Methods to ensure long-term stability of contaminated groundwater remediation effects

Abstract

This invention belongs to the field of contaminated groundwater remediation and relates to a method for ensuring the long-term stability of contaminated groundwater remediation effects. The invention is used to maintain the long-term stability of contaminated groundwater remediation effects and specifically includes the following steps: injecting an alkaline solution into the soil through an injection well while simultaneously extracting groundwater at the extraction well until the concentration of pollutants in the extracted groundwater drops to a target value, at which point the injection of the alkaline solution is stopped; then injecting a calcium and / or magnesium solution into the soil through the injection well until the soil is filled with calcium and / or magnesium solution and the concentration of pollutants in the groundwater is below the target value, thus completing the long-term stabilization treatment of the contaminated groundwater remediation. This invention injects alkaline and calcium and / or magnesium solutions into the soil through injection wells, forming a separation zone at the boundary between low-permeability and high-permeability zones of the soil. This prevents pollutants not removed during the remediation process in the low-permeability zone from diffusing into the high-permeability zone and entering the groundwater flow channel, thereby ensuring the long-term stability of the groundwater remediation effect.

Description

Technical Field

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

[0002] In-situ leaching is the most common method used in contaminated groundwater remediation projects. It involves burying injection wells and extraction wells in the soil, extracting contaminated groundwater from the extraction wells, and simultaneously injecting leaching fluid into the injection wells. Depending on the contaminant, the leaching fluid may contain acids, alkalis, surfactants, oxidants, or reducing agents. However, the biggest problem this technology faces in engineering applications is that the uneven distribution of soil permeability at the remediation site often leads to unstable long-term remediation results. This problem is particularly prominent in the groundwater remediation of heavily chromium-contaminated sites (such as former sites of chromate production plants), which will be illustrated below as an example.

[0003] In natural soil and groundwater environments, chromium exists in the trivalent (Cr) state. 3+ ) and hexavalent (CrO4) 2- Chromium exists in two forms: trivalent chromium, which is its naturally occurring form, has low toxicity, and low solubility in water; and hexavalent chromium, which originates from human industrial activities, is nearly a thousand times more toxic than trivalent chromium, is a carcinogen, and has high solubility in water. Remediation of chromium-contaminated groundwater typically employs leaching technology, especially when the contamination area is extensive or when surface buildings cannot be demolished. Leaching involves injecting a leaching solution into the soil through injection wells, and then extracting the hexavalent chromium-containing leaching solution from the soil through extraction wells until the concentrations of hexavalent chromium and total chromium in the water meet the remediation target requirements. If necessary, in the latter half of the leaching process, reducing agents such as ferrous iron are added to the leaching solution to reduce any remaining hexavalent chromium, thereby improving the remediation effect and efficiency.

[0004] The biggest problem facing this groundwater remediation technology is the inability to effectively remove hexavalent chromium from the soil in low-permeability zones. During long-term monitoring after remediation acceptance, it gradually infiltrates into the groundwater channels of high-permeability zones, leading to excessive hexavalent chromium concentrations in later monitoring results. This is mainly due to the different migration patterns of hexavalent chromium when contaminating groundwater compared to leaching remediation. Taking a heavily contaminated, large-area chromium salt production site as an example, hexavalent chromium released from leaks and spills in the production workshop and chromium slag dumps infiltrates the soil from top to bottom with rainwater within the plant area, polluting the soil and groundwater. When this infiltration encounters high-permeability zones (areas with high permeability coefficients) with lateral water flow channels, it migrates laterally out of the plant area, also polluting groundwater and soil outside the plant. Simultaneously, hexavalent chromium continues to infiltrate, polluting deeper low-permeability zones (areas with lower permeability coefficients). Hexavalent chromium exists in the form of chromate (CrO4). 2-Hexavalent chromium exists and has a high permeability, similar to nitrate and chloride ions. Site investigations have found that hexavalent chromium has been continuously contaminating the site for decades, reaching depths of tens of meters and penetrating into the weathered bedrock of low-permeability zones. The concentration of hexavalent chromium in groundwater exceeds 1000 mg / L. This prolonged and high concentration allows hexavalent chromium to enter low-permeability zones through concentration gradient diffusion.

