This project reduces pollutants in streams, reservoirs and groundwater of Santa Clara County by supporting surface water quality pollution prevention activities. These programs address water quality concerns currently identified by local and state regulatory agencies, as well as contaminants of emerging concern. Initiatives under this project are consistent with the Regional Water Quality Control Board (RWQCB) impaired water bodies designation and Total Maximum Daily Loads (TMDLs), which are the maximum amount of a pollutant that a water body can receive and still safely meet water quality standards. Under this project, Valley Water studies and implements methods to reduce methylmercury formation in reservoirs, and helps create and carry out realistic plans to reduce contaminants, such as nutrients, bacteria, pesticides, polychlorinated biphenyls (PCBs) and others, in local creeks and reservoirs.
This project addresses both greenhouse gas (GHG) reduction and climate change adaptation, as reservoirs are a major source of GHG emissions (i.e. methane, a potent greenhouse gas) during low oxygen conditions. Microbes in the low-oxygen bottom waters of reservoirs and lakes produce methane seasonally. Oxygenation and other interventions may reduce methane production in reservoirs. Oxygenation is the current mechanism to control mercury in fish and may reduce methane emissions. Oxygenation can also reduce the formation of harmful algal blooms, which may become more frequent with warmer temperatures.
See Environmental & Community Benefits section for complete description of Key Performance Indicators (KPIs).
KPI #1: (Reduce methylmercury)
- The TMDL Monitoring Plan calls for monthly water quality monitoring and spring and summer fish monitoring. Valley Water completed monthly water quality monitoring at Almaden, Calero, Guadalupe, and Stevens Creek reservoirs, and quarterly monitoring at Almaden Lake. FY25 summer fish monitoring was completed at Calero, Guadalupe, and Stevens Creek reservoirs. Almaden Reservoir fish were not collected due to low water levels that made boat access difficult. FY25 spring fish monitoring is scheduled to begin in April 2025. The data will be included in the next biennial progress report to the San Francisco Bay Regional Water Quality Control Board in 2026.
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In accordance with the adaptive implementation plan for the Guadalupe River Watershed Mercury TMDL Program, Valley Water continued a collaborative research project with the University of California, Merced (UC Merced) to study sorbent treatment methods for mercury control as an alternative to reservoir oxygenation. Sorbents are solid materials that bind to specific compounds. In this case, the study is researching sorbents that preferentially bind to mercury or methylmercury, making it unavailable for entry into the food web. Sorbent treatment methods have the benefit that they do not cause warming or mixing of reservoir water. The project aims to identify effective and appropriate sorbents and application methods that could be used in a field trial in Guadalupe Reservoir. The project began in early FY23 and will continue throughout FY25. The initial tasks of this project have been completed and show promising results. Sediment core samples were collected from Guadalupe Reservoir in March 2025 for use in follow-up chamber studies with different sorbent materials.
- Valley Water coordinated with Santa Clara County, Midpeninsula Regional Open Space District, Guadalupe Rubbish Disposal Company, and the Regional Water Quality Control Board to complete the second 5-year phase of the Coordinated Monitoring Program for the Guadalupe River Watershed Mercury TMDL project. According to the Monitoring Plan, two of the several large storms in January 2023 were sampled for suspended sediment, mercury, and methylmercury in water. The final report was submitted in April 2024 and approved by the Water Board after edits in July 2024. In FY25, the partners will collaborate with Regional Water Quality Control Board staff on the next steps for the TMDL. More information on the TMDL project is available here.
- In June 2023, Valley Water entered into an agreement with the University of California, Davis (UC Davis) to study methylmercury sources and formation pathways in Guadalupe Reservoir. In FY24, researchers partnered with Valley Water staff to conduct augmented monthly sampling and analysis of various parameters to achieve the goals of the study. More intensive bi-monthly sampling was carried out from April 2024 and was completed in September 2024. Sampling will continue until the end of FY25. These intensive sampling events will investigate the seasonal formation pathways of methylmercury production by examining the biological and chemical makeup of bottom water and sediment. A final report is expected in early 2026.
