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f 1 <br /> 1. r S yl <br />' 23 June 2003 <br /> AGE-NC Project No 00-0769 <br />' Page 12 of 13 <br /> a, <br /> below mean sea level during the November 2002 monitoring event HU-1 ground water was <br /> Inferred to be flowing generally toward the south under a gradient of 0 03 ft/ft,HU-2,HU-3 <br /> and HU-4 ground water flow directions were Inferred to be towards the north and northeast <br /> at approximate gradients of 0 03 ft/ft or less (Figures 7 through 10) <br /> ' The most highly Impacted ground water appears to be located near the former UST locations, <br /> figures 11 through 15 Illustrate the lateral extent of hydrocarbon-Impacted ground water <br /> Vertically, hydrocarbon-Impacted ground water was detected in each of the screened <br /> Intervals of multi-level wells MW-4 through MW-7,only up-gradient multi-level well MW-9 <br /> and cross-gradient multi-level well MW-8 had low to non-detectable concentrations of <br /> petroleum hydrocarbon compounds <br /> • Concentrations of benzene and 1,2-DCA detected in ground water samples collected from <br /> wells MW-4 and MW-5 screened in each of the five Identified hydrogeologic units were <br /> above the DHS's Maximum Contaminant Levels(MCLs)of 1 µg/1 and 0 5 µg/l,respectively <br /> • In general,petroleum hydrocarbon concentrations in multi-level wells MW-4 and MW-5 are <br /> high in HU 1,decline in HU2 and HU3,then Increase again in HU4 and HUS At the location <br /> ofwell MW-4,the BTEX concentrations in the deepest hydrologic unit(HU5)were all above <br /> the DHS's MCL for drinking water <br /> • Ethanol was detected In ground water samples MW-4A, MW-4B and MW-4C, the source <br /> of the ethanol is unknown at this time However, the vertical and lateral extent of the <br /> contaminant is defined, and appears to be localized in the area of well MW-4 <br /> • The lateral and vertical extent of hydrocarbon-Impacted ground water has not been <br /> delineated <br />' 6.0. RECOMMENDATIONS <br />' Based on the findings of the fourth quarter 2002 site Investigation and previous Investigations,AGE <br /> recommends <br /> • Continued quarter ground water monitoring, and <br /> . <br /> Preparation of a work plan to further define the lateral k and vertical extent of hydrocarbon- <br /> impacted ground water ; <br /> 1 <br /> < 1 <br /> ` , Advanced GeoEnvironmental,Inc <br />