2025-10-13_item_4.8_adopt_iwrmp_amendments_to_the_water_wastewater_and_recycled_water_master_plans_pw_22-19_and_ww_22-24 — Lathrop City Council, October 13, 2025 (part 1 of 2)

ITEM 4. 8

CITY MANAGER' SREPORT
OCTOBER 13, 2025 CITY COUNCIL REGULAR MEETING
ITEM: ADOPT IWRMP AMENDMENTS TO THE WATER,

WASTEWATER AND RECYCLED WATER MASTER
PLANS ( PW 22- 19 AND WW 22-4) AND CEQA

DETERMINATION
RECOMMENDATION: Adopt Resolution to Approve the Integrated Water Resources Master Plan Amendments to the Water,
Wastewater and Recycled Water Master Plans ( PW
22- 19 and WW 22-4), and to Approve an Addendum
to the City of Lathrop Integrated Water Resources
Master Plan Environmental Impact Report in
Accordance with CEQA Guidelines Sections 15162
and 15164
SUMMARY:

The Integrated Water Resources Master Plan ( IWRMP) Amendments associated with CIPs PW 22- 19 and WW 22-4, provide a comprehensive update to the City' s water, wastewater and recycled water system master plan documents, which were originally adopted in 2019. Implementation of the IWRMP Amendments is a discretionary project for the City and is therefore subject to environmental review under the California Environmental Quality Act ( CEQA).

Staff request Council adopt a resolution approving the City of Lathrop IWRMP Amendments to the water, wastewater and recycled water master plans and approve an Addendum to the City of Lathrop IWRMP Environmental Impact Report ( EIR), in accordance with CEQA Guidelines Sections 15162 and 15164.

BACKGROUND:

The IWRMP Amendments update water and sewer demand projections and address changes in regulatory requirements, population and growth forecasts, land use planning, climate change, and other evolving conditions. The original IWRMP and its EIR were prepared by EKI and De Novo and approved by City Council in December 2019.

Since then, several developments have necessitated updates. These include revised water demand factors and projections, completed in July 2020 to support the River Islands Phase 2 development Water Supply Assessment; and the City obtaining a National Pollutant Discharge Elimination System ( NPDES) permit, allowing surface water discharge from the City' s
Consolidated Treatment Facility ( CTF). The updates
also include the decommissioning of ponds and spray fields previously used for CTF effluent disposal.

CITY MANAGER' S REPORT PAGE 2
OCTOBER 13, 2025 CITY COUNCIL REGULAR MEETING

ADOPT IWRMP AMENDMENTS TO THE WATER, WASTWATER AND RECYCLED WATER MASTER PLANS ( PW 22- 19 AND WW 22-4) AND CEQA

DETERMINATION
On April 11, 2022, the City Council approved an agreement with EKI to update the IWRMP. Amendment No. 1 to this agreement was approved by staff in August 2022 to reallocate the scope of work toward evaluating wastewater strength sent to the Manteca Water Quality Control Facility ( MWQCF), in lieu of flow monitoring. On February 13, 2023, Council approved Amendment No. 2 to update geodatabases for the water, sewer and recycled water systems.

On August 12, 2024, the City Council approved an agreement with EKI for additional services needed to complete the IWRMP Amendments, including updates to the City' s planned expansion of the recycled water system. The City Council also approved an agreement with DeNovo to perform the CEQA analysis.

CEQA REVIEW:

As a discretionary project, the IWRMP Amendments require compliance with the California Environmental Quality Act ( CEQA) prior to formal adoption.

To consider an amendment to the IWRMP, the City must ensure that environmental review consistent with CEQA and the State CEQA Guidelines has been completed.

Because the City previously complied with CEQA for the IWRMP, and the current discretionary action involves changes to an already - approved project, the City may rely on the certified Environmental Impact Report ( EIR) previously prepared for the IWRMP, to the extent it remains adequate. Pursuant to CEQA Guidelines Section 15162, the City must, determine whether any changed circumstances or new information of substantial importance trigger the need for a subsequent EIR.

CEQA Guidelines Section 15164 provides that a lead agency shall prepare an addendum to a previously certified EIR if some changes or additions are necessary, but none of the conditions outlined in Section 15162 have occurred. A subsequent EIR is only required if substantial evidence in the record demonstrates that one or more of the following conditions apply:
1) Substantial changes are proposed in the project that would require major revisions to the previous EIR or negative declaration due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects;
2) Substantial changes occur with respect to the circumstances under which the project is undertaken, requiring major revisions to the previous EIR or negative declaration due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified effects; or 3) New information of substantial importance, which was not known and could not have been known with the exercise of reasonable diligence at the time the previous EIR was certified as complete or the negative declaration was adopted, shows any of the following:

CITY MANAGER' S REPORT PAGE 3
OCTOBER 13, 2025 CITY COUNCIL REGULAR MEETING

ADOPT IWRMP AMENDMENTS TO THE WATER, WASTWATER AND RECYCLED WATER MASTER PLANS ( PW 22- 19 AND WW 22- 24) AND CEQA

DETERMINATION
A) The project will have one or more significant effects not discussed in the previous EIR or negative declaration;
B) Significant effects previously examined will be substantially more severe than shown in the previous EIR;
C) Mitigation measures or alternatives previously found infeasible would, in fact, be feasible and would substantially reduce one or more significant effects of the project, but the project proponents decline to adopt the mitigation measure or alternative; or
D) Mitigation measures or alternatives considerably different from those analyzed in the previous EIR would substantially reduce one or more significant effects on the environment, but the project proponents decline to adopt the mitigation measure or alternative.

If any of the above conditions are met, the City must prepare a subsequent EIR, unless only minor additions or changes would be needed to make the previous EIR adequately apply to the modified project. In such cases, a supplement to an EIR would be appropriate under CEQA Guidelines, Section 15163. If none of the conditions requiring a subsequent or supplemental EIR are met, the City may prepare an addendum under Section 15164. An addendum explains why some changes or additions to the certified EIR are necessary, but none of the conditions described in Section 15162 have occurred.

As demonstrated in the environmental analysis provided in Section 4 ( Environmental Analysis), the proposed changes do not meet the criteria for subsequent EIR or negative declaration. An addendum is appropriate here because, as explained in Section 4, none of the conditions requiring a subsequent EIR or negative declaration have occurred.

As detailed in the EIR Addendum, the revisions in the IWRMP Amendments do not alter the environmental conclusions presented in the EIR, which found impacts to be either less significant or less than significant with mitigation.

RECOMMENDATION:

Staff recommend that the City Council consider all submitted information and public testimony and, if deemed appropriate, adopt a Resolution approving the City of Lathrop Integrated Water Resources Master Plan ( IWRMP) Amendments to the water, wastewater, and recycled water master plans, and approving an Addendum to the IWRMP Environmental Impact Report ( EIR) in accordance with CEQA Guidelines Sections 15162 and 15164.

CITY MANAGER' S REPORT PAGE 4
OCTOBER 13, 2025 CITY COUNCIL REGULAR MEETING

ADOPT IWRMP AMENDMENTS TO THE WATER, WASTWATER AND RECYCLED WATER MASTER PLANS ( PW 22- 19 AND WW 22-4) AND CEQA

DETERMINATION
FISCAL IMPACT:

There is no direct fiscal impact associated with the recommended action. The IWRMP will support Capital Improvement Planning ( CIP), budgeting, and rate studies for water, wastewater and recycled water projects.

ATTACHMENTS:

A. Resolution to Approve the Integrated Water Resources Master Plan Amendments to the Water, Sewer and Recycled Water Master Plans PW 22- 19 and WW 22-4 and to Approve an Addendum to the City of Lathrop Integrated Water Resources Master Plan Environmental Impact Report in accordance with CEQA Guidelines Sections 15162 and 15164
B. Addendum to the City of Lathrop Integrated Water Resources Master Plan Amendments Environmental Impact Report ( SCH # 2019029106), August 2025
C. 2024 Water Master Plan Amendment, December 2024
D. 2024 Wastewater System Master Plan Amendment, December 2024 E. 2025 Recycled Water System Master Plan Amendment, May 2025 CITY MANAGER' S REPORT PAGE 5
OCTOBER 13, 2025 CITY COUNCIL REGULAR MEETING

ADOPT IWRMP AMENDMENTS TO THE WATER, WASTWATER AND RECYCLED WATER MASTER PLANS ( PW 22- 19 AND WW 22- 24) AND CEQA

DETERMINATION
APPROVALS:

Greg bson Date
Senior Civil Engineer
BradQfaylor
City Engineer
1/ I6/ 74)
Date
Ito• Zoz. s'
Michael King Date
Assistant City Manager
Salvador Navarrete
City Attorney
Date
to • Z - Z.

Stephen J. Salvatore Date
City Manager
RESOLUTION NO. 25 -

A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF LATHROP APPROVE

THE INTEGRATED WATER RESOURCES MASTER PLAN AMENDMENTS TO THE WATER, WASTEWATER AND RECYCLED WATER MASTER PLANS ( PW 22- 19 AND WW 22- 24), AND TO APPROVE AN ADDENDUM TO THE CITY OF

LATHROP INTEGRATED WATER RESOURCES MASTER PLAN

ENVIRONMENTAL IMPACT REPORT IN ACCORDANCE WITH CEQA
GUIDELINES SECTIONS 15162 AND 15164
WHEREAS, the Integrated Water Resources Master Plan ( IWRMP) Amendments associated with CIPs PW 22- 19 and WW 22-4, provide a comprehensive update to the City' s water, wastewater and recycled water system master plan documents that were originally adopted in 2019; and WHEREAS, the IWRMP Amendments update water and sewer demand projections and address changes in regulatory requirements, population and growth forecasts, land use planning, climate change, and other evolving conditions; and WHEREAS, previously, EKI and De Novo assisted the City with preparation of the IWRMP and associated project Environmental Impact Report which were approved by Council in December 2019; and
WHEREAS, since then, several developments have necessitated updates.

These include revised water demand factors and projections, completed in July 2020 to support the River Islands Phase 2 development Water Supply Assessment; and the City obtaining a National Pollutant Discharge Elimination System ( NPDES) permit, allowing surface water discharge from the City' s Consolidated Treatment
Facility ( CTF). The updates also include the decommissioning of ponds and spray fields previously used for CTF effluent disposal; and
WHEREAS, on April 11, 2022, Council approved an agreement with EKI to update the IWRMP. Amendment No. 1 to this agreement was approved by staff in August 2022 for EKI to evaluate the strength of wastewater sent to the Manteca Water Quality Control Facility in lieu of a task for wastewater flow monitoring; and WHEREAS, on February 13, 2023, Council approved Amendment No. 2 with EKI to update the geodatabases for the water, sewer and recycled water systems.

On August 12, 2024, Council approved an agreement with EKI for additional services needed to complete the IWRMP Amendments including changes in the City' s planned expansion of the recycled water system and an agreement with DeNovo to perform the CEQA analysis; and
WHEREAS, On August 12, 2024 Council approved an agreement with EKI for additional services needed to complete the IWRMP Amendments including changes in the City' s planned expansion of the recycled water system and an agreement with DeNovo to perform the CEQA analysis; and
WHEREAS, implementation of the IWRMP Amendments is a discretionary project for the City and are therefore subject to environmental review under CEQA; and
WHEREAS, the completion of CEQA is required prior to formal adoption of the IWRMP Amendments by the City; and
WHEREAS, De Novo has completed the CEQA analysis and an Environmental Addendum, to provide analysis of the water and sewer master plan components of the IWRMP Amendments PW 22- 19 and WW 22- 24; and
WHEREAS, as detailed in the EIR Addendum the revisions in the IWRMP Addendum do not change the environmental conclusions of less than significant, or less significant with mitigation that was provided in the certified EIR.

NOW, THEREFORE, BE IT RESOLVED that the City Council of the City of Lathrop, hereby approves the proposed Integrated Water Resources Master Plan Amendments to be used to support the General Plan and as the basis for regulatory compliance documents, to support utility operations, budget, rate studies, land use planning and development fees; and
NOW THEREFORE, BE IT FURTHER RESOLVED that the City Council of the City of Lathrop, hereby approves the proposed Addendum to the City of Lathrop Integrated Water Resources Master Plan Environmental Impact Report ( EIR) in accordance with CEQA Guidelines Sections 15162 and 15164.

The foregoing resolution was passed and adopted this 13th day of October 2025, by the following vote of the City Council, to wit:

AYES:

NOES:

ABSTAIN:

ABSENT:

Paul Akinjo, Mayor
ATTEST: APPROVED AS TO FORM:

Teresa Vargas, City Clerk Salvador Navarrete, City Attorney A Land Use Planaiflg, Design, and En

ADDENDUM
TO THE

CITY OF LATHROP INTEGRATED WATER RESOURCES MASTER PLAN

ENVIRONMENTAL IMPACT REPORT ( EIR)
SCH # 2019029106)
AUGUST 2025
Prepared for:

City of Lathrop
Planning Division
390 Towne Centre Drive
Lathrop, CA 95330
Prepared by:

De Novo Planning Group
1020 Suncast Lane, Suite 106
El Dorado Hills, CA 95762
916) 997- 1865
EIR Addendum

1. INTRODUCTION
This Addendum was prepared in accordance with the California Environmental Quality Act ( CEQA) and the CEQA Guidelines. This document has been prepared to serve as an Addendum to the previously certified Environmental Impact Report ( EIR) (State Clearinghouse [ SCH] # 2019029106) for the Lathrop Integrated Water Resources Master Plan ( Original Project). The City of Lathrop is the lead agency for the proposed amendments to the IWRMP, which consists of updates to the Water System Master Plan ( WSMP), the Wastewater System Master Plan ( WWSMP), and the Recycled Water System Master Plan ( RWSMP) (hereafter proposed Project).

For the City to consider an amendment to the IWRMP, the City must ensure that, if needed, environmental review consistent with the requirements of the California Environmental Quality Act CEQA) and the State CEQA Guidelines has been completed. Because the City has previously complied with CEQA for the IWRMP project and the new discretionary action before the City would be a change in an already -approved project, the City can rely on information in the certified EIR previously prepared for the IWRMP, to the extent they remain adequate. Consistent with the requirements of CEQA Guidelines Section 15162, the City must, therefore, determine whether any changed circumstances or " new information of substantial importance" will trigger the need for a subsequent EIR.

As described in CEQA Guidelines Section 15164, a lead agency shall prepare an addendum to a previously adopted EIR if some changes or additions to an EIR certified for a project are necessary, but none of the of conditions identified in CEQA Guidelines Section 15162 have occurred. No subsequent EIR shall be prepared for that project unless the lead agency determines, based on substantial evidence in the light of the whole record, one or more of the following conditions to be applicable:
1) Substantial changes are proposed in the project which will require major revisions of the previous EIR or negative declaration due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects; 2) Substantial changes occur with respect to the circumstances under which the project is undertaken which will require major revisions of the previous EIR or negative declaration due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects; or 3) New information of substantial importance, which was not known and could not have been known with the exercise of reasonable diligence at the time the previous EIR was certified as complete or the negative declaration was adopted, shows any of the following:

A) The project will have one or more significant effects not discussed in the previous EIR or negative declaration;
Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 1 EIR Addendum
B) Significant effects previously examined will be substantially more severe than shown in the previous EIR;
C) Mitigation measures or alternatives previously found not to be feasible would in fact be feasible and would substantially reduce one or more significant effects of the project, but the project proponents decline to adopt the mitigation measure or alternative; or D) Mitigation measures or alternatives which are considerably different from those analyzed in the previous EIR would substantially reduce one or more significant effects on the environment, but the project proponents decline to adopt the mitigation measure or alternative.

If any of the triggers set forth above occurs, the City would be required to prepare a subsequent EIR, unless " only minor additions or changes would be necessary to make the previous EIR adequately apply to the project in the changed situation," in which case a " supplement to an EIR" would suffice see CEQA Guidelines, Section 15163). If there are no grounds for either a subsequent EIR or a supplement to an EIR, then the City must prepare an addendum pursuant to CEQA Guidelines Section 15164, explaining why " some changes or additions" to the 2019 IWRMP EIR " are necessary but none of the conditions described in Section 15162 calling for preparation of a subsequent EIR have occurred."
As demonstrated in the environmental analysis provided in Section 4 ( Environmental Analysis), the proposed changes do not meet the criteria for preparing a subsequent EIR or negative declaration.

An addendum is appropriate here because, as explained in Section 4, none of the conditions calling for preparation of a subsequent EIR or negative declaration have occurred.

Information and technical analyses from the IWRMP EIR are utilized throughout this Addendum.

Relevant passages from this document ( consisting of the IWRMP EIR) are cited and available for review at:

City of Lathrop — City HaII
390 Towne Centre Drive
Lathrop, CA 95330
https:// www. ci. lathrop. ca. us/ community- development/ page/ communitv- developmentdocuments 2 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum

2. BACKGROUND AND PURPOSE OF THE EIR ADDENDUM
The City' s 2019 IWRMP, which includes the City' s
Water System Master Plan,' Wastewater System
Master Plan,' and Recycled Water Master Plan,' was finalized and approved by the City Council in December 2019 after a California Environmental Quality Act ( CEQA) process. The Lathrop Integrated Water Resources Master Plan EIR was certified by the Lathrop City Council in December 2019. The Project site is generally contiguous with the City limits, and includes the Sharpe Army Depot and the Rail Cargo Container Yard.

ORIGINAL PROJECT
The Original Project consisted of adoption and implementation of the IWRMP, which included the improvement projects summarized in the Water System Master Plan ( 2019), Wastewater System Master Plan ( 2019), and Recycled Water System Master Plan ( 2019).

WATER SYSTEM MASTER PLAN
The Water System Master Plan focused on development of water demand unit factors and projections, hydraulic assessment of the City' s existing water infrastructure and key planned improvements, and development of recommended water system capital improvement projects CIPs). Recommended CIPs were developed to support the City' s water supply strategy and address the deficiencies identified in the hydraulic assessment. A project was developed to address each identified fire flow capacity deficiency, either by replacing existing mains, installing new mains, or replacing undersized hydrants. Additional projects were developed to improve transmission of supply sources within the City' s distribution system.

WASTEWATER SYSTEM MASTER PLAN
The Wastewater System Master Plan focused on development of wastewater flow unit factors and projections, hydraulic assessment of the City' s existing infrastructure and key planned conveyances, and development of recommended wastewater CIPs.

Recommended CIPs were developed to address the potential deficiencies identified in the hydraulic assessment. For each identified gravity sewer capacity deficiency, a project was developed to remove and replace the existing pipe with a larger diameter pipe. Existing pipe slopes and depths were preserved when upsizing sewers in -place. Proposed increases in pipe diameters were optimized to meet the applicable criteria, while preventing oversizing and resulting low velocities during dry weather conditions. Improvements were also identified to address the potential deficiency at the City' s pump stations, including construction of parallel force mains and/ or pump EKI, 2019. Wastewater System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2019. Water System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2019. Recycled Water System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 3 EIR Addendum
upgrades. The WWSMP also suggested installation of permanent flow meter and flow monitoring programs in the Historic Lathrop and Crossroads areas.

RECYCLED WATER SYSTEM MASTER PLAN
The Recycled Water System Master Plan focuses on an evaluation of recycled water use and disposal alternatives, recycled water balance analyses, hydraulic assessment of the City' s existing recycled infrastructure and key planned improvements, and development of recommended recycled water system improvements and operational recommendations.

The City' srecycled water system supports the disposal of the effluent produced by the City -owned Lathrop Consolidated Treatment Facility ( CTF). The RWSMP evaluated the expansion of its recycled water distribution system to meet disposal requirements for the Phase 2 expansion of the Lathrop CTF, and increase from 1. 0 million gallons per day ( MGD) to 2. 5 MGD. It was assumed that the Phase 2 recycled water system expansion would be completed in two phases: Phases 2A and 2B. For expansion of permitted recycled water uses in Phase 2B, the RWSMP implemented a series for improvements including increasing capacity of PMP- 1, installing two ponds, and constructing a pump station.

APPROVALS
As part of the Original Project, the City undertook the following actions:

Certified the Integrated Water Resources Master Plan EIR; Adopted the Mitigation Monitoring and Reporting Program for the project; and Approved the Integrated Water Resources Master Plan.

3. PROPOSED PROJECT
The City' s 2019 IWRMP, which includes the City' s
Water System Master Plan, 4 Wastewater System
Master Plan,' and Recycled Water Master Plan,' was finalized and approved by the City Council in December 2019 after a California Environmental Quality Act ( CEQA) process. Since the IWRMP was completed, new information has become available and certain planning assumptions have changed that require an amendment to the IWRMP, including the following:

Land Use Information: The City completed a General Plan Update in September 2022 which included updated growth projections for the City.' In addition, development projections 4 EKI, 2019. Wastewater System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2019. Water System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019. 6 EKI, 2019. Recycled Water System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

City of Lathrop, 2022. City of Lathrop General Plan, August 2022. Available: https:// lathrop. generalplan. org/. 4 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
have changed significantly in the River Islands planning area with approval of the modified River Islands Phase 2 project in June 2021 and in the Central Lathrop Specific Plan area.' Water Demand Factors and Projections: The City' s unit water demand factors and water demand projections were updated in July 2020 to support the River Islands Phase 2 development Water Supply Assessment, which were later incorporated into the City' s 2020 Urban Water Management Plan ( UWMP). 9 The updated demand evaluation was based on the City' s water use patterns observed since the 2014-017 drought, which are significantly lower compared to those included in the 2019 IWRMP which had been based on the City' s pre -drought water patterns.

Water Supply Information: The City' s water supply reliability and water supply infrastructure investments need to be reassessed based on the updated water supply projections presented in the 2020 UWMP and any subsequent management efforts. For example, the City' s imported surface water from the South County Water Supply Project SCWSP) could experience significant cutbacks in light of the Bay Delta Plan Amendment and the resolution of the resultant settlement negotiations. Future, the City has experience water quality issues with its groundwater supply associated with the nearby former Occidental Chemical Corporation remediation site and detections of per- and polyfluoroalkyl substances ( PFAS). These issues limit the City' s ability to expand groundwater production in the future. The City conducted engineering feasibility studies for adding PFAS treatment of the Louise Avenue Water Treatment Facility ( LAWTF) and an aquifer storage and recovery ( ASR) project to improve water supply reliability.

River Discharge Permit: The City has obtained a National Pollutant Discharge Elimination System ( NPDES) permit to dispose a portion of the wastewater treated at the Lathrop Consolidated Treatment Facility ( CTF) in the San Joaquin River, with the remaining portioned delivered as recycled water to City owned parks and landscaping as well as retail customers.

To support use of recycled water for landscape irrigation, the City obtained coverage under General Order WQ- 2019- 0058- DDW- R5017 and submitted a Title 22 Report Addendum in 2020. The City began delivering recycled water for urban uses in the summer of 2021. These changes reduce the City' s potable water demand, and affect the operations and infrastructure needed of the City' s
wastewater effluent disposal and recycled water
distribution systems.

WATER SYSTEM MASTER PLAN AMENDMENT
For this project, a comprehensive update of the water system hydraulic model was undertaken to reflect various system improvements and planned expansions. The model was updated to include system improvements completed since the 2019 Water System Master Plan ( WSMP), as well as ongoing projects such as system expansions due to new developments and capital improvement projects by the City. Additionally, the backbone water system infrastructure was updated to account e
9 City
project.

EKI,
of
2021.

Lathrop,
2020
2022.

Urban
River
Water
Islands
Management
Phase 2 Project.

Plan for
Available:
the City of
https:// www. ci. lathrop. ca. us/ planning/ page/ river- islandsphase- 2 Lathrop, June 2021. Available:
https:// www. ci. lath rop. ca. us/ publicworks/ page/ urba n -water - management -plan.

Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 5 EIR Addendum
for future development areas, incorporating recent utility plans from both the City and developers, including specific plans like the River Islands Phase 2 and Mossdale Landing West Tentative Map.

To ensure the accuracy of the model, operational settings for pumps and tanks were verified with input from City operations staff, and adjustments were made where necessary. The water demand factors were updated based on water use data from 2017 to 2021, and parcel -by -parcel average day demands were reallocated to reflect new developments added since the previous update.

Projections for future water demand were developed based on the land projections from the General Plan Update ( adopted in September 2022) and the River Islands Phase 2 project ( approved in June 2021).

The evaluation of water supply reliability included analysis based on the 2020 Urban Water Management Plan ( UWMP) and the City' s PFAS treatment and Aquifer Storage and Recovery ( ASR) feasibility studies. Fire flow demands were assigned to each new fire hydrant, taking into account associated land uses. The water system' s performance under both existing ( 2022) and buildout 2045) conditions was assessed through steady- state model simulations, evaluating system pressures, velocity, head loss deficiencies, and fire flow coverage. The evaluation also extended to storage and booster pump station capacities. Furthermore, the list of capital improvement projects CIPs) from the 2019 WSMP was verified and updated. Finally, the findings and updates were compiled into an amended WSMP document for review and future planning purposes.

SYSTEM IMPROVEMENTS
Since 2019, several major water system improvements have been completed. These completed projects were considered for the WSMP amendment.

BPSs 5 and 6 and Storage Tanks: BPS 5 and 6 and associated storage tanks ( 1. 2 MG and 1. 6 MG, respectively) were constructed in 2018 and 2019 to provide additional storage and flow capacity to the new development at River Islands and Central Lathrop Phase 1 ( Stanford Crossing).

BPS 5 and Tank 5 Site Expansion: The Tank 5 site expansion project, including construction of an additional fire pump of 4, 000 gpm design flow and two new 1. 8 MG water storage tanks ( Tank 5B and Tank 5C) is near completion during the preparation of this master plan.

SSJID Turnout 2: SSJID Turnout 2 was constructed in 2018 with three 2, 000 gpm pumps and one 1. 0 MG tank owned by SSJID.

J Street Improvement Project: The previous 8" to 10" pipes on J St between approximately 140 feet west of Avon St and approximately 210 feet east of 5th St were replaced by new 12" PVC pipe. The previous 10" line on Avon St between J St and Sunflower Dr was replaced by new 12" PVC pipe. The previous 12" BPS -1 discharge line was replaced by new 16" PVC pipe.

South Harlan Road Improvement Project: A new 8" pipe on South Harlan Road, north of Louise Avenue, was constructed to loop the existing 8 -inch dead- end on South Harlan Road to the 8 -inch pipe on Old Harlan Road.
6 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
River Islands Water Infrastructure: Water system improvements for Phases 1, 2A, and parts of 2B of the River Islands Development.

Central Lathrop Stanford Crossing Infrastructure: Water system improvements for the Central Lathrop Stanford Crossing development.

Louise Avenue Water Transmission Main Project: A new 12 - inch transmission line was installed in parallel to the existing 12 -inch transmission line along Louise Avenue from I-5 to Howland Road.

South Lathrop Offsite Backbone Infrastructure: A new 12 - inch transmission line was constructed on Yosemite Avenue between Highway 120 and D' Arcy Parkway.

Backbone Infrastructure, South Lathrop Commerce Center: A new 12 -inch transmission loop was constructed around the South Lathrop Commerce Center.

Murphy Parkway Off -Site Civil Improvement: A new 10 -inch transmission line was constructed on the new development ( Tesla Service Distribution Center) at 17100 Murphy Pkwy, Lathrop, CA 95330.

POPULATION GROWTH
The City anticipates that population will continue to grow in the future given the existing entitlements for several large residential developments. The population projections for 2025 through 2045, summarized in Table 1, are estimated using the existing population and adding the amount of new housing anticipated to be permitted in each five- year increment based on anticipated growth in the service area. The anticipated population in 2045 is now less than the population anticipated in the 2019 WSMP.

Table 1. Current and Projected Service Area Population
Current and Projected Service Area Population
Year 2016 2020 2023 2025 2030 2035 2040
2045
Buildout)
2019 WSMP 22, 174 32,95 46,34 58, 653 67, 844 74, 581 93, 485 2024 WSMP 35, 080 40, 531 55, 471 72, 513 84,97 86, 013 Difference 5, 903 3, 182 4, 669 10, 316 7, 472
Sources:

EKI, 2019. Water System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2024. 2024 Water System Master Plan Amendment, December.

DEMANDS
The City' stotal potable water use was 5, 277 acre- feet (AF) in 2022, with a per capita water use of 149 gallons per capita per day ( GPCD). Water demand rebounded from the recent 2014-017 as water use restrictions were lifted and new development projects were constructed. However, water use decreased again as a result of the 2021-022 drought and remains below 2020 levels.

Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 7 EIR Addendum
The City' s water demand factors presented in the 2020 UWMP were verified and updated using 2017 through 2022 data. The water demand factors serve as the basis to estimate average annual water demands for future developments. The updated water demand factors in gallons per day per dwelling unit ( gpd/ du) or gallons per day per acre ( gpd/ ac) are presented in Table 2. In all land use categories except Commercial, the water demand is less than that anticipated in the 2019 WSMP.

Table 2. Water Demand Factors
Land Use Category
2019 WSMP Potable Water Use
Factors
2024 WSMP Updated Potable
Water Use Factors
City- wide City- wide River Islands
Low Density Residential 430 gpd/ du 330 gpd/ du 315 gpd/ du Medium Density Residential 330 gpd/ du 250 gpd/ du 235 gpd/ du High Density Residential 265 gpd/ du 170 gpd/ du
Commercial 1, 300 gpd/ ac 1, 550 gpd/ ac
Industrial 1, 400 gpd/ ac 1, 200 gpd/ ac
Parks / Public Landscaping 3, 500 gpd/ ac 2, 450 gpd/ ac Schools / Institutional 2, 100 gpd/ ac 1, 250 gpd/ ac
Sources:

EKI, 2019. Water System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2024. 2024 Water System Master Plan Amendment, December.

Water demand projections were updated and calculated as the sum of (1) the City' s existing potable water demand in 2022, and ( 2) the anticipated potable water demands associated with the future development projects and planning areas post 2022. It is anticipated that the City' stotal demand in 2045 will be 12, 405 acre- feet per year ( AFY), which is significantly lower than the demand projections included in the 2019 WSMP ( 18, 977 AFY).

WATER SYSTEM SUPPLIES
The City obtains water from both imported surface water and local groundwater sources. The City receives Stanislaus River water through SCWSP that is operated by SSJID. The City currently operates five groundwater production wells and a groundwater treatment facility — the LAWTF.

Due to the relatively high cost of SCWSP water, the City has historically relied upon its groundwater wells as the primary source of supply. The City' s annual water production increased from 4, 168 AF in 2017 to 5, 277 AF in 2022 as a result of development growth and rebound from the 2014-017 drought. Surface water production ( i.e., SCWSP purchases) steadily increased from 921 AF in 2017 to 3, 866 AF in 2022. At the same time, the City reduced its groundwater production from 3, 247 AF or 78% of its total supplies in 2017 to 1, 411 AF or 27% in 2022 due to groundwater quality concerns.

The City is evaluating treatment options to meet upcoming regulations for per- and polyfluoroalkyl substances ( PFAS) and an Aquifer Storage and Recovery ( ASR) project to boost its water supply reliability. With future groundwater treatment and purchase of SCWSP Phase II, the City has adequate supplies through 2045 during normal and dry years, as shown in Table 3, Table 4, and Table 5.
8 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
Table 3. Projected Potable Supply vs. Demand for Normal Year Scenario Estimated Supply and Demand (AFY)
2025 2030 2035 2040 2045
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 11, 607 11, 607 11, 607 11, 607 11, 607 Surplus or Deficit
Percent Shortfall
5, 479 3, 508 1, 825 524 798
6%
Projected Supply - Current and Future 12,07 12,07 12,07 15, 981 15, 981 Surplus or Deficit
Percent Shortfall
5, 979 4, 008 2, 325 4, 898 3, 576
Source:

EKI, 2024. 2024 Water System Master Plan Amendment, December. Table 5- 10.

Table 4. Projected Potable Supply vs. Demand for Single Dry Year Scenario Estimated Supply and Demand (AFY)
2025 2030 2035 2040 2045
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 10, 498 11, 048 11, 597 10,07 10, 505 Surplus or Deficit
Percent Shortfall
4, 370 2, 949 1, 815 976
9%
1, 901
15%
Projected Supply - Current and Future 10, 998 11, 548 12, 097 13, 637 14, 259 Surplus or Deficit
Percent Shortfall
4, 870 3, 449 2, 315 2, 554 1, 854
Source:

EKI, 2024. 2024 Water System Master Plan Amendment, December. Table 5- 11.

Table 5. Projected Supply vs. Demand for Multiple Dry Years Scenario Estimated Supply and Demand ( AFY)
2025 2030 2035 2040 2045
First Dry Year
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 11, 607 11, 607 11, 607 11, 607 11, 607 Surplus or Deficit
Percent Shortfall
5, 479 3, 508 1, 825 524 798
6%
Projected Supply - Current and Future 12,07 12,07 12,07 15, 981 15, 981 Surplus or Deficit
Percent Shortfall
5, 979 4, 008 2, 325 4, 898 3, 576
Second Dry Year
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 9 EIR Addendum
Estimated Supply and Demand ( AFY)
2025 2030 2035 2040 2045
Projected Supply - Current Sources 11, 607 11, 607 11, 607 11, 607 11, 607 Surplus or Deficit
Percent Shortfall
5, 479 3, 508 1, 825 524 798
6%
Projected Supply - Current and Future 12,07 12,07 12,07 15, 981 15, 981 Surplus or Deficit
Percent Shortfall
5, 979 4, 008 2, 325 4, 898 3, 576
Third Dry Year
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 10, 498 11, 048 11, 597 10,07 10, 505 Surplus or Deficit
Percent Shortfall
4, 370 2, 949 1, 815 976
9%
1, 901
15%
Projected Supply - Current and Future 1Q998 11, 548 12, 097 13, 637 14, 259 Surplus or Deficit
Percent Shortfall
4, 870 3, 449 2, 315 2, 554 1, 854
Fourth Dry Year
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 10, 498 11, 048 11, 597 10,07 10, 505 Surplus or Deficit
Percent Shortfall
4, 370 2, 949 1, 815 976
9%
1, 901
15%
Projected Supply - Current and Future 10, 998 11, 548 12, 097 13, 637 14, 259 Surplus or Deficit
Percent Shortfall
4, 870 3, 449 2, 315 2, 554 1, 854
Fifth Dry Year
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 11, 607 11, 607 11, 607 11, 607 11, 607 Surplus or Deficit
Percent Shortfall
5, 479 3, 508 1, 825 524 798
6%
Projected Supply - Current and Future
12,07 12,07 12,07 15, 981 15, 981
Surplus or Deficit
Percent Shortfall
5, 979 4, 008 2, 325 4, 898 3, 576
Source:

EKI, 2024. 2024 Water System Master Plan Amendment, December. Table 5- 12. 10 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum

HYDRAULIC ASSESSMENT
The water system hydraulic model was updated to represent the City' s utility infrastructure as of January 2023. The hydraulic model, along with the updated demand projections, was used to evaluate capacity needs for current and future demand conditions and to complete the hydraulic assessment portion of the WSMP. The updated model was validated by comparing the model results to system operations data.

Existing infrastructure and key planned infrastructure were assessed under an Existing ( 2022) scenario and a Buildout ( 2045) scenario.

The City' s water distribution system is primarily assessed against its ability to supply required pressures under peak demand and fire flow conditions. Pipe velocity and head loss criteria are secondary criteria that indicate which pipes could be upsized to increase downstream pressures and improve water movement within the system. Due to the updated water demand projections, no new hydraulic deficiencies are identified compared to the 2019 WSMP.

SUPPLY, STORAGE, AND PUMPING CAPACITY ASSESSMENT
The City currently has adequate supply, storage, and peaking pumping capacity to meet design criteria. Additional supply, storage, and peak pumping capacity will be required to support future development, as shown in Table 6.

Table 6. Projected Citywide Pumping Requirements
Available or Required Capacity( a)
Existing Buildout
gpm mgd gpm mgd
Available
Pumping
Capacity
SSJIDTurnout 1 5, 210 7. 5 5, 210 7. 5
LAWTF Booster Station 6, 300 9. 1 6, 300 9. 1
BPS - 1 1, 050 1. 5 1, 050 1. 5
BPS - 2 3, 000 4. 3 3, 000 4. 3
BPS - 3 4, 750 6. 8 4, 750 6. 8
BPS -4 4, 600 6. 4, 600 6.

BPS -5(') 8, 000 11. 5 12, 000 17. 3
BPS -6 5, 300 7. 6 5, 300 7. 6
Planned BPS at the former Well 21 site 3, 000 4. 3
Planned River Islands Phase II BPS 8, 000 11. 5
Total Available Firm Pumping Capacity 38, 210 55. 0 53, 210 76. 6 Criteria 1: Max
Day Plus Fire
Flow
MDD Plus Two Concurrent Fires(`) 11, 562 16. 6 19, 075 27. 5 Max Day Plus Two Concurrent Fires Pumping
Capacity Surplus 26, 648 38. 4 34, 135 49. 2
Criteria 2: Peak
Hour Demands
PHD 8, 506 12. 2 19, 996 28. 8
Peak Hour Demand Pumping Capacity 29, 704 42. 8 33, 214 47. 8 Pumping Capacity Surplus r(Deficit) el 26, 648 38. 4 33, 214 47. 8 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 11 EIR Addendum
Notes:
a) Firm pumping capacity reflects the capacity of the pumping station with the largest domestic pump offline. b) Firm pumping capacity at buildout from City of Lathrop Phase I Potable Water Booster Pump station and Storage Tank Expansion Plan at River Islands 100% Plans ( PACE, 2022).
c) Value is equal to the MDD plus the fire flow criteria for one high density residential fire ( 2, 000 gpm) and one industrial fire ( 4, 000 gpm)•
d) Total pumping capacity surplus or deficit reflects the most stringent criteria. Deficits will be made up by future booster pump stations. e) SSJID Turnout 2 was designed to pump directly to Tank 5 or BPS -5 therefore it' s not accounted for in the total pumping capacity.

Source: EKI, 2024. 2024 Water System Master Plan Amendment, December. Table 8-7.

RECOMMENDED CAPITAL IMPROVEMENT PROGRAM CHANGES
The WSMP recommends modifications to the list of Capital Improvement Projects ( CIPs) included in the 2019 WSMP and the City' s CIP. The following improvements were identified:

Modifications to Water Supply CIPs
o Groundwater Treatment Improvements
o Aquifer Storage and Recovery
Modification to Water Distribution System CIPs
o Harlan Road and South Harlan Road Fire Flow Improvement Project o Murphy Parkway Fire Flow Loop to Harlan Road
o East J Street Alley Residential Fire Flow Improvement Project o Lathrop Transmission Main Improvement Project

WASTEWATER SYSTEM MASTER PLAN AMENDMENT
The WWSMP amendment includes a comprehensive update of the wastewater system hydraulic model to reflect improvements completed since the 2019 WWSMP, as well as ongoing projects currently under design or construction. The amendment includes a review of the City' s basic assumptions and criteria for wastewater planning, including system design, pump station operations, and infiltration and inflow rates. Additionally, the wastewater flow unit factors would be updated based on data collected from 2017 to 2021, which reflect both wastewater flow and water usage patterns.

Wastewater generation projections have been developed using land use data consistent with the General Plan Update ( adopted in September 2022) and the River Islands Phase 2 project ( approved in June 2021). The peaking curve would be verified and updated to accurately evaluate peak wet - weather flows. The updated flow projections would then be assessed against the wastewater treatment capacity to ensure the system' s adequacy to handle future demand. The existing collection system would also be evaluated under both current and future flow conditions through steady- state model simulations.

Further analysis focused on pump stations, force mains, and alternative conveyance methods to optimize the system' sperformance. The list of Capital Improvement Programs ( CIPs) from the 2019 WWSMP was verified and updated, ensuring that all improvements are accounted for. Finally, the 12 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
findings and updates from these analyses were compiled into an amended WWSMP document to guide future planning and improvements.

UPDATED DEVELOPMENT PROJECTIONS
The City has experienced significant growth in recent years and is anticipating growth to continue, as shown in Table 7, particularly in several approved or pending large development projects within the City. Infrastructure needs for these projects are evaluated in the WWSMP. The development areas considered for buildout projections are:

Central Lathrop Specific Plan
Mossdale Landing
Mossdale Landing East
Mossdale Landing South
Mossdale Landing West
River Islands
Lathrop Gateway Business Park Specific Plan
South Lathrop Specific Plan
Historic Lathrop Infill and Other Developments East of I-5 Sharpe Army Depot
Table 7. Current and Projected City of Lathrop Population Current and Projected Service Area Population ( a)( b)
Year 2023 2025 2030 2035 2040
2045
Buildout)
Population Served 35, 080 40, 531 55, 471 72, 513 84,97 86, 013 Notes:
a) Current population is based on population estimates by the California DOF for the City of Lathrop included in DOF, 2023.
b) Projected populations for 2025 through buildout ( 2045) are based on residential unit counts from Table 2- 1 of the WWSMP, multiplied by 4. 02 persons per dwelling unit for low density developments ( U. S. Census, 2023) and

3. 0 persons per dwelling unit for medium and high density developments.

Source: EKI, 2024. 2024 Wastewater System Master Plan Amendment, December. Table 2-3.

CITY' SEXISTING WASTEWATER INFRASTRUCTURE
Wastewater from the City is treated at two facilities: (1) the Lathrop Consolidated Treatment Facility Lathrop CTF, or LCTF), and (2) the Manteca Wastewater Quality Control Facility ( MWQCF). The City' s allocated capacity at the MWQCF is 1. 451 million gallons per day (MGD) of dry weather flow per the City' s 2002 Agreement Amendment with Manteca. The Lathrop CTF has a treatment capacity of 2. 5 MGD. The City is currently planning a Phase 3 Expansion that will expand CTF' scapacity to a total of

5. 0 MGD.

Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 13 EIR Addendum
The City' s wastewater collection system consists of approximately 102 miles of gravity mains, 23. 6 miles of force mains, as well as 15 lift stations and pump stations. The City has a Supervisory Control and Data Acquisition ( SCADA) system for control and monitoring of facilities.

Land use -specific wastewater generation factors were updated using the 2017 through 2022 historic wastewater flow and parcel -level water use data. The wastewater generation factors serve as the basis to estimate ADWF for future developments. The IWRMP updated wastewater generation factors ( in units of gallons per day per dwelling unit or gallons per day per acre; gpd/ du or gpd/ ac) are presented in Table 8.

Table 8. Wastewater Flow Factors
Wastewater Flow Factor
City -Wide River Islands
Low Density Residential 240 gpd/ du 200 gpd/ du
Medium Density Residential 200 gpd/ du 155 gpd/ du
Medium Density Residential 110 gpd/ ac
Commercial 755 gpd/ ac
Industrial 240 gpd/ ac
Parks 55 gpd/ ac
Schools/ Institutional 220 gpd/ ac
Source: EKI, 2024. 2024 Wastewater System Master Plan Amendment, December. Table ES - 1.

Wastewater ADWF projections were calculated as the sum of the two major components of future wastewater flow: (1) the volume of wastewater that best represents existing wastewater generation within the City, and ( 2) the anticipated wastewater generation associated with the future development projects and planning areas.

The City' s projected wastewater generation by sector and by development area are estimated in five- year increments between 2025 and buildout in 2045. It is anticipated that the City' stotal ADWF at buildout in 2045 is estimated to be 5. 67 MGD, which is 12. 5% lower than the projections included in the 2019 WWSMP of 6. 48 MGD. An ADWF of L36 MGD is anticipated to flow to MWQCF from Historic Lathrop and 4. 31 MGD is projected to flow to the Lathrop CTF at buildout. The vast majority of the projected increase in wastewater generation at the CTF above current rates is associated with new development in River Islands and Central Lathrop.
14 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum

WASTEWATER TREATMENT CAPACITY ASSESSMENT
The City' s allocation at the MWQCF is sufficient to meet the projected wastewater flows to MWQCF at buildout ( Table 9). Flows to the CTF is anticipated to exceed the current CTF capacity between 2030 and 2035. As shown in Table 10, flows to the Lathrop CTF is anticipated to exceed the current CTF capacity of 2. 5 MGD between 2030 and 2035. The City anticipates completing the Lathrop CTF Phase 3 Expansion within the next three years to meet the projected wastewater flows. The Phase 3 Expansion will expand the CTF' s capacity to a total of 5. 0 MGD, which is sufficient to meet projected flows through buildout.

Table 9. Projected Wastewater Flow and Treatment Capacity at MWQCF Estimated ADWF Influent and Treatment Capacity ( MGD)
Existing
2022)
2025 2030 2035 2040 2045
Projected Influent ADWF (a)
ADWF Projection 1.1 1. 22 1. 28 1. 30 1. 30 1. 31
MWQCF Capacity
Allocated Capacity ( b) 1. 451 1. 451 1. 451 1. 451 1. 451 1. 451 Projected Deficit
Notes:
a) Wastewater influent to MWQCF is the wastewater flow from the Historic Lathrop area and Sharpe Army Depot. b) The City of Manteca indicated that increases in influent wastewater nutrient concentrations reduce MWQCF' streatment capacity and Lathrop' sshare of MWQCF' scapacity to 0. 935 MGD ( see Section 5. 2 of the WWSMP). The City is assessing the information provided by Manteca and whether the City will participate in improvements at the MWQCF to increase the City' s share of capacity.

Source: EKI, 2024. 2024 Wastewater System Master Plan Amendment, December. Table 5-1.

Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 15 EIR Addendum
Table 10. Projected Wastewater Flow and Treatment Capacity at Lathrop CTF Estimated ADWF Influent and Treatment Capacity ( MGD)
Existing
2022)
2025 2030 2035 2040 2045
Projected Influent ADWF ( a)
ADWF Projection 1. 08 1. 51 2. 44 3.7 4. 03 4. 31
Existing Capacity and Future Expansions
Lathrop CTF Phase 0 - 2 ( b) 2. 50 2. 50 2. 50 2. 50 2. 50 2. 50 Lathrop CTF Phase 3 0.0 0.0 2. 50 2. 50 2. 50 2. 50
Total Capacity 2. 50 2. 50 5. 00 5. 00 5. 00 5. 00
Projected Deficit
Notes:
a) Wastewater influent to Lathrop CTF is the combination of wastewater flow from all city areas except for the Historic Lathrop area and Sharpe Army Depot.
b) Higher influent wastewater nutrient concentrations recently observed at the CTF may limit its hydraulic capacity to approximately 2. 0 MGD ( see Section 55. 2of the WWSMP).

Source: EKI, 2024. 2024 Wastewater System Master Plan Amendment, December. Table 5-2.

Both the MWQCF and the Lathrop CTF are observing increasing wastewater strength ( i.e., concentration of pollutants and nutrients in wastewater) likely due to improved water use efficiency during the recent droughts and in response to state regulations. According to capacity studies conducted by the City of Manteca, the City' s share of treatment capacity at the MWQCF is reduced to 0. 935 MGD because of the increased wastewater strength. The City has requested additional information from Manteca and assessing its rights to capacity at the MWQCF. An analysis performed by PACE Engineers ( PACE) in 2021 suggested that higher pollutant loading in CTF influent reduces CTF' s hydraulic capacity to approximately 2. 0 MGD.

HYDRAULIC ASSESSMENT
As part of the WWSMP Amendment, the sewer system hydraulic model was updated to represent the City' sutility infrastructure as ofJanuary 2023. The hydraulic model was used to assess the ability of the City' s existing infrastructure to support the wastewater flow projections summarized in Section 4 of the WWSMP. Existing infrastructure was assessed under two scenarios: Existing ( 2022) and Buildout ( 2045).

The City' scollection system was primarily assessed against the capacity criteria, including depth to diameter ( d/ D) ratio in gravity mains and maximum velocity in force mains. Model results have shown that approximately 3% of City' s existing gravity mains will not meet the capacity criteria by 2045. Most capacity deficiencies identified in the Buildout scenario already exist in the existing system, although the degree of deficiency may increase with projected development ( Table 11). 16 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
Table 11. Summary of Collection System Capacity Deficiencies Scenario
Percent Length of Gravity Mains
Meeting
Capacity
Criteria
d/ D Ratio
Greater
Than 0. 5
a)
d/ D Ratio
Greater
Than 0. 75
d/ D Ratio
Greater Than 1
Surcharged)
Existing 98% 1.4% 0.1% 0.2%
Buildout 97% 2.0% 0.2% 0.3%
Notes:
a) Gravity mains less than 18 -inch diameter and exceeding the capacity criteria.

Source: EKI, 2024. 2024 Wastewater System Master Plan Amendment, December. Table 7-2.

Pump stations are evaluated against the ability to convey peak wet weather flow ( PWWF) within a station' sfirm capacity. A capacity deficiency has been identified in the Stonebridge Lift Station ( LS) in both the Existing and Buildout scenario ( Table 12). All other pump stations are projected to have sufficient capacities to meet existing and future PWWFs.

Table 12. Summary of Hydraulic Capacity Analysis for Pump Stations Pump Station
Existing
Firm
Capacity
gpm)
Existing Scenario Buildout
Firm
Capacity
gpm) (b)
Buildout Scenario
PWWF
gpm)
TDH
ft)
PWWF
gpm)
TDH
ft)
MWQCF Collection System
North Harlan PS 1, 075 53 11. 4 117 21.

Stonebridge LS 350 390 47. 5 390 43. 0
Woodfield LS 820 744 47. 5 752 50. 2
Valley Crossing LS ( c) 83 27 47. 5 27 50. 2
J Street LS 700 584 27. 8 651 28. 1
Easy Court LS 500 223 37. 9 227 65. 1
O Street PS 2, 800 915 27. 8 994 28. 1
McKinley Avenue PS 1, 675 971 34. 1 984 35. 5
Lathrop CTF Collection System
Stanford Crossing PS 2, 300 194 37. 9 1, 049 65. 1
Mossdale PS 4, 050 989 43. 2 3, 450 1, 328 58. 9
River Islands 2A PS 3, 975 437 19. 4 2, 018 19. 9
River Islands Main PS ( e) 1, 700 884 37. 9 15, 000 3, 785 65. 1 Lathrop Gateway PS 280 126 13. 5 155 22.

South Lathrop PS 1, 850 1 27. 8 94 28. 1
Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 17 EIR Addendum
Notes:
a) Bolded text indicates PWWF exceeded pump station' s firm capacity. b) If different from existing firm capacity.

C) Capacity of the 8" outlet is listed as the lift station capacity, as it is the capacity limiting component of this pump station. d) Flow information is not available for the Louise Avenue PS, therefore, its capacity is not analyzed. e) It is anticipated that the River Islands Sewer PS will be constructed in phases to include a total of six pumps.

Source: EKI, 2024. 2024 Wastewater System Master Plan Amendment, December. Table 7-4.

The City' s existing and planned force mains are able to convey projected wastewater flow through 2045.

RECOMMENDED CAPITAL IMPROVEMENT PROGRAM
The recommended collection system capital improvement projects ( CIPs) from the 2019 WWMP have been reviewed and confirmed to address the potential deficiencies identified in the updated hydraulic assessment. The WWSMP Amendment recommends additional analyses be conducted to confirm the required project extents and infrastructure sizing. Modifications and additions were made to treatment projects based on findings from the wastewater treatment capacity assessment.

The WWSMP Amendment recommends modifications and additions to the list of recommended CIPs included in the 2019 WWSMP. The following modifications to the City' s wastewater treatment
CIPs are identified to reflect recent wastewater strength at MWQCF and the City' s progression on CTF expansions.

Manteca Interim Improvements
The City of Manteca indicated that increases in influent wastewater nutrient concentrations reduce MWQCF' streatment capacity to 6. 36 MGD and, therefore, Lathrop' sshare of MWQCF' scapacity to

0. 935 MGD. The City' s ADWF conveyed to the MWQCF was 1.1 MGD in 2022 and was above this estimated reduced allocation. Moreover, the City anticipates a total of 1. 31 MGD of wastewater will flow to MWQCF at buildout.

The City of Manteca is planning interim improvement projects which would increase the MWQCF' s capacity to 8. 23 MGD and Lathrop' sshare of capacity to 1. 21 MGD. The cost estimate of interim improvement projects to MWQCF was estimated at a total 32. 8 million in the August 2022 letter and updated to 79. 6 million in Manteca' s 2023 draft Wastewater Master Plan ( Manteca, 2022; 2023).

The draft Manteca Wastewater Master Plan additionally evaluated a Phase IV Expansion Project that would further increase MWQCF' scapacity from 8. 23 MGD to 17. 5 MGD to serve projected population growth in its service area. The recommended Phase IV Expansion Project includes two

4. 65 MGD stages, with the cost of Stage 1 estimated at $ 146. 3 million and Stage 2 at $ 70. 6 million. 18 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
The City is currently assessing its appropriate level of contribution to improvements at the MWQCF to meet its current and buildout wastewater treatment needs. It is anticipated that the City will identify such improvements as a CIP once an agreement is established.

Lathrop CTF Phase 3 Expansion
The current Phase 2 expansion Lathrop CTF has a hydraulic capacity of 2. 5 MGD at elevated wastewater strength levels. As discussed in Section 5.2, wastewater ADWF to the Lathrop CTF is projected to soon exceed this capacity before 2025. The City has initiated Phase 3 expansion of the facility to a total ADWF capacity of 5. 0 MGD. The total projected OPC for the Phase 3 expansion is approximately $23. 7 million based on the City' s FY 2023-4 CIP plan ( WW 22- 38).

The Phase 3 expansion is projected to meet flows from the new development areas through 2040, until when the City may need a fourth expansion of the facility.

Modification to Collection System CIPs
The hydraulic evaluation in the WWSMP Amendment showed a reduction in hydraulic deficiency locations compared to those presented in the 2019 WWSMP as a result of CIPs completed since the 2019 WWSMP and lower wastewater flow projections. In particular, (1) the Woodfield Pump Station upgrade was completed in 2019; and ( 2) the Crossroads gravity main replacement project is no longer necessary. As such, these projects are removed or modified from the list of recommended CIPs.

The remaining collection system CIPs from the 2019 WWSMP have been reviewed and have been retained to address the potential deficiencies identified in the hydraulic assessment. However, the findings in the WWSMP Amendment recommend additional analysis be conducted to confirm the required project extents and sizing.

RECYCLED WATER SYSTEM MASTER PLAN AMENDMENT
The RWSMP amendment includes a comprehensive update to the recycled water system hydraulic model network to incorporate system improvements completed since the 2019 RWSMP. The amendment takes into consideration the backbone infrastructure in the future recycled water system hydraulic model network based on utility plans completed by City or individual land developers as development projects were approved. Existing recycled water landscape irrigation areas were identified, and the future uses of recycled water evaluated and used to create demand projections. Based on the existing usage of recycled water and the demand for recycled water in the future, the amendment reevaluated the City' s conclusions regarding recycled water planning including design criteria, balance analyses, and pump station operations. Based on future demands for recycled water and steady- state model simulations, the RWSMP amendment provides an operation strategy resulting in river discharge. Specific capital improvements to the recycled water system are identified to optimize the City' s distribution system at buildout with implementation of river discharge. Finally, the findings and updates were compiled into an amended RWSMP document for review and future planning purposes.

Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 19 EIR Addendum

CITY' SEXISTING RECYCLED WATER INFRASTRUCTURE
The City' srecycled water system was originally built to support the disposal of the effluent produced by the City -owned Lathrop Consolidated Treatment Facility ( CTF) via agricultural land application areas ( LAAs) and use of recycled water for urban landscape irrigation ( LI). The land use required for LAAs and the necessary seasonal storage ponds limited the potential development areas within the City. Thus, the City obtained a National Pollutant Discharge Elimination System ( NPDES) permit 2021 to discharge effluent to the San Joaquin River to eliminate the need for LAAs and large storage ponds. The City has been discharging CTF effluent to the San Joaquin River since February 2024 and plans to remove the land application areas, storage ponds, and selected pump stations to optimize the system for a smaller amount of recycled water demands associated with urban landscape irrigation.

The City is currently providing recycled water to 54. 7 acres of landscape irrigation ( LI) areas located primarily in the Central Lathrop and Mossdale development areas. Projected future uses of recycled water will continue to consist of landscape irrigation to a total of 174. 9acres by buildout ( 2045).

River Islands is supplementing its non -potable demand with its own non -potable sources.

RECYCLED WATER SUPPLY AND DEMAND EVALUATION
The City provided a total of 194 acre- feet of recycled water to LI areas in 2022. By its buildout in 2045, the City anticipates a total annual recycled water demand of 2. 4 MGD or 2, 688 acre- feet per year (AFY), which is a significant reduction from demands estimated in prior planning documents due to river discharge of effluent.

The City provided a total of 194 acre- feet of recycled water to LI areas in 2022. Projected recycled water demand is estimated assuming average precipitation and evaporation. The City' s projected annual and maximum month recycled water demand in 5 -year increments through buildout ( 2045) is summarized in Table 13. The City anticipates a total recycled water demand of 2. 38 MGD or 2, 669 acre- feet per year ( AFY) by 2045.

