WO2020165562A1

WO2020165562A1 - Leak monitoring system

Info

Publication number: WO2020165562A1
Application number: PCT/GB2020/050292
Authority: WO
Inventors: Jon CROWTHER; Vladimir Nosko
Original assignee: Sensor (Uk) Limited; Sensor, Spol. S R.O.
Priority date: 2019-02-11
Filing date: 2020-02-10
Publication date: 2020-08-20
Also published as: GB201901888D0

Abstract

A geosynthetic clay liner comprising a first geotextile layer, a second geotextile layer, and a clay layer provided between the first and second geotextile layers. The geosynthetic clay liner comprises electrically conductive material.

Description

Leak Monitoring System

[0001] The present invention is related to a leak monitoring system for monitoring integrity of membranes.

[0002] Geotextiles are permeable fabrics that can be used in association with soil to separate, filter, reinforce, protect or drain. Geotextiles are typically made from polypropylene or polyester and conventionally come in one of the three different forms: woven (resembling mail- bag sacking), needle punched (resembling felt) or heat-bonded (resembling ironed felt).

[0003] Geotextiles have many applications in the fields of construction and civil engineering, including reservoirs, canals, dams, leach pads (heap leach mining), landfills, ponds, construction site silt fences or geotubes. Typically, geotextiles are placed at the tension surface to strengthen the soil or are used as a protective layer over geomembranes in an attempt to limit damage to the geomembrane as a result of the covering process.

[0004] Geocomposites are composite structures in which various geosynthetic products have been assembled together, for example to create products that are more effective, are easier to install or are augmented to provide a functional characteristic. Geogrids, plastic meshes and perforated tubes can be used to enhance drainage; and stainless steel meshes, carbon fibres and graphene enhanced polyurethane paint can be used to enhance electrical conductivity.

[0005] A further example of a geocomposite is a synthetic clay liner. Synthetic clay is used as a component in the geocomposite to reduce leak transmissivity. A geosynthetic clay liner provides a hydraulic barrier to liquids, and sometimes gases. Geosynthetic clay liners are used to form a composite with geomembrane liner materials and regular compacted clay in order to augment security against accidental leakage. Geosynthetic clay liners are often used in a variety of geosynthetic designs.

[0006] Geosynthetic clay liners are typically factory-manufactured and comprise a layer of clay or other low-permeability material, supported by geotextiles and/or geomembranes and mechanically held together by needling, stitching or chemical adhesives. Bentonite composed predominantly of montmorillonite or other expansive clays are most commonly used. Bentonite composed predominantly of montmorillonite or other expansive clays are most commonly used in geosynthetic clay liners. Natural or processed sodium bentonite is typically used, with woven and/or non-woven textile geosynthetics enclosing the clay layer. However, polyethylene geomembrane layers have also been incorporated in place of a textile layer, to support and enclose the clay layer. [0007] Electrically conductive geotextiles have been developed to augment the conductivity of the surface immediately beneath a plastic geomembrane layer. The purpose of this is to enhance the sensitivity of electronic leak detection and location techniques, including arc testing, water lance, water puddle, dipole and permanent point sensor leak monitoring systems.

[0008] Existing methods of achieving conductivity include using carbon fibres during the production process of the geotextile, often combined with a sprayed latex to fix the fibres in place; use of a stainless steel mesh supported on a polypropylene grid that is then needle- punched between two geotextile layers; and use of a graphene-enhance polyurethane paint that is sprayed onto the surface of the geotextile.

[0009] Various methods are used for detection of leaks in plastic membranes during construction. These methods employ impressed electrical signals that flow through the membrane at the point of defects or damage.

[0010] It is desirable to enhance the conductivity beneath the membrane, to improve electronic leak detection and location. In particular, enhancement of conductivity is desirable to improve detectability of holes in the membrane. It is also desirable to homogenise conductivity such that the ability to detect holes is constant across the entire membrane installation.

