Medium-and-long-term remediation method for plant groundwater pollution

Abstract

The invention discloses a medium and long term remediation method for plant groundwater pollution, and relates to the technical field of water treatment.The medium and long term remediation method comprises the steps that S1, pollutant concentration data of plant soil and groundwater is obtained, and plant pollution areas are divided; s2, determining a remediation method based on the polluted area of the factory; s3, establishing an underground water migration-reaction coupling model for simulating pollutant diffusion and restoration; s4, based on the groundwater migration-reaction coupling model, simulating to obtain a predicted restoration period and predicted restoration parameters, and then adopting a restoration method and the predicted restoration parameters to restore the groundwater pollution of the factory area; according to the method, a systematic and scientific factory groundwater pollution remediation scheme is provided, the diffusion and remediation process of pollutants can be simulated by establishing the groundwater migration-reaction coupling model, the remediation cost can be reduced as much as possible while the environment remediation effect is guaranteed, and the balance of environmental benefits and economic benefits is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and specifically relates to a medium- and long-term remediation method for groundwater pollution in a factory area. Background Art

[0002] Due to the current situation of medium- and long-term remediation of groundwater pollution in factory areas involving the application of multiple technologies, such as in-situ chemical oxidation, two-phase extraction, vapor extraction, bioventing, and groundwater circulation wells, these technologies aim to gradually reduce the concentration of pollutants and restore the quality of groundwater.

[0003] However, the remediation work faces many challenges, including the complexity of pollutants, the uncertainty of the pollution range, the complexity of geological conditions, high costs, and long remediation times. The complexity of pollutants is reflected in that the pollutants in the groundwater of the factory area may include various organic and inorganic compounds, and the properties and migration behaviors of these pollutants are different, increasing the difficulty of remediation; the uncertainty of the pollution range is reflected in that the pollutants may have spread to a large area, and the pollution boundary may be difficult to determine, which will bring difficulties to the formulation of remediation strategies; the complexity of geological conditions is reflected in that different geological conditions will affect the migration of pollutants and the effectiveness of remediation technologies. Different technologies have different application conditions and limitations, and need to be selected and adjusted according to specific situations; the uncertainty of remediation time is reflected in that the remediation of groundwater pollution may take a long time, and the remediation progress may be affected by various factors, such as seasonal changes and groundwater level fluctuations; the cost issue is reflected in that long-term remediation work may involve high costs, including technology implementation, monitoring, and maintenance costs. How to effectively control costs is an important issue; to solve these problems, a comprehensive method needs to be adopted for remediation. Summary of the Invention

[0004] To solve the above problems, the present invention provides a medium- and long-term remediation method for groundwater pollution in a factory area.

[0005] A medium- and long-term remediation method for groundwater pollution in a factory area includes the following steps: S1. Obtain the pollutant concentration data of the soil and groundwater in the factory area, and divide the polluted areas in the factory area according to the pollutant concentration data of the soil and groundwater in the factory area; the polluted areas in the factory area include: pure soil pollution area, soil pollution area with limited remediation, vadose zone soil pollution area, pure slightly polluted groundwater area, pure heavily polluted groundwater area, and heavily co-polluted soil and groundwater area; S2. Determine the remediation method based on the polluted areas in the factory area; The in-situ injection chemical oxidation method is used to repair the pure soil pollution area; the repair-restricted soil pollution area is repaired by first using the two-phase extraction method and then the in-situ injection chemical oxidation method; the vadose zone soil pollution area is repaired by combining the gas extraction method and the bioventing method; the pure slightly polluted groundwater area is repaired by using a groundwater circulation well; for the pure heavily polluted groundwater area or the heavily co-polluted soil and groundwater area, the groundwater circulation well method and the in-situ injection chemical oxidation method at multiple depths are successively used for repair; S3. According to the pollutant concentration data of the soil and groundwater in the factory area, establish a groundwater transport-reaction coupling model for simulating pollutant diffusion and repair; S4. Based on the groundwater transport-reaction coupling model, simulate and obtain the predicted repair period and predicted repair parameters, and then use the corresponding repair methods and predicted repair parameters to repair the groundwater in the factory area; the repair parameters include the oxidant concentration in the in-situ injection chemical oxidation method, the extraction rate in the two-phase extraction method and the gas extraction method, the pumping and injection water flow rate in the groundwater circulation well, the added amount of acclimated hydrocarbon-degrading bacteria in the bioventing method, and the air injection flow rate.

