Static chamber and method for determining gas flux and diffusion coefficient of a full-surface contaminated site

Abstract

The application discloses a static box and method for measuring full-surface pollution site gas flux and diffusion coefficient. The device mainly comprises a metal chamber, a detachable 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 geomembrane. When used, the multifunctional base is inserted into the soil body on the soil surface and fixed by clay, the sealing water tank is placed on the base and filled with water to keep the sealing of the metal chamber; after the contaminated gas is accumulated in the static box, a rigid sampling gas box is taken out every fixed time, then the surface gas release flux is obtained according to the time-concentration gradient, and the gas diffusion coefficient of the site can be obtained by inverting the release flux through a gas migration model. The device has the advantages of simple structure, simple operation, anti-cracking erosion, full-surface universality, multifunctional combination, wide applicability and the like, and has a popular research background in the background of pollution gas management and improvement of atmospheric environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of urban contaminated site soil gas sampling device, especially relates to a static box and method for determining gas flux and diffusion coefficient of full-surface contaminated site, which can monitor the gas release flux and diffusion coefficient of the surface of the contaminated site. TECHNICAL BACKGROUND

[0002] Urban contaminated sites will produce a lot of contaminated gases, including greenhouse gases and some toxic and harmful malodorous gases, etc., among which the more common gases include methane, carbon dioxide and other greenhouse gases, hydrogen sulfide, ammonia and other toxic and harmful malodorous gases, and benzene, toluene, ethylbenzene and dimethylbenzene (p-, m-, o-dimethylbenzene) and other volatile organic compounds (VOCs). These gases will continue to be released and cause serious impact on the atmospheric environment. The contaminated gases in the contaminated site will migrate through diffusion, penetration and other ways, so it is very important to obtain the release flux and diffusion coefficient of the contaminated gases on the site surface under the field conditions for studying the migration law of the contaminated gases and controlling the contaminated gases.

[0003] At present, the field gas release flux is mainly obtained by static box test monitoring. However, the traditional static box has limitations such as easy erosion and cracking, poor air tightness, and complex operation, and the traditional static box is only suitable for soil surface, while the geomembrane surface of the contaminated site is not suitable for monitoring by the traditional static box.

[0004] Therefore, it is of great significance to seek a static box that is suitable for full-surface for monitoring the release flux and diffusion coefficient of the contaminated gases on the site surface under the field conditions, which can help to study the migration law of the contaminated gases and control the diffusion of the contaminated gases, and has great practical value for the sustainable development of the economy and society. SUMMARY

[0005] The present application aims at the deficiencies of the prior art, and provides a static box and method for determining gas flux and diffusion coefficient of full-surface contaminated site.

[0006] The present application discloses a static box for determining gas flux and diffusion coefficient of full-surface contaminated site, which comprises a metal chamber, a separable water tank, a multifunctional base and a rigid sampling gas box.

[0007] The metal chamber is in a cylindrical structure, a plurality of windows are arranged at different heights on the side surface of the metal chamber, the windows are made of transparent organic glass; a plurality of gas sampling ports and a plurality of standby sampling ports are arranged on the top surface of the metal chamber, the gas sampling ports and the standby sampling ports are both provided with three-way valves, the three-way valves are connected with the rigid sampling gas box through air pipes; and the rigid sampling gas box is provided with two air valves.

[0008] The separable sink is a circular ring structure, which has a water injection groove, and the water injection groove is circumscribed by an extension edge; the bottom of the metal chamber is arranged in the water injection groove;

[0009] The multifunctional base is a circular ring structure, which is arranged with a lap joint platform capable of being connected with the extension edge of the separable sink; the inner diameter of the multifunctional base is greater than the outer diameter of the metal chamber.

[0010] Further, the metal chamber is integrated, not easy to crack, and resistant to high temperature and corrosion, and can adapt to various sampling environments; the view window of the metal chamber is arranged on the opposite side and located close to the top and the bottom, respectively, which can be matched with a portable laser methane detector to directly determine the methane concentration gradient, facilitate rapid acquisition of methane flux, and also take into account the functions of light transmission and observation.

