COMPLIANCE INFO - Laserfiche WebLink

Home Browse Search

1 � GROUND-WATER RECHARGE AND DISTRIBUTION OF HIGH-CHLORIDE WATER FROM WELLS,SAN JOAQUIN COUNTY,CALIFORNIA By: John A.Izbicki SUMMARY Water levels are declining and chloride concentrations are increasing in eastern San Joaquin County as a result of pumping in excess of recharge.Declining water levels and decreases in ground-water quality may decrease agricultural and public supplies for Stockton and other cities—increasing reliance of surface sources,which may adversely impact the San Joaquin Delta and threaten water exports to cities in southern California during periods of low flow. The purpose of this study is to quantify 1)source,areal extent,and vertical distribution of high-chloride water to wells,and 2)the sources,distribution,and rates of recharge to aquifers in eastern San Joaquin County.The scope of this study includes: 1)assembly and review of existing geologic,hydrologic,and water-quality data,2) collection of geochemical and geophysical data(including well-bore flow and depth-dependent water-quality data), 3)test drilling and well installation,and 4)construction of a spatial GIS database to be used for 3-D visualization of aquifer materials and ground-water chemistry.The study is to be completed in October 2008 with interim papers describing the 1)sources of high-chloride water and 2)ground-water recharge along selected study flowpaths published in 2006 and 2007,respectively. PROBLEM AND STUDY AREA:Water levels are declining and chloride concentrations are increasing in eastern San Joaquin County(figure 1)as a result of pumping in excess of recharge.Previous studies(Montgomery Watson, Inc.,2000)have defined the area of high-chloride ground water near the delta of the San Joaquin River on the basis of the 300 mg/L contour and water from some wells have chloride concentrations in excess of 2,000 mg/L. However,the areal extent and vertical distribution of the high-chloride water are poorly defined and the source of the high-chloride water is not known.High-chloride water may result from a combination of the movement of poor- quality water from the San Joaquin Delta,irrigation return,or movement of water from older deposits underlying alluvial deposits pumped for water supply.Local water management agencies recharge water to augment natural recharge,but the cumulative effect of ongoing ground water recharge projects on water levels and water quality in aquifers is not known.