ARRANGEMENT, APPARATUS AND METHOD FOR SOIL AIR MONITORING AND PAVING SEALING EXAMINATION

Abstract: Arrangement and apparatus for soil air monitoring, paving sealing examination and soil air extraction with regard to the soil (25) under a liquid-tight and/or gas-tight floor (27) of a location, in particular for examining the degree of liquid-tightness of such floor (27). The arrangement comprises soil air monitoring units (15), which extend from the floor surface (28) into the soil (25), which units are positioned in such a manner that their operational area preferably comprises the soil (25) under the entire floor (27), but at least those parts of the soil (25) under or in the direct vicinity of parts of the floor (27) where there is a specific risk of contaminated substances penetrating from the floor (27) into the soil (25). The interface between the floor surface (28) and a soil air monitoring unit (15) is fluid-tight, and the soil air monitoring units (15) are individually accessible from the floor surface (28) via a closable opening (41).

Description: Arrangement, apparatus and method for soil air monitoring and paving sealing examination. The invention generally relates to paving sealing examination and to soil air monitoring of the soil under a liquid-tight and/or gas-tight floor or paving of a location, which arrangement comprises soil air monitoring units and air supply units. In order to prevent contamination of the soil and the ground water by pollutants such as carbohydrates, national and international regulations prescribe that measures be taken, such as the provision of 1 iquid-tight and/or gastight floors (hereinafter called fluid- tight floors) at locations where there is a high or an increased risk of contamination of the soil. In this context sales outlets for fuel (petrol stations), service stations, carwashes and the like, industrial production facilities, storage facilities for chemical substances, storage facilities for dredge spoil and, for example in the agricultural industry, stable floors, manure storage facilities and the like may be considered. Besides the specific requirements and other relevant environmental requirements which such fluid-tight floors or paved surfaces have to meet, it is also necessary, of course, to install a monitoring system by means of which any contamination of the soil and/or of the ground water caused by leakage into the floors in question can be detected at the earliest possible stage. In practice monitoring can for example take place by sampling the ground water via standpipes. Standpipes have this drawback, however, that in many cases they cannot be installed sufficiently close to the high-risk points. Another drawback of sampling via standpipes is the fact that when the contamination is detected, it has already reached the ground water and drastic remediation measures are inevitable, as is described in US patent specifications Nos. 5,286,141 and 5,525,008. Another possibility for detecting contamination of the soil by organic compounds is by so-called soil air examination. Soil air measurements comprise the capturing and analysing of air and diffuse vapours from the soil. The analysis takes place by means of sophisticated chemical analysing apparatus, and it is carried out by qualified personnel who are highly experienced in this field. Usually a borehole is formed in the soil to be examined, in order to make the soil accessible for soil air sampling, whereby the air present in the borehole or in an adsorption material provided in the borehole is analysed after some time. A hollow pipe containing a filtering material may be placed in the borehole for monitoring purposes, with a view to analysing the soil air from time to time. In practice soil air monitoring units in the form of horizontal filters inserted into the ground at a depth of about 1 metre below ground level are utilized for use with fluid-tight floors or paving. These filters, which are usually tubular and which comprise openings provided in the wall, through which soil air and diffuse vapour can enter the pipe, are positioned at all high-risk points. Each filter is connected, via a separate pipe of plastic material, to a central measuring unit. In this manner the soil air can be periodically checked and monitored for contamination in a simple manner, without the integrity of the fluid-tight floor or paving being affected. If any contamination is detected, it will be possible in many cases to extract soil air directly, via a control unit in the measuring unit, without any further drastic measures being imme diately necessary. The source of the contamination can be established with reasonable precision, so that immediate measures can be taken at said source as well . A drawback of this system of soil air monitoring is, among others, the fact that the installation of the filters makes it necessary to repave the surface completely or construct a completely new fluid-tight floor. In many cases such a drastic measure is undesirable for financial and constructional reasons. Furthermore, the system itself does not allow validated measurement, because of the different lengths of the pipes from the filters to the central measuring unit. As is known to those skilled in the art, the time it takes before soil air which has diffused into the filter becomes available at the end of the pipe in the central measuring unit depends, among others, on the length of said pipe and on the extent of the diffusion through said pipe. Suppose that a certain part of the soil is contaminated by leakage, which part lies within the operational area of a first filter, which is connected to the central measuring unit via a relatively short pipe, and within that of an adjacent filter, which is connected to the measuring unit via a relatively long pipe. Due to the different lengths of the pipes, it is possible that, although the contamination in question " has also entered the area covered by the second filter, it is concluded upon early measurement that the contamination is limited to the area covered by the first filter, because no contaminated soil air from the second filter is detected in the measuring unit, due to the longer propagation time in the connecting pipe. Measurements on the pipes in the measuring unit furthermore require corrections for a reproducibly correct detection and interpretation. The validation of the measurements is subject to parameters to be estimated, such as influences of moisture in the system of pipes, contamination of the pipe under the influence of diffuse vapours, temperature corrections for the location, and the weather conditions at the time of the measurement at the measuring unit compared to the situation in the ground. When air is supplied to the filters for testing the fluid-tightness of the floor or the paving under which the filters in question are present, the different lengths of the connecting pipes make it more difficult to control the air that is injected under the floor or the paving, because the pressure data and the added volume of air per unit time cannot be directly detected and/or corrected at a filter. In the first instance the object of the invention is to provide an arrangement for soil air monitoring of the soil present under a fluid-tight floor of a location, which arrangement can be provided in existing floors or paved surfaces without drastic measures being required, such as the complete breaking up of a floor or a paved surface and reconstruction of said floor or said paved surface, and which furthermore enables precise, validated measurement of possible soil air contamination. In order to accomplish that objective the invention provides an arrangement for soil air monitoring of the soil under a fluid- tight floor of a location, which arrangement comprises soil air monitoring units extending from the floor surface into the soil, which units are positioned in such a manner that their operational area preferably comprises the entire area of the soil under the fluid-tight floor, but at least those parts of the soil under or in the direct vicinity of parts of the floor where there is a specific risk of fluid penetrating from the floor into the soil, wherein the interface between the floor and a soil air monitoring unit is fluid-tight, and wherein the soil air monitoring units are individually accessible from the floor surface via a closable opening. In accordance with the invention, the soil air monitoring units can be individually accessed from the floor surface or the ground level via a closable opening. This means that soil air measurements can be carried out directly on the soil air monitoring units, without there being a need for various connecting pipes of different lengths, and without the pipe losses emanating therefrom. Unlike horizontal filters, soil air monitoring units extending vertically from the floor surface into the ground have a radial operational area. In accordance with the invention, the soil