[0005] During leaching remediation, the leaching fluid, driven by the pressure gradient between the injection and extraction wells, selectively forms flow channels in high-permeability zones. These channels gradually expand with leaching time (due to the removal of some soil), especially when acid is present in the leaching fluid, which dissolves carbonates in the soil, leading to a significant expansion of the flow channels. This results in the leaching fluid primarily passing through high-permeability zones, bypassing low-permeability zones to reach the extraction wells and return to the surface. In high-permeability zones, hexavalent chromium in groundwater and soil is mainly washed out through convection or reduced by contact with reducing agents. Typically, after several weeks or months of remediation, the concentration of hexavalent chromium in the high-permeability groundwater can be reduced to meet the remediation target, and the remediation project is complete. However, only a small portion of the hexavalent chromium in the low-permeability soil and groundwater surrounding the high-permeability flow channels is removed through concentration gradient diffusion into the flow channels. This is because decades of concentration gradient diffusion cannot be reversed within a few months. This process is very slow, but sufficient to cause a "rebound" and exceedance of the hexavalent chromium concentration in groundwater after remediation stops, failing to meet the requirement for long-term stable remediation results. For example, after more than 20 years of natural rainwater leaching and remediation at a former chromium salt plant site, the concentration of hexavalent chromium in the groundwater only decreased from >1000 mg / L to around 200 mg / L, but the rate of decrease showed a decreasing trend year by year. Meanwhile, the limit for Class IV water quality in the "Groundwater Quality Standard" (GB / T14848-2017) is no more than 0.1 mg / L. Similarly, the remediation of other types of contaminated groundwater (such as groundwater contaminated by other metals and metalloids, and groundwater contaminated by various organic substances) also faces the same long-term stability challenge. To solve these problems, there is an urgent need 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 this invention is to provide a method to ensure the long-term stability of the remediation effect of contaminated groundwater. A "separation zone" with a lower permeability coefficient is established at the boundary between high-permeability and low-permeability zones to seal off pollutants (such as hexavalent chromium) in the low-permeability zone, preventing or slowing down their entry into the high-permeability zone. This ensures that the concentration of pollutants in the groundwater after remediation does not exceed the groundwater quality standards, thus achieving long-term stability of the leaching remediation effect on contaminated groundwater.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for ensuring the long-term stability of the remediation effect of contaminated groundwater, specifically including the following steps:

[0009] Step 1. Inject the alkaline solution into the soil through the injection well, while simultaneously extracting groundwater at the extraction well end until the concentration of pollutants in the extracted groundwater drops to the target value, then stop injecting the alkaline solution.

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

[0011] Furthermore, the alkaline solution is a sodium hydroxide solution or a 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 one or more of calcium citrate, calcium lactate, calcium gluconate, calcium chloride, calcium oxide, calcium hydroxide, magnesium chloride, magnesium citrate, or magnesium sulfate.

[0014] Further, 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, step 1 is performed under heating conditions of ≤100°C to shorten the time of step 1;

[0016] The heating methods are as follows: heating the alkaline solution before 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 high-permeability and low-permeability zones, or heating the alkaline solution in the soil after heating the alkaline solution.

[0017] Furthermore, before proceeding to step 1, the contaminated groundwater needs to be remediated to reduce the concentration of pollutants in the groundwater to below the target value. Then, this method can be used to maintain the long-term stability of the remediation effect of the contaminated groundwater.

