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Former Beacon Station No 12419 March 18, 2002 Stockton California Problem Assessment Report/Corrective Action Plan Soil analytical results from the air sparge well AS-3 boring indicate that gasolene-impacted soil does not extend laterally northward of the soil boring SB-6 area to the area of air sparge well AS-3 and monitoring bell MW-11 The dissolved TPHg and oxygenate concentrations reported in the monitoring well MW-lI groundwater sample and the absence of gasolene constituents in the air sparge well AS-3 groundwater sample indicate the approximate northern extent of dissolved gasoline constituents in groundwater The ethanol reported in the groundwater sample collected from air sparge well AS-3 is likely from the Pel Plug bentonite because of its high concentration value and the absence of other gasoline constituents en the sample, and is localized in the vicinity of the well Utilizing fourth quarter 2001 (30 November 2001) groundwater monitoring data, a vertical potenteometrec gradient between the top of the AS-2 screened interval (approximately 123 feet bsg) and the water table in the vicinity of air sparge well AS-2 (approximately 54 feet bsg as measured in monitoring well MW-9) can be estimated from groundwater level data collected from monitoring well MW-9 and air sparge well AS-2 which are situated approximately 12 feet apart The potenteometrec elevations calculated for monitoring well MW-9 and air sparge well AS-2 were —33 46 and —32 39 feet, respectively The upward potenteometrec gradient is calculated to be approximately 0 001 The vertical potenteometrec gradient suggests that dissolved gasolene constituents will not tend to migrate downward because of differences in hydrostatic potential 7.0 PROBLEM ASSESSMENT The distribution of petroleum hydrocarbons in soil was interpreted on the basis of soil analytical data from previous investigations The distribution of petroleum hydrocarbons in groundwater was interpreted on the basis of groundwater analytical data from third quarter 2001 quarterly monitoring 419PARCAP3-42 doe l I Project No 1419 23 HORIZON ENVIRONMENTAL INC.