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' 01 October 2004 AGE-NC Project No 95-0173 ' Page 8 of 10 ' • The rapid decrease of dissolved petroleum hydrocarbon concentrations at AW-2A and AW-2B can be attributed to the ongoing air sparging activities at well AW-2B between December 2003 and June 2004 However, previous analytical ground water data has Indicated this concentration reduction may later rebound • The overall decreasing trend in hydrocarbon concentrations observed at well AW-1B may be attributed to the September, October and November 2003 IAS activities performed at ' AW-1B, furthermore, the rapid, upward movement of volatilized hydrocarbons was substantiated with the observed `spike' in the September, October and November 2003 ' influent air flow samples • Generally, an overall apparent trend of decreasing dissolved petroleum concentrations is evident in water samples collected from wells MW-1, MW-2, MW-3, MW-4, MW-6, ' AW-2A and AW-2B, the trend of decreasing concentrations may be attributed to the air sparge activities being performed at well AW-2B (Table 3) ' • A moderate increase in dissolved hydrocarbons was still evident from well AW-1 (A and B), the increase in hydrocarbon concentrations may be attributed to a `rebound' effect from the fourth quarter 2003 IAS activities previously conducted from well AW-1B ' • Previous and current laboratory results of ground water samples suggest that there is a minor MTBE- and 1,2-DCA-Impact to ground water in the areas of wells MW-2 through MW-5, IMW-9, MW-11, AW-1B and AW-2A (Tables 3 and 4) Based on SVE remediation data collected between 24 March 2004 and 22 June 2004, AGE ' concludes • The average SVE inlet vapor concentration was approximately 93 }Ig/l, the average SVE ' inlet flow rate was approximately 74 cubic feet per minute (Table 6) • The volume of hydrocarbons extracted by the SVE system was calculated to be ' approximately 9 gallons of petroleum hydrocarbons(Appendix F)during the second quarter 2004 monitoring periods (Table 7) • Since Initiation of the SVE system,the total volume of petroleum hydrocarbons extracted is a t o ,. 1 1 ll3Q 11, 110 esulilUlZu w b� apprvniiiiatCiy i,�✓c� gaiavi,o k a.avis. r� • A spike in the PID field measurements and influent SVE air samples was evident during the fourth quarter 2003 monitoring period and coincided with the operation ofIAS well AW-1B and the reconfiguration of the SVE well network from VW-1 through VW-7 to VW-1 through VW-4 SVE Wells VW-5 through VW-7 were closed at the well-heads due to only trace levels of petroleum hydrocarbons observed at these wells from PID field measurements (Table 6) However, during the first and second quarter 2004 monitoring periods, IAS well ' AW-2B was utilized and concentrations steadily declined to non-detect levels Advanced GeoEnviron mental,Inc I