[0006] Note: The above method can systematically and scientifically complete the repair of soil and groundwater pollution in the factory area. From data collection, regional division, repair method selection, model establishment to parameter optimization, it provides clear guidance and an operation framework for pollution control. By establishing a groundwater transport-reaction coupling model, the diffusion and repair process of pollutants can be simulated, providing a scientific basis for the selection of repair plans and parameter optimization. At the same time, it allows the optimization of key parameters before actual repair to improve the repair efficiency and effect. This model- and data-driven method can not only monitor the repair effect in real time and adjust according to the actual situation, but also minimize the repair cost as much as possible while ensuring the environmental repair effect, achieving a balance between environmental benefits and economic benefits.

[0007] Furthermore, the pure soil pollution area is an area where only the soil is polluted and the groundwater is not polluted; the repair-restricted soil pollution area is a pure soil pollution area with restricted working space or the presence of waste gas pipelines in the area; the vadose zone soil pollution area is a pure soil pollution area located above the groundwater level; the pure slightly polluted groundwater area is an area where pollutants only exist in the groundwater and the soil is not polluted; the pure heavily polluted groundwater area is a heavily polluted groundwater area; the heavily co-polluted soil and groundwater area is an area where both the groundwater and the soil are heavily polluted.

[0008] Description: The above method defines different types of polluted areas in the factory area. This classification method helps to accurately identify and locate pollution situations, providing a clear basis for the selection and implementation of subsequent remediation strategies, thereby improving the efficiency and pertinence of pollution control.

[0009] Furthermore, the method of dividing the polluted areas in the factory area according to the pollutant concentration data of the factory area soil and groundwater includes: processing the pollutant concentration data of the factory area soil and groundwater by Kriging interpolation method or inverse distance weighted method to obtain multiple simulated concentration data, using the multiple concentration data, generating the spatial distribution of pollutant concentration through GIS software, and then dividing the polluted areas in the factory area.

[0010] Description: Through the Geographic Information System (GIS) and interpolation methods (i.e., Kriging interpolation method or inverse distance weighted method), not only the accuracy and efficiency of data processing are improved, but also a visualization tool is provided for the accurate division of polluted areas.

[0011] Furthermore, the method of establishing a groundwater flow and reaction coupling model for simulating pollutant diffusion and remediation according to the pollutant concentration data of the factory area soil and groundwater in S3 includes: S3-1. Obtain the factory area model parameters; S3-2. Based on the pollutants and their concentration distributions, and the factory area model parameters, use PHT3D software to couple a water flow module for simulating the direction and rate of groundwater flow, a solute transport module for simulating the migration and diffusion of pollutants with groundwater flow, and a reactive transport module for simulating the dynamic attenuation of pollutant concentration with remediation to obtain a groundwater flow and reaction coupling model.

[0012] Description: The above method can simultaneously simulate the flow of groundwater, the migration and diffusion of pollutants, and the dynamic changes of pollutant concentration during the remediation process, providing a scientific basis for predicting the remediation effect and optimizing the remediation parameters, thereby improving the efficiency and reliability of pollution remediation.

[0013] Furthermore, the factory area model parameters include the aquifer permeability coefficient, porosity, pollutant degradation rate, and pollutant adsorption coefficient.

[0014] Description: The above parameters are the basis for constructing the groundwater flow and reaction coupling model, and they directly affect the accuracy and prediction ability of the model. By clarifying these parameters, it can be ensured that the model can more realistically reflect the actual situation of groundwater flow and pollutant migration.

