Method and system for analyzing dnapsl contamination in a typical groundwater system

Abstract

The present application relates to the method and system for analyzing DNAPLs pollution in typical groundwater system, in particular to collecting the information of DNAPLs pollution research area, determining the research area range based on the information of DNAPLs pollution research area, generalizing the characteristics affecting the distribution of DNAPLs pollution, judging the groundwater flow direction and flow state, determining the corresponding initial condition, boundary condition, recharge condition and discharge condition, constructing the typical groundwater system, and identifying the properties of DNAPLs pollutants, pollution source, pollution release mechanism and pollution source structure in the groundwater system based on the typical groundwater system, determining the migration path and migration conversion mechanism of DNAPLs in the groundwater system, constructing the DNAPLs pollution model in the typical groundwater system, and then analyzing the DNAPLs pollution by using the numerical model of DNAPLs migration; the present application solves the problem that the conceptual model established by the research on DNAPLs pollution in the groundwater system is greatly different from the overall accuracy of the actual DNAPLs pollution in the groundwater system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of DNAPLs pollution analysis in groundwater, and particularly relates to a DNAPLs pollution analysis method and system in a typical groundwater system. BACKGROUND

[0002] There are various types of pollutants in a groundwater system, and the harm caused by organic pollutants is the most serious and the most difficult to treat and repair. Since the solubility of most organic pollutants in water is small, such organic pollutants are commonly known as non-aqueous phase liquids (NAPLs), and the ones with a density greater than water are called DNAPLs (Dense NAPLs), i.e., heavy non-aqueous phase liquids.

[0003] DNAPLs pollutants have various sources, including halogenated hydrocarbon organic solvents such as tetrachloroethylene (PCE), trichloroethylene (TCE), and other industrial pollution sources such as polychlorinated biphenyl (PCB), creosote (Creosote), coal tar (Coal Tar), and mixed organic solvents. DNAPLs pollutants have characteristics such as low water solubility, weak migration, and difficult degradation, can pass through the unsaturated zone into the saturated aquifer, and slowly and persistently dissolve into the surrounding water, resulting in an increasing pollution range and causing great harm to the safety of the groundwater environment. Therefore, research on DNAPLs pollutants in a groundwater system, especially the establishment of a DNAPLs pollution model, can provide a scientific basis for pollution liability identification by relevant departments, and provide strong support for subsequent scientific monitoring and treatment and prevention of DNAPLs-polluted groundwater, which is of great significance to the safety of groundwater resources and the environment and the realization of sustainable development of human society.

[0004] However, current research on DNAPLs pollution in a groundwater system generally studies DNAPLs pollution in a single structural layer of the groundwater system, for example, some only study DNAPLs pollution in a porous medium structural layer of the groundwater system, and some only study DNAPLs pollution in a karst medium structural layer of the groundwater system. In fact, the migration process of DNAPLs in a typical key zone often includes complex heterogeneous structures, some of which include multiple porous aquifers, and some of which include porous and fractured composite media. Therefore, there is still a lack of complete understanding of the migration, dissolution, volatilization, adsorption, degradation, and multi-coupling processes of DNAPLs pollutants in a groundwater system, which leads to a large difference between the current DNAPLs pollution model in a groundwater system and the actual DNAPLs pollution in the groundwater system in terms of overall accuracy.

[0005] The research finds that the DNAPLs pollutants have a density greater than water, and after leaking from the surface, the DNAPLs pollution source area formed can penetrate the entire groundwater system, and the research on the DNAPLs pollution in a single structure layer of the groundwater system is insufficient to accurately establish the DNAPLs pollution model in the water system, and it is necessary to take the typical groundwater system composed of the aeration zone, the phreatic water-bearing layer, the porous confined water-bearing layer and the bedrock weathering fissure medium and other structure layers as a whole framework to carry out the DNAPLs pollution research, that is, taking different structure layers of the groundwater system as a whole to study the DNAPLs pollution, establishing a DNAPLs pollution model in the actual and complex groundwater system, so that the established DNAPLs pollution model in the groundwater system is in line with the actual DNAPLs pollution in the groundwater system, and for this purpose, a DNAPLs pollution analysis method and system in a typical groundwater system are proposed. SUMMARY

[0006] In order to comprehensively understand, recognize and master the DNAPLs in the groundwater system, it is necessary to take different structure layers of the groundwater system as a whole to study the DNAPLs pollution based on the scientific thought of the system, and establish a DNAPLs pollution model in a typical groundwater system to analyze the DNAPLs pollution.

