Static box and method for measuring gas flux and diffusion coefficient of full-surface polluted site

Abstract

The invention discloses a static box and a method for measuring gas flux and diffusion coefficient of a full-surface polluted site. The device mainly comprises a metal chamber, a separable sealing water tank, a multifunctional base, a rigid sampling gas box and the like. The device can be used on the surface of contaminated soil and the surface of a geomembrane, when the device is used, the multifunctional base is inserted into a soil body on the surface of the soil and fixed through clay, and the sealing water tank is placed on the base and filled with water to keep the sealing performance of the metal cavity; after pollution gas is accumulated in the static box, one rigid sampling gas box is taken down every fixed time, then the surface gas release flux is obtained according to the time-concentration gradient, and the release flux can be inverted through a gas migration model to obtain the field gas diffusion coefficient. The device has the advantages of being simple in structure, easy and convenient to operate, resistant to cracking and corrosion, universal in whole surface, capable of achieving multifunctional combination, wide in applicability and the like, and has the great popularization and research background under the background of pollution gas management and atmospheric environment improvement.

Description

Technical Field

[0001] The present invention belongs to the field of soil gas sampling devices for urban contaminated sites, and in particular relates to a static box and method for measuring the gas flux and diffusion coefficient of the entire surface of the contaminated site, which can monitor the gas release flux and diffusion coefficient on the surface of the contaminated site. Technical Background

[0002] Urban polluted sites will produce a lot of pollutants, including greenhouse gases and some toxic and harmful odorous gases. The more common gases include greenhouse gases such as methane and carbon dioxide, toxic and harmful odorous gases such as hydrogen sulfide and ammonia, and volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene and xylene (para-, meta-, and o-xylene). These gases will be continuously released and have a serious impact on the atmospheric environment. Polluted gases in polluted sites will migrate by diffusion, infiltration, etc. Therefore, it is very important to obtain the release flux and diffusion coefficient of polluted gases on the surface of the site under field conditions to study the migration law of polluted gases and control of polluted gases.

[0003] At present, the on-site gas release flux is mainly obtained by static chamber test monitoring. However, the traditional static chamber has the limitations of easy erosion and cracking, poor air tightness, and complex operation. In addition, the traditional static chamber is only applicable to the soil surface, and in reality, the contaminated site also has a geomembrane surface that is not suitable for monitoring with the traditional static chamber.

[0004] Therefore, seeking a static box that is universal on the entire surface is of great significance for monitoring the release flux and diffusion coefficient of polluted gases on the surface of the site under field conditions. It can help study the migration laws of polluted gases and control the diffusion of polluted gases. It is of great significance to improving the atmospheric environment for human survival and has great practical value for the sustainable development of the economy and society. Summary of the invention

[0005] The purpose of the present invention is to provide a static box and method for measuring the gas flux and diffusion coefficient of a full-surface contaminated site in view of the deficiencies of the prior art.

[0006] The invention discloses a static box for measuring gas flux and diffusion coefficient of a full-surface contaminated site, comprising a metal chamber, a detachable water tank, a multifunctional base, and a rigid sampling gas box;

[0007] The metal chamber is a cylindrical structure, wherein a plurality of windows are provided at different heights on the side of the metal chamber, and the windows are made of transparent organic glass; the metal chamber is provided with a plurality of gas sampling ports and a plurality of spare sampling ports on the top surface, and the gas sampling ports and spare sampling ports are both equipped with three-way valves, and the three-way valve is connected to the rigid sampling gas box through an air pipe; the rigid sampling gas box is provided with two ventilation valves;

[0008] The detachable water tank is a circular ring structure, which has a water injection groove, and the water injection groove is connected to the extension edge; the bottom of the metal chamber is arranged in the water injection groove;

[0009] The multifunctional base is a circular ring structure, in which a lap platform is provided, which can be connected with the extended edge of the detachable water tank; the inner diameter of the multifunctional base is larger than the outer diameter of the metal chamber.

[0010] Furthermore, the metal chamber is one-piece, not easy to crack, and resistant to high temperature and corrosion, and can adapt to a variety of sampling environments; the windows of the metal chamber are arranged on opposite sides and are respectively located near the top and the bottom, and can be used with a portable laser methane detector to directly measure the methane concentration gradient, which is convenient for quickly obtaining methane flux and can also take into account the functions of light transmission and observation.

[0011] Furthermore, the detachable water tank and the multifunctional base can be used simultaneously or separately to adapt to the surface characteristics of different sampling locations, thereby achieving precise setting of the airtightness of the metal chamber.

