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S+ 1 07 October 2403 AGE-NC Project No 95-0121 ' Page 5 of 7 • On two separate occasions, approximately 0 9 feet and 0 49 feet of floating petroleum ' product was encountered at soil vapor extraction well VW-1, approximately 4 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 Solinst Interface Probe Well VW-1 has a screen interval between 15 and 30 feet bsg, which is screened across the lower sand of the site aquifer, thus demonstrating the 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 ' success of the operation of the soil vapor extraction system • 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 (Figure 5) and more apparent at the top of the water table at,depths between 17 feet and 20 feet bsg 1n vapor wells VW-1 and to a lesser in vapor well VW-4 and VW-6 (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, MTBE (Table 3) The detection of 1,2-DCA • in the shallow water table suggests that the deeper wells may also be impacted with 1,2-DCA due to the sinking nature of this compound The 1,2-DCA compound will need to be fully assessed and mitigated prior to closure IThe 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 north-east of well MW-4 (Figures 4 and 5) „ In Corrective Action Plan - November 1995, dated 14 November 1995, AGE recommended implementation of soil vapor extraction in conjunction with in-situ air sparging for remediation of the petroleum hydrocarbon,Impacted soil and ground water at the site At the time the CAP was F prepared, other dissolved'petroleum treatment methods (i e ground water pump-and-treat, ozone I spargmg,air stripping)were generally not,viewed as an effective and cost efficient method of ground water remediation However, the above methods have gained more favor recently as methods to address hydrocarbon-impacted ground water due impart to improved engineering,reduced treatment costs and reduced disposal costs, where as previous technologies (air-sparging) may not be as controllable,or as effective ISince the approval ofthe'CAP in December 1995,the local and regional ground water elevation has increased significantly(approximately 10 feet) and has maintained a depth to water of near 15 feet bsg The CAP was properly designed to mitigate dissolved and adsorbed shallow contamination, with a water table level at approximately 25 to 30 feet bsg AGE believes that the sustained increase of ground water elevation has significantly decreased the potential effectiveness of SVEAAS as a S Advanced GeoEnvironmental, [nc