air monitoring units are positioned at strategic locations, where there is an increased and high risk of contamination of the soil. In any case in such a manner that the locations in question lie within the operational area of a soil air monitoring unit. The soil air monitoring units in the arrangement according to the invention may be installed directly upon construction of a floor or paving, but they may also be installed at a later stage in existing floors. To this end holes extending into the soil for receiving soil air monitoring units are provided in the floor. These openings or bores may be provided vertically in the ground, so that, unlike the situation with the horizontal filter pipes, no pipes present under an existing floor need to be crossed. In order to maintain the fluid-tightness of the floor or the paving, the soil air monitoring units of the arrangement according to the invention are installed in the floor in a fluid-tight manner. In a preferred embodiment of the invention the soil air monitoring units, which have a radial operational area, are positioned in such a manner that the relevant parts of the soil are completely covered by their mutual overlapping operational areas. Preferably in such a manner that also the ground area some distance beyond the boundaries of said location falls within the operational area of the arrangement. For an optimum operation of the arrangement according to the invention, the soil air monitoring units extend from the floor surface at least into the unsaturated soil zone, that is, that part of the soil which, in addition to granulate, contains an amount of pores, because soil air and water vapour will be present mainly in said pores. The soil air monitoring units extending vertically into " the ground, may also be used advantageously for examining ground water, to which end the soil air monitoring units of yet another embodiment of the invention extend into the ground water portion of the soil. Soil air monitoring units which are positioned in this manner are preferably arranged for extracting not only soil air, but also ground water via their closable opening. In addition to being arranged for soil air and ground water examination, the soil air monitoring units of a preferred embodiment of the arrangement according to the invention are also arranged for injecting air under pressure into the ground via their closable opening. That is, air can be injected into the soil under a specified pressure via the soil air monitoring units, so that the liquid-tightness and/or gas- tightness of the floor or the paving in which the arrangement is provided can be tested by injecting air in this manner. In a method according to the invention for examining the paving sealing of a floor in this manner, a soap-like solution, preferably a biodegradable soap solution, is applied to the floor surface to be examined, as a result of which air escaping from the floor via cracks or other leakage spots will become visible in the form of soap bubbles to indicate leakage. Since air can be directly injected on the soil air monitoring units in the arrangement according to the invention, it is possible to effect a desired air penetration profile in the soil in a controlled manner, which can be checked for each unit individually, for carrying out an adequate sealing examination, specifically adapted to the soil in question, of the respective floor or paving. The volume of air which is supplied to one or more of the soil air monitoring units while the method according to the invention is being implemented, is preferably metered to reach the limit level at which omnidirectional displacement of the air present in the pore volume of the soil is started. By utilizing an air filtering unit, ambient air can be used advantageously for testing the floor. In order to interfere as little as possible with the normal use of a floor provided with an arrangement according to the invention, the soil air monitoring units are mounted in such a manner that their closable opening is recessed with respect to the floor surface or the ground surface. In a preferred embodiment of the invention the soil " air monitoring units are tubular, and extend substantially vertically from the floor surface into the soil . Preferably they are mounted in a receiving hole or bore, which has been formed in the ground via the floor, where they are surrounded by filtering gravel. The term filtering gravel is understood to include a group of fine-grained, sandy materials. The fluid- tight mounting of the soil air monitoring units is provided by a fluid- tight sleeve, which engages the outer wall of the soil air monitoring unit and the inner wall of the receiving hole or bore. Preferably a layer of a moisture-absorbing material, such as bentonite grains and/or a foam filling, is provided between the sleeve and the filtering gravel so as to prevent any form of penetration of liquid into the ground via the receiving hole. In many cases the arrangement will be provided in a liquid-tight, concrete floor, so that the inner wall of the receiving hole is strong enough for the sleeve to engage thereon. It will be apparent, that the sleeve will have to extend along a specified length of the receiving hole in order to provide a desired degree of fluid-tightness. If such a length is not available, for example if the floor is too thin for recessed mounting of the soil air monitoring unit and the sleeve, or if the inner wall of the receiving hole is not smooth enough, or if the floor material is less suitable for taking up forces in longitudinal direction, that is, parallel to the floor, if will be advantageous according to another embodiment of the invention to insert a guide pipe from the floor surface into the receiving opening hole. In that case the tubular soil air monitoring unit guide pipe will extend into the ground via said guide pipe. The guide pipe must extend so far into the ground that the soil air monitoring unit can be mounted so that it is recessed with respect to the floor surface, and that the sleeve can engage the inner wall of the guide pipe in a reliable manner. The guide pipe itself is joined to the floor in a fluid-tight manner. In new floors, guide pipes for soil air monitoring units can be advantageously incorporated into the floor in prefabricated form at desired places upon construction of the floor. The guide pipes or the receiving holes are preferably closed at the floor surface by a closure, comprising a cover plate having a first diameter, for covering the receiving hole from the floor, a further plate to be fitted in the receiving hole or the guide pipe, and an elastic sealing material confined between said plates, whilst means such as tightening bolts are provided for moving the plates together so as to clamp the elastic material therebetween. That is, the diameter of the elastic material, such as a rubber disc or ring, in non-clamped condition is such that it can be placed into the receiving hole or the guide pipe, whereby the circumferential dimension of the elastic material is increased to such an extent by the clamping action of the plates, that it cla pingly engages the inner wall of the receiving hole or the guide pipe, thus forming a fluid-tight joint. Soil air monitoring units which are suitable for the purpose of the invention comprise an elongated member, which is closed at one end and which is provided with apertures along part of its length from this end, whereby the closable opening is formed by a so-called "rapid-action coupling". In a preferred embodiment of the soil air monitoring unit, which can be used in many cases, the elongated member consists of an HDPE pipe having a length of up to approx. 1 , and an outside diameter of 25 - 50 mm. The apertures are openings or slots having a diameter of approx. 0.3 mm, which extend over an operative length of up to approx. 0.8 m. Filtering material having a mesh size of approx. 