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' 15 November 1995 <br /> • AGE-NC Project No 95-0142 <br />' Page 16 of 19 <br /> 7 2 5 COST <br /> Ground water extraction is usually a very costly method of ground water treatment Cost for <br />' installation of a"pump and treat" system typically ranges from $20,000 to $30,000, including the <br /> installation of one large-diameter extraction well However, once extracted, the contaminated water <br /> must be treated or disposed Treatment is highly dependant upon the concentrations of dissolved <br />' hydrocarbons in the ground water For the Stockton Plating site,the cost per gallon could be as great <br /> as $2 00, based upon the extraction/treatment of approximately 200,000 to 300,000 gallons of <br /> contaminated groundwater Costs for the entire treatment project would likely be between $200,000 <br />' and $650,000 <br />' 7 3 IN-SITU BIOREMEDIATION/BIOENHANCEMENT <br />' 7 3 1 BASIC PRINCIPLES <br /> Bioremediation involves the introduction of hydrocarbon-degrading nucrobes or supplemental <br /> nutrients to enhance naturally-occurring bacteria, through wells into the ground water The microbes <br /> degrade hydrocarbons and spread laterally(and vertically) by migration and reproduction <br />' Hydrocarbon-degrading microbes are able to metabolize hydrocarbons and assuYulate the resulting <br /> organic chemicals into biomass for reproduction and growth Typically, the light-end hydrocarbons <br /> are degraded first, followed by heavier compounds <br /> 7 3 2 NUTRIENT REQUIREMENTS AND TOXICITY <br />' The microbes require certain essential nutrients that are sometimes available to ground water If <br /> supplemental nutrients are required, which consist of nitrogen and phosphorus as ammonium <br />' phosphate in liquid phase, the quantity is usually very low However, a Waste Discharge Permit is <br /> required by the Regional Water Quality Control Board for the injection,of nutrients into ground <br /> water ' <br />' Typically, microbes utilized in bioremediation are aerobic and usually require additional oxygen to <br /> supplement dissolved oxygen concentrations in ground water Generally, several air sparging or in- <br /> well aeration sources are sufficient to provide the necessary oxygen However, in some cases the <br /> addition of hydrogen peroxide is necessary <br />