A bedrock fissure site VOCs vapor invasion risk assessment method

Abstract

The application discloses a bedrock fissure site VOCs vapor invasion risk assessment method, comprising the following steps: S1, identifying the area where the bedrock and groundwater in the site exist VOCs pollution; S2, establishing a pollutant transport flux simulation test system; S3, using the pollutant transport flux simulation test system, carrying out the target pollutant transport flux test of the pollution area, setting a first transport flux test point at the center position of the pollution area, and calculating the maximum influence area of the first transport flux test point during the test; S4, selecting a second transport flux test point in the pollution area outside the maximum influence area of the first transport flux test point, and repeating step S3 to calculate the maximum influence area of the second transport flux test point during the test; S5, repeating steps S3 to S4 until the maximum influence areas of all transport flux test points are superimposed and cover the whole pollution area; and S6, predicting the future indoor vapor invasion health risk of the population in the pollution area.

Description

Technical Field

[0001] This invention relates to the field of risk assessment technology for contaminated sites, and specifically to a method for assessing the risk of VOCs vapor intrusion into bedrock fissure sites. Background Technology

[0002] Indoor vapor intrusion risk refers to the risk of health hazards to people indoors due to inhaling gaseous volatile organic compounds (VOCs) that evaporate from soil or groundwater into the indoor air. According to domestic and international research, indoor vapor intrusion is a major driver of VOCs pollution risk at sites and a primary basis for determining whether remediation and control measures are necessary. Current technical specifications provide vapor intrusion risk assessment models; however, these models are only applicable to characterizing the transport and risk of VOCs in loose porous strata. They are not suitable for bedrock fissure sites where transport channels are primarily random and discrete. Furthermore, there is currently a lack of mature international experience and methods for accurately characterizing VOCs transport in bedrock fissures and objectively quantifying their potential indoor vapor intrusion risk. my country has diverse topography, with the vast southwest region and the piedmont areas of plains cities primarily characterized by bedrock fissures. Therefore, there is an urgent need to provide a method for assessing VOCs vapor intrusion risk in bedrock fissure sites. Summary of the Invention

[0003] The purpose of this invention is to provide a method for assessing the risk of VOCs vapor intrusion in bedrock fracture sites, in order to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides a method for assessing the risk of VOCs vapor intrusion in bedrock fracture sites, comprising the following steps:

[0005] S1. Identify areas within the site where bedrock and groundwater are contaminated with VOCs, and delineate the boundaries of the contaminated areas;

[0006] S2. Level the ground of the designated contaminated area and establish a pollutant transport flux simulation test system;

[0007] S3. Using the established pollutant transport flux simulation test system, conduct target pollutant transport flux tests in the polluted area, set up the first transport flux test point at the center of the polluted area, and calculate the maximum impact area of ​​the first transport flux test point during the test period.

[0008] S4. In the contaminated area outside the maximum influence area of ​​the first transmission throughput test point, select the second transmission throughput test point and repeat step S3 to calculate the maximum influence area during the test of the second transmission throughput test point.

[0009] S5. Repeat steps S3 to S4 until the maximum influence area of ​​all transmission throughput test points is superimposed and covers the entire contaminated area.

[0010] S6. Predict the health risks of indoor vapor intrusion into polluted areas for future residents.

[0011] In a preferred embodiment, in step S2, the pollutant transport flux simulation test system includes a concrete cover layer, a gravel air-conducting layer, an extraction pipe, an extraction pump, an extraction pipeline valve, and a gas sampling port. The concrete cover layer and the gravel air-conducting layer are arranged sequentially from top to bottom above the bedrock fissure layer. The extraction pipe includes a horizontal pipe and a vertical pipe that are interconnected. The lower end of the vertical pipe extends to the bottom of the gravel air-conducting layer and above the bedrock fissure layer. A gas sampling port is provided on one side of the upper part of the vertical pipe. An extraction pump and an extraction pipeline valve are installed inside the horizontal pipe, with an opening on the side of the horizontal pipe away from the vertical pipe. The concrete cover layer has a thickness of 15–20 cm, a compressive strength of not less than C35, and a permeability grade of not less than P8. The gravel air-conducting layer has a thickness of 15 cm, an average gravel diameter of not more than 5 mm, and a non-uniformity coefficient of less than 5.