[0007] A technical solution for achieving the object of the application is a DNAPLs pollution model establishment method in a typical groundwater system, comprising the following steps:

[0008] S1, collecting DNAPLs pollution research area information;

[0009] The DNAPLs pollution research area information collection sources include: monitoring data of the atmosphere, soil, surface water and groundwater in the research area; comprehensive or special investigation and research reports, monographs, papers and charts and the like of topography, geomorphology, geology, hydrogeology and the like; field experiment and laboratory test data, necessary supplementary field investigation, monitoring sampling, drilling and geophysical measurement data, related intermediate comprehensive analysis research results; land use, economic and social development and investigation and statistical data related to DNAPLs pollution sources and the like;

[0010] S2, based on the DNAPLs pollution research area information, determining the DNAPLs pollution research area range, generalizing the characteristics influencing the DNAPLs pollution distribution, judging the groundwater flow direction and flow state and determining the initial conditions, boundary conditions, recharge conditions and discharge conditions of the groundwater, and constructing a typical groundwater system model;

[0011] Wherein the water flow direction and flow state include laminar flow, turbulent flow, planar flow and three-dimensional flow; the initial conditions include water level, flow and pollutant concentration distribution in the study area; the boundary conditions include the type of natural boundary or man-made boundary, i.e. determining which type of boundary belongs to one, two and three types of boundaries, and determining the corresponding numerical value; the recharge condition and discharge condition include the recharge source, the discharge mode, the path of recharge and discharge, the recharge amount and the discharge amount, etc.

[0012] S3, on the basis of the typical groundwater system model, identifying DNAPLs pollutant properties, DNAPLs pollution sources, DNAPLs pollution release mechanism and DNAPLs pollution source structure, determining the migration path and migration and transformation mechanism of DNAPLs pollutants in the typical groundwater system, and constructing a DNAPLs pollution model in the typical groundwater system;

[0013] Wherein, the DNAPLs pollutant properties refer to its physical and chemical properties, which are embodied in related physicochemical parameters, including molecular weight, density, vapor pressure, solubility, n-octanol or water partition coefficient, n-octanol or air partition coefficient, Henry's constant, etc.; the DNAPLs pollution source refers to the source of DNAPLs pollutants in soil-groundwater; the DNAPLs pollution release mechanism refers to the mechanism of DNAPLs entering the soil-groundwater environment; and the DNAPLs pollution source structure refers to the existence form and distribution of NAPL phase in the groundwater system;

[0014] S4, on the basis of the DNAPLs pollution model in the typical groundwater system, using the numerical model of DNAPLs migration to analyze the DNAPLs pollution.

[0015] According to the above technical scheme, the DNAPLs pollution research area information includes DNAPLs pollution research area geological information, hydrogeological information, hydro-meteorological information, drilling information and water level information;

[0016] The geological information: namely the geological conditions of the research area, which is divided into two aspects of stratum lithology and geological structure;

[0017] The hydrogeological information: including groundwater occurrence and distribution law, groundwater recharge, runoff and discharge conditions, groundwater dynamic characteristics and groundwater chemical characteristics;

[0018] The hydro-meteorological information: including annual average temperature, multi-year average precipitation, multi-year average evaporation and climate type in the research area; river, belonging to the river system, drainage area, annual runoff volume, salinity, etc. in the research area;

[0019] The drilling information: including drilling position, hole diameter, depth, elevation, etc.;

[0020] The water level information: combined with the drilling, the pumping test can be carried out, the water level amplitude and flow are recorded, and the hydrogeological parameters can be obtained;

[0021] Among them, the hydrogeological information accurately describes the non-homogeneity of the medium by using the three-dimensional geological statistical method, and the distribution of the spatial classification variable is simulated by the transfer probability and Markov chain method.

[0022] According to the above technical scheme, the characteristics affecting the distribution of DNAPLs pollution include medium type, aquifer type, spatial distribution of aquifer, and spatial distribution of relative aquiclude continuity and tendency.

[0023] Medium type: generally divided into pore, fracture and karst medium.