[0015] Further, the water flow module is simulated through a three-dimensional heterogeneous aquifer network with boundary conditions and source-sink terms set; the advection-dispersion solute transport module is simulated based on the three-dimensional heterogeneous aquifer network by setting the advection-dispersion coefficient and adsorption parameters of pollutants; the reactive transport module is simulated based on the simulation results of the advection-dispersion solute transport module by setting a degradation reaction equation.

[0016] Explanation: The above method clarifies the simulation methods and parameters used in each module of the groundwater flow-reaction coupling model, which helps to understand the working principle of the model, ensure the accuracy and reliability of the model, and thus provide a scientific basis for pollution remediation.

[0017] Further, the method for predicting the remediation period and remediation parameters of the polluted area in the factory area based on the groundwater flow-reaction coupling model in S4 includes: S4-1. Define the pollutant remediation threshold. S4-2. Use the Monte Carlo simulation method to generate multiple simulated remediation parameters, and input the multiple simulated remediation parameters into the groundwater flow-reaction coupling model for simulation respectively. During the simulation process, when the pollutant concentration decays to the pollutant remediation threshold, it is taken as the simulation end point to obtain the simulated remediation periods corresponding to the multiple simulated remediation parameters. S4-3. Based on the multiple simulated remediation parameters and the simulated remediation periods, calculate the total remediation cost, and then find the predicted remediation parameter that minimizes the total cost and the predicted remediation period corresponding to the predicted remediation parameter among the multiple simulated remediation parameters.

[0018] Explanation: The above method uses the groundwater flow-reaction coupling model and the Monte Carlo simulation method to predict the remediation period of the polluted area in the factory area and optimize the remediation parameters. This method can find the predicted remediation parameter with the minimum cost and the corresponding predicted remediation period. This method based on model and cost optimization not only improves the scientificity and feasibility of the remediation plan, but also ensures the economic benefits of the remediation work.

[0019] Further, the remediation parameters further include the spacing of extraction wells, the composition of oxidants, and the composition of hydrocarbon-degrading bacteria.

[0020] Explanation: The above content further expands the scope of remediation parameters, including the spacing of extraction wells, the composition of oxidants, and the composition of hydrocarbon-degrading bacteria. The addition of these parameters makes the remediation plan more comprehensive and detailed, and can be more precisely adjusted and optimized according to the specific pollution situation and site conditions, thereby improving the remediation effect and efficiency.

[0021] The beneficial effects of the present invention are: The method of the present invention provides a systematic and scientific method for the remediation of contaminated soil and groundwater in industrial areas. From regional division, selection of remediation methods, model establishment to parameter optimization, it provides clear guidance and an operation framework for pollution control. By establishing a coupled groundwater transport-reaction model, it is able to simulate the diffusion and remediation processes of pollutants, providing a scientific basis for the selection of remediation schemes and parameter optimization. At the same time, it allows for the optimization of key parameters before actual remediation to improve the remediation efficiency and effect. This model- and data-driven method can not only monitor the remediation effect in real time and make adjustments according to the actual situation, but also minimize the remediation cost as much as possible while ensuring the environmental remediation effect, achieving a balance between environmental and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the flowchart of the processing method of the embodiment of the present invention; Figure 2 is the pH trend chart of the GWA contaminated area after the start of remediation in the embodiment of the present invention; Figure 3 is the electrical conductivity EC trend chart of the GWA contaminated area after the start of remediation in the embodiment of the present invention; Figure 4 is the oxidation-reduction potential ORP trend chart of the GWA contaminated area after the start of remediation in the embodiment of the present invention; Figure 5 is the PID concentration trend chart of the tail gas of the DPE device in the GWA contaminated area after the start of remediation in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] To further elaborate on the methods adopted and the effects achieved by the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with experiments.