As shown in the water balance evaluations in the RWSMP Amendment, monthly landscape irrigation demands were estimated based on average annual precipitation and evaporation within the City.

The resulting total annual recycled water demand per unit area is equivalent to 48. 7 ac- inch/ ac.

Using the unit area recycled water demand factor, the City anticipates a total recycled water demand of 2. 38 MGD or 2, 669 acre- feet per year ( AFY) by 2045 ( Table 14). The projected demand is well below the projected recycled water supply at 4. 31 by 2045. 20 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
Table 13. Projected Average Annual and Maximum Month Recycled Water Demand Units 2025 2030 2035 2040 2045
Total Annual Demand
ac - inch 11, 592 19, 227 25, 323 32, 032 32, 032
acre- feet 966 1, 602 2, 110 2, 669 2, 669
MGD 0. 86 1. 43 1. 88 2. 38 2. 38
Maximum Month Demand
ac - inch 1, 994 3,07 4, 356 5,10 5,10
MGD 1. 75 2. 90 3. 82 4. 83 4. 83
Source: EKI, 2025. 2025 Recycled Water System Master Plan Amendment, May. Table 4-3.

Table 14. Projected Average Annual Recycled Water Demand by Development Area Development Area
Projected Recycled Water Demand ( acre- feet)
2025 2030 2035 2040 2045
Central Lathrop 146 305 325 445 445
Mossdale 182 217 262 262 262
River Islands 635 1, 078 1, 521 1, 960 1, 960
Lathrop Gateway 0. 81 0. 81 0. 81 0. 81 0. 81
Crossroads 1. 6 1. 6 1. 6 1. 6 1. 6
TOTAL 966 1, 602 2, 110 2, 669 2, 669
Source: EKI, 2025. 2025 Recycled Water System Master Plan Amendment, May. Table 4-.

RECYCLED WATER SYSTEM OPERATION STRATEGY
The City anticipates a smaller amount of recycled water demands associated with urban landscape irrigation and implementation of river discharge. Only 61. 4to 71. 5 MG of seasonal storage is needed to meet the City' sseasonal recycled water demands under 2030 and 2045 conditions, respectively.

This can be met by retaining existing ponds S5 and S16 with a total storage capacity of 129. 5 MG, as summarized in Table 15, and their respective booster pump stations PMP- 1 and PMP- 10 with upgrades.

Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 21 EIR Addendum
Table 15. Existing Storage Pond Characteristics
Pond ID
Assessor' sParcel
Number
Storage Capacity
million gallons) a
Storage Capacity
acre -inches)
S5
198-30- 47
198-30- 48 28 1, 048
S16 213-90- 02 101 3, 719
Note: (a) Storage capacities are rounded to the nearest million gallons.

Source: EKI, 2025. 2025 Recycled Water System Master Plan Amendment, May. Table 5-1.

Pump stations PMP- 1and PMP- 10 will need to be upgraded to expand their capacities to supply peak recycled water demands and continually pressurize the recycled water system. To optimize its recycled water system, it is recommended that the City install pressure reducing valve stations to create two pressure zones, one for River Islands and one for the rest of the City. In addition, new transmission mains are recommended to improve distribution system capacity and support new development.

Pump stations PMP- 10and PMP- 1 will need to be upgraded to supply peak demands and pressurize the recycled water system at the necessary pressures. A significant portion of the City' s buildout recycled water demand will be driven by the River Islands non -potable water system. The City' s recycled water system is planned to connect to River Islands through the existing RI - PS and the future RI Phase 2 PS. Recycled water will be discharged to the wet wells of these pump stations, which will then pump water into River Islands' distribution system. As such, PMP- 10 should be upgraded to meet peak demands at RIPS and RI Phase 2 PS and maintain positive pressures within the City' srecycled water transmission system in River Islands. In addition, PMP- 1 will be upgraded to meet demands and maintain required pressures in areas east of the San Joaquin River.

Due to the high cost of operating and maintaining pump stations and storage ponds, as well as the phased nature of future developments, the RWSMP recommends that the City phase the expansion of the BPSs. This should begin with upgrading and operating the existing PMP- 1, followed by upgrading PMP- 10 when system - wide projected peak demands approach the firm capacity of PMP1.

The recommended buildout recycled system also includes new transmission mains to improve the system' s hydraulic capacity. These new mains are facilities conceptualized previously in backbone infrastructure plans or through discussion with City staff, which are listed below:

Mossdale Landing West development area backbone infrastructure; A New 16 -inch transmission main along River Islands Parkway, Cambay Parkway, and Golden Valley Parkway, connecting the RI Phase 2 PS with the City' s existing 16 -inch main on Golden Valley Parkway near Cirrus Court; and
22 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
A 24 -inch transmission main and railroad crossing that connects PMP- 10 to the new 16 - inch main at the intersection of Cambay Parkway and Golden Valley Parkway.

To optimize the efficiency of PMP- 1 and PMP- 10 when both pump stations are in operation simultaneously, the RWSMP recommends installing pressure reducing valve ( PRV) stations between portions of the River Islands system and the remaining areas of the City' s recycled water system.

This will create two separate pressure zones to improve system performance and reliability. The new PRV stations are intended to maintain appropriate pressure within each zone to meet the City' s design criteria.

The PRVs will be set to remain closed when both PMP- 1and PMP- 10 are operating concurrently, and to open when S16 is being filled or when only one pump station is in operation. Each station will be equipped with two sets of low -flow and high -flow PRVs to allow bidirectional water transfer, along with flow meters to monitor volume flowing in both directions between the City and River Islands.

The RWSMP recommends the following PRV locations and pressure settings to ensure the valves remain closed during peak demand conditions.

PRV- 1: On the existing 16 - inch main along River Islands Parkway between Somerston Parkway and Cohen Road
o From the City to River Islands: 12 psi
o From River Islands to the City: 50 psi
PRV- 2: On the existing 16 -inch main along Manthey Road near the intersection of Manthey Road and Steward Road
o From the City to River Islands: 30 psi
o From River Islands to the City: 45 psi
Additionally, at each connection point between the River Islands' non -potable water system and the City' s recycled water system, pressure sustaining valve ( PSV) stations are recommended to be installed to maintain positive pressure in the City' s system during periods of low demand. A PSV station will also be required at S16' sinflow pipe to sustain the pressure during pond filling periods.

This configuration allows the City to manage flows during peak and non -peak seasons and keep the recycled water system pressurized.

Algae growth within the City' s storage ponds has been impacting distribution and irrigation system equipment. To address this, the City is exploring options to add filtration or other treatment to the recycled water pumped from the ponds. Additionally, with the reduced recycled water demand projections, only a portion of the existing capacity of ponds S5 and S16 is required to meet peak seasonal demands. As a result, the City could consider reducing the capacity of these ponds or partitioning them into smaller cells, provided that the remaining storage is sufficient to meet the estimated required seasonal storage during average rainfall years of 6L4 MG by 2030 and 71. 5 MG Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 23 EIR Addendum
by 2045. Reducing storage capacity could also help improve water quality and repurpose a portion of the parcel for other beneficial uses. Hydraulic Assessment The RWSMP includes an updated recycled water system hydraulic model to assess the recommended optimizations in the near -term and at buildout. Modeling results verify that design criteria are met throughout the system under peak hour demand conditions with the recommended optimizations.

RECOMMENDED CAPITAL IMPROVEMENT PROGRAM
Recommended CIPs were developed to optimize the design of the City' s distribution system at buildout with implementation of river discharge. Planning level opinions of probable costs ( OPCs) are developed based on bid information from recent similar projects in California.

The OPC for construction is presented in December 2024 dollars based on Engineering News Record ENR) Construction Cost Index ( CCI) of 13, 632. 41 (20 -city average). The total CIP OPC also includes allowances equal to 60% for construction contingency ( 30%), design ( 15%), construction management ( 5%), permitting (5%), and project implementation (5%).

Table 16 summarizes the RWSMP- recommended CIPs and the City' s existing CIPs with their estimated planning level OPCs. The estimated OPC totals $ 17. 8 million for City CIP projects.

Table 16. Summary of Recommended Recycled Water System Capital Improvement Projects Project # Improvement Description OPC ( a)
City Projects
RW- 1 Pump Station PMP- 1Upgrade 6, 060,00
RW- 2 Pump Station PMP- 10 Upgrade 10,20, 000
RW- 3 Treatment at Storage Ponds S5 and S16 1, 547, 000 (b) RW- 6 Conversion of Potable Irrigation Areas to Recycled Water TBD ( c) RW- 7 Recycled Water Metering and Billing Improvements TBD ( c) RW- 8 Recycled Water Operations and Permitting ( City RW 23- 02) 69, 915 (d) Total City CIP OPC 17, 797, 000
Developer Funded Projects
RW- 4 River Islands Phase 2 Backbone Main Improvement 17, 880, 000 RW- 5 Pressure Reducing Valve Station Improvement 860, 00 Abbreviations:

CIP = capital improvement projects
OPC = Opinion of Probable Construction Cost
Notes:
a) Detailed costs for RW- 1, RW- 2, RW- 4 and RW- 5 are estimated in following sections and are presented in December 2024 dollars.
b) Costs for RW- 3are based on estimates provided by City staff on 7 February 2025. Projects RW- 6and RW- 7 are recommended to be further refined in the near future.
24 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
C) Costs for RW- 8 was carried over from the City' s Capital Improvement Programs Fiscal Years d) 2023 - 2025 ( Lathrop, 2023).
e) Total may not sum due to rounding.

Source: EKI, 2025. 2025 Recycled Water System Master Plan Amendment, May. Table 8-1

4. ENVIRONMENTAL ANALYSIS

ANALYSIS OF IMPACTS FOUND TO BE LESS THAN SIGNIFICANT
Specific impacts within the following categories of environmental effects were found to be less than significant as set forth in more detail in the certified EIR. Following each bullet is a conclusion on whether the proposed revisions change the impact conclusion found in the original EIR.

Biological Resources: The following specific impacts were found to be less than significant: 3.1- 2, 3. 1-, and 3. 1-4.
o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.

Geology and Soils: The following specific impact was found to be less than significant: 3.-1 o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.

Hazards and Hazardous Materials: The following specific impacts were found to be less than significant: 3. 4-2, 3. 4-, 3. 4-, 3.-5, and 3.-6.
o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.

Hydrology and Water Quality: The following specific impacts were found to be less than significant: 3. 5-2, 3.5-, 3. 5-4, 3. 5-, and 3. 5-6.
o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.

Utilities: The following specific impacts were found to be less than significant: 3. 6-1, 3. 6-2, 3. 6- 3, 3.6-4, 3. 6-5, 3.6-, 3.6-7, and 3.6-8.

Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 25 EIR Addendum
o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.

Analysis of Impacts Found to be Less Than Cumulatively Considerable Specific impacts within the following categories of environmental effects were found to be less than cumulatively considerable contribution as set forth in more detail in the certified EIR. Following each bullet is a conclusion on whether the proposed revision change the impact conclusion found in the original EIR.

Biological Resources: The following specific impact was found to be less than cumulatively considerable: 4. 1.
o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.

Cultural and Tribal Resources: The following specific impact was found to be less than cumulatively considerable: 4. 2.
o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.

Geology and Soils: The following specific impact was found to be less than cumulatively considerable: 4.3.
o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.

Hazards and Hazardous Materials: The following specific impact was found to be less than cumulatively considerable: 4.
o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.

Hydrology and Water Quality: The following specific impacts were found to be less than cumulatively considerable: 4.5, 4.6, 4.7, and 4.8.
o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.
26 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
Utilities: The following specific impacts were found to be less than cumulatively considerable:

4.9, 4. 10, 4. 11, 4. 12, and 4. 13.
o The revisions do not increase the severity of any impact. However, the revisions do not change the environmental conclusion of less than significant that was provided in the certified EIR.

ANALYSIS OF IMPACTS FOUND TO BE LESS THAN SIGNIFICANT WITH

MITIGATION
Specific impacts within the following categories of environmental effects were found to be less than significant with mitigation as set forth in more detail in the certified EIR. Following each bullet is a conclusion on whether the proposed revisions change the impact conclusion found in the original EIR.

Biological Resources
Impact 3. 1-: The proposed Project has the potential to have direct or indirect effects on special - status species. The potential for the Project to have direct or indirect effects on special - status species is discussed on pages 3.1- 23 through 3.1- 28 of the Draft EIR. The following mitigation measure was adopted and will be implemented as provided by the Mitigation Monitoring Program: Mitigation Measure 3.1-. The revisions do not have a net change in impact as it relates to this environmental topic. The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

Impact 3.1-5: The proposed Project has the potential to conflict with an adopted Habitat Conservation Plan. The potential for the Project to conflict with an adopted Habitat Conservation Plan is discussed on pages 3. 1-1 through 3.1-2 of the Draft EIR. The following mitigation measure was adopted and will be implemented as provided by the Mitigation Monitoring Program: Mitigation Measure 3. 1-. The revisions do not have a net change in impact as it relates to this environmental topic. The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

Cultural and Tribal Resources
Impact 3. 2-1: The proposed Project has the potential to cause a substantial adverse change to a significant historical resource, as defined in CEQA Guidelines § 15064. 5, or a significant tribal cultural resource, as defined in Public Resources Code § 21074. The potential for the Project to cause a substantial adverse change to a significant historical resource is discussed on pages 3. 2- 11 through 3.2- 12 of the Draft EIR. The following mitigation measure was adopted and will be implemented as provided by the Mitigation Monitoring Program: Mitigation Measure 3. 2-1. The revisions do not have a net change in impact as it relates to this Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 27 EIR Addendum
environmental topic. The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

Impact 3.2-: The proposed Project has the potential to cause a substantial adverse change to a significant archaeological resource, as defined in CEQA Guidelines § 15064. 5. The potential for the Project to cause a substantial adverse change to a significant archaeological resource is discussed on page 3. 2- 13 of the Draft EIR. The following mitigation measure was adopted and will be implemented as provided by the Mitigation Monitoring Program: Mitigation Measure 3.2-1. The revisions do not have a net change in impact as it relates to this environmental topic. The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

Impact 3. 2-: The proposed Project has the potential to directly or indirectly destroy a unique paleontological resource or site or unique geologic feature. The potential for the Project to cause a substantial adverse change to a significant paleontological resource or site or unique geologic feature is discussed on page 3. 2- 13 of the Draft EIR. The following mitigation measure was adopted and will be implemented as provided by the Mitigation Monitoring Program: Mitigation Measure 3. 2-1. The revisions do not have a net change in impact as it relates to this environmental topic. The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

Impact 3. 2-4: The proposed Project has the potential to disturb human remains, including those interred outside of formal cemeteries. The potential for the Project to disturb human remains is discussed on page 3.2- 14 of the Draft EIR. The following mitigation measure was adopted and will be implemented as provided by the Mitigation Monitoring Program:

Mitigation Measure 3. 2-. The revisions do not have a net change in impact as it relates to this environmental topic. The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

Geology and Soils
Impact 3.-2: The proposed Project may result in substantial soil erosion or the loss of topsoil.

The potential for the Project to result in soil erosion is discussed on pages 3.- 14 through

3.- 17 of the Draft EIR. The following mitigation measure was adopted and will be implemented as provided by the Mitigation Monitoring Program: Mitigation Measure 3.-

1. The revisions do not have a net change in impact as it relates to this environmental topic.

The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

Impact 3.-: The proposed Project has the potential to be located on a geologic unit or soil that is unstable, or that would become unstable as a result of project implementation, and potentially result in landslide, lateral spreading, subsidence, liquefaction or collapse. The potential for the Project to be located on an unstable geologic unit such that landslide, lateral spreading, subsidence, liquefaction, or collapse could occur is discussed on pages 3.- 28 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR EIR Addendum
17 through 3.- 18 of the Draft EIR. The following mitigation measure was adopted and will be implemented as provided by the Mitigation Monitoring Program: Mitigation Measure

3.-2. The revisions do not have a net change in impact as it relates to this environmental topic. The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

Impact 3.-4: The proposed Project has the potential to be located on expansive soils which may create substantial risks to life or property. The potential for the Project to be located on expansive soils such that risks to life or property could occur is discussed on page 3.- 19 of the Draft EIR. The following mitigation measure was adopted and will be implemented as provided by the Mitigation Monitoring Program: Mitigation Measure 3.-2. The revisions do not have a net change in impact as it relates to this environmental topic. The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

Hazards and Hazardous Materials
Impact 3. 4-1: The proposed Project has the potential to create a significant hazard through the routine transport, use, or disposal of hazardous materials or through the reasonably foreseeable upset and accident conditions involving the release of hazardous materials into the environment. The potential for the Project to create a significant hazard through the release of hazardous materials into the environment is discussed on pages 3.4- 15 through

3.4- 16 of the Draft EIR. The following mitigation measures were adopted and will be implemented as provided by the Mitigation Monitoring Program: Mitigation Measures 3.4- 1 and 3.4-2. The revisions do not have a net change in impact as it relates to this environmental topic. The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

Hydrology and Water Quality
Impact 3.5-1: The proposed Project has the potential to violate water quality standards or waste discharge requirements or otherwise substantially degrade surface or ground water quality during construction. The potential for the Project to degrade surface or ground water quality during construction is discussed on pages 3.5- 17 through 3.5- 18 of the Draft EIR. The following mitigation measures were adopted and will be implemented as provided by the Mitigation Monitoring Program: Mitigation Measures 3.-1. The revisions do not have a net change in impact as it relates to this environmental topic. The revisions do not change the environmental conclusion of less than significant with mitigation that was provided in the certified EIR.

IMPACTS FOUND TO BE SIGNIFICANT AND UNAVOIDABLE
There were no impacts in the certified EIR that were found to be significant and unavoidable.

Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR 29 EIR Addendum
30 Addendum to the City of Lathrop Integrated Water Resources Master Plan EIR

ATTACHMENT C
eki
2024 WATER SYSTEM MASTER PLAN

AMENDMENT
City of Lathrop
December 2024
EKI C20049. 01
environment
water
EKI ENVIRONMENT & WATER, INC. 2001
www. ekiconsult. com
Junipero Serra Blvd, Suite 300 • Daly City, CA 94014
ek, environment
water
2024 Water System Master Plan Amendment
City of Lathrop
December 2024
Prepared for:

City of Lathrop
390 Towne Centre Drive
Lathrop, CA 95330
Prepared by:

EKI Environment & Water, Inc.
2001 Junipero Serra Blvd., Suite 300
Daly City, California 94014
650) 292- 9100
www. ekiconsult. com
EKI C20049. 01
Jonathan Sutter, P. E.

Project Manager/ Supervising Engineer
k 0
con
Tina Wang, P. E.

Assistant Project Manager/ Associate Engineer
L4,,-, Acr, 1
Gi- e,...

Yuqing Gao, EIT
Project Engineer
2024 Water System Master Plan Amendment
City of Lathrop

TABLE OF CONTENTS
EXECUTIVE SUMMARY ES -1
1 INTRODUCTION 1-

1. Project Background 1-

1. 2 Scope of Work 1-2

1. 3 Report Organization 1- 2
2 STUDY AND WATER SERVICE AREAS 2-1

2. 1 City Limits, Sphere of Influence, and Service Boundaries 2-1

2. Specific Plans and Large Planned Unit Development 2-1

2. 3 Current and Projected Population 2-7
3 EXISTING WATER SYSTEM 3-1

3. 1 Water Supply and Treatment Facilities 3- 1

3. 1. Groundwater Wells, Raw Water Pipelines, and Treatment Facilities 3- 1

3. 1. 2 Surface Water Turnouts 3-1

3. 1. Emergency Interties 3-2

3. 2 Water Distribution System Facilities 3- 5

3. 2. 1 Treated Water Storage Facilities and Booster Pump Stations 3-5

3. 2. Water Distribution Pipelines 3-5

3. 2. SCADA System 3- 5

3. Summary of Major Water System Improvements Since 2019 3- 5 4 EXISTING AND FUTURE WATER DEMANDS 4-1

4. 1 Current and Historical Water Demand 4-1

4. 2 Water Demand Projections 4-8

4. 2. 1 Baseline Potable Water Demand 4-8

4. 2. Demand Associated with Planned Development 4-8

4. 2.3 Total Projected Potable Water Demand 4-8

4. 3 Peak Demands 4- 12
5 WATER SYSTEM SUPPLIES 5-1

5. 1 Imported Surface Water 5- 2

5. 2 Groundwater 5-

5. 3 Total Water Supplies 5-6

5. 4 Water Supply Reliability 5-8

5. 4. 1 Projected Supply Reliability by Source 5-8

5. 4. 2 Projected Supply Reliability by Year Type 5- 13

5. Supply and Demand Assessment 5- 18

5.1 City -Wide Supply and Demand by Year Type 5- 18

5. 6 Recommended Water Supply Strategy 5- 23

5. 6. 1 SSJID SCWSP Phase II 5- 23
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5. 6.2 Treatment for PFAS 5- 23

5. 6. 3 Aquifer Storage and Recovery 5- 24
6 WATER SYSTEM PERFORMANCE AND OPERATIONS CRITERIA 6- 1

6. 1 Distribution System Performance Criteria 6- 1

6. 1. Peaking Factors 6-1

6. 1. 2 Fire Flows 6-1

6. 1. 3 Water Supply Capacity 6-1

6. 1. 4 Distribution System Pressures 6-2

6. 2 Water Facilities Criteria 6- 7

6. 2. 1 Water Transmission and Distribution Pipeline Sizing Criteria 6-7

6. 2. Booster Pump Stations 6-7

6. 2. 3 Water Storage Capacity 6-8
7 DISTRIBUTION SYSTEM HYDRAULIC CAPACITY EVALUATION 7-1

7. 1 Hydraulic Modeling Approach 7-1

7. 2 Hydraulic Model Update 7-1

7. 2. 1 Model Platform 7-1

7. 2. Model Update 7-1

7. 2.3 Model Validation and Calibration 7-2

7. 3 Modeling Scenarios 7- 2

7. 4 Water Distribution System Performance Evaluation 7-

7. 4.1 Existing System Evaluation 7-

7. 4. 2 Future System Evaluation 7- 12
8 WATER SUPPLY, STORAGE, AND PUMPING CAPACITY EVALUATION 8-1

8. 1 Existing Water System Evaluation 8-1

8. 1. Water Supply Capacity 8- 1

8. 1.2 Water Storage Capacity 8-1

8. 1. 3 Peak Pumping Capacity 8-1

8. 2 Future Water System Evaluation 8-3

8. 2.1 Water Supply Capacity 8-3

8. 2. Water Storage Capacity 8-4

8. 2. 3 Peak Pumping Capacity 8-6
9 RECOMMENDED CAPITAL IMPROVEMENT PROGRAM CHANGES 9-1

9. 1 Modifications to Water Supply CIPs 9-1

9. 1. Groundwater Treatment Improvements 9-1

9. 1. 2 Aquifer Storage and Recovery 9- 1

9. 2 Modification to Water Distribution System CIPs 9- 2

9. 2. 1 Harlan Road and South Harlan Road Fire Flow Improvement Project 9- 2

9. 2. Murphy Parkway Fire Flow Loop to Harlan Road 9- 3

9. 2. 3 East J Street Alley Residential Fire Flow Improvement Project 9- 3

9. 2. 4 Lathrop Transmission Main Improvement Project 9- 3 eki environment
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10 REFERENCES 10-
TABLES
Table ES - 1. Water Demand Factors ES -2
Table ES -2. Summary of Recommended Water System Capital Improvement Projects ES -7 Table 2-1. City of Lathrop Development Projections by Development Area 2-5 Table 2-. Historical Service Area Population 2- 8
Table 2-3. Current and Projected Service Area Population 2-9 Table 3-1. Active Groundwater Well Information 3-4
Table 3-2. Existing Treated Water Storage Facilities 3-7 Table 3-. Treated Water Storage Facility Booster Pump Station Characteristics 3-8 Table 3-4. Pipeline Lengths by Diameter 3-9
Table 4-1. Current and Historical Potable Water Use and Population 4-3 Table 4-2. Number of Current ( 2022) Potable Water Services by Sector 4-5 Table 4-3. Current and Historical Potable Water Use by Sector 4-6 Table 4-. Updated Water Demand Factors 4-8
Table 4-5. Projected Water Demand by Development Area 4- 10 Table 4-6. Historical Potable Water Peak Demands and Peaking Factors 4- 14 Table 5-1. Current and Historical Potable Water Supply 5-1 Table 5- 2 Lathrop SSJID Turnouts — Basis of Design 5-3 Table 5-3. Groundwater Production Well Capacities and Annual Yields 5-6 Table 5-4. Current and Projected Potable Water Supply Entitlements 5-7 Table 5-. Projected SCWSP Supply Availability 5-9
Table 5-6. Projected SCWSP Supply Available to City of Lathrop 5-9 Table 5-7. Projected Potable Water Supply in Normal Years 5- 14 Table 5-8. Projected Potable Water Supply in Single Dry Years 5- 15 Table 5-9. Projected Potable Water Supply in Multiple Dry Years 5- 16 Table 5- 10. Projected Potable Supply vs. Demand for Normal Year Scenario 5- 19 Table 5- 11. Projected Potable Supply vs. Demand for Single Dry Year Scenario 5- 20 Table 5- 12. Projected Supply vs. Demand for Multiple Dry Years Scenario 5- 21 Table 6-1. Summary of Recommended Potable Water System Performance and Operational Criteria... 6-3 Table 6-2. Required Fire Flow and Storage Requirements 6- 5 Table 7-1. Summary of Water Demands by Scenario 7-5
Table 8-1. Existing Water Supply Capacity 8- 2
Table 8-2. Existing Water Storage Capacity and Requirements 8-2 Table 8-3. Evaluation of Existing Firm Pumping Capacity 8- 3 Table 8-4. Projected Water Supply Capacity 8-4
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Table 8-5. Projected Storage Requirements by Development Area 8- 5 Table 8-6. Projected Citywide Storage Requirements 8- 5 Table 8-7. Projected Citywide Pumping Requirements 8-6
Table 9-1. Summary of Recommended Water System Capital Improvement Projects 9-4

FIGURES
Figure ES -1. Existing Potable Water System Infrastructure ES -4 Figure ES -2. Modeled Future Water Infrastructure ES -5 Figure ES -3. Recommended Water System Capital Improvement Projects ES - 6 Figure 2-1. City of Lathrop Boundaries and Development Areas 2-4 Figure 2-. Historical and Projected Service Area Population 2-9 Figure 3-1. Existing Water System Infrastructure 3-
Figure 4-1. Current and Historical Potable Water Use and Population 4- Figure 4-2. Current and Historical Per Capita Potable Water Use 4- Figure 4-3. Number of Current Potable Water Services by Sector 4-5 Figure 4-. Annual Water Use by Sector: 2017-022 4-7
Figure 4-5. Percentage of Total Water Use by Sector: 2017-022 4-7 Figure 4-6. City of Lathrop Monthly Water Production 4- 13 Figure 5-1. Current and Historical Potable Water Supply 5-2 Figure 5-2. Water Supply Infrastructure 5-4
Figure 5-3. Current and Projected Potable Water Supply Entitlements 5-7 Figure 5-4. Projected Normal Year Potable Water Supply 5- 14 Figure 5-. Projected Single Dry Year Potable Water Supply 5- 15 Figure 5-6. Projected Multiple Dry Year Potable Water Supply 5- 17 Figure 5-7. Normal Year Potable Supply vs. Demand 5- 19 Figure 5-8. Single Dry Year Potable Supply vs. Demand 5- 20 Figure 5-9. Multiple Dry Year Supply vs. Demand 5- 22
Figure 6-1. Fire Flow Requirement 6-
Figure 7-1. Modeling Scenarios 7-4
Figure 7-2. Modeled Existing and Future Infrastructure 7-6 Figure 7-3. Existing Water System Hydraulic Evaluation — Peak Hour Demand — Pressure 7- 8 Figure 7-4. Existing Water System Hydraulic Evaluation — Peak Hour Demand — Pipe Velocity 7-9 Figure 7-5. Existing Water System Hydraulic Evaluation — Peak Hour Demand — Pipe Head Loss 7- 10 Figure 7-6. Existing Water System Hydraulic Evaluation — Maximum Day Demand — Available Fire Flow . 7- 11 Figure 7-. Buildout Water System Hydraulic Evaluation — Peak Hour Demand — Pressure 7- 13 Figure 7-8. Buildout Water System Hydraulic Evaluation — Peak Hour Demand — Pipe Velocity 7- 14 Figure 7-9. Buildout Water System Hydraulic Evaluation — Peak Hour Demand — Pipe Head Loss 7- 15 eki environment
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Figure 7- 10. Buildout Water System Hydraulic Evaluation — Maximum Day Demand — Available Fire Flow 7- 16

APPENDICES
Appendix A Water Demand Factor Evaluations
Appendix B Recommended CIP Details

ABBREVIATIONS AND ACRONYMS
AAFES Army & Air Force Exchange Services
ac acres
AC asbestos cement
ACE Altamont Commuter Express
ADD average day demands
AF acre feet
AFY acre feet per year
AOI Area of Interest
ASR Aquifer Storage and Recovery
BBID Byron -Bethany Irrigation District
BCID Banta- Carbona Irrigation District
BPS booster pump station
CCI Construction Cost Index
CEQA California Environmental Quality Act
CII commercial, industrial and institutional
CIP Capital Improvement Program or Capital Improvement Project City City of Lathrop
CLSP Central Lathrop Specific Plan
CTF Consolidated Treatment Facility
DBCP 1, 2- dibromo- 3- chloropropane
Depot Sharp Army Depot
DDW Department of Drinking Water
DGWTP Nick C. DeGroot Water Treatment Plant
DIP ductile iron pipe
DOF California Department of Finance
du dwelling unit
DWR Department of Water Resources
EDB ethylene dibromide
EKI EKI Environment & Water
ENR Engineering News Record
EPA Environmental Protection Agency
FF Fire Flow
fps feet per second
ft feet
ft bgs feet below ground surface
ft/ k-t feet per thousand feet
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FY Fiscal Year
GAC granulated activated carbon
GIS geographic information system
GPCD gallons per capita per day
gpd gallons per day
gpm gallons per minute
GSA Groundwater Sustainability Agency
GSP Groundwater Sustainability Plan
HFPO- DA hexafluoropropylene oxide dimer acid
HI Hazard Index
hp horsepower
I-5 Interstate 5
IWRMP Integrated Water Resources Master Plan
LAWTF Louise Avenue Water Treatment Facility
LF linear feet
LMFD Lathrop Manteca Fire District
MCL Maximum Contaminant Levels
MDD max day demands
MFR multi -family residential
MG Million Gallons
mg/ L milligrams per liter
MGD million gallons per day
MMD maximum month demand
MOU Memorandum of Understanding
MSL mean sea level
NL Notification Level
OCC Occidental Chemical Corporation
OID Oakdale Irrigation District
OPC Opinion of Probable Cost
PFAS per- and polyfluoroalkyl substances
PFBS perfluorobutane sulfonic acid
PFHxS perfluorohexane sulfonic acid
PFNA perfluorononanoic acid
PFOA perfluorooctanoic acid
PFOS perfluorooctanesulfonic acid
PHD peak hour demand
psi Pounds per square inch
PVC polyvinyl chloride
RL Response Level
SB Senate Bill
SCADA Supervisory Control and Data Acquisition
SCWSP South County Water Supply Program
SFR single family residential
SGMA Sustainable Groundwater Management Act
Sharpe Sharpe Army Depot
SOI sphere of influence
SSJID South San Joaquin Irrigation District
SWRCB State Water Resources Control Board
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EKI C20049. 01
2024 WSMP Amendment
City of Lathrop
TDS Total Dissolved Solids
Title 22 California Code of Regulations, Title 22
UCMR Unregulated Contaminant Monitoring Rule
USBR United States Bureau of Reclamation
UWMP Urban Water Management Plan
VFD Variable Frequency Drive
WSMP Water System Master Plan
WTF Water Treatment Facility
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EKI C20049. 01
2024 WSMP Amendment
EXECUTIVE SUMMARY City of Lathrop

EXECUTIVE SUMMARY
EKI Environment & Water, Inc. (EKI) has prepared this Water System Master Plan Amendment ( WSMP Amendment) for the City of Lathrop, California ( City). This WSMP Amendment was developed as part of the 2024 amendment to the City' s Integrated Water Resources Master Plan ( IWRMP Amendment), a comprehensive planning process involving the City' s
Potable Water, Wastewater and Recycled Water
Master Plans. This WSMP Amendment incorporates new information that has become available and changed planning assumptions since the completion of the 2019 IWRMP.

STUDY AND SERVICE AREAS
The City completed a General Plan Update in September 2022 ( Lathrop, 2022a) which included updated growth projections for the City. In addition, development projections have changed significantly in the River Islands area with approval of the modified River Islands Phase 2 project in June 2021 and in the Central Lathrop area.

The current population within the City is approximately 35, 080 as of January 2023 ( California DOF, 2023).

The City has experienced significant growth and anticipates growth to continue in the future given the existing entitlements for several large residential developments.

CITY' SEXISTING WATER INFRASTRUCTURE
As of December 2023, the City' s existing water supply facilities consists of five groundwater wells ( Wells 6, 7, 8, 9, 10), the Louise Avenue Water Treatment Facility ( LAWTF) for treatment of groundwater from Wells 6 through 10, two surface water turnouts for delivery of South County Water Supply Program SCWSP) from the South San Joaquin Irrigation District ( SSJID), and 2. 5 miles of raw water pipelines to deliver untreated well water to the LAWTF. The City' s water distribution system consists of a single pressure zone with seven storage tanks and booster pump stations, and approximately 156 miles of distribution pipelines. Figure ES - 1 shows the City' sservice area and locations of the City' s major water system facilities.

EXISTING AND FUTURE WATER DEMANDS
The City' stotal potable water use was 5, 277 acre- feet (AF) in 2022, with a per capita water use of 149 gallons per capita per day ( GPCD). Water demand rebounded from the recent 2014-017 as water use restrictions were lifted and new development projects were constructed. However, water use decreased again as a result of the 2021-022 drought and remains below 2020 levels.

The City' s water demand factors presented in the 2020 UWMP were verified and updated using 2017 through 2022 data. The water demand factors serve as the basis to estimate average annual water demands for future developments. The updated water demand factors in gallons per day per dwelling unit (gpd/ du) or gallons per day per acre (gpd/ ac) are presented in Table ES -1 below. eki environment
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EKI C20049. 01

EXECUTIVE SUMMARY
2024 WSMP Amendment
City of Lathrop
Table ES - 1. Water Demand Factors
Land Use Category
Low Density Residential
Updated Potable Water
City- wide
330 gpd/ du
Use Factors ( a)
River Islands
315 gpd/ du
Medium Density Residential 250 gpd/ du 235 gpd/ du
High Density Residential 170 gpd/ du
Commercial 1, 550 gpd/ ac
Industrial 1, 200 gpd/ ac
Parks / Public Landscaping 2, 450 gpd/ ac
Schools / Institutional 1, 250 gpd/ ac
Water demand projections were updated and calculated as the sum of (1) the City' s existing potable water demand in 2022, and ( 2) the anticipated potable water demands associated with the future development projects and planning areas post 2022. It is anticipated that the City' stotal demand in 2045 will be 12, 405 acre- feet per year (AFY), which is significantly lower than the demand projections included in the 2019 WSMP.

Due to the relatively high cost of SCWSP water, the City has historically relied upon its groundwater wells as the primary source of supply. However, the City reduced its groundwater production during recent years due to groundwater quality issues. The City is evaluating treatment options to meet upcoming regulations for per- and polyfluoroalkyl substances ( PFAS) and an Aquifer Storage and Recovery ( ASR) project to boost its water supply reliability. With future groundwater treatment and purchase of SCWSP Phase II, the City has adequate supplies through 2045 during normal and dry years.

HYDRAULIC ASSESSMENT
EKI updated the water system hydraulic model to represent the City' s utility infrastructure as of January 2023. The hydraulic model, along with the updated demand projections developed in Section 4, was used to evaluate capacity needs for current and future demand conditions and to complete the hydraulic assessment portion of the WSMP. EKI validated the updated model by comparing the model results to system operations data.

Existing infrastructure and key planned infrastructure were assessed under an Existing ( 2022) scenario and a Buildout ( 2045) scenario. Planned future infrastructure to support future development is shown in Figure ES -2.

The City' s water distribution system is primarily assessed against its ability to supply required pressures under peak demand and fire flow conditions. Pipe velocity and head loss criteria are secondary criteria that indicate which pipes could be upsized to increase downstream pressures and improve water movement within the system. Due to the updated water demand projections evaluated herein, no new hydraulic deficiencies are identified compared to the 2019 WSMP. eki environment
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December 2024
EKI C20049. 01
2024 WSMP Amendment
EXECUTIVE SUMMARY City of Lathrop

SUPPLY, STORAGE, AND PUMPING CAPACITY ASSESSMENT
The City currently has adequate supply, storage, and peaking pumping capacity to meet design criteria.

Additional supply, storage, and peak pumping capacity will be required to support future development.

RECOMMENDED CAPITAL IMPROVEMENT PROGRAM
EKI recommended modifications and additions to the list of recommended capital improvement projects CIPs) included in the 2019 WSMP. Two new water supply projects ( PFAS treatment at the LAWTF and ASR) are identified in Section 5.6. No new distribution system CIPs are required; several remaining CIPs identified in the 2019 IWRMP are no longer recommended or have been modified.

Figure ES -3 shows an overview of the collection system capacity project locations, and Table ES - 2 summarizes all the identified capacity improvement projects and their estimated planning level opinion of probable costs ( OPCs).
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EKI C20049. 01
1 Emergency Stockton Intertie

ATRROP RD
JI
1- TurnouSSDt l7
WeII 8• LOUISE AV
LAWTF Tank
a- d BPS
Well 10
TWell9 YOSEMITE AY
VVell 21
WeII21
l®
Imo
Sphere of Influence
Existing City Infrastructure
Treatment Plant
al Pump Station
Enclosed Storage Facility
Ej SSJID Turnout
Fb Production Well
Emergency Intertie
Raw Water Main
Existing Pipe Diameter, Inches
Less than and equal to4
8 10
16 20
24 30
Abbreviations
BPS = booster pump station
LAWTF = Louise Avenue Water Treatment Facility
SOI = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations locations are approximate.

2. Well9 is currentty offline due to water quality issues.

Well 21 and the Well 21 WTF are inactive.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 13 November 2024. o 3, 000 6, 000
soeie e, Feet)
Existing Water System Infrastructure
Water System Master Plan Amendment
CM or Lathrop
Lathrop, CA
ekienvironment Dec` m0049. 0ber
e
water Figure ES -
1 Legend
L1Sphere of Influence
Existing Infrastructure
Treatment Plant
W Pump Station
Enclosed Storage Facility
C SSJID Turnout
Pipe
Future Facilities
Pump Station
Enclosed Storage Facility
SSJID Turnout
Future Pipe Diameter, Inches
8 — 18
10 20
12 - 24
16 - 30
Abbreviations
BPS = booster pump station
LAWTF = Louise Avenue Water Treatment Facility
SOI = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS
Online, 13 November 2024.

N 0 3, 000 6, 000
15cek in Feet)
Modeled Existing and Future Infrastructure
Water System Mater Plan Amendment
CO of Lathrop
Lathrop, CA
December 2020 ek December
I & C20049.
water
01 Figure ES -2
i River Islands Phase 2 • „> j
e
I Tankgnd: BPS_ , < 4- ' rt.'
BPS - 3,
DOS REIs RD r
r
I
I
1 r
rr, rT.. f 10
i ,-; : Iirri1 i,l_q I
I._. '
r, Yi i
7 El i
I
r+iY'; WD -3: Northern ' McKinley
I S _ ri
Industrial Area Fire Flow

14.-=.: t Improvement Proect
9 --_ J
yv% \ KA' lif FF. BPsY• 1 WD4: Murphy Parkway Fire t.F t i-` , • `40 1•` i
Flow Improvement Project,] r, r` yCr e e
f1 t'
LArnRop RD
L_ SSJID
Turnout 1
1 t
i~
j ` a ! Ilii-:-_„?\ ;',. _ ,./> )
1 I w LAWiF
04 y t' :. vfu„' 7. i "1. 0 • • 1`y) 4.1 -_ J.
1 1;:-... 4:: 2‘;‘::;. ..(' d tr . a,• iM, T•_.__ c-.±= 4,7_,_..),.• ' 1_z^I *v..,„ '--" i ,/// rr I — f-... yvv` I-"`•-• ; t ;' < ` T'
I
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1-----...
i _`.\
S i-1:: tili hbet- i '---,- J
Tank `
t
i ,. r` Y` ; / I
1-• r; I L / •
WD - 2: Harlan Road and South Harlan Road
Fire Flow Improvement Project
WD - 5: Lathrop Transmission Main Improvement Project
WD -1: East J Street Alley Residential Fire Flow Improvement Project s i.

I '
a ` a __ di t -
I
i r BPS -5
y
k-• •-/'SSJID-- Ltv `
Tank
f
I____% Tumout2 0,
f
1 BPS -2
Tank
s
L"-

LOUISE AV
ank and BPS
WS - 3: I.AWTF Centralized
PFAS Treatment Project
1 Tank
an BPS
WS - 6: Tank and BPS
at Well 21 site

YOSEMITE AU
L+e. oend
Sphere of Influence
Existing Infrastructure
Treatment Plant
Pump Station
e Enclosed Storage Facility
SSJID Turnout
Existing Pipe
Future Infrastructure
Future Pump Station
Future Enclosed Storage Facility
Future SSJID Turnout
Future Pipe
Recommended CIPS
a Replace existing hydrant with 8 -inch hydrant & lateral Future Pump Station
Future Enclosed Storage Facility
Future SSJID Turnout
Replacement Pipe, inches
6 8
12 New Pipe, inches
6 8
Abbreviations
BPS = booster pump station
LAWfF = Louise Avenue Water Treatment Facility
SOI = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' sArcGIS
Online, 13 November 2024.

N 0 3, 000 6, 000
A ( Bub In Feet)
Recommended Water System Improvements
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Nieta, System Master Plan Amendment
City of Lathrop
Lathrop, CA
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water
C2o04a. 01
Figure ES - 3

EXECUTIVE SUMMARY
2024 WSMP Amendment
City of Lathrop
Table ES -2. Summary of Recommended Water System Capital Improvement Projects Project #
Water Supply
Time
Addresses Fire Total Project OPC
Project ( a) Frame
b)
Flow Deficiency ( c)( d)
Improvements
WS -1
Well 10 Testing, Analysis and
Modifications ( PW 22- 37) (e)
Existing 844, 527
WS -2
Booster Pump Stations Upgrade
Project ( PW 24- 10) (e)
Existing 800, 00
WS -3
Groundwater Treatment
Improvements ( PW 20- 16) (e)
Existing 25, 564, 010
WS 4
SSJID Turnout 1 Emergency Backup
Power ( f)
Buildout 930, 00
WS -5 Tank and BPS at the Well 21 Site ( g) Buildout 5, 640, 000 WS -6 SSJID SCWSP Phase 2 ( f) Buildout 28,80, 000
WS -7 SSJID Turnout 2 Expansion ( f) Buildout 4,90, 000 WS 8
Aquifer Storage and Recovery
PW 22- 36) (d) (e)
Buildout 9, 000,0
TOTAL WATER SUPPLY IMPROVEMENTS OPC $ 75, 550, 000
Water Distribution System Improvements
WD -1
East J Street Alley Residential Fire
Flow Improvement Project ( PW 25-
10)
Existing Yes 400, 00
WD 2
Harlan Road Fire Flow Improvement
Project ( PW 25- 10) (e) (h) (i)
Existing Yes 1,90, 000
WD 3
Northern McKinley Industrial Area
Fire Flow Improvement Project
Existing Yes h)
WD -4
Murphy Parkway Fire Flow
Improvement Project
PW 24- 11) (e) (j)
Existing Yes 180, 00
WD -5
Lathrop Transmission Main
Improvement Project ( PW 25- 10) Existing Yes 570, 00
WD -6
Lathrop Water Main and
Lateral Upgrade Project ( PW 24- 12)
e)
Existing Yes 120, 00
TOTAL WATER DISTRIBUTION SYSTEM IMPROVEMENTS OPC 2, 460, 000 Notes:
a) Project information is obtained from Table 9- 1 of the 2019 WSMP with their costs escalated to December 2024 dollars, and includes modifications recommended in Sections 9. 1 and 9. 2. b) Time frame refers to when projects are identified to be required. c) Costs shown are presented in December 2024 dollars based on an ENR CCI of 13, 632. 41 (20 -city average), with totals rounded to the nearest $10, 000, except for projects called out in footnote e).
d) Costs include mark- ups equal to 60% for construction contingency (25%), design ( 10%), construction management ( 10%), permitting ( 10%), and Project Implementation ( 5%). eki environment
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EXECUTIVE SUMMARY City of Lathrop
e) Improvements and associated costs have been carried over from the City of Lathrop Capital Improvement Programs Fiscal Years 2023 - 2025 ( City of Lathrop, 2023). f) Construction costs for improvements have been carried over from estimates in the 2013 Draft Water Master Plan, escalated to December 2024 dollars.

Construction costs for Tank and BPS at the former Well 21 site reflect the engineer' s estimate
prepared by H2O Urban Solutions in July 2017, escalated to December 2024 dollars. h) This project will be conditioned for private development to complete. i) For planning purpose, cost estimated shown in the table was based on 6 -inch for existing water mains along Old Harlan Road between Shilling Avenue and Lathrop Road, City to verify the actual size since inconsistent pipe diameters observed in available documentation. j) Costs were updated to reflect reduced project scale as recommended in Section 9. 1. g)
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Section 1

INTRODUCTION
2024 WSMP Amendment
City of Lathrop
1 INTRODUCTION
EKI Environment & Water, Inc. (EKI) has prepared this Water System Master Plan Amendment ( WSMP Amendment) for the City of Lathrop, California ( City). This WSMP Amendment was developed as part of the 2024 amendment to the City' s Integrated Water Resources Master Plan ( IWRMP Amendment), a comprehensive planning process involving the City' s
Potable Water, Wastewater and Recycled Water
Master Plans. This WSMP Amendment updates the City' s 2019 WSMP ( EKI, 2019a). The IWRMP Amendment was completed through a coordinated effort between multiple City departments and provides a unifying framework to support utility operations and capital improvement program ( CIP) development and implementation.

1. Project Background
The City' s 2019 IWRMP, which includes the City' s
Water System Master Plan, Wastewater System Master
Plan, and Recycled Water Master Plan, was finalized and approved by the City Council in December 2019 after a California Environmental Quality Act ( CEQA) process ( EKI, 2019a; 2019b; 2019c). Since the IWRMP was completed, new information has become available and certain planning assumptions have changed that require an amendment to the IWRMP, including the following:

Land Use Information: The City completed a General Plan Update in September 2022 which included updated growth projections for the City ( Lathrop, 2022a). In addition, development projections have changed significantly in the River Islands planning area with approval of the modified River Islands Phase 2 project in June 2021 and in the Central Lathrop Specific Plan area Lathrop, 2022b).

Water Demand Factors and Projections: The City' s unit water demand factors and water demand projections were updated in July 2020 to support the River Islands Phase 2 development Water Supply Assessment, which were later incorporated into the City' s 2020 Urban Water Management Plan ( UWMP). The updated demand evaluation was based on the City' s water use patterns observed since the 2014-017 drought, which are significantly lower compared to those included in the 2019 IWRMP which had been based on the City' s pre -drought water patterns.

Water Supply Information: The City' s water supply reliability and water supply infrastructure investments need to be reassessed based on the updated water supply projections presented in the 2020 UWMP and any subsequent management efforts. For example, the City' s imported surface water from the South County Water Supply Project (SCWSP) could experience significant cutbacks in light of the Bay Delta Plan Amendment and the resolution of the resultant settlement negotiations. Future, the City has experience water quality issues with its groundwater supply associated with the nearby former Occidental Chemical Corporation remediation site and detections of per- and polyfluoroalkyl substances ( PFAS). These issues limit the City' s ability to expand groundwater production in the future. The City conducted engineering feasibility studies for adding PFAS treatment of the Louise Avenue Water Treatment Facility ( LAWTF) and an aquifer storage and recovery ( ASR) project to improve water supply reliability.

River Discharge Permit: The City has obtained a National Pollutant Discharge Elimination System NPDES) permit to dispose a portion of the wastewater treated at the Lathrop Consolidated Treatment Facility ( CTF) in the San Joaquin River, with the remaining portion delivered as recycled water to irrigate urban parks and landscaping. To support use of recycled water for landscape irrigation, the City obtained coverage under General Order WQ- 2019- 0058- DDW- R5017 and submitted a Title 22 Report Addendum in 2020. The City began delivering recycled water for urban uses in the summer of 2021. These changes reduce the City' s potable water demand, and affect eki environment
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Section 1

INTRODUCTION
2024 WSMP Amendment
City of Lathrop
the operations and infrastructure needed of the City' s wastewater effluent disposal and recycled water distribution systems.

1. 2 Scope of Work
The scope of work for the WSMP Amendment included the following primary tasks:

Update of the water system hydraulic model network to incorporate system improvements completed since the 2019 WSMP or those currently in design or under construction, including system expansions related to new development and capital improvement projects completed by the City.

Update the backbone water system infrastructure included in the future water system hydraulic model network for future development areas based on recent utility plans completed by City or Developers ( e.g., the River Islands Phase 2 plans, the Mossdale Landing West Tentative Map); Verification of operational settings with input from City operations staff and update of the settings in the hydraulic model for pumps and tanks, as needed;
Verification and update of land use -specific water demand factors based on water use between 2017 and 2021;
Reallocation of parcel -by -parcel average day demands ( ADD) in the model based on an updated demand evaluation and allocation of demands associated with new development added since the prior hydraulic model update;
Development of water demand projections based on the land projections included in the General Plan Update (adopted September 2022) and River Islands Phase 2 project (approved in June 2021); Evaluation of water supply reliability based on information from the 2020 UWMP and the City' s PFAS treatment and ASR feasibility studies;
Assignment of fire flow demands to each new fire hydrant based on associated land use; Assessment of the Existing ( 2022) and Buildout ( 2045) water system performance under current and future flow conditions using steady- state model simulations; Evaluation of water distribution system performance, e.g., system pressures, velocity, and head loss deficiencies, and fire flow deficiencies;
Evaluation of storage and booster pump station ( BPS) capacities; Verification and update of the list of capital improvement projects ( CIPs) included in the 2019 WSMP; and
Preparation of the amended WSMP document.

1. 3 Report Organization
The WSMP is organized into the following sections:

Section 1- Introduction
Section 2 - Study and Water Service Area
Section 3 - Existing Water System
Section 4 - Existing and Future Water Demands
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Section 1

INTRODUCTION
2024 WSMP Amendment
City of Lathrop
Section 5 - Water System Supplies
Section 6 - Water System Performance and Operations Criteria Section 7 - Distribution System Hydraulic Capacity Evaluation Section 8 - Water Supply, Storage, and Pumping Capacity Evaluation Section 9 - Recommended Capital Improvement Program
Section 10 - References
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Section 2 2024 WSMP Amendment
STUDY AND WATER SERVICE AREAS City of Lathrop
2 STUDY AND WATER SERVICE AREAS
The City of Lathrop ( also referred to herein as the City) was incorporated on July 1, 1989 and is located in San Joaquin County, approximately 10 miles south of the City of Stockton and directly west of the City of Manteca. The City lies east of the Coastal Range that separates California' s Central Valley from the San Francisco Bay Area. Interstate 5 ( I-5), a major north -south interstate corridor, bisects the City. The City is also connected by Highway 120 which runs east -west through the southeastern - most part of the City, and by Interstate 205, which connects Interstate 580 to I-5. The City is also served by the Altamont Commuter Express ( ACE) train, which travels along the southern and eastern border of the City. The community was originally developed primarily east of I-5. Beginning in 2003, major new developments have been constructed west of I-5 and others are currently planned or under construction in this area.

This section provides an overview of the City' sservice area, including discussions of the City' sservice area boundaries, planned developments, and population.

2. 1 City Limits, Sphere of Influence, and Service Boundaries The City currently encompasses an area of approximately 13, 400 acres, or about 20. 9square miles. The City' s Sphere of Influence ( SO1) is slightly larger with an area of about 13, 600 acres, or 21. square miles.

The City' s SOI includes two unincorporated areas:

1. Approximately 134 acres northeast of the City boundary and along Roth Road that is designated Freeway Commercial and Limited Industrial, and

2. Approximately 62 acres southeast of the City boundary that is designated Service Commercial and part of the Lathrop Gateway Business Park Specific Plan area.

The City reduced their SOI in 2016 to exclude an additional unincorporated area ( approximately 2, 100 acres) located north of the Central Lathrop Specific Plan ( Central Lathrop or CLSP) area and west of I-5.

Much of this area does not have a General Plan land use designation. The City has designated this area as an Area of Interest (AOI) (Lathrop, 2016). Figure 2-1 shows the City limits, SOI, and AOI.

As shown in Figure 2-1, the City' s water service area is generally contiguous with the City limits and includes the railroad cargo container commercial enterprise that is outside of the City limits.

The City currently provides water service to approximately 9,22 residential, commercial, industrial institutional/ governmental, irrigation, agricultural, and other/ construction service connections, of which approximately 223 services are dedicated for irrigation uses. All of the City' s water services are metered.

The City began providing water to the 724 -acre Sharpe Army Depot in 2022. 1

2. Specific Plans and Large Planned Unit Development
The City has experienced significant growth in recent years and is anticipating growth to continue, particularly in several approved or pending large development projects within the City. Infrastructure needs for these projects are evaluated in this document. These projects are described below and shown on Figure 2-1 and Table 2-1, based on City and developer projections. Specifically, Table 2- 1 lists the number of new residential dwelling units and commercial, industrial, and institutional ( CII) acreage that is 1 As of the September 2024, only the Army & Air Force Exchange Service ( AAFES) along with a couple of buildings on Roth Road receive potable water from the City, while Sharpe Army Depot still operates its onsite drinking water system for the remainder of the facility.
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anticipated to be served by the City' spotable water system in five- yearincrements between 2025 and the anticipated buildout in 2045. A general description of the development areas and the total development planned at buildout is described below.

Central Lathrop Specific Plan. The Central Lathrop Specific Plan proposes development of 1, 520 acres located west of I-5. Phase 1 of the project is anticipated to be completed by 2040 and consists of a total 579 high density units, 1, 483 variable density residential units, and 146 acres of commercial land uses. The project also includes two schools and 161 acres of recreational land use and open space. Phase 2 of the project includes 682 acres of light industrial use and a 5 -acre park.

Mossdale Landing. Mossdale Landing is a mixed - use master planned community that is anticipated to be completed by 2030. Construction at Mossdale Landing began in 2003 and approximately 1, 640 residential units have been constructed thus far. An additional 66 low density residential units are anticipated by project completion. In addition, the development is allocating a total of 35 acres land for two schools, 40 acres for parks, and 25 acres for commercial development.

Mossdale Landing East. Mossdale Landing East ( formerly referred to as Lathrop Station) is anticipated to be completed by 2030. Approximately 490 residential units have been constructed so far. An additional 37 low density units are anticipated by project completion. The development plan also includes a total of 6. 5 acres of village commercial, 13. 2acres of service commercial, and

27. 5 acres of highway commercial land uses.

Mossdale Landing South. Mossdale Landing South is a proposed 104 -acre development that is anticipated to be completed by 2030. Approximately 140 medium and high density units have been constructed so far. An additional 85 medium density units are anticipated by project completion. In addition, the project includes a total of 28 acres of commercial, 25 acres of open space, and 9. 5 acres of parks.

Mossdale Landing West. Mossdale Landing West is a proposed residential development that is anticipated to be completed by 2032. The project will be located on the Silveira property and consist of 829 low density dwelling units and 11 acres of parks.

River Islands. The 4, 995 -acre River Islands development is located west of the San Joaquin River and east of Paradise Cut on land known as the Stewart Tract. The development proposes a mixture of low, medium, and high density residential units. According to its recently amended Specific Plan, River Islands will consist of two phases and a total of 15, 000 homes, a 260 -acre employment center, a 79 -acre town center, 235 acres of parks and ten schools. About 2, 800 low density residential units were constructed and occupied by late 2022. The estimated project completion date is 2040 ( Lathrop, 2022b; Woodard & Curran, 2020).

