th Percentile event via infiltratio n
2.Retain 95 th Percentile event via storage, harvesting, infiltration and/or evapotranspiratio n
3.N/A
4.Retain 95 th Percentile event via infiltration where overlying Groundwater Basi n
5.Retain 85 th Percentile event via infiltratio n
6.Retain 85 th Percentile event via storage, harvesting, infiltration and/or evapotranspiratio n
7.Retain 95th Percentile event via infiltration where overlying Groundwater Basi n
8.Retain 85th Percentile event via infiltratio n
9.Retain 85th Percentile event via storage, harvesting, infiltration and/or evapotranspiratio n
10.Retain 95 th Percentile event via infiltration where overlying Groundwater Basi n
No additiona l
Stormwater
Requirements
Project in WMZ 1, 2, 3, 6, or 9 ?
Project creates >22,500 ft 2 of new an d
replaced impervious surface
Apply Performanc e
Requirement #4
(Peak Management )
Figure 1c . Requirements for Large Development Project s
Yes
SS2-105
CITY STAFF REPORT - ATTACHMENT 2 - 7 9
Detached Single Family Residential Project s
Project i s
> 2,500 ft 2 bu t
< 15,000 ft 2 new an d
replaced imperviou s
surfac e
Performance
Requirement
#1
Project i s
> 15,000 ft 2 but <
22,500 ft 2 new an d
replaced imperviou s
surface
Performance
Requirement #s
1, 2, and 3
Project i s
> 22,500 ft 2 ne w
and replace d
imperviou s
surfac e
Performanc e
Requirement It s
1, 2, 3, and 4
Figure 1d . Requirements for Single Family Residential projects
SS2-106
ATTACHMENT 3 -1
Definition s
Impervious Surfaces are those surfaces that do not allow water to penetrate them, but rathe r
result in runoff . Standard asphalt concrete paving, commonly used in parking lots and on streets ,
is a typical example .
Low Impact Development (LID)is a group of practices that work together to mimic,to th e
extent possible, the natural processes of the land . This could be something as simple as avoidin g
development near a creek or providing areas for rain to infiltrate .
Net impervious is the sum of reconstructed impervious areas and new impervious areas, minu s
new pervious areas created through removal of previous impervious areas . For example,a
property has 10,000 square feet (ft) of building and paving on it at the time redevelopment i s
proposed . The new development removes all the impervious surfaces, restoring all imperviou s
areas but 2,000 ft2 of what was parking lot to put in landscaping, adds 1,000 ft2 of new building
area where landscape previously existed, and replaces another 3,000 ft 2 of parking area with a
pervious surface . The total is then 8,000 (10,000-2,000) reconstructed + 1,000 new impervious —
3,000 pervious = 6,000 ft 2 net impervious for purposes of regulation where the term "ne t
impervious" is used .
Peak Management is for the largest developments and entails keeping the highest flow s
managed to a level that does not exceed the flows that left the site prior to the new development .
If the site was previously developed, this may not be that difficult . If the site was undeveloped, it
would be more challenging . This form of stormwater management is similar to what is currentl y
required by the City for flood control and generally achieved through detention basins . Th e
basins store large flows and meter them out to the drainage system .
Retention of stormwater entails preventing water from leaving the site . The majority of the area s
available for development in the City are designated as Water Management Zone 1
Development in Zone 1 must comply with the retention regulation through infiltration . Thos e
areas have been designated to pursue infiltration of water because they naturally infiltrate wate r
into soil layers or overlay a groundwater basin . The soils are still of a clay type and in areas o f
existing development, compacted, making infiltration between the surface and the sub-surfac e
problematic .
Site Design is a process through which a prospective developer looks at the site and creates a
design that minimizes impacts to natural features and minimizes runoff There are no set runoff
reduction requirements .
Special Circumstances covers situations where it does not make sense to pursue retention o r
peak management . The recognized special circumstances include discharge to concrete line d
channels, and infiltration in areas that naturally accrue water, such as low spots .
