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'• 18 July 2002 <br /> AGE-NC Project No 96-0254 <br /> ' Page 16 of 17 <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 on the <br /> duration and type of monitoring required <br /> ' Fate and Transport modeling may be used to demonstrate the potential for hydrocarbons to impact <br /> nearby groundwater receptors Quarterly groundwater monitoring may also be used to demonstrate <br /> ' a stable and declining ground water plume <br /> 7.0. RECOMMENDATIONS FOR REMEDIATION OF HYDROCARBON- <br /> IMPACTED SOIL <br /> ' Vadose zone soil impacted by TPH-d,TPH-g,BTEX and MTBE extends vertically to the saturated <br /> zone under the former UST and surrounding areas to an approximate depth of 10 feet bsg(Figure 3) <br /> Excavation would require the removal of a minor volume of overburden soil in the former UST and <br /> ' surrounding areas Figure 7 illustrates the approximate area of proposed excavation Because there <br /> appears to be a low feasibility for bioremediation and monitored natural attenuation,AGE believes <br /> that excavation would be most effective for remediating impacted soil at the site,Soil remediation <br /> I• methods, estimated durations and associated costs are summarized on Table 5 <br /> A Remedial Action Work Plan detailing the proposed excavation should be prepared <br /> i <br /> 8.0. RECOMMENDATIONS FOR REMEDIATION OF HYDROCARBON- <br /> IMPACTED GROUND WATER <br /> AGE believes that an in-situ method would be more effective in both cost and performance over a <br /> "pump and treat" method Both in-situ methods described in this CAP could be effective in <br /> remediating the site However,due tolimited regulatory acceptance,in-situ bioremediahonofground <br /> r water may not be the most cost-effective remedial alternative for the site, and should not be relied <br /> ` upon as the primary method for remedtatton of impacted ground water <br /> Because there appears to be a low feasibility for bioremediation and pump and treat,AGE believes <br /> that coupled with the excavation of the hydrocarbon source (impacted soil), monitored natural <br /> attenuation would be the most feasible method for remediating impacted ground water at the site <br /> ' Ground water remediation alternatives,estimated durations and associated costs, as applied to the <br /> whole site,are summarized on Table 5 <br /> IAdvanced GeoEnwonmental,Inc <br /> I <br />