[0012] In a preferred embodiment, step S3, calculating the maximum influence area during the test of the first transmission flux test point, includes: fitting and calculating the air conductivity, leakage coefficient, and the maximum influence radius (ROI) of the local area where the first transmission flux test point is located. max and the target pollutant transport flux, in terms of ROI max Draw a circle with a radius of 1, and use the area covered by the circle as the maximum influence area during the first transmission throughput test point.

[0013] In a preferred embodiment, in step S3, the first transmission throughput test point includes one air extraction point and six pressure monitoring points. The six pressure monitoring points are arranged at different positions around the air extraction point in the horizontal direction. The angle between two adjacent pressure monitoring points and the air extraction point is 60°. The pressure monitoring point closest to the air extraction point is 0.5m away from the air extraction point. The radial distance between two adjacent pressure monitoring points is no more than 5m. Each pressure monitoring point is equipped with an online pressure monitoring and recording device.

[0014] In a preferred embodiment, step S3 involves conducting a target pollutant transport flux test in the contaminated area, including: after the pollutant transport flux simulation test system is connected, starting the air pump and continuously pumping air at a constant flow rate of 600 L / min for 4 hours; continuously sampling at the gas sampling port at a sampling flow rate of 1 L / min; after 4 hours of continuous pumping, shutting off the air pump and the air pump pipeline valve, closing the air pump inlet sampling device, and sending the collected samples to the laboratory to test the target pollutant concentration; continuously monitoring and recording pressure changes at each pressure monitoring point until the readings at each pressure monitoring point return to the readings before the air pump was started; exporting the monitoring data for each pressure monitoring point; and using AQTESOLV software to fit the pressure change curve of each pressure monitoring point over time to automatically calculate the gas conductivity T. i and leakage coefficient B i The average value of the six pressure monitoring points was calculated as the air conductivity and leakage coefficient of the local area where the corresponding transmission flux test point is located.

[0015] In a preferred embodiment, in step S3, the gas velocity V(r) in the gravel gas-conducting layer at a horizontal distance r from the extraction point is calculated using formula (1), and a curve showing the velocity variation with r is plotted:

[0016]

[0017] Where V(r) is in cm / min; Q ssv ρ is the pumping rate during the transmission throughput test, in L / min; b is the thickness of the gravel air-conducting layer, in cm; n is the effective porosity of the gravel air-conducting layer, dimensionless, with n taking a value of 0.3. The value of the first-order Bessel function of the second kind when the independent variable takes the value r / B is obtained by looking up the function table;

[0018] The time t for gas to migrate from the gravel gas-conducting layer at a horizontal distance r from the extraction point to the extraction point is calculated using formula (2):

[0019]

[0020] Wherein, V(r0) is the velocity of gas migrating from the gravel gas-conducting layer at a distance r0 from the extraction point to the extraction point, in cm / min, and is calculated using formula (1);

[0021] Using the calculation results of formula (2), the curves of the time for gas to migrate from the gravel gas-conducting layer to the pumping point at different distances from the pumping point are plotted as a function of distance. The distance corresponding to the migration time of 4 hours is read from the curve and used as the maximum influence radius (ROI) during the transmission flux test of the first transmission flux test point. max .

[0022] In a preferred embodiment, in step S3, the transport flux MF of the target pollutant at the first transport flux test point is calculated using formula (3). i :

[0023]

[0024] Among them, C i The average concentration of the target pollutant in the gas sample collected from the intake pipe of the pump during the transfer flux test is expressed in mg / m³. 3 ΔP represents the indoor-outdoor pressure difference at the building's foundation slab, in cm air column height; T represents the average air conductivity of the gravel air-conducting layer in the local area where the transmission flux test point is located, in cm. 2 / min; B is the average leakage rate of the concrete cover layer in the local area where the transmission flux test point is located, in cm.

[0025] In a preferred embodiment, in step S6, the area-weighted average of the target pollutant transport flux within the exposure unit is calculated using formula (4):

[0026]

[0027] Among them, MF i Let mg / (m³) be the transport flux of the target pollutant at the i-th test point within a certain exposure unit. 2 ·s); ROI maxi Let A be the maximum influence radius during the test of the i-th transmission throughput test point within a certain exposed unit, in meters; and let A be the area of ​​the exposed unit, in meters. 2 .

[0028] In a preferred embodiment, step S6, predicting the future health risk of indoor vapor intrusion into the contaminated area, includes: calculating the carcinogenic health risk of indoor vapor intrusion of the target pollutant within the exposure unit using formula (5), and calculating the non-carcinogenic health risk of indoor vapor intrusion of the target pollutant using formula (6).

