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W.. �sii <br /> November 10, 1992 Working-To Restore Nature <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 (RESNA, June 2, 1992, Report No. 86102-9). Results of <br /> laboratory analyses of the soil sample collected from the boring indicated that <br /> concentrations of gasoline and diesel.hydrocarbons were below laboratory detection limits. <br /> Total .lead was detected:at a concentration of '6:6 parts per million and is interpreted as <br /> 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. The laboratory analyses on water samples collected during the most recent sampling <br /> event (col.lected.July 13,. 1992) indicated that hydrocarbons are not present•in the ground <br /> water. The cumulative results of ground-water sampling,.beginning from December 1986; <br /> are shown in the July Status Report (RESNA; September 28, 1992, report No. 86102-8). <br /> Ultramar installed and operated- a vapor-extraction system (VES).from June 6, 1992 to <br /> September 18, 1992. The VES:utilized a 100 CFM, King,Buck .catalytic oxidizer as the <br /> abatement device. -The vapor concentrations of total petroleum.,hydrocarbons as gasoline <br /> ( (TPHg) in the initial influent sample, collected on June 30, 1992, was 1000 Molar ppm. <br /> After approximately three months of operating the system, the results of the influent vapor <br /> concentrations, collected on September 8, 1992,were less than the laboratory detection limit <br /> of 8.0 Molar ppm, indicating that the vapor concentrations have decreased over this time <br /> period. <br /> ADDITIONAL INVESTIGATION. <br /> On October 8, 1992, a RESNA geologist returned to the site to observe drilling of three soil <br /> borings (B-9, B-10 and B-11) to confirm the VES had been effective. Our field 'methods are <br /> presented as an .attachment. Results of the soil samples are presented in Table 1 and <br /> indicate hydrocarbon compounds were not present at detectable concentrations. It is our <br /> opinion that the total lead concentrations.represent background levels. Copies of Lags of <br /> Bogs are also attached. <br /> Based on our finding of the additional work, it is our opinion that additional environmental <br /> investigation is not warranted. We recommend that the monitoring and vapor-extraction <br /> wells be destroyed and the environmental,investigation be closed.. We also recommend that <br /> this document be forwarded to Ms. Diane Hinson of the San Joaquin County Public Health <br /> Services, Environmental Health Division, P.O. Box 2009; Stockton, California 95201, and <br /> Ms. Elizabeth Thayer of the California Regional Water Quality Control.'Board, Central <br /> Valley Region, 3443 Routier.'Road, Sacramento, California 95827"3098.- <br /> 86102-9 <br /> 5827-3098:86102-9 <br /> 1029kear 2 <br />