HomeMy WebLinkAboutItem 4b. WATER AND WASTEWATER ELEMENT UPDATE CONSISTING OF AN UPDATED WASTEWATER CAPACITY CONSTRAINED AREA MAP
PLANNING COMMISSION AGENDA REPORT
SUBJECT: WATER AND WASTEWATER ELEMENT UPDATE CONSISTING OF AN
UPDATED WASTEWATER CAPACITY CONSTRAINED AREA MAP
BY: Shawna Scott, Special Projects Manager FROM: Tyler Corey, Deputy Director
Phone Number: 805-781-7176 Phone Number: 805-781-7169
Email: sscott@slocity.org Email: tcorey@slocity.org
APPLICANT: City of San Luis Obispo, Public Utilities Department
RECOMMENDATION
Adopt a Resolution recommending the City Council approve an amendment to the City’s
Water and Wastewater Element of the General Plan (GENP-0762-2025) and find the
action categorically exempt from the California Environmental Quality Act (CEQA).
1.0 COMMISSION'S PURVIEW
It is the Planning Commission’s purview to review the proposed General Plan Amendment
and proposed CEQA exemption, and provide a recommendation to the City Council.
2.0 SUMMARY
The City’s guiding policy document for water and wastewater planning is the General
Plan, Water and Wastewater Element (WWE). The City first adopted the WWE in 1987
to address water and wastewater services because of the vital role these resources play
in the community and the far-reaching impacts of water and wastewater related policies
on community growth and character. The WWE translates the General Plan’s Land Use
Element capacity for development into potential demand for water supply and wastewater
service.
The WWE includes goals, policies, and programs as it relates to wastewater capacity and
service, and includes a wastewater capacity constrained area map (WWE, Figure 3) that
was initially included in the WWE in 2018. The WWE also references a 2012 Flow
Monitoring and Inflow/Infiltration Study and 2016 Wastewater Collection System
Infrastructure Renewal Strategy, which provided the data and analysis used to determine
the capacity-constrained areas currently identified in WWE Figure 3. An updated
wastewater flow study, informing system modeling and analysis, has been completed and
incorporated into the 2025 Wastewater Collection System Infrastructure Renewal
Strategy (2025 WWCIRS) to evaluate and document current conditions and provide
recommendations for future capital projects and programming related to the sewer
system.
Meeting Date: 10/22/2025
Item Number: 4b
Time Estimate: 30 minutes
Page 247 of 268
Item 4b
GENP-0762-2025
Planning Commission Report – October 22, 2025
With the completion of the 2025 WWCIRS, significant changes in capacity constrained
conditions were determined. Therefore, staff are proposing revisions to the WWE,
including text updates specific to the 2025 WWCIRS. The more substantial amendment
consists of an updated Figure 3, which identifies existing capacity constrained areas in
the City’s wastewater collection system based on the 2025 analysis. Staff is also
recommending minor text amendments to update the status of the Water Resource
Recovery Facility (WRRF) upgrade project, which was completed in October 2025.
Recommended revisions to the WW E are provided in Attachment A in legislative draft
format.
3.0 PREVIOUS REVIEW
City Utilities staff presented the draft updated capacity-constrained area map to the City
Council during a Council study session on August 19, 2025. The City Council directed
staff to proceed with the General Plan Amendment process, based on review of the draft
maps (Council Minutes). Additional items presented at the August study session related
to the Wastewater Flow Offset and Sewer Lateral Inspection Programs that will be
brought back to City Council for consideration in 2026, following staff’s further community
outreach and analysis of the potential Program modifications.
4.0 PROJECT ANALYSIS
This analysis section provides background information regarding the City’s adopted
General Plan and relevant goals, policies, and programs and the recommended action’s
consistency with the General Plan, provides an overvie w of the City’s sewer system and
capacity-related causes and issues, briefly summarizes the analysis and study behind the
recommendation for updated capacity-constrained area boundaries, and presents the
proposed updated figure recommended for the WWE amendment.
