Bedrock fracture site VOCs steam invasion risk assessment method

Abstract

The invention discloses a VOCs steam invasion risk assessment method for a bedrock fracture site. The method comprises the following steps: S1, identifying an area where VOCs pollution exists in bedrock and underground water in the site; s2, establishing a pollutant transmission flux simulation test system; s3, carrying out a target pollutant transmission flux test in the polluted area by using the pollutant transmission flux simulation test system, setting a first transmission flux test point at the central position of the polluted area, and calculating a maximum influence area of the first transmission flux test point during a test period; s4, selecting a second transmission flux test point in a polluted area outside the maximum influence area of the first transmission flux test point, repeating the step S3, and calculating the maximum influence area of the second transmission flux test point during the test period; s5, repeating the steps S3 to S4 until the maximum influence areas of all the transmission flux test points are overlapped and then cover the whole pollution area; and S6, predicting the indoor steam invasion health risk of future crowds in the polluted area.

Description

Technical Field

[0001] The present invention relates to the technical field of contaminated site risk assessment, and in particular to a VOCs vapor intrusion risk assessment method for bedrock fissure sites. Background Art

[0002] Indoor vapor intrusion risk refers to the potential health risks posed to people indoors by breathing volatile organic compounds (VOCs) volatilized from soil or groundwater into the indoor air. According to international and domestic research, indoor vapor intrusion is the primary driver of VOC contamination risk at a site and the primary basis for determining whether remediation and control measures are necessary. Currently published technical specifications provide vapor intrusion risk assessment models, but these models are only suitable for characterizing the transport and risk of VOCs in loose porous strata. They are not applicable to bedrock fracture sites, where the transmission pathways are primarily characterized by random, discrete patterns. Furthermore, there is currently a lack of established international experience and methodologies to accurately characterize the transport of VOCs in bedrock fractures and objectively quantify their potential indoor vapor intrusion risk. my country has a diverse topography, with bedrock fractures dominating the vast southwestern region and the piedmont areas of plain cities. Therefore, a VOC vapor intrusion risk assessment method for bedrock fracture sites is urgently needed. Summary of the Invention

[0003] The purpose of the present invention is to provide a VOCs vapor intrusion risk assessment method for bedrock fissure sites to solve the problems raised in the above background technology.

[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 of VOCs contamination in bedrock and groundwater within the site and define the boundaries of the contaminated areas;

[0006] S2. Level the entire ground in the designated polluted area and establish a pollutant transmission flux simulation test system;

[0007] S3. Conduct a target pollutant transmission flux test in the polluted area using the established pollutant transmission flux simulation test system. Set a first transmission flux test point at the center of the polluted area and calculate the maximum impact area during the test at the first transmission flux test point.

[0008] S4. Select a second transmission flux test point in the contaminated area outside the maximum impact area of ​​the first transmission flux test point, and repeat step S3 to calculate the maximum impact area during the test of the second transmission flux test point;

[0009] S5. Repeat steps S3 to S4 until the maximum impact areas of all transmission flux test points are superimposed to cover the entire contaminated area;

[0010] S6. Predict the future health risks of indoor vapor intrusion to people in polluted areas.

[0011] In a preferred embodiment, in step S2, the pollutant transmission flux simulation test system includes a concrete cover layer, a gravel air conducting layer, an exhaust pipe, an exhaust pump, an exhaust pipe valve and a gas sampling port. The concrete cover layer and the gravel air conducting layer are arranged in sequence from top to bottom above the bedrock fracture layer. The exhaust pipe includes a horizontal pipe and a vertical pipe that are interconnected. The lower end of the vertical pipe extends into the bottom of the gravel air conducting layer and above the bedrock fracture layer. A gas sampling port is provided on one side of the upper part of the vertical pipe. An exhaust pump and an exhaust pipe valve are provided in the horizontal pipe. The horizontal pipe is opened on one side away from the vertical pipe. The thickness of the concrete cover layer is 15 to 20 cm, the compressive strength of the concrete is not less than C35, and the impermeability grade is not less than P8. The thickness of the gravel air conducting layer is 15 cm, the average diameter of the gravel is not greater than 5 mm, and the unevenness coefficient is less than 5.

