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• In the CP stem Cyclo-Purge S the air is circulated within a closed loop flow y i ? path, consisting of VOC removal equipment at the surface (up to 98% removal), and well casing leading to and from the subsurface zone of contamination. The device used for contaminant removal is a heat pump, which simultaneously condenses the saturated VOC vapor mixture extracted from the ground and reheats the treated air which is returned to the subsurface zone of contamination or groundwater. The elevated temperature of the injected air enhances the rate of VOC removal it (evaporation) from the soil Metal well-screens are installed exactly at the level where volatile contaminants f are located in the vadose formation The wells are used In two ways, each group consisting of one or more well-screens One group Is used for Injgglion of the heated } air into the ground, and the other group for the ex ction of the air/vapor mixture from t the contaminated zone. Tha depth of well-screens is selected by the supervising engineer or geologist to direct the flow path, such that the air will pass through the contaminated zone Heating the air enhances the rate of evaixration by providing the VOC latent heat of vaporization, while holding the temperatUre at or above ambient soil The saturated vapor is collected at the surface from the group of extraction well-screens and passed over the cold coils of the heat pump The saturated vapors are condensed and the liquid solvent is collected in a proper receiver. The residual air is then forced i through the hot coils of the heat pump by the blower (compressor). This raises the temperature, thereby decreasing the relative saturation of the VOC in the air strear".. The unsaturated air stream then flows into the "injection group" of well-screens, where the cycle is repeated at a slightly higher temperature With each cycle of air in the closed loop, the soil temperature is raised slightly until equilibrium is reached and the soil is progressively dried An optional, auxiliary heater is available to raise the temperature of the air medium even higher than is possible with the heat pump as the only heat source The auxiliary heat source greatly enhances the rate of evaporation of the contaminant and, indeed, makes practical the r9moval of semi-volatile contaminants having a higher boiling point (I e. relatively low vapor pressure). This latter option will allow remediation of contaminants formerly thought to be amenable only to relatively high cost remediation techniques, e g : excavation, and off-site disposal . 2