[0012] Furthermore, the static box can be used for all types of surface sampling at the same time. When used on the surface of geomembrane, the multifunctional base can be used as the edge of the metal chamber, and glass glue is applied on the outer side of the metal chamber and the inner side of the multifunctional base to fix it on the surface of geomembrane. Water is injected between the metal chamber and the multifunctional base to check the air tightness of the metal chamber. At this time, the detachable water tank can be omitted; when used on the soil surface, the extended edge of the detachable water tank can be placed on the overlapping platform of the multifunctional base, and the metal chamber can be placed in the water injection groove and sealed by water injection.

[0013] Furthermore, the rigid sampling gas box is provided with two vent valves at the top and bottom, which can be used for flushing the gas box before the test, and can also be used for connection with the metal chamber and gas sampling and detection. The rigid sampling gas box and the metal chamber are quick-detachable and can be directly used for gas sampling without using a vacuum pump, which is convenient for rapid sampling and does not affect the air pressure stability in the metal chamber. The number of rigid sampling gas boxes can be arbitrarily set according to site conditions and test requirements.

[0014] The present invention also discloses a method for measuring the gas flux and diffusion coefficient of a full-surface contaminated site using the device, comprising the following steps:

[0015] S1. At the beginning of the test, all the gas sampling ports on the top of the metal chamber are opened and connected to one of the opened vent valves of the rigid sampling gas box through the air pipe, and the other vent valve and the three-way valve of the spare sampling port are kept closed; the static box is fixedly installed on the contaminated site and ensured to be airtight;

[0016] S2. After the metal chamber is in a well-sealed state, gas accumulates in it; at time 0, a rigid sampling gas box is removed and the vent valve and the three-way valve are closed; thereafter, a rigid sampling gas box is removed every 30 to 60 minutes for a total of 90 to 180 minutes, and the gas sample concentration in the rigid sampling gas box is analyzed by gas chromatograph;

[0017] S3. After the test, the gas release flux on the surface of the contaminated site is calculated according to the following formula:

[0018]

[0019] ΔC=C t+Δt -C t (3)

[0020] Where V0 is the volume of the metal chamber (m 3 );V s is the volume of a single rigid sampling gas box (m 3 ); n is the number of rigid sampling gas boxes; i is the number of sampling times; t is the time (min); △t is the time interval between two gas samplings (min); C t is the gas concentration in the device at time t (mg / m 3 );C t+△t is the gas concentration at time t+△t (mg / m 3 ); S is the bottom area of ​​the metal chamber (m 2 ); j is the gas release flux on the surface of the contaminated site (mg / m 2 / h);

[0021] S4. Establish mathematical models for the migration of polluted gases in soil and geomembrane respectively; according to the gas release flux measured on site calculated in step S3, the diffusion coefficient of the gas under field conditions is obtained by inverting the established mathematical model for migration.

[0022] Furthermore, the sampling time and the number of sampling times can be flexibly changed according to different site conditions and experimental requirements.

[0023] The device and method of the present invention can be used to measure the gas release flux in contaminated sites with different surfaces, can directly sample without using a vacuum pump to avoid affecting the air pressure stability in the metal chamber, and can be used with a portable gas detector for rapid measurement. Compared with traditional static boxes, the device of the present invention has the advantages of simple structure, easy operation, resistance to cracking and erosion, universal use of all surfaces, multifunctional combination and wide applicability. In the context of increasingly serious impacts of polluted gases, it is of great significance to the release, diffusion and control of polluted gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is a schematic diagram of the use of a static box on the soil surface for measuring the gas flux and diffusion coefficient of the full-surface contaminated site;

[0025] Figure 2 It is a schematic diagram of the use of a static box on the surface of a geomembrane for measuring the gas flux and diffusion coefficient of a full-surface contaminated site;

[0026] Figure 3 It is a schematic diagram of the top surface of a static box for determining the gas flux and diffusion coefficient of a full-surface contaminated site;

[0027] Figure 4 Schematic diagram of a static box detachable water tank for measuring gas flux and diffusion coefficient of a full-surface contaminated site; (a) front view, (b) top view, (c) stereogram;

[0028] Figure 5 Schematic diagram of a multifunctional base of a static box for measuring gas flux and diffusion coefficient of a full-surface contaminated site, including (a) a front view, (b) a top view, and (c) a stereogram;

[0029] Figure 6 is a gas release flux diagram of a field test in an embodiment of the present invention;

[0030] Figure 7 It is a gas diffusion coefficient diagram of the field test in the embodiment of the present invention.