- In December 2021, Valley Water entered into a collaborative agreement with the University of California, Santa Cruz (UC Santa Cruz) to study local atmospheric mercury deposition near the New Almaden Mining District using lichens as bioindicators. Field data collection was completed in the spring of 2022. Sample analysis and reporting were completed in FY23. Following this study, a second agreement was established to study the sources of atmospheric mercury using lichen. Sampling has been completed, and a final report will be delivered in FY25.
- Valley Water deploys hypolimnetic oxygenation systems (HOSs) to reduce toxic methylmercury production in some reservoirs' bottom waters. HOSs consist of a large oxygen gas generator and distribution lines that bubble oxygen into the bottom waters. This prevents the waters from being hypoxic, an environment low in oxygen that promotes the production of toxic methylmercury. However, HOS operation can increase the temperature of reservoir releases and stimulate surface algae growth, particularly when reservoir storage volume is low. In FY24, Valley Water deployed HOSs at Almaden and Calero Reservoirs from June to September 2024. HOSs were not deployed at Guadalupe and Stevens Creek reservoirs to preserve cold water releases for fish downstream.
KPI #2: (Prioritization plan)
- Valley Water periodically reviews the Prioritization and Implementation of Pollution Prevention and Reduction Activities Plan to Address Impaired Water Bodies in Santa Clara County (Prioritization Plan). The review uses various sources of information, including the San Francisco Bay RWQCB Triennial Review of the Basin Plan and the State’s list of impaired water bodies, to evaluate potential projects in water bodies within our jurisdiction. Since RWQCB priorities change over time as impairments are addressed and new problems are identified, the Prioritization Plan is a living document that is updated according to changing priorities. In FY23, Valley Water surveyed all data available in the California Environmental Data Exchange Network and internal environmental data to develop an objective assessment to identify and prioritize potential projects. A review of the existing data was completed in FY24, and a draft updated Prioritization Plan was completed in July 2024 and is under review. A final updated Prioritization Plan is expected in FY25. The June 2017 Prioritization Plan can be accessed here.
KPI #3: (Surface water quality improvement activities)
- Surface Water Quality Improvement Activity #1: Accumulation Point Mapping and Removal (Coyote Creek and Guadalupe River)
- The Memorandum of Agreement with the City of San José that supported this project by allowing Valley Water to remove trash rafts on City of San José property was terminated at the end of FY24. Valley Water staff analyzed internal and MOA-derived trash raft data collected from 2019 to 2024 to guide Q2 and Q3 field assessments to identify and prioritize locations on Valley Water property for trash raft removal in FY25. Utilizing the completed analysis, Valley Water staff completed field assessments to identify potential cleanup sites in Q2 and Q3. Five trash rafts (three on Coyote Creek and two on Guadalupe River) were identified for removal and are expected to be removed in Q4.
- Surface Water Quality Improvement Activity #2: Reservoir Greenhouse Gas Emission Study
- Valley Water is collaborating with UC Davis to study greenhouse gas emissions from the surfaces of Almaden, Chesbro, Stevens Creek, and Uvas reservoirs. Since January 2021, researchers have completed sampling events to measure gas storage in reservoir sediments (measured quarterly) and greenhouse gas (primarily methane) fluxes from reservoir surfaces in conjunction with atmospheric and water quality data (measured monthly). Data collection continued through 2023, and results will be synthesized in a final report or manuscript. To date, two manuscripts have been published in peer reviewed journals presenting results of these studies. A second agreement with UC Davis for an additional study in FY25 to further refine methane flux estimates and collect additional data on carbon dioxide and nitrous oxide was finalized and is underway. The study’s primary goal is to better estimate greenhouse gas emissions from all Valley Water reservoirs. Valley Water will evaluate the inclusion of reservoir-related emissions into its agencywide greenhouse gas inventory after the completion of this study.
- Surface Water Quality Improvement Activity #3 Microbial Source Tracking Support
- Due to the lack of participation and accessibility barriers with the RV waste disposal vouchers for the previous Unhoused Best Practices pilot, the South County Partners discussed alternative projects to address human and animal waste sources of fecal bacteria in South County waterbodies for FY25. In Q3, South County Partners began planning a Special Study for the Pajaro River Fecal Coliform TMDL to monitor potential recreation sites and flowing outfalls for human fecal microbial genetic markers. Valley Water is providing additional funding to analyze samples for animal microbial genetic markers in tandem with the South County partners, which may help track sources and determine additional management practices. While human fecal sources pose the most risk to humans, there are several animal sources that pose a lower but still meaningful risk to those recreating in the waterways.
