GB2301133A

GB2301133A - Treating contaminated land

Info

Publication number: GB2301133A
Application number: GB9610350A
Authority: GB
Inventors: Neil Andrew Mcleod
Original assignee: Envirotreat Ltd
Current assignee: Envirotreat Ltd
Priority date: 1995-05-20
Filing date: 1996-05-17
Publication date: 1996-11-27
Anticipated expiration: 2016-05-17
Also published as: GB9510255D0; GB2301133B; GB9610350D0

Abstract

Contaminated land A is treated by forming a barrier B around the contaminated area A by boring into the land, mixing the material undergoing boring with an appropriate treatment agent to form a plurality of columns 21 containing a treatment agent selected to react with or bind with the contaminants present in the land. Optionally, containment columns 20 may be formed around the treatment zone formed by the treatment columns 21. In some cases, a gate G may be formed in the barrier wall to receive a replaceable cartridge 22 of treatment material. Where necessary the treatment columns 21 may be formed into a continuous array C to provide an extended area of treatment.

Description

Title: Treating contaminated land.

Description of Invention This invention relates to a process for treating contaminated land at least to reduce migration of contaminants from such land with or without elimination of contaminant by neutralisation, degradation or other processes.

Broadly, the invention resides in a process for treating contaminated land by forming a barrier which is substantially impervious to the contaminant(s) so as effectively to prevent migration of the contaminant(s), the barrier being formed by boring into the land, mixing the material undergoing said boring with a treatment agent which is selected according to the nature of the contaminant(s) so as to form a treatment column containing said treatment agent, and further forming a plurality of similar such treatment columns in the same manner, each of which is contiguous or overlapping with adjacent such columns to form a continuous treatment zone to comprise the barrier.

The treatment agent may include an active material selected to react with the contaminant so as to neutralise or destroy it, and/or a binding material to bind the contaminant and prevent physical migration thereof.

The treatment agent may comprise a mixture of one or more active materials and/or one or more binding materials.

The treatment column is preferably permeable to water so as to enable the contaminant(s) to be brought into the treatment zone by movement of water from the contaminated land.

The barrier formed by said treatment columns may be formed around the entire periphery of an area of contaminated land, so that migration of the contaminant is arrested by a continuous "wall" of such treatment columns in which the contaminant is treated by the treatment agent therein.

In some cases, the barrier formed by said treatment columns may extend around the only part of periphery of contaminated area. For example if drainage is entirely in one direction, the barrier may be generally of U-shape in plan, remaining open at the upstream side of the area.

In an alternative arrangement, the treatment zone may extend over the whole, or part of, the contaminated area within the barrier by forming additional similar treatment columns within the barrier. Such additional treatment columns may be contiguous with said barrier or be formed at one or more separate locations within the area enclosed by the barrier, particularly at any point where contamination is especially high, to produce "spot treatment" at appropriate positions within a larger area of contamination.

In addition to said treatment columns, the treatment zone is itself preferably surrounded by a further, outer wall of containment columns formed by boring into the land, mixing the material undergoing boring with a containment agent which forms a physical barrier to migration of the contaminant.

The containment columns may be less pervious to water than the treatment columns. The containment columns may be contiguous with, and preferably overlap with, the treatment columns, but in some cases may be spaced from and around the treatment columns to form an outer barrier.

In such a case the outer barrier, which may extend partly or completely around the treatment zone comprising said treatment columns, may be formed with one or more gaps which contain water-pervious material incorporating said treatment agent so as to allow water to flow from the area within the outer barrier subject to treatment of any residual contaminant therein by said treatment agent.

Whilst the function of the containment columns is primarily to contain the contaminant and prevent migration thereof from the contaminated site, such columns may also include a treatment agent (the same as, or different to, that used in the treatment columns) as well as a containment agent, or the containment agent itself may also in part serve as a treatment agent for the contaminant.

The containment agent may comprise any appropriate material, such as a slurry of sodium bentonite or cement, etc., which is mixed with the soil or other such material as the column is formed by boring into the land so as to form a mechanically stable column which is substantially impervious.

