Underground water pollution risk assessment method based on underground water environment background value

Abstract

The invention provides a groundwater pollution risk assessment method based on a groundwater environment background value, and aims to solve the problems that the influence of a natural process and human activities on a groundwater environment is difficult to discriminate in the prior art, the background value is inaccurate to determine, the risk management mode is extensive and the like. The method comprises the following steps: dividing a human activity influence area and a natural dominant area by constructing a human activity quantification model and a judgment model, and determining an underground water environment background value; introducing an underground water dynamic field activeness index, and establishing a water quality dynamic threshold model associated with the activeness; dividing main control factor subareas of different groundwater qualities according to the activeness-water quality discrimination relation and the pollution source analysis result; and the zoning result is verified by adopting methods such as isotopic tracing or specific pollutant analysis, a risk management and control strategy matched with the characteristics of each zone is provided, scientific improvement of underground water background value determination is realized, and a refined technical support is provided for underground water environment protection and restoration work.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of groundwater environment protection, and specifically provides a dynamic water quality threshold evaluation and influencing factor discrimination method based on a groundwater fluctuation environment. BACKGROUND

[0002] Groundwater is an important source of freshwater supply in many parts of the world, and is a key link between the biosphere, lithosphere and atmosphere, and plays an important role in material migration and energy transfer. Due to the strong concealment and weak self-purification ability of the groundwater system, once it is polluted, it is difficult to control and costly to treat. Therefore, preventive control of groundwater pollution has more significant environmental and economic value than post-treatment. Building an effective groundwater pollution risk early warning technology is the key to early identification and active intervention. However, the existing technology generally has the problem that it is difficult to effectively distinguish between natural background values and human pollution, which seriously restricts the accuracy and reliability of the early warning. In addition, the current evaluation system uses fixed thresholds for water quality evaluation, ignoring the dynamic influence of groundwater dynamic conditions on water quality safety thresholds, which is easy to misjudge natural high background values as pollution, resulting in "false positive" results, and thus the risk control measures lack pertinence.

[0003] In the prior art, there are several related patents involving groundwater environment early warning and evaluation. For example, CN120217159A proposes a groundwater environment monitoring and early warning method, which couples real-time early warning and prediction early warning modules to build a monitoring model, and identifies potential pollution sources and enterprise types with the help of pollutant inversion; CN120494621A discloses a groundwater quality grading prediction method based on multi-source data and machine learning, which uses a trained model to predict water quality grades; CN106932549B provides a comprehensive groundwater water quality early warning method, which uses an improved Nemerow index method and VisualMODFLOW simulation to perform water quality state early warning and warning degree determination. Although the early warning function is realized, the separation of natural and human influences is not systematically solved, and there is also a lack of dynamic correction mechanism for water quality safety thresholds.

[0004] In summary, the existing groundwater water quality evaluation and early warning technology still has deficiencies in the scientific judgment of groundwater environmental background values, especially lacking systematic consideration of the dynamic changes of water quality safety thresholds caused by water level fluctuations, which is difficult to adapt to the needs of precise early warning and fine management under complex hydrogeological conditions. SUMMARY

[0005] The technical problem to be solved by the present application is that the existing groundwater quality evaluation and early warning technology still has deficiencies in the scientific determination of groundwater environmental background value, especially lacks systematic consideration of the dynamic changes of water quality safety threshold caused by water level fluctuation, and is difficult to adapt to the precise early warning and fine management needs under complex hydrogeological conditions.

