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1 <br /> community has grown in recent years, due in large part to <br /> encouraging results in California and elsewhere (see Appendices D <br />' & E) . <br /> GeoAudit and its affiliates have achieved impressive results with <br />' both ex--situ and in-situ bioremediation at sites in northwestern <br /> and southern California. At the Desert Knolls Texaco site in Apple <br /> Valley, California, in-situ bioremediation of sandy soil was <br /> completed successfully in less than 2 years . Original contaminant <br />' concentrations equalled or exceeded the present concentrations at <br /> the Geweke site, but were reduced to non-detect within 14 months of <br /> initial inoculation (see Appendix D) . Ex-situ bioremediation of <br />' 3 , 000 cubic yards of soil was completed in approximately 8 months <br /> at a site in Ukiah, California (see Appendix E) . <br />' In the Waco-GeoAudit application of the method, hydrocarbon <br /> consuming bacteria are isolated and grown specifically for use at <br /> hydrocarbon-contaminated sites. These bacteria are then inoculated <br /> into vadose-zone "inoculation" wells that are screened through the <br />' contaminant plume. After inoculation, a low-pressure air source is <br /> manifolded to the wells to provide additional oxygen and accelerate <br /> the bioremediation process . <br /> Once in the ground, the bacteria consume the hydrocarbon <br /> contaminants . The light-end hydrocarbons are consumed first, <br /> I followed by heavier molecular-weight compounds. Essential nutrients <br /> are generally available in the soil and if supplements are needed, <br /> the amounts are generally very low, comparable to light <br /> agricultural use. <br /> When the bacteria reach the ground water, if no contaminants are <br /> available for consumption, they will die back to background levels . <br /> If contaminants are present , the bacteria will consume them prior <br /> to dying back. Because of the above factors, the potential <br /> effectiveness of bioremediation is high and the health risks are <br /> I low. <br /> Bioremediation requires no elaborate equipment and creates minimal <br /> site disruptions . The only equipment required is a blower unit, <br /> which can easily be housed in a small, locked box near a power <br /> source. <br /> As with vapor extraction, completion time for in-situ <br /> bioremediation projects is difficult to estimate. The time depends <br /> on the number of inoculation wells, the number of inoculation <br /> events, the rate of bacterial migration in the soil, and the <br /> suitability of the selected bacterial cultures to the particular <br /> contaminants. At the sites investigated by Waco, where sandy soils <br /> predominate, completion times of 12 to 24 months have been <br /> required. completion time in clayey soils can be longer (up to 36 <br /> months) . <br /> I 8 <br />