Water Quality Treatment is a lower level of requirement for addressing runoff. Where
impervious surfaces are created on a site, the development will be required to treat a specifie d
volume of water to remove pollutants . The preferred method is through infiltration o r
SS2-107
ATTACHMENT 3 -2
evapotranspiration which will also reduce runoff. The use of soils and plant material to clea n
water is also acceptable, where water is directed through a drainage channel and passes throug h
vegetation and soil before reaching a piped system that carries it to a traditional drainage system .
SS2-108
'or3nwat'erQua/it /~.)tt t ro ,+("IC'IICt'Rl7t l
July 6, 201 2
Mr . Dominic Roque s
California Regional Water Quality Control Boar d
Central Coast Region
Subject : Comments on the Draft Resolution Approving Post-Construction Stormwate r
Management Requirements for Developing Projects in the Central Coast Regio n
Dear Mr . Roques :
The California Stormwater Quality Association appreciates this opportunity to comment on th e
subject Draft Resolution Approving Post-Construction Stormwater Management Requirements for
Developing Projects in the Central Coast Region ("Draft Resolution") and Attachment 1 of the Draf t
Resolution containing the Post-Construction Stormwater Management Requirements ("Post -
Construction Requirements"). CASQA typically comments on regional requirements only whe n
there is an issue of potential statewide significance . Accordingly, we are compelled to provid e
specific comments on some of the provisions of the Post-Construction Requirements for the Centra l
Coast Region . However, before we provide our specific comments we offer the followin g
observations and comments :
CASQA is very concerned with the apparent escalation in permit requirements being conducte d
by the various Water Board permit writers in drafting provisions for land development . Over
the last few years we have seen the ratcheting up of new development requirements in eac h
MS4 permit renewal without allowing time to assess the impact/effectiveness of the prio r
development requirements . This lack of a cohesive approach-and standard has created a n
uneven playing field for communities and developers . Furthermore, the clear absence of an y
consensus within the State on what the requirements are for land development (particularly wit h
respect to Hydromodification Management) is damaging to the credibility of the entir e
stormwater program .
The proposed Central Coast requirements ignore the 1993 State Water Board definition o f
maximum extent practicable (MEP)1 that clearly established public acceptance and a
reasonable cost :benefit calculation as fundamental tenets of MEP .
Our specific concerns are listed below and expanded upon in the remaining part of the letter :
The requirement to retain runoff from storm events up to the 9 5 th percentile 24-hour rainfall
event is unreasonable, infeasible for many projects, has no demonstrated additiona l
environmental benefit and is not cost-effective .
See E . Jennings, Office of Chief Counsel, 2/11/93 memo to A . Mathews, Division of Water Quality regardin g
"Definition of Maximum Extent Practicable".
J't.i . i3,,x Nlon?t,t'dr .C1<a 1O2 ' 1)1t,3nr,,lU}%wIvtv.<osqri .olz
CASQA comments on the Draft Resolution Approving Post-Construction Stormwate r
Management Requirements for Developing Projects in the Central Coast Regio n
The hydromodification management (HM) standard requiring matching post-project t o
pre-project peak flows for the 2- through 100-year events, in combination with a runof f
retention standard, is inconsistent with HM studies and approaches to date and may no t
be as protective of creek channels as a flow duration control approach . There is no
technical basis to deviate from the extensive study that has been completed o n
hydromodification elsewhere in the State .
3.The retention and HM requirements, and some of the LID requirements, are inconsisten t
and go beyond those of existing or proposed statewide, regional, or local Phase I or Phas e
II MS4 permits in California .
4.Schedules for adoption of the Draft Resolution and Draft Phase II Permit need to b e
better coordinated, and the adoption of the Draft Resolution should be delayed .
A discussion of our specific concerns is presented below :
1 . The requirement to retain runoff from storm events up to the 95 th percentile 24-
hour rainfall event is unreasonable, infeasible for many projects, has n o
demonstrated additional environmental benefit, and is not cost-effective .