[0012] In a preferred embodiment, in step S3, the maximum impact area during the test of the first transmission flux test point is calculated, including: fitting and obtaining the air permeability, leakage coefficient, and maximum impact radius ROI of the local area where the first transmission flux test point is located during the test of the first transmission flux test point. max and target pollutant transport flux, with ROI max Draw a circle with the radius as the maximum impact area during the test of the first transmission flux test point.

[0013] In a preferred embodiment, in step S3, the first transmission flux test point includes 1 air pumping point and 6 pressure monitoring points. The 6 pressure monitoring points are arranged at different positions around the air pumping point in the horizontal direction with the air pumping point as the center. The angle formed by two adjacent pressure monitoring points and the air pumping point is 60°, and the pressure monitoring point closest to the air pumping point is 0.5m away from the air pumping point. The distance between two radially adjacent pressure monitoring points is not more than 5m, and each pressure monitoring point is installed with an online pressure monitoring and recording device.

[0014] In a preferred embodiment, in step S3, a target pollutant transmission flux test is carried out in the polluted area, including: after the pollutant transmission flux simulation test system is connected, the vacuum pump is started, and continuous air is pumped at a constant flow rate of 600 L / min for 4 hours, and continuous sampling is performed at the gas sampling port with a sampling flow rate of 1 L / min. After continuous air pumping for 4 hours, the vacuum pump and the vacuum pipeline valve are turned off, the vacuum pump inlet pipe sampling device is turned off, and the collected samples are sent to the laboratory for detection of target pollutant concentrations. The pressure changes at each pressure monitoring point are continuously monitored and recorded until the readings at each pressure monitoring point return to the readings before the vacuum pump is started, and the monitoring data of each pressure monitoring point are derived. The pressure change curve of each pressure monitoring point over time is fitted using AQTESOLV software to automatically calculate the gas conductivity T i and leakage coefficient B i , calculate the average value of the six pressure monitoring points as the air permeability 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 flow velocity V(r) of the gas in the gravel gas conduction layer at a distance r from the extraction point in the horizontal direction is calculated using formula (1), and a curve of the change of the flow velocity with r is plotted:

[0016]

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

[0018] Formula (2) is used to calculate the time t for gas to migrate from the gravel gas-conducting layer at a distance r from the gas extraction point in the horizontal direction:

[0019]

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

[0021] Using the calculation results of formula (2), a curve of the time of gas migration from the gravel gas-conducting layer to the gas extraction point at different distances from the gas extraction point is drawn. The distance corresponding to the migration time of 4 hours is read from the curve 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 transmission flux MF of the target pollutant at the first transmission flux test point is calculated using formula (3): i :

[0023]

[0024] Among them, C i The average concentration of target pollutants in the gas sample collected from the air inlet pipe of the air pump during the transmission flux test, in mg / m 3 ; ΔP is the pressure difference between the indoor and outdoor areas of the future building base, in cm air column height; T is the average air permeability of the gravel air conduction 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 weighted average of the target pollutant transmission flux in the exposure unit by area is calculated using formula (4):

[0026]

[0027] Among them, MF i is the target pollutant transmission flux at the i-th test point in a certain exposure unit, in mg / (m 2 ·s); ROI maxi is the maximum influence radius of the i-th transmission flux test point in a certain exposure unit during the test, in m; A is the area of ​​the exposure unit, in m 2 .