Lathrop Gateway Business Park Specific Plan. The Lathrop Gateway Business Park Specific Plan Lathrop Gateway) proposes commercial and industrial development of approximately 384 acres to be completed by 2040. The City annexed 213 acres of this area in June 2012 and 99 acres of the remaining 117 acres in May 2016. This would result in approximately 4. 7 million square feet of service commercial, limited industrial, distribution, and research and development related uses, and approximately 741, 000 square feet of commercial office and retail uses. The first phase of the project includes approximately 167 acres of limited industrial, 83 acres of service commercial, and 57 acres of office and commercial retail uses and is anticipated to be completed by 2030.
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Section 2 2024 WSMP Amendment
STUDY AND WATER SERVICE AREAS City of Lathrop
South Lathrop Specific Plan. The South Lathrop Specific Plan ( South Lathrop) was approved by the City Council on 20 July 2015 and includes a 315 - acre plan area. The Specific Plan proposes approximately 10 acres of commercial office uses, 246 acres of limited industrial, 31 acres of open space, and 27 acres of roads and public facilities. The City South Lathrop Specific Plan area was annexed into the City in May 2016. The South Lathrop Commerce Center, approximately 272 acres within the South Lathrop Specific Plan, is anticipated to be completed by 2030. The South Lathrop Commerce Center will encompass all of the South Lathrop Specific Plan area with the exception of approximately 24 acres of light industrial, 1. 2 acres of office commercial, and 19 acres of open space and public roads.

Historic Lathrop Infill and Other Developments East of I-5. The portion of the City east of I-5 is anticipated to include infill development and added density in the future. Currently, this area consists of approximately 3, 160 low density and 455 medium density units, commercial and industrial areas, and a few public parks. Future residential growth of this area is expected on undeveloped/ underutilized and redeveloped parcels consolidated from large lots where low density residential units would be demolished. New residential projects are estimated to consist of 52 low density, 218 medium density, and 48 high density residential units, increasing the total existing residential unit count by 318 units.

Sharpe Army Depot. During World War II, the US Army created the Sharpe Army Depot ( Depot) in the rural Lathrop Community to allow shipment of major army supplies to the western United States. The Depot is comprised of a 724 - acre facility south of Roth Road and has served both the Army and Airforce with a variety of supplies depending on the demand of goods and supplies created by war time efforts. The Depot is occupied by the Army & Air Force Exchange Services AAFES) West Coast Distribution Center that employs 348 workers. Prior to 30 September 2014 the Defense Logistics Agency was also housed at the Depot; its workforce of 700 workers has since been transferred to the larger Tracy Army Depot. The City began providing water and sewer services to the Sharpe Army Depot in 2022, including the AAFES and California National Guard properties.
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tallow
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South
Lathrop
ya
Sherpa
Army
Depot
and Other Deveipmts
Legend
IJj city Limit
EDSphere of Influence
EnArea of Interest
Rail Cargo Container Yard
Development Areas
3 Central Lathrop
Crossroads
Q Historic Lathrop Infill and Other Developments
QLathrop Gateway
Mossdale Landing
Mossdale Landing West
Mossdale Landing East
Mossdale Lending South
ORiver Islands
Sharpe Army Depot
izzi South Lathrop
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 13 November 2024.

N
0 A

4. 000 8, 000
Sala in Feat)
City of Lathrop Boundaries
and Development Areas
Water System Master Plan Amendment
City of Lathrop
Lathrop, CA
er 2024 ski environment DecC20048 czD0481 4e 0
water Figure 2. 1
Section 2

STUDY AND WATER SERVICE AREAS
2024 WSMP Amendment
City of Lathrop
Table 2-1. City of Lathrop Potable Water Development Projections by Development Area Land Use Designation
Central Lathrop- Phase 1
Low Density Residential du 500 264 764
High Density Residential du 246 210 123 579
Mixed Use ac 51 51
Commercial ac 13 61 72 146
Central Lathrop - Phase 2
Light Industrial / R&D Flex ac
ac
90 592 682
Parks 5. 0 5. 0
Mossdale Landing
Low Density Residential du 66 66
Commercial ac 4. 6 1. 5 6. 1
Schools ac 16. 2 16. 2
Mossdale Landing East
Low Density Residential du 37 37
High Density Residential du 84 84
Commercial ac 7. 0 7. 0
Mossdale Landing South
Medium Density Residential du 85 85
Commercial ac 8 17 25
Parks ac 4. 0 4. 0
Mossdale Landing West
Low Density Residential du -- -- 829 -- -- 829
River Islands
Low Density Residential du 768 1, 218 1, 218 1, 218 4,22 Medium Density Residential du 676 945 945 945 3, 511
High Density Residential du 1, 395 1, 395 1, 395 4, 185 Town Center ac 22 22 22 67
Commercial ac 73 73 73 220
Schools ac 11 5. 4 5. 3 5. 1 26. 9
Parks ac 1. 3 4. 3 4. 3 4. 3 14. 4
Landscape Areas ac 1. 5 1. 1. 1. 4. 7
Street Landscape Area ac 0. 3 1. 1. 1. 3. 6
South Lathrop
Light Industrial / R&D Flex ac 67. 0 32. 8 99. 75
Office Commercial ac 8. 1. 2 10. 0
Lathrop Gateway
Light Industrial / R&D Flex ac 66 17 83
Commercial ( Office and Service) ac 51 12 63
Open Space ac 2. 5 1. 6 4. 1
Public Landscaping ac 2. 6 8. 11. 4
Crossroads
Industrial ac 23 23
Commercial ac 1. 5 1. 5
Incremental
Incremental New Development ( a)( b)( c)
New
Units 2025 2030 2035 2040 2045 By Buildout
Buildout )
ek, environment
water 2- 5
December 2024
EKI C20049. 01
Section 2

STUDY AND WATER SERVICE AREAS
2024 WSMP Amendment
City of Lathrop
Table 2-1 (Cont.). City of Lathrop Potable Water Development Projections by Development Area Land Use Designation
Historic Lathrop and Other Developmen
Low Density Residential du 12 6 5 29 52
Medium Density Residential du 27 26 26 26 113 218
High Density Residential du 48 48
Commercial ac 22 14 8 44
Industrial ac 18 24 42
Sharpe Army Depot
Incremental New Development ( a)( b)( c)
Units 2025 2030 2035 2040 2045
Buildout)
Areas
Total New
Development
Industrial ac d) d)
Notes:
a) Dwelling unit counts and acreages were based on information provided by developers and the City in November 2016, December 2016, May 2017, July 2017, July 2020, and April 2023 and adjusting for the future development to be supplied by recycled water in Central Lathrop and River Islands. b) Includes dwelling units and acreages that are assumed to be developed during the preceding five- year period. c) Area of landscape parcels and parks includes areas to be irrigated with potable water only. d) The existing facilities at the Sharpe Army Depot has been connected to City' s water service in summer 2022. Due to
incomplete billing records from the Sharpe facility, water demands are estimated using historical metered consumption from the AAFES facility and projections provided on 12 April 2018 for the California Military Department facility, as seen in Table 4-5.

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G & water 2-6
December 2024
EKI C20049. 01
Section 2
2024 WSMP Amendment
STUDY AND WATER SERVICE AREAS City of Lathrop

2. 3 Current and Projected Population
Values for the historical and current population within the City' s water service area were obtained from
data reported by the California Department of Finance ( DOF) within the City Limits. Although Lathrop' s water service area includes a railroad cargo container commercial enterprise that is outside the City limits, the service area population is estimated to be equivalent to the City population. As of January 2023, the population estimate for Lathrop was 35, 080 (California DOF, 2023). The historical and current population data within the City' swater service area are presented in Table 2-.

Population in the City has grown by approximately 410% over the 32 -year period between 1990 through 2023, from approximately 6, 800 to 35, 100 (California DOF, 2007, 2012, and 2023). Between 2005 and 2023, population increased by 174%, from approximately 12, 800 to 35, 100.

STUDY AND WATER SERVICE AREAS
2024 WSMP Amendment
City of Lathrop
Table 2-. Historical Service Area Population
Year
1990
Service Area Population ( a)
6, 841
Annual Growth Rate
1991 7, 018 2.6%
1992 7, 063 0.6%
1993 7, 434 5.3%
1994 8, 410 13.%
1995 8, 713 3.6%
1996 9, 031 3.6%
1997 9, 172 1.6%
1998 9, 508 3.7%
1999 9, 786 2.9%
2000 10, 445 6.7%
2001 10, 802 3.4%
2002 11, 616 7.5%
2003 12, 089 4.1%
2004 12, 482 3.%
2005 12, 768 2.3%
2006 14, 489 13. 5%
2007 16, 271 12. 3%
2008 17, 282 6.2%
2009 17, 589 1.8%
2010 18, 023 2.5%
2011 18, 688 3.7%
2012 19, 090 2.%
2013 19, 642 2.9%
2014 20, 158 2.6%
2015 20, 796 3.2%
2016 22, 174 6.%
2017 23, 117 4.3%
2018 24, 185 4.6%
2019 25, 401 5.0%
2020 26, 833 5.6%
2021 29, 384 9.5%
2022 31, 575 7.5%
2023 35, 080 11.%
Notes:
a) Historical and current population is based on population estimates by the California DOF for the City of Lathrop included in DOF, 2007; DOF, 2012; DOF, 2022; and DOF, 2023.

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i & water 2-8
December 2024
EKI C20049. 01
Section 2

STUDY AND WATER SERVICE AREAS
2024 WSMP Amendment
City of Lathrop
Population
Served
Table 2-3. Current and Projected Service Area Population Current and Projected Service Area Population ( a)( b)
Year 2023 2025 2030 2035 2040
2045
Buildout)
Population Served 35, 080 40, 531 55, 471 72, 513 84,97 86, 013 Notes:
a) Current population is based on population estimates by the California DOF for the City of Lathrop included in DOF, 2023.
b) Projected populations for 2025 through buildout (2045) are based on residential unit counts from Table 2-1, multiplied by 4. 02 persons per dwelling unit for low density developments ( U. S. Census, 2023) and 3. 0 persons per dwelling unit for medium and high density developments.
100, 00
90, 000
80, 000
70, 000
60, 000
50, 000
40, 000
30, 000
20, 000
10, 000
eki
0 1990 1995 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 Year
4—Historical Population — 6 — Projected Population
Figure 2-. Historical and Projected Service Area Population i
environment
water 2- 9
December 2024
EKI C20049. 01
Section 3 2024 WSMP Amendment
EXISTING WATER SYSTEM City of Lathrop
3 EXISTING WATER SYSTEM
The City' s existing water system facilities consist of five groundwater wells ( Wells 6, 7, 8, 9, 10), the Louise Avenue Water Treatment Facility ( LAWTF) for treatment of groundwater from Wells 6- 10, two surface water turnouts for delivery of South County Water Supply Program ( SCWSP) from South San Joaquin Irrigation District ( SSJID), seven storage tanks and booster pump stations, and approximately 156 miles of pipeline. The City' s distribution system operates as a single pressure zone. Figure 3-1shows the City' sservice area and locations of the City' s major water system facilities. These facilities will be described in further detail in the following sections.

3. 1 Water Supply and Treatment Facilities
The City' s water supply and treatment facilities are described in the following sections. The City' s water supply facilities and an assessment of the City' s water supply reliability are discussed further in Section 5.

3. 1. Groundwater Wells, Raw Water Pipelines, and Treatment Facilities The City currently operates five municipal groundwater supply wells: Wells 6, 7, 8, 9, and 10. WeII 9 is currently offline due to water quality issues and may be used in the future as an emergency well until water quality issues are addressed to meet drinking water standards. A sixth City well, WeII 21, is currently not in operation. Table 3-1 provides information about well age, depth, status, design and measured flow rates, and treatment. As shown on Figure 3-1, these wells are located on the eastern side of the City' sdistribution system. Groundwater from wells 6, 7, 8, 9, and 10 is conveyed via 12 -inch and 16 -inch water mains along the eastern border of the City along the railroad tracks to the LAWTF, where the groundwater is treated to remove arsenic. The LAWTF began operating in 2012 and has a treatment capacity of 6, 250 gallons per minute (gpm).

A series of sampling events in the City' s production wells during 2019 and 2020 showed that perfluorooctanoic acid ( PFOA) and perfluorooctanesulfonic acid ( PFOS) concentrations in groundwater from WeII 9 exceeding both the Notification Levels ( NLs) and Response Levels ( RLs), which were established by the State Water Resources Control Board Division of Drinking Water ( SWRCB DDW). The NLs for PFOS were also exceeded in one or more samples collected from Wells 6, 7, 8, and 10. PFOA concentrations in groundwater from Wells 6, 7, 8, and 10 were below reporting limits. Based on these and historical sampling results, the City took WeII 9 offline so that the PFOA concentrations in the blended flow from remaining wells is well below the RLs.

The WeII 21 site includes a treatment facility ( Well 21 WTF), designed for disinfection and manganese treatment. The City last operated WeII 21 and WeII 21 WTF between January 2012 and November 2013.

WeII 21 has remained inactive since November 2013 due to sanding in the well and elevated levels of PFAS, arsenic and uranium. The City does not currently plan to bring the well or WTF back online due to poor groundwater quality.

3. 1. 2 Surface Water Turnouts
The City purchases imported surface water from SSJID through SCWSP, which supplies treated Stanislaus River water ( see Section 5.1). There are two SSJID turnouts ( SSJID Turnout 1 and SSJID Turnout 2). SSJID Turnout 1 is located on Lathrop Road, east of McKinley Avenue, and has a peak capacity of 7. 5 million gallons per day ( MGD). Due to downstream distribution system capacity limitations, the current maximum capacity of SSJID Turnout 1 is approximately 3 MGD.

SSJID Turnout 2 is located west of the Manthey Road and Stewart Road intersection and north of the railroad tracks ( i.e., adjacent to the City' s
BPS -5 site) and has a peak capacity of 11. 52 MGD.
eki environmentwater 3- 1
December 2024
EKI C20049. 01
Section 3 2024 WSMP Amendment
EXISTING WATER SYSTEM City of Lathrop
SSJID Turnouts 1 and 2 both include 1. 0 -million -gallon ( MG) SSJID tanks, which are not owned by the City and are therefore not included in storage calculations ( see Section 3. 2.1).

3. 1. Emergency Interties
The City has an emergency intertie located near Roth Road, at the northern city limits near the City of Stockton. Further investigation is needed to confirm the status of this intertie and the connecting water system ( i.e. City of Stockton, California Water Service, or County of San Joaquin) and whether an agreement exists to operate the intertie in the event of an emergency.

The City does not have an intertie with the City of Manteca, which may be considered in the future. ek, environment
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December 2024
EKI C20049. 01
Emergency Stockton Intenie •
F. -
L.,
t
BPS -7
Tank,
s
BI16
rTarik
ui- HooP RD
SSJID
7' I Turnout 1
Well?
1Jwell
Well 8.
8P r
LAWTF Tank and BPS
1•
Well 10
Well 9
ilYOSEMITE A
Well 21 1
Well 21
WT...,
SSJI »
BPS - 5
Tank
Turnout 2
Lepend
Sphere of Influence
Existing City Infrastructure
Treatment Plant
O Pump Station
Enclosed Storage Facility
C SSJID Turnout
Production Well
Emergency Intertie
Raw Water Main
Existing Pipe Diameter, Inches
Less than and equal to 4
8 10
12 16
18 20
24 30
Abbreviations
BPS = booster pump station
LAWTF = Louise Avenue Water Treatment Facility
SOI = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

2. Well 9 is currently offline due to water quality issues.

Well 21 and the Well 21 WTF are inactive.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 13 November 2024.

N
o
A _

3. 000 6, 000
MuA in reey
Existing Water System Infrastructure
Wafer System Master Plan An endrna t
cM or Lathrop
Lathrop, CA
December 2024 ek December
IC20049. water 01Figure 3- 1
Section 3

EXISTING WATER SYSTEM
2024 WSMP Amendment
City of Lathrop
WeII ID Location
WeII 6
1991
Park Street
Current Backup
Status ( b) Power
Active
Table 3-1. Active Groundwater Well Information
VFD
Date
Drilled
1986
Age of
WeII
years)
36 Completed Design
Well Casing Flow
Depth Rate
ft bgs) ( gpm)
270 1, 200
Measured Design
Flow Rate Head
gpm) ( feet)
1, 650 221
Well 7 15800 5` hStreet Active 1989 33 270 1, 500 1, 400 210 WeII 8
2444 E Louise
Avenue
Active 1991 31 273 1, 200 1,00 221
WeII 9
17550 Shideler
Parkway
Temporarily
Offline
1993 29 282 1, 200 1, 400 221
WeII 10
17400 Shideler
Parkway
Active 2007 15 275 1, 300 1, 700 258
Current Treatment
Arsenic treatment and
chlorine disinfection at
LAWTF. Chlorine injection
possible at well heads in
case of emergency.

Notes:
a) WeII 9 is currently offline due to water quality issues and may be used in the future as an emergency well until water quality issues are addressed to meet drinking water standards.
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water 3-4
December 2024
EKI C20049. 01
Section 3
2024 WSMP Amendment
EXISTING WATER SYSTEM City of Lathrop

3. 2 Water Distribution System Facilities

3. 2. 1 Treated Water Storage Facilities and Booster Pump Stations As seen in Table 3-2, the City has approximately 7. 4 MG of total storage in seven existing ground -level storage tanks. Two additional 1. 0 MG storage tanks are located at the two SSJID Turnouts but are owned and operated by SSJID. The City' stanks are used to help meet system demands during peak hours, provide emergency storage, and provide fire flow storage.

As seen in Table 3-, the City has seven booster pump stations associated with each storage tank and the LAWTF, and two additional BPS at the two SSJID Turnouts. The SSJID Turnout 1 BPS is the only station without backup power. BPS -1 is the only domestic pump station without variable frequency drive pumps.

In total, the City has approximately 21, 660 gpm of existing firm domestic pump capacity ( i.e., without the largest domestic pump at each BPS), and an additional 16, 550 gpm of fire pump capacity. The discharge from the SSJID Turnout 2 is directly pumped to the BPS - 5 and therefore not included in the total firm pumping capacity.

3. 2. Water Distribution Pipelines
The City' s water distribution network consists of approximately 157 miles of pipe ranging from 2 inches to 30 inches in diameter. Table 3-4summarizes the City' s distribution pipelines by diameter. Distribution system pipe sizes are shown spatially on Figure 3-1.

Pipe material is not well documented in the older Historic Lathrop and Crossroads areas, but materials are known to include asbestos cement ( AC) pipe, cast iron pipe, ductile iron pipe ( DIP), and polyvinyl chloride ( PVC) pipe. DIP is used near the LAWTF and the former Well 21 site. Newer areas of the City west of I-5 are exclusively served by PVC pipe, which is the City' scurrent standard pipe material.

3. 2. SCADA System
The City has Supervisory Control and Data Acquisition ( SCADA) system monitoring for all wells, pump stations, storage tanks, the LAWTF and the SSJID turnouts. The system monitors discharge flows, discharge pressures, tank levels, pump speeds, and chlorine residual. Alarms are set for minimum and maximum levels and pressures.

3. Summary of Major Water System Improvements Since 2019 The following major water system improvements were completed since the 2019 WSMP:

SSJID Turnout 2: SSJID Turnout 2 was constructed in 2018 with three 2, 000 gpm pumps and one

1. 0 MG tank owned by SSJID.

J Street Improvement Proiect: The previous 8" to 10" pipes on J St between approximately 140 feet west of Avon St and approximately 210 feet east of 5th St were replaced by new 12" PVC pipe. The previous 10" line on Avon St between J St and Sunflower Dr was replaced by new 12" PVC pipe. The previous 12" BPS - 1 discharge line was replaced by new 16" PVC pipe. eki environment
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December 2024
EKI C20049. 01
Section 3 2024 WSMP Amendment
EXISTING WATER SYSTEM City of Lathrop
South Harlan Road Improvement Project: A new 8" pipe on South Harlan Road, north of Louise Avenue, was constructed to loop the existing 8 -inch dead- end on South Harlan Road to the 8 -inch pipe on Old Harlan Road.

River Islands Water Infrastructure: Water system improvements for Phases 1, 2A, and parts of 2B of the River Islands Development.

Central Lathrop Stanford Crossing Infrastructure: Water system improvements for the Central Lathrop Stanford Crossing development.

Louise Avenue Water Transmission Main Project: A new 12 -inch transmission line was installed in parallel to the existing 12 -inch transmission line along Louise Avenue from I-5 to Howland Road.

South Lathrop Offsite Backbone Infrastructure: A new 12 -inch transmission line was constructed on Yosemite Avenue between Highway 120 and D' Arcy Parkway.

Backbone Infrastructure, South Lathrop Commerce Center: A new 12 -inch transmission loop was constructed around the South Lathrop Commerce Center.

Murphy Parkway Off -Site Civil Improvement: A new 10 -inch transmission line was constructed on the new development ( Testa Service Distribution Center) at 17100 Murphy Pkwy, Lathrop, CA 95330.
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water 3- 6
December 2024
EKI C20049. 01
Section 3

EXISTING WATER SYSTEM
2024 WSMP Amendment
City of Lathrop
Table 3-2. Existing Treated Water Storage Facilities
Storage Facility
Tank 1
Location
J Street and Ruby Court
Date Constructed
1986
Material
Steel
Capacity
MG)

0. 4
Diameter
feet)
55 Height
ft)

22. 9
MSL Elevation
ft)

15. 0
Tank 2
Howland Road and
D' Arcy Parkway
1993 Steel 1. 0 75 30. 7 17. 5
Tank 3
Tracywood Avenue and
Shadywood Avenue
2003 Steel 1. 0 85 24. 1 15. 0
Tank 4
Brookhurst Boulevard
and Manthey Road
2005 Steel 1.7 100 23. 5 15. 25
Tank 5
Golden Valley Parkway
and W Stewart Rd
2018 Steel 1. 2 106 27. 0 16. 0
Tank 6
Stanford Crossing and
Spartan Way
2021 Steel 1. 6 97 32. 5 12. 0
LAWTF Tank 2112 Louise Avenue 2013 Steel 1.0 92 24. 0 24. 0 Notes:
a) Sources: Draft Water Master Plan, November 2013 and Water Supply Wells Arsenic Reduction Facilities Louise Avenue Water Treatment Facility, CIP Project PW05- 07, January 2013. Asbuilts provided by the City on May 2022. b) Listed water storage facilities do not include the 1.0 MG tanks at SSJID turnout 1 and SSJID Turnout 2, which are owned and operated by SSJID.
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water 3-7
December 2024
EKI C20049. 01
Section 3

EXISTING WATER SYSTEM
2024 WSMP Amendment
City of Lathrop
Table 3-. Treated Water Storage Facility Booster Pump Station Characteristics Variable
Design
Booster Pump Head Frequency Horsepower Installation Standby Pump No. Flow
Station (
gpm) (
ft) Drive ( hp) Date ( b) Power
VFD)
1 1A 1, 800 133 50 1986
V
1FP 1, 050 138 100 1986
2 2A 1, 750 180 V 75 1993
V
2FP 3, 000 116 1993
3 3A 1, 250 142 60 1999
3B V 1, 250 142 V 60 1999
3FP 3, 500 173 266 1999
4 4A 600 130 V 25 2006
V
4B 1, 000 92. 3 60 2006
4C 1, 000 92. 3 60 2006
4D 1, 000 92. 3 60 2006
4FP 2, 000 155 125 2006
5 ( c)
1 2, 000 197 125 2018
V
2 2, 000 197 V 125 2018
3 2, 000 197 V 125 2018
FP1 4, 000 197 250 2018
FP2 4, 000 197 250
Under
Construction
6 ( d)
1 1,50 162 V 60 2019
V
2 1,50 162 V 60 2019
3 1,50 162 V 60 2019
FP 3, 000 162 200 2019
LAWTF
LAWTF1 2, 100 165 V 125 2012
V
LAWTF2 2, 100 165 V 125 2012
LAWTF3 2, 100 165 V 125 2012
LAWTF4 2, 100 165 V 125 2012
SSJID Turnout 1
SSJ1 2, 605 203 V 200 2004
SSJ2 2, 605 203 V 200 2004
SSJ3 2, 605 203 V 200 2004
SSJID Turnout 2
e)
1 2000 30 25 2018
2 2000 30 25 2018 V
3 2000 30 25 2018
Notes:
a) Source: Water Master Plan, December 2019.
b) Date of original installation.
c) Firm pumping capacity at buildout from City of Lathrop Phase I Potable Water Booster Pump station and storage Tank Expansion Plan at River Islands 100% Plans ( PACE, 2022). d) Central Lathrop Specific Plan Tank & Booster Pump Station, dated 2019. ek, environment
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December 2024
EKI C20049. 01
Section 3 2024 WSMP Amendment
EXISTING WATER SYSTEM City of Lathrop
Table 3-4. Pipeline Lengths by Diameter
Pipeline Diameter
inches)
2 Length
feet)
2, 788
Length
miles)

0. 53
Percent of Water
System

0. 34%
3 165 0.3 0.2%
4 7, 627 1. 44 0. 92%
6 61,15 11. 67 7. 45%
8 433, 362 82. 08 52. 43%
10 77, 477 14. 67 9. 37%
12 158, 84 30. 09 19. 22%
16 49, 103 9. 30 5. 94%
18 7, 081 1. 34 0. 86%
20 18, 385 3. 48 2.2%
24 9, 557 1. 81 1.6%
30 580 0. 11 0.7%
Total 826, 624 156. 56 100%
Notes:
a) Data includes all active potable water transmission and distribution pipelines present in the geographic information system ( GIS) data provided by the City and updated by EKI.
ekienvironment water 3- 9
December 2024
EKI C20049. 01
Section 4 2024 WSMP Amendment
EXISTING AND FUTURE WATER DEMANDS City of Lathrop
4 EXISTING AND FUTURE WATER DEMANDS
The City updated its demand projections as part of this IWRMP Amendment. The following sections summarize the City' s historical and current water demands, water demand projections, and water peaking factors.

4. 1 Current and Historical Water Demand
Table 4-1, Figure 4-1, and Figure 4-2 provide historical context by summarizing the City' s potable water use, service area population, and per capita potable water use for the years 2000 through 2022. Historical potable water use is calculated based on total annual SCWSP water purchases and groundwater production. Total potable water use in 2022 was 5, 277 acre feet ( AF).

Potable water use has generally increased over the past two decades, although significant variations have occurred from year to year and are believed to be associated with changing hydrologic and economic conditions. During the extended drought of 2014-017, the City' s water production decreased dramatically due to the voluntary and mandatory water conservation efforts that were implemented by the City' s water customers. Water production rebounded between 2017 and 2020 as water use restrictions were lifted and new development projects were constructed. However, water use decreased again as a result of the 2021-022 drought. The City' scurrent ( 2022) total potable demand and per capita water demand remain below 2020 levels due to the current drought.

Although population has steadily increased over the past 21 years, the increase in total water demand has been buffered by a general decline in per capita water use since 2004, as shown in Figure 4-2. Specifically, per capita water use dropped to below the City -adopted 2020 Senate Bill x7- 7 (SBx7- 7) Target of 188 gallons per capita per day (GPCD) 2in 2014 and has remained lower than the Target ever since. The City' s current ( 2022) per capita water use is 149 GPCD. While recent declines may be attributed in part to behavioral changes and regulatory mandates during the past and current droughts, the longer -term decline in per capita water use is likely representative of ( 1) new residential development, which has increased population and minimized the portion of per capita water demands associated with nonresidential uses and ( 2) increases in water use efficiency through retrofits of existing properties and the construction of new, water - efficient development.

The City' s potable water demands were quantified in terms of the following water use sectors, which were established based upon the categories assigned to each account in the City' s water billing system: Single Family Residential ( SFR), Multi -Family Residential ( MFR), Commercial, Industrial, Institutional/ Governmental, and Other/ Construction. Additionally, dedicated irrigation accounts were separated into an Irrigation sector, which includes both separate irrigation accounts and those accounts in other sectors that have irrigation sub -meters.

Table 4-2 summarizes the current number of customer service connections in each water use sector. The City currently provides water service to approximately 9,22 residential, commercial, industrial and institutional/ governmental service connections. The SFR and MFR sectors comprise respectively 91% and 4% of all customer service connections in the City. The CII sectors comprise 3% of all customer service The Water Conservation Act of 2009 ( SBx7- 7) required water retailers to set a total GPCD water use reduction target of 20% by year 2020 from a calculated baseline water use. The target is measured in GPCD, which represents the total water use divided by the population, as opposed to Residential GPCD ( R- GPCD), which only includes residential water use divided by the population. The City adopted its 2020 SBx7- 7 target in 2012. ek, environment
water 4-1
December 2024
EKI C20049. 01
Section 4 2024 WSMP Amendment
EXISTING AND FUTURE WATER DEMANDS City of Lathrop
connections in the City. The remaining accounts are dedicated irrigation meters and construction/ temporary meters. All the City' s
water services are metered.

In addition to the metered water consumption described above, the City' s potable water demand also includes non -revenue water, including water used for fire hydrant flushing and testing and for water main flushing, as well as distribution system water losses. The volume of non -revenue water is estimated herein by comparing metered water demand ( i.e., consumption) against total water purchases and groundwater production.

Current and historical potable water demands for the customer sectors discussed above are provided in Table 4-3 and on Figure 4- and Figure 4-5. Over the period 2017 through 2022, SFR water use comprised approximately half of all water use in the City ( 48%). Of the metered water consumption, the Industria/ and Irrigation sectors comprised 24% and 15% of the City' s water demands, respectively. Water use in the Commercial ( 3%), Institutional/ Governmental (3%), MFR ( 2%), and Agricultural ( 2%) sectors was relatively minor compared to total water use. The relative percentage of the total potable water demand represented by most sectors remained relatively constant from 2017 through 2022.

The City' s non - revenue water use over this period, as calculated by subtracting metered consumption from production, averaged approximately 1% of total use from 2017 to 2022. This unusually low average and several negative annual water loss volumes recorded during this period are likely indicative of meter errors, and the actual non -revenue water use is likely higher. ek, environment
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December 2024
EKI C20049. 01
Section 4

EXISTING AND FUTURE WATER DEMANDS
2024 WSMP Amendment
City of Lathrop
Table 4-1. Current and Historical Potable Water Use and Population Year
Potable Water Use
acre feet)
a)
Service Area
Population
b)
Per Capita
Potable Water Use
GPCD) (c)
2000 2, 518 10, 445 215
2001 2, 689 10, 802 222
2002 3, 105 11, 616 239
2003 3,26 12, 089 246
2004 3, 471 12, 482 248
2005 3,72 12, 768 236
2006 3, 640 14, 489 224
2007 4, 076 16, 271 224
2008 4, 528 17, 282 234
2009 4, 214 17, 589 214
2010 3, 672 18, 023 182
2011 3, 798 18, 688 181
2012 4, 332 19, 090 203
2013 4, 686 19, 642 213
2014 4, 008 20, 158 177
2015 3, 445 20, 796 148
2016 3, 646 22, 174 147
2017 4, 168 23, 117 161
2018 4, 551 24, 185 168
2019 4,52 25, 401 156
2020 5, 485 26, 833 182
2021 5, 285 29, 384 161
2022 5, 277 31, 575 149
Notes:
a) Detailed historical and current water demand data from 2011 through 2020 are documented in the City' s 2020 UWMP. The 2021 and 2022 demands are documented in Table 4-2. b) Historical and current population is based on population estimates by the California DOF for the City of Lathrop included in DOF, 2007; DOF, 2012; DOF, 2022, and DOF, 2023. c) Per capita potable water use is calculated by dividing the total annual potable water demand by service area population and the number of days in a year.
eki environment
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December 2024
EKI C20049. 01
Section 4 2024 WSMP Amendment
EXISTING AND FUTURE WATER DEMANDS City of Lathrop
Figure 4-1. Current and Historical Potable Water Use and Population 6, 000
5, 000
d
4, 000
a
3, 000
a
a, 2, 000
n
In
0 a
1, 000
0 300
u
w 250
a
ra
E 200
3 150
a
m
c 100
a
Ns
a.
50 IL
0 et Ln LO N CO rn 0 .--I N m V1 lD N oo rn
0 0 0 0 0 0 0 0 00 e - I N N
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

N N NCNINNN N N N N N N N N N N N N N N N
Year
Potable Water Usage - Population
Figure 4-2. Current and Historical Per Capita Potable Water Use O N m ct V1 le) I, CO D1 O .-- I N Cr) in co N co cn O .- 1 N O O O o O e - I .-- 1 ei r -N ei e - I ei ei ei ei N N N O O O o O O O O O O O O O O O O O O

N N N N N N N N N N N N N N N N N N
000

O O O O O N N N N N
Year
35, 000
30, 000
25, 000
20, 000
15, 000
10, 000
5, 000
N
N
O
N
Per Capita Potable Water Use — 2020 SBX7- 7Target ( 188 GPCD) Service
Area
Population
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December 2024
EKI C20049. 01
Section 4

EXISTING AND FUTURE WATER DEMANDS
2024 WSMP Amendment
City of Lathrop
Table 4-2. Number of Current ( 2022) Potable Water Services by Sector Water Use Sector 2022
Residential Service Connections
Single Family Residential 9, 028
Multi -Family Residential 387
Subtotal Residential 9, 415
CII Service Connections
Commercial 143
Industrial 53
Institutional/ Governmental 60
Subtotal CII 256
Other Service Connections
Irrigation 223
Other/ Construction 28
Subtotal Other 251
Total Number of Services 9,22
Notes:
a) Number of accounts were based on the December 2022 billing data provided by the City on 25 July 2023.

Figure 4-3. Number of Current Potable Water Services by Sector Multi -Family Residential
Institutional/ Governmental
Commercial
Irrigation
Single Family Residential
Industrial
Other/ Construction
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December 2024
EKI C20049. 01
Section 4

EXISTING AND FUTURE WATER DEMANDS
2024 WSMP Amendment
City of Lathrop
Table 4-3. Current and Historical Potable Water Use by Sector Water Use Sector
Potable Water Demand ( acre- feet) (a)
2017 2018 2019 2020 2021 2022
Residential Water Use
Single Family Residential 1, 991 2, 112 2, 136 2, 559 2, 681 2, 696 Multi - Family Residential 76 80 79 99 106 133
Subtotal Residential 2, 067 2, 191 2,15 2, 658 2, 788 2, 829 CI! Water Use
Commercial 155 184 150 132 146 179
Industrial 856 1,43 1,71 1, 206 1, 210 1, 287
Institutional/ Governmental 100 110 94 150 140 146
Subtotal Cll 1,11 1, 437 1, 414 1, 488 1, 497 1, 612
Other Water Use
Irrigation 719 730 664 894 837 815
Agricultural 119 226 212
Other/ Construction 75 157 122 172 146 58
Recycled Water Use ( b) 94) 194)
Subtotal Other 912 1,13 999 1, 066 889 679
Total Water Consumption 4, 090 4, 741 4, 627 5, 211 5, 174 5, 120 Non -revenue Water ( c)
2% 4% 4% 5% 2% 3%
78 190 175 273 111 158
Total Water Demand (d) 4, 168 4, 551 4,52 5, 485 5, 285 5, 277 Notes:
a) Water use data was processed from water billing data provided by the City on 4 August 2022 and 27 April 2023.
b) Recycled water use based on CalSense meter data and subtracted from total water use data. c) Non -revenue water includes water used for fire hydrant flushing and testing, for water main flushing, as well as distribution system water losses. This value is calculated as the difference between metered water consumption and total water production.
d) Total water demand is the sum of metered water consumption and non -revenue water. e) Totals may not add exactly due to rounding.
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December 2024
EKI C20049. 01
Section 4
2024 WSMP Amendment
EXISTING AND FUTURE WATER DEMANDS City of Lathrop
Figure 4-. Annual Water Use by Sector: 2017-022
6, 000
5, 000
5 4, 000
Q
ai
D
i
3, 000
ry
Q 2, 000
1, 000
0 2017
Single Family Residential
Industrial
Other/ Construction
2018 2019 2020 2021 2022
Multi - Family Residential ip- Commercial
Institutional/ Governmental • Irrigation
Non -revenue Water • Agricultural
Figure 4-5. Percentage of Total Water Use by Sector: 2017-022 3%
Single Family Residential
Multi - Family Residential
Commercial
Industrial
Institutional/ Governmental
Irrigation
Agricultural
Other/ Construction
Non -revenue Water
ekienvironment water 4-7
December 2024
EKI C20049. 01
Section 4 2024 WSMP Amendment
EXISTING AND FUTURE WATER DEMANDS City of Lathrop

4. 2 Water Demand Projections
Potable water demand projections were calculated as the sum of the two major components of future water demands: ( 1) baseline water demand based on the City' s existing potable water demand in 2022, and ( 2) the anticipated potable water demands associated with the future development projects and planning areas post 2022. Components of potable water demand projections are described in the sections below.

4. 2.1 Baseline Potable Water Demand
The baseline water demand is based on the City' s potable demand in 2022. As discussed above, water demand in 2022 was slightly suppressed due to water use restrictions implemented during the 2021-022 drought. However, it is anticipated that the City' s water use efficiency will continue to improve over the long term, driven by its compliance to the State' s upcoming water use efficiency regulations. As such, the water demand in 2022 is considered as a reasonable " baseline".

Baseline water demand does not include water uses by construction and temporary meters and is estimated to be 5, 061 acre- feet per year (AFY).

4. 2. Demand Associated with Planned Development
To estimate demands for future developments, water use factors shown in Table 4- were applied to the anticipated acreages and number of dwelling units associated with each proposed development listed in Table 2-1. As part of this IWRMP Amendment, EKI reviewed City' s water use during 2017 through 2022 to verify and update the water demand factors presented in the City' s 2020 UWMP. The factors assign a unit volume of potable water demand to an individual dwelling unit ( gallons per day per dwelling unit, or, gpd/ du) or to each acre of CI' development ( gallons per day per acre, or, gpd/ ac). The methodology used to develop the factors is described in Appendix A.

Table 4-. Updated Water Demand Factors
Land Use Category
Updated Potable Water Use Factors ( a)
City- wide River Islands
Low Density Residential 330 gpd/ du 315 gpd/ du
Medium Density Residential 250 gpd/ du 235 gpd/ du
High Density Residential 170 gpd/ du
Commercial 1, 550 gpd/ ac
Industrial 1, 200 gpd/ ac
Parks / Public Landscaping 2, 450 gpd/ ac
Schools / Institutional 1, 250 gpd/ ac
The resulting calculation is shown in Table 4-5. Potable water demand associated with planned development also includes 5% non-revenue water.

4. 2.3 Total Projected Potable Water Demand
Table 4-5 summarizes the City' s projected water demand and by development area in five- year increments between 2025 and buildout, based on the City' s projected developments shown in Table 2-1. eki environment
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December 2024
EKI C20049. 01
Section 4 2024 WSMP Amendment
EXISTING AND FUTURE WATER DEMANDS City of Lathrop
The total projected potable water demand also includes non -revenue water, which is estimated to be 5% of demands. 3The City anticipates that total potable water demand will be 12, 405 AFY by 2045. 3 Non - revenue water is assumed to be 5% consistent with the 2019 WSMP. Actual non -revenue water observed between 2017 and 2022 appears to be unusually low and included negative values, likely due to meter errors. ek, environment
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December 2024
EKI C20049. 01
Section 4

EXISTING AND FUTURE WATER DEMANDS
2024 WSMP Amendment
City of Lathrop
Table 4-5. Projected Water Demand by Development Area
Updated Projected New
Land Use Designation
Demand Factor 2025 2030
Central Lathrop - Phase 1
Water Demand ( AFY) (a)
2035 2040 Buildout
Low Density Residential 330 gpd/ du 0 185 282 282 282
High Density Residential 170 gpd/ du 0 47 87 110 110
Commercial 1, 550 gpd/ ac 23 128 128 128 253
New Central Lathrop Phase 1 Demand
Existing Central Lathrop Phase 1 Demand
23 223
359
223
497
223
520
223
734
223
Projected Central Lathrop Phase 1 Demand 246 583 720 744 957 Central Lathrop - Phase 2
Light Industrial / R&D Flex 1, 200 gpd/ ac 121 121 121 121 916 Parks 2, 450 gpd/ ac 0 0 0 0 14
New Central Lathrop Phase 2 Demand
Existing Central Lathrop Phase 2 Demand
121
0 121
0 121
0 121
0 930
0 Projected Central Lathrop Phase 2 Demand 121 121 121 121 930 Mossdale Landing
Low Density Residential 330 gpd/ du 0 0 0 0 24
Commercial 1, 550 gpd/ ac 8 11 11 11 11
Schools 1, 250 gpd/ ac 0 0 0 0 23
New Mossdale Landing Demand
Existing Mossdale Landing Demand
8 660
11 660
11 660
11 660
58 660
Projected Mossdale Landing Demand 668 671 671 671 718
Mossdale Landing East
Low Density Residential 330 gpd/ du 0 14 14 14 14
High Density Residential 170 gpd/ du 0 0 0 0 16
Commercial 1, 550 gpd/ ac 0 12 12 12 12
New Mossdale Land ng East Demand
Existing Mossdale Landing East Demand
0 204
26 204
26 204
26 204
42 204
Projected Mossdale Landing East Demand 204 229 229 229 245 Mossdale Landing South
Medium Density Residential 250 gpd/ du 24 24 24 24 24
Commercial 1, 550 gpd/ ac 0 0 14 14 43
Parks 2, 450 gpd/ ac 0 11 11 11 11
New Mossdale Landing South Demand
Existing Mossdale Landing South Demand
24 49
35 49
49 49
49 49
78 49
Projected Mossdale Landing South Demand 73 85 100 101 127 Mossdale Landing West
Low Density Residential 330 gpd/ du 0 0 306 306 306
New Mossdale Landing West Demand
Existing Mossdale Landing West Demand
0 0
0 0
306
0 306
0 306
0 Projected Mossdale Landing West Demand 0 0 306 306 306 River Islands
Low Density Residential 315 gpd/ du 271 701 1,31 1, 560 1, 560 Medium Density Residential 235 gpd/ du 178 427 675 924 924 High Density Residential 170 gpd/ du 0 266 531 797 797
Commercial 1, 550 gpd/ ac 0 166 332 499 499
Schools 1, 250 gpd/ ac 16 23 31 38 38
Parks and Landscaping Parcels 2, 450 gpd/ ac 9 27 44 62 62 New River Islands Demand
Existing River Islands Demand
473
851
1, 609
851
2, 745
851
3, 880
851
3, 880
851
Projected River Islands Demand 1, 324 2, 460 3, 596 4, 731 4, 731 eki environment
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December 2024
EKI C20049. 01
Section 4

EXISTING AND FUTURE WATER DEMANDS
2024 WSMP Amendment
City of Lathrop
Table 4- 5 (Cont.). Projected Water Demand by Development Area Updated Projected New Water Demand (AFY) (a)
Land Use Designation
Demand Factor
2025 2030 2035 2040 Buildout
South Lathrop
Light Industrial / R&D Flex 1, 200 gpd/ ac 0 90 90 90 134 Office Commercial 1, 550 gpd/ ac 0 15 15 15 17
New South Lathrop Demand
Existing South Lathrop Demand
0 25
105
25 105
25 105
25 151
25 Projected South Lathrop Demand 25 130 130 130 176
Lathrop Gateway
Light Industrial / R&D Flex 1, 200 gpd/ ac 0 89 89 111 111 Office Commercial 1, 550 gpd/ ac 0 89 89 109 109
Open Space 2, 450 gpd/ ac 0 7 7 11 11
Public Landscaping 2, 450 gpd/ ac 0 7 7 31 31
New Lathrop Gateway Demand
Existing Lathrop Gateway Demand
0 27
191
27 191
27 262
27 262
27 Projected Lathrop Gateway Demand 27 218 218 290 290
Crossroads
Industrial 1, 200 gpd/ ac 0 31 31 31 31
Commercial 1, 550 gpd/ ac 0 3 3 3 3
New Crossroads Demand
Existing Crossroads Demand
0 582
34 582
34 582
34 582
34 582
Projected Crossroads Demand 582 616 616 616 616
Historic Lathrop and Other Development Areas
Low Density Residential 330 gpd/ du 0 4 7 9 19
Medium Density Residential 250 gpd/ du 8 15 22 29 61
High Density Residential 170 gpd/ du 0 0 0 0 9
Commercial 1, 550 gpd/ ac 38 62 62 62 76
Industrial 1, 200 gpd/ ac 24 24 24 24 56
New Historic Lathrop / Other Demand
Existing Historic Lathrop / Other Demand
70 2, 437
105
2, 437
115
2, 437
124
2, 437
222
2, 437
Projected Historic Lathrop / Other Demand 2, 507 2, 542 2, 552 2, 561 2, 659 Sharpe Army Depot ( b)
AAFES 16 16 16 16 16
California Military Department 41 41 41 41 41
New Sharpe Army Depot Demand
Existing Sharpe Army Depot Demand
56 56
3 3
56 3
56 3
56 3
Projected Sharpe Army Depot Demand 59 59 59 59 59
Notes:
a) Projected residential water demand calculated as the total number of projected residential dwelling units ( Table 2-1) multiplied by the applicable water demand factor (Table 4-4). Projected non- residential water demand calculated as the total projected acreage (Table 2- 1) multiplied by the applicable water demand factor ( Table 4-). b) Water demand for the AAFES facility is estimated using historical metered consumption. Water demand for the California Military Department based on projections provided on 12 April 2018. c) Totals may not add exactly due to rounding.
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December 2024
EKI C20049. 01
Section 4 2024 WSMP Amendment
EXISTING AND FUTURE WATER DEMANDS City of Lathrop

4. 3 Peak Demands
EKI reviewed the City' s historical water production data to identify the peaking factors relative to average day demand ( ADD) that best estimate maximum month demand ( MMD), maximum day demand ( MDD), and peak hour demand ( PHD). To determine the MMD peaking factor, EKI evaluated the City' s monthly production data. Monthly production between January 2005 and December 2022 is shown on Figure 4-6.

Citywide monthly production exhibits seasonal trends with peak flows occurring during the summer months, when irrigation demands are high, and lower flows in winter months, when there are minimal irrigation demands. Figure 4-6 shows that peak flows declined significantly from previous years in the summer of 2015, after the SWRCB imposed mandatory restrictions. Peak flows began to rebound in summer of 2016 and continued as of December 2022, as the restrictions were lifted.

EKI reviewed data collected from the City' sSCADA system to determine the MDD and PHD peaking factors.

The City provided flow data from each of its supply sources ( LAWTF and SSJID Turnouts 1 and 2) and elevation data from each of its storage tanks in 30 -minute increments between June 2013 and August 2016 and the flow data in 5 -minutes increments between 1 January 2017 to 20 July 2022. Using this data, EKI calculated Citywide hourly production by summing the flow into the system from each source and the change in storage in each tank.

Table 4-6 lists the historical ADDs and MMDs between 2005 and 2021 and the MDD and PHD between 2013 and 2021. 4Also, listed in Table 4- 6 are the calculated peaking factors in each year.

Based on the recent water use pattern, EKI updated the peaking factors to estimate existing and future peak flows, as follows, based on the average factors between 2013 and 2022:

MMD Peaking Factor = 1. 5 x ADD
MDD Peaking Factor = 1. 7 x ADD
PHD Peaking Factor = 2. 6 x ADD
The application of these peaking factors to assess system capacity and performance is described in Section 6.
4 2022 ADD was calculated separately based on annual water production data due to SCADA availability. ekienvironment water 4- 12
December 2024
EKI C20049. 01
Section 4 2024 WSMP Amendment
EXISTING AND FUTURE WATER DEMANDS City of Lathrop
Figure 4-6. City of Lathrop Monthly Water Production
8, 000,00
7, 000,00
6, 000,00
a
5, 000,00
a

0. c 4, 000,00
IT
3, 000,00
2, 000,00
1, 000,00
o
L. r1 lD N o0 O1 O N M Tr u1 IX) r-- CO O1 O .- 1 N m
O O O O O a - I c -I a- I - ti ,— I ,— I ,— I a - I N N N N

C C C C C C C C C C C C C C C C C C C
CO CD co Co ro CD CO ca CO CO co CO co CO co co CO CO CO 4,— Potable Water Production 12 -Month Running Ave. Water Production eki environment
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December 2024
EKI C20049. 01
Section 4

EXISTING AND FUTURE WATER DEMANDS
2024 WSMP Amendment
City of Lathrop
Table 4-6. Historical Potable Water Peak Demands and Peaking Factors Updated
2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 Avg. Peaking Factor
a)
Demands ( MGD)
ADD ( b) (c) 4. 18 3. 58 3. 08 3. 19 3. 73 4. 06 4. 06 4. 71 4. 73 4. 71 3. 79 MMD (b)( c) 6. 04 5. 45 3. 94 4. 81 5.2 5. 99 6. 91 6.9 6. 48 5. 65 MDD (d)( e) 6. 80 6. 49 4. 66 5.3 6. 32 6. 85 8. 08 7. 19 7. 39 6. 59 PHD ( e)( f) 14.7 9. 05 7. 91 8. 75 8.0 10. 0 10. 9. 83 Peaking Factors (-)
MMD to ADD 1. 44 1. 52 1. 28 1. 51 1. 48 1. 47 1. 47 1. 41 1. 38 1. 50 1. 5 MDD to ADD 1. 63 1. 82 1. 51 1. 73 1. 69 1. 69 1. 71 1. 52 1. 57 1. 65 1. 7 PHD to ADD 3.9 2. 53 2. 57 2. 74 2. 36 2. 12 2. 14 2. 55 2. 6 Notes:
a) IWRMP Amendment peaking factors selected based on averages rounded up to the nearest tenth. b) ADD and MMD are based on the monthly production data provided by the City. c) ADD for 2022 was calculated based on the City' s provided annual water production from groundwater wells and SSJID turnout. MDD, MMD, and PHD were derived from the SCADA data recorded from January 1st through July 20th. Taking into consideration that the City' s historical MMD tends to occur between June and August ( Note (e)), and considering the data available to EKI, this analysis assumed that MMD occurred in June 2022. Subsequently, MDD was observed on June 29, 2022. d) MDD and PHD calculated from the City provided SCADA flow data from each of its supply sources ( LAWTF, Well 21 WTF, and the SSJID Turnout L1) and elevation data from each of its storage tanks in 30 -minute increments between June 2013 and August 2016 and 5 -minute increments between January 2017 to December 2021. For the periods of 2019 and 2020, SSJID flow reports were used due to lack of SCADA data in the temporary SSJID turnout. The 2018 SCADA data appeared to be erroneous and not included in the peaking factor analysis.

MDDs for 2013 to 2016 were observed on 11 July 2013, 13 June 2014, 23 June 2015, and 27 July 2016 respectively. MDD for 2017 and 2021 were observed on 1 August 2017 and July 2021, respectively.

PHD for 2013 to 2016, 2017, and 2021 is equal to the peak hourly demand during the maximum demand days listed in Note ( d). PHD factors for 2019 and 2020 were not able to be calculated due to the lack of SCADA data in the temporary SSJID turnout.
e)
f)
eki environment
water 4- 14
December 2024
EKI C20049. 01
Section 5 2024 WSMP Amendment
WATER SYSTEM SUPPLIES City of Lathrop
5 WATER SYSTEM SUPPLIES
The City obtains water from both imported surface water and local groundwater sources. The City receives Stanislaus River water through the SCWSP that is operated by the SSJID and discussed' in Section 5. 1. The City also owns and operates five groundwater production wells, discussed in Section 5. 2. The City' ssurface water and groundwater production over the period 2017 through 2022 is summarized in Table 5- 1 and Figure 5-1. Due to the relatively high cost of SCWSP water, the City has historically relied upon its groundwater wells as the primary source of supply.

The City' s annual water production increased from 4, 168 AF in 2017 to 5, 277 AF in 2022 as a result of development growth and rebound from the 2014-017 drought. Surface water production ( i.e., SCWSP purchases) steadily increased from 921 AF in 2017 to 3, 866 AF in 2022. At the same time, the City reduced its groundwater production from 3, 247 AF or 78% of its total supplies in 2017 to 1, 411 or 27% in 2022 due to groundwater quality concerns. The City' s current and potential future water supplies are further described in the following sections.

Table 5-1. Current and Historical Potable Water Supply
Annual Production ( acre- feet) (a)
Potable Water Source 2017 2018 2019 2020 2021 2022
Surface Water
SCWSP 921 1, 946 2, 892 3, 429 2, 401 3, 866
Percentage of Supply 22% 43% 65% 63% 45% 73%
Groundwater Production
Production Wells ( b) 3, 247 2, 605 1, 560 2, 055 2, 884 1, 411 Percentage of Supply 78% 57% 35% 37% 55% 27%
Total 4, 168 4, 551 4,52 5, 485 5, 285 5, 277
Notes:
a) Production data from 2017 to 2020 were obtained from the 2020 UWMP and others were provided by the City in April and May 2022 and May 2023. eki environment
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December 2024
EKI C20049. 01
Section 5

WATER SYSTEM SUPPLIES
2024 WSMP Amendment
City of Lathrop
Annual
Potable
Water
Supply (
feet) acre6, 000
5, 000
4, 000
3, 000
2, 000
1, 000
0 Figure 5-1. Current and Historical Potable Water Supply 2016 2017 2018 2019 2020 2021 2022
Year
O Surface Water 0 Groundwater Production

5. 1 Imported Surface Water
The City purchases imported surface water from SSJID through the SCWSP, which supplies Stanislaus River water. Information related to the contractual entitlements and treatment processes for the surface water source is detailed further in the City' s 2020 UWMP ( EKI, 2021a). The reliability of this water supply is discussed in Section 5.1.

The SCWSP is a partnership between the City, SSJID, and the cities of Manteca, Tracy, and Escalon. 5The SCWSP water supply is based on SSJID' ssenior, pre -1914 appropriative water rights to the Stanislaus River, a tributary of the San Joaquin River, coupled with a 1988 agreement with the United States Bureau of Reclamation ( USBR) to store water in the New Melones Reservoir. 6The SCWSP was planned to be implemented in two phases. Phase I was completed in 2005 with a total capacity of 31, 500 AFY. Per SSJID' s 2020 UWMP, Phase II is anticipated to be completed before 2040 and will increase the SCWSP' s capacity
to approximately 43, 090 AFY ( EKI, 2021b).

The 1995 Water Supply Development Agreement between the City and SSJID provided the City with a Phase I allocation of 8, 007 AFY and a total allocation of 11, 791 AFY after completion of Phase II. In August 5 The City of Escalon is under contract to purchase water from the SCWSP but has not yet constructed a pipeline to convey the water to its facilities.
6 This agreement recognized and protected SSJID' s senior water rights on the Stanislaus River, because those rights could potentially be affected by the USBR' s
operation of the New Melones Reservoir as part of the Central Valley Project. The agreement entitles the senior water rights holders, SSJID and Oakdale Irrigation District, to access up to 600, 00 AFY of water from New Melones Reservoir in years in which inflow to the reservoir exceeds 600, 00 AF.

SSJID' sshare of this allotment is 300, 00 AF. In years in which inflow does not meet this threshold, the entitlement is reduced based on a pre -determined formula.
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December 2024
EKI C20049. 01
Section 5 2024 WSMP Amendment
WATER SYSTEM SUPPLIES City of Lathrop
2013, the City sold 1,20 AFY of SCWSP water to the City of Tracy.' Therefore, the City' sremaining SSJID allocation is 6, 887 AFY for Phase I and a total of 10, 671 AFY after completion of Phase II.

The SCWSP transmission system has been designed to deliver seasonal peak flows to each City through a transmission pipeline to turnout facilities. The transmission system is currently operated by gravity flow.

In Phase II, a treated water pump station will be installed at the DGWTP to deliver pumped flows. The SCWSP delivers flows to Lathrop at two locations:

The turnout at Lathrop Road, east of McKinley Avenue ( Lathrop SSJID Turnout 1); and The turnout at Stewart Road, west of Manthey Road ( Lathrop SSJID Turnout 2).

The City' sSSJID Turnouts 1 and 2 supply Lathrop' s allocated Phase 1 peak flows. Lathrop SSJID Turnout 2 will be expanded in the future to deliver Lathrop' sPhase II peak allocation. The planned capacity of each Lathrop turnout according to the SSJID SCWSP Basis of Design Report ( Black & Veatch, 2002), modified to account for the Tracy sale, is listed in Table 5-2.

Table 5-2. Lathrop SSJID Turnouts — Basis of Design
Phase 1 Flows Phase 2 Flows
Cumulative)

AFY) ( MGD) ( AFY) ( MGD)
Lathrop SSJID Design Rows
Contractual Allocation 8, 007 7. 1 11, 791 10. 5
Sale to City of Tracy ( b) 1,20 1. 0 1,20 1. 0
Remaining Allocation 6, 887 6. 1 10, 671 9. 5
Peaking Factors 2. 1 2. 0
Remaining Peak Flow 14, 462 12. 9 21, 342 19.

Lathrop Design Turnout Capacity
Lathrop SSJID Turnout 1 8, 401 7. 5 8, 401 7. 5
Lathrop SSJID Turnout 2 ( c) 6, 061 5. 4 12, 938 11. 6
Notes:
a) Source: South San Joaquin irrigation District South County Water Supply Program Basis of Design Report ( Black and Veatch, 2002).
b) The City sold 1,20 AFY ( 1 MGD) of its Phase 1 SSJID allocation to the City of Tracy in 2013. c) Turnout design flow based on SSJID SCWSP Basis of Design, less the sale to the City of Tracy.

