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' 05 May 1997 <br /> i AGE-NC Project No 95-0173 <br /> Page 17 of 29 <br /> hydrocarbons are typically consumed first, followed by"heavier" hydrocarbon molecules <br /> 7 3 2 Nutrient Requirements and Toxicity <br /> The hydrocarbon-degrading bacteria require certain essential nutrients, which are usually available <br />' in native soil If supplemental nutrients are needed, the quantities and concentrations are generally <br /> very low, comparable to the quantities and concentrations utilized for light agriculture <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 degrade 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 However, free oxygen does increase the metabolic rates of <br /> reaction in the bacteria A small blower delivering atmospheric air to the subsurface at a rate of two <br /> to five cfm per well can be used to enhance air flow and oxygen concentrations during the process <br /> The bacteria are tolerant to a wide range of soil conditions For instance, pH can range from 4 to 9 5 <br />'. and electrical conductivity has little or no effect on bacterial metabolism unless sodium <br /> concentrations exceed 5% on a weight basis <br /> 7 3 3 Inoculation Wells <br />' The effective radius of influence of inoculatidn wells is generally 15 to 20 feet Existing monitoring <br /> wells can be used for inoculation of ground water and the smear zone A greater radius of influence <br />' is usually obtained for ground water inoculation, since ground water movement can assist the <br /> bacterial migration However, temporary or additional permanent inoculation points may be needed <br /> to adequately address the vadose zone <br /> 7 3 4 Monitoring Activities <br /> The inoculation wells and ground water monitoring wells should be monitored for several months <br /> after initial inoculation by collecting periodic field measurements of organic vapor, carbon dioxide, <br /> tand oxygen concentrations Quarterly or semi-annual monitoring activities should include the <br /> installation of soil borings to collect soil samples to monitor bacterial populations, nutrient <br /> availability and soil remediation progress If monitoring indicates areas of slow remediation <br />' additional inoculations may be required <br /> • <br />' Advanced GeoEmironmental,Inc <br />