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0 <br /> ' GEOMATREX <br /> 4.0 CORRECTIVE ACTION ALTERNATIVES EVALUATION <br /> ' Corrective action alternatives evaluated for the affected soil and groundwater include <br /> ' • Alternative 1 -Natural attenuation of affected soil and water (including attempted free <br /> product removal and human health risk evaluation) <br /> ' + Alternative 2 -Enhanced bioremediation using air sparging and soil vapor extraction <br /> Alternative 3—Shallow excavation of affected soil in the former UST excavation area <br /> ' and off-site disposal of soil, including free phase petroleum removal and enhanced <br /> bioremediation <br /> ' 0 Alternative 4—Excavation of soil in the former UST excavation area(to 30 feet bgs) and <br /> off-site disposal of soil <br /> Alternative 5—Excavation of on-site affected soil and off-site disposal of soil <br /> Alternative 6-Complete excavation and on-site thermal desorption of soil <br /> ' • Alternative 7-Complete excavation and off-site disposal of soil <br /> ' Table 5 presents a description of each alternative and an evaluation of the site-specific effectiveness, <br /> implementability, time to achieve WQOs,and cost Detailed cost analyses used to develop the costs <br /> ' for each option are included in Appendix B <br /> We consider Alternative 1 (natural attenuation with attempted free product removal and a human <br /> ' health risk evaluation)to be the best available corrective action strategy for this site The technical <br /> facts at this site indicate that with no further action,the residual detectable"TPH" is stable and will <br /> ' remain localized and continue to attenuate naturally over time Concentrations of TPH below WQOs <br /> will likely be attained, although the time period is expected to be very long Meaningful calculations <br /> ' predicting when the WQO for TPHd and TPHg will be obtained using natural attenuation cannot be <br /> performed because initial concentrations are unknown, however this time period is expected to be <br /> decades to centuries Alternative I assumes that prior to implementation,a site specific human health <br /> ' risk assessment will be completed and that active free product removal (by pumping from two <br /> proposed extraction wells for a period of 6 months)will be attempted to confirm whether or not <br /> significant free product removal is practicable at the site <br /> ' As shown in Table 5, for all alternatives except complete excavation of all petroleum-affected soil at <br /> the site and within the site vicinity,the timeframe to achieve WQOs for TPHd and TPHg likely is <br /> very long Geomatnx attempted to develop relatively "precise"remedial time frame estimates for <br /> ' 11D0c_Safe19000s199631CAP1CAP txt doe 8 <br />