[0029]

[0030] Wherein, CR represents the carcinogenic health risk of the target pollutant, which is dimensionless; EF represents the exposure factor, which is taken as 0.075m when the land is planned for sensitive use. 3 / (kg body weight·d), when planned as non-sensitive land use, is taken as 0.121m. 3 / (kg body weight·d); IUR is the inhalation carcinogenicity rate factor for the target pollutant, expressed in m³ / d. 3 / mg, obtained by querying a toxicology database; RfD i The target pollutant respiration reference concentration is expressed in mg / m³. 3The value was obtained by querying a toxicology database; ER is the indoor air conversion rate of a building, and when the land is planned as a sensitive area, the value is taken as 1.39 × 10⁻⁶. -4 s -1 When the land is designated as a non-sensitive use, the value is taken as 2.78 × 10. -4 s -1 L b The interior clear height of the building is 2.2m when the land is designated as a sensitive area and 3.0m when the land is designated as a non-sensitive area.

[0031] In a preferred embodiment, step S6 further includes: comparing the predicted risk of indoor vapor intrusion in the contaminated area with a preset acceptable level; if it exceeds the acceptable level by 1×10⁻⁶, the prediction is further subtracted from the predicted risk. -6 If so, control or remedial measures will be implemented.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] Existing technical specifications provide VOCs indoor vapor intrusion health risk assessment models that correspond to the physical scenario of VOCs transport driven by molecular diffusion in loosely connected porous media. These models cannot characterize the indoor vapor intrusion health risk in bedrock fracture sites where VOCs are transported and diffused through random discrete fracture channels. Furthermore, although research results on discrete fracture network models simulating VOCs transport processes in bedrock fracture sites have been reported, the highly random and discrete nature of fracture distribution in actual sites makes accurate risk quantification using such models extremely costly. Firstly, extensive drilling tests in the contaminated area are required to finely characterize the three-dimensional spatial distribution of fractures and contaminants within the site. Otherwise, simulation assessment results are prone to overestimating or underestimating the risk, leading to increased uncertainty in management decisions.

[0034] This invention, combined with real-world VOCs indoor vapor intrusion risk exposure scenarios, proposes a risk assessment method for bedrock fracture sites based on measured VOCs transport flux at key indoor vapor intrusion interfaces, filling a gap in this field. Furthermore, the transport flux testing method proposed in this invention typically covers an area exceeding 500m² for a single test point. 2 However, when using the traditional discrete fracture network model to achieve the same evaluation accuracy, at least 50 points need to be tested to achieve a detailed characterization of the fracture and contaminated space, thereby ensuring the accuracy of the model's risk prediction. Therefore, this invention can reduce costs by at least 90%. Attached Figure Description

[0035] Figure 1 This is a flowchart of the method of the present invention;

[0036] Figure 2 This is a schematic diagram of the pollutant transport flux simulation test system of the present invention;

[0037] Figure 3 This is a graph showing the variation of flow velocity V(r) with r according to the present invention;

[0038] Figure 4 This is a graph showing the time it takes for gas to migrate from the gravel gas-conducting layer at different distances from the extraction point to the extraction point, as a function of distance.

[0039] Explanation of reference numerals in the attached figures:

[0040] 201. Concrete cover layer; 202. Gravel air-conducting layer; 203. Air extraction pipe; 213. Vertical pipe; 204. Air extraction pump; 205. Air extraction pipeline valve; 206. Gas sampling port; 207. Pressure monitoring point; 210. Unsaturated bedrock fissure layer; 211. Saturated bedrock fissure layer. Detailed Implementation

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention.

[0042] Example 1:

[0043] like Figures 1 to 2 As shown, the preferred embodiment of the VOCs vapor intrusion risk assessment method for bedrock fracture sites of the present invention includes the following steps:

[0044] Step S1: By comprehensively utilizing on-site pollution trace identification and rapid detection, historical monitoring data analysis, drilling sampling and laboratory testing, etc., identify areas in the site where bedrock and groundwater are contaminated with VOCs, and delineate the boundaries of the contaminated areas.

[0045] Step S2: Level the ground of the designated contaminated area and establish a simulation test system for the transport flux of pollutants under the building foundation.

