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r <br /> � I <br /> Evaluation of Contamination January 3, 1989 <br /> Former Texaco Service Station, Manteca, California AGS 38053-1 <br /> I <br /> installation, collect soil samples, and subjectively evaluate the <br /> soil for contamination. Subjective evidence of contamination was <br /> present in soil samples collected from the boring located north <br /> of the former product storage tanks (B-1) . The results of <br /> laboratory analyses of soil samples collected from the <br /> unsaturated zone in this boring indicate that contaminants are <br /> present at relatively low levels. No subjective evidence of soil <br /> contamination was present in the boring located on the southern <br /> edge, adjacent to the former tank cavity. <br /> r' On October 26, 1988, a geologist from Applied GeoSystems was <br /> present at the site to develop the monitoring wells; and on <br /> October 27, a geologist from Applied GeoSystems was at the site <br /> to measure depths to water, subjectively analyze ground water in <br /> the monitoring wells, purge the monitoring wells, and collect <br /> ground-water samples for laboratory analyses. Analyses of ground <br /> water from each monitoring well revealed relatively low levels of <br /> gasoline. Laboratory analyses of samples from monitoring wells <br /> MW-2 and M11-3 showed concentrations of benzene in excess of <br /> action levels for drinking water recommended by the California <br /> Department of Health Services. <br /> Because of the detected contamination at 18 feet below grade, <br /> Applied GeoSystems recommends that additional subsurface work be <br /> conducted at the site. This work should include excavating the <br /> initial tank cavity to the ground--water surface at approximately <br /> 23 feet below grade. If subjective evidence of soP. <br /> contamination exists to the north, this soil shoula also he <br /> removed. A sanitary sewer line is present at the eastern edgs of <br /> the former tank location, and the station building is present <br /> adjacent to the western edge of the former tank location. The <br /> presence of the sewer line and site building precludes excavating <br /> to the east or west. Monitoring well MW-3 is located south of <br /> the former tank cavity, and the soil sample analyzed from this <br /> boring indicated no detectable hydrocarbons. <br /> It is our further recommendation that quarterly monitoring of the <br /> ground water be continued for a period of one year. During this <br /> period, the monitoring wells should be purged in an attempt to <br /> remove a portion of the ground-water contamination. If gasoline <br /> concentrations do not increase in this period, we recommend that <br /> this site be re-evaluated. <br /> 2 <br /> AVV11ed GeaSYWe1nS <br />