A method for determining a soil risk control value suitable for protecting bedrock fissure water

Abstract

This invention provides a method for determining soil risk control values ​​applicable to the protection of bedrock fissure water, belonging to the field of pollution prevention and control technology. The method includes: sequentially determining the comprehensive first-order attenuation coefficient and the comprehensive retardation factor of the vadose zone; determining the vertical migration leaching factor based on the comprehensive first-order attenuation coefficient and the comprehensive retardation factor of the vadose zone; further determining the comprehensive leaching factor based on the vertical migration leaching factor and the horizontal mixing and dilution factor; and calculating the soil risk control value of the pollutant using a risk concept model based on the comprehensive leaching factor and the maximum allowable concentration limit of pollutants in groundwater. The method of this invention considers the characteristics of pollutants in different vadose zones and their diffusion performance at the horizontal level, obtaining a more accurate leaching factor through multi-dimensional calculations, thereby making the obtained soil risk control value more precise.

Description

Technical Field

[0001] This invention relates to the field of pollution control technology, and in particular to a method for determining soil risk control values ​​applicable to the protection of bedrock fissure water. Background Technology

[0002] Soil risk control values ​​refer to the maximum permissible concentration limits of pollutants in soil set under specific land use patterns to prevent unacceptable risks to human health and the ecological environment (especially groundwater).

[0003] Soil risk control values ​​are calculated based on the maximum concentration limits of pollutants in groundwater and the leaching factor of pollutants migrating into groundwater. However, the existing calculation model for the leaching factor of pollutants migrating into groundwater is a mass flux balance model. This model is developed based on the theory of convection-dispersion migration of pollutants in homogeneous loose porous media. It is only applicable to scenarios where there is pore water and the water table is close to the contaminated soil layer. It is not applicable to bedrock fissure water, especially not applicable to scenarios with thick vadose zones where the water table is deeper than the contaminated soil layer.

[0004] This is because, firstly, when using existing mass flux balance models to calculate leaching factors, the input parameters, including Darcy rate and groundwater mixing zone thickness, are based on the porous media settings under the scenario of unconfined groundwater, and are not applicable to the parameter definitions, testing methods, and value standards corresponding to bedrock fractured media. Consequently, existing mass flux balance models can only characterize the solute migration characteristics of loose porous aquifers, and cannot adapt to the heterogeneity of bedrock fractured media and the migration patterns of the fracture-matrix dual media. For the widely distributed bedrock mountainous and karst areas in my country, the model's physical concepts are completely inconsistent with the actual hydrogeological conditions, resulting in severely distorted calculation results.

[0005] Second, the model completely ignores the adsorption and hindrance, biological and abiotic attenuation effects of pollutants during vertical migration in the thick vadose zone, resulting in a significantly larger calculated leaching factor. Consequently, the soil risk control value obtained is too conservative, which greatly increases the unnecessary remediation cost of the site. Summary of the Invention

[0006] This invention proposes a method for determining soil risk control values ​​applicable to the protection of bedrock fissure water, which solves the core problem in the prior art that the leaching factor model is not applicable to bedrock fissure media and the water table is deeper than the contaminated soil scenario. This method improves the accuracy and rationality of soil risk control values ​​and avoids the waste of resources caused by over-remediation.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for determining soil risk control values ​​suitable for protecting bedrock fissure water includes: Based on the attenuation coefficient of pollutants in the loose vadose zone Attenuation coefficient of bedrock fracture vadose zone Determine the comprehensive first-order attenuation coefficient of the outflow vadose zone According to the loose vadose zone resistance factor and bedrock fracture vadose zone blocking factor Determine the comprehensive retardation factor of the vadose zone The vertical thickness of the loosely packed air-filled zone Vertical thickness of the vadose zone in bedrock fissures satisfy ≥thickness threshold Based on the first-order attenuation coefficient of the vadose zone Vadose zone comprehensive blocking factor Determine the vertical migration leaching factor The vertical migration leaching factor This refers to the leaching factors of pollutants in the soil that enter groundwater; further, based on the aforementioned vertical migration leaching factors... With horizontal mixing dilution factor Determine the comprehensive leaching factor ; According to the comprehensive leaching factor Maximum allowable concentration limits of pollutants in groundwater Soil risk control values ​​for pollutants were calculated using a risk concept model. .

[0008] In one implementation of the present invention, the first-order attenuation coefficient λ of the vadose zone satisfies the following formula: when At that time, the overall first-order attenuation coefficient of the vadose zone Satisfy the following formula: when At that time, the overall first-order attenuation coefficient of the vadose zone Satisfy the following formula: In the formula, λ is the bedrock fracture ratio, dimensionless, and λ is the comprehensive first-order attenuation coefficient of the vadose zone, in units of d. -1 , The attenuation coefficient of pollutants in the loose vadose zone, in units of d. -1 , The attenuation coefficient of the vadose zone in bedrock fractures, in units of d. -1 ; The vertical thickness of the loose vadose zone is expressed in cm. The vertical thickness of the vadose zone in bedrock fractures, in cm. The thickness threshold =2, the unit is m.

