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. Ms.Devra Lewis • June 7,2001 Page 2 collected for the ongoing DDJC-Tracy groundwater investigation reported detections of chloroform and carbon tetrachloride, among other volatile organic compounds, in groundwater samples collected north of the Pioneer facility. Pond Closure Ponds 1 and 2,former wastewater storage impoundments constructed prior to 1980, were located along the northeastern boundary of the site(Figure 2). The ponds were lined with a polyvinyl chloride(PVC) liner. In addition to process wastewater, these ponds occasionally received water used to clean spills within the process area of the plant. Sediments and soil samples collected from above and below the PVC liner in August 1998 reported elevated concentrations of sodium and chloride. In October 1998 the pond sediments and liner, approximately 570 tons of material, were removed and disposed of at a Class 3 landfill. Soils remaining beneath the liner were excavated as part of the pond closure activities in 1999. The Closure Report, submitted on February 4, 2000, documented soil excavation conducted in August 1999 at Ponds 1 and 2, and subsequent trenching and soil sampling conducted in September 1999. In the course of closure activities, Pioneer excavated and disposed of approximately 3,200 cubic yards of sodium and chloride impacted soil. The RWQCB approved the Closure Report in a letter dated February 24,2000. 1999-2000 Offsite CPT Investigation The RWQCB requested in a December 16, 1998, letter that the offsite investigation at the site be expanded to"determine the relationship between the ...site and the carbon tetrachloride/chloroform plume,and to define the extent of the plume." A Groundwater Investigation Work Plan was submitted to the RWQCB on March 3, 1999, and approved in a letter from the RWQCB dated March 24, 1999. The initial investigation,completed in November 1999, included 12 cone penetrometer test(CPT)points to a depth of 100 feet below ground surface(bgs)and the collection of groundwater samples at three discrete intervals between the surface and 100 feet bgs adjacent to each of the twelve CPT locations. Chloroform and carbon tetrachloride were the only VOC constituents detected in the samples. A letter report summarizing the results of the November 1999 offsite groundwater investigation was submitted to the RWQCB on April 12,2000. The data from the investigation were considered to be insufficient to assess the northern extent of chloroform and carbon tetrachloride concentrations detected in the groundwater north and northeast of the site. The April 12, 2000 letter report recommended additional investigation consisting of three CPT points and associated groundwater sampling. The additional investigation was approved by the RWQCB in a phone call on April 28, 2000. The three additional CPT soundings and associated groundwater sampling were completed in November 2000. The report documenting the results off the offsite CPT investigation was submitted on April 30, 2001. The results of the CPT investigation indicated chloroform and carbon tetrachloride present in shallow groundwater at the Site have migrated north of the Site. Three of the 45 groundwater samples analyzed reported detections of chloroform that exceeded the California MCL of 0.100 mg/L. Nineteen of the 45 groundwater samples analyzed reported detections of carbon tetrachloride that exceeded the California MCL of 0.0005 mg/L. CPT sample locations are shown on Figure 3 and results are tabulated in Table 1. Based on the results of the offsite CPT investigation, the RWQCB issued the May 11, 2001 letter requesting installation of offsite monitoring wells. H:\Pioneer-Tracy\WorkPlan2001\workplan.doc SECOR International Inc.