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Y <br /> July 27, 1992 ��� <br /> Beacon Station No.492, Manteca, California <br /> On February 14, 1992, RESNA observed drilling of one soil boring and installation of a <br /> ground-water monitoring well Results of laboratory analyses of the soil sample collected <br /> from the boring indicated that concentrations of gasoline and diesel hydrocarbons were <br /> below laboratory detection limits. Total lead was detected at a concentration of 6 6 parts <br /> per million and is interpreted as representative of natural soil conditions <br /> RESNA began monitoring the ground water underlying the site in December 1986 <br /> Concentrations of hydrocarbons have been below detection limits in the wells since March <br /> 1991 <br /> REMEDIAL ACTION IN PROGRESS <br /> Currently Ultramar is operating a vapor-extraction system (VES) The VES consists of a 100 <br /> CFM King Buck catalytic oxidizer as the abatement device At start up (June 6, 1992), the <br /> initial organic vapor analyzer (OVA) reading was approximately 550 parts per million by <br /> volume (ppmv) in the influent stream On June 30, and July 8 and 17, the influent vapor <br /> concentrations were 850, 625, and 245, respectively which indicate that the vapor <br /> concentrations have decreased over this time period. Ultramar will continue to operate the <br /> VES and evaluate data <br /> ADDITIONAL INVESTIGATION <br /> On the basis of results of our previous investigations, RESNA will perform confirmation soil <br /> sampling Our proposed tasks include the following <br /> o Updating the Site Safety Plan <br /> o Contracting an underground line locating service to mark the locations of <br /> onsite underground structures before drilling <br /> o Contracting a licensed driller to drill two 8-inch-diameter vertical soil borings <br /> and one 8-inch-diameter angle boring near the product tanks to dust above <br /> ground water(estimated at approximately 35 feet below grade) The locations <br /> of the borings are shown on the attached Plate 2 <br /> o Collecting relatively undisturbed soil samples at 5-foot intervals from the soil <br /> borings <br /> o Backfilling the borings to surface grade with a slurry of neat cement and <br /> bentonite <br />• 86102-9w 2 <br />