Lathrop - Tracy Purchase, Sale and Amendment Agreement," dated 6 August 2013. eki environment
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December 2024
EKI C20049. 01
San Joaquin Valley
Tracy Subbasin
DWR #5- 022. 15)
113LUil
Highway
J City Limit
DWR Groundwater Basins
5- 22. 01 Eastern San Joaquin Subbasin
Q 5- 22. 15 Tracy Subbasin
Other ( Subbasin or Basin)
Infrastructure Features
W Production Well
Water Treatment Facility
o SSJID Turnout
Abbreviations
CASGEM = California Statewide Groundwater Elevation
Monitoring Program
DWR = California Department of Water Resources
LAWfF = Louise Avenue Water Treatment Facility
SSJID = South San Joaquin Irrigation District
WTF = Water Treatment Facility
Notes

1. All locations are approximate.

Sources

1. DWR groundwater basins are based on the boundaries
defined in California' s Groundwater, Bulletin 118- 2016 Update.

2. Basemap: Esri' s World Reference and World Terrain
Base, accessed 16 January 2024.

N
0 4, 000 8, 000
Water Supply Infrastructure
Wet. rSystem Mester Plen Amendment
Cay of Lathrop
Lathrop, CA
ek
I environment DecemberC200490101
water Figure 5- 2
Section 5 2024 WSMP Amendment
WATER SYSTEM SUPPLIES City of Lathrop

5. 2 Groundwater
The City only overlies the Tracy Groundwater Subbasin ( Department of Water Resources [ DWR] 5- 22. 15) of the San Joaquin Valley Groundwater Basin ( DWR 5-22), as a result of DWR' s approval on the Basin Boundary Modification Request, dated February 11, 2019. The Basin Boundary Modification incorporated all of the City in the Tracy Subbasin and removed the City from the Eastern San Joaquin Groundwater Subbasin ( DWR 5- 22. 01). The groundwater basin and subbasin areas underlying the City and the locations of the City' s production wells are shown on Figure 5-3.

The Tracy Subbasin is designated as a Medium priority basin by DWR and is therefore subject to the Sustainable Groundwater Management Act ( SGMA). In the Tracy Subbasin, six Groundwater Sustainability Agencies ( GSAs), including Byron -Bethany Irrigation District ( BBID), Banta- Carbona Irrigation District BCID), the City of Tracy, the City of Lathrop, San Joaquin County, and Stewart Tract, worked cooperatively and were awarded a DWR Grant to develop the Tracy Groundwater Sustainability Plan ( GSP). The GSP for the Tracy Subbasin was completed in November 2021 and will be updated every 5 years as additional information becomes available. The chapters of the GSP can be found on the Tracy Subbasin website:
https:// tracysubbasin. org/ gsp- chapters/.

As discussed in Section 3. 1., the City currently operates five municipal groundwater supply wells: Wells 6, 7, 8, 9, and 10. Well 9 is currently offline due to water quality issues. Groundwater from Wells 6, 7, 8, 9 when operating), and 10 is treated to remove arsenic at the LAWTF, which came online in 2012. The City currently has no plans to install additional groundwater wells or expand its groundwater production.

However, the City is actively exploring treatment options to meet emerging water quality regulations which will facilitate bringing Well 9 back online, as well as groundwater - surface water conjunctive use and/ or Aquifer Storage and Recovery ( ASR).

Information regarding the City' sgroundwater production wells are summarized in Table 3- 1 and Table 5-3.

The combined maximum pumping capacity of the City' s
wells ( including Well 9) is 7, 250 gpm, which is
higher than the treatment capacity of the LAWTF ( 6, 250 gpm). However, for the purposes of this evaluation, it is assumed that Wells 6, 7, 8, and 10 are pumped at 50% of their maximum capacity on an annual basis. Given this supply assumption, the City' scurrent annual groundwater supply capacity is equivalent to approximately 4, 720 AFY. As described in Section 5. 6, an annual pumping of approximately 500 AFY from WeII 9 is assumed to be necessary to hydraulically control PFAS in groundwater sourcing from the south of the City' s
wells. As such, it is assumed that future reactivation of Well 9 with PFAS treatment will add another 500 AFY to the City' s annual groundwater supply yield for a total of 5, 220 AFY.

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Table 5-3. Groundwater Production Well Capacities and Annual Yields Groundwater Wells (a)
Existing Maximum Pumping Capacity
Measured Flow Rate Estimated Annual Yield ( b)
gpm) ( AFY)
Well 6 1, 650 1, 330
Well 7 1, 400 1,30
Well 8 1,00 890
Well 10 1, 700 1, 370
Total Exiting Groundwater Capacity 5, 850 4, 720
Well 9 1, 400 500 ( c)
Total Future Groundwater Capacity 7, 250 (d) 5, 220
Notes:
a) Well 21, currently inactive, is not listed above. The City currently has no plans or designs underway to bring it back on- lie due to water quality issues associated with the well ( including PFAS issue). b) Assumes wells are operated at 50% maximum capacity on an annual basis except for Well 9. c) It is assumed that Well 9 will be operated in the future with an annual production rate of 500 AFY to control migration of groundwater with higher concentrations of PFAS. d) Maximum capacity of LAWTF is 6, 250 gpm. Estimated annual yield assumes that annual yield of Wells 6- 10 is not limited by LAWTF capacity on an annual basis.

5. 3 Total Water Supplies
The City' s projected potable water supply entitlements are summarized in Table 5-4 and Figure 5-3. The values presented in this table reflect the City' s contractual allotments from the SCWSP and the City' s current and planned future groundwater production. The actual availability of these water supplies depends on several factors and is discussed in detail in Section 5. ek, environment
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Table 5-4. Current and Projected Potable Water Supply Entitlements Potable Water Water Right or
Source Contract Reliability 2023 2025 2030 2035 2040 2045 Current Supplies
SCWSP SSJID Contract ( a) Pre -1914 6, 887 6, 887 6, 887 6, 887 6, 887 6, 887 Groundwater b) 4, 720 4, 720 4, 720 4, 720 4, 720 4, 720 Anticipated Future Supplies
SCWSP SSJID Contract ( c) Pre -1914 3, 784 3, 784
Groundwater d) 500 500 500 500 500
Total 11, 607 12,07 12,07 12,07 15, 891 15, 891
Notes:
a) The City' stotal Phase I allotment of SCWSP water, following the 2013 sale to the City of Tracy of 1,20 AFY, is 6, 887 AFY.
b) Reflects the City' s firm groundwater capacity, without Well 9. c) The City' s total Phase I & II allotment of SCWSP water, following the 2013 sale to the City of Tracy, is 10, 671 AFY.
d) it is anticipated that Well 9 will be brought online in 2025 with completion of future PFAS treatment with an annual production rate of 500 AFY.
18, 000
16, 000
14, 000
cu
12, 000
to
J10000
a`, 8, 000
co
To 6, 000
a 4, 000
2, 000
0 Figure 5-3. Current and Projected Potable Water Supply Entitlements 2023 2025 2030
Year
2035 2040 2045
Groundwater ( Future) SCWSP ( Phase II) Groundwater ( Current) D SCWSP ( Phase I) eki environment
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5. 4 Water Supply Reliability
This section describes the constraints on the City' s potable water supply sources, as well as the management strategies that the City has employed or will employ to address these constraints. This section also provides an estimate of the supply volumes available to the City and the corresponding supply and demand reliability assessments in normal years, single dry years, and multiple dry year periods.

5. 4.1 Projected Supply Reliability by Source
The following sections describe the projected reliability of each of the City' s water supplies, including the water supply from SCWSP and groundwater production.

5. 4.1. Surface Water Supply Reliability
The City has access to 6, 887 AFY of Stanislaus River water provided by the SCWSP ( see Section 5. 1.).

Phase II of the SCWSP is anticipated to increase the City' s allocation to 10, 671 AFY by 2040. Due to the seniority of the water rights underlying the SCWSP, SSJID' s pre -1914 appropriative rights to Stanislaus
River water, the City has historically assigned a high reliability to SCWSP water.

However, the future reliability of the City' sfull SCWSP allocation is potentially uncertain due to recent planning efforts by the SWRCB. In December 2018, the SWRCB adopted amendments to the Water Quality Control Plan for the San Francisco Bay/ Sacramento- San Joaquin Delta Estuary ( Bay -Delta Plan Amendment). The adopted changes include increasing flows on three San Joaquin River tributaries ( the Stanislaus, Merced, and Tuolumne Rivers) and the Bay -Delta, with a range of 30% to 50% depending on
biological conditions from February to June in every year type. The SWRCB also approved a framework for accepting voluntary agreements to pursue a combination of flow and " non -flow" measures that improve conditions for fish and wildlife where allowances for reduced river flows may be developed.

Oakdale Irrigation District ( OID) and SSJID began voluntary negotiations on the Stanislaus River prior to adoption of the Bay -Delta Plan Amendment ( OID and SSJID, 2019). On 29 March 2022, a Memorandum of Understanding ( MOU) was signed by the SWRCB and multiple water supply agencies to work to settle litigation over endangered species protections in the Sacramento - San Joaquin Delta. The MOU outlines broad areas of agreement and anticipates the need for further negotiations to develop detailed implementation agreements. OID and SSJID are not among the signatories of the MOU, however, additional parties have been added to the MOU as agreements move forward in more watersheds.

The Lower San Joaquin River flow and southern Sacramento - San Joaquin Delta salinity updates to the Bay - Delta Plan Amendment are not self -implementing and require addition actions by the State ( SWRCB, 2022). Uncertainties including difficult legal process ahead and considerations of senior water rights are challenging the implementation of the Bay -Delta Plan Amendment, which included significant changes and could result in significant surface water cutbacks. SSJID presented its water reliability analysis assuming that the Bay -Delta Plan Amendment will not be implemented in its 2020 UWMP ( EKI, 2020b).

As a retail agency, the City relies on SSJID for the reliability projections. Consistent with SSJID' s approach,
this Water Service Reliability and Drought Risk Assessment section of the City' s 2020 UWMP presents results for the SCWSP water reliability assessment assuming that the Bay -Delta Plan Amendment will not be implemented.

SSJID anticipates that 100% of the contract volumes ( 31, 522 AFY during Phase I and 43, 090 AFY during Phase II) will be available to SCWSP participants in normal years. In single dry years, SSJID projects that SCWSP participants will receive 79% to 99% of their contract volumes based upon the analog of SSJID' s water supplies in 1977. In a five- year, multiple dry year scenario, SSJID projects that SCWSP participants will receive 79% to 99% of their contract volumes during the third and fourth dry years, while 100% of the eki environment
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contract volumes will be available in the remaining years. The multiple dry year supply reliability is based on the analog of SSJID' s water supplies over the period of 2012 through 2016.

Section 8(a) of the 1995 Water Supply Development Agreement stipulates that reductions in SCWSP deliveries shall be distributed pro -
allotment. Therefore, it is assumed
rata
that the
among
City' s
the
supply
SCWSP
availability
participants
will be
based
proportionate
upon each
to
participant' s
the SCWSP
supply availability presented in Table 5-. The City' s projected SSJID supply in normal years, single dry years, and multiple dry years is summarized in Table 5-6.

Table 5-. Projected SCWSP Supply Availability
Estimated Supply and Demand
Year Type
2025 2030 2035
AFY)
2040 2045
Average Year 31, 522 31, 522 31, 522 43, 090 43, 090
Single - Dry Year 26, 448 28, 962 31, 475 33, 988 36, 501 Multiple Dry Years - First Year 31, 522 31, 522 31, 522 43, 090 43, 090 Multiple Dry Years - Second Year 31, 522 31, 522 31, 522 43, 090 43, 090 Multiple Dry Years - Third Year 26, 448 28, 962 31, 475 33, 988 36, 501 Multiple Dry Years - Fourth Year 26, 448 28, 962 31, 475 33, 988 36, 501 Multiple Dry Years - Fifth Year 31, 522 31, 522 31, 522 43, 090 43, 090 Notes:
a) Source: City of Lathrop 2020 Urban Water Management Plan Table 7-1.

Table 5-6. Projected SCWSP Supply Available to City of Lathrop Year Type
2025
Estimated Supply and Demand ( AFY)
2030 2035 2040 2045
Average Year 6, 887 6, 887 6, 887 10, 761 10, 761
Single -Dry Year 5, 778 6, 328 6, 877 8, 417 9, 039
Multiple Dry Years - First Year 6, 887 6, 887 6, 887 10, 761 10, 761 Multiple Dry Years - Second Year 6, 887 6, 887 6, 887 10, 761 10, 761 Multiple Dry Years - Third Year 5, 778 6, 328 6, 877 8, 417 9, 039 Multiple Dry Years - Fourth Year 5, 778 6, 328 6, 877 8, 417 9, 039 Multiple Dry Years - Fifth Year 6, 887 6, 887 6, 887 10, 761 10, 761 Notes:
a) Source: City of Lathrop 2020 Urban Water Management Plan Table 7-2. eki environment
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5. 4.1.2 Groundwater Supply Reliability
The City currently relies upon groundwater production from its five active wells ( Wells 6 through 10) to meet its demands. The City' s ability to utilize its existing groundwater wells within the Tracy Subbasin is not likely be affected by SGMA8. It is anticipated that the future GSP will not require the City to limit groundwater production to maintain a sustainable groundwater budget. Based on the available information, it is anticipated that 100% of the City' scurrent estimated groundwater yield is available for the planning horizon of this Plan.

Groundwater production has historically been constrained by the City' s well production and treatment
capacity, as well as by the groundwater quality. Considering the current water quality constraints discussed below, the City is anticipating that Well 9 will remain offline until 2025 when PFAS treatment is added to the LAWTF as described in Section 5. 6.2. The groundwater supplies from Wells 6 through 10 are expected to be 100% reliable and available during all year types at the volumes shown in Table 5-3.

5. 4.1.3 Groundwater Quality
One of the biggest threats to the City' s ability to use groundwater to meet potable water demands is water quality. The primary water quality concerns in the City' s groundwater are arsenic, manganese, uranium, total dissolved solids ( TDS), groundwater contamination from industrial processes, and per- and polyfluoroalkyl substances ( PFAS).

5. 4.1.Arsenic and Uranium
As discussed in Section 5. 2.3., the City' s groundwater supplies have been limited by groundwater quality constraints. Wells 6 through 10 are currently treated for arsenic at LAWTF to reduce concentrations below the maximum contaminant level ( MCL) of 0.10 milligrams per liter (mg/ L). The City' sinactive Well 21 also experienced elevated concentrations of arsenic and uranium and is assumed to remain inactive in the future.

The presence of arsenic and uranium in groundwater underlying the City impacts the reliability of the City' s groundwater supply. Expansion of groundwater production in the future is limited by the costs associated with treatment and the availability of adequate supplies to conduct blending.

5. 4.1. Total Dissolved Solids
The City' s groundwater supply reliability is also impacted by the migration of groundwater with TDS concentrations in excess of the secondary MCL of 500 mg/ L. Wells 6 through 10 are located immediately east of groundwater with high TDS concentrations, based on water quality data from City wells and sampling and analysis data from both shallow and deep monitoring wells collected by private entities ( SGI, 2008). Previous studies have indicated that TDS concentrations may be higher in the vicinity of Well 21 than in Wells 6 through 10. In September 2014, TDS concentrations in WeII 9 and Well 10 ranged from 270 mg/ Lto 310 mg/ L (UNICO Engineering, 2015). 9During the same sampling event, concentrations of 8 The final Tracy Subbasin GSP anticipated an increasing groundwater production from 7, 020 AFY in 2020 to 8, 483 AFY in buildout, or beyond 2040. (GEI, 2021).
9 These values are generally confirmed by the City' s Consumer Confidence Reports for 2014 and 2015, where TDS concentrations in groundwater ranged from 280 mg/ Lto 387 mg/ L. Since WeII 21 was inactive during this period, these values are representative of water quality within Wells 6 through 10. ekienvironment water 5- 10
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TDS within Well 21 ranged from 630 mg/ Lto 660 mg/ L. 10 The City has historically investigated the option of drilling a new wellfield near Well 21 and determined that it would not be feasible due to the potential for expanded pumping to induce the migration of high TDS water.

5. 4.1.6 Industrial Contamination
Groundwater contamination has been identified at several locations in the City due to industrial processes. Contamination plumes are associated with pollution from Sharpe Army Depot and the former Occidental Chemical Corporation (OCC) site."
Contamination of groundwater at the Sharpe Army Depot consists primarily of trichloroethene, tetrachloroethene, and cis- 1,2- dichloroethene. The plume is located at depths of approximately 50 to 150 feet below ground surface ( ft bgs). Due to concerns of potential contamination from the plume, the City abandoned Well 5 and constructed Well 10 as a replacement well. Three groundwater extraction and treatment systems located at Sharpe Army Depot are used to treat existing groundwater contamination RBF, 2009).

The OCC plume consists primarily of the pesticides 1, 2- dibromo- 3- chloropropane ( DBCP) and ethylene dibromide ( EDB), and the chemical solvent sulfolane. The OCC has been conducting investigation and remediation activities at the site since 1979, and a groundwater remedial system has been in place since 1982. The groundwater remedial system consists of extraction and injection wells as well as granular activated carbon and aeration treatment. Treated water is then re - injected into the confined aquifer beneath the Corcoran Clay layer, which is located between 230 ft bgs and 300 ft bgs.

To help prevent a sulfolane containment plume originating from the former OCC site from impacting the City' s groundwater supply, the City temporarily reduced its groundwater production and significantly limited groundwater production between 2018 and 2020. Efforts to improve the OCC groundwater extraction and treatment system were completed in March 2020. The City restarted Wells 6, 7, 8, and 10 and the LAWTF beginning in April of 2020. And the City has been continuously monitoring for sulfolane in its groundwater wells.

5. 4.1.7 Nitrate
Nitrate concentrations detected at Well 10 had historically shown increasing trends in 2020. During April and November 2020, nitrate ( as nitrogen) at WeII 10 was detected at 8. 1 mg/ Land 7. 5 mg/ L, respectively, approaching the MCL of 10 mg/ L. Since then, in response to this issue, the City has been closely monitoring for nitrate in WeII 10 at least once per quarter and evaluating the possible contaminant source. From June 2021 to September 2023, the monitoring results for WeII 10 showed the nitrate concentrations decreased to 1. 4 mg/ L — 4. 9 mg/ L, above the SCWRCB required reporting level of 0. 4 mg/ L but significantly lower than the MCL.
io Samples were also collected in two private wells in the vicinity of WeII 21. Concentrations of TDS in these wells ranged from 500 mg/ Lto 570 mg/ L.
11 The OCC site is now owned by J. R. Simplot.
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5. 4.1.8 Per- and Polyfluoroalkyl Substances ( PFAS)
PFAS is a group of emerging man-ade contaminants that were used in firefighting foam, protective coatings, and stain and water- resistant products until the 2000s. The current regulatory setting for PFAS is as follows:

The SWRCB Division of Drinking Water ( DDW) established drinking water Notification Levels ( NLs) and Response Levels ( RLs) for PFOA and PFOS12. Under the authority of Health and Safety Code section 116400, detections above the NL require agencies to notify the governing body for the areas where the water has been served within 30 days of receiving verified test results. If the RL is exceeded in drinking water provided to consumers, DDW recommends that the water agency remove the water source from service or provide treatment.

On March 14, 2023, the U. S. Environmental Protection Agency ( EPA) proposed federal MCLs for six PFAS compounds at ( 1) 4. 0 ppt for PFOA, (2) 4. 0 ppt for PFOS, (3) and a Hazard Index of 1. 0 calculated based on the concentrations of erfluorononanoic acid ( PFNA), hexafluoropropylene oxide dimer acid ( HFPO- DA, commonly known as GenX Chemicals), perfluorohexane sulfonic acid PFHxS), and perfluorobutane sulfonic acid ( PFBS). 13 The proposed MCLs are anticipated to be promulgated in early 2024 and effective in early 2027 ( U. S. EPA, 2023).

In response to the EPA' s Third Unregulated Contaminant Monitoring Rule ( UCMR3), the City of Lathrop sampled its supply sources for a suite of contaminants including six PFAS in 2013 and 2014. PFOA and PFOS were detected in groundwater samples collected from City' s Well 21 in April and October 2013.

Samples of water were also collected at the LAWTF and at SSJID Turnout 1, but neither PFOA nor PFOS was detected above laboratory reporting limits in either source.

In April 2019, pursuant to section 116400, the State Water Resources Control Board Division of Drinking Water ( DDW) sent monitoring orders to more than 200 public water systems across the state including Lathrop to test for PFAS. In its April 2019 Order, DDW ordered the City to collect and analyze samples for PFOA and PFOS from groundwater collected at Wells 9 and 10 because Wells 9 and 10 are within a one - mile radius of Well 21. In response to DDW' s 2019 monitoring order, Lathrop analyzed groundwater samples collected from Well 9 and Well 10 in May, June, and July 2019 and every quarter thereafter. The City also voluntarily began collecting groundwater samples from Wells 6, 7, and 8 in 2019. The City is currently required by DDW to collect and analyze samples for PFOA and PFOS from groundwater collected at each of its wells on a quarterly basis.

Sampling results showed that PFOA and PFOS concentrations in groundwater from Well 9 exceeded both the NLs and RLs. The NLs for PFOS were also exceeded in one or more samples collected from Wells 6, 7, 8, and 10. PFOA concentrations in groundwater from Wells 6, 7, 8, and 10 were below reporting limits.

Based on these and historical sampling results, the City took Well 9 offline in 2019 so that the PFOA concentrations in the blended flow from remaining wells are below the RLs.

The City anticipates installing centralized PFAS treatment at the LAWTF to treat groundwater from all of its wells ( EKI 2020; Carollo Engineers, 2022). Detections of PFOS in groundwater collected from each of the City' swells have exceeded the proposed PFOS MCL; detections of PFOA and the mixture of PFNA, PFHxS, PFBS, and GenX compounds in Well 9 have also exceeded the proposed MCLs. In addition, recent The NLs were 5. 1 ng/ Lfor PFOA and 6. 5 ng/ Lfor PFOS. The RL was 10 ng/ Lfor PFOA and 40 ng/ Lfor PFOS. 13 The HI is described in more detail on the EPA' s PFAS Drinking Water Regulation page:
https:// www. epa. gov/ sdwa/ and- polyfluoroalkyl- substances- pfas. eki environment
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sampling results found an increase in PFAS concentrations in Well 9, particularly the doubling of the observed PFOS concentrations.

The abovementioned water quality issues impact the reliability of the City' s groundwater supply.

Expansion of groundwater production in the future is limited by the costs associated with treatment and the availability of adequate supplies to conduct blending. Given the above issues, the City is not currently pursuing development of any additional wells or increased groundwater production.

5. 4. 2 Projected Supply Reliability by Year Type
The City' s projected water supply reliability in normal years, single dry years, and multiple dry years is described in the following sections.

5. 4.2.1 Normal Years
The City' s projected water supplies in normal years are presented in Table 5-7 and Figure 5-4. In normal years, the City expects to receive 100% of its SCWSP supplies ( see Section 5.1.) and 100% of its groundwater supply ( see Section 5.1.2). The normal year supply reliability is based upon SSJID' s water supplies in 2020.

5. 4.2. Single Dry Year
The City' s projected water supplies in single dry years are presented in Table 5-8 and Figure 5-. In single dry years, the City expects to receive between 79% and 99% of its SCWSP supplies ( see Section 5.1.) and 100% of its groundwater supply. The single dry year supply reliability is based upon SSJID' s water supplies in 1977.

5. 4.2.3 Multiple Dry Years
The City' s projected water supplies in multiple dry years are presented in Table 5- 9 and Figure 5-6. In multiple dry years, the City expects to receive between 79% and 100% of its SCWSP supplies ( see Section 5.1.) and 100% of its groundwater supply. The multiple dry year supply reliability is based upon SSJID' s water supplies over the period 2012 through 2016. eki environment
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Table 5-7. Projected Potable Water Supply in Normal Years Supply Volume ( AFY)
Potable Water Source Reliability 2025 2030 2035 2040 2045 Current Sources
SSJID SCWSP Phase I 100% of Contract ( a) 6, 887 6, 887 6, 887 6, 887 6, 887 Groundwater 100% Reliable 4, 720 4, 720 4, 720 4, 720 4, 720 Current Sources 11, 607 11, 607 11, 607 11, 607 11, 607 Anticipated Future Sources
SSJID SCWSP Phase II 100% of Contract ( a) 3, 874 3, 874 Groundwater 100% Reliable 500 500 500 500 500
Current and Future Sources 12,07 12,07 12,07 15, 981 15, 981 Notes:
a) The projected normal year availability of SSJID SCWSP supplies is obtained from Table 7-4 of the City' s 2020 UWMP ( EKI, 2021a).
18, 000
16, 000
14, 000
a
12, 000
10, 000
8, 000
6, 000
4, 000
2, 000
0 2025
Figure 5-4. Projected Normal Year Potable Water Supply
2030 2035
Year
2040 2045
El SCWSP ( Phase 1) Groundwater (Current) SCWSP ( Phase 2) Groundwater ( Future) eki environment
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Table 5-8. Projected Potable Water Supply in Single Dry Years Supply Volume ( AFY)
Potable Water Source Reliability 2025 2030 2035 2040 2045 Current Sources
SSJID SCWSP Phase I 79%- 99% of Contract ( a) 5, 778 6, 328 6, 877 5, 387 5, 785 Groundwater 100% Reliable 4, 720 4, 720 4, 720 4, 720 4, 720 Current Sources 10, 498 11, 048 11, 597 10,07 10, 505
Anticipated Future Sources
SSJID SCWSP Phase II 79%- 99% of Contract ( a) 3, 030 3, 254 Groundwater 100% Reliable 500 500 500 500 500
Current and Future Sources 10, 998 11, 548 12, 097 13, 637 , 14, 259 Notes:
a) The projected single dry year availability of SSJID SCWSP supplies is obtained from Table 7- 5 of the City' s 2020 UWMP ( EKI, 2021a).

Annual
Water
Supply (
feet) acre16, 000
14, 000
12, 000
10, 000
8, 000
6, 000
4, 000
2, 000
0 2025
Figure 5-. Projected Single Dry Year Potable Water Supply 2030 2035 2040 2045
Year
SCWSP ( Phase 1) Groundwater ( Current) SCWSP ( Phase 2) Groundwater ( Future) eki environment
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Table 5-9. Projected Potable Water Supply in Multiple Dry Years Supply Volume ( AFY)
Potable Water Source Allocation 2025 2030 2035 2040 2045 Multiple Dry Years - First Year
Current Supplies
SCWSP Phase I 100% of Contract ( a) 6, 887 6, 887 6, 887 6, 887 6, 887 Groundwater 100% Reliable 4, 720 4, 720 4, 720 4, 720 4, 720 Current Sources ( First Year) 11, 607 11, 607 11, 607 11, 607 11, 607 Anticipated Future Supplies
SCWSP Phase II 100% of Contract ( a) 3, 874 3, 874
Groundwater 100% Reliable 500 500 500 500 500
Current and Future Sources ( First Year) 12,07 12,07 12,07 15, 981 15, 981 Multiple Dry Years - Second Year
Current Supplies
SCWSP Phase I 100% of Contract ( a) 6, 887 6, 887 6, 887 6, 887 6, 887 Groundwater 100% Reliable 4, 720 4, 720 4, 720 4, 720 4, 720 Current Sources ( Second Year) 11, 607 11, 607 11, 607 11, 607 11, 607 Anticipated Future Supplies
SCWSP Phase II 100% of Contract ( a) 3, 874 3, 874
Groundwater 100% Reliable 500 500 500 500 500
Current and Future Sources ( Second Year) 12,07 12,07 12,07 15, 981 15, 981 Multiple Dry Years - Third Year
Current Supplies
SCWSP Phase I 79%- 99% of Contract ( a) 5, 778 6, 328 6, 877 5, 387 5, 785 Groundwater 100% Reliable 4, 720 4, 720 4, 720 4, 720 4, 720 Current Sources ( Third Year) 10, 498 11, 048 11, 597 10,07 10, 505 Anticipated Future Supplies
SCWSP Phase II 79%- 99% of Contract ( a) 3, 030 3, 254
Groundwater 100% Reliable 500 500 500 500 500
Current and Future Sources ( Third Year) 10, 998 11, 548 12, 097 13, 637 14, 259 Multiple Dry Years - Fourth Year
Current Supplies
SCWSP Phase I 79%- 99% of Contract ( a) 5, 778 6, 328 6, 877 5, 387 5, 785 Groundwater 100% Reliable 4, 720 4, 720 4, 720 4, 720 4, 720 Current Sources ( Fourth Year) 10, 498 11, 048 11, 597 10,07 10, 505 Anticipated Future Supplies
SCWSP Phase II 79%- 99% of Contract ( a) 3, 030 3, 254
Groundwater 100% Reliable 500 500 500 500 500
Current and Future Sources ( Fourth Year) 10, 998 11, 548 12, 097 13, 637 14, 259 eki environment
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Table 5-9. (Continued)
Supply Volume ( AFY)
Potable Water Source Allocation 2025 2030 2035 2040 2045 Multiple Dry Years - Fifth Year
Current Supplies
SCWSP Phase I 100% of Contract ( a) 6, 887 6, 887 6, 887 6, 887 6, 887 Groundwater 100% Reliable 4, 720 4, 720 4, 720 4, 720 4, 720 Current Sources ( Fifth Year) 11, 607 11, 607 11, 607 11, 607 11, 607 Anticipated Future Supplies
SCWSP Phase II 100% of Contract ( a) 3, 874 3, 874
Groundwater 100% Reliable 500 500 500 500 500
Current and Future Sources ( Fifth Year) 12,07 12,07 12,07 15, 981 15, 981 Notes:
a) The projected availability of SSJID SCWSP supplies during multiple dry years is obtained from Table 7- 6 of the City' s 2020 UWMP ( EKI, 2021a).

Annual
Water
Supply (
feet) acre18, 000
16, 000
14, 000
12, 000
10, 000
8, 000
6, 000
4, 000
2, 000
0 Figure 5-6. Projected Multiple Dry Year Potable Water Supply d--
rr
2025 2030 2035
Year
2040 Buildout
SCWSP ( Phase I) Groundwater ( Current) SCWSP ( Phase II) Groundwater ( Future) ek, environment
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2024 WSMP Amendment
WATER SYSTEM SUPPLIES City of Lathrop

5. Supply and Demand Assessment
The City' s projected water demands are described in Section 4.2, the City' s projected water supplies are discussed in Section 5. 4, and the reliability of these supplies in normal years and dry years is described in Section 5.. The following sections compare the City' stotal water supplies to its projected demands.

5.1 City -Wide Supply and Demand by Year Type
The following sections compare the City' s total water supplies under each year type discussed in Section 5.3 — normal years, single dry years, and multiple dry years — to the City' s projected water demands through 2045.

5.1. Normal Years
As shown in Table 5- 10 and Figure 5-7, the City' scurrent water supplies are sufficient supplies to meet projected demands in normal years through 2040. Without planned water supply projects, the City would experience supply shortfalls up to 798 AFY ( 6%) in 2045. SCWSP Phase II and restart of WeII 9 with PFAS treatment will allow the City to have sufficient supplies to meet projected demands through 2045.

5.1.2 Single Dry Year
As shown in Table 5- 11 and Figure 5-8, the City is projected to have adequate supplies to meet projected demands in single dry years through 2035 with its current water supplies. Without planned projects, the projected single dry year supply shortfall in 2040 and 2045 would be 967 AFY (9%) and 1, 901 AFY ( 15%), respectively. Future planned SCWSP Phase II and restart of WeII 9 will allow the City to have sufficient supplies to meet projected demands in single dry years through 2045.

5.1.3 Multiple Dry Years
As shown in Table 5- 12 and Figure 5-9, the City is projected to have adequate supplies to meet projected demands in multiple dry years through 2035 with its current water supplies. Without planned projects, the projected supply shortfall in multiple dry years would range from 798 AFY ( 6%) during the first, second, and fifth dry year to 21, 901 AFY ( 15%) during the third and fourth dry year in 2045, respectively. Future planned SCWSP Phase II and restart of Well 9 will allow the City to have sufficient supplies to meet projected demands in multiple dry years through 2045.
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Section 5

WATER SYSTEM SUPPLIES
2024 WSMP Amendment
City of Lathrop
Table 5- 10. Projected Potable Supply vs. Demand for Normal Year Scenario Projected Potable Water Demand
Estimated
2025
6, 128
Supply
2030
8, 099
and Demand
2035
9, 782
AFY) (a)( b)
2040
11, 083
2045
12, 405
Projected Supply - Current Sources 11, 607 11, 607 11, 607 11, 607 11, 607 Surplus or Deficit
Percent Shortfall
5, 479 3, 508 1, 825 524 798
6%
Projected Supply - Current and Future 12,07 12,07 12,07 15, 981 15, 981 Surplus or Deficit
Percent Shortfall
5, 979 4, 008 2, 325 4, 898 3, 576
Notes:
a)
b)
eki
Values for projected potable water demand are summarized in Table 4-5.

Projected available potable water supplies during normal years are summarized in Table 5-7. 18, 000
16, 000
14, 000
12, 000
10, 000
8, 000
6, 000
4, 000
2, 000
0 Figure 5-7. Normal Year Potable Supply vs. Demand
2025 2030 2035 2040 Buildout
Year
Projected Supply - Current Sources I I Projected Supply - Future Sources 4—Projected Normal Year Demand
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Section 5

WATER SYSTEM SUPPLIES
2024 WSMP Amendment
City of Lathrop
Table 5- 11. Projected Potable Supply vs. Demand for Single Dry Year Scenario Projected Potable Water Demand
Estimated
2025
6, 128
Supply
2030
8, 099
and Demand
2035
9, 782
AFY) (a)( b)
2040
11, 083
2045
12, 405
Projected Supply - Current Sources 10, 498 11, 048 11, 597 10,07 10, 505 Surplus or Deficit
Percent Shortfall
4, 370 2, 949 1, 815 976
9%
1, 901
15%
Projected Supply - Current and Future 10, 998 11, 548 12, 097 13, 637 14, 259 Surplus or Deficit
Percent Shortfall
4, 870 3, 449 2, 315 2, 554 1, 854
Notes:
a) Projected available potable water supplies during single dry years are summarized in Table 5-8. b) Values for projected potable water demand are summarized in Table 4-5. 16, 000
14, 000
12, 000
10, 000
8, 000
6, 000
4, 000
2, 000
0 Figure 5-8. Single Dry Year Potable Supply vs. Demand 2025 2030 2035
Year
2040 Buildout
Projected Supply - Current Sources ,, ' Projected Supply - Future Sources Projected Single Dry Year Demand
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City of Lathrop
Table 5- 12. Projected Supply vs. Demand for Multiple Dry Years Scenario Estimated Supply and Demand ( AFY) (a)( b)
2025 2030 2035 2040 2045
First Dry Year
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 11, 607 11, 607 11, 607 11, 607 11, 607 Surplus or Deficit
Percent Shortfall
5, 479 3, 508 1, 825 524 798
6%
Projected Supply - Current and Future 12,07 12,07 12,07 15, 981 15, 981 Surplus or Deficit
Percent Shortfall
5, 979 4, 008 2, 325 4, 898 3, 576
Second Dry Year
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 11, 607 11, 607 11, 607 11, 607 11, 607 Surplus or Deficit
Percent Shortfall
5, 479 3, 508 1, 825 524 798
6%
Projected Supply - Current and Future 12,07 12,07 12,07 15, 981 15, 981 Surplus or Deficit
Percent Shortfall
5, 979 4, 008 2, 325 4, 898 3, 576
Third Dry Year
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 10, 498 11, 048 11, 597 10,07 10, 505 Surplus or Deficit
Percent Shortfall
4, 370 2, 949 1, 815 976
9%
1, 901
15%
Projected Supply - Current and Future 10, 998 11, 548 12, 097 13, 637 14, 259 Surplus or Deficit
Percent Shortfall
4, 870 3, 449 2, 315 2, 554 1, 854
Fourth Dry Year
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 10, 498 11, 048 11, 597 10,07 10, 505 Surplus or Deficit
Percent Shortfall
4, 370 2, 949 1, 815 976
9%
1, 901
15%
Projected Supply - Current and Future 10, 998 11, 548 12, 097 13, 637 14, 259 Surplus or Deficit
Percent Shortfall
4, 870 3, 449 2, 315 2, 554 1, 854
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Section 5

WATER SYSTEM SUPPLIES
2024 WSMP Amendment
City of Lathrop
Table 5- 12. Projected Supply vs. Demand for Multiple Dry Years Scenario ( Continued) Estimated Supply and Demand ( AFY) (a)( b)
2025 2030 2035 2040 2045
Fifth Dry Year
Projected Potable Water Demand 6, 128 8, 099 9, 782 11, 083 12, 405 Projected Supply - Current Sources 11, 607 11, 607 11, 607 11, 607 11, 607 Surplus or Deficit
Percent Shortfall
5, 479 3, 508 1, 825 524 798
6%
Projected Supply - Current and Future 12,07 12,07 12,07 15, 981 15, 981 Surplus or Deficit
Percent Shortfall
5, 979 4, 008 2, 325 4, 898 3, 576
Notes:
a) Projected available potable water supplies during multiple dry years are summarized in Table 5-9. b) Values for projected potable water demand are summarized in Table 4-5. 0 E
a
o
QQ
c
H
L u
co
d
CO
o
a
18, 000
16, 000
14, 000
12, 000
10, 000
8, 000
6, 000
4, 000
2, 000
0 Figure 5-9. Multiple Dry Year Supply vs. Demand
2025 2030 2035 2040 Buildout
Year
Potable Water Supply —— Projected Potable Water Demand
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Section 5 2024 WSMP Amendment
WATER SYSTEM SUPPLIES City of Lathrop

5. 6 Recommended Water Supply Strategy
The supply versus demand assessment presented above has shown that the City is projected to have adequate supplies to meet projected demands in all year types through 2045 with implementation of SCWSP Phase II by 2040 and PFAS treatment to allow for the City to operate WeII 9. The City would experience up to a 6% shortfall without implementation of SCWSP Phase II and restart of WeII 9 in 2045 under the normal year scenario.

However, future reliability of SCWSP water is uncertain due to adoption of the Bay -Delta Plan Amendment, which could result in significant surface water cutbacks. The SSJID and others are continuing negotiations with SWRCB on implementation of the Bay -Delta Plan Amendment for water supply cutbacks, particularly during droughts. This is a dynamic situation and the projected drought cutback allocations may change depending on the outcome of ongoing negotiations. A conservative estimate of the potential impacts of the Bay -Delta Plan Amendment on the SCWSP is provided in Appendix H of the 2020 UWMP ( EKI, 2021a).

In the near -term, EKI recommends that the City complete the treatment for PFAS to meet proposed regulatory requirements that are anticipated to be effective by early 2027. In addition, the City should monitor the outcomes of the Voluntary Agreement negotiations. In the event that the Bay -Delta Plan Amendment is implemented or if highly restrictive Voluntary Agreements with the SWRCB are implemented, additional water projects such as ASR ( see Section 5. 6.3) may be needed to supplement the City' sexisting supplies and boost drought reliability.

The City relies on implementation of SWCSP Phase II to meet demands from 2040 and onwards. In the long- term (i.e., before 2040), EKI recommends that the City purchase its Phase II SCWSP allocations and expand its SSJID Turnout 2 capacity to meet its Phase II design criteria ( see Section 5. 1.). As this project will require the expansion of SSJID' s DGWTP, the City will need to initiate efforts to secure SCWSP Phase II supplies at least 5- 10 years prior to when the allocations are needed, because this project will likely require significant lead time for planning, design, and construction.

The abovementioned water supply projects are discussed in more detail below. In addition to these projects, EKI is aware that potential water transfer opportunities may exist with Stockton East Water District (SEWD) water contractors. It is recommended that the City explore such opportunities to increase its available supplies.

5. 6. 1 SSJID SCWSP Phase II
As discussed in Section 5.1., the City' s
SSJID supply is anticipated to increase from 6, 887 AFY to 10, 671 AFY with the implementation of Phase II of the SCWSP ( see Section 5.1). The timing of Phase II is unknown, but for water supply planning purposes it is assumed that SSJID Phase II water will be available to the City by 2040.

5. 6. 2 Treatment for PFAS
As mentioned above, the City detected emerging contaminants belonging to the group of PFAS in its groundwater production wells. The City took WeII 9 offline in 2019 so that the PFOA concentration in the blended flow from the remaining wells is below California' s RLs for PFOA. With the proposed MCLs issued by the USEPA in March 2023, the City anticipates treatment for all of its groundwater wells.

In 2020, EKI evaluated 11 alternatives for PFAS management and treatment and conducted a bench -scale granular activated carbon ( GAC) test to explore the performance of treating the City' s groundwater with GAC pressure vessels ( EKI, 2020). In 2022, the City contracted with Carollo Engineers ( Carollo) to further study and develop the City' s options for GAC treatment of only groundwater from WeII 9 and blended groundwater from all the City' s wells ( Wells 6- 10) at the LAWTF ( Carollo Engineers, 2022). Treatment for eki environment
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Section 5 2024 WSMP Amendment
WATER SYSTEM SUPPLIES City of Lathrop
PFAS consists of passing water through GAC media beds contained in pressure vessels in a lead/ag configuration. The treatment process will contain key components including the PFAS treatment pressure vessels, GAC backwashing facilities, and booster pumps, with a full capacity of 7, 000 gpm. The PFAS treated water will reenter the existing treatment processes at the LAWTF upstream of chemical addition before being sent to the LAWTF storage tank.

EKI is currently assisting the City with evaluating the City' s groundwater for the presence, potential transport, and sources of PFAS, and proposed treatment options. The study aims to better understand ( 1) the extent of PFAS contamination, (2) if the elevated levels of PFAS detected in Well 9 or other locations will impact the City' sother drinking water supply wells, and ( 3) how these potential impacts may impact planned PFAS treatment. Preliminary groundwater modeling results as of December 2023 reveal that a 500 AFY of production at Well 9 is needed to hydraulically control PFAS in groundwater sourcing from south of the City' swells.

5. 6. 3 Aquifer Storage and Recovery
ASR is defined as the recharge of water through a well into a suitable aquifer during times when water is available or is the best quality for recharge, storage for a period of weeks to months or years, and recovery from the same well during times when the stored water is needed. The ASR operation forms a buffer zone around the ASR well, separating the native groundwater and the stored water, which in the City' scase will be treated, higher -quality SCWSP water. The stored water will be available for recovery during times when it is needed to meet peak or emergency demands or during severe droughts.

The City contracted with Carollo Engineers and completed an engineering feasibility study for ASR in 2023.

The feasibility study included drilling of an ASR test hole, water quality sampling and testing, and recommendations for well design ( Carollo Engineers, 2023).

The site selected for the ASR well is at the River Islands potable water storage and sewer pumping project, located at 950 Stewart Road. The test well was completed to 800 ft bgs where a favorable zone for storage was found in the last 60 feet of drilling. From the initial monitoring well results, the City' s ASR well capacity
is estimated at 1, 000 gpm, or approximately 1. 44 MGD.

An ASR project will boost the City' ssupply reliability during water supply emergencies ( e.g. due to water quality concerns) or severe droughts, especially with the uncertain outcomes of the Bay - Delta Plan Amendment implementation, as discussed above.
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Section 6 2024 WSMP Amendment
WATER SYSTEM PERFORMANCE AND OPERATIONS CRITERIA City of Lathrop 6 WATER SYSTEM PERFORMANCE AND OPERATIONS CRITERIA
This section describes the recommended performance and operational criteria by which the City' sexisting and key planned infrastructure will be evaluated. These criteria are based on California Code of Regulations Title 22 ( Title 22) requirements, 2022 Lathrop Design and Construction Standards Standards"; Lathrop, 2022c), and the 2019 WSMP. These criteria can be grouped into two categories:
1) criteria used to evaluate the water distribution system' sperformance ( Section 6.1) and ( 2) criteria used to evaluate the sizing of the systems water facilities, including pipelines, turnouts, tanks and pump stations (Section 6.2).

The water distribution system criteria include maximum and minimum allowable system pressures, required fire flows and pressure, and requirements for minimum supply capacity. The water supply and storage facilities criteria include maximum allowable pipeline velocity and head loss, pumping capacity and water storage capacity for normal and emergency conditions. These criteria are summarized in Table 6- 1 and described in further detail in the following section.

6. 1 Distribution System Performance Criteria

6. 1. Peaking Factors
The WSMP uses peaking factors to estimate MDDs and PHDs for purposes of evaluating the distribution system performance under peak demand conditions. As discussed in Section 4.3, the following peaking factors are applied as part of this IWRMP Amendment:

MDD Peaking Factor = 1. 7 x ADD
PHD Peaking Factor = 2. 6 x ADD
In addition, a 5% water loss ( non -revenue water) factor is applied to the water demand projections to estimate ADDs ( see Section 4.2). These peaking factors are also used to size facilities for peak demand conditions, as discussed in Section 6. 2.

6. 1. 2 Fire Flows
The Lathrop Manteca Fire District ( LMFD) has established minimum fire flow and residual pressure requirements for firefighting purposes, which the City is responsible for providing in its water distribution system. Required fire flows are based on land use designation and are designed to be conservative for long- term planning. The required fire flow requirements are summarized in Table 6-2. LMFD has reviewed and approved these requirements for planning purposes. These fire flows must be provided in conjunction with maximum day demand conditions while maintaining a minimum residual pressure of 20 pounds per square inch ( psi) at all system nodes. The distribution of the required fire flows within the City are shown on Figure 6-1.

As discussed below, these flows and durations are used to establish supply capacity criteria, pipe sizing, and storage and pumping capacity requirements.

6. 1. 3 Water Supply Capacity
As discussed in Section 3, the City' s water distribution system consists of a single pressure zone, with both groundwater and surface waters supplied to meet customer demands. Maximum day demand plus fire flow and peak hour demand conditions will be used to assess the adequacy of the City' s potable water supply and distribution system capacities. The following sections describe the supply assumptions and criteria for each demand condition.
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Section 6 2024 WSMP Amendment
WATER SYSTEM PERFORMANCE AND OPERATIONS CRITERIA City of Lathrop

6. 1.3. Peak Conditions — Peak Hour Demand
During normal operation conditions, the City' s
water supply system is required to be capable of meeting peak hour demand conditions, while meeting minimum and maximum system pressure criteria. This demand condition can be met with a combination of storage, surface, and groundwater sources. This includes firm pumping capacity at all existing and planned storage tanks, existing and planned SSJID turnouts, and the LAWTF. The firm capacity is defined for each facility as its capacity with its highest capacity domestic pump offline.

6. 1.3.2 Peak Conditions — Maximum Day Demand with Fire Flow During emergency fire flow conditions, the City' sfirm water supply system capacity is required to be capable of meeting maximum day demand conditions in conjunction with two concurrent fires, with one industrial fire and one residential fire, while meeting minimum and maximum system pressure criteria.

This demand condition can be met with a combination of storage, surface, and groundwater sources. This includes firm pumping capacity at all existing and planned storage tanks, existing and planned SSJID turnouts, and the LAWTF.

6. 1.4 Distribution System Pressures
The distribution system' s ability to maintain adequate system pressures is the primary indicator of acceptable system performance. Under normal operating conditions, the distribution is required to maintain a minimum pressure of 40 psi ( Title 22 requirement) and a maximum pressure of 80 psi. As discussed above, the system must be able to maintain a minimum of 20 psi under fire flow conditions to comply with Title 22.
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Section 6

WATER SYSTEM PERFORMANCE AND OPERATIONS CRITERIA
2024 WSMP Amendment
City of Lathrop
Table 6-1
Summary of Recommended Potable Water System Performance and Operational Criteria Component Criteria

WATER SYSTEM PERFORMANCE
FireFlow Requirements
Data Sources/ Remarks (a)
Single Family 1, 250 gpm for 2 hours. Based on review and approval by Multi Family 2, 000 gpm for 2 hours. the Fire Marshal for master General
Commercial and
Office
3, 000 gpm for 2 hours.
planning. Requirements are general
requirements for master planning
purposes, and may not be indicative
Heavy Commercial 4, 000 gpm for 2 hours. of requirements for specific Industrial 4, 000 gpm for 2 hours. developments.

Peaking Factors For System Analysis
Water Loss ( NonRevenue Water)
5% increase to average day demands for unaccounted for
water.

Max Day to Average
Day Peaking Factor

1. 7 times average day demand.

IWRMP recommendation based on
demand evaluation.

Peak Hour to
Average Day

2. 7 times average day demand.

Water System Supp y Requirement
Demand Condition
To Be Met
Peak Conditions - Normal Operations: Provide firm water supply capacity to meet maximum day demand.

Peak Conditions - Emergencies: Provide firm water supply and storage capacity to meet maximum day and two concurrent fires, or peak hour demands, whichever is larger.

Distribution System Pressures
Maximum Pressure 80 psi at customer service connections Minimum Pressure -
Normal Operating
Conditions for
System Expansions
40 psi at customer service connections excluding fire flow Title 22 requirements for system
expansions that expand the number
of existing system service
connections by 20 percent or more.

Minimum Pressure -
Max Day Plus Fire
Flow Conditions
20 psi
Title 22 requirement for minimum
allowable pressure.
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EKI C20049. 01
Section 6

WATER SYSTEM PERFORMANCE AND OPERATIONS CRITERIA
2024 WSMP Amendment
City of Lathrop
Table 6- 1 (Cont.)
Summary of Recommended Potable Water System Performance and Operational Criteria Component Criteria Data Sources/ Remarks ( a)

FACILITIES SIZING
Pipelines
Distribution Main
Diameter
General: 8 -inch diameter or larger
Cul- de- sacs and end runs: 6 -inch diameter acceptable within culde -sacs and end runs of less than 500 feet where future extensions will not occur and no fire hydrants are located.

Commercial and industrial: 10 -inch diameter or larger serving commercial or industrial areas.

Dead -End Main
Diameter and
Length
6 -inch diameter limited to max length of 100 feet.
8 -inch diameter limited to max length of 1, 200 feet.
12 -inch diameter limited to max length of 2, 400 feet.

Maximum
Velocity
6 ft/ s, all system mains, peak hour demand
10 ft/ s, all system mains, maximum day plus fire flow
IWRMP recommendation based
Maximum Head
Loss
3 ft per 1, 000 ft, mains 16", peak hour demands
7 ft per 1, 000 ft, mains < 16", peak hour demands
10 ft per 1, 000 ft, all system mains, maximum day plus fire flow on industry practice, modified
from 2013 Draft Water Master
Plan.

Hazen Williams
C" Factor
New Piping = 140
Existing System Piping = 120 - 130 per model calibration New Piping C -factor based on
City Design and Construction
Standards. Existing system piping
C -factors confirmed by EKI
calibration.

Pipeline Material
All Domestic Water Mains: PVC C900 or C905 Class 150
All Fire Lines: PVC C900 or C905 Class 200
Booster Pump Station Capacity
Pumping Capacity
Citywide, firm pumping capacity equal to maximum day demand plus fire flow ( one industrial and one residential) or peak hour demand, whichever is larger.

Per development area, firm pumping capacity equal to peak hour demand plus ability to meet single largest fire flow requirement ( confirm by modeling).

Firm pumping capacity defined
as the total capacity of all pumps
minus the capacity of one
domestic pump.

Backup Power Equal to firm pumping capacity of facility.

IWRMP recommendation for
system reliability.

Water Storage Capacity
Operational
Equalization)
Equal to 25 percent of maximum day demand calculated per development.

Fire Supply flow for simultaneously fighting one residential (2, 000 gpm) and one industrial fire (4, 000 gpm) for 2 hours (City- wide).

Emergency
Equal to 75 percent of maximum day demand calculated per development.

Emergency
Groundwater
Credit
Equal to the firm groundwater supply that can be reliably pumped (facilities equipped with auxiliary power) (Citywide).

The maximum emergency
storage credit is equal to the
reliable pumping capacity over
an 18 -hour period.

Total Water
Storage Capacity
100 percent of max day demand plus fire volume.

Summation of operational, fire,
and emergency storage minus
emergency groundwater credit.

Notes:
a) Source: Water System Standards, City of Lathrop Department of Public Works Design and Construction Standards, January 2014, unless noted otherwise.
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WATER SYSTEM PERFORMANCE AND OPERATIONS CRITERIA
2024 WSMP Amendment
City of Lathrop
Table 6-2. Required Fire Flow and Storage Requirements
General Land Use Designation
Very Low Density
Medium Density Residential
Examples of Specific Developments
All existing single family residential developments, as wells as planned unit development and recreation
residential.

Fire Flow
gpm)
1, 250
High Density Residential All existing apartment and condominium developments. 2, 000 General Commercial and
Office
Highway, Village, Regional, Service, Neighborhood
Commercial designations. Includes Professional Offices
and Community Commercial designations.
3, 000
Heavy Commercial Areas designated as Recreation and/ or Hotels. 4, 000 Industrial Limited and General Industrial 4, 000
Notes:
a) Fire flow requirements were reviewed by LMFD with the City on 15 August 2017 and were determined to be consistent with Lathrop' s City Standards and the LMFD Master Plan for long term master planning purposes.
b) Fire flows imported into model were based on zoning land use designations. eki environment
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EKI C20049. 01
egend
Sphere of Influence
IN Treatment Plant
W Pump Station
ID Enclosed Storage Facility
0 SSJID Turnout
Pipe
Hydrant Fire Flow Requirement
1250 GPM
O 2000 GPM
3000 GPM
4000 GPM
Abbreviations
BPS = booster pump station
GPM = gallons per minute
LAWTF = Louise Avenue Water Treatment Facility
Sol = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 13 November 2024.

N
o 3, 00D 6, 000
lewk S Feet:

Fire Flow Requirement
Wkler 6y. Nm Metier Hen Amendment
City of Lennon
Lathrop CA
Denember 2024 ekenvironment I & 020048.
water
01 Figure 6-1
Section 6 2024 WSMP Amendment
WATER SYSTEM PERFORMANCE AND OPERATIONS CRITERIA City of Lathrop

6. 2 Water Facilities Criteria
The following sections describe the performance and sizing criteria for City water facilities.

6. 2. 1 Water Transmission and Distribution Pipeline Sizing Criteria The following pipeline velocity and head loss criteria will be used for sizing new transmission and distribution pipelines. However, when evaluating the existing system, velocity and head loss criteria are secondary to the system pressure criteria ( Section 6. L4). For example, if system pressures are satisfied under normal and fire flow conditions, an existing pipe that exceeds maximum velocity or head loss criteria will not necessarily be indicative of a problem that requires system improvements. Any identified exceedances will be reviewed on a case - by -case basis to determine if they are influencing any deficient system pressures or if improving these pipes to meet velocity or head loss criteria would benefit the water movement within the system or increase system redundancy.

6. 2.1. Velocity Criteria
The following velocity criteria, in conjunction with head loss criteria described below, are recommended for sizing of new water mains:

PHD conditions: Maximum velocity of 6 feet per second ( fps) for all mains MDD plus fire flow conditions: Maximum velocity of 10 fps for all mains As discussed above, for existing infrastructure these criteria are secondary to pressure criteria and are evaluated to identify potential bottlenecks in the system that could be upsized to address pressure deficiencies.

6. 2.1. Head loss Criteria
In addition to velocity criteria, the following head loss criteria must also be met for sizing of new water mains:

PHD conditions:
o Pipes < 16 inches in diameter: Maximum head loss of 7 feet per 1, 000 feet of pipe ( ft/ kft) o Pipes 16 inches in diameter: Maximum head loss of 3 ft/ k-t MDD plus fire flow conditions: Maximum head loss of 10 ft/ k-tfor all mains The PHD head loss criteria distinguish between pipes less than 16 inches and those greater or equal to 16 inches in diameter. The larger pipes are generally used to transmit water long distances from sources to smaller distribution pipelines which serve customer connections.

For existing pipelines these criteria are used to identify bottlenecks in the system that if upsized could relieve downstream pressure to meet pressure criteria and improve connectivity of major supply sources and storage facilities to outlying areas.

6. 2. Booster Pump Stations
In order to meet varying demand conditions, the City Standards require that firm pumping capacity among all water supply sources and booster pump stations be able to provide the greater of:

Maximum day demand conditions with two simultaneous fires, with one being high density residential and one being industrial or heavy commercial; or Peak hour demands.
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Section 6 2024 WSMP Amendment
WATER SYSTEM PERFORMANCE AND OPERATIONS CRITERIA City of Lathrop This criterion exists to ensure there is sufficient pumping capacity distributed throughout the system to meet peak demand conditions. EKI also recommends the City establish criteria to provide backup power for all facilities to provide firm pumping capacity.