[0018] The beneficial effects of this invention are as follows:

[0019] For contaminated groundwater that has undergone in-situ leaching remediation (such as chromium-contaminated groundwater), or when the concentration of hexavalent chromium in chromium-contaminated groundwater is low and the leaching effect is unstable over a long period or the cost-effectiveness of the leaching method is very low, this invention provides a method to ensure the long-term stability of the remediation effect of contaminated groundwater. By injecting alkaline and calcium solutions into the soil through injection wells, calcium aluminosilicate and / or magnesium aluminosilicate gel are generated in the soil, thereby sealing the gaps between fine soil particles and forming a low-permeability isolation zone at the boundary between low-permeability and high-permeability zones. This prevents hexavalent chromium that has not been leached from the low-permeability zone from diffusing into the groundwater flow channel in the high-permeability zone. Simultaneously, it coats and seals the surface of soil particles, preventing the further desorption of hexavalent chromium from the soil particle surface into the soil solution, thus ensuring the long-term stability of the groundwater remediation effect.

[0020] Secondly, this invention can also be used in other types of groundwater pollution remediation where long-term stability is required, such as maintaining the remediation effect of groundwater contaminated by other metals and metalloids, and groundwater contaminated by various organic substances. Furthermore, the operation method of this invention is simple, the cost is low, and the remediation cycle is short, making it a promising application in practical applications for maintaining the long-term stability of groundwater remediation effects.

[0021] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0023] Figure 1 This is a schematic diagram illustrating the implementation of a method for ensuring the long-term stability of the remediation effect of contaminated groundwater according to the present invention.

[0024] Figure 2 This is a schematic diagram (with heating device) illustrating an implementation of a method for ensuring long-term stable remediation effects of contaminated groundwater according to the present invention.

[0025] Attached reference numerals: 1. Injection well; 2. Extraction well; 3. Groundwater flow channel; 4. High-permeability zone; 5. Low-permeability zone; 6. Isolation zone; 7. Heating device. Detailed Implementation

[0026] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed 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 are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0027] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0028] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0029] Example 1

[0030] like Figure 1 As shown, the soil at a contaminated site contained high levels of aluminum-silicon minerals such as kaolinite and montmorillonite, with hexavalent chromium content ranging from 210 to 860 mg / kg in the soil and 80 to 150 mg / L in the groundwater. After leaching with an acid solution for 52 days, the hexavalent chromium concentration in the extraction well water decreased to 0.1 mg / L. After stopping injection and extraction for one week and then resuming extraction, the hexavalent chromium concentration rebounded to 2.3 mg / L. This process was repeated multiple times, and the hexavalent chromium concentration continued to rebound, making it impossible to maintain the long-term stability of the remediation effect for chromium-contaminated groundwater.

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

[0032] Subsequently, a 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. Injection was stopped once the soil was deemed saturated with calcium chloride solution and the hexavalent chromium concentration was below 0.1 mg / L. Four weeks later, water samples were taken from extraction well 2 to monitor the hexavalent chromium concentration in groundwater flow channel 3. The hexavalent chromium concentration remained below 0.1 mg / L. Monitoring was conducted monthly for the following year, and the hexavalent chromium concentration showed a decreasing trend month by month, ultimately falling below 0.05 mg / L, meeting the Class III water quality requirements of the Groundwater Quality Standard (GB / T14848-2017).

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

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

[0035] Specifically, sodium hydroxide and calcium chloride solutions rapidly distribute through convection in the water flow channels, the entire high-permeability zone 4, and the transition zone between high-permeability zone 4 and low-permeability zone 5. They then slowly infiltrate into low-permeability zone 5 via concentration gradient diffusion (higher concentrations and temperatures result in faster and deeper diffusion). In the groundwater flow channels 3 of high-permeability zone 4 (wide enough to be several mm or cm), the pores between soil particles are relatively large and cannot be completely sealed; only the hexavalent chromium on the surface of the soil particles can be sealed. As the flow extends towards the surrounding low-permeability zone 5, the pores between soil particles gradually shrink, and the sealing effect on the pores becomes apparent, leading to a decrease in soil permeability and forming an isolation zone 6. Therefore, this isolation zone 6 is a region with a transitional boundary extending from the groundwater flow channels 3 around high-permeability zone 4 to low-permeability zone 5, where the permeability coefficient at one end of low-permeability zone 5 is lower than the original soil permeability coefficient. The groundwater remediation process will significantly alter the structure and flow distribution of the original groundwater channels on the site. The channels widened by the leaching fluid will become the main channels for groundwater in the remediated site. The presence of the isolation zone 6 prevents the diffusion of hexavalent chromium remaining in the low-permeability zone 5 into the groundwater flow channel 3.

