COMMITTEE AGENDA MEMORANDUM
Recycled Water Committee
Government Code § 84308 Applies: Yes ☐ No ☒
(If “YES” Complete Attachment A - Gov. Code § 84308)
SUBJECT: title
Receive an Update on the Desalination Engineering Feasibility Study.
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RECOMMENDATION: Recommendation
Receive an update on the Desalination Engineering Feasibility Study.
Body
SUMMARY:
This memorandum provides an update on the Desalination Engineering Feasibility Study (DEFS). Since the last update to the Recycled Water Committee (RWC) on December 16, 2025, Valley Water is completing the draft final DEFS and will present the findings to date.
BACKGROUND
In 2023, Valley Water (VW) completed a Desalination Environmental Feasibility and Planning Study (DEFPS), which identified intake options, facility locations, and brine management strategies. These elements formed the foundation for the DEFS currently underway by Black and Veatch. Building on the conclusions of the DEFPS, the current work is focused on evaluating additional siting locations, intake options, brine management and conveyance options. In December 2025, the Fatal Flaw Analysis was completed, and more recently the Alternatives Analysis was completed, including a rough cost estimate for various alternatives. The following sections present the findings from these latest efforts, and provide an update on outreach efforts with regulators, stakeholders and other interested parties.
STUDY APPROACH
The DEFS evaluated the feasibility of a treatment facility with a production capacity of 10 to 40 million gallons per day (MGD) with the feed source from the Lower South San Francisco Bay (LSB). The four major components evaluated include a bay-water intake, facility siting, brine management and conveyance for distribution.
Intake locations including both subsurface and open intake options were evaluated as well as four intake types and five screen options for the protection of aquatic life while meeting hydraulic needs. Twelve sites were evaluated for multiple constraints such as constructability, environmental sensitivity, flood resilience and future facility expansion potential. Brine management options include commingling with treated effluent from a wastewater treatment facility, deep bay discharge, nature-based solution, beneficial use of salt production and discharge to the East Bay Discharges Authority (EBDA). Finally, conveyance was evaluated as conceptual level connections to local distribution systems and VW’s existing infrastructure.
Following a progressive screening approach, the first screen applied fatal flaw criteria to remove concepts that were determined to be infeasible based on regulatory, environmental or technical constraints. Concepts that passed this screening step were then evaluated using a multivariable scoring framework that compared the intake, facility siting and brine management. In addition, feedback from environmental organizations obtained through several outreach efforts over the past 20 months was also considered.
FEASIBLE ALTERNATIVES
Intake Options
A hydrogeologic evaluation of the area determined that subsurface intake options were infeasible due to the lack of a direct lateral connection between the LSB and shallow aquifer system which leads to low well yields and would require a large number of intake wells. For ocean desalination intakes, the California Ocean Plan (COP) requires subsurface intakes as the primary inlet type. However, this does not apply to an enclosed bay including the LSB, as was communicated to VW by the California State Water Resources Control Board (Water Board) in September 2025. Screened surface intakes were determined to be the only viable option to carry forward in this study. Further analysis included estimating intake volumes and pipe size as well as tunneling requirements, constructability, hydraulics, marine growth control mechanisms and other environmental considerations. Specifically, intake locations are required to be continuously submerged at water depths that allow steady water flow at all times and are not affected by tidal effects. The geologic setting, parcel ownership, designated land uses, environmental constraints, water quality and navigation impacts were also considered resulting in four possible intake locations at Guadalupe Slough, Coyote Creek, Deep Bay and Interconnecting Channel (South of Pond A4).
