801 T Street
Sacramento, CA 94811
www.woodardcurran.com
T 800.426.4262
T 916.999.8700
F 916.999.8701
Via Electronic Mail
June 23, 2025
Maria Encinas
City of Patterson
1 Plaza
Patterson, CA 95363
RE: Amendment to Proposal to Update Hexavalent Chromium Treatment Feasibility Study, P.O. 002025-0199
Dear Ms. Encinas:
Woodard & Curran is pleased to provide the City of Patterson (City) with the following amendment to our contract to update the Hexavalent Chromium (Chrome 6) Feasibility Study originally completed in 2017 and reinitiated in 2025. This revised scope incorporates additional evaluation criteria as requested by the City following submittal of initial proposal in October of 2023. The updated feasibility study will address the same overall objectives as the original study, evaluating feasible treatment approaches for compliance with the new Chrome 6 maximum contaminant level (MCL), while also integrating new planning factors related to aquifer management, SGMA compliance, system hydraulics, and regional growth.
The updated study will provide an expanded evaluation of wellhead vs. centralized treatment strategies, options for using Upper Aquifer groundwater and surface water sourced from Patterson Irrigation District (PID) or others, and planning-level evaluation of conveyance system hydraulics. It also incorporates updated demand projections and reduced Lower Aquifer groundwater pumping targets as contained in the Delta-Mendota Subbasin Groundwater Sustainability Plan (GSP). The study will focus on Chrome 6 but also considers the co-treatment of potential emerging contaminants (e.g. 1,2,3-TCP), TDS and nitrate, when necessary.
PROJECT BACKGROUND
On July 1, 2014, the State Water Resources Control Board (SWRCB), Division of Drinking Water (DDW) adopted a maximum contaminant level (MCL) for Chrome 6 of 0.010 mg/L. Although the MCL was later rescinded in 2017, the State subsequently re-initiated rulemaking starting on June 16, 2023, and held a public hearing on August 2, 2023 to receive oral comments, with written comments due August 18, 2023. In August of 2024, the State Water board adopted the same Chrome 6 MCL of 0.010 mg/L with an effective date of October 1, 2024.
The water quality of the City's water supply has generally remained unchanged; the seven groundwater wells that constitute the entirety of its potable supply all exceed the proposed MCL of 10 ug/L. As such, it is expected that DDW will issue a Compliance Order (CO) to the City requiring the City to take measures to meet compliance with the new MCL, including submitting an updated Corrective Action Plan. As before, subsequent evaluations, including an updated feasibility study, will need to consider the levels of nitrate and Total Dissolved Solids (TDS) in potable wells in evaluating treatment alternatives and associated engineering, as well as the City of Patterson (0012768.00) 2 Woodard & Curran, Inc.
Amendment to Proposal to Update Chrome 6 Treatment Feasibility Study June 23, 2025 Chrome 6 concentrations. It is also recommended that the City use this opportunity to consider the potential need for future treatment of other emerging contaminants such as 1,2,3- TCP.
As previously, the Feasibility Study will require evaluating the following elements:
• Treatment technologies to reduce Chrome 6 from the source water as identified in the California Code of Regulation (CCR) Section 64447.2 as best available technologies (BAT) for Chrome 6 treatment. These technologies include:
o Reduction/coagulation/filtration (RCF)
o Strong based anion exchange (SBA)
o Weak based anion exchange (WBA)
o Reverse Osmosis (RO)
• The potential treatment for nitrate and/or total dissolved solids (TDS) in addition to Chrome 6 using the technologies listed above. Both nitrate and TDS have been identified as long- term water quality (WQ) improvement goals in the City's Water Master Plan.
• Potential siting options for a treatment facility (i.e., centralized treatment facility or individual well head treatment systems).
• For siting of a potential centralized facility, evaluation of conceptual pipeline alignments to convey raw well water from the individual well locations to a centralized location, treated water to the existing potable distribution system, and residuals (e.g. spent backwash, spent regenerants, brine, etc.) to the existing sewer.
