Method for ensuring long-term stability of remediation effect of polluted groundwater

Abstract

The invention belongs to the field of polluted groundwater remediation, and relates to a method for ensuring long-term stability of a polluted groundwater remediation effect, which is used for maintaining the long-term stability of the polluted groundwater remediation effect, and specifically comprises the following steps: injecting an alkali solution into soil through an injection well, and simultaneously extracting groundwater at an extraction well end, after the concentration of the pollutants in the extracted underground water is reduced to a target value, the injection of the alkaline solution is stopped; and injecting the calcium and / or magnesium solution into the soil through the injection well until the soil is filled with the calcium and / or magnesium solution and the concentration of pollutants in the underground water is lower than a target value, so as to finish the long-term stabilization treatment of the polluted underground water remediation. Alkali liquor and calcium and / or magnesium solution are injected into the soil through the injection well, and calcium aluminosilicate and / or magnesium aluminosilicate gel are / is generated at the junction of the low-permeability area and the high-permeability area of the soil to form an isolation belt, so that pollutants which are not removed in the remediation process of the low-permeability area are prevented from diffusing to the high-permeability area and entering an underground water flow channel; therefore, the long-term stability of the groundwater remediation effect is ensured.

Description

Technical Field

[0001] The invention belongs to the field of contaminated groundwater remediation and relates to a method for ensuring long-term stability of the contaminated groundwater remediation effect. Background Art

[0002] In-situ leaching is the most commonly used method for contaminated groundwater remediation projects, that is, by burying injection wells and extraction wells in the soil, extracting contaminated groundwater from the extraction wells, and injecting leaching fluid into the injection wells at the same time. Depending on the pollutants, the leaching fluid may contain acid, alkali, surfactant, oxidant or reductant, etc. However, the biggest problem faced by this technology in engineering applications is that the remediation effect cannot be stable for a long time due to the uneven distribution of soil permeability at the remediation site. This problem is particularly prominent in the remediation of groundwater at heavily chromium-contaminated sites (such as the original site of chromate production enterprises). The following example will be used to illustrate this.

[0003] In natural soil and groundwater environments, chromium is present in trivalent form (Cr 3+ ) and hexavalent (CrO4 2- ) exists in two forms. Trivalent chromium is its natural form with low toxicity and low solubility in water. Hexavalent chromium comes from human industrial activities and is nearly a thousand times more toxic than trivalent chromium. It is a carcinogen and has high solubility in water. The remediation of chromium-contaminated groundwater usually uses leaching technology, especially when the pollution range is wide or ground buildings cannot be demolished. The leaching technology is to inject the leaching solution into the soil through an injection well, and then extract the leaching solution containing hexavalent chromium from the soil through an extraction well until the concentrations of hexavalent chromium and total chromium in the water meet the remediation target requirements. If necessary, add ferrous iron or other reducing agents to the leaching solution in the second half of the leaching operation to reduce the hexavalent chromium that has not been leached out, so as to improve the remediation effect and efficiency.

[0004] The biggest problem facing this contaminated groundwater remediation technology is that the hexavalent chromium in the soil of the low-permeability area cannot be effectively removed. During the long-term monitoring process after the remediation acceptance, it gradually seeps into the groundwater channels in the high-permeability area, resulting in excessive hexavalent chromium concentrations in the later monitoring results. This is mainly due to the different migration mode of hexavalent chromium when it pollutes the groundwater and during leaching remediation. Taking the contaminated sites of chromium salt production enterprises with heavy pollution and large pollution areas as an example, hexavalent chromium released from leakage in the production workshop and chromium slag yard infiltrates into the soil from top to bottom with rainwater in the factory area, causing pollution to the soil and groundwater in the factory area. When the infiltration encounters a high-permeability area (an area with a higher permeability coefficient) with a lateral water flow channel, it migrates laterally out of the factory area and also pollutes the groundwater and soil outside the factory area. At the same time, hexavalent chromium continues to infiltrate and pollute deeper low-permeability areas (areas with a lower permeability coefficient). Hexavalent chromium is in the form of chromate (CrO4 2-) exists, and its penetration ability is very strong, close to that of nitrate ions and chloride ions. A site survey found that hexavalent chromium has been polluting the site for more than decades, with a depth of tens of meters and has entered the weathered bedrock in the low-permeability area. The hexavalent chromium concentration in the groundwater is more than 1000 mg / L. Long-term and high concentrations allow hexavalent chromium to enter the low-permeability area through the concentration diffusion mechanism.

