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hydrocarbon plume. The trench must extend several <br /> feet below the expected lowest seasonal fluctuation <br /> of the water table or to the geologic barrier which <br /> is perching the hydrocarbons. Liquid hydrocarbons <br /> will migrate into the trench under the influence of <br /> the natural ground water gradient and can be <br /> collected by pumping. Pumping from the trench <br /> lowers the water table in the trench, thereby <br /> inducing free product flow to the trench. Use of <br /> trenches is limited by construction costs and <br /> feasibility and soil disposal costs. <br /> a Recovery Wellg <br /> There are three basic types of recovery well <br /> pumping systems: s}Timmer, single-pump, and <br /> dual-pump. Ski �,ming pump systems are designed to <br /> remove liquka hydrocarbons from the fluid surface <br /> in a well or sump with little or no water <br /> production. Single-pump systems produce both water <br /> and free product and require aboveground separation <br /> of fluids. In a dual--pump system, water is <br /> withdrawn at a controlled rate to create a cone of <br /> depression while a suspended hydrocarbon pump is <br /> place above the water pump to remove immiscible <br /> phase hydrocarbons. Single-pump and dual-pump <br /> A` systems can be used to both collect free product <br /> and to treat dissolved phase hydrocarbons in around <br /> water. <br /> A Q Activated Carbon Adsorption <br /> -a Activated carbon adsorption is a long proven <br /> a technology for removal of organic compounds from <br /> water. The technology is based on the principle <br /> that certain organic constituents preferentially <br /> adsorb to organic carbon. Activated carbon systems <br /> are capable of efficiently removing very low <br /> concentrations of dissolved organics from ground <br /> water including BTEX and most other gasoline and <br /> .� diesel constituents. The most common application <br /> of carbon adsorption is passing ground water under <br /> pressure through a product/water separator followed <br /> -� by two or three separate carbon treatment units. <br /> Due to high carbon costs, this method is not <br /> suitable for high levels of O?issolved hydrocarbons. <br /> Expended carbon is normally transported to a <br /> suitable recycling facility. <br /> J <br /> k 22 <br /> 3 . <br /> Vv <br /> ,S <br />