WO1995007773A1

WO1995007773A1 - Method and device for detecting soil pollution or cleaning up polluted soil in situ, respectively

Info

Publication number: WO1995007773A1
Application number: PCT/NL1994/000225
Authority: WO
Inventors: Leonardus Gerardus Catharina Mathia Urlings; Henricus Bernardus Reinerus Jozef Van Vree
Original assignee: Tauw Milieu B.V.
Priority date: 1993-09-15
Filing date: 1994-09-15
Publication date: 1995-03-23
Also published as: NL9301596A; CA2171833A1; EP0804299A1

Abstract

The invention relates to a method and device for detecting soil pollution or cleaning up polluted soil in situ, respectively, in which: polluted air is extracted via one or more air drainage lines, which are located in the soil above the groundwater level, and/or polluted liquid is extracted via one or more further liquid drainage lines, which are located in the soil below the groundwater level, from the polluted soil, and the air and/or liquid thus extracted is analyzed or decontaminated, respectively. The air drainage lines extend principally horizontally and preferably lie at least 1 metre above the groundwater level. The liquid drainage lines extend principally horizontally and lie preferably at least 1 metre under the groundwater level. A reduced pressure of preferably 3 to 6 kPa is applied to the air drainage lines. To further prevent environmental pollution, vapours and waste fluids which are released are also collected and supplied preferably to the same decontamination device.

Description

Method and device for detecting soil pollution or cleaning up polluted soil in situ, respectively.

The present invention relates to a method for detecting soil pollution or cleaning up polluted soil in situ, respectively. The detection of soil pollution by taking samples of soil material and analyzing these samples elsewhere is generally known. Taking such a sample is very time-consuming, since, for this purpose, a tube is driven into the ground vertically or at an angle and then pulled out of the ground again together with the soil material to be analyzed. Such taking of samples is considerably impeded by buildings, cables, sewer systems and the like. If, subsequently, soil pollution is observed upon chemical analysis, the polluted soil often has to be excavated and taken to a purifying installation for purification. The purified soil material can then be put back or new, clean soil material is put back. Cleaning up polluted soil in this way is very costly.

The aim of the present invention is to provide a method for detecting soil pollution or cleaning up polluted soil in situ, respectively, which, inter alia, does not have these drawbacks.

A further object of the invention is to provide a method to prevent environmental pollution at a chemical installation.

This object is achieved according to the invention, in that polluted (soil) air is extracted via one or more air drainage lines, which are located in the soil above the groundwater level, and/or - polluted liquid is extracted via one or more further liquid drainage lines, which are located in the soil below the ground- water level, from the polluted soil, and the air and/or liquid thus extracted is analyzed or decontaminated, respectively. By means of such drainage lines which are preferably permanently provided in the soil, air and/or liquid can be extracted from the soil and subsequently analyzed. Moreover, the air and/or liquid extracted can also be decontaminated so that the polluted soil can be cleaned up in situ without being excavated and purified elsewhere. If samples are taken and analyzed with sufficiently great frequency via the air and/or liquid drainage lines, pollution of the soil is detected in good time so that it can be cleaned up quickly via the drainage lines before said pollution has been able to spread far out into the soil. The method according to the invention may be used at locations where environmentally damaging substances (such as, for example, solvents, mineral oils, volatile hydrocarbons or mixtures thereof) can penetrate into the soil, and contamination of the soil and/or the groundwater and/or the soil air may occur. The method according to the invention lends itself particularly to fuel sales outlets (filling stations), transfer stations, storage depots and other locations where there is an increased risk of soil pollution as a result of aboveground and underground activities, such as, inter alia, at chemical production sites, bus garages, car repair premises, etc.

