Diffuse hydraulic control using low viscosity, long duration gelation and in SITU distributed colloidal silica solutions

Abstract

Colloidal silica can be used in advanced techniques for environmental and geotechnical engineering, such as for groundwater control, mine water management, and the formation of in-situ containment structures. Colloidal silica can be used to immobilize groundwater plumes, manage mine water in high hydraulic conductivity areas, and construct in-situ cutoff walls and diversion structures.

Description

Docket No. 255432.000088GEOSYN13PCTDIFFUSE HYDRAULIC CONTROL USING LOW VISCOSITY, LONG DURATION GELATION AND IN SITU DISTRIBUTED COLLOIDAL SILICA SOLUTIONSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 689,553 filed August 30, 2024, the content of which is incorporated by reference herein in its entirety.BACKGROUND OF THE DISCLOSURE1. Field

[0002] The present disclosure relates to advanced methodologies for employ ing colloidal silica in environmental and geotechnical engineering, specifically for groundwater control, mine water management, and the formation of in-situ containment structures. The disclosed techniques utilize colloidal silica to immobilize groundwater plumes, manage mine water in high hydraulic conductivity areas, and construct in-situ cutoff walls, diversion structures, and the like.2. Description of Related Art

[0003] In the field of geotechnical engineering, colloidal silica, bentonite, laponite and carbon nanotube are nanomaterials that have been recently applied to soil improvement. Nanomaterials can be properly added to various kinds of soil to modify and improve some physical / mechanical properties of the natural material.

[0004] The conventional techniques for using colloidal silica and the like have been considered satisfactory for their intended purpose. However, there is an ever-present need to immobilize groundwater plumes, manage mine water in high hydraulic conductivity areas, and construct in-situ cutoff walls, diversion structures, and the like. Employing colloidal silica in environmental and geotechnical engineering, specifically for groundwater control, mine water management, and the formation of in-situ containment structures can prove beneficial. This disclosure provides a solution for these needs.318615202vl 1Docket No. 255432.000088GEOSYN13PCTSUMMARY

[0005] A system includes a subsurface formation having an impermeable base formation, an aquifer above the base formation, and a vadose zone above the aquifer extending to a surface. A column of activated colloidal silica gel extends into the aquifer from a boundary where the aquifer meets the vadose zone downward to the impermeable base formation. A mineshaft extends through the column of activated colloidal silica gel to reduce or prevent leaking of groundwater from the aquifer into the mineshaft.

[0006] The impermeable base formation can include ore. The mineshaft can extend from the surface, through the column of activated colloidal silica gel to the ore. A portion of the mineshaft between the surface and the column of activated colloidal silica gel can extend at least partially through a vadose zone. The column of activated colloidal silica gel can be a gel with a higher viscosity than the groundwater. The column of activated colloidal silica gel can form a semi-permeable barrier to reduce groundwater flow. The column of activated colloidal silica gel can be solidified. The mineshaft can have a cross-sectional perimeter. For at least a portion of a length of the mineshaft, the cross-sectional perimeter can be fully surrounded by the column of activated colloidal silica gel.

[0007] A system includes a subsurface formation including an impermeable base formation, an aquifer above the base formation, and a vadose zone above the aquifer extending to a surface. A volume of activated colloidal silica is within the aquifer. A contaminant is included, wherein the volume of activated colloidal silica forms a containment barrier that at least reduces or prevents spread of the contaminant migrating into groundwater in the aquifer.

[0008] The volume of activated colloidal silica can completely envelop the contaminant. At least some of the contaminant can be chemically altered or rendered inert after by chemical reaction with at least one of a colloidal silica after activation of the activated colloidal silica. The activated colloidal silica can form a barrier layer between groundwater in the aquifer and the contaminant. The column of activated colloidal silica can be a gel with a higher viscosity than water. The column of activated colloidal silica can be solidified.

