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feet north of the site, respectively. PW-1 is shown on Figure 2. The most recent sampling in the third quarter of 1998 detected carbon tetrachloride at a concentration of 1.56 µg/1 in water from PW- 1,but carbon tetrachloride was not detected in a water sample from PW-5. The carbon tetrachloride concentration reported in PW-1 from quarterly samples collected from the fourth quarter of 1996 though the third quarter of 1998 sampling period ranged from 0.927 µg/1 to 1.56 4g/1. Carbon tetrachloride was also detected at concentrations of 0.729 µg/l and 0.749 4g/1 in samples collected from PW-3 during the third quarters of 1996 and 1998,respectively. The California MCL for carbon tetrachloride is 0.5 µg/l. Additionally, groundwater grab samples collected from Geoprobe sampling locations north of the site(Figure 2)were reported to contain chloroform and carbon tetrachloride. Chloroform detections were reported from samples from GP011, GP012, GP013, and GP014. Chloroform concentrations ranged from 1.62 µg/1 in GP 013 to 30.9 µg/L in GP012. Carbon tetrachloride was detected in the sample from GPO12 at a concentration of 1.03 µg/L (Montgomery Watson 1995b). The recently completed Record of Decision for DDJC-Tracy stated that the "chloroform and carbon tetrachloride plume appears to be emanating from an offsite source (other than DDJC-Tracy)" (Montgomery Watson, 1998b). The RWQCB requested in a December 16, 1998 letter to All-Pure that the offsite investigation of groundwater at the All-Pure facility be expanded to "determine the relationship between the All Pure Chemical site and the carbon tetrachloride/chloroform plume, and to define the extent of the plume." 1.2 Scope and Objectives The objectives of this investigation are to assess the presence and concentration of chloroform and carbon tetrachloride within the groundwater north and northwest of the site. This work plan describes the scope of work for the investigation. 2.0 Site Conditions - The site is located within the San Joaquin Valley, west of the San Joaquin River. The site covers approximately 10 acres. The site is bounded on the west by South Banta Road, on the south by agricultural lands, and by California Northern Railroad Company right-of-way along the northwest property line (Figure 1). The surrounding area consists primarily of agricultural usage, with some mixed-use light industrial and residential areas. 2.1 Regional Geology and Hydrogeology The site's location in the San Joaquin Valley overlies recent Quaternary deposits and the Tulare Formation. Recent Quaternary silt and clay alluvial deposits are predominant in the upper 30 feet of the subsurface. These shallow subsurface deposits are difficult to distinguish from the underlying deposits of the Tulare Formation. The Tulare Formation has been divided into Upper, Middle, and Lower Members in the vicinity of the site. The Upper Tulare deposits display rapid variation in grain size and consist of interbedded gravels,sands,silts,and clays. The Upper Tulare reaches a thickness Work Plan IT Corporation 2 All Pure,Tracy