[0011] Previous methods that aim to enhance conductivity for this purpose include using conductive backed geomembranes (coextruded with conductive polyethylene, by bonding conductive geotextile and by printing onto the membrane during the production process) and by separately placing conductive geotextiles.

[0012] There are several problems that are encountered in the augmentation of conductivity in geosynthetics. The enhanced-conductivity material can be expensive. The process of installing an additional layer can be costly. A specialist in leak detection and location is needed to test the membrane installation. The incorporation of a conductive geotextile beneath a membrane can undesirably increase the transmissivity beneath that membrane of any liquid that has leak through a hole. Conductive-backed membranes inhibit dipole testing and permanent monitoring of the membrane due to the electrical earthing effect of the membrane, and in particular the weld sleeve.

[0013] Additionally, the placement of both a separate conductive layer (e.g. conductive geotextile, conductive netting or a mesh) or a bonded conductive layer (e.g. a conductive geotextile bonded to an impermeable plastic membrane, printing conductivity onto a membrane or coextruding a conductive plastic membrane to a non-conductive impermeable plastic membrane) has the effect that resistance measurements are unusable due to the homogeneous nature of the conductivity provided by these means. In other words, existing methods of providing conductivity for the purposes of leak detection do not affect the resistivity of the conductive material itself.

[0014] It is therefore desirable to provide means for enhancing leak location technology wherein non-specialists are able to test the membrane after covering and determine whether there are any integrity issues.

[0015] It is also desirable to provide means for detecting and locating leaks in low temperatures, in particular freezing conditions. This is becoming a more common requirement as exploration and mining of precious metals takes place in arctic and Antarctic regions. There is a desire to utilise geosynthetics to protect the environment from leaks or industrial process chemicals in polar or tundra regions. Although processes have been developed for the installation of geosynthetics in freezing conditions, the lack of moisture in freezing conditions is a huge challenge for leak detection.

[0016] According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

[0017] According to a first aspect of the invention there is provided a geosynthetic clay liner comprising a first geotextile layer, a second geotextile layer, and a clay layer provided between the first and second geotextile layers, wherein the geosynthetic clay liner comprises electrically conductive material.

[0018] The introduction of a conductive material in the geosynthetic clay liner allows the reception of an electrical signal from a layer above a hole in a membrane. The electrical signal, that may be electric current, may be received by the conductive material in the geosynthetic clay liner. This electric signal may be transmitted via a connected cable to a monitoring means. The monitoring means may comprise electronics to allow online and/or offline analysis of the signal.

[0019] The use of a geosynthetic clay liner comprising an electrically conductive material provides the advantage that it eliminates the need to use conductive backed membranes in environments where it is already planned to use a geosynthetic clay liner for providing a hydraulic barrier.

[0020] The clay layer may be configured to expand upon becoming hydrated in the vicinity of a leak. The expanded area of the clay layer in the vicinity of the leak may stop the leak. The use of a geosynthetic clay liner comprising an electrically conductive material thereby provides the advantage that, unlike a typical geotextile or membrane, the geosynthetic clay liner inhibits further transmission of a liquid in the event of a leak. There is no effect on transmission of a leak through a membrane layer above the geosynthetic clay liner, which would occur if a separate conductive geotextile layer were used above the geosynthetic clay liner.

[0021] The expanded area of the clay layer may be locatable by measuring changes in resistivity. The changes in resistivity may be measurable using a small handheld multimeter. It may thereby be easy to detect and locate a leak. The use of a geosynthetic clay liner comprising an electrically conductive material can also reduce or eliminate the requirement for a specialist to determine whether damage to the covered membrane has occurred. Where a specialist is required, the specialist can be directed to the area exhibiting problems by using the resistivity measurements.

[0022] The electrically conductive material may be a conductive layer. The conductive layer may be provided between the first geotextile layer and a third geotextile layer, such that the first geotextile layer is provided between the conductive layer and the clay layer.