The treatment agent may comprise any of a range of known treatment agents appropriate for different contaminants, preferably mixed with a suitable slurry of cementitious products, including inter alia, cement, pozzolans, lime, etc.

to form a mechanically stable column which is sufficiently porous to allow contaminants to enter the column. A pillared clay may be employed to provide the required porosity.

Where the contaminants include organics, the slurry preferably also contains a modified pillared clay adapted to bind such organics in order to prevent them interfering with the curing of the cementitious products.

The invention will now be described by way of example with reference to the accompanying drawings wherein: FIGURE 1 is a diagrammatic illustration of part of a barrier wall comprising columns of treated material formed by boring and mixing in appropriate materials in accordance with the invention; FIGURE 2 illustrates part of such a barrier wall in plan view; FIGURE 3 illustrates part of a continuous treatment zone formed in a similar manner; FIGURE 4 is a diagrammatic plan view of a treatment site enclosed by a barrier wall comprising outer containment columns and inner treatment columns, with an inner treatment zone comprising an array of treatment columns bounded by a ring of containment columns; FIGURE 5 is a plan similar to Figure 4 wherein the barrier wall is formed with an outlet gate;; FIGURE 6 is a plan similar to Figure 4 wherein the barrier wall and inner zone are made up entirely of treatment columns; FIGURE 7 is a plan similar to Figure 5 in which the barrier wall is formed entirely of containment columns; and FIGURE 8 is a plan of a site comprising a barrier wall with outlet gate as illustrated in Figure 5 in combination with an inner treatment zone made up entirely of treatment columns as illustrated in Figure 6.

Referring firstly to Figures 1 and 2, a barrier wall 10 is formed by forming at least one row of contiguous or overlapping bores 11, which extend vertically into the ground 12 and into underlying bedrock 13. In the bores 11 the material which makes up the ground 12 is mixed with an appropriate stabilising material to form a physically stable column, but preferably without compaction.

The function of the columns thus formed is primarily to provide a treatment for contaminant in the ground material enclosed by the barrier wall 10 so as effectively to eliminate said contaminant therein and/or prevent migration thereof. For this purpose the material making up each treatment column has additionally mixed therein one or more treatment agents appropriate to the contaminant or contaminants present on the site.

The treatment agent may include biological systems for biodegradation, chemical systems for neutralisation or chemical degradation, systems designed to promote reactions such as polymerisation of contaminant materials, or agents which function mainly to bind a specified contaminant in the column formed in the bore, for example a pillared clay, and combinations thereof as appropriate at any specific site.

The wall 10 may include one or more further rows of such treatment columns containing the same, or a different, treatment agent and optionally an outermost row of columns is formed in a similar manner, whose function is primarily to serve as containment columns which prevent migration of contaminant material from the site. For this purpose, in the outermost row of containment columns the stabilising material, and the proportion thereof relative to the ground material, are so chosen that the columns thus formed are substantially impervious, and these columns may or may not also include said treatment agent.

As shown in Figure 3, a cluster 15 of bores 11 may be formed in the same manner to provide an array of columns over an extended treatment zone instead of a barrier wall.

Figures 4 to 8 illustrate various typical practical applications for the treatment of contaminated land. In each case, the contaminated area A is at least partially surrounded by a peripheral barrier wall B and includes, for the purposes of illustration only, a concentrated treatment zone C, which may not in all cases be necessary.

In the case shown in Figure 4, the barrier wall B comprises a continuous outer row of containment columns 20 and an adjacent, inner row of treatment columns 21, extending around the entire periphery of the area A.

Within the area A, a patch of greater contamination is treated by the concentrated treatment zone C which also comprises an outer ring of containment columns 20 and an inner array of treatment columns 21.