[0005] During the leaching remediation, the eluent, driven by the pressure gradient between the injection well and the extraction well, chooses to form a water flow channel in the hyperpermeable area, and as the leaching time increases, the channel gradually expands (because some soil is taken away), especially when there is acid in the eluent, it will dissolve the carbonate in the soil, causing the water flow channel to expand significantly. This causes the eluent to pass mainly through the hyperpermeable area and return to the ground at the extraction well without passing through the hypopermeable area. In the hyperpermeable area, the hexavalent chromium in the groundwater and soil is mainly washed out by convection or reduced by contact with the reducing agent. Usually after weeks or months of remediation, the hexavalent chromium concentration in the groundwater in the hyperpermeable area can be reduced to meet the remediation target requirements, and the remediation project is completed. However, only a small part of the hexavalent chromium in the soil and groundwater in the hypopermeable area surrounding the water flow channel in the hyperpermeable area enters the water flow channel through concentration diffusion and is removed, because the result of decades of concentration diffusion cannot be reversely diffused within a few months. This process is very slow, but it is enough to cause the hexavalent chromium concentration in the groundwater to "rebound" and exceed the standard after the remediation is stopped, which cannot meet the requirements of long-term stability of the remediation effect. For example, after more than 20 years of natural rainwater leaching and restoration at the site of a chromium salt factory, the concentration of hexavalent chromium in the groundwater dropped from >1000mg / L to about 200mg / L, but the rate of decline has been decreasing year by year, while the limit value required for Class IV water quality in the Groundwater Quality Standard (GB / T14848-2017) is no more than 0.1mg / L. Similarly, the remediation of other types of contaminated groundwater (such as other metals and metalloids, various organic polluted groundwater) also faces the same long-term stability problem. In order to solve the above problems, it is urgent to propose a method to ensure the long-term stability of the remediation effect of contaminated groundwater. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a method to ensure the long-term stability of the remediation effect of contaminated groundwater, establish an "isolation zone" with a lower permeability coefficient at the junction of the hyperpermeable zone and the hypopermeable zone, and seal the pollutants (such as hexavalent chromium) in the hypopermeable zone, so that they cannot enter the hyperpermeable zone or slow down their speed, thereby ensuring for a long time that the concentration of pollutants in the groundwater after the remediation of the contaminated groundwater does not exceed the groundwater quality standard requirements, thereby achieving long-term stability of the leaching remediation effect of contaminated groundwater.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for ensuring the long-term stability of the contaminated groundwater remediation effect is used to maintain the long-term stability of the contaminated groundwater remediation effect, specifically comprising the following steps:

[0009] Step 1. Inject the alkaline solution into the soil through the injection well, and extract groundwater at the extraction well end at the same time, until the pollutant concentration in the extracted groundwater drops to the target value, and then stop injecting the alkaline solution;

[0010] Step 2. Inject the calcium and / or magnesium solution into the soil through the injection well until the calcium and / or magnesium solution fills the soil to complete the long-term stabilization treatment of the contaminated groundwater remediation.

[0011] Furthermore, the alkaline solution is sodium hydroxide or potassium hydroxide solution or a mixture of the two.

[0012] Furthermore, the concentration range of the alkaline solution is: 1.5 mol / L to 38 mol / L.

[0013] Furthermore, the calcium and / or magnesium solution is prepared by mixing one or more of calcium citrate, calcium lactate, calcium gluconate, calcium chloride, calcium oxide, calcium hydroxide, magnesium chloride, magnesium citrate or magnesium sulfate.