[0006] The purpose of the present application is achieved in the following manner: A groundwater pollution risk assessment method based on a groundwater environmental background value, the method comprising: S1: selecting key social, economic and environmental pressure factors, establishing a human activity quantification model, calculating the human activity intensity index of each unit in the study area, and constructing a human activity influence index database; S2: based on the human activity influence index database, establishing a natural-human impact discrimination model, setting a human activity influence threshold, and dividing the study area into a natural dominant area and a human activity influence area with the threshold as the boundary; S3: performing a reasonableness test on the zoning results of S2; if the test fails, feeding back to S1 to optimize the model; if the test passes, determining the groundwater environmental background value according to the groundwater quality data in the natural dominant area; S4: introducing a groundwater dynamic field activity index calculated from water level depth, hydraulic gradient and water level fluctuation speed, and constructing a quantitative relationship model between the activity index and the groundwater quality threshold, thereby establishing a groundwater quality dynamic threshold model; S5: combining the activity-water quality discrimination relationship established in S4 with the pollution source analysis results to perform groundwater quality control factor zoning; S6: verifying the zoning results of S5 using isotope tracing or characteristic pollutant analysis methods, and integrating the dynamic threshold and zoning information to form a targeted groundwater pollution risk management and control scheme.

[0007] In S1, the human activity intensity index is calculated by the following formula: In the formula, H represents the human activity intensity, represents the weight corresponding to the n pressure indicators; represents the standardized value of the n pressure indicators.

[0008] In S1, the human activity intensity index H is further corrected by groundwater depth and hydraulic slope to obtain the human activity influence intensity HI, and the correction formula is: In the formula, representing the groundwater flow gradient, k and b are the flow gradient influence coefficients; is the depth coefficient.

[0009] In S2, the method for establishing the natural-human influence discrimination model is as follows: taking the cumulative frequency of the correlation coefficient between the groundwater level at different points and the natural influence factor as the vertical coordinate, taking the human activity intensity obtained in S1 as the horizontal coordinate, drawing a cumulative frequency curve, and determining the human activity influence threshold by identifying the inflection point on the curve.

[0010] In S4, the groundwater dynamic field activity index a is calculated by the following formula: In the formula, is the groundwater activity, is the normalized depth, is the normalized hydraulic gradient, is the normalized water level fluctuation speed.

[0011] In S4, the quantitative relationship between the activity index a and the water quality threshold C is established by using the Greenberg logarithmic model, and the model expression is as follows: In the formula, is the standard concentration of groundwater of three types of water, is the activity of the point in the study area meeting the three types of water standards, is the groundwater activity, is the groundwater water quality threshold.

[0012] In S5, the following sub-steps are specifically included: S51: In the human activity influence area, based on the cumulative frequency of the groundwater dynamic field activity and the corresponding water quality index data, a cumulative frequency curve is drawn, and a characteristic inflection point on the curve is identified; S52: Comparing the groundwater environmental background value determined in S3 with the water quality concentration at the inflection point, and according to the comparison result, different water quality control factor types are divided.

[0013] In S52, according to the comparison result, different water quality control factor types are divided, specifically as follows: When the groundwater environmental background value is less than the inflection point water quality: If the groundwater water quality concentration C is less than the background value, it is determined that the dilution of the artificial recharge clean water source is dominant; If the groundwater water quality concentration C is between the background value and the inflection point water quality, it is determined that the human activity pollutants enter the aquifer with recharge water; If the concentration C of the groundwater quality is greater than the inflection point water quality, it is determined that evaporation concentration or pollutant migration and accumulation dominates.

[0014] In S6, the targeted risk control scheme is formed, specifically: the dynamic water quality threshold zoning map obtained in S4 is superimposed and fused with the groundwater quality control factor zoning map obtained in S5 to generate a comprehensive zoning management map, and a differentiated pollutant input control strategy is formulated for each zone based on the comprehensive zoning management map.

[0015] The beneficial effects of the present application are: (1) Based on key socio-economic indicators such as population density, land use, and fertilizer application amount, the weight is determined by the analytic hierarchy process, and the intensity of human activity is quantified; then, by establishing a natural-human impact discrimination model, the natural dominant area and human activity impact area are reasonably divided, and a feedback mechanism is set to iteratively optimize the zoning results, and finally the background value is determined according to the water quality data of the natural dominant area. This technical path effectively overcomes the bottleneck problem that natural high background value and human pollution are difficult to separate in traditional methods, significantly improves the scientificity and accuracy of the determination of background value, and provides a reliable benchmark for subsequent risk assessment.