[0009] A method includes injecting colloidal silica into a groundwater in a subsurface formation. The method includes activating the colloidal silica to form a stable gel matrix barrier to separate the groundwater from a second fluid.Docket No. 255432.000088GEOSYN13PCT

[0010] The method can include forming a mineshaft through the gel matrix barrier. The second fluid can be air within the mineshaft. Separating the ground water from the second fluid can include at least reducing migration of the groundwater into the mineshaft.

[0011] The method can include activating the colloidal silica using an activator compound to induce gelation of the treated groundwater.

[0012] The second fluid can be contaminated groundwater. Injecting colloidal silica can include in-situ mixing of colloidal silica with the contaminated groundwater. Forming a stable gel barrier can separate the contaminated ground water from non-contaminated groundwater. Activating the colloidal silica can immobilize the contaminated groundwater within a stable gel matrix. Injecting colloidal silica and activating the colloidal silica can include forming a solidified barrier upon gelation including at least one of an in-situ cutoff wall, an in-situ containment barrier, and an in-situ diversion stmcture. The method can include recirculating the colloidal silica to control at least one of distribution of the colloidal silica and activation of the colloidal silica.

[0013] These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the disclosed embodiments taken in conjunction with the drawings.Docket No. 255432.000088GEOSYN13PCTBRIEF DESCRIPTION OF THE DRAWINGS

[0014] So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, embodiments thereof will be described in detail herein below with reference to certain figures, wherein:

[0015] FIG. 1 is a schematic elevation view of an embodiment of a system constructed in accordance with the present disclosure, showing recirculation of colloidal silica in a subsurface formation;

[0016] FIG. 2 is a schematic elevation view of an exemplary embodiment of a system constructed in accordance with the present disclosure, showing a secondary' containment structure beneath a development such as a landfill, tailings management facility, lagoon, pond, or the like;

[0017] FIG. 3 is a schematic elevation view of another exemplary' embodiment of the system of FIG. 2, showing the mineshaft extending from the surface to an ore deposit;

[0018] FIG. 4 is a schematic plan view of the system of FIG. 3. showing the mineshaft passing through the column of activated colloidal silica;

[0019] FIG. 5 is a schematic elevation view of the system of FIG. 3, showing the crosssection of the mineshaft completely surrounded by the column of activated colloidal silica;

[0020] FIG. 6 is a schematic elevation view of another exemplary’ embodiment of a system constructed in accordance with the present disclosure, showing a land formation with an aquifer having ground water separated from a contaminant within a containment barrier made from activated colloidal silica;

[0021] FIG. 7 is a schematic plan view of the sy stem of FIG. 6, showing a perimeter formed by the containment barrier;

[0022] FIG. 8 is a schematic elevation view of another exemplary' embodiment of a system constructed in accordance with the present disclosure, showing activated colloidal silica gel encasing a contaminant within an aquifer to separate the contaminant from groundwater;

[0023] FIG. 9 is a schematic plan view of the system of FIG. 8 showing a full perimeter of the activated colloidal silica gel encasing the contaminant;

[0024] FIG. 10 is a schematic elevation view of another exemplary' embodiment of a system constructed in accordance with the present disclosure, showing a column of activatedDocket No. 255432.000088GEOSYN13PCT colloidal gel forming a diversion or barrier wall between groundwater and a contaminant in an aquifer;

[0025] FIG. 11 is a schematic plan view of the system of FIG. 10, showing the portion of the aquifer with contaminated groundwater separated from the clean groundwater by the diversion or barrier wall; and

[0026] FIG. 12 is a diagram of a method in accordance with the present disclosure.Docket No. 255432.000088GEOSYN13PCTDETAILED DESCRIPTION

[0027] Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an embodiment of a system in accordance with the disclosure is shown in FIG. 1 and is designated generally by reference character 100. Other embodiments of systems in accordance with the disclosure, or aspects thereof, are provided in FIGS. 2-12. as will be described. The systems and methods described herein can be used to form in-situ barriers for groundwater in applications such as reduction or prevention of migration of groundwater into mine structures, or prevention of migration and mixing of contaminants into groundwater.

