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1 <br /> ' 01 June 1999 <br /> AGE-NC Project No 95-0137 <br /> Page 21 of 26 <br /> ' 6 2 4 Cost <br /> Ground water extraction Is usually a very costly method of ground water treatment Costs for <br /> ' installation of a"pump and treat" system typically ranges from $20,000 to $35,000, including the <br /> installation of large-diameter extraction wells Once extracted, the contaminated water must be <br /> treated or disposed Treatment Is highly dependant upon the concentrations of dissolved <br /> ' hydrocarbons in the ground water For the Ripon Farm site, the cost per gallon could be as great as <br /> $2 based on the extraction/treatment of approximately 100,000 gallons of contaminated ground <br /> water Costs for the entire treatment project would likely be between $100,000 and $300,000 <br /> 1 <br /> 6 3 IN SITU BIOREMEDIATION/BIOENHANCEMENT <br /> ' In-situ bioremediation involves of es the introduction of hydrocarbon-degrading microbes and/or <br /> ' supplemental nutrients to enhance naturally-occurring or injected bacteria, through wells into the <br /> ground water The microbes degrade hydrocarbons and spread laterally (and vertically) by migration <br /> and reproduction <br /> There is considerable variation in the types of bacteria used by different remediation consultants for <br /> bioremediation The bacteria are cultured and selected for their ability to degrade petroleum <br /> ' hydrocarbons They are microaerophilic and facultatively anaerobic, and therefore abundant oxygen <br /> is not necessary for the process to occur Exotic forms of oxygen (such as hydrogen peroxide) are <br /> usually not required, but free oxygen does increase the metabolic rates in the bacteria Therefore a <br /> ' compressed or pressurized source of delivering atmosphene air to the subsurface at a rate of at least <br /> 4 to 6 scfm per injection well can be used to enhance air flow and oxygen concentrations during the <br /> process <br /> ' For in-situ bioremediation of the ground water, hydrocarbon-degrading bacteria are <br /> propagated In <br /> a liquid medium or solid, which is then injected directly into ground water and inoculation wells <br /> ' screened into ground water Once In the contaminant plume, the bacteria metabolize and therefore <br /> degrade hydrocarbons and spread laterally by migrating and reproducing, creating an advancing <br /> ' remediation front <br /> ' 6 3 1 Nutrient Requirements And Toxicity <br /> The bacteria are not tolerant to a wide range of ground water conditions For instance, pH should <br /> ' range from 6 to 8 5 The possible presence of high concentrations of pesticides or fumlcldes at the <br /> site may have a biotoxic effect on some bacteria <br /> Adtianeed GeoEnvironmental,Inc <br />