[0016] (2) The groundwater dynamic field activity index is introduced, and a dynamic water quality threshold evaluation system based on the Greenberg logarithmic model is constructed. This system comprehensively considers key hydrodynamic parameters such as water depth, hydraulic gradient, and water level fluctuation speed, and establishes a quantitative functional relationship between activity index and water quality threshold through standardization processing and weighted average calculation. This method can dynamically adjust the water quality safety threshold according to the hydrodynamic characteristics of different regions and different periods, effectively avoiding misjudgment caused by "one-size-fits-all" evaluation, and significantly improving the spatial adaptability and temporal dynamics of water quality evaluation and risk identification.

[0017] (3) Based on the identification of characteristic inflection points by cumulative frequency curve, combined with groundwater environmental background value for multi-scenario zoning discrimination, the dominant control process in different zones is clearly revealed, and further scientific verification of the zoning results is carried out by using isotope tracing and characteristic pollutant analysis means. Finally, by superimposing dynamic threshold zoning and influence factor zoning, a comprehensive management zoning map is generated, which directly presents the management and control targets and dominant factors of each zone, providing direct technical basis for formulating differentiated and precise risk control strategies, and greatly improving the pertinence and operability of groundwater environmental protection and remediation measures. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the flow chart of the discrimination method of the present application; Figure 2 is the natural-human impact discrimination result for the study area; Figure 3 is the active-water quality discrimination graph. Specific Embodiments

[0019] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0020] It should be noted that the following detailed description is exemplary and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same technical meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0021] A method for assessing groundwater pollution risk based on the background value of the groundwater environment, the method comprising: S1: Select key socio-economic and environmental stress factors, establish a quantification model of human activities, calculate the human activity intensity index of each unit in the study area, and construct a human activity impact index database; S2: Based on the human activity impact index database, establish a natural-artificial impact discrimination model, set a human activity impact threshold, and divide the study area into a natural-dominated area and a human activity impact area with the threshold as the boundary; S3: Conduct a rationality test on the zoning results of S2; if the test fails, feedback to S1 to optimize the model; if the test passes, determine the groundwater environment background value based on the groundwater quality data in the natural-dominated area; S4: Introduce an index of groundwater dynamic field activity comprehensively calculated from the water level depth, hydraulic gradient, and water level fluctuation speed, and construct a quantitative relationship model between the activity index and the groundwater quality threshold, thereby establishing a groundwater quality dynamic threshold model; S5: Based on the activity-water quality discrimination relationship established in S4 and the results of pollution source analysis, conduct zoning of groundwater quality control factors; S6: Use isotope tracing or characteristic pollutant analysis methods to verify the zoning results of S5, and integrate the dynamic threshold and zoning information to form a targeted groundwater pollution risk control plan.

[0022] Select environmental stress factors such as population density, land use, and chemical fertilizer application amount that characterize the impact of human activities, determine their weights using the analytic hierarchy process, and calculate the human activity intensity index of each unit in the study area using the weighted superposition method. In S1, the human activity intensity index is calculated by the following formula: In the formula, H (taking values from 0 to 1) represents the human activity intensity, where 0.75 < H ≤ 1 indicates extremely strong human activities, 0.5 < H ≤ 0.75 indicates strong human activities, 0.25 < H ≤ 0.5 indicates medium human activities, and 0 < H ≤ 0.25 indicates weak human activities. represent the weight of n pressure indicators; represent the standardized values of n pressure indicators.

[0023] In view of the fact that the depth and the hydraulic gradient control the rate and the possibility of the migration of pollutants, in S1, the groundwater depth and the hydraulic gradient are further used to correct the human activity intensity index H, to obtain the human activity influence intensity HI, and the correction formula is: In the formula, represent the groundwater flow gradient, k and b are the flow gradient influence coefficients (the value range is 0.1-1); is the depth coefficient (assigned according to the lithology of the stratum).

