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f <br /> GOLDEN GRAIN COMPANY 45 <br /> December 21, 1989 <br /> 202/799--5045.06 <br /> 5.6 IN SITU BIODEGRADATION <br /> The remedial action of in situ biodegradation involves the <br /> development of a hydraulic control system similar to the ground- <br /> water extraction and treatment method. In addition, a site-- <br /> specific nutrient mix is developed to increase hydrocarbon- <br /> utilizing microbe populations in bath the vadose-zone soils and <br /> in the groundwater. The nutrients are introduced through the <br /> soil and into the groundwater through a well or infiltration <br /> gallery to stimulate the growth of the hydrocarbon-utilizing <br /> microbes. Oxygen is supplied through the use of an oxidizing <br /> agent or through air transfer in a soil-vent system. The advan•- <br /> tages and disadvantages of in situ biodegradation are as follows: <br /> In situ Biodegradation Advantages: <br /> 1. Treatment of both the adsorbed and dissolved <br /> hydrocarbon phases. <br /> 2. Decreases the overall length and cost of remediation <br /> project. <br /> 3. Water is infiltrated back into the subsurface, creating <br /> a closed-loop system. <br /> In situ Biodegradation Disadvantages: <br /> 1. Moderate to high initial cost to implement system. <br /> 2. Moderate operational and maintenance costs. <br /> 3. Requires continued monitoring and sampling. <br /> GROUNDWATER <br /> TECHNOLOGY,INC. <br />