Groundwater pollution risk assessment method for fly ash backfill field based on double module analytical model

Abstract

The application discloses a fly ash backfill field groundwater pollution risk assessment method based on a double-module analytical model, and comprises the following steps: obtaining geological parameters, hydrological parameters and pollutant parameters of a backfill field area; constructing a vadose zone pollutant migration model based on the parameters, and calculating the concentration of the pollutant when the pollutant enters an aquifer; taking the output as the input, constructing an aquifer pollutant migration model, and predicting the pollutant concentration at a target sensitive point; comparing the predicted concentration with a groundwater quality standard value, and judging whether the groundwater pollution risk is controllable; determining a risk sensitive area based on the simulation result, and identifying key control parameters affecting the pollutant migration. The application adopts a double-model series analytical calculation method, simplifies the operation process, improves the accuracy and consistency of the risk assessment, and is suitable for groundwater pollution risk prediction and control of a fly ash backfill field.

Description

Technical Field

[0001] This invention relates to the field of groundwater pollution risk assessment technology, specifically to a method for groundwater pollution risk assessment of fly ash backfill sites based on a dual-module analytical model. Background Technology

[0002] Fly ash, as a major solid waste from coal-fired power plants, poses a potential risk to groundwater environments due to pollutant migration during its backfilling disposal process. Currently used three-dimensional overall models cannot accurately simulate the transport of pollutants in the vadose zone (soil), and their application is primarily limited to academic research, offering limited applicability for on-site engineering backfilling guidance. For example, Ji Wenjia of the Chinese Research Academy of Environmental Sciences established a method for assessing the health risks of hazardous waste landfill disposal to groundwater environments based on the US EPACMTP model and health risk assessment model. Li Tiankui of Tsinghua University used a multi-media model of pollutant migration and transformation, employing regional sensitivity analysis, global sensitivity analysis, and empirical case verification methods; however, the simulated scenario was a closed or relocated enterprise site, unsuitable for dynamic guidance on engineering sites.

[0003] Existing technologies, such as the US EPACMTP model, have parameter systems that do not fully match my country's hydrogeological conditions. Due to the unsystematic identification of key risk factors, the simulation of pollutant migration processes in the vadose zone is limited, and the coupled simulation of pollutant migration processes in the vadose zone and aquifer is not accurate enough. As a result, the assessment results of different sites cannot provide a relatively accurate reference for standardized assessment processes at the management level and for guiding on-site monitoring and risk control. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a simple, accurate and reliable method and system for assessing the migration risk of groundwater pollutants in fly ash backfill sites, which is suitable for the characteristics of fly ash backfill sites in China.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The method for risk assessment of groundwater pollution at fly ash backfill sites based on a dual-module analytical model includes the following steps: (1) Obtain geological parameters, hydrological parameters, and pollutant parameters of the backfill site; (2) Construct a pollutant migration model in the vadose zone based on the parameters, and calculate the concentration of pollutants when they enter the aquifer; (3) Using the output of step (2) as input, construct an aquifer pollutant migration model to predict the pollutant concentration at the target sensitive point; (4) Compare the predicted concentration with the groundwater quality standard value (Groundwater Quality Standard (GB / T 14848-2017) Class III) to determine whether the groundwater pollution risk is controllable; (5) Based on the simulation results, determine the risk-sensitive areas and identify the key control parameters that affect the migration of pollutants.

[0006] Furthermore, the pollutant migration model in the vadose zone described in this invention is calculated analytically using the following migration equilibrium equation:

[0007] in, The concentration of pollutants entering the aquifer, Percolation duration, For the thickness of the vadose zone, As a lag factor, The dispersion coefficient is... The pore water flow velocity, The degradation coefficient of pollutants; The analytical solution is used to calculate the following when the following preset conditions are met. value:

[0008] C 0i The initial concentration of pollutant component i in the landfill leachate, mg / L, is obtained by equation (1). The concentration of pollutant i in the leachate entering the aquifer from the vadose zone is calculated by the solver using equation (2). C i ,Will C i The value is used as the input value for the aquifer pollutant migration model.