[0028] In a preferred embodiment, in step S6, predicting the future health risk of indoor vapor intrusion for people in the polluted area includes: using formula (5) to calculate the carcinogenic health risk of indoor vapor intrusion of the target pollutant in the exposure unit, and using formula (6) to calculate the non-carcinogenic health risk of indoor vapor intrusion of the target pollutant:

[0029]

[0030] Among them, CR is the carcinogenic health risk of the target pollutant, which is dimensionless; EF is the exposure factor, which is 0.075m when it is planned as sensitive land. 3 / (kg body weight·d). When it is planned as non-sensitive land, the value is 0.121m 3 / (kg body weight·d); IUR is the target pollutant's unit carcinogenicity slope factor for inhalation, unit is m 3 / mg, obtained by querying the toxicology database; RfD i is the target pollutant breathing reference concentration, in mg / m 3, obtained by querying the toxicology database; ER is the conversion rate of indoor air in buildings. When it is planned as sensitive land, the value is 1.39×10 -4 s -1 When it is planned as non-sensitive land, the value is 2.78×10 -4 s -1 ;L b It is the indoor net height of the building. When it is planned as sensitive land, the value is 2.2m. When it is planned as non-sensitive land, the value is 3.0m.

[0031] In a preferred embodiment, step S6 further includes comparing the predicted result of the vapor intrusion risk in the contaminated area with a preset acceptable level, and if the risk exceeds the acceptable level by 1×10 -6 , control or remediation measures will be implemented.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The VOCs indoor vapor intrusion health risk assessment model provided by existing technical specifications corresponds to the physical scenario of VOCs transmission driven by molecular diffusion in loosely connected porous media. It cannot describe the indoor vapor intrusion health risk scenario of VOCs transmission and diffusion through random discrete fracture channels in bedrock fractured sites. In addition, although research results have been reported on discrete fracture network models that simulate the VOCs transmission process in bedrock fractured sites, the strong random discreteness of the fracture distribution in actual sites makes the use of such models to accurately quantify the risk first require extensive drilling tests in the contaminated area to accurately characterize the three-dimensional spatial distribution of the fractures and contamination in the site, which is costly. Otherwise, the simulation assessment results are likely to overestimate or underestimate the risk, leading to increased uncertainty in management decisions.

[0034] This paper combines the VOCs indoor vapor intrusion risk exposure scenario in actual sites and proposes a risk assessment method based on the measured transmission flux of VOCs at key interfaces of indoor vapor intrusion in bedrock fracture sites, filling the gap in this field. At the same time, the transmission flux test method proposed in this paper usually covers an area of ​​more than 500m2 at a single test point. 2 However, when using the traditional discrete fracture network model to achieve the same assessment accuracy, at least 50 points need to be tested to achieve a detailed depiction of the fractures and contaminated space, thereby ensuring the accuracy of the model's risk prediction. Therefore, the present invention can reduce costs by at least 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a flow chart of the method of the present invention;

[0036] Figure 2 Schematic diagram of the pollutant transmission flux simulation test system of the present invention;

[0037] Figure 3 Graph showing the change of flow velocity V(r) with r according to the present invention;

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

[0039] Description of reference numerals:

[0040] 201. Concrete cover layer; 202. Gravel gas-conducting layer; 203. Exhaust pipe; 213. Vertical pipe; 204. Exhaust pump; 205. Exhaust pipe valve; 206. Gas sampling port; 207. Pressure monitoring point; 210. Unsaturated bedrock fracture layer; 211. Saturated bedrock fracture layer. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention are described clearly and completely below. The embodiments of the present invention and all other embodiments obtained by persons of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0042] Example 1:

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

[0044] Step S1: Comprehensively utilize on-site pollution trace identification and rapid detection, historical monitoring data analysis, drilling sampling, and laboratory testing to identify areas within the site where VOCs contamination exists in bedrock and groundwater, and delineate the boundaries of the contaminated area.

[0045] Step S2: Level the entire ground in the designated polluted area and establish a pollutant transmission flux simulation test system under the building floor.