[0011] Further, the separable sink and the multifunctional base can be used simultaneously or separately to adapt to the surface features of different sampling sites, and realize precise setting of the air tightness of the metal chamber.

[0012] Further, the static box can be used for full type surface sampling at the same time. When used on the geomembrane surface, the multifunctional base can be used as the surrounding edge of the metal chamber, and glass glue is used on the outside of the metal chamber and the inside of the multifunctional base to fix it on the geomembrane surface, and water is injected between the metal chamber and the multifunctional base to check the air tightness of the metal chamber, at this time, the separable sink can not be used; when used on the soil surface, the extension edge of the separable sink can be placed on the lap joint platform of the multifunctional base, and the metal chamber can be placed in the water injection groove for sealing by injecting water.

[0013] Further, the rigid sampling gas box is provided with two air valves at the top and the bottom, which can be used for gas box flushing before the test starts, 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 release type, which can be directly used for gas sampling without using a gas pump, facilitating rapid sampling and not affecting the stability of the air pressure in the metal chamber, and the number of rigid sampling gas boxes can be arbitrarily set according to the site conditions and test requirements.

[0014] The application also discloses a method for determining the gas flux and diffusion coefficient of a full surface contaminated site by using the device, which comprises the following steps:

[0015] S1. When the test starts, the gas sampling ports at the top of the metal chamber are all opened and connected with one of the opened air valves of the rigid sampling gas box through the air pipe, and the other air valve and the three-way valve of the standby sampling port are kept closed; the static box is fixedly installed on the contaminated site and the air tightness is ensured;

[0016] S2. After the metal chamber is in good sealing state, gas is accumulated therein; at 0 moment, a rigid sampling gas box is taken and the air valve and the three-way valve are closed; then every 30-60 minutes, a rigid sampling gas box is taken, and the process lasts for 90-180 minutes in total, and the gas sample concentration in the rigid sampling gas box is analyzed by a gas chromatograph;

[0017] S3. After the test is completed, 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] Wherein, 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 sampling times; t is the time (min) ; △t is the time interval of two gas sampling (min) ; C t is the gas concentration in the device at t moment (mg / m 3 ) ; C t+△t is the gas concentration at t+△t moment (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. The migration mathematical models of the contaminated gas in the soil and the geomembrane are respectively established; according to the measured gas release flux calculated in the step S3, the diffusion coefficient of the gas under the site condition is obtained by the established migration mathematical model.

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

[0023] The device and the method of the present application can measure the gas release flux on the contaminated site with different surfaces, can directly sample without using a gas pump to avoid affecting the stability of the air pressure in the metal chamber, and can also be matched with a portable gas detector for rapid determination. Compared with the traditional static box, the device of the present application has the advantages of simple structure, easy operation, anti-cracking erosion, universal surface, multifunctional combination, wide applicability and the like, and has important significance for the release, diffusion and control of the contaminated gas under the background of the increasingly serious influence of the contaminated gas. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0026] Figure 3 is a schematic diagram of the use of a static chamber on the surface of a geomembrane for measuring gas flux and diffusion coefficient of a full-surface contaminated site;

[0027] Figure 4 is a schematic diagram of the use of a static chamber on the surface of a geomembrane for measuring gas flux and diffusion coefficient of a full-surface contaminated site;

[0028] Figure 5 is a schematic diagram of the use of a static chamber on the surface of a geomembrane for measuring gas flux and diffusion coefficient of a full-surface contaminated site;

[0029] Figure 6 is a schematic diagram of the use of a static chamber on the surface of a geomembrane for measuring gas flux and diffusion coefficient of a full-surface contaminated site;

[0030] Figure 7 is a schematic diagram of the use of a static chamber on the surface of a geomembrane for measuring gas flux and diffusion coefficient of a full-surface contaminated site.

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

[0032] The present application will be further described and explained with reference to the accompanying drawings and examples. The following examples are taken as examples of 4 times of sampling in tests. The technical features of each embodiment of the present application can be combined accordingly without conflict.

