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i r F It . 15 Novemb `er 1995 AGE-NC Project No 95-0142 ' Page 12 of 19 6 3 4 MONITORING ACTIVITIES After inoculation, the inoculation wells and groundwater monitoring wells should be monitored for several months by periodic field measur=ements 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 soil remediation progress If monitoring indicates areas of slow remediation, additional inoculations may be required 6 3 5 DURATION Duration(and cost) are dependent on the volume of soil to be remediated, the number of moculation ' and monitoring wells and inoculation events, the average concentrations of contaminants and nutrients, and the temperature and permeability of the soil Theoretically, the radius of influence of the inoculation well should increase rapidly at first, then gradually decline as the affected volume N increases and the bacteria encounter decreasing hydrocarbon concentrations toward the margins of the contaminant plume We estimate that remediation will take between 18 and 36 months I6 3 6 FEASIBILITY ' Results of the microbiological analysis of soil samples (Appendix C) indicate that populations of indigenous hydrocarbon-degrading bacteria are low at the site The low concentrations of hydrocarbon-degrading bacteria may be due to the low concentrat:ons of nitrogen, both oxidized and ' reduced, low levels of biologically available carbon sources and,the possible presence of high concentrations of metals which may have a biotoxic effect on bacteria ' For an in-situ bioremediation program at the Stockton Plating site, the soil would need to be supplemented with ammonium nitrate as well as undergo metal analysis to determine possible biotoxic sources I , 6 3 7 ESTIMATED COSTS ' 1 The cost for in-situ bioremediation will vary, depending upon the volume of inoculant required and ' the number of remediation wells to be inoculated The cost for in-situ bioremediation at the Stockton Plating site would likely range from $50,000 to $75,000 Weekly and monthly monitoring costs are generally between $10,000 and $20,000 annually Soil probes to monitor bioremediation progress ' typically average$5,000 to$10,000 annually Total costs for bioremediation of soil at the subject site `