HomeMy WebLinkAboutA23004 Onsite Drainage Analysis PDF (1)
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ONSITE DRAINAGE
ANALYSIS
For
Crockers Lockers Self-Storage
3745 Sueldo Street (n/o Innovation Way)
San Luis Obispo, CA 93401
(APN: 053-251-083 & -084)
February 16, 2024
Prepared For:
Crocker’s Lockers/Darme Holding Co, Inc.
7036 Valley Greens Circle
Carmel, CA 93923
831-582-7352
Prepared By:
Robert A. Karn & Associates, Inc.
707 Beck Avenue
Fairfield, CA 94533
(707) 435-9999
Project #A23004
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INTRODUCTION:
This Onsite Storm Drain Analysis summarizes the existing and proposed drainage flows for the
project site. The City of San Luis Obispo Design Guidelines were used for the sizing of the
proposed onsite storm drain facilities. The flood control detention and the sizing of the stormwater
quality treatment facilities were designed consistent with the City’s Post Construction and Runoff
Retention Performance Requirements.
EXISTING CONDITIONS:
The project site is 3.06 acres in size and is undeveloped with native grasses. The site gently slopes in
a southeasterly direction, where excess runoff generated from the project site that does not infiltrate
or evaporate is picked up in the existing flood control detention ditch immediately east of the project
site. This ditch was not sized to provide flood control or stormwater treatment for the private
properties- only the public streets.
Sueldo Street drains in a southerly direction with a slope of 0.5% towards Vanguard Way/Innovation
Way. Innovation Way drains in an easterly direction to a drain inlet along the curb return, which
discharges into the adjacent drainage ditch mentioned above.
PROPOSED CONDITIONS:
The City of San Luis Obispo requires the following:
1. Site Design requirements for projects of >2,500 SF of new and replaced impervious surface.
2. Water Quality Treatment for projects of >5,000 SF of net impervious area.
3. Runoff Retention requirements typically apply to projects of >15,000 SF of new and
replaced impervious surface.
4. Peak Management requirements typically apply to projects of >22,000 SF of new and
replaced impervious surface.
Since the proposed project is creating approximately 101,200 SF of impervious surface, the project
is conditioned to take into consideration all four of the above Post Construction Requirements.
The proposed work includes the construction of: two (2) 1-story and three (3) 2-story self-storage
buildings, a Manager’s Office, as well as associated drive aisles, parking, and landscaping. The site
will be graded to drain surficially to a valley gutter within the drive aisles, then to an underground
storm drain vault through drainage inlets within the valley gutter. Runoff will then be released at
pre-development rates to a stormwater treatment device before discharging to the existing adjacent
drainage ditch.
The sizing of the underground storm drain vault was based on the need to provide peak management
to contain flows to pre-development conditions. The proposed underground storm drain system is
comprised of 60-inch diameter corrugated metal pipes sized to store 13,500 cubic feet of runoff,
with a single outlet sized to regulate outflow to pre-development conditions. Stormwater will enter
the underground storm drain by way of drainage inlets placed directly above the storm drain lines.
The product and manufacturer are the CMP Detention System from Contech (or approved equal).
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The stormwater treatment device chosen for the project is an internal bypass vault, containing a filter
media designed to treat stormwater runoff before leaving the site. The product and manufacturer are
the Filterra Bioscape Vault Internal Bypass from Contech (or approved equal).
SUMMARY:
The proposed onsite storm drain system including underground detention and stormwater quality
treatment are designed to provide runoff retention and manage peak, and to treat the onsite
stormwater, to the standards of the City of San Luis Obispo and their Municipal Regional Permit
with the Regional Water Quality Control Board.
Attachments:
Preliminary Grading & Utility Plan
Preliminary Stormwater Control Plan
Contech CMP Detention System Sizing Sheet
Filterra Bioscape Vault Internal Bypass Site Layout and Configuration Detail
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STORMWATER
CONTROL PLAN
For
Crockers Lockers Self-Storage
3745 Sueldo Street (n/o Innovation Way)
San Luis Obispo, CA 93401
(APN: 053-251-083 & -084)
January 18, 2024
Prepared For:
Crocker’s Lockers/Darme Holding Co, Inc.
7036 Valley Greens Circle
Carmel, CA 93923
831-582-7352
Prepared By:
Robert A. Karn & Associates, Inc.
