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T 2-2 TPE's investigation are presented in their Preliminary Site Assessment Report, dated September 3, 1992 HETI installed three off-site groundwater monitoring wells (Wells MW-6, MW-7, and ' MW-8), to depths of approximately 90 feet bgs, between December 1 and 3, 1993 (Figure 2-1) Groundwater was initially encountered during this investigation at a depth of approximately 78 feet bgs Depth to groundwater on December 9, 1993, was approximately 74 feet bgs Results of laboratory analyses performed on the soil and groundwater samples collected during this investigation did not identify petroleum hydrocarbon constituents in the soil samples collected from the three soil bonngs However,TPHg and BTEX were identified, ' above the analytical method reporting limit, in the groundwater sample collected from Well MW-7. Results of HETI's investigation are presented in their Phase II Subsurface Investigation Report, dated January 20, 1994. Brown and Caldwell was contracted by E-Z Serve in July 1994, to continue the environmental investigation at this facility Brown and Caldwell completed,groundwater monitoring events on September 23 and December 9, 1994 Results of these sampling events indicate that the extent to which groundwater has been affected by TPHg and BTEX has been ' sufficiently delineated to the east and west of the Site. The analytical laboratory results of the groundwater samples collected during these and previous sampling events are summarized in Table 2-2. Analytical results of the soil samples collected from the previous site investigations presented above are summarized in Table 2-1 Geology and Hydrogeology The following information has been compiled from previous NEI, TPE, and HETI reports Regional Geology and Hydrogeology. Stockton lies in the San Joaquin Valley which is a north-south trending structure bounded by the Sierra Nevada Mountain Range to the East and the Costal Ranges to the West Within the Stockton area the valley floor consists of Quarternary age alluvial sediments deposited by the San Joaquin River and its tributaries Soil lithology in the Stockton area includes sands, silty sands, silts, clayey silts and clays. The San Joaquin River is the mayor surface drainage within the Stockton area of the. San Joaquin Valley. The river flows approximately 40 miles from its point of origin, in the central San Joaquin Valley to Suisun Bay Groundwater in the valley flows west, from the Use or disclosure of data contained on this sheet is subject to the restnctwn specified at the beginning of this document OSV 18195e%RP30RM150%10OM61MAP-Z W P5 QMS-PS410