[0014] Furthermore, the Ca in the calcium and / or magnesium solution 2+ With Mg 2+ The sum of their concentrations ranges from 0.27 to 7.2 mol / L.

[0015] Furthermore, the step 1 is carried out under a heating condition of ≤100°C to shorten the time of step 1;

[0016] The heating method is: heating the alkaline solution first and then injecting it into the soil, or injecting the alkaline solution into the soil and then heating it using a heating device buried in the soil at the junction of the hypertonic zone and the hypotonic zone, or after heating the alkaline solution, heating the alkaline solution in the soil again using a heating device.

[0017] Furthermore, before carrying out step 1, the contaminated groundwater needs to be repaired to reduce the concentration of pollutants in the contaminated groundwater to below the target value, and then the method is used to maintain the long-term stability of the contaminated groundwater repair effect.

[0018] The beneficial effects of the present invention are:

[0019] For contaminated groundwater (such as chromium-contaminated groundwater) after in-situ leaching and repair, or when the hexavalent chromium concentration in the chromium-contaminated groundwater is low and the leaching water effect is long-term unstable or the cost-effectiveness of the leaching method is very low, the present invention provides a method for ensuring the long-term stability of the contaminated groundwater repair effect. Alkali solution and calcium solution are injected into the soil through an injection well to generate calcium aluminosilicate and / or magnesium aluminosilicate gel in the soil, thereby sealing the tiny gaps between soil particles and forming a low-permeability isolation zone at the junction of the low-permeability zone and the high-permeability zone, preventing the hexavalent chromium that has not been leached away in the low-permeability zone from diffusing into the high-permeability zone and entering the groundwater flow channel, and at the same time wrapping and sealing the surface of the soil particles to prevent the hexavalent chromium on the surface of the soil particles from continuing to desorb into the soil solution, thereby ensuring the long-term stability of the groundwater repair effect.

[0020] Secondly, the invention can also be used in situations where long-term stability needs to be achieved in other types of groundwater pollution remediation, such as maintaining the remediation effects of groundwater polluted by other metals and metalloids, and groundwater polluted by various organic substances. The operation method of the present invention is simple, the cost is low, and the remediation cycle is short. It has good application prospects in the practical operation of maintaining long-term stability of the remediation effect of contaminated groundwater.

[0021] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0023] Figure 1 A schematic diagram of the implementation of a method for ensuring long-term stability of the contaminated groundwater remediation effect in the present invention;

[0024] Figure 2 It is a schematic diagram of the implementation of a method for ensuring long-term stability of the contaminated groundwater remediation effect in the present invention (with a heating device).

[0025] Figure numerals: injection well 1, extraction well 2, groundwater flow channel 3, high permeability zone 4, low permeability zone 5, isolation zone 6, heating device 7. DETAILED DESCRIPTION

[0026] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0027] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0028] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0029] Example 1

[0030] like Figure 1 As shown in the figure, the soil of a contaminated site contains high content of aluminum-silicon minerals such as kaolinite and montmorillonite, the hexavalent chromium content in the soil is 210-860 mg / kg, and the hexavalent chromium concentration in the groundwater is 80-150 mg / L. After 52 days of elution with an acid solution eluent, the hexavalent chromium concentration in the effluent from the extraction well dropped to 0.1 mg / L. After stopping injection and extraction for a week and then resuming extraction, it was found that the hexavalent chromium concentration rebounded to 2.3 mg / L. After repeated repeated attempts, the hexavalent chromium concentration still rebounded, resulting in the inability to maintain the long-term stability of the remediation effect of chromium-contaminated groundwater.

