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Table 1 - Results of Certified Laboratory Analyses of Soil Samples Acquired from Boring S-3 March, 1991 Ethyl- Sample TPH-D TPH-G Benzene Toluene benzene Xylenes Number (Rpm) (Ppm) (]RPM) (ppm) ( m) ( m) ' S3-15 ' 75 1400 N.D. 6 . 5 14 120 S3-20 ' 54 1200 N.D. 16 14 95 ' --------r Method Detect 10 1 . 003 . 003 . 003 . 003 Limit ------------------------------------------------------------- TPH-D. . .Total Petroleum Hydrocarbons as Diesel TPH-G. . .Total Petroleum Hydrocarbons as Gasoline ' ppm. . . Parts per million N.D. —Not detected at or above laboratory detection limits To further define the vertical and horizontal extent of hydrocarbon contamination, three additional soil borings were dvanced and sampled during December, 1991 . The data acquired during December revealed detectable concentrations of fuel ydrocarbons in soil samples acquired from borings EB-5 and EB-6 (Figure 2 ) . Concentrations of TPH-G between 40 and 150 ' ppm were present in EB--5 at 21 and 22 . 3 feet. TPH-D was present in these samples (at 29 and 200 ppm, respectively) . Low levels of benzene, toluene, ethylbenzene, and xylenes (BTEX) were also present in EB-5 at 22 . 3, 31 , 36, 41 , and 46 feet. Concentrations of TPH-G and TPH-D in boring EB-6 did not exceed ' 1 . 1 ppm and BTEX was detected in the samples from 36 and 41 feet. Total lead was present in all samples, ranging from 1 . 4 to 4 . 4 ppm (well below the 16 ppm average for the Earth' s crust) . Grab water samples collected from borings EB-4 and EB-5 contained 170-200 parts per billion (ppb) TPH-G and 82-98 ppb TPH-D. The Halogenated Volatile Organic (HVO) compounds 1 , 2 Dichloro- ethane ( 1 , 2 DCA) and Perchloroethene ( PCE) were present at 33-100 ppb and N.D. -11 ppb, respectively. ' GEOLOGICAL AND HYDROGEOLOGICAL SETTING The site is located on an alluvial plain and is underlain by ' Quarternary alluvium of the Great Valley or Central Valley that consists of generally horizontal, interbedded clay, silt, 2 .