Method for acquiring key parameters for pollutant migration under influence of site scale temperature-hydrodynamic coupling

Abstract

Disclosed in the present invention is a method for acquiring key parameters for pollutant migration under the influence of site scale temperature-hydrodynamic coupling, which method involves acquiring a permeability parameter, a heat conductivity coefficient and a dispersion coefficient of a pollution site on the basis of multi-field coupling numerical simulation of a hydrodynamic field, a temperature field and a concentration field. The pollutant migration parameter of a site is a key indicator for the investigation and management of organic pollution of the site. At present, the acquisition of parameters of an aquifer mainly depends on hydrogeological survey work, so a test method and a physical field are simplistic. On this basis, the method is provided in the present invention. The method illustrated in the present invention comprises: for an organic pollution site, establishing a water-heat-salt coupling model in an early stage by means of site drilling data and an on-site physical test result; on the basis of a site model and in view of on-site multi-party data, performing multi-field coupling numerical inversion; and adjusting model parameters by means of a manual trial-and-error method, so as to improve the model precision and obtain an optimal model.

Description

A method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling Technical Field

[0001] The present invention relates to the field of obtaining key parameters of site pollutant migration, and in particular to a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling. Background Art

[0002] During the treatment and remediation of contaminated sites, the acquisition of various aquifer parameters depends on hydrogeological surveys. Through various hydrogeological tests, geophysical exploration, and hydrogeological drilling, the geological structure and hydrogeological parameters of the aquifer are determined, which is conducive to making qualitative and quantitative judgments on the concentration, distribution range, and migration characteristics of pollutants.

[0003] The dynamic evolution of seepage and temperature fields, as well as the solute transport characteristics of aquifers, are crucial for site remediation and the evaluation of remediation effectiveness. Permeability, thermal conductivity, and diffusion coefficient are key parameters for characterizing these fields, as well as the solute transport characteristics of aquifers. They also serve as fundamental data for groundwater resource calculations and pollution prevention and control. Improving the accuracy of these parameters is crucial for guiding site management and remediation efforts. Currently, aquifer parameters are acquired using a combination of multiple survey methods and multi-physics field coupling, a method that offers the advantages of high accuracy and low multi-solution complexity.

[0004] Currently, there is limited research on obtaining key aquifer parameters through multi-field coupled numerical modeling. Furthermore, groundwater multi-field coupled experiments are primarily laboratory-scale. Few field experiments have been conducted in China to simultaneously obtain multiple key site parameters through coupled tracer experiments at the site scale. Therefore, by constructing a site-scale water-heat-salt coupled tracer test platform and conducting field experiments, combined with the results of previous pumping tests, micro-water tests, and geotechnical tests, multi-field coupled numerical simulations were implemented to obtain key parameters such as site contaminant permeability, thermal conductivity, and diffusion coefficient.

[0005] Summary of the Invention

[0006] Purpose of the invention: In response to the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a coupled simulation method and system for site-scale water-heat-salt multi-physical fields. First, a site-scale water-heat-salt coupled tracer test platform is constructed to perform three-dimensional multi-parameter monitoring (temperature, water pressure, conductivity, etc.) to obtain hydraulic, temperature and concentration response signals of low permeability formations, and accumulate three-dimensional long-term series data of hydrodynamic fields, temperature fields and concentration fields, which serve as the basis for adjusting model parameters.

[0007] Technical Solution: To achieve the above objectives, the present invention proposes a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling, which includes the following specific steps:

[0008] 1) For the contaminated site, an injection well H1, a pumping well H4, and observation wells H0, H2, and H3 were arranged. Preliminary experiments were conducted on each well, including geotechnical tests, pumping tests, and micro-water tests, to obtain the initial value of the site's aquifer permeability coefficient, which served as the standard for subsequent model calibration.