[0031] Then, a method for ensuring long-term stability of the contaminated groundwater remediation effect provided by the present invention is used, and the injection well 1 and the extraction well 2 used for in-situ elution are directly used to inject the alkaline solution and the calcium solution and extract the groundwater, and a 30 mol / L sodium hydroxide solution is injected into the soil through the injection well 1 instead of the elution solution. When the hexavalent chromium concentration in the effluent of the extraction well 2 drops below 0.1 mg / L, the injection and extraction are stopped and maintained for one week;

[0032] After that, 7.2 mol / L calcium chloride solution was injected, and the concentrations of calcium chloride and hexavalent chromium in the effluent from the extraction well were monitored. The injection was stopped after it was determined that the calcium chloride solution had filled the soil and the hexavalent chromium concentration was lower than 0.1 mg / L. Four weeks later, water samples were extracted from extraction well 2 to monitor the hexavalent chromium concentration in groundwater flow channel 3, and the hexavalent chromium concentration was still lower than 0.1 mg / L. Monitoring was conducted once a month in the following year, and the hexavalent chromium concentration showed a decreasing trend month by month, and the last time it was lower than 0.05 mg / L, meeting the Class III water quality requirements in the Groundwater Quality Standard (GB / T14848-2017).

[0033] The principle of the method for ensuring the long-term stability of the contaminated groundwater remediation effect is that, in the first step, sodium hydroxide is injected into the soil through the injection well 1 to dissolve and soften the silicon and aluminum minerals on the surface of the soil particles, and sodium silicate and sodium aluminate with a certain viscosity are generated on the surface of the soil particles and between the soil particles;

[0034] In the second step, calcium ions are injected into the soil through the injection well 1. The injected calcium ions react with sodium silicate and sodium aluminate to generate calcium aluminosilicate with a gelling effect to seal the pores on the surface of soil particles and between adjacent soil particles. The sealing of the surface of soil particles fixes the undesorbed hexavalent chromium, and the sealing of the pores between adjacent soil particles reduces the soil permeability, thereby forming an isolation zone 6 between the high permeability zone 4 and the low permeability zone 5, making it more difficult for the hexavalent chromium in the soil solution of the low permeability zone 5 to diffuse into the high permeability zone 4 through the concentration difference.

[0035] Specifically, the sodium hydroxide solution and the calcium chloride solution are rapidly distributed in the water flow channel, the entire hypertonic zone 4, and the transition zone between the hypertonic zone 4 and the hypotonic zone 5 through convection, and slowly penetrate into the hypotonic zone 5 through concentration diffusion (the higher the concentration and the higher the temperature, the faster the diffusion speed and the greater the depth). In the underground water flow channel 3 (the wide band can reach several mm or several cm) in the hypertonic zone 4, the pores between the soil particles are large and cannot be closed, and only the hexavalent chromium on the surface of the soil particles can be closed. With the expansion to the surrounding hypotonic zone 5, the pores between the soil particles gradually shrink, and the sealing effect on the pores begins to appear, causing the soil permeability to decrease, forming an isolation zone 6. Therefore, the isolation zone 6 is an area with a transition boundary that extends from the underground water flow channel 3 around the hypertonic zone 4 to the periphery until the hypotonic zone 5, and its permeability coefficient at one end of the hypotonic zone 5 is lower than the original permeability coefficient of the soil. The groundwater remediation process will largely change the structure and flow distribution of the original groundwater flow channel on the site. The flow channel widened by the elution fluid will become the mainstream channel of groundwater in the site after the remediation. The existence of the isolation zone 6 blocks the diffusion of hexavalent chromium retained in the low-permeability zone 5 to the groundwater flow channel 3.

[0036] The penetration capacity of sodium hydroxide is more than twice that of hexavalent chromium (Na2CrO4). Therefore, as long as the time, concentration and temperature reach a certain level, its diffusion depth can exceed the diffusion depth of hexavalent chromium. This means that in theory, the entire low-permeability area 5 where hexavalent chromium exists can be sealed. In actual remediation projects, the underground conditions of various sites are ever-changing. During the implementation of the project, the basic technical requirement is to meet the standards based on the conditions of each site, and comprehensive consideration is given to limiting factors such as cost and construction period. Various technical parameters are determined through small-scale field experiments. There is no need to seal the entire low-permeability area contaminated by hexavalent chromium.

