Las Flores basin hydrogeology, camp Pendleton marine corps base, San Diego County, California.
The Las Flores basin is located in northwest San Diego County, California, on the Camp Pendleton Marine Corps base. The Las Flores basin is one of four groundwater basins that supply drinking water to Camp Pendleton. Groundwater in the Las Flores basin is extracted from the alluvial aquifer and the San Mateo aquifer located in the coastal basin. The San Mateo aquifer is overlain by unconsolidated alluvial deposits and underlain by the San Onofre Breccia. Groundwater in the basin is unconfined except for a locally occurring confining conditions in the vicinity of Interstate 5. The direction of groundwater flow is southwest along the axis of Las Pulgas Canyon. Well log data and electrical resistivity surveys conducted using the Schlumberger sounding technique were evaluated to estimate the thickness of the alluvial aquifer and the San Mateo aquifer. The minimum thickness of the water-bearing units ranges from 33 to 1,400 feet. Aquifer tests have been conducted at five locations within the coastal basin. The estimated transmissivity of the water-bearing units ranges from 1.2 to 22.4 square feet per minute (ft2/min), the specific yield is 0.12, and the hydraulic conductivity ranges from 0.03 to 0.19 feet per minute (ft/min), based on the aquifer test data. Groundwater from this basin is an acceptable drinking water supply with total dissolved solids concentrations less than 900 milligrams per liter and nitrate concentrations less than 7 milligrams per liter.