[0046] Specifically, the pollutant transmission flux simulation test system includes a concrete cover layer 201, a gravel gas conducting layer 202, an exhaust pipe 203, an exhaust pump 204, an exhaust pipe valve 205 and a gas sampling port 206. The concrete cover layer 201 and the gravel gas conducting layer 202 are arranged in sequence from top to bottom above the bedrock fracture layer (the lower part of which is a saturated bedrock fracture layer 211 and the upper part is an unsaturated bedrock fracture layer 210). The exhaust pipe 203 includes a horizontal pipe and a vertical pipe 213 that are interconnected. The lower end of the vertical pipe extends to the bottom of the gravel gas conducting layer 202 and above the unsaturated bedrock fracture layer 210. A gas sampling port 206 is arranged on one side of the upper part of the vertical pipe. The exhaust pump 204 and the exhaust pipe valve 205 are arranged in the horizontal pipe. The horizontal pipe is opened on one side away from the vertical pipe. The thickness of the concrete cover layer 201 is usually 15 to 20 cm, the concrete compressive strength is not less than C35, and the anti-permeability grade is not less than P8; the thickness of the gravel air conducting layer is 15 cm, the average diameter of the gravel is not more than 5 mm, and the unevenness coefficient is less than 5.

[0047] Step S3: Use the established pollutant transmission flux simulation test system to carry out the target pollutant transmission flux test in the polluted area, set the first transmission flux test point at the center of the polluted area, and fit the air permeability, leakage coefficient, and maximum influence radius ROI of the local area where the first transmission flux test point is located during the test. max and target pollutant transport flux, with ROI max Draw a circle with a radius of , and take the area covered by the circle as the maximum impact area during the test of the first transmission flux test point.

[0048] Specifically, the first transmission flux test point includes one air pumping point and six pressure monitoring points 207. The six pressure monitoring points 207 are arranged at different positions around the air pumping point in the horizontal direction with the air pumping point as the center. The angle formed by two adjacent pressure monitoring points 207 and the air pumping point is 60°, and the pressure monitoring point closest to the air pumping point is 0.5m away from the air pumping point. The distance between two radially adjacent pressure monitoring points 207 is not 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 not more than 0.1Pa, and one pressure data is read and stored every 1 second.

[0049] Furthermore, a target pollutant transmission flux test in the polluted area was carried out, including: after the pollutant transmission flux simulation test system was connected, the vacuum pump 204 was started, and the air was continuously pumped at a constant flow rate of 600L / min for 4 hours. Continuous sampling was performed at the gas sampling port 206, and the sampling flow rate was 1L / min. After continuous pumping for 4 hours, the vacuum pump 204 and the vacuum pipeline valve 205 were turned off, and the vacuum pump inlet pipe sampling device was turned off. The collected samples were sent to the laboratory to detect the target pollutant concentration. Each pressure monitoring point continuously monitored and recorded the pressure changes until the readings of each pressure monitoring point returned to the readings before the vacuum pump was started, and the monitoring data of each pressure monitoring point was derived. The AQTESOLV software was used to fit the pressure change curve of each pressure monitoring point over time, and the gas conductivity T was automatically calculated. i and leakage coefficient B i , calculate the average value of the 6 pressure monitoring points as the air permeability T and leakage coefficient B of the local area where the corresponding transmission flux test point is located.

[0050] Formula (1) is used to calculate the gas velocity V(r) in the gravel gas-conducting layer at a distance r from the extraction point in the horizontal direction, and a curve of the change of the velocity V(r) with r is plotted:

[0051]

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

[0053] Formula (2) is used to calculate the time t for gas to migrate from the gravel gas-conducting layer at a distance r from the gas extraction point in the horizontal direction:

[0054]

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

[0056] Using the calculation results of formula (2), a curve of the time of gas migration from the gravel gas-conducting layer to the gas extraction point at different distances from the gas extraction point is drawn. The distance corresponding to the migration time of 4h (240min) 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] Formula (3) is used to calculate the transmission flux MF of the target pollutant at the first transmission flux test point: i :

[0058]

[0059] Among them, C i The average concentration of target pollutants in the gas sample collected from the air inlet pipe of the air pump during the transmission flux test, in mg / m 3 ; ΔP is the pressure difference between the indoor and outdoor areas of the future building base, in cm air column height, usually 10Pa, about 83cm air column height; T is the average air permeability of the gravel air conduction 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.

