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' CC 10 1990- - lrpif 1H T£AN L)U[_S NC 39.3 P 1E/51 contaminated unsaturated zone at many sites Stripped air and possibly soil air are transported through the ventilator and across activated carbon, onto which the contamination is adsorbed. Thus, only clean air escapes into the atmosphere ' The cleaning effect of the well is based on reduced pressure, which reinforces the escape of volatile contamination out of the water, and as a result of the air intermixing, onto the considerable surface area of the air bubbles and onto the concentration gradient In this sense, the permanent vibration caused by the air bubbles is beneficial to the escape process of the contamination This vibration is transmuted as compression and shear waves into sediment and fluid, and presumably influences the mobility of the ' contaminants, even outside the well. The upward-streaming, stripped groundwater leaves the well casing through the upper screen section in the reach of the groundwater surface, which is lifted in a phreatic ' aquifer by the previously explained pump processes and the below-atmosphenc pressure. It then returns in an extensive circulation to the well bottom In this way, the groundwater surrounding the well is also remediated The expansion of groundwater circulation is positively influenced by the anisotropy existing in each natural aquifer possessing greater horizontal than vertical hydraulic conductivities. The artificial groundwater circulation determines the sphere of influence of a well and is overlapped ' with the natural groundwater flow (as described below) The pinhole plate and all the installations within the well casing are designed as a float so they can adjust automaticly to changing groundwater levels. For special contaminants of lower density than water, a special installation within the well is available: the contaminated water enters the well through the upper screen, is stripped there, and with help of the additional pump, leaves the well through the lower screen Both installations can be used within the same well casing. At many remediation sites, the UVB is used without an additional pump and separating plate (see Fig 2) In this case, a circulation flow occurs within the well casing, which is Produced by the strong pumping effect of the rising air bubbles. For the most part, the stripped water follows the path of least resistance and flows down to the end of the suction pipe. Thus, a water of uniform temperature and oxygen content appears in the entire well casing The water temperature is influenced by the withdrawn evaporation heat in the stripping zone and by the temperature of the fresh air. ' Depending on the groundwater temperature around the well, the water leaves the well casing through the upper screen section and contaminated water enters the UVB at the lower screen section. This occurs when the groundwater is colder than the circulation water in the well casing. On the other hand, when the water in the well is colder than the surrounding groundwater, an outer circulation occurs which is opposite to that shown m Figure 2.The water leaves the well at the lower screen section and enters it at the upper. ' Both cases, influenced by density differences of the involved water bodies, have been observed at different sites. SPHERE OF INFLUENCE AND CAPTURE ZONE OF A UVB OR UVB FIELD The extended circulation field outside the well is of special interest. In this paper numerical results of only UVB installations with additional pump and separation plate will be discussed (Fig. 1). The effect of the above-mentioned permanent vibrations, caused by the air bubbles, will not be considered. In principle, two different cases have 3 1