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Ms. Laurie Casias <br /> September 3, 1993 <br /> Page 5 <br /> b. The highest soil contamination levels at the <br /> Site occur between the depths of 15 and 20 <br /> feet below the ground surface, while the <br /> highest historical groundwater level in the <br /> area occurred at a depth of about 38 feet <br /> according to historic groundwater elevations <br /> obtained from Stockton East Water District <br /> and San Joaquin County, indicating <br /> approximately 18 feet of unsaturated soils <br /> above the highest historic groundwater level; <br /> C. Dichloroethane and dichloropropane were not <br /> found in the soil samples in the area <br /> collected by one of Petitioner's consultants; <br /> however, these halogenated organic compounds <br /> were found in the groundwater indicating that <br /> there may be another source for the organic <br /> contaminants in the groundwater; <br /> d. The relatively low horizontal groundwater <br /> velocity which results from a flat hydraulic <br /> gradient (0. 002 to 0 . 005 ) and low hydraulic <br /> conductivity silty-clayey silt, when <br /> considered with the very low levels of <br /> groundwater contamination below the areas of <br /> highest soil contamination, further reduce <br /> the likelihood that the groundwater <br /> contamination is related to the soil <br /> contamination; and <br /> e. The presence of the asphalt layer over the <br /> entire site since approximately 1978 has <br /> significantly minimized the vertical <br /> migration of TPH in the soils by effectively <br /> capping the soils at the Site, thereby <br /> preventing surface water from entering the <br /> system and providing the pressure (head) to <br /> drive the contaminants vertically toward and <br /> into the water table. <br /> This data, combined with substantial hydrocarbon <br /> contamination documented immediately up-gradient at 101 South <br /> Wilson Way, is sufficient evidence to include Adjacent Landowners <br /> as additional responsible parties for the groundwater <br /> contamination at the Site. <br /> PHS/EHD takes a limited view of its authority to name <br /> additional responsible parties pursuant to the LOP. PHS/EHD <br /> F:\TRN\17093\D\ROHR3.HHH <br /> 75376-17093/./09/03/93/4 <br />