50 - 80 μm is provided adjacently to these apertures. In another embodiment the invention provides a soil air monitoring unit, wherein the elongated tubular member is tapered or rounded at one end, defining an opening therein, in such a manner that a jet pipe can be mounted therein from the other end so as to engage in this opening with its jet nozzle. Preferably coupling means are provided for detachably coupling the jet pipe to the closable opening of the tubular member. This embodiment of the soil air monitoring unit according to the invention is in particular suitable for installing the soil air monitoring unit from a floor surface into the soil present thereunder. To this end, after a receiving hole extending at least as far as the ground surface has been formed in the floor, the elongated tubular member containing the jet pipe, which is detachably mounted therein, is placed into the hole with its tapered or rounded end. Then a fluid such as air or, preferably, water is connected to the jet pipe under such a pressure that soil material present at the location of the tapered end ' or the jet nozzle of the jet pipe is displaced, so that the tubular member can be easily inserted into the ground. Once the tubular member has been installed, the jet pipe is removed and the joint between the tubular member and the floor can be made fluid-tight, for example in the manner as described above. When a guide pipe is used, the tubular member containing the jet pipe is inserted into the soil via said guide pipe. The invention also provides apparatus for supplying air to one or more soil air monitoring units forming part of an arrangement according to the invention, for the purpose of examining the fluid- tightness of a floor or paving. The apparatus generally comprises a movable frame provided with an inlet opening for supplying air under pressure, one or more outlet openings provided with control means, and means for measuring air pressure, and preferably filter means for filtering air delivered from an outlet opening. Furthermore, an air pump may be connected to the frame, so that ambient air can be directly compressed for implementing the invention. In a sophisticated embodiment, the apparatus comprises means for electronically adjusting and recording the pressure and the volume of air delivered from an inlet opening, for example for effecting a desired air penetration profile in soil, as described above. The strategic position of the soil air monitoring units makes the arrangement according to the invention particularly suitable for extracting contaminated soil air and diffuse vapour from the ground in those cases where leakage has caused contamination. To that end the invention also provides a method for connecting an air extraction arrangement to the closable opening of one or more of the soil air monitoring units for extracting contaminated soil air from the soil via said soil air monitoring units. In the case of contaminated soil, air or another suitable gas and/or nutrients can be introduced into the ground for the purpose of promoting a biological decomposition process. The invention also relates to a closure for closing or sealing an opening in a surface, in particular for use in an arrangement for soil air monitoring as described above, comprising a plate-shaped cover part and a clamping part, between which parts a defor able member of elastic sealing material is provided, and clamping means for clamping said deformable member between the cover part and the clamping part, in such a manner that the circumference thereof in clamped condition is larger " than in non-clamped condition. A closure of this type is known per se in practice as a so-called bushing closure. Bushing closures are for example used in practice for sealing pre-formed openings or boreholes for pipes, ducts, conduits and the like, either temporarily or permanently, with the cover part, whereby the closure clampingly engages the wall of an opening or borehole with said deformable member. With the known bushing closures, the clamping means consist of tightening screws, whose threaded end portion either projects some distance outwards beyond the cover part or beyond the clamping part. A corresponding nut engages said threaded end for clamping the deformable member between the cover part and the clamping part as a result of being tightened. These known bushing closures are by no means suitable for use as closures for closing or sealing an opening in a floor or ground surface. The embodiment comprising a bolt end which projects outwards from the cover part constitutes a risk of damage to objects moving across the floor, such as vehicle tyres or wheels, but also of injury to persons walking on the floor. It stands to reason that bushing closures comprising a threaded bolt which projects some distance outwards, beyond the tensioning part, and on which a nut engages, are not suitable for sealing blind openings or holes in a floor or in the ground, because there is no possibility in that case for clamping the deformable member by means of a suitable tool. After all, the nut cannot be reached. Accordingly, it is another object of the invention to provide a closure of the kind referred to in the introduction, which is in particular suitable for sealing openings or holes in floor or ground surfaces, which closure must not constitute a danger to vehicles or persons or the like moving across said floor or said ground surface. In order to accomplish that objective the closure according to the invention is characterized in that said clamping means are recessed tightening bolts engaging the clamping part and are accessible from the side of the cover part that faces away from the deformable member, and wherein the cover part comprises a gradually flattened portion on its side facing away from the deformable member, which flattened portion extends over a specified distance in the direction of the circumferential edge of said cover part. Due to the fact that its tightening bolts are recessed, the closure according to the invention does not comprise any parts that project outwards beyond the cover part, as a result of which the risk of damage and/or injury as described above is effectively eliminated. Since the clamping part is gradually flattened at its circumferential edge, a practically stepless transition between the floor surface and the cover part surface is obtained, as a result of which also the risk of the closure being "grabbed" by a tyre of for example a car or a lorry is effectively reduced. In particular in the case of stepped transitions between the floor surface and the surface of a closure, there is a danger that the closure is grabbed by a tyre rolling over the cover plate, which may cause the closure to twist and/or turn in the opening, thus affecting its sealing action, or that the closure as a whole is pulled or flung from the opening, with all the dangers and risks this may involve. In one preferred embodiment of the closure according to the invention the cover part is flattened along a radius of curvature. Said radius of curvature is selected such that a ery smooth, nearly stepless transition to the floor surface is effected. In order to enable clamping of the deformable member with a force that can be controlled sufficiently precisely, another embodiment of the invention is characterized in that the clamping part is provided with internal screw thread, into which tightening bolts engage for clamping the deformable member between the cover part and the clamping part. Preferably the clamping part is provided with threaded bushes, which extend between the cover part and the clamping part, in which threaded bushes the tightening bolts engage. In particular in the case of a deformable member of a stiff elastic sealing material , such threaded bushes facilitate the clamping, because the tightening bolts only engage the deformable member over a small distance. The threaded bushes also effect a smooth, fluid-tight engagement with the material of the deformable member compared to the threaded surface of a tightening bolt. In another embodiment of the closure according to the invention, the cover part intended for use in floor or ground surfaces is a massive, plate-shaped member, in order to give the closure sufficient stability to withstand point loads being exerted thereon, for example by wheels of cars, lorries and the like. In yet another embodiment the cover part is provided with slots or grooves on its side facing away from the deformable member, which function to provide skid resistance, so as to prevent people from being injured as a result of slipping and falling as much as possible. This applies in particular in areas where people work with oil or other slippery substances that may land on the floor or on the closure. Although the recessed engagement of the tightening bolt on the clamping part can be made fluid-tight by means of suitable sealing means, for example by using sealing rings or sealing discs of plastic material, another preferred embodiment of the invention is characterized in that the cover part is provided with tapered or conical holes tapering off from the side of the cover part that faces away from the deformable member for receiving in these holes a correspondingly tapered or conical head of a tightening bolt, whereby such a hole and such a head are formed with sufficient surface precision to provide a fluid-tight joint between the head and the hole in clamped condition. It has become evident that tightening bolts which are for example provided with a socket-like recess for moving the cover part and the clamping part towards each other or away from each other by means of a rotational movement, provide adequate protection against easy removal of closures by unauthorized persons. Instead of using socket-1 ike recesses, it is also possible, of course, to use tightening bolts having other, suitably shaped heads, and which may or may not have the advantage of providing additional protection against