[0009] In one implementation of the present invention, the For loose vadose zone blocking factor, The following formula must be satisfied; The It is a barrier factor for the vadose zone in bedrock fractures. The following formula must be satisfied; when At that time, the comprehensive blocking factor of the vadose zone Satisfy the following formula: when At that time, the comprehensive blocking factor of the vadose zone Satisfy the following formula: In the formula, This refers to the soil bulk density, expressed in kg / dm³. 3 , Soil organic carbon partition coefficient, unit: cm 3 / g, The organic carbon mass fraction is given by the loose vadose zone soil, dimensionless. The volumetric water content of the loose vadose zone is dimensionless. The solid-water partition coefficient of the bedrock matrix, in cm. 3 / g, This refers to the density of bedrock matrix particles, expressed in kg / dm³. 3 In one implementation of the present invention, the vertically migrating leaching factor Satisfy the following formula: In the formula, The unit is kg / L.

[0010] In one implementation of the present invention, the vertical migration leaching factor... With horizontal mixing dilution factor The method for determining the comprehensive leaching factor is as follows: calculate the vertical migration leaching factor. With horizontal mixing dilution factor The product of is calculated using the following formula: In the formula, The leaching factor is expressed in kg / L. Vertical migration leaching factor, in kg / L. The horizontal mixing dilution factor is dimensionless. The horizontal mixing dilution factor The calculation formula is: In the formula, This represents the thickness of the bedrock fissure water mixing zone, in cm. This represents the dilution factor of the bedrock fracture saturation zone, dimensionless. The dilution factor of the bedrock fracture saturation zone The calculation formula is: in, This represents the groundwater runoff in the bedrock fracture saturation zone, in cubic meters (m³). 3 / d, This represents the leachate flow rate of pollutants entering the bedrock saturated zone from the bottom of the vadose zone in bedrock fissures, expressed in m³. 3 / d.

[0011] Furthermore, the risk conceptual model satisfies the following formula: In the formula, This is the soil risk control value, in mg / kg. The maximum concentration limit for pollutants in groundwater, in mg / L. The leaching factor is expressed in kg / L.

[0012] In one implementation of the present invention, the pollutants include: heavy metals, benzene compounds, petroleum hydrocarbons, and polycyclic aromatic hydrocarbons.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The method for determining soil risk control values ​​provided by this invention addresses a bedrock fissure water scenario where the water table is deeper than the contaminated soil layer and a thick vadose zone exists in between. The thick vadose zone is divided into a loose vadose zone and a bedrock fissure vadose zone. The method fully considers the adsorption and hindrance, as well as biological and abiotic attenuation effects, of pollutants during their vertical migration within the thick vadose zone. The method calculates the corresponding hindrance factor and attenuation coefficient for each of the two vadose zones, including the hindrance factor for the loose vadose zone. and bedrock fracture vadose zone blocking factor Attenuation coefficient of loose vadose zone Attenuation coefficient of bedrock fracture vadose zone Then, further based on the dispersion gas belt resistance factor and bedrock fracture vadose zone blocking factor Attenuation coefficient of loose vadose zone Attenuation coefficient of bedrock fracture vadose zone Calculate the vertical migration leaching factor applicable to bedrock fracture water scenarios. And considering the dilution and diffusion of pollutants in the horizontal direction, further based on the vertical migration leaching factor. With horizontal mixing dilution factor To determine more accurate leaching factors, thereby obtaining more accurate soil risk control values. Attached Figure Description

[0014] Figure 1 This is a vertical division structure diagram of the land parcel according to an embodiment of the present invention. Detailed Implementation

[0015] In the specification and claims of this invention, the terms "first" and "second," etc., are used to distinguish different objects, rather than to describe a specific order of objects.

[0016] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0017] Soil risk control values ​​refer to the maximum permissible concentration limits of pollutants in soil set under specific land use patterns to prevent unacceptable risks to human health and the ecological environment (especially groundwater).

[0018] Groundwater is often classified according to the lithology of the aquifer, such as pore water (found in loose sediments), bedrock fissure water (found in rock fissures), and karst water (found in karst caves in soluble rocks).

[0019] For bedrock fissure water, especially in scenarios where the water table is deeper than the contaminated soil layer and a thick vadose zone exists in between, this application divides the thick vadose zone into a loose vadose zone and a bedrock fissure vadose zone. It fully considers the adsorption and retardation effects, as well as the biological and abiotic attenuation processes of pollutants during their vertical migration within the thick vadose zone. The application calculates the corresponding retardation factors and attenuation coefficients for both the loose vadose zone and the bedrock fissure vadose zone, including the retardation factor for the loose vadose zone. and bedrock fracture vadose zone blocking factor Attenuation coefficient of loose vadose zone Attenuation coefficient of bedrock fracture vadose zone Then, further based on the dispersion gas belt resistance factor and bedrock fracture vadose zone blocking factor Attenuation coefficient of loose vadose zone Attenuation coefficient of bedrock fracture vadose zone Calculate the vertical migration leaching factor applicable to bedrock fracture water scenarios. Further based on vertical migration leaching factors With horizontal mixing dilution factor To determine a more accurate leaching factor.

