Los Osos Valley – Los Osos Area

Source: CA DWR

Los Osos Valley – Los Osos Area


  • Basin Name
  • Los Osos Valley – Los Osos Area
  • Basin Number
  • 3-008.01
  • SGMA Basin Priority
  • Very Low
  • Critically Overdrafted
  • No
  • Hydrologic Region Name
  • Central Coast
  • Counties
  • San Luis Obispo
  • Adjacent Basins
  • Los Osos Valley - Warden Creek 3-008.02,


Located in California’s hydrologic region, the Los Osos Valley – Los Osos Area is 4,232.03 acres in size. This Very Low priority basin is home to an estimated 13,703 people (2010 value), which have been at a rate of .

Los Osos Valley – Los Osos Area is a(n) basin with approximately 50 wells, of which approximately 15 are water supply wells. Groundwater accounts for approximately 100 percent of the basin’s water supply.

Source: CA DWR
Source: CA DWR

Basin Notes

2019: Created in by subdivision of Los Osos Valley 3-008. Priority went from critical overdraft to very low by dint of basin boundary modification and excision of adjudicated areas. For plans to do with gestating GSA required under former critical overdraft status, contact SLO County, contacts below.

Water quality comments collected by DWR:

“The primary constraint on water availability in the Los Osos Valley Groundwater Basin is deteriorating water quality due to sea water intrusion and nitrate contamination. Source: 3-008_01_7a_L_Appendix_SLOGWBasins.pdf pg L-15 … Basins with Coast-Known Seawater Intrusion and/or Nitrate Contamination: This factor relates to the target constituents an SNMP seeks to address salt and nitrates. The following basins are Coast-Known to have seawater intrusion and/or nitrate issues: Morro and Chorro Valley, Los Osos Valley, North Coast (Santa Rosa and San Simeon Valley). Source: 3-008_01_7c_SLO-IRWMP_Appendix_O.pdf pg. 8 2) Los Osos CSD: The district has suffered from a high turnover of general managers in recent years. It is also must deal with saltwater intrusion into the aquifers beneath the town. Source: 3-008_7c_SLOCountyspecialdistrictCSDelectionresultsNovember2016.pdf pg. 1 3) In order to control seawater intrusion in the basin, the purveyors and other groundwater users need to reduce their production from the Lower Aquifer in the western area. That action will allow freshwater levels to rise, thereby preventing further seawater intrusion and pushing the freshwater-seawater interface seaward and away from the Los Osos community. Source: 3-008_7c_LosOsosBasin Plan-2015.pdf pg. 101 4) The Basin Plan established two methods for measuring progress in management of seawater intrusion (ISJ Group, 2015): one based on comparing annual groundwater extractions with the sustainable yield of the basin as calculated by the basin numerical groundwater model, and one based on evaluating water level and water quality data from the LOBP Groundwater Monitoring Program. …The Chloride Metric is defined as the weighted average concentration of chlorides in four key Lower Aquifer wells. One key well (LA10) is within the historical path of seawater intrusion (Cleath & Associates, 2005). Reduction in pumping from the Lower Aquifer should result in measurable declines in chloride concentrations at this well, as the hydraulic head in the Lower Aquifer increases and the hydraulic gradient toward land decreases or reversed. The LOBP Groundwater Monitoring Program schedule for measuring the Chloride metric is in the Spring and Fall. There are also three key wells on the perimeter of the seawater intrusion front (LA8, LA11, and LA12). Source: 3-008_7c_LosOsos-2015AnnualReportFINALDRAFT062716.pdf pg. 31

GSA Information