Santa Clara Plain Groundwater Basin

Santa Clara Plain Groundwater Basin
Name	Santa Clara Plain Groundwater Basin
Location	Santa Clara County, California
Coordinates	37°21′N 121°57′W
Area	~120 sq mi
Aquifer type	Alluvial aquifer
Principal river	Guadalupe River
Managing agency	Santa Clara Valley Water District

Santa Clara Plain Groundwater Basin

The basin underlies central Santa Clara County, California on the southern end of San Francisco Bay and forms a primary water source for cities including San Jose, California, Santa Clara, California, Sunnyvale, California, and Mountain View, California. Bounded by the Santa Cruz Mountains, the Diablo Range, and the baylands adjacent to Alviso, California and Palo Alto, California, the basin interacts with regional surface-water systems such as the Guadalupe River (California) and engineered infrastructure like the Almaden Reservoir and Vasona Reservoir. Stakeholders range from the Santa Clara Valley Water District to federal entities such as the United States Geological Survey and state agencies including the California Department of Water Resources.

Overview and Geography

The plain occupies the central portion of Santa Clara Valley and includes urbanized plains, reclaimed salt ponds near San Francisco Bay, and remnant wetlands adjoining Don Edwards San Francisco Bay National Wildlife Refuge. Major urban corridors include Interstate 280 (California), U.S. Route 101 in California, and the Caltrain corridor, with transit hubs near Diridon Station. Surface drainage networks feed into estuarine systems near Alviso Marina County Park and the South San Francisco Bay Shoreline National Wildlife Refuge. Other geographic features influencing the basin are the Llagas Creek watershed, the Coyote Creek corridor, and upland feeders from the Santa Teresa Hills.

Hydrogeology and Aquifer Characteristics

The basin consists of Quaternary alluvium and older Pleistocene deposits forming layered aquifers with discontinuous confining units; notable lithologies include coarse gravels derived from the Santa Cruz Mountains and finer silts from bay-margin deposition. Aquifer transmissivity and storativity vary across the plain, with high-permeability channels beneath former fluvial corridors mapped by the United States Geological Survey and the California State Water Resources Control Board. Groundwater flow is generally toward the San Francisco Bay with local gradients influenced by pumping near municipal well fields such as those serving San Jose Water Company and industrial extraction near Moffett Field. Potentiometric surfaces and aquifer tests have been documented by the Santa Clara Valley Water District and academic partners at Stanford University and San Jose State University.

History of Groundwater Use and Management

Indigenous inhabitants including the Ohlone people historically relied on surface springs and riparian resources prior to European settlement associated with Spanish colonization of the Americas and the establishment of Mission Santa Clara de Asís. Intensive municipal and agricultural pumping accelerated during the California Gold Rush era and 20th-century urbanization, prompting subsidence concerns similar to other basins studied by the U.S. Geological Survey. Basin management practices evolved through creation of the Santa Clara Valley Water District and regulatory frameworks tied to the California Environmental Quality Act and regional water planning efforts backed by organizations like the Bay Area Air Quality Management District for allied environmental issues. Landmark projects include coordinated recharge programs and importation of surface water from the Central Valley Project and the California State Water Project via interties and local reservoirs.

Water Quality and Contamination Issues

Groundwater quality across the plain exhibits spatial variability with contaminants of concern historically including industrial volatile organic compounds documented near former aerospace sites like Moffett Federal Airfield and defense contractors, agricultural nitrates in periurban zones, and naturally occurring constituents such as arsenic in localized geologic settings. Contamination episodes prompted involvement by the Environmental Protection Agency and the California Regional Water Quality Control Board, San Francisco Bay Region with response actions coordinated with municipal water utilities and remediation contractors. Emerging issues include salts and total dissolved solids from recycled water and urban runoff pathways influenced by stormwater conveyance tied to Santa Clara Valley Transportation Authority infrastructure projects.

Groundwater Recharge and Sustainability Measures

Recharge strategies on the plain combine managed aquifer recharge via spreading basins, injection wells, and conjunctive use of surface supplies from reservoirs like Anderson Reservoir (California) and the Lexington Reservoir. Natural recharge is facilitated by permeable valley-fill deposits and engineered projects within floodplains of Coyote Creek and the Guadalupe River (California)]. Water reuse, stormwater capture initiatives driven by local ordinances in San Jose, California and regional plans such as the One Water approach promote sustainability alongside demand-management programs implemented by entities like California Public Utilities Commission-regulated utilities. Climate-change projections by the Intergovernmental Panel on Climate Change inform long-term recharge planning to address sea-level rise impacts on shallow aquifers and saltwater intrusion risks studied by researchers at Lawrence Berkeley National Laboratory.

Governance, Monitoring, and Regulation

Oversight is led by the Santa Clara Valley Water District in coordination with county and municipal water agencies, state regulators including the California Department of Water Resources under frameworks like the Sustainable Groundwater Management Act where applicable governance mechanisms, monitoring networks of observation wells, and interagency data sharing guide resource allocation. Scientific monitoring relies on networks run with technical support from the United States Geological Survey and academic partners at Stanford University for groundwater modeling, geophysical surveys, and long-term potentiometric mapping. Public engagement and stakeholder processes involve local elected bodies such as the Santa Clara County Board of Supervisors, community organizations, and utilities like San Jose Water Company to reconcile municipal supply, environmental protection for refuges including Don Edwards San Francisco Bay National Wildlife Refuge, and regional infrastructure investments.

Category:Water supply in California Category:Hydrology of California