[0020] The technical solution of this application will now be described in detail with reference to specific implementation methods.

[0021] Specifically, this application provides a method for determining soil risk control values ​​suitable for protecting bedrock fissure water, including S1~S2.

[0022] S1, based on the attenuation coefficient of pollutants in the loose vadose zone Attenuation coefficient of bedrock fracture vadose zone f Determine the comprehensive first-order attenuation coefficient of the outflow vadose zone According to the loose vadose zone resistance factor and bedrock fracture vadose zone blocking factor Determine the comprehensive retardation factor of the vadose zone The vertical thickness of the loosely packed air-filled zone Vertical thickness of the vadose zone in bedrock fissures satisfy ≥thickness threshold Based on the first-order attenuation coefficient of the vadose zone Vadose zone comprehensive blocking factor Determine the vertical migration leaching factor The vertical migration leaching factor This refers to the leaching factors of pollutants in the soil that enter groundwater; further, based on the aforementioned vertical migration leaching factors... With horizontal mixing dilution factor Determine the comprehensive leaching factor .

[0023] In this embodiment of the application, for the site to be evaluated, the thick vadose zone in the site is divided into a loose vadose zone and a bedrock fissure vadose zone. That is, the loose vadose zone is between the bottom of the contaminated soil layer and the top of the bedrock top plate, and the bedrock fissure vadose zone is between the bottom of the bedrock top plate and the water table. Figure 1 As shown, the plot, from top to bottom, consists of: a contaminated soil layer, a loose vadose zone layer, a bedrock fissure vadose zone layer, and a bedrock fissure saturated zone. The vertical thickness of the loose vadose zone is denoted as... The vertical thickness of the vadose zone in bedrock fissures is denoted as . Vertical thickness of loose vadose zone Vertical thickness of the vadose zone in bedrock fissures Must meet ≥thickness threshold In this application embodiment, for example, the thickness threshold =2, in meters (m). Of course, for those skilled in the art, this thickness threshold... The thickness threshold can also be adjusted according to the actual application scenario. This embodiment does not specify the thickness threshold. Make specific limitations.

[0024] The aforementioned S1 specifically includes S101 to S104.

[0025] S101, Based on the attenuation coefficient of pollutants in the loose vadose zone Attenuation coefficient of bedrock fracture vadose zone Determine the comprehensive first-order attenuation coefficient of the outflow vadose zone The first-order attenuation coefficient λ of the vadose zone satisfies the following formula: when At that time, the overall first-order attenuation coefficient of the vadose zone Satisfy the following formula: when At that time, the overall first-order attenuation coefficient of the vadose zone Satisfy the following formula: In the formula, λ is the bedrock fracture ratio, dimensionless; λ is the comprehensive first-order attenuation coefficient of the vadose zone, in units of d. -1 , The attenuation coefficient of pollutants in the loose vadose zone, in units of d. -1 , The attenuation coefficient of the vadose zone in bedrock fractures, in units of d. -1 ; The vertical thickness of the loose vadose zone is expressed in cm. The vertical thickness of the vadose zone in bedrock fractures, in cm. Specifically, the attenuation coefficient of the loose vadose zone Attenuation coefficient of bedrock fracture vadose zone The confirmation method is as follows: Uncirculated soil samples from the loose vadose zone and uncirculated rock samples from the bedrock fissure vadose zone were collected from the site. Indoor static batch attenuation tests were conducted in accordance with the "Technical Specification for Soil Environmental Monitoring" (HJ / T 166). The attenuation coefficient of pollutants in the loose vadose zone was fitted using a first-order kinetic equation. Attenuation coefficient of bedrock fracture vadose zone ; The process of the above indoor static batch attenuation test is as follows: The undisturbed soil sample from the loose vadose zone of the site was divided into three equal parts. Each part was mixed with a solution containing contaminants at a solid-liquid ratio of 1g:10mL in brown centrifuge tubes, and three parallel experiments were performed. The initial liquid phase concentration of the contaminants in the solution was recorded. The concentration of contaminants in the bedrock fissure water was set at 5 to 10 times the concentration of the bedrock fissure water in the sample. Brown centrifuge tubes were placed in a constant-temperature incubator to simulate the temperature of the sample. Samples were taken at t=0, 1, 3, 7, and 14 days, and the concentration of contaminants in the liquid phase of the sample solution at time t was measured. The pollutant concentration was plotted as a function of time. The decay followed first-order kinetics, and the fitting equation is as follows: In the formula, Let t be the liquid phase concentration of the pollutant at time t, in mg / L; The initial liquid phase concentration of the pollutant is expressed in mg / L; t represents the experimental incubation time in days.

[0026] For each parallel experiment, a nonlinear fit is performed on the sampled data. The significance test result of the fit results for each parallel experiment is required to yield the coefficient of determination R0. 2 If the value is ≥0.85, the experiment needs to be repeated; after the fit is qualified, the fitted data obtained from the sampling data of each parallel experiment is used. The average value is used as the attenuation coefficient of the loose vadose zone. .