In the case shown in Figure 5, the arrangement is generally similar to that of Figure 4, except that the barrier wall B is formed, at at least one point in its periphery, with an outlet gate G. The outlet gate G comprises a gap in the barrier wall B which is formed from water-pervious material containing an appropriately selected treatment agent which effectively removes the contaminant from water leaving the site through the gate. It will be appreciated that the gate may be formed from treatment columns 21 similar to those which form the inner row of columns of the barrier wall B, or alternatively it may comprise a readily replaceable "cartridge" 22 of similar material, so that it can readily be exchanged when its treatment capacity becomes depleted.

In the case shown in Figure 6 both the barrier wall B and the concentrated treatment zone C are formed entirely from treatment columns 21.

In the case shown in Figure 7 the concentrated treatment zone C comprises an array of treatment columns 21 surrounded by a ring of containment columns 20, as shown in Figures 4 and 5, but the barrier wall B is formed entirely of containment columns 20 with an outlet gate G having a cartridge 22 of treatment material.

In the case shown in Figure 8, the concentrated treatment zone C is formed entirely as an array of treatment columns 21, as illustrated in Figure 6, and the barrier wall B is formed as illustrated in Figure 7.

It will be appreciated that in all the above examples the area A is shown as including one concentrated treatment zone C, but it will be understood that it may not be necessary for such a concentrated treatment zone C to be provided in all cases, and in other cases more than one such concentrated treatment zone may be necessary. Indeed, in an extreme case the concentrated treatment zone C may extend to cover the whole of the area A within the barrier wall B.

If the contaminant tends to migrate primarily in one specific direction, the barrier wall B, may in some cases not extend around the entire periphery of the contaminated site A, but may be open at the side of the site opposite that towards which contaminant migration occurs.

The containment columns 20 will be typically constructed using a slurry of bentonite and water (unmodified clay apart from possible conversion of Ca2+ to Na + to improve expansive properties). Cernent may be added for strengthening purposes only.

The treatment columns 21 will normally comprise of a mix of cementitious products, pozzolanic materials/silicates and modified pillared clays.

The clays will be incorporated into the overall mix strategy to facilitate chemical bonding (fixation) and immobilisation of organic contaminants in particular (but not exclusively) within the treated soil matrix. The prime stabilisation agent in environmental terms will be cement and/or cementitious products/pozzolanic materials. The use of these materials as an alkaline precipitation medium/encapsulation method for the treatment of inorganics/heavy metals is well documented and is an accepted known technology. Other additives will be used for specific applications. These include both naturally occurring materials such as humic acids and inorganic/organic additives such as metal salts and polymers.

The treatment columns 21 may be designed to facilitate other complementary treatment techniques such as in-situ bioremediation or chemical degradation. Alternatively, the treatment columns will be designed to form part of a composite treatment approach operating in combination with adjacent in-situ bioremediation, soil washing or other treatment processes. The combination of these processes would aim to optimise the treatment efficiency of a complete active containment system.

Where appropriate, in addition to the columns 20,21 intended for the treatment and/or containment of contaminant within the area A, conventional constructional piles may be formed as appropriate to enable the land to be developed by the construction of buildings or the like.

The features disclosed in the foregoing description, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS:

1. A process for treating contaminated land by forming a barrier which is substantially impervious to the contaminant(s) so as effectively to prevent migration of the contaminant(s), the barrier being formed by boring into the land, mixing the material undergoing said boring with a treatment agent which is selected according to the nature of the contaminant(s) so as to form a treatment column containing said treatment agent, and further forming a plurality of similar such treatment columns in the same manner, each of which is contiguous or overlapping with adjacent such columns to form a continuous treatment zone to comprise the barrier.

2. A process according to Claim 1 wherein the treatment agent includes an active material selected to react with the contaminant so as to neutralise or destroy it.

3. A process according to Claim 1 wherein the treatment agent includes a binding material to bind the contaminant and prevent physical migration thereof.

4. A process according to Claim 1 wherein said treatment agent comprises one or more active materials selected to react with the contaminant so as to neutralise or destroy the contaminant, and/or one or more binding materials to bind the contaminant and prevent physical migration thereof.