[0028] To facilitate an understanding of the principles and features of the various embodiments of the systems and methods, various illustrative embodiments are explained below. Although exemplary embodiments are explained in detail, it is to be understood that other embodiments are contemplated. Accordingly, it is not intended that the systems and methods are limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The systems and methods are capable of other embodiments and of being practiced or carried out in various ways. Also, in describing the exemplary7embodiments, specific terminology' will be resorted to for the sake of clarity'.

[0029] It must also be noted that, as used in the specification and the appended claims, the singular forms "a.” “an” and “the” include plural references unless the context clearly dictates otherwise. For example, reference to a component is intended also to include composition of a plurality7of components. References to a composition containing “a” constituent is intended to include other constituents in addition to the one named.

[0030] Also, in describing the exemplary embodiments, terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents which operate in an analogous manner to accomplish a similar purpose.

[0031] Ranges may be expressed herein as from “about” or “approximately” or “substantially” one particular value and / or to “about” or “approximately” or “substantially” another particular value. When such a range is expressed, other exemplary7embodiments include from the one particular value and / or to the other particular value.

[0032] Similarly, as used herein, “substantially free” of something, or “substantially pure”, and like charactenzations. can include both being “at least substantially free” of something,Docket No. 255432.000088GEOSYN13PCT or “at least substantially pure’", and being “completely free’' of something, or “completely pure”.

[0033] By “comprising” or “containing” or “including” is meant that at least the named compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

[0034] It is also to be understood that the mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Similarly, it is also to be understood that the mention of one or more components in a composition does not preclude the presence of additional components than those expressly identified.

[0035] The materials described as making up the various elements of the systems and methods are intended to be illustrative and not restrictive. Many suitable materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of this disclosure. Such other materials not described herein can include, but are not limited to, for example, materials that are developed after the time of the development of the disclosure.

[0036] In an exemplary embodiment, the present disclosure provides diffuse hydraulic control using low viscosity, long duration gelation and in situ distributed colloidal silica solutions for groundwater control, mine water management, and in-situ containment structures.

[0037] The present disclosure leverages the unique properties of colloidal silica to address key challenges in groundwater control, mine water management, and the construction of in- situ containment structures. By exploiting the gelation properties of colloidal silica, the methods provide effective, sustainable solutions for controlling fluid flow in both contaminated and uncontaminated subsurface environments.

[0038] Significant changes in plasticity characteristics and hydraulic conductivity are induced in cohesive soils by the addition of nano-clay, and a significant decrease in the hydraulic conductivity can be achieved in sandy soils by grouting them with nano-silica solutions. Nanosilica grout treatments can be used for soil remediation, e.g., to remove contaminants or to form impervious barriers, or in tunneling industry to prevent piping and to prevent water leaking through cracks.Docket No. 255432.000088GEOSYN13PCT

[0039] Colloidal silica (CS) is an aqueous suspension of silica nanoparticles produced from saturated solutions of silica acid. The particle size is generally between 2 and 100 nm. During manufacturing, CS solutions are stabilized against gelation with alkali solutions. Alkaline solutions ionize the nanoparticles so that they repel each other.

[0040] Gelation that relies on the interaction between particles is induced by weakening these repulsive forces, resulting in the formation of a coherent network of siloxane (Si-O-Si) bonds that bind the soil particles together and restrain the pore fluid. The mam factors that influence the transferal of colloidal silica in liquefiable sand are the viscosity of the colloidal silica stabilizer, hydraulic gradient, and the hydraulic conductivity7of the liquefiable soil.

[0041] Additionally, the time of formation of the gel is mainly affected by the percentage of silica in the solution, the size of the silica particles, pH value, ionic strength and the temperature of the solution.Colloidal Silica Groundwater Immobilization / Contaminant Isolation:

[0042] An aqueous 5% silica sol solution with density and viscosity' similar to water (approximately 15-20 Pa; water = 10 Pa) is used. Typically, a 5% solution of colloidal silica is employed.