[0009] Furthermore, the aquifer pollutant migration model of the present invention employs the following analytical predictions:

[0010] in, The target point pollutant concentration, As coordinates, The dispersion coefficient is... Groundwater flow velocity, It is a first-order reaction constant. For the thickness of the aquifer, This represents the leachate flow rate.

[0011] Furthermore, the present invention also includes sensitivity analysis of at least one of the following parameters: observation well distance, groundwater depth, aquifer thickness, and initial concentration of pollutants.

[0012] Furthermore, the sensitivity analysis described in this invention is used to determine: (a) Pollution risk distribution within 2000 meters of the backfill site; (b) Risk-sensitive areas where groundwater depth is between 10 and 80 meters; (c) Quantitative relationship between initial pollutant concentration and receptor concentration; (d) The propagation pattern of pollutant concentration when the aquifer thickness is less than 20 meters.

[0013] Furthermore, the present invention also includes: combining the vadose zone model and the aquifer model in series to form a composite analytical model, and realizing automated calculation through programming tools.

[0014] Furthermore, the programming tool described in this invention is MATLAB, and the analytical model achieves batch calculation and result visualization through scripts or functions.

[0015] This invention also provides a groundwater pollution risk assessment system for fly ash backfill sites based on a dual-module analytical model, comprising: The parameter input module is used to receive geological parameters, hydrological parameters, and pollutant parameters input by the user. The model calculation module includes a cascaded vadose zone migration submodule and an aquifer migration submodule, used to execute the method described in this invention; The results output module is used to output pollutant concentration prediction results, risk levels, and sensitive area information. The comparison and judgment module is used to compare the prediction results with preset standard values ​​and generate risk assessment conclusions.

[0016] Furthermore, the system of the present invention is characterized by further comprising: The visualization module is used to display the curves of pollutant concentration changes with distance, time, burial depth, or thickness. The report generation module is used to automatically generate risk assessment reports, including key parameter tables, risk distribution maps, and control recommendations.

[0017] A non-transitory storage medium storing a computer program that, when executed by a processor, implements the method described in this invention.

[0018] The beneficial effects of this invention are: This invention employs independent computational modules to establish two analytical models for pollutant migration in the vadose zone and aquifer, respectively. These models are then cascaded and combined to form a composite model. This overcomes the limitation of the overall conceptual model in accurately simulating pollutant migration in the vadose zone, resulting in accurate and reliable risk assessment results. The analytical calculation method using dual-model cascade simplifies the computational process and improves assessment efficiency and consistency. The model parameter system is tailored to typical hydrogeological conditions in my country, making it suitable for groundwater pollution risk assessment in various fly ash backfill sites and facilitating widespread application. Sensitivity analysis can identify key risk factors. This management-oriented risk assessment software tool, based primarily on analytical models, provides a scientific basis for risk control. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a graph illustrating the impact of the risk factor backfill distance on pollutant concentration in Example 2. Figure 3 This is a graph showing the impact of risk factor pollutant concentration on pollutant concentration in Example 3; Figure 4 This is a diagram illustrating the impact of groundwater burial depth on pollutant concentration in Example 4. Figure 5 This is a graph illustrating the impact of aquifer thickness on pollutant concentration in Example 5. Figure 6 This is a simulation diagram of pollutant migration in the fly ash backfilling project area in Example 1. Detailed Implementation

[0020] The present invention will now be further described with reference to the accompanying drawings and embodiments. Example 1

[0021] This embodiment takes a fly ash backfill site in Ordos as an example. The geological parameters, hydrological parameters, and pollutant parameters of the backfill site are shown in Table 1:

[0022] The above parameters are input into the vadose zone pollutant migration model of this invention to calculate the concentration of pollutants when they enter the aquifer; the concentration in the aquifer is then input into the aquifer pollutant migration model of this invention to predict the pollutant concentration at the target sensitive point. The migration calculation process in the aquifer and the process in the vadose zone are two independent calculation units, but they are treated as a single calculation process in the software program, ultimately outputting only the pollutant concentration value in the aquifer. The calculation shows that the molybdenum concentration in the observation well after 5 years is 0.026 mg / L (this calculation process is performed by running the built-in software program, and the result is automatically output after completion; the solver program is EPACMTP), which is lower than the Class III standard limit (0.07 mg / L) of the "Groundwater Quality Standard" (GB / T 14848-2017), indicating that the risk is controllable. Figure 6 As shown, Figure 6 Wells 1#, 2#, 3#, and 7# are identified as high-risk locations, while wells 5#, 6#, and 9# are identified as low-risk locations. This is consistent with the conclusions of the completed official risk assessment report. Furthermore, wells 1#, 2#, 3#, and 7# are identified as high-risk monitoring locations, which is consistent with the on-site monitoring results. Example 2