[0009] 2) Based on the preliminary experiments, coupled tracer tests were conducted on each well: pumping tests—calculating the permeability coefficient by observing changes in the aquifer water level; heat tracer tests—calculating the thermal conductivity by observing the relationship between depth and temperature in each well; and salt tracer tests—calculating the diffusion coefficient by converting the conductivity into concentration by observing the relationship between depth and conductivity. Probes were then deployed at the locations of the test and observation wells to monitor the temperature, conductivity, and permeability coefficient of the aquifers at different depths.

[0010] 3) Construct a three-dimensional groundwater flow field model. Process the contaminated site data in the test area into spatial coordinates, set initial and boundary conditions, and input the permeability, thermal conductivity, and diffusion coefficient obtained from the field test into the simulation software COMSOL Multiphysics 5.6 for three-dimensional modeling. The model is divided into three layers based on the locations of the test wells and observation wells to obtain a three-dimensional groundwater flow field model of the contaminated site.

[0011] 4) Collect groundwater level data from observation wells H0, H2, and H3 at the contaminated site, and obtain groundwater level data for the same observation period in the constructed three-dimensional groundwater flow field model of the contaminated site. Compare the measured water level values ​​with the simulated water level values ​​to obtain the root mean square error (RMS) of the groundwater level. Adjust the model parameters based on the initial value of the aquifer permeability coefficient obtained in the preliminary test so that the RMS error of the groundwater level is within the preset range.

[0012] 5) Use the calibrated three-dimensional groundwater flow field model of the contaminated site to perform multi-field coupled simulations of the groundwater flow field, temperature field, and solute concentration field. For groundwater flow field simulation, use the Darcy's law module in COMSOL Multiphysics 5.6. For temperature field simulation, use the porous media heat transfer module in the software. For solute concentration field distribution, use the porous media dilute species transport module in the software. Perform multi-physics simulations of the groundwater flow field-temperature field, groundwater flow field-solute concentration field, and groundwater flow field-temperature field-solute concentration field, respectively, to obtain the influence relationship between each field under fully coupled conditions.

[0013] 6) Using the monitoring data at different depths in the tracer test, adjust the permeability coefficient, thermal conductivity coefficient, and diffusion coefficient in the groundwater flow field model to determine the optimal model for the contaminated site;

[0014] 7) Predict pollutant migration parameters based on the optimal model of the contaminated site. Input the water level, temperature, conductivity or concentration of the aquifer into the optimal model to obtain the pollutant migration parameters, namely, permeability, thermal conductivity and diffusion coefficient.

[0015] Furthermore, in step 1), the experimental area of ​​the contaminated site is a 3×3m square, wherein the injection well H1, the pumping well H4 and the observation wells H2 and H3 are located at the four corners of the square experimental area, and the observation well H0 is located in the center of the square experimental area.

[0016] Furthermore, in step 1), the pumping test and the sluice test data are both processed using the Theis fitting method, and the geological parameters of the aquifer are determined by comparing the measured curves with the theoretical curves.

[0017] Furthermore, in the step 2), the probes in each well are HR8801 water level and temperature monitoring recorder and HR-206A online conductivity sensor, which are a group connected to the underground measurement and control terminal. Among them, the observation wells H0, H2, and H3 are respectively equipped with water level and temperature integrated sensors and conductivity sensors at depths of 8.5m, 9.5m, 10.5m, 11.5m, and 12.5m; the pumping well is equipped with a group of water level and temperature integrated sensors and conductivity sensors at a depth of 11.5m; and the injection well is equipped with a group of water level and temperature integrated sensors and conductivity sensors at a depth of 12.5m.

[0018] Furthermore, in the step 3), the plane range of the three-dimensional structural model is a rectangle, the long axis of the rectangle is parallel to the line connecting the pumping and injection wells, the long axis is 18.55m, the short axis is 10.11m, and the average vertical height is 18.67m; according to the positions of the test wells and observation wells, the model is divided into three layers, specifically: the surface to a burial depth of 4m is generalized as a fill layer, the burial depth of 4m to 13.5m is generalized as a clay layer, and the burial depth of 13.5m to the bottom of the model is generalized as a bedrock layer.