The Draft Resolution designates 10 watershed management zones (WMZs) based o n
receiving water type, geology and percent slope . Projects that create and/or replac e
15,000 square feet of impervious surface in WMZs 1 and 2, and portions of WMZs 4, 7 ,
and 10 that overlie designated Groundwater Basins are required to retain runoff fro m
storm events up to the 95 th percentile 24-hour rainfall event . Based on Table 5 of th e
Draft Technical Support Document (Attachment 2 of the Draft Resolution), thi s
requirement would apply to 72-86% of the Central Coast's urban area (depending on th e
extent of the groundwater basins), so this requirement will have a significant impact o n
development projects in the region .
It is well established that water quality control measures are most economical an d
efficient when they target small, frequent storm events that over time produce more tota l
runoff than the larger, infrequent storms targeted for design of flood control facilities .
Typically, design criteria for water quality control BMPs are set to coincide with th e
"knee of the curve", i .e ., the point of inflection where the magnitude of the event (an d
corresponding cost of facilities) increases more rapidly than the number of event s
captured. In other words, targeting design storms larger than this point will produc e
volume retention gains but at considerable incremental cost2 . Capturing this additional
incremental volume beyond the 85 th percentile has not been demonstrated to be mor e
protective than the standard adopted by the rest of the State .
In fact, this is the very basis of the criteria in most Phase I MS4 permits and the draf t
Phase II permit for sizing stormwater control measures to capture the 85 th percentile, 24 -
hour storm . This storm event was determined to be the "maximized" or "optimized "
2 CASQA Stormwater BMP Handbook, New Development and Redevelopment, 2003 .
July 6, 2012
2
SS2-11 -0
CASQA comments on the Draft Resolution Approving Post-Construction Stormwate r
Management Requirements for Developing Projects in the Central Coast Regio n
capture volume based on studies by Urbonas, et . al . in the 1990s . These studies led to the
development of an approach for estimating the maximized stormwater quality captur e
volume presented in "Urban Runoff Quality Management", which is referenced by mos t
permits as one of the acceptable approaches for computing the water quality desig n
volume3 .
The technical analysis of the feasibility of the 95 th percentile storm standard did not take
total facility cost or cost-effectiveness into account . The 95 th percentile, 24-hour storm
volume is approximately twice that of the 85 th percentile 24-hour storm . A sensitivit y
analysis performed for the City of Denver showed that doubling the maximized captur e
volume results in a very small increase in the total annual runoff captured .4 While
doubling the size of a facility to retain the 95 th vs . the 85 th percentile storm may not
completely double the capital cost of the facility, it will likely double the opportunit y
cost, i .e., the surface area of the site that must be used for the stormwater control measur e
and can't be used for other purposes .
During the public workshop on the Draft Resolution held on June 6, 2012, Mr . Robert
Ketley of the City of Watsonville presented a case study demonstrating the difficulty o f
retaining the 95 th percentile storm in the Central Coast development environments The
case study involved a 3-acre commercial redevelopment project in Watsonville that
would be 89% impervious (11% landscaped area). The site is in WMZ 1 and would have
to retain the 95th percentile event (1 .23 inches) by infiltration . The case study use d
median values for soil infiltration rates for Hydrologic Group A, B, C, and D soils an d
assumed a 72-hour maximum drawdown time . Given these assumptions, it was estimate d
that the surface area of the infiltration facilities would require 7% of the site area for A
and B soils, 16% of the site area for C soils, and 69% of the site area for D soils .Water
Board staff replied that these were conservative assumptions, and that by their estimates ,
type A/B soils, C soils, and D soils require about 5%, 10% and 40% of the site are a
dedicated to the BMP, respectively . However, these values are still significantly greate r
than the amount of the site needed for retention of the 85 th percentile storm .
CASQA appreciates that the . Draft Resolution includes some incentives for smart growt h
and redevelopment in currently urbanized areas of the Central Coast . These include
allowing redevelopment projects to retain the runoff volume from only half of th e
replaced or new/replaced impervious surface (depending on whether or not the project i s
in an Urban Sustainability Area). However, retention of the 95 th percentile storm wil l
still be challenging for redevelopment projects, and infeasible for those with D soils .