[0024] Due to the multiple challenges faced in the medium- and long-term remediation of industrial area groundwater pollution, the diversity of pollutants (such as heavy metals, organic substances, and combined pollution) and the migration and retention of non-aqueous phase liquids (NAPLs) result in a long remediation cycle. Reverse diffusion and tailing effects are likely to cause concentration rebound, and hydrogeological heterogeneity and dynamic changes in groundwater flow exacerbate the uncertainty of pollution distribution. Existing analyses show that the combined pollution left by industrial activities continues to spread through geochemical processes such as adsorption-desorption and oxidation-reduction. Therefore, in the remediation of the embodiments of the present invention, a coupled design of a prediction model and a classification strategy is adopted to address the problem of pollutant diversity, providing a remediation scheme that takes into account both cost and remediation effect, as follows; A medium- and long-term remediation method for industrial area groundwater pollution includes the following steps: S1. Obtain the pollutant concentration data of the factory area soil and groundwater, and divide the polluted areas of the factory area according to the pollutant concentration data of the factory area soil and groundwater; the polluted areas of the factory area include: pure soil pollution area, soil pollution area with limited restoration, vadose zone soil pollution area, pure groundwater mild pollution area, pure groundwater severe pollution area, and severe co-pollution area of soil and groundwater; Specifically, the pure soil pollution area is the area where only the soil is polluted and the groundwater is not polluted; the soil pollution area with limited restoration is the pure soil pollution area with limited working space or the existence of waste gas pipelines in the area; the vadose zone soil pollution area is the area where the pure soil is polluted and above the groundwater level; the pure groundwater mild pollution area is the area where pollutants only exist in the groundwater and the soil is not polluted; the pure groundwater severe pollution area is the area with severe groundwater pollution; the severe co-pollution area of soil and groundwater is the area with severe pollution of groundwater and soil; the above judgment criteria for whether pollution occurs and mild and severe pollution adopt the methods in "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Agricultural Land (Trial)" (GB 15618-2018) and "Groundwater Quality Standard" (GB / T 14848-2017); Dividing the polluted areas of the factory area according to the pollutant concentration data of the factory area soil and groundwater includes: processing the pollutant concentration data of the factory area soil and groundwater by Kriging interpolation method or inverse distance weighted method to obtain multiple simulated concentration data, using the multiple concentration data, generating the spatial distribution of pollutant concentration through GIS software, and then dividing the polluted areas of the factory area; S2. Determine the restoration method based on the polluted areas of the factory area; For the pure soil pollution area, in-situ injection chemical oxidation method is used for restoration; for the soil pollution area with limited restoration, the method of first using two-phase extraction method and then in-situ injection chemical oxidation method is used for restoration; for the vadose zone soil pollution area, the method of combining gas extraction method and bioventing method is used for restoration; for the pure groundwater mild pollution area, the groundwater circulation well method is used for restoration; for the pure groundwater severe pollution area or the severe co-pollution area of soil and groundwater, the groundwater circulation well method and the in-situ injection chemical oxidation method with multiple depths are used for restoration in sequence; Specifically, for the pure soil pollution area: in in-situ injection chemical oxidation method (ISCO), the oxidant type is preferably persulfate (such as sodium persulfate) or hydrogen peroxide; for heavy metal pollution, potassium permanganate is added for synchronous oxidation and fixation; the method of pressurized injection + multi-depth well combination is adopted, and through layered slotted pipe design (such as single well multi-slotted pipe with packer isolation), ensure that the oxidant is evenly distributed in the 0-3 m polluted soil layer; For the remediation of restricted soil pollution areas: In the two-phase extraction + in-situ chemical oxidation method, in the first stage, a vacuum pump negative pressure of ≥0.5 bar is set for two-phase extraction, and the extraction flow rate is 20 - 50 L / min to remove volatile organic compounds and light non-aqueous phase liquids; Thermal enhancement assistance: Inject hot air (80 - 100 °C) during the extraction process to improve the desorption efficiency of pollutants and shorten the extraction cycle; In the second stage, in in-situ chemical oxidation, the oxidant is a combined injection of sodium persulfate and hydrogen peroxide (mass ratio 1:1); Staged injection: First inject a high concentration of oxidant (such as 3 wt% sodium persulfate), and subsequently use slow-release oxidant capsules (such as slow-release materials coated with sodium persulfate) to prevent concentration rebound; For the vadose zone soil pollution area, in the gas-phase extraction + bioventing combined method, extraction wells are arranged in a triangular grid with a spacing of 2 - 5 m (preferably 4 m), and the extraction flow rate is 20 mL / min to mainly remove volatile pollutants in the vadose zone of 1 - 3 m; Microbial domestication: Add domesticated hydrocarbon-degrading bacteria (such as Pseudomonas), and continuously inject nutrient solution (the nutrient solution uses commercially available products with a nitrogen-phosphorus ratio of 10:1) to promote biodegradation; Maintain the dissolved oxygen ≥2 mg / L through an in-well aeration system (such as an air injection flow rate of 30 L / min) to accelerate the mineralization of pollutants into CO 2 and H 2 O; For the simple lightly polluted groundwater area: In the groundwater circulation well remediation, an ozone generator + activated carbon adsorption layer is built in the in-well treatment unit, with an ozone concentration of 10 - 20 ppm to treat VOCs and some SVOCs; Hydraulic circulation mode: Adopt reverse circulation and pump water through the bottom of the well; (Flow rate 5 - 10 m 3 / d) to form a three-dimensional circulation with an influence radius of 15 - 20 m, and simultaneously activate the degradation of indigenous microorganisms; For the severely polluted groundwater or soil - groundwater co-pollution area: In the first stage of the GCW + multi-depth ISCO method: Combine air stripping technology to inject compressed air to strip adsorbed pollutants and improve the mobility of groundwater, and inject low-concentration sodium persulfate (0.5 - 1 wt%) downstream of the circulation well; In the second stage: Adopt multi-well group layered injection, use potassium permanganate (0.1 - 3 wt%) in the shallow layer (0 - 5 m), and use slow-release persulfate capsules in the deep layer (10 m) to avoid MnO 2 precipitation clogging; Add zero-valent iron and oxidant at the edge of the pollution plume to form an oxidation-reduction gradient to simultaneously degrade chlorinated hydrocarbons and immobilize heavy metals (for example, Cr(Ⅵ) is reduced to Cr(Ⅲ)); S3. According to the pollutant concentration data of the factory area soil and groundwater, establish a groundwater flow and reaction coupling model for simulating pollutant diffusion and remediation; The method for establishing a groundwater flow-reaction coupling model includes: S3-1. Obtain the plant area model parameters; the plant area model parameters include the aquifer permeability coefficient, porosity, pollutant degradation rate, and pollutant adsorption coefficient; S3-2. Based on the pollutants and their concentration distributions, and the plant area model parameters, use the PHT3D software to couple the water flow module for simulating the groundwater flow direction and rate, the advection-dispersion solute transport module for simulating the migration and diffusion of pollutants with groundwater flow, and the reactive transport module for simulating the dynamic attenuation of pollutant concentration with remediation to obtain a groundwater transport-reaction coupling model (this model is implemented using existing software MODFLOW-MT3DMS or FEFLOW); Among them, the water flow module completes the simulation through a three-dimensional heterogeneous aquifer network with boundary conditions and source-sink terms set; the advection-dispersion solute transport module completes the simulation based on the three-dimensional heterogeneous aquifer network by setting the advection-dispersion coefficient and adsorption parameters of the pollutants; the reactive transport module completes the simulation based on the simulation results of the advection-dispersion solute transport module by setting the degradation reaction equation.

