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III. CONCLUSIONS <br /> Soil samples collected and analyzed during the Phase I tank removal activities of T1 and T2 <br /> showed that nondetectable concentrations of TPH-Diesel and Gasohn were found in the <br /> native soils under both ends of the two tanks During Phase I tank removal activities, the <br /> two soil samples that were taken from under T3 showed nondetectable concentrations of <br /> TPH-D and TPH-G at one end of the tank and 850 ppm at the fill pipe end of the tank <br /> Soil samples collected and analyzed during the Phase TI investigation show that <br /> hydrocarbon contaminated soil remains to the ground at the former T3 UST site Three <br /> out of twenty-one soil samples taken indicate concentrations between 380 and 8,000 ppm <br /> TPH-D in a localized zone around B4 <br /> The subsurface geology is characteristic of outer or distal alluvial fan deposits The fine <br />. grained soils, i e , clays and silts, are typical outer fan deposits The gravelly clay, sandy <br /> gravel, and clayey gravel deposits are derived from mobile debris flows, which originate in <br /> the mountains and flow down the face of the alluvial fan, with subsequent stream incision <br /> and infilling creating deposits, some of which contain lenses and others of which are <br /> channel deposits <br /> The soil borings show that the site is not underlain strictly with gravels, but a variety of fine <br /> grained sods and some coarser discontinuous layers <br /> Comparing these boring logs, the subsurface geology at T3 is composed of a clay to <br /> approximately 4 feet bgs, a gravelly clay sand (5 to 10 feet bgs) which is thicker in B-4, B-5 <br /> and B-b Below the gravelly clay/sand are interbedded clays and silts to approximately <br /> 25 feet bgs, where clayey gravels and sandy gravels extend to the bottom of the soil borings <br /> This interbedded clay/silt layer has contained the contamination, preventing it from <br />. r2h1d 08(ml4) Page 10 <br /> AMERICAN <br />