[0023] The first and third geotextile layers may be joined to opposing sides of the conductive layer. The first and third geotextile layers may be joined to the conductive layer using an adhesive. The adhesive may be glue that comprises an electrically conductive material. The electrically conductive material provided in the glue may be at least one of graphene, conductive black and silver nitrate.

[0024] The electrically conductive material may be provided in the clay layer. This may provide the advantage that it eliminates the need to install an additional layer for providing electrical conductivity. Additionally, the cost of enhancing the clay layer such that it is electrically conductive can be low.

[0025] The clay layer may comprise clay and an electrically conductive element provided within the clay. Alternatively, the clay layer may comprise clay and an electrically conductive element provided adjacent the clay, between the clay and the first or second geotextile layer.

[0026] The electrically conductive element may comprise wire. The wire may be provided as a singular wire or a wire mesh. The wire may be a metallic wire. The wire may be a graphene-doped conductive plastic thread, wire, tube or rod and may include metallic wires to improve resistance to snapping. The wire may be a carbon doped conductive plastic thread, wire, tube or rod and may include metallic wires inside to improve resistance to snapping. The metallic wires may be formed of materials such as carbon fibres, stainless steel, titanium, aluminium or copper.

[0027] The wire may be arranged in a curved configuration. Preferably, the wire may be arranged in an undulating or S-shaped configuration. This provides the advantage that the required conductivity is provided, but the use of grid or net pattern is avoided, thereby saving the cost of those parts missing from a grid pattern, which the undulating pattern replaces.

[0028] The electrically conductive element comprising a wire is advantageous in that a user could measure the electrical resistivity of the geosynthetic clay liner using a simple multimeter while the covering work proceeds to check that the resistivity of the geosynthetic clay liner remains in a predetermined range. If the range is exceeded, the user could mark that area as an area to be further investigated by a specialist.

[0029] The electrically conducting element may be a sensing element comprising two parallel coaxial cables. The sensing element may comprise a non-conductive insulator joining and surrounding the two coaxial cables. The sensing element may comprise an electrically conductive outer layer provided on an outer surface of the non-conductive insulator. The outer layer may be plastic that is extruded onto an outer surface of the non-conductive insulator. The outer layer may be ink that is printed onto the outer surface of the non-conductive insulator. The outer layer may be paint that is painted onto the outer surface of the non- conductive insulator. The outer layer plastic, ink or paint may be enhanced with a conductive material. The conductive material that enhances the outer face plastic, ink or paint may be at least one of graphene, carbon black, and silver nitrate. Alternatively, the outer surface of the non-conductive insulator may be wrapped with a conductive medium. The conductive medium may be foil, braided material or wire. The foil, braided material or wire may be formed of carbon fibres and/or metallic material such as stainless steel, titanium, aluminium or copper.

[0030] Use of the sensing element as the electrically conductive element is particularly beneficial in situations where the area of detection is small, for example in the construction industry for waterproofing building foundations, for the verification of integrity of covered ground gas protection membranes, or in connection with roof membranes. In traditional leak location techniques, complications arise due to the size of the surface area relative to the length of the perimeter and the electrically conductive items required to pass through the membrane (such as lighting conductors, pipes, vents, etc.) exert an undue influence on the testing process, which can lead to leaks or damage to the membranes being undetected. Use of the sensing element provides the user with a means for testing resistivity of the geosynthetic clay liner after it has been covered, using a simple multimeter connected to the externally conductive part of the sensing element, while the twin coaxial cables would permit the locating of the most hydrated parts of the clay layer (thereby locating the position of leaks) using a measurement of relative dielectric permittivity.

[0031] The clay layer may comprise clay, wherein a component of the clay is electrically conductive. The clay may comprise bentonite and a conductive material. The conductive material may be conductive powder or conductive fibres. The conductive material may comprise at least one of urea, sodium chloride, silver nitrate, metallic filings, carbon black, carbon fibres, and graphene.