[0024] Aquifer type: according to the rock layer transmission and water supply properties of the saturated zone, it is divided into aquifer, aquiclude and weakly permeable layer; according to the burial condition, it is divided into phreatic aquifer and confined water aquifer; according to the aquifer medium, it is divided into pore aquifer, fracture aquifer and karst aquifer; it can also be divided into heterogeneous aquifer and homogeneous aquifer.

[0025] Spatial distribution of aquifer: each aquifer is distinguished in the vertical direction, and the layer thickness is recorded; the distribution area is recorded in the horizontal direction.

[0026] Spatial distribution of relative aquiclude continuity and tendency: the lithology data at different depths obtained by continuous drilling, if the continuous drilling obtains the stratum with relatively weak permeability, the aquiclude is continuous, otherwise it may be discontinuous; the tendency can be determined by the position of the weakly permeable stratum obtained by different drilling, and the aquiclude obtained by different drilling is connected to see the general trend of the aquiclude.

[0027] According to the above technical scheme, the structure of the typical groundwater system includes a heterogeneous pore medium vadose zone, a phreatic aquifer, a confined aquifer and a bedrock weathered fracture medium.

[0028] Among them, the vadose zone of the heterogeneous pore medium is also called the unsaturated zone, the groundwater system refers to the boundary limited, unified hydraulic connection of the aquifer geological body, which is the basic unit of groundwater resource evaluation, and the basic unit of groundwater and its combination with water quantity, water quality input, migration and output.

[0029] According to the above technical scheme, the migration path of the DNAPLs pollutant in the typical groundwater system:

[0030] Under the comprehensive action of gravity, capillary pressure and viscous force, the DNAPLs pollutant leaks from the surface into the underground environment, and can continuously migrate downward in water from the unsaturated zone to the saturated aquifer, and to the bottom bedrock.

[0031] In the process, the heterogeneous spatial variability of the water-bearing medium can cause lateral spreading, preferential flow and local accumulation of the DNAPLs pollutants; in the unsaturated zone, the DNAPLs pollutants can penetrate the lens composed of low-permeability medium, and can also exist in the gaseous phase due to volatilization; in the saturated zone, the DNAPLs pollutants generally accumulate on the lens composed of low-permeability medium and produce flow around, and when the vertically continuous DNAPLs pollutants can overcome the capillary resistance, they can also penetrate the relatively thin low-permeability interlayer and continue to migrate downward; the DNAPLs pollutants accumulated on the weakly permeable layer or the impervious floor will flow to the low-lying place along the slope of the corresponding weakly permeable layer or the impervious floor, and thus the situation that the flow direction of the DNAPLs pollutants is opposite to the flow direction of the groundwater can occur.

[0032] According to the technical scheme, the migration and transformation mechanism of the DNAPLs pollutants in the typical groundwater system is a mechanism affecting the migration and transformation process of the DNAPLs in the soil-groundwater system, including physical mechanisms, chemical mechanisms and biological mechanisms, and coupling between different mechanisms.

[0033] In the process, the heterogeneous spatial variability of the water-bearing medium can cause lateral spreading, preferential flow and local accumulation of the DNAPLs pollutants; in the unsaturated zone, the DNAPLs pollutants can penetrate the lens composed of low-permeability medium, and can also exist in the gaseous phase due to volatilization; in the saturated zone, the DNAPLs pollutants generally accumulate on the lens composed of low-permeability medium and produce flow around, and when the vertically continuous DNAPLs pollutants can overcome the capillary resistance, they can also penetrate the relatively thin low-permeability interlayer and continue to migrate downward; the DNAPLs pollutants accumulated on the weakly permeable layer or the impervious floor will flow to the low-lying place along the slope of the corresponding weakly permeable layer or the impervious floor, and thus the situation that the flow direction of the DNAPLs pollutants is opposite to the flow direction of the groundwater can occur.

[0034] The migration and transformation mechanism of the DNAPLs pollutants in the typical groundwater system specifically includes:

[0035] The DNAPLs pollutants migrate downward through the aeration zone, and their existence forms in the infiltration process are various, including the gaseous phase volatilized in the air in the aeration zone, the immobile phase intercepted on the migration path and not continuously distributed in the pores / fractures, and the mobile phase in the continuous state accumulated on the low-permeability medium such as the weakly permeable layer / bedrock floor, and the latter two existence forms of the DNAPLs are collectively referred to as the NAPL phase or the organic phase.

