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:.s <br /> A brief description of each remedial option is presented <br /> below: <br /> single-pump and dual-pump systems can be used to collect <br /> both free product and dissolved-phase hydrocarbons in <br /> ground water. In this case, a single-pump system with <br /> electrical pumps would be used since no free product is <br /> �. anticipated. Air-displacement pumps would be used in lieu <br /> of electric pumps if significant free product was expected <br /> since these pumps fill from the top and are less <br /> susceptible to material damage caused by petroleum <br /> products. In single recovery wells or well clusters, a <br /> vacuum can be applied, using regenerative, positive <br /> displacement blowers, that may induce enhanced fluid flow <br /> - to the recovery well. <br /> TrenrhPs and = ina <br /> Interceptor trenches and drains are used to recover <br /> hydrocarbon-affected ground water in a shallow water table <br /> or a perching stratum of low hydraulic conductivity. <br /> Trenches or drains can be excavated within and/or <br /> downgradient of the hydrocarbon plume. The recovery trench <br /> depth must extent several feet below the expected lowest <br /> seasonal fluctuation of the water table or to the geologic <br /> barrier which is restricting vertical migration of <br /> hydrocarbons. Liquid hydrocarbons will migrate into the <br /> ed <br /> trench under the influence of the natural or pump <br /> ground water gradient and can be extracted by pumping. Use <br /> of trenches is limited by construction costs, technical <br /> feasibility, and soil disposal factors. This ground water <br /> recovery method was determined not to be applicable at this <br /> site due to the limited extent of the dissolved-phase plume <br /> and limited accessibility downgradient of the site. <br /> Biological treatment techniques used by municipal <br /> wastewater facilities can be scaled down and applied to <br /> removal of dissolved-phase hydrocarbons from ground water. <br /> The hydrocarbons can serve as a food source for specific <br /> microorganisms that aerobically metabolize organic <br /> compounds into carbon dioxide, water, energy, and <br /> biological solids. Disadvantages of biological treatment <br /> include higher capital, operating, and maintenance costs. <br /> optimum natural-. conditions. are..required .for.successful <br /> biological treatment. The technology involves numerous <br /> variables and biological systems are more complex than <br /> other treatment systems and are more prone to operational <br /> problems. For these reasons, biological treatment was <br /> determined not to be applicable to this site. <br />