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• MEMORANDUM • CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD - CENTRAL VALLEY REGION 3443 Routier Road, Suite A Phone: (916) 361-5600 Sacramento, CA 95827-3098 ATSS Phone: 8-495-5600 TO: Antonia K. J. Vorster FROM: Camilla Williams Senior WRC Engineer Engineering Geologist DATE: 22 November 1991 SIGNATURE: SUBJECT: OFF-SITE DOMESTIC SUPPLY WELLS ALONG BANTA ROAD, DEFENSE DISTRIBUTION REGION WEST (DDRW), TRACY, SAN JOAQUIN COUNTY During the 10 to 11 October 1991 Project Manager's Meeting, DDRW, Tracy's consultant, Woodward-Clyde, presented the results of the May 1991 Quarterly Ground Water Monitoring Program. Based on these data, it appeared that the off-site volatile organic (VOC) plume threatened to impact two domestic supply wells to the east of the site at 25516 and 25080 South Banta Road. During the meeting, it was agreed that the Regional Board would collect ground water samples from these domestic supply wells and analyze for VOCs using Methods 601 and 602 because we could provide the quickest turn around to determine if the wells had been impacted using our in-house State certified laboratory. On 6 November 1991 and on 14 November 1991, the Regional Board and the Department of Toxic Substances Control collected ground water samples at the Rose (25516 South Banta Road) and Robertson (25080 South Banta Road) properties. The analytical results for volatile organic constituents (VOCs) revealed that carbon tetrachloride was present in concentrations exceeding the State Primary Maximum Contaminant Level (MCL) of 0.5 micrograms per liter (µg/1 ) in both wells in both sampling events. The results also revealed that trichloroethylene (TCE) was present in the Rose well samples on both sampling occasions and that the concentration exceeded the Federal and California Primary MCL of 5 µg/l only in the 6 November 1991 sample. The analytical results for Standard Minerals and Title 22 Metals, collected on 6 November 1991, were sent to our contract laboratory and have not yet been received. All of the analytical results will be forwarded to DDRW, Tracy. On 14 November 1991, a meeting was held with representatives of the Environmental Protection Agency (EPA) , the State, San Joaquin County, DDRW, Tracy and the Corps of Engineers to discuss the preliminary analytical results for VOCs from the 6 November 1991 sampling event. At that time, all of the regulatory agencies indicated that DDRW, Tracy should supply bottled water as an interim measure to both the Rose and Robertson residences. During the meeting, I recommended that DDRW, Tracy conduct a comprehensive off-site well survey to determine what off-site supply wells should be incorporated into the quarterly ground water monitoring program. We had previously written DDRW, Tracy on 31 July 1991 and indicated that off-site agricultural and domestic supply wells had been contaminated by VOCs above State Action Levels and requested that off- site supply wells be incorporated into the quarterly monitoring program. The monitoring program has not yet been changed. Since our 14 November 1991 meeting, I have been informed that bottled water has been supplied to the Rose residence, but not to the Robertson residence. It my understanding that DDRW, Tracy will not voluntarily supply bottled water to the Robertson residence because DDRW, Tracy believes that it is not the source of the carbon tetrachloride ground water contamination and the supply of bottled water may be construed as an admission of guilt. DDRW, Tracy also plans monthly monitoring of the Rose and Robertson domestic supply wells.