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} <br /> 1 <br /> L <br /> ''•lr. Chuck Carmel <br /> December 31. 1991 <br /> Pace 16 <br /> Discussion <br /> The general groundwater flow direction to the south and the general hydraulic gradient of <br /> 0.003 has not changed significantly since October 1990. In October 1990 and from September <br /> 1988 to October 1989, the gradient beneath the station was steeper--at approximately 0..-1. <br /> From July 1991 to October 1991, water levels in all monitoring wells decreased 1.11 to 1.71 <br /> feet. Hydrographs show seasonal variations and art overall decline of water table elevation <br /> in all monitoring wells. The groundwater elevations in monitoring wells W-2,W-3,W-5,W- <br /> 6,W-7,and W-8 show an average drop of 13.10 feet from April 1987 to October 1991,while <br /> W-lA and W-9 through W-12 have dropped 5.90 feet on average from April 1990 to October <br /> 1991. <br /> In all monitoring wells sampled. from July to October 1991, there was a decrease in <br /> concentration of BETX and TPH-G, except for the benzene concentration in. W-12. The <br /> benzene concentration in W-12 increased from 6.9 to 25 parts per billion from July to October <br /> 1991. <br /> Monitoring of the wells will continue through 1992. A vapor extraction and treatment system <br /> is operating on site, and groundwater extraction and trea'trnent is expected to begin in the <br /> spring of 1992. <br /> If you have any questions regarding this quarterly report, please contact me or Ms. Wendy <br /> Linck at (916) 444-0123. <br /> `:ery urtly yours, <br /> BROWN AND CALDWELL CONSULTANT'S <br /> CO <br /> �G :pGEQ(pCi <br /> /ay7ucas. R.-G. 1 Nay CR;k1Z �= <br /> Project Manager <br /> JL:NVL:mkw sT'•�...a.••'E ; <br /> Enclosures r <br /> cc: Mr. Gordon Boggs, California Regional Water Qualiry Control Board. <br /> Central Valley Region <br /> Ms. Laurie Cotulla, San Joaquin County Local Health District <br /> Mr. Chris Winsor, ARCO Products Company <br /> Brown and Caldwell 53&MUP0RTTXX7r9IMAY• <br />