[0031] The reference numerals in the figure are: metal chamber 1, window 2, detachable water tank 3, multifunctional base 4, gas sampling port 5, three-way valve 6, air pipe 7, rigid sampling gas box 8, ventilation valve 9, spare sampling port 10, water injection groove 11, extension edge 12, overlapping platform 13. DETAILED DESCRIPTION

[0032] The present invention is further described and illustrated below in conjunction with the accompanying drawings and embodiments, wherein the following embodiments take a total of 4 samplings as an example. The technical features of each embodiment of the present invention may be combined accordingly without conflicting with each other.

[0033] like Figure 1 and 2 The figure is a schematic diagram of the use of a static box for measuring the gas flux and diffusion coefficient of a full-surface contaminated site. The device is placed on the soil surface ( Figure 1 ) and geomembrane surface ( Figure 2 ) can be used; the device mainly includes a metal chamber 1, a detachable water tank 3, a multifunctional base 4, and a rigid sampling gas box 8; wherein, when used on the surface of a geomembrane, the detachable water tank 3 may not be provided. In some embodiments of the present invention, the metal chamber 1 is a cylindrical structure, wherein two viewing windows 2 are provided at different heights on the side of the metal chamber 1, and the viewing windows 2 are square structures and are made of transparent organic glass.

[0034] like Figure 3 As shown, the metal chamber 1 is provided with 4 gas sampling ports 5 and 3 spare sampling ports 10 on the top surface, and the gas sampling ports 5 and spare sampling ports 2 are both equipped with three-way valves 6, and the three-way valve 6 is connected to the rigid sampling gas box 8 through an air pipe 7; the rigid sampling gas box 8 is provided with two ventilation valves 9;

[0035] like Figure 4 As shown, the detachable water tank 3 is a circular ring structure, in which a water injection groove 11 is provided and an external extension edge 12 is connected.

[0036] like Figure 5 As shown, the multifunctional base 4 is a circular ring structure, in which a lap platform 13 is provided, which can be connected with the extended edge 12 of the detachable sink 3.

[0037] In a specific embodiment of the present invention, the metal chamber 1 is an integrated type and can be made of metal materials such as stainless steel. It is not easy to crack and is resistant to high temperature and corrosion, and can adapt to a variety of sampling environments. The window 2 of the metal chamber 1 is arranged on opposite sides and is located close to the top and the bottom respectively. It can be used with a portable laser methane detector to directly measure the methane concentration gradient, which is convenient for quickly obtaining the methane flux, and can also take into account the functions of light transmission and observation.

[0038] In a specific embodiment of the present invention, the detachable water tank 3 and the multifunctional base 4 can be used simultaneously or separately to adapt to the surface characteristics of different sampling locations, thereby achieving precise setting of the airtightness of the metal chamber 1 .

[0039] In a specific embodiment of the present invention, when used on a geomembrane surface, Figure 2 As shown, the multifunctional base 4 can be used as the surrounding edge of the metal chamber 1 (the inner diameter of the multifunctional base 4 is larger than the outer diameter of the metal chamber 1), glass glue is applied on the outer side of the metal chamber 1 and the inner side of the multifunctional base 4 to fix it on the surface of the geomembrane, and water is injected between the metal chamber 1 and the multifunctional base 4 to check the air tightness of the metal chamber 1; when used on the soil surface, Figure 1 As shown, the extended edge 12 of the detachable water tank 3 can be placed on the overlapping platform 13 of the multifunctional base 4, and the metal chamber 1 can be placed in the water injection groove 11 and sealed by water injection.

[0040] In a specific embodiment of the present invention, two vent valves 9 are provided at the top and bottom of the rigid sampling gas box 8, which can be used for flushing the gas box before the test, and can also be used for connection with the metal chamber 1 and sampling and testing of gas. The rigid sampling gas box 8 and the metal chamber 1 are quick-detachable and can be directly used for gas sampling without using a vacuum pump, which is convenient for rapid sampling and does not affect the air pressure stability in the metal chamber 1. The number of rigid sampling gas boxes 8 can be arbitrarily set according to site conditions and test requirements.

