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. _ Former Beacon Station No 12419 March 18,2002 Stockton California Problem Assessment Re ort/Corrective Action Plan Ethanol was reported in initial groundwater samples at concentrations of 130 ppb in monitoring well MW-11, 610 ppb in air sparge well AS-2, and 81000 ppb in air sparge well AS-3 In subsequent sampling, no ethanol was reported in air sparge well AS-2, and the ethanol concentration in air sparge well AS-3 decreased by two orders of magnitude The source of ethanol reported in the groundwater samples is likely due to the bentonite pellets used in the construction of air sparge wells AS-2 and AS-3 The coating on the pellets, which contains ethanol, allow the pellets to drop through standing water before hydrating On the basis of soil analytical results from the air sparge well AS-2 boring, gasoline- impacted soil extends down to approximately 90 feet bsg The relatively consistent TPHg and BTEX concentrations reported in soil samples collected from the air sparge well AS-2 boring at depths of 100 to 125 feet bsg suggest that this sandy interval was below a groundwater level which stood between 90 and 100 feet bsg The gasoline constituent concentrations reported in the soil samples are likely the result of dissolved phase petroleum hydrocarbons present during the time of the low groundwater level The 0 0052 ppb xylenes (reporting limit 0 0050 ppb) reported in the soil sample collected in a sandy silt at 130 feet bsg is likely because of the drilling process Analytical data for groundwater samples coIIected from air sparge well AS-2 indicate dissolved TPHg and BTEX compounds No MTBE or other ether, alcohol or methanol oxygenates were reported in the air sparge well AS-2 groundwater sample The reported ethanol concentration is likely due to the Pel Plug bentonite pellets filter pack seal material Bentonite chips, which do not contain ethanol, were utilized in the construction of monitoring well MW-11 The ethanol concentration reported in the initial groundwater sample (130 ppb) collected from monitoring well MW-11 may be due to ethanol from the bentonite pellets used in the construction of air sparge well AS-3 The ethanol concentration decreased to 17 ppb in June 2001 419PARCAP3-02 doe 10 Project No 1419 23 HORIZON ENVIRONMENTAL INC.