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31 October 1996 <br /> �a. AGE-NC Project No. 95-0190 <br /> Page 2 of 7 <br /> of igneous and metamorphic-rock. <br /> 2.3. GROUND WATER DEPTH AND REGIONAL FLOW DIRECTION <br /> According to the San Joaquin County Flood Control and Water Conservation District map titled <br /> Lines of Equal Depth of Water Wells-- Fall 1993, ground water depth in the area of the site is <br /> approximately 10 feet below surface grade (bsg). Regional ground-water flow direction in the area <br /> is westerly, although, flow direction can vary locally and seasonally:As will be discussed below, <br /> ground water on the site was encountered at depths of 12 to 18'!feet bsg during the course of the site <br /> `y investigation, and between 8.42 and 16.54 feet below,tops of-the well casings during monitoring <br /> events.The flow direction calculated from data collected during the monitoring events was north 60° <br /> east,on.average. <br /> 2.4. UNDERGROUND STORAGE TANK REIMOVAL <br /> LM <br /> ' Two 1,000-gallon USTs, suction pump dispensers and related piping were removed from the site in <br /> I February 1990. Both USTs were utilized to dispense unleaded gasoline.Numerous holes were noted <br /> in the piping during removal; however the condition of the USTs was not noted in the PHS-EHD <br /> inspection report. Soil excavated during UST removal was noted to have"strong hydrocarbon odors' <br /> and was stockpiled on-site. A small quantity of soil has been aerating on-site, since removal of the <br /> USTs. <br /> Four soil samples were collected by FGL Environmental from'the tank excavation and analyzed for <br /> total petroleum hydrocarbons quantified as gasoline (TPH-g) and volatile aromatic hydrocarbons <br /> (benzene,toluene,ethylbenzene and xylenes: BTE&X).TPH-g and.BTE&X were detected in all the. <br /> samples at concentrations as high as-5,000 mg/kg (milligrams per kilogram or parts per million: <br /> f ppm). Analytical data from all soil samples collected at the site are summarized on Table 1. A copy <br /> of the laboratory report (FGL laboratory Nos. 26884-1 to..26884-4)'and .chain-of,-custody are <br /> included in Appendix A. <br /> Le <br /> 3.0. SITE ASSESSMENT <br /> 3.1. MONITORING WELL INSTALLATION <br /> Geological Audit Services,Inc. (GAS)conducted an assessment-to determine the lateral and vertical <br /> extent of contamination at the,site. On 10 and 11 February 1993; five soil borings were drilled at the <br /> �- site. Boring B 1 was advanced to a depth of 32 feet bsg; borings B2 through B5 were advanced to <br />