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The Site release has resulted in a dissolved petroleum hydrocarbon groundwater water <br /> plume of limited extent. Free-phase petroleum hydrocarbons and MTBE have not been <br /> detected at the Site. The lateral extent of soil impacts has been identified. Hydrocarbon <br /> impacts in the soil appear to be limited to the area around the former product islands. The <br /> lateral extent of groundwater impacts has been identified and is constrained by data from the <br /> monitoring well array. The downgradient extent of impacts to groundwater by TPHg and <br /> be�zeng (greater than 1 ug/L) are both less than 100 ft_ Based on data from the new <br /> monitoring point, NP-1, the vertical extent of soil impacts at the Site have been identified and <br /> the impacts are comprised of a 30 foot thickness below 30 ft bfs and above 70 ft bgs. While the <br /> vertical extent of groundwater impacts have not been fully delineated, concentrations of TPHg <br /> Fl and benzene are significantly attenuated below 50 to 60 ft bgs. Field sampling evidence <br /> indicates that the impacted water at depths below 60 ft is moving in "stringers" of somewhat <br /> permeable soil interlayered with soils of lower permeability. <br /> i <br /> Based on the presence of significant thicknesses of low permeability zones as evidenced <br /> by the NP-1 boring log, the significant attenuation of concentrations with depth, and the <br /> pattern of electron acceptor data consistent with natural biodegradation, it can be reasonably <br /> r., concluded that the vertical migration is also being stabilized and remediated by natural <br /> r <br /> bioremedial processes. <br /> 4 <br /> Concentrations of petroleum hydrocarbons in groundwater have declined significantly <br /> over the 11-year period of the monitoring record. An examination of the longest record of <br /> f continuous monitoring data available at the site (9 years) shows that the groundwater plume <br /> front is stable and has not substantially moved. Multiple lines of biogeochemical data(including <br /> r dissolved oxygen, nitrates, iron (11), sulfates, and dissolved methane data) indicate that the <br /> groundwater plume is undergoing microbial mediated biodegradation. <br /> The data collected, analyzed, and evaluated in this report indicate that the Site has been <br /> adequately characterized and is self-remediating through the mechanisms of natural attenuation <br /> L• <br /> l <br />