unauthorized rotation and removal of closures. It has become evident that when clamping means consisting of tightening bolts, which are arranged in mutual rotational symmetry, are used in combination with plate-shaped cover parts and clamping parts so as to provide a uniform clamping force to be exerted on the deformable member, it is possible to achieve a fluid-tight sealing of openings having a relatively large diameter (in the order of 10 cm or more) . A preferred embodiment of the invention is characterized in that the cover part is a circular plate having a first diameter, that the clamping part is a circular plate having a smaller second diameter, and that the deformable member of elastic sealing material is a ring or ring-shaped rubber disc having a third diameter, which third diameter ranges between said first and said second diameters. The deformable member may be made of a suitable elastic sealing material, which is selected in dependence on the field of application of the closure, for example a deformable member which is made of an oil and fuel-resistant elastic sealing material for use in environments such as floors of petrol stations, workshops, in particular motorcar repair shops and the like. In an embodiment of the closure according to the invention the cover part, the clamping part and the clamping means are made of stainless steel, in order to ensure a high-quality seal for a prolonged period of time, also in the outside air and/or in aggressive environments. In practice the dimensions of the cover part and the tensioning part, as well as those of the deformable member, are for example selected such that when the closure is fitted for the purpose of closing an opening in a floor or in the ground in a fluid-tight manner, the cover part is supported on the ground or on the floor, and the clamping part and the deformable member are accommodated in the opening, whereby the deformable member engages the circumferential wall of the opening in a fluid-tight manner in its clamped condition. The invention will be described and explained in more detail hereafter with reference to the accompanying drawings. Figure 1 is a schematic view of an arrangement according to the invention, which is used at a fuel outlet. Figure 2 schematic shows the operational area or sphere of influence of a soil air monitoring unit, which in accordance with the invention extends from a floor surface into the soil present thereunder. Figure 3 is a schematic, partly elevational and partly sectional view, of a preferred soil air monitoring unit mounted in accordance with a preferred embodiment of the invention. Figure 4 is a schematic plan view of a closure in particular for use with the arrangement according to the invention. Figure 5 is a schematic sectional view along line V-V in Figure 4. Figure 6 is a schematic view of a device according to the invention for injecting air into individual soil air monitoring units present in an arrangement according to the invention. Figure 7 is a schematic, partly elevational and partly " sectional view, not to scale, of an embodiment of a soil air monitoring unit according to the invention, with a jet pipe mounted therein. Figure 1 shows by way of example a typical fuel outlet 1 for motor fuels, such as various types of petrol, diesel fuel and for example LPG. Sales outlet 1 comprises a shop and paying room 2, vehicle washing locations 3, 4, fuel storage tanks 5, 6, 7, a pump unit 8, for example for diesel fuel, a pump unit 9, for example for LPG, and pump units 10 for the various types of petrol. Vehicle washing facilities 3, 4 and pump units 8, 9 and 10 are disposed on a liquid-tight floor or paved surface 11. Subsoil pipes (not shown) extend from storage tanks 5, 6, 7 to a so-called filling points trough 12 for filling the fuel tanks 5, 6, 7. Filling points trough 12 is likewise provided with fluid-tight paving 11. The requirements which liquid-tight paving for use at fuel outlets has to meet are laid down in various national regulations, with the addition of possible further stipulations imposed by insurance companies or the like. Said regulations are not of importance for a correct understanding of the present invention. In accordance with the invention, soil air monitoring units indicated by reference numeral 13 are installed in the liquid-tight floor 11 at various strategic locations. The soil air monitoring units 13 extend from the liquid-tight floor 11 into the ground present under said floor. The soil air monitoring units 13 are positioned in such a manner that their operational area comprises at least those parts of the soil that lie under or in the direct vicinity of those areas of the floor 11 where there is an increased risk of contamination. In the present example said areas are made up of fuel pump units 8, 9 and 10 and by the filling points trough 12. At these locations there is a relatively large risk of spillage of fuel, which will contaminate the soil present thereunder if it should leak into floor 11. Also washing locations 3 and 4 constitute a fairly high risk of contamination of the soil. The soil air monitoring unit according to the invention (not shown) may also be placed near storage tanks 5, 6, 7, if desired, whereby there is generally no requirement that storage tanks 5, 6, 7 have to be disposed on a fluid-tight floor. The soil air monitoring units 13 are preferably disposed in such a manner that their operational area or area of influence comprises the entire area of the soil under a fluid-tight floor or a paved surface. The soil air monitoring units present in the arrangement according to the invention have an approximately radial operational area, as is illustrated with reference numeral 14 in Figure 2. The operational area of a soil air monitoring unit is determined by the specific dimensions thereof as well as by the soil conditions. In the case of relatively open soil, that is, porous soil, the soil air monitoring units will have a larger operational area 14 than in denser soil containing fewer pores. In practice data are known with regard to the permeability of the soil to air or vapours and to water. It will be apparent thereby that the permeability of gravel, for example, to air as well as to water, is many times larger than to fine sand or for example clay. Furthermore, the operational area of a soil air monitoring unit also includes a time component, that is, soil air contamination occurring further away from the soil air monitoring unit will be detected later by the soil air monitoring unit than contamination which occurs nearer the soil air monitoring unit, due to the permeability of the soil. Accordingly, the operational area of a soil air monitoring unit for soil air testing in the arrangement according to the invention may be characterised as the area surrounding the respective soil air monitoring unit within which soil air contamination that has occurred can be detected after some time by a respective soil air monitoring unit. Figure 3 shows an embodiment of a soil air monitoring unit 15 according to the invention in the form of an elongated tubular pipe member 16 having a first end 17 and a second end 18. First end 17 of pipe 16 is closed by a cap 19, and a closable opening 20, for example in the form of a so-called "rapid-action coupling" 21, is provided at the second end 18. Said rapid-action coupling preferably comprises an insert nipple of standardised dimensions. Rapid-action couplings which are suitable for use in the invention are known per se, they do not require any further explanation. In the illustrated embodiment, rapid-action coupling 21 is mounted in the elongated tubular member 16 in a fluid-tight manner by means of screw thread, using teflon tape. Those skilled in the art will appreciate that also other fluid-tight coupling techniques which are known per se may be used for the purpose according to the invention J Apertures or slots 22 are provided in the wall of the pipe 16 over a specified distance, from the first end 17 of the pipe 16 towards the second end 18. Preferably a filter in the form of a nylon filter sleeve, for example, has been provided over the apertures 22 from the first end 17, which filter sleeve is clamped on the pipe 16 near the second end 18, for example with a clamping strip. For illustrative purposes, filter sleeve 23 is shown in partly broken-away view in Figure 3. The soil air monitoring unit 15, that is, the substantially vertically disposed pipe 16, extends into the so-called unsaturated zone of the soil 25, that is, that part which, besides granulate, contains an amount of pores. As is schematically indicated in Figure 3, the end 17 of the pipe 16 may extend further to a position in the ground water 26, so that in addition to soil air, also ground water 26 becomes available for examination via the soil air monitoring unit 15. It stands to reason that the closable opening 15 at the first end 17 has to be arranged for providing access to the ground water 26 present in soil air monitoring unit 15. Cap 19 may be provided with suitable openings for allowing ground water into pipe 15, if desired. In a preferred embodiment of the soil air monitoring unit 15, which can be used in many cases, the elongated member consists of an HDPE pipe 16 having a length of up to approx. 