[0019] Furthermore, in step 3), the initial conditions and boundary conditions of the groundwater flow field model of the contaminated site are set as follows:

[0020] The boundaries parallel to the artificial groundwater flow field are set as no-flow boundaries, the top and bottom surfaces of the model are no-flow boundaries, and the two side boundaries perpendicular to the main groundwater direction are set at the observation well position and set as constant head boundaries, whose head values ​​are set by the interpolation function; the top and bottom surfaces of the model are set as thermal insulation boundaries, the sides are set as open boundaries, and the injection wells are set as line heat source boundaries; the parameter settings of the porous medium dilute species transfer module are the same as those of the heat conduction module, the initial concentration of the model dilute species NaCl is set to 0, the top and bottom surfaces of the model are set as no-flux boundaries, the sides are set as open boundaries, and the injection wells are set as line mass sources, and the mass flow rate of the solute species is controlled by a piecewise function.

[0021] Furthermore, in step 4), when describing the accuracy of the groundwater flow field model, the root mean square error (RMSE) of the model is calculated, and the model parameters whose root mean square error (RMSE) meets the preset conditions are selected. The calculation formula of the root mean square error (RMSE) is as follows:

[0022] Where C i0 is the numerical simulation value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, C ie The actual measured value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, where n is the number of sampling points.

[0023] Furthermore, in step 5), the mass conservation equation and Darcy velocity equation are used to simulate the groundwater flow field under the unsteady flow state of the site. The energy conservation equation and Darcy velocity equation are as follows:

[0024] Where, t is time, unit is s; ε p is the porosity; ρ is the liquid density, in kg / m 3 ;Q m is the input mass source, in kg / (m 3 *s); κ is the permeability, unit is m 2 ; μ is dynamic viscosity, unit is MPa*s; is the pressure difference, the unit is MPa; g is the acceleration due to gravity, the unit is m / s 2 ; u is the groundwater velocity, unit is m / s 2 .

[0025] Furthermore, in step 5), the energy conservation equation, heat conduction equation, and effective thermal conductivity calculation formula are used to simulate the heat transfer of the porous media in the site. The energy conservation equation, heat conduction equation, and effective thermal conductivity calculation formula are as follows: k eff =θ s k s +ε1k f +k disp (6)

[0026] Where C p,f is the constant pressure heat capacity of the fluid, in J / (kg*K); ρ f is the fluid density, its unit is kg / m 3 ; u is the groundwater velocity, unit is m / s 2 ; T is Kelvin temperature, unit is K; Q is heat source term, unit is J; q is heat flow, unit is W / m 2 ;k effis the effective thermal conductivity, in W / (m*K), which is determined by the solid matrix k s , fluid thermal conductivity k f The weighted average of thermal diffusion coefficient k disp Determine, where θ s and ε1 are weights.

[0027] Furthermore, in step 5), the following porous media dilute species transfer module control equation is selected to simulate salt migration:

[0028] Where ρ is the liquid density in kg / m 3 ; C is the concentration of the dilute substance, in mol / m 3 ; t is time, unit is s; v is the velocity vector of the fluid, unit is m / s; D is the diffusion coefficient of the dilute substance, unit is m 2 / s; R is the source term, the unit is mol / (s*m 3 ).

[0029] Principle of the Invention: Acquiring aquifer parameters relies on hydrogeological surveys. A single test method or single physical field cannot explore multi-parameter relationships. However, combining multiple survey methods and coupling multiple physical fields to acquire relevant aquifer parameters allows for exploring the interplay between various physical fields, offering the advantages of high accuracy and rapid prediction. To address the changing hydrodynamic conditions and temperature and concentration fields involved in contaminated site management, this invention conducts site-scale coupled tracer tests and multi-field coupled numerical simulations to determine the permeability, thermal conductivity, and diffusion coefficient of the test site.

