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and MW-4) The initial detection of TPH-G, ethylbenzene, and xylenes in well MW-4 <br /> on July 15, 1991 appears to have been anomalous A summary of the quarterly <br /> groundwater analytical results are presented in Table 1 Upgradient monitoring well <br /> MW-1 was temporarily removed from the quarterly sampling program, with approval <br /> ' of the San Joaquin County Department of Public Health Services (SJCDPHS) <br /> ' 30 HYDROGEOLOGIC SETTING <br /> ' The hydrogeology of the site is defined from the soils encountered in soil borings and <br /> water level elevations measured in the monitoring wells The regional hydrogeologic <br /> ' setting and the site boring logs are presented in Appendices A and B (Mrttelhauser's <br /> Preliminary Investigation and Evaluation Report dated January 31, 1992, and <br /> ' Mittelhauser's Monitoring Well MW-3A Installation Report dated December 3, 1993, <br /> respectively) <br /> The site is generally underlain with a poorly graded sand fill that is between 6 inches <br /> and 3 feet thick A dark gray clay or silty clay was observed to a depth of <br /> ' approximately 8 feet below ground surface (bgs) Below the clay, and extending to <br /> the maximum depth of the monitoring well borings, the soil generally consists of <br /> ' clayey silt to sandy silt. Areas that were excavated during the recent remediation <br /> activities were backfilled with compacted Class-2 base rock The portion of the UST <br /> excavation below the water table was backfilled with gravel drain rock <br />' The depth to groundwater is generally between 8 and 10 feet bgs The groundwater <br /> gradient has been determined during five quarterly monitoring events between July <br />' 1991 and September 1992 The groundwater gradient direction has varied between <br /> N51OW and N390E with all but one of the quarterly gradient directions being toward <br />' the northwest <br /> /Mittelhauser <br /> C O R P O R A 7 I O N <br /> P21 SBRO06 wp1031941 2 <br />