[0036] The continuous and discontinuous organic-phase DNAPLs entering the groundwater system will continuously dissolve into water to form the dissolved-phase DNAPLs, and the dissolved-phase DNAPLs will also undergo adsorption and degradation reactions while flowing with the groundwater, causing the DNAPLs pollution plume to continuously expand in the flow direction of the groundwater, and under the condition that the time is sufficient, all the organic-phase DNAPLs can disappear, and only the dissolved-phase DNAPLs remain.

[0037] The evolution of DNAPL plume is controlled by the comprehensive action of physical, chemical and biological processes, including two categories of destructive and non-destructive comprehensive actions.

[0038] The non-destructive comprehensive actions include convection, diffusion, volatilization, dilution and adsorption, which change the concentration of pollutants in different media and different phases, but do not reduce the total amount of pollution. The destructive comprehensive actions include biological degradation and non-biological degradation. The process of microorganisms decomposing DNAPL pollutants through direct oxidation, aerobic cometabolism or reductive dechlorination is biological degradation; the reductive process of DNAPL pollutants in the stratum mediated by active minerals is non-biological degradation. The destructive action not only can reduce the concentration of pollutants, but also can decompose pollutants, realizing the reduction of the total amount of pollutants;

[0039] According to the above technical scheme, the DNAPLs pollution model construction steps in the typical groundwater system are:

[0040] Different structural layers in the groundwater system are taken as a whole, the multi-coupling process of DNAPL pollutants in different structural layers is clarified, and the DNAPLs pollution model of the typical groundwater system is established according to the migration path and migration and transformation mechanism of DNAPLs pollutants in the typical groundwater system.

[0041] According to the above technical scheme, the numerical model of DNAPLs migration uses the T2VOC module in the TOUGH2 algorithm to calculate volatile organic compounds; the T2VOC module assumes that air, water and organic chemicals are included, and air, water and organic chemicals are distributed in any one or more phases of gas phase, water phase and NAPL phase, and the gas phase, water phase and NAPL phase are unified as β phase, and the mass balance equation of DNAPLs migration is:

[0042]

[0043] Where t is time, φ is porosity, S β is the saturation of β phase, ρ β is the density of β phase, X β κ is the mass fraction of component κ in β phase, V n is any flow region, Γ n is the surface area, k is the absolute permeability rate, k rβ is the relative permeability of β phase, μ β is the dynamic viscosity of β phase, P β is the fluid pressure in β phase, g is the acceleration of gravity, n is the unit inward normal vector, q κ is the rate of heat generation per unit volume, in formula (1), the pressure P β and the saturation Sβ defined by capillary pressure function and relative permeability function, which are called relative permeability-moisture content constitutive relationship, i.e. constitutive model;

[0044] For multiphase flow simulation, capillary pressure and relative permeability are important factors to determine fluid migration and distribution in groundwater system, Stone model and Parker model are used as constitutive model to simulate DNAPLs migration process, where Stone model is used to define relative permeability function, Parker model is used to define capillary pressure function;

[0045] Stone model expression is as follows:

[0046]

[0047]

[0048]

[0049] S w +S g +S n =1

[0050] Where, k rg , k rw , k rn are relative permeability of gas phase, water phase and NAPL phase respectively, S w , S g , S n are saturation of water phase, gas phase and NAPL phase respectively, S wr , S gr , S nr are remaining saturation of water phase, gas phase and NAPL phase respectively, f is fitting parameter;

[0051] Parker model expression is as follows:

[0052]

[0053]

[0054]

[0055]

[0056] Where, S we is effective saturation of water phase, S le is effective saturation of liquid phase, S m is remaining saturation of liquid phase, P cgn is gas phase-DNAPL capillary pressure, Pcgw is the gas-water capillary pressure, a gn is the inverse of the gas-DNAPL air entry pressure, a nw is the inverse of the DNAPL-water liquid entry pressure, m, f are fitting parameters, S n , S w are the saturations of the NAPL and water phases, respectively, g is the gravitational acceleration.

[0057] The T2VOC module ignores dynamic dispersion of the fluid, only simulates molecular diffusion in the gas phase, and mass transfer in all phases is described by convection. It is assumed that the fluid phase of each element is in local chemical equilibrium, so that interphase mass transfer between all phases can be described by equilibrium partitioning relationships. Water in the NAPL phase is ignored, and the relevant mechanisms of NAPL phase mass transfer include evaporation state NAPL, dissolved state NAPL, and gas-liquid mass transfer.