[0036] Sodium hydroxide has a permeability more than twice that of hexavalent chromium (Na2CrO4). Therefore, given sufficient time, concentration, and temperature, its diffusion depth can exceed that of hexavalent chromium. This means that, theoretically, the entire low-permeability zone containing hexavalent chromium can be sealed off. However, in actual remediation projects, the underground conditions of each site vary greatly. During project implementation, the basic technical requirement is to meet the standards based on the conditions of each site. Taking into account factors such as cost and construction period, various technical parameters are determined through small-scale field experiments. It is not necessary to completely seal off the entire low-permeability zone contaminated with hexavalent chromium.

[0037] This invention, when used in conjunction with existing leaching technologies or alone when the cost-effectiveness of leaching is very low, can effectively solve the problem of maintaining long-term stability in the remediation of chromium-contaminated groundwater.

[0038] Example 2

[0039] like Figure 2 As shown, the hexavalent chromium content in the soil of a contaminated site ranged from 910 to 3100 mg / kg, while the concentration in the groundwater ranged from 230 to 360 mg / L. After leaching with an acid solution for 30 days, the concentration of hexavalent chromium in the effluent from the extraction well decreased to 12–15 mg / L. Reduction treatment using a reducing agent further reduced the concentration of hexavalent chromium in the effluent to 0.6–1.1 mg / L, after which it stopped decreasing.

[0040] Continuing with the method of the present invention, a 38 mol / L sodium hydroxide solution was injected into the soil through injection well 1 instead of the leaching solution. At the same time, the soil temperature was heated to about 90°C using an electric heating rod (heating device 7). When the concentration of hexavalent chromium in the effluent from extraction well 2 dropped to below 0.1 mg / L, the injection and extraction were stopped. After maintaining this for 12 hours, the concentration of hexavalent chromium was retested and found to have increased by only about 12%.

[0041] A 7.2 mol / L calcium chloride solution was then injected, and the concentrations of calcium chloride and hexavalent chromium in the effluent from extraction well 2 were monitored. Injection was stopped once the soil was deemed sufficiently saturated with calcium chloride and the hexavalent chromium concentration was below 0.1 mg / L. Four weeks later, water samples were taken from the extraction well for monitoring, and the hexavalent chromium concentration was below 0.1 mg / L. Monitoring was conducted monthly for the following year, and the hexavalent chromium concentration gradually decreased to below 0.05 mg / L each month.

[0042] Example 3

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

[0044] Because the site was relatively lightly polluted and had undergone natural leaching for more than 20 years, the cost-effectiveness of leaching was very low. Therefore, the method of this invention was 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 concentration of hexavalent chromium in the water from the extraction well dropped to below 0.1 mg / L, the injection and extraction were stopped.

[0045] Then, a 0.5 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. Injection was stopped once the soil was deemed sufficiently saturated with calcium chloride and the hexavalent chromium concentration was below 0.1 mg / L. Four weeks later, water samples were taken from the extraction well for monitoring, and the hexavalent chromium concentration was below 0.1 mg / L. Monitoring was conducted monthly for the following year, and the hexavalent chromium concentration gradually decreased to below 0.05 mg / L.

[0046] Example 4

[0047] like Figure 2 As shown, the soil and groundwater at the site of a pesticide factory were contaminated with pesticides such as dimethoate. Chemical in-situ oxidation technology was used for remediation, in which oxidants were injected into the soil through injection wells. After 35 days of remediation, although the pesticide concentration in the water extracted from the wells had basically met the standards, the odor was still strong and could not meet the requirements.

[0048] Continuing with the method of this invention, a 5 mol / L sodium hydroxide solution heated to above 95°C was injected into the soil through an injection well. Simultaneously, a heating rod (heating device 7) was used to heat the soil. Injection and extraction were stopped once the pesticide concentration and odor in the extraction well met the standards. Subsequently, a 0.27 mol / L calcium chloride solution was injected. Water samples were taken from the extraction well four weeks later for monitoring; both pesticide concentration and odor met the standards. No rebound was observed during monthly monitoring over the following year.

