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i <br />: f <br /> 10 years or so. Therefore, replacement of an air stripper/vapor-phase GAC system with a ) <br /> liquid-phase GAC system after a 10-year service life is a viable long-range treatment scheme. <br /> The treatment system selected for cost estimating of Option B consists of air stripping <br /> followed by vapor phase GAC. <br /> Long-Term Monitoring and Contingency Plan <br /> Long-term monitoring and reporting will occur until data indicate that the site may be clean <br /> + enough to seek closure. A set of criteria will be established that will initiate a contingency <br /> plan if (1) the plume migrates beyond the compliance monitoring points, (2) constituent <br /> concentrations are not degrading at a satisfactory rate, or (3) the risk to human health <br /> increases significantly. The contingency plan will consist of more aggressive remedial <br /> intervention that may require augmentingmentin <br /> the natural rate of contaminant removal through <br /> groundwater aeration or nutrient addition. <br /> Remediation Options Evaluation <br /> The two groundwater remediation options were evaluated by considering the following <br /> } <br /> criteria: <br /> • Overall Protection of Human Health and the Environment <br /> (4 . Reduction of Toxicity, Mobility, and Contaminant Mass or Volume <br /> Short-Term Effectiveness (ability to demonstrate initial progress) <br /> • Long-Term Effectiveness (reliability) <br /> • Implementation (technical and administrative feasibility) <br /> • Cost Effectiveness <br /> t The extent to which each remediation option satisfies these criteria is summarized in <br /> Table 4-1. Cost estimates for each option are presented in Tables 4-2 and 4-3. The primary <br /> differences and similarities between Options A and B with respect to the evaluation criteria <br /> are listed below. <br /> Overall Protection of Health and the Environment <br /> Migration is controlled in either option. ' The mechanism of control is passive in. Option A <br /> and active in Option B. Option B creates a slightly greater risk of human contact with <br /> contamination. <br /> Reduction in Toxicity, Mobility, Contaminant Mass, or Volume <br /> l <br /> Reduction in toxicity and mass removal occurs with either option. Option A would produce <br /> evidence of natural biodegradation through enhanced sampling and analysis. The same <br /> natural biodegradation would occur under Option B, but without the documentation. Option <br /> B would have added removal through stripping of 1.0 gpm of groundwater. <br /> r <br /> SF010030983.DOC 4-8 <br />