5. A process according to Claim 1 wherein the treatment column is permeable to water so as to enable the contaminant(s) to be brought into the treatment zone by movement of water from the contaminated land.

6. A process according to any one of the preceding claims wherein the barrier formed by said treatment columns is formed around the entire periphery of an area of contaminated land, so that migration of the contaminant is arrested by a continuous wall of such treatment columns in which the contaminant is treated by the treatment agent therein.

7. A process according to any one of Claims 1 to 5 wherein the barrier formed by said containment columns extends around only part of the periphery of an area of contaminated land.

8. A process according to Claim 1 wherein the treatment zone also includes the whole, or part of, the contaminated area within the barrier by forming additional similar treatment columns within the area enclosed by the barrier.

9. A process according to Claim 8 wherein said additional treatment columns are contiguous with said barrier.

10. A process according to Claim 8 wherein said additional treatment columns are provided at one or more separate locations within the area enclosed by the barrier and spaced from the barrier.

11. A process according to Claim 1 wherein in addition to said treatment columns, the treatment zone is itself surrounded by a further, outer wall of containment columns formed by boring into the land, mixing the material undergoing boring with a containment agent which forms a physical barrier to migration of the contaminant.

12. A process according to Claim 11 wherein the containment columns are less pervious to water than the treatment columns.

13. A process according to Claim 11 wherein the containment columns are contiguous with the treatment columns.

14. A process according to Claim 11 wherein the containment columns overlap with the treatment columns.

15. A process according to Claim 11 wherein the containment columns are spaced from and around the treatment columns to form an outer barrier.

16. A process according to Claim 15 wherein the outer barrier is formed with one or more gaps which contain water-pervious material incorporating said treatment agent so as to allow water to flow from the area within the outer barrier subject to treatment of any residual contaminant therein by said treatment agent.

17. A process according to any one of Claims 11 to 16 wherein said containment columns also include a treatment agent.

18. A process according to Claim 1 wherein the containment agent comprises a slurry of sodium bentonite, cement, or other similar material, which is mixed with the ground material as the column is formed by boring into the land so as to form a mechanically stable column which is substantially impervious.

19. A process according to Claim 1 wherein the treatment agent comprises one or more treatment materials selected in accordance with the contaminant(s) present in the land mixed with a slurry of cementituous material to form a mechanically stable column which is sufficiently porous to allow contaminant(s) to enter the column.

20. A process according to Claim 19 wherein a pillared clay is included with the treatment agent to achieve the required porosity.

21. A process according to Claim 18 or 19 wherein the slurry further includes a modified clay adapted to bind organic contaminant materials in order to prevent such materials interfering with the curing of cementitious materials.

22. A barrier for the treatment and/or containment of contaminant materials within an area of contaminated land comprising a plurality of treatment and/or containment columns substantially as hereinbefore described with reference to and as shown in Figures 1 and 2 of the accompanying drawings.

23. A construction for the treatment and/or containment of contaminant materials within an area of contaminated land comprising treatment and/or containment columns substantially as hereinbefore described with reference to and as shown in Figure 3 of the accompanying drawings.

24. A method of treating contaminated land comprising the construction of a barrier wall around the periphery of such land substantially as hereinbefore described with reference to and as shown in Figure 4 of the accompanying drawings.

25. A method of treating contaminated land comprising the construction of a barrier wall around the periphery of such land substantially as hereinbefore described with reference to and as shown in Figure 5 of the accompanying drawings.

26. A method of treating contaminated land comprising the construction of a barrier wall around the periphery of such land substantially as hereinbefore described with reference to and as shown in Figure 6 of the accompanying drawings.

27. A method of treating contaminated land comprising the construction of a concentrated treatment zone in such land substantially as hereinbefore described with reference to and as shown in Figure 4 of the accompanying drawings.

28. A method of treating contaminated land comprising the construction of a concentrated treatment zone in such land substantially as hereinbefore described with reference to and as shown in Figure 6 of the accompanying drawings.