fig1 schematically shows a well shaft 10 which was driven into a ground region 11 contaminated with hydrocarbon chloride , to a ground water region 12 . a line 13 identifies the ground water table . the wall of the well shaft is reinforced with known interrupted well pipes 14 . the upper end of the well shaft is closed with a cover 15 in an air - tight manner . a ventilator 16 is arranged on the cover 15 for producing a negative pressure in the well shaft . the air which is aspirated by the ventilator 16 from the well shaft 10 is discharged through a filter 17 into the atmosphere . under the action of the negative pressure in the well shaft 10 , the ground water table in the well shaft and the surrounding ground region is lifted in correspondence with a line region 13a . the table of the ground water inside the well shaft 10 is identified with reference numeral 13 &# 39 ;. a bell - shaped sieve plate 18 is arranged inside the well shaft 10 in the ground water 12 &# 39 ; with a distance above the ground water level 13 &# 39 ;. an air conduit 20 extends in an inner chamber 19 of the bell through the well shaft 10 . fresh air is supplied from outside through the air conduit 20 and raises through the sieve opening of the sieve plate 18 which is spaced a predetermined amount from the water table 13 &# 39 ; in form of individual air bubbles to the liquid table 13 &# 39 ;. in a cleaning region 21 of the well shaft this air entrains the volatile matter contained in the ground water 12 &# 39 ; and discharges the same . in the region which is identified in fig1 with reference numeral ii the wall of the well shaft 10 is designed differently and not provided with the conventional slotted well pipe . fig2 and 3 show this wall region in which a filter pipe 23 is inserted between the known well pipes provided with a slot bridge opening 22 . the filter pipe 23 has an inner sieve wall 24 and an outer sieve wall 25 . they are arranged at a distance from and concentrically to one another . they can be composed of metal or synthetic plastic material . the walls have a greater permeability than the adjoining well pipes 14 . the intermediate space which is formed between both sieve walls 24 and 25 is filled with a granulate 26 . as can be seen from fig3 both sieve walls 24 and 25 are supported relative to one another by radially extending webs 27 and a meander - shaped inner sieve wall 28 . at their inner upper end and their inner lower end the sieve walls 24 and 25 are reinforced by limiting rings 29 . the granulate provide for a plurality of fine capillary passages through which the ground water can flow in a laminar flow with relatively high flow speed . fig4 shows a preferable embodiment of the arrangement in accordance with the present invention . in this embodiment the bell - shaped sieve plate 18 is suspended on a floating ring 31 through chains 30 . the air conduit 20 &# 39 ; is formed as a flexible hose . between the cover 15 which closes the well shaft 10 and the floating ring 31 a hose bellows wall 32 is provided . it prevents the penetration of gases from the ground 11 above the ground water table 13 into the well shaft 10 . the raising fresh air bubbles are shown as pearl chains in the cleaning region 21 between the sieve plate 18 and the liquid table 13 of the well shaft 10 . the ground water located in the cleaning region 21 moves due to bubble induced to oscillations , upwardly together with the bubbles and then moves downwardly along the wall . a greater part of it flows outwardly through the sieve walls 24 and 25 . the vibrations improve the lateral discharge of the ground water through the capillary openings of the sieve walls 24 and 25 . a circular flow of the ground water takes place in the vicinity of the well shaft 10 , as identified in fig1 with the arrow 33 . the expansion of this circular stream into the surrounding area of the well shaft 10 can be influenced by the power of the negative pressure produced in the well shaft which is free of the ground water . in the upper third of the well shaft region 10 ; in which the ground water 12 &# 39 ; flows predominantly outward , the outflow of the ground water is especially strong in the region of the sieve walls 24 and 25 . in the lower half of the well shaft region 10 &# 39 ; in contrast , the inflow of the ground water into the well shaft is predominant . this is shown in fig4 by a pressure distribution curve 34 identified with a dash - dot line . because of this circular flow formation , an upward stream of the ground water 12 &# 39 ; from the lower region of the well shaft is produced in the interior of the well shaft 10 . fig5 shows a different embodiment of the inventive arrangement . in this embodiment , the well shaft 10 up to a sieve wall region 35 corresponds to the sieve wall region 24 / 25 of the previous embodiment . then over a lower sieve wall region 36 it is coated with water - impermeable enclosures 37 . in the region which is free from the ground water up to the upper sieve wall region 35 , double - walled water - impermeable enclosures 38 are provided . in this arrangement an inflow and a backflow