[0032] In use, when the geosynthetic clay liner is in contact with water, the area of the clay layer that is hydrated may expand and may expand through a hole in the membrane. When a component of the clay is electrically conductive, the conductive clay may make a mechanical connection between the lower and upper side of the membrane, thereby allowing an electrical signal to pass through the hole in the membrane whilst preventing further liquid flow through the hole in the membrane by the clay blocking the hole.

[0033] The electrically conductive material may be a coating. An electrically conductive coating may be provided on a surface of the first geotextile layer, between the clay layer and the first geotextile layer. Additionally or alternatively, an electrically conductive coating may be provided on a surface of the second geotextile layer, between the clay layer and the second geotextile layer. The coating may coat all or only part of the surface of the first and/or second geotextile layer.

[0034] The electrically conductive coating may be electrically conductive ink or paint that may be printed or sprayed onto the surface of the first and/or second geotextile layer. The electrically conductive ink or paint may be ink or paint enhanced with at least one of graphene, silver nitrate and carbon black.

[0035] The geosynthetic clay liner may form a sheet sensor or tile sensor.

[0036] According to another aspect of the invention, there is provided a leak monitoring system comprising a geosynthetic clay liner and a conductive tracer fluid, wherein the geosynthetic clay liner comprising a first geotextile layer, a second geotextile layer, and a clay layer provided between the first and second geotextile layers, wherein the geosynthetic clay liner comprises electrically conductive material.

[0037] The geosynthetic liner may comprise any of the features described in relation to the first aspect of the invention.

[0038] The tracer fluid may be a fluid with a low freezing temperature, such that the tracer fluid remains in a liquid state in polar and tundra regions. Preferably, the tracer fluid may remain in a liquid state at a temperature of -26°C. The tracer fluid may comprise propylene glycol. The tracer fluid may be configured to reduce the temperature at which leak detection is possible, by providing conductive liquid that will flow through a hole in a damaged membrane when otherwise no leak would occur due to the frozen state of all other naturally occurring moisture. The tracer fluid may not present a risk to the local or wider ecology. [0039] Often, geosynthetics products are laid on top of permafrost and then are covered with gravel, sand or other overburdening materials. The ground is frozen beneath and the material placed above then also freezes. The tracer fluid may enable leak detection in these environments.

[0040] In use, the geosynthetic clay liner may be laid over permafrost and a membrane may be provided over the clay liner. The membrane may then be covered by a covering layer, such as gravel, sand or other overburdening materials. In use, the tracer fluid may be poured over the covering layer and may permeate through the covering layer to the membrane. If there is a hole in the membrane, the tracer fluid may pass through the hole into the geosynthetic clay liner. The leak may then be detectable using the geosynthetic clay liner.

[0041] The tracer fluid may be configured to remain conductive and in a liquid state to detect a leak when all other naturally occurring moisture would otherwise be frozen and therefore would not be suitable for leak detection. Ice is non-conductive and does not flow, so when frozen the presence of damage in a membrane is not detectable using electricity to flow through an area of damage with any present moisture. At sub-zero temperatures, the use of water would not reach an area of geomembrane damage before freezing, and in temperatures lower than 25°C, even heated water would freeze on contact with gravel, and would not reach the area of geomembrane damage. The tracer fluid permits the operation of leak detection techniques that are currently considered unachievable in freezing conditions.

[0042] The tracer fluid may comprise propylene glycol and an additive for lowering the electrical resistivity of the tracer fluid. The additive may be at least one of water, urea, sodium chloride, graphene, metallic powders and carbon black. Propylene glycol has a high electrical resistivity, which is prohibitive for electric leak detection and so the additive may enable the tracer fluid to be used in electronic leak detection.

[0043] The tracer fluid may comprise an additive for increasing the viscosity of the tracer fluid. The additive for increasing the viscosity of the tracer fluid may be a food thickener, for example sodium alginate, ground arrowroot, or cornflour. Increasing the viscosity of the tracer fluid may leave a deposit on the gravel overburden as it passes through to areas of geomembrane damage, thereby permitting the use of electricity for the purposes of leak detection.