[0046] Specifically, the pollutant transport flux simulation test system includes a concrete cover layer 201, a gravel air-conducting layer 202, an extraction pipe 203, an extraction pump 204, an extraction pipeline valve 205, and a gas sampling port 206. The concrete cover layer 201 and the gravel air-conducting layer 202 are arranged sequentially from top to bottom above the bedrock fissure layer (the lower part of which is a saturated bedrock fissure layer 211, and the upper part is an unsaturated bedrock fissure layer 210). The extraction pipe 203 includes a horizontal pipe and a vertical pipe 213 that are interconnected. The lower end of the vertical pipe extends into the bottom of the gravel air-conducting layer 202 and above the unsaturated bedrock fissure layer 210. A gas sampling port 206 is set on one side of the upper part of the vertical pipe. The extraction pump 204 and the extraction pipeline valve 205 are installed in the horizontal pipe. The horizontal pipe has an opening on the side away from the vertical pipe. The thickness of the concrete cover layer 201 is usually 15-20cm, the concrete compressive strength is not lower than C35, and the impermeability grade is not lower than P8; the thickness of the gravel air-conducting layer is 15cm, the average diameter of the gravel is not greater than 5mm, and the non-uniformity coefficient is less than 5.

[0047] Step S3: Using the established pollutant transport flux simulation test system, conduct target pollutant transport flux tests in the polluted area. Set up the first transport flux test point at the center of the polluted area, and calculate the gas conductivity, leakage coefficient, and maximum influence radius (ROI) of the local area where the first transport flux test point is located during the test. max and the target pollutant transport flux, in terms of ROI max Draw a circle with a radius of 1, and use the area covered by this circle as the maximum influence area during the first transmission throughput test point.

[0048] Specifically, the first transmission throughput test point includes one extraction point and six pressure monitoring points 207. The six pressure monitoring points 207 are arranged at different positions around the extraction point in the horizontal direction. The angle between two adjacent pressure monitoring points 207 and the extraction point is 60°. The nearest pressure monitoring point to the extraction point is 0.5m away from the extraction point. The radial distance between two adjacent pressure monitoring points 207 is no more than 5m. Each pressure monitoring point is equipped with an online pressure monitoring and recording device. The pressure monitoring resolution of the device is no more than 0.1Pa, and it reads and stores one pressure data every second.

[0049] Furthermore, the target pollutant transport flux test of the contaminated area was conducted, including: after the pollutant transport flux simulation test system was connected, the vacuum pump 204 was started and continuously pumped at a constant flow rate of 600 L / min for 4 hours. Continuous sampling was performed at the gas sampling port 206 at a sampling flow rate of 1 L / min. After 4 hours of continuous pumping, the vacuum pump 204 and the vacuum pipeline valve 205 were shut off, and the sampling device in the vacuum pump inlet pipe was closed. The collected samples were sent to the laboratory to test the target pollutant concentration. Pressure changes at each pressure monitoring point were continuously monitored and recorded until the readings at each pressure monitoring point returned to the readings before the vacuum pump was started. The monitoring data for each pressure monitoring point was exported. The pressure change curve of each pressure monitoring point over time was fitted using AQTESOLV software, and the gas conductivity T was automatically calculated. i and leakage coefficient B i The average value of the six pressure monitoring points is calculated as the air conductivity T and leakage coefficient B of the local area where the corresponding transmission flux test point is located.

[0050] The gas velocity V(r) in the gravel gas-conducting layer at a horizontal distance r from the extraction point is calculated using formula (1), and the curve of velocity V(r) versus r is plotted:

[0051]

[0052] Where V(r) is in cm / min; Q ssv ρ is the pumping rate during the transmission throughput test, in L / min; b is the thickness of the gravel air-conducting layer, in cm; n is the effective porosity of the gravel air-conducting layer, dimensionless, with n taking a value of 0.3. The value of the first-order second-kind Bessel function is given when the independent variable takes the value r / B, obtained by looking up the function table; the unit of r is cm.

[0053] The time t for gas to migrate from the gravel gas-conducting layer at a horizontal distance r from the extraction point to the extraction point is calculated using formula (2):

[0054]

[0055] Wherein, V(r0) is the velocity of gas migrating from the gravel gas-conducting layer at a distance r0 from the extraction point to the extraction point, in cm / min, and is calculated using formula (1);

[0056] Using the calculation results of formula (2), the curves of the time for gas to migrate from the gravel gas-conducting layer to the pumping point at different distances from the pumping point are plotted as a function of distance. The distance corresponding to the migration time of 4 hours (240 minutes) is read from the curve and used as the maximum influence radius (ROI) during the transmission flux test of the first transmission flux test point. max .