[0025] Specifically, a three-dimensional heterogeneous aquifer grid is established through the water flow module (MODFLOW module), boundary conditions (such as constant head boundary, zero flux boundary) and source-sink terms (production wells, recharge areas) are set to simulate the groundwater flow direction and rate; the solute transport module inputs the initial pollutant concentration field, defines the advection-dispersion coefficient and adsorption parameters, and simulates the migration and diffusion of pollutants with groundwater flow; the reactive transport module (RT3D module) sets the degradation reaction equation (such as the first-order reaction kinetic equation) according to the pollutant type, and considers chemical processes such as oxidation-reduction and biodegradation to achieve the simulation of the dynamic attenuation of pollutant concentration; S4. Based on the groundwater transport-reaction coupling model, simulate and obtain the predicted remediation period and predicted remediation parameters, and then use the corresponding remediation methods and predicted remediation parameters to remediate the groundwater in the plant area; the remediation parameters include the oxidant concentration in in-situ chemical oxidation, the extraction rate in two-phase extraction and air sparging, the pumping and injection flow rates in groundwater circulation wells, the added amount of acclimated hydrocarbon-degrading bacteria in bioventing, and the air injection flow rate; Among them, the method for predicting the remediation period and remediation parameters of the polluted area in the plant area based on the groundwater transport-reaction coupling model includes: S4-1. Define the pollutant remediation threshold, and the screening values in the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Agricultural Land (Trial)" (GB 15618-2018) and the "Groundwater Quality Standard" (GB / T 14848-2017) can be used; S4-2. Generate multiple simulated remediation parameters using the Monte Carlo simulation method, and input the multiple simulated remediation parameters into the groundwater transport-reaction coupling model for simulation. During the simulation, when the pollutant concentration decays to the pollutant remediation threshold, it is taken as the simulation end point to obtain the simulated remediation periods corresponding to the multiple simulated remediation parameters. S4-3. Based on the multiple simulated remediation parameters and the simulated remediation periods, calculate the total remediation cost, and then find the predicted remediation parameter that minimizes the total cost and the predicted remediation period corresponding to the predicted remediation parameter among the multiple simulated remediation parameters.