At a large number of fuel sales outlets the ground is polluted as a result of leakages from the installations or as a result of spills, for example, during filling. A great number of measures are currently taken against this. However, despite these measures, such as the cathodic protection of the tanks, overfill safety devices, liquid-tight containers around filling outlets, and liquid-tight surfacing around the so-called pump islands, etc., it cannot be ruled out that further instances of pollution will arise. On the one hand, this may occur as a result of accidents and, on the other hand, also because the efficiency and the service life of the materials used for the measures are not totally known. With the method according to the invention it is possible, for example in the case of such fuel sales outlets, to extract air and/or liquid from the soil at regular intervals, to analyze this air and/or liquid for pollution, and, if pollution is observed, to clean up the polluted soil directly, if appropriate, by removing polluted air and/or liquid from the soil and decontaminating it. The spread of soil pollution can in this way be prevented at an early stage. To purify the air and/or liquid extracted from the soil, use may be made, for example, of a device as described in EP-Bl-0,385,555- The method according to the invention may also be used to continuously extract air and/or liquid from the soil and to purify it without pollution having first being observed. The detection and cleaning-up can thus take place simultaneously or interdependently and also independently of each other. According to an advantageous embodiment, the air and/or liquid drainage lines extend principally horizontally. In this manner, a large area can be covered with one drainage line.

It is also advantageous according to the invention if a number of air and/or liquid drainage lines are arranged in a principally horizontal plane parallel to one another and with a mutual spacing of preferably at least 2 to 3 m. In this manner a large area of soil can be covered efficiently with a number of drainage lines.

To extract air and/or liquid from the soil, a reduced pressure is advantageously applied in the air and/or liquid drainage lines, for example a reduced pressure of 1 to 10 kPa and, preferably, from 3 to 6 kPa. At such a reduced pressure, the extraction of air and/or liquid from the soil is such that the concentrations of any pollutants are not too small (this is not, for example, conducive to analysis), whilst, moreover, not too little air and/or liquid is extracted from the soil. By sucking up air via the air drainage lines, air is also sucked into the soil from the environment. This environmental air is beneficial to any bioactivity in the soil. Such bioactivity may have a favourable influence in combating soil pollution. According to an advantageous embodiment, the bioactivity of the soil is further stimulated by introducing biomass and/or nutrients for biomass into the soil, which can be effected, for example, via the air and/or liquid drainage lines. During this introduction of biomass and/or nutrients therefor into the soil, in the latter case the extraction of air and/or liquid from the soil will be halted temporarily, if required.

Moreover, according to the invention, it is advantageous if the decontamination installation for decontaminating air and/or liquid extracted from the soil is also used for treating waste fluids. In this case, waste fluids includes fluids other than air and/or liquid extracted from the soil, such as domestic waste water, vapours collected above ground, fluids originating from production processes, etc.

In a chemical installation, for example a filling station for fuel, volatile vapours originating at fuel pumps, filling outlets, venting points, etc. are preferably collected and conveyed to the same decontamination installation in order to be purified. Such a method offers a complete concept to prevent environmental pollution. It may be sufficient to have one decontamination device to purify both polluted air and/or liquid extracted from the soil and to purify volatile vapours collected elsewhere. The pjjj-ifi-ertion devices described in EP-Bl-385.555 and EP-^2,1 7 are very suitable for purifying both gases and liquids and may be used particularly advantageously according to the invention.

In this context, it is advantageous according to the invention if the waste water, such as domestic waste water is, furthermore, collected and supplied to the decontamination device in order to be decontaminated. This waste water may be released directly into the environment which, in the case of remote chemical installations which are often not connected to the sewers, is very favourable in preventing environmental pollution. Since, at chemical installations, such as filling stations for fuel, potentially polluting substances are often spilt, it is furthermore advantageous according to the invention if the rinse water flowing away from the chemical installation (such as, for example, that used for clearing out and removing the spill) and/or rain water, which has taken up volatile pollutants, is collected and is supplied to said purification device.

The invention further relates to a method for the construction, conversion or renovation of a chemical installation, such as a filling station, in which a number of drainage lines preferably extending principally horizontally are provided in the soil under the chemical installation, said drainage lines are provided above and/or under the groundwater level, - the drainage lines are connected to suction means for the application of a reduced pressure in the drainage lines, and the drainage lines are connected to a treatment device. The treatment device can, in this case, be a .device for sampling, and/or analyzing, and/or purifying fluid extracted from the soil. Using this method, it is possible, on the one hand, to ensure that existing and future filling stations do not cause further environmental pollution and, on the other hand, that all soil pollution present can be cleaned up, whilst a filling station located on this polluted soil can be or remain in operation. When a filling station is to be built, less time is lost by thoroughly cleaning up the soil prior to constructing the filling station. In the case of an existing filling station, one to be converted or to be renovated, this means that the filling station will be out of operation for less time.