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

[0034] As Figure 3 shown, the metal chamber 1 is provided with 4 gas sampling ports 5 and 3 standby sampling ports 10 on the top surface, the gas sampling ports 5 and standby sampling ports 2 are provided with three-way valves 6, the three-way valves 6 are connected with rigid sampling gas boxes 8 through air pipes 7; the rigid sampling gas boxes 8 are provided with two air valves 9;

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

[0036] As Figure 5 shown, the multifunctional base 4 is a circular ring structure, which is provided with a lap joint platform 13 and can be connected with the extension edge 12 of the detachable water tank 3.

[0037] In one embodiment of the present application, the metal chamber 1 is integrated and can be made of stainless steel and other metal materials, which is not easy to crack, resistant to high temperature and corrosion, and can adapt to various sampling environments; the windows 2 of the metal chamber 1 are arranged on the opposite sides and located near the top and bottom respectively, which can be matched with a portable laser methane detector to directly determine the methane concentration gradient, facilitate rapid acquisition of methane flux, and also can be used for light transmission and observation.

[0038] In one embodiment of the present application, the detachable water tank 3 and the multifunctional base 4 can be used simultaneously or separately to adapt to the surface features of different sampling sites and realize precise setting of the airtightness of the metal chamber 1.

[0039] In one embodiment of the present application, when used on the geomembrane surface, as Figure 2 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 greater than the outer diameter 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 geomembrane surface, and water is injected between the metal chamber 1 and the multifunctional base 4 to check the airtightness of the metal chamber 1; when used on the soil surface, as Figure 1 shown, the extension edge 12 of the detachable water tank 3 can be placed on the lap joint platform 13 of the multifunctional base 4, and the metal chamber 1 can be placed in the water injection groove 11 for sealing by water injection.

[0040] In one embodiment of the present application, the rigid sampling gas box 8 is provided with two vent valves 9 at the top and bottom, which can be used for flushing the gas box before the test begins, and for connecting with the metal chamber 1 and sampling and detecting the gas. The rigid sampling gas box 8 and the metal chamber 1 are quick-release type, which can be directly used for gas sampling without using a gas pump, facilitating rapid sampling and not affecting the stability of the gas pressure in the metal chamber 1. The number of rigid sampling gas boxes 8 can be arbitrarily set according to the site conditions and test requirements.

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

[0042] S1. Device installation. When the test begins, the gas sampling ports 5 at the top of the metal chamber 1 are all opened and connected with one of the open vent valves 9 of the rigid sampling gas box 8 through the gas pipe 7, and the other vent valve 9 and the three-way valve 6 of the standby sampling port 10 are kept closed. When used on the surface of soil, 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 with the lap joint 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 airtightness of the metal chamber 1. When used on the surface of geomembrane, the metal chamber 1 and the multifunctional base 4 are directly fixed on the surface of the geomembrane with glass cement, the multifunctional base 4 can serve as the surrounding edge of the metal chamber 1, and water is injected into the groove between the two to check the airtightness of the metal chamber 1 on the surface of the geomembrane.

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

[0044] S3. Release flux calculation. After the test is completed, 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] Wherein, 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 sampling number; t is the time (min) ; Δt 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 of the contaminated site surface (mg / m 2 / h).

[0048] S4. Diffusion coefficient calculation. The mathematical models of the migration of the contaminated gas in the soil and the geomembrane are respectively established. S4.1 The control equation of the mathematical model of the soil system is represented as

[0049]

[0050] wherein 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 the gas in the soil (m 2 / s) ; v is the convection velocity of the gas in the soil (m 2 / s).

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

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

[0053] At the bottom boundary, it is assumed to be a constant concentration boundary condition:

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

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

[0056] The gas release flux J s of the soil surface is represented as:

[0057]

[0058] wherein θ g is the soil air porosity.

