OVERVIEW

Prior to the formation of the District, early farmers made use of groundwater for irrigation. In 1968, the delivery of surface water from the San Luis Unit largely replaced the use of groundwater for irrigation. However, in response to drought conditions and other surface water shortfalls, farmers reactivated old wells and constructed new wells in order to pump groundwater to irrigate their crops. In 1977, groundwater pumping increased to nearly 500,000 acre-feet and the piezometric surface declined about 90 feet, resulting in localized subsidence of approximately four inches. The groundwater basin underlying Westlands is essentially comprised of two water-bearing zones: (1) an upper zone above a nearly impervious Corcoran Clay layer containing the Coastal and Sierra aquifers and (2) a lower zone below the Corcoran Clay containing the Sub-Corcoran aquifer. These water-bearing zones are recharged by subsurface inflow from the east and northeast, the compaction of water-bearing sediments, percolation of pumped groundwater, and percolation from imported and natural surface water. Today, about one-third of the total goundwater pumped within the District is by farmers from privately owned and operated wells. The remaining groundwater pumped comes from wells enrolled in the Groundwater Management Program, through which the wells are integrated into the District's comprehensive water supply system. The District surveys the static water levels in all wells, and the water quantity and quality of pumped groundwater, and publishes the results in the Deep Groundwater Conditions Report. Contour maps showing the depth and elevation to deep groundwater in the District are compiled annually.