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!1 i <br /> 1, EXECUTIVE SUMMARY <br /> I This report presents the results and findings of a supplemental Site characterization <br /> I field investigation, file reviews, and analyses conducted by ARCADIS Geraghty&Miller, Inc, <br /> on behalf of Union Oil Company of California(UNOCAL), between August, 1998 and March, <br /> 1999, regarding the former UNOCAL service station number 2859, located at 1665 Pacific <br /> Avenue, Stockton, California Additionally, the histoncal record of data and events regarding <br /> the Site has been examined, analyzed, and presented The results of a sitewide monitoring <br /> event conducted February 4, 1999 are also presented and evaluated <br /> I � <br /> The primary petroleum hydrocarbon sources, relating to the dispensing of gasoline <br /> products at the Site, have been removed Approximately 2,745 pounds(450 gallons) of TPHg <br /> and 12 pounds (1 6 gallons) of benzene have been removed by an SVE pilot study at the Site <br /> The amount of excavated impacted soul removed at the Site is in question However, previous <br /> consultants report having excavated impacted soil to a depth of approximately 30 feet in the <br /> area of the 1988 tank excavation <br /> The Site release occurred during at a tune when groundwater levels were lower and <br /> groundwater has subsequently risen into the zone of impacted soils Based on data from a 90- <br /> foot boring(NP-1)advanced at the Site, impacts from the removed surface source and residual <br /> concentrations in vadose zone soils are not the result of ongoing migration downward and <br /> impact to saturated zone soils <br /> - General water quality in the vicinity of the Site is poor and does not meet California <br /> State standards (MCLs) for acceptable drinking water All of the wells at the Site have Total <br /> Dissolved Solids concentrations above the California State Maximum Contamuiant Level The <br /> Iwater sampled in the deepest well at the Site is of clearly different quality than that from water <br /> sampling points higher in the profile It appears that the water sampled in the deep zone <br /> represents the influence of the intruding salt water front documented in the 1997 San Joaquin <br /> a <br /> County Flood Control&Water Conservation Report <br />