[0023] In this embodiment, except for changing the distance between the observation point and the backfill site (the distance between the observation point and the backfill site is set to 50m, 100m, 200m, 500m, 1000m, 2000m respectively), the other pollutant parameters are the same as in Example 1.

[0024] The distance between the aforementioned observation points and the backfill site was used as the "x" coordinate input into the aquifer pollutant migration model described in this invention. The model was then used in a pre-programmed solver for batch calculations (the solver did not separate the two calculation processes; instead, it automatically input the first calculation and performed the second model calculation, ultimately outputting only one final value). Simulation results showed that within 200 meters of the backfill site, the pollutant concentration was high and the decay rate was fast; as the distance increased further, the concentration decay trend gradually slowed down, reaching 0.026 mg / L at 500 meters; when the distance exceeded 500 meters, the concentration change curve tended to flatten. Figure 2 As shown, within a 500-meter radius, pollutant concentrations decrease rapidly with increasing distance; beyond 500 meters, concentration changes tend to level off, indicating a higher risk within this range, requiring close monitoring. Example 3

[0025] In this embodiment, the system changes the groundwater burial depth parameters (set to 2m, 5m, 10m, 20m, 40m, 60m, and 80m respectively), while other pollutant parameters remain the same as in Example 1. Different burial depth values ​​(groundwater burial depth) are substituted into the vadose zone pollutant migration model described in this invention for calculation, and their impact on the final well concentration is analyzed. Simulation results show: Figure 3 As shown, pollutant concentration changes are sensitive within the burial depth range of 0-10 meters; changes are not significant within the 10-40 meter range; sensitivity increases above 40 meters; and the risk is extremely low above 80 meters. Example 4

[0026] In this embodiment, the initial concentration of molybdenum in the fly ash leachate was changed (set to 0.1 mg / L, 0.5 mg / L, 0.833 mg / L, 1.2 mg / L, and 2.0 mg / L, respectively). Other pollutant parameters remained the same as in Example 1. Different initial concentration values ​​were input into the model editor, and the predicted concentration at the observation well (500 meters) was recorded for each initial concentration. Linear regression analysis was performed on the data, revealing a significant linear proportional relationship between the pollutant concentration in the observation well and the initial concentration of the leachate, with a slope k = 0.0844 (R² > 0.99). The observation well concentration = leachate concentration × 0.0844. Figure 4 As shown, the simulation results show that the concentration in the observation well is linearly related to the initial concentration (slope 0.0844), which can be used to reverse control the leachate concentration to meet the standard. If the molybdenum concentration at the observation well is to meet the Class III water standard (<0.07 mg / L), the molybdenum concentration in the fly ash leachate needs to be controlled below 0.07 / 0.0844 ≈ 0.833 mg / L. Example 5

[0027] In this embodiment, the aquifer thickness parameter was systematically changed (set to 5m, 10m, 20m, 50m, 100m, 150m, and 200m respectively), while other pollutant parameters remained the same as in Example 1. The aquifer pollutant migration model of this invention, based on the above model, was calculated using different thickness values. Simulation results show that when the aquifer thickness is in the range of 0-20 meters, the pollutant concentration increases rapidly with increasing thickness, having a significant impact; when the thickness exceeds 20 meters, the rate of increase in concentration with thickness slows down, reaching a maximum concentration around 150 meters; when the thickness exceeds 150 meters, the concentration shows a slow decreasing trend. Figure 5 As shown in the figure, the simulation results show that the pollutant concentration increases significantly with increasing thickness in the range of 0-20 meters; the effect gradually weakens above 20 meters. Comparative Example 1

