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07 November 2004 <br /> AGE-NC Project No 96-0232 <br /> Page 10 of 11 <br /> 4 4 1 Principles <br /> As with natural attenuation in soil, biodegradation is the most important natural attenuation <br /> mechanism for impacted ground water No additional bacteria or nutrients are added to the ground <br /> water Essential nutrients required for biodegradation are usually naturally present in the saturated <br /> zone However,where high concentrations of hydrocarbons are present,nutrients maybe consumed <br /> before hydrocarbon remediation is complete Oxygen depletion in ground water is another <br /> characteristic of passive biodegradation Natural attenuation is normally used where low <br /> concentrations of hydrocarbons are present or after completion of another method of remediation <br /> 4 4 2 Duration <br /> The duration for natural attenuation can be many, many years Costs for natural attenuation are <br /> generally lower than most active remediation options However, costs can be highly variable <br /> depending on the duration and type of monitoring required Fate and transport modeling maybe used <br /> to demonstrate the potential for hydrocarbons to impact nearby ground water receptors <br /> • <br /> 4 4 3 Feasibility <br /> No feasibility testing or studies concerning natural attenuation have been performed at the site Prior <br /> to initiation of natural attenuation, additional ground water characterization would probably be <br /> necessary at the site to demonstrate natural attenutation Fate and Transport modeling may be used <br /> to determine whether or not hydrocarbons in ground water pose a threat to area receptors <br /> MTBE concentrations are relatively high at the site (MW-8), and therefore, natural attenuation is <br /> probably not a cost-effective method of remediation <br /> 4 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 /> Advanced GcoEnvironmental,Inc <br />