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i I18 February 1997 AGE-NC Project No 95-0104 Page 12 of 22 concentrations 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 I6 3 5 DURATION Duration(and cost) are dependent on the volume of soil and water 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 of the inoculation 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 compositions typically takes between 18 and 36 months b 3 6 FEASIBILITY No feasibility studies for in-situ bioremediation have been performed at the site If bioremediation is � C� chosen as the method of remediation, soil samples should be collected and analyzed for physicochemical properties The results will be used to evaluate the need for parameter adjustment, if necessary, to facilitate effective biodegradation Due to the high concentrations of hydrocarbons, additional nutrients may be required to replace those consumed during remediation 6 3 7 ESTIMATED COSTS FOR IN-SITU BIOREMEDIATION The cost for in-situ bioremediation will vary, depending upon the volume of inoculant required and the number of remediation wells to be inoculated Generally, the initiation cost for in-situ bioremediation will range from $35,000 to $75,000 Weekly and monthly monitoring generally costs between $10,000 to $20,000 annually, soil probings to monitor bioremediation progress typically averages $5,000 to $10,000 annually Total costs for bioremediation of soil at the subject site is estimated to be between $55,000 and $106,000 00 64 NATURAL ATTENUATION Natural attenuation, or passive bioremediation, is a remedial alternative that relies on natural processes to degrade hydrocarbons Natural attenuation is not an "inactive" remediation method and does require specific characterization and long-term monitoring