[0024] The natural influence factors of the groundwater level in the study area are determined, a relationship coefficient database is established based on the correlation between the water level time series data of different points for many years and the natural indicators, in S2, the establishment method of the natural-human influence discrimination model is: taking the cumulative frequency of the correlation coefficient of the groundwater level of different points and the natural influence factors as the vertical coordinate, taking the human activity intensity obtained in S1 as the horizontal coordinate, an accumulated frequency curve is drawn, the human activity influence threshold is determined by identifying the inflection point on the curve. Taking the threshold as the limit, the natural dominant area and the human activity influence area are divided.

[0025] Considering the fact that the groundwater salt concentration is usually negatively correlated with the depth, the hydraulic gradient and the water level fluctuation speed, in order to comprehensively reflect the dynamic characteristics of the water level in the vertical fluctuation and the horizontal flow, the average values of the water level depth, the hydraulic gradient and the water level fluctuation speed after standardization are introduced as the comprehensive indicators representing the activity degree of the groundwater dynamic field. The calculation formula of the water level fluctuation speed is: In the formula, and represent the time corresponding to two adjacent inflection points, and represent the water level values corresponding to two adjacent inflection points.

[0026] In S4, the groundwater dynamic field activity degree index is calculated by the following formula: In the formula, is the groundwater activity degree, is the standardized depth, is the standardized hydraulic gradient, is the standardized water level fluctuation speed.

[0027] In S4, the quantitative relationship between the activity index a and the water quality threshold C is established by using the Greenberg logarithmic model, and the water quality safety threshold evaluation based on dynamic hydrodynamic conditions is realized. The model expression is: In the formula, is the concentration of the third-class water standard of groundwater, is the activity of the point in the study area that meets the third-class water standard, is the groundwater activity, is the groundwater quality threshold.

[0028] In S5, the following sub-steps are specifically included: S51: In the human activity affected area, based on the cumulative frequency of the groundwater dynamic field activity and the corresponding water quality index data, a cumulative frequency curve is drawn, and a characteristic inflection point on the curve is identified; S52: The groundwater environmental background value determined in S3 is compared with the water quality concentration at the inflection point, and different water quality control factor types are divided according to the comparison result.

[0029] In S52, the different water quality control factor types are divided according to the comparison result, specifically: When the groundwater environmental background value is less than the inflection point water quality: If the groundwater water quality concentration C is less than the background value, it is determined that the artificial recharge clean water source dilution is dominant; If the groundwater water quality concentration C is between the background value and the inflection point water quality, it is determined that the human activity pollutants enter the aquifer with recharge water; If the groundwater water quality concentration C is greater than the inflection point water quality, it is determined that the evaporation concentration or pollutant migration and accumulation is dominant.

[0030] In S6, the formation of the targeted risk control scheme is specifically: the dynamic water quality threshold zoning map obtained in S4 is superimposed and fused with the groundwater water quality control factor zoning map obtained in S5 to generate a comprehensive zoning management map, and a differentiated pollutant input control strategy is developed for each zone based on the comprehensive zoning management map.

[0031] Embodiment: Taking the typical groundwater salinization problem in Yinchuan Plain as an application example, according to step S1, the indexes closely related to the groundwater environment of living and production activities are selected, and the social and economic development characteristics of the irrigation area are fully considered. When quantifying the intensity of human activities, the social indexes are summarized as population distribution density, land use / cover change, distribution of diversion canals (including length and lining degree), distribution of groundwater pumping sources (reflecting the intensity of exploitation), and fertilizer load of cultivated land. The economic indexes are integrated as total grain output and total industrial output. On this basis, the main environmental pressure factors in the irrigation area are quantitatively characterized, and the weights of each factor are determined by using the analytic hierarchy process. Finally, the human activity intensity index of each unit in the study area is calculated by weighted superposition, and the calculation formula is as follows: In the formula, H (representing human activity intensity, wherein represents extremely strong human activity, represents strong human activity, represents moderate human activity, represents weak human activity; represents the weight corresponding to the 7 pressure indexes; represents the standardized value of the 7 pressure indexes.