707 Beck Avenue
Fairfield, CA 94533
(707) 435-9999
Project #A23004
TABLE OF CONTENTS
I. Project Data .................................................................................................................1
II. Setting ..........................................................................................................................1
II.A. Project Location and Description ................................................................................................................ 1
II.B. Existing Site Features and Pre-Development Conditions ....................................................................... 2
II.C. Post-Development Conditions ..................................................................................................................... 2
II.D. Opportunities and Constraints for Stormwater Control ......................................................................... 2
III. Post Construction Design Strategies ...........................................................................3
III.A. Optimization of Site Layout.......................................................................................................................... 3
III.A.1. Limitation of development envelope 3
III.A.2. Preservation of natural drainage features 3
III.A.3. Setbacks from creeks, wetlands, and riparian habitats 3
III.A.4. Minimization of imperviousness 3
III.A.5. Use of drainage as a design element 3
III.B. Use of Permeable Pavements ....................................................................................................................... 3
III.C. Dispersal of Runoff to Pervious Areas ....................................................................................................... 3
III.D. Bioretention or other Integrated Management Practices ......................................................................... 3
IV. Documentation of Drainage Design .............................................................................4
IV.A. Descriptions of each Drainage Management Area ................................................................................... 4
IV.A.1. Table of Drainage Management Areas 4
IV.A.2. Drainage Management Area Descriptions 4
IV.B. Integrated Management Practice Descriptions .......................................................................................... 4
IV.B.1. Areas Draining to Non-LID Treatment 4
IV.C. Tabulation and Sizing Calculations .............................................................................................................. 4
V. Source Control Measures .............................................................................................4
V.A. Site activities and potential sources of pollutants ...................................................................................... 4
V.B. Source Control Table ..................................................................................................................................... 5
V.C. Features, Materials, and Methods of Construction of Source Control BMPs ..................................... 6
V.D. Trash Capture Compliance ........................................................................................................................... 6
VI. Stormwater Facility Maintenance ................................................................................6
VI.A. Ownership and Responsibility for Maintenance in Perpetuity ............................................................... 6
VI.B. Summary of Maintenance Requirements for Each Stormwater Facility ............................................... 6
VII. Construction Plan Checklist ........................................................................................7
VIII. Certifications ................................................................................................................7
Tables
Table 1. Project Data ........................................................................................................................................... 1
Table 2. Drainage Management Areas .............................................................................................................. 4
Table 3. Source Controls .................................................................................................................................... 5
Table 4. Construction Plan Checklist ............................................................................................................... 7
Robert A. Karn & Associates, Inc. Page 1 of 7 Crocker’s Lockers Stormwater Control Plan
I. PROJECT DATA
Table 1. Project Data
Project Name/Number Crocker’s Lockers
Application Submittal Date
Project Location Northeast corner of Sueldo Street & Innovation Way
San Luis Obispo, CA 93401
Assessor Parcel Number (s) APN: 053-251-083 & 084
Name/Address of Developer Darme Holding Co, Inc.
7036 Valley Greens Circle
Carmel, CA 93923
831-582-7352
Project Phase No. N/A
Project Type and Description Self-Storage
Project Watershed San Luis Obispo Creek
Total Project Site Area (acres) 3.06 Acres (133,431 SF)
Total Area of Land Disturbed (acres) 3.06 Acres (133,431 SF)
Total New Impervious Surface Area (sq. ft.) 2.32 Acres (101,200 SF)
Total Replaced Impervious Surface Area 0
Total Pre-Project Impervious Surface Area 0
Total Post-Project Impervious Surface Area 2.32 Acres (101,200 SF)
Post Construction Requirements Level 4 (Greater than 22,000 SF of impervious surface)
II. SETTING
II.A. Project Location and Description
The 3.06-acre project site is situated along the northeast corner of Sueldo Street and Innovation Way,
within the City of San Luis Obispo, in San Luis Obispo County, California. The proposed work
includes the construction of: two (2) 1-story and three (3) 2-story self-storage buildings, a Manager’s
Office, as well as associated drive aisles, parking, and landscaping.
Robert A. Karn & Associates, Inc. Page 2 of 7 Crocker’s Lockers Stormwater Control Plan
Figure 1: Vicinity Map
II.B. Existing Site Features and Pre-Development Conditions
The site is undeveloped with native grasses and generally drains in a southeasterly direction to an
existing detention basin just east of the project site that serves the industrial park. Frontage
improvements exist along Sueldo Street and Innovation Way, which include curb, gutter, and
separated sidewalk.
II.C. Post-Development Conditions
The entirety of the site is graded to drain to an underground storage system, then into a bio-filtration
fault near the southerly border, just north of Innovation Way. From there, runoff will be directed to
the existing detention basin east of the project site. The sizing of both the underground storage and
bio-filtration fault will be designed to City Standards.
II.D. Opportunities and Constraints for Stormwater Control
Constraints: None.