[0043] Silica sol, initially low in viscosity7, begins gelation when mixed with an accelerator like NaCl. This reaction destabilizes the suspension, causing the particles to bond and form a low-permeability gel.

[0044] Common accelerators include NaCl. K.C1. CaCk, and NHrCl. The addition of the accelerator may or may not be required depending on the groundwater and geological conditions. It may be added concurrently or sequentially.

[0045] Gel time can be controlled by varying the concentrations of the reactant or accelerator, or both.Potential Applications:In situ Recirculation and Mixing:

[0046] One important element of the present disclosure includes maintaining the colloidal silica solution at a low viscosity7, allowing for wide distribution in the vadose zone through a combination of injection pumping, recirculation, and slow activation. Gelation may take several days or weeks to complete.Docket No. 255432.000088GEOSYN13PCTMass Flux Reduction of Groundwater Flow:

[0047] In order to use the present innovative technology, to effectively reduce the mass flux the site desired for treatment site should comprise geological materials such as gravel, sand, silt. The hydraulic conductivity of the transmissive units should be. as just one example, 5x10-4 cm / sec or higher to allow for the amendment solutions to be injected and mixed in situ.

[0048] Once the colloidal silica has been amended and gelled, groundwater flux through the treated zone is expected to decrease significantly, potentially by four orders of magnitude or more, resulting in a substantial reduction in post-treatment groundwater flow.

[0049] Advantages of the present disclosure are many and include being cost-effective: Compared to ground freezing and conventional grouting the present disclosure should be less costly to use.

[0050] Minimal maintenance and operating costs can be achieved. Once activated nothing substantial should be required to preserve the achieved effect of groundwater control.

[0051] Biodegradation and resistance to potential changes in pH can be achieved. Once complete, the resulting changes should not be affected by biological activity7and pH conditions between 3 and 10 pH units.

[0052] Systems and methods as disclosed herein can provide source zone or plume isolation. By greatly reducing hydraulic conductivity, treated groundwater flow can be greatly reduced, reducing mass discharge.

[0053] Compared to clays, treated areas should behave like clays from a hydraulic conductivity perspective. As such amended geology can be compared to low-permeable clays.

[0054] Potential applications of the present disclosure include those shown in FIGS. 1 and 2. As indicated by the flow arrows in FIG. 1, recirculation is an aspect of the present disclosure where the injected colloidal silica solutions remain of a sufficiently low viscosity7to allow the solution to be widely distributed in the vadose zone by a combination of injection pumping and recirculation and pumping, followed by potentially7very slow activation and gelation taking several days or weeks to complete.

[0055] More generally, once the colloidal silica solution is added to a site and distributed using a combination of inject and recirculation, the resulting treatment zone can be amended with an activator solution such as NaCl, KC1, CaCh, NH4CI to start the gelation,Docket No. 255432.000088GEOSYN13PCT solidification and hardening processes that ultimately provide the reduced hydraulic conductivity that is the desired outcome.

[0056] With reference now to FIG. 2, such a barrier can be formed beneath tailings dams, landfills, or other similar sites that may generate contaminants. Using a direction boring machine 117, a more directional injection well 115 be formed, e.g., laterally, to inject colloidal silica in-si tu beneath a site for forming hydraulic control (liner type) structures beneath the site.Gelation ProcessHydrogen Bond Formation:

[0057] Silica particles begin to form hydrogen bonds under changes in pH or ionic strength, reducing particle repulsion and leading to aggregation.Network Formation:

[0058] The aggregated particles connect into a three-dimensional network throughout the liquid, forming a semi-solid gel that traps water.Solidification ProcessOngoing Gelation and Densification:

[0059] Structural changes continue as silica particles move closer together, stabilizing the network.Particle Coalescence:

[0060] The silica network densifies, resulting in a stronger, cohesive gel structure while retaining water within the matrix.Hardening ProcessSiloxane Bond Formation (Si-O-Si):

