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1.0 Introduction This work plan has been prepared by IT Corporation (IT) to present the scope of work for a groundwater investigation for the All-Pure Chemical Company (All-Pure) facility (site) located at 26700 South Banta Road,Tracy, San Joaquin County,California(Figure 1). This work plan is being presented in response to California Regional Water Quality Control Board's (RWQCB) December 16, 1998 letter requesting investigation of carbon tetrachloride and chloroform concentrations in groundwater north of the site. 1.1 Background The All-Pure facility at 26700 South Banta Road has manufactured swimming pool supplies and bleach,and has repackaged chlorine gas and sulfur dioxide from railroad cars, since 1975. The site was previously used for tire sorting and storage between 1957 and 1970 and for alfalfa dehydration between 1948 and 1957. During a January 1988 RWQCB inspection,water samples were collected from wastewater treatment Pond 1 and Pond 2 at the site(Figure 1). These samples were analyzed by the RWQCB for volatile organic compounds(VOCs)using U.S. Environmental Protection Agency (EPA) Method 601 and were determined to contain chloroform at concentrations of 120 micrograms per liter (µg/l) in both ponds and carbon tetrachloride at concentrations of 7.5 4g/1 and 4.3 4g/1, respectively (RWQCB, 1995). At the request of the RWQCB, groundwater monitoring wells were installed at the site. The wells have been monitored quarterly since installation and reports submitted to the RWQCB. Chloroform and/or carbon tetrachloride have been detected in groundwater samples collected from monitoring wells MW-1, MW-2, and MW-3 since 1989. The U.S. Department of Defense Distribution Depot San Joaquin, Tracy Facility (DDJC-Tracy), covering approximately 910 acres, is located approximately 1,500 feet west of the site. DDJC-Tracy is a storage and distribution facility for the U.S. military services. In 1991, DDJC-Tracy was listed on the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List(NPL)as a Superfund site,primarily due to VOC releases to the groundwater (Radian, 1998). Monitoring data collected for the ongoing DDJC-Tracy groundwater investigation detected chloroform and carbon tetrachloride in groundwater samples collected north of the All-Pure facility. Groundwater samples from private well PW-3, located approximately 1,000 feet north of the site (Figure 2)has consistently contained chloroform since 1992. The most recent sampling in the third quarter of 1998 reported a chloroform concentration of 21.3 micrograms per liter(4g/1). Chloroform was detected at concentrations of 6.09 µg/1 and 24 E.cg/l during the fourth quarter of 1996 and the third quarter of 1997, respectively. The California maximum contaminant level (MCL) for chloroform is 100 µg/1. Carbon tetrachloride has been detected in the majority of water samples collected from private wells PW-1 and PW-5 since April 1992. PW-1 and PW-5 are located approximately 3,800 feet and 5,500 Work Plan IT Corporation 1 All Pure,Tracy