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Work Plan for Temporary Soil Vapor Probes Boyett Petroleum-Manteca June 17, 2008 419 S. Main Street, Manteca, California The groundwater gradient in the shallow wells has been primarily to the west and southwest with an average gradient of approximately 0.007 feet per foot (ft/ft). Shallow groundwater flow has also been measured on occasion to the northwest and northeast. The groundwater gradient in the deep wells has been primarily to the southwest with an average gradient of approximately 0.009 ft/ft. However, the gradient changes to a north to northwest direction during the summer. 1.2 Summary of Soil Impact Initial soil sampling conducted at the Site in November 1996 indicated the presence of petroleum hydrocarbons in soil beneath the dispenser islands. Toluene, ethylbenzene, total xylenes and MTBE were detected at maximum concentration of 8.6 µg/L, 25 µg2, 430 µg/L and 740 µg/L all in sample Disp #3, respectively. No other petroleum hydrocarbons or fuel oxygenates/additives were detected at or above the laboratory detection limits. Approximately 44 cubic yards of soil from the demolition and retrofit activities at the Site were transported off the Site and used as fill material. Laboratory analytical results of a composite soil sample collected from the soil stockpile on October 5 1998 indicated that P p p , BTEX, TPHg and MTBE were not detected at or'above the laboratory detection limits. During the most recent soil sampling conducted at the Site (October 30, 2003) only MTBE was detected at a maximum concentration of 53 µg/l, in sample MW-11 at 26 feet bgs. No other petroleum hydrocarbons or fuel oxygenates/additives were detected at or above the laboratory detection limits. 1.3 Summary of Groundwater Impact Groundwater monitoring began at the Site in 1999. To date a total of ten monitoring wells MW-2 MW- - - ( 3, MW 4R, MW 6 through MW-11 and EW-1) are monitored and sampled on a quarterly basis. Laboratory analytical results collected from the shallow wells (MW-2, MW-3, MW-4R, MW-6, MW-7, MW-8 and MW-10) indicate that BTEX and TPHg have not been detected in any of the samples collected from these wells since December 2001 and MTBE has not been detected since December 2005. Laboratory analytical results collected _ from the deep wells (MW79, MW-11 and EW-1) indicate that BTEX and TPHg have not been detected in any of the samples collected from these wells since December 2001. MTBE has been reported at levels below Maximum Contaminant Level (MCL) in all wells since r December 2006. L. Page 2 of 8 Closure Solutions,Inc