[0041] The specific working process of this device is as follows:

[0042] S1. Installation of the device. At the beginning of the test, the gas sampling ports 5 on the top of the metal chamber 1 are all opened and connected to one of the opened vent valves 9 of the rigid sampling gas box 8 through the air pipe 7, and the other vent valve 9 and the three-way valve 6 of the spare sampling port 10 are kept closed. When used on the soil surface, the multifunctional base 4 is inserted into the soil and fixed in place with clay, the extended edge 12 of the detachable water tank 3 is connected to the overlapping platform 13 of the multifunctional base 4, and the metal chamber 1 is placed in the water injection groove 11. Water is injected into the groove 11 to protect the air tightness of the metal chamber 1. When used on the geomembrane surface, the metal chamber 1 and the multifunctional base 4 are directly fixed to the geomembrane surface with glass glue. The multifunctional base 4 can be used as the surrounding edge of the metal chamber 1. Water is injected into the groove between the two to check the air tightness of the metal chamber 1 on the geomembrane surface.

[0043] S2. Gas sampling. After the metal chamber 1 is in a well-sealed state, gas accumulates in it. At time 0, remove a rigid sampling gas box 8 and close the vent valve 9 and the three-way valve 6. After that, remove a rigid sampling gas box 8 every 30 to 60 minutes for a total of 90 to 180 minutes. The specific time and sampling times are determined according to the site conditions and test requirements. The gas sample concentration in the rigid sampling gas box 8 is analyzed by a gas chromatograph.

[0044] S3. Release flux calculation. After the test, the gas release flux on the surface of the contaminated site is calculated according to the following formula:

[0045]

[0046] ΔC=C t+Δt -C t (3)

[0047] Where V0 is the volume of the metal chamber 1 (m 3 );V s is the volume of a single rigid sampling gas box 8 (m 3 ); n is the number of rigid sampling gas boxes 8; i is the number of samplings; t is the time (min); △t is the time interval between two gas samplings (min); C tis the gas concentration in the device at time t (mg / m 3 );C t+△t is the gas concentration at time t+△t (mg / m 3 ); S is the bottom area of ​​the metal chamber 1 (m 2 ); j is the gas release flux on the surface of the contaminated site (mg / m 2 / h).

[0048] S4. Calculation of diffusion coefficient. Mathematical models of the migration of polluted gases in soil and geomembrane are established respectively. The control equation of the mathematical model of S4.1 soil system is expressed as

[0049]

[0050] Among them, C s (z) is the gas concentration in the soil (mg / m 3 ); z is the depth (m); D s is the effective diffusion coefficient of gas in soil (m 2 / s); v is the convection velocity of gas in the soil (m 2 / s).

[0051] At the top boundary, the soil surface is directly connected to the atmosphere, and the concentration of the gas is assumed to be zero at the top boundary:

[0052] C s (0)=0 (5)

[0053] A constant concentration boundary condition is assumed at the bottom boundary:

[0054] C s (H)=C0 (6)

[0055] Where C0 is the gas source concentration at the bottom of the soil (mg / m 3 ), H is soil thickness (m).

[0056] The gas release flux J on the soil surface can be obtained from this s It is expressed as:

[0057]

[0058] Among them, θ g is the air porosity of the soil.

[0059] S4.2 The governing equation of the mathematical model of the geomembrane system is expressed as

[0060]

[0061] Among them, C g (z) is the gas concentration in the geomembrane (mg / m3 ); z is the depth (m); D g is the diffusion coefficient of gas in geomembrane (m 2 / s). w (z) is the gas concentration in the pollutant pile under the geomembrane (mg / m 3 );D w is the effective diffusion coefficient of gas in the pollutant pile (m 2 / s).

[0062] There is a distribution relationship between the gas concentration on the upper and lower surfaces of the geomembrane and the concentration in the membrane:

[0063]

[0064] Among them, C g *(z) is the gas concentration on the upper and lower surfaces of the geomembrane (mg / m 3 );S gf To monitor the distribution coefficient between gas and geomembrane.

[0065] The top and bottom boundary conditions of the geomembrane system are consistent with the boundary conditions of the soil system. The boundary conditions at the interface between the geomembrane and the pollutant pile are expressed as:

[0066]

[0067] Where n is the total porosity in the pollutant pile and h is the thickness of the geomembrane (m).

[0068] The gas release flux J on the geomembrane surface can be obtained from this g It is expressed as:

[0069]

[0070] S4.3 The gas release flux measured on site calculated in step S3 is inverted by equation (7) or equation (11) to obtain the diffusion coefficient of the gas under on-site conditions.