The Draft Resolution's standard for retention of the 95 th percentile storm seems to b e
based, in part, on the Technical Guidance on Implementing the Stormwater Runof f
Requirements for Federal Projects under Section 438 of the Energy Independence an d
Security Act of 2007 (EISA). However, the Draft Resolution takes only part of th e
3 WEF Manual of Practice No . 23/ASCE Manual and Report on Engineering Practice No . 87, 1998 .4 Ibid ., Table 5 .3, p . 174 .
5 See the workshop presentation posted on the Central Coast Water Board's website :http ://www .waterboards .ca.gov/centralcoast/wateris sues/p rograms/stormwater/dots/lid/workshop 2 .pd f
July 6, 2012 3
SS2-111
CASQA comments on the Draft Resolution Approving Post-Construction Stormwate r
Management Requirements for Developing Projects in the Central Coast Regio n
Section 438 Technical Guidance and does not include specific language and options i n
the federal Act that could make implementation feasible . Specifically :
•Section 438 Technical Guidance provides an option for site specific hydrologi c
analysis to demonstrate a match to pre-development flow rates and volumes instead
of using the generalized 95 th percentile approach .
•Section 438 Technical Guidance always provides options of evapotranspiration an d
harvesting and reuse as opposed to the Draft Resolution, which requires onl y
infiltration, be used for most areas where development will occur.
Section 438 Technical Guidance includes specific conditions that can be used to
justify a determination that it is not technically feasible to fully implement th e
criteria, such as small project sites, soils that cannot be sufficiently amended t o
provide for the requisite infiltration rates, and where rainwater harvesting and use i s
not practical .
Where a determination of technical infeasibility has been made, projects can b e
approved based on implementation to the maximum extent technically feasibl e
whereas the Draft Resolution requires off-site compliance regardless of whether a
feasible off-site option is available to the applicant .
CASQA strongly requests that either the retention standard be reduced to the 85 th
percentile storm or that more flexibility be provided in implementing the standard up to
a certain level offeasibility or cost.
2 . The hydromodification management standard requiring matching post-project t o
pre-project peak flows for the 2- through 100-year events, in combination with a
runoff retention standard, is inconsistent with hydromodification managemen t
studies and approaches to date and may not be as protective of creek channels as a
flow duration control approach . There is no technical basis to deviate from th e
extensive study that has been completed on hydromodification elsewhere in th e
State .
The hydromodification management standard used in many Phase I permits throughou t
the State is that "increases in runoff flow and volume shall be managed so that post -
project runoff shall not exceed pre-project peak flows, volumes and durations"6 .
Numerous studies have documented that matching peak flows alone for a range of storm s
is not protective of streams because flow durations are increased and can cause advers e
erosive impacts . This fact is recognized by the Central Coast Water Board in Attachmen t
2 of the Draft Resolution, which states that :
6 Example taken from the San Francisco Bay Region, Municipal Regional Stormwater NPDES Permit, Order No .
R2-2009-0074,as revised November 28, 2011, Provision C .3 .g .
July 6, 2012 4
SS2-112
CASQA comments on the Draft Resolution Approving Post-Construction Stormwate r
Management Requirements for Developing Projects in the Central Coast Regio n
"Water Board staff recognizes that peak management alone is not sufficient to protec t
downstream receiving waters due to the extended flow durations that can still caus e
adverse impacts . However, Water Board staff anticipates that the Peak Management
criterion, when used in combination with the Runoff Retention requirement, wil l
achieve a broad spectrum of watershed process protection while also protectin g
stream channels from hydromodification impacts . Water Board staff's judgment i s
based on the fact that the retention requirement is expected to avoid gross changes i n
the distribution of runoff between surface and subsurface flow paths for smalle r
events, and that peak management is expected to provide critical stream protectio n
from the larger events, starting conservatively at then-year storm event."
This combination standard has not been thoroughly studied as to its effectiveness in
protecting streams, nor is it consistent with current approaches throughout the State that
have been studied . We also have concerns about 1) using retention of the 95 th percentil e
storm as the method to address the effects of smaller events, which appears to go beyon d
requirements to replicate the pre-project (as well as the pre-development) condition ; and
2) requiring peak flow matching up to the 100-year event .