[0030] Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0031] The present invention provides a novel method for obtaining key parameters of pollutant migration based on site-scale water-heat-salt multi-field coupled tracer tests and numerical simulations. There are relatively few groundwater multi-field coupled tests in my country that obtain important parameters from the site scale. At the same time, related numerical calculations mainly focus on studying the impact of temperature on moisture distribution, ignoring the transient changes of moisture field to temperature. The method described in the present invention implements multi-field coupled tracer tests of groundwater hydrodynamic field, temperature field, and concentration field at the site scale to obtain data from each field, and uses trial and error combined with numerical simulation to more accurately solve the permeability coefficient, thermal conductivity coefficient, and diffusion coefficient of the aquifer, which has a more efficient and accurate application value. The present invention provides a new technical idea for obtaining key parameters of groundwater pollutant migration during the investigation and remediation of contaminated sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0033] FIG1 is a flow chart of a method for obtaining key parameters of pollutant migration based on the influence of site-scale temperature-hydrodynamic coupling designed by the present invention;

[0034] FIG2 is a perspective schematic diagram of a three-dimensional conceptual model of a field-scale pumping and injection well according to Example 1 of the present invention;

[0035] FIG3 is a boundary setting diagram of a three-dimensional conceptual model of a field-scale pumping and injection well involved in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0037] As shown in FIG1 , the present invention proposes a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling, which includes the following specific steps:

[0038] 1) For the contaminated site, an injection well H1, a pumping well H4, and observation wells H0, H2, and H3 were arranged. Preliminary experiments were conducted on each well, including geotechnical tests, pumping tests, and micro-water tests, to obtain the initial value of the site's aquifer permeability coefficient, which served as the standard for subsequent model calibration.

[0039] 2) Based on the preliminary experiments, coupled tracer tests were conducted on each well: pumping tests—calculating the permeability coefficient by observing changes in the aquifer water level; heat tracer tests—calculating the thermal conductivity by observing the relationship between depth and temperature in each well; and salt tracer tests—calculating the diffusion coefficient by converting the conductivity into concentration by observing the relationship between depth and conductivity. Probes were then deployed at the locations of the test and observation wells to monitor the temperature, conductivity, and permeability coefficient of the aquifers at different depths.

[0040] 3) Construct a three-dimensional groundwater flow field model. Process the contaminated site data in the test area into spatial coordinates, set initial and boundary conditions, and input the permeability, thermal conductivity, and diffusion coefficient obtained from the field test into the simulation software COMSOL Multiphysics 5.6 for three-dimensional modeling. The model is divided into three layers based on the locations of the test wells and observation wells to obtain a three-dimensional groundwater flow field model of the contaminated site.

[0041] 4) Collect groundwater level data from observation wells H0, H2, and H3 at the contaminated site, and obtain groundwater level data for the same observation period in the constructed three-dimensional groundwater flow field model of the contaminated site. Compare the measured water level values ​​with the simulated water level values ​​to obtain the root mean square error (RMS) of the groundwater level. Adjust the model parameters based on the initial value of the aquifer permeability coefficient obtained in the preliminary test so that the RMS error of the groundwater level is within the preset range.

[0042] 5) Use the calibrated three-dimensional groundwater flow field model of the contaminated site to perform multi-field coupled simulations of the groundwater flow field, temperature field, and solute concentration field. For groundwater flow field simulation, use the Darcy's law module in COMSOL Multiphysics 5.6. For temperature field simulation, use the porous media heat transfer module in the software. For solute concentration field distribution, use the porous media dilute species transport module in the software. Perform multi-physics simulations of the groundwater flow field-temperature field, groundwater flow field-solute concentration field, and groundwater flow field-temperature field-solute concentration field, respectively, to obtain the influence relationship between each field under fully coupled conditions.

[0043] 6) Using the monitoring data at different depths in the tracer test, adjust the permeability coefficient, thermal conductivity coefficient, and diffusion coefficient in the groundwater flow field model to determine the optimal model for the contaminated site;

[0044] 7) Predict pollutant migration parameters based on the optimal model of the contaminated site. Input the water level, temperature, conductivity or concentration of the aquifer into the optimal model to obtain the pollutant migration parameters, namely, permeability, thermal conductivity and diffusion coefficient.

[0045] Furthermore, in the step 1), the experimental area of ​​the contaminated site is a 3×3m square, wherein the injection well H1, the pumping well H4 and the observation wells H2 and H3 are located at the four corners of the square experimental area, and the observation well H0 is located in the center of the square experimental area.