[0057] The transport flux MF of the target pollutant at the first transport flux test point is calculated using formula (3). i :

[0058]

[0059] Among them, C i The average concentration of the target pollutant in the gas sample collected from the intake pipe of the pump during the transfer flux test is expressed in mg / m³. 3 ΔP represents the pressure difference between the interior and exterior of the building's foundation slab, measured in cm of air column height, typically taken as 10 Pa (approximately 83 cm of air column height). T represents the average air conductivity of the gravel air-conducting layer in the local area where the transport flux test point is located, measured in cm³. 2 / min; B is the average leakage rate of the concrete cover layer in the local area where the transmission flux test point is located, in cm.

[0060] Step S4: In the contaminated area outside the maximum influence area of ​​the first transmission throughput test point, select another second transmission throughput test point and repeat step S3 to calculate the maximum influence area during the test of the second transmission throughput test point.

[0061] Step S5: Repeat steps S3 to S4 until the maximum influence areas of all transmission throughput test points are superimposed and cover the entire contaminated area.

[0062] Step S6: Predict the health risks of future indoor vapor intrusion into the polluted area.

[0063] Specifically, the area-weighted average of the target pollutant transport flux within the exposure unit is calculated using formula (4):

[0064]

[0065] Among them, MF i Let mg / (m³) be the transport flux of the target pollutant at the i-th test point within a certain exposure unit. 2 ·s); ROI maxi Let A be the maximum influence radius during the test of the i-th transmission throughput test point within a certain exposed unit, in meters; and let A be the area of ​​the exposed unit, in meters. 2 .

[0066] Predicting the future health risks of indoor vapor intrusion into contaminated areas includes: calculating the carcinogenic health risk of indoor vapor intrusion of the target pollutant within the exposure unit using formula (5), and calculating the non-carcinogenic health risk of indoor vapor intrusion of the target pollutant using formula (6).

[0067]

[0068] Wherein, CR represents the carcinogenic health risk of the target pollutant, which is dimensionless; EF represents the exposure factor, which is taken as 0.075m when the land is planned for sensitive use. 3 / (kg body weight·d), when planned as non-sensitive land use, is taken as 0.121m. 3 / (kg body weight·d); IUR is the inhalation carcinogenicity rate factor for the target pollutant, expressed in m³ / d. 3 / mg, obtained by querying a toxicology database; RfD i The target pollutant respiration reference concentration is expressed in mg / m³. 3 The value was obtained by querying a toxicology database; ER is the indoor air conversion rate of a building, and when the land is planned as a sensitive area, the value is taken as 1.39 × 10⁻⁶. -4 s -1 When the land is designated as a non-sensitive use, the value is taken as 2.78 × 10. -4 s -1 L b The interior clear height of the building is 2.2m when the land is designated as a sensitive area and 3.0m when the land is designated as a non-sensitive area.

[0069] Step S6 further includes: comparing the predicted risk of indoor vapor intrusion in the contaminated area with a preset acceptable level; if it exceeds the acceptable level by 1×10⁻⁶, the risk is assessed. -6 If so, control or remedial measures will be implemented.

[0070] Example 2:

[0071] This embodiment uses the risk assessment of chloroform vapor intrusion in a bedrock fissure contaminated site as an example to describe in detail the method of the present invention.

[0072] In this example: The total area of ​​a bedrock fissure site located in front of a mountain is approximately 50,000 m². 2 Historically, the site was primarily used as a chemical plant. According to relevant management requirements, a site survey and risk assessment must be conducted to ensure the safe use of the land.

[0073] Step S1: In accordance with the specifications, by comprehensively utilizing on-site pollution trace identification and rapid detection, historical monitoring data analysis, and multiple batches of progressively denser drilling and sampling tests, approximately 16,000 m² of the site was ultimately delineated. 2 The bedrock and groundwater in the area are contaminated with chloroform.

[0074] Step S2, for 16000m 2 The chloroform-contaminated area was leveled, underground pipes and other facilities were removed, and a negative pressure extraction simulation system was established under the building's foundation. Figure 2The pollutant transport flux simulation test system is shown. On the leveled ground, a gravel air-conducting layer approximately 15cm thick is first laid. The gravel uses quartz sand with a diameter of 3-5mm, and screening ensures the uniformity coefficient of the quartz sand in the gravel air-conducting layer is 3-5. A 15cm thick concrete cover layer with a compressive strength of C35 and a permeability grade of P8 is then laid on top of the gravel air-conducting layer. The concrete cover layer is oxidized according to specifications to prevent cracking.