General Plan Consistency
The City’s Land Use Element states that the Water and Wastewater Element provides
policies and programs to support adequate water and wastewater services to the
community. The current WWE includes the following goals, policies, and programs related
to wastewater capacity and service:
Goal B 2.1: Adequate wastewater collection and treatment service to meet
the long-term needs of the City.
Policy B 2.2.2: Service Capacity
The City's wastewater collection system and Water Resource Recovery
Facility shall support population and related service demands consistent with
the General Plan.
Page 248 of 268
Item 4b
GENP-0762-2025
Planning Commission Report – October 22, 2025
Policy B 2.2.3: Wastewater Service for New Development
New development shall pay its proportionate or “fair share” of expanded
treatment and collection system capacity and upgrades. New development
will only be permitted if adequate capacity is available within the wastewater
collection system and/or Water Resource Recovery Facility.
Program B 2.3.1: Expand capacity in the City’s collection system and Water
Resource Recovery Facility in support of projected wastewater flows.
Program B 2.3.2: Evaluate the potential for the wastewater flows of a
proposed project to exceed the capacity of collection and treatment systems.
Program B 2.3.3: The City will conduct periodic updates to its wastewater
development impact fees.
Goal B 4.1: Collect and convey all wastewater under safe and sanitary conditions
to the Water Resource Recovery Facility.
Policy B 4.2.1: Collection System Maintenance
The City will manage the collection system to ensure that the proper level of
maintenance is provided and that the flow in sanitary sewers does not exceed
design capacity.
Policy B 4.2.2: Infiltration and Inflow
The City will minimize stormwater and groundwater infiltration and inflow into the
sewer system.
Program B 4.3.1: Investigate and carry out cost-effective methods for reducing
infiltration and inflow into the wastewater collection system.
Program B 4.3.2: Develop education and outreach materials to increase public
awareness of problems associated with excessive infiltration and inflow (I & I) into
the wastewater collection system and the City’s efforts to reduce I & I.
Program B 4.3.3: Support the retrofit of commercial and residential sewer
laterals to reduce infiltration and inflow into the wastewater collection system.
Program B 4.3.4: Update the Sewer System Management Plan to maintain its
applicability.
Program B 4.3.5: Maintain, and revise as necessary, master plans for the extension
of wastewater services to developing areas of the City and to ensure orderly
replacement of aged infrastructure.
Program B 4.3.6: Review development proposals to ensure new development does
not adversely impact existing infrastructure and that necessary infrastructure will be
in place to support the development.
Program B 4.3.7: Provide a Pretreatment Program pursuant to the Clean Water
Act to ensure that all discharge requirements are met.
Page 249 of 268
Item 4b
GENP-0762-2025
Planning Commission Report – October 22, 2025
Staff’s proposed amendments to the General Plan WWE (Attachment A) consist of the
replacement of WWE Figure 3 (Capacity Constrained Areas) with an updated capacity-
constrained area map and text amendments specific to the 2025 WWCIRS and recently
completed WRRF upgrade. The proposed amendments are consistent with all other
General Plan Elements, as the amendments provide the updates necessary to reflect
currently accurate information. The WWE would continue to provide the goals, policies,
and programs for adequate wastewater services to the community, and would continue
to provide the policy basis for the City Council to cons ider and adopt wastewater-related
programs that facilitate and support build-out of the General Plan.
Impact of Inflow and Infiltration on the City’s Wastewater Collection System
The City has separate public stormwater and public sewer systems; however, during wet
weather, the City’s wastewater collection system experiences a significant increase in
volume due to storm-related flows. Though not intended to be conveyed or treated by the
wastewater system, stormwater enters wastewater pipes directly through improperly
plumbed drains (inflow) and/or as groundwater that seeps through cracked wastewater
pipes (infiltration). An illustration of common sources of inflow and infiltration (I &I) is
presented below in Figure 1. Significant I&I in the collection system can result in sanitary
sewer overflows (SSOs), which can have public and environmental health impacts. Under
these conditions, peak flows to the City's WRRF have exceeded 20 million gallons a day
(MGD) in a 24-hour period, where expected flows are under four MGD in a typical 24 -
hour period. Treatment of this excess wastewater flow increases energy used for
pumping, treatment, and chemical usage. I&I also consumes capacity in the co llection
system, resulting in increased capital requirements to increase pipeline size, energy, and
other costly treatment expenses.