[0046] Furthermore, in step 1), the pumping test and the sluice test data are both processed using the Theis fitting method, and the geological parameters of the aquifer are determined by comparing the measured curves with the theoretical curves.

[0047] Furthermore, in the step 2), the probes in each well are HR8801 water level and temperature monitoring recorder and HR-206A online conductivity sensor, which are a group connected to the underground measurement and control terminal. Among them, the observation wells H0, H2, and H3 are respectively equipped with water level and temperature integrated sensors and conductivity sensors at depths of 8.5m, 9.5m, 10.5m, 11.5m, and 12.5m; the pumping well is equipped with a group of water level and temperature integrated sensors and conductivity sensors at a depth of 11.5m; and the injection well is equipped with a group of water level and temperature integrated sensors and conductivity sensors at a depth of 12.5m.

[0048] Furthermore, in the step 3), the plane range of the three-dimensional structural model is a rectangle, the long axis of the rectangle is parallel to the line connecting the pumping and injection wells, the long axis is 18.55m, the short axis is 10.11m, and the average vertical height is 18.67m; according to the positions of the test wells and observation wells, the model is divided into three layers, specifically: the surface to a burial depth of 4m is generalized as a fill layer, the burial depth of 4m to 13.5m is generalized as a clay layer, and the burial depth of 13.5m to the bottom of the model is generalized as a bedrock layer.

[0049] Furthermore, in step 3), the initial conditions and boundary conditions of the groundwater flow field model of the contaminated site are set as follows:

[0050] The boundaries parallel to the artificial groundwater flow field are set as no-flow boundaries, the top and bottom surfaces of the model are no-flow boundaries, and the two side boundaries perpendicular to the main groundwater direction are set at the observation well position and set as constant head boundaries, whose head values ​​are set by the interpolation function; the top and bottom surfaces of the model are set as thermal insulation boundaries, the sides are set as open boundaries, and the injection wells are set as line heat source boundaries; the parameter settings of the porous medium dilute species transfer module are the same as those of the heat conduction module, the initial concentration of the model dilute species NaCl is set to 0, the top and bottom surfaces of the model are set as no-flux boundaries, the sides are set as open boundaries, and the injection wells are set as line mass sources, and the mass flow rate of the solute species is controlled by a piecewise function.

[0051] Furthermore, in step 4), when describing the accuracy of the groundwater flow field model, the root mean square error (RMSE) of the model is calculated, and the model parameters whose root mean square error (RMSE) meets the preset conditions are selected. The calculation formula of the root mean square error (RMSE) is as follows:

[0052] Where C i0 is the numerical simulation value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, C ie The actual measured value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, where n is the number of sampling points.

[0053] Furthermore, in step 5), the mass conservation equation and Darcy velocity equation are used to simulate the groundwater flow field under the unsteady flow state of the site. The energy conservation equation and Darcy velocity equation are as follows:

[0054] Where, t is time, unit is s; ε p is the porosity; ρ is the liquid density, in kg / m 3 ;Q m is the input mass source, in kg / (m 3 *s); κ is the permeability, unit is m 2 ; μ is dynamic viscosity, unit is MPa*s; is the pressure difference, the unit is MPa; g is the acceleration due to gravity, the unit is m / s 2 ; u is the groundwater velocity, unit is m / s 2 .

[0055] Furthermore, in step 5), the energy conservation equation, heat conduction equation, and effective thermal conductivity calculation formula are used to simulate the heat transfer of the porous media in the site. The energy conservation equation, heat conduction equation, and effective thermal conductivity calculation formula are as follows: k eff =θ s k s +ε1k f +k disp (6)

[0056] Where C p,f is the constant pressure heat capacity of the fluid, in J / (kg*K); ρ f is the fluid density, its unit is kg / m 3 ; u is the groundwater velocity, unit is m / s 2 ; T is Kelvin temperature, unit is K; Q is heat source term, unit is J; q is heat flow, unit is W / m 2 ;k eff is the effective thermal conductivity, in W / (m*K), which is determined by the solid matrix k s , fluid thermal conductivity k f The weighted average of thermal diffusion coefficient k disp Determine, where θ s and ε1 are weights.

