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Former Beacon Station No 12419 March 18,2002 Stockton California Problem Assessment Report/Corrective Action Plan 6.3 Results of Additional Site Assessment Static groundwater elevations in the new wells varied from approximately -21 feet mean sea level (msl) in air sparge well AS-2 to -25 feet msl in air sparge well AS-3, and -28 feet msl in monitoring well MW-11 Higher static groundwater elevations in the deeper-screened wells and lower static groundwater elevations in the shallower-screened wells indicate an upward potentiometric gradient Soil analytical data from the air sparge well AS-2 boring indicate generally decreasing TPHg and BTEX concentrations from 90 to 130 feet bsg Concentrations of 100 milligrams per kilogram (parts per million or ppm) TPHg and 0 16 ppm benzene were reported in the soil sample collected at 90 feet bsg Concentrations of TPHg in soil samples collected from 100 to 125 feet bsg ranged from l 8 to 8 3 ppm Concentrations of BTEX compounds displayed a similar trend with benzene concentrations ranging up to 0 16 ppm at 90 feet bsg to 0 034 ppm at 125 feet bsg No TPHg or benzene concentrations were reported in the soil sample collected from 130 feet bsg No oxygenates (including MTBE) or lead scavenger compounds were reported in soil samples collected from the air sparge well AS-2 boring No TPHg, BTEX or oxygenate concentrations were reported in soil samples from the air sparge well AS-3 boring A concentration of 0 0062 ppm 1,2-DCA (reporting limit 0 0050 ppm) was reported in the air sparge well AS-3 soil sample collected from 61 feet bsg Groundwater analytical data indicate 29,000 micrograms per liter (parts per billion or ppb) TPHg in air sparge well AS-2 and 240 ppb TPHg in monitoring well MW-1 i No TPHg was reported in groundwater collected from air sparge well AS-3 Concentrations of BTEX compounds were reported in the groundwater sample from air sparge well AS-2 only with a benzene concentration of 140 ppb and concentrations of other BTEX compounds ranging from 650 to 3I00 ppb Concentrations of TBA, 1,2-DCA and 1,2-DBA were reported in groundwater samples from air sparge well AS-2 and monitoring well MW-1 l as summarized in Table I 419PARCAP3-02 doc 9 Pr41ect No 1419 23 HORIZON ENVIRONMENTAL INC.