[0044] In areas such as polar or tundra regions, it may also be necessary to designers to use large particle size gravel with little blinding/dust or small particles therein as the covering layer. This is in order to maximise the drainage throughput of process fluids once such facilities are in operational phase. This means that any conductive tracer fluid may actually not maintain conductivity long enough to carry out leak detection processes and may need to be thickened so that it adheres to the gravel in the covering layer, thereby creating a conductive path from above the membrane, through the hole in the membrane, to the conductive geosynthetic clay liner beneath the membrane.

[0045] The system may comprise monitoring means electrically connected to the geosynthetic clay liner.

[0046] According to another aspect of the invention there is provided a system for monitoring leaks comprising a geosynthetic clay liner and monitoring means electrically connected to the geosynthetic clay liner, wherein the geosynthetic clay liner comprises a first geotextile layer, a second geotextile layer, and a clay layer provided between the first and second geotextile layers, wherein the geosynthetic clay liner comprises electrically conductive material.

[0047] According to another aspect of the invention there is provided a tracer fluid for use in leak monitoring systems, wherein the tracer fluid is a fluid with a low freezing temperature, such that the tracer fluid remains in a liquid state in polar and tundra regions.

[0048] The tracer fluid may comprise propylene glycol and an additive for lowering the electrical resistivity of the tracer fluid. The additive for lowering the electrical resistivity of the tracer fluid may be at least one of water, urea, sodium chloride, graphene, metallic powders and carbon black. The tracer fluid may comprise an additive for increasing the viscosity of the tracer fluid. The additive for increasing the viscosity of the tracer fluid may be a food thickener, for example sodium alginate, ground arrowroot, wheat flour or cornflour.

[0049] According to another aspect of the invention there is provided a conductive element for a leak detection system, wherein the conductive element is a conductor comprising an s- shaped portion. The conductor may comprise a plurality of s-shaped portions, such that the conductor has an undulating configuration.

[0050] According to another aspect of the invention there is provided a geotextile sensor comprising a non-conductive first geotextile layer, a non-conductive second geotextile layer, and a conductive layer provided between the first geotextile layer and the second geotextile layer, wherein the first and second geotextile layers are joined to opposing sides of the conductive material with an adhesive.

[0051] The adhesive may be electrically conductive. The adhesive may be glue that comprises an electrically conductive material. The electrically conductive material provided in the glue may be at least one of graphene, metallic powders, conductive black, and silver nitrate.

[0052] The advantage of joining the geotextile layers using an electrically conductive adhesive is that the electrical conductivity of the geotextile is further enhanced. [0053] The first and second geotextile layers may be permeable to liquid and/or gas. Preferably, the first and second geotextile layers are permeable to water. In use, the geocomposite can be provided beneath a plastic geomembrane and can enhance the sensitivity of electronic leak detection and improve localisation of leaks in leak monitoring systems.

[0054] Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[0055] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:

[0056] Figure 1 shows a cross-section view of a geotextile sensor;

[0057] Figure 2 shows a partially cut-away perspective view of the geotextile sensor;

[0058] Figure 3 shows a cross-section view of a geosynthetic clay liner;

[0059] Figure 4 shows a partially-assembled perspective view of the geosynthetic clay liner of figure 3.

[0060] Figure 5 shows a cross-section view of another geosynthetic clay liner;

[0061] Figure 6 shows a partially installed geosynthetic clay liner;

[0062] Figure 7 shows another partially installed geosynthetic clay liner;

[0063] Figure 8 shows a cross-section view of a sensing element; and [0064] Figure 9 shows a cross-section view of a conductive element.

