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• 16 January 2003 AGE-NC Project No. 98-0450 ' Page 7 of 8 ' hydrocarbons was calculated for each time interval using average hydrocarbon concentrations of influent soil-vapor sample data and average air flow rates. Approximately 112 kg, 247.7 lbs or 40 gallons of hydrocarbons as gasoline (TPH-g) were removed at the site between June and ' December 2002. The volume/mass calculations are attached in Appendix E. ' 4.0. DISCUSSION AND CONCLUSIONS Based on confirmation soil sampling, SVE remediation data collected between'July and December ' 2002, and the fourth quarter monitoring event, AGE concludes: • TPH-g and TPH-d were detected in confirmation soil samples collected from boring CB at ' maximum concentrations of 580 mg/kg and 800 mg/kg, respectively; prior to SVE remediation, the maximum TPH-g concentration in soil at the immediately adjacent well BMW-4 was 9,600 mg/kg (sample SB4-15). BTEX compounds and MTBE were not ' detected in boring CB 1,compared to maximum BTEX concentrations of 24 mg/kg benzene, 520 mg/kg toluene, 190 mg/kg ethylbenzene and 1,200 mg/kg xylenes and a maximum MTBE concentration of 9.2 mg/kg in adjacent, pre-SVE well BMW-4 (sample SB4-15 in ' Table 2). TBA was detected in boring CBI at a maximum concentration of 0.59 mg/kg, compared o 6.6 mg/kg in pre-SVE well BMW-4. ' • Prior to SVE remediation, TPH-g, TPH-d and BTEX compounds were detected in soil samples collected at the vapor extraction well VW-1 (SB5), at maximum concentrations of 1,800 mg/kg TPH-g, 1.7 mg/kg TPH-d, 0.021 mg/kg benzene, 7.2 mg/kg toluene,35 mg/kg ' ethylbenzene and 170 mg/kg xylenes (Table 2); in addition, MTBE and TBA were detected at maximum concentrations of 0.095 mg/kg and 0.33 mg/kg,respectively.No target analytes were detected in the immediately adjacent confirmation soil boring CB2. ' • Ground water was encountered in the monitoring wells at approximately 50 feet bsg and was inferred to have a southerly flow direction during the December 2002 monitoring event, consistent with the historical ground water flow direction. ' • The maximum hydrocarbon concentrations in ground water were detected in monitoring well BMW-4 at the former UST excavation;maximum BTEX concentrations were also detected ' in BMW-4,but at concentrations that are below the DHS' Primary Maximum Contaminant Levels (MCL) for drinking water. ' MTBE was.detected in two ground water samples (BMW-2 and MW-5) down-gradient of the former UST location (Figure 2); only sample MW-5, at a concentration of 45 µg/1, was significantly above the DHS' Secondary MCL of 5 pg/l. Trendlines plotted on a graph of MTBE concentration versus time for wells BM-W-2 and BMW-5 showed declining trends from initiation of monitoring in 1998 to the present (5/98-12/02 in Figure 4); however, the MTBE trendlines showed a more steeper decline at a better than 80% correlation from ' Advanced Geo Environmental,Inc.