[0028] The same site in Examples 1-5 was simulated using a traditional overall conceptual model (Modflow), with the same model parameters as in Example 1. The concentration obtained after 5 years was 0.053 mg / L, lower than the Class III groundwater standard (0.07 mg / L), indicating a low and controllable risk. The risk status of each monitoring point was simultaneously confirmed as follows: wells 1#, 2#, 3#, and 7# were identified as high-risk points, while points 5#, 6#, and 9# were identified as low-risk points. Although both met the standard, the analytical model results of this invention are more accurate and simpler in simulating vadose zone migration, making it relatively safer for guiding the backfilling process and able to withstand more risks.

[0029] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the scope of the present invention are still within the scope of the present invention.

Claims

1. A method for risk assessment of groundwater pollution in fly ash backfill sites based on a dual-module analytical model, characterized in that, Includes the following steps: (1) Obtain geological parameters, hydrological parameters, and pollutant parameters of the backfill site; (2) Construct a pollutant migration model in the vadose zone based on the parameters, and calculate the concentration of pollutants when they enter the aquifer; (3) Using the output of step (2) as input, construct an aquifer pollutant migration model to predict the pollutant concentration at the target sensitive point; (4) Compare the predicted concentration with the groundwater quality standard value to determine whether the groundwater pollution risk is controllable; (5) Based on the simulation results, determine the risk-sensitive areas and identify the key control parameters that affect the migration of pollutants.

2. The method according to claim 1, characterized in that, The vadose zone pollutant migration model is calculated analytically using the following migration equilibrium equation: ； in, The concentration of pollutants entering the aquifer, Percolation duration, For the thickness of the vadose zone, As a lag factor, The dispersion coefficient is... The pore water flow velocity, The degradation coefficient of pollutants; The analytical solution is used to calculate the following when the following preset conditions are met. value: ; C 0i The initial concentration of pollutant component i in the landfill leachate, mg / L, is obtained by equation (1). The concentration of pollutant i in the leachate entering the aquifer from the vadose zone is calculated by the solver using equation (2). C i ,Will C i The value is used as the input value for the aquifer pollutant migration model.

3. The method according to claim 2, characterized in that, The aquifer pollutant migration model uses the following analytical predictions: ; in, The target point pollutant concentration, As coordinates, The dispersion coefficient is... Groundwater flow velocity, It is a first-order reaction constant. For the thickness of the aquifer, This represents the leachate flow rate.

4. The method according to claim 1, characterized in that, It also includes sensitivity analysis of at least one of the following parameters: observation well distance, groundwater depth, aquifer thickness, and initial concentration of pollutants.

5. The method according to claim 4, characterized in that, The sensitivity analysis was used to determine: (a) Pollution risk distribution within 2000 meters of the backfill site; (b) Risk-sensitive areas where groundwater depth is between 10 and 80 meters; (c) Quantitative relationship between initial pollutant concentration and receptor concentration; (d) The propagation pattern of pollutant concentration when the aquifer thickness is less than 20 meters.

6. The method according to claim 1, characterized in that, Also includes: The vadose zone model and the aquifer model are combined in series to form a composite analytical model, and automated calculations are achieved through programming tools.

7. The method according to claim 6, characterized in that, The programming tool is MATLAB, and the analytical model is used to perform batch calculations and visualize the results through scripts or functions.

8. A groundwater pollution risk assessment system for fly ash backfill sites based on a dual-module analytical model, characterized in that, include: The parameter input module is used to receive geological parameters, hydrological parameters, and pollutant parameters input by the user. The model calculation module includes a cascaded vadose zone migration submodule and an aquifer migration submodule, used to perform the method as described in any one of claims 1-7; The results output module is used to output pollutant concentration prediction results, risk levels, and sensitive area information. The comparison and judgment module is used to compare the prediction results with preset standard values ​​and generate risk assessment conclusions.

9. The system according to claim 8, characterized in that, Also includes: The visualization module is used to display the curves of pollutant concentration changes with distance, time, burial depth, or thickness. The report generation module is used to automatically generate risk assessment reports, including key parameter tables, risk distribution maps, and control recommendations.

10. A non-transitory storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-7.

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