1 m, and an outside diameter of 25 - 50 mm. Apertures 22 are openings or slots having a dimension of approx. 0.3 mm, which extend over an operative length of up to approx. 0.8 m from pipe 16. Filter 23 thereby has a mesh size of approx. 50 - 80 μ . Near the fluid-tight, in particular liquid-tight floor 27, the soil air monitoring unit 15 is surrounded by a guide pipe 29, which extends partly into the soil 25 from the floor surface 28. Said guide pipe 29 may be made of metal, of plastic material or for example of ceramic material. Guide pipes which are suitable for this purpose are known in practice, they are inter alia used as lead-throughs in domestic and in commercial and industrial buildings. A fluid-tight joint 31 is provided in the space between the outer wall of the guide pipe 29, that is, seen from the soil air monitoring unit 15, and the inner wall of a receiving hole 30 provided " in the floor 27. In the case of for example a concrete floor, a non-shrink mortar joint sealer may be used, whether or not in combination with a foam filling. With other types of floors, a non-shrink adhesive may be used, or elastic putty, for example. All this adapted to the specific requirements set for the properties of the floor and of the material of the guide pipe 29, which can be selected in dependence thereon. The opening between the outer wall of the pipe 16 of the soil air monitoring unit 15 and the inner wall 29 is sealed by means of a sleeve 32, which in fact consists of an elastic material, which can be clamped between the outer wall of the pipe 16 and the inner wall of the guide pipe 29 in a fluid-tight manner via a clamping device 33. Sleeves which are suitable for this purpose are known per se in practice, and they are also known for use in domestic and in commercial and industrial buildings. In the case of an existing floor 27, a borehole or receiving hole 30 extending into the soil 25 is provided in the floor for the purpose of mounting the soil air monitoring unit 15 therein. Then a guide pipe 29 may be mounted in the floor 27, as described above. The use of a guide pipe 29 is not necessary per se if the floor 27 is thick enough for recessing the closable opening 20 therein, and if the floor 27 is sufficiently strong, or if the inner wall of receiving hole 30 is sufficiently smooth for clamping the sleeve 32 therein in a liquid-tight manner. Sufficiently strong means, capable of taking up pressure forces parallel to the floor surface 28. Then a soil air monitoring unit 15 is mounted in the receiving hole 30, after which the space between the receiving hole 30 and the pipe 16 of the soil air monitoring unit 15 is filled with filtering gravel 34 to a point some distance below the closable opening 20. Then a layer of a moisture-absorbing and moisture-repelling material, such as bentonite grains, is provided on top of the filtering gravel 34. Subsequently the whole is sealed by means of the sleeve 32. The bentonite grains 35, which may or may not be provided, function to capture very small amounts of liquid which may leak out along the pipe 16 in spite of the presence of the seal formed by means of the sleeve 32. The bentonite will swell and provides a further seal against the leakage. Filtering gravel 34 is a generic name for a granular material having a sufficiently large amount of pores for admitting soil air into the soil air monitoring unit 15. Receiving hole 30 and guide pipe 29 are sealed by means of a closure 41 at the level of the floor surface 28. Said closure 41 is shown in more detail in Figures 4 and 5. Figure 7 shows another embodiment of a soil air monitoring unit according to the invention in the form of an elongated tubular pipe member 63, which comprises a tapered or rounded first end 64, with an opening 65 present therein. The tubular member 63 is provided with a closable opening at its second end 66, as described above in connection with Figure 3, for example for receiving a rapid-action coupling. In the illustrated embodiment the tubular member 63 is provided with screw thread at its second end 66. The wall of the tubular member 63 is furthermore provided with perforations or slots 67, which are distributed over the length thereof. A jet pipe 68 is present in tubular member 63, which jet pipe comprises a spray nozzle 69 which extends into the opening 65 at the tapered or rounded first end 64 of pipe 63. A suitable fluid, such as air or, preferably, water, can be supplied to the end 70 of the jet pipe 68. Jet pipe 68 is strongly and detachably attached to the second end 66 of the tubular member 63 by means of a clamping bolt 71. Also other or additional clamping means, which are known to those skilled in the art, may be used for this purpose, if desired. The tubular member 63 integral with the jet pipe 68, can now be readily inserted into the ground by placing the rounded or tapered end 64 thereof into a hole present in the floor. When subsequently water, for example, is supplied to the jet pipe 68 under high pressure, the soil present under the jet nozzle 69 of the jet pipe 68 is displaced under the influence of the powerful water jet. The amount of water to be used may be small, but the pressure must be high, so that sand, granular material and the like present in the area of influence of the exiting water jet is moved aside by the force of said water jet and is caused to move upwards along the jet pipe. In this way a deepening hole is formed in the ground, into which hole the tubular member 63 can be inserted. Once a receiving hole extending to the ground beneath a floor has been formed in the floor, a soil air monitoring unit as shown can be installed in the above-described manner, without any further mechanical operations being required. After the installation of the soil ' air monitoring unit, that is, the tubular member 63, the jet pipe 70 is removed by disconnecting clamping bolt 71, and the interface, or the transition from tubular member 63 to the floor, can be made fluid-tight, as described above in connection with Figure 3. Then a rapid-action coupling 20 can be mounted on the second end 66 of tubular member 63, etc. To those skilled in the art it will be apparent that instead of using a screwed connection as shown, it is also possible to use a bayonet coupling or another suitable coupling technique for securing the jet pipe 68 to tubular member 63 and mounting a rapid-action coupling 20 therein. The above-described manner of installing the soil air monitoring units according to the invention has the advantage that damage to pipes, cables and the like present in the ground is prevented as much as possible, partially because of the fact that the end 64 of tubular member 63 is tapered or rounded. Tubular member 63 may also be made of HDPE or of a metal, it may be provided with suitable apertures 67 and an outside diameter of 25 mm. With such dimensions it becomes possible to limit the dimension of the receiving hole in the ground to as little as 50 mm. Arrows 36 in Figure 3 illustrate the entry of soil air from the soil 25 into the pipe 16 of the soil air monitoring unit 15. Said air can be subjected to closer examination via the closable opening 20, for example by sucking out an amount of air, or by inserting a measuring probe into the pipe 16. A measuring probe may also be used for sampling ground water 26 in the pipe 16. Arrow 37 indicates that the soil air monitoring unit 15 also checks its own fitting for fluid-tightness, because any leakage, for example via the space between the receiving hole 30 and the guide pipe 29, can be directly sampled via the soil air monitoring unit 15. In other words, the arrangement according to the invention comprises its own inherent fluid-tightness test. Soil air measurements mainly demonstrate the presence of gaseous or volatile organic compounds. In practice those groups or compounds that can be detected by means of soil air measurements include: - volatile alkanes (petrol); - aromatic compounds (benzene, toluene, ethyl benzene, xylene); - volatile halogenated hydrocarbons (trichloroethylene, tetrachloroethylene, monochlorobenzene, etc.); - organic solvents (acetone, diethyl ether, etc.). In addition to these, also permanent gases can be detected: oxygen, carbon dioxide, hydrogen sulphide, methane, nitrogen oxides. The soil air monitoring unit 15 may also be used for extracting contaminated soil air from the soil 25, by connecting an air extracting arrangement, for example an air exhaust arrangement, to the closable opening 20. This makes it possible to achieve a certain decontamination of polluted ground 25, without taking drastic measures such as breaking open and