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30,July 2004 AGE-NC Project No 95-0121 h Page 5 of 6 F • Due to the low gradient at the site, slight variations in ground water measurements or changes of recharge/discharge of the local ground water could greatly modify ground water flow direction • Between February 1991 and May 1998, ground water elevations at the site significantly increased from 26 feet to 7 feet belowMSL,however,ground water measurements collected between May 1998 and present have generally fluctuated very little between 7 feet and 12 feet below MSL (Table 2) • Ground water data collected from VW-1 through VW-7 are most likely representative of ' shallow ground water conditions, however, ground water data collected from wells MW-1 through MW-9 were generally between 5 and 14 feet below the ground water table, and probably yields samples more representative of deeper ground water conditions (Table 2) IDuring October 2003,approximately 0 06 feet to 0 37 feet of floating petroleum product was encountered at soil vapor extraction well VW-1 on five separate occasions, between 2 and 6 gallons of ground water was hand-bailed from the well during each Incident until the petroleum product was no longer observed and no longer detected utilizing a Sohnst Interface Probe Well VW-1 has a screen Interval between 15 and 30 feet bsg, which is screened across an upper semi-confined to confined silt/clay unit and a lower sand unit,thus demonstrating the potential for release of adsorbed hydrocarbons from the fine grained soils at approximately twenty to twenty-five feet, Into the lower sand • Free product was not detected in any other vapor wells(screened 5 to 20 feet bsg),which are exclusively screened across the upper sand unit at the site, most likely demonstrating the I success of the operation of the shallow soil vapor extraction system between February 2000 and late 2001 • The core of the dissolved petroleum hydrocarbon plume appears to be located at depths between 25 feet and 53 feet bsg in the area of deeper screened wells MW-1 through MW-4, MW-7 and more apparent at the top of the water table at depths between 17 feet and 20 feet bsg in vapor wells VW-1 and to a lesser degree in vapor well VW-4(Figure 4) A review of current and previous ground water samples suggest the core of the plume is impacted by TPH-g, TPH-d, BTEX and MTBE (Table 3) The dissolved concentrations of TPH and I BTEX compounds from the deeper screened well MW-1 has Increased since April 2000 The dissolved contaminants in the remaining deeper screened wells have not decreased over the ? same period, but rather have remained stable This Increase of the dissolved plume at well ' MW-1 is likely due to desorption of contamination from soil at the well screen's depth • The lateral and vertical extent of dissolved petroleum hydrocarbons Is not fully defined at the site, further assessment Is warranted west-northwest of well MW-7, north of MW-2 and ' northeast of well MW-4 (Figure 4) i ' Advanced CeoEnvyronmental,Inc I 4