ARCHIVED REPORTS XR0012684 - Laserfiche WebLink

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