[0026] The remediation parameters also include the spacing of extraction wells, the composition of oxidants, and the composition of hydrocarbon-degrading bacteria.

[0027] Preferably, in the specific implementation process, Pareto front analysis can be used to screen the parameter combinations that simultaneously meet the concentration compliance (constraint condition) and the minimum total cost (objective function); for example, use genetic algorithms or particle swarm optimization algorithms to extract the optimal solution from the Monte Carlo simulation results and verify its robustness (such as parameter sensitivity analysis); Based on the groundwater transport-reaction coupling model, record the remediation period T for the dynamic process of the pollutant concentration decaying to the remediation threshold; construct a cost function according to the chemical dosage, energy consumption, and time cost of the parameter combination ; ( is the total amount of chemicals or the total amount of energy consumption, and a, b, c are unit price coefficients), calculate the total cost of each group of parameters; finally, select the parameter combination with the minimum total cost from all simulation results; Exemplarily, define the pollutant remediation threshold (such as the concentration of TCE (trichloroethylene) ≤ 0.005 mg / L); secondly, input the remediation parameters into the coupling model, simulate the spatio-temporal evolution of pollutants under different scenarios, and record the duration of the concentration decaying to the threshold; optimize the parameter combination in combination with the cost function (chemical dosage × time); finally, use Monte Carlo simulation to quantify the uncertainty of geological and reaction parameters, and output the confidence interval of the remediation period (such as 12 - 18 months under 90% probability) and the optimal parameter scheme (such as injection rate 50 L / min, extraction well spacing 30 m).

[0028] Short-term remediation results: For a certain polluted area, the results after remediation are as Figure 2 、 Figure 3 、 Figure 4 and Figure 5 shown.

[0029] In the embodiments of the present invention, GCW refers to groundwater circulation well remediation, ISCO refers to in-situ chemical oxidation remediation, DPE refers to dual-phase extraction, and SVE refers to soil vapor extraction; PID refers to a Photo Ionization Detector for detecting volatile organic compounds (VOCs). (1) It entered the operation and maintenance period in March 2020 and operated until September 2021. First, multiple NL wells (wells for recovering non-aqueous phase liquids (NAPLs)) with relatively high concentrations and containing oil were suction-treated to extract high-concentration groundwater and pure-phase substances. According to the monitoring data, the concentration of the target pollutant 1,2-dichloroethane decreased fluctuatingly. Subsequently, while maintaining the suction treatment of some wells continuously, GCW was operated intermittently for groundwater circulation, and the circulating flow field could accelerate the removal of pollutants. Then it entered the groundwater pumping and injection circulation stage, and auxiliary drug injection was used to enhance remediation. With the addition of the drug, the concentration of the target pollutant 1,2-dichloroethane decreased significantly, a large amount of pollutants were removed, and the polluted area gradually shrank.