April 2025
- Stevens Creek Reservoir Temperature, Turbidity, and Dissolved Oxygen Study 2020-2021
- Stevens Creek Reservoir Temperature, Turbidity, and Dissolved Oxygen Data Report 2020-2021
- Guadalupe River Watershed Mercury TMDL: 2020-2021 Progress Report on Methylmercury Control Measures in Reservoirs
Coordinated Monitoring Program
- CA Water Boards: TMDL
- Final Monitoring Plan
- Regional Board Approval Letter
- Guadalupe River Coordinated Monitoring Program 5-Year Report (2011-2016)
- Coordinated Monitoring Program Interim Monitoring Report 2018-2019
- Coordinated Monitoring Program 2019 Annual Progress Report
- The Prioritization and Implementation of Pollution Prevention and Reduction Activities Plan to Address Impaired Water Bodies in Santa Clara County, rev June 2017
- Coyote Creek and Guadalupe River Trash Accumulation Point GIS map FY23
- Coyote Creek and Guadalupe River Trash Accumulation Point GIS map FY24
FY22-36 Key Performance Indicators for the Safe, Clean Water Program
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Investigate, develop, and implement actions to reduce methylmercury in fish and other organisms in the Guadalupe River Watershed.
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Prepare and update a plan for the prioritization of surface water quality improvement activities, such as addressing trash and other pollutants.
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Implement at least two (2) priority surface water quality improvement activities identified in the plan per 5-year implementation period.
Benefits
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Reduces contaminants in streams and reservoirs
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Improves water quality, including water slated for drinking water treatment plants
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Increases understanding of mercury cycling in reservoirs to develop strategies that reduce toxic methylmercury in fish consumed by people and wildlife
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Increases the scientific understanding of environmental pollutants to assist in developing actions to manage them
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Supports regulatory compliance with surface water quality standards for local creeks and reservoirs
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Addresses climate change by providing data on the production of methane in reservoirs to estimate the magnitude of those emissions
Geographic Area of Benefit
Countywide
About the Safe, Clean Water and Natural Flood Protection Program
In November 2020, voters in Santa Clara County overwhelmingly approved Measure S, a renewal of Valley Water’s Safe, Clean Water and Natural Flood Protection Program.
The program was first passed by voters in 2000 as the Clean, Safe Creeks and Natural Flood Protection Plan, then again in 2012 as the Safe, Clean Water and Natural Flood Protection Program. The renewal of the Safe, Clean Water Program will continue to provide approximately $47 million annually for local projects that deliver safe, clean water, natural flood protection, and environmental stewardship to all the communities we serve in Santa Clara County.
While evaluating ways to improve the 2012 program, Valley Water gathered feedback from more than 21,000 community members. That helped Valley Water create the six priorities for the renewed Safe, Clean Water Program, which are:
- Priority A: Ensure a Safe, Reliable Water Supply
- Priority B: Reduce Toxins, Hazards and Contaminants in our Waterways
- Priority C: Protect our Water Supply and Dams from Earthquakes and Other Natural Disasters
- Priority D: Restore Wildlife Habitat and Provide Open Space
- Priority E: Provide Flood Protection to Homes, Businesses, Schools, Streets and Highways
- Priority F: Support Public Health and Public Safety for Our Community
Each year, Valley Water prepares a report providing a progress update for each of these program priorities, along with fiscal year accomplishments.
To ensure transparency and accountability to the voters, the ballot measure also created an Independent Monitoring Committee, appointed by the Santa Clara Valley Water District Board of Directors. The Independent Monitoring Committee annually reviews the program’s progress to ensure the outcomes are achieved in a cost-efficient manner and reports its findings to the Board. Additionally, the IMC also reviews each proposed 5-year implementation plan prior to its submittal for Board approval.
In addition, the program requires three independent audits.