[0061] The gel hardens over time as siloxane bonds form, contributing to structural integrity' and strength, even in the presence of water.Docket No. 255432.000088GEOSYN13PCTFurther Densification:

[0062] Continued densification can occur through chemical bonding and reorganization of silica particles.Crystallization ProcessNucleation:

[0063] Under fully saturated conditions, crystallization occurs if temperature and pressure conditions are met. Nucleation sites develop as crystalline silica forms.Crystal Growth:

[0064] Cry stals grow as SiO2 molecules organize into an ordered structure. Water presence may slow the rate but does not inhibit growth.Phase Transition:

[0065] Crystalline regions expand, potentially leading to a phase transition where crystalline silica predominates.Completion of Crystallization:

[0066] Crystallization can result in a material that is harder and more thermally stable than before crystallization. Water presence may influence final crystallinity and mechanical properties.Final Structure and Properties (Under Saturated Conditions)Hydraulic Conductivity:

[0067] The final material exhibits greatly reduced hydraulic conductivity , potentially by four orders of magnitude or more.Docket No. 255432.000088GEOSYN13PCTMechanical Properties:

[0068] The final material can exhibit good mechanical strength and stability, though water presence may reduce hardness compared to dried equivalents. Mechanical strength improvements may not be significant depending on the application, so that tunnelling through the gelled matrix may require ground improvement engineering to make it possible.Effects Regarding Final Matrix Shrinkage:

[0069] Minimal or no shrinkage occurs in a fully saturated environment, as water prevents collapse that could otherwise occur during drying.

[0070] Referring now to FIGS. 3-11, systems and methods implementing the foregoing aspects of colloidal silica are further described. With reference to FIG. 3, a system 100 includes a subsurface formation 102 having an impermeable base formation 104, an aquifer 106 above the base formation 104. and a vadose zone 108 above the aquifer 106 extending to the surface 110. A column 112 of activated colloidal silica gel extends into the aquifer 106 from a boundary 114 where the aquifer 106 meets the vadose zone 108 downward to the impermeable base formation 104. The colloidal silica gel can be injected and optionally recirculated using wells or pipes 136, 138 and a mixing tank 134 much as described below with reference to FIG. 1.

[0071] A mineshaft 116 extends through the column 112 of activated colloidal silica gel to reduce or prevent leaking of groundwater 118 from the aquifer 106 into the mineshaft 116. FIG. 4 shows a top-down view of how the mineshaft 116 passes through the column 112 of activated colloidal silica gel. Those skilled in the art will readily appreciate that the discussion herein with respect to mineshafts can readily be applied to any other tunneling activities such as but not limited to subway tunnels, roadways, utility corridors, shelters, storage facilities, data centers, or the like.

[0072] Those skilled in the art will readily appreciate that applications for colloidal silica as disclosed herein are for use in the saturated zone, and that structures generated in the vadose zone are not to be expected to be permanent. In the vadose zone, it is expected that over time, the colloidal silica gel may desiccate leading to reduced lifespan.

[0073] The activated colloidal silica gel in the column 112 is formed by activating colloidal silica gel during or after placing the colloidal silica gel in place in the formation 102. The column 112 of activated colloidal silica gel can remain as a gel that form a semi -permeableDocket No. 255432.000088GEOSYN13PCT barrier to reduce groundwater flow or can be completely or partially solidified for the same function. This can reduce, inhibit, or completely eliminate groundwater ingress into mining areas and can provide an effective means of managing mine water in challenging hydrogeological conditions.

[0074] The impermeable base formation 104 includes ore 120. The mineshaft 116 extends from the surface 110, through the column 112 of activated colloidal silica gel to the ore 120. A portion of the mineshaft 116 between the surface 110 and the column 112 of activated colloidal silica gel can extend at least partially through the vadose zone 108. The column 112 of activated colloidal silica gel is a gel with a higher viscosity than the groundwater 118. In addition to preventing ingress of the groundwater 118 into the mineshaft 116, the column 112 also prevents any contaminants that may be in the mineshaft 116 from migrating into the groundwater 118. The mineshaft has a cross-sectional perimeter 122, as shown in FIG. 5. For at least a portion of a length of the mineshaft 116, the cross-sectional perimeter 122 is fully surrounded by the column 112 of activated colloidal silica gel. The column 112 can be formed using any of the methods as disclosed herein, e.g., as shown in FIG. 1.

