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' 17 March 1996 AGE-NC Project No 95-0128 ' Page 7 of 8 ' 5.0. CONCLUSIONS AND RECOMMENDATIONS 51 CONCLUSIONS I' The following conclusions were drawn fiom the results of this investigation ' 0 Hydrocarbon-impacted soil within the upper vadose zone (depths of 15 feet or less) is laterally limited to the area northeast of the former UST excavation and near the northern two dispenses islands • Hydrocarbon impacted soil within the lower vadose zone (depths between 15 and 35 feet bsg) is present in the area north of MW-3, south of MW-1, east of MW-7 and east of wells MW-2 and MW-4 The greatest concentrations of hydrocarbon-impacted soil is present near well VW-1 The lateral extent of the hydrocarbon impacted vadose zone soil is depicted in Figure 5 - Hydrocarbon Impuc.ted Sod ' Hydrocarbon-impacted soil is also present below the static water level at the site • The soil samples analyzed for geotechnical parameters indicted that soil in the saturated zone I• demonstrates a low organic carbon content, and therefore lacks the ability to adsorb and retard the migration of hydrocarbons through the saturated zone Additionally, the penmeability of the saturated zone at the site is characterized by a relatively high tendency to transinit fluids Therefore, it does not appear that the lateral movement of the petrolcuni hydiocaibons dissolved in water is limited by the sediment type and distribution at the site • Natural attenuation utilizing passive bioremediation does not appear to be a viable soil ieniediation alternative for the site However, the potential feasibility of enhanced bao iennediation of the hydiocaibon-impacted soil is possible, due to the adequate chemical parameters of the soil at the site The highest concentration of dissolved hydrocarbons in ground water continues to be in the I vicinity of vapor well VW-1 However, concentrations of most analyzed hydiocarbons decreased in vapor well VW-1 between September 1996 and February 1997, most likely due to the successful removal of free product - it IS likely that well t'vi`w-7 represenrs the western edge of the dissolved plume However, it appears that dissolved hydrocarbons extend off-site north, northeast and east of the property I 52 RECOMMENDATIONS Based on the results of this investigation, AGE recommends the following • If determining the lateral extent of the off-site migration of dissolved hydrocarbons is I