[0027] The bedrock fractured vadose zone rock samples were subjected to indoor static batch attenuation tests using the same experimental procedure described above, and the attenuation coefficient of the bedrock fractured vadose zone was obtained. .

[0028] It is understandable that, in the prior art, when calculating the attenuation coefficient of pollutants in the vadose zone, different types of vadose zones (such as the loose vadose zone and the bedrock fissure vadose zone in the embodiments of this application) are usually calculated as a whole vadose zone, ignoring the differences in hydraulic characteristics, pore structure, mineral composition and adsorption capacity of different vadose zones, which makes the calculated vadose zone attenuation coefficient not accurate enough. Specifically, the differences between loose vadose zones and bedrock fracture vadose zones are as follows: The loose vadose zone is mainly composed of porous media with a relatively continuous distribution of pore size. Therefore, the seepage is relatively uniform, continuous, and slow. Sandy soils in the loose vadose zone have high permeability, while clays have low permeability. They are usually isotropic, have good connectivity, and are widely connected between pores to form a continuous network. The bedrock fracture vadose zone is a typical dual medium: secondary pores (fractures) and primary pores (matrix micropores). Secondary pores are the main channels for the rapid migration of water flow and pollutants. The fluid in the primary pores hardly flows, but can exchange solutes with the fractures through diffusion. Therefore, the water flow is highly non-uniform, discontinuous and rapid. Its permeability mainly depends on the density, opening, connectivity and filling of the fractures. It has extremely strong anisotropy, poor connectivity and high non-uniformity, and depends entirely on whether the fractures cut each other to form a network.

[0029] In contrast, the loose vadose zone is mainly composed of secondary clay minerals (such as montmorillonite and kaolinite), iron and aluminum oxides, and organic matter. These components are strong adsorbents with abundant and easily accessible adsorption sites, resulting in strong attenuation of pollutants. On the other hand, the fracture walls of the bedrock fissure vadose zone may be covered with secondary alteration minerals or precipitates, but the main matrix is ​​primary minerals (such as quartz, feldspar, and calcite), which have weak adsorption capacity, resulting in a slow adsorption rate and thus weaker attenuation of pollutants.

[0030] Considering that pollutants have different attenuation effects in loose vadose zones and bedrock fissure vadose zones, and that the attenuation of pollutants depends not only on the medium but also on the path the pollutants take, i.e., the thickness of the vadose zone, this application embodiment calculates the attenuation coefficients of pollutants in loose vadose zones and bedrock fissure vadose zones separately, and then calculates a new comprehensive attenuation coefficient of the vadose zone by weighting the values ​​of the thickness of each vadose zone. This reduces the uncertainty of the attenuation coefficient of the vadose zone caused by averaging the overall medium of the vadose zone in the prior art.

[0031] S102, Based on the loose vadose zone resistance factor and bedrock fracture vadose zone blocking factor Determine the comprehensive retardation factor of the vadose zone ; Among them, the loose vadose zone blocking factor The following formula must be satisfied; Bedrock fracture vadose zone blocking factor The following formula must be satisfied; when At that time, the comprehensive blocking factor of the vadose zone Satisfy the following formula: when At that time, the comprehensive blocking factor of the vadose zone Satisfy the following formula: In the formula, This refers to the soil bulk density, expressed in kg / dm³. 3 , Soil organic carbon partition coefficient, unit: cm 3 / g, The volumetric water content of the loose vadose zone is dimensionless. This refers to the density of bedrock matrix particles, expressed in kg / dm³. 3 ; This represents the mass fraction of organic carbon in loose vadose zone soil. , dimensionless, among which, Soil organic matter content, in g·kg -1 ; The solid-water partition coefficient of the bedrock matrix. The unit is cm. 3 / g; Organic carbon content of bedrock matrix, in g·kg -1 .

[0032] It should be noted that the loose vadose zone is mainly composed of secondary clay minerals (such as montmorillonite and kaolinite), iron and aluminum oxides, and organic matter. These components are strong adsorbents with abundant and easily accessible adsorption sites, thus significantly hindering the migration of pollutants. In contrast, the fracture walls of the bedrock fissure vadose zone may be covered with secondary alteration minerals or precipitates, but the main matrix is ​​primary minerals (such as quartz, feldspar, and calcite), which have weak adsorption capacity, resulting in a slow adsorption rate and thus a poor effect on hindering the migration of pollutants.

[0033] Therefore, the vadose zone in different media types has varying degrees of impediment effect on pollutants. However, existing technologies treat vadose zones with different impediment effects as a single entity, thus exaggerating the impediment capacity of the bedrock fracture vadose zone and underestimating the overall penetration velocity of pollutants. Consequently, the calculated impediment factor becomes distorted. Conversely, this application calculates the impediment factors of loose vadose zones and bedrock fracture vadose zones separately, and then weights the calculation by combining the thickness values ​​of each vadose zone. This approach more closely approximates the true situation dominated by the weakly impeding bedrock fracture vadose zone, thereby obtaining a more accurate comprehensive vadose zone impediment factor.

