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• 16 August 2001 <br /> r 1 <br /> AGE-NC Project No 97-0312 A - <br /> Page 17 of 20 _ <br /> ' Typical costs for monthly monitoring,of an in-situ bioremediation systern, in addition to standard <br /> r s quarterly sampling,would be approximately$1,500 00 per month Based on a one and one-half year <br /> treatment period, the total cost for in-situ bioremediation at the site would be between $70,000 00 <br />' and $95,000 00 <br /> 83 NATURAL ATTENUATION <br /> Natural attenuation, or passive bioremediation, is a remedial alternative that relies on natural <br />' processes to degrade hydrocarbons Natural attenuation is a passive remediation method and does <br /> require a high degree of site characterization and long-tern monitoring <br /> 8 3 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 to 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 /> T <br /> 8 3 2 'Duration <br />' f The duration for natural attenuation can be many years Costs for natural attenuation are generally <br /> Iower than most active remediation options However,costs can be highly variable depending on 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 /> 8 3 3 Feasibility , <br /> Quarterly ground water mamtoring may be used to monitor,and document development of a stable <br /> and declining ground water plume and declining hydrocarbon concentrations Data collected to date <br /> is not sufficient to adequately assess the feasibility of utilizing natural attenuation for site <br /> remediation <br /> Adwnced CeoEnviranmental,Inc <br />