New booster pump stations should be sized for a firm capacity equal to peak hour demands of the area to be served, at a minimum, and modeling must confirm that this capacity is sufficient to meet required fire flows in this area.

6. 2. 3 Water Storage Capacity
Treated water storage capacity includes equalization storage, fire storage, and emergency storage. The following storage criteria were established in prior master plan updates and have already been incorporated into the City Standards ( 2022). The following sections explain each storage requirement in detail. Existing storage capacity is evaluated system -wide to meet the following criteria. Future development will be required to provide requisite equalization and emergency storage based on their projected demands.

6. 2.3.1 Equalization Storage
As discussed in Section 6. 1, peaking factors are developed to capture varying water use conditions. Higher water demand periods occur during summer months as compared to winter months when irrigation demands are higher. Over the course of the day, usage peaks in the early morning when people are preparing for their day and at night when people return home and begin irrigating their landscapes.

As discussed in Section 6. 1.3, the water supply criterion requires firm treatment plant and supply turnout capacity provide MDD. Additional pumping capacity from booster pump stations is used to meet peak demand conditions ( Section 6. 2.). This storage volume is then refilled during low demand periods when water supply is greater than water demand.

The storage volume used to meet these high demand periods is called operational or equalization storage.

Recommended equalization storage is equal to 25% of MDD.

6. 2.3. Emergency Storage
Emergency storage is required to meet demands during various emergencies, such as natural disasters, pipeline failures, treatment failures, power outages or pump station failure. No standard requirements exist for determining the appropriate amount of emergency storage, and each utility establishes these requirements based on their judgement. Currently, the City has an emergency storage requirement of 75% of MDD. EKI finds this requirement to be appropriately conservative.

6. 2.3. Fire Storage
As discussed in Section 6. 1.2, fire flow and duration requirements were established for long- term planning purposes by the City and LMFD. The total system -wide fire storage volume is required to supply a concurrent industrial fire ( 4, 000 gpm for 2 hours) and high -density residential fire (2, 000 gpm 2 hours).

This results in a total storage requirement of 0. 72 MG which should be distributed throughout the system.

6. 2.3.4 Groundwater Storage Credit
The City' s groundwater basin can account for a portion of the City' s emergency storage requirement.

Groundwater credit for emergency storage is defined as the quantity of groundwater which can reliably be produced in the event of an emergency over an 18 -hour period. The groundwater credit is calculated based on the firm groundwater supply of facilities equipped with backup power (i.e., the total capacity of the all the wells with backup power minus the capacity of the largest well with backup power). Additional eki environment
water 6- 8
December 2024
EKI C20049. 01
Section 6 2024 WSMP Amendment
WATER SYSTEM PERFORMANCE AND OPERATIONS CRITERIA City of Lathrop considerations should be made as to the system' s ability to transmit this water to outlying areas of the City.
eki environment
water 6- 9
December 2024
EKI C20049. 01
Section 7 2024 WSMP Amendment
DISTRIBUTION SYSTEM HYDRAULIC CAPACITY EVALUATION City of Lathrop 7 DISTRIBUTION SYSTEM HYDRAULIC CAPACITY EVALUATION
EKI updated the City' s water system hydraulic model to evaluate the ability of the City' s distribution system to meet the recommended performance and operational criteria described in Section 6. 1. A hydraulic model transforms information about the physical facilities and system into a mathematical model to analyze the water system under various demand conditions. The hydraulic model generates information on pressure, flows, velocities, and head loss that can be used to assess system performance and identify deficiencies. The hydraulic model can also be used to verify the adequacy of recommended or proposed system improvements.

7. 1 Hydraulic Modeling Approach
To evaluate distribution system performance against performance criteria, EKI conducted steady- state model simulations of (1) PHD, and ( 2) MDD plus fire flows for existing and buildout scenarios. Key planned infrastructure was added to the future scenarios to support future developments.

All model runs except for the fire flow simulations were conducted with the fire pumps offline and with firm domestic capacity available at each BPS. These results provided information on junction pressures and pipeline head loss and velocity.

To determine available fire flow and pressure at each node, fire flow simulations were modeled during MDD conditions. Pump controls were set such that fire pumps switched on when firm domestic pumping capacity was unable to meet discharge pressure requirements. The fire flow simulations determine the fire flow availability at each hydrant while maintaining a minimum of 20 psi everywhere in the system.

These results were compared to required fire flows to determine which hydrants are not meeting the required criteria. Additional fire flow analyses were conducted by applying fire demands on individual hydrant nodes to evaluate pipeline head loss and velocity criteria for recommended new pipes under MDD plus fire flow conditions.

7. 2 Hydraulic Model Update
This section documents the updates of the City' s existing water system hydraulic model. The section provides an overview of the model expansion process, the water system improvements incorporation, and model validation and calibration.

7. 2. 1 Model Platform
The City' s existing water system hydraulic model was developed on Innovyze InfoWater platform by EKI for the 2019 WSMP. The model has been migrated to Innovyze InfoWater Pro, which provides enhanced analytical tools and higher geographical information system ( GIS) integration capabilities. This software upgrade allows not only for automatic synchronization between the model and infrastructure GIS to limit future maintenance efforts but also for the City' s emerging water system simulation needs.

7. 2. Model Update
The City maintains a GIS geodatabase of its infrastructure assets, which was used as the basis of information to construct the existing water system hydraulic model. EKI updated the City' s GIS database
to incorporate recent infrastructure improvements, identified and filled data gaps to make sure the GIS database accurately represented the City' s existing utility infrastructure as of January 2023.

Significant efforts were required after the City' s geodatabase updates were completed to update and validate the hydraulic model. After importing the City' s GIS data into the hydraulic model, the following
steps were performed to address data gaps, validate network data, and create a fully connected network:
eki environment
water 7- 1
December 2024
EKI C20049. 01
Section 7 2024 WSMP Amendment
DISTRIBUTION SYSTEM HYDRAULIC CAPACITY EVALUATION City of Lathrop New water system infrastructure, including tanks, BPSs, pipeline improvements constructed post 2019 WSMP, has been digitized in the geodatabase and incorporated into the new hydraulic model. 14,s
Planned transmission mains, tanks, and BPSs were added for the buildout scenario.

The model network was reviewed and refined for connectivity. Using the software' stools, each pipe was connected to a model node or junction. Orphan and duplicate elements were corrected.

Elevations were assigned to each new model node by extracting elevations from publicly available light detection and ranging ( LiDAR) data.

Hazen -Williams friction C -Factors were applied to each pipe.

Tank and pump station configurations were verified and updated as needed. Pump operational settings were initially imported from the City' s prior hydraulic model and updated with City' s September 2023 setpoints.

Parcel -level existing water demand and future projections were allocated to the nearest node.

Fire flow requirements were allocated to each hydrant node based on land use type.

7. 2. 3 Model Validation and Calibration
Given that the City' s distribution system is largely comprised of newer PVC pipes, the pipeline C -factors are unlikely to have changed significantly since the 2019 WSMP. As a substitution of typical model calibration, EKI retained the C -factors from the existing hydraulic model for pipes constructed prior 2019 WSMP, which was calibrated with field hydrant test data. A C -factor of 140 was assigned to planned new pipes or pipes constructed post the 2019 WSMP, based on the City' s Design Standards ( 2022).

After model construction, EKI validated the model to verify correct model construction, controls, and correct assignment of model variables. EKI conducted model validation runs of the existing system scenario to check the accuracy of the model' srepresentation of real system operations. EKI compared the results of these validation runs against SCADA system data provided by the City to determine if modeled system pressures were generally consistent with actual system pressures. Based on these runs, EKI updated the operational settings of the pump stations in the model and modeled the pumps with variable frequency drives accordingly to better represent actual pump operations.

7. 3 Modeling Scenarios
Existing infrastructure and key planned infrastructure were assessed under two scenarios: Existing (2022), and Buildout ( 2045) development scenarios. Figure 7- 1 shows parcels and future development included in each scenario.

Water infrastructure included in the Existing scenario is described in Section 3 and shown on Figure 3-1.

Key planned infrastructure was initially separated by anticipated development timing ( i.e., the Near - Term Future, Long -Term Future, and Selected Buildout scenarios) in the 2019 WSMP based on available drawings, design reports, and prior planning documents. However, as the development projections have 14 New infrastructure includes Tanks 5 and 6 with their onsite BPSs, installation of new 12" main on Louise Avenue and new 8" main on S Harland Road, as well as distribution network expansion in River Islands, Mossdale, and Central Lathrop.
15 Pipeline improvements include upsizing of existing 8" - 12" pipelines on J Street, Avon Street, and at the BPS - 1 site.
eki environment
water 7- 2
December 2024
EKI C20049. 01
Section 7 2024 WSMP Amendment
DISTRIBUTION SYSTEM HYDRAULIC CAPACITY EVALUATION City of Lathrop been changed significantly since then, to minimize the variations associated with development timing change and account for the overall impact caused by the system expansion, the prior future scenarios were consolidated as a single Buildout scenario with all key planned infrastructure. Figure 7-2 shows the locations of planned infrastructure.

The following planned development -related infrastructure is included in the Buildout scenario:

Lathrop Gateway: A new 1. 0 MG storage tank, a booster pump station with a firm pumping capacity of 3, 000 gpm, and 16 -inch transmission line connecting the booster pump station to Yosemite Avenue at the former Well 21 site, south of the intersection of Yosemite Avenue and McKinley Avenue.

River Islands: Two additional 1. 8 MG storage tanks ( Tank 5B and Tank 5C) at the existing Tank 5 site and one additional 4, 000 fire pump at the existing BPS -5 site.

River Islands Phase 2: The River Islands Phase 2 storage tanks ( 3. 6 MG total) and BPS with three domestic variable speed pumps with capacities of 2, 000 gpm each and a 4, 000 gpm fire pump 8, 000 gpm firm capacity) located southwest of the intersection of S Paradise Rd and W Stewart Rd; expansion of backbone water mains required to support the River Islands phase 2 development. 16
Central Lathrop: Expansion of backbone water mains to support CLSP development, including an 8 -inch I-5 crossing at Lathrop Road'. Diameter of the backbone water mains were optimized and downsized to serve lower projected water demands in the Central Lathrop area, as verified in Section 7. 4.2.

Mossdale Landing West: Planned water distribution mains, ranging from 8" to 10" in diameter, to support the Mossdale Landing West development.

Parcel -level potable water ADDs for the Existing scenario were assigned based on each parcel' s actual 2022 water billing data. Incremental ADDs were added in the Buildout scenario using the land -use specific water demand factors to match the water demand projections described in Section 4. Table 7- 1 summarizes the total ADD, MDD, and PHD under each scenario.

As discussed in Section 7.1, EKI conducted steady- state model simulations of PHD and MDD plus fire flows for each scenario.
le Tank and pipe information extracted from River Islands' WaterCAD model, provided on May 30, 2023. The phase 2 BPS characteristics were assumed to be consistent with Tank 5 BPS without SSJID Turnout 2 expansion. 17 The I-5 crossing at Lathrop Road was originally anticipated to be completed by developers but is now incorporated in the City' s
CIP as project PW 25- 10 and Section 9. 2.
ek, environment
water 7- 3
December 2024
EKI C20049. 01
f,egend 7.Sphere of Influence
Development Areas
Central Lathrop
Crossroads
Historic Lathrop Infill and Other Developments
Lathrop Gateway
Mossdale Landing
Mossdale Landing East
Mossdale Landing West
Mossdale Landing South
0 River Islands
Sharpe Army Depot
r) South Lathrop
Incremental Development by Model Scenario
Existing ( 2022)
Buildout ( Beyond 2040)
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s AroGIS Online, 13 November 2024.

Aa _ 4, 000 8, 000
scale in reef)
eki
Modeling Scenarios
Water System Master Plan Amendment
Clty of Lathrop
Lathrop. CA
environment ana20er202a czooae. m
water Figure 7- 1
Section 7

DISTRIBUTION SYSTEM HYDRAULIC CAPACITY EVALUATION
2024 WSMP Amendment
City of Lathrop
Table 7-1. Summary of Water Demands by Scenario
Demand Scenario
ADD ( a)
MDD ( b)
PHD ( c)
Existing
gpm
3, 272
5,62
8, 506
MGD

4. 7

8. 0

12. 2
Buildout ( 2045) (d)
gpm MGD
7, 691
13, 075
19, 996

11. 18. 8

28. 8
Notes:
a) Existing ADD is based on Table 4- 3 which includes the City' s 2022 billed water use. The buiidout average day demands are based on demand projections in Table 4-5 and a 5 percent unaccounted for water use factor to estimate total water use. b) MDD is calculated using a peaking factor of 1. 7 times the ADD. c) PHD is calculated by using a peaking factor of 2. 6 times the ADD. eki environment
water 7- 5
December 2024
EKI C20049. 01
1 River Islands Phase 2
X, Tank andBPS
BPS6
Tarik
Tumout
SSJID BPS - 5
2 Tank
f

LATHROP RD
SSJID
Turnout 1 I

LOUISE AV
LAWTF Tank and BPS
Q
Well 21 Tank,
land BF, S,
e~
YOSEMITE.,
epend
1 Sphere of Influence
Existing Infrastructure
lam. Treatment Plant
G Pump Station
Enclosed Storage Facility
0 SSJID Turnout
Pipe
Future Facilities
Pump Station
Enclosed Storage Facility
SSJID Turnout
Future Pipe Diameter, Inches
8 ---- 18
10 20
12 — 24
16 — 30
Abbreviations
BPS = booster pump station
tAWfF = Louise Avenue Water Treatment Facility
Sot = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS
Online, 13 November 2024.

N 0 3, 000
A
Modeled Existing and Future Infrastructure
6, 000
Seale in Feet)
eki
Water System Master Plan Amendment
CO of Lathrop
Lathrop, CA
December 2024
environment C20049. 01
water Figure 7- 2
Section 7 2024 WSMP Amendment
DISTRIBUTION SYSTEM HYDRAULIC CAPACITY EVALUATION City of Lathrop

7. 4 Water Distribution System Performance Evaluation
The following sections discuss the hydraulic model results and distribution system deficiencies identified in each scenario.

7. 4.1 Existing System Evaluation
Existing scenario model simulations were evaluated to identify existing system deficiencies, as are discussed in the following sections.

Note that the existing scenario simulations were modeled with SSJID Turnout 1 flowing at 1, 381 gpm per the City' scurrent operations. The City currently uses the SSJID Turnout 1, LAWTF and storage tanks to meet peak demands, and then uses a combination of the LAWTF and the SSJID Turnouts 1 and 2 during off- peak hours to refill the storage tanks.

7. 4.1. PHD Results
Model results indicate that the existing system can meet minimum pressure criteria of 40 psi system -wide under PHD conditions. Modeled system pressures ranged from 44 psi to 60 psi, as shown on Figure 7-3.

Results show that velocities are elevated in the discharge lines from each of the BPSs. However, no modeled velocity in the distribution mains exceeds the maximum velocity criteria ( Figure 7-4). As shown in Figure 7-5, head losses exceed criteria in the discharge lines from BPS -5 and SSJID Turnout 1. As discussed in Section 6. 2.1, these exceedances do not necessarily indicate there is a problem unless the pipe velocity or head loss is contributing to pressure deficiencies.

7. 4.1.2 MDD Plus Fire Flow Results
Modeled fire flow availability and deficiencies are shown on Figure 7-6. Several locations cannot meet fire flow requirements, including:

Multiple hydrants in the commercial area near the intersection of Harlan Road and Lathrop Road.

Multiple hydrants in the CLSP along Dos Reis Road. As described in Section 7. 4.2., these deficiencies are addressed by planned future infrastructure to support development of the CLSP.

As such, no improvements were developed to address these deficiencies.

Multiple hydrants in the northern McKinley industrial area including areas bounded by W. Lathrop Road and Park street.

Multiple hydrants on South Harlan Road north of Lathrop Road and along Old Harlan Road south of Lathrop Road, which are addressed by future 8 -inch I-5 crossing, as discussed in Section 7. 4.2.

Two hydrants along Old Harland Road between Shilling Avenue and Lathrop Road.

Two hydrants off the 4 -inch and 6 -inch lines, serving residential areas of Historic Lathrop in the alley between 5th and 6th Streets.

Two hydrants in the Crossroads area on one dead end line along Murphy Road. The south deficiency is addressed in buildout scenario with additional supply from planned tank and BPS at the former Well 21 site. The north deficiency can be addressed by installing a new water main connecting the 10 -inch dead- end pipe on Murphy Road with the existing 12 -inch pipe on South Harlan Road.
eki environment
water 7-
December 2024
EKI C20049. 01
r.J
SSJID BPS - 5
Tumout 2
Tank
BPS - 2
Tank

LATHROP RD
SSJID
Tumout 1

LOUISE AV
LAWFF Tank and BPS
E
r '

YOSEMITE AU
Leaend
Sphere of Influence
Existing Infrastructure
Ikg Treatment Plant
W Pump Station
Enclosed Storage Facility
SSJID Tumout
Pipe
Junction Pressure, psi
Less than 40 ( Not Meeting Criteria)
40-5
O 45- 50
C 50-5
55- 65
Abbreviations
BpS = booster pump station
9pm = gallons per minute
LAWtF = Louise Avenue Water Treatment Facility
PHD = Peak Hour Demand
psi = pounds per square inch
SOI = Sphere of Influence
smo = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

2. Well 9, Well 21, and Well 21 WTF are not active in the existing system analysis.

3. SSJID Turnout 1 is operating at 1, 381 gpm flow rate in the existing modeling scenario.

Sources

1. Aerial photograph provided by ESRI' sArcGIS Online,
13 November 2024.

N 0
A _
3, 000 6, 000
Scale , nFeet)
Existing Water System Hydraulic Evaluation
Peak Hour - Pressure
Water System Master Plan Amendment
Coy of Lathrop
Lathrop, CA
environment
December2024
C20046, 01
water Figure 7- 3
awe,
BP46
pTadk
BPS - 2
Tank
SSJID"
BPS - 5
Tumout 2
Tank

LATHROP AD
LOUISE A.
e
LAVVTF Tank and BPS
s
I
YOSEMITE or
eki
r.egend 1 Sphere of Influence
Existing Infrastructure
Treatment Plant
W Pump Station
Enclosed Storage Facility
SSJID Turnout
Pipe
Pipe Velocity, fps
Less than 4
4-6
Greater than 6 ( Not Meeting Criteria)
Abbreviations
BPS = booster pump station
a/ s = feet per second
gpm = gallons per minute
LAWTF = Louise Avenue Water Treatment Facility
PHD = Peak Hour Demand
O1 = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. 8,1 locations are approximate.

2. Well 9, Well 21, and Well 21 WTF are not active in the existing system analysis.

3. SSJID Turnout 1 is operating at 1, 381 gpm flow rate in the existing modeling scenario.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 13 November 2024.

N o
A
3, 000 6, 000
Scale in Feel)
Existing Water System Hydraulic Evaluation
Peak Hour - Pipe Velocity
Water System Master Plan Amendment
City or Lathrop
Lathrop, CA
December 2024
environment C2004901
water Figure 7-4
BPS16
Tarick
SSJI [
BPS - 5
Turnout 2
Tank
BPS - 2
Tank

LATHROP FD
SSJID
Tumout 1 I

LOUISE AV
e
LAVVTF Tank and BPS

YOSEMITE AU
r,eoendSphere of Influence
Existing Infrastructure
Treatment Plant
C=J Pump Station
Enclosed Storage Facility
Ct SSJID Turnout
Pipe
Pipe Head Loss, ftlk-t
Less than 3
3-5
5-7
7- 10
Greater than 10
Pipe Head Loss Not Meeting Criteria
t • Head Loss Exceeds Requirement
Abbreviations
BPS = booster pump station
ft/ k-B = feet per thousand feet
gpm = gallons per minute
LAWTF = Louise Avenue Water Treatment Facility
PHD = Peak Hour Demand
SOI = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

2. Well 9, Well 21, and Well 21 WTF are not active in the existing system analysis.

3. SSJID Turnout 1 is operating at 1, 381 gpm flow rate in the existing modeling scenario.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 13 November 2024.

A _
3, 000 6000
Scale in Feet)
Existing Water System Hydraulic Evaluation
Peak Hour - Pipe Head Loss
Water System Master Plan Amendment
Gilt' or Lathrop
Lathrop, CA
environment
een1cer2ovu
I & water
December
Figure 7-5
k
SSJID
Tumoutt
LAWIF Ta nk
and
BPS

YOSEMITE
A
Legend
1L7Sphere of Influence
Existing Infrastructure
Treatment Plant
Pump Station
Enclosed Storage Facility
Cti SSJID Turnout
Pipe
Available Fire Flow, Gallons per Minute
Less than 1250
C 1250 - 2000 C 2000 - 3000
3000 - 4000
iL Greater than 4000
Hydrant Residual Pressure Not Meeting Criteria
Residual Pressure Below Requirement
Abbreviations
BPS = booster pump station
gpm = gallons per minute
LAWTF = Louise Avenue Water Treatment Facility
5O1 = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

2. Well 9, Well 21, and Well 21 WTF are not active in the existing system analysis.

3. SSJID Turnout
1 is operating at 1, 381 gpm flow rate
in the existing modeling scenario.

4. Evaluated with fire pumps online at booster pump
stations where effluent pressure drops below effluent
pressure set points.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 13 November 2024. N o
A _
3, 000 6, 000
yule In Feet)
Existing Water System Hydraulic Evaluation
Maximum Day Demands - Available Fire Flow
Water System Master Plan Amendment
Cay of Lathrop
Lathrop, CA
December 2020
Ienvironment C20Dde. 01
water Figure 74
Section 7
2024 WSMP Amendment
DISTRIBUTION SYSTEM HYDRAULIC CAPACITY EVALUATION City of Lathrop

7. 4. 2 Future System Evaluation
Model results for the buildout scenario were evaluated to anticipate future system deficiencies. As discussed in Section 7.3, the sizes of facilities needed to support future development added to each scenario were verified by the modeling efforts. As such, the following sections discuss how future development and planned infrastructure improvements affect the existing water distribution system facilities.

Given the SSJID Turnout 1 is required to provide sufficient flow to meet demand conditions, the buildout PHD and MDD plus fire flow scenarios were modeled with SSJID Turnout 1 BPS operating at 3, 900 gpm i.e., 50% of buildout ADD) to conservatively mimic the City' s current operational scheme. Currently, the
City utilizes existing tanks, SSJID Turnout 1 ( operating at 1, 381 gpm), and the LAWTF to meet peak demands, and then utilizes SSJID Turnout 1 and LAWTF to refill tanks during the off- peak hours.

7. 4.2.1 PHD Results
Model results indicate that the system can meet minimum pressure criteria of 40 psi system -wide under PHD conditions at buildout, as shown on Figure 7-. Pressures at the nodes with potable water demand range from 44 psi to 62 psi.

Results show that velocities remain elevated near each of the BPSs in the future scenarios ( Figure 7-). As shown in Figure 7-, head losses exceed recommended normal operational head losses ( 7 ft/ k-tfor pipes smaller than 16 inches in diameter or 3 ft/ k-tfor pipes larger than 16 inches in diameter) in the discharge lines of multiple BPSs and SSJID Turnout 1. This exceedance does not necessarily indicate there is a problem unless the head loss is contributing to pressure deficiencies.

7. 4.2. MDD Plus Fire Flow Results
Modeled future fire flow availability and deficiencies are shown on Figure 7- 10. The existing fire flow deficiencies remain in the future scenarios, with exception of hydrants in CLSP which are addressed by future CLSP infrastructure improvements, hydrants on Old Harlan Road and Avon Avenue which are addressed by future I-5 crossing at Lathrop Road, and one hydrant on Murphy Road which is addressed by future tank and BPS at the former Well 21 site.
eki environment
water 7- 12
December 2024
EKI C20049. 01
k
BPS) 6
rTank
r
River Islands Phase2
Tank -
a
d BPS

LATHROP RD
SSJID
Turnout1 I

LOUISE AV
LAWTFTaTank nd BPS L

YOSEMITE AV
L, eoend
f, Sphere of Influence
Existing Infrastructure
Treatment Plant
Pump Station
Enclosed Storage Facility
SSJID Turnout
Pipe
Buildout Facilities
Pump Station
Enclosed Storage Facility
SSJID Turnout
Junction Pressure, psi
Less than 40 ( Not Meeting Criteria)
O 40-5 o 45- 50
50 - 55
55- 65
Abbreviations
BPS = booster pump station
gpm = gallons per minute
LAWTF = Louise Avenue Water Treatment Facility
PHD = Peak Hour Demand
psi = pounds per square inch
SOI = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

2. Well 21 and Well 21 WTF is not active in the
buildout system analysis.

3. SSJID Tumout1 is operating at 3, 900 gpm flow rate
in the buildout modeling scenarios.

Sources

1. Aerial photograph provided by ESRI' sArcGIS Online,
13 November 2024. 0 3, 000 6, 000
Sule In Feel)
Buildout Water System Hydraulic Evaluation
Peak Hour - Pressure
Wafer System Master Plan Amendment
cay or Lathrop
Lathrop, CA
December
Q environment 01C20049.
i & water Figure 7-
River Islands Phase 2
Tank idBPS
BPS3- 6
Tank
r;
SSJID` J
BPS - 5
Turnout 2
Tank

LATHROP RD
SSJID
Turnout 1

OUISE A
IN
LAWTF Tank andd BPS

YOSEMITE AV
Well 21 Tank:
land BBS11.
f,egendSphere of Influence
Existing Infrastructure
PI Treatment Plant
Ex Pump Station
Enclosed Storage Facility
SSJID Turnout
Pipe
Buildout Facilities
Pump Station
Enclosed Storage Facility
SSJID Tumout
Pipe Velocity, fps
Less than 4
4-6
Greater than 6 ( Not Meeting Criteria)
Abbreviations
BpS = booster pump station
f/s = feet per second
gpm = gallons per minute
LAWTF = Louise Avenue Water Treatment Facility
PHD = Peak Hour Demand
SOI = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

2. Well 21 is not active in the buildout system analysis.

3. SSJID Turnout 1 is operating at 3, 900 gpm flow rate in the buildout modeling scenarios.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 13 November 2024.

N 0
az _
3, 000 6, 000
Soak in Feat)
Buildout Water System Hydraulic Evaluation
Peak Hour - Pipe Velocity
Water System Master Plan Amendment
City of Lathrop
Lathrop. CA
eki environment
December
C2004901
water Figure 7-8
River Islands RI -lase
2 Tan - dBPS
des
w'
SSJID
BPS- 5
Turnout2
Tank
i
J ``
BPS -2
Tank

SSJID '
Turnout1

ATHROP RD

LOUISE AV
LAWFF Tank
nd
BPS
Y0SEMITEA.
a® -
Well 21 Tank.
iand
Legend
CZ! Sphere of Influence
Existing Infrastructure
Ea' Treatment Plant
Pump Station
Enclosed Storage Facility
SSJID Turnout
Pipe
Buildout Facilities
Pump Station
Enclosed Storage Facility
SSJID Turnout
Pipe Head Loss, ft/ k-t
Less than
3 3-5
5-7
7- 10
Greater than 10
Pipe Head Loss Not Meeting Criteria
aa Head Loss Exceeds Requirement
Abbreviations
BPS = booster pump station
ft/ k-t = feet per thousand feet
gpm = gallons per minute
LAWTF = Louise Avenue Water Treatment Facility
PHD = Peak Hour Demand
SOI = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. All locations are approximate.

2. Well 21 is not active in the buildout system analysis.

3. SSJID Turnout1 is operating at 3, 900 gpm flow rate
in the buildout modeling scenarios.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 13 November 2024. N o
A _
3, 000 6, 000
Scale in Feet)
Buildout Water System Hydraulic Evaluation
Peak Hour - Pipe Head Loss
Water System Master Plan Amendment
City of Lathrop
Lathrop. CA
environment
December 20x4
C20069. 01
I & water Figure 7- 9
5 River Islands Vhase 2
Tank_ an -BPS
i
BPS) 6
rTank

SSJID '
BPS - 5
L.

LATHRO'
SSJID
Tumout 1 I

LOUISEAV
Ta
x
WTFTank
a
d BPS
BPS -2
Tank
Well 21 Tank.•
land BP, S#

YOSEMITE AV
Legend
L1Sphere of Influence
Existing Infrastructure
Treatment Plant
Pump Station
Enclosed Storage Facility
SSJID Turnout
Pipe
Buildout Facilities
MI Pump Station
Enclosed Storage Facility
SSJID Turnout
Available Fire Flow, Gallons per Minute
Less than 1250
i 1250- 2000
O 2000 - 3000
3000 - 4000
C Greater than 4000
Hydrant Residual Pressure Not Meeting Criteria
Residual Pressure Below Requirement
Abbreviations
BPS = booster pump station
gpm = gallons per minute
LAWTF = Louise Avenue Water Treatment Facility
SOI = Sphere of Influence
SSJID = South San Joaquin Irrigation District
Notes

1. NI locations are approximate.

2. Well 21 is not active in the buildout system analysis.

3. SSJID Turnout 1 is operating at 3, 900 gpm flow rate in the buildout modeling scenarios.

4. Evaluated with fire pumps online at booster pump
stations where effluent pressure drops below effluent
pressure set points.

Sources

1. Aenal photograph provided by ESRI' s ArcGIS Online,
13 November 2024.

N
3000 6, 000
some tr, Peen
Buildout Water System Hydraulic Evaluation
Maximum Day Demands - Available Fire Flow
Water System Master Plan Amendment
coy or Lathrop
Lathrop, DA
rnber eki environment DeceC2006920 c2004s 01
water Figure 7- 10
Turnout 2
Tank
Section 8
2024 WSMP Amendment
WATER SUPPLY, STORAGE, AND PUMPING CAPACITY EVALUATION City of Lathrop 8 WATER SUPPLY, STORAGE, AND PUMPING CAPACITY EVALUATION This section evaluates the City' s water system storage and pumping capacity to meet the recommended performance and operational criteria described in Section 6. 2 under existing and future scenarios. Note that the demands used for sizing these facilities include landscaping and park demands which may be supplied by recycled water in the future. If recycled water is used to supply these demands, then the City can opt to reduce facility sizing requirements accordingly.

8. 1 Existing Water System Evaluation
As discussed below, the City' s existing water system currently has sufficient storage and pumping capacity to meet performance criteria.

8. 1. Water Supply Capacity
The City' s required supply capacity must be greater than MDD. This supply capacity can currently be provided by the firm pumping capacity at the existing SSJID Turnout 1, SSJID Turnout 2, and the LAWTF.

Table 8-1 presents a summary of required and existing firm supply pumping capacity and indicates that the City currently has a supply pumping capacity of approximately 13, 400 gpm, and a surplus capacity of approximately 7, 800 gpm.

8. 1. 2 Water Storage Capacity
The City' s required storage capacity is composed of equalization ( 25% of MDD), fire ( 0. 72 MG based on concurrent industrial and high -density residential fires of 2, 000 and 4, 000 gpm with durations of two hours), and emergency storage ( 75% of MDD). Total existing required storage is equal to 8. 7 MG.

The City currently has 7. 4 MG of storage between LAWTF and Tanks 1 through 6. In addition, the City has a groundwater credit of 4. 5 MG ( see Section 6. 2.3.4). 18 Thus, the City currently has a storage surplus of

3. 1 MG. Table 8-2 provides a summary of existing storage requirements and capacity.

8. 1. 3 Peak Pumping Capacity
The City' srequired peak pumping capacity is equal to the greater of MDD plus concurrent industrial and high -density residential fires or PHD. Peak pumping capacity can be met with a combination of the existing SSJID Turnout 1, the LAWTF, and the BPSs associated with each Tank. The total firm capacity of these pumps is approximately 38, 200 gpm.

Existing MDD is equal to approximately 5,00 gpm and the two concurrent fires are equal to 6, 000 gpm.

Thus, MDD plus fire flow pumping requirement is equal to approximately 11, 500 gpm. PHD pumping requirement is approximately 8, 500 gpm. Therefore, MDD plus fire flow pumping requirements governs.

Table 8- 3 provides an evaluation of firm pumping capacity and indicates that the City currently has a surplus pumping capacity of approximately 26, 600 gpm.

Groundwater credit is calculated as the firm capacity of the wells with backup power ( i.e., with highest -capacity well with backup power out of service) over an 18 -hour period. This is equal to the 18 -hour maximum capacity of Wells 6, 7, and 8. Well 10 is not included because it is highest - capacity well with backup power. Well 9 is temporarily offline due to water quality issues. The City currently don' thave plan to put Well 21 back online. ekienvironment water 8-1
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EKI C20049. 01
Section 8

WATER SUPPLY, STORAGE, AND PUMPING CAPACITY EVALUATION
2024 WSMP Amendment
City of Lathrop
Table 8-1. Existing Water Supply Capacity
Supply Component
Required or Available Firm Supply
Capacity ( a)
gpm MGD
Available Supply Capacity
SSJID Turnout 1 BPS Firm Capacity ( b) 5, 210 7. 5
LAWTF Production Capacity ( c) 4, 150 6. 0
SSJID Turnout 2 BPS Firm Capacity ( b) 4, 000 5. 8
Total Supply Capacity 13, 360 19. 2
Required Supply Capacity Existing Maximum Day Demand ( d) 5,62 8. 0 Notes:
a) Firm pumping capacity reflects the capacity of the pumping station with the largest pump offline. b) Refer to Table 3-1.
c) LAWTF production capacity equals the firm of capacity of Wells 6, 7, and 8. Well 10 is not included because it is highest -capacity well. Well 9 is temporarily offline due to water quality issues. d) Refer to Table 7-1.

Table 8-2. Existing Water Storage Capacity and Requirements Available Storage Capacity
Tank Storage Capacity (a) 7. 4
Groundwater Credit ( b) 4. 5
Total Storage Capacity 11. 9
Required Storage Capacity
Operational 2. 0
Fire ( c) 0. 7
Emergency
Total Required Storage

6. 0

8. 7
Notes:
a) Tank storage capacity includes total capacity of Tanks 1, 2, 3, 4, 5, 6 and the LAWTF Tank. The tank storage capacity does not include the tank at the SSJID turnouts, which are not City facilities. b) Groundwater credit is calculated as the firm capacity of the wells with backup power ( i.e., with highest - capacity well with backup power out of service) over an 18 -hour period. This is equal to the 18 -hour maximum capacity of Wells 6, 7, and 8. Well 10 is not included because it is highest -capacity well with backup power. Well 9 is temporarily offline due to water quality issues. The City currently does not have plan to put Well 21 and Well 21 WTF back online.
c) Required fire storage for one high density residential ( 2, 000 gpm) fire and one industrial or heavy commercial fire ( 4, 000 gpm).
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EKI C20049. 01
Section 8

WATER SUPPLY, STORAGE, AND PUMPING CAPACITY EVALUATION
2024 WSMP Amendment
City of Lathrop
Table 8-3. Evaluation of Existing Firm Pumping Capacity Firm Capacity (a)
Pumping Component
gpm MGD
Available Pumping
Capacity
SSJID Turnout 1 5, 210 7. 5
LAWTF BPS 6, 300 9. 1
BPS - 1 1, 050 1. 5
BPS -2 3, 000 4. 3
BPS - 3 4, 750 6. 8
BPS -4 4, 600 6.

BPS - 5 8, 000 11. 5
BPS -6 5, 300 7. 6
Total Available Firm Pumping Capacity 38, 210 55. 0
Criteria 1: Max Day
Plus Fire Flow
Max Day Plus Two Concurrent Fires ( b) 11, 562 16. 6
MDD+ FF Pumping Capacity Surplus 26, 648 38. 4
Criteria 2: Peak Hour
Demands
Peak Hour Demand 8, 506 12. 2
PHD Pumping Capacity Surplus 29, 704 42. 8
Notes:
a) Firm pumping capacity reflects the capacity of the pumping station with the largest domestic pump offline.
b) Reflects MDD plus one high density residential ( 2, 000 gpm) fire and one industrial or heavy commercial fire ( 4, 000 gpm).
c) MDD with fire flow governs as the more stringent criteria. d) SSJID Turnout 2 was designed to pump directly to Tank 5 or BPS - 5, therefore it' s not accounted for in the total pumping capacity.

8. 2 Future Water System Evaluation
The following sections evaluate the City' s future pumping and storage capacity and requirements at buildout. These sections also describe the storage and pumping capacity that each future development will need to provide to meet the City Standards.

8. 2. 1 Water Supply Capacity
At buildout, the City' sfirm supply capacity is anticipated to increase because of reactivation of Well 9 and the future expansion of SSJID Turnout 2. The total supply pumping capacities at buildout is approximately 18, 760 gpm.

Future supply pumping requirements ( equal to total MDD) are 13, 075 gpm. Table 8- 4 shows the itemized projected Citywide pumping capacity availability and requirements. At buildout, the City is anticipated to have a supply pumping surplus of approximately 5, 685 gpm. eki environment
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EKI C20049. 01
Section 8

WATER SUPPLY, STORAGE, AND PUMPING CAPACITY EVALUATION
2024 WSMP Amendment
City of Lathrop
Table 8-4. Projected Water Supply Capacity
Available Supply
Capacity
Supply Component
SSJID Turnout 1 Capacity
Required or Available Firm Supply Capacity (a)
Existing Buddout
gpm gpm MGD
5, 210 7. 5 5, 210 7. 5
LAWTF Capacity ( b) 4, 150 6. 0 5,50 8. 0
SSJID Turnout 2 Capacity 4, 000 5. 8 8, 000 11. 5
Total Supply Capacity 13, 360 19. 2 18, 760 27. 0
Required Supply
Capacity
Maximum Day Demand 5,62 8. 0 13, 075 18. 8
Notes:
a) Firm supply capacity reflects the capacity of the supply source with the largest pump offline. b) LAWTF production capacity at buildout equals the firm capacity of Wells 6, 7, 8, and 9. Well 10 is not included because it is highest capacity well.

8.2. Water Storage Capacity
The City' s water storage capacity is anticipated to expand to support future development. Table 8- 5 shows the existing and required storage that each development area will need to provide in the future to meet the City' sstorage criteria for emergency and equalization storage.

River Islands already has plans to build an additional 3. 6 MG of storage at the existing Tank 5 site and plans to design two additional 1. 8 MG tanks ( 3. 6 MG total) to support the River Islands Phase 2 development. A 1. 0 MG storage tank at the former Well 21 site is also planned to provide additional storage capacity. Reactivation of Well 9 will increase the City' s groundwater credit to 6. 0 MG. Table 8-6 shows these planned storage projects can support the projected Citywide future storage needs. The City is anticipated to maintain a storage surplus of 2. 0 MG at buildout. eki environment
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EKI C20049. 01
Section 8

WATER SUPPLY, STORAGE, AND PUMPING CAPACITY EVALUATION
2024 WSMP Amendment
City of Lathrop
Table 8-5. Projected Storage Requirements by Development Area Development Area
Projected Storage Requirement
Existing
MG) (a)
Buildout
Central Lathrop Specific Plan ( b) 0. 36 3. 01
Mossdale Landing 1. 05 1.4
Mossdale Landing East 0. 32 0. 39
Mossdale Landing West 0.0 0. 49
Mossdale Landing South 0.8 0. 20
River Islands 1. 36 7. 54
South Lathrop 0.4 0. 28
Lathrop Gateway 0.4 0. 46
Crossroads 0. 93 0. 98
Historic Lathrop 3. 88 4. 24
Sharpe Army Depot 0.1 0.9
Notes:
a) Storage requirement includes equalization storage ( 0. 25 x MDD) and emergency storage ( 0. 75 x MDD). b) Includes CLSP phase 1 and 2 developments.
c) Totals may not sum due to rounding.

Table 8-6. Projected Citywide Storage Requirements
Available Storage
Capacity
Planned
MG)
Storage Component
Existing Storage Capacity ( a)
Existing

7. 4
Buildout

7. 4
Groundwater Credit (b) 4. 5 6. 0
Storage Capacity ( c) 8. 2
Total Existing and Planned Storage Capacity 11. 9 21. 6 Required Storage
Capacity
MG)
Operational 2. 0 4. 7
Emergency 6. 0 14.

System Wide Fire Storage 0. 7 0. 7
Total Projected Required Storage Capacity 8. 7 19. 5
Notes:
a) Tank storage capacity includes total capacity of Tanks 1, 2, 3, 4, 5, 6, and the LAWTF Tank. The tank storage capacity does not include the tank at the SSJID turnout, which is not a City facility. b) Groundwater credit is calculated as the firm capacity of the wells with backup power ( i.e., with highest - capacity well with backup power out of service) over an 18 -hour period. This is equal to the 18 -hour maximum capacity of Wells 6, 7, 8, and 9 at buildout. Well 10 is not included because it is highest -capacity well with backup power.
c) Planned storage includes 1 MG for the planned tank at the Well 21 site, 3. 6 MG for Tanks 5B and 5C, and

3. 6 MG for the River Island Phase 2 tanks.
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December 2024
EKI C20049. 01
Section 8
WATER SUPPLY, STORAGE, AND PUMPING CAPACITY EVALUATION City of Lathrop 2024 WSMP Amendment

8. 2. 3 Peak Pumping Capacity
As with storage capacity, the City' s peak pumping capacity is anticipated to expand to support future development. Table 8-7 shows the Citywide required pumping capacities under MDD plus two simultaneous fire flows and PHD scenarios in the future to meet the City' s pumping requirement criteria.

River Islands has planned Tank 5 BPS expansion, which will provide an additional 4, 000 gpm firm pumping capacity and the planned phase 2 BPS is assumed to provide 8, 000 gpm firm pumping capacity. 19 The planned BPS at the previous Well 21 site is anticipated to provide 3, 000 gpm firm pumping capacity. Table 8- 7 shows these planned BPSs at buildout on top of the projected Citywide pumping capacity needs.

Table 8-7. Projected Citywide Pumping Requirements
Available or Required Capacity ( a)
Existing
gpm mgd
Buildout
gpm mgd
Available
Pumping
Capacity
SSJID Turnout 1 5, 210 7. 5 5, 210 7. 5
LAWTF Booster Station 6, 300 9. 1 6, 300 9. 1
BPS - 1 1, 050 1. 5 1, 050 1. 5
BPS -2 3, 000 4. 3 3, 000 4. 3
BPS - 3 4, 750 6. 8 4, 750 6. 8
BPS -4 4, 600 6. 4, 600 6.

BPS -5 ( b) 8, 000 11. 5 12, 000 17. 3
BPS - 6 5, 300 7. 6 5, 300 7. 6
Planned BPS at the former Well 21 site 3, 000 4. 3
Planned River Islands Phase II BPS 8, 000 11. 5
Total Available Firm Pumping Capacity 38, 210 55. 0 53, 210 76. 6 Criteria 1: Max
Day Plus Fire
Flow
MDD Plus Two Concurrent Fires ( c) 11, 562 16. 6 19, 075 27. 5 Max Day Plus Two Concurrent Fires
Pumping Capacity Surplus
26, 648 38. 4 34, 135 49. 2
Criteria 2: Peak
Hour Demands
PHD 8, 506 12. 2 19, 996 28. 8
Peak Hour Demand Pumping Capacity 29, 704 42. 8 33, 214 47. 8 Notes:
a) Firm pumping capacity reflects the capacity of the pumping station with the largest domestic pump offline. b) Firm pumping capacity at buildout from City of Lathrop Phase I Potable Water Booster Pump station and Storage Tank Expansion Plan at River Islands 100% Plans ( PACE, 2022). c) Value is equal to the MDD plus the fire flow criteria for one high density residential fire ( 2, 000 gpm) and one industrial fire ( 4, 000 gpm).
d) Total pumping capacity surplus or deficit reflects the most stringent criteria. Deficits will be made up by future booster pump stations.
e) SSJID Turnout 2 was designed to pump directly to Tank 5 or BPS -5 therefore it' s not accounted for in the total pumping capacity.
19 Based on 2022 BPS - 5 configurations.
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EKI C20049. 01
Section 9 2024 WSMP Amendment
RECOMMENDED CAPITAL IMPROVEMENT PROGRAM CHANGES City of Lathrop 9 RECOMMENDED CAPITAL IMPROVEMENT PROGRAM CHANGES
This section recommends modifications to the list of CIPs included in the 2019 WSMP and the City' s Fiscal Year ( FY) 2023 - 2025 Capital Improvement Program ( Lathrop, 2023). Table 9-1 summarizes CIPs from the 2019 WSMP and the City' s Capital Improvement Program and incorporates the modifications recommended herein. Figure 9- 1 shows an overview of the distribution system project locations and improvements. Each project is shown in detail in Appendix C. In addition to these CIPs, the analysis presented herein assumes that the development -related improvements identified in Section 7 will also be implemented.

Opinions of probable costs ( OPCs) presented below are conceptual level estimates, considered to have an estimated accuracy range of -30% to +50%, suitable for use for budget forecasting, CIP development, and project evaluations, with the understanding that refinements to the project details and costs would be necessary as projects proceed to design and construction. OPCs for each project are escalated to December 2024 dollars based on an Engineering News Record ( ENR) Construction Cost Index ( CCI) of 13, 632 (20 -city average).

9. 1 Modifications to Water Supply CIPs
The following modifications to the City' s water supply CIPs are identified to reflect the discussion of water supply strategy in Section 5. 6. In addition to these CIPs, it is recommended that the City explore water transfer opportunities with regional water projects to increase the available supplies.

9. 1. Groundwater Treatment Improvements
The City will need treatment for all of its groundwater wells to meet the USEPA' s proposed PFAS MCLs, anticipated to be effective by 2026. As described in Section 5. 6.2, the City completed a feasibility study in 2022 for centralized PFAS treatment at the existing LAWTF. The project OPC for a 7, 000 gpm GAC treatment system was estimated to be $ 22 million, escalated to December 2024 dollars ( Carollo Engineers, 2022). The City currently has budgeted $ 25, 564, 010 for overall groundwater treatment improvements through FY 2026 (Lathrop, 2023).

9. 1. 2 Aquifer Storage and Recovery
As discussed in Section 5. 6.3, the City' ssupplies have historically been highly reliable. However, the City' s surface water supplies face uncertainties with implementation of the Bay -Delta Plan Amendment and new water quality regulations. The City should continue to monitor Bay -Delta Plan Amendment negotiations for the Stanislaus River. If the Bay -Delta Plan Amendment or a Voluntary Agreement with high cutbacks is implemented that significantly impacts the reliability of the SCWSP, an ASR project would boost the City' s dry year water supply and mitigate the impacts of severe droughts. Additionally, an ASR project would be capable of supplying water during water supply emergencies related to water quality concerns or treatment downtime.

Per the City' sfeasibility assessment, ASR wellfields are typically constructed in phases. To pursue the project, the City would construct a full- size ASR well with one or two monitoring wells, and conduct cycle testing to verify operational performance. During the next phase, additional ASR wells would be constructed and placed into operation ( Carollo Engineers, 2023).

The City' s 2023 assessment estimates that constructing the first ASR well for the City, including well construction and equipment costs, would cost $ 5. 6 million escalated to December 2024 dollars. The City' s current Capital Improvement Program includes $ 6. million for project design, construction, acceptance, and commission. EKI estimates a total project OPC at $ 9. 0 million considering a 60% markup for eki environment
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December 2024
EKI C20049. 01
Section 9
2024 WSMP Amendment
RECOMMENDED CAPITAL IMPROVEMENT PROGRAM CHANGES City of Lathrop construction contingency, design, construction management, permitting, and project implementation consistent with other CIPs.

9. 2 Modification to Water Distribution System CIPs
Due to the updated water demand projections evaluated herein, which are significantly lower than those included in the 2019 WSMP, the following projects are removed or modified from the list of the City' s existing CIPs and recommended CIPs in the 2019 WSMP:

The BPS -2 and BPS -3 Pipeline Replacement Projects are no longer necessary ( portion of PW 22- 22);
Well 21 WTF Phase 2 Improvements are no longer necessary, except for the construction of the 1 MG tank and BPS at the Well 21 location;
The Sadler Oak Transmission Improvement Project is no longer necessary; Multiple fire flow improvement projects are no longer necessary or have reduced in scale, including the E. Louise Avenue project ( PW 22- 21), Harlan Road project ( PW 22-2), Easy J Street Alley project near BPS -1 and Crossroads project; and
The I-5 crossing at Lathrop Road was originally anticipated to be completed by developers but is now incorporated as City CIP PW 25- 10 East Lathrop Water Distribution System Improvement project. The project connects the distribution system between Golden Valley Parkway and Old Harlan Road on Lathrop Road.

Modifications to the Harlan Road project ( PW 22-2) are discussed further in Section 9. 2. 1below.

In addition, the following projects recommended in the 2019 WSMP have been completed as of the date of this update:

LAWTF Transmission Improvement Project ( Louise Avenue 12" CIP) BPS -1 Pipeline Replacement Project
Old Harlan Road Fire Flow Improvement Project
One new CIP has been identified to address the fire flow deficiency identified on Murphy Parkway.

9. 2. 1 Harlan Road and South Harlan Road Fire Flow Improvement Project The hydraulic modeling results indicate the fire flow deficiencies at the intersection of Harlan Road and South Harlan Road can be addressed by the City' scurrent CIP PW 25- 10 (previously PW 22- 22), the Harlan Road Fire Flow Improvement Project, in a reduced scale.

The recommended scaled down project consists of:

Replacing approximately 1, 270 LF of existing 6 -inch mains on Harlan Road between Lathrop Road and Shilling Avenue20;
Replacing approximately 600 LF of existing 2 -inch mains on Harlan Road between Shilling Avenue and Warren Avenue with a new 8 -inch main; and
Installing approximately 490 LF of 8 -inch main along Harlan Road to connect to the existing mains at the intersection of Warren Avenue and Harlan Road.
20 This existing pipeline section has been identified with inconsistent diameters of 6" and 8" across various record documents. Further verification may be required to confirm the actual pipe size. ek, environment
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December 2024
EKI C20049. 01
Section 9
2024 WSMP Amendment
RECOMMENDED CAPITAL IMPROVEMENT PROGRAM CHANGES City of Lathrop Installing approximately 70 LF of 8 -inch main connecting new 8 -inch mains on Harlan Road and Old Harlan Road at the intersection of Harlan Road and Shilling Avenue.

To eliminate dead- end pipes and improve system resilience, EKI recommends retaining the original project scope to install approximately 580 LF 12 -inch main connecting the 12 -inch main on South Harlan Road to the new 8 -inch main on Harlan Road.

The total project OPC is approximately $ 1,90, 000.

9. 2. Murphy Parkway Fire Flow Loop to Harlan Road
The City' s existing CIP PW 24- 11 includes installing a new 12 -inch water main from Murphy Parkway across to Harlan Road to loop the dead- end of the 10 -inch water main on Murphy Parkway. The loop is currently completed by an old private 8 -inch main and not included in the City' s hydraulic model. The hydraulic modeling results indicate that replacing the private 8 -inch main with a new 8 -inch line can address the fire flow deficiency identified on Murphy Parkway and increase system reliability. The updated OPC is approximately $ 180, 00.

9. 2. 3 East J Street Alley Residential Fire Flow Improvement Project This project updates BPS -1 Pipeline Replacement and Residential Fire Flow Improvement Project recommended in the 2019 WSMP due to completion of improvements of the BPS -1 discharge main and distribution mains on J Street and Avon Street.

The recommended East J Street Alley Residential Fire Flow Improvement Project addresses existing fire flow deficiencies along the residential alley between 5th and 6th Streets and eliminates the dead- end of the 6" pipe near H Street for higher system resilience. This project consists of:

Replacing approximately 1, 020 LF of existing 4 -inch mains in the alley between 5th and 6th Streets with a new 8 -inch main; and
Installing an approximately 80- LF 6 -inch connection between the existing 10 -inch main on East H Street and the existing 6 -inch main in the alley between 5th and 6th Streets.

Total project OPC is $ 400, 00.

9. 2.4 Lathrop Transmission Main Improvement Project
The City' s existing CIP PW 25- 10 includes installing approximately 1, 450 LF of new 8 -inch transmission main connection between the existing 8 -inch dead- end mains on Lathrop Road on both sides of Interstate Highway 5. The total project OPC is approximately $ 570, 00. eki environment
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December 2024
EKI C20049. 01
Section 9

RECOMMENDED CAPITAL IMPROVEMENT PROGRAM CHANGES
2024 WSMP Amendment
City of Lathrop
Table 9-1. Summary of Recommended Water System Capital Improvement Projects Project #
Water Supply Improvements
Time Frame
Addresses
Total Project OPC
Project ( a) Fire Flow
b) d
Deficiency (
c )( )
WS 1
Well 10 Testing, Analysis and
Modifications ( PW 22- 37) (e)
Existing 844, 527
WS -2
Booster Pump Stations Upgrade
Project ( PW 24- 10) (e)
Existing 800, 00
WS -3
Groundwater Treatment
Improvements ( PW 20- 16) (e)
Existing 25, 564, 010
WS 4
SSJID Turnout 1 Emergency Backup
Power (f)
Buildout 930, 00
WS - 5 Tank and BPS at the Well 21 Site ( g) Buildout 5, 640, 000 WS -6 SSJID SCWSP Phase 2 ( f) Buildout 28,80, 000
WS -7 SSJID Turnout 2 Expansion ( f) Buildout 4,90, 000 WS -8
Aquifer Storage and Recovery
PW 22- 36) (d) (e)
Buildout 9, 000,00
TOTAL WATER SUPPLY IMPROVEMENTS OPC $ 75, 550, 000
Water Distribution System Improvements
WD -1
East J Street Alley Residential Fire
Flow Improvement Project ( PW 25-
10)
Existing Yes 400, 00
WD 2
Harlan Road Fire Flow Improvement
Project ( PW 25- 10) (e) (h) (i)
Existing Yes 1,90, 000
WD -3
Northern McKinley Industrial Area
Fire Flow Improvement Project
Existing Yes h)
WD -4
Murphy Parkway Fire Flow
Improvement Project
PW 24- 11) (e) (j)
Existing Yes 180, 00
WD -5
Lathrop Transmission Main
Improvement Project ( PW 25- 10) Existing Yes 570, 00
WD -6
Lathrop Water Main and
Lateral Upgrade Project ( PW 24- 12)
e)
Existing Yes 120, 00
TOTAL WATER DISTRIBUTION SYSTEM IMPROVEMENTS OPC 2, 460, 000 Notes:
a) Project information is obtained from Table 9- 1 of the 2019 WSMP with their costs escalated to December 2024 dollars, and includes modifications recommended in Sections 9. 1 and 9. 2. b) Time frame refers to when projects are identified to be required. c) Costs shown are presented in December 2024 dollars based on an ENR CCI of 13, 632. 41 (20 -city average), with totals rounded to the nearest $10, 000, except for projects called out in footnote e).
d) Costs include mark- ups equal to 60% for construction contingency ( 25%), design ( 10%), construction management ( 10%), permitting ( 10%), and Project Implementation ( 5%). ekienvironment water 9- 4
December 2024
EKI C20049. 01
Section 9 2024 WSMP Amendment
RECOMMENDED CAPITAL IMPROVEMENT PROGRAM CHANGES City of Lathrop Improvements and associated costs have been carried over from the City of Lathrop Capital Improvement Programs Fiscal Years 2023 - 2025 ( City of Lathrop, 2023).

Construction costs for improvements have been carried over from estimates in the 2013 Draft Water Master Plan, escalated to December 2024 dollars.

Construction costs for Tank and BPS at the former Well 21 site reflect the engineer' sestimate prepared by H2O Urban Solutions in July 2017, escalated to December 2024 dollars.

This project will be conditioned for private development to complete.

For planning purpose, cost estimated shown in the table was based on 6 -inch for existing water mains along Old Harlan Road between Shilling Avenue and Lathrop Road, City to verify the actual size since inconsistent pipe diameters observed in available documentation.

Costs were updated to reflect reduced project scale as recommended in Section 9. 1. eki environment
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EKI C20049. 01
Section 10

REFERENCES
2024 WSMP Amendment
City of Lathrop
10 REFERENCES
Black and Veatch, 2002. South San Joaquin Irrigation District South County Water Supply Program Basis of Design Report, May 2002.

California DOF, 2007. E- 4 Revised Historical City, County and State Population Estimates, 1991- 2000, with 1990 and 2000 Census Counts, August 2007.

California DOF, 2012. E- 4 Population Estimates for Cities, Counties, and the State, 2001- 2010, with 2000 2010 Census Counts, November 2012.

California DOF, 2022. E- 4 Population Estimates for Cities, Counties, and the State, 2011-020, with 2010 Census Benchmark, May 2022.

California DOF, 2023. E- 5 Population and Housing Estimates for Cities, Counties, and the State, January 2021-023, with 2020 Benchmark, May 2023.

DWR, 2021. California' sGround Water Bulletin 118 - Update 2020, California Department of Water Resources, November 2021.

