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1 <br /> t <br /> f 20 March 1996 <br /> AGE-NC Project No 95-0130 <br /> Page 13 of 23 <br />' suspended for at least two to three weeks if off-site disposal is selected, and as much as six to twelve <br /> months if on-site treatment and backfilling is selected Other disadvantages include air pollution <br />' control concerns, backfilling and compaction costs <br />' 6 2 3 ESTIMATED COSTS FOR EXCAVATION <br />' At the subject site, impacted soil could not be excavated with traditional equipment Shoring and <br /> engineering of the excavation would be required Approximately 20,000 cubic yards of soil would <br /> have to be excavated from the site, of which approximately 5,000 cubic yards would require <br />' treatment or disposal Approximately 15,000 cubic yards of excavated soil would be "clean' <br /> overburden <br /> However, since the hydrocarbon-impacted soil extends off-site, it is unlikely that all of the impacted <br /> soil can be removed, thereby leaving impacted soil as a potential source of hydrocarbon-impact on <br /> the ground water <br /> Once excavated, the soil must then be treated on-site or disposed of off-site Replacement backfill <br /> material must be imported if off-site disposal is chosen The cost for excavation, treatment/disposal <br /> and backfilling would likely be between $80 00 and $120 00 per cubic yard, depending upon <br /> concentrations of hydrocarbons Total costs for excavation and treatment or disposal could therefore <br /> approach $750,000 00 <br /> 6 3 IN-SITU BIOREMEDIATION <br /> Acceptance of this treatment technology by the regulatory community has grown in recent years, as <br /> success has been achieved at sites in California and elsewhere <br /> 6 3 1 PRINCIPLES <br /> The bioremediation method utilizes hydrocarbon-degrading bacteria, which are propagated in a liquid <br /> medium and then injected into inoculation wells screened through the interval of contamination If <br /> ground water has been impacted, strategically located ground water monitoring wells can be used for <br /> inoculation Once in the contaminant plume, the bacteria degrade the hydrocarbons and spread <br /> laterally and vertically by migrating and reproducing, creating an advancing remediation front <br /> Hydrocarbon-degrading bacteria metabolize hydrocarbons and assimilate the resulting organic <br /> chemicals into biomass for reproduction and growth, and release water and carbon dioxide as waste <br /> products The light-end hydrocarbons are consumed first, followed by heavier hydrocarbon <br />