[0037] The present invention can be used in conjunction with existing leaching technology, or used alone when the leaching cost-effectiveness ratio is very low, to effectively solve the problem of how to maintain long-term stability in the remediation of chromium-contaminated groundwater.

[0038] Example 2

[0039] like Figure 2 As shown in the figure, the hexavalent chromium content in the soil of a contaminated site is 910-3100 mg / kg, and the hexavalent chromium concentration in the groundwater is 230-360 mg / L. After leaching with an acid solution eluent for 30 days, the hexavalent chromium concentration in the effluent from the extraction well dropped to 12-15 mg / L. After the reduction treatment was carried out by injecting a reducing agent, the hexavalent chromium concentration in the effluent dropped to 0.6-1.1 mg / L and stopped decreasing.

[0040] The method of the present invention is then used to inject a 38 mol / L sodium hydroxide solution into the soil instead of the eluent through the injection well 1, and the soil temperature is heated to about 90° C. by using an electric heating rod (heating device 7). When the hexavalent chromium concentration in the effluent from the extraction well 2 drops below 0.1 mg / L, the injection and extraction are stopped. After 12 hours, the hexavalent chromium concentration is only increased by about 12% after re-testing.

[0041] After that, 7.2 mol / L calcium chloride solution was injected, and the concentrations of calcium chloride and hexavalent chromium in the water from extraction well 2 were monitored. The injection was stopped after it was determined that the calcium chloride had filled the soil and the hexavalent chromium concentration was lower than 0.1 mg / L. Water samples were taken from the extraction well for monitoring after 4 weeks, and the hexavalent chromium concentration was lower than 0.1 mg / L. Monitoring was carried out once a month for the next year, and the hexavalent chromium concentration decreased to below 0.05 mg / L month by month.

[0042] Example 3

[0043] like Figure 1 As shown, the hexavalent chromium content in the soil of a contaminated site is 120-250 mg / kg, and the hexavalent chromium concentration in the groundwater is 6.1-11.7 mg / L.

[0044] The site is less polluted and has been naturally leached for more than 20 years. The cost-effectiveness of leaching is very low. Therefore, the method of the present invention is directly used to inject a 1.5 mol / L sodium hydroxide solution heated to above 95°C into the soil through an injection well. When the hexavalent chromium concentration in the effluent from the extraction well drops below 0.1 mg / L, the injection and extraction are stopped.

[0045] Then, 0.5 mol / L calcium chloride solution was injected, and the concentrations of calcium chloride and hexavalent chromium in the water from the extraction well were monitored. The injection was stopped after it was determined that the calcium chloride had filled the soil and the hexavalent chromium concentration was lower than 0.1 mg / L. After 4 weeks, water samples were taken from the extraction well for monitoring, and the hexavalent chromium concentration was lower than 0.1 mg / L. Monitoring was performed once a month for the following year, and the hexavalent chromium concentration gradually dropped to below 0.05 mg / L.

[0046] Example 4

[0047] like Figure 2 As shown in the figure, the soil and groundwater at the site of a pesticide factory were contaminated by pesticides such as dimethoate. Chemical in situ oxidation technology was used for remediation, and the oxidant was injected into the soil through an injection well. After 35 days of remediation, although the pesticide concentration in the water from the extraction well had basically reached the standard, the odor was still strong and could not meet the requirements.

[0048] The method of the present invention is then used to inject a 5 mol / L sodium hydroxide solution heated to above 95°C into the soil through the injection well, and the soil is heated using a heating rod (heating device 7). The injection and extraction are stopped after the pesticide concentration and odor in the extraction well meet the standards. Then, a 0.27 mol / L calcium chloride solution is injected, and water samples are taken from the extraction well for monitoring after 4 weeks. The pesticide concentration and odor meet the standards. No rebound phenomenon was observed in the monthly monitoring within the next year.

