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' 18 July 2002 AGE-NC Project No 96-0254 Page 9 of 17 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 scfin 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 injection of distilled water to each well The hydrocarbon-degrading bacteria are also tolerant to a wide range ofsoll 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 5 2 3 Inoculation Wells ' The effective radius of influence in soil of inoculation wells is typically 15 feet Existing monitoring wells can be used for inoculation of the smear zone as wcll as ground water,but the inoculum will tend to go to the bottom of a monitoring well and pass into the saturated ground water zone from the annular space near the bottom Although a greater radius of influence is usually obtained for ground water inoculation, since ground water movement can assist the bacterial migration, additional inoculation points would be needed for In-situ soil treatment of the vadose zone,utilizing temporary '• Inoculation points or soil borings 5 2 4 Monitoring Activities ' After inoculation,the inoculation wells and groundwater monitoring wells should bemonitoredover a period of several months through periodic field measurements of organic vapor, carbon dioxide, and oxygen concentrations Quarterly or semi-annual monitoring activities should also include the ' installation of soil borings to collect soil samples to monitor bacterial populations, nutrient availability and soil remediation progress If monitoring Indicates areas of slow remediation, additional inoculation or addition of nutrients maybe required 5 2 5 Duration tDuration(and cost) is dependent on the volume of soil and i,,rater to be remediated, the number of inoculation and monitoring wells,the average concentrations of contaminants and nutrients,and the ' temperature and permeability of the soil Theoretically,the radius of influence oftheinoculation well should increase rapidly at first, then gradually decline as the affected volume Increases and the bacteria encounter decreasing hydrocarbon concentrations toward the margins of the hydrocarbon ' plume Shorter-chain hydrocarbons are typically consumed first and longer-chain hydrocarbons later • Remediation at sites with similar soil composition typically takes between 12 and 48 months IAdvanced GwEnvimnnwnhl,Inc