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12 September 2002 <br /> AGE-NC Project No 95-0137 <br /> ' Page 6 of 8 <br /> where M= cumulative mass recovered (kg) <br /> C = soil-vapor concentration (kg/m-) <br /> Q= extraction flow rate (m3/hr) <br /> ' t= operational period, in hours <br /> The estimated mass of hydrocarbons removed was based on laboratory analysis of soil-vapor <br /> samples, the flow rate and operational time The operational time for the two quarters was divided <br /> into six time periods The mass of extracted hydrocarbons was calculated for each time period using <br /> average influent soil-vapor sample hydrocarbon concentrations and average air flow rates The <br /> ' operational results are summarized on Table EYP 1b,4 <br /> A total of 30 66 gallon, or 87 2 kg hydrocarbons as gasoline removed and destroyed by the SVE <br /> ' network between 13 December 2001 and 13 June 2002 The volume and mass calculations are <br /> attached in Appendix C <br /> 3 4 GROUND WATER GRADIENT AND FLOW DIRECTION <br /> ' The elevation of ground water in each well was calculated by subtracting the depth to ground water <br /> from the relative well casing elevations of monitoring wells MW-1 through MW-5 (Table 2) <br /> i <br /> 3.4 1 First Quarter 2002 <br /> 1 � <br /> Depths to ground water during February ranged from 19 25 to 20 23 feet below the well casing tops <br /> The relative ground water elevations ranged from 79 25 feet to 79 35 feetincreasing an average of <br /> ' 0 8 feet over the fourth quarter 2001 A contoured map of ground water elevations infers a ground <br /> water depression at the remediation area(Figure 3), ground water appears to be near equal-gradient <br /> north and east of the remediation area, with an average gradient of 0 001 feet/feet The hydraulic <br /> ' gradient may be slightly steeper west of the former UST and remediation area (Figure 3) <br /> 4� <br /> ' 3 4 2 Second Quarter 2002 A-1��1 <br /> V r <br /> Depths to ground water during June ranged from 2040 to 21 28 feet below the well casing tops The <br /> ' relative ground water elevations ranged from 78 "feet to 78 30 feet, decreasing an average of <br /> 1 1 feet over the first quarter A contoured map of ground water elevations infers a trough-shaped <br /> water table at the remediation area,extending towards the sc theast(Figure 4),ground water appears <br /> ' to be near equal-gradient north and east of the remediation area, with an average gradient of <br /> 0 001 feet/feet The hydraulic gradient may have been slightly steeper west of the former UST and <br /> ' remediation area (Figure 4) <br /> Advanced GcoEnvironmcntal,Inc <br />