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• 15 November 1995 AGE-NC Project No 95-0142 Page 11 of 19 , which is then mjected into inoculation wells screened through the interval of contamination If ground I water has been impacted, strategically located ground water monitoring wells can be used for inoculation Once in the contaminant-plume, the bacteria degrade the hydrocarbons and spread laterally and vertically by migrating and reproducing, creating an advancing remediation front Hydrocarbon-degrading bacteria metabolize hydrocarbons and assimilate the resulting organic ichemicals into biomass for reproduction and growth, and release water and carbon dioxide as waste products The light-end hydrocarbons are consumed first, followed by heavier hydrocarbon molecules 63 2 NUTRIENT REQUIREMENTS AND TOXICITY The bacteria require certain essential nutrients, which are usually available in native soil If I supplemental nutrients are needed, the quantities and concentrations are generally very low, comparable to the quantntes and concentrations utilized for light agricultural use There is considerable variation in the types of bacteria used by different remediation consultants for bioremediation The bacteria are cultured and selected for their ability to degrade petroleum hydrocarbons They are rmcroaerophnhc and facultatively anaerobic, and therefore abundant oxygen is not necessary for the process to occur No exotic forms of oxygen(such as hydrogen peroxide or hgwd oxygen)are needed Free oxygen does increase the metabolic rates of reaction in the bacteria A small blower delivering atmospheric am to the subsurface at a rate of 2 to 5 psi per well can be used ' to enhance air flow and oxygen concentrations during the process This may result in unwanted dehydration of the soil,but dehydration can be ameliorated by monthly infection of distilled water to each well ' The bacteria are also tolerant to a wide range of soil conditions For instance H can range from 4 $ , P g to 9 5 and electrical conductivity has little or no effect unless sodium concentrations exceed 5% on a weight basis ' 6 3 3 INOCULATION WELLS The effective radius of influence of inoculation wells is typically 15 feet Existing extraction wells could be used for inoculation, however additional wells would likely have to be installed Temporary inoculation points could also be utilized I