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I31 May 2002 <br /> . AGE-NC Project No 97-0290 <br /> IPage 5 of 7 <br /> 3 4 MASS OF RECOVERED HYDROCARBONS <br /> The hydrocarbon mass (TPH-g) removed during the operating period was calculated using the <br /> following equation M =C-Q-t <br /> where M = cumulative mass recovered (kg) <br /> C = soil-vapor concentration (kg/m') <br /> Q = extraction flow rate (m'/hr) <br /> t= operational period, in hours <br /> IThe operational time was divided into at least three time periods The calculated mass of <br /> hydrocarbons removed was based on laboratory analysis of soil-vapor samples The mass of <br /> extracted hydrocarbons was calculated for each time period using average hydrocarbon <br /> concentrations of influent soil-vapor samples collected and average air flow rates Total of 230 <br /> gallons or 656 kg of gasoline (TPH-g and BTEX) were removed over the first three months of <br /> Ioperation <br /> The volume/mass calculations are attached in Appendix D <br /> 3 5 GROUND WATER GRADIENT AND FLOW DIRECTION <br /> The depths to ground water ranged from 44 78 feet to 49 85 feet below the tops of the well casings <br /> I on 25 February 2002 Groundwater elevations calculated from the well monitoring data ranged from <br /> 2 11 feet to 2 73 feet above mean sea level (msl) Ground water data is summarized in Table 4 The <br /> depth to ground water increased an average 16 feet since the previous quarter The ground water <br /> flow direction was southwest with a gradient of 0 002 ft/ft Ground water elevation contours based <br /> upon the data for the monitoring event are illustrated on Figure 3 <br /> 3 6 ANALYTICAL RESULTS OF WATER SAMPLES <br /> TPH-g was detected in water samples collected from wells MW-2, MW-4, MW-6 and MW-7 at <br /> concentrations of 3,000 micrograms per liter (µg/1), 440 µg/l, 180 µg/1 and 230 µg/1, respectively <br /> IBenzene was detected in ground water samples collected from wells MW-2 and MW-4 at <br /> concentrations of 470µg/1 and 8 0µg/1,respectively,other BTEX compounds were detected in wells <br /> I MW-2 and MW-4 at maximum concentrations of 120 µg/1 (xylene in MW-2) MTBE was detected <br /> in ground water samples MW-4 and MW-6 at concentrations of 8 3 µg/1 and 97 µg/1, respectively <br /> • Petroleum hydrocarbons were not detected in the samples collected from wells MW-5 and MW-8 <br /> IAdvanced GeoEnvironmental,Inc <br />