Page 250 of 268
Item 4b
GENP-0762-2025
Planning Commission Report – October 22, 2025
Figure 1. Sources of Inflow and Infiltration
The City completed an updated WWCIRS in July 2025 , which provided a new sewer
hydraulic model based on real data collected during the peak wet-weather flows of
December 2023 through March 2024. This comprehensive flow study identified multiple
locations in the collection system that experienced elevated flows due to I&I, which i s
discussed in detail in the 2025 WWCIRS. These elevated flows result in the identification
of capacity-constrained areas of the wastewater collection system that are unable to
accommodate the impacts of I&I safely. A detailed summary of the 2025 WWCIRS and
additional background information regarding the City’s current Wastewater Flow Offset
and Sewer Lateral Inspection Programs is provided in the City Council Study Session
Agenda Report dated August 19, 2025.
Page 251 of 268
Item 4b
GENP-0762-2025
Planning Commission Report – October 22, 2025
Proposed Updated Capacity Constrained Area Map
One of the primary deliverables of the 2025 WWCIRS was an updated capacity-
constrained area boundary map. Projects located within the WWE capacity-constrained
areas are subject to the City’s Wastewater Flow Offset Program, as currently mandated
by Municipal Code Section 13.08.396. The current Program requires that new or
intensified development in capacity constrained areas offset new wastewater flow in the
existing wastewater collection system to accommodate the project’s additional demand.
In addition to these offsets, the City implements capital and maintenance projects to
increase capacity in the sewer system and better monitor flows. Figure 2 presents the
updated capacity-constrained areas boundaries as identified in the 2025 WWCIRS, which
are superimposed over the existing boundaries for comparison.
Figure 2: Comparative Updates to Capacity-Constrained Area Boundaries
At the Council Study Session in August, staff recommended including Proposed Areas 1
and 3 on the updated capacity-constrained areas map in the WWE, and excluding
Proposed Area 2, which is small enough to be addressed through City capital
improvement projects that are currently funded in the adopted 25-27 Financial Plan. This
is the most efficient way to address current and forecasted future capacity constraints in
this area, which would not place additional burden on property owners and developers in
this area. At the Council Study session, the City Council supported this recommendation.
Page 252 of 268
Item 4b
GENP-0762-2025
Planning Commission Report – October 22, 2025
Figures 3 and 4, below, show the proposed capacity-constrained area boundaries for
these areas, and include the condition of private sewer laterals located within this area
based on currently available data collected through the City’s Sewer Lateral Inspection
Program mandated by Municipal Code Section 13.08.395.
Proposed Area 1 (Figure 3) retains much of the original boundaries and includes some
minor revisions to reflect the current operating conditions of the system, as demonstrated
in the 2023-24 sewer flow study, and discussed in the 2025 WWCIRS report. Updated
conditions include consideration of the buildout and future flow conditions of the California
Polytechnic State University, including development of the University’s Water
Reclamation Facility (i.e. wastewater treatment plant), which is anticipated to be
commissioned sometime in 2026 and will initially reduce flows to the City’s sewer system
(but later increase with campus buildout).
Figure 3: Proposed Capacity-Constrained Area 1
Page 253 of 268
Item 4b
GENP-0762-2025
Planning Commission Report – October 22, 2025
Proposed Area 3 (Figure 4) has shifted significantly north, which reflects the current
operating conditions of the system, as demonstrated in the 2023 -24 sewer flow study.