Retention of the 95 th percentile storm – The specific criterion that addresses th e
smaller events is to "prevent offsite discharge from events up to the 95t h percentil e
rainfall event as determined by local rainfall data". This statement means tha t
projects need to be designed to discharge runoff only during rare events . For
example, in the City of Salinas, the 95 th percentile rainfall event is 0 .98 inches .
There were only 42 days during the 30-year period from 1979 through 2008, a n
average of 1 .4 days per year, when rainfall exceeded this depth . Limitin g
discharge of runoff to an average of 1 .4 days per year is not consistent wit h
maintaining predevelopment hydrologic conditions in most areas . Pre-developmen t
conditions would have typically resulted in 10 to 20 percent of rainfall from the 9 5 th
percentile event becoming runoff, depending on soil type, and more of it would ru n
off when the ground is saturated from previous rainfall . It is not reasonable, o r
environmentally beneficial, to require runoff to be reduced to less than pre -
development conditions .
Peak flow matching to the 100-year event - Discrete event criteria such as thes e
have not been shown to be an appropriate basis for hydromodification management .
This type of criteria may be appropriate to size detention basins to mitigate fo r
potential impacts to local storm drainage systems, but because determination o f
peak flows is dependent on time of concentration, the approach is not generall y
applicable to a receiving stream that has a time of concentration significantl y
different than the site being developed . In addition, requiring discrete even t
matching up to the 100-year storm is excessive and not cost-effective . Studie s
conducted for the Santa Clara Valley Urban Runoff Program on the effects o f
increased flows on the erosion potential of streams showed that a significan t
amount of erosive "work done" (90-95%) on the channel bed and bank is associate d
Pers . comm. with Harvey Oslick, RBF Consulting, consultant to the City of Salinas, who conducted the rainfal lanalysis.
July 6, 2012
SS2-1 13-
CASQA comments on the Draft Resolution Approving Post-Construction Stormwate :r
Management Requirements for Developing Projects in the Central Coast Regio n
with flows up to the 10-year peak flow . Flows higher than the 10-year peak flo w
perform a very small percentage of the total work (5-10%) because they occu r
infrequently over the period of record .8
The flow duration control approach being used by Phase I communities in the State ha s
proven to be feasible, numerous technical studies have shown that the approach i s
protective of streams, and technical tools such as the Bay Area Hydrology Mode l
(BAHM) have simplified the use of continuous simulation models . Taking a simila r
approach to Phase I permits would also make implementation more straightforward fo r
Central Coast MS4s that are Phase I MS4s (i .e ., City of Salinas) as well as those
adjoining Phase I MS4s (i .e ., south Santa Clara County).
CASQA recommends that the Draft Resolution be revised to contain a HM approac h
that is consistent with other permits.
The retention and HM requirements, and some of the LID requirements, ar e
inconsistent with and go beyond those of existing or proposed state-wide, regional ,
or local Phase I or Phase H MS4 permits in California .
The Draft Resolution states that the maximum extent practicable standard "is an ever-
evolving, flexible, and advancing concept, which considers technical and economi c
feasibility", and that the proposed Post-Construction Requirements "are consistent wit h
the evolving MEP standard ." CASQA is very concerned that the "evolving ME P
standard" expressed by the proposed Post-Construction Requirements is inconsistent wit h
the MEP standard in all other California stormwater permits, is not technically well
supported, and did not consider economic feasibility, as discussed earlier in ou r
comments .
In addition to the concerns we have raised about the 95 th percentile storm retentio n
standard and the HM peak flow matching standard, we are also concerned about th e
following inconsistencies with other California permits :
Thresholds for HM requirements are much lower than existing or proposed permit s
(15,000 square feet and 22,500 square feet of created/replaced impervious surfac e
for runoff retention and peak matching, respectively).
Post-project vs . pre-project peak matching is required up to the 100-year storm ,
which is beyond most existing requirements and more appropriate for flood contro l
facilities .