[0065] A conductive geotextile 10, shown in figure 1 , comprises a first geotextile layer 12, a second geotextile layer 14 and an electrically-conductive layer 16 provided between the first geotextile layer 12 and the second geotextile layer 14. As shown in figure 2, the conductive layer 16 comprises a mesh; however in other examples, the conductive layer may be an s- shaped conductor. [0066] The first geotextile layer 12 is joined to the second geotextile layer 14 by means of an electrically-conductive adhesive, with the electrically-conductive layer sandwiched between the first and second geotextile layers and secured with the electrically-conductive adhesive.

[0067] A geosynthetic clay liner 100, shown in figure 3, comprises a first geotextile layer 102, a second geotextile layer 104, and a clay layer 106 provided between the first geotextile layer and the second geotextile layer.

[0068] A third geotextile layer 108 is also provided facing an opposite side of the first geotextile layer to the clay layer. A conductive layer 1 10 is provided between the third geotextile layer and the first geotextile layer. As shown in figure 4, the conductive layer 1 10 comprises a mesh; however, in other examples the conductive layer 1 10 may be an s-shaped conductor. The third geotextile layer and the first geotextile layer are fixed to the conductive layer with a conductive adhesive.

[0069] Figure 5 shows another example of a geosynthetic clay liner 200 comprising a first geotextile layer 202, a second geotextile layer 204 and a clay layer 206 provided between the first geotextile layer 202 and the second geotextile layer 204. The clay layer 206 comprises an electrically conductive material. The electrically conductive material may be an ingredient in the clay, or may be a conducting element provided within the clay.

[0070] Figure 6 shows a plurality of geosynthetic clay liners 300 being installed at a site. A liner 300 can be provided as a roll. Each liner 300 is unrolled and positioned adjacent another liner 300. The membrane 310 then covers the geosynthetic clay liner, and a covering layer 320, such as gravel can be provided over the membrane 310. The geosynthetic clay liner 300 comprises a mesh conductive element 302. A connecting cable 304 electrically connects the conductive element 302 to a monitoring means 306. A source electrode (not shown) electrically connected to the monitoring means 306 provides an electric pole above the membrane 310, whilst the geosynthetic clay liner comprises the second electric pole. A current can therefore flow from the source electrode, through the hole in the membrane to the geosynthetic clay liner and through the connecting cable 304 to be detected by the monitoring means 306. The leak can therefore be detected and located using the methods disclosed in US4947470 and WO2016/001639.

[0071] In use, liquid, for example rain water, permeates through the covering layer 320 and contacts the membrane 310. If the membrane is damaged, the water travels through the hole in the damaged membrane and permeates through the first geotextile layer of the geosynthetic clay liner and is absorbed by the clay layer. Electricity flows from above the source electrode through the leak to the geosynthetic clay liner [0072] In conditions below zero, it is not possible to detect the leak using water, and so a tracer fluid that remains in a liquid state in these conditions is poured over the covering layer 320. The tracer fluid flows through the hole in the membrane 310 to the geosynthetic clay liner 300 and is absorbed by the clay in the clay layer. The tracer fluid and the geosynthetic clay liner are electrically conductive, and so an electric current flows from the source electrode, through the hole in the membrane to the geosynthetic clay liner and is detected by the monitoring means.

[0073] Figure 7 shows a plurality of geosynthetic clay liners 400 being installed at a site. The arrangement of the installation is similar to that shown in figure 6. However, instead of a mesh conductive element, the conductive element in each geosynthetic clay liner 400 is wire 402 having an undulating form. Each wire is electrically connected to the monitoring means 406 via the connecting cable 404.

[0074] Figure 8 shows a cross-section view of an example of a sensing element 500 that may be used as the conducting element in the geosynthetic clay liner. The sensing element comprises first and second coaxial cables 502, 504 that are arranged substantially parallel to each other. A non-conductive material 506 is provided between and surrounding the first and second coaxial cables 502, 504. A conductive material 508 is provided on an outer surface of the non-conductive material 506. The conductive material 508 may be plastic that is extruded onto the outer surface of the non-conductive material or ink that is printed onto the outer surface of the non-conductive material or paint that is painted onto the outer surface of the non-conductive insulator. The outer layer plastic, ink or paint may be enhanced with a conductive material. Alternatively, the conductive material 508 may be foil, braided material or wire that is wrapped around the non-conductive material 506. The foil, braided material or wire may be formed of carbon fibres and/or metallic material such as stainless steel, titanium, aluminium or copper. Other example sensing elements that may be used as the conducting element in the geosynthetic clay liner include those disclosed in EP2538192 and PCT/GB2019/050256.

