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' 07 December 2004 AGE-NC Project No 98-0448 ' Page 8 of 9 ' Ground water elevation data collected on 03 September 2004 did not suggest that ground water mounding was occurring due to air spargmg at the site (Figure 3) • Ground water flow direction at the site was toward the southwest, the ground water gradient ' was estimated to be approximately 0 013 ft/ft (Figure 3) • The September 2004 concentrations of petroleum hydrocarbons detected in the samples ' collected from wells MW-2 and MW-4A indicate that these wells are still within the dissolved petroleum hydrocarbon"core area"of the plume(Figure 4), lesser concentrations were detected from wells MW-1 and MW-6 and are probably representative of the south and ' west margins of the plume • Generally, an overall apparent trend of decreasing dissolved petroleum concentrations is evident in water samples collected from wells MW-1, MW-2, MW-4A and MW-4B, the trend of decreasing concentrations may be attributed to the air sparge activities being performed at wells AW-1 through AW-5 and MW-4B (Table 3) ' Between August 1998 and May 2002 (fourteen consecutive quarters), well MW-6 had detected TPH-g and/or BTEX at concentrations as high as 480 µg/1, thereafter, dissolved petroleum hydrocarbons were not detected at MW-6 between August 2002 and July 2004 • (eight consecutive quarters), however, low concentrations of TPH-g, toluene,"ethylbenzene and xylenes were once again detected at MW-6 during the September 2004 monitoring event The September 2004 TPH-g/BTEX detections at MW-6 are still within the range of hydrocarbons that were previously detected and are most likely the result of a slight shift in the margin of the ground water plume towards the south ' Based on SVE/IAS remediation data collected between 22 July 2004and 23 September 2004,AGE concludes ' The volume of hydrocarbons extracted b the SVE system was calculated to be • Y Y Y , ' approximately 71 pounds during the third quarter 2004, or equivalent to an approximate volume of 10 8 gallons of gasoline extracted (Appendix F) - - The average SVE inlet flow rate was estimated to '6&-2 3 cubic feef per rnmute(C-fin)at an ' average differential pressure of 0 23 inches of water(Table 6) • Since initiation ofthe SVE system(April 2001),the total volume ofpetroleum hydrocarbons ' extracted is estimated to be approximately 281 gallons (Table 7) • The SVE system appears to have extracted the majority of the available adsorbed soil contamination, as based on the decline trend in vapor samples collected Advanced GeoEnvironmentai,Inc ' r y