The conditions and capacities of the city’s wastewater collection system change over time
due to a number of dynamic factors. Collectively, reasons for the removal of the downtown
capacity-constrained area and the development of a new capacity-constrained area
further north include 1) significant replacement of public and private infrastructure in the
formerly capacity-constrained downtown area, 2) aging private and public infrastructure
in the northern area, as it has been ten years since the last assessment, 3) ground
settlement and impacts from drought, such as increased root intrusion into legacy
materials such as vitrified clay pipe, and 4) significant differences in the severity of
weather monitored between the two flow studies (2012 vs 2023-24).
California entered a multi-year drought beginning in 2012, which became one of the most
severe in state history (lasting through 2016). The National Centers for Environmental
Information classified large portions of the Central Coast (San Luis Obispo, Santa
Barbara, and Monterey counties) as being in “severe to extreme drought” by late 2012.
While keeping these significant changes in mind, the city’s contractor utilized best -
practice industry standards to conduct an unbiased and current evaluation of the system,
using real data, to produce an updated model of current and future build -out conditions,
which ultimately led to the development of new capacity-constrained boundaries. The
process of determining these updated boundaries included over a year of data analysis
and system modeling/verification.
Figure 4: Proposed Capacity-Constrained Area 3
The updated map proposed for the WWE amendment was developed based on the
results of a wastewater flow study, wastewater flow modeling, and the 2025 WWCIRS.
Page 254 of 268
Item 4b
GENP-0762-2025
Planning Commission Report – October 22, 2025
The updated capacity-constrained area boundaries were presented to City Council in
August 2025, and staff was directe d to proceed with the General Plan Amendment to
replace the capacity-constrained area map (WWE Figure 3) with the updated map (Figure
5, below) and update associated text amendments in the WWE. No changes to policy or
program language are proposed. The legislative draft WWE amendment is provided as
Attachment A for the Planning Commission’s consideration and recommendation to City
Council.
Figure 5: Proposed WWE Map Amendment
Page 255 of 268
Item 4b
GENP-0762-2025
Planning Commission Report – October 22, 2025
5.0 ENVIRONMENTAL REVIEW
The proposed General Plan Amendment is exempt from the California Environmental
Quality Act pursuant to CEQA Guidelines Sections 15307 (Actions by Regulatory
Agencies for Protection of Natural Resources) and 15308 (Actions by Regulatory
Agencies for the Protection of the Environment) because the intent of the capacity-
constrained area map is to identify these areas in the City’s general plan such that land
use planning can occur with these capacity limitations in mind. In addition, the updated
map and policies to remain provide a basis in the General Plan for programs that reduce
I&I and the potential for SSOs. Implementation of programs that address these capacity-
related issues would have a beneficial impact on the environment by reducing the
potential for I&I and overflows due to reduced flows from groundwater and stormwater.
6.0 OTHER DEPARTMENT COMMENTS
The Community Development Department concurs with the proposed General Plan
amendment. The City Attorney’s Office has reviewed the legislative draft amendment and
has approved to form.
7.0 ALTERNATIVES
1. Continue review of the amendment. The Commission may continue action if additional
information is needed. Specific direction should be given to staff if continued.
2. The Planning Commission may recommend that the City Council not amend the
General Plan capacity-constrained boundaries map. Impacts of this alternative include
subjecting private property owners to the Wastewater Flow Offset Program, including
requiring private sewer lateral replacements, in areas that have not been identified as
capacity-constrained by the 2025 WWCIRS. By not updating the capacity-constrained
boundaries map, staff would be carrying out a program that would be informed by data
from ten years prior, which does not take into account the current condition s informed
by the 2025 WWCIRS.
8.0 ATTACHMENT
A - Draft Planning Commission Resolution recommending that the City Council adopt
amendments to the General Plan Water and Wastewater Element.