[0060] Step S4: Select a second transmission flux test point in the contaminated area outside the maximum impact area of ​​the first transmission flux test point, and repeat step S3 to calculate the maximum impact area of ​​the second transmission flux test point during the test period;

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

[0062] Step S6: predicting the future health risk of indoor steam intrusion to people in the polluted area.

[0063] Specifically, formula (4) is used to calculate the area-weighted average of the target pollutant transmission flux within the exposure unit:

[0064]

[0065] Among them, MF i is the target pollutant transmission flux at the i-th test point in a certain exposure unit, in mg / (m 2 ·s); ROI maxi is the maximum influence radius of the i-th transmission flux test point in a certain exposure unit during the test, in m; A is the area of ​​the exposure unit, in m 2 .

[0066] Predicting the future health risk of indoor vapor intrusion for people in the polluted area includes: using formula (5) to calculate the carcinogenic health risk of indoor vapor intrusion of the target pollutant in the exposure unit, and using formula (6) to calculate the non-carcinogenic health risk of indoor vapor intrusion of the target pollutant:

[0067]

[0068] Among them, CR is the carcinogenic health risk of the target pollutant, which is dimensionless; EF is the exposure factor, which is 0.075m when it is planned as sensitive land. 3 / (kg body weight·d). When it is planned as non-sensitive land, the value is 0.121m 3 / (kg body weight·d); IUR is the target pollutant's unit carcinogenicity slope factor for inhalation, unit is m 3 / mg, obtained by querying the toxicology database; RfD i is the target pollutant breathing reference concentration, in mg / m 3 , obtained by querying the toxicology database; ER is the conversion rate of indoor air in buildings. When it is planned as sensitive land, the value is 1.39×10 -4 s -1 When it is planned as non-sensitive land, the value is 2.78×10 -4 s -1 ;L b It is the indoor net height of the building. When it is planned as sensitive land, the value is 2.2m. When it is planned as non-sensitive land, the value is 3.0m.

[0069] Step S6 also includes comparing the predicted result of the steam intrusion risk in the contaminated area with the preset acceptable level. If the risk exceeds the acceptable level by 1×10 -6 , control or remediation measures will be implemented.

[0070] Example 2:

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

[0072] The situation of this embodiment: a bedrock fissure site located in front of a mountain with a total area of ​​about 50,000m 2 Historically, it was primarily used as a chemical plant. According to relevant management requirements, a site investigation and risk assessment must be conducted to ensure the land can be used safely.

[0073] Step S1: According to the requirements of the regulations, the site pollution trace identification and rapid detection, historical monitoring data analysis, and multiple batches of gradually intensified drilling sampling and testing were used to finally delineate the site. 2 Chloroform contamination of bedrock and groundwater in the region.

[0074] Step S2: 16000m 2 The ground of the chloroform contaminated area was leveled, underground pipelines and other facilities in the area were removed, and a negative pressure exhaust simulation system under the building floor was established. Figure 2The pollutant transmission flux simulation test system shown in the figure. On the leveled ground, a 15cm-thick gravel air-conducting layer is first laid. The gravel is made of quartz sand with a diameter of 3-5mm. Screening is performed to ensure that the unevenness 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 an impermeability grade of P8 is laid above the gravel air-conducting layer. The concrete cover layer is oxidized according to regulatory requirements to prevent cracks.

[0075] Step S3: After the concrete cover reaches curing conditions, a first transmission flux test point is established at the center of the concrete cover laid in the contaminated area. The pressure changes over time at negative pressure monitoring points at different distances from the extraction point are recorded at a constant extraction rate. Simultaneously, gas sampling ports on the extraction pipes are regularly sampled to detect target pollutant concentrations.