Facility Siting
Twelve sites for a desalination facility were evaluated across Palo Alto, Mountain View, Sunnyvale and San José. Approximately four to twelve acres of land would be required for a 10 to 40 MGD facility, respectively. After detailed evaluations of the twelve sites, it was determined that three would move forward for further analysis and could be located in Palo Alto (Site 11), Sunnyvale (Sites 6 and 7) and San José (Site 12). Other sites were not selected due to various reasons including geotechnical complications, land acquisition complexity, sensitive habitat, and flooding potential. For the three selected sites, facility layout, treatment technology process and additional environmental considerations were evaluated. The facility treatment technology assumed for this study was a two-pass reverse osmosis (RO) process with an average recovery rate of 42%. In essence, a 24 MGD production facility would require approximately 57 MGD of bay-water at the inlet. The modular nature of a RO system would allow for the system to operate at different flow rates depending on demand and drought conditions.
Brine Management
Based on existing guidance and regulations for discharges to the LSB, several brine management options were evaluated. The analysis assessed the environmental, technical, and regulatory considerations for the viability of the three brine management options: shallow water discharge commingled with treated wastewater, deep bay discharge and nature-based solutions. For the first option, brine would be blended with available fully treated wastewater effluent from an existing wastewater treatment plant and discharged to a shallow water outfall in the LSB. The Basin Plan requires discharges to achieve a minimum of 10 to 1 initial dilution or provide an equivalent level of environmental protection. Variances in dilution credits are allowed provided hydrodynamic modeling demonstrates mixing zones can achieve the required dilution for salinity or other constituents. Deepwater bay discharges could be achieved by building a pipeline with multi-port diffusers to the northern LSB meeting the 10 to 1 dilution requirement, complying with water quality standards and protection of aquatic ecosystems.
A nature-based solution such as a horizontal levee could also be an alternative for brine management, but is an emerging technology primarily used to remove nutrients. Horizontal levees, characterized by a long slope, require extensive land to build and operate making them a less favored option. The use of salt obtained from brine processing was also evaluated for use at the Cargill Newark salt production facility. Limitations to this option are the constant rate of brine produced from a desalination facility compared to the much slower salt production from evaporation ponds. Discharge to EBDA was another option evaluated. However, this option would require a long pipeline and does not have sufficient capacity. As a result, these approaches were also discarded as viable options.
Conveyance and Distribution
Conveyance from a new desalination facility to an existing water distribution system in the South Santa Clara County was evaluated and included options for pipeline alignments, redundant connection points, storage needs and surge protection. Blending strategies were also considered to ensure existing infrastructure is protected. This comprehensive evaluation also identified some challenges such as seasonal demand fluctuations.
Five key factors evaluated are pipeline ownership and size, storage and hydraulic considerations, length and alignment of pipelines, water recipient and agency partnerships, and water quality compatibility. Several potential connections near the shortlisted sites in Palo Alto, Sunnyvale and San José were developed as well as benefits and challenges. While this evaluation provided enough information to develop cost estimates, there is additional work that needs to be completed to better address some of the unknowns like hydraulics, operations, capacity and storage.
DEVELOPMENT AND SELECTION OF ALTERNATIVES
Following the completion of the fatal flaw and alternatives analysis, VW proceeded to rank components and compare alternatives to identify combinations offering the greatest feasibility across environmental, permitting, supply reliability, engineering and financial considerations. The highest ranked components were then evaluated as conceptual configurations and cost estimates were also developed for each component and combinations.
Top Ranked Components and Cost
To determine the overall ranking of each component, two multi-criteria decision-making methods were used to evaluate and compare results. Of the shortlisted intake sites, the Interconnecting Channel ranked the highest followed by Guadalupe Slough. The treatment facility site ranking identified Site 12 (San José) as the top option. Finally, the highest ranked brine management option was commingling with treated wastewater followed by a Deep Bay Discharge. Unlike the intake and facility site rankings which were not affected by excluding financial criteria, the brine management options did swap places resulting in the Deep Bay Discharge ranking highest after the financial criteria was removed.
