process not shown such as an activated charcoal filter in order to alter the flow path of the air through the soil it has been suggested to block the flow through the upper portion of the screen thereby causing air to flow through areas more distant from the well and deeper than the soil through which air previously flowed according to the present invention the sealing device 26 of the present invention closes off the upper portion of the screened casing section 16 referring to fig2 the sealing device 26 comprises a pipe 28 having an outside diameter less than the inside diameter of the well casing in which it is to be located surrounding the pipe is a sleeve 30 of flexible air impermeable material the inside diameter of the sleeve is slightly greater than the outside diameter of the pipe so that an annulus 32 is formed between the sleeve and pipe the upper and lower ends of the sleeve are tightly secured against the pipe as by clamps or rings 34 to seal off the annulus and a tube 36 extends from the annulus to a point outside the device a pipe support 38 which may comprise a rod or cable or any other suitable support arrangement is attached to the upper end of the pipe as by bolts or pins 40 to enable the device to be raised or lowered by a line referring to fig3 in practice the device is introduced to the well through the upper end of the casing 14 and is lowered by line 42 to a point adjacent the portion of the casing screen to be sealed the line 42 extends to the surface through a rubber stopper 44 or.