[0057] Furthermore, in step 5), the following porous media dilute species transfer module control equation is selected to simulate salt migration:

[0058] Where ρ is the liquid density in kg / m 3 ; C is the concentration of the dilute substance, in mol / m 3 ; t is time, unit is s; v is the velocity vector of the fluid, unit is m / s; D is the diffusion coefficient of the dilute substance, unit is m 2 / s; R is the source term, the unit is mol / (s*m 3 ).

[0059] Example 1

[0060] The present invention proposes a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling. The embodiment of the present invention takes the constructed site pumping and injection well model as an example.

[0061] (1) Based on the borehole catalog data of the test site, a borehole information text was established. In combination with the pumping test, micro-water test and geotechnical test, a conceptual model of the pumping and injection well with the same physical parameters as the actual scenario was established. As shown in Figure 2, the plane range of this three-dimensional structural model is a rectangle, with the long axis of the rectangle parallel to the line connecting the pumping and injection wells, that is, the direction of the groundwater flow in the artificial flow field. The long axis of the rectangle is 18.55m, the short axis is 10.11m, and the average vertical height is 18.67m. The model range is determined by the location of the test well and the observation well. The aquifer is mainly generalized into three layers. From the surface to the 4m burial depth, it is generalized as a fill layer. From the 4m to 13.5m burial depth, it is generalized as a clay layer. The 8-13m depth layer is subdivided into 5 fine layers for the subsequent characterization of the heterogeneity of the test layer. The 13.5m burial depth to the bottom of the model is generalized as the bedrock layer. The 8.5m to 13.5m burial depth is the main test hole section, and each 1m interval is subdivided into a small layer. Considering the overall low groundwater gradient at the site, the boundaries parallel to the artificial groundwater flow field were set as no-flow boundaries, as were the top and bottom surfaces of the model. Furthermore, given the distribution of the on-site observation wells and the long test period, the water level in the test area continued to drop with pumping. Therefore, the boundaries perpendicular to the main groundwater flow direction were set as constant-head boundaries, with the head values ​​representing interpolation functions (see Figure 3). The groundwater seepage parameters in the model are shown in Table 1.

[0062] Table 1 Parameters related to groundwater seepage calculation

[0063] (2) Simulation of the groundwater flow field. The reliability of the model was determined by comparing the simulated and measured water level values ​​of the H0, H2, and H3 observation wells. In this phase, only the groundwater flow field was simulated, without multi-field coupling calculations. The model was divided into three groups according to different time steps and simulation times. First, a groundwater flow field simulation calculation with a time step of 1 minute and a simulation time of 2400 minutes was performed to calibrate parameters such as the permeability coefficient. The simulation time was then extended to observe the stability of the model. See Table 2 for details.

[0064] (3) Based on the groundwater flow field, a combination simulation of different physical fields was performed to compare the effects of different physical fields under fully coupled conditions. The specific working condition settings are shown in Table 3. The root mean square error of the simulation results is generally kept within a small range, indicating that the model calculation values ​​are highly reliable, providing a good foundation for the groundwater flow model for subsequent simulation calculations involving the addition of temperature and solute concentration fields.

[0065] (4) Based on the data from sensor probes at different depths, the parameters of the different formations in the test section were adjusted through trial and error to improve the overall accuracy of the model. The selection of simulation time and step size was mainly based on the specific experimental process. The parameters of the fluid properties and solid matrix properties of the heat transfer module are shown in Table 4.