[0032] Table 1 Human activity intensity in different regions The degree of influence of human activities on the groundwater environment is also restricted by natural environmental factors. In order to accurately quantify the human influence, the groundwater depth and hydraulic slope are used to correct the human activity intensity index calculated, so as to obtain the influence intensity of human activities on the water environment which is more in line with the actual situation. The correction principle is that the shallower the groundwater depth and the smaller the hydraulic slope, the slower the migration speed of pollutants in the aquifer, and the weaker the dilution and self-purification ability, so the influence of human activities is relatively more significant.

[0033] In the formula, represents the influence intensity of human activities; H represents the action intensity of human activities; represents the groundwater flow slope, and is the flow slope influence coefficient (the value range is 0.1-1); is the depth coefficient (assigned according to the lithology of the stratum), which is set as follows.

[0034] Table 2 Depth correction coefficient table of human activity influence intensity in Yinchuan Plain According to step S2, the characteristics of establishing a natural-anthropogenic impact discrimination model and determining the threshold of human activity impact are as follows: First, identify the natural influencing factors of groundwater level in the study area, and construct a correlation coefficient database based on multi-year water level time series data and corresponding natural indicators at different monitoring points; then, plot a cumulative frequency curve with the cumulative frequency of this correlation as the ordinate and the intensity of human activity obtained in S1 as the abscissa to construct the discrimination model; furthermore, determine the critical threshold of human activity impact by identifying the characteristic inflection points on the curve (in this example, the threshold HI is 0.1); finally, use this threshold as the boundary to divide the study area into a naturally dominated area and a human activity-affected area (see...). Figure 2 ).

[0035] The rationality of the threshold division results was verified in step S3. This verification shows that the division results are consistent with the actual situation in the region. Accordingly, the groundwater environmental background value was determined as the average value of groundwater quality indicators at all monitoring points within the natural dominant area, which was calculated to be 911 mg / L.

[0036] The groundwater quality thresholds under different hydrodynamic characteristics are determined according to S4. Considering that groundwater salinity concentration is usually negatively correlated with burial depth, hydraulic gradient, and water level fluctuation velocity, in order to comprehensively reflect the dynamic characteristics of water level in both vertical fluctuation and horizontal flow, the average values ​​of water level burial depth, hydraulic gradient, and water level fluctuation velocity after standardization are introduced as a comprehensive index characterizing the activity of the groundwater hydrodynamic field. The formula for calculating the water level fluctuation velocity is: In the formula, t 1 and t 2 represents the time corresponding to two adjacent inflection points. H t2 and H t1 This represents the water level value corresponding to two adjacent inflection points. The formula for calculating the groundwater dynamic field activity index is: In the formula, For groundwater activity, To standardize burial depth, To standardize the hydraulic gradient, This is to standardize the water level fluctuation rate.

[0037] Preferably, a Greenberg logarithmic model is introduced to establish a quantitative relationship between groundwater hydrodynamic field activity and water quality threshold, thereby achieving water quality safety threshold evaluation based on dynamic hydrodynamic conditions. The model expression is as follows: In the formula,C 0 is the groundwater three-class water standard concentration, is the point activity of the study area that meets the three-class water standard, is the groundwater activity, C is the groundwater water quality threshold. The phreatic water in the study area basically exceeds the safety threshold, and further judgment of the pollution control factor is required.

[0038] Table 3 fluctuation threshold of a typical area According to the groundwater water quality control factor partitioning method according to step S5, the specific implementation manner is as follows: the human activity affected area is selected as the research object, the activity-accumulation frequency determined in S4 is taken as the vertical coordinate, the corresponding water quality index is taken as the horizontal coordinate, the cumulative frequency curve is constructed based on the activity-water quality discrimination relationship, and thus the activity-water quality discrimination model is established; the inflection point of the model is identified, and the human activity affected threshold is set, and thus the partitioning and division of the groundwater water quality control factor are realized.