In this case, it is furthermore advantageous according to the invention if a portion of the soil is firstly excavated and replaced with a sandy soil material, and drainage lines are provided in said sandy soil material. In this case, it is particularly advantageous if a number of trenches are firstly dug in the soil and replaced by moderately fine to coarse sand, and drainage lines are provided in said moderately fine to coarse sand. This is particularly advantageous in the case of clay and/or loamy soils, since the permeability of such soils is low, which renders the extraction of air and/or liquid via drainage lines more difficult. A soil with moderately fine to coarse sand is, however, very suitable for extracting air and/or liquid from the soil by means of drainage lines.

To further prevent environmental pollution it is, in this case, advantageous also to provide collector means for collecting vapours originating from fuel pumps, filling outlets, venting points, etc. and to connect said collector means to the decontamination installation. According to a further advantageous method, collection means for waste water, such as domestic waste water, are also provided and connected to the decontamination installation. Preferably, the collection means are provided in such a manner that they also collect rinse water and/or rain water. The invention further relates to the application of an underground drainage system having: air drainage lines located in the soil above the groundwater level, and/or liquid drainage lines located in the soil under the groundwater level, for analyzing (soil) air and/or groundwater and optionally cleaning up polluted (soil) air and/or polluted groundwater.

Finally, the invention also relates to a device'for applying the methods according to the invention. In the text which now follows, the invention will be further described on the basis of an illustrative embodiment illustrated in the attached figure.

The figure shows a service station for filling up cars 6 with fuel. A number of fuel pumps 5 are placed on liquid-tight surfacing k . Under the liquid-tight surfacing •, and above the groundwater level 3. a number of parallel air drainage lines 1 are provided in the unsaturated zone of the soil. Moreover, a number of parallel liquid drainage lines 2 are provided in the soil under the groundwater level 3- The fuel pumps 5 are connected to supply tanks 7 via lines 9. It is advantageous according to the invention if, along the lines 9. yet further drainage lines (not shown) are provided. These may, depending on the depth at which the lines 9 lie, be air or liquid drainage lines. At the fuel tanks 7, further air and fluid drainage lines 1 and 2 are also advantageously provided.

The drainage lines 1 and 2 are connected to a treatment device 8 via suction means which can create a reduced pressure in the drainage lines. This treatment device may comprise sampling means and/or analyzing means and/or detection means and/or purification means for purifying air and/or liquid extracted from the soil. When extracting air from the soil, a forced evaporation of volatile components present in the soil takes place as a result of the reduced pressure provided in the air drainage lines. The soil air with the evaporated components is collected in the air drainage lines and conveyed to the treatment device 8. Here, the soil air is treated, in the sense that pollutants are detected or analyzed, or that soil air is sampled for, for example, laboratory analysis, and/or that the soil air is purified.

For the detection and analyzing means, use may be made of a PID meter (PID = Photo Ionization Detector), FID meter (FID = Flame Ionization Detector), the Drager method, activated carbon tubes, air bags with supplementary GC analysis (GC = Gas Chromatography) , the FTIR method (FTIR = Fourier Transformed Infra Red), etc. For the purification means use may be made advantageously of a device such as described in EP-Bl-0,385,555- However, it will be obvious that other detection/ analyzing means and purification means are also perfectly usable. The air and/or liquid drains are provided particularly at those points where the risk of soil pollution is great. In the case of a fuel sales outlet, these points are located particularly: under and around the liquid-tight surfacing; around the storage tanks 7; around the fuel lines 9; and close to the filling points for the storage tanks 7- In particular, the portion of soil above the groundwater level

(the unsaturated zone) is outstandingly suitable for handling any pollution since, by extracting soil air from this portion of soil, micro¬ organisms present in said portion of soil are stimulated. As a result of the reduced pressure in the air drainage lines, there will also be a transfer of oxygen from the ambient air to the portion of soil lying above the groundwater level. This oxygen is an outstanding source of oxygen for microorganisms living in this portion of soil. These microorganisms may then biologically degrade any pollutants to form non- harmful compounds or less harmful compounds. Such biostimulation can be enhanced by adding biomass and nutrients therefor to said portion of soil lying above the groundwater level. This biomass and these nutrients may optionally be introduced into the soil via the air drainage lines. The availability for biodegradation of the pollutant may be enhanced by introducing surface-active substances, such as detergents. These substances may also enhance the effectiveness of flushing or leaching of the soil as a result of enhanced absorption. During this introduction via the drainage lines, the extraction of fluids from the soil may be halted for a shorter or longer period, if required.