[0075] With reference to FIG. 6, in another configuration a volume 124 of activated colloidal silica is within the aquifer 106. A contaminant 126 is included, wherein the volume 124 of activated colloidal silica forms a containment barrier 128 that at least reduces or completely prevents the spread of the contaminant 126 migrating into the groundwater 118 in the aquifer 106. The containment barrier 128 in FIGS. 6-7 is in the form of a barrier wall the forms a complete perimeter 123 around the contaminant 126, acting as a storage tank with the impermeable base formation, so that contaminant from a site 132 above the containment barrier 128 ends up in the storage volume inside the perimeter 123 of the containment barrier 128, as indicated by the arrows in FIG. 6. For example, if the contaminant 126 is heavier than water, it may settle at the bottom of the containment volume of the containment barrier 128. A water well 130 formed outside the containment barrier 128 into the aquifer 106 can provide clean groundwater 118.

[0076] With reference now to FIG. 8, it is also contemplated that the volume 124 of activated colloidal silica can completely envelop the contaminant 126. Completely enveloping the contaminant 126 can include a level of safety margin, e.g., a boundary thickness of at least 1 meter on all sides, including the top side, beyond the extent of contaminant impacts above levels where adverse effects are expected based on contaminant concentration and the like. As used herein, enveloping can include enclosing wherein the activated colloidal silica andDocket No. 255432.000088GEOSYN13PCT contaminant remain separate, but can also include partial or complete incorporation of the contaminant together with the activated colloidal silica. At least some of the contaminant 126 can be rendered inert or chemically changed by chemical reaction with the colloidal silica after to form the containment barrier 128. Fig. 8 shows the top-down perimeter 123 of the volume 124 surrounding the contaminant 126, which can be in the form of a plume. The activated colloidal silica of the volume 124 forms a barrier layer between groundwater 118 in the aquifer 106 and the contaminant 126. As with any of the embodiments in FIGS. 1-11, the column 112 or volume 124 of activated colloidal silica can either be a gel with a higher viscosity than water, or partially or completely solidified. A well 130 can access clean groundwater 118 from the aquifer 106 outside of the volume 124.

[0077] Referring now to FIG. 10, it is not necessary for the volume 124 to form a complete perimeter or encasement around the contaminant on its own. It is possible to separate groundwater 118 from a contaminant 126 using a volume 124 or column 112 of activated colloidal silica gel or crystal structure as a cut-off wall or diversion (depending on whether or not the groundwater 118 flows through the aquifer proximate the volume 124). or any other suitable type of barrier. In the case of FIGS. 10 and 11, impermeable base formation 104 and the volume 124 cooperate to separate the contaminant 126 from reaching the groundwater 118 in the aquifer 106, so a well into the aquifer on the opposite side of the volume 124 from the contaminant 126 can access clean groundwater 118. In another configuration, e.g., as shown in FIG. 1. the volumes 124 build a container above a salt brine contamination 126 to keep that from migrating up into the aquifer 106.

[0078] With reference again to FIGS. 6, 8, 10, the volume 124 can be used as a diversion structure to divert or contain a flow of groundwater to separate it from reaching a contaminant or an undesirable location. For instance, in Fig. 10, instead of a contaminant 126, there could be moving groundwater on the right-hand side of the volume 124, which is prevented from going to an undesirable location by the presence of the activated gel structure in the volume 124. This could be used, e.g., to mitigate undesirable ground water extraction effects like subsidence or dry wells on neighboring properties. For instance, a mine operation can use a barrier as described herein to prevent their pumping to dewater a mining operation from reducing ground water elevation on neighboring properties.