[0071] In a specific embodiment of the present invention, a total of 4 samplings were carried out, and the device was used to monitor the release flux of hydrogen sulfide gas on the working surface and geomembrane surface of the landfill respectively, and the release flux of hydrogen sulfide gas on different surfaces was measured and calculated as shown in Table 1, Figure 6 As shown in the figure, the diffusion coefficients of gases in different media under the field conditions obtained by inversion are as follows: Figure 7 As shown, it can be seen that the hydrogen sulfide flux measured on the working surface is generally greater than the flux on the geomembrane surface, and the diffusion coefficient of the gas in the garbage pile is also much greater than the diffusion coefficient on the geomembrane.

[0072] Table 1 Hydrogen sulfide gas flux between the landfill working surface and the geomembrane surface measured by the static box method

[0073]

[0074]

[0075] The above examples are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples, and many variations are possible. All variations that can be directly derived or associated with the contents disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A static chamber for measuring gas flux and diffusion coefficient of full-surface contaminated sites, characterized in that: It comprises a metal chamber (1), a detachable water tank (3), a multifunctional base (4), and a rigid sampling gas box (8); The metal chamber (1) is a cylindrical structure, wherein a plurality of viewing windows (2) are provided at different heights on the side of the metal chamber (1), and the viewing windows (2) are made of transparent organic glass; the metal chamber (1) is provided with a plurality of gas sampling ports (5) and a plurality of spare sampling ports (10) on the top surface, and the gas sampling ports (5) and the spare sampling ports (10) are both equipped with three-way valves (6), and the three-way valve (6) is connected to a rigid sampling gas box (8) through an air pipe (7); the rigid sampling gas box (8) is provided with two ventilation valves (9); The detachable water tank (3) is a circular ring structure, having a water injection groove (11), and the water injection groove (11) is connected to an extension edge (12); the bottom of the metal chamber (1) can be arranged in the water injection groove (11) and filled with water to seal; The multifunctional base (4) is a circular ring structure, wherein a lap platform (13) is provided for cooperating and connecting with the extended edge (12) of the detachable water tank (3); the inner diameter of the multifunctional base (4) is larger than the outer diameter of the metal chamber (1).

2. The static box for measuring the gas flux and diffusion coefficient of the full-surface contaminated site according to claim 1 is characterized in that: The metal chamber (1) is of an integrated type; the viewing window (2) of the metal chamber (1) is arranged on opposite sides and is located close to the top and the bottom, and is used in conjunction with a portable laser methane detector to directly measure the methane concentration-time gradient.

3. The static box for measuring the gas flux and diffusion coefficient of the full-surface contaminated site according to claim 1 is characterized in that: The detachable water tank (3) and the multifunctional base (4) can be used simultaneously or separately to adapt to the surface characteristics of different sampling locations, thereby achieving precise setting of the airtightness of the metal chamber (1).

4. The static box for measuring the gas flux and diffusion coefficient of the full-surface contaminated site according to claim 3 is characterized in that: When used on the surface of a geomembrane, the multifunctional base (4) serves as the surrounding edge of the metal chamber (1), glass glue is applied on the outside of the metal chamber (1) and the inside of the multifunctional base (4) to fix it on the surface of the geomembrane, and water is injected between the metal chamber (1) and the multifunctional base (4) to check the air tightness of the metal chamber (1); When used on the soil surface, the extended edge (12) of the detachable water tank (3) is placed on the overlapping platform (13) of the multifunctional base (4), and the metal chamber (1) is placed in the water injection groove (11) and sealed by water injection.

5. The static box for measuring the gas flux and diffusion coefficient of the full-surface contaminated site according to claim 1 is characterized in that: The rigid sampling gas box (8) is provided with two ventilation valves (9) at the top and bottom, and the ventilation valves (9) are used for flushing the gas box before the test, connecting it to the metal chamber (1), and sampling and detecting the gas; the rigid sampling gas box (8) and the metal chamber (1) are connected in a quick-release manner, and can be directly used for gas sampling without using a vacuum pump, which is convenient for rapid sampling and does not affect the stability of the gas pressure in the metal chamber (1).

