Groundwater Studies

Groundwater Benefit Zones

Valley Water protects and replenishes local groundwater supplies to ensure water supply reliability. Sustainable groundwater management is funded by groundwater charges, which are applied to groundwater pumpers within zones benefiting from Valley Water activities. These activities include replenishing groundwater with local and imported surface water, monitoring and protecting groundwater from pollutants, and constructing, operating, and maintaining facilities that help sustain groundwater supplies. After a comprehensive scientific study of the zones and extensive community outreach, the Valley Water Board of Directors adopted changes to the zones in 2020. More information is available here.

Seawater Intrusion, Groundwater Rise and Emergence (May 2025)

Valley Water conducted a multi-year study on groundwater in the Santa Clara Subbasin adjacent to the southern San Francisco Bay to advance understanding of the impacts from tides, seawater intrusion, and sea-level rise on groundwater rise and emergence at land surface. 

The report provides an overview for the public and policymakers, as well as relevant technical details for practitioners in groundwater science, engineering, and management. The report includes major advances in the hydrogeologic conceptual model of the Santa Clara Subbasin shallow aquifer system near the Bay. 

Report: Groundwater Response to Tides, Seawater Intrusion, and Sea-Level Rise in Santa Clara County, California 

Fact Sheet: Groundwater Response to Tides, Seawater Intrusion, and Sea-Level Rise in Santa Clara County, California

Salt and Nutrient Management Plans

Valley Water lead the effort to prepare Salt and Nutrient Management Plans (SNMP) for the Santa Clara and Llagas Groundwater Subbasins in Santa Clara County. This stakeholder-driven process assessed all salt and nutrient loading in the subbasins to evaluate existing and projected future assimilative capacity, as required by the State Water Resources Control Board 2009 Recycled Water Policy.

Recycled Water Irrigation and Groundwater Study (August 2011)

Valley Water initiated this multi-year study in 2007 to advance water district policies of aggressively protecting groundwater and supporting recycled water development in Santa Clara County.

The goal of this study was to evaluate the potential effects of recycled water used for irrigation on groundwater quality and to identify best management practices to protect groundwater quality.

The study included laboratory testing of soils irrigated with recycled water and an 18-month field study at a site using recycled water for irrigation.

Groundwater Vulnerability Study (October 2010)

The goal of this study was to predict the vulnerability of groundwater to potentially contaminating land use activities to allow Valley Water to prioritize groundwater protection efforts and resources on the most vulnerable areas, evaluate groundwater quality impacts from land use changes, and provide information to decision makers at the district, land use agencies, and regulatory agencies to improve groundwater protection.

Solvent Studies

Valley Water has conducted several studies related to solvents and the related threat to groundwater resources. This includes a study on the threat posed by current and former dry cleaning sites in Santa Clara County and a white paper on solvent stabilizers, including 1,4-dioxane.