Page 256 of 268
[Type here]
RESOLUTION NO. XXXX-2025
A RESOLUTION OF THE PLANNING COMMISSION OF THE CITY OF
SAN LUIS OBISPO RECOMMENDING THE CITY COUNCIL ADOPT
AMENDMENTS TO THE WATER AND WASTEWATER ELEMENT OF
THE GENERAL PLAN. THE PROJECT IS EXEMPT FROM
ENVIRONMENTAL REVIEW (CEQA) AS REPRESENTED IN THE
PLANNING COMMISSION AGENA REPORT AND ATTACHMENTS
DATED OCTOBER 22, 2025 (GENP-0762-2025)
WHEREAS, Government Code Section 65300 mandates all cities and counties to
adopt a comprehensive, long-term general plan to guide their physical development; and
WHEREAS, the Water and Wastewater Element of the City of San Luis Obispo
General Plan was last updated in 2020 in compliance with State law; and
WHEREAS, General Plan Water and Wastewater Element Policies state that the
City’s wastewater collection system shall support population and related service demands
consistent with the General Plan (Policy B 2.2.2), and the City shall collect and convey all
wastewater under safe and sanitary conditions to the Water Resource Recovery Facility
(Goad B 4.1), and maintain, and revise as necessary, master plans for the extension of
wastewater services to developing areas of the City and to ensure orderly replacement
of aged infrastructure (Program B 4.3.5); and
WHEREAS, the City of San Luis Obispo has prepared amendments to the General
Plan Water and Wastewater Element to incorporate current information including an
updated wastewater collections system capacity-constrained area map and associated
references to current wastewater flow and infrastructure studies (2025 Wastewater
Collections Infrastructure Renewal Strategy), and minor text edits to provide currently
available information regarding the wastewater collections system and Water Resource
Recovery Facility (Exhibit A); and
WHEREAS, the Planning Commission, at the hearing of October 22, 2025,
considered the amendments to the General Plan Water and Wastewater Element and
proposed categorical exemptions to the California Environmental Quality Act.
NOW, THEREFORE, BE IT RESOLVED by the Planning Commission of the City
of San Luis Obispo as follows:
SECTION 1. Findings. The Planning Commission, after considering the proposed
amendments to the Water and Wastewater Element, staff presentation and
recommendation, public testimony and correspondence, and reports thereon, make the
following finding:
1) The proposed amendments to the Water and Wastewater Element are
consistent with the General Plan.
Page 257 of 268
Planning Commission Resolution No. PC-XXXX-2025
GENP-0762-2025 (Citywide)
Page 2
SECTION 2. Recommendation to City Council. The Planning Commission, after
considering the proposed amendments to the Water and Wastewater Element, staff
presentation and recommendation, public testimony and correspondence, and reports
thereon, recommend the following to the City Council:
1) Find the amendments to the Water and Wastewater Element consistent with
the General Plan.
2) Find the amendments to the Water and Wastewater Element exempt from the
California Environmental Quality Act (CEQA) pursuant to CEQA Guidelines
Sections 15307 (Actions by Regulatory Agencies for Protection of Natural
Resources) and 15308 (Actions by Regulatory Agencies for the Protection of
the Environment) because the intent of the capacity-constrained area map is
to identify these areas in the City’s general plan s uch that land use planning
can occur with these capacity limitations in mind. In addition, the updated map
and policies to remain provide a basis in the General Plan for programs that
reduce I&I and the potential for SSOs. Implementation of programs that
address these capacity-related issues would have a beneficial impact on the
environment by reducing the potential for I&I and overflows due to reduced
flows from groundwater and stormwater.
Upon motion of Commissioner , seconded by
Commissioner , and on the following roll call vote:
AYES:
NOES:
REFRAIN:
ABSENT:
The foregoing resolution was adopted this day of 2025.