[0058] The DNAPLs pollution analysis system in a typical groundwater system includes:

[0059] An information collection module is configured to collect information of a DNAPLs pollution study area.

[0060] A typical groundwater system construction module is configured to determine a DNAPLs pollution study area range based on the information of the DNAPLs pollution study area, to generalize characteristics affecting DNAPLs pollution distribution, to determine groundwater flow direction and flow state, and to determine initial conditions, boundary conditions, recharge conditions, and discharge conditions of the groundwater, and to construct a typical groundwater system model.

[0061] A DNAPLs pollution model construction module is configured to identify DNAPLs pollutant properties, DNAPLs pollution sources, DNAPLs pollution release mechanisms, and DNAPLs pollution source area structures based on the typical groundwater system model, to determine migration paths and migration and transformation mechanisms of the DNAPLs pollutants in the typical groundwater system, and to construct a DNAPLs pollution model in the typical groundwater system.

[0062] A DNAPLs pollution analysis module is configured to analyze DNAPLs pollution by using a numerical model of DNAPLs migration based on the DNAPLs pollution model in the typical groundwater system.

[0063] An output end of the information collection module is connected to an input end of the typical groundwater system construction module, an output end of the typical groundwater system construction module is connected to an input end of the DNAPLs pollution model construction module, and an output end of the DNAPLs pollution model construction module is connected to an input end of the analysis module.

[0064] Compared with the prior art, the present application has the following advantages:

[0065] The DNAPLs pollution analysis method and system in the typical groundwater system of the present application carries out DNAPLs pollution research by taking the typical groundwater system composed of multiple structural layers underground as a whole framework, i.e. taking different structural layers of the groundwater system as a whole to research DNAPLs pollution, and establishes a DNAPLs pollution model in a complex groundwater system in accordance with the actual situation, so as to achieve that the established DNAPLs pollution model in the groundwater system conforms to the actual DNAPLs pollution situation in the groundwater system, can provide a scientific basis for pollution liability identification by relevant departments, at the same time, can provide strong support for subsequent scientific monitoring and treatment and prevention of DNAPLs pollution in groundwater, has important significance for guaranteeing groundwater resource environmental safety and realizing human social sustainable development, and solves the problem that the conceptual model established by the current research on DNAPLs pollution in the groundwater system is often quite different from the overall accuracy of the actual DNAPLs pollution situation in the groundwater system. BRIEF DESCRIPTION OF DRAWINGS

[0066] Figure 1 is a migration path diagram of DNAPLs pollutants in a typical groundwater system in an embodiment of the present application.

[0067] Figure 2 is a migration and transformation mechanism diagram of DNAPLs pollutants in a typical groundwater system in an embodiment of the present application.

[0068] Figure 3 is a DNAPLs pollution schematic diagram in a typical groundwater system composed of a pore aquifer, a karst aquifer and a bedrock fissure in an embodiment of the present application. DETAILED DESCRIPTION

[0069] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0070] It is found by analysis that the current research on DNAPLs pollution in groundwater system generally adopts the research on DNAPLs pollution in a single structural layer of the groundwater system, for example, some only research DNAPLs pollution in the porous medium structural layer of the groundwater system, and some only research DNAPLs pollution in the karst medium structural layer of the groundwater system. In fact, the migration process of DNAPLs in a typical key zone often includes a complex heterogeneous structure, some of which include multiple porous aquifers, and some of which include porous and fissured composite media. Therefore, at present, the migration, dissolution, volatilization, adsorption, degradation and multi-coupling process of DNAPLs pollutants in the groundwater system are still lacking of complete understanding, which leads to a large difference between the current DNAPLs pollution model in the groundwater system and the actual DNAPLs pollution in the groundwater system. It is found that the density of DNAPLs pollutants is greater than that of water, and after the leakage from the ground surface, the DNAPLs pollution source area formed can penetrate the entire groundwater system. The research on DNAPLs pollution in a single structural layer of the groundwater system is insufficient to accurately establish a DNAPLs pollution model in the groundwater system, and it is necessary to take the "typical groundwater system" composed of the structural layers such as the aeration zone, the porous phreatic aquifer, the porous confined aquifer and the bedrock weathered fissured medium as a whole framework to carry out the DNAPLs pollution research, that is, to take different structural layers of the groundwater system as a whole to research the DNAPLs pollution, and to establish a DNAPLs pollution model in the groundwater system which conforms to the actual situation and is complex, so as to achieve that the established DNAPLs pollution model in the groundwater system conforms to the actual DNAPLs pollution in the groundwater system. Therefore, a DNAPLs pollution analysis method and system in a typical groundwater system are proposed.