[0079] With reference now to FIG. 12, a method 200 includes injecting colloidal silica into a groundwater in a subsurface formation, as indicated in box 202. The method 200 includes activating the colloidal silica. The method 200 includes activating the colloidal silicaDocket No. 255432.000088GEOSYN13PCT simultaneous or post-distribution with the colloidal silica itself. This can include using an activator compound to induce gelation of the treated groundwater, e.g., over time. As indicated in box 204, this the activator can be injected into the subsurface formation together with the colloidal silica gel or separately. Optionally, the method 200 can include recirculation, as indicated in box 206, of the colloidal silica and / or its activator as described above with reference to FIG. 1. The method includes forming a stable gel matrix barrier, e.g., column 112 or volumel24 shown in FIGS. 3-11, to separate the groundwater from a second fluid, as indicated in box 208.

[0080] The method can include crystallizing the gel, as indicated in box 210 to form a solidified barrier against flow and diffusion upon gelation. The gel or solid barrier can include at least one of an in-situ cutoff wall, an in-situ containment barrier, and an in-situ diversion structure, or the like as described above with reference to FIGS. 3-11. The solidified barrier can effectively divert or contains groundwater or other fluids, offering a cost-effective and environmentally friendly solution for various geotechnical and environmental applications.

[0081] With reference again to FIG. 1, the method can include recirculating the colloidal silica and or its activator to control at least one of distribution of the colloidal silica and activation of the colloidal silica. This can include using a mixing tank 134 to mixt the silica in water and to optionally mix in the activator before during, or after injecting and / or recirculating the colloidal silica. The mixture from the mixing tank 134 can be pumped down into the subsurface formation 102 through the down pipes or wells 136 and can optionally be recirculated up to the mix tank suing up pipes or wells 138. Those skilled in the art will recognize that in addition to or in lieu of a mixing tank 134. mixing may be accomplished using metering pumps, inline mixers, dosing systems or the like, to add both the colloidal silica materials as wells as any activators. A ratio of one extraction well 138 can be used for every’ 3 to 4 injection wells 136, however those skilled in the art will readily appreciate that any suitable number or ratio of injection wells and extraction wells can be used. The cumulating or circulating volume of colloidal silica and or activated gel can form columns 112 or volumes 124. When it is determined that the colloidal silica and / or activated gel from colloidal silica is properly distributed in the subsurface formation 102, and optionally that the activator is sufficiently mixed in, recirculation through the system 100 can be stopped to allow the gel to form and potentially to allow the gel to crystallize.Docket No. 255432.000088GEOSYN13PCT

[0082] With reference again to FIGS. 2-5, the method 200 of FIG. 12 can include forming a mineshaft 116 through the gel matrix barrier, whether that is crystallized or in gel form, as indicated in box 212. In this case, the second fluid mentioned above is air within the mineshaft 11 . Separating the groundwater 118 from the second fluid includes at least reducing or fully preventing migration of the groundwater 118 into the mineshaft 116. This provides for controlling mine water inflows in areas with high hydraulic conductivity by in- situ mixing of colloidal silica within the groundwater 118 surrounding proposed or existing mine workings.

[0083] With reference now to FIGS. 6-11, the method 200 of FIG. 12 can also be used to prevent the spread of groundwater 118 impacted by various contaminants 126. The second fluid in such applications is contaminated groundwater. Injecting colloidal silica can include in-situ mixing of colloidal silica with the contaminated groundwater, e.g., as in FIGS. 8-9. It is also contemplated that the method 200 of FIG. 12 can include forming a containment barrier 128 of stable gel, e.g., as in FIGS. 6-7 and 10-11, that separates the contaminated ground water from non-contaminated groundwater. Activating the colloidal silica immobilizes the contaminated groundwater within a stable gel matrix in any of FIGS. 3-11, effectively reducing their migration through the subsurface and mitigating the spread of pollution. This can prevent contamination of surrounding groundwater systems.

