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27 December 1996 <br /> AGE-NC Project No 95-0143 <br />' Page 11 of 19 <br />' 5 3 7 ESTIMATED COSTS FOR IN-SITU BIOREMEDIATION <br /> The cost for in-situ bioremediation will vary, depending upon the volume of inoculant required and <br />' the number of remediation wells to be inoculated Generally, the initiation cost for in-situ <br /> bioremediation will range from $35,000 00 to $75,000 00 Weekly and monthly monitoring <br /> generally costs between$10,000 00 to $20,000 00 annually, soil probings to monitor bioremediation <br /> progress typically averages $5 000 00 to $10,000 00 annually Total costs for bioremediation of soil <br /> at the subject site is estimated to be between $80,000 00 and $130,000 00 <br /> 5 4 NATURAL ATTENUATION <br /> Natural attenuation, or passive bioremediation, is a remedial alternative that relies on natural <br /> processes to degrade hydrocarbons Biodegradation is the most important natural attenuation <br /> mechanism No additional bacteria or nutrients are added to the soil Essential nutrients requued for <br />' biodegradation are usually naturally present in the subsurface However, where high concentrations <br /> of hydrocarbons are present, nutrients may be consumed before hydrocarbon remediation is <br /> complete Oxygen depletion in the subsurface is another characteristic of passive biodegradation <br /> The core of a contaminant plume typically exists under anaerobic conditions and only the margins <br /> are aerobic Therefore, even though anaerobic biodegradation is much slower than aerobic <br />' biodegradation, anaerobic processes may dominate the degradation of contaminants Natural <br /> attenuation is normally used where low concentrations of hydrocarbons are present or after <br /> completion of another method of remediation <br /> The natural attenuation process is time consuming, it will take many years for the hydrocarbon <br /> plume to reach levels comparable to those of active remediation methods Costs for natural <br /> attenuation are definitely lower than the active remediation options However, the periodic costs <br /> could accumulate over time and potentially be considerable depending on the duration and type of <br /> monitoring requirements <br /> Fate and Transport modeling g ma y be used to demonstrate that hydrocarbons in soil do not pose a <br /> threat to ground water Where ground water has been impacted or has a high potential to become <br /> impacted,modeling may be used to evaluate the possibility of hydrocarbons to impact nearby ground <br /> water receptors <br />