[0071] The DNAPLs pollution analysis method in a typical groundwater system comprises the following steps:

[0072] Collecting DNAPLs pollution research area information;

[0073] In an embodiment, the collection of DNAPLs pollution research area information in step S1 includes DNAPLs pollution research area geological information, hydrogeological information, hydro-meteorological information, drilling information and water level information.

[0074] The geological information is the geological conditions of the research area, which is divided into two aspects of stratum lithology and geological structure.

[0075] The stratum lithology can be divided into several boundaries, a boundary is divided into several systems, and a system is divided into several groups. When describing each group, the following information is included: the specific location of the stratum outcrop, the lithology, the thickness, whether it contains a lens, and the contact relationship with the overlying or underlying stratum; the geological structure includes the regional tectonic position, and the typical folds and fault structures in the research area.

[0076] In the lithology, color, granularity, composition, structure are included, and whether there are special minerals such as gravel, chert, oolitic particles; in the fold structure, starting, axis length, dip angle, whether there is rock body intrusion, etc. are included; in the fracture structure, starting, full length, tendency, strike, dip angle, information of rock blocks intercalated in the middle, etc. are included.

[0077] The hydrogeological information includes the occurrence and distribution law of groundwater, the recharge, discharge and dynamic characteristics of groundwater, and the chemical characteristics of groundwater. The information given in the first point includes the type of groundwater, the characteristics of the aquifer, and preferably the hydrogeological map and hydrogeological section; the information given in the second point includes the recharge, discharge and flow direction of groundwater in the study area; the information given in the third point includes the annual variation amplitude of water level in the study area, the monthly water level monitored by the wells in the study area, and the statistical rainfall, and the relationship between the two; the fourth point is based on the water quality analysis results, the chemical characteristics of the study area;

[0078] In the groundwater type, according to the burial condition, it is divided into phreatic water, confined water and upper perched water; according to the water-bearing medium, it is divided into pore water, fissure water and karst water;

[0079] The characteristics of the aquifer include distribution, thickness, lithology, whether there are local fractures, dissolution pores, dissolution caves, and water abundance, etc.; the recharge of groundwater includes rainfall or lateral runoff or artificial; the discharge includes evaporation or outflow or spring or artificial.

[0080] The hydro-meteorological information includes the average annual temperature, the average annual precipitation, the average annual evaporation, and the climate type in the study area; the river in the study area, the water system to which it belongs, the basin area, the total annual runoff, and the mineralization, etc.

[0081] The drilling information includes the drilling location, hole diameter, depth, elevation, etc. Through drilling sampling, for the drilling sediment, the stratum and lithology in which it is located can be recorded, and the lithology includes water permeability or water resistance.

[0082] The water level information: combined with the drilling, pumping test can be carried out, the water level amplitude and flow rate are recorded, and the hydrogeological parameters can be calculated.

[0083] Based on the DNAPLs pollutant research area information, the DNAPLs pollutant research area range is determined, the characteristics affecting the distribution of DNAPLs pollutants are generalized, the groundwater flow direction and flow state are judged, and the initial conditions, boundary conditions, recharge conditions and discharge conditions of groundwater are determined, and a typical groundwater system model is constructed;

[0084] In an embodiment, the characteristics affecting the distribution of DNAPLs pollutants include medium type, aquifer type, spatial distribution of aquifer, and spatial distribution of relative aquiclude continuity and tendency.

[0085] Medium type: Generally, it can be divided into pore, fracture and karst medium.

[0086] Aquifer type: According to the rock transmission and water giving property of saturated zone, it is divided into aquifer, aquiclude and weakly permeable layer; according to the buried condition, it is divided into phreatic aquifer and confined water aquifer; according to the contained medium, it is divided into pore aquifer, fracture aquifer and karst aquifer; it can also be divided into heterogeneous aquifer and homogeneous aquifer.

[0087] Aquifer spatial distribution: In vertical direction, each aquifer is distinguished and the layer thickness is recorded; in horizontal direction, the distribution area is recorded, and the aquifer includes phreatic water, confined water and weakly permeable layer.

