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18 February 1997 <br /> AGE-NC Project No 95-0104 <br />' Page 11 of 22 <br />' remediation front <br /> Hydrocarbon-degrading bacteria metabolize hydrocarbons and assinulate 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 /> 6 3 2 NUTRIENT REQUIREMENTS AND TOXICITY <br />' The bacteria require certain essential nutrients, which are usually available in native soil If <br /> supplemental nutrients are needed, the quantities and concentrations are generally very low, <br /> comparable to the quantities and concentrations utilized for light agricultural use <br /> There is considerable variation in the types of bacteria used b different remediation consultants for <br /> y <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 /> This may result in unwanted dehydration of the soil, but dehydration can be ameliorated by monthly <br /> injection of distilled water to each well <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 unless sodium concentrations exceed 5% on a weight <br /> basis <br /> I <br /> 6 3 3 INOCULATION WELLS <br /> The effective radius of influence of inoculation wells is typically 15 feet Existing monitoring wells <br /> can be used for inoculation of ground water and the smear zone A greater radius of influence is <br /> usually obtained for ground water inoculation, since ground water movement can assist the bacterial <br /> migration However, additional vadose zone inoculation points would also be needed Temporary <br /> inoculation points could also be utilized <br /> 6 3 4 MONITORING ACTIVITIES <br /> . After inoculation, the inoculation wells and ground water monitoring wells should be monitored for <br /> several months by periodic field measurements of organic vapor, carbon dioxide, and oxygen <br /> I <br />