[0030] On October 25, 2020, the self-evaluation detection sampling work for the remediation effect was carried out. The monitoring data showed that the remediation effect was initially achieved. On December 4, 2020, the detection sampling work for the remediation effect evaluation was carried out. The detection data showed that there were still individual soil exceedance situations on the northeast side of the SA area (SA refers to the area number exemplified in this embodiment) and SE1 (SE1 refers to the area number exemplified in this embodiment). Subsequently, supplementary remediation was carried out on this area, using DPE, ISCO processes, and GCW pumping and injection circulation combined with drug injection to enhance remediation. The detection results of the soil exceedance points in January 2021 showed that the soil pollutants were lower than the remediation target. To ensure the remediation effect, starting from February 2021, the SA1+GWA1 area (SA1, GWA1 refer to the area numbers exemplified in this embodiment) maintained the GCW pumping and injection circulation mode; later, four batches of groundwater detections were carried out, and samples were sent to a third-party qualified laboratory for testing in October 2020, January 2021, June 2021, and September 2021 respectively. According to the detection results, it was initially judged that the remediation target was achieved.

[0031] (2) In this project, the ISCO process uses sodium persulfate as the oxidant and sodium hydroxide as the activator, which are injected into the formation by solution addition. The basic water quality self-inspection items carried out in this project mainly include pH, conductivity EC, and oxidation-reduction potential ORP. The pH of the groundwater in the SA+GWA1 (SA and GWA1 refer to the area numbers exemplified in this embodiment) pollution area is around 7-8 recently. With the addition of the chemicals, the pH, EC, and ORP have all increased. Before the start of the remediation activities, the ORP of some wells showed negative values, indicating a reducing state and the presence of certain pollutants. As the remediation activities ended, the pH and conductivity EC gradually returned to the state before the start of the remediation.

[0032] (3) It can be seen from the PID monitoring data and trend chart that the PID values in the SA1 area fluctuate and decline as a whole, with local rebounds. The PID drops significantly in the initial stage of operation and slows down significantly in the later stage of operation, indicating that DPE has an effect on the remediation of this site. However, as a new phase equilibrium is established, the amount of pollutants extracted decreases.

Claims

1. A medium- and long-term remediation method for groundwater pollution in a factory area, characterized in that: The following steps are involved: S1. Obtain the pollutant concentration data of the soil and groundwater in the plant area, and divide the plant area into polluted areas according to the pollutant concentration data of the soil and groundwater in the plant area; the plant area polluted areas include: pure soil pollution area, restricted soil pollution area, vadose zone soil pollution area, pure groundwater light pollution area, pure groundwater heavy pollution area, and soil and groundwater heavy co-pollution area; S2. Determine the remediation method based on the polluted area of ​​the plant; The simple soil contaminated area is repaired by in-situ injection chemical oxidation method; the restricted soil contaminated area is repaired by first two-phase extraction method and then in-situ injection chemical oxidation method; the aeration zone soil contaminated area is repaired by gas phase extraction method combined with biological ventilation method; the simple groundwater lightly polluted area is repaired by groundwater circulation well method; the simple groundwater heavily polluted area or the soil and groundwater heavily co-polluted area is repaired by groundwater circulation well method and in-situ injection chemical oxidation method in sequence; S3. Based on the pollutant concentration data of the soil and groundwater in the plant area, establish a groundwater transport-reaction coupling model for simulating pollutant diffusion and remediation; S4. Based on the groundwater migration-reaction coupling model, the predicted remediation cycle and predicted remediation parameters are simulated, and then the corresponding remediation method and predicted remediation parameters are adopted to remediate the groundwater in the plant area; the predicted remediation parameters include the oxidant concentration in the in-situ injection chemical oxidation method, the extraction rate in the two-phase extraction method and the gas phase extraction method, the injection and pumping flow rate in the groundwater circulation well, the amount of hydrocarbon-degrading bacteria added after domestication in the biological ventilation method, and the air injection flow rate.

