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6A� 27 December 1996 <br /> AGE-NC Project No 95-0143 <br /> Page 9 of 19 <br /> number of sites in California and elsewhere <br /> 5 3 1 PRINCIPLES <br /> For in-situ bioremediation, hydrocarbon-degrading bacteria are propagated in a liquid medium, <br /> which is then infected 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 metabolize and therefore degrade <br /> hydrocarbons and spread laterally and vertically by migrating and reproducing, creating an <br /> 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 typically consumed first, followed by "heavier ' <br /> hydrocarbon molecules <br /> 5 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 by different remediation consultants for <br /> bioremediation The bacteria are cultured and selected for their ability to degzade 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 two to five cfm per <br /> well can be used to enhance air flow and oxygen concentrations during the process This may result <br />' in unwanted dehydration of the soil, but dehydration can be ameliorated by monthly infection 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 or no effect unless sodium concentrations exceed 5% on <br /> a weight basis <br />