[0066] Table 2 Groundwater flow field simulation grouping table

[0067] Table 3 Multi-field coupling simulation grouping table

[0068] Table 4 Parameters of porous media heat transfer module

[0069] Through manual trial and error, the permeability coefficient of the aquifer's fine layers in the test section was adjusted based on the temperature signal variations at different depths at each well location. Within a 2400-minute simulation, the simulated water levels at each test well were closer to the measured values, and the root mean square error (RMS) decreased. The largest reduction in RMS error was observed for injection well H1, which decreased by 0.0383, followed by H4 and H0, which decreased by 0.0169 and 0.016, respectively. This demonstrates that the model's precise characterization results in simulations closer to the actual values, effectively predicting key parameters of aquifer contaminant migration.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling, characterized in that: The method comprises the following specific steps: 1) For the contaminated site, water injection well H1, pumping well H4, observation wells H0, H2, H3 are arranged, and preliminary experiments are carried out on each well, including geotechnical test, pumping test and micro-water test, to obtain the initial value of the permeability coefficient of the site aquifer, which will serve as the standard for subsequent model correction; 2) Based on the preliminary experiment, coupled tracer tests were carried out on each well: pumping test - calculating the permeability coefficient by observing the water level change of the aquifer, heat tracer test - calculating the thermal conductivity by observing the relationship between the depth and temperature change in each well, salt tracer test - calculating the diffusion coefficient by converting the conductivity into concentration by observing the relationship between the depth and conductivity change, and setting probes according to the positions of the test wells and observation wells to monitor the temperature, conductivity and permeability coefficient of aquifers at different depths; 3) Construct a three-dimensional groundwater flow field model, process the contaminated site data of the test area into spatial coordinates, set initial conditions and boundary conditions, and input the permeability, thermal conductivity, and diffusion coefficient obtained from the field test into the simulation software COMSOL Multiphysics 5.6 for three-dimensional modeling. According to the locations of the test wells and observation wells, the model is divided into three layers to obtain a three-dimensional groundwater flow field model of the contaminated site; 4) Collect groundwater level data from observation wells H0, H2, and H3 of the contaminated site, and obtain groundwater level data within the same observation period in the constructed three-dimensional groundwater flow field model of the contaminated site, compare the measured water level value with the simulated water level value, and obtain the root mean square error of the groundwater level. Adjust the model parameters according to the initial value of the permeability coefficient of the aquifer obtained in the preliminary test, so that the root mean square error of the groundwater level is within the preset range; 5) Use the corrected three-dimensional groundwater flow field model of the contaminated site to perform multi-field coupling simulation of groundwater flow field, temperature field, and solute concentration field. For groundwater flow field simulation, select the Darcy's law module in COMSOL Multiphysics 5.6 software, for temperature field simulation, select the porous medium heat transfer module in the software, and for solute concentration field distribution, select the porous medium dilute species transfer module in the software. Perform multi-physics field simulations of groundwater flow field-temperature field, groundwater flow field-solute concentration field, and groundwater flow field-temperature field-solute concentration field, respectively, to obtain the influence relationship between the fields under full coupling conditions; 6) Using the monitoring data at different depths in the tracer test, adjust and calibrate the permeability coefficient, thermal conductivity coefficient and diffusion coefficient in the groundwater flow field model to determine the optimal model for the contaminated site; 7) Based on the optimal model of the contaminated site, the pollutant migration parameters are predicted. The water level, temperature, conductivity or concentration of the aquifer are input into the optimal model to obtain the pollutant migration parameters, namely, permeability, thermal conductivity and diffusion coefficient.

2. According to claim 1, a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling is characterized in that: In the step 1), the experimental area of ​​the contaminated site is a 3×3m square, wherein the injection well H1, the pumping well H4 and the observation wells H2 and H3 are located at the four corners of the square experimental area, and the observation well H0 is located in the center of the square experimental area.

3. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 1 is characterized in that: In the step 1), the data of the pumping test and the micro-water test are processed by the Theis matching method, and the geological parameters of the aquifer are determined by comparing the measured curve with the theoretical curve.

4. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 1 is characterized in that: In the step 2), the probes in each well are HR8801 water level temperature monitoring recorder and HR-206A online conductivity sensor, which are a group connected to the underground measurement and control terminal, wherein the observation wells H0, H2, and H3 are respectively provided with water level temperature integrated sensors and conductivity sensors at depths of 8.5m, 9.5m, 10.5m, 11.5m, and 12.5m; the pumping well is provided with a group of water level temperature integrated sensors and conductivity sensors at a depth of 11.5m; and the injection well is provided with a group of water level temperature integrated sensors and conductivity sensors at a depth of 12.5m.

5. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 1 is characterized in that: In the step 3), the plane range of the three-dimensional structural model is a rectangle, the major axis of the rectangle is parallel to the line connecting the pumping and injection wells, the major axis is 18.55m, the minor axis is 10.11m, and the average vertical height is 18.67m; the model is divided into three layers according to the locations of the test wells and the observation wells, specifically: the surface to a burial depth of 4m is generalized as a fill layer, the burial depth of 4m to 13.5m is generalized as a clay layer, and the burial depth of 13.5m to the bottom of the model is generalized as a bedrock layer.

6. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 1 is characterized in that: In the step 3), the initial conditions and boundary conditions of the groundwater flow field model of the contaminated site are set as follows: The boundaries parallel to the artificial groundwater flow field are set as no-flow boundaries, the top and bottom surfaces of the model are no-flow boundaries, and the two side boundaries perpendicular to the main groundwater flow direction are set at the observation well position and set as constant head boundaries, and their head values ​​are set by the interpolation function; the top and bottom surfaces of the model are set as thermal insulation boundaries, the sides are set as open boundaries, and the injection wells are set as line heat source boundaries; the parameter settings of the porous medium dilute species transfer module are the same as those of the heat conduction module, the initial concentration of the model dilute species NaCl is set to 0, the top and bottom surfaces of the model are set as no flux boundaries, the sides are set as open boundaries, and the injection wells are set as line mass sources, and the mass flow rate of the solute substance is controlled by a piecewise function.

7. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 6 is characterized in that: In the step 4), when describing the accuracy of the groundwater flow field model, the root mean square error RMSE of the model is calculated, and the model parameters whose root mean square error RMSE meets the preset conditions are selected. The calculation formula of the root mean square error RMSE is as follows: In the formula, C i0 is the numerical simulation value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, C ie The actual measured value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, where n is the number of sampling points.

8. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 7 is characterized in that: In the step 5), the mass conservation equation and Darcy velocity equation are used to simulate the groundwater flow field under the unsteady flow state of the site. The energy conservation equation and Darcy velocity equation are as follows: Where t is time, unit is s; ∈ p is the porosity; ρ is the liquid density, in kg / m 3 ;Q m is the input mass source, in kg / (m 3 *s); κ is the permeability, unit is m 2 ; μ is dynamic viscosity, unit is MPa*s; is the pressure difference, in MPa; g is the acceleration due to gravity, in m / s 2 ; u is the groundwater velocity, in m / s 2 .

9. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 8, characterized in that: In the step 5), the energy conservation equation, heat conduction equation and effective thermal conductivity calculation formula are used to simulate the heat transfer of the porous medium in the site. The energy conservation equation, heat conduction equation and effective thermal conductivity calculation formula are as follows: k eff =θ s k s +∈1k f +k disp (6) In the formula, C p,f is the constant pressure heat capacity of the fluid, in J / (kg*K); ρ f is the fluid density, its unit is kg / m 3 ; u is the groundwater velocity, in m / s 2 ; T is Kelvin temperature, unit is K; Q is heat source term, unit is J; q is the heat flow, unit is W / m 2 ;k eff is the effective thermal conductivity, in W / (m*K), which is determined by the solid matrix k s , fluid thermal conductivity k f The weighted average of the thermal diffusion coefficient k disp Determine, where θ s and ∈1 are weights.

10. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 1, characterized in that: In the step 5), the following porous medium dilute species transfer module control equation is selected to simulate salt migration: Where ρ is the liquid density in kg / m 3 ; C is the concentration of the dilute substance, in mol / m 3 ; t is time, in seconds; v is the velocity vector of the fluid, in meters per second; D is the diffusion coefficient of the dilute substance, in meters 2 / s; R is the source term, the unit is mol / (s*m 3 ).

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