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1 I <br /> • Historical Background - Chet's Automotive <br /> ' Page 2 of 3 <br /> I <br /> ' between 1 foot and 2 feet below the depth of the UST inverts The excavated soil was transported <br /> to an appropriate landfill for disposal Following the excavation and sampling,clean and appropriate <br /> backfill was placed into the excavation <br /> 1 <br /> PREVIOUS SITE INVESTIGATION <br /> rOn 23 and 24 October 2001,four soil probe borings(B 1 through 134)were advanced at the site under <br /> the oversight of the San Joaquin County Environmental Health Department(EHD) Probe borings <br /> ' were advanced in the former UST excavation area and west, southwest,and east of the former UST <br /> area to collect soil and grab ground water samples Probe boring B 1 was advanced to a total depth <br /> of 65 feet bsg and borings B2 through B4 were advanced to 40 feet bsg Analytical data is presented <br /> ' in the attached tables Locations of the soil probe borings are illustrated on Figure 2 of the report <br /> The most intensely hydrocarbon-impacted soil was encountered in the area of the former USTs <br /> ' (boring B I), contaminants were not detected in analyzed soil samples collected from borings B2 <br /> through B4 At boring location B 1,petroleum hydrocarbons were detected in soil samples to depths <br /> of 30 feet bsg,but generally were not detected in soil samples collected at 40 feet bsg and below The <br /> ' highest hydrocarbon concentrations were encountered at depths between 10 feet and 20 feet bsg <br /> ' Hydrocarbon-impacted ground water was encountered in all four soil borings The highest <br /> concentration of dissolved hydrocarbons quantified as gasoline and diesel (TPH-g and TPH-d, <br /> respectively)and overall BTEX compounds(benzene,toluene,ethylbenzene,and total xylenes)were <br /> present in aground water sample collected at 40 feet bsg from boring B 1 However,dissolved TPH-g <br /> and BTEX concentrations decreased radially northwest, southwest, and east away from the area of <br /> the UST release In addition,dissolved TPH and BTEX were detected at low concentrations in a grab <br /> ' ground water sample collected from 60 feet bsg at boring BI <br /> ' GROUND WATER MONITORING WELL INSTALLATION <br /> On 13 and 14 August 2002, five ground water monitoring wells (MW-1 though MW-5) were <br /> ' installed near the UST area to monitor ground water flow and hydrocarbon concentrations in ground <br /> water <br /> i <br /> Results of the well installation and subsequent sampling delineated the dissolved hydrocarbons and <br /> indicated direction of ground water flow generally toward the northeast Ground water monitoring <br /> enabled delineation ofthe dissolved hydrocarbon plume The dissolved hydrocarbon plume has been <br /> vertically delineated Analytical data is presented in the attached tables <br /> Advanced GcoEnvironmentai,Inc <br /> I <br />