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Mr Michael Infurna, SJCBHD June 17, 2005 Site Investigation Work Plan Palisades Station No 835, Stockton,CA Page 3 (May 2003) naming Palisades as the primary responsible party for the subsurface petroleum hydrocarbon impact 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 Table 1 summarizes drilling and well construction activities completed to date Site Geology and Hydrogeology • Based on soil boring logs prepared by previous environmental consultants, Stratus has developed a geologic cross section illustrating interpreted geologic relationships (see Figure 5) The surface trace of this cross section is included on Figure 2 Fine grained soils are generally observed from surface grade to depths ranging from approximately 8 to 17 feet below ground surface (bgs) Sand, interbedded with silty sand, sandy silt, and clayey sand mixtures, underlie these fine grained soils, extending to depths ranging from approximately 20 to greater than 36 feet bgs, the maximum depth explored at the site Clayey soils were observed beneath these sandy strata at borings SB-7 (20 to 29 feet bgs), SB-8 (25 to 31 feet bgs), and SB-9 (30 to 36 feet bgs) Depth to groundwater beneath the site has ranged from approximately 7 to 17 feet bgs (well MW-1) since monitoring was initiated in August 1991 Groundwater elevations have generally increased (approximately 10 feet between 1991 and 2004) 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 8 5 to 11 feet bgs during the fourth quarter 2004 Northeast and southeast groundwater flow directions have predominately been observed, at consistently low groundwater gradients Given the historical groundwater flow direction, the 7-11 facility#14117 is situated immediately upgradient of the site Extent of Subsurface Petroleum hydrocarbon Impact TPHG and BTEX impact was reported in soil samples collected during site investigation and compliance soil sampling activities during the early and mid 1990's TPHG and benzene were reported at maximum concentrations of 880 milligrams per kilogram K\USA Gasohne\0835\Work Plans\pahsades835 workplan 06-17-05 doc 5TRATU5