Cost estimates for construction or capital expenditures (CAPEX) and operating expenditures (OPEX) for the alternatives were developed as Class 5 (AACE, accuracy range -50%/+100%) baseline estimates. These estimates are planning level and reflect conceptual design including pipeline conveyance for distribution. While no specific desalination goal has been established, a range of 10 to 40 MGD was evaluated as bookends should there be a need to evaluate a facility in this range at a later date. A total of 18 combinations were developed of the different intake, facility siting and brine management components to assess how design choices affect the overall cost. In addition, a facility similar in size to the Pure Water Silicon Valley (PWSV) direct potable reuse (DPR) project of 24 MGD was also evaluated for CAPEX/OPEX and unit costs.
The resulting total CAPEX for the 18 different combinations ranges between $800 million (M) and $3.7 billion (B) in 2025 dollars. Unit costs are influenced by facility size, and this economy of scale results in a gradual increase in OPEX from a 10 to 40 MGD facility, ranging between $30M and $100M annually.
In addition, staff also compared cost estimates to PWSV, since both desalination and potable reuse are identified in the 2050 Water Supply Master Plan (WSMP) as possible water supply alternatives that could help meet a future water supply shortfall. The cost estimate for a 24 MGD desalination facility, assuming the top ranked components, resulted in an average CAPEX of $1.7B, equal to a DPR facility of the same size. Due to the longer conveyance distances, the desalination costs for the intake and brine management are higher compared to a DPR facility. The DPR facility has higher treatment facility costs due to more complex and multi-barrier advanced treatment processes. On a unit cost basis, both the desalination and DPR facility have a CAPEX unit cost of $2,100 per acre-foot (AF). The OPEX unit costs for a desalination and DPR facility are $2,525/AF and $2,133/AF, respectively. The primary difference for a higher OPEX unit cost is the energy consumption needed for both the intake and RO pumps at a desalination facility.
In summary, costs between a desalination facility and PWSV are similar, with OPEX costs for a desalination facility estimated to be slightly more than PWSV. As described in the WSMP, pursuing DPR is the preferred option with desalination as a backup project.
OUTREACH
VW reached out to interested parties over the past 20 months and received positive feedback from various agencies and environmental partners. These included meeting with regulators at the Water Board, San Francisco Bay Regional Water Quality Control Board (RWB), Bay Conservation and Development Commission (BCDC), Midpeninsula Regional Open Space District (Mid-Pen), Citizens Committee to Complete the Refuge (CCCR), Sierra Club, and the Environmental and Water Resources Committee.
REGULATORY CONSIDERATIONS
While a future desalination project is technically feasible, the permitting pathway is complex and will require additional studies and extensive coordination with agencies such as the U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service, National Marine Fisheries Service, California Department of Fish and Wildlife, Water Board, RWB, BCDC and Don Edwards San Francisco Bay National Wildlife Refuge (Refuge). At this time, feedback has only been obtained from the Water Board, RWB, and BCDC. The permitting and environmental review process (California Environmental Quality Act and National Environmental Policy Act) is likely to take a minimum of six years. This is a planning level schedule and could be extended depending on factors such as additional studies which may be needed to further support facility sitting, design development, technology selection, mitigation measures and the level of public and stakeholder engagement during the environmental review process.
NEXT STEPS
Staff will continue engagement with regulatory agencies and environmental partners as the DEFS is completed this summer. A final update on the DEFS will be presented to the Board of Directors (Board) upon completion in late summer of 2026.
As a result of the extensive work completed to date, there are certain areas which have been identified as needing further development. These areas include hydrodynamic modeling for the two brine management options (commingling with treated wastewater or deep bay outfall) and further investigation of the intake location near the Interconnecting Channel and adjacent Pond A4 to determine if impacts from the pond could affect water quality in the channel. To complete this additional scope of work, staff will develop an amendment to the Agreement upon the final study presentation to the Board.
ENVIRONMENTAL JUSTICE IMPACT:
There are no environmental justice impacts associated with this item. This action is unlikely to or will not result in adverse impacts and is not associated with an equity opportunity.
ATTACHMENTS:
Attachment 1: PowerPoint
Attachment 2: PowerPoint: Alternative Site Evaluation
UNCLASSIFIED MANAGER:
Manager
Kirsten Struve, 408-630-3138