[0049] Example 5

[0050] In a site contaminated with arsenic, the arsenic content in the soil ranges from 270 to 630 mg / kg, and the arsenic concentration in the groundwater ranges from 0.6 to 1.1 mg / L. Arsenic exists in the form of arsenate ions, and its desorption efficiency in alkaline solutions is higher than that in acidic solutions; therefore, the method of this invention can be used directly.

[0051] like Figure 2 As shown, a 20 mol / L sodium hydroxide solution was injected into the soil through injection well 1. A gas-fired heating element (heating device 7) was used to heat the soil to approximately 60°C. Injection and extraction were stopped when the arsenic concentration in the effluent from extraction well 2 dropped below 0.05 mg / L. After maintaining the temperature for 24 hours, a retest showed no increase in arsenic concentration. Subsequently, a 1.8 mol / L calcium chloride solution was injected, and the concentrations of calcium chloride and arsenic in the effluent from the extraction well were monitored. Injection was stopped once the soil was deemed sufficiently saturated with calcium chloride and the arsenic concentration was below 0.05 mg / L. Four weeks later, water samples were taken from the extraction well for monitoring, and the arsenic concentration was below 0.05 mg / L. Monitoring was conducted monthly for the following year, and the arsenic concentration gradually decreased 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 prepared from one or more of magnesium chloride, magnesium citrate, or magnesium sulfate, and the magnesium solution contains Mg. 2+ Concentration (all using magnesium solution) or Ca 2+ With Mg 2+ The sum of their concentrations (a mixed solution of calcium and magnesium) ranges from 0.27 to 7.2 mol / L, corresponding to the generation of magnesium aluminosilicate or a mixture of calcium aluminosilicate and magnesium aluminosilicate in subsequent step 2.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for ensuring the long-term stability of remediation effects for contaminated groundwater, characterized in that, To maintain the long-term stability of the remediation effect of contaminated groundwater, the following steps are specifically included: Step 1. Inject the alkaline solution into the soil through the injection well, while simultaneously extracting groundwater at the extraction well end until the concentration of pollutants in the extracted groundwater drops to the target value, then stop injecting the alkaline solution. Step 2. Inject calcium and / or magnesium solution into the soil through injection wells until the soil is filled with calcium and / or magnesium solution to complete the long-term stabilization treatment for the remediation of contaminated groundwater. In step 1, the alkaline solution is used to dissolve and soften the silicon and aluminum minerals on the surface of soil particles, generating silica compounds and aluminate compounds on the surface of soil particles and between soil particles. In step 2, the calcium and / or magnesium ions injected into the calcium and / or magnesium solution react with silicate and aluminate compounds to form calcium aluminosilicate and / or magnesium aluminosilicate with a gelling effect. This seals the pores on the surface of soil particles and between adjacent soil particles. The sealing of the soil particle surface fixes the undesorbed hexavalent chromium, and the sealing of the pores between adjacent soil particles reduces soil permeability. This forms an isolation zone between the high-permeability zone and the low-permeability zone, making it more difficult for hexavalent chromium in the soil solution of the low-permeability zone to diffuse into the high-permeability zone through concentration gradient.

2. The method according to claim 1, characterized in that: The alkaline solution is a sodium hydroxide solution, a 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 calcium and / or magnesium solution contains Ca 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: Step 1 is performed under heating conditions of ≤100℃ to shorten the time of step 1; The heating methods are as follows: heating the alkaline solution before 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 high-permeability and low-permeability zones, or heating the alkaline solution in the soil and then continuing to heat it using the heating device after heating the alkaline solution.

7. The method according to any one of claims 1 to 6, characterized in that: Before proceeding to step 1, the contaminated groundwater needs to be remediated to reduce the concentration of pollutants in the groundwater to below the target value. Then, this method can be used to maintain the long-term stability of the remediation effect of the contaminated groundwater.

Images