[0034] S103, Based on the first-order attenuation coefficient of the vadose zone Vadose zone comprehensive blocking factor Determine the vertical migration leaching factor Vertical migration leaching factor These are leaching factors that allow pollutants from the soil to enter groundwater; Vertical migration leaching factor Satisfy the following formula: In the formula, The unit is kg / L.

[0035] In this embodiment, based on the combined attenuation coefficient and retardation factor of the vadose zone combining the loose vadose zone and the bedrock fracture vadose zone, the strong attenuation and retardation effects experienced by pollutants in the loose vadose zone and the weak attenuation and retardation effects in the bedrock fracture vadose zone are accurately quantified. Compared with the prior art, which ignores the problem that pollutants in thick vadose zones have different adsorption retardation and biological and non-biological attenuation effects during vertical migration due to the different vadose zone media, resulting in a significantly larger calculated vertical migration leaching factor, the solution of this embodiment strengthens the influence of the bedrock fracture vadose zone on pollutants, and is more accurate.

[0036] S104, Based on vertical migration leaching factor With horizontal mixing dilution factor Determine the comprehensive leaching factor The calculation formula is as follows: In the formula, The leaching factor is expressed in kg / L. Vertical migration leaching factor, in kg / L. The horizontal mixing dilution factor is dimensionless. Among them, horizontal mixing dilution factor The calculation formula is: In the formula, This represents the thickness of the bedrock fissure water mixing zone, in cm. This refers to the dilution factor of the bedrock fracture saturation zone. bedrock fracture saturation zone dilution factor The calculation formula is: in, This represents the groundwater runoff in the bedrock fracture saturation zone, in cubic meters (m³). 3 / d, This represents the leachate flow rate of pollutants entering the bedrock saturated zone from the bottom of the vadose zone in bedrock fissures, expressed in m³. 3 / d.

[0037] Understandably, in bedrock fissure water environments, the risk level of pollutants depends not only on their rapid infiltration (vertical migration leaching factor) but also on whether they can be effectively diluted after entering the aquifer (horizontal mixing dilution factor). Current technologies typically only calculate the vertical migration leaching factor, neglecting the horizontal dilution and diffusion of pollutants. Furthermore, the porosity of bedrock fissure water influences the degree of pollutant diffusion; a high porosity means the water flow is concentrated in a few wide fissures, making it difficult for pollutants to diffuse into the surrounding rock matrix, resulting in extremely poor dilution capacity. Conversely, a low porosity results in a complex fissure network, strong dispersion, a thick mixing zone, and a high dilution factor. Ignoring horizontal dilution leads to an overestimation of the pollution risk in low-fissure areas and an underestimation of the pollution risk in high-fissure areas, resulting in severely distorted calculations of the leaching factor.

[0038] Therefore, the solution in this application fully considers the horizontal mixing and dilution factor of pollutants, and calculates the leaching factor in multiple dimensions, which fully covers the complete exposure path of pollutants from the contaminated soil layer to the bedrock fissure water, making the final calculation result of the comprehensive leaching factor more accurate.

[0039] S2, based on the aforementioned comprehensive leaching factor Maximum allowable concentration limits of pollutants in groundwater Soil risk control values ​​for pollutants were calculated using a risk concept model. .

[0040] The risk concept model satisfies the following formula: In the formula, This is the soil risk control value, in mg / kg. The maximum concentration limit for pollutants in groundwater, in mg / L. The leaching factor is expressed in kg / L.

[0041] It is understood that the method for determining soil risk control values ​​in this application is applicable to various common soil pollutants, including heavy metals, benzene compounds, petroleum hydrocarbons, and polycyclic aromatic hydrocarbons.

[0042] Example 1: This example uses benzo[a]pyrene as a pollutant and determines the soil risk control value of benzo[a]pyrene according to the method provided in this application.

[0043] Specifically, taking a certain industrial legacy site in Hechi City, Guangxi Zhuang Autonomous Region (planned as Class I land use) as the target, the vertical structure of the site is divided into a 0-2m contaminated soil layer and a 2-10m silty clay loose vadose zone (i.e., =800cm), 10~35m limestone fissure vadose zone (i.e. =2500cm), satisfying =33m≥thickness threshold =2m Furthermore, the measured fracture rate of the limestone was n=0.12>0.1.

[0044] S1. Determine the comprehensive leaching factor S101. Determine the comprehensive first-order attenuation coefficient of the vadose zone. Three equal portions of undisturbed silty clay loose vadose zone soil were divided and mixed with a solution containing benzo[a]pyrene at a solid-liquid ratio of 1 g:10 mL in brown centrifuge tubes. Three parallel experiments were performed. The initial liquid phase concentration of benzo[a]pyrene in the solution was recorded. =8 times the bedrock fissure water concentration, brown centrifuge tubes were placed in a constant temperature incubator to simulate the ground temperature; samples were taken at t=0, 1, 3, 7, and 14 days, and the liquid phase concentration of benzo[a]pyrene in the sample solution at time t was measured. The concentration of benzo[a]pyrene was plotted as a function of time. The decay followed first-order kinetics, and the fitting equation is as follows: In the formula, Let t be the liquid phase concentration of the pollutant at time t, in mg / L; The initial liquid phase concentration of the pollutant is expressed in mg / L; t represents the experimental incubation time in days.