The air drainage lines and the liquid-tight surfacing are preferably provided near the fuel pumps in a service station, as illustrated in the figure. In order to extract soil air from the soil, it is advantageous if the air drainage lines lie at least approximately 1 metre above the groundwater level, since, in that case, little or no groundwater is sucked up. The air drainage lines also have to lie sufficiently deep in the soil so that they are not damaged during laying of, interalia, the liquid-tight surfacing and other installations on the ground. The air drainage lines along the underground lines 9 and/or at the storage tanks 7 preferably lie in the vicinity of these lines 9 and storage tanks 7, respectively.

The liquid drainage lines are preferably laid principally perpendicularly under the air drainage lines, but at a greater depth than the air drainage lines. Preferably, these liquid drainage lines lie at least 1 metre under the groundwater level, in a sandy environment.

Depending on, inter alia, the condition of the soil and the groundwater level, it is possible to provide both air drainage lines and liquid drainage lines, but it is also conceivable to provide only air drainage lines or only liquid drainage lines. If, for example, the groundwater is very high, it will, in practice, be very difficult if not impossible to provide air drainage lines. In the case of a lower level of the groundwater, such as from 4 metres under the surface, and in the case of soils with solid rock, the drainage lines can also be provided vertically, optionally combined with horizontal drainage lines, in which case they are suitable for so-called deep-well and/or controlled drainage. Furthermore, in the case of low groundwater, and thus in the case of a large unsaturated zone, there can be provided a number of layers or levels with horizontal air drainage lines. However, liquid drainage lines at greater depth levels are also conceivable in principle. The frequency of taking samples from the soil air and/or groundwater must particularly be adjusted to the spread of the pollution in the groundwater. A decisive factor in this case is, on the one hand, the natural flow rate of the groundwater and, on the other hand, the possibility of using the installed drainage system to draw polluted groundwater against the natural direction of flow of the groundwater.

Taking into account a specific time interval between the taking of samples, analysis and the taking of organizational and logistic measures, a sampling frequency of preferably twice per year is desirable. The sampling frequency must be such that any pollution of the groundwater can still be controlled with the aid of the drainage lines so that drainage lines present in the ground are sufficient for cleaning-up and no additional measures have to be taken. A soil pollution situation may serve as an example, where a soil having a water permeability factor (k) of 30 m/day, a groundwater flow rate (v) of 30 m/year, a pack thickness (D) of 50 m and an extraction rate (Q) of 353 m³/day (=15m /hour) and a pollution spot which has spread in the groundwater to 25 m in the downstream direction can be controlled with a sampling frequency of twice per year. In soils in which the flow rate of the groundwater is very high or very low, the sampling frequency can be adjusted.

Many variants and extensions are possible with the methods and device according to the invention. Thus, in the case of a petrol station, it is conceivable to guide the (domestic) waste water, optionally after preliminary decontamination, for example, by means of a septic tank, to the treatment device 8 and to purify it there and to collect vapours originating from the fuel pumps, filling points, venting points 10, etc., to guide them to the treatment device 8 and to purify them there.

When building new chemical installations, the extraction means for groundwater and soil air may be provided at very limited cost. In existing chemical installations, the installation costs will be higher, since aboveground and underground infrastructure has to be removed and replaced. Removal and replacement of aboveground and underground infrastructure can be avoided, if desired, by providing the drainage pipes in the ground under the existing installation in another manner known per se in the prior art. The drainage pipes may, in this case, be provided both horizontally and vertically.

A further advantage of the methods and devices according to the invention is that the time between observation of soil pollution and the commencement of the clean-up can be kept extremely short (for example, a few days), and that, during the clean-up, the operation of the chemical installation can be continued.