digging out portions of the contaminated ground 25. The cleanup process may also be carried out by introducing air or a suitable gas and/or nutrients into the ground via a soil air monitoring unit, in order to promote biological decomposition of the contaminated substances. On the other hand, the soil air monitoring unit 15 according to the invention may also be used for paving sealing examination by testing the floor 27 for fluid-tightness. To this end clean air or another suitable test gas is injected into soil air monitoring unit 15, which gas penetrates the soil 25 via apertures or openings 22, as is indicated by arrows 38. Reference numeral 39 illustrates a crack in the floor 27, through which leakage of liquid into the soil 25 might occur. When a soap solution, for example a biodegradable soap solution, is applied to the floor surface 28, air 38 escaping via said crack 39 will become visible on floor surface 28 in the form of soap bubbles 40. The presence of soap bubbles 40 is a direct indication of the degree of fluid-tightness of the floor 27. Also in this case it applies that the fluid-tightness of the fitting of the soil air monitoring unit 15 is inherently checked, because any leakage, for example at the sleeve 32 or at the guide pipe 29, will result in the formation of soap bubbles. In other words, the arrangement according to the invention may be called intrinsically safe. The operational area of a soil air monitoring unit is now also characterised as the area surrounding the respective soil air monitoring unit, where a volume of air can be added to the soil compartment within a controlled period of time, such that the sphere of influence of " the tightness test covers at least the entire area of the liquid-tight facility (floor) (see Figure 2). The soil air monitoring unit 15 will of course have to be installed sufficiently firmly to enable injection of air 38 into the soil 25 under pressure. As already mentioned before, a suitable measuring apparatus, such as a manometer, can be mounted directly on the rapid-action coupling 21, permanently if desired, in order to achieve precise metering of the injected air. The possibility of regulating the air pressure directly on the soil air monitoring unit 15 means that measurements can be made in a reproducible manner. Conversely, this also applies to the extraction of air from the soil air monitoring unit 15. Since there are no connecting pipes to a central measuring unit, no pipe losses will occur, and even the presence of small amounts of contaminated soil air in the soil air monitoring unit 15 can be established in a manner which is reproducible as regards the measuring conditions. Preferably, the soil air monitoring units 15 in the arrangement according to the invention are disposed in such a manner that their operational area also extends partly beyond the boundaries of the floor 11, in order to be able to determine the extent of any soil air contamination and also to test the tightness of the floor or paving. Figure 4 is a plan view of a closure 41 in a preferred embodiment of the invention. Closure 41 comprises a circular, plate-shaped cover part 42, which is provided with openings or holes 48 and with circular grooves or slots 47 for providing skid resistance. Figure 5 is a sectional view along line V-V in Figure 4, showing a further plate 43, which is positioned in a spaced parallel relationship with respect to the cover part or cover plate 42, and which functions as a plate-shaped clamping part. A deformable member 44 of an elastic sealing material, for example a circular cylindrical disc or ring made of rubber, is provided between said cover part 42 and said clamping part 43. In the illustrated embodiment, the plate-shaped clamping part is likewise circular. From said cover part 42, tightening bolts 45 engage into corresponding threaded bushes 46 on the clamping part 43. The openings or holes 48 in the cover part 42 have an inwardly tapered shape from the outside of the cover part 42, i.e. the outside surface 51 or the side facing away from the deformable member 44, in which the correspondingly shaped heads 49 of the threaded bolts 45 are recessed. That is, the head 49 of a threaded bolt 45 does not extend outwards beyond the outside surface 51 of the cover part 42. In the illustrated embodiment the head 49 of a threaded bolt 45 is provided with a hexagonal or socket-like recess 50, for moving the clamping part 43 towards and away from the cover part 42 by rotating a threaded bolt 45 by means of a suitable tool. When the cover part 42 and the clamping part 43 are moved together by screwing, the deformable member 44 will attempt to enlarge its circumference, and when the cover part 42 and the clamping part 43 are moved away from each other by screwing, the deformable member 44 will more or less return to its original circumferential dimension. In this manner the closure 41 according to the invention can be clampingly retained in an opening or borehole in a floor or a wall, whereby the cover part 42 engages the surface of the floor or the wall, and whereby the deformable member 44 and the clamping part 43 are positioned in the opening or borehole. In its clamped condition, the deformable member 44 will engage the wall of the opening or the borehole. When a flat ring-shaped or disc-shaped deformable member 44 and flat, plate-shaped cover parts and clamping parts 42, 43 are used, and when the tightening bolts 45 are arranged in symmetrical relationship, as shown in Figure 4, a uniform clamping action of the deformable member 44 on the wall of a cylindrical opening or a cylindrical borehole is obtained, so as to seal an opening or a borehole in a fluid-tight manner. The force of the clamping action can be precisely controlled via tightening bolts 45. The interface between the head 49 of the tightening bolt 45 and the recessed hole 48 in the cover part 42 can be made fluid- tight by means of plastic rings, if desired. If the surface of the wall of the conical or tapered hole 48 of the cover part 42 and the surface of the engaging conical or tapered circumferential wall of the head 49 are formed with sufficient precision, a fluid-tight seal can likewise be effected between the head 49 and the hole 48 upon clamping of the closure 41. When sufficiently hard materials are used, fluid-tightness is guaranteed, also when a closure 41 is repeatedly clamped down and detached, which is not always the case when plastic sealing rings and the like are used, which exhibit a static deforming behaviour, and which are liable to fracture in the long run, due to ageing and the like. The use of threaded bushes 46 provides an excellent, fluid-tight engagement of the deformable member 44 at the interface between the tightening bolt and the clamping part, and the turning of the tightening bolts 45 is facilitated, because they only need to be in contact with the deformable member 44 over a small part of their length, depending on the length of the threaded bushes 46, when the deformable member is being clamped. Threaded bushes 46 preferably have a sufficiently smooth outer surface, which is in contact with the deformable member 44 for providing a fluid-tight engagement. Instead of using threaded bushes 46, or in addition thereto, it is also possible to provide the plate-shaped clamping part 43 with internal screw thread, into which tightening bolts 45 can engage. Undesired access to an opening which is sealed by a closure 41, or undesired removal of a closure 41 can be prevented, for example by providing the tightening bolts 45 with a specially shaped head 49, in such a manner that it can only be turned with a special tool. Threaded bolts which are suitable for this purpose are known in practice, or they can be designed by a person skilled in the art, for example a head 49 formed with a socket-like recess 50. The elastic sealing material from which the deformable member 44 is made can be selected in dependence on its intended use, for example an oil or fuel -resistant rubber for sealing holes in floors of workshops, such as motorcar repair shops, petrol stations and the like. Of course also other applications and sealing materials which are adapted thereto are conceivable. As is clearly shown in Figure 5, the cover part 42 is a massive, plate-shaped member, so that it will be sufficiently capable of withstanding point loads by wheels of cars, lorries and the like. Said point loads are taken up by the plate-shaped cover part 42 itself, and they are exchanged with the floor or the ground on which the cover part 42 is supported in mounted condition. The exchange of such point loads via the deformable member 44 and the wall of an opening or a borehole against which the deformable member abuts is thus largely eliminated. The closure 41 is thus capable of providing a guaranteed, prolonged, fluid- tight seal of openings and boreholes in floors or walls which can be subjected to varying loads, and which can also be removed and