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All Pure Chemical Company -6- Tracy Plant Chronology 14 May 93 Letter from Mr. Norwood discussing the results of the third quarter 1993 ground water monitoring report. Total petroleum hydrocarbons as diesel was detected for the first time in MW-3. 24 May 93 Letter from City of Tracy to All Pure stating the City does not wish to accept All Pure's wastewater due to the very high level of total dissolved solids (TDS). 26 Oct 94 Meeting between Mr. Norwood and Board staff to discuss third quarter monitoring report. TDD, Lyoth Loading Station, the pipeline in the railroad right-of-way, and possible use of carbon tetrachloride as an herbicide by the railroad were discussed as possible sources of carbon tetrachloride present in MW-1 and MW-2. Board staff requested Mr. Norwood to provide logs and construction details of onsite production wells at the All Pure facility, a list of chemicals and products presently or historically used or produced at the site. Mr. Norwood informed staff that All Pure would be asking for permission to close the ponds. 28 Dec 95 Board report titled Tracy Well Survey Report completed. The Board survey was conducted to identify potential sources of carbon tetrachloride in the ground water east of the TDD. Domestic supply wells and monitoring wells in the vicinity of potential source areas were sampled. Potential sources considered include All Pure, Triple E Produce, TDD, and the Lyoth Loading Station. The report concludes that a plume of carbon tetrachloride exists along the north-south path in the vicinity of South Banta Road. Concentrations are highest in ground water from wells at the All Pure site and decrease in ground water wells to the north. Since 1991, the concentration of carbon tetrachloride in ground water at All Pure has increased considerably. Based on local gradient and distribution of carbon tetrachloride in ground water, carbon tetrachloride may be migrating southwest across the All Pure site, and into All Pure's production wells. These production wells may be acting as a conduit for contaminant flow into the middle horizon within the Tulare Formation. The carbon tetrachloride may then be migrating to the northeast with the regional ground water during periods when pumping from the production well is substantially decreased or the pumps are shut off. Sources of chloroform identified were All Pure and the Triple E Produce facility over a mile southwest of All Pure. The Triple E chloroform plume is migrating to the northwest, away from All Pure. Staff recommended delineation of the nature and extent of carbon tetrachloride and chloroform plumes which exist beneath All Pure. Potential effects of local pumping should be evaluated as part of a focused ground water investigation. PAL:pal/lsb