[0076] Specifically, the vertical tube 213 of the exhaust pipe is used as the exhaust point, and a total of 6 pressure monitoring points 207 are set with the exhaust point as the center, at intervals of 0.5m, 6m, 10m, 15m, 20m, and 25m, respectively. The angle between two adjacent pressure monitoring points and the exhaust point is 60°. Connect the exhaust pipe 203, install the online pressure monitoring and recording device, start the exhaust pump 204, adjust the exhaust flow rate to 600L / min, and continuously exhaust for 4 hours. During the exhaust process, a Suma tank is used to continuously collect gas samples at the gas sampling port 206 of the exhaust pipe, with a sampling flow rate of 1L / min. After 4 hours of exhaust, close the exhaust pump 204 and the exhaust pipe valve 205. When the pressures of the 6 pressure monitoring points are restored to the readings before the exhaust pump is started, the data in the pressure monitoring and recording devices of the 6 pressure monitoring points are exported, and the AQTESOLV software is used to fit the pressure change curve of each pressure monitoring point over time, and the gas conductivity T is automatically calculated. i and leakage coefficient B i , calculate the average value as T and B of the local area where the transmission flux test point is located. The fitting results show that the T of the pressure variation curve of the 6 pressure monitoring points set around the transmission flux test point is i 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. The fitted B i They are 905.6cm, 901.6cm, 908.2cm, 915.8cm, 902.2cm and 921.2cm respectively, with an average value of 909.1cm.

[0077] Use formula (1) to calculate the gas velocity in the gravel gas-conducting layer at a distance r from the pumping point in the horizontal direction, and draw a curve of V(r) varying with r, as shown in the attached figure. Figure 3 shown.

[0078]

[0079] Formula (2) is used to calculate the time t of gas migration from the gravel gas-conducting layer at a distance r from the pumping point in the horizontal direction to the pumping point. The curve of the time of gas migration from the gravel gas-conducting layer at different distances from the pumping point to the pumping point is plotted as a function of distance, as shown in the attached figure. Figure 4 shown.

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

[0081]

[0082] During the entire transmission flux test, the gas sampling port of the exhaust pipe continuously collected gas samples using a Suma tank, and the average chloroform concentration was 0.5 mg / m 3 , use formula (3) to calculate the transmission flux MF of chloroform at the test point with a pressure difference of 10Pa (83cm air column height) i 5.3×10 -6 mg / (m 2 ·s).

[0083]

[0084] Step S4: Select another transmission flux test point outside the maximum impact area of ​​the transmission flux test point in step S3 and within the contaminated area, and repeat step S3.

[0085] Step S5, repeating steps S3 and S4 until the maximum impact areas of all transmission flux test points cover the entire contaminated area, and finally testing 16 transmission flux test points.

[0086] Step S6: The land is planned to be used as residential land in the future. 2 The polluted area is divided into four zones with an area of ​​4000m 2 Each exposure unit includes 4 transmission flux test points. Formula (4) is used to calculate the weighted average of the chloroform transmission flux in each exposure unit. The results are shown in Table 1:

[0087]

[0088] Table 1 Weighted average values ​​of chloroform transmission flux in different exposure units

[0089]

[0090]

[0091] Formula (5) is used to calculate the carcinogenic health risk of indoor vapor intrusion of target pollutants in the exposure unit, and formula (6) is used to calculate the non-carcinogenic health risk of indoor vapor intrusion of target pollutants.

