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15 June 1999 <br /> AGE-NC Project No 98-0450 <br />' Page 16 of 27 <br /> attenuation Periodic soil vapor monitoring would be required for the duration of the remediation <br />' Additionally, monitoring activities would include the installation of soil borings for the collection <br /> of confirmatory soil samples to verify the effectiveness of the alternative <br /> 4 4 3 Feasibility <br /> Although it is difficult to determine the feasibility of natural attenuation, fate and transport modeling <br /> may be used to determine the probabilities of hydrocarbon-impacted soil affecting ground water and <br /> migration to potential receptor sites Where ground water has already been impacted, fate and <br /> transport modeling may also be used to evaluate the migration and dilution of hydrocarbons Under <br /> current site conditions, natural attenuation is not a feasible remedial alternative for the contaminant <br />' concentrations and the perceived environmental receptors Typically, natural attenuation is a viable <br /> remedial alternative once active remediation methods are not longer remedially or cost effective <br /> 4 4 4 Duration <br /> Natural attenuation is a slow process that can take more than 30 years for the hydrocarbon plume to <br /> reach levels comparable to those achieved by active remediation methods The duration required fol <br />' natural attenuation is prohibitive as a viable remediation alternative for the site at this time <br /> 4 4 5 Estimated Cost <br /> It is likely that some additional assessment, including additional laboratory analysis of soil samples <br /> 1 and/or confirmation soil sampling would be required to monitor and verify natural attenuation <br /> Furthermore,a long-term monitoring program,perhaps exceeding 25 years,would be required Costs <br /> for natural attenuation can be significantly lower than the active remediation options However, <br /> additional characterization costs and periodic monitoring costs would accumulate over time and <br /> could potentially be significant depending on the duration and type of monitoring requirements <br />' Generally, the initial cost to evaluate contaminant fate and transport as well as installation of <br /> monitoring wells would range from $10,000 to $30,000 Monitoring and reporting costs for natural <br />' attenuation would range from$5,000 to$10,000 annually Collection and evaluation of conf rmatoiy <br /> soil samples would cost from$5,000 to$15,000 The total cost of natural attenuation for the duration <br /> (10 to 25 years) is estimated to range from $65,000 to $295,000 <br /> 1 <br /> • <br /> 1 <br /> Advanced CeoEmLronmental,Inc <br />