SITE INFORMATION AND CORRESPONDENCE

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STATE OF CALIFORNIA-Environmental Protection Agency • PETE WILSON, Governor CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD CENTRAL VALLEY REGION 3443 Routier Road, Suite A Sacramento,CA 958273098 ass PHONE: (916)2553000 FAX (916)2553015 10 December 1992 Mr. James Wang Diamond Properties 2546 Derby Drive San Ramon, CA 94583 RESCISSION OF CLEANUP AND ABATEMENT ORDER NO. 90-700 AND SITE CLOSURE, 701, 825, AND 835 WEST 11TH STREET, TRACY, SAN JOAQUIN COUNTY Staff have received your request for closure and have reviewed the file for this site. The review showed that the site was a former service station, surface structures were removed a number of years ago, and three underground tanks were removed by 1982. In 1987, during site assessment activities, four borings were drilled and contamination was found down to the ground water surface, at approximately 12 feet. In 1988, several borings were drilled and three monitoring wells were installed. Ground water contamination was detected in MW-2. A year later, in 1989, ground water contamination was found in all three wells with up to 45 ppb benzene and 17.5 ppm gasoline in MW-2. In February 1990, Cleanup and Abatement Order No. 90-700 was issued by the Executive Officer in order to expedite the investigation and cleanup due to planned road construction over the site. In August 1990, 5000 cubic yards of soil were excavated and aerated to nondetectable levels. The excavation extended to ground water. Monitoring wells MW-2 and MW-4 were abandoned during excavation activities, in accordance with San Joaquin County regulations. Due to the proximity of sidewalks and streets, it was necessary to leave contaminated soil , up to 27 ppm gasoline, in the southeast corner and eastern sidewalls of the excavation to depths of 12 feet. A ground water sample collected from the bottom of the excavation did not contain detectable levels of contamination. Quarterly ground water samples have been collected since September 1990. Low levels of BTEX were detected intermittently in MW-1 and MW-3 until June 1991 when 3.3 ppb toluene was detected in MW-3. Due to the low levels of ground water contamination, Board staff agreed that it was unnecessary to use the soil vapor extraction system which had been installed during the tank excavation/backfill operation in August 1990. Ground water samples analyzed in September and December 1991 and March and October 1992 did not have detectable levels of contamination. Based on the removal of the majority of contaminated soil and a year of ground water samples with no detected contamination, we agree that sufficient work has been completed to protect beneficial uses of water. Therefore, Cleanup and Abatement Order No. 90-700 is hereby rescinded.