Tyler Corey, Secretary
Page 258 of 268
Planning Commission Resolution No. PC-XXXX-2025
GENP-0762-2025 (Citywide)
Page 3
Exhibit A
Legislative Draft Water and Wastewater Element Amendment
Page 259 of 268
Page 8-25
Water and Wastewater Element
WASTEWATER SERVICE
B 2.0 Background
The City is the sole provider of wastewater service within the City. The service provides collection and treatment
for residential, commercial, and industrial users on properties within the city limits. In 20182025, the number of
service connections is estimated to be 12,00013,421. Through agreement, the City also provides service to the
San Luis Obispo campus of California Polytechnic State University (Cal Poly) and the County of San Luis Obispo
Airport.
The collection system is primarily a gravity flow system. Where gravity flow is not feasible due to the topography,
wastewater lift stations and pressurized force mains are used to move wastewater to the City’s Water Resource
Recovery Facility on Prado Road. Sewer pipelines measure from six inches to 48 inches in diameter.
The City completed a two-year Flow Monitoring and Inflow/Infiltration Study in 2012. Using data from this
Study, pipeline condition data from its asset management database, and growth assumption from the General
Plan’s Land Use (2014) and Housing (2015) elements, the City completed hydraulic modeling and its
Wastewater Collection System Infrastructure Renewal Strategy in 2016. The Renewal Strategy identified a
prioritized list of capital projects to address the City’s aging infrastructure. The Renewal Strategy also
identified capacity constrained areas during wet weather events due to inflow and infiltration, shown in Figure
3. Inflow and infiltration is discussed further in section B.4.0.
The City completed an updated Wastewater Collection System Infrastructure Renewal Strategy (WWCIRS) in
July 2025. Development of the 2025 WWCIRS included the collection of wastewater flow data, the completion
of a system-wide capacity modeling study in 2024, the incorporation of growth estimates based on build-out
of the City’s General Plan and underlying zoning for each parcel, including assumptions for accessory dwelling
units and developments that include a density bonus, and the completion of an updated wastewater flow
model. Based on the results of the analysis, recommendations for capital improvement sewer projects are
included in the 2025 WWCIRS. The WWCIRS also identified updated capacity-constrained areas during wet
weather events due to inflow and infiltration. The updated capacity-constrained area map is included in this
Element as Figure 3. Inflow and infiltration, and is discussed further in section B.4.0.
Following completion of a major upgrade in 2025 to increase capacity to serve the City’s build-out population
outlined in the Land Use Element, Tthe Water Resource Recovery Facility (WRRF) is designed for an average dry-
weather flow of 5.1 5.4 million gallons per day (mgd). Instantaneous peak flows exceeding 20 mgd are not
uncommon during storm events due to infiltration and inflow into the wastewater collection system, discussed
further in subsection B 4.0. As the City grows to its build-out population outlined in the Land Use Element, the
average dry-weather flow of wastewater is expected to reach 5.4 mgd. In 2018, design for the expansion of the
Water Resource Recovery Facility to accommodate General Plan buildout is underway. When the WRRF is
expanded in the future it will have a treatment capacity of 5.4 mgd.
B 2.1 Goal
Adequate wastewater collection and treatment service to meet the long-term needs of the City.
Page 260 of 268
Page 8-26
Chapter 8
B 2.2 Policies
B 2.2.1 Service Outside the City Limits
To receive City wastewater service, property must be annexed to the City. The City Council may authorize
exceptions to this policy provided it is found to be consistent with the General Plan.
B 2.2.2 Service Capacity
The City's wastewater collection system and Water Resource Recovery Facility shall support
population and related service demands consistent with the General Plan.
B 2.2.3 Wastewater Service for New Development
New development shall pay its proportionate or “fair share” of expanded treatment and collection
system capacity and upgrades. New development will only be permitted if adequate capacity is available
within the wastewater collection system and/or Water Resource Recovery Facility.
B 2.2.4 City as Exclusive Provider
The City will be the only provider of public wastewater treatment within the City (but on-site
pretreatment of wastewater to meet City Standards may be required).
