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vg <br /> Chevron U.S.A. - Page 18 <br /> 12.0 CONCLUSIQNS <br /> Based upon review of the data collected from our field and laboratory study, <br /> coupled with review of reports from previous investigation and published data. <br /> Dames & Moore has reached the following general conclusions: <br /> The subsoils encountered at the subject property were generally <br /> comprised of fine sandy silts and clays with interbedded silt and clay. <br /> At the time of our field study, ground water was encountered beneath the <br /> _ subject property at an approximate depth of 71 feet below the existing <br /> grade, with an interpreted relatively flat gradient of approximately <br /> 8.3x10-4 (0.00083 ft./ft.) flowing in a east-northeasterly direction. <br /> Results of chemical analysis conducted on soil samples suggests <br /> petroleum hydrocarbons contamination is present in subsoils. Iii our <br /> opinion, the residual liquid vertical migration of contamination <br /> encountered at each of the previous dispenser island locations (B-1 and <br /> B-2) attenuates at an approximate depth of 20 feet below the existing <br /> grade, with passible-vapor-phase migration extending to greater depths'. <br /> ` - In our opinion, the sporadic distribution of low levels of banzene' and <br /> toluene (0.08 to 0.15 parts per million concentrations) reported from <br /> analysis of samples obtained from the B-3 boring advanced through the <br /> previous tank burial pit, does not suggest residual contamination from <br /> ' liquid vertical migration of petroleum hydrocarbons from the previous <br /> underground tanks at that soil boring location. <br /> In our opinion, the low levels of benzene and toluene (less than 1 part <br /> per million concentrations) encountered in samples obtained from below <br /> the 26 foot depth at the subject property may be attributable to vapor- <br /> phase migration of volatile petroleum hydrocarbons. <br /> g The results of chemical analysis conducted on ground water samples <br /> obtained from monitoring wells installed at the subject property were <br /> reported as non-detected for petroleum hydrocarbons as referenced to <br /> gasoline at the time of our field and laboratory study. <br /> -000- <br /> DAMES S 2S�OORE <br />