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.. ... . . <br /> 27 June 1996 <br /> AGE-NC Project No. 95-0115 <br /> Page 14 of 23 <br /> 7.3. IN-SITU BIOREMEDIATION <br /> Acceptance of this treatment technology by the regulatory community has grown in recent years,due <br /> to success achieved at sites in California and elsewhere. <br /> f <br /> 7.3.1. PRINCIPLES <br /> _ For in-situ bioremediation, hydrocarbon-degrading bacteria are propagated in a liquid medium, <br /> which is 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 <br /> for 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 /> c 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 /> f.==- molecules. <br /> 1.•.�'..�� <br /> F� 7.3.2. NUTRIENT REQUIREMENTS AND TOXICITY <br /> The bacteria require certain essential nutrients, which are usually available in native soil. If <br /> fj supplemental nutrients are needed, the quantities and concentrations are generally very low, <br /> corriparable to the quantities and concentrations utilized for light agricultural use. <br /> `J 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. Free oxygen increases the metabolic rates of reaction in the <br /> bacteria. A small blower delivering atmospheric air to the subsurface at a rate of 2 to 5 psi per well <br /> can be used to enhance air flow and oxygen concentrations during the process. This may result in <br /> unwanted dehydration of the soil, but dehydration- can be ameliorated by monthly injection of <br /> distilled water to each well. <br /> The bacteria are also tolerant to a wide range of soil conditions. For instance, pH can range from 4 <br /> to 9.5 and electrical conductivity has little to no effect unless sodium concentrations exceed 5% on <br /> ' a weight basis. <br /> -J <br />