Opportunities: Stormwater treatment will be handled through a proposed bio-filtration fault located
on the southerly portion of the site. Flows entering the bio-filtration vault will first be reduced to
pre-development flows through an onsite underground storage system. Once treated, the stormwater
will be directed into the existing detention basin located immediately east of the project site.
SITE
Robert A. Karn & Associates, Inc. Page 3 of 7 Crocker’s Lockers Stormwater Control Plan
The requirement to manage increases in runoff peak flows and durations is based on methods
described in the San Luis Obispo Stormwater Control Plan for Post Construction Requirements, as
well as the Post Construction Requirements from the Central Coast Regional Water Quality Control
Board (Level 4- Peak Management, based on greater than 22,000SF of impervious surface created).
III. POST CONSTRUCTION DESIGN STRATEGIES
III.A. Optimization of Site Layout
III.A.1. Limitation of development envelope
Development is designed to impact the minimum area possible. Landscaped areas are proposed to
limit the project’s impact.
III.A.2. Preservation of natural drainage features
No existing natural drainage features are disturbed or removed with the construction of the project.
Proposed drainage features shall contain elements of vegetation for both function and aesthetics.
III.A.3. Setbacks from creeks, wetlands, and riparian habitats
No natural creeks, wetlands or riparian habitats are present on the project site.
III.A.4. Minimization of imperviousness
The project minimizes the amount of impervious area onsite with the use of landscaping.
III.A.5. Use of drainage as a design element
The site drainage is conveyed to a proposed onsite underground storage system, which will drain to a
bio-filtration vault at the southerly end of the project site, which will then be conveyed into the
existing detention basin immediately east of the project site.
III.B. Use of Permeable Pavements- No permeable pavement is proposed for the project.
III.C. Dispersal of Runoff to Pervious Areas
The site drainage is conveyed to a proposed onsite underground storage system, which will drain to a
bio-filtration vault at the southerly end of the project site. This bio-filtration vault will serve as the
pervious area.
III.D. Bio-retention or other Integrated Management Practices
The proposed bio-filtration vault has been designed per the San Luis Obispo Stormwater Control
Plan for Post Construction Requirements, as well as the Post Construction Requirements from the
Central Coast Regional Water Quality Control Board (Level 4- Peak Management, based on greater
than 22,000SF of impervious surface created).
Robert A. Karn & Associates, Inc. Page 4 of 7 Crocker’s Lockers Stormwater Control Plan
IV. DOCUMENTATION OF DRAINAGE DESIGN
IV.A. Descriptions of each Drainage Management Area
IV.A.1. Table of Drainage Management Areas
Table 2. Drainage Management Areas
DMA Name Area (SF) Surface Type/Desc. DMA Type/Drains to
ROOF-1 63,165 Conventional Roof BF-1
PAVE-1 38,035 Concrete/Asphalt BF-1
LAND-1 32,233 Landscaping BF-1
ROOF-1, totaling 63,165 SF, drains the roof area into BF-1, a bio-filtration vault via roof downspouts
into surface drainage.
PAVE-1, totaling 38,035 SF, drains the parking area into BF-1, a bio-filtration vault via surface drainage
and underground piping within the parking area.
LAND-1, totaling 32,233 SF, drains the landscape area into BF-1, a bio-filtration vault.
IV.B. Integrated Management Practice Descriptions
The proposed bio-filtration fault was sized per the San Luis Obispo Stormwater Control Plan for
Post Construction Requirements, as well as the Post Construction Requirements from the Central
Coast Regional Water Quality Control Board.
IV.B.1. Areas Draining to Non-LID Treatment
None.
IV.C. Tabulation and Sizing Calculations
See IMP sizing calculations on the attached Spreadsheet and Stormwater Control Plan.
V. SOURCE CONTROL MEASURES
V.A. Site activities and potential sources of pollutants
The following activities planned for the project have the potential to allow pollutants to enter runoff:
Potential dumping of washwater or other liquids into storm drain inlets.
Landscape maintenance.
Trash refuse areas.
All In-Lieu areas where these activities occur will drain to a stormwater treatment bio-retention area.
To further reduce the potential to enter runoff, permanent and operational source control BMP’s will
be implemented as described in Table 3 below.
Robert A. Karn & Associates, Inc. Page 5 of 7 Crocker’s Lockers Stormwater Control Plan
V.B. Source Control Table
Table 3. Source Controls
Potential Source
of Runoff
Pollutants
Permanent Source Control BMPs Operational Source
Control BMPs
On-site storm drain
inlets
Mark inlets that could be easily accessed with
a “No Dumping-Drains to Creek” or similar
message.
• Maintain and
periodically repaint or
replace inlet
markings.
