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i ' 01 June 1999 AGE-NC Project No 95-0137 Page 13 of 25 ' 5 3 I Principles Hydrocarbon-degrading bacteria metabolize hydrocarbons and assimilate the resulting organic t chemicals into biomass for reproduction and growth, and release water and carbon dioxide as waste products The light-end hydrocarbons are typically consumed first, followed by "heavier" hydrocarbon molecules For in-situ bioremediation, hydrocarbon-degrading bacteria are propagated in a liquid medium, which is then infected into inoculation wells screened in the interval of contamination If ground ' water has been impacted, strategically located ground water monitoring wells can be used for inoculation Once in the contaminant plume,the bacteria metabolize and degrade hydrocarbons and spread laterally and vertically by migrating and reproducing, thereby creating an advancing ' remediation front ' 5 3 2 Nutrient Requirements And Toxicity The hydrocarbon-degrading bacteria require certain essential nutrients, which are commonly available in native soil If supplemental nutrients are needed, the quantities and concentrations are generally very low,comparable 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 microaeroplulic and facultatively anaerobic, and therefore abundant oxygen is not necessary for the process to occur Exotic forms of oxygen (such as hydrogen peroxide or liquid oxygen) are usually not required Free oxygen increases the metabolic rates of reaction in the ' bacteria A small blower delivering atmospheric air to the subsurface at a rate of two to five scfm 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 hydrocarbon-degrading bacteria are also tolerant 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 1 5 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 and the smear zone However, inoculum will tend to go to the bottom of a well and pass into from the annular space near the bottom A greater radius of Advanced GeoEn%ironmental,Inc