Carollo Engineers, 2022. Technical Memorandum 1: PFAS Centralized Treatment Feasibility Study. Carollo Engineers, June 2022.

Carollo Engineers, 2023. City of Lathrop Aquifer Storage Recovery Feasibility Assessment, final March 2023.

EKI, 2019a. Water System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2019b. Wastewater System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2019c. Recycled Water System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2020. Technical Memorandum: Alternative Evaluation for Use of Groundwater with Detections of Per - and Polyfluoroalkyl Substances, draft 6 March 2020.

EKI, 2021a. 2020 Urban Water Management Plan for the City of Lathrop, June 2021. Available at:

EKI, 2021b.
https:// www. ci. lathrop. ca. us/ publicworks/ page/ urban- water- management- plan 2020 Urban Water Management Plan for South San Joaquin Irrigation District. Available at:
https:// www. ssjid. com/ wp- content/ uploads/ 2020 UWMP SSJID. pdf Lathrop, 2016. Municipal Service Review and Sphere of Influence Plan, 14 April 2016.

Lathrop, 2022a. City of Lathrop General Plan, August 2022. Available at: https:// lathrop. generalplan. org/ Lathrop, 2022b. River Islands Phase 2 Project, https:// www. ci. lathrop. ca. us/ planning/ page/ river- islandsphase- 2- project Lathrop, 2022c. City of Lathrop Department of Public Works Design & Construction Standards. Available at: https:// www. ci. lathrop. ca. us/ publicworks/ page/ design- construction- standards Lathrop, 2023. Capital Improvement Programs Fiscal Years 2023-025. Available at:
https:// www. ci. lathrop. ca. us/ finance/ page/ budget OID and SSJID, 2019. Stanislaus River Basin Proposal, dated 1 March 2019.

RBF, 2009. Water Supply Study, prepared for the City of Lathrop, January 2009. eki environment
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EKI C20049. 01
Section 10

REFERENCES
2024 WSMP Amendment
City of Lathrop
SGI, 2008. Technical Memorandum for the Groundwater Model Update, City of Lathrop Water Supply Study. Source Group, Inc., 25 April 2008.

SWRCB, 2022. Revised Notice of Preparation and California Environmental Quality Act Scoping Meeting, dated 8 August 2022.

UNICO Engineering, 2015. Technical Memorandum to City of Lathrop, Evaluate Uranium Levels Near the Vicinity of Well 21, 19 March 2015.

U. S. Census, 2023. QuickFacts, Lathrop city, California, https:// www. census. Rov/ quickfacts/ lathropcitycalifornia, accessed December 15, 2023.

U. S. EPA, 2023. EPA' s PFAS Strategic Roadmap: Second Annual Progress Report, December 2023. Available at:
2023508v2. pdf
https:// www. epa. gov/ system/ files/ documents/ 2023- 1/ epas- pf- strategic- roadmap- decWoodard & Curran, 2020. River Islands Phase 2 Development Water Supply Assessment, dated September 2020.
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EKI C20049. 01
2024 WSMP Amendment
City of Lathrop

APPENDIX A
Water Demand Factor Evaluation
ekienvironment water
Appendix A

WATER DEMAND FACTOR EVALUATION
2024 WSMP Amendment
City of Lathrop
A. WATER DEMAND FACTOR EVALUATION
EKI evaluated the City' s billing data to develop representative unit water use factors for each anticipated land use category. The water use factors assign a unit volume of water demand to each acre of commercial, industrial, and institutional ( CII) development ( gpd/ acre) or an individual dwelling unit ( gpd/ du). The factors described herein update those developed by EKI in 2020, which were included as part of the City' s 2020 Urban Water Management Plan ( UWMP).

The methodology utilized to verify and update the City' s water demand factors is summarized in
this section.

As discussed in Section 4. 1, the City' s water use has fluctuated over the past several years, responding to changing economic and drought conditions. During the extended drought of 2014- 2017, the City' s
water production decreased dramatically due to the voluntary and mandatory water conservation efforts that were implemented by the City' s water customers. Water
production rebounded between 2017 and 2020 as water use restrictions were lifted and new development projects were constructed, however, is again affected by the recent drought of 2021-022. The City' s water demand factors were last updated in July 2020 based on post - drought water use between 2017 and 2019. The analysis herein verifies the 2020 water demand factors against water use trends through 2021.

Based on these data, 2022 was selected as the " representative year" (i.e., it reflects the latest water use behavioral changes and moderate drought conditions). The total production and per capita water use in 2022 are slightly below the average values over the past 10 years. This level of optimism is appropriate for future projections, given that this number accounts for both the water use behavioral changes and construction of new water -efficient development along with retrofits of existing properties, both of which significantly impacted water use.

A. 1 Residential Water Use Factors
Development of residential water use factors focused on quantifying water use in homes within the City, as a whole and by development area. Historical residential water use was evaluated on a parcel - by -parcel basis based on the City' s water billing data. Annual water use was extracted for residential accounts with complete billing records between 2017 and 2021.

To simplify the evaluation, various development area -specific zoning classes were grouped into one of three categories Low Density Residential ( LDR), Medium Density Residential ( MDR), and High Density Residential (HDR). LDR accounts for Single - Family accounts with lot sizes larger than 4, 000 square feet, while MDR includes Multi -Family accounts and Single - Family accounts with lot sizes equal to or less than 4, 000 square feet. 1 HDR exclusively represents apartment land use. 1 Account type extracted from the City' s potable water billing data. Lot size information based on San Joaquin County Assessor data.
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December 2024
EKI C20049. 01
Appendix A

WATER DEMAND FACTOR EVALUATION
2024 WSMP Amendment
City of Lathrop
Figure A- 1 shows which individual parcels fell into each land use category, according to the San Joaquin County Assessor parcel data. Only accounts with full year of billing data in each year were considered as qualified data for the LDR and MDR water use factor analysis. Figure A- 2 shows the breakdown of total qualified residential accounts in the LDR and MDR categories between 2017 and 2021 by development area. HDR water use were only available between November 2022 and May 2023 with construction and occupation of the Towne Centre Apartment and were evaluated separately.
ekienvironment water A- 2
December 2024
EKI C20049. 01
fL, egendSphere of Influence
Development Areas
Central Lathrop
QCrossroads
L_j
Historic Lathrop Infill and Other Developments
0Lathrop Gateway
Mossdale Landing
Mossdale Landing East
E.]
Mossdale Landing West
u] Mossdale Landing South
ORiver Islands
Sharpe Army Depot
South Lathrop
Land Use Categories
Low Density Residential
Medium Density Residential
High Density Residential
Notes

1. All locations are approximate.

2. Includes all residential accounts with at least one full year of billing data.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 13 November 2024.

N
4, 000 8, 000
Scale in
Residential Land Use Categories
yMter System Master Plan Amendment
Day of Lathrop
Lathrop, CA
December 2024 ekenvironment I & C20009.
water
01 Figure A- 1
Appendix A

WATER DEMAND FACTOR EVALUATION
2024 WSMP Amendment
City of Lathrop
Number
of
Accounts
Figure A- 2 Qualified Low Density and Medium Density Residential Accounts Qualified Low Density Residential Accounts
3, 500
3, 000
2, 500
2, 000
1, 500
1, 000
500
0 316
2017
325
2018
285
2019
Year
314
2020
304
2021
Historic Lathrop Infill Mossdale Landing Mossdale Landing East • Mossdale Landing South • River Islands 500
450
400
350
0 300
c
250
N
12 200
3 Z
150
100
50 0
43 Qualified Medium Density Residential Accounts
42 41
2017 2018 2019
Year
w Historic Lathrop Infill Mossdale Landing Mossdale Landing East • Mossdale Landing South • River Islands 2020
43 2021
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Appendix A

WATER DEMAND FACTOR EVALUATION
2024 WSMP Amendment
City of Lathrop
The available data were further evaluated to assess the extent to which each development area had unique water use patterns. Figure A- 3
presents the average per unit water use between 2017
and 2021 by land use category and development area. These figures indicate that ( 1) while certain patterns are apparent, residential units in each development area, broken down by the selected land use categories, used similar amounts of water per dwelling unit annually, and exhibited similar water use trends during this period; and ( 2) the water use in medium density residential units in the River Islands area are consistently lower than those in the other parts of the City. This confirms the methodology of developing a specific set of factors based on River Islands residential water use for the future water demand projection in this area, and " City- wide" factors to project residential uses for the rest of the City.

As Figure A- 3 shows, though the average water use varied slightly year by year, no significant change in Low Density Residential and Medium Density Residential water use pattern has been identified between 2020 and 2022 compared to 2017 through 2019. As such, the City' s 2020 water demand factors for Low Density Residential and Medium Density Residential categories are confirmed to be ( 1) 330 gpd/ duand 250 gpd/ du for City- wide low and medium - density residential units, respectively, and ( 2) 315 gpd/ du and 235 gpd/ dufor River Islands low and medium density residential units, respectively. A uniform, City- wide high density residential water use factor of 170 gpd/ du was determined by water use in the Towne Centre Apartments in the Mossdale Landing area, since no water use from high density water units are available from River Islands as of the date of this report.
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WATER DEMAND FACTOR EVALUATION
2024 WSMP Amendment
City of Lathrop
Figure A- 3 Low and Medium Density Residential Water Demand Factor Evaluation Per Unit Low Density Residential Water Use
a
450
O. 400
350
c
t
300
250
a
0 200
a
3 150
u • 100
a
50 d
b.° 0
Average
Water Consumption
Per Dwelling
Unit (
gpd/ du)
350
300
250
200
150
100
50 0
2017
Historic Lathrop Infill
327
2018 2019
Year
Mossdale Landing
Mossdale Landing South Mil River Islands
2 2017
351
2020
339
2021
Mossdale Landing East
Low Density Average
Per Unit Medium Density Residential Water Use
Historic Lathrop Infill
Mossdale Landing South
249
2018 2019 2020
Year
toroo Mossdale Landing
moo River Islands
IND
2021
Mossdale Landing East
Medium Density Average
e
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December 2024
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Appendix A

WATER DEMAND FACTOR EVALUATION
2024 WSMP Amendment
City of Lathrop
A. 2 CII Water Use Factors
Per acre water use factors for commercial, industrial, parks/ irrigation, and schools/ institutions were updated based on the City' s billing data from 2017 to 2021. For each CII land use, the total water use each year, including sub - metered irrigation accounts, was divided by the total acreage to determine water use factors. Acreages were calculated by cross- referencing the City' s billing database with the San Joaquin County parcel database. Land use categories were extracted from the City' s billing data account types for each customer.

As part of this update, City staff identified inconsistencies within the City' s billing data account types and reclassified certain CII users, which significantly altered the results compared to the 2020 water demand factors analysis. Figure A- 4 shows which individual parcels fell into each land use category, as confirmed by City staff. Figure A- 5 presents the historical average per acre water use and total area evaluated each year for commercial and industrial land uses.

General commercial and industrial water use factors were evaluated based on the average commercial and industrial water uses between 2017 and 2021, including on -parcel irrigation, respectively. The water use factor was determined to be 1, 550 gpd/ ac for Commercial land uses.

The commercial water demand factor increased significantly compared to the 2020 factor of 860 gpd/ acre, likely due to that a significant portion of commercial accounts were corrected as industrial, government, or park land uses. The average water use by industrial water users between 2017 and 2021 was 1,32 gpd/ ac, generally consistent with the 1, 200 gpd/ ac water use factor for Industrial land uses.

The water use factor for parks and landscape irrigation was quantified based on historical water use data for the following parks:

Apolinar Sangalang Park
Armstrong Park
Crescent Park
Crystal Cove Park
Green Belt Park
Historical Marker
Homsen Park
Islanders Field
Lathrop Dog Park
Lathrop Generations Center
Lathrop Generations Fitness Park
Lathrop Squares
Leland and Jane Stanford Park
Libby Lane Park
Manuel Valverde Park
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Michael Vega Park
Milestone Park
Mossdale Crossing Regional Park
Mossdale Landing Community Park
Park West
River Park North
River Park South
Somerston Park
The Commons at Mossdale Landing
The Green at Mossdale Landing
Tidewater Park
Woodfield Park
William S. Moss Park
Other unnamed community park in
River Islands, Mossdale, and CLSP
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EKI C20049. 01
L, egend
Sphere of Influence
Development Areas
Central Lathrop
QCrossroads
U Historic Lathrop Inn and Other Developments
Lathrop Gateway
QMossdale Landing
Mossdale Landing East
J Mossdale Landing West
Mossdale Landing South
River Islands
Sharpe Army Depot
South Lathrop
Land Use Categories
Commercial
Industrial
sr Park
School
IMP Government
Notes

1. All locations are approximate.

2. Includes all residential accounts with at least one full year of billing data.

Sources

1. Aenal photograph provided by ESRI' s ArcGIS Online,
13 November 2020.

N o
A
eki
a O00 6, 000
Scale In Fee)
CII Land Use Categories
Water System Mester Plan Amendment
CM of Lemrop
Lathrop, CA
024
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December
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water Figure A- 5
Appendix A

WATER DEMAND FACTOR EVALUATION
2024 WSMP Amendment
City of Lathrop
2, 000
1, 800
OD 1, 600
a
1, 400
c 1, 200
E 1, 000
0 • 800
v
600
400
a • 200
0 1, 000
900
800
700
600
v 500
400
300
200
100
eki
0 969
Figure A- 5 Commercial Water Demand Factor Evaluation
1, 770
Commercial Water Demand Factors
1, 362
2017 2018
Industrial
1, 380
1,75
1, 309
1, 540
1, 074
1, cg2
2019 2020 2021
Year
so Commercial
Commercial and Industrial Land Use Acreage Included in Analysis 876
118
2017
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872
2018
El Industrial
856
2019
A- 9
Year
896
2020
WI Commercial
872
2021
December 2024
EKI C20049. 01
Appendix A 2024 WSMP Amendment
WATER DEMAND FACTOR EVALUATION City of Lathrop
Historical water use for parks evaluated herein presents total water use, inclusive of both potable water and recycled water uses, to determine the total irrigational demand of park acreages.

Figure A- 6 shows that park water use increased between 2017 and 2021, likely due to construction of new parks in the new development areas and water use rebound post the 2014 and 2017 drought. Irrigation water demand was suppressed in 2019 due to insufficient water main pressure when the Louise Avenue Water Treatment Facility ( LAWTF) was offline. The average park water use from 2017 to 2021 excluding 2019 was approximately 2, 383 gpd/ ac, generally consistent with the water use factor for Parks/ Irrigation at 2, 450 gpd/ ac.

Historical water use data was reviewed for the following schools and City services for the Schools/ Institutional land use category: 2
Joseph Widmer Jr. Elementary School
Lathrop Elementary School
Lathrop High School
Mossdale Elementary School
NextGeneration STEAM Academy
one. Lathrop
River Islands Technology Academy
Other City institutional uses including fire stations, City Hall, and post offices.

Figure A- 6 shows the schools/ institutional water use has been generally consistent over the past five years and averaged at 1, 322 gpd/ ac, which is generally consistent with the water use factor for Schools/ Institutional at 1, 500 gpd/ ac.
2 Water use in 2020 from the NextGeneration STEAM Academy and River Islands Technology Academy were excluded from analysis due to irregular water billing data. eki environment
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Appendix A

WATER DEMAND FACTOR EVALUATION
2024 WSMP Amendment
City of Lathrop
Figure A- 6 Park and School Water Demand Factor Evaluation 3, 000
m
to 2, 500
2, 128
V
Q
a`, :::
a
c
O
d,.

E
O • 1, 000
a
M
Q 0
140
120
100
80 t) 60
40 20
0 2017
119
2017
ek,1 & water
2018
Park and School Unit Water Demand
2, 095
2018
Park
2019
Year
School
2, 617
2020
Park and School Land Use Acreage Included in Analysis
119
113 — 113
119
2019
Year
DPark I2 School
A- 11
120
2020
2, 695
2021
129
2021
December 2024
EKI C20049. 01
Appendix A

WATER DEMAND FACTOR EVALUATION
2024 WSMP Amendment
City of Lathrop
A. 3 Summary of Water Use Factors
Based on the information presented above, Table A- 1 summarizes the water use factors developed for the 2023 IWRMP Amendment.

Table A- 1. Updated 2022 Water Use Factors
Land Use Category
Low Density Residential 330
Updated
City- wide
Potable Water
gpd/ du
Use Factors
River
315
a)
Islands
gpd/ du
Medium Density Residential 250 gpd/ du 235 gpd/ du
High Density Residential 170 gpd/ du
Commercial 1, 550 gpd/ ac
Industrial 1, 200 gpd/ ac
Parks / Public Landscaping 2, 450 gpd/ ac
Schools / Institutional 1, 250 gpd/ ac
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EKI C20049. 01
2024 WSMP Amendment
City of Lathrop

APPENDIX B
Recommended CIP Details
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6"
12"
8"
12 BPS -1 Tank
Thomsen Rd.
6"
12"
12\ WSMP
Ma
Legend
Sphere of Influence
Existing Pipe
8" PVC Inch -Diameter and Pipe Material
Abbreviations
PVC = polyvinyl chloride
Replacement Pipe, Inches
8 New Pipe, Inches
6 Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' sArcGIS Online, obtained 13 November 2024.
0 375 750
Feet
East J Street Alley Residential
Fire Flow Improvement Project
Water System Master Plan Amendment
City of Lathrop
December 2024
e
environment EKI C20049. 01
I & water Figure B- 1
Legend
f.III"
049\ Maps\ 2023 1\ WSMP
Maps
Orioinal. aprx
U
X

MI MI MI
Sphere of Influence
Existing Pipe
Future Pipe
8" PVC Inch -Diameter and Pipe Material
Abbreviations
PVC = polyvinyl chloride
Notes

1. All locations are approximate.

Replacement Pipe, Inches
8 New Pipe, Inches
8 12
Sources

1. Aerial photograph provided by ESRI' sArcGIS Online, obtained 13 November 2024.
ti 0 425 850
Feet
Old Harlan Road and South Harlan Road
Fire Flow Improvement Project
eki environment
water Figure B- 2
Water System Master Plan Amendment
City of Lathrop
December 2024
EKI C20049. 01
WSMP 12\
MaDS
a
ath:

X_\ C20040\ Maps 20
12 12"
12" 12"
12"
12"
Legend
Sphere of Influence
Existing Pipe
8" PVC Inch - Diameter and Pipe Material
Abbreviations
PVC = polyvinyl chloride
Notes

1. All locations are approximate.

Replacement Pipe, Inches
12 New Pipe, Inches
12 Sources

1. Aerial photograph provided by ESRI' sArcGIS Online, obtained 13 November 2024.
450 900
Feet
Northern McKinley Avenue Industrial
Area Fire Flow Improvement Project
eki
Water System Master Plan Amendment
City of Lathrop
December 2024
environment EKI C20049. 01
water Figure B- 3
Legend
LM

MI MI MI
8" PVC
0 n
2 Sphere of Influence
Existing Pipe
Future Pipe
Inch -Diameter and Pipe Material
Abbreviations
PVC = polyvinyl chloride
Notes

1. All locations are approximate.

New Pipe, Inches
8 Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, obtained 14 November 2024.
0 425 850
Feet
Murphy Parkway
Fire Flow Improvement Project
Water System Master Plan Amendment
City of Lathrop
December 2024
e1( environment EKIC20049. 01
water Figure B- 4
0 Co
C
0 O
Maos\ 2023 t2\ WSMP
Ma
N
V
X
Legend
Sphere of Influence
Existing Pipe
8" PVC Inch - Diameter and Pipe Material
Abbreviations
PVC = polyvinyl chloride
Notes

1. All locations are approximate.

New Pipe, Inches
8 Sources

1. Aerial photograph provided by ESRI' sArcGIS Online, obtained 14 November 2024.
0 150 300
Feet
Lathrop Road Transmission Main
Improvement Project
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City of Lathrop
December 2024
environment EKI C20049. 01
water Figure B- 5

ATTACHMENT D
eki environment
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2024 WASTEWATER SYSTEM MASTER PLAN

AMENDMENT
City of Lathrop
December 2024
EKI C20049. 02
EKI ENVIRONMENT & WATER, INC. 2001
www. ekiconsult. com
Junipero Serra Blvd, Suite 300 • Daly City, CA 94014
eki environment
water
2024 Wastewater System Master Plan Amendment
City of Lathrop
December 2024
Prepared for:

City of Lathrop
390 Towne Centre Drive
Lathrop, CA 95330
Prepared by:

EKI Environment & Water, Inc.
2001 Junipero Serra Blvd., Suite 300
Daly City, California 94014
650) 292- 9100
www. ekiconsult. com
EKI C20049. 02
Jonathan Sutter, P. E.

Project Manager/ Supervising Engineer
A) cotl
Tina Wang, P. E.

Assistant Project Manager/ Associate Engineer
Chris Pittner, P. E.

Project Engineer
2024 WWSMP Amendment
City of Lathrop
2024 Wastewater System Master Plan Amendment
City of Lathrop

TABLE OF CONTENTS
1 INTRODUCTION 1-

1. Project Background 1-

1. 2 Scope of Work 1-

1. 3 Report Organization 1-
2 STUDY AND SERVICE AREAS 2-3

2. 1 City Limits, Sphere of Influence, and Service Boundaries 2-3

2. Specific Plans and Large Planned Unit Development 2- 3

2. 3 Current and Projected Population 2-9
3 CITY' SEXISTING WASTEWATER INFRASTRUCTURE 3-1

3. 1 Wastewater Collection 3-1

3. 1. Gravity System 3- 1

3. 1. 2 Pump Stations and Force Mains 3-5

3. 1. Collection System Intertie 3-5

3. 1. 4 Major Collection System Improvements Completed Since 2019 3-5

3. 2 Wastewater Treatment 3-8

3. 2. 1 Manteca Water Quality Control Facility 3-8

3. 2. Lathrop Consolidated Treatment Facility 3-8
4 EXISTING AND FUTURE WASTEWATER GENERATION 4-1

4. 1 Current and Historical Wastewater Flow 4-1

4. 2 Wastewater Generation Projections 4-5

4. 2.1 Existing Wastewater Generation 4-5

4. 2. Wastewater Generation Associated with Planned Development 4-5

4.2. 3 Total Projected Wastewater Generation 4-5

4. 3 Wastewater Peaking Factors 4-9
5 WASTEWATER TREATMENT CAPACITY ASSESSMENT 5-1

5. 1 Wastewater Treatment Capacity Assessment 5- 1

5. 2 Impacts of Wastewater Strength on Treatment Capacity 5-

5. 2. 1 Manteca Water Quality Control Facility 5-

5.2. Lathrop Consolidated Treatment Facility 5-
6 COLLECTION SYSTEM PERFORMANCE AND DESIGN CRITERIA 6- 1

6. 1 Capacity Criteria 6- 1
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City of Lathrop

6. 2 Minimum Velocity and Slope Criteria 6-1
7 HYDRAULIC ASSESSMENT OF THE COLLECTION SYSTEM 7-1

7. 1 Hydraulic Modeling Approach 7-1

7. 2 Hydraulic Model Update 7-1

7. 2. 1 Model Platform 7- 1

7. 2. Model Update 7- 1

7. 3 Sewer System Hydraulic Modeling Scenarios 7-2

7. 4 Collection System Hydraulic Evaluation 7- 5

7. 5 Force Main and Pump Station Capacity Evaluation 7-8 8 CAPITAL IMPROVEMENT PROGRAM CHANGES TO THE 2019 WWSMP 8-1

8. 1 Modifications to Wastewater Treatment CIPs 8-1

8. 1. Manteca Interim Improvements 8- 1

8. 1. 2 Lathrop CTF Phase 3 Expansion 8- 1

8. 2 Modification to Collection System CIPs 8-2
9 REFERENCES 9- 1
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EKI C20049. 02
2024 WWSMP Amendment
City of Lathrop
TABLES
Table 2-1. City of Lathrop Development Projections by Development Area 2-7 Table 2-. Historical City of Lathrop Population 2- 10
Table 2-3. Current and Projected City of Lathrop Population 2- 11 Table 3-1. Collection System Inventory 3-4
Table 3-2. Summary of Wastewater Pump Station Characteristics 3-6 Table 3-. Wastewater Capacity Allocation at MWQCF 3-8
Table 4-1. Current and Historical Wastewater AAF and Per Capita AAF 4-2 Table 4-2. Current and Historical ADWF and Per Capita ADWF 4-3 Table 4-3. Wastewater Flow Factors 4-5
Table 4-. Projected New Wastewater Flow by Development Area 4-6 Table 4-5. Existing and Future Wastewater Flow by Development Area 4-8 Table 5-1. Projected Wastewater Flow and Treatment Capacity at MWQCF 5-2 Table 5-2. Projected Wastewater Flow and Treatment Capacity at Lathrop CTF 5- 3 Table 5-3. Projected Wastewater Flow and Treatment Capacity, Citywide 5-4 Table 6-1. Minimum Gravity Main Slopes 6-1
Table 7-1. Peak Wet Weather Flow at Pump Stations 7-3
Table 7-2. Summary of Collection System Capacity Deficiencies 7-5 Table 7-3. Force Main Hydraulic Analysis Results 7-9
Table 7-4. Summary of Hydraulic Capacity Analysis for Pump Stations 7- 10 Table 8-1. Summary of Capital Improvement Projects 8-3

FIGURES
Figure 2-1. City of Lathrop Municipal Boundaries and Development Areas 2-6 Figure 2-. Historical and Projected City of Lathrop Population 2- 11 Figure 3-1. City' s Wastewater Infrastructure 3-2
Figure 3-2. City' s
Wastewater Pump Station Drainage Areas 3-
Figure 3-. City' s Wastewater Collection System Schematic 3-7 Figure 4-1. Current and Historical Wastewater Flow by Collection System 4- Figure 4-2. Current and Historical Per Capita Wastewater Flow 4- Figure 4-3. Average Dry Weather Flow and Peaking Factors 4-9 Figure 5-1. Projected Wastewater Flow and Treatment Capacity at MWQCF 5- 2 Figure 5-2. Projected Wastewater Flow and Treatment Capacity at Lathrop CTF 5-3 Figure 5-3. Projected Wastewater Flow and Treatment Capacity, Citywide 5- 4 eki environment
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2024 WWSMP Amendment
City of Lathrop
Figure 7-1. Modeling Scenarios 7-4
Figure 7-2. Existing Collection System Capacity Deficiencies 7-6 Figure 7-3. Buildout Collection System Capacity Deficiencies 7- Figure 8-1. Recommended Collection System Improvement Projects 8-4

APPENDICES
Appendix A
Appendix B
Appendix C
Appendix D
Wastewater Generation Factor Evaluation
Wastewater Peaking Factor Evaluation
Summary of Monitoring Results from Evaluation of Biochemical Oxygen Demand Contribution to Manteca Water Quality Control Facility
Recommended CIP Details

APPENDIX D FIGURES
Figure D- 1. Stonebridge Gravity Main Replacement and Parallel Force Main Project Figure D- 2. Woodfield West Deficiency Project - Alternative A Figure D- 3. Woodfield West Deficiency Project - Alternative B Figure D- 4. J Street Gravity Main Replacement Project
Figure D- 5. Easy Court/ O Street Gravity Main Replacement Project ekienvironment water
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EKI C20049. 02
2024 WWSMP Amendment
City of Lathrop

LIST OF ABBREVIATIONS
AAF Average Annual Flow
AAFES Army & Air Force Exchange Services
ac acre
ADWF Average Dry Weather Flow
AOI Area of Interest
BSF Base Sanitary Flow
BOD Biological Oxygen Demand
CCI Construction Cost Index
CII Commercial, Industrial, and Institutional
CIP Capital Improvement Projects
City City of Lathrop
CLSP Central Lathrop Specific Plan
d/ D depth to Diameter
Depot Sharpe Army Depot
DOF Department of Finance
du dwelling unit
EKI EKI Environment & Water, Inc.

ENR Engineering News Record
fps feet per second
GIS Geographical Information System
gpd gallons per day
I-5 Interstate 5
I& Infiltration and Inflow
IWRMP Integrated Water Resources Master Plan
Lathrop CTF Lathrop Consolidated Treatment Facility
LF Linear Feet
LS Lift Station
MGD Million Gallons per Day
MWQCF Manteca Wastewater Quality Control Facility
NPDES National Pollution Discharge Elimination System
OPC Opinion of Probable Cost
PS Pump Station
PVC Polyvinyl Chloride
PWWF Peak Wet Weather Flow
SCADA Supervisory Control and Data Acquisition
SLSP South Lathrop Specific Plan
SOI Sphere of Influence
TDH Total Dynamic Head
UWMP Urban Water Management Plan
VC Vitrified Clay
WDR Waste Discharge Requirements
WWSMP Wastewater System Master Plan
WWTF Wastewater Treatment Facility
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EKI C20049. 02
2024 WWSMP Amendment
EXECUTIVE SUMMARY City of Lathrop

EXECUTIVE SUMMARY
EKI Environment & Water, Inc. ( EKI) has prepared this Wastewater System Master Plan Amendment WWSMP Amendment) for the City of Lathrop, California ( City). This WWSMP Amendment was developed as part of the 2024 Amendment to the City' s Integrated Water Resources Master Plan IWRMP Amendment), a comprehensive planning process involving the City' s Potable Water System,
Wastewater System, and Recycled Water System Master Plans. This WWSMP Amendment incorporates new information that has become available and changed planning assumptions since the completion of the 2019 IWRMP.

The current population within the City is approximately 35, 080 as of January 2023 ( California DOF, 2023). The City has experienced significant growth and anticipates growth to continue in the future given the existing entitlements for several large residential developments.

CITY' S EXISTING WASTEWATER INFRASTRUCTURE
Wastewater from the City is treated at two facilities: ( 1) the Lathrop Consolidated Treatment Facility Lathrop CTF, or LCTF), and ( 2) the Manteca Wastewater Quality Control Facility ( MWQCF). The City' s allocated capacity at the MWQCF is 1. 451 million gallons per day ( MGD) of dry weather flow per the City' s 2002 Agreement Amendment with Manteca. The Lathrop CTF has a treatment capacity of

2. 5 MGD. The City is currently planning a Phase 3 Expansion that will expand CTF' s capacity to a total of

5. 0 MGD.

The City' s wastewater collection system consists of approximately 102 miles of gravity mains, 23. 6 miles of force mains, as well as 15 lift stations and pump stations. The City has a Supervisory Control and Data Acquisition ( SCADA) system for control and monitoring of facilities. The City' s wastewater infrastructure is shown on Figure ES -1.

EXISTING AND FUTURE WASTEWATER GENERATION
In 2022, the City generated a total average annual flow (AAF) of 2. 17 MGD, including 1.1 MGD treated at the MWQCF ( 51%) and 1. 06 MGD treated at the CTF ( 49%). The City' s average dry weather flow ADWF) was essentially equal to its AAF between 2017 and 2022, indicating minimal rainfall - induced infiltration and inflow ( I&). The total per capita ADWF is approximately 70 gallons of wastewater per capita per day.
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December 2024
EKI C20049. 02
fL. eoendSphere of Influence
n Approximate Area of WWTF
Oa Pump Station or Lift Station
River Islands 2A PS
Valley Crossings LS
Stanford CrossingrPS
Mossdale PS'
BEIM
River Island
Mein PS

DE LIMA RD

DOS REIS RO
in North
Harlan PS
Stonebndge PS t.

Easy Ct LS
O St. PS
j1 Crossroads PS
I
Southoegrop PS
Lathrop CTF
Sherpe[ PS
Private)
Woodfield LS;

ILATHROP RD
California :
t Natural ProdLcts
PS ( Private)
McKinley I
Ave PS
Louise Ave PS
t LOWSE AV
SSI PS
ovate)
LIP LSet
fPn ate)
Lathrop
MWQCF Flow Getaway PS
YO3EMITE AV
Ga
Meter
MWQCF, r
Gravity Main Diameter, Inches
4-14-6
8 20-1
10 - 24
12 - > 30
Force Main Diameter, Inches
4 ••• 14-6
8 20-1
10 --- 24
12 - - > 30
Abbreviations
CTF = Consolidated Treatment Facility
LIP = Lathrop Industrial Park
LS = lift station
MWQCF = Manteca Water Quality Control Facility
pg = pump station
SSI = Super Store Industries
WWTF = wastewater treatment facility
Notes
1 All locations are approximate.

Sources
1 Aenel photograph provided by ESRI' s ArcGIS
Online, 14 May 2024.
3, 000 6, 000
SuN in Fmk)
City' s
Wastewater Infrastructure
Wastewater Svatem Master Plan Amendment
City of LethrOp
Lathrop, CA
ekiDecember, environment C20A8 00480A2
Water Figure ES -1

EXECUTIVE SUMMARY
2024 WWSMP Amendment
City of Lathrop
Land use -specific wastewater generation factors were updated using the 2017 through 2022 historic wastewater flow and parcel -level water use data. The wastewater generation factors serve as the basis to estimate ADWF for future developments. The IWRMP updated wastewater generation factors ( in units of gallons per day per dwelling unit or gallons per day per acre; gpd/ du or gpd/ ac) are presented in Table ES -1 below.

Table ES -1 Wastewater Flow Factors
Low Density Residential
Wastewater Flow
City -Wide
240 gpd/ du
Factor
River Islands
200 gpd/ du
Medium Density Residential 200 gpd/ du 155 gpd/ du
High Density Residential 110 gpd/ ac
Commercial 755 gpd/ ac
Industrial 240 gpd/ ac
Parks 55 gpd/ ac
Schools/ Institutional 220 gpd/ ac
Wastewater ADWF projections were calculated as the sum of the two major components of future wastewater flow: (1) the volume of wastewater that best represents existing wastewater generation within the City, and ( 2) the anticipated wastewater generation associated with the future development projects and planning areas.

The City' s projected wastewater generation by sector and by development area are estimated in fiveyear increments between 2025 and buildout in 2045. It is anticipated that the City' s total ADWF at buildout in 2045 is estimated to be 5. 67 MGD, which is 12. 5% lower than the projections included in the 2019 WWSMP of 6. 48 MGD. An ADWF of 1. 36 MGD is anticipated to flow to MWQCF from Historic Lathrop and 4. 31 MGD is projected to flow to the Lathrop CTF at buildout. The vast majority of the projected increase in wastewater generation at the CTF above current rates is associated with new development in River Islands and Central Lathrop.

WASTEWATER TREATMENT CAPACITY ASSESSMENT
The City' s allocation at the MWQCF is sufficient to meet the projected wastewater flows to MWQCF at buildout. Flows to the CTF is anticipated to exceed the current CTF capacity between 2030 and 2035.

The planned Phase 3 Expansion at the CTF will provide sufficient capacity to meet projected flows through buildout.

Both the MWQCF and the Lathrop CTF are observing increasing wastewater strength ( i.e. concentration of pollutants and nutrients in wastewater) likely due to improved water use efficiency during the recent droughts and in response to state regulations. The increases in influent wastewater strength may further limit treatment capacities at the treatment plants. To review the pollutant concentration in Lathrop' s
wastewater conveyed to the MWQCF, EKI conducted monitoring study during October 2022.

HYDRAULIC ASSESSMENT
EKI updated the sewer system hydraulic model to represent the City' s utility infrastructure as of January 2023. The hydraulic model was used to assess the ability of the City' s existing infrastructure to support the wastewater flow projections summarized in Section 4. Existing infrastructure was assessed under two scenarios: Existing ( 2022) and Buildout ( 2045).
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December 2024
EKI C20049. 02
2024 WWSMP Amendment
EXECUTIVE SUMMARY City of Lathrop
The City' s collection system was primarily assessed against the capacity criteria, including depth to diameter ( d/ D) ratio in gravity mains and maximum velocity in force mains. Model results have shown that approximately 3% of City' s existing gravity mains will not meet the capacity criteria by 2045. Most capacity deficiencies identified in the Buildout scenario already exist in the existing system, although the degree of deficiency may increase with projected development.

Pump stations are evaluated against the ability to convey peak wet weather flow ( PWWF) within a station' sfirm capacity. A capacity deficiency has been identified in the Stonebridge Lift Station ( LS) in both the Existing and Buildout scenario. All other pump stations are projected to have sufficient capacities to meet existing and future PWWFs.

The City' s existing and planned force mains are able to convey projected wastewater flow through 2045.

RECOMMENDED CAPITAL IMPROVEMENT PROGRAM
The recommended collection system capital improvement projects ( CIPs) from the 2019 WWSMP and the City' s existing Capital Improvement Programs ( Lathrop, 2023) have been reviewed and confirmed to address the potential deficiencies identified in the updated hydraulic assessment. However, EKI recommends additional analyses be conducted to confirm the required project extents and infrastructure sizing. Modifications and additions were made to treatment projects based on findings from the wastewater treatment capacity assessment in Section 5.

Figure ES -2 shows an overview of the collection system capacity project locations, and Table ES -2 summarizes all the identified collection system improvement projects, including location, proposed improvements, estimated planning level costs, and alternatives.

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December 2024
EKI C20049. 02

EXECUTIVE SUMMARY
2024 WWSMP Amendment
City of Lathrop
Table ES -2. Recommended Capital Improvement Projects
Addresses
Project Modeled
Project Timeframe
Number Surcharging in
Existing Scenario
Treatment Facility Improvement Projects
Total Project OPC ( a)
WWT- 1 Manteca Interim Improvements Near -term (b)
WWT 2 CTF8; Phase 3 Expansion ( WW 22 -
Near
3CTF
term ( c) 23, 700, 000
WWT 3
Surface Water Discharge ( WW
20- 17) (d)
Existing 12, 699, 000
Total Treatment Facility Improvements OPC 36,99, 000
Collection System Improvement Projects
WW -1
Stonebridge Gravity Main
Replacement and Pump Station
Upgrade ( WW 22-5) (e)
Existing No 850, 00
WW 2A
Woodfield West Deficiency Project
Alternative A ( WW 22-6) Existing ( f) No 2, 730, 000
WW 26
Woodfield West Deficiency Project
Alternative B ( WW 22- 26) Existing ( f) No 2, 400, 000 WW -4
J Street Gravity Main Replacement
Project
Existing ( f) Yes 1, 690, 000
WW 5
Easy Court / O Street Gravity Main
Replacement Project
Existing No 1, 370, 000
WW -6 O Street Pump Station Upgrade Existing No 1, 560, 000 Total Collection System Improvements OPC 10, 600, 000
Miscellaneous Collection System Projects
WW -8 Temporary Flow Monitoring 100, 00
WW 9
Wastewater Lift Station Access
Modifications ( PW 24- 14) (d)
FY 23-5 CIP 475, 000
WW 9
Ozone Upgrade for Wastewater
Pump Stations ( PW- 24- 15) (d)
FY 23-5 CIP 75, 000
Total Miscellaneous Collection System Improvements OPC 650, 00 Notes:
a) Costs shown are presented in December 2024 dollars based on an ENR CCI of 13, 632. 41 (20 -city average).
b) City is currently evaluating the appropriate level of contribution to improvements at the MWQCF. c) City is currently issuing a request for proposal to PACE which may update this project OPC. d) Project included as a part of the City of Lathrop Capital Improvement Programs Fiscal Years 2023-025 report.
e) Connecting North Harlan Rd businesses which currently pump into the Stonebridge collection system to the North Harlan Rd SSFM can be considered as an alternative. f) Project addresses existing deficiencies, however future development influences recommended pipe or pump sizes to be installed.
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December 2024
EKI C20049. 02
WW -2B: Woodfield West
Deficiency Project
Alternative B

DE LIMA RD

DOS REIS R
WW - 4: J Street
Gravity Main
Replacement
J
L WW- 1: Stonebridge Gravity Main
Replacement and Parlllel
Force Main
i
I/
WW -6: O Street
P, S Replacement
WW -5: Easy Court/ 0Street\
Gravity Main Replacement
Ia QQgp
CTF
WW -2A: Woodfield West
Deficiency Pioject - Alternative A
1 LATH ROP RD

MCKINLEY
AV

LLILOUISE AV
a
I
S1. ja' OSEMITE AV
egend
Sphere of Influence
i Approximate Area of WVVTF
D Pump Station or Lift Station
MO Pump Station or Lift Station Upgrade
Force Main
Gravity Main
Diameter of Replacement Sewer
e•
10"
12"
15"
18"
Diameter of New Force Main
Abbreviations
CTF = Consolidated Treatment Facility
MWQCF = Manteca Water Quality Control Facility
WWTF = wastewater treatment facility
Notes

1. All locations are approximate.

2. A detailed map for each project is Included in Appendix D.

Sources

1. Aerial photograph provided by ESRI• s ArcGIS Online, 12 March 2024.

N o
A _
2, 500 5, 000
Soak = Feel)
Recommended Collection System
Improvement Projects
Wastewater System Master Plan Amendment
City of Lahop
Lathro, CA
December ek,I
environment C2004802
water Figure ES -2
Section 1
Introduction
2024 WWSMP Amendment
City of Lathrop
1 INTRODUCTION
EKI Environment & Water, Inc. (EKI) has prepared this Wastewater System Master Plan Amendment WWSMP Amendment) for the City of Lathrop, California ( City). This WWSMP Amendment was developed as part of the 2024 amendment to the City' s Integrated Water Resources Master Plan IWRMP Amendment), a comprehensive planning process involving the City' s Potable Water System,
Wastewater System, and Recycled Water System Master Plans. This WWSMP Amendment updates the City' s 2019 WWSMP ( EKI, 2019a). The IWRMP Amendment was completed through a coordinated effort between multiple City departments and provides a unifying framework to support utility operations and capital improvement program ( CIP) development and implementation.

Since the 2019 IWRMP was completed, new information has become available and certain planning assumptions have changed that require an amendment to the IWRMP. The factors that influence this WWSMP Amendment include the following:

Land Use Information: The City completed a General Plan Update in September 2022 which included updated growth projections for the City. In addition, development projections have changed significantly in the River Islands area with approval of the modified River Islands Phase 2 project in June 2021 and in the Central Lathrop area.

River Discharge Permit: The City has obtained a National Pollutant Discharge Elimination System NPDES) permit to discharge a portion of the wastewater treated at the Lathrop Consolidated Treatment Facility ( CTF) in the San Joaquin River and deliver the remaining recycled water to retail customers. To support use of recycled water for landscape irrigation, the City obtained coverage under General Order WQ- 2019- 0058- DDW- R5017 and submitted a Title 22 Report Addendum in 2020. The City began delivering recycled water for urban uses in the summer of 2021 and discharging to the San Joaquin River in February 2024. These changes reduce the City' s potable water demand, and affect the operations and infrastructure needed of the City' s wastewater effluent disposal and recycled water distribution systems.

Increases in Wastewater Strength: both the Manteca Wastewater Quality Control Facility MWQCF) and the Lathrop Consolidated Treatment Facility ( Lathrop CTF) are observing increasing wastewater strength ( i.e. concentration of pollutants and nutrients in wastewater) likely due to improved water use efficiency during the recent droughts and in response to state regulations. The recent increases in wastewater strength have resulted in decreased hydraulic capacities at the treatment plants and requires a reassessment of the City' streatment capacity against projected wastewater flows.

1. 2 Report Organization
The WWSMP is organized into the following sections:

Section 1 - Introduction
Section 2 - Study and Service Areas
Section 3 - City' s Existing Wastewater Infrastructure
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December 2024
EKI C20049. 02
Section 1
Introduction
2024 WWSMP Amendment
City of Lathrop
Section 4 - Existing and Future Wastewater Generation
Section 5 - Wastewater Treatment Capacity Assessment
Section 6 - Hydraulic Assessment of the Collection System Section 7 - Capital Improvement Program Changes to the 2019 WWSMP Section 8 - References

1. 3 Scope of Work
The scope of work for the WWSMP Amendment included the following primary tasks:

Update of the wastewater system hydraulic model network to incorporate system improvements completed since the 2019 WWSMP or those currently in design or under construction;
Review of the City' s basic assumptions, criteria and conclusions in wastewater planning, e.g., wastewater system design criteria, pump station operations, and infiltration and inflow rates; Update of the land use -specific wastewater flow unit factors based on wastewater flow and water use between 2017 and 2021;
Development of wastewater generation projections based on land use consistent with the General Plan Update ( adopted September 2022) and River Islands Phase 2 project ( approved June 2021);
Verification and update of the peaking curve to evaluate peak wet -weather flows; Assessment of wastewater treatment capacity against updated wastewater flow projections; Assessment of the existing collection system under existing and future flow conditions using steady- state model simulations;
Evaluation of pump stations, force mains, and conveyance alternatives; Verification of the list of Capital Improvement Programs ( CIPs) included in the 2019 WWSMP; and
Preparation of the amended WWSMP document.
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EKI C20049. 02
Section 2 2024 WWSMP Amendment
Study and Service Areas City of Lathrop
2 STUDY AND SERVICE AREAS
The City of Lathrop ( also referred to herein as the City) was incorporated on July 1, 1989 and is located in San Joaquin County, approximately 10 miles south of the City of Stockton and directly west of the City of Manteca. The City lies east of the Coastal Range that separates California' s Central Valley from the San Francisco Bay Area. Interstate 5 ( I-5), a major north -south interstate corridor, bisects the City. The City is also connected by Highway 120 which runs east -west through the southeastern -most part of the City, and by Interstate 205, which connects Interstate 580 to 1-5. The City is also served by the Altamont Commuter Express ( ACE) train, which travels along the southern and eastern border of the City. The community was originally developed primarily east of I-5. Beginning in 2003, major new developments have been constructed west of I-5 and others are currently planned or under construction in this area.

This section provides an overview of the City' s service area, including discussions of the City' sservice area boundaries, planned developments, and population.

2. 1 City Limits, Sphere of Influence, and Service Boundaries The City currently encompasses an area of approximately 13, 400 acres, or about 20. 9 square miles. The City' s Sphere of Influence ( SOI) is slightly larger with an area of about 13, 600 acres, or 21. square miles.

The City' sSOI includes two unincorporated areas:

1. Approximately 134 acres northeast of the City boundary and along Roth Road that is designated Freeway Commercial and Limited Industrial, and

2. Approximately 62 acres southeast of the City boundary that is designated Service Commercial and part of the Lathrop Gateway Business Park Specific Plan area.

The City reduced their SO1 in 2016 to exclude an additional unincorporated area ( approximately 2, 100 acres) located north of the Central Lathrop Specific Plan ( Central Lathrop or CLSP) area and west of 1-5. Much of this area does not have a General Plan land use designation. The City has designated this area as an Area of Interest ( AOI) (Lathrop, 2016). Figure 2-1 shows the City limits, SOI, and AOI.

The City' s wastewater collection system service area is generally contiguous with the City limits. The City currently provides wastewater service to approximately 6, 100 residential, commercial, industrial and institutional/ governmental properties.

A few large industrial facilities ( e.g., Simplot and California Natural Products) manage their wastewater onsite. California Natural Products independently treats and land applies most of their wastewater onsite and sends the remaining flows to the City' scollection system. The City began sewer service to the 724 - acre Sharpe Army Depot in 2022.

2. Specific Plans and Large Planned Unit Development
The City has experienced significant growth in recent years and is anticipating growth to continue, particularly in several approved or pending large development projects within the City. Infrastructure needs for these projects are evaluated in this document. These projects are described below and shown on Figure 2- 1 and Table 2-1, based on City and developer projections. Specifically, Table 2- 1 lists the number of new residential dwelling units and commercial, industrial, and institutional ( CII) acreage that is anticipated to be connected to the City' ssewer system in five- year increments between 2025 and the anticipated buildout at 2045. A general description of the development areas and the total development planned at buildout is described below.
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EKI C20049. 02
Section 2 2024 WWSMP Amendment
Study and Service Areas City of Lathrop
Central Lathrop Specific Plan. The Central Lathrop Specific Plan proposes development of 1, 520 acres located west of I-5. Phase 1 of the project is anticipated to be completed by 2040 and consists of a total of 579 high density units, 1, 483 variable density residential units, and 144 acres of commercial land uses. The project also includes two schools and 161 acres of recreational land use and open space. Phase 2 of the project includes 682 acres of light industrial use and a 5 -acre park.

Mossdale Landing. Mossdale Landing is a mixed - use master planned community that is anticipated to be completed by 2030. Construction at Mossdale Landing began in 2003 and approximately 1, 640 residential units have been constructed thus far. An additional 66 low density are anticipated by project completion. In addition, the development is allocating a total of 35 acres of land for two schools, 40 acres for parks, and 25 acres for commercial development.

River Islands. The 4, 995 -acre River Islands development is located west of the San Joaquin River and east of Paradise Cut on land known as the Stewart Tract. The development proposes a mixture of low, medium and high density residential units. According to its recently amended Specific Plan, River Islands will consist of two phases and a total of 15, 000 homes, a 260 -acre employment center, a 79 -acre town center, 235 acres of parks and ten schools. About 2, 800 low density residential units were constructed and occupied by late 2022. The estimated project completion date is 2040 ( Lathrop, 2022b; Woodard & Curran, 2020).

Lathrop Gateway Business Park Specific Plan. The Lathrop Gateway Business Park Specific Plan proposes commercial and industrial development of approximately 384 acres to be completed by 2040. The City annexed 213 acres of this area in June 2012 and 99 acres of the remaining 117 acres in May 2016. This would result in approximately 4. 7 million square feet of service commercial, limited industrial, distribution, and research and development related uses, and approximately 741, 000 square feet of commercial office and retail uses. The first phase of the project includes approximately 167 acres of limited industrial, 83 acres of service commercial, and 57 acres of office and commercial retail uses and is anticipated to be completed by 2030.

South Lathrop Specific Plan. The South Lathrop Specific Plan was approved by the City Council on 20 July 2015 and includes a 315 - acre plan area. The Specific Plan proposes approximately 10 acres of commercial office uses, 246 acres of limited industrial, 31 acres of open space, and 27 acres of roads and public facilities. The City South Lathrop Specific Plan area was annexed into the City in May 2016. The South Lathrop Commerce Center, approximately 272 acres within eki environment
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December 2024
EKI C20049. 02
Section 2 2024 WWSMP Amendment
Study and Service Areas City of Lathrop
the South Lathrop Specific Plan, is anticipated to be completed by 2030. The South Lathrop Commerce Center will encompass all of the South Lathrop Specific Plan area with the exception of approximately 24 acres of light industrial, 1. 2 acres of office commercial, and 19 acres of open space and public roads.

Historic Lathrop Infill and Other Developments East of I-5. The portion of the City east of I-5 is anticipated to expand and add density in the future. Currently, this area consists of approximately 3, 160 low density and 455 medium density units, commercial and industrial areas, and a few public parks. Future residential growth of this area is expected on undeveloped/ underutilized and redeveloped parcels consolidated from large lots where low density residential units would be demolished. New residential projects are estimated to consist of 52 low density, 218 medium density, and 48 high density residential units, increasing the total existing residential unit count by 318 units.

Sharpe Army Depot. During World War II, the US Army created the Sharpe Army Depot ( Depot) in the rural Lathrop Community to allow shipment of major army supplies to the western United States. The Depot is comprised of a 724 -acre facility south of Roth Road and has served both the Army and Airforce with a variety of supplies depending on the demand of goods and supplies created by war time efforts. The Depot is occupied by the AAFES West Coast Distribution Center that employs 348 workers. Prior to 30 September 2014 the Defense Logistics Agency was also housed at the Depot; its workforce of 700 workers has since been transferred to the larger Tracy Army Depot. The City began providing water and sewer services to the Sharpe Army Depot in 2022, including the AAFES and the California National Guard properties. eki environment
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December 2024
EKI C20049. 02
River
Islands
ti5\
Area of ! Mao*
Central
enkn
Alley
Doom
IPstorro Lathrop ! Moll
and Oliser Developments
ari c.w
cwara.. nm
lDrLe_ endCity Limit
173 Sphere of Influence
EDArea of Interest
EDRail Cargo Container Yard
Development Areas
Central Lathrop
QCrossroads
Historic Lathrop lab and Other Developments
ED Lathrop Gateway
EZI Mossdale Landing
r- Mossdale Landing West
Mossdale Landing East
Mossdale Landing South
River Islands
Sharpe Army Depot
Q South Lathrop
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 12 March 2024.

N
o
A
4, 000 8, 000
Sole in FM)
eki
City of Lathrop Boundaries
and Development Areas
Wastewater System Master Plan Amendment
City of Latnron
Lathrop, CA
mber
environment DaceC2004a02 czoo4e Dz
water Figure 2- 1
Section 2
Study and Service Areas
2024 WWSMP Amendment
City of Lathrop
Table 2-1
City of Lathrop Wastewater Development Projections by Development Area Land Use Designation
Central Lathrop Phase 1
Units
2025 2030 2035 2040
Incremental New Development ( a)( b) Total New
2045 Development
Buildout)
Low Density Residential du 500 264 764
High Density Residential du 246 210 123 579
Commercial ac 13. 0 60. 72. 0 145. 6
Mixed Use ac 51. 0 51. 0
Parks ac 39 5. 0 44. 1
CentralLathrop - Phase 2
Light Industrial / R&D Flex ac 90 592 682
Parks ac 5 5
Mossdale - All Developments ( c)
Low Density Residential du 37 829 66 932
Medium Density Residential du 85 85
High Density Residential du 84 84
Commercial ac 4. 6 8. 5 8. 0 17. 0 38. 1
Parks ac 4. 0 11. 0 15. 0
Schools ac 16. 2 16. 2
Mossdale Landing
Low Density Residential du 66 66
Medium Density Residential du 0
High Density Residential du 0
Commercial ac 4. 6 1. 5 6
Schools ac 16. 2 16
Mossdale Landing East
Low Density Residential du 37 37
High Density Residential du 84 84
Commercial ac 7. 0 7
Mossdale Landing South
Medium Density Residential du 85 85
Commercial ac 8. 0 17. 0 25
Parks ac 4. 0 4
Mossdale Landing West
Low Density Residential du 829 829
Parks ac 11. 0 11
River Islands
Low Density Residential du 768 1, 218 1, 218 1, 218 4,22 Medium Density Residential du 676 945 945 945 3, 511
High Density Residential du 1, 395 1, 395 1, 395 4, 185 Town Center ac 26. 3 26. 3 26. 3 79
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December 2- 024
EKI C20049. 02
Section 2
Study and Service Areas
2024 WWSMP Amendment
City of Lathrop
Table 2-1
City of Lathrop Wastewater Development Projections by Development Area Land Use Designation Units
ac
Incremental
2025 2030

86. 1
New Development
2035

86. 1
2040

86. 1
a)( b)
2045
Buildout)
Total New
Development
Commercial 258
Schools ( d) ac 32. 5 15. 0 15. 0 14. 0 77
Parks ac 19. 0 60. 9 61. 0 61. 0 201. 9
South Lathrop
Light Industrial / R&D Flex ac 67. 0 32. 8 99. 8
Office Commercial ac 8. 1. 2 10. 0
Lathrop Gateway
Light Industrial / R&D Flex ac 66. 0 16. 6 82. 6
Office Commercial ac 51. 0 11. 7 62. 7
Open Space ac 2. 5 1. 6 4. 1
Crossroads ( c)
Industrial ac 23. 0 23. 0
Commercial ac 1. 5 1. 5
Historic Lathrop and Other Development Areas ( c)
Low Density Residential du 12 6 5 29 52
Medium Density Residential du 27 26 26 26 113 218
High Density Residential du 48 48
Commercial ac 22. 0 13. 6 8. 0 43. 6
Industrial ac 18. 0 24. 0 42. 0
Sharpe Army Depot
Industrial ac d) d)
Notes:
a) Dwelling unit counts and acreages were based on information provided by developers and the City in July 2020 and April 2023.
b) Includes dwelling units and acreages that are assumed to be developed during the preceding five- year period. Dwelling units and acreages shown for 2025 are those assumed to be developed between January 2023 and December 2025. Dwelling units and acreages developed before December 2022 are included in baseline wastewater flow (see Table 4-6).
c) Future development located in the Historic Lathrop Development Area that are anticipated to be discharging to the CTF are listed under the Crossroads Development Area for the purposes of this document.
d) The AAFES facility and the CMD facility at the Sharpe Army Depot are connected to City' ssewer system as of January 2023.
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EKI C20049. 02
Section 2 2024 WWSMP Amendment
Study and Service Areas City of Lathrop

Population in the City has grown by approximately 410% over the 32 -year period between 1990 through 2023, from approximately 6, 800 to 35, 100 (California DOF, 2007, 2012, and 2023). Between 2005 and 2023, the population increased by 174%, from approximately 12, 800 to 35, 100.

