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Mr.Michael Infurna,SJCEHD April 7,2006 Well Installation Work Plan Palisades Station No. 835, Stockton,CA Page 3 Previous Environmental Investigations Six groundwater monitoring wells (MW-1 through MW-6), and 10 exploratory soil borings (B-1 through B-10), were completed at the site between August 1991 and February 1992. Petroleum hydrocarbons were reported in soil samples collected from borings B-6 through B-10, and in groundwater samples collected from well MW-3. A quarterly groundwater monitoring program was initiated in August 1991. Additional subsurface investigations were completed in March 1994 (wells MW-7 and MW-8), January 1995 (wells VEW-1 and VEW-2, borings SB-1 through SB-3), May 1997 (well VEW-3), and May 1999 (wells MW-9 and MW-10, borings SB-4 through SB-9) to further evaluate the extent of subsurface petroleum hydrocarbon impact. Stratus directed the advancement of 7 cone penetrometer test (CPT) borings (CPT-1 through CPT-7) in September 2005. Table 1 summarizes drilling and well construction activities completed to date. Soil boring and well locations are depicted on Figure 2 and Figure 3. Site Geology and Hydrogeology The following summarizes information from available boring logs prepared by previous consultants, and the boreholes logged by CPT. Fine grained soils are generally observed from surface grade to depths ranging from approximately 8 to 17 feet below ground surface (bgs). Predominately sandy soils, approximately 10 to 12 feet in thickness, are observed beneath these shallow fine grained soils and extend to depths ranging from approximately 20 to 30 feet bgs. Laterally continuous sandy strata, with thicknesses of approximately 5 to 12 feet, were logged by CPT at depths ranging from approximately 35 to 48 feet bgs. Silt and clay mixtures were predominately logged by CPT below these laterally continuous sandy strata, extending to approximately 80 feet bgs. Sandy soils were observed from approximately 80 to 85 feet bgs at boring CPT-6, and 80 to 94 feet bgs at boring CPT-7. The lateral or vertical extent of these deepest encountered sandy strata is not currently known. Interpreted geological relationships are illustrated in cross sections A to A' (Figure 5), and B to B' (Figure 6). The surface trace of each cross section is included on Figure 2. Depth to groundwater beneath the site has ranged from approximately 6 to 17 feet bgs (well MW-1) since monitoring was initiated in August 1991. Fine and coarser grained soils encountered at these depths appear to represent a "smear zone" for the petroleum hydrocarbon impact resulting from the variable groundwater elevations. Groundwater elevations have generally increased (approximately 10 feet between 1991 and 2005) since the initiation of monitoring. Seasonal depth to groundwater fluctuations of 2 to 5 feet annually have also generally been observed. Depth to groundwater was measured at depths ranging from approximately 6.0 to 8.5 feet bgs during the fourth quarter 2005. Northeast and southeast groundwater flow directions have predominately been observed, at consistently low groundwater gradients. Northeast groundwater flow directions are KAUSA Gasoline\0835\Work Plans\palisades835 workplan2006.doc STRATUS