be replaced again as required. In an embodiment of the invention the cover part 42, the clamping part 43 and the tightening bolts 45 are made of stainless steel, in order to provide a high-quality seal, for example in aggressive environments. It will be apparent to those skilled in the art that also suitable plastic materials may be used for this purpose, with this understanding that the mechanical loads which are expected to be exerted on the closure 41 in its mounted condition will have to be taken into account in that case. As is clearly shown in Figure 5, the cover part 42 comprises a gradually flattened portion on its outwardly facing side, which extends over some distance towards its circumferential edge 52. The figure shows a gradual rounding along a radius of curvature which may be in the order of the radius of the plate-shaped cover part 42. In this way a practically stepless transition between the cover part 42 and a floor or wall is obtained. When the closure is mounted in the floor, this will prevent the closure from being grabbed, for example, via the profile of the tyres of wheels of cars and lorries rolling over cover part 42, and be turned or moved otherwise in the opening in which it is mounted, which is by no means desirable in the case of a fluid-tight mounting. Furthermore, this will prevent the closure 41 from being turned or flung out of an opening as a whole, which may constitute a danger in the vicinity thereof. It should be considered that the closure 41 is suitable for being mounted in the ground or the floor of petrol stations and the like, where there is traffic of heavy lorries. Figure 6 shows an apparatus 60 for supplying air or another suitable test gas under pressure to the soil air monitoring units of an arrangement according to the invention. The apparatus comprises a movable frame 61, which is provided with an inlet opening 62 for air and several outlet openings 53. Present on the frame are control means 54 for each outlet opening 53, and means 55 for measuring pressure and volume, by means of which the pressure and the volume of air being delivered from an outlet opening 53 can be adjusted. Air present at the inlet opening 62 is compressed via a pump or a compressor 56, and preferably delivered as pure, clean air at the outlet openings 53 via a filter 57. The volume of air flowing in can be read from a gauge 58. If, for example, clean compressed air is used, filter " means 57 need not be used. The compressor 56 does not necessarily have to be mounted on the frame 61, it may also be a separate unit. Frame 61 is preferably movable, so that it can be used with any arrangement. The outlet openings 53 are preferably provided with rapid-action couplings for coupling the apparatus 60 to the rapid-action couplings 21 of the soil air monitoring units via hoses. The control means 54 and the measuring means 55 may be electronically controlled means, if desired, whereby electronic recording means may be fed with the measured values, as is schematically indicated by reference numeral 59. Although the invention has been illustrated by means of an elongated, tubular, vertically mounted soil air monitoring unit for use in a motor fuel outlet, it will be apparent to those skilled in the art that various forms of soil air monitoring units and arrangements may be used at other locations within the scope of the invention. In this context garages, carwashes, industrial production facilities, storage facilities, facilities for receiving fire extinguishing water, soil decontamination/recycling facilities, storage facilities for industrial waste, container storage facilities/collecting depots for chemical substances, storage facilities for dredge spoil/sludge, stable floors and manure storage facilities may be considered. The term "air" which is used as an independent word or as part of a compound in the accompanying claims, is understood to be a collective noun comprising vaporous and/or gaseous media.

Claims: CLAIMS 1. An arrangement for soil air monitoring of the soil under a fluid-tight floor of a location, in particular for examining the degree of liquid-tightness of said floor, said arrangement comprising soil air monitoring units, characterized by soil air monitoring units extending from the floor surface into the soil, which units are positioned in such a manner that their operational area comprises at least those parts of the soil under or in the direct vicinity of parts of the floor where there is a specific risk of fluid penetrating from the floor into the soil, wherein the interface between the floor and a soil air monitoring unit is fluid-tight, and wherein said soil air monitoring units are individually accessible from the floor surface via a closable opening. 2. An arrangement according to claim 1, characterized in that said soil air monitoring units have an approximately radial operational area, and are positioned in such a manner that the relevant parts of the soil are completely covered by radially overlapping operating areas. 3. An arrangement according to one or more of the preceding claims, characterized in that said soil air monitoring units extend at least into the unsaturated soil zone, that is, such part of the soil which, in addition to granulate, contains an amount of pores. 4. An arrangement according to claim 3, characterized in that said soil air monitoring units extend into the ground water portion of said soil . 5. An arrangement according to claim 4, characterized in that soil air monitoring units are arranged for extracting ground water via their closable opening. 6. An arrangement according to one or more of the preceding claims, characterized in that said soil air monitoring units are arranged for injecting air under pressure into the soil via their closable opening. 7. An arrangement according to one or more of the preceding claims, characterized in that said soil air monitoring units are mounted in such a manner that their closable opening is recessed with respect to the floor surface. 8. An arrangement according to one or more of the preceding claims, characterized in that said soil air monitoring units are tubular, and extend substantially vertically from the floor surface into the soil. 9. An arrangement according to claim 8, characterized in that said tubular soil air monitoring units extend, surrounded by filtering gravel, into a receiving hole of the soil, whereby the space between the soil air monitoring unit and the receiving hole is sealed at the closable opening of the soil air monitoring units by a fluid-tight sleeve engaging the outer wall of the soil air monitoring unit and the inner wall of the receiving hole. 10. An arrangement according to claim 9, characterized in that a layer of a moisture-absorbing material, such as bentonite grains, is provided on said filtering gravel, under said sleeve. 11. An arrangement according to claim 8, 9 or 10, characterized in that said soil air monitoring units extend into the soil and surrounded by a guide pipe, which guide pipe extends from the floor surface to below the closable opening of the soil air monitoring unit, in such a manner that said sleeve engages the inner wall of the guide pipe for sealing the space between the guide pipe and the soil air monitoring unit, and wherein the guide pipe at its outer wall is joined to the floor in a fluid-tight manner. 12. An arrangement according to claim 8, 9, 10 or 11, characterized in that said receiving hole or the guide pipe is sealed from the floor surface by means of a closure, which closure comprises a cover plate which engages in or on the floor, and a further plate in the receiving hole or the guide pipe, between which plates an elastic sealing material is present which engages the inner wall of the receiving hole or the guide pipe, whereby said cover plate and said further plate can be moved towards each other so as to clamp the sealing material under force against said inner wall. 13. A soil air monitoring unit for use in an arrangement according to one or more of the preceding claims, characterized by an elongated, tubular member, which is closed at one end and which is provided with a closable opening at its other end, which tubular member is provided with apertures along part of its length from said closed end, whereby the closable opening is formed by a so-called "rapid-action coupling". 14. A soil air monitoring unit according to claim 13, characterized in that said elongated member consists of an HDPE pipe having a length of up to approx. 1 m and an outside diameter of 25 - 50 mm, whereby said apertures are openings having a diameter of approx. 0.3 mm, "" which extend over an operative length of up to approx. 0.8 m, whereby filtering material having a mesh size of approx. 50 - 80 μm is provided adjacently to said apertures. 15. A soil air monitoring unit according to claim 14, characterized in that said filtering material is a nylon filter sleeve, which extends from the closed end to a position under the closable opening in non-stretched condition. 