SITE INFORMATION AND CORRESPONDENCE

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STATE OF CALIFORNIA - Environmental Protet%rn Agency PETE WILSON, Governor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARDl`�� 60m, CENTRAL VALLEY REGION91 3443 Routier Road, Suite A Sacramento, CA 95827-3098 PHONE: (916) 255-3000 U p� FAX: (916) 255-3015 17 August 1993 Harlin Knoll San Joaquin County Public Health Services, Environmental Health Division P.O. Box 2009 Stockton CA 95201 STAN MORRI FORD, 104 WEST ELEVENTH STREET, TRACY, SAN JOAQUIN COUNTY In your 6 August 1992 letter you requested concurrence with site closure for the above site. I have reviewed the file and have the following concerns. On the last reported ground water sampling, dated July 1991, the chemicals 1,1,1 trichloroethane, 1,1 dichloroethane, tetrachloroethylene, 1,1 dichioroethylene, and tetrachloroethane were detected in the site's three ground water monitoring wells. Monitoring well 1, which has detected halocarbons in all four monitoring episodes, is immediately downgradient of the previous waste oil tank. It is very possible that cleaning solvents containing such chemicals as 1,1,1 trichloroethane were placed in the waste oil tank when working on cars. No solvents were found in the soil samples during tank removal; however, heavy solvents such as 1,1,1 trichloroethane may degrade in soil while not degrading in water. In the 27 August 1991 Final Report, the site consultant, Murray and Associates, argued that the halocarbons may have come from the car wash operation on the southern end of the property. This argument is supported by pointing out that halocarbons were detected in monitoring well 2, which is upgradient of the former waste oil tank location, but downgradient from the car wash area. However, the ground water gradient was based on only one episode of water surface elevations, 31 January 1990. Also, it seems unlikely with the entire area cover by asphalt that the solvents could travel to the ground water directly below the site. I have sent a letter to Lambert Barnum (see enclosed), the property owner, informing him of this information. We will request that ground water from the three monitoring wells continue to be analyzed for the same chemicals as the July 1991 sampling event. Water surface elevations should be measured and gradients calculated each time ground water samples are taken. After four consecutive quarters of ground water analysis have taken place with no detectable ground water contamination, Mr. Barnum may wish to request closure from the Regional Board. Therefore, we will keep this site open in our underground tanks unit until the continued ground water contamination is resolved.