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. Mr. Harlin Knoll <br /> San Joaquin County Public Health Services, <br /> Environmental Health Division <br /> Page 4 <br /> May 18, 1995 <br /> Therefore, in July 1994 Hunter & Associates drilled two additional <br /> soil borings (Location A and Location B) to a depth of <br /> approximately 41 feet bgs in the vicinity of previously drilled <br /> soil boring B--5 and former UST excavation sidewall sample SW-2W, <br /> respectively in order to evaluate reductions in soil gasoline <br /> concentrations since 1990 . Benzene was detected at concentrations <br /> of 0. 008 ppm in soil samples collected from boring Location A at <br /> depths of approximately 25. 5 and 31. 0 feet bgs. Ethylbenzene and <br /> xylenes were detected at concentrations of 0. 020 ppm and 0. 048 ppm, <br /> respectively in soil samples collected from boring Location A at a <br /> depth of approximately 31 feet bgs. BTEX were not detected in soil <br /> samples collected from other sample intervals in the boring. TPHg <br /> was not detected in soil samples collected from the boring. BTEX <br /> were detected at maximum concentrations of 0. 08 ppm, 0 . 18 ppm, 0. 07 <br /> ppm, and 0. 19 ppm, respectively in soil samples collected from <br /> boring Location B at depths of 16 feet, 26 feet, and 31 feet bgs. <br /> TPHg was detected at a maximum concentration of 19 . 0 ppm at a depth <br /> of 16 feet bgs. TPHg was also detected at a concentration of 2 . 5 <br /> . ppm , and 3 . 6 ppm at depths of 26 feet, and 31 feet bgs, <br /> respectively. TPHg and BTEX were not detected in soil samples <br /> collected from the other sample intervals. Hunter & Associates <br /> concluded that the vertical and horizontal extent of soil <br /> contamination had been defined, that groundwater had not been <br /> impacted, and that the levels of residual gasoline contamination <br /> had decreased significantly over a period of 3 . 5 years . <br /> In a letter dated January 25, 1995 San Joaquin County Public Health <br /> Services-Environmental Health Division (SJCPHS-EHD) stated that <br /> based on the results of the additional investigation performed by <br /> Hunter & Associates residual soil contamination remains at <br /> unacceptable levels, and recommended a groundwater investigation be <br /> conducted to evaluate groundwater conditions and gradient. <br /> PROPOSED WORK <br /> Ground Zero proposes drilling three soil borings (SB-1 through SB- <br /> 3) at locations shown on the attached Generalized Site Plan (Figure <br /> 2) . The borings will be advanced 15 feet into the first <br /> encountered groundwater bearing zone using a drill rig equipped <br /> with 8-inch diameter hollow-stem augers. we anticipate <br /> encountering groundwater at approximately 70 feet below ground <br /> surface. During drilling, soil samples will be collected at five <br /> • foot intervals for logging purposes. <br />