[0075] Step S3: After the concrete cover layer reaches the curing conditions, firstly, a first transmission flux test point is set at the center of the concrete cover layer laid in the contaminated area. The pressure values ​​of the negative pressure monitoring points at different locations at different distances from the extraction point are recorded over time under a constant extraction rate. At the same time, the gas sampling port of the extraction pipe is sampled periodically to detect the concentration of the target pollutants.

[0076] Specifically, the vertical pipe 213 of the extraction pipe is designated as the extraction point. Six pressure monitoring points 207 are set at intervals of 0.5m, 6m, 10m, 15m, 20m, and 25m around this extraction point, with an angle of 60° between adjacent monitoring points and the extraction point. The extraction pipe 203 is connected, and an online pressure monitoring and recording device is installed. The extraction pump 204 is started, and the extraction flow rate is adjusted to 600 L / min, with continuous extraction for 4 hours. During extraction, gas samples are continuously collected at the gas sampling port 206 of the extraction pipe using a soma canister at a sampling flow rate of 1 L / min. After 4 hours of extraction, the extraction pump 204 and the extraction pipe valve 205 are closed. Once the pressure at the six monitoring points returns to the readings before the pump was started, the data from the pressure monitoring and recording device is exported. AQTESOLV software is used to fit the pressure change curve of each monitoring point over time, and the gas conductivity T is automatically calculated. i and leakage coefficient B i The average value was calculated as T and B for the local area where the corresponding transmission flux test point was located. The fitting results show that the T values ​​obtained from the pressure-time variation curves of the six pressure monitoring points surrounding this transmission flux test point are... i They are 59.4cm respectively. 2 / min, 61.5cm 2 / min, 63.8cm 2 / min, 68.4cm 2 / min, 63.5cm 2 / min, 58.6cm 2 / min, with an average of 62.5cm 2 / min. Fitted B i The measurements were 905.6cm, 901.6cm, 908.2cm, 915.8cm, 902.2cm, and 921.2cm respectively, with an average of 909.1cm.

[0077] The gas velocity in the gravel gas-conducting layer at a horizontal distance r from the extraction point is calculated using formula (1), and the curve of V(r) versus r is plotted as shown in the attached figure. Figure 3 As shown.

[0078]

[0079] Using formula (2), calculate the time t for gas to migrate from the gravel gas-conducting layer at a horizontal distance r from the extraction point to the extraction point. Plot the curves of the time for gas to migrate from the gravel gas-conducting layer at different distances from the extraction point as a function of distance, as shown in the attached figure. Figure 4 As shown.

[0080] From the appendix Figure 4 The distance r = 20m corresponding to a migration time of 240min (4h) is taken as the maximum radius of influence (ROI) during the transmission throughput test at this test point. max Draw a circle with the transmission throughput test point as the center and a radius of 20m. The area covered by this circle is taken as the maximum coverage area for the transmission throughput test of this test point.

[0081]

[0082] Throughout the entire transmission throughput test, the average concentration of chloroform in the gas sample collected continuously from the gas sampling port of the extraction tube using a soma canister was 0.5 mg / m³. 3 The transport flux MF of chloroform at the test point with a pressure difference of 10 Pa (83 cm air column height) was calculated using formula (3). i 5.3×10 -6 mg / (m 2 ·s).

[0083]

[0084] Step S4: Outside the maximum influence area of ​​the transmission throughput test point in step S3, within the contaminated area, select another transmission throughput test point and repeat step S3.

[0085] Step S5: Repeat steps S3 and S4 until the maximum influence area of ​​all transmission throughput test points covers the entire contaminated area, and finally test 16 transmission throughput test points.

[0086] Step S6: The land parcel is planned for future residential use, with a planned area of ​​16,000 square meters. 2 The pollutant zone is divided into four areas, each with an area of ​​4000m². 2 The exposed units consist of 4 transmission flux test points. The weighted average of the chloroform transmission flux in each exposed unit is calculated using formula (4). The results are shown in Table 1.

[0087]

[0088] Table 1 Weighted average chloroform transport flux in different exposure units

[0089]

[0090]

[0091] Formula (5) was used to calculate the carcinogenic health risk of indoor vapor intrusion of the target pollutant in the exposed unit, and Formula (6) was used to calculate the non-carcinogenic health risk of indoor vapor intrusion of the target pollutant.

[0092]

[0093] The calculation results are shown in Table 2. Among them, the carcinogenic health risk of chloroform indoor vapor intrusion in exposure units 2 and 3 exceeds the acceptable level of 1×10⁻⁶. -6 Control or remedial measures need to be implemented.