2. A method for medium- and long-term restoration of groundwater pollution in a factory area as claimed in claim 1, characterized in that: The simple soil contamination area is an area where only pollution occurs in the soil and no pollution occurs in the groundwater; the remediation restricted soil contamination area is an area where simple soil contamination occurs but the working space is limited or there are exhaust gas pipelines in the area; the vadose zone soil contamination area is an area where simple soil contamination occurs and is located above the groundwater level; the simple groundwater lightly contaminated area is an area where pollutants only exist in the groundwater and no pollution occurs in the soil; the simple groundwater heavily contaminated area is an area where groundwater is heavily contaminated; the soil and groundwater heavily co-contaminated area is an area where groundwater and soil are heavily contaminated.

3. A method for medium- and long-term restoration of groundwater pollution in a factory area as claimed in claim 2, characterized in that: The dividing of the plant area pollution area according to the pollutant concentration data of the plant area soil and groundwater includes: processing the pollutant concentration data of the plant area soil and groundwater by Kriging interpolation method or inverse distance weighted method to obtain multiple simulated concentration data, using the multiple concentration data to generate the spatial distribution of pollutant concentration through GIS software, and then dividing the plant area pollution area.

4. A method for medium- and long-term restoration of groundwater pollution in a factory area as claimed in claim 1, characterized in that: The method for establishing a groundwater transport-reaction coupling model for simulating pollutant diffusion and remediation according to the pollutant concentration data of the soil and groundwater in the plant area described in S3 includes: S3-1, obtaining plant model parameters; S3-2. Based on the distribution of pollutants and pollutant concentrations and plant model parameters, PHT3D software is used to couple the water flow module for simulating the direction and rate of groundwater flow, the solute transport module for simulating the migration and diffusion of pollutants with the flow of groundwater, and the reactive transport module for simulating the dynamic attenuation of pollutant concentration with remediation, to obtain a groundwater transport-reaction coupling model.

5. A method for medium- and long-term restoration of groundwater pollution in a factory area as claimed in claim 4, characterized in that: The plant model parameters include aquifer permeability, porosity, pollutant degradation rate and pollutant adsorption coefficient.

6. A method for medium- and long-term restoration of groundwater pollution in a factory area as claimed in claim 4, characterized in that: The water flow module completes the simulation by setting a three-dimensional heterogeneous aquifer network with boundary conditions and source and sink terms; the migration and diffusion solute transport module completes the simulation by setting the convection-diffusion coefficient and adsorption parameters of pollutants based on the three-dimensional heterogeneous aquifer network; the reactive transport module completes the simulation by setting the degradation reaction equation based on the simulation results of the migration and diffusion solute transport module.

7. A method for medium- and long-term restoration of groundwater pollution in a factory area as claimed in claim 1, characterized in that: The method for predicting the restoration period and restoration parameters of the contaminated area in the plant area based on the groundwater migration-reaction coupling model described in S4 includes: S4-1. Define pollutant remediation thresholds; S4-2. Generate multiple simulated remediation parameters using the Monte Carlo simulation method, input the multiple simulated remediation parameters into the groundwater transport-reaction coupling model for simulation, and take the decay of pollutant concentration to the pollutant remediation threshold as the simulation end point during the simulation process to obtain the simulated remediation cycle corresponding to the multiple simulated remediation parameters; S4-3. Calculate the total repair cost based on multiple simulated repair parameters and simulated repair cycles, and then find the predicted repair parameters and the predicted repair cycle corresponding to the predicted repair parameters that minimize the total cost among the multiple simulated repair parameters.

8. A method for medium- and long-term restoration of groundwater pollution in a factory area as claimed in claim 7, characterized in that: The remediation parameters also include the spacing of extraction wells, the composition of oxidants, and the composition of hydrocarbon-degrading bacteria.

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