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i <br /> 10 10 June 1999 <br /> AGE-NC Project No 97-0290 <br />' Page 14 of 26 <br /> I7 3 1 Principles <br /> For in-situ bioremediation, hydrocarbon-degrading bacteria are propagated in a liquid medium and <br />' infected into impacted soil via inoculation wells screened through 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 /> hydrocarbons are typically consumed first, followed by "heavier" hydrocarbon molecules <br /> 1 <br /> 7 3 2 Nutrient Requirements and Toxicity <br />' The hydrocarbon-degrading bacteria require certain essential nutrients, which are commonly <br /> available in native soil If supplemental nutrients are needed, the quantities and concentrations are <br /> generally very low, comparable to the quantities and concentrations utilized for light agriculture <br /> There is considerable variation in the types of bacteria used by different remediation consultants for <br />' bioremediation The bacteria are cultured and selected for their ability to degrade petroleum <br /> hydrocarbons They are microaerophilic and facultatively anaerobic, and therefore abundant oxygen <br /> is not necessary for the process to occur Exotic forms of oxygen (such as hydrogen peroxide or <br />' liquid oxygen) are usually not required However, free oxygen does increase the metabolic rates of <br /> reaction in the bacteria A small blower delivering atmospheric air to the subsurface at a rate of two <br />' to five cfm per well can be used to enhance air flow and oxygen concentrations during the process <br /> The bacteria are tolerant to a wide range of soil conditions For instance, pH can range from 4 to 9 5 <br />' and electrical conductivity has little or no effect on bacterial metabolism unless sodium <br /> concentrations exceed 5% on a weight basis <br /> I7 3 3 Inoculation Wells <br />' The effective radius of influence of inoculation wells is assumed to be 15 to 20 feet Existing <br /> monitoring wells can be used for inoculation of ground water and the smear zone A greater radius <br /> of influence is usually obtained for ground water inoculation, since ground water movement can <br />' assist the bacterial migration However,temporary or additional permanent inoculation points would <br /> be needed to adequately address the vadose zone <br /> I <br /> Advanced GeoEnN ironmental,Inc <br />