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' 29 April 2005 . . AGE-NC Project No. 98-0440 '. ' Page 15 of 1.8 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 'i§;not necessary for the process:to occur.Exotic forms of oxygen(such as hydrogen peroxide)are.. ' -usually not required, but free oxygen does,increase the metabolic rates in the bacteria. Therefore a. compressed or pressurized source of delivering atmospheric air to the subsurface at a rate of at least 4 to 6 scfm per injection well can be used to enhance,air flow and•oxygen concentrations during the, process. ' For in-situ bioremediation of,the ground water, hydrocarbon-degrading bacteria are-propagated in, a liquid medium or solid',which is then_injected directly into ground water and inoculation' wells screened into ground water.°Once in the contaminant plume, the bacteria metabolize,and'therefore.r:, ' degrade hydrocarbons and spread'laterally by migrating-and reproducing, creating an advancing remediation front. :7.2.1. Nutrient Requirements and Toxicity •` The bacteria are not tolerant to a wide range of ground water conditions. For instance, pH should ' range from 6 to 8.5. In addition the ossible presence of high concentrations of pesticides or g � P p g fiunicides at the site may have a biotoxic effect on some bacteria. The microbes require certain essential nutrients that are commonly available in ground water. if supplemental nutrients are-required, such as nitrogen and phosphorus as ammonium phosphate in 'liquid phase;the quantity is usually very low.However,a Waste Discharge Permit is required'by thee. RWQCB°for the injection of nutrients into ground water. Typically,the microbes utilized,in bioremediation are aerobic and usually require additional oxygen to supplement dissolved oxygen concentrations-in ground water. Generally, several air sparging or 1 in-Well aeration,sources are sufficient to provide the necessary oxygen.-In•some cases,,addition of hydrogen•peroxide•is beneficial. '. 7.2.2. Monitorin• Activities ' After inoculation,the inoculation wells and ground water monitoring well should be monitored for 'several months by periodic field'measurements of organic vapor, carbon dioxide;'and, dissolved oxygen-concentration. Ground'-water samples ;should be collected and analyzed for petroleum ' hydrocarbons, bacterial popWations and nutrient availability. If monitoring indicates areas of slow: remediation; additional inoculum and/or nutrients may be required. Advanced GeoEnvironmentnl,Ine.