BAT treatment technologies for Chrome 6 (RCF, SBA, WBA, RO) have not changed from the time of the 2017 study. Therefore this information will be reviewed for consistency with current designs, but it's anticipated that design criteria or individual well site treatment footprints will not change significantly.
After the previous proposal to update the Hexavalent Chromium Treatment Feasibility Study was submitted, the City requested that several additional considerations be evaluated as part of the study update. These include:
• Evaluation of feasibility to replace or supplement existing wells by using water from other wells in the City’s service area that are not currently owned or operated by the City.
• Options to meet conservation requirements, and Sustainable Groundwater Management Act (SGMA) Lower Aquifer pumping reduction target as estimated by EKI Environment & Water, Inc. (EKI).
• Use of a second centralized treatment facility near the Arambel Tank or other nearby locations.
City of Patterson (0012768.00) 3 Woodard & Curran, Inc.
Amendment to Proposal to Update Chrome 6 Treatment Feasibility Study June 23, 2025 • Impacts of these changes on system hydraulics and the need for new conveyance, pressure boosting, or other potential system adjustments. • Use of surface water from Patterson Irrigation District (PID) or California Valley Project (CVP) to offset Lower Aquifer pumping and for blending to potentially reduce or eliminate treatment for Chrome 6 or other contaminants.
These items have been discussed with City staff and other stakeholders over the course of several meetings and the outcomes are reflected in this revised scope of work. A slide deck deliverable was prepared to explain our initial findings, conclusions, and suggestions. In addition to the original objectives of the 2017 study, the updated feasibility study will now also consider:
• Revised demand projections
• The SGMA-mandated Lower Aquifer pumping reduction target (as estimated by EKI) • Use of new or existing Upper Aquifer wells to meet potable demand and reduce lower aquifer pumping
• Treatment of Upper Aquifer groundwater for potable supply at a centralized facility • Use of Diablo Grande/CVP
• Use of surface water for potable augmentation and blending Once the alternatives evaluated in the 2017 study have been reviewed and conceptually redefined as needed, the planning level configurations from the 2017 study will be updated using conservative values for design and operating criteria for each revised alternative. Lifecycle costs will then be updated for each alternative, factoring in capital cost, operational and maintenance (0&M) costs, and residual management costs, as well as the findings as applicable from the prior Well Evaluation study. The results from this effort will be used as a basis to recommend one overall alternative for the City to consider for pilot testing or further evaluation.
SCOPE OF SERVICES
Task 1: Project Management and QA/QC
Task 1 includes coordination of project activities, budget tracking, and incidental communication and correspondence, as well as quality assurance and quality control (QA/QC) to execute this project.
Task 2: Chrome 6 Treatment Feasibility Study Update
Woodard & Curran will update the 2017 feasibility study using the original analysis as a foundation, incorporating revised planning assumptions and newly requested evaluation elements described above. The updated feasibility study will re-evaluate wellhead and City of Patterson (0012768.00) 4 Woodard & Curran, Inc.
Amendment to Proposal to Update Chrome 6 Treatment Feasibility Study June 23, 2025 centralized treatment options for Chrome 6 and co-contaminants, considering both revised system demands and potential new sources such as Upper Aquifer wells and surface water.
The majority of the Task 2 and Task 4 budget was expended completing the additional scope items described above while also making significant progress on the original subtasks. The following subtasks detail the remaining scope required for Task 2 and have been revised to match the City’s newly determined needs. Note the addition of Subtask 2.5, which represents the relatively small number of activities needed to complete the additional work previously described above.
Subtask 2.1 - Treatment Technology Analysis Update
This subtask will reassess the design basis for the previously evaluated BAT technologies for Chrome 6 treatment. Conceptual design information for each technology to be reviewed and updated as necessary in this subtask include the following:
• Treated water quality objectives.