Page 261 of 268
Page 8-27
Water and Wastewater Element
Figure 3 Capacity Constrained Areas [delete and replace]
Page 262 of 268
Page 8-28
Chapter 8
Figure 3 Capacity Constrained Areas
B 2.3 Programs
B 2.3.1 Expand capacity in the City’s collection system and Water Resource Recovery Facility in support of
projected wastewater flows.
B 2.3.2 Evaluate the potential for the wastewater flows of a proposed project to exceed the capacity of
collection and treatment systems.
B 2.3.3 The City will conduct periodic updates to its wastewater development impact fees.
Page 263 of 268
Page 8-29
Water and Wastewater Element
WASTEWATER TREATMENT
B 3.0 Background
The Water Resource Recovery Facility processes wastewater in accordance with standards set by the State's
Regional Water Quality Control Board (RWQCB). The RWQCB issues a permit to the City under the National
Pollutant Discharge Elimination System (NPDES), setting standards for the discharge of treated wastewater. The
standards are to protect beneficial uses of the receiving water (San Luis Obispo Creek), including recreation,
agricultural supply, and fish and wildlife habitat.
The Water Resource Recovery Facility removes solids, reduces the amount of nutrients, and eliminates bacteria in
the treated wastewater, which is then discharged into San Luis Obispo Creek. Solids are separated and treated to
create biosolids. Biosolids are beneficially reused as compost and/or soil amendment. As described in Section A
7.0, the Water Resource Recovery Facility has been producing tertiary-treated recycled water for delivery to
water customers in the City since 2006.
The design phase for theA comprehensive upgrade of the Water Resource Recovery Facility is underway with
completion of construction anticipated in 2022was completed in 2025. The upgrade increased average daily dry
weather capacity at the facility to 5.4 mgd, and included, but was not limited to, expansion of an equalization basin
that provides additional flood protection measures and operational flexibility, and construction of a new membrane
and ultra-violet disinfection (MBR-UV) facility. The upgrade will also enable the City to consider potable reuse, part
of a One Water concept, in the future.
B 3.1 Goals
B 3.1.1 Wastewater treatment that meets or exceeds regulatory requirements and ensures the protection of public
health and the environment.
B 3.1.2 Maximize recycled water production.
B 3.2 Policies
B 3.2.1 Treating Wastewater
The City will treat all wastewater in compliance with approved discharge permits.
B 3.2.2 Recycled Water Production
The City will produce high-quality, dependable recycled water, suitable for a wide range of uses.
B 3.2.3 Beneficial Use
The City will pursue treatment and disposal methods which provide for further beneficial use of wastewater
and biosolids.
B 3.3 Programs
B 3.3.1 Prepare and implement Water Resource Recovery Facility master plan consistent with regulatory
requirements.
B 3.3.2 Work cooperatively on regional water quality issues.
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Page 8-30
Chapter 8
COLLECTION SYSTEM
B 4.0 Background
The first sanitary sewers were built in San Luis Obispo in the late 1800s. Today, portions of the collection system
are over 100 years old. It includes nine lift stations, approximately 1385 miles of gravity sewer line, and three
miles of force main. Approximately 2,9003,184 manholes provide access to the collection system. The sewer
lines are made of a variety of materials, including ductile iron pipe, terra cotta salt-glazed pipe, vitrified clay pipe
(VCP), polyvinyl chloride (PVC), high-density polyethylene (HDPE) and asbestos concrete.
The City’s wastewater collection system requires maintenance to ensure uninterrupted flows and minimize
sanitary sewer overflows. Area and preventive maintenance programs are regularly evaluated to ensure their
effectiveness. The City also utilizes video inspection to prioritize problem areas for replacement, maintenance,
assess overall mainline conditions, conduct inflow and infiltration evaluations, and assess new construction.
The City issues discharge permits to and conducts inspections of facilities that have the potential to discharge
pollutants in concentrations that could pose a threat to worker safety, the wastewater collection system, and/or
the Water Resource Recovery Facility. Through its Pretreatment Program, the City also implements programs to
target constituents of special concern.
