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Ff- �f ,._.. r 27 June 1996 AGE-NC Project No. 95-0118 Page 20 of 23 nutrients to,enhance naturally-occurring bacteria,through wells into the ground water. The microbes degrade hydrocarbons and spread laterally (and vertically) by migration and reproduction. Hydrocarbon-degrading microbes are able to metabolize hydrocarbons and assimilate the resulting . organic chemicals into biomass for reproduction and growth. Typically, the light-end hydrocarbons are degraded fust, followed by heavier compounds. 8.3.2. NUTRIENT REQUIREMENTS AND TOXICITY k--' The microbes require certain essential nutrients that are sometimes available in ground water. If supplemental nutrients are required, such as nitrogen and phosphorus as ammonium phosphate in tliquid phase,the quantity is usually very low. However,a Waste Discharge Permit is required by the `- Regional Water Quality Control Board for the injection of nutrients into ground water. .:i Typically, the microbes utilized in bioremediation are aerobic and usually require additional oxygen to supplement dissolved oxygen concentrations in ground water. Generally, several air sparging or in-well aeration sources are sufficient to provide the necessary oxygen. However, in some cases the ` r # addition of hydrogen peroxide is necessary. �i 8.3.3. FEASIBILITY STUDIES Feasibility studies for in-situ bioremdiation of impacted ground water have not been performed at the site. 8.3.4. DURATION Cleanup durations for in-situ bioremediation will vary, depending upon specific site characteristics. However a 18 to 36 month treatment period is generally achievable. Based upon the dissolved hydrocarbon concentrations at the Elkhorn site, a cleanup period of 24 months is likely. :_ 8.3.5. COST Bioremediation of ground water can be a very cost-effective method of treatment. With little on-site > equipment required beyond the initial inoculation,the cost for in-situ bioremediation at the Elkhorn = site would be between $40,000 and$55,000.-However, monitoring costs will vary depending upon regulatory require M' encs which could significantly increase the total cost of the project.