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rn 04 February 2000 <br /> AGE Project No. 95-0118 <br /> Page 5 of 7 <br /> 3.3. MASS OF RECOVERED HYDROCARBONS <br /> E <br /> The hydrocarbon mass removed during the operating period was calculated using the following <br /> equation: M=C•Q•t <br /> where: M= cumulative mass recovered(kg) <br /> r'r C —vapor concentration(kg/m') <br /> Q =extraction flow rate (m /hr) <br /> t=operational period, in hours <br /> _a The operational time was divided into three time periods. Mass of hydrocarbons removed was based <br /> on laboratory analysis from collected soil-gas vapor samples. The mass of extracted hydrocarbons <br /> 1.. was calculated for each time periods using the average hydrocarbon concentrations of influent vapor <br /> samples collected and average air flow rates.A total of approximately 78.5 gallons of gasoline were <br /> calculated to have been removed between 15 September 1999 and 03 January 2000. <br /> On average,the following mass of petroleum hydrocarbons were extracted: 19.2 gallons of gasoline <br /> =' were removed between 15 September 1999 and 30 October 1999; 43.2 gallons of gasoline were <br /> removed between 01 October and, 01 November 1999; 11.1 gallons of gasoline were removed <br /> between 01 November and 06 December 1999; and 5 gallons of gasoline were removed between 06 <br /> ff December and 03 January 2000. <br /> The mass calculations are attached in Appendix C. <br /> i- <br /> 3.4. RELATIVE GROUND WATER ELEVATION AND GRADIENT <br /> The relative ground water elevation in each well was calculated by subtracting the ground water <br /> depth from the surveyed casing elevations. The depth to ground water and the relative ground water <br /> elevations are summarized in Table 1. <br /> During the final quarter sampling event,the depth to ground water from the casing tops at the site <br /> `.; ranged from 35.28 feet to 37.16 feet below well casing. The average relative ground water elevation <br /> decreased 5.3 feet over the quarter. <br /> During this monitoring event the ground water flow was directed toward the northwest in the central <br /> ` portion of the site, away from the former UST area. The gradient measured from well MW-3 toward <br /> well MW-2 was 0.005. Relative ground water elevation contours are illustrated in Figure 3. <br /> Advanced GenEnvironmental,Inc. <br /> -f <br />