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HydroGeo Consultants Based on the drilling logs, sediments beneath the Site consist mostly of silty clay and clayey silt from the surface to approximately 65-70 feet below grade At this depth a sand layer occurs which is approximately 5 to 10 feet thick and contains various fractions of ' silt and clay Underlying the sand layer at approximately 75 feet, the section is characterized by the silty clay/clayey silt sediments typical of the upper section, to at ' least 90 feet below grade Generalized geologic cross-sections for the Site are included as Figures 3A and 3B for A-A' and B-B', respectively Groundwater was encountered at a depth of approximately 50 feet below ground surface ' in 1988 within the silty clay sediments Well MW-3 was installed to 50 feet below grade and wells MW-1 and MW-2 were installed to a depth of approximately 60 feet below ' grade Because only two wells contained significant quantities of water, the hydraulic gradient could not be measured at that time During drilling in November 1992, groundwater was encountered 80 feet below grade, , indicating a significant drop in the local water table had occurred Because of this decrease in groundwater elevation, none of the shallow monitoring wells contained ' groundwater and only wells MW-3R, MW-4, MW-5, and MW-6 were available for groundwater monitoring The static groundwater level has continued to fluctuate between 1992 and present Results of quarterly monitoring show a steady rise of the water table ' through 1993 and 1994 The hydraulic gradient has generally been 0 001-0 003 to the east through this period During drilling in 1995, groundwater was encountered at a depth of approximately 60 feet below grade The hydraulic gradient was measured to be about 0 003 to the northeast During the I" Quarter 2002, depth to groundwater beneath the Site ranged from 42 80 ' feet below grade in monitoring well MW-5 to 44 79 feet below grade in monitoring well ' MW-6 Groundwater was estimated to be flowing towards the east with an approximate gradient ranging from 0 005 to 0 008 feet per foot 3.2 Previous Site Assessment Activities ' Hydrotech Consultants, Inc performed the initial investigation at the Site in December of ' 1987 The details of this investigation are presented in the Hydrotech report titled "Limited Subsurface Investigation, Thrifty Oil Company Station No 171, 1250 N Wilson Way, Stockton, California", dated January 7, 1988 The investigation consisted of ' advancing four exploratory borings (B1, B2, B3, 134) to depths of 20 feet below grade near the former USTs Laboratory results indicated the presence of a maximum of 1,983 mg/kg total petroleum hydrocarbons (TPH) in one soil sample at 10 feet below grade , A second assessment of the Site was conducted by Woodward-Clyde Consultants (WCC) in August, 1988 The details of this investigation are presented in the WCC report titled ' "Subsurface Assessment Report, Thrifty Oil Service Station 171, Stockton, California", dated October 6, 1988 The investigation consisted of advancing three exploratory Page 2 TOC#111 Aquifer Test and RAP Rpt '