• Distribute stormwater
pollution prevention
information to
Owner.
Landscape/outdoor
pesticide use • Any native trees, shrubs, and ground
cover on the site will be preserved to the
maximum extent possible.
• Landscaping will be designed to minimize
required irrigation and runoff, to promote
surface infiltration, and to minimize the
use of fertilizers and pesticides that can
contribute to storm water pollution.
• Plantings for bio-filtration vault will be
selected to be appropriate to anticipated
soil and moisture conditions.
• Where possible, pest resistant plants will
be selected, especially for locations
adjacent to hardscape.
• Plants will be selected appropriate to site
soils, slopes, climates, sun, wind rain, land
use, air movement, ecological consistency,
and plant interactions.
• Owner will receive
integrated pest
management
information.
• All site landscaping is
to be maintained with
minimal or no use of
pesticides.
Vehicle washing
• Driveways and parking areas drain to bio-
filtration vault.
Distribute stormwater
pollution prevention
information to Owner.
Trash Refuse Area
• Provide adequate number of
receptacles. Inspect receptacles
regularly; repair or replace leaky
receptacles. Prohibit/prevent dumping of
liquid or hazardous wastes. Post “no
hazardous materials” signs. Inspect and
pick up litter daily and clean up spills
immediately. Keep spill control materials
available on-site. See fact Sheet SC-34,
“Waste Handling and Disposal” in the
CASQA Stormwater Quality Handbooks.
Trash enclosure will be covered.
Distribute stormwater
pollution prevention
information to Owner.
Post “Do Not Dump
Hazardous Materials
Here” signs near
receptacles.
Robert A. Karn & Associates, Inc. Page 6 of 7 Crocker’s Lockers Stormwater Control Plan
V.C. Features, Materials, and Methods of Construction of Source Control BMPs
Construction of the bio-filtration vault includes:
• Excavation per the elevations provided on the grading plan and installation of the bio-filtration
vault.
• Placement of the 6” underdrain stone layer.
• Placement of the perforated pipe within a 6” underdrain stone layer.
• Placement of the 21” soil media layer provided by the Manufacturer.
• Placement of the 3” mulch layer.
• Placement of an energy dissipation rock layer.
• Installation of the landscaping.
All material submittals will be reviewed and approved by the Civil Engineer to confirm compliance
with the approved plans.
V.D. Trash Capture Compliance
Trash capture is being accomplished with the proposed bio-filtration vault, which by definition is a
trash capture device, to meet the specifications of the Regional Water Quality Control Board. All
trash within the proposed bio-filtration vault will be removed on a routine basis.
VI. STORMWATER FACILITY MAINTENANCE
VI.A. Ownership and Responsibility for Maintenance in Perpetuity
All storm water treatment facilities in this plan will be owned and maintained in perpetuity by the
private owner of the subject property. The applicant accepts responsibility for operation and
maintenance of the facilities until such time as this responsibility is formally transferred to a
subsequent owner.
The applicant will execute, prior to completion of project construction, a Stormwater Facilities
Operation and Management Agreement. Such an Agreement will “run with the land” and be
enforceable on subsequent property owners. The applicant will provide the City access to stormwater
treatment devices for inspection.
VI.B. Summary of Maintenance Requirements for Each Stormwater Facility
The planted areas will be weeded by hand approximately monthly. At this time, plants will be
inspected for health and the irrigation system will be turned on manually and checked for any leaks
or broken lines, misdirected spray patterns etc. Any dead plants will be replaced. Inspect bank
between curb cuts and treatment facility. Look for gullies, washouts, evidence of uncontrolled
surface water flow or any other evidence of distress to the slope. Inspect all subdrains where it
enters the catch basin to see whether the subdrain pipe is dry, or is clogged with vegetation. Storm
drain system to be inspected from the upstream end to the outfall, including catch basins. Observe
the flow of water. Any evidence of ponding in the catch basins indicates a blockage.
Robert A. Karn & Associates, Inc. Page 7 of 7 Crocker’s Lockers Stormwater Control Plan
VII. CONSTRUCTION PLAN CHECKLIST
Table 4. Construction Plan Checklist
Stormwater
Control
Plan
Page # BMP Description See Plan Sheet #s
5 Bio-Filtration Vault Description C2
5 Bio-Filtration Vault (BF-1) Detail C2
6 Bio-Filtration Vault Sizing Criteria C2
VIII. CERTIFICATIONS
The selection, sizing, and preliminary design of stormwater treatment and other control measures in
this plan meet the requirements of Central Valley Regional Water Quality Control Board.
By
Print Name
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GRAPHIC SCALE
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