[0088] Relative aquiclude continuity and spatial distribution of tendency: through the lithology data of different depths obtained by continuous drilling, if the relatively weakly permeable stratum is obtained in the continuous drilling, the aquiclude is continuous, otherwise it can be discontinuous; the tendency can be determined by the position of the weakly permeable stratum obtained by different drilling, and the aquiclude obtained by different drilling is connected to see the general trend of the aquiclude.

[0089] On the basis of regional topography and geomorphology type and division, stratum lithology and geological structure, the characteristics of the study area affecting the distribution of DNAPLs pollution are generalized according to the following contents:

[0090] (1) the lithology, thickness and structure of the study area air zone, etc.

[0091] (2) the structure, lithology, distribution range, thickness, buried condition, water enrichment property of the aquifer, etc.

[0092] (3) the lithology, structure, thickness and distribution of the relative aquiclude, especially the continuity and tendency of the relative aquiclude, which can significantly affect the characteristics of the distribution of DNAPLs pollution;

[0093] (4) the groundwater recharge, runoff and discharge conditions, the dynamic characteristics of water quantity, water quality, water level and water temperature, the analysis data of the chemical composition of the groundwater in the study area, the pollution condition, the distribution characteristics, composition, concentration and change of the DNAPLs pollution, etc.

[0094] In an embodiment, according to the relevant meteorological, geological, hydrogeological information of the DNAPLs pollution study area, the groundwater flow direction and flow state are determined, the corresponding initial condition, boundary condition, recharge condition and discharge condition are determined; the flow direction and flow state include laminar flow, turbulent flow, plane flow and three-dimensional flow; the initial condition includes the water level, flow and pollutant concentration distribution of the study area; the boundary condition includes the type of natural boundary or man-made boundary, that is, to determine which one of the first, second and third boundary, and to determine the corresponding numerical value; the recharge condition and discharge condition include the recharge source, discharge mode, recharge and discharge path, recharge and discharge amount, etc.

[0095] On the basis of a typical groundwater system model, DNAPLs pollutant properties, DNAPLs pollution sources, DNAPLs pollution release mechanisms and DNAPLs pollution source zone structures are identified, migration paths and migration and transformation mechanisms of DNAPLs pollutants in a typical groundwater system are determined, and a DNAPLs pollution model in a typical groundwater system is constructed. Specifically, different structural layers in the groundwater system are taken as a whole, the multi-coupling process of DNAPLs pollutants in different structural layers is clarified, and the DNAPLs pollution model in the typical groundwater system is established according to the migration paths and migration and transformation mechanisms of DNAPLs pollutants in the typical groundwater system.

[0096] In the formula, the DNAPLs pollutant properties refer to physical and chemical properties, which are embodied in relevant physicochemical parameters, including molecular weight, density, vapor pressure, solubility, n-octanol or water partition coefficient, n-octanol or air partition coefficient, Henry's constant and the like; the DNAPLs pollution source refers to the source of DNAPLs pollutants in the soil-groundwater; the DNAPLs pollution release mechanism refers to the mechanism of DNAPLs entering the soil-groundwater environment; and the DNAPLs pollution source zone structure refers to the existence form and distribution of the NAPL phase in the groundwater system.

[0097] In an embodiment, the migration path of the DNAPLs pollutant in the groundwater system is as shown in FIG. 1.

[0098] Under the combined action of gravity, capillary pressure and viscous force, after the DNAPLs pollutant leaks from the ground surface into the underground environment, it can continuously migrate downward in water from the unsaturated zone to the saturated aquifer, and to the bottom bedrock, in the process, the heterogeneous spatial variability of the water-bearing medium can cause lateral diffusion, preferential flow and local accumulation of the DNAPLs pollutant, as shown in FIG. 2. Figure 1

[0099] In the unsaturated zone, the DNAPLs pollutant can penetrate the lens composed of low-permeability media, and in addition, it can exist in the gas phase due to volatilization; in the saturated zone, the DNAPLs pollutant generally accumulates on the lens composed of low-permeability media and produces flow around, and when the vertically continuous DNAPLs pollutant can overcome the capillary resistance, it can also penetrate the relatively thin low-permeability interlayer and continue to migrate downward; the DNAPLs pollutant accumulated on the weakly permeable layer or the impervious bottom plate will flow to the low-lying place along the slope of the corresponding weakly permeable layer or the impervious bottom plate, and therefore, the situation that the flow direction of the DNAPLs pollutant is opposite to the direction of the groundwater flow may occur, as shown in FIG. 3. Figure 2

[0100] The structure of the groundwater system is complex, in addition to the pore and fracture aquifer, there may also be karst aquifer,​​Figure 3 DNAPLs pollution in groundwater system composed of pore water, karst water and bedrock fissure is illustrated.