[0049] Example 5

[0050] In a certain arsenic contaminated site, the arsenic content in the soil is 270-630 mg / kg, and the arsenic concentration in the groundwater is 0.6-1.1 mg / L. Arsenic exists in the form of arsenate, and the desorption efficiency in alkaline solution is higher than that in acid solution, so the method of the present invention is directly used;

[0051] like Figure 2 As shown, a 20 mol / L sodium hydroxide solution is injected into the soil through an injection well 1, and the heating rod (heating device 7) uses a gas heat source to heat the soil temperature to about 60°C. When the arsenic concentration in the effluent water of the extraction well 2 drops below 0.05 mg / L, the injection and extraction are stopped. After 24 hours of insulation, the arsenic concentration in the effluent water is re-tested and does not increase. Then, a 1.8 mol / L calcium chloride solution is injected, and the concentrations of calcium chloride and arsenic in the effluent water of the extraction well are monitored. The injection is stopped after it is determined that the calcium chloride has filled the soil and the arsenic concentration is lower than 0.05 mg / L. After 4 weeks, water samples are taken from the extraction well for monitoring, and the arsenic concentration is lower than 0.05 mg / L. Monitoring is performed once a month in the following year, and the arsenic concentration gradually drops to below 0.01 mg / L.

[0052] In another embodiment, part or all of the calcium solution may be replaced by a magnesium solution, wherein the magnesium solution is a mixture of one or more of magnesium chloride, magnesium citrate or magnesium sulfate, and the Mg in the magnesium solution is 2+ concentration (all magnesium solutions) or Ca 2+ With Mg 2+ The sum of their concentrations (mixed solution of calcium and magnesium) ranges from 0.27 to 7.2 mol / L, and magnesium aluminosilicate or a mixture of calcium aluminosilicate and magnesium aluminosilicate is generated in the subsequent step 2.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for ensuring long-term stability of the remediation effect of contaminated groundwater, characterized in that: To maintain the long-term stability of the contaminated groundwater remediation effect, the following steps are included: Step 1. Inject the alkaline solution into the soil through the injection well, and extract groundwater at the extraction well end at the same time, until the pollutant concentration in the extracted groundwater drops to the target value, and then stop injecting the alkaline solution; Step 2. Inject the calcium and / or magnesium solution into the soil through the injection well until the calcium and / or magnesium solution fills the soil to complete the long-term stabilization treatment of the contaminated groundwater remediation.

2. The method according to claim 1, characterized in that: The alkaline solution is sodium hydroxide or potassium hydroxide solution or a mixture of the two.

3. The method according to claim 2, characterized in that: The concentration range of the alkaline solution is: 1.5 mol / L to 38 mol / L.

4. The method according to claim 1, characterized in that: The calcium and / or magnesium solution is prepared by mixing one or more of calcium citrate, calcium lactate, calcium gluconate, calcium chloride, calcium oxide, calcium hydroxide, magnesium chloride, magnesium citrate or magnesium sulfate.

5. The method according to claim 4, characterized in that: The Ca in the calcium and / or magnesium solution 2+ With Mg 2+ The sum of their concentrations ranges from 0.27 to 7.2 mol / L.

6. The method according to claim 1, characterized in that: The step 1 is carried out under a heating condition of ≤100°C to shorten the time of step 1; The heating method is: heating the alkaline solution first and then injecting it into the soil, or injecting the alkaline solution into the soil and then heating it using a heating device buried in the soil at the junction of the hypertonic zone and the hypotonic zone, or after heating the alkaline solution, continuing to heat the alkaline solution in the soil through the heating device.

7. The method according to any one of claims 1 to 6, characterized in that: Before carrying out step 1, the contaminated groundwater needs to be repaired to reduce the concentration of pollutants in the contaminated groundwater to below the target value, and then the method is used to maintain the long-term stability of the contaminated groundwater repair effect.

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