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f r- 27 June 1996 AGE-NC Project No. 95-0118 -; Page 15 of 23 7.3.3. INOCULATION WELLS The effective radius of influence of inoculation wells is typically 15 feet. Existing extraction wells could be used for inoculation; however additional wells might have to be installed. Temporary inoculation points could also be utilized. `.' 7.3.4. MONITORING ACTIVITIES -`3 After inoculation,the inoculation wells and ground water monitoring wells should be monitored for -' several months by periodic field measurements of organic vapors, carbon dioxide, and oxygen. Ground water samples should be collected and analyzed for petroleum hydrocarbon concentrations to monitor remediation progress. Quarterly or semi-annual monitoring activities should include the installation of soil borings to collect soil samples to monitor bacterial populations, nutrient availability and the soil remediation progress. If monitoring indicates areas of slow remediation, additional inoculations may be required. 7.3.5. DURATION f Duration(and cost)are dependent on the volume of soil to be remediated,the number of inoculation and monitoring wells and inoculation events, the average concentrations of contaminants and nutrients, and the temperature and permeability of the soil. Theoretically,the volume of soil affected l-j by the inoculation well should increase rapidly atfirst,then gradually decline as the affected volume increases and the bacteria encounter decreasing hydrocarbon concentrations toward the margins of the contaminant plume. In-situ remediation of soil at the Elkhorn site would likely require 6 to 18 Fa months to reduce hydrocarbon concentrations to acceptable levels. 7.3.6: FEASIBILITY ;.._ Results of the rinicrobiological analysis of soil samples (Appendix C) indicate that indigenous hydrocarbon-degrading bacteria constitute a high proportion of the total microbiological population at the site,however,the total microbiological population is low. The concentrations of hydrocarbon- degrading bacteria may be due to the presence of hydrocarbons in the soil providing a food source for the bacteria. The total colony units (CFUs) of the soil at the site are inadequate for bioremediation, without inoculation of additional microbes and nutrients. . i The low concentrations of nitrogen,both oxidized and reduced, low levels of biologically available carbon sources and the possible presence of high concentrations of inorganic constituents may have __J