of the ground water can occur only through the lower sieve region 36 , whereby the ground water circulation in the area surrounding the well shaft 10 is further increased . this arrangement is designed for a biological cleaning of the contaminated ground . an aqueous nutrient solution mixed with microbes can be supplied into an annular chamber 39 of the double - walled enclosure 38 through an upper inlet 40 . it flows to the sieve wall region 35 and there is entrained by the ground water which discharges through the sieve wall region 35 outwardly and is enriched with oxygen , to flow to the surrounding ground . before increasing the biological purification effect , the inner side of the water - impermeable wall enclosure 37 of the arrangement is provided with an electrical heating body coating 41 for heating the ground water located in the well shaft 10 . this creates a favorable temperature for the growth of the microbes . a conduit 42 connects the coating 41 with a heat source 43 . fig6 shows a further embodiment of the arrangement in accordance with the present invention . in this embodiment a nozzle body 118 is provided . its upper limiting wall 118 &# 39 ; has a plurality of nozzle pipes 126 which are distributed uniformly and at identical distances from the central air supply pipe 120 . the nozzle pipes 126 extend in the longitudinal direction of the well shaft 110 . the nozzles pipes are above the limiting wall 118 , extend through an air chamber 119 which is formed in the nozzle member 118 , and end below the air chamber 119 in the well shaft 110 filled with the ground water 112 &# 39 ;. in the region of their lower ends the nozzle pipes are provided with an outer thread 127 whereby they can be connected with extension pipes 129 by threaded bushes 128 . the walls of the nozzles pipes 126 are provided with air inlet openings 130 in the region of the air chamber 119 underneath the nozzle limiting wall 118 &# 39 ; which forms a nozzle plate . air which flows through the air inlet openings 130 from the air chamber 119 into the nozzle pipes 126 produces a suction which aspirates the ground water 112 &# 39 ; as shown by the arrow 131 . in the purification region 121 it is transported upwardly through the air chamber region 119 . reinforced circulating movement of the ground water develops through the nozzle pipes 126 in the purification region 121 of the well shaft 110 and is identified with the arrow 132 . a part of this flow is discharged outwardly in direction of the arrow 125 through the filter wall 123 , while another part moves in the direction of the arrow 134 downwardly to the nozzle member 118 . fig7 shows a further embodiment of the arrangement , in accordance with the present invention . in this embodiment the nozzle pipes 126 are formed with different lengths . a partition 136 is mounted on the longer nozzle pipes of which only one nozzle pipe is shown . the partition 136 subdivides the well shaft 110 . it is arranged on the height of a watertight ground layer 140 , under which pressurized ground water 112 &# 34 ; is collected and presses through a lower filter wall region 123 &# 39 ; of the well shaft coating into the well shaft 110 . when desired , the pressurized ground water 112 &# 39 ; is guided through the nozzle pipe 126 which extends through the partition 136 , upwardly into the purification region 121 . the long nozzle pipes 126 which are supported in the partition 136 can be closed at their lower ends , and instead lateral water inlet openings can be provided above the partition 136 . this can be done when it is desired to convey upwardly only the base water 112 &# 39 ; from the well shaft region located above the partition 136 to the purification region 121 . in the well shafts provided with the arrangement in accordance with the embodiments of fig6 and 7 , an inner ground water circulation through the purification region 121 is reinforced and simultaneously , a vertical ground water movement to the surrounding area of the well shaft is intensified . instead of the individual nozzle pipes 126 , it is also possible to provide nozzle shafts which are designed in a different manner , for example as nozzle shafts with a cross - section shaped as a hollow ring segment . it will be understood that each of the elements described above , or two or more together , may also find a useful application in other types of constructions differing from the types described above . while the invention has been illustrated and described as embodied in an arrangement for driving out volatile impurities from ground water , it is not intended to be limited to the details shown , since various modifications and structural changes may be made without departing in any way from the spirit of the present invention . without further analysis , the foregoing will so fully reveal the gist of the present invention that others can , by applying current knowledge , readily adapt it for various applications without omitting features that , from the standpoint of prior art , fairly constitute essential characteristics of the generic or specific aspects of this invention .