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t 1 z and MW-4) The initial detection of TPH-G, ethylbenzene, and xylenes in well MW-4 on July 15, 1991 appears to have been anomalous A summary of the quarterly . groundwater analytical results are presented in Table 1 . Upgradkent monitoring well MW-1 was temporarily removed from the quarterly sampling program, with approval of the San Joaqu:n,County Department of Public Health Services,(SJCDPHS) 3.0HYDROGEOLOGIC SETTING The hydrogeology of the site is defined from the soils encountered in soil borings and __water level eIevat:ons-measured in the monktorkng_wells _ The regional hydrogeologic setting and the site boring logs are presented :n Appendices A and B (Mittelhauser's Preliminary Investigation and Evaluation Report dated January, 31 , 1992, and Mittelhauser's Monitoring Well MW-3A Installation Report dated December 3, 1993, respectively) The site is generally underlain with a poorly graded sand fill that is between 6 inches and 3 feet thick A dark gray clay or silty clay was observed to a depth of S approximately 8 feet below ground surface (bgs) Below the clay, and extending to , the maximum depth of the monitoring well borings, the soil generally consists of �— clayey silt to sandy silt Areas that were excavated during the recent remediation _ activities were backfilled with compct aed Class-2 base rock The f the portion oUST excavation below the water table was backfilled with gravel drain rock The depth to groundwater is generally between 8 and 10 feet bgs The groundwater , gradient has been determined during five quarterly monitoring events between July 1991 and September 1992 The groundwater gradient direction has varied between N51°W and N39°E with all but one of the quarterly gradient directions being toward the northwest /Mittelhauser P2168R006 wpf031941 2 C O R P 0 R A T 1 0 N