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1 \ 04 March 1996 AGE-NC Project No 95-0144 Page 11 of 18 4 , ' 6 3 I PRINCIPLES For this remediation method, hydrocarbon-degrading bacteria are propagated in a liquid medium, which is then infected into inoculation wells screened through the interval of impact If ground 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 and assimilate hydrocarbons, generating biomass, water and carbon dioxide as waste products- The light-end hydrocarbons are typically consumed first, followed by heavier hydrocarbon molecules ` r 6 3 2 NUTRIENT REQUIREMENTS AND TOXICITY The bacteria require certain essential nutrients, which are usually available in native soil If r supplemental nutrients are needed, the quantities and concentrations are generally low, comparable 1 to the quantities 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 microaerophilic and facultatively anaerobic, and therefore abundant oxygen is not necessary for the process to occur No exotic forms of oxygen (such as hydrogen peroxide of liquid oxygen) are needed Free oxygen does increase the metabolic rates of reaction in the bacteria A small blower delivering atinosphenc air 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 alleviated by monthly infection of distilled water to + each well ' The bacteria are also tolei ant to a wide range of soil conditions For instance, pH can range from 4 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 monitoring wells can be used for inoculation of ground water A greater radius of influence is usually obtained for ground water inoculation, since ground water mo,,ement can assist the bacterial migration However, additional ground water inoculation points would also be needed Y r