[0075] Figure 9 shows a cross-section view of an example of a conductive element 600 that may be provided in the electrically conductive layer 16 of the geotextile in figure 1 or as the electrically conductive element in the geosynthetic clay liners of figures 3-7. The conductive element 600 is a wire formed of a conductive plastic thread 602 doped with graphene or carbon. Metallic wires 604 are provided in the plastic thread to improve resistance to snapping. The metallic wires may be formed of materials such as carbon fibres, stainless steel, titanium, aluminium or copper.

[0076] Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the components) specified but not to the exclusion of the presence of others.

[0077] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0078] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0079] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0080] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1 . A geosynthetic clay liner comprising a first geotextile layer, a second geotextile layer, and a clay layer provided between the first and second geotextile layers, wherein the geosynthetic clay liner comprises electrically conductive material.

2. The geosynthetic clay liner according to claim 1 , wherein the electrically conductive material is an electrically conductive element provided within the clay layer.

3. The geosynthetic clay liner according to claim 2, wherein the electrically conductive element is a wire.

4. The geosynthetic clay liner according to claim 3, wherein the wire is any one of:

a metallic wire;

a graphene-doped conductive plastic thread, wire tube or rod; or

a carbon-doped conductive plastic thread, wire, tube or rod.

5. The geosynthetic clay liner according to claim 3 or claim 4, wherein the wire comprises an undulating form in a length direction.

6. The geosynthetic clay liner according to claim 2, wherein the electrically conductive element comprises a sensing element formed of two substantially parallel coaxial cables and a non-conductive insulator joining and surrounding the two coaxial cables, wherein the sensing element comprises an electrically conductive outer layer provided on an outer surface of the non-conductive insulator.

7. The geosynthetic clay liner according to claim 2, wherein the clay layer comprises clay and a component of the clay is electrically conductive.

8. The geosynthetic clay liner according to claim 7, wherein the electrically conductive component of the clay is at least one of silver nitrate, metallic filings, carbon black, carbon fibres, and graphene.

9. The geosynthetic clay liner according to claim 1 , wherein the electrically conductive material is a coating provided on a surface of the first geotextile layer and/or the second geotextile layer, between the clay layer and the first and/or second geotextile layer.

10. The geosynthetic clay liner according to claim 9, wherein the electrically conductive coating is electrically conductive ink or paint that is printed or sprayed onto the surface of the first and/or second geotextile layer, wherein the electrically conductive ink or paint is enhanced with at least one of graphene, silver nitrate and carbon black.

1 1 . The geosynthetic clay liner according to claim 1 , wherein the electrically conductive material is a conductive layer provided between the first geotextile layer and a third geotextile layer, wherein the first geotextile layer is provided between the conductive layer and the clay layer.

12. The geosynthetic liner according to claim 1 1 , wherein the first and third geotextile layers are joined to opposing sides of the conductive layer by an adhesive that comprises an electrically conductive additive.

13. A leak monitoring system comprising the geosynthetic clay liner according to any preceding claim and a conductive tracer fluid, wherein the tracer fluid is a fluid with a low freezing temperature, such that the tracer fluid remains in a liquid state in polar and tundra regions.

14. The leak monitoring system according to claim 13, wherein the tracer fluid comprises propylene glycol and an additive for lowering the electrical resistivity of the tracer fluid.

15. The leak monitoring system according to claim 13 or claim 14, wherein the tracer fluid comprises an additive for increasing the viscosity of the tracer fluid.