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— v r - d i Monitoring Well Installation Report-,Tosco(Former BP)Service Station No '11192 September 26.2001 groundwater monitoring wells (MW-1 and MW-3 through MW-7) Properties in the site vicinity are developed primarily for residential and retail use A former Shell service station was previously, located across Pershing Avenue to the cast of the subject site Six groundwater monitoring wells have been installed by,others at the former Shell site Pertinent site features are shown on Figure 2 2.2 Geology and Hydrogeology The site is situated on generally flat topography at an elevation of approximately six feet above sea r level Smith Canal is located approximately 1,300 feet south of the site and the Calaveras River is approximately 3,500 feet north of the site F Boring logs from the existing wells indicate that the site is predominantly underlain by clay and clayey sand with lesser amounts of silt, except in monitoring will MW-6, in which poorly graded sand with gravel was encountered from 25 to 40 feet north of the site (IT, 1991), The static depth to groundwater in the six existing wells was measured at 1181 to 13 14 feet below the tops of well casings on April 12, 2001 The groundwater flow direction was inferred to be to the north-northeast at an approximate gradient of 0 06 (Blaine Tech, 2001) The historical .� groundwater flow direction generally ranges from north to northeast at a gradient of 0 001 to 0 009 Soils encountered during GR's previous investigation (Installation of Geoprobes® B-1 through B-8 and Cone Penetrometer Test [CPT] boring CPT-1) consisted primarily of an overlying layer of clay existing from approximately 6 inches below ground surface (bgs) to depths ranging from 3 feet to 1 I bgs The clay is underlain by silty sand containing a high percent of fine sand In most of the Geoprobes, this layer was observed to the total explored depth In Geoprobes B-3 and B-4, a layer of well-graded sand was encounter beneath the silty sand and extend to the total explored depth Groundwater was encountered during probing at approximately 15 5 to 16 5 feet bgs The locations of B-1 through B-8 and CPT-1 are shown on the attached Figure 2 The results of the CPT boring confirm the subsurface conditions observed in the Geoprobes The _ silty sand observed Geoprobes B-1 through B-8 locations was also observed in CPT-1 from approximately 13 feet bgs to approximately 27 feet bgs From 27,to approximately 55 feet bgs an interval of fine-grained soil was encountered This fine-grained interval was interpreted by the CPT onboard computer to be clay with several smaller interbeds of silty clay and clayey silt At \ approximately 55 5 feet bgs the CPT detected an approximately one foot thick layer of sandy silt to clayey silt At 57 feet bgs the CPT probe experienced refusal and the test was terminated While advancing the groundwater sampling probe, the CPT operator, Mr David Fisch of Fisch Environmental Exploration Services, felt a change in lithology at 68 bgs, which he interpreted as being sand According to Mr Fisch, the sand interval extended to the total depth explored (75 feet bgs) (GR, 2001) 14024505-2 2