Santa Clara Valley – San Mateo Plain

Source: CA DWR

Santa Clara Valley – San Mateo Plain



Located in California’s San Francisco Bay hydrologic region, the Santa Clara Valley – San Mateo Plain is 48,100 acres in size. This Very Low priority basin is home to an estimated 292,819 people (2010 value), which have been at a rate of .

Santa Clara Valley – San Mateo Plain is a(n) basin with approximately 348 wells, of which approximately 10 are water supply wells. Groundwater accounts for approximately 10 percent of the basin’s water supply.

Source: CA DWR
Source: CA DWR

Basin Notes

2003: Bulletin 118 basin description

2018: Basin prioritization comments –

  • Declining groundwater levels: 1) CASGEM/WDL/GWIDS: No data or data insufficent to determine GWL status. Source: DWR 2) One hydrograph in Groundwater Reliability Partnership for the San Mateo Plain Sub-basin presentation, Slide 12, showed groundwater levels increasing 1962 to 2015. Source: GRP_Presentation_10_19_15_FINAL.pdf
  • Salt intrusion: 1) According to the Regional Water Quality Control Board (RWQCB), saltwater intrusion has occurred to groundwater within the San Mateo Plain sub-basin. The DWR found that groundwater quality in the sub-basin contains high concentrations of sodium; samples from wells in the area also found concentrations of nitrates/nitrogen in excess of maximum contaminant levels established by the California Department of Health Services and the United States Environmental Protection Agency.

County of San Mateo Watershed Navigator

2017: San Mateo Plain Groundwater Subbasin: A Local Case Study, Stanford University

2018: San Mateo Plain subbasin given draft medium priority, subjecting it to SGMA

2018 Final Basin Prioritization: Basin remains unchanged at very low priority.