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15 February 2000 <br /> AGE-NC Project No 98-0448 <br />' Page 30 of 33 <br /> i 9 4 2 Duration <br /> The duration for natural attenuation can be many years Costs for natural attenuation are generally <br />' - lower than most active remediation options However,costs can be highly variable depending nn the <br /> duration and type of monitoring required Fate and transport modeling may be used to demonstrate <br /> the potential for hydrocarbons to impact nearby ground water receptors <br /> 1 { <br /> 9 4 3 Feasibility <br /> Natural attenuation at the site has a low feasibility, the results of the microbial enumeration and <br /> physicochemical analysis in soil Indicated that hydrocarbon degrading organisms were generally <br /> inadequate to support microbial growth and bioremedial activity The analysis Indicated that <br /> biodegradation was occurring at a slow rate due to the small percentage of biodegraders. The <br /> laboratory suggested that an alternative carbon sources (I a organic debris) may be the dominant <br /> food source for native microorganisms Based on the assumption that the gasoline release occurred <br /> a minimum of 20 years ago, laboratory analysis of soil and ground water samples collected during <br /> the ongoing site investigation suggests that little apparent natural attenuation has occurred during <br /> the last 20 years <br />' 9 4 4 Estimated Costs <br />' It is likely that some additional laboratory analysis of ground water samples would be required to <br /> monitor and verify natural attenuation A long-term monitoring program, perhaps 25-years, would <br /> be Initiated Quarterly monitoring and sampling could costs between $5,000 to $15,000 annually, <br /> and report preparation could cost between $1,000 to $5,000 annually Therefore, the total cost for <br /> natural attenuation could range from $6,000 to $20,000 annually <br /> 1 10.0. RECOMMENDATIONS <br />' AGE has considered four remedial methods for hydrocarbon-impacted soil'and ground water on the <br /> subject site Consideration of site specific conditions, remedial principles, advantages and <br /> disadvantages of each remedial method and AGE's experience with each method, AGE recommends <br />' that impacted soil`and ground water at the site be addressed as described below <br /> Advanced CeoEnvironmental,Inc <br />