The City anticipates that population will continue to grow in the future given the existing entitlements for several large residential developments, discussed above in Section 2.. The population projections for 2025 through 2045, summarized in Table 2-3, are estimated using the existing population ( as determined by California DOF) and adding the amount of new housing anticipated to be permitted in each five- year increment based on Table 2-1. The population added each year is projected by multiplying the most recent number of new housing units by ( 1) 4. 02 person per dwelling unit based on Census data for low density developments, which consists of a large majority of the City' s existing land uses and ( 2) 3. 0 persons per dwelling units for future medium density and high -density dwelling units U. S. Census, 2023). Current and projected population trends are shown on Figure 2-. eki environment
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December 2024
EKI C20049. 02
Section 2
Study and Service Areas
2024 WWSMP Amendment
City of Lathrop
Table 2-. Historical City of Lathrop Population
Year
1990
Service Area Population ( a)
6, 841
Annual Growth Rate
1991 7, 018 2.6%
1992 7, 063 0.6%
1993 7, 434 5.3%
1994 8, 410 13.%
1995 8, 713 3.6%
1996 9, 031 3.6%
1997 9, 172 1.6%
1998 9, 508 3.7%
1999 9, 786 2.9%
2000 10, 445 6.7%
2001 10, 802 3.4%
2002 11, 616 7.5%
2003 12, 089 4.1%
2004 12, 482 3.%
2005 12, 768 2.3%
2006 14, 489 13. 5%
2007 16, 271 12. 3%
2008 17, 282 6.2%
2009 17, 589 1.8%
2010 18, 023 2.5%
2011 18, 688 3.7%
2012 19, 090 2.%
2013 19, 642 2.9%
2014 20, 158 2.6%
2015 20, 796 3.2%
2016 22, 174 6.%
2017 23, 117 4.3%
2018 24, 185 4.6%
2019 25, 401 5.0%
2020 26, 833 5.6%
2021 29, 384 9.5%
2022 31, 575 7.5%
2023 35, 080 11.%
Notes:
a) Historical and current population is based on population estimates by the California DOF for the City of Lathrop included in DOF, 2007; DOF, 2012; DOF, 2022; and DOF, 2023. eki environment
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December 2024
EKI C20049. 02
Section 2
Study and Service Areas
2024 WWSMP Amendment
City of Lathrop
Population
Served
Table 2-3. Current and Projected City of Lathrop Population Current and Projected Service Area Population ( a)( b)
Year 2023 2025 2030 2035 2040
2045
Buildout)
Population Served 35, 080 40, 531 55, 471 72, 513 84,97 86, 013 Notes:
a) Current population is based on population estimates by the California DOF for the City of Lathrop included in DOF, 2023.
b) Projected populations for 2025 through buildout ( 2045) are based on residential unit counts from Table 2-1, multiplied by 4. 02 persons per dwelling unit for low density developments ( U. S. Census, 2023) and 3. 0 persons per dwelling unit for medium and high density developments.
100, 00
90, 000
80, 000
70, 000
60, 000
50, 000
40, 000
30, 000
20, 000
10, 000
eki
0 1990 1995 2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 Year
Figure 2-. Historical and Projected City of Lathrop Population Historical Population — 8 — Projected Population
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EKI C20049. 02
Section 3
2024 WWSMP Amendment
City' sExisting Wastewater Infrastructure City of Lathrop 3 CITY' SEXISTING WASTEWATER INFRASTRUCTURE
Wastewater from the City is treated at two facilities: the regional MWQCF and the City -owned Lathrop CTF. The City' s wastewater collection system, including the City' s lift station and pump station drainage areas, 1is shown on Figure 3-1. The City' s wastewater utilities are discussed in more detail in the sections below.

3. 1 Wastewater Collection
The City' s wastewater collection system consists of approximately 102 miles of gravity mains, 23. 6 miles of force mains, as well as 16 lift and pump stations. The City has a supervisory control and data acquisition ( SCADA) system for control and monitoring of facilities.

As shown on Figure 2-, most of the City' s wastewater generated in the areas east of I-5 is conveyed to the MWQCF; wastewater generated in the Crossroads, South Lathrop, and Lathrop Gateway industrial areas and the areas west of I-5, including the Mossdale, River Island, and Central Lathrop areas, is conveyed to the Lathrop CTF.

A few large industrial facilities ( e. g., Simplot and California Natural Products) manage their wastewater onsite. California Natural Products manages the majority of their wastewater and sends the remaining flows to either the J Street Lift Station ( LS) or the McKinley Avenue Pump Station ( PS).

3. 1. Gravity System
Table 3-1 summarizes the City' s gravity main inventory by diameter. Gravity main sizes are also shown on Figure 3-1.

Approximately 66% of gravity mains are polyvinyl chloride ( PVC) pipes, and the remaining 34% are vitrified clay ( VC) pipes. All the VC pipes are located in the older Historic Lathrop and Crossroads areas.

Newer areas of the City west of I-5 are exclusively served by PVC pipe, which is the City' s current standard pipe material.
1 Generally, lift stations add hydraulic head to the wastewater flow within the gravity collection system; pump stations pressurize wastewater flow for conveyance via force mains. eki environment
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River Islands 2A PS
L Sphere of Influence
nApproximate Area of W WfF
CD Pump Station or Lift Station
Stanford Cross_ ing. PS
Mossdale P31
Valley Crossings LS

DE LIMA RD

DOS REIS RD
I
North
Harlan PS
tonebridge PS
i
Sharpe[ PS
Private))
Woodfield LS:

II. ATHROP RD
California
t Natural Products
ps I
PS ( Private)
McKinley
Ave PS
Louise Ave PS
Easy Ct LS
O St PS
Z
Lathrop CTF
t -

OUISE AV
SSI PS
i` vale)
2 LIP LS!
Private)
1 Lathrop ''— .

OSEMITEAV
Ga away PS MWQCF, FIow
j
I
Crossroads PS 0. Met r
River Islands , •• tc
i
Mein PS ‘/
oth• Lhrop PS
y ..

Gravity Main Diameter, Inches
4-14-6
6 - 18
8 20-1
10 - 24
12 - > 30
Force Main Diameter, Inches
8 20-1
12 - - > 30
Abbreviations
CTF = Consolidated Treatment Facility
LIP = Lathrop Industrial Perk
LS = lift station
MWQCF = Manteca Water Quality Control Facility
PS = pump station
SSI = Super Store Industries
WWTF = wastewater treatment facility
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS
Online, 14 May 2024.

N
o 3, 000 o, 000
A ( scale in Feet)
Citys Wastewater Infrastructure
Wastewater System Master Plan Amendment
Ciry of Lathrop
Lathrop, CA
ski environment DecemberC2004902
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C20043
Figure 3- t1
River Islands 2A PS
Stanford Crossin
f
Mossoale F'
River Islands
Main PS
North
Harlan.. PS
Valley Crossings LS Stonebndg

DE LIMA RD
South
Lathrop CTF
La hrop
Gateway PS
Lathrop PS
pe PS
vale)

LATHROP RD
ducts
owse Ave PS
t CHASE AV
SSI PS
Rnvate)
te)

SEMRE AV
MWQCFFlow
Meter

MWOCCFF
Legend
rJ Sphere of Influence
r Approximate Area of W WTF
NI Pump Station or Lift Station
Force Main
Gravity Main
WWTP Drainage Area Boundaries
Lathrop CTF Collection System
MWQCF Collection System
Pump Station Drainage Areas
MIN Stanford Crossing - Mossdale
Crossroads ` O St
ME Easy Ct River Islands
t"L,` J St South Lathrop
Lathrop Gateway Stonebridge
MI Manteca FiSN, Valley Crossing
NE McKinley Woodfield
Abbreviations
CTF = Consolidated Treatment Facility
LIP = Lathrop Industrial Perk
LS = lift station
MWQCF = Manteca Water Quality Control Facility
PS = pump station
SSI = Super Store Industries
W WTF = wastewater treatment facility
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS
Online, 12 March 2024.

N
o 3, 000 6O00
A ( Scale in Eeen
City' s Wastewater Pump Station Drainage Areas
Wastewater System Master Plan Amendment
Cry of Lathrop
Lathrop, CA
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Figure 3-2
Section 3 2024 WWSMP Amendment
City' sExisting Wastewater Infrastructure City of Lathrop Table 3-1. Collection System Inventory
Pipe Diameter Total Pipe Length
Percent of System
inches) ( miles)
Gravity Mains
6 8. 6 8%
8 71. 9 70%
10 6. 7 6.%
12 5. 8 5.7%
14 0. 5 0.5%
15 2. 9 2.8%
16 0. 1 0.1%
18 1. 3 1.3%
20 0. 4 0.4%
21 0.2 0.2%
24 1. 5 1.5%
30 1. 9 1.9%
36 0. 6 0.6%
42 0. 1 0.1%
Total 102. 2 100%
Force Mains
4 1. 2 5%
6 4. 3 18%
8 2. 5 11%
10 0. 7 3%
12 7. 3 31%
14 3. 1 13%
16 1. 8 8%
18 2. 7 11%
Total 23. 6 100%
Notes:
a) Does not include laterals.
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3. 1. 2 Pump Stations and Force Mains
Table 3- 2 summarizes the characteristics of each of the City' s lift and pump stations and their associated force mains. The direct tributary areas of each lift station or pump station, or " drainage areas", are shown on Figure 3-2. A schematic of the City' s lift stations and pump stations that shows how wastewater flows through the collection system is illustrated on Figure 3-. An inventory of the City' s force main sizes is summarized in Table 3-1.

The City' s wastewater generated east of I-5 and north of Louise Avenue in the Historic Lathrop area is conveyed via gravity sewers and lift stations to either the O Street PS or the McKinley Avenue PS.

Wastewater from the McKinley Avenue PS and O Street PS converge at the McKinley intertie, which is capable of sending converged flow via a 12 -inch and/ or a 16 -inch diameter force main to the MWQCF.

These force mains also convey wastewater from the Louise Avenue pump station and other private pump stations that serve the industrial areas east of I-5 to the MWQCF.

Wastewater from the CLSP, Mossdale, River Islands, South Lathrop, and Lathrop Gateway areas are conveyed via gravity sewers to a main pump station within each development area. These pump stations then send wastewater directly to the Lathrop CTF.

3. 1. Collection System Intertie
The City' stwo collection systems are connected by the 8 -inch Mossdale Intertie, which crosses beneath I-5 on River Islands Parkway and Louise Avenue. The intertie may convey flow from the Mossdale PS to sewer mains upstream of the East Street LS but is limited by the capacity of sewers in the Easy Street area. The intertie is not routinely operated but could potentially be utilized in the future to reroute a portion of flows from the Mossdale PS to the MWQCF tributary area.

3. 1. 4 Major Collection System Improvements Completed Since 2019 The following major wastewater collection system improvements were completed since the 2019 WSMP:

CLSP sewer infrastructure and Stanford Crossing Pump Station: infrastructure improvements in the Central Lathrop Phase 1 ( Stanford Crossing) area were constructed including gravity mains, pump station, and connection to existing 14 - inch and 18 - inch force mains which convey wastewater flow from buildout of Central Lathrop Specific Plan ( CLSP) area to the CTF.

River Islands: sewer infrastructure was expanded for Phase 2A/B of the River Islands development, including a gravity collection system, the River Islands 2A PS, and the River Islands Main PS which connects to existing 12 -inch and 18 -inch diameter force mains conveying flows to the Lathrop CTF.

South Lathrop: a new gravity collection system along Yosemite Ave was constructed to collect wastewater from commercial facilities in its vicinity to a new pump station, which then conveys flows to the CTF via dual 6 -inch force mains.

Lathrop Gateway: a new 10 -inch diameter gravity collection system along Business Park Court. was constructed to collect wastewater from commercial facilities in its vicinity to a new pump station, which then conveys flows to the CTF via a new 4 -inch and 6 -inch diameter force mains.

Woodfield Pump Station: the Woodfield PS was upgraded and connected to the 10 -inch diameter force main that flows to the gravity mains upstream of the McKinley Avenue PS.

North Harlan PS: the private pump station has been upgraded to a public pump station.

These completed projects are incorporated in the WWSMP evaluation of the existing wastewater collection system.
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Table 3-2. Summary of Wastewater Pump Station Characteristics Number
Force Main Existing Existing Firm
Pump Station
of Pumps
Rated Power Diameter Design Capacity Capacity
in) ( gpm) ( gpm)( a)
MWQCF Collection System
North Harlan PS 2 10 HP 6" 2, 150 1, 075
Stonebridge LS 2 10 HP 6" 700 350
Woodfield LS 3 5 HP 8" (b) 1, 230 820
Valley Crossing LS ( b) 2 3 HP 4" 83 83
J Street LS 2 10 HP 8" 1, 400 700
Easy Court LS 2 3 HP 1, 000 500
O Street PS 3
Two at 70 HP;
one at 5 HP
12" 4, 200 2, 800
McKinley Avenue PS 3
Two at 25 HP;
one at 5 HP
16" 2, 513 1, 675
Louise Avenue PS 2 5 HP 4" d) d)
Lathrop CTF Collection System
Stanford Crossing 2
One at 90 HP;
One at 45 HP
14" & 18" 4, 100 2, 300
Mossdale PS 4 30 HP 8" & 12" 5, 400 4, 050
River Islands Main PS 2 ( c) 110 HP 12" & 18" 3, 400 1, 700 River Islands 2A PS 4 15 HP 30" 5, 300 3, 975
Lathrop Gateway PS 2 23 HP 4" & 6" 560 280
South Lathrop PS 3 12 HP 6" & 6" 2, 775 1, 850
Notes:
a) Firm pumping capacity defined as the total capacity of all pumps minus the capacity of the largest pump. b) Capacity of the 8" outlet is listed as the lift station capacity, as it is the capacity limiting component of this pump station.
c) River Islands Sewer PS will be constructed in phases with addition of two pumps during each phase. eki environment
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Stanford
Crossing PS
River Islands
Main PS
River Islands
2A
Figure 3-. City' s Wastewater Collection System Schematic Mossdale PS
Lathrop
CIF
South
Lathrop PS
Mossdale
Intertie
Valley
Crossing LS
Easy Court
LS
Crossroads
PS
Lathrop
Gateway PS
North
Harlan PS
Stonebridge
LS
Woodfield
PS
CNP PS
private)
J Street PS
O Street PS
4 Louise Ave
PS
McKinley
Intertie
Valve Box
SSI PS
private)
Notes:
a) The Stonebridge PS receives wastewater from four private pump stations: Panattoni, Gordon Trucking, Boise Cascade, and Utility Trailer. These pump stations convey wastewater collected by the private North Harlan Gravity System, which serves industrial parcels north of Brookfield Street. b) Heinz - Kraft, Sharpe, and LIP private pump stations not shown. eki environment
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3. 2 Wastewater Treatment
Wastewater treatment at the MWQCF and the Lathrop CTF are discussed in the following sections.

3.2. 1 Manteca Water Quality Control Facility
The City owns approximately 14. 7% of the existing MWQCF capacity by contract with the City of Manteca. However, the City does not participate in the operation of the plant, nor does it receive recycled water from MWQCF. Per the City' s 2002 Agreement Amendment with Manteca and as listed in Table 3-, the total current MWQCF design capacity is 9. 87 million gallons per day ( MGD) and the City' s allocated capacity is 1. 451 MGD ( Lathrop County Water District and the City of Manteca, 2002). Under the Agreement Amendment, the City has the right to 1. 451 MGD dry weather flow, 2. 321 MGD peak wet weather flow, 3, 751 pounds per day of biochemical oxygen demand ( BOD), and 3, 812 pounds per day of total suspended solids ( TSS). However, as discussed in Section 5. 2, recent increases in wastewater strength may limit MWQCF' streatment capacity and, as a result, the City' sshare of MWQCF capacity.

The MWQCF is permitted for future expansions of up to 26. 97 MGD, of which the City would be allocated up to 3. 97 MGD, should the City elect to fund its share of the expansions to maintain its proportional allotment.

Treatment at the MWQCF consists of primary sedimentation followed by roughing biotowers, conventional activated sludge, secondary clarification, tertiary filtration, and ultraviolet disinfection.

Disinfected tertiary effluent is discharged to the San Joaquin River. A portion of the secondary effluent is not disinfected and is used to irrigate crops on 190 acres of land owned by the City of Manteca ( WDR Order No. R5- 2015- 0026).

Table 3-. Wastewater Capacity Allocation at MWQCF
Phase
Existing
Build - Out ( 2050)
Allocated Capacity at MWQCF ( MGD)
City of Manteca City of Lathrop

8. 42

23. 00

1. 45

3. 97
Total

9. 87

26. 97

3. 2. Lathrop Consolidated Treatment Facility
The City owns a membrane bio reactor (MBR) treatment facility, the Lathrop CTF, that also incorporates portions of the old Crossroads Industrial Wastewater Treatment Plant. Daily operations of the Lathrop CTF are contracted to Veolia Water, North America. The City completed the Phase 2 Expansion of the Lathrop CTF in 2019 which increased the plant' streatment capacity to 2. 5 MGD. The City has the ability to further upgrade Lathrop CTF to increase the treatment capacity up to 9. 0 MGD as needed. 2 As discussed in Section 5.2, recent increases in wastewater strength may limit the CTF' streatment capacity.

Wastewater treatment and recycled water disposal at the City' s Lathrop CTF is regulated under Waste Discharge Requirements ( WDR) Order No. R5- 2016- 0028-1by the Central Valley Regional Water Quality Control Board ( RWQCB). Wastewater treatment processes at the Lathrop CTF include secondary 2 The City had previously completed a project -level Environmental Impact Report ( EIR) for treatment capacity up to

6. 0 MGD at the CTF. Post combination with Crossroads WWTF, the program - level EIR treatment capacity at the CTF has increased to 9. 0 MGD.
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City' s Existing Wastewater Infrastructure City of Lathrop treatment, tertiary membrane filtration, and disinfection prior to storage and disposal. The current Lathrop CTF is capable of treating Peak Day Flows of 4. 0 MGD at a loading of 14, 000 pounds of BOD per day and Peak Hour Flows of 7. 5 MGD.

With the rapid increase of wastewater generation anticipated within the City and the CTF drainage area, the City is planning Phase 3 expansion of the Lathrop CTF in the near future. The Phase 3 expansion is anticipated to add 2. 5 MGD of capacity to a total of 5. 0 MGD capacity.

The Lathrop CTF produces disinfected tertiary recycled water suitable for irrigation at parks, landscape strips, median islands, pond berms, and agricultural fields. The City is covered under General Order WQ2016- 0068- DDW (General Order) for recycled water use in a total of 196 acres of landscape irrigation areas in the River Islands, Mossdale, and Central Lathrop areas.

In 2021, the City obtained a National Pollutant Discharge Elimination System ( NPDES) permit for surface water discharge ( Order R5- 2022- 0004). This permit allows the City to discharge a portion of the treated effluent to the river, while using the remaining portion for meeting landscape irrigation demands and other permitted non -potable uses.

The City completed the following infrastructure improvements to implement its NPDES permit and began discharging to the San Joaquin River in February 2024:

CTF
o Retrofitting of the existing chlorine contact exit structure to a new dechlorination station with overflow pipes to send chlorinated effluent ( Title 22 recycled water) to S5 and dechlorinated effluent to the Crossroads Pump Station. o New piping from the dechlorination station to the existing Crossroads Pump Station. o Abandoning of the piping from Ponds A, B and C to the Crossroads Pump Station o New piping that connects the existing discharge line from the Crossroads Pump Station to the CTF headworks, which will divert substandard effluent from the outfall, and disconnection of the existing discharge line from PB- 1. o New piping to connect PMP- 1to percolation pond PB- 1.

Effluent Discharge Pipeline
o Approximately 2, 000 linear feet ( LF) of a new dedicated discharge line and railway crossing from the Crossroads Pump station along Tesla Way to connect to an existing 18" pipeline at Murphy Parkway and Tesla Way.
o Reuse of approximately 3,00 LF of existing 18 - inch pipeline along Tesla Way and Harlan Road from Murphy Parkway to Sadler Oak.
o Reuse of approximately 1, 800 LF of existing 20 -inch pipeline along Sadler Oak from Harlan Road to the RD - 17 levee.
o Reconstruction of the 20 -inch pipeline where it crosses the levee and extension of the pipeline to a new outfall approximately 350 feet further downstream ( north).

Outfall Structure
o A new side bank outfall located approximately 350 feet downstream from the Crossroads storm drain pump station outfall.
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City' sExisting Wastewater Infrastructure City of Lathrop The City began discharging CTF effluent to the San Joaquin River in February 2024 and plans to retire its agricultural land application areas and decommission the majority of its recycled water storage ponds and percolation pond PB- 1 (EKI, 2024).
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Existing and Future Wastewater Generation City of Lathrop 4 EXISTING AND FUTURE WASTEWATER GENERATION
As part of the IWRMP, the City evaluated its existing wastewater flows and updated its flow projections.

The following sections summarize the City' s historical and current wastewater generation, wastewater flow projections, and wastewater peaking factors.

Wastewater flows in a sanitary sewer system typically consist of the following components:

Base sanitary flow ( BSF): BSF is the sanitary wastewater flow from domestic, commercial, industrial, and institutional uses.

Infiltration: Infiltration refers to groundwater that enters a sewer system through defective pipes, pipe joints, connections, or manholes.

Inflow: Inflow refers to stormwater that enters a sewer system through direct connections, such as manhole covers and defective sewer service cleanouts or ( illegal) roof drains, foundation drains, catch basins, or area drain connections.

Infiltration and Inflow are collectively referred to as " I&". The amount of I&tends to be smaller in new collection systems but is generally observed to increase over time due to wear and tear on the collection system.

The following terminology is used throughout this document to describe variations in wastewater flow:

Average annual flow ( AAF): AAF refers to the average daily flow over the entire year and is inclusive of BSF and I&.

Average dry -weather flow ( ADWF): ADWF refers to the average daily flow for the months of June, July, and August ( i.e., during the dry season). ADWF includes BSF and infiltration, but not inflow.

Peak wet weather flow ( PWWF): PWWF refers to the peak hourly flow, which includes peak diurnal BSF, infiltration, and inflow from storm events.

EKI reviewed the following available information for evaluation of wastewater flows as part of this WWSMP update:

Daily flow data collected between January 2017 and December 2022 from the headworks of the Lathrop CTF;
Daily flow data collected between January 2017 and December 2022 from the flow meter on Yosemite Avenue that measures the City' sflow to the MWQCF; Available discharge flow and level data recorded in 5 -minute intervals from the City' s lift stations and pump stations by the SCADA system between January 2017 and December 2021; and
Daily discharge flow for the City' s lift stations and pump stations recorded by the City' s operators between January 2017 and December 2021.

4. 1 Current and Historical Wastewater Flow
Table 4-1 and Table 4-2 provide historical context by summarizing the City' s wastewater generation, service area population, and per -capita wastewater generation for the years 2009 through 2022.

Table 4- 1 lists the total AAF, citywide and by treatment facility, and per -capita AAF. Table 4-2 lists the same information on an ADWF- basis, and compares AAF to ADWF along with Figure 4- 1 and Figure 4-2. eki environment
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The City' s total AAF and ADWF showed a steady increasing trend between 2009 and 2022. Although there was a period of slower growth between 2014 and 2016, the City' s wastewater flow appears to be insensitive to the recent droughts. During the period between 2017 and 2022, the City' s AAF increased at an annual rate of approximately 7%, comparable to the City' s population growth. In 2022, the City generated a total AAF of 2. 171 MGD, including 1.06 MGD treated at the MWQCF ( 51%) and 1. 065 MGD treated at the CTF ( 49%).

The comparison between AAF and ADWF is calculated in Table 4-2, which is an indication of the amount of rainfall -induced l&I collected during a given year. The ADWF to AAF ratio between 2017 and 2022 averaged 103%, indicating that the ADWF is essentially equal or at times, higher than the AAF.

The total per capita AAF and ADWF also showed an increasing trend between 2009 and 2022, despite temporary declines during the economic recession between 2009 and 2012 and the historic drought between 2014 and 2015. The per capita ADWF varied between 67 and 75 gallons of wastewater per day per capita between 2017 and 2022.

Table 4-1. Current and Historical Wastewater AAF and Per Capita AAF Year
2009
Average
MWQCF
MGD)

0. 706
Annual Flow ( AAF)
CTF ( b)
MGD)

0. 287
a)
Total
MGD)

1.54 City
Population ( c)
17, 589
Per Capita
Wastewater Flow
d)
gallons per
capita per day)
66 2010 0. 705 0. 286 1.45 18, 023 64
2011 0. 724 0. 294 1.57 18, 688 62
2012 0. 781 0. 280 1.71 19, 090 61
2013 0. 919 0. 301 1. 333 19, 642 68
2014 0. 897 0. 315 1. 359 20, 158 67
2015 0. 873 0. 348 L360 20, 796 65
2016 0. 918 0. 405 1. 463 22, 112 66
2017 0. 911 0. 642 1. 553 23, 098 67
2018 1. 046 0. 678 1. 724 24, 124 71
2019 1.04 0. 708 1. 812 25, 332 72
2020 1. 068 0. 831 1. 899 26, 806 71
2021 0. 939 1. 002 1. 941 29, 608 66
2022 1.06 1. 065 2. 171 31, 575 69
Notes:
a) Wastewater flow data from 2009 to 2022 are obtained from the treatment plants' semi- annual monitoring reports. Totals may not sum due to rounding. b) Flows to the CTF includes flows to the Crossroads WWTF prior to its conversion and connection to the CTF in August 2015.
c) City sewered population is assumed to be approximate to City population, which is based on population estimates by the California DOF for the City of Lathrop included in E- 5 Population and Housing Estimates.
d) Per capita wastewater flow is calculated by dividing the total annual wastewater flow by City population and the number of days in a year.
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Table 4-2. Current and Historical ADWF and Per Capita ADWF Year
2009
Average Dry
MWQCF
MGD)

0. 701
Weather Flow ( ADWF)
CTF ( b)
MGD)

0. 257
a)
Total
MGD)

1.34 ADWF
vs.

AAF (c)
98%
Annual
Rainfall ( d)
in)

10. 48
Per Capita
ADWF ( e)
gallon per
capita per
day)
64 2010 0. 697 0. 266 1.16 97% 18. 70 62
2011 0. 710 0. 276 1.20 97% 10. 09 60
2012 0. 779 0. 274 1.52 98% 13. 54 60
2013 0. 950 0. 299 1. 358 102% 14. 59 69
2014 0. 896 0. 304 1. 342 99% 14. 23 67
2015 0. 857 0. 335 1. 328 98% 7. 43 64
2016 0. 874 0. 383 1. 405 96% 18. 28 64
2017 0. 97 0. 701 1. 673 108% 16. 60 72
2018 1.0 0. 705 1. 803 105% 14.5 75
2019 1.1 0. 663 1. 771 98% 17. 05 70
2020 1.4 0. 880 2. 020 106% 5. 97 75
2021 0. 97 1. 007 1. 974 102% 14.8 67
2022 1.2 1. 083 2.03 101% 11. 41 70
Notes:
a) ADWF is calculated as the average daily flow between June and August of the year. Totals may not sum due to rounding.
b) Flows to the CTF includes flows to the Crossroads WWTF prior to its conversion and connection to the CTF in August 2015.
c) The ratio of AAF to ADWF is calculated using AAF values from Table 4-1. d) Precipitation data obtained from National Oceanic and Atmospheric Administration Stockton Airport Station ( USW00023237).
e) Per capita ADWF is calculated using City population data in Table 4-1. eki environment
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Figure 4-1. Current and Historical Wastewater Flow by Collection System

2. 5

2. 0
2 d
U)
Ua
Per
Capita
Wastewater
Generation (
GPCD)
eki

0. 5

0. 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022

CTF- AAF CTF- ADWF MWQCF- AAF MWQCF- ADWF
Figure 4-2. Current and Historical Per Capita Wastewater Flow 80 75
70 65
60 55
50 2008 2010 2012 2014 2016 2018 2020 2022
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0— Per Capita AAF — • — Per Capita ADWF
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Existing and Future Wastewater Generation City of Lathrop

4. 2 Wastewater Generation Projections
Wastewater ADWF projections were calculated as the sum of the two major components of future wastewater flow: (1) the volume of wastewater that represents existing wastewater generation within the City in 2022, and ( 2) the anticipated wastewater generation associated with the future development projects and planning areas post 2022. Components of wastewater generation projections are described in the sections below.

4.2. 1 Existing Wastewater Generation
The City' s existing wastewater generation is based on the City' s wastewater flow data in 2022, representing development within the City as of the end of 2022. The City decided to apply a 10% safety factor to the 2022 flows to account for anticipated future increases in I&. A major portion of the City' s collection system consists of the newer systems in the areas west of I-5, which will likely produce more I&in the future as the infrastructure ages.

4. 2. Wastewater Generation Associated with Planned Development Wastewater generation associated with anticipated future development are estimated using land use - specific wastewater flow factors and the anticipated acreages and number of dwelling units associated with each proposed development ( Table 2-1). The land use -specific wastewater flow factors were developed using historic wastewater flow and parcel -level water use data with a safety factor, as described in detail in Appendix A. These factors are developed based on 2017 to 2021 wastewater flows and update those included in the 2019 WWSMP. The updated wastewater generation factors ( in units of gallons per day per dwelling unit or gallons per day per acre; gpd/ du or gpd/ ac) are presented in Table 4-3, below.

Table 4-3. Wastewater Flow Factors
Land Use
Low Density Residential
Wastewater
Historic Lathrop
240 gpd/ du
Flow Factor
West Lathrop
200 gpd/ du
Medium Density Residential 200 gpd/ du 155 gpd/ du
High Density Residential 110 gpd/ du
Commercial 755 gpd/ ac
Industrial 240 gpd/ ac
Parks 55 gpd/ ac
Schools / Institutional 220 gpd/ ac
Table 4- summarizes the volume of wastewater generation associated with anticipated future developments by development area in five- year increments between 2025 and 2045.

4.2. 3 Total Projected Wastewater Generation
Table 4- 5 summarizes the City' stotal projected wastewater generation in five- year increments between 2025 and buildout, as a sum of the existing and new wastewater flow. Based on these projections, it is anticipated that total ADWF in 2045 will be 5. 67 MGD. Of these totals, ADWFs of 1. 36 MGD and

4. 31 MGD are anticipated to flow to MWQCF and the Lathrop CTF, respectively. The majority of the anticipated increase in wastewater generation at the CTF is associated with the River Islands and Central Lathrop development areas.
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Existing and Future Wastewater Generation
2024 WWSMP Amendment
City of Lathrop
Table 4-
Projected New Wastewater Flow by Development Area
Land Use Designation
Central Lathrop Phase 1
Wastewater
Flow Factor
Projected New Wastewater Flow (gpd) (a)
2025 2030 2035 2040 Buildout 2045
Low Density Residential
High Density Residential
240 gpd/ du
110 gpd/ du
0 0
120, 00

27. 060
183, 360
50, 160
183, 360
63,90
183, 360
63,90
Commercial 755 gpd/ ac 9, 815 55,38 55,38 55,38 109, 88 Mixed Use 755 gpd/ ac 0 0 0 0 38, 505
Parks 55 gpd/ ac 0 2, 149 2, 424 2, 424 2, 424
New Central Lathrop ADWF 9, 815 204, 77 291, 482 305, 012 397, 87 Central Lathrop - Phase 2
Light Industrial / R&D Flex 240 gpd/ ac 21, 557 21, 557 21, 557 21, 557 163, 620 Parks 55 gpd/ ac 0 0 0 0 275
New Central Lathrop ADWF 21, 557 21, 557 21, 557 21, 557 163, 895 Mossdale Landing
Low Density Residential 240 gpd/ du 0 0 0 0 15, 840
Medium Density Residential 200 gpd/ du 0 0 0 0 0
High Density Residential 110 gpd/ du 0 0 0 0 0
Commercial 755 gpd/ ac 3, 443 4, 575 4, 575 4, 575 4, 575 Schools 220 gpd/ ac 0 0 0 0 3, 573
New Mossdale ADWF 3, 443 4, 575 4, 575 4, 575 23, 988
Mossdale Landing East
Low Density Residential 240 gpd/ du 0 8,80 8,80 8,80 8,80 High Density Residential 110 gpd/ du 0 0 0 0 9, 240
Commercial 755 gpd/ ac 0 5, 285 5, 285 5, 285 5, 285
New Mossdale ADWF 0 14,65 14,65 14,65 23, 405
Mossdale Landing South
Medium Density Residential 200 gpd/ du 17, 000 17, 000 17, 000 17, 000 17, 000 Commercial 755 gpd/ ac 0 0 6, 040 6, 040 18, 875
Parks 55 gpd/ ac 0 220 220 220 220
New Mossdale ADWF 17, 000 17, 220 23,60 23,60 36, 095
Mossdale Landing West
Low Density Residential 240 gpd/ du 0 0 198, 960 198, 960 198, 960 Parks 55 gpd/ ac 0 0 603 603 603
New Mossdale ADWF 0 0 199, 563 199, 563 199, 563
River Islands
Low Density Residential 200 gpd/ du 153, 600 397, 200 640, 80 884, 400 884, 400 Medium Density Residential 155 gpd/ du 104, 780 251,55 397, 730 544, 205 544, 205 High Density Residential 110 gpd/ du 0 153, 450 306, 900 460, 350 460, 350 Town Center 755 gpd/ ac 0 19, 857 39, 713 59,70 59,70
Commercial 755 gpd/ ac 0 65, 006 130, 011 195, 017 195, 017 Schools 220 gpd/ ac 7, 150 10, 450 13, 750 16, 830 16, 830 Parks 55 gpd/ ac 1, 045 4, 395 7,50 11,05 11,05
New River Islands ADWF 266, 575 901, 62 1, 536, 654 2, 171, 476 2, 171, 476 South Lathrop
Light Industrial / R&D Flex 240 gpd/ ac 0 16, 080 16, 080 16, 080 23, 940 Office Commercial 755 gpd/ ac 0 6,44 6,44 6,44 7, 550
Open Space 55 gpd/ ac 0 0 0 0 0
New South Lathrop ADWF 0 22, 724 22, 724 22, 724 31, 490 Lathrop Gateway
Light Industrial / R&D Flex 240 gpd/ ac 0 15, 840 15, 840 19, 824 19, 824 Office Commercial 755 gpd/ ac 0 38, 505 38, 505 47, 339 47, 339 Open Space 55 gpd/ ac 0 138 138 226 226
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New Lathrop Gateway ADWF
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0 54A83 54, 483 67, 388 67, 388
December 2024
EKI C20049. 02
Section 4
Existing and Future Wastewater Generation
2024 WWSMP Amendment
City of Lathrop
Table 4-
Projected New Wastewater Flow by Development Area
Land Use Designation
Wastewater Projected New Wastewater Flow (gpd) (a)
Flow Factor
2025 2030 2035 2040 Buildout2045
Crossroads
Industrial 240 gpd/ ac 0 5,20 5,20 5,20 5,20
Commercial 755 gpd/ ac 0 1,33 1,33 1,33 1,33
New Crossroads ADWF 0 6,53 6,53 6,53 6,53
Historic Lathrop and Other Development Areas
Low Density Residential 240 gpd/ du 0 2, 880 4, 320 5,20 12, 480 Medium Density Residential 200 gpd/ du 5, 400 10, 600 15, 800 21, 000 43, 600 High Density Residential 110 gpd/ du 0 0 0 0 5, 280
Commercial 755 gpd/ ac 16, 610 26, 878 26, 878 26, 878 32, 918 Industrial 240 gpd/ ac 4, 320 4, 320 4, 320 4, 320 10, 080 New Historic Lathrop / Other ADWF 26, 330 44, 678 51, 318 57, 718 104, 358 Sharpe Army Depot
Industrial I -- 32, 000 32, 000 32, 000 32, 000 32, 000 New Sharpe Army Depot ADWF 32, 000 32, 000 32, 000 32, 000 32, 000 Total Projected New ADWF 376, 720 1, 324, 413
PROJECTED NEW ADWF AT CTF 318,90 1, 247, 735
PROJECTED NEW ADWF AT MWQCF 58, 330 76, 678
2,58, 433 2, 926, 091 3, 258, 188
2, 175,15 2, 836, 373 3, 121, 830
83, 318 89, 718 136, 358
Notes:
a) Projected residential wastewater generation calculated as the total number of projected residential dwelling units multiplied by the applicable wastewater flow factor (Table 4-3). Projected non- residential wastewater flow are calculated as the total projected acreage multiplied by the applicable wastewater flow factor ( Table 4-3). Projected residential dwelling units and non- residential acreage are listed in Table 2-1. eki environment
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December 2024
EKI C20049. 02
Section 4
Existing and Future Wastewater Generation
2024 WWSMP Amendment
City of Lathrop
Table 4-5. Existing and Future Wastewater Flow by Development Area Wastewater Generation ( MGD) (a)
Development Area (a) Baseline Buildout
2025 2030 2035 2040
b) 2045
Lathrop CTF
Central Lathrop and
Mossdale ( c)

0. 46 0. 51 0. 73 1. 02 1. 03 1. 31
River Islands 0. 44 0. 71 1. 35 1. 98 2. 62 2. 62
South Lathrop 0.02 0.02 0.25 0.25 0.25 0.34
Lathrop Gateway and
Crossroads ( c)

0. 28 0. 28 0. 34 0. 34 0. 36 0. 36
ADWF at CTF 1.9 1. 51 2. 44 3.7 4. 03 4. 31
Manteca
Historic Lathrop and Other
Development Areas

1. 22 L28 1. 30 1. 30 1. 31 1. 36
ADWF at MWQCF 1. 22 1. 28 1. 30 1. 30 1. 31 1. 36
TOTAL EXISTING ADWF ( b) 2. 41 2. 79 3. 73 4. 67 5. 34 5. 67 Notes:
a) Projected wastewater generation calculated as the sum of baseline wastewater generation and the incremental new wastewater generation associated with future development shown in Table 4-. b) Baseline wastewater generation is based on the existing wastewater generation in 2022 at 2. 12 MGD with a 10% factor of safety to account for future I&.
c) Development areas served by the Lathrop CTF are grouped due to the availability of existing pump station flow data. Central Lathrop and Mossdale ADWF is estimated using flow from the Mossdale PS. Crossroads and Lathrop Gateway ADWF are estimated as the LCTF flow minus flow from the River Islands, Mossdale, and South Lathrop pump stations.
d) Totals may not sum due to rounding.
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December 2024
EKI C20049. 02
Section 4 2024 WWSMP Amendment
Existing and Future Wastewater Generation City of Lathrop

4. 3 Wastewater Peaking Factors
EKI reviewed the City' s historical wastewater flow data between 2017 and 2022 to verify and update the peaking factor curve that best estimates PWWF. PWWF is the highest hourly flow experienced during the year due to rainfall -induced I&and peak diurnal sanitary flows and is used to evaluate the hydraulic capacity of a wastewater collection system. The PWWF peaking factors are typically higher in smaller drainage areas, in which there is little flow attenuation. Larger drainage areas provide a greater capacity to attenuate flows, as peak flows generated in the upstream reaches of the system take a longer
amount of time to travel downstream. EKI developed a new peaking factor curve shown on Figure 4-3.

The methodologies used to develop this curve are described in Appendix B.

Figure 4-3. Average Dry Weather Flow and Peaking Factors 6 0
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Peaking Factor = e(- 3. t"ADWF( MGD)+ 0.9) + 2. 05
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500, 00 1, 000,00 1, 500, 000
Average Dry Weather Flow ( gpd)
4- 9
2, 000,00
December 2024
EKI C20049. 02
Section 5 2024 WWSMP Amendment
Wastewater Treatment Capacity Assessment City of Lathrop 5 WASTEWATER TREATMENT CAPACITY ASSESSMENT
This section compares the City' s projected wastewater generation through 2045 to its treatment capacity at the two treatment plants. The City' s collection system and treatment plant capacity are described in Section 3. 2.

5. 1 Wastewater Treatment Capacity Assessment
Table 5-1 and Figure 5-1 compares the projected ADWF with the City' s allocation at 1. 451 MGD at the MWQCF ( Section 3. 2.1). The City' s allocation at the MWQCF is sufficient to meet projected wastewater flows to the MWQCF through buildout.

As shown in Table 5-2 and on Figure 5-2, flows to the Lathrop CTF is anticipated to exceed the current CTF capacity of 2. 5 MGD between 2030 and 2035. The City anticipates completing the Lathrop CTF Phase 3 Expansion within the next three years to meet the projected wastewater flows. The Phase 3 Expansion will expand the CTF' s capacity to a total of 5. 0 MGD, which is sufficient to meet projected flows through buildout.

Collectively, wastewater treatment capacity at the CTF ( including the Phase 3 Expansion) and MWQCF is projected to be sufficient to meet Citywide projected wastewater flows through buildout ( Table 5- 3 and Figure 5-3). However, as discussed below in Section 5. 2, recent increases in wastewater strength observed at the treatment plants may limit their treatment capacities. eki environment
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December 2024
EKI C20049. 02
Section 5
Wastewater Treatment Capacity Assessment
2024 WWSMP Amendment
City of Lathrop
Table 5-1. Projected Wastewater Flow and Treatment Capacity at MWQCF Estimated ADWF Influent and Treatment Capacity ( MGD)
Existing
2022)
2025 2030 2035 2040 2045
Projected Influent ADWF (a)
ADWF Projection 1.1 1. 28 1. 30 1. 30 1. 31 1. 36
MWQCF Capacity
Allocated Capacity 1. 451 1. 451 1. 451 1. 451 1. 451 1. 451 Projected Deficit
Notes:
a) Wastewater influent to MWQCF is the wastewater flow from the Historic Lathrop area and Sharpe Army Depot.

Wastewater
Flow /
Treatment
Capacity (
MGD)

1. 6

1. 4

1. 2

1. 0

0. 8

0. 6

0. 4

0. 2

0. Figure 5-1. Projected Wastewater Flow and Treatment Capacity at MWQCF Existing ( 2022) 2025 2030 2035 2040 2045
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Emil Allocated Capacity — 1r—ADWF Projection
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December 2024
EKI C20049. 02
Section 5
Wastewater Treatment Capacity Assessment
2024 WWSMP Amendment
City of Lathrop
Table 5-2. Projected Wastewater Flow and Treatment Capacity at Lathrop CTF Estimated ADWF Influent and Treatment Capacity ( MGD)
Existing
2022)
2025 2030 2035 2040 2045
Projected Influent ADWF ( a)
ADWF Projection 1. 08 1. 51 2. 44 3.7 4. 03 4. 31
Existing Capacity and Future Expansions
Lathrop CTF Phase 0 - 2 ( b) 2. 50 2. 50 2. 50 2. 50 2. 50 2. 50 Lathrop CTF Phase 3 0.0 0.0 2. 50 2. 50 2. 50 2. 50
Total Capacity 2. 50 2. 50 5. 00 5. 00 5. 00 5. 00
Projected Deficit
Notes:
a) Wastewater influent to Lathrop CTF is the combination of wastewater flow from all city areas except for the Historic Lathrop area and Sharpe Army Depot.
b) Higher influent wastewater nutrient concentrations recently observed at the CTF may limit its hydraulic capacity to approximately 2. 0 MGD ( see Section 5.2).

Wastewater
Flow /
Treatment
Capacity (
MGD)

6. 0

5. 0

4. 0

3. 0

2. 0

1. 0

0. eki
Figure 5-2. Projected Wastewater Flow and Treatment Capacity at Lathrop CTF Existing ( 2022) 2025 2030 2035 2040 2045
Lathrop CTF Phase 0 - 2
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Lathrop CTF Phase 3 Lathrop CTF ADWF Projection
5-3
December 2024
EKI C20049. 02
Section 5
Wastewater Treatment Capacity Assessment
2024 WWSMP Amendment
City of Lathrop
Table 5-3. Projected Wastewater Flow and Treatment Capacity, Citywide Estimated ADWF Influent and Treatment Capacity ( MGD)
Existing
2022) 2025 2030 2035 2040 2045
Projected Influent ADWF (a)
Total ADWF Projection 2. 19 2. 79 3. 73 4. 67 5. 34 5. 67 Existing Capacity and Future Expansions
Manteca WQCF 1. 451 1. 451 1. 451 1. 451 1. 451 1. 451
Lathrop CTF Phase 0 - 2 2. 50 2. 50 2. 50 2. 50 2. 50 2. 50 Lathrop CTF Phase 3 0.0 0.0 2. 50 2. 50 2. 50 2. 50
Total Capacity 3. 95 3. 95 6. 45 6. 45 6. 45 6. 45
Projected Deficit

7. 0

6. 0
2 Y
a 5. 0
v

4. 0
a)
a

3. 0
LL
w 2. 0
f6
co 1. 0
o.

Figure 5-3. Projected Wastewater Flow and Treatment Capacity, Citywide Existing ( 2022) 2025 2030 2035 2040 2045
Manteca WQCF MEI Lathrop CTF Phase 0 - 2
Lathrop CTF Phase 3 -*- Total ADWF Projection
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December 2024
EKI C20049. 02
Section 5 2024 WWSMP Amendment
Wastewater Treatment Capacity Assessment City of Lathrop

5. 2 Impacts of Wastewater Strength on Treatment Capacity Both the MWQCF and the Lathrop CTF are observing increasing influent wastewater strength ( i.e. concentration of pollutants and nutrients in wastewater) likely due to improved water use efficiency during the recent droughts and in response to state regulations. The increases in influent wastewater strength may further limit treatment capacities at the treatment plants.

5. 2. 1 Manteca Water Quality Control Facility
In March 2022, Stantec Consulting Services ( Stantec) and Herwit Engineering ( Herwit) completed a MWQCF Capacity Study that indicates a reduction in MWQCF treatment capacity due to increased wastewater strength over recent years among other factors. To review the pollutant concentration in Lathrop' s wastewater conveyed to the MWQCF, EKI conducted monitoring study during October 2022, summarized in Appendix C.

The current wastewater influent to MWQCF, including flows from the Cities of Lathrop and Manteca, has an average BOD concentration of 372 mg/ L over the period of 2016 to 2021 ( Stantec and Herwit, 2022). To investigate the contribution of wastewater strength, EKI performed monitoring of flow and BOD, TSS, and total kjeldahl nitrogen ( TKN) concentrations during October 2022 at selected locations in the City' s wastewater collection system connected to the MWQCF. The results indicate there was relatively little variation in BOD, TSS, and TKN concentrations across the six monitored locations. BOD and TKN concentrations in the collection system samples were generally similar to concentrations typically measured from the Lathrop combined influent samples that are collected at the MWQCF, however, the TSS concentrations in the collection system were generally significantly lower than the concentrations from MWQCF samples. BOD concentrations in the collection system samples ranged from 208 mg/ Lto 312 mg/ L. A summary of sampling results is detailed in Appendix C.

5.2. Lathrop Consolidated Treatment Facility
The current capacity of the Lathrop CTF at 2. 5 MGD was designed in 2015 based on a pollutant loading of 420 mg/ L BOD ( carbon) and 60 mg/ Ltotal nitrogen (TN) (nitrogen). However, current sewer flows to the CTF contain higher dissolved and particulate BOD and TN concentrations. In its 2021 sewershed analysis, PACE Engineers ( PACE) showed an increase of 15 to 20% in pollutant load per gallon of water or hydraulic load in wastewater samples collected in the Mossdale, River Islands, and Crossroads areas compared to the CTF design concentrations ( PACE 2021). The higher pollutant loading limits the treatment capacity and reduces the CTF hydraulic capacity to 2. 0 MGD at current pollutant loading conditions ( PACE, 2021).

In the City' s collection system draining to the Lathrop CTF, PACE conducted sampling and analysis of BOD and TN during August of 2021. Samples were collected from four locations including Mossdale, River Islands, Crossroads, and combined CTF influent. Filtered chemical oxygen demand ( COD), TN, and total dissolved solids ( TDS) were analyzed for each sample and BOD was estimated from COD / filtered COD. The average BOD for the Mossdale, River Islands, Crossroads, and combined CTF locations were 554. 2mg/ L, 466. 8mg/ L, 544. 3mg/ L, and 355. 8mg/ L, respectively ( PACE, 2021). 3 3 PACE indicated that the results for the combined CTF influent were artificially low due to the auto -sampling equipment being located too far from the sample location and treatment occurring within the sample tubing. eki environment
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December 2024
EKI C20049. 02
Section 6 2024 WWSMP Amendment
Collection System Performance and Design Criteria City of Lathrop 6 COLLECTION SYSTEM PERFORMANCE AND DESIGN CRITERIA
The criteria used to evaluate the City' s existing collection system is based on 2022 Lathrop Design and Construction Standards (" Standards"; Lathrop, 2022) and the 2019 WWSMP. A summary of the wastewater system design criteria is provided below:

For hydraulic analyses, a Manning' s "n" of 0.13 is assumed for all sewers.

Pipes 15 inches in diameter and smaller are designed for peak flows with a maximum depth to diameter ( d/ D) ratio of 0. 50. Pipes 18 inches in diameter and larger are designed for peak flows at a maximum d/ D ratio of 0. 75.

Design velocity and head loss for force mains calculated using Hazen - Williams formula with a roughness constant of 110.

Minimum velocity greater than 2 feet per second ( fps) for pipes flowing half full.

Minimum gravity main slopes are summarized in Table 6-1.

Maximum velocity less than 10 fps.

Pump stations should be designed to convey PWWF within its firm capacity'.

Table 6-1. Minimum Gravity Main Slopes
Pipe Size ( inch)
6 Minimum Slope (ft/t)

0.050
8 0.035
10 0.025
12 0.020
15 0.015
18 0.012

6. 1 Capacity Criteria
The collection system is primarily evaluated against its ability to carry projected PWWF. Specifically, the d/ D ratio for gravity mains under PWWF are compared to the design criteria. Force mains are considered to be capacity deficient if maximum velocity exceeds 10 fps. For pump stations, the required total head and flow under PWWF are compared to their firm capacity.

6. 2 Minimum Velocity and Slope Criteria
Minimum velocity and slope criteria for gravity mains are of the same nature and independent of flow, i.e. velocity in a pipe flowing at half full is determined by its slope. These criteria ensure an appropriate flushing velocity and prevents sediment buildout in the pipes. However, it is unnecessary to correct an existing pipe with a mild slope if the pipe is sufficient to carry PWWF. The minimum velocity and slope criteria evaluation were not updated as part of this WWSMP Amendment. 4 Defined as pumping capacity with the largest pumping unit out of service. ek, environment
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December 2024
EKI C20049. 02
Section 7 2024 WWSMP Amendment
Hydraulic Assessment of the Collection System City of Lathrop 7 HYDRAULIC ASSESSMENT OF THE COLLECTION SYSTEM
EKI updated the City' s wastewater system hydraulic model to assess the ability of City' s existing collection system and key planned infrastructure under various wastewater flow scenarios to meet the recommended performance and operational criteria described in Section 6. A hydraulic model transforms information about the physical facilities and system into a mathematical model used to analyze the sewer system under various demand conditions. The hydraulic model then generates information on flow, velocity, flow depth, and head that can be used to assess system performance and identify system capabilities and deficiencies. The hydraulic model can also be used to verify the adequacy of recommended or proposed system improvements.

7. 1 Hydraulic Modeling Approach
To evaluate collection system performance against hydraulic design criteria, EKI ( 1) conducted steadystate model simulations of PWWF conditions, and ( 2) evaluated capacity and head requirements at PWWF for each lift station or pump station for existing and buildout scenarios.

The PWWF were modeled for all pipes as the total ADWF upstream of the pipe multiplied by the corresponding peaking factor from Figure 4-3. Pump stations were first modeled as ideal pumps that can pump at a rate equal to the inflow to determine the estimated PWWF influent to each pump station.

The modeling results were then evaluated against actual pump hydraulics to determine if each pump station has sufficient capacity to pump the modeled PWWF.

7. 2 Hydraulic Model Update
This section provides an overview of the updates to the City' ssewer system hydraulic model as part of this WWSMP amendment.

7. 2. 1 Model Platform
The City' s existing sewer system hydraulic model was developed on the Innovyze InfoSWMM model platform for the 2019 WWSMP. This selection was partially based on the platform' s geographical information system ( GIS) integration capabilities. To optimize the modeling building and maintenance process, a key objective of the IWRMP modeling effort was to construct hydraulic models that are integrated with the City' sinfrastructure GIS and allow for automatic synchronization between the model and infrastructure GIS to limit future maintenance efforts.

After importing the City' sGIS data into the hydraulic model, the following steps are performed to address data gaps, validate network data, and create a fully connected network:

New wastewater system infrastructure, including lift stations, pipeline improvements constructed post 2019 WSMP, were digitized in the geodatabase and incorporated into the new hydraulic model.
ekienvironment water
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December 2024
EKI C20049. 02
Section 7 2024 WWSMP Amendment
Hydraulic Assessment of the Collection System City of Lathrop The model network was reviewed and refined for connectivity. Using the software' stools, each pipe was connected to a model nodes and identified for upstream and downstream directions.

Orphan and duplicate elements were corrected.

Node and pipe invert data were reviewed and corrected for data errors. Missing invert data were inferred based on the City' s
minimum slope requirement, known invert of connecting
pipes, and ground slope.

Global parameters including Manning' sconstant and the Hazen - Williams C -Factors were applied to pipes based on City' s design criteria.

All scenarios were created with associated active facilities and conveyance configurations Parcel -level wastewater flow projections were allocated to the nearest upstream manhole.

EKI also obtained data for pump stations including wet well dimensions and elevations, pump types, operating levels, and head -discharge curves. These data are summarized in Table 3- 2 and are the basis for the pump station evaluation in Section 7. 5. Modeled PWWF at each pump station are summarized in Table 7-1.

EKI did not recalibrate the hydraulic model due to lack of sewer flow monitoring data. However, flow monitoring recommended as a CIP ( see Section 8) could be used to calibrate the model in the future.

7. 3 Sewer System Hydraulic Modeling Scenarios
The Existing ( 2022) and Buildout ( 2045) scenarios respectively assess existing infrastructure and regional infrastructure needs for the City' scurrent and planned developments described in Section 2.

Parcel - level wastewater ADWFs for the existing scenario were developed based on parcel land use and wastewater generation factors summarized in Section 4.2. Future ADWF included in the Buildout scenario is consistent with flow projections described in Section 4.2.3. Figure 7-1 shows parcels and future development included in each scenario.
s
either a manhole, a force main fitting, or a network structure ek, environment
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December 2024
EKI C20049. 02
Section 7
Hydraulic Assessment of the Collection System
2024 WWSMP Amendment
City of Lathrop
Table 7-1. Peak Wet Weather Flow at Pump Stations.

Existing Buildout
Lift Station or Pump Station
ADWF Peaking PWWF ADWF Peaking PWWF
mgd) Factor ( mgd) ( mgd) Factor ( mgd)
MWQCF Collection System
North Harlan PS 0.17 4. 0.76 0.40 4. 2 0. 168
Stonebridge LS 0. 158 3. 6 0. 561 0. 158 3. 6 0. 561
Woodfield LS 0. 382 2. 8 1. 071 0. 389 2. 8 1. 083
Valley Crossing LS 0.09 4. 0.39 0.09 4. 0.39
J Street LS 0. 270 3. 1 0. 842 0. 315 3. 0 0. 938
Easy Court LS 0.81 4. 0 0. 322 0.83 4. 0 0. 327
O Street PS 0. 518 2. 5 1. 317 0. 583 2. 5 1. 431
McKinley Avenue PS 0. 564 2. 5 1. 398 0. 575 2. 5 1. 417 Lathrop CTF Collection System
Central Lathrop PS 0.69 4. 0 0. 279 0. 630 2. 4 1. 511
Mossdale PS 0. 579 2. 5 1. 424 0. 861 2. 1. 913
River Islands 2A PS 0. 183 3. 4 0. 629 1. 395 2. 1 2. 905 River Islands Main PS 0. 493 2. 6 1. 273 2. 658 2. 1 5. 45 Crossroads PS 0.43 4. 2 0. 182 0.54 4. 1 0. 223
South Lathrop PS 0.003 4. 5 0.01 0.32 4. 3 0. 136
Lathrop Gateway PS 0.1 4. 5 0.3 0.7 4. 0 0. 286
Notes:
a) Flow information is not available for the Louise Avenue PS. eki environment
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EKI C20049. 02
f,egendSphere of Influence
Development Areas
Central Lathrop
QCrossroads
f
Historic Lathrop Infill and Other Developments
OLathrop Gateway
Mossdale Landing
Mossdale Landing East
Mossdale Landing West
Mossdale Landing South
River Islands
Sharpe Army Depot
Q South Lathrop
Incremental Development by Model Scenario
Itat Existing ( 2022)
Buildout ( Beyond 2040)
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 16 January 2024.

NA
4, 000 8, 000
Scale in Feet)
Modeling Scenarios
Wastewater System Master Plan Amendment
Coy of Lathrop
Lathrop, CA
December2024
Ienvironment 02004901
water Figure 7- 1
Section 7
Hydraulic Assessment of the Collection System City of Lathrop 2024 WWSMP Amendment

7. 4 Collection System Hydraulic Evaluation
As discussed in Section 6.1, the City' scollection system is primarily assessed against the capacity criteria, including d/ D ratio in gravity mains and maximum velocity in force mains. Figure 7-2 and Figure 7-3 show the modeled d/ D ratio under PWWF for each scenario. Gravity mains are highlighted where the modeled d/ D ratio exceeds the design criteria.

