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15 .lune 1999 <br /> AGE-NC Project No 98-0450 <br /> Page 13 of 27 <br />' 4 3 1 Principles <br /> For in-situ bioremediation, hydrocarbon-degrading bacteria are propagated in a liquid medium and <br /> ' injected into impacted soil via inoculation wells screened into the hydrocarbon-impacted soil If <br /> ground water has been impacted, strategically located ground water monitoring wells can be used <br /> for inoculation Once in the contaminant plume, the bacteria metabolize 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 material into biomass <br /> for reproduction and growth, and release water and carbon dioxide as waste products The light-end <br /> (gasoline-range) hydrocarbons are typically consumed first, followed by "heavier" hydrocarbon <br /> molecules <br /> 4 3 2 Requirements <br /> There is considerable variation in the types of microorganisms utilized by for bioremediation The <br /> microorganisms are cultured and selected for their ability to degrade select petroleum hydrocarbon <br /> compounds Bacteria and microbes in soil require certain essential nutrients which are commonly <br /> available in native soil The activity of the microorganisms often may be enhanced by inducing air <br /> ' flow and increasing oxygen concentrations into the unsaturated zone through extraction or injection <br /> wells (Bioventing), an by injecting supplemental nutrients <br /> ' Installation of an array of inoculations wells would be required within the impacted area As with <br /> SVE (Section 4 2 4), the effective radius of influence of an inoculation well is dependant on the <br /> intrinsic permeability of soil The intrinsic permeability and effective radius of influence of the <br /> ' microbial action decreases with increasing clay content Typically, a small blower is required to <br /> deliver atmospheric air and increase oxygen concentration in the subsurface through inoculation <br /> ' wells Based on soil permeability and microorganism activity, additional inoculation points may be <br /> needed to adequately address the vadose zone Furthermore, additional nutrients may be required to <br /> replace those consumed during remediation due to the high concentrations of iemaining petroleum <br /> ' hydrocarbons Also, biotoxicity to the microbes can occur due to agents such as heavy metals in the <br /> soil or to excessive concentrations of gasoline constituents <br /> ' 43 -3- Monitoring Activities <br /> ' Subsequent to initial inoculation, soil vapor from the inoculation wells would need to be periodically <br /> monitored for organic vapor, carbon dioxide, and oxygen concentrations to assess microbial activity <br /> Quarterly or semi-annual monitoring activities should include the installation of soil borings for the <br /> 1 <br /> Advanced GeoEnrironmental,Inc <br />