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Ms.Margaret Lagorio, SJCEHD October 21,2003 Joe's Truck Plaza Project No. 2033-15600-01 Work Plan for Additional Site Assessment Page 3 In November 1998, Avalon advanced fifteen soil borings in the vicinity of the former northern and southern UST pits. TPHD and MTBE were reported in soil samples collected from a depth of approximately 9 feet bgs, at maximum concentrations of 200 mg/Kg and 0.064 mg/Kg, respectively. Avalon concluded that petroleum hydrocarbon impact extended to groundwater. TPHD, benzene, and MTBE were reported in grab groundwater samples at maximum concentrations of 11,000 µg/L, 16 µg/L, and 1,700 µg/L, respectively. Avalon concluded that the lateral and vertical extent of hydrocarbon impact was adequately characterized beneath the southern tank pit, but that the lateral extent of petroleum hydrocarbon impact beneath the northern tank pit had not been adequately assessed. In February 2000, Avalon installed six groundwater monitoring wells (MW-1 through MW-6). Depth to water beneath the site ranged from 6.24 to 7.26 feet bgs. Avalon d -: 7 concluded that groundwater beneath the site was impacted with TPHD, TPHG, benzene, and MTBE at maximum concentrations of 120 µg/L, 440 µg/L, 3.1 µg/L, and 1,800 µg/L, respectively. The site was subsequently placed on a quarterly groundwater monitoring program. In January 2001, Avalon conducted additional subsurface assessment activities to further evaluate the lateral extent of petroleum hydrocarbon impact to soil and groundwater in the northern half of the site and beneath the adjacent property to the north. Four soil borings were advanced along the northern border of the site, and six soil borings were advanced on the adjacent property to the north for further lateral characterization of the dissolved plume to the northeast (predominant groundwater flow direction). MTBE was reported in the grab groundwater samples collected from every boring advanced, with the maximum concentration of MTBE reported at 2,600 µg/L. Avalon concluded that the lateral extent of petroleum hydrocarbon impact to soil was adequately characterized. However, Avalon concluded that the vertical extent of dissolved hydrocarbons beneath the site, and the lateral extent of dissolved hydrocarbons to the north and northeast were not adequately characterized by this investigation. In February 2002, Avalon installed four more monitoring wells to further evaluate the vertical the lateral extent of petroleum hydrocarbon impact to groundwater. Three of these wells (MWO-1 through MWO-3) were installed on the adjacent property to the north and northeast of the study site. The fourth well (MWO-1X) was installed in the vicinity of monitoring well MW-2, but screened into a deeper horizon. Avalon concluded that the lateral extent of petroleum hydrocarbon impact to groundwater was adequately characterized to the north and northeast, but the vertical extent of dissolved petroleum hydrocarbons remained uncharacterized. P:\Joe's Truck Plaza\Work Plans\Joes workplan 102103.doc