Like most cities in California, San Luis Obispo has separate sewer and storm drain systems. This means each
system of pipes in the ground is designed to accommodate either sewer or stormwater flows. One set of pipes
takes sanitary waste to the Water Resource Recovery Facility while a second set carries stormwater runoff from
street drains directly into bioswales, detention basins, or creeks.
The City’s wastewater collection system and the Water Resource Recovery Facility have long experienced
problems associated with wet weather infiltration and inflow (I & I). Inflow is water that enters the collection
system at points of direct connection (non-soil) such as around manhole covers or through illegal connection of
roof drains, downspouts, or landscape drains. Infiltration is water that flows through the ground into the
collection system usually through cracks in public sewer mains and/or private sewer laterals (See Figure 4). I & I
overloads the collection system during heavy rains and can result in sanitary sewer overflows. During periods of
significant rain events, the Water Resource Recovery Facility can become hydraulically overwhelmed (as
mentioned previously, instantaneous peak flows exceeding 20 mgd are not uncommon during storm events),
increasing the chance of effluent violations and the release of partially treated wastewater to San Luis Obispo
Creek. Table 6 includes data on the highest average daily flows experienced at the Water Resource Recovery
Facility during rain events over a nine-19-year period.
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Page 8-31
Water and Wastewater Element
Table 6. Highest Average Daily Flows to the Water Resource Recovery Facility, 2006 to
20172024
Average Daily Flows 1 Year
19.75 mgd 2006 (April)
7.24 mgd 2007(December)
9.83 mgd 2008 (January)
11.67 mgd 2009 (October)
13.51 mgd 2010 (December)
13.23 mgd 2011 (March
7.10 mgd 2012 (January)
5.17 mgd 2013 (January)
5.12 mgd 2014 (March)
5.24 mgd 2015 (February)
5.63 mgd 2016 (March)
9.00 mgd 2017 (February)
10.626 2018 (March)
10.19 2019 (March)
6.86 2020 (March)
11.18 2021 (January)
6.92 2022 (December)
172 2023 (January)
9.26 2024 (April)
Notes:
1. Instantaneous peak flows are higher.
August dry weather flow to the Water Resource Recovery Facility was 1.91 mgd in 2016 and 2.80 mgd in 2017.
Source: City of San Luis Obispo Utilities Department, 2018.
2. At the time of measurement, during the WRRF upgrade project, maximum measurement limit was 17 mgd.
Actual flows exceeded this amount.
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Page 8-32
Chapter 8
Figure 4 Inflow and Infiltration Illustrated
B 4.1 Goal
Collect and convey all wastewater under safe and sanitary conditions to the Water Resource Recovery Facility.
B 4.2 Policies
B 4.2.1 Collection System Maintenance
The City will manage the collection system to ensure that the proper level of maintenance is provided and that the
flow in sanitary sewers does not exceed design capacity.
B 4.2.2 Infiltration and Inflow
The City will minimize stormwater and groundwater infiltration and inflow into the sewer system.
B 4.3 Programs
B 4.3.1 Investigate and carry out cost-effective methods for reducing infiltration and inflow into the wastewater
collection system.
B 4.3.2 Develop education and outreach materials to increase public awareness of problems associated with excessive
infiltration and inflow (I & I) into the wastewater collection system and the City’s efforts to reduce I & I.
B 4.3.3 Support the retrofit of commercial and residential sewer laterals to reduce infiltration and inflow into the
wastewater collection system.
B 4.3.4 Update the Sewer System Management Plan to maintain its applicability.
B 4.3.5 Maintain, and revise as necessary, master plans for the extension of wastewater services to developing areas of the
City and to ensure orderly replacement of aged infrastructure.
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B 4.3.6 Review development proposals to ensure new development does not adversely impact existing infrastructure and
that necessary infrastructure will be in place to support the development.
B 4.3.7 Provide a Pretreatment Program pursuant to the Clean Water Act to ensure that all discharge requirements are
met.
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