• Initial and ultimate treatment capacity requirements for centralized facility. • Establish design raw water quality for use as design basis for treatment, both for individual wells and combined well flow, for both Lower and Upper Aquifer wells, and for surface water based on publicly available water quality data. • Design criteria as appropriate for each technology (e.g., loading rates, allowable bed volumes for treatment, recovery/brine flow rate, etc.). • Conceptual process configurations with number of unit operations and redundancy requirements.
• Determine capability to reduce nitrate and/or TDS from the raw water, particularly for Upper Aquifer well treatment for potable use.
• Equipment sizing.
The potential and need to add and coordinate other treatment methods (such as granular activated carbon) to the treatment system to address other constituents (such as 1,2,3-TCP) will also be considered.
Subtask 2.2 – Siting Re-evaluation
This subtask will update siting feasibility of both wellhead and centralized treatment systems, and consider use of surface water to supplement supply and offset Lower Aquifer pumping:
1. Wellhead Treatment: Footprint feasibility assessments for onsite treatment of Chrome 6 will be updated to include new Well 14 using parametric comparisons of required vs. available space. Footprint feasibility assessment for onsite treatment of 1,2,3-TCP at Well 6 will also be evaluated.
City of Patterson (0012768.00) 5 Woodard & Curran, Inc.
Amendment to Proposal to Update Chrome 6 Treatment Feasibility Study June 23, 2025 o Conceptual level layouts will not be generated as the estimated square footage required versus space available at each well site will be used as a basis to determine feasibility.
2. Centralized Treatment: Revised well water quality, demand projections, and source water configurations will be used to:
o Recalculate facility design capacity and footprint estimates based on revised demand forecast and reduced Lower Aquifer pumping
o Develop a revised conceptual treatment system design for one centralized treatment facility at the previously identified site located at 1st and Orange.
This will include:
One (1) new layout for RO treatment of blended Lower Aquifer and Upper Aquifer wells, potentially including the City’s Keystone and Floragold wells, for simultaneous removal of Chrome 6, nitrate, and TDS, sized to offset Lower Aquifer pumping for potable use sufficient to meet the Lower Aquifer pumping target.
• A detailed brine management study is not included. It will be assumed that liquid waste brine streams like RO concentrate can be discharged to the local sewer.
o The updated layout will inform lifecycle cost and hydraulic evaluations in subsequent tasks.
3. Surface Water Supplementation: A narrative conceptual evaluation of supplementing or offsetting supply with surface water will be prepared. Due to limited availability of water quality data for potential supply sources and the conceptual nature of this study, no detailed surface water treatment design criteria or layouts will be included. The following two alternative sources of surface water and approaches will be evaluated:
A. Diablo Grande partnership to obtain Central Valley Project (CVP) surface water.
Evaluate options for expanded treatment at Diablo Grande’s existing surface water treatment plant, conveyance to the City, and exchange programs with neighboring districts.
Explore funding opportunities.
This option may have the benefit of an expedited timeline given the existing agreement between Diablo Grande and the CVP, some existing treatment, and ongoing water quality sampling and data collection. Given the implementation timeline, interim treatment of local groundwater for Chrome 6 will likely still be required to meet DDW’s compliance timeframe. As part of this approach, Woodard & Curran will narratively evaluate a short-term, centralized treatment City of Patterson (0012768.00) 6 Woodard & Curran, Inc.
Amendment to Proposal to Update Chrome 6 Treatment Feasibility Study June 23, 2025 option using anion exchange specifically for Lower Aquifer water to remove Chrome 6 only. This option is recommended due to its relative affordability, ease of deployment, and the advantage of generating no residuals that require off-site management. Due to uncertainty of lead time for this option, it may require short-term exceedance of Lower Aquifer pumping, but long-term would significantly reduce all groundwater pumping once completed. The ramifications of this option under DDW regulations may need to be investigated.