[0094] Table 2 Health Risks of Indoor Chloroform Vapor Intrusion in Different Exposure Units

[0095] Exposed Unit Number unit Exposed Unit 1 Exposed Unit 2 Exposed Unit 3 Exposed Unit 4 area <![CDATA[m 2 ]]> 4000 4000 4000 4000 Transmission throughput weighted average <![CDATA[mg / (m 2 ·s)]]> 5.5E-09 1.7E-08 3.9E-08 1.7E-09 IUR <![CDATA[m 3 / mg]]> 0.023 0.023 0.023 0.023 RfC <![CDATA[mg / m 3 ]]> 0.098 0.098 0.098 0.098 ER <![CDATA[s -1 ]]> 1.39E-04 1.39E-04 1.39E-04 1.39E-04 Lb m 2.2 2.2 2.2 2.2 CR Dimensionless 4.11E-07 1.26E-06 2.91E-06 1.24E-07 HQ Dimensionless 5.53E-04 1.69E-03 3.91E-03 1.67E-04

[0096] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A bedrock fissure site VOCs vapor intrusion risk assessment method characterized by: Comprise the following steps: S1, identify the bedrock and groundwater in the area of the region contaminated by VOCs, delineate the boundary of the contaminated area; S2, the overall pollution area is flat, and a pollutant transport flux simulation test system is established; S3, using the established pollutant transport flux simulation test system, the target pollutant transport flux test is carried out, the first transport flux test point is set in the center of the contaminated area, and the maximum influence area of the first transport flux test point during the test is calculated; S4, in the contaminated area outside the maximum influence area of the first transport flux test point, a second transport flux test point is selected, and steps S3 are repeated to calculate the maximum influence area of the second transport flux test point during the test; S5, repeat steps S3 to S4 until the maximum influence area of all transport flux test points is superimposed and covers the entire contaminated area; S6, predict the health risk of indoor vapor intrusion of future population in the contaminated area; In step S3, the maximum influence area of the first transport flux test point during the test is calculated, including: fitting the air permeability of the local area where the first transport flux test point is located, the leakage coefficient, the maximum influence radius ROImax of the first transport flux test point during the test, and the target pollutant transport flux, drawing a circle with ROImax as the radius, and taking the area covered by the circle as the maximum influence area of the first transport flux test point during the test; the first transport flux test point is taken as the center, including one air extraction point and six pressure monitoring points, the six pressure monitoring points are arranged at different positions around the air extraction point in the horizontal direction, the included angle formed by the adjacent two pressure monitoring points and the air extraction point is 60°, and the pressure monitoring point closest to the air extraction point is 0.5m away from the air extraction point, the distance between the radially adjacent two pressure monitoring points is not more than 5m, and each pressure monitoring point is provided with an online pressure monitoring and recording device.

2. The bedrock-fissure site VOCs vapor intrusion risk assessment method of claim 1, wherein: In step S2, the pollutant transport flux simulation test system comprises a concrete cover layer, a gravel air guide layer, an air extraction pipe, an air extraction pump, an air extraction pipeline valve and a gas sampling port, the concrete cover layer and the gravel air guide layer are sequentially arranged above the bedrock fissure layer from top to bottom, the air extraction pipe comprises a horizontal pipe and a vertical pipe which are in communication, the lower end of the vertical pipe extends into the bottom of the gravel air guide layer above the bedrock fissure layer, the gas sampling port is arranged on one side of the upper part of the vertical pipe, the air extraction pump and the air extraction pipeline valve are arranged in the horizontal pipe, and the opening of the horizontal pipe is arranged on the side away from the vertical pipe.

3. The bedrock-fissure site VOCs vapor intrusion risk assessment method of claim 1, wherein: In step S3, the target pollutant transmission flux test of the contaminated area is carried out, including: after the pollutant transmission flux simulation test system is connected, the air suction pump is started, the constant flow of 600 L / min is continuously sucked for 4 h, the continuous sampling is carried out at the gas sampling port, the sampling flow rate is 1 L / min, after the continuous suction for 4 h, the air suction pump and the air suction pipeline valve are closed, the sampling device of the air suction pump inlet is closed, the collected sample is sent to the laboratory to detect the concentration of the target pollutant, the pressure change of each pressure monitoring point is continuously monitored and recorded until the reading of each pressure monitoring point returns to the reading before the air suction pump is started, the monitoring data of each pressure monitoring point is exported, the AQTESOLV software is used to fit the pressure change curve of each pressure monitoring point with time, the air permeability T i and the leakage coefficient B i are automatically obtained, and the average value of the six pressure monitoring points is calculated as the air permeability and the leakage coefficient of the local area where the transmission flux test point is located.

