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27 June 1996 <br /> AGE-NC Project No. 95-0118 <br /> Page 16 of 23 <br /> j <br /> a biotoxic effect on bacteria. <br /> For an in-situ bioremediation program at the Elkhorn site,the soil will need to be supplemented with <br /> r: ammonium nitrate as well as to undergo additional inorganic(metals)analysis to determine possible <br /> is= biotoxic sources. Bioinoculation will be required to supplement the indigenous hydrocarbon- <br /> degrading bacteria at the site. <br /> 7.3.7. ESTIMATED COSTS <br /> The cost for in-situ bioremediation will vary, depending upon the volume of inoculant required and <br /> the number of remediation wells to be inoculated. The initial cost for in-situ bioremediation at the <br /> Elkhorn site would likely range from$30,000 to $50,000. Weekly and monthly monitoring costs are <br /> generally between $10,000 and $20,000 annually. Soil probe borings to monitor bioremediation <br /> F progress typically average $5,000 to $10,000 amivally. Based upon a two to three year treatment <br /> period, total costs for bioremediation of soil at the Elkhorn site would be between $60,000 and <br /> $.140,000, depending upon regulatory requirements for monitoring. <br /> 8.0. GROUND WATER REMEDIATION ALTERNATIVES <br /> 8.1. IN-SITU AIR SPARGING <br /> _. � In-situ air sparging (IAS) utilizes air injection to volatilize dissolved hydrocarbons and strip <br /> hydrocarbon vapors into the vadose zone, where they can be withdrawn by the vapor extraction <br /> system..Air sparging is commonly conducted concurrently with vapor extraction. <br /> 8.1.1. PRINCIPLES <br /> IAS induces the transfer of hydrocarbons from ground water to, soil gas in the vadose zone by <br /> creating a strong concentration gradient between the two regimes. Commonly, an extraction well is <br /> surrounded by specifically designed air injection wells that are screened only within the saturated <br /> zone (i.e. below.ground water). A low capacity blower connected to the injection wells forces air <br /> under pressure into the saturated zone producing air channels that strip dissolved contaminants from <br /> the ground water and rise to the sail-air-water interface. Upon reaching the unsaturated zone, the <br /> volatilized hydrocarbons are drawn into the extraction well by the subsurface air flow induced by <br /> E the vacuum potential. <br /> 7 • ' <br /> I <br />