The options for LID treatment or runoff retention on project sites do not includ e
infiltration trenches, basins, and drywells, and no explanation for this is provided i n
the Draft Resolution or attachments . The Draft Resolution states that these so -
called "conventional designs" are only allowed for use in meeting retentio n
8 SCVURPPP, 2005 . Hydromodification Management Plan - Final Report .
July 6, 2012 6
SS2-114
CASQA comments on the Draft Resolution Approving Post-Construction Stormwate r
Management Requirements for Developing Projects in the Central Coast Regio n
requirements where LID measures are infeasible . When properly sited an d
designed, these facilities are considered acceptable in other permits as part of th e
suite of options for LID retention and/or treatment, and should be available option s
for Central Coast MS4s as well .
• A minimum planting media depth of 24 inches is required in a biofiltration system ,
which differs from other permits and guidance across the state, and no technica l
justification is provided .
CASQA strongly requests that the Post-Construction Requirements be revised to b e
more consistent with requirements in other Phase I and Phase II permits in the Stat e
and not be allowed to define an "evolving MEP" without sufficient technical an d
economic analysis and coordination with the State Water Board and other Regiona l
Boards .
4 . Schedules for adoption of the Draft Resolution and the Draft Phase II Permit nee d
to be better coordinated and the adoption of the Draft Resolution should be delayed .
The Draft Resolution containing post-construction requirements for Central Coast MS4 s
is inextricably linked to the draft Phase II Permit, which is in a concurrent process o f
public review . Linkages or potential linkages include the following :
Provision E .12 .i of the draft Phase II Permit states that Central Coast small MS4 s
shall comply with the Central Coast post-construction requirements develope d
pursuant to the Central Coast Water Board Joint Effort for Hydromodificatio n
Control, in place of complying with the requirements set forth in Provision E .1 2
(except for two provisions on Planning and Building Document Updates and Sourc e
Control Requirements).
Provision E . 12 .d .2 .(ii)(3)c . of the draft Phase II Permit includes a reopener for LI D
requirements that states that the State Water Board Executive Director may evaluat e
newly available technical data and other information regarding the effectiveness o f
source control, runoff reduction, stormwater treatment, and baseline hydrograp h
modification management measures and may propose revisions to these criteria .
• Provision E .12 .f. of the draft Phase II Permit states that, within the second year o f
permit implementation, the State and Regional Water Boards will determin e
whether the LID and hydromodification management requirements in E .12 .d an d
E .12 .e . are protective of specified watershed processes [similar to those identified i n
the Draft Resolution] or if modified criteria should apply .
Because of these linkages, and the possibility that Central Coast requirements could serv e
as model for modified criteria in the Phase II Permit, final adopted language in the Draf t
Resolution could affect final or future language in the Phase II Permit . The date for
Central Coast Water Board consideration of adoption of the Draft Resolution i s
September 6, 2012, whereas the date for State Water Board consideration of adoption o f
July 6, 2012 7
SS2-115
CASQA comments on the Draft Resolution Approving Post-Construction Stormwate r
Management Requirements for Developing Projects in the Central Coast Regio n
the draft Phase II permit is expected to be sometime in October 2012 .The earlie r
adoption of the Draft Resolution could result in inconsistencies or preclude revisions to
the Phase II Permit . In addition, there are many small MS4s in regions other than th e
Central Coast that may be unaware of the effect that the Central Coast requirements ma y
have on their future Phase II requirements . There should be sufficient time allowed t o
raise awareness of these linkages at public hearings .
CASQA strongly recommends that the adoption of the Draft Resolution be delaye d
until after the adoption of the Phase II Permit .
We thank you again for the opportunity to provide our comments and we ask that the Centra l
Coast Water Board carefully consider them . If you have any questions, please contact CASQA
Executive Director Geoff Brosseau at (650) 365-8620 .
Sincerely ,
Richard Boon, Chair
cc : Tom Howard, State Water Board
Jonathan Bishop, State Water Boar d
Vicky Whitney, State Water Boar d
Bruce Fujimoto, State Water Boar d
CASQA Board of Directors and Executive Program Committe e
July 6,2012 8
SS2-116