[0092]

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

[0094] Table 2 Health risks of chloroform indoor vapor intrusion in different exposure units

[0095] Exposure unit number unit Exposure Unit 1 Exposure Unit 2 Exposure Unit 3 Exposure Unit 4 area <![CDATA[m 2 ]]> 4000 4000 4000 4000 Transmission flux 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] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for assessing the risk of VOCs vapor intrusion in bedrock fissure sites, characterized by: The steps include: S1. Identify areas of VOCs contamination in bedrock and groundwater within the site and define the boundaries of the contaminated areas; S2. Level the entire ground in the designated polluted area and establish a pollutant transmission flux simulation test system; S3. Conduct a target pollutant transmission flux test in the polluted area using the established pollutant transmission flux simulation test system. Set a first transmission flux test point at the center of the polluted area and calculate the maximum impact area during the test at the first transmission flux test point. S4. Select a second transmission flux test point in the contaminated area outside the maximum impact area of ​​the first transmission flux test point, and repeat step S3 to calculate the maximum impact area during the test of the second transmission flux test point; S5. Repeat steps S3 to S4 until the maximum impact areas of all transmission flux test points are superimposed to cover the entire contaminated area; S6. Predict the future health risks of indoor vapor intrusion to people in polluted areas.

2. The VOCs vapor intrusion risk assessment method for bedrock fissure sites according to claim 1, characterized in that: In step S2, the pollutant transmission flux simulation test system includes a concrete cover layer, a gravel air conducting layer, an exhaust pipe, an exhaust pump, an exhaust pipe valve and a gas sampling port. The concrete cover layer and the gravel air conducting layer are arranged in sequence from top to bottom above the bedrock fracture layer. The exhaust pipe includes a horizontal pipe and a vertical pipe that are interconnected. The lower end of the vertical pipe extends into the bottom of the gravel air conducting layer and above the bedrock fracture layer. A gas sampling port is provided on one side of the upper part of the vertical pipe. An exhaust pump and an exhaust pipe valve are provided in the horizontal pipe. The horizontal pipe is opened on one side away from the vertical pipe. The thickness of the concrete cover layer is 15 to 20 cm, the compressive strength of the concrete is not less than C35, and the impermeability grade is not less than P8. The thickness of the gravel air conducting layer is 15 cm, the average diameter of the gravel is not greater than 5 mm, and the unevenness coefficient is less than 5.

3. The VOCs vapor intrusion risk assessment method for bedrock fissure sites according to claim 1, characterized in that: In step S3, the maximum impact area during the test of the first transmission flux test point is calculated, including: fitting and obtaining the air permeability, leakage coefficient, and maximum impact radius ROI of the local area where the first transmission flux test point is located during the test of the first transmission flux test point. max and target pollutant transport flux, with ROI max Draw a circle with the radius as the maximum impact area during the test of the first transmission flux test point.

4. The VOCs vapor intrusion risk assessment method for bedrock fissure sites according to claim 3, characterized in that: In step S3, centered around the first transmission flux test point, there is one pumping point and six pressure monitoring points. The six pressure monitoring points are arranged horizontally at different positions around the pumping point. The angle between two adjacent pressure monitoring points and the pumping point is 60°, and the pressure monitoring point closest to the pumping point is 0.5m away from the pumping point. The distance between two radially adjacent pressure monitoring points is no more than 5m, and each pressure monitoring point is equipped with an online pressure monitoring and recording device.

5. The VOCs vapor intrusion risk assessment method for bedrock fissure sites according to claim 4, characterized in that: In step S3, a target pollutant transmission flux test is carried out in the polluted area, including: after the pollutant transmission flux simulation test system is connected, the vacuum pump is started, and air is continuously pumped at a constant flow rate of 600L / min for 4 hours. Continuous sampling is performed at the gas sampling port with a sampling flow rate of 1L / min. After continuous pumping for 4 hours, the vacuum pump and the vacuum pipeline valve are turned off, the vacuum pump inlet pipe sampling device is turned off, and the collected samples are sent to the laboratory for detection of target pollutant concentrations. The pressure changes at each pressure monitoring point are continuously monitored and recorded until the readings at each pressure monitoring point return to the readings before the vacuum pump is started. The monitoring data of each pressure monitoring point is exported, and the pressure change curve of each pressure monitoring point with time is fitted using AQTESOLV software to automatically calculate the gas conductivity T. i and leakage coefficient B i , calculate the average value of the six pressure monitoring points as the air permeability and leakage coefficient of the local area where the corresponding transmission flux test point is located.

