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E <br /> Response to Letter October 18, 1990 <br /> Former Texaco Station, Manteca, California AGS 38053-2 <br /> analyses of soil and ground-water samples collected during this investigation indicated the <br /> presence of hydrocarbons in soil and the presence of low levels of dissolved hydrocarbons <br /> in ground wa*r. On the basis of the results of this investigation, we recommended <br /> excavation of soil containing hydrocarbons to remove the source for future migration of <br /> hydrocarbons into ground water and one year of quarterly monitoring of ground water to <br /> evaluate fluctuations of hydrocarbon concentrations in the ground water beneath the site. <br /> At the request of the SJPHSD/EHD, prior to excavating the soil containing hydrocarbons, <br /> Applied GeoSystems arranged for the removal of the underground product-delivery lines left <br /> at the site. In August 1989, Don Lambert & Sons of Waterford, California, removed the <br /> product-delivery lines. A geologist from Applied GeoSystems collected soil samples from <br /> soil beneath the former lines. The results of analyses indicate that hydrocarbons were <br /> present in soil directly beneath the former dispenser. <br /> In October 1989, Applied GeoSystems observed Don Lambert & Sons removed <br /> approximately 1,100 cubic yards of soil from the vadose zone beneath the site. We removed <br /> this soil to eliminate the source of hydrocarbons that could migrate into ground water. <br /> Approximately 23 vertical feet of soil were removed from the ground surface to the lateral <br /> r <br /> limits of hydrocarbons in soil beneath the former tanks and service station building, and <br /> approximately 8 vertical feet of soil were removed beneath the former dispenser island. <br /> Results of analyses of soil samples collected from the sidewalls of the excavation indicate <br /> that hydrocarbons in the vadose zone have been effectively removed by excavation in each <br /> direction. Laboratory analyses of sidewall samples did not show concentrations of <br /> hydrocarbons above detection limits established by the laboratory. A sample collected from <br /> the base of the excavation (23 feet deep) contained a concentration of total petroleum <br /> hydrocarbons as gasoline (TPHg) of 16 parts per million (ppm) and a concentration of TPH <br /> as mineral spirits of 5 ppm. Because ground water has previously been higher than 23 feet <br /> below grade, we believe this sample was collected from the zone of ground-water <br /> fluctuation. <br /> Applied GeoSystems collected 30 soil samples from the soil excavated and stockpiled at the <br /> site. Results of analyses of these soil samples showed a maximum concentration of TPHg <br /> in the stockpiled soil of 12 ppm, no detectable benzene, no detectable TPH as diesel fuel, <br /> and a maximum concentration of TPH as mineral spirits of 7.4 ppm. After reviewing the <br /> report of the excavation and sampling, in a letter from the California Regional Water <br /> Quality Control Board, Central Valley Region (CRWQCBCVR) to the SJPHSD/EHD, � �� <br /> dated November 20, 1989, the CRWQCBCVR concluded that backfilling the excavation with <br /> the stockpiled soil would pose no additional threat to the beneficial uses of the ground <br /> c �4 <br /> tN CT' <br /> 2 <br /> i <br /> -_ Applied GeoSystems __ ._......_----------- --------. ..._._.... .. _ _.... <br />