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�Aw"FuA► <br /> ir�Zjr7 <br /> Working to Restore Nature <br /> highest concentrations were detected in wells near the western and southern <br /> perimeter of the site and offsite <br /> 7.0 DISCUSSION AND CONCLUSION <br /> Based on data collected at the subject site, sediment with the highest concentrations of <br /> residual hydrocarbons is present in the capillary fringe zone from 26 to 41 feet bsg <br /> Sediment in the overlying vadose zone (above 26 feet bsg) contains relatively low <br /> concentration of residual hydrocarbons In contrast, relatively high concentrations of <br /> residual hydrocarbons have been detected in soil above the capillary fringe zone in the <br /> offsite soil borings ARCO has thoroughly assessed the soil underlying the potential sources <br /> of hydrocarbons at the site 1 e the USTs, dispensers and piping) A residual hydrocarbon <br /> plume emanating from a potential source and extending to groundwater has not been <br /> identified Such a plume would represent a migration pathway from the source of a release <br /> to the capillary fringe zone Therefore, in our opinion, the residual hydrocarbon plume in <br /> the capillary fringe zone underlying the ARCO site is not the result of a release from the <br /> ARCO facilities <br /> Dissolved hydrocarbons were detected in the onsite and offsite monitoring wells, however, <br /> free product has not been present in onsite monitoring wells Free product has been <br /> reported in wells located upgradient at the Texaco station. The groundwater gradient has <br /> i31004-10 11 <br />