6. The VOCs vapor intrusion risk assessment method for bedrock fissure sites according to claim 5, characterized in that: In step S3, the flow velocity V(r) of the gas in the gravel gas-conducting layer at a distance r from the extraction point in the horizontal direction is calculated using formula (1), and a curve of the change of flow velocity with r is plotted: Where, V(r) is in cm / min; Q ssv is the pumping rate during the transmission flux test, in L / min; b is the thickness of the gravel gas-conducting layer, in cm; n is the effective porosity of the gravel gas-conducting layer, dimensionless, and n is 0.3; The value of the first-order second-kind Bessel function when the independent variable is r / B is obtained by looking up the function table; Formula (2) is used to calculate the time t for gas to migrate from the gravel gas-conducting layer at a distance r from the gas extraction point in the horizontal direction: Wherein, V(r0) is the velocity of gas migration from the gravel gas-conducting layer at a distance r0 from the extraction point to the extraction point, in cm / min, calculated using formula (1); Using the calculation results of formula (2), a curve of the time of gas migration from the gravel gas-conducting layer to the gas extraction point at different distances from the gas extraction point is drawn. The distance corresponding to the migration time of 4 hours is read from the curve as the maximum influence radius ROI during the transmission flux test of the first transmission flux test point. max .

7. The VOCs vapor intrusion risk assessment method for bedrock fissure sites according to claim 6, characterized in that: In step S3, the transmission flux MF of the target pollutant at the first transmission flux test point is calculated using formula (3): i : Among them, C i The average concentration of target pollutants in the gas sample collected from the air inlet pipe of the air pump during the transmission flux test, in mg / m 3 ; Δp is the pressure difference between the indoor and outdoor areas of the future building base, in cm air column height; T is the average air permeability of the gravel air conduction 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.

8. The VOCs vapor intrusion risk assessment method for bedrock fissure sites according to claim 7, characterized in that: In step S6, the weighted average of the target pollutant transmission flux within the exposure unit by area is calculated using formula (4): Among them, MF i is the target pollutant transmission flux at the i-th test point in a certain exposure unit, in mg / (m 2 ·s); ROI maxi is the maximum influence radius of the i-th transmission flux test point in a certain exposure unit during the test, in m; A is the area of ​​the exposure unit, in m 2 .

9. The VOCs vapor intrusion risk assessment method for bedrock fissure sites according to claim 8, characterized in that: In step S6, the future health risk of indoor vapor intrusion for people in the polluted area is predicted, including: using formula (5) to calculate the carcinogenic health risk of indoor vapor intrusion of the target pollutant in the exposure unit, and using formula (6) to calculate the non-carcinogenic health risk of indoor vapor intrusion of the target pollutant: Among them, CR is the carcinogenic health risk of the target pollutant, which is dimensionless; EF is the exposure factor, which is 0.075m when it is planned as sensitive land. 3 / (kg body weight·d). When it is planned as non-sensitive land, the value is 0.121m 3 / (kg body weight·d); IUR is the target pollutant's unit carcinogenicity slope factor for inhalation, unit is m 3 / mg, obtained by querying the toxicology database; RfD i is the target pollutant breathing reference concentration, in mg / m 3 , obtained by querying the toxicology database; ER is the conversion rate of indoor air in buildings. When it is planned as sensitive land, the value is 1.39×10 -4 s -1 When it is planned as non-sensitive land, the value is 2.78×10 -4 s -1 ;L b It is the indoor net height of the building. When it is planned as sensitive land, the value is 2.2m. When it is planned as non-sensitive land, the value is 3.0m.

10. The VOCs vapor intrusion risk assessment method for bedrock fissure sites according to claim 9, characterized in that: Step S6 also includes comparing the predicted result of the steam intrusion risk in the contaminated area with the preset acceptable level. If the risk exceeds the acceptable level by 1×10 -6 , control or remediation measures will be implemented.

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