West Mojave Plan FEIR/S - Desert Managers Group

Rosamond Faults and the San Andreas Fault Zone.Alluvium and interbedded lacustrine deposits of Quaternary age are the importantaquifers within the closed basin and have accumulated to a thickness of as much as 1,600 feet.The alluvium is unconsolidated to moderately consolidated, poorly sorted gravel, sand, silt, andclay. Older units of the alluvium are more compact and consolidated, somewhat coarser grained,more weathered, and more poorly sorted than the younger units. The rate at which water movesthrough the alluvium (the hydraulic conductivity of the alluvium) decreases with increasingdepth.Two aquifers, which are separated by the lacustrine deposits, are in the alluvial material.The upper aquifer is the principal and most used aquifer and contains water under unconfined, orwater table, conditions. Where the lower, or deep, aquifer underlies lacustrine deposits, itcontains water under confined, or artesian, conditions. Elsewhere, unconfined conditions prevail.The use of ground water for agriculture in Antelope Valley began about 1880, whenwells were drilled near the center of the valley and yielded flowing water in quantities sufficientfor irrigation. In 1891, more than 100 wells were in use, but most had stopped flowing. About1915, intense use of ground water began when a large number of wells were drilled and equippedwith pumps. The maximum rate of withdrawal of about 400,000 acre-feet per year is about 10times the estimated annual recharge to the basin. Water removed from storage in the aquifers wasa major part of the ground-water withdrawals, and severe water-level declines resulted. By about1950, studies showed that ground-water withdrawals in the valley were greatly in excess ofnatural recharge and withdrawals were curtailed. The Antelope Valley-Eastern Kern WaterDistrict is still serviced by ground water.Antelope Valley illustrates the potential for overdraft in the groundwater basins in theplan area.Water Quality: Although there are vast quantities of water within the ground waterbasins, some of the water is of poor quality. The mineral quality of the ground water within thestudy area varies greatly. The geologic setting of the basins directly affects the degree of groundwater mineralization. In general, basins near the source of recharge are less mineralized thanthose that are more distant.Very short flow paths generally characterize small local flow systems, usually no morethan a few miles in length. Springs connected to these systems are usually located in or near themountains and have highly variable annual ranges in discharge which respond to theprecipitation that year or a few years previous. Discharge waters have small concentrations ofdissolved sodium plus potassium and chloride plus sulfate, large concentrations of tritium, andwater temperatures that commonly approach average air temperatures.Large local flow systems are characterized by interbasin flow or flow confined to onebasin with longer flow paths. Springs connected to these systems have moderate concentrationsof the major salts, no significant concentrations of tritium and water temperatures from 50 to 60degrees Fahrenheit.Chapter 3 3-62