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Campbell Taggart Inc. December 14, 1990 202/029000-390 Page 3 Low-temperature thermal strippers (LTTS) have also been used In recent years for treatment of hydrocarbon-contaminated soils, however, this technology primarily volatilizes rather than destroys the hydrocarbons. The effectiveness of a LTTS Is dependent on the volatility of the hydrocarbons and may not be suitable for oil contamination, as only 10 percent of the components may readily volatilize. The advantage of thermal treatment is that it can reduce hydrocarbon concentrations in soils to very low levels when operated under optimum conditions. The costs associated with thermal treatment are still relatively high due to the capital costs and supplemental fuel requirements of the system. An air discharge permit is required to operate an incinerator, and the permitting process is often lengthy. Many units come equipped with a liquid scrubber to cool effluent gases, remove particulates, and neutralize any acids that may be produced. Sludges are produced during scrubber operation which must ultimately be disposed of along with the ash produced during incineration. The time to remediate soils containing hydrocarbons varies depending on the type of unit utilized and the volatility of the hydrocarbons present. In general, processing rates for mobile units average one cubic yard per hour. Because of the high temperatures involved,the operation requires constant monitoring, and the potential exists for the formation of by-products from incomplete combustion. In summary,thermal treatment units have been shown to be effective at remediating contaminated soils; however, large volumes of soil are needed to financially justify this technology, operation costs are relatively high, processing and permitting time for large projects can be lengthy, and by-products are produced which require disposal. 4.3 BIOREMEDIATION Biodegradation is a natural-occurring process whereby indigenous microorganisms utilize hydrocarbons as an energy source. The microorganisms eventually break down the hydrocarbons to carbon dioxide and water. Groundwater Technology has shown that indigenous microorganisms can be stimulated to grow and degrade hydrocarbons at an increased rate when nutrients(containing nitrogen and phosphorus) and air are supplied. Because the microorganisms degrade hydrocarbons most efficiently under aerobic conditions, biodegradation Is combined with controlled aeration to induce air flow through the soil treatment cell. In the case of motor-oil, the hydrocarbon concentrations will primarily be reduced through biodegradation due to the low volatility of the oil. The duration of the project is dependent on the existing levels of hydrocarbons in the soil and the present bacteria population. The aeration of soils serves two functions: (1) contaminant volatilization,and (2) soils oxygenation. Typical landfarming techniques involve spreading the soil approximately two feet deep across a large area and periodically turning the soil to promote exposure of all the soil surface to the air. This requires a large 1J�GROUNDWATER TECHNOLOGY,INC.