B. Regional Project: Procurement and use of PID water for blending and treatment at centralized facility location.
This option is a longer Term solution, 10+ years as indicated in discussion with DDW, due to the need to identify and develop partnerships and agreements for the project, collect water quality data to meet the USEPA Long-Term 2 Enhanced Surface Water Rule monitoring requirements, procure funding, and design and construct treatment and conveyance.
Opportunities to expedite this process will be evaluated based on Woodard & Curran’s experience with expedited surface water treatment projects in Florida and other locations.
High-level review of possible funding opportunities and potential opportunities with neighboring disadvantaged communities. Narrative evaluation of treatment at centralized facility site. Note, required treatment likely to be more robust than for CVP surface water if San Joaquin River water is used.
This option, as with the Diablo Grande partnership, would also require an interim Chrome 6 treatment solution. Opportunity to integrate surface water treatment at the future existing centralized treatment facility for Chrome 6 will be considered. Longer lead time would likely require short-term exceedance of Lower Aquifer pumping, but longterm would significantly reduce all groundwater pumping across the Delta-Mendota Subbasin once completed. The ramifications of this option under DDW regulations may need to be investigated.
Please note that, for the purposes of this proposal, it was assumed that surface water sourced from PID would be used for a regional surface water treatment project. However, surface water supplies may also be sourced from other entities within the Delta-Mendota Subbasin (e.g., Central California Irrigation District, West Stanislaus Irrigation District) to support a regional surface water supply project.
Subtask 2.3 - Conceptual Pipeline Alignment Re-evaluation City of Patterson (0012768.00) 7 Woodard & Curran, Inc.
Amendment to Proposal to Update Chrome 6 Treatment Feasibility Study June 23, 2025 For this subtask, Woodard & Curran will re-assess the conceptual level evaluation of the raw water, treated water, and residuals management pipelines previously conducted for a centralized treatment facility. This will include reviewing the pipeline alignments previously identified based on available public right-of-way and City land/easements; pipeline length; known utility congestion; major crossings such as highways, railroad tracks, and flood control facilities; general traffic congestion, and other factors. Utility mapping from outside utility agencies will not be obtained; however, Woodard & Curran will use Google Earth and newly available City-provided information to confirm the pipeline alignments and constructability, as well as optimal connection points.
Within Subtask 2.3, Woodard & Curran will evaluate system hydraulics for the proposed raw water alignments to the centralized treatment facility (CF-1), including tying in the non-potable system for the ability to supply CF-1 with water from the Upper Aquifer. This will include evaluating existing well pumping pressures and determining adequate sizing (diameter) for the alignments. The CF-1 alignments that will be evaluated include:
• Baseline scenario of connecting Wells 8, 9, 11, and 14 to CF-1 o Addition of Well 6
o Addition of Wells 5 and 7
• Tying Well 2 to the non-potable system
• Tying in the non-potable system to CF-1 via a new pipeline to CF-1 • Tying in the connection point from PID to CF-1. It is assumed PID water will be supplied at adequate pressures to convey the required flow to CF-1.
Additionally, Woodard & Curran will develop a conceptual alignment from Diablo Grande to a connection point in the City’s distribution system and evaluate what the expected maximum available pressure is at that point.
Woodard & Curran will also re-assess the point of connection of the treated water pipeline based on the current potable water system configuration along with the proposed pipeline route from the centralized treatment facility to the point of connection along with the proposed sizing for a treated water pump station based on system pressure requirements.
Finally, as part of this subtask, Woodard & Curran will re-evaluate the proposed residuals management methods recommended in the original feasibility study. This assessment will include consideration of the additional hydraulic loading and proposed point of connection based on the existing sewer capacity evaluation and location preference. This project does not include a new sewer capacity evaluation. As before, it is assumed that all residuals flows from the treatment plant will be disposed to the sewer and no other options for residuals disposal will be considered (such as drying beds, deep well injection, haul off, etc.).
Assumptions:
City of Patterson (0012768.00) 8 Woodard & Curran, Inc.