4. The bedrock-fissure site VOCs vapor intrusion risk assessment method of claim 3, wherein: In step S3, the flow velocity V(r) of the gas in the gravel air guide layer at a position with a distance of r from the air extraction point in the horizontal direction is calculated by formula (1), and the curve of the flow velocity with r is drawn: where V(r) has the unit of cm / min; Q ssv is the pumping rate during the transmission flux test, with the unit of L / min; b is the thickness of the gravel gas guide layer, with the unit of cm; n is the effective porosity of the gravel gas guide layer, dimensionless, and n is 0.3; is the first-order second-type Bessel function value when the independent variable is r / B, and is obtained by looking up a function table; B is the average leakage rate of the concrete cover layer in the local area where the transmission flux test point is located, with the unit of cm; The time t of the gas in the gravel air guide layer at a position with a distance of r from the air extraction point in the horizontal direction to migrate to the position of the air extraction point is calculated by formula (2): Wherein, V(r0) is the velocity of gas migration to the pumping point at the position with a distance of r0 from the pumping point, in cm / min, calculated by formula (1); Using the calculation results of formula (2), a curve of the time for gas in the gravel gas guide layer at different distances from the gas extraction point to migrate to the gas extraction point is drawn, and the distance corresponding to the migration time of 4h is read from the curve as the maximum influence radius ROI during the transmission flux test of the first transmission flux test point max .

5. The bedrock-fissure site VOCs vapor intrusion risk assessment method of claim 4, wherein: In step S3, the transfer flux MF of the target pollutant of the first transfer flux test point is calculated using formula (3) i : Wherein, MF i is the target pollutant transmission flux of the i th test point in a certain exposure unit, with the unit of mg / (m 2 ·s); C i is the average concentration of the target pollutant in the gas sample collected by the suction pump inlet pipe during the transmission flux test, with the unit of mg / m 3 ; ΔP is the indoor and outdoor pressure difference of the building floor, with the unit of cm air column height, T is the average air guide rate of the gravel air guide layer in the local area where the transmission flux test point is located, with the unit of cm 2 / min; B is the average leakage rate of the concrete cover layer in the local area where the transmission flux test point is located, with the unit of cm.

6. The bedrock-fissure site VOCs vapor intrusion risk assessment method of claim 5, wherein: In step S6, the weighted average value of the target pollutant transmission flux per area in the exposure unit is calculated by formula (4): wherein MF i is the target pollutant transfer flux for the ith test point within a certain exposure unit, in mg / (m 2 ·s); ROI maxi is the maximum influence radius during the test period for the ith transfer flux test point within a certain exposure unit, in m; and A is the area of the exposure unit, in m 2 .

7. The bedrock-fissure-site VOCs vapor intrusion risk assessment method according to claim 6, wherein: In step S6, the future population indoor vapor intrusion health risk of the contaminated area is predicted, including: the carcinogenic health risk of the target pollutant indoor vapor intrusion in the exposure unit is calculated by formula (5), and the non-carcinogenic health risk of the target pollutant indoor vapor intrusion is calculated by formula (6): Wherein, CR is the carcinogenic health risk of target pollutants, dimensionless; EF is the exposure factor, which is 0.075 m 3 / (kg·d) when the planning is sensitive land, and is 0.121 m 3 / (kg·d) when the planning is non-sensitive land; IUR is the slope factor of respiratory inhalation unit of target pollutants, with the unit of m 3 / mg, which is obtained by querying the toxicology database; RfD i is the respiratory reference concentration of target pollutants, with the unit of mg / m 3 , which is obtained by querying the toxicology database; is the indoor air conversion rate of building, which is 1.39×10 -4 s -1 when the planning is sensitive land, and is 2.78×10 -4 s -1 when the planning is non-sensitive land; L b is the net height of indoor building, which is 2.2 m when the planning is sensitive land, and is 3.0 m when the planning is non-sensitive land.

8. The bedrock-fissure-site VOCs vapor intrusion risk assessment method of claim 7, wherein: Step S6 further comprises comparing the prediction of the risk of intrusion of the contaminated compartment with a pre-set acceptable level, and if the acceptable level 1 x 10 -6 is exceeded, implementing control or repair measures.

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