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{ <br /> I <br /> _ Mr. Steven Schneider Page Two <br /> January 3, 1991 <br /> . I <br /> i <br /> The contaminated groundwater was generally encountered at <br /> approximately 45 feet below grade and appears to be confined because static <br /> water levels in the monitoring wells have risen to approximately 38 feet j <br /> below ,grade. As with the soil contamination, the plume of the <br /> contaminated groundwater is fairly well defined and is shown in Figure 3-4 <br /> of the report. <br /> Site Remediation <br /> After reviewing the results of the soil and groundwater investigation, we <br /> did a preliminary evaluation of different remediation alternatives with an <br /> eye towards filling in the excavation as an immediate objective. <br /> Although we are doing further research, we anticipate that the <br /> groundwater contamination will be pumped out of the ground through <br /> extraction wells and will be treated by an acceptable method. <br /> The two principal approaches to remediating the contamination in the soil <br /> are to ::either (1) excavate and treat (either on-site or off-site) the <br /> contaminated soil or (2) remediate the contaminated soil in place. <br /> Accordingly, after examining various remediation methods, we evaluated <br /> excavation and on-site bioremediation as the one alternative and in-situ <br /> vacuum extraction.as another alternative. <br /> After careful evaluation taking into account cost, safety, and the likelihood ` <br /> of success, we do not believe that excavatio and treating the contaminated <br />_ g g a ated <br /> soil is feasible for safety and cost reasons. In order to remove the estimated <br /> 8500 cubic yards of contaminated soil, the pit would have to be excavated to a <br /> depth of 45 feet and expanded on all sides. To excavate the contaminated <br /> soil would require excavating 35 feet of overburden representing 30,000 <br /> cubic yards of soil. Due to the extensive depth of the excavation and <br />- presence of groundwater, sheet piling would be required around the <br /> a <br /> perimeter of the excavation. All of these features increase safety risks on <br /> the site and would require corresponding safeguards to mitigate their <br /> effects, .which, in turn, would increase costs. Furthermore, an expanded <br /> excavation may require excavating through the road or excavating to the <br /> edge of the road. In either case the road could be damaged and may need to <br /> be rebuilt. Once excavated, additional problems are caused simply because <br /> of the difficulties posed in treating such large volumes of soil. Finally, we <br /> estimated the cost of the excavation and treatment by bioremediation to be <br /> prohibitively expensive. <br />