Amendment to Proposal to Update Chrome 6 Treatment Feasibility Study June 23, 2025 • Woodard & Curran will not conduct a system-wide hydraulic analysis of the distribution system, including analyzing specific water demands across the system which could be used to inform that there would be adequate distribution of water from the Diablo Grande connection point or the connection point of CF-1 across the entire potable distribution system. For the purposes of this study, it is assumed that the four solutions evaluated in Subtask 2.2 are feasible hydraulically.
• The feasibility study will not include a sewer capacity evaluation. Available sewer capacity information will be used in the study.
Subtask 2.4 - Cost Analysis Update
Subtask 2.4 will update the conceptual level lifecycle cost for each treatment option included in the feasibility study to confirm the most cost-effective alternative for the City. Lifecycle costs will be generated for both the wellhead and centralized treatment options for each of the technologies. Lifecycle costs will factor in the following:
• Constructed project capital cost. Wellhead treatment options will not include additional conveyance piping. The centralized treatment facility options will include raw water, treated water, and residual disposal conveyance piping. • Lifecycle operations and maintenance (O&M) cost. O&M costs will include labor, consumables (e.g., chemicals, power, etc.), residuals management and disposal (e.g., RO brine, spent salt regenerant, backwash, resin replacement, etc.), and major equipment parts replacements anticipated during the lifecycle of the system. • Lifecycle costs will be normalized to current year (i.e. 2025) dollars through a net present value analysis. The 20-year U.S. treasury bond and ENR CCI national index rate will be applied in the analysis for discount and escalation rates, respectively. • Possible project phasing options for financing flexibility and planning.
The lifecycle costs generated for this effort will be developed on a conceptual level (i.e., - 50%/+ 100%) in accordance with the AACE International (formerly the Association for the Advancement of Cost Engineering) for Class 5 planning level projects. To facilitate costing efforts, the City will provide recent cost of construction for pertinent projects such as pipeline installation, construction of pumping station, connection fees, etc.
Subtask 2.5 – Design Flows and Water Quality Update
This subtask will reassess design flows and water quality in Section 2 of the Feasibility Study, considering the following:
• Recent water quality data provided by the City
• Revised demand projections using:
City of Patterson (0012768.00) 9 Woodard & Curran, Inc.
Amendment to Proposal to Update Chrome 6 Treatment Feasibility Study June 23, 2025 o The California Department of Water Resources (DWR) Office of Water Use Efficiency capped objective on annual water use, which results in a water use objective of 141 gallons per capita per day (GPCD)
o 2045 population projections based on 2.5% annual growth • The GSP-mandated Lower Aquifer pumping reduction target (as estimated by EKI) • Use of new or existing Upper Aquifer wells to meet potable demand and reduce Lower Aquifer pumping
• Additional pumping necessary to offset the concentrate waste stream and maintain capacity to meet estimated demand if reverse osmosis is used as the treatment approach at a centralized facility.
Task 3 - Report Development
This task will consist of preparing the draft and final reports for this updated feasibility study.
The draft report will be submitted in PDF format and present the updated findings of the evaluation along with recommendations and point out any issues that may be outstanding. The draft report will be submitted for City review prior to finalizing; a virtual meeting will be held to discuss comments and questions if needed. The City‘s comments will be addressed in a final report for submittal to the City. It is assumed that all comments from the City will be provided in a single consolidated conformed set of comments.
Task 4 - Meetings
This scope assumes four (4) total meetings for the project -these will consist of the following:
• One (1) virtual kickoff meeting (TEAMS meeting) – COMPLETED • Two to three (2-3) coordination meetings as needed. Each will consist of a virtual meeting with an estimated duration of 1 to 2 hours. – COMPLETED • Three (3) coordination meetings as needed. Each will consist of a virtual meeting with an estimated duration of up to two (2) hours. – NEW
Please note that this scope does not include formal coordination activities or meetings with the DDW nor presentations to the City Council.
