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11 April 2001 <br /> AGE-NC Project No 95-0143 <br /> Page 5 of 6 <br /> reports(MAI sample Nos 498375 50566, 55237, 56314 and 57076) and chain-of-custody forms are <br /> included in Appendix C <br /> 3 5 MASS OF HYDROCARBONS REMOVED <br /> A total of approximately 10,969,344 cubic feet of soil vapor was extracted from the site between 01 <br /> October 2000 and 31 December 2000 Approximately 70 kilograms, or 25 2 gallons, of gasoline <br /> were removed from the site during the same time period Calculations for the mass of hydrocarbons <br /> removed are included in Appendix E <br /> 4.0. SUMMARY/CONCLUSIONS <br /> Based upon data collected from the site, AGE concludes <br /> • Ground water elevation decreased approximately 1 13 feet between August 2000 and <br />� .� November 2000 Ground water elevation was within the screened interval of MW-17 and the <br /> five vapor extraction wells, but above the screened interval of the other eight monitoring <br /> wells The exposed portion of the screened interval in the five vapor extraction wells was <br /> within a silty layer and dust above a sandy layer The inferred ground water flow direction <br /> remains variably toward the north to northeast at the site <br /> • Petroleum hydrocarbons were detected in four of the nine wells sampled at concentrations <br /> ranging from 780 pLg/1 (MW-7) to 110,000 �ig/l (MW-3) Measurable free product was not <br /> encountered during the November 2000 monitoring event Fuel oxygenates were not detected <br /> in ground water samples collected during the November 2000 monitoring event Only minor <br />' concentrations (less than 7 µg/1) of DIPE and TBA have been detected since monitoring <br /> began in 1997 <br />' • TPH-g was detected at an average concentration of 103 µg/l over the quarter m the soil vapor <br /> samples from the intake of the SVE unit Significant decreases in soil vapor concentrations <br /> have occurred since early April 2000 The drop in soil vapor concentrations coincides with <br />' an increase in ground water elevation Historically,average depth to ground water at the site <br /> has been well below the elevation of the SVE's horizontal extraction wells (approximately <br />' 13 feet bsg) During the May 2000 ground water monitoring event, average depth to ground <br /> water was 13 14 feet bsg m MW-9, MW-14 and MW 15, the closest monitoring wells to the <br /> northern horizontal well field Elevated ground water levels appear to degrade the <br />' effectiveness of the horizontal vapor extraction system Additionally, the exposed screened <br /> intervals of the vertical extraction wells were within a sandy to clayey silt layer, the <br /> characteristics of which, combined with the high ground water elevation, may limit the <br /> Advanced GeoEnvironmental,Inc <br /> 1 <br />