[0084] Numerous characteristics and advantages have been set forth in the foregoing description, together with details of structure and function. While the systems and methods above has been disclosed in several forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions, especially in matters of shape, size, and arrangement of parts, can be made therein without departing from the spirit and scope of the disclosure and its equivalents as set forth in the following claims. Therefore, other modifications or embodiments as may be suggested by the teachings herein are particularly reserved as they fall within the breadth and scope of the claims here appended.

Claims

Docket No. 255432.000088 GEOSYN13PCTWhat is claimed is;1. A system comprising: a subsurface formation including an impermeable base formation and an aquifer above the base formation; a column of activated colloidal silica gel extending into the aquifer downward to the impermeable base formation; and a mineshaft extending through the column of activated colloidal silica gel to reduce leaking of groundwater from the aquifer into the mineshaft.

2. The system as recited in claim 1, wherein the impermeable base formation includes ore, and wherein the mineshaft extends from the surface, through the column of activated colloidal silica gel to the ore.

3. The system as recited in claim 2, wherein a portion of the mineshaft between the surface and the column of activated colloidal silica gel extends through at least a portion of a vadose zone.

4. The system as recited in claim 1, wherein the column of activated colloidal silica gel is a gel with a higher viscosity than the groundwater.

5. The system as recited in claim 1. wherein the column of activated colloidal silica gel is solidified.Docket No. 255432.000088GEOSYN13PCT6. The system as recited in claim 1, wherein the mineshaft has a cross-sectional perimeter, and wherein for at least a portion of a length of the mineshaft, the cross-sectional perimeter is fully surrounded by the column of activated colloidal silica gel.

7. The system as recited in claim 1, wherein the column of activated colloidal silica gel forms a semi-permeable barrier to reduce groundwater flow.

8. A system comprising: a subsurface formation including an impermeable base formation, an aquifer above the base formation, and a vadose zone above the aquifer extending to a surface; a volume of activated colloidal silica within the aquifer; and a contaminant, wherein the volume of activated colloidal silica forms a containment barrier that at least reduces spread of the contaminant migrating into groundwater in the aquifer.

9. The system as recited in claim 8, wherein the volume of activated colloidal silica completely envelops the contaminant.

10. The system as recited in claim 9, wherein at least some of the contaminant is chemically altered by chemical reaction with at least one of a colloidal silica after to activation of the activated colloidal silica.

11. The system as recited in claim 8, wherein the activated colloidal silica forms a barrier layer between groundwater in the aquifer and the contaminant.Docket No. 255432.000088 GEOSYN13PCT12. The system as recited in claim 1, wherein the column of activated colloidal silica is a gel with a higher viscosity than water.

13. The system as recited in claim 1, wherein the column of activated colloidal silica is solidified.

14. A method comprising: injecting colloidal silica into a groundwater in a subsurface formation; and activating the colloidal silica to form a stable gel matrix barrier to separate the groundwater from a second fluid.

15. The method as recited in claim 14, further comprising forming a mineshaft through the gel matrix barrier, wherein the second fluid is air within the mineshaft, wherein separating the groundwater from the second fluid includes at least reducing migration of the groundwater into the mineshaft.

16. The method as recited in claim 14, wherein activating the colloidal silica includes using an activator compound to induce gelation of the treated groundwater.

17. The method as recited in claim 14, wherein the second fluid is contaminated groundwater, wherein injecting colloidal silica includes in-situ mixing of colloidal silica with the contaminated groundwater, wherein forming a stable gel barrier separates the contaminated ground water from non-contaminated groundwater.Docket No. 255432.000088GEOSYN13PCT18. The method as recited in claim 17, wherein activating the colloidal silica immobilizes the contaminated groundwater within a stable gel.

19. The method as recited in claim 14, wherein injecting colloidal silica and activating the colloidal silica include forming a solidified barrier upon gelation including at least one of an in-situ cutoff wall, an in-situ containment barrier, and an in-situ diversion structure.

20. The method as recited in claim 19, further comprising recirculating the colloidal silica to control at least one of distribution of the colloidal silica and activation of the colloidal silica.

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