Islais Valley

Source: CA DWR

Islais Valley



Located in California’s hydrologic region, the Islais Valley is 5,941 acres in size. This Very Low priority basin is home to an estimated 131,671 people (2010 value), which have been at a rate of 2.05.

Islais Valley is a(n) basin with approximately 16 wells, of which approximately 0 are water supply wells. Groundwater accounts for approximately 3.45 percent of the basin’s water supply.

Source: CA DWR

Basin Notes

2003: Bulletin 118 basin description

2014: CASGEM basin prioritization – very low

2018: Draft basin priority – very low.

Groundwater level comments:

  • 1) CASGEM/WDL/GWIDS: No data or data insufficent to determine GWL status. Source: DWR
  • 2) No available documentation on groundwater level decline past or present in the basin

Salt Intrusion comment: 1) Natural sources of TDS to groundwater in the San Francisco Bay study unit (Marina, Lobos, Downtown, Islais Valley, South San Francisco, Visitacion Valley, Westside, and the Santa Clara Valley groundwater basins ) include saltwater intrusion from the Bay and interaction between recharge water and aquifer materials derived from marine or estuarine sediments. On the east side of the Bay, high and moderate concentrations of TDS were detected in areas with a history of intrusion of water from the Bay in response to pumping of freshwater from aquifers. Source: USGS

San Mateo County Office of Sustainability links to groundwater storage and recovery (GSR)

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

GSA Information


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