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Page 6,c" ARCO muu awn <br /> The site has been recently renovated with new dispensers and tanks, which would have to <br /> be removed if excavation were attempted Operation of the site would be suspended for <br />' weeks or months while excavation took place <br /> Adequate space for spoils storage is not available <br />' 4.2 In-situ Bioremediation <br /> One alternative to excavation is m-place soil treatment using hydrocarbon-degrading bacteria <br />' This technique has the advantages of minimal disruption of site operations and relatively low <br /> overall cost Its primary disadvantages are the somewhat inconsistent results that have been <br /> achieved and the burdensome and relatively expensive implementation and monitoring activities <br /> that are often required <br /> Although in-situ bioremediation is more feasible than excavation at this site, the technique is not <br /> recommended, for the following reasons <br /> In-situ bioremediation projects are typically burdened with extensive requirements for <br /> soil, vapor, and groundwater monitoring Monitoring must be continued over a relatively <br /> long time, which can largely negate the method's advantage of low cost Typically, <br /> monitoring costs exceed $ 5,000 per quarter when the cost of confirmatory soil borings is <br /> included <br /> ' It is often difficult to deliver the bacterial mixture to the site of the contamination Due to <br /> the depth and lateral extent of soil contamination at this site, a large number of infection <br /> wells would be needed to fully affect the contaminant plume Based on recent <br /> ' experience with other sites, a well spacing of 10 to 15 feet would probably be necessary, <br /> and some wells would need to be nested so that the inoculant could be isolated within <br /> specific depth intervals <br /> Maintaining the proper moisture and oxygen ranges in the soil is commonly difficult <br /> ' Without sufficient oxygen and water, bacterial] growth and migration are diminished or <br /> prevented <br /> 4.3 Soil Vapor Extraction <br /> The third method of soil remediation that has been considered for this site is in-situ vapor <br /> ' extraction In this method, hydrocarbons are vaporized and withdrawn from the soil under a <br /> vacuum The vapors are then treated or destroyed above-ground Advantages of this technique <br /> are proven effectiveness and minimal site disruption Application of vapor extraction is limited <br /> to saes with moderate-to-high soil permeability and volatile contaminants <br /> 1 <br />