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' 26 February 2004 AGE-NC Project No 98-0448 ' Page 5 of 10 ' The rebound response test was initiated at the site on 29 December 2003 by collecting baseline field vapor measurements at the well-heads of VW-1 through VW-5, MW-4A and from the SVE remediation system influent Each field measurement was collected in a Tedlar bag using a hand air- vacuum pump,and measured with an OVA equipped with a photo-ionization detector(PID Thermo Environmental 580B, 10 0 eV,calibrated to isobutylene) Field vapor measurements are summarized in Table 7 Following collection of field vapor measurements,the SVE/LAS remediation system was ' shut-down, and ground water samples collected from wells MWA, MW-2, MW-4 (A & B) and MW-6 (Fourth Quarter 2003 ground water monitoring event) ' On 28 January 2004,ground water samples were collected from wells MW-1,MW-2,MW-4(A and B) and MW-6 Thereafter, the SVE/IAS remediation system was re-started, and field vapor measurements collected at the well-heads of VW-1 through VW-5, MW-4A and from the SVE ' remediation system influent Each field measurement was collected in a Tedlar bag using a hand air- vacuum pump, and measured with an OVA Field vapor measurements are summarized in Table 7 5 0. FINDINGS ' • AGE determined ground water flow direction and gradient from the field data collected on 29 December 2003 and on 28 January 2004,the contaminant impact to ground water was assessed from ' the laboratory data From field data collected at the SVE remediation system between 09 October and 29 December ' 2003, AGE determined the average TPH-g concentration and the average flow rate and calculated the approximate mass and volume of hydrocarbons removed ' 5 1 GROUND WATER ELEVATION AND GRADIENT ' Between December 2003 and January 2004, the depths to ground water were measured at between 18 74 and 21 46 feet below the tops of the well casings(Table 2) The December 2003 ground water elevations at the site were calculated to be between 8 99 feet (MW-7) and 12 05 feet (MW-4B) ' below mean sea Ievel,the January 2004 ground water elevations were calculated to be between 9 95 feet(MW-7) and 11 81 feet(MW-4B)below mean sea level(Table 2), ground water elevations are depicted in Figures 3 and 4 Generally, ground water elevation at the site increased an average 0 38 ' feet between the September 2003 and the December 2003 ground water monitoring events The December 2003 ground water flow direction at the site was inferred to be southwest, at an approximate gradient of 0 017 ft/ft (Figure 3), the January 2004 ground water flow direction was . inferred to be southwest, at an approximate gradient of 0 011 ft/ft (Figure 4) Advanced Geo Environmental,Inc