SCHEDULE
Woodard & Curran proposes the following schedule for the feasibility study update:
• Draft feasibility study update submittal no later than August 12, 2025. • Two weeks for City review of the draft feasibility study. • Two to three weeks following receipt of comments on the draft feasibility study update to incorporate City comments into the final feasibility study update, followed by City of Patterson (0012768.00) 10 Woodard & Curran, Inc.
Amendment to Proposal to Update Chrome 6 Treatment Feasibility Study June 23, 2025 submittal of the final updated feasibility study to the City. This will be no later September 16, 2025.
FEE ESTIMATE
Woodard & Curran proposes to complete the above Scope of Services for a time and materials cost of $84,980 as shown in the attached fee estimate. Please note that this fee corresponds to a level of effort that has streamlined labor and staffing allowing for cost efficiency but limiting the flexibility to accommodate scope deviations and contingencies. All work will be completed on a time and materials basis in accordance with the attached Woodard & Curran rate schedule.
We appreciate this opportunity to work with the City on this important project. If you have any questions, please feel free to contact me at (925) 627-4152 or Leslie Dumas at (916) 999-8778.
Sincerely,
WOODARD & CURRAN, INC.
Ryker Brown, P.E.
Senior Project Manager, Principal
Fee Estimate
City of PattersonUpdate Hexavalent Chromium Treatment Feasibility Study - Amendment Tasks Labor Total
Leslie Dumas Ryker Brown Nate McLaughlin Tyler Abercrombie Erika Wilson Staff Engineer Kris Rosner PIC Project Manager Lead Technical Engineer - Treatment Technical Manager - Treatment Technical Manager - Conveyance Engineer 2 Cost Estimator Graphics Admin $365 $355 $365 $320 $280 $240 $300 $170 $145
Task 1: Project Management and QA/QC
1.1 Project Management 6 4 10 $2,710 $2,7101.2 QA/QC and Technical Oversight 8 6 4 18 $6,310 $6,310 Subtotal Task 1: 8 6 6 0 0 0 4 0 4 28 $9,020 $9,020
Task 2: Chrome 6 Treatment Feasibility Study Update
2.1 Treatment Technology Analysis Update 2 2 4 8 $2,720 $2,7202.2 Siting Re-evaluation 2 4 26 12 44 $13,350 $13,3502.3 Conceptual Pipeline Alignment Re-evaluation 2 8 4 28 42 $12,690 $12,6902.4 Cost Analysis Update 2 6 16 10 4 38 $11,980 $11,9802.5 Design Flows and Water Quality Update 2 2 8 4 16 $4,960 $4,960 Subtotal Task 2: 10 22 0 58 38 16 4 0 0 148 $45,700 $45,700 Task 3: Report Development
3.1 Draft Feasibility Study Update 2 8 24 16 4 54 $16,410 $16,4103.2 Final Feasiblity Study Update 2 4 6 4 4 2 22 $6,490 $6,490 Subtotal Task 3: 4 12 0 30 20 4 0 6 0 76 $22,900 $22,900 Task 4: Meetings
4.1 Kickoff Meeting 0 $0 $04.2 Coordination Meetings 6 6 6 4 22 $7,360 $7,360 Subtotal Task 5: 6 6 0 6 4 0 0 0 0 22 $7,360 $7,360
TOTAL 28 46 6 94 62 20 8 6 4 274 $84,980 $84,980
2. Subconsultants will be billed at actual cost plus 10%. 5. Completion of Subtask 2.3 requires that we receive the data already requested.1. The individual hourly rates include salary, overhead and profit.3. Other direct costs (ODCs) such as reproduction, delivery, mileage (rates will be those allowed by current IRS guidelines), and travel expenses, will be billed at actual cost plus 10%.
4. Woodard & Curran reserves the right to adjust its hourly rate structure and ODC markup at the beginning of the calendar year for all ongoing contracts.
Total Hours Total Labor Costs (1) Total Fee