[0045] Nonlinear fitting was performed on the sampled data of the three parallel experiments, and the significance test results of the fitting results of each parallel experiment were evaluated, with the determination coefficient R0. 2 ≥0.85, obtained by fitting the sampled data from three parallel experiments. The average value is used to obtain the attenuation coefficient of the loose vadose zone. =0.0001d -1 Since n > 0.1, the attenuation coefficient of the vadose zone in bedrock fractures is... =0d -1 ; Then, the attenuation coefficient of the loose vadose zone is... Attenuation coefficient of bedrock fracture vadose zone Vertical thickness of loose vadose zone Vertical thickness of the vadose zone in bedrock fissures Substitute into the following formula: The calculated first-order attenuation coefficient of the vadose zone is obtained. = (0.0001 × 800) / 3300 = 2.42 × 10 -5 d -1 .

[0046] S102. Determine the comprehensive vadose zone resistance factor. The bulk density of soil in the contaminated soil layer was measured. =1.5kg / dm 3 Soil organic carbon partition coefficient =5.87×10 5 cm 3 / g, soil organic matter content =15g / kg and the organic carbon content of the loose vadose zone in silty clay. = 15 / 1.724 = 0.0087, Loose vadose zone volumetric water content =0.3; Substitute the above parameters into the following formula; The resistance factor of the loose vadose zone was calculated. =1+(1.5×5.87×10 5 (×0.0087) / 0.3 = 25535.5; Since n=0.12>0.1, the hindering effect of the vadose zone in the bedrock fractures is ignored, and the hindering factor of the loose vadose zone is considered. Vertical thickness of loose vadose zone Vertical thickness of the vadose zone in bedrock fissures Substitute into the following formula: The comprehensive retardation factor was calculated. = (25535.5 × 800) / (800 + 2500) = 6190.

[0047] S103, Determine the vertical migration leaching factor The overall first-order attenuation coefficient obtained from S101 The comprehensive blocking factor obtained from S102 Loose vadose zone volumetric moisture content Substitute into the following formula: The vertical migration leaching factor was calculated. =e -10950×2.42×10-5 / (6190 × 0.3) = 4.13 × 10 -4 kg / L.

[0048] S104. Determine the comprehensive leaching factor. Measured groundwater runoff in the saturated zone of limestone fissures =120m 3 / d, leaching flow rate of benzo[a]pyrene from the bottom of the vadose zone in limestone fractures into the saturated zone of limestone fractures. =0.15m 3 / d; Substitute the above parameters into the following formula: The dilution factor of the bedrock fracture saturation zone was calculated. =120 / 0.15=800; The thickness of the bedrock fissure water mixing zone was measured. =200cm, dilution factor of bedrock fracture saturation zone Thickness of the mixing zone with bedrock fissure water Substitute into the following formula: Calculate the horizontal mixing dilution factor =800 / 200=4; Vertical migration of leaching factors and horizontal mixing dilution factor Substitute into the following formula: The comprehensive leaching factor was calculated. =4.13×10 -4 ×4=1.65×10 -3 kg / L.

[0049] S2. Calculate the soil risk control value for benzo[a]pyrene. .

[0050] According to GB / T 14848 Class III water standard, the maximum allowable concentration limit of benzo[a]pyrene in groundwater is... =0.00001mg / L, The maximum permissible concentration limit of benzo[a]pyrene in groundwater and comprehensive leaching factors Substitute into the following formula: Soil risk control values ​​were calculated. =0.00001 / (1.65×10 -3 =0.00606mg / kg.

[0051] When using the existing technology in the "Technical Guidelines for Risk Assessment of Soil Pollution in Construction Land" (HJ25.3-2019) to calculate the risk, the method cannot identify the rapid migration characteristics of high-fracture-rate soil. The resulting soil risk control value for protecting groundwater is 0.012 mg / kg, which is too large and too lenient. If this standard is used to remediate only areas with excessive benzo[a]pyrene concentration, the remediation of benzo[a]pyrene-contaminated soil will be insufficient, and the risk of benzo[a]pyrene migrating to groundwater cannot be controlled, threatening the safety of drinking water sources.

[0052] The method used in this application takes into account the hindrance and attenuation weakening characteristics under high fissure rate. The resulting soil risk control value of 0.00606 mg / kg is more in line with the actual migration risk. It can comprehensively remediate the 0-2m contaminated soil layer, expand the remediation range, effectively control the migration of benzo[a]pyrene to bedrock fissure water, and ensure the safety of drinking water sources.

[0053] Example 2: This example uses toluene as a pollutant and determines the soil risk control value of toluene according to the method provided in this application.