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

[0060]

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

[0062] The concentration of the gas on the upper and lower surfaces of the geomembrane has a distribution relationship with the concentration in the membrane:

[0063]

[0064] Wherein, C g *(z) is the concentration of the gas on the upper and lower surfaces of the geomembrane (mg / m 3 ) ; S gf is the distribution coefficient between the monitoring gas and the 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 waste pile are expressed as:

[0066]

[0067] Wherein, n is the total porosity in the waste pile, and h is the thickness of the geomembrane (m).

[0068] The gas release flux J g on the surface of the geomembrane is expressed as:

[0069]

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

[0071] In one specific embodiment of the present application, four samplings are performed, and the hydrogen sulfide gas release flux is monitored by using the device on the working surface and the geomembrane surface of the landfill, and the hydrogen sulfide gas release flux on different surfaces is measured and calculated as shown in Table 1, Figure 6 The diffusion coefficient of the gas in different media under on-site conditions obtained by inversion is shown in Table 2, Figure 7 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 waste pile is also much greater than the diffusion coefficient on the geomembrane.

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

[0073]

[0074]

[0075] The above listed are only specific embodiments of the present application. It is clear that the present application is not limited to the above embodiments, but can have many variations. All variations that can be directly derived or conceived by those of ordinary skill in the art from the disclosure of the present application should be considered as falling within the scope of the present application.

Claims

1. A static chamber for determining the gas flux and the diffusion coefficient of a full-surface contaminated site, 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 in a cylindrical structure, and a plurality of windows (2) are arranged on the side surface of the metal chamber (1) at different heights, wherein the windows (2) are made of transparent organic glass; a plurality of gas sampling ports (5) and a plurality of standby sampling ports (10) are arranged on the top surface of the metal chamber (1), and the gas sampling ports (5) and the standby sampling ports (10) are respectively provided with three-way valves (6), the three-way valves (6) are connected with the rigid sampling gas box (8) through gas pipes (7), and the rigid sampling gas box (8) is provided with two air valves (9). The detachable water tank (3) is in a circular ring structure, has a water injection groove (11), and an extension edge (12) is arranged outside the water injection groove (11); the bottom of the metal chamber (1) can be arranged in the water injection groove (11) and sealed by water injection. The multifunctional base (4) is in a circular ring structure, and a lap joint platform (13) is arranged therein and used for being connected with the extension edge (12) of the detachable water tank (3); the inner diameter of the multifunctional base (4) is greater than the outer diameter of the metal chamber (1).

2. The static chamber for determining the gas flux and the diffusion coefficient of a full-surface contaminated site according to claim 1, characterized in that, The metal chamber (1) is integrated; the windows (2) of the metal chamber (1) are arranged on opposite side surfaces and located close to the top and the bottom, and are matched with a portable laser methane detector to directly determine the methane concentration-time gradient.

3. The static chamber for determining the gas flux and the diffusion coefficient of a full-surface contaminated site according to claim 1, characterized in that, The detachable water tank (3) and the multifunctional base (4) can be used simultaneously or separately to adapt to the surface features of different sampling sites and realize accurate setting of the air tightness of the metal chamber (1).

4. The static chamber for determining the gas flux and diffusion coefficient of the full-surface contaminated site according to claim 3, characterized in that, When used on the geomembrane surface, the multifunctional base (4) is used as a 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 be fixed on the geomembrane surface, 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 extension edge (12) of the detachable water tank (3) is placed on the lap joint 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 chamber for determining the gas flux and the diffusion coefficient of a full-surface contaminated site according to claim 1, characterized in that, The top and the bottom of the rigid sampling gas box (8) are provided with two air valves (9), the air valves (9) are used for gas box flushing before the test starts, connection with the metal chamber (1), and gas sampling and detection, the rigid sampling gas box (8) and the metal chamber (1) are fast-release connected, can be directly used for gas sampling without using a gas pump, are convenient for rapid sampling and do not affect the air pressure stability in the metal chamber (1).

