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' Mr Harlan Knoll <br /> September 20, 1993 <br /> Page 2 <br /> PREVIOUS WORK <br /> Three underground diesel storage tanks (2-10,000 and 1-5,400-gallon) and one <br />' 515-gallon waste oil storage tank were removed from the site on June 12, 1989, by <br /> Wathall Construction of Stockton, California Associated piping and dispensers were also <br />' removed Soil contamination was detected in the waste oil excavation pit at a depth of <br /> 12'/z ft Analytical test results indicated a total petroleum hydrocarbon concentration of <br /> 4,500 parts per million (ppm) in soil below the former tank Soil contamination was <br />' detected in the diesel tanks excavation pit in the western wall near the center tank area at a <br /> depth of 13 feet Analytical test results indicated a total petroleum hydrocarbon as diesel <br />' (TPHd) concentration of 650 ppm Analytical test results indicated no concentrations of <br /> suspected contaminants in the northwestern, southwestern, and all eastern samples <br /> I collected from the diesel pit, all three piping samples, and the one eastern dispenser <br /> sample <br />' On November 27, 1989, soil was excavated from the waste oil tank area by Water <br /> Works of Escalon, California to a depth of 18 ft Soil contamination was detected in the <br /> pit in the southern and eastern walls No confirmation samples were collected and the pit <br /> was evidently backfilled with clean soil Water Works then installed one groundwater <br /> I monitoring well (B1/MW1) east of the tank area and one angle boring (ASB-1) south of <br /> the tank area that was advanced beneath the existing shop building Analytical test results <br /> on soil samples collected from B1/MW1 indicate low concentrations of TPH in soil <br /> samples from depths of 15 ft (1 5 ppm), 20 ft (2 7 ppm), and 30 ft (4 1 ppm) No <br /> detectable concentrations of BTEX were detected in the soil or in the groundwater <br /> Water samples collected in February 1990 indicated a concentration of 350 ppm TPHd <br /> A concentration of 59 ppm TPHd was detected in April 1990 Analytical test results from <br /> ASB-1 indicate no concentrations of TPHd nor BTEX <br /> On December 15, 1989, soil was excavated from the western wall near the former <br /> Idiesel tank area Analytical test results indicate a TPHd concentration of 30 6 ppm at 6 ft <br /> TPHd was not detected in the 2 ft nor the 16 ft sample <br /> LOCAL GEOLOGY <br /> The site is located in the central portion of the Great Valley physiographic <br /> province and is situated approximately 10 ft above mean sea level The site is underlain by <br /> ROGER <br /> 323-001 sew F®TT <br /> ASSOCIATES <br />