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1444 MARIPOSA <br /> WKA No. 2938.03 <br /> February 1, 1996 <br /> Page 2 <br /> underground storage tanks. Ten soil samples were obtained from the sidewalls and bottom of the <br /> excavation. Laboratory test results for the sidewall samples, obtained from a depth of <br /> approximately 22 feet, revealed non-detectable concentrations of Total Petroleum Hydrocarbons <br /> (TPH) as gasoline, diesel, and motor oil and non-detectable concentrations of Benzene, Toluene, <br /> Ethylbenzene, and Total Xylenes (BTEX). Results for the bottom samples, obtained from depths <br /> of 27 to 30 feet, revealed TPH as gasoline (TPHg) concentrations ranging from non-detectable to <br /> 25,000 mg/kg. Based on these results, the excavation was deepened to approximately 36 feet <br /> below grade on November 9, 1992. <br /> At approximately 36 feet below surface grade, petroleum hydrocarbon odors were still noticeable <br /> in the soils, so an exploratory trench was dug in the center of the excavation to a depth of <br /> approximately 44 feet below surface grade. Because further excavation would require sloping of <br /> the side walls, the decision was made to drill exploratory soil borings to further evaluate the <br /> vertical and lateral extent of hydrocarbon contamination. <br /> March 1993 <br /> Four soil borings (B1 through B4) were drilled between March 29-31, 1993 at the site. Boring <br /> B1 was constructed approximately five feet easterly of the excavation and extended to a depth of <br /> 86.5 feet. Drilling was discontinued when ground water was encountered in the boring at a <br /> depth of approximately 85 feet. <br /> Soil borings B2 and B3 were drilled at approximate 30° angles from vertical beneath the location <br /> of former underground storage tanks to vertical depths of 71 and 81 feet below site grade. The <br /> soils in these borings consisted primarily of silty clays and clayey silts; two thin sand layers were <br /> observed at depths of approximately 49 to 53 feet and 63 to 68 feet. Boring B4 was constructed <br /> approximately ten feet westerly of the excavation to a depth of 49.5 feet. A slight petroleum <br /> odor was noted in each of the four soil borings. Analytical results of selected soil samples from <br /> the four soil borings revealed relatively low concentrations of petroleum constituents at a depth of <br /> 75 feet below surface grade. <br /> WK <br /> WALLACE•KUHL <br /> Recycled paper 6ASSOQIU•ES INC <br />