16. A soil air monitoring unit according to claim 13, 14 or 15, characterized in that said elongated tubular member is tapered or rounded at one end, defining an opening therein, in such a manner that a jet pipe can be mounted therein from the other end so as to engage in said opening with its jet nozzle. 17. A soil air monitoring unit according to claim 16, characterized by coupling means for detachably coupling the jet pipe to the closable opening in the tubular member. 18. A method for installing a soil air monitoring unit according to claim 16 or 17 from a floor surface into the soil beneath, characterized in that a receiving hole extending at least as far as the ground surface is formed in the floor, that an elongated tubular member containing a jet pipe which is detachably mounted therein is placed into the receiving hole with its tapered end, after which a fluid is connected to the jet pipe under such a pressure that soil material present at the location of the tapered end or the jet nozzle of the jet pipe is displaced, so that the tubular member can be inserted into the ground, and that the jet pipe is removed once the tubular member has been installed, and the interface between the tubular member and the floor is made fluid-tight. 19. A method according to claim 18, characterized in that a guide pipe is provided in said receiving hole, which is connected to the wall of said hole in a fluid-tight manner, after which the elongated tubular member containing the jet pipe mounted therein is installed in the soil from said guide pipe, and the tubular member is connected to the guide pipe in a fluid-tight manner. 20. A method for examining the paving sealing of a fluid- tight, in particular liquid-tight, floor preferably a location provided with an arrangement according to one or more of the claims 1 - 12, characterized in that a soap-like solution is applied to the floor surface to be examined, and that air is injected into the ground under pressure " via the soil air monitoring units, in such a manner that air escaping from the floor surface becomes visible in the form of soap bubbles in the soaplike material, whereby the pressure at which the air is injected via one or more of the soil air monitoring units is individually adjusted on the soil air monitoring units so as to effect a desired air penetration profile in the ground. 21. A method according to claim 20, characterized in that the volume of air which is supplied to one or more of the soil air monitoring units is metered to reach the threshold level at which omnidirectional displacement of the air present in the pore volume of the soil is started. 22. A method according to claim 20 or 21, characterized in that the air to be supplied to the soil air monitoring units is filtered through an air filter, in such a manner that air having a desired degree of purity is injected into the soil. 23. Apparatus for supplying air to one or more soil air monitoring units forming part of an arrangement according to one or more of the claims 1 - 12 for the purpose of implementing the method according to one or more of the claims 20 - 22, characterized by a movable frame provided with an inlet opening for receiving air under a specified pressure, one or more outlet openings provided with control means, and means for measuring air pressure and air volume, for supplying air under an adjustable pressure to a soil air monitoring unit via a connecting hose. 24. Apparatus according to claim 23, further characterized by filter means for filtering air delivered from an outlet opening, which filter means are connected to the inlet opening. 25. Apparatus according to claim 23 or 24, further characterized by an air pump for delivering compressed air from an outlet opening, which air pump is connected to the inlet opening. 26. Apparatus according to one or more of the claims 22 - 25, characterized by means for electronically adjusting and recording the pressure and the volume of air delivered from an inlet opening. 27. A method for extracting contaminated soil air in an arrangement according to one or more of the claims 1 - 12, characterized in that an air extracting arrangement is connected to the closable opening of one or more of the soil air monitoring units for extracting contaminated soil air via said soil air monitoring units. 28. A method for introducing air or substances into the ground in an arrangement according to one or more of the claims 1 - 12, characterized in that air and/or nutrients are added for the purpose of promoting chemical decomposition of pollutants present in the soil. 29. A closure for closing or sealing an opening in a surface, in particular for use in an arrangement according to one or more of the claims 1 - 12, comprising a plate-shaped cover part and a clamping part, between which parts a deformable member of elastic sealing material is provided, and clamping means for clamping said deformable member between the cover part and the clamping part, in such a manner that the circumference thereof in clamped condition is larger than in non-clamped condition, characterized in that said clamping means are recessed tightening bolts engaging the clamping part and are accessible from the side of the cover part that faces away from the deformable member, and wherein the cover part comprises a gradually flattened portion on its side facing away from the deformable member, which flattened portion extends over a specified distance in the direction of the circumferential edge of said cover part. 30. A closure according to claim 29, characterized in that said cover part is flattened along a radius of curvature. 31. A closure according to claim 28 or 29, characterized in that said clamping part is provided with internal screw thread, into which tightening bolts engage for clamping the deformable member between the cover part and the clamping part. 32. A closure according to claim 31, characterized in that said clamping part is provided with threaded bushes, which extend between the cover part and the clamping part, in which threaded bushes the tightening bolts engage. 33. A closure according to one or more of the claims 29 - 33, characterized in that said cover part is a massive, plate-shaped member. 34. A closure according to one or more of the claims 29 - 33, characterized in that said cover part is provided with slots or grooves on its side facing away from the deformable member to provide skid resistance. 35. A closure according to one or more of the claims 29 - 34, characterized in that said cover part is provided with tapered or conical holes tapering off from the side of the cover part that faces away from the deformable member for receiving in said holes a correspondingly tapered or conical head of a tightening bolt, whereby such a hole and such a head are formed with sufficient surface precision to provide a fluid-tight joint between the head and the hole in clamped condition. 36. A closure according to one or more of the claims 29 - 35, characterized in that said tightening bolts are provided with a socket-like recess for moving the cover part and the clamping part towards each other or away from each other by means of a rotational movement. 37. A closure according to one or more of the claims 29 - 36, characterized in that said clamping means are tightening bolts, which are arranged in mutual rotational symmetry. 38. A closure according to one or more of the claims 29 - 37, characterized in that said cover part is a circular plate having a first diameter, said clamping part is a circular plate having a smaller second diameter, and said deformable member of elastic sealing material is a ring or ring-shaped rubber disc having a third diameter, which third diameter ranges between said first and said second diameters. 39. A closure according to one or more of the claims 29 - 38, characterized in that said deformable member is made of an oil and fuel -resistant elastic sealing material. 40. A closure according to one or more of the claims 29 - 39, characterized in that said cover part, said clamping part and said clamping means are made of stainless steel. 41. A closure according to one or more of the claims 29 - 40, characterized in that said closure is fitted for the purpose of closing an opening in a floor or in the ground in a fluid-tight manner, whereby the cover part is supported on the floor or ground, and the clamping part and the deformable member are accommodated in the opening, whereby the deformable member in its clamped condition engages the circumferential wall of the opening in a fluid-tight manner. 42. A closure according to claim 41, characterized in that said closure is fitted in an opening of an arrangement for soil air monitoring.

Inventors: DE JONG GERARDUS MAJELLA, DE JONG, GERARDUS, MAJELLA
Applicants: JONG GERARDUS MAJELLA DE, DE JONG, GERARDUS, MAJELLA
Application year: 1998
Main classification: E02D31
IPC codes: E02D31