[0054] Specifically, taking a chemical plant site in Shijiazhuang City, Hebei Province (planned as Class II land use) as an example, the site's vertical structure is divided into a 0-1.5m contaminated soil layer and a 1.5-8m silty clay loose vadose zone (i.e., =650cm), 8~28m dolomite fracture vadose zone (i.e. =2000cm), satisfying =26.5m≥thickness threshold =2m Furthermore, the measured fracture rate of the dolomite was n=0.03<0.1.

[0055] S1. Determine the comprehensive leaching factor S101. Determine the comprehensive first-order attenuation coefficient of the vadose zone. The undisturbed soil sample of loose vadose zone of silty clay was divided into three equal parts, and each part was mixed with a solution containing toluene at a solid-liquid ratio of 1g:10mL in brown centrifuge tubes. Three parallel experiments were performed. The initial liquid phase concentration of toluene in the solution was recorded. =8 times the bedrock fissure water concentration, brown centrifuge tubes were placed in a constant temperature incubator to simulate the ground temperature; samples were taken at t=0, 1, 3, 7, and 14 days, and the toluene liquid phase concentration in the sample solution at time t was measured. The toluene concentration was plotted as a function of time. The decay followed first-order kinetics, and the fitting equation is as follows: In the formula, Let t be the liquid phase concentration of the pollutant at time t, in mg / L; The initial liquid phase concentration of the pollutant is expressed in mg / L; t represents the experimental incubation time in days.

[0056] Nonlinear fitting was performed on the sampled data of the three parallel experiments, and the significance test results of the fitting results of each parallel experiment were evaluated, with the determination coefficient R0. 2 ≥0.85, obtained by fitting the sampled data from three parallel experiments. The average value is used to obtain the attenuation coefficient of the loose vadose zone. =0.0004d -1 Then, undisturbed soil samples from the dolomite fracture vadose zone were taken, and the attenuation coefficient of the bedrock fracture vadose zone was obtained using the same method. =0.00002d -1 ; Then, the attenuation coefficient of the loose vadose zone is... Attenuation coefficient of bedrock fracture vadose zone Vertical thickness of loose vadose zone Vertical thickness of the vadose zone in bedrock fissures Substitute into the following formula: The calculated first-order attenuation coefficient of the vadose zone is obtained. = (0.0004 × 650 + 0.00002 × 2000) / (650 + 2000) = 1.13 × 10 -4 d -1 .

[0057] S102. Determine the comprehensive vadose zone resistance factor. The bulk density of soil in the contaminated soil layer was measured. =1.6kg / dm 3 Soil organic carbon partition coefficient =195cm 3 / g, Organic matter content of polluted soil =8g / kg, organic carbon content in the loose vadose zone of silty clay = 8 / 1.724 = 0.00464, Loose vadose zone volumetric water content =0.28; The organic carbon content of the bedrock matrix in the fractured vadose zone of dolomite was measured. =0, bedrock matrix particle density =2.70kg / dm 3 The solid-water partition coefficient of the bedrock matrix was calculated. cm 3 / g.

[0058] Substitute the above parameters into the following formulas; The resistance factor of the loose vadose zone was calculated. =1 + (1.6 × 195 × 0.00464) / 0.28 = 6.17; The bedrock fracture vadose zone retardation factor was calculated. =1; Since n=0.03<0.1, the loose vadose zone will be blocked by a certain factor. bedrock fracture vadose zone blocking factor Vertical thickness of loose vadose zone Vertical thickness of the vadose zone in bedrock fissures Substitute into the following formula: The comprehensive retardation factor was calculated. = (6.17 × 650 + 1 × 2000) / (650 + 2000) = 2.27.

[0059] S103, Determine the vertical migration leaching factor The overall first-order attenuation coefficient obtained from S101 The comprehensive blocking factor obtained from S102 Loose vadose zone volumetric moisture content Substitute into the following formula: The vertical migration leaching factor was calculated. =e -10950×1.13×10-4 / (2.27 × 0.28) = 0.4565 kg / L.

[0060] S104. Determine the comprehensive leaching factor. Measured groundwater runoff in the saturated zone of limestone fissures =150m 3 / d, leaching flow rate of benzo[a]pyrene from the bottom of the vadose zone in limestone fractures into the saturated zone of limestone fractures. =0.12m 3 / d; Substitute the above parameters into the following formula: The dilution factor of the bedrock fracture saturation zone was calculated. =150 / 0.12=1250; The thickness of the bedrock fissure water mixing zone was measured. =300cm, dilution factor of bedrock fracture saturation zone Thickness of the mixing zone with bedrock fissure water Substitute into the following formula: Calculate the horizontal mixing dilution factor =1250 / 300=4.17; Vertical migration of leaching factors and horizontal mixing dilution factor Substitute into the following formula: The comprehensive leaching factor was calculated. =0.4565×4.17=1.90kg / L.

[0061] S2. Calculate the soil risk control value for benzo[a]pyrene. .

[0062] According to GB / T 14848-2017 Class III water standard, the maximum allowable concentration limit of toluene in groundwater is... =0.7mg / L, The maximum permissible concentration limit of benzo[a]pyrene in groundwater and comprehensive leaching factors Substitute into the following formula: Soil risk control values ​​were calculated. =0.7 / 1.90=0.368mg / kg.