[0039] According to the relationship between the groundwater environmental background value and the fluctuation inflection point water quality as shown in FIG. 5, it is confirmed that the region meets the condition of “groundwater environmental background value < fluctuation inflection point water quality”. Based on this, the groundwater water quality control factor is partitioned and judged as follows according to different water quality concentration intervals: Figure 3 When the water quality concentration is less than 911 mg / L, it is determined that the dilution effect of artificial recharge water dominates, and the typical cases include the dilution of clean water source introduced by the seepage of water diversion channels to the groundwater body; When the water quality concentration is between 911 mg / L and 2350 mg / L, it is determined that the pollutants caused by human activities enter the aquifer with the infiltration recharge water, for example, the groundwater pollution caused by the infiltration of fertilizers in the agricultural irrigation process; C When the water quality concentration is greater than 2350 mg / L, it indicates that the groundwater activity in the region is extremely low, and the water quality deterioration is not related to artificial recharge, and is mainly controlled by the evaporation concentration effect or the migration and accumulation of pollutants from upstream to downstream. C According to the verification results of the final isotope tracing and characteristic pollutant analysis, when the water quality concentration is less than 911 mg / L, the groundwater activity is high, and the dilution effect of artificial recharge water dominates; when the water quality concentration is between 911 mg / L and 2350 mg / L, the nitrate content reaches the peak value, indicating that the interval is mainly affected by agricultural non-point source input; and when the water quality concentration is greater than 2350 mg / L, the groundwater activity value is significantly low, reflecting the strong evaporation fractionation effect. C The above verification results show that the groundwater water quality control factor partitioning result realized by the method is scientific and reasonable.

[0040] According to the verification results of the final isotope tracing and characteristic pollutant analysis, when the water quality concentration is less than 911 mg / L, the groundwater activity is high, and the dilution effect of artificial recharge water dominates; when the water quality concentration is between 911 mg / L and 2350 mg / L, the nitrate content reaches the peak value, indicating that the interval is mainly affected by agricultural non-point source input; and when the water quality concentration is greater than 2350 mg / L, the groundwater activity value is significantly low, reflecting the strong evaporation fractionation effect. C C The above verification results show that the groundwater water quality control factor partitioning result realized by the method is scientific and reasonable.

[0041] ​​​Based on the risk management scheme described in S6, the dynamic water quality threshold zoning map is spatially superimposed with the groundwater quality control factor zoning map to generate a comprehensive zoning management map, which clearly defines the corresponding water quality management target values and their dominant influencing factors for each zone. Based on the existing hydrodynamic conditions, a differentiated pollutant input control measure is developed with the dynamic water quality safety threshold as the core target.

[0042] Through superposition analysis, it is known that human activities such as water diversion irrigation, although to some extent, increase the water dynamic activity by increasing the infiltration recharge, dilute the salt in the short term and increase the apparent safety threshold, but still need to prevent the potential risks brought by the downward movement of pollutants carried by the recharge water; while groundwater exploitation activities will reduce the water dynamic activity and safety threshold, and the water quantity regulation and pollution source control in this region need to be strengthened.

[0043] The above is only the preferred embodiment of the present application, it should be noted that for those skilled in the art, without departing from the overall concept of the present application, a number of changes and improvements can be made, which should be considered as the protection scope of the present application.

Claims

1. A groundwater pollution risk assessment method based on groundwater environmental background values, characterized in that: The method includes: S1: Select key socio-economic and environmental pressure factors, establish a quantitative model of human activities, calculate the human activity intensity index of each unit in the study area, and construct a database of human activity impact index. S2: Based on the aforementioned human activity impact index database, establish a natural-human impact discrimination model, set a human activity impact threshold, and divide the study area into a natural-dominated area and a human activity-affected area using the threshold as the boundary. S3: Perform a rationality check on the zoning results of S2; if the check fails, it is fed back to S1 to optimize the model; if the check passes, the groundwater environmental background value is determined based on the groundwater quality data in the natural dominant area. S4: Introduce the groundwater dynamic field activity index, which is calculated by combining water level depth, hydraulic gradient and water level fluctuation velocity, and construct a quantitative relationship model between the activity index and the groundwater quality threshold, thereby establishing a dynamic threshold model for groundwater quality. S5: Based on the activity-water quality discrimination relationship established in S4 and the results of pollution source analysis, the groundwater quality control factors are zoned. S6: Verify the zoning results of S5 using isotope tracing or characteristic pollutant analysis methods, and integrate the dynamic threshold and zoning information to form a targeted groundwater pollution risk management plan.