Modeled results are generally similar to the 2019 WWMP update and show that approximately 3% of City' s existing gravity mains will not meet the capacity criteria by 2045 ( see Table 7-2). As shown on Figure 7-2 and Figure 7-3, areas with capacity deficiencies are mostly consistent in the two scenarios, indicating that most capacity deficiencies identified in the Buildout scenario already exist in the existing system, although the degree of deficiency may increase with projected development.

Table 7- 2 summarizes modeled d/ D ratio results for each scenario.

Table 7-2. Summary of Collection System Capacity Deficiencies Scenario
Percent Length of Gravity Mains
Meeting
Capacity
Criteria
d/ D Ratio
Greater
Than 0. 5
a)
d/ D Ratio
Greater
Than 0. 75
d/ D Ratio
Greater Than 1
Surcharged)
Existing 98% 1.4% 0.1% 0.2%
Buildout 97% 2.0% 0.2% 0.3%
Notes:
a) Gravity mains less than 18 -inch diameter and exceeding the capacity criteria. eki environment
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EKI C20049. 02
Stanford Cro5sing. PS
Mossdale S1
Valley Crossings LS

DE LIMA RD

DOS REIS RD
N
Harlaorthn PS
I
j
1 r
i
PS
Easy Ct LS
0 St. PS
Crossroads PSG
Stonebridge PS
Sharp+ Private)
Lathrop CTF
Woodfield Li

LATHROP RD
California
i Natural Prodjcts
PS ( Private) I
McKinley l
Ave PS
EouiseAvePS
I

LOUISE AV
SSI PS
su( F
ivate)
Lathrop
Gateway PS
outh4ethrop PS

LIP LSI
Private)
i I YOSEMITE AV
MWQCFFFlow Meter
MWQCF
environment
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fL, egendSphere of Influence
OApproximate Area of WWTF
Pump Station or LA Station
Force Main
Gravity Mains
Meeting Capacity Criteria
Modeled Deficiencies
d/ D ratio 0. 51 - 0. 75
d/ D ratio 0. 76 - 0. 99
d/ D ratio >= 1. 0 (Surcharged)
Abbreviations
CTF = Consolidated Treatment Facility
d/ D = flow depth vs. pipe diameter
LIP = Lathrop Industrial Park
LS = lift station
MWQCF = Manteca Water Quality Control Facility
PS = pump station
SSI = Super Store Industries
WWTF = wastewater treatment facility
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 12 March 2024.

N
0 2, 000 0.00
Sao u Fat)
Existing Collection System Capacity Deficiencies
Wastewater System Master Plan Amendment
Cry or LeMrop
Lathrop, CA
December 2024
C20040 02
Figure 7- 2
River Islands P
Stanford Crossing. PS
UF
Mossdale PS. (;
r•• ,-\Y\\\, yam\
River Islands
Main PS
Valley Crossings LS

DE LIMA RD

DOS REIS RD
Ili`
Crossroads PS
i
North
Harlan PS
t
PS
Easy Ct LS
O St. PS
Stonebridge PS !
SharpelPS Private)
Woodfield Li

LATHROP RD
1 -California
Natural Prod cts
i
PS ( Private)
McKinley
Ave PS
Louise Ave PS

ILOUISE AV
SSI PS
a( PPivate)
Lathrop CTF
Lathrop
Gateway PS
Soyitheathrop PS

LIP LS(
Private)
i I
tOSEMITE AV
MWQCFFFlow Meter
MWQCF
ekenvironment 1 & water
r.egendSphere of Influence
nApproximate Area of WWTF
90 Pump Station or Lift Station
Force Main
Gravity Mains
Meeting Capacity Criteria
Modeled Deficiencies
d/ D ratio 0. 51 - 0. 75
d/ D ratio 0. 76 - 0. 99
d/ D ratio >= 1. 0 (Surcharged)
Abbreviations
CTF = Consolidated Treatment Facility
d/ D = flow depth vs. pipe diameter
LIP = Lathrop Industrial Park
LS = lift station
MWQCF = Manteca Water Quality Control Facility
PS = pump station
SSI = Super Store Industries
WWTF = wastewater treatment facility
Notes

1. All locations are approximate.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 28 March 2024.

N o 2, 600 5, 000
SUM In FM)
Buildout Collection System Capacity Deficiencies
Wastewater System Master Plan Amendment
City of Lathrop
Lathrop, CA
December 2024
C20040 O2
Figure 7-3
Section 7 2024 WWSMP Amendment
Hydraulic Assessment of the Collection System City of Lathrop

7. 5 Force Main and Pump Station Capacity Evaluation
The hydraulic requirements at each lift station or pump station depend on configuration of its downstream force main, specifically, size and head loss. Therefore, EKI ran the model and reviewed the resulting velocities to optimize force main configuration in the Buildout scenario before conducting the hydraulic assessment.

Table 7-3 summarized the force main configurations under PWWF in each scenario, as well as the head loss and velocity of each force main. As shown on the table, the City' s existing and planned force mains are able to convey projected wastewater flow through buildout.

Table 7-4 summarizes the flow and total head requirements under PWWF for each pump station. The table also lists the firm capacities of each pump station under Existing and Buildout scenarios, which may be affected by a pump station expansion or significant change in the total head requirement due to development. When compared to the pump stations' capacities, deficiencies are identified in the Stonebridge LS in both scenarios.
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December 2024
EKI C20049. 02
Section 7
Hydraulic Assessment of the Collection System
2024 WWSMP Amendment
City of Lathrop
Table 7-3. Force Main Hydraulic Analysis Results
Upstream Pump Station
Force Main
Diameter
in)
Existing Buildout
Velocity Velocity
fps)( b) ( fps)( b)

CLSP PS
18 14" Capacity Sufficient ( b)
14 0. 40 2. 14
Mossdale PS
8 1. 60 1. 75
12 2. 05 2.4
River Islands 2A 30 1. 89 2. 57
River Islands Main PS
18 1. 09 3. 45
12 18" Capacity Sufficient ( b) 2. 71
Crossroads PS 8 1. 21 1. 44
South Lathrop PS
6 0. 10 0. 53
6 6" Capacity Sufficient ( c)
Lathrop Gateway PS
6 0. 68 2. 39
4 6" Capacity Sufficient ( c)
North Harlan PS 6 0. 59 1. 31
Stonebridge PS 6 4. 36 4. 36
Woodfield LS 10 2. 98 3. 02
Valley Crossings LS 4 0. 98 0. 98
J St. PS 8 4. 10 4.7
Easy Ct LS 8 2. 32 2. 33
O St. PS 12 2. 55 2. 76
McKinley Ave PS 10 5. 44 5. 47
Notes:
a) Blue bolded text indicates velocity does not meet minimum criteria of 2 fps. b) Velocity in the force mains under steady- state hydraulic modeling is evaluated as a secondary criterion. In reality, force main and pump station operations can be adjusted from time -to -time to ensure there is enough velocity to prevent sedimentation.
c) For pump stations with parallel force mains, a single force main was modeled when velocities were below 2 fps.
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December 2024
EKI C20049. 02
Section 7
Hydraulic Assessment of the Collection System
2024 WWSMP Amendment
City of Lathrop
Table 7-4. Summary of Hydraulic Capacity Analysis for Pump Stations Existing
Existing Scenario Buildout
Buildout Scenario
Firm
Firm
Pump Station
Capacity
Capacity
gpm)
PWWF TDH ( gpm) PWWF TDH
gpm) ( ft) ( b) ( gpm) ( ft)
MWQCF Collection System
North Harlan PS 1, 075 53 11. 4 117 21.

South Lathrop PS 1, 850 1 27. 8 94 28. 1
Notes:
a) Red bolded text indicates PWWF exceeded pump station' s firm capacity. b) If different from existing firm capacity.
c) Capacity of the 8" outlet is listed as the lift station capacity, as it is the capacity limiting component of this pump station.
d) Flow information is not available for the Louise Avenue PS, therefore, its capacity is not analyzed. e) It is anticipated that the River Islands Sewer PS will be constructed in phases to include a total of six pumps.
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December 2024
EKI C20049. 02
Section 8 2024 WWSMP Amendment
Capital Improvement Program Changes to the 2019 WWSMP City of Lathrop 8 CAPITAL IMPROVEMENT PROGRAM CHANGES TO THE 2019 WWSMP This section recommends modifications and additions to the list of recommended CIPs included in the 2019 WWSMP and the City' s current Capital Improvement Program ( Lathrop, 2023). Table 8- 1 summarizes the current CIPs and incorporates the modifications recommended herein. The Opinion of Probable Cost ( OPC) for each project is escalated to December 2024 dollars based on an Engineering News Record ( ENR) Construction Cost Index ( CCI) of 13, 632 (20 -city average). The OPCs are conceptual level estimates, considered to have an estimated accuracy range of - 30% to+ 50%, suitable for use for budget forecasting, CIP development, and project evaluations, with the understanding that refinements to the project details and costs would be necessary as projects proceed to design and construction.

Figure 8- 1 shows an overview of the collection system project locations and improvements. Each project is shown in detail in Appendix D .

8. 1 Modifications to Wastewater Treatment CIPs
The following modifications to the City' s wastewater treatment CIPs are identified to reflect recent wastewater strength at MWQCF and the City' s progression on CTF expansions.

8. 1. Manteca Interim Improvements
As discussed in Section 5. 1, the City of Manteca indicated that increases in influent wastewater nutrient concentrations reduce MWQCF' streatment capacity to 6. 36 MGD and, therefore, Lathrop' sshare of MWQCF' scapacity to 0. 935 MGD ( Stantec and Herwit, 2022; Manteca, 2022). The City' s ADWF
conveyed to the MWQCF was 1.1 MGD in 2022 and was above this estimated reduced allocation.

Moreover, the City anticipates a total of 1. 31 MGD of wastewater will flow to MWQCF at buildout.

The City of Manteca is planning interim improvement projects which would increase the MWQCF' s capacity to 8. 23 MGD and Lathrop' sshare of capacity to 1. 21 MGD. The cost estimate of interim improvement projects to MWQCF was estimated at a total $ 32. 8 million in the August 2022 letter and updated to $79. 6 million in Manteca' s2023 draft Wastewater Master Plan ( Manteca, 2022; 2023).

The City is currently assessing its rights to capacity at the MWQCF and the appropriate level of contribution to improvements at the MWQCF to meet its current and buildout wastewater treatment needs. It is anticipated that the City will identify such improvements as a CIP once an agreement is established.

8. 1.2 Lathrop CTF Phase 3 Expansion
The current Phase 2 expansion Lathrop CTF has a hydraulic capacity of 2. 5 MGD at elevated wastewater strength levels. As discussed in Section 5. 1, wastewater ADWF to the Lathrop CTF is projected to soon exceed this capacity before 2025. The City has initiated Phase 3 expansion of the facility to a total ADWF capacity of 5. 0 MGD. As shown in Table 8-1, the total projected OPC for the Phase 3 expansion is approximately $ 23. 7 million based on the City' s FY 2023-4 CIP plan ( WW 22- 38).

The Phase 3 expansion is projected to meet flows from the new development areas through 2040, until when the City may need a fourth expansion of the facility. eki environment
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December 2024
EKI C20049. 02
Section 8 2024 WWSMP Amendment
Capital Improvement Program Changes to the 2019 WWSMP City of Lathrop

8. 2 Modification to Collection System CIPs
The hydraulic evaluation presented in Section 7 showed a reduction in hydraulic deficiency locations compared to those presented in the 2019 WWSMP as a result of CIPs completed since the 2019 WWSMP and lower wastewater flow projections. In particular, (1) the Woodfield Pump Station upgrade WW 22- 26) was completed in 2019; and ( 2) the Crossroads gravity main replacement project ( WW 22- 27) is no longer necessary. As such, these projects are removed or modified from the list of recommended CIPs.

The Stonebridge LS is approximately 40- gpm over capacity and the North Harlan PS has significant excess capacity. As an alternative to Project WW -1, North Harlan Rd businesses which currently pump into the Stonebridge collection system could instead tie -into North Harlan Rd SSFM.

The remaining collection system CIPs from the 2019 WWSMP have been reviewed and have been retained to address the potential deficiencies identified in the hydraulic assessment. However, EKI recommends additional analysis be conducted to confirm the required project extents and sizing. ek, environment
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December 2024
EKI C20049. 02
Section 8
Capital Improvement Program Changes to the 2019 WWSMP
2024 WWSMP Amendment
City of Lathrop
Table 8-1. Summary of Capital Improvement Projects
Addresses
Project Modeled
Project Timeframe
Number Surcharging in
Existing Scenario
Treatment Facility Improvement Projects
Total Project OPC ( a)
WWT- 1 Manteca Interim Improvements Near -term (b)
WWT 2
CTF Phase 3 Expansion ( WW 22 -
Near
3WW-1-
term (c) 23, 700, 000
CTF Surface Water Discharge ( WW
20- 17) (d) Existing 12, 699, 000
Total Treatment Facility Improvements OPC 36,99, 000
Collection System Improvement Projects
WW -1
Stonebridge Gravity Main
Replacement and Pump Station
Upgrade ( WW 22-5) (e)
Existing No 850, 00
WW 2A
Woodfield West Deficiency Project
Alternative A (WW 22 26)
Existing (f) No 2, 730, 000
WW 26
Woodfield West Deficiency Project
Alternative B ( WW 22 26) Existing ( f) No 2, 400, 000
WW 4
J Street Gravity Main Replacement
Project
Existing ( f) Yes 1, 690, 00
WW -5
Easy Court / O Street Gravity Main
Replacement Project
Existing No 1, 370, 000
WW -6 O Street Pump Station Upgrade Existing No 1, 560, 000 Total Collection System Improvements OPC 10, 500, 000
Miscellaneous Collection System Projects
WW -8 Temporary Flow Monitoring 100, 00
WW 9
Wastewater Lift Station Access
Modifications ( PW 24- 14) (d)
FY 23-5 CIP 475, 000
WW 9
Ozone Upgrade for Wastewater
Pump Stations ( PW- 24- 15) (d)
FY 23-5 CIP 75, 000
Total Miscellaneous Collection System Improvements OPC 650, 00 Notes:
a) Costs shown are presented in December 2024 dollars based on an ENR CCI of 13, 632. 41 (20 -city average).
b) City is currently evaluating the appropriate level of contribution to improvements at the MWQCF. c) City is currently issuing a request for proposal to PACE which may update this project OPC. d) Project included as a part of the City of Lathrop Capital Improvement Programs Fiscal Years 2023-025 report.
e) Connecting North Harlan Rd businesses which currently pump into the Stonebridge collection system to the North Harlan Rd SSFM can be considered as an alternative. f) Project addresses existing deficiencies, however future development influences recommended pipe or pump sizes to be installed.
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December 2024
EKI C20049. 02
r
WW -4: J Street
Gravity Main
Replacement
t_L LJ
WW -2B: Woodfield West
Deficiency Project
Alternative B

DE LIMA RD

DOS REIS R
WW -1: Stonebridge Gravity Main
Replacement and Pantie'
i Force Main
t/W- 6: O Street
PS Replacement w
1 WW -5: EasyCourUO Street\
Gravity Main Replacement
Lathr
CTF
WW -2A: Woodfield West
Deficiency Project - Alternative A

LATHROP RD
1I
1 1 LOUISE AV
1 a
ti
I—I ,
s. . tVOSEMITE AV
lit MWQj
Ll, e
end
7I. Sphere of Influence
Approximate Area of W WTF
E7a Pump Station or Lift Station
MI Pump Station or Lift Station Upgrade
Force Main
Gravity Main
Diameter of Replacement Sewer
10"
12"
15"
t
18"
Diameter of New Force Main
Abbreviations
CTF = Consolidated Treatment Facility
MWQCF = Manteca Water Quality Control Facility
WWTF = wastewater treatment facility
Notes

1. All locations are approximate.

2. A detailed map for each project is included in Appendix D Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 12 March 2024.

N 0
A
2, 500 5, 000
SP. in Fecal
Recommended Collection System
Improvement Projects
Wastewater System Master Plan Amendment
City of Lathrop
Lathrop. CA
environment
December 2024 Cthrop, 2
water Figure & 1
Section 9
References
2024 WWSMP Amendment
City of Lathrop
9 REFERENCES
California DOF, 2007. E- 4 Revised Historical City, County and State Population Estimates, 1991- 2000, with 1990 and 2000 Census Counts, August 2007.

California DOF, 2012. E- 4 Population Estimates for Cities, Counties, and the State, 2001-10, with 2000 2010 Census Counts, November 2012.

California DOF, 2022. E- 4 Population Estimates for Cities, Counties, and the State, 2011-020, with 2010 Census Benchmark, May 2022.

California DOF, 2023. E- 5 Population and Housing Estimates for Cities, Counties, and the State, January 2021-023, with 2020 Benchmark, May 2023.

EKI, 2019a. Wastewater System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2019b. Water System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2019c. Recycled Water System Master Plan, City of Lathrop Integrated Water Resources Master Plan Update, final December 2019.

EKI, 2024. Recycled Water System Master Plan Amendment, City of Lathrop Integrated Water Resources Master Plan, draft November 2024.

Stantec and Herwit, 2022. City of Manteca WQCF 2021 Capacity Assessment, prepared for the City of Manteca, dated 18 March 2022.

Lathrop, 2022a. City of Lathrop General Plan, August 2022. Available at: https:// lathrop. generalplan. org/ Lathrop, 2022b. River Islands Phase 2 Project, https:// www. ci. lathrop. ca. us/ planning/ page/ river- islandsphase- 2- project Lathrop, 2022c. City of Lathrop Department of Public Works Design & Construction Standards. Available at: https:// www. ci. Iathrop. ca. us/ publicworks/ page/ design- construction- standards Lathrop, 2023. Capital Improvement Programs Fiscal Years 2023-025. Available at:
htt ps:// www. ci. lath rop. ca. us/ finance/ page/ budget Lathrop County Water District and the City of Manteca, 2002. Amendment to Agreement dated March 5, 1984 between Lathrop County Water District and the City of Manteca Concerning Waste Water Treatment.

Manteca, 2022. City of Manteca — Wastewater Quality Control Facility Capacity, letter dated 30 August, 2022.

Stantec, 2023. City of Manteca Wastewater Master Plan, prepared for the City of Manteca, Final Draft dated November 2023.

PACE, 2021. Technical Memorandum: City of Lathrop CTF Phase 3 Expansion Discussion, dated 15 September 2021.

SWRCB, 2016. Order WQ- 2016- 008- DDWWater Reclamation Requirements for Recycled Water Use, 7 June 2016.
eki environment
water
9-1
December 2024
EKI C20049. 02
Section 9
References
2024 WWSMP Amendment
City of Lathrop
RWQCB, 2016. Order R5- 2016- 0028-1 Waste Discharge Requirements and Master Recycling Permit for City of Lathrop, Lathrop Consolidated Treatment Facility, San Joaquin County, California Regional Water Quality Control Board Central Valley Region, 21 April 2016.

RWQCB, 2022. National Pollutant Discharge Elimination System ( NPDES) CA0085359 Order R5- 2022- 0004, Waste Discharge Requirements for the City of Lathrop Consolidated Treatment Facility San Joaquin County, California Regional Water Quality Control Board Central Valley Region, 14 March 2022.
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EKI C20049. 02
Appendix A
WASTEWATER GENERATION FACTOR EVALUATION eki

APPENDIX A

WASTEWATER GENERATION FACTOR EVALUATION
environment
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Appendix A

WASTEWATER GENERATION FACTOR EVALUATION
A. WASTEWATER GENERATION FACTOR EVALUATION
eki environment
water
The following section describes the analysis performed to verify and update land -use specific wastewater generation factors developed by EKI in the City' s 2019 Integrated Water Resources Master Plan ( IWRMP).

As the City meters wastewater flows only at pump stations or at treatment plants, it is difficult to determine existing wastewater flow rates by individual land uses or sectors. However, wastewater use by individual sector can be estimated using historical water billing data. The analysis herein estimates wastewater flow rates using historical minimum month water use data and its ratio compared with measured average dry weather flow (ADWF).

EKI first evaluated the City' s water billing data for each applicable land use category and calculated the unit volume of minimum month water use for an individual dwelling unit ( gpd/ du) or each acre of commercial, industrial, and institutional ( CII) development ( gpd/ acre). This factor was then multiplied by either the uniform City- wide or development -area - specific ratios between water use and the ADWF ( see Section A. 1) to estimate the unit volume of wastewater ADWF, or gallons of wastewater per day per dwelling unit or acre ( gpd/ du and gpd/ acre, respectively). These unit flow factors represent estimated ADWF measured downstream at the wastewater treatment plants, which includes base sanitary flow (BSF) and year- round groundwater infiltration into the collection system.

The updated wastewater flow factors are listed in Table A- 4. As discussed below, a separate set of factors for River Islands low and medium density residential land uses has been developed to account for the unique residential per unit water use and existing lower I&due to the age of the collection system in this development area. A safety factor of 15% has been applied to the unit wastewater flow for the River Islands factors to account for the expected increase in I&in the future as the sewer system ages. A lower safety factor of 10% has been applied to the City- wide per unit wastewater generation factors to account for the relatively new developments and their local wastewater collection systems in Mossdale and Central Lathrop Specific Plan ( CLSP) development areas.

The process used to develop updated wastewater factors for each land use category is described in the following sections.

A. 1 Wastewater Flow and Water Use Comparison
To evaluate the relationship between water use and wastewater generation, EKI compared monthly water use derived from the City' s account - level water billing data to wastewater generation within each drainage area. By comparing water use to wastewater flows during the winter months, when little water is typically used outdoors, one can assess the amount of I&. For example, without significant I&, wastewater flows are typically only slightly lower than water use in winter, assuming the majority of indoor water use drains to the wastewater collection system. Wastewater flows in excess of water use during the winter would be indicative of contributions from I&.

Monthly average wastewater flow and water use from non -irrigation accounts between January 2017 and December 2021 for each collection system are shown on Figure A- 1. Wastewater flows in the MWQCF Manteca Water Quality Control Facility) drainage area was based on the SCADA at the MWQCF site, while the LCTF ( Lathrop Consolidatedh Treatment Facility) no River Islands drainage area wastewater flows was calculated by subtracting the River Islands pump station SCADA from the SCADA data at the LCTF site, City of Lathrop A- 1
Wastewater System Master Plan Amendment
December 2024
EKI C20049. 02
Appendix A
WASTEWATER GENERATION FACTOR EVALUATION e
environment
1 & water
which treats wastewater from Mossdale, River Islands, CLSP, South Lathrop, and Lathrop Gateway development areas as shown in the system schematic shown in Section 3. 1, 2 While water use generally exhibits strong seasonal trends largely due to landscape irrigation, wastewater generation appears similar from month to month. During the winter months, overall wastewater flows in the MWQCF drainage area ( i.e., Historic Lathrop Infill areas) and LCTF drainage area ( i.e., the rest development areas within the City) without River Islands are nearly equivalent to water use. Specifically, in the River Islands development area, wastewater flows are approximately 80% of winter water use. 3 Table A- 1
compares ADWF to water use during the month with the least water use ( Le. "minimum month water use") for each winter from 2017 to 2022 to assess the amount of infiltration. Wastewater flows range from 84% to approximately 115% of minimum month water use in the MWQCF drainage area. In LCTF drainage area, the 5 -year average ADWF is 95% of minimum month water use, while in River Islands, the ADWF is approximately 84% of minimum month water use. Without River Islands' wastewater flow contributions, the LCTF ADWF to water use increased to as high as 110%. It may be indicative of I&from the rest LCTF development areas draining to the LCTF collection system. 4 Citywide, the ADWF to water use ratio during minimum water use months is about 98% during the five- year window.

The May 2019 wastewater flow spike at the MWQCF station resulted from an abnormal meter reading, impacting the City- wide data, which is the sum of LCTF and MWQCF flows. 2 May 2018 and July 2019 wastewater flow SCADA data in the LCTF drainage area and River Islands were excluded due to negative readings at the River Islands pump station. The spike observed in June 2021 was considered an irregular meter reading compared to the historical flow pattern at the station. All reading errors at this station were not reflected in the LCTF flow data.
3 A 80% ratio between wastewater flows and winter water use is lower than typically expected and may indicate that there is significant winter -time landscape irrigation in River Islands. One potential reason may be because these newer homes are equipped with irrigation timers that residents forget to reset in the winter. 4 Significant I&had been identified in Crossroads in the previous Wastewater System Mater Plan ( EKI, 2019), however, Crossroads Pump Station SCADA data was not available during this preparation of this update.

City of Lathrop A- 2
Wastewater System Master Plan Amendment
December 2024
EKI C20049. 02
Appendix A

WASTEWATER GENERATION FACTOR EVALUATION
0 a
on
a)
m
Ia)
0 C
0 2, 500, 000
2, 000,00
1, 500, 00
1, 000,00
500, 00
eki environment
water
Figure A- 1 Monthly Water Use and Wastewater Flow by Collection System A. LCTF
0 Jan - 17 Aug -17 Feb -18 Sep -18 Mar -19 Oct -19 Apr -20 Nov -20 Jun - 21 Dec -21 Month
1— Water Use -— WW Flow - SCADA
B. MWQCF
3, 000,00
2, 500, 000
2, 000,00
1, 500, 000
1, 000,00
500, 00
0 Jan - 17 Aug -17 Feb -18 Sep -18 Mar - 19 Oct -19 Apr -20 Nov -20 Jun - 21 Dec -21 Month
41-- Water Use — I-- WW Flow - SCADA
City of Lathrop A- 3
Wastewater System Master Plan Amendment
December 2024
EKI C20049. 02
Appendix A

WASTEWATER GENERATION FACTOR EVALUATION
Monthly
Average (
gpd)
1, 200, 00
1, 000,00
800, 00
600, 00
400, 00
200, 00
eki
Figure A- 1 (Continued)
Monthly Water Use and Wastewater Flow by Collection System C. Mossdale
environment
water
0 Jan - 17 Aug -17 Feb - 18 Sep -18 Mar -19 Oct -19 Apr -20 Nov - 20 Jun - 21 Dec -21 Month
tWater Use — 4— WW Flow - SCADA
D. City -Wide
5, 000,00
4, 500, 000
4, 000,0
a
0-
3, 500, 000
0o
m 3, 000,00
m
2, 500, 000
Q
2, 000,00
c
0 1, 500, 000
1, 000,00
500, 00
0 Jan - 17 Aug -17 Feb -18 Sep -18 Mar -19 Oct -19 Apr -20 Nov -20 Jun - 21 Dec - 21 Month
4--- Water Use - AI-- WW Flow - SCADA
City of Lathrop A- 4
Wastewater System Master Plan Amendment
December 2024
EKI C20049. 02
Appendix A
WASTEWATER GENERATION FACTOR EVALUATION e
environment
8( water
Table A- 1 Minimum Month Water Use and ADWF
ADWF as a Percentage
MWQCF ( b) LCTF ( c)
of Minimum Month Water Use (%) ( a)
LCTF ( no RI) River Islands City -Wide
2017 99% 97% 94% 112% 98%
2018 110% 90% 96% 68% 101%
2019 115% 104% 110% 86% 110%
2020 98% 87% 91% 80% 93%
2021 84% 96% 108% 76% 90%
2022 73% 89% 85% 77% 80%
Average 101% 95% 100% 84% 98%
Notes:
a) Calculated as the ADWF of a given year divided by the water use during the minimum water use month of the previous winter. Dedicated irrigation accounts are excluded from this evaluation. b) Because it is difficult to discern the portion of wastewater that is managed onsite or discharged to the city' s wastewater system, historical water use in the McKinley drainage area is assumed to be equal to wastewater generation in this evaluation. c) Including River Islands, Mossdale, CLSP, South Lathrop, and Lathrop Gateway development areas.

A. 2 Residential Wastewater Flow Factors
Similar to the residential water use evaluation presented in the IWRMP Water System Master Plan Amendment ( EKI, 2024), various development - area -specific zoning classes were simplified into one of three categories: Low Density Residential ( LDR), Medium Density Residential ( MDR), and High Density Residential ( HDR). LDR accounts for Single -Family accounts with lot sizes larger than 4, 000 square feet, while MDR includes Multi -Family accounts and Single - Family accounts with lot sizes equal to or less than 4, 000 square feet. 5 HDR exclusively represents apartment land use. According to the San Joaquin County Assessor data and the account type from the billing records, the residential classes were assigned to each residential land use category are shown on Figure A- 2.

After grouping the residential parcels, minimum month water use in each year between 2017 and 2021 was evaluated on a parcel -by -parcel basis and multiplied by the ADWF ratios ( Table A-1) to develop residential wastewater flow factors for each existing residential land use category.

The HDR wastewater flow factor was exclusively derived from the water usage of the Towne Centre Apartments from November 2022 to June 2023 due to limited prior occupancy rates and billing data availability. Therefore, HDR flow factor was evaluated separately.

Account type extracted from the City' s potable water billing data. Lot size information based on San Joaquin County Assessor data.

City of Lathrop A- 5
Wastewater System Master Plan Amendment
December 2024
EKI C20049. 02
VINSC
OS MI
1 Legend
Sphere of Influence
Development Areas
Central Lathrop
Qf -1Crossroads
LJ Historic Lathrop Ingll and Other Developments
C3 Lathrop Gateway
Mossdale Landing
Mossdale Landing East
Mossdale Landing West
Mossdale Landing South
ORiver Islands
Sharpe Army Depot
South Lathrop
Land Use Categories
Low Density Residential
Medium Density Residential
High Density Residential
Notes

1. All locations are approximate.

2. Includes all residential accounts with at least one full year of billing data.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online. 7 March 2024.

N o O00 8. 000
A Isv. nr_, l
Residential Land Use Categories
Water System Master Plan Amendment
City of Lathrop
Lefton. CA
environment
December 2024
C200490t
water Figure A- 1
Appendix A
WASTEWATER GENERATION FACTOR EVALUATION eki environment water
As shown in Table A- 3, the available data were then evaluated to assess the extent to which each collection system had unique wastewater generation patterns. Figure A- 3 and Figure A- 4 show the results of this evaluation for LDR and MDR units, respectively. The data show that estimated unit wastewater generation in River Islands was approximately 20% lower than the minimum month water use per unit, and average water usage per unit at these homes was generally lower than City- wide average water use per unit. It may be caused by significant winter -time landscape irrigation in this development area ( see footnote 3 above). For the rest of the City, the estimated residential wastewater generation was generally equal to or slightly higher than the estimated minimum month water use per unit. This is likely due to the aging of the wastewater collection system within older historic Lathrop collection system which makes it more subject to I&compared to the newer West Lathrop collection system.

The ADWF in the MWQCF drainage area ( i.e., Historic Lathrop) and LCTF drainage area ( excluding River Islands) observed during 2017-021 are similar to the observed Historic Lathrop average flow during the 2018 flow monitoring period, while ADWF in River Islands is slightly lower than the observed West Lathrop flow. Additionally, the 2018 flow monitoring results provided further evidence that unit wastewater generation is different between the two portions of the City.

Based on the analysis and flow monitoring results described above, separate LDR and MDR wastewater flow factors were developed for the River Islands and the remaining City- wide units. There were no HDR i.e., apartments) in River Islands as of the preparation of this evaluation. Therefore, a uniform high density flow factor was assumed. Due to the newer age of the sewer system in River Islands, a 15% safety factor is applied to units in this development area to account for the expected increase in infiltration in the future as the sewer system ages. Therefore, a wastewater flow factor of 200 gpd/ du was selected for the River Islands LDR units based on calculated maximum wastewater generation per unit between 2017 and 2021 and the 15% safety factor. A safety factor of 10% was applied to the City- wide wastewater flow factors, assuming sewer conditions and infiltration will not be significantly worsened in the Historic Lathrop area and the collection system will gradually age in the remaining LCTF drainage area. As such, a wastewater flow factor of 240 gpd/ du was selected for City- wide LDR units, which is consistent with the previously developed Historic Lathrop LDR wastewater flow factor.

Similarly, wastewater flow factors of 200 gpd/ du and 155 gpd/ du were selected for City- wide and River Islands MDR units, respectively. A wastewater flow factor of 170 gpd/ du was selected for HDR units. The HDR flow factor is assumed to apply to all apartment units within the City.

City of Lathrop A- 7
Wastewater System Master Plan Amendment
December 2024
EKI C20049. 02
Appendix A
Wastewater Generation Factor Evaluation
Table A- 2
Residential Wastewater Flow Factor Evaluation
Year MWQCF ( Historic Lathrop) LCTF ( West Lathrop, no RI) Estimated
Unit ADWF
d)
bpd/ du)
River Islands
Unit Water
Use h)
gpd/ du)
Citywide
Minimum
Month Water
Use ( a)
gpd)
Number of
Active
Accounts
a)
Unit Water
Use( b)
gpd/ du)
ADWF vs.

Water Use
Ratio ( c)
Estimated
Unit ADWF
d)
Igpd/ du)
Minimum
Month Water
Use ( a)
gpd)
Number of
Active
Accounts
a)
Unit Water
Use (b)
gpd/ du)
ADWF vs.

Water Use
Ratio ( c)
Minimum
Month Water
Use ( a)
gpd)
Number of
Active
Accounts
a)
ADWF vs.

Water Use
Ratio (c(
Estimated
Unit ADWF
d)
gpd/ du)
Estimated
Unit ADWF
e)
gpd/ du)

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a) Water use data are obtained from the City' s billing system. b) Unit water use equals the minimum month water use divided by the number of active accounts. c) The ADWF to Water Use Ratio for each drainage area is obtained from Table A- 2. 4) Estimated ADWF is calculated by muhiplying the Unit Water Use by the ADWF to Water Use Ratio. e) Citywide Estimated Unit ADWF is calculated using the citywide estimated ADWF in gallons per day, divided by the city' stotal number of active accounts. eki A- 8 December 2024
EKI C20049. 02
Appendix A

WASTEWATER GENERATION FACTOR EVALUATION
Y

4. 250
200
o
LL` 150
v
a
m
ai 100
aa) 50
L
ai
f0 0
eki environmentwater
Figure A- 3 Low Density Residential Wastewater Flow Factor Evaluation 300
176
228
209
205
218
2017 2018 2019 2020 2021
Year
Water Use - MWQCF
Water Use- River Islands
Wastewater Flow- LCTF
Citywide Wastewater Flow
Water Use - LCTF
Wastewater Flow- MWQCF
Wastewater Flow - River Islands
300
250
200
150
100
50 Figure A- 4 Medium Density Residential Wastewater Flow Factor Evaluation 300
00 250
w
411
200
3 150
v
a
3 "
N 100
50 w
0 156
189
177
157
184
2017 2018 2019 2020 2021
Year
Water Use - MWQCF
Water Use - River Islands
Wastewater Flow - LCTF
Citywide Wastewater Flow
Water Use - LCTF
Wastewater Flow - MWQCF
Wastewater Flow - River Islands
300
250
200
150
100
50 City of Lathrop A- 9
Wastewater System Master Plan Amendment
December 2024
EKI C20049. 02
Appendix A
WASTEWATER GENERATION FACTOR EVALUATION e
environment
water
A. 3 CII Wastewater Flow Factors
Per acre wastewater flow factors were developed for commercial, industrial, parks, and schools/ institutional land uses based on minimum month water use and ADWF between 2017 and 2021.

For each CII land use, minimum month water use for each year between 2017 and 2021 was divided by the total land use acreage of active accounts, then multiplied by the ADWF ratio, to determine wastewater flow factors. Acreages were calculated by cross- referencing the City' s billing database with the San Joaquin County parcel database.

As discussed in the City' s
Water System Master Plan Amendment, City staff identified certain CII users need reclassification in regard to the account type from the billing data, which significantly altered the results compared to the CII wastewater generation factors developed in the City' s 2019 IWRMP. Figure A- 5 shows which individual parcels fell into each land use category, as confirmed by City staff.

General commercial and industrial water use factors were updated based on commercial and industrial minimum month water use, respectively. Table A- 3 shows an evaluation of commercial and industrial estimated water flow between 2017 and 2021. Estimated wastewater flows are compared between each collection system, as the MWQCF system represents the Historic Lathrop area, the LCTF drainage area represents new developments in West Lathrop. 6
Estimated commercial wastewater flow varies
significantly across the systems, ranging from less than 300 gpd/ acre in the LCTF area to more than 900 gpd/ acre in the MWQCF area.' This is likely due to highly variable water use between the types of commercial businesses across the City. The evaluations of commercial and industrial wastewater flows are illustrated on Figure A- 6 and Figure A- 7, respectively.

As parcel -level commercial and industrial wastewater flow is largely determined by the specific type of business, uniform or " Citywide" factors were developed to project future commercial and industrial wastewater generation, assuming that the existing profile of business and industries within the City will continue into the future. The wastewater flow factors were determined to be 755 gpd/ acre for Commercial land uses and 240 gpd/ acre for Industrial land uses including a 10% safety factor to account for the average future increase in infiltration in old and new sewers City- wide. Compared to the 2019 IWRMP, the commercial wastewater flow factor increased by approximately 28% from 590 gpd/ acre, which is likely due to a significant portion of commercial accounts were corrected as industrial, government, or park land uses.

The industrial wastewater flow factor decreased by approximately 28% from 335 gpd/ acre, which may be partially attributed to the improved I&conditions within the Crossroads development area. As shown in Table A- 1, the 5 -year average ADWF to Minimum Month Water Use ratio in the LCTF drainage area, where the Crossroads located within, is 95%, approximately 32% lower than the prior Crossroads 5 -year average ratio of 140%.

Since no industrial units currently exists or has been planned in River Islands, no separation of River Islands and the rest of LCTF was performed for CII wastewater flow factor evaluation.

Water use in during the minimum water use month in the Crossroads area in 2014 is likely to be an anomaly.

City of Lathrop A- 10
Wastewater System Master Plan Amendment
December 2024
EKI C20049. 02
Legend
Sphere of Influence
Development Areas
L _ __- 1 Central Lathrop
OCrossroads
O Historic Lathrop Inflll and Other Developments
QLathrop Gateway
Q Mossdale Landing
Mossdale Landing East
Mossdale Landing West
Mossdale Landing South
O River Islands
Sharpe Army Depot
CD South Lathrop
Land Use Categories
Commercial
Inn Industrial
an Park
School
MI Government
Notes

1. All locations are approximate.

2. Includes all residential accounts with at least one full year of billing data.

Sources

1. Aerial photograph provided by ESRI' s ArcGIS Online, 6 March 2024.

N o 4, 000 8, 000
ISw4 n Fri)
CII Land Use Categories
Water System Master Plan Amendment
City or Lathrop
Lathrop, CA
environment
December 2024
C2004a O1
water Figure A- 5
Appendix A
Wastewater Generation Factor Evaluation
Table A- 3
Commercial and Industrial Wastewater Generation Factor Evaluation Year MWQCF ( Historic Lathrop) LCTF ( West Lathrop) Citywide Minimum
Month Water
Use
gpd)
Land Use of
Active
Accounts
acres)
Unit Water
Use
gpd/ ac)
ADWF vs.

Water Use
Ratio
Estimated
Unit ADWF
gpd/ ac)
Minimum
Month Water
Use
gpd)
Land Use of
Active
Accounts
acres)
Unit Water
Use
gpd/ ac)
ADWF vs.

Water Use
Ratio
Estimated
Unit ADWF
gpd/ ac)
Estimated
Unit ADWF
gpd/ ac)
minec, c
2017 62,13 68 919 99% 906 18, 806 50 374 97% 361 675
2018 77, 839 71 1096 110% 1204 20, 065 80 251 90% 227 686 2019 63, 903 74 864 115% 990 25, 774 84 306 104% 318 633 2020 70,10 82 862 98% 843 20, 000 55 365 87% 320 634
2021 82, 323 97 853 84% 715 17, 419 51 340 96% 325 580
2017 85, 097 449 189 99% 187 85, 548 427 200 97% 194 190 2018 105, 097 436 241 110% 264 79, 452 436 182 90% 165 215 2019 57, 290 447 128 115% 147 73, 129 409 179 104% 186 165 2020 96, 419 516 187 98% 183 56, 419 381 148 87% 130 160 2021 63, 935 501 128 84% 107 70, 194 371 189 96% 181 139 Notes:
a) Water use data are obtained from the City' sbilling system. b) The ADWF to Water Use Ratio for each drainage area is obtained from Table A- 2. c) Estimated ADWF is calculated by multiplying the Unit Water Use by the ADWF to Water Use Ratio. d) Citywide Estimated Unit ADWF is calculated using the citywide estimated ADWF in gallons per day, divided by the city total number land use in acres. eki1 & water
A- 12 December 2024
EKI C20049. 02
Appendix A

WASTEWATER GENERATION FACTOR EVALUATION
u
1200
a
ao
1000
800
o0
rz 600
w
v 400
V)
200
Q1 0 1-+
300
250
200
150
100
50 0
e
environment
water
Figure A- 6 Commercial Wastewater Flow Factor Evaluation 2017 2018 2019 2020 2021
Year
Water Use - MWQCF Water Use - LCTF
Wastewater How - MWQCF= Wastewater Flow - LCTF
Citywide Wastewater Flow
Figure A- 7 Industrial Wastewater Flow Factor Evaluation 2017 2018 2019 2020 2021
Water Use - MWQCF
Wastewater Flow - MWQCF
Citywide Wastewater Flow
Year
Water Use - LCTF
Wastewater Flow - LCTF
1200
1000
800
600
400
200
300
250
200
150
100
50 0
City of Lathrop
Wastewater System Master Plan Amendment
A- 13 December 2024
EKI C20049. 02
Appendix A
WASTEWATER GENERATION FACTOR EVALUATION e
environment
1 & water
The wastewater flow factor for parks was quantified based on minimum month water use data for the following parks with indoor ( i.e., restroom) water use:

Apolinar Sangalang, • Milestone Park,
Crescent Park, • Mossdale Landing Community Park,
Greens Park, • Park West,
Islanders Field, • William S. Moss Park,
Lathrop Generations Fitness Park, • Woodfield Park, and Manuel Valverde Park, • River Island Fields.

Michael Vega Park,
The wastewater flow factor for parks was determined to be 55 gpd/ ac including a City- wide 10% safety factor, which is consistent with the 2019 park wastewater flow factor.

School water use varies seasonally depending on the school calendar ( i.e., the highest water use months) were reviewed to evaluate wastewater flow. Water use data were reviewed for the Lathrop High School, one. Lathrop, NextGeneration STEAM Academy, River Islands Technology Academy, and the Lathrop Elementary School."
Minimum month water use data for several institutional uses ( i.e., fire stations, City HaII, post office) had been reviewed and determined to be similar to schools in the 2019 IWRMP, and there was no significant change observed in institutional water use since then. Therefore, wastewater generation for institutional uses and schools was combined into a single factor. Based on minimum month water use between 2017 and 2021 and the City- wide 10% safety factor, the wastewater flow factor for Schools/ Institutional was determined to be 220 gpd/ ac.

A. 4 Summary of Wastewater Flow Factors
Based on the information presented above, Table A- 4 summarizes the wastewater flow factors developed for the 2024 IWRMP Amendment.

Note that these wastewater flow factors are planning -level factors for evaluating infrastructure, while the City uses site -specific wastewater allocations to manage discharge and capacity fees. 8 Water use data from non -irrigation meters for schools such as the Mossdale Elementary School and the Joseph Widemer Jr. Elementary School showed significant seasonal patterns due to irrigation water use and were therefore excluded from this analysis.
9 Water use in 2020 from the NextGeneration STEAM Academy and River Islands Technology Academy were excluded from analysis due to irregular water billing data.

City of Lathrop A- 14
Wastewater System Master Plan Amendment
December 2024
EKI C20049. 02
Appendix A
WASTEWATER GENERATION FACTOR EVALUATION eki
Table A- 4 Updated Wastewater Flow Generation Factors
environment
water
Low Density Residential
Wastewater
City -Wide
240 gpd/ du
Flow Factor
River Islands
200 gpd/ du
Medium Density Residential 200 gpd/ du 155 gpd/ du
High Density Residential 110 gpd/ ac
Commercial 755 gpd/ ac
Industrial 240 gpd/ ac
Parks 55 gpd/ ac
Schools/ Institutional 220 gpd/ ac
City of Lathrop A- 15
Wastewater System Master Plan Amendment
December 2024
EKI C20049. 02
Appendix B
WASTEWATER PEAKING FACTOR EVALUATION eki environment
water

APPENDIX B

WASTEWATER PEAKING FACTOR EVALUATION
Appendix B 2024 WWSMP Amendment
Wastewater Peaking Factor Evaluation City of Lathrop
B. WASTEWATER PEAKING FACTOR EVALUATION
As part of the Wastewater System Master Plan ( WWSMP) Amendment, EKI updated the peaking factor curve that estimates peak wet weather flow (PWWF) using wastewater flow data collected between 2017 and 2022. PWWF is the highest hourly flow experienced during the year due to rainfall -induced I&and peak diurnal sanitary flows and is used to evaluate the hydraulic capacity of a wastewater collection system. PWWF peaking factors are typically higher in smaller drainage areas, in which there is little flow attenuation. Larger drainage areas provide a greater capacity to attenuate flows, as peak flows generated in the upstream reaches of the system take a longer
amount of time to travel downstream.

B. 1 Historical Peak Hourly Flow
The City provided discharge flow data and sump elevation data from several pump stations in 5 - minute increments between January 2017 and July 2022. Using these data, EKI calculated hourly inflow to each pump station by summing discharge and sump storage change.

EKI has observed occasional abnormal patterns in the SCADA flow data, possibly due to incorrectly registered flows in the SCADA system, or artificial flow peaks due to large scale construction and wastewater infrastructure maintenance. The data sets were processed in the programming language " R" in order to convert the 5 -minute SCADA data into useable hourly and daily averages. Additionally, manual processing was conducted in order to remove erroneous zero data and outliers. Summarized by pump station the following adjustments were made to the SCADA data:

Mossdale PS — Removed small portion of erroneous data from 2018 ( 124 data points) Stonebridge PS — Removed erroneous peak in 2021 ( 5 data points) Woodfield PS — Data from 1 January 2017 to 15 May 2021 was determined to be unreliable reliable due to incorrectly registered flows River Islands Main PS — November and December 2021 data was combined with the 2022 dataset
McKinley and O Street PS — Data was split into two sets for before and after 2 April 2021 for changes in pumping configuration.

To review data in detail, EKI calculated the Cumulative Distribution Function ( CDF) of peak hourly flow within each day, normalized by ADWF, for each pump station. The result of this analysis is shown together with CDFs calculated for the 2019 WWSMP on Figure B- 1. A typical CDF resembles a sigmoid function ( or " S -curve"), which can be observed during most years at each pump station. Several exceptionally high peak periods were observed at the Mossdale, Stonebridge, and O Street Pump Stations that were not found to be associated with rainfall. To eliminate anomalies in flow data, EKI selected the 99. 5 -percentile peak hourly flow as the PWWF during each year, as listed in Table B- 1.
ek, environment
water
B- 1 December 2024
EKI C20049. 02
Appendix B 2024 WWSMP Amendment
Wastewater Peaking Factor Evaluation City of Lathrop
B. 2 Peaking Factor Curve
Figure B- 2 plots historical PWWF versus ADWF for the City' s pump stations from 2013 through 2022 as well as peak hourly flow versus average flow for the 2018 flow monitoring locations by year and then by pump station. As shown on Figure B- 2, there is not an observed yearly trend of PWWF versus ADWF.

EKI fit a peaking factor curve based on these flow data, as shown on Figure B- 2, which EKI recommends be adopted for future evaluations to assess pumping and conveyance capacities. It can be observed that while other pump stations with long periods of records, such as Stonebridge, Mossdale, and McKinley, have data points scattered both above and below the estimate line, data from the O Street Pump Station concentrated below the estimated line. This indicates that peak flow observed at the 0 Street Pump Station are smaller than what is anticipated for pump stations at its size.

Given that the City' sdesign standard requires that 50% capacity be retained in most pipes1 under PWWF and that pump stations meet PWWF with their firm capacity, EKI believes that use of the calculated PWWF curve is appropriate. The design standard provides surplus capacity to accommodate flows from larger rain events to prevent capacity -related sanitary sewer overflows.
1 The City' s design standard requires 50% capacity to be retained in pipes with a diameter of 15 inches or smaller and 75% capacity to be retained in pipes with a diameter greater than 15 inches. ekienvironment water
B- 2
December 2024
EKI C20049. 02
Appendix B 2024 WWSMP Amendment
Wastewater Peaking Factor Evaluation City of Lathrop
Figure B- 1. Cumulative Distribution Functions of Historical Peak Hourly Flow Mossdale
Cumulative
Distribution
Frequency
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
i f • •
0 1 2 3 4 5 6
Peak Hourly Flow within Each Day / ADWF
2013 2014 • 2015 • 2016 • 2017 • 2018 • 2019 • 2020 • 2021 100%
90%
o80%
a,
U- 70%
c
60%
50%
v,
G 40%
30%
20%
10%
0% • _
0 Stonebridge
1 2 3 4
Peak Hourly Flow within Each Day / ADWF
5 2013 2014 2015 • 2016 • 2017 • 2018 • 2019 • 2020 • 2021 eki environment
water
B- 3
6 December 2024
EKI C20049. 02
Appendix B
Wastewater Peaking Factor Evaluation
2024 WWSMP Amendment
City of Lathrop
Cumulative
Distribution
Frequency
Cumulative
Distribution
Frequency
Figure B- 1. Cumulative Distribution Functions of Historical Peak Hourly Flow (Cont.) 100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
O St
0 0. 5 1 1. 5 2 2. 5
Peak Hourly Flow within Each Day / ADWF
2013 2014 • 2015 • 2016 • 2017 • 2018 • 2019 • 2020 • 2021 RI Main
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
3 0. 0. 5 1. 0 1. 5 2. 0 2. 5 3. 0 3. 5
Peak Hourly Flow within Each Day / ADWF
ek, environment
water
2021&022
B- 4
December 2024
EKI C20049. 02
Appendix B 2024 WWSMP Amendment
Wastewater Peaking Factor Evaluation City of Lathrop
Figure B- 1. Cumulative Distribution Functions of Historical Peak Hourly Flow ( Cont.) RI PS 2A
Cumulative
Distribution
Frequency
Cumulative
Distribution
Frequency
100% I .•....•• • rte• ..
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
100% - - • • • ,,.• • ••

0. 0. 5 1. 0 1. 5 2. 0 2. 5 3. 0 3. 5 4. 0
Peak Hourly Flow within Each Day / ADWF
2020 • 2021 • 2022
McKinley
90%
80%
70%
60%
50%
40%
30%
20%
10%
eki
0%

0. 0. 5 1. 0 1. 5 2. 0 2. 5 3. 0 3. 5 4. 0
Peak Hourly Flow within Each Day / ADWF
2020 Pre 4/ 2/021 • Post 4/ 2/021 • 2022
environment
water
B- 5

4. 5
December 2024
EKI C20049. 02
Appendix B 2024 WWSMP Amendment
Wastewater Peaking Factor Evaluation City of Lathrop
Figure B- 1. Cumulative Distribution Functions of Historical Peak Hourly Flow ( Cont.) Woodfield
Cumulative
Distribution
Frequency
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%

0.0 0. 50 1. 00 1. 50 2. 00 2. 50 3. 00 3. 50 4. 00 4. 50 Peak Hourly Flow within Each Day / ADWF
2021
eki environment
water
B- 6
December 2024
EKI C20049. 02
Appendix B
Wastewater Peaking Factor Evaluation
2024 WWSMP Amendment
City of Lathrop
Table B- 1. Historical Wastewater Flow and Peaking Factors ADWF PWWF Peaking Factor
Year
gpd) ( gpd) (a) ( b)
Mossdale Pump Station ( c)
2013 307, 410 830, 547 2. 70
2014 312, 268 732, 557 2. 35
2015 335, 693 1, 636, 267 4. 87
2016 408, 363 2, 008, 720 4. 92
Stonebridge Pump Station
2013 128, 478 367,26 2. 86
2014 121, 054 512, 057 4. 23
2015 116, 383 497, 90 4. 28
2016 120, 371 603, 360 5. 01
O St Pump Station
2013 675, 465 1, 406, 948 2. 08
2014 638, 801 1, 371, 470 2. 15
2015 612, 014 1, 393, 241 2.8
2016 622, 13 1, 310, 883 2. 11
MWQCF Flow Meter
2014 0 0 2. 02
Notes:
a) A 99. 5 -percentile daily peak flow was selected for the PWWF of each pump station to eliminate anomalies in the City' s
SCADA system data.
b) Peaking factor is calculated as the ratio of PWWF to ADWF. c) The City began weekly flushing of River Islands sewer system in 2015, which likely accounts for the significantly higher peak flows in 2015 and 2016. eki environment
water
B- 7
December 2024
EKI C20049. 02
Appendix B
Wastewater Peaking Factor Evaluation City of Lathrop
2024 WWSMP Amendment
Peak
Wet
Weather
Flow /
Average
Dry
Weather
Flow
6 5
4 3
2 1
0 eki
0 500, 00 1, 000,00 1, 500, 000
Figure B- 2. Historical Wastewater Flow and Peaking Factors Average Dry Weather Flow ( gpd)
IWRMP Peaking Factor
2014
2016
2017
2019
2021
2023 IWRMP Peaking Factor
environment
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B- 8
2013
e 2015
2018 ( Flow Monitoring)
e 2018
2020
2022
2, 000,00
December 2024
EKI C20049. 02
Appendix B
Wastewater Peaking Factor Evaluation City of Lathrop
2024 WWSMP Amendment
Peak
Wet
Weather
Flow /
Average
Dry
Weather
Flow
6 5
4 3
2 1
0 0 500, 00 1, 000,00 1, 500, 000
Figure B- 2. Historical Wastewater Flow and Peaking Factors ( Cont.) Average Dry Weather Flow ( gpd)
2, 000,00
2016 IWRMP Peaking Factor • O Street
Mossdale e Stonebridge
Woodfield RI Main
McKinley 2023 IWRMP Peaking Factor
eki environment
water
B- 9
December 2024
EKI C20049. 02
Appendix C ekienvironment water

APPENDIX C
Summary of Monitoring Results from
Evaluation of Biochemical Oxygen Demand
Contribution to Manteca Water Quality
Control Facility
eki
DRAFT — 13 December 2023

MEMORANDUM
To:

From:

Subject:

Greg Gibson, P. E. (City of Lathrop)
Dave Umezaki, P. E. (EKI Environment & Water, Inc.)
Tina Wang, P. E., (EKI Environment & Water, Inc.)
environment
water
Summary of Monitoring Results from Evaluation of Biochemical Oxygen Demand Contributions to Manteca Water Quality Control Facility Wastewater System Master Plan Amendment Evaluation
City of Lathrop, California
EKI C20049. 02)
On behalf of the City of Lathrop ( City), EKI Environment & Water, Inc. has prepared this memorandum to summarizing the results of monitoring performed for evaluation of the City' s biochemical oxygen demand BOD), total suspended solids (TSS), and Total Kjeldahl Nitrogen (TKN) contributions to the Manteca Water Quality Control Facility ( MWQCF).

BACKGROUND AND MONITORING APPROACH
During October 2022, EKI performed monitoring to evaluate flows and BOD, TSS, and TKN concentrations at selected locations within the City' s wastewater collection system. The purpose of the monitoring was to provide additional data in response to correspondence from the City of Manteca indicating that the City of Lathrop was exceeding its allotted BOD loading limit from the Wastewater Capacity Agreement between the two cities.

Based on a review of the City of Lathrop wastewater collection system, EKI selected a total of five monitoring locations, generally shown on Figure 1 and in more detailed views on Figures 2 through 6.

These monitoring locations included the following:

A monitoring location at the North Harlan Pump Station wet well ( Figure 2) to capture the sewershed served by that pump station;
A monitoring location at the Stonebridge Lift Station wet well (Figure 3) to capture the sewershed served by that lift station;
A monitoring location at the Woodfield Lift Station wet well ( Figure 4), to capture the sewershed that is served by the North Harlan Pump Station, Stonebridge Lift Station, and Woodfield Lift Station;
A monitoring location at an O Street manhole located upstream of the Easy Court Lift Station Figure 5), to capture the sewershed that is served by that lift station; A monitoring location at the O Street Pump Station wet well ( Figure 6), to capture the sewershed that is served by the Valley Crossing Lift Station, J Street Pump Station, Easy Court Lift Station, and O Street Pump Station; and
Greg Gibson, P. E.

City of Lathrop
DRAFT — 13 December 2023

Page 2 of 3 ends

Lathrop City CouncilOctober 13, 2025

Lathrop City Council
October 13, 2025