[0063] When using the existing technology in the "Technical Guidelines for Risk Assessment of Soil Pollution in Construction Land" (HJ25.3-2019) to calculate the risk, the leaching factor is too high because the method ignores the blocking and attenuation effect of the thick vadose zone. The resulting soil risk control value for protecting groundwater is 0.02 mg / kg, which is too conservative. The contaminated soil layer from 0 to 1.5 m in depth needs to be fully remediated.

[0064] The soil risk control value calculated using the method of this application embodiment is 0.368 mg / kg. Combined with the actual pollution monitoring results of the site, only the local areas with excessive toluene concentration need to be remediated. Compared with the prior art, this saves remediation costs and avoids ecological disturbance caused by excessive remediation, thus verifying the scientific and economic nature of the present invention.

[0065] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for determining soil risk control values ​​suitable for protecting bedrock fissure water, characterized in that, include: Based on the attenuation coefficient of pollutants in the loose vadose zone Attenuation coefficient of bedrock fracture vadose zone Determine the comprehensive first-order attenuation coefficient of the outflow vadose zone According to the loose vadose zone resistance factor and bedrock fracture vadose zone blocking factor Determine the comprehensive retardation factor of the vadose zone The vertical thickness of the loosely packed air-filled zone Vertical thickness of the vadose zone in bedrock fissures satisfy ≥thickness threshold Based on the first-order attenuation coefficient of the vadose zone Vadose zone comprehensive blocking factor Determine the vertical migration leaching factor The vertical migration leaching factor This refers to the leaching factors of pollutants in the soil that enter groundwater; further, based on the aforementioned vertical migration leaching factors... With horizontal mixing dilution factor Determine the comprehensive leaching factor ; According to the comprehensive leaching factor Maximum allowable concentration limits of pollutants in groundwater Soil risk control values ​​for pollutants were calculated using a risk concept model. .

2. The method as described in claim 1, characterized in that, The overall first-order attenuation coefficient λ of the vadose zone satisfies the following formula: when At that time, the overall first-order attenuation coefficient of the vadose zone Satisfy the following formula: when At that time, the overall first-order attenuation coefficient of the vadose zone Satisfy the following formula: In the formula, λ is the bedrock fracture ratio, dimensionless, and λ is the comprehensive first-order attenuation coefficient of the vadose zone, in units of d. -1 , The attenuation coefficient of pollutants in the loose vadose zone, in units of d. -1 , The attenuation coefficient of the vadose zone in bedrock fractures, in units of d. -1 ; The vertical thickness of the loose vadose zone is expressed in cm. The vertical thickness of the vadose zone in bedrock fractures, in cm. The thickness threshold =2, the unit is m.

3. The method as described in claim 2, characterized in that, The For loose vadose zone blocking factor, The following formula must be satisfied; The It is a barrier factor for the vadose zone in bedrock fractures. The following formula must be satisfied; when At that time, the comprehensive retardation factor of the vadose zone Satisfy the following formula: when At that time, the comprehensive retardation factor of the vadose zone Satisfy the following formula: In the formula, This refers to the soil bulk density, expressed in kg / dm³. 3 , Soil organic carbon partition coefficient, unit: cm 3 / g, The organic carbon mass fraction is given by the loose vadose zone soil, dimensionless. The volumetric water content of the loose vadose zone is dimensionless. The solid-water partition coefficient of the bedrock matrix, in cm. 3 / g, This refers to the density of bedrock matrix particles, expressed in kg / dm³. 3 .

4. The method as described in claim 3, characterized in that, The vertical migration leaching factor Satisfy the following formula: In the formula, The unit is kg / L.

5. The method as described in claim 4, characterized in that, The vertical migration leaching factor With horizontal mixing dilution factor The method for determining the comprehensive leaching factor is as follows: calculate the vertical migration leaching factor. With horizontal mixing dilution factor The product of is calculated using the following formula: In the formula, The leaching factor is expressed in kg / L. Vertical migration leaching factor, in kg / L. The horizontal mixing dilution factor is dimensionless. The horizontal mixing dilution factor The calculation formula is: In the formula, This represents the thickness of the bedrock fissure water mixing zone, in cm. This represents the dilution factor of the bedrock fracture saturation zone, dimensionless. The dilution factor of the bedrock fracture saturation zone The calculation formula is: in, This represents the groundwater runoff in the bedrock fracture saturation zone, in cubic meters (m³). 3 / d, This represents the leachate flow rate of pollutants entering the bedrock saturated zone from the bottom of the vadose zone in bedrock fissures, expressed in m³. 3 / d.

6. The method as described in claim 5, characterized in that, The risk conceptual model satisfies the following formula: In the formula, This is the soil risk control value, in mg / kg. The maximum concentration limit for pollutants in groundwater, in mg / L. The leaching factor is expressed in kg / L.

7. The method as described in claim 1, characterized in that, The pollutants include: heavy metals, benzene compounds, petroleum hydrocarbons, and polycyclic aromatic hydrocarbons.

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