6. A method for measuring the gas flux and diffusion coefficient of a full-surface contaminated site based on the static box according to any one of claims 1 to 5, characterized in that: The steps include: S1. At the beginning of the test, the gas sampling ports (5) on the top of the metal chamber (1) are all opened and connected to one of the opened vent valves (9) of the rigid sampling gas box (8) through the air pipe (7), and the other vent valve (9) and the three-way valve (6) of the spare sampling port (10) are kept closed; the static box is fixedly installed on the contaminated site and ensures air tightness; S2. After the metal chamber (1) is in a well-sealed state, gas accumulates therein; at time 0, a rigid sampling gas box (8) is removed and the vent valve (9) and the three-way valve (6) are closed; thereafter, a rigid sampling gas box (8) is removed every 30 to 60 minutes for a total of 90 to 180 minutes, and the concentration of the gas sample in the rigid sampling gas box (8) is analyzed by a gas chromatograph; S3. After the test, the gas release flux on the surface of the contaminated site is calculated according to the following formula: [V0+(n+1-i)V s ]C t+Δt =[V0+(n+1-i)V s ]C t +jSΔt (1) ΔC=C t+Δt -C t (3) Where V0 is the volume of the metal chamber (1) (m 3 );V s is the volume (m 3 ); n is the number of rigid sampling gas boxes (8); i is the number of sampling times; t is the time (min); Δt is the time interval between two gas samplings (min); C t is the gas concentration in the device at time t (mg / m 3 );C t+△t is the gas concentration at time t+△t (mg / m 3 ); S is the bottom area of ​​the metal chamber (1) (m 2 ); j is the gas release flux on the surface of the contaminated site (mg / m 2 / h); S4. Establish mathematical models for the migration of polluted gases in soil and geomembrane respectively; according to the gas release flux measured on site calculated in step S3, the diffusion coefficient of the gas under field conditions is obtained by inverting the established mathematical model for migration.

7. The method according to claim 6, characterized in that As described in S1, the static box is fixedly installed on the contaminated site and its airtightness is ensured, specifically: When the static box is used on the soil surface, the multifunctional base (4) is inserted into the soil and fixed in an appropriate position with clay, the extended edge (12) of the detachable water tank (3) is connected to the overlapping platform (13) of the multifunctional base (4), the metal chamber (1) is placed in the water injection groove (11), and water is injected into the groove (11) to protect the air tightness of the metal chamber (1); When the static box is used on the surface of the geomembrane, the metal chamber (1) and the multifunctional base (4) are directly fixed on the geomembrane surface with glass glue, and the multifunctional base (4) serves as the surrounding edge of the metal chamber (1). Water is injected into the groove between the two to check the air tightness of the metal chamber (1) on the geomembrane surface.

8. The method according to claim 6, characterized in that The S4 includes: S4.1 Establish a mathematical model for the migration of polluted gases in the soil: The governing equation of the mathematical model of the soil system is expressed as: Among them, C s (z) is the gas concentration in the soil (mg / m 3 ); z is the depth (m); D s is the effective diffusion coefficient of gas in soil (m 2 / s); v is the convection velocity of gas in the soil (m 2 / s); At the top boundary, the soil surface is directly connected to the atmosphere, and the concentration of the gas is assumed to be zero at the top boundary: C s (0)＝0 (5) A constant concentration boundary condition is assumed at the bottom boundary: C s (H)=C0 (6) Where C0 is the gas source concentration at the bottom of the soil (mg / m 3 ); H is soil thickness (m); The gas release flux J on the soil surface can be obtained from this s It is expressed as: Among them, θ g is the soil air porosity; S4.2 Establish a mathematical model for the migration of polluted gases in the geomembrane system: The governing equation of the mathematical model of the geomembrane system is expressed as: Among them, C g (z) is the gas concentration in the geomembrane (mg / m 3 ); z is the depth (m); D g is the diffusion coefficient of gas in geomembrane (m 2 / s); C w (z) is the gas concentration in the pollutant pile under the geomembrane (mg / m 3 );D w is the effective diffusion coefficient of gas in the pollutant pile (m 2 / s); There is a distribution relationship between the gas concentration on the upper and lower surfaces of the geomembrane and the concentration in the membrane: Among them, C g *(z) is the gas concentration on the upper and lower surfaces of the geomembrane (mg / m 3 );S gf To monitor the distribution coefficient between gas and geomembrane; The top and bottom boundary conditions of the geomembrane system are consistent with those of the soil system; the boundary conditions at the interface between the geomembrane and the pollutant pile are expressed as: Where n is the total porosity in the pollutant pile, and h is the thickness of the geomembrane (m); The gas release flux J on the geomembrane surface can be obtained from this g It is expressed as: S4.3 The gas release flux measured on site calculated in step S3 is inverted by equation (7) or equation (11) to obtain the diffusion coefficient of the gas under on-site conditions.

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