Ground water in north Monterey County, California, 1980

Present ground-water demands exceed long-term recharge throughout much of North Monterey County in the shallow Quaternary deposits--principally the upper part of the Aromas Sand--and the overlying alluvium. Recharge occurs largely from local precipitation, although small quantities of potable ground water from outside areas also recharge these aquifers. Water levels in the Pajaro and Salinas River valleys north and south of the study area are lower than most of the intervening area, and recharge from the east is blocked by faults and impervious rock. Ocean water moves in from the west to replace depleted freshwater storage in the upper part of the Aromas Sand, alluvium, and terrace deposits. The North County area was divided into subareas to estimate pumpage demands and to evaluate ground-water yields. Pumpage near the granitic ridge, an area of limited storage, nearly matches local recharge. West of the granitic ridge, pumpage exceeds available recharge but draws upon a large storage potential. Deeper units than those now tapped by wells in the Aromas Sand and the underlying Purisima Formation may have substantial water-bearing potential for additional ground-water development. Extensive development of water from these formations might be limited, however, by the remoteness of the recharge source and by the proximity to the ocean. (USGS)