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' 01 June 1999 AGE-NC Project No 95-0137 Page 24 of 26 ' 7.0. RECOMMENDATIONS FOR REMEDIATION OF HYDROCARBON- IMPACTED SOIL Vadose zone soil Impacted by TPH-d and TPH-g extends vertically to the saturated zone under the former UST area and extends under the building on-site Additional Impacted soil extends laterally in the saturated "smear" zone or capillary fnnge zone Excavation would require the removal of minor volume of overburden soil in the UST area, however, significant `clean' overburden soil would have to be removed to clean up Impacted soil in the surrounding capillary fringe or"smear zone" at approximately 15 to 20 feet bsg AGE believes that natural attenuation processes are too slow to rely on for Impacted ground water already in the Immediate vicinity of a domestic water well Therefore, AGE recommends that in-situ methods of remediation be considered ' Both In-situ methods described in this CAP could be effective for remediating the site SVE is effective for gasoline range hydrocarbons, but is moderately effective for diesel range hydrocarbons Diesel range hydrocarbons can be effectively addressed through bioremediation From a cost basis, ' Implementation of an in-situ bioremediation program is comparable to soil vapor extraction, although monitoring requirements, duration and limited control of the bio-technology could Increase the cost significantly AGE recommends installation of an SVE system at the site in the former UST area to address the BTEX compounds, TPH-g and lighter-end TPH-d components that are impacting the underlying ground water and posing a threat to the domestic well on the Jimco property AGE ' also recommends addressing the TPH-d impacted"smear"zone soil through enhancement of natural biodegradation through bioventing associated with sparging, which is discussed below Soil remediation methods, estimated durations and associated costs are summarized on Table 8 1 An extraction unit capable of approximately 100 scfm will be required for remediation of vadose soil in the former UST area Due to the concentration of contaminants at the site, an IC unit would be the ' most cost-effective choice An electric blower and carbon filtration system may be used during the final stages of remediation A 12 to 18 month soil remediation period can be expected Installation of an SVE syatem would include installation of soil vapor extraction wells within the contaminated ' soil plume Installation of sparge lines, which would provide oxygen for bioventing is discussed below 1 8.0. RECOMMENDATIONS FOR REMEDIATION OF HYDROCARBON- IMPACTED GROUND WATER AGE believes that an in-situ method would be more effective in both cost and performance over a ' "pump and treat" method Both in-situ methods described in this CAP could be effective in remediating the site However,due to limited regulatory acceptance in-situ bioremediation of ground water may not be the most cost-effective remedial alternative for the site, and should not be relied upon as the primary method for remediation of impacted ground water Advanced GeoEnvironmental,Inc