By coupling the drainage lines, collector means, collection means and suction means to, preferably, one purification system, it is possible to reduce the emission of pollutants considerably. In this connection, in the case of a petrol station, it is conceivable for there to be additional suction of air originating from fuel pumps, filling points and venting points. Waste water and rain water originating at the petrol station can also be purified via the same purification system which further combats environmental pollution. For it was found that rain water flowing away may be slightly polluted, on the one hand as a result of the washing-out of the air near to the chemical installation and, on the other hand, through contact with, for example, oil and petrol residues at the fuel pumps and at parking spaces. The various air and water flows are brought to a purification device (purification installation) . This purification installation has to be able to treat gases (air and soil air) and liquids (such as soil water, waste water and rain water) simultaneously. For this purpose, purification installations may be used such as those described in European Patent EP-0,385,555 and EP-0,442,157- The content of said

European Patents must be regarded as a component of the present patent application as regards the purification device.

Claims

1. Method for detecting soil pollution or cleaning up polluted soil in situ, respectively, in which polluted air is extracted via one or more air drainage lines, which are located in the soil above the groundwater level, and/or polluted liquid is extracted via one or more further fluid drainage lines, which are located in the soil below the ground water level, from the polluted soil, and the air and/or liquid thus extracted is analyzed or decontaminated, respectively.

2. Method according to one of the preceding claims, in which the air drainage lines extend principally horizontally and lie preferably at least 1 metre above the groundwater level. 3- Method according to one of the preceding claims, in which the liquid drainage lines extend principally horizontally and preferably lie at least 1 metre under the groundwater level.

4. Method according to one of the preceding claims, in which a number of air and/or fluid drainage lines are arranged in a principally horizontal plane, parallel to one another and with a mutual spacing of preferably at least 2 to 3 ta .

5. Method according to one of the preceding claims, in which a reduced pressure, for example of 1 to 10 kPa and preferably from 3 to 6 kPa, is applied in the air drainage lines. 6. Method according to one of the preceding claims, characterized in that the bioactivity of the soil is stimulated by introducing biomass and/or nutrients for biomass into the soil, preferably via the air and/or liquid drainage lines.

7- Method according to one of the preceding claims, characterized in that air and/or liquid extracted from the soil is analyzed for volatile compounds.

8. Method according to one of the preceding claims, in which a decontamination device is provided for decontaminating air and/or liquid extracted from the soil. 9. Method according to Claim 8, in which waste fluids are treated in said decontamination device.

10. Device for application of the method according to one of the preceding claims. 11. Method for the construction, conversion or renovation of a chemical installation, such as a filling station, in which a number of drainage lines are provided in the soil under the chemical installation, - said drainage lines are provided above and/or under the groundwater level, the drainage lines are connected to suction means for the application of a reduced pressure in the drainage lines, and the drainage lines are connected to a treatment device. 12. Method according to Claim 11, in which a number of drainage lines are provided in such a manner that they extend principally horizontally.

13. Method according to Claim 11 or 12, in which a liquid- and/or gas-tight layer is provided between the drainage lines and the chemical installation. lA. Method according to one of Claims 11-13, in which a portion of the soil is firstly dug out and replaced with a sandy soil material, and drainage lines are provided in said sandy soil material.

15. Method according to one of Claims 11-14, in which a number of trenches are dug in the soil and replaced by moderately fine to coarse sand, and drainage lines are provided in said moderately fine to coarse sand.

16. Method according to one of Claims 11-15, in which the drainage lines are provided at least 1 metre above the groundwater level. 17- Method according to one of Claims 11-16, in which the liquid drainage lines are provided at least 1 metre under the groundwater level. l8. Method according to one of Claims 11-17, in which the treatment device comprises a decontamination device, and in which lines for waste fluids are connected to the decontamination device. 19. Method for the construction, conversion or renovation of a filling station according to Claim 18, in which the lines for waste fluids comprise lines for domestic waste water and/or lines for fuel vapours which were released and collected aboveground. 20. Application of an underground drainage system having: ~ air drainage lines located in the soil above the groundwater level, and/or liquid drainage lines located in the soil under the groundwater level, for analyzing and optionally cleaning up polluted soil. 21. Application according to Claim 20, in which the air and/or liquid drainage lines extend, horizontally in the soil.