6. A method for determining the gas flux and the diffusion coefficient of a full surface contaminated site based on the static chamber according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: 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 with one of the opened air valves (9) of the rigid sampling gas box (8) through the gas pipes (7), and the other air valve (9) and the three-way valve (6) of the standby sampling port (10) are kept closed; the static chamber is fixedly installed on the contaminated site and the air tightness is ensured. S2. After the metal chamber (1) is in good sealing state, the gas accumulates therein; at 0 time, take a rigid sampling gas box (8) and close the air valve (9) and the three-way valve (6); then take a rigid sampling gas box (8) every 30-60 minutes, for a total of 90-180 minutes, analyze the gas sample concentration in the rigid sampling gas box (8) by a gas chromatograph; S3. After the test is completed, 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) AC = C t+Δt - C t (3) Where V0 is the volume (m³) of the metal chamber (1). 3 );V s It is the volume (m³) of a single rigid sampling gas cell (8). 3 ); n is the number of rigid sampling gas boxes (8); i is the number of samplings; t is the time (min); Δt is the time interval between two gas samplings (min); C t The gas concentration (mg / m³) in the device at time t. 3 ); C t+△t It is the gas concentration (mg / m³) at time t+Δt. 3 S is the bottom area (m²) of the metal chamber (1). 2 j is the surface gas emission flux of the contaminated site (mg / m³). 2 / h); S4. The migration mathematical models of the contaminated gas in the soil and the geomembrane are respectively established; the gas diffusion coefficient under the field conditions is obtained by the established migration mathematical model according to the field measured gas release flux calculated in the step S3.

7. The method of claim 6, wherein, The static box is fixedly installed on the contaminated site and the air tightness is ensured according to the step S1, specifically: When the static box is used on the soil surface, the multifunctional base (4) is inserted into the soil body and fixed in the appropriate position by clay, the extended edge (12) of the detachable water tank (3) is connected with the lap joint 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 geomembrane surface, the metal chamber (1) and the multifunctional base (4) are directly fixed on the geomembrane surface by glass cement, the multifunctional base (4) is used as the surrounding edge of the metal chamber (1), and 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 of claim 6, wherein, The step S4 includes: S4.1 The migration mathematical model of the contaminated gas in the soil is established: The control equation of the mathematical model of the soil system is represented as: where C s (z) is the concentration of the gas in the soil (mg / m 3 ); z is the depth (m); D s is the effective diffusion coefficient of the gas in the soil (m 2 / s); v is the convective velocity of the gas in the soil (m 2 / s); At the top boundary, the soil surface is directly connected with the atmosphere, and it is assumed that the concentration of the gas at the top boundary is zero: C s (0)＝0 (5) At the bottom boundary, it is assumed to be a constant concentration boundary condition: C s (H) = Co (6) wherein Co is the concentration of the gas source at the bottom of the soil (mg / m 3 ); H is the thickness of the soil (m); From this the gas release flux J from the soil surface can be obtained s is represented as: where θ g is the soil air porosity; S4.2 The migration mathematical model of the contaminated gas in the geomembrane system is established: The control equation of the mathematical model of the geomembrane system is represented as: where C g (z) is the concentration of the gas in the geomembrane (mg / m 3 ); z is the depth (m); D g is the diffusion coefficient of the gas in the geomembrane (m 2 / s); C w (z) is the concentration of the gas in the waste pile below the geomembrane (mg / m 3 ); D w is the effective diffusion coefficient of the gas in the waste pile (m 2 / s); There is a distribution relationship between the gas concentrations on the upper and lower surfaces of the geomembrane and the concentration in the membrane: wherein C g (z) is the concentration of the gas on the upper and lower surfaces of the geomembrane (mg / m 3 ); S gf is the distribution coefficient between the monitoring gas and the geomembrane; The top and bottom boundary conditions of the geomembrane system are consistent with the boundary conditions of the soil system; the boundary condition at the interface between the geomembrane and the contaminated pile is represented as: Wherein, n is the total porosity in the contaminated pile, and h is the thickness of the geomembrane (m); From this the gas release flux J of the geomembrane surface can be obtained g is represented as: The gas diffusion coefficient under the field conditions is obtained by formula (7) or formula (11) according to the field measured gas release flux calculated in the step S3.

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