2. The groundwater pollution risk assessment method based on groundwater environmental background values ​​according to claim 1, characterized in that: In S1, the human activity intensity index is calculated using the following formula: In the formula, H represents the intensity of human activity. Represents the weights corresponding to n pressure indicators; The standardized values ​​represent n stress indicators.

3. The groundwater pollution risk assessment method based on groundwater environmental background values ​​according to claim 2, characterized in that: In S1, the human activity intensity index H is further corrected using groundwater depth and hydraulic gradient to obtain the human activity impact intensity HI. The correction formula is as follows: In the formula, represents the groundwater flow gradient, and k and b are the influence coefficients of the water flow gradient; This is the burial depth coefficient.

4. The groundwater pollution risk assessment method based on groundwater environmental background values ​​according to claim 1, characterized in that: In S2, the method for establishing the natural-human impact discrimination model is as follows: using the cumulative frequency of the correlation coefficient between groundwater level and natural influencing factors at different locations as the vertical axis and the intensity of human activities obtained in S1 as the horizontal axis, a cumulative frequency curve is plotted, and the threshold of human activity impact is determined by identifying the inflection point on the curve.

5. The groundwater pollution risk assessment method based on groundwater environmental background values ​​according to claim 1, characterized in that: In S4, the groundwater dynamic field activity index α is calculated using the following formula: In the formula, For groundwater activity, To standardize burial depth, To standardize the hydraulic gradient, This is to standardize the water level fluctuation rate.

6. The groundwater pollution risk assessment method based on groundwater environmental background values ​​according to claim 5, characterized in that: In S4, the Greenberg logarithmic model is used to establish a quantitative relationship between the activity index α and the water quality threshold C. The model expression is as follows: In the formula, The concentration is the Class III standard concentration for groundwater. To study the activity levels of monitoring points in the study area that meet the Class III water quality standards, For groundwater activity, This refers to the groundwater quality threshold.

7. The groundwater pollution risk assessment method based on groundwater environmental background values ​​according to claim 1, characterized in that: In S5, the following sub-steps are specifically included: S51: Within the area affected by human activities, based on the cumulative frequency of groundwater dynamic field activity and corresponding water quality index data, a cumulative frequency curve is plotted, and characteristic inflection points on the curve are identified. S52: Compare the groundwater environmental background value determined in S3 with the water quality concentration at the inflection point, and classify different water quality control factor types based on the comparison results.

8. The groundwater pollution risk assessment method based on groundwater environmental background values ​​according to claim 7, characterized in that: In S52, the classification of different water quality control factor types based on the comparison results is specifically as follows: When the groundwater environmental background value is less than the inflection point water quality: If the groundwater concentration C is less than the background value, it is determined that the groundwater is mainly diluted by artificial replenishment of clean water. If the groundwater concentration C is between the background value and the inflection point water quality, it is determined that pollutants from human activities have entered the aquifer with the recharge water. If the groundwater concentration C is greater than the inflection point water quality, it is determined that the groundwater is dominated by evaporation and concentration or the accumulation of pollutants.

9. The groundwater pollution risk assessment method based on groundwater environmental background values ​​according to claim 1, characterized in that: In S6, the formation of a targeted risk management plan specifically involves: overlaying and merging the dynamic water quality threshold zoning map obtained in S4 with the groundwater quality control factor zoning map obtained in S5 to generate a comprehensive zoning management map, and formulating differentiated pollutant input control strategies for each zoning based on the comprehensive zoning management map.

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