[0101] Therefore, the accurate description of DNAPLs migration path and pollution source area is crucial in establishing DNAPLs pollution model in typical groundwater system.

[0102] In an embodiment, the migration and transformation mechanism of DNAPLs pollutants in groundwater system is as follows:

[0103] DNAPLs pollutants migrate downward through the aeration zone, and exist in various forms during the infiltration process, including gas phase volatilized in the air of the aeration zone, part of DNAPLs pollutants will be intercepted on the migration path rather than continuously distributed in the organic phase DNAPL in the pore or fissure, the organic phase DNAPL includes non-continuous distribution of immobile phase and continuous existence of mobile phase;

[0104] The immobile phase is also called residual phase; the mobile phase is also called pool, which is often accumulated on the weak permeable layer or bedrock floor;

[0105] The continuous and non-continuous distribution of organic phase DNAPL entering the groundwater system will continue to dissolve in water, and the dissolved phase DNAPL formed will also undergo adsorption and degradation reactions while flowing with the groundwater, causing the continuous expansion of the DNAPL pollution plume in the direction of groundwater flow; under sufficient time conditions, all organic phase DNAPLs may disappear, leaving only dissolved phase DNAPLs;

[0106] The organic phase DNAPL is the source of the pollution plume, and the evolution of the DNAPL pollution plume is controlled by the comprehensive action of physical, chemical and biological processes, including destructive comprehensive action and non-destructive comprehensive action;

[0107] The non-destructive comprehensive action includes convection, dispersion, volatilization, dilution and adsorption, the destructive comprehensive action includes biodegradation and non-biodegradation, the non-destructive action changes the concentration of pollutants in different media and different phases, but does not reduce the total amount of pollution; the destructive action not only reduces the concentration of pollutants, but also decomposes the pollutants, achieving the reduction of the total amount of pollutants;

[0108] In the destructive action, the process of microorganisms decomposing DNAPLs pollutants through direct oxidation, aerobic cometabolism or reductive dechlorination is biodegradation; correspondingly, the reductive process of DNAPLs pollutants in the formation mediated by active minerals and the like is non-biodegradation.

[0109] On the basis of the DNAPLs pollution model in typical groundwater system, DNAPLs pollution is analyzed by using the numerical model of DNAPLs migration.

[0110] In one embodiment, a numerical model of DNAPLs transport is used to simulate and predict the migration and distribution of DNAPLs in the groundwater system;

[0111] DNAPLs is a fluid that is immiscible with water, and its transport process is also called a multiphase flow process. The movement process of each phase (such as the water phase and the DNAPL phase) in the multiphase flow can be described by the pressure and gravity in the heterogeneous form of Darcy's law. The numerical model of DNAPLs transport uses the T2VOC (Tough2 Volatile Organic Compound) module in the TOUGH2 algorithm to calculate volatile organic compounds; the T2VOC module assumes that air, water, and organic chemicals are distributed in any one or more of the gas phase, the water phase, and the NAPL phase, and the gas phase, the water phase, and the NAPL phase are collectively represented as the β phase. The mass balance equation for the DNAPLs transport is:

[0112]

[0113] where t is time, φ is porosity, S β is the saturation of the β phase, ρ β is the density of the β phase, X β κ is the mass fraction of component κ in the β phase, V n is an arbitrary flow region, Γ n is the surface area, k is the absolute permeability, k rβ is the relative permeability of the β phase, μ β is the dynamic viscosity of the β phase, P β is the fluid pressure in the β phase, g is the acceleration of gravity, n is the unit inward normal vector, q κ is the rate of heat generation per unit volume, in equation (1), the pressure P β and the saturation S β are defined by the capillary pressure function and the relative permeability function, respectively, which are called the relative permeability-moisture content constitutive relationship, i.e., the constitutive model;

[0114] For multiphase flow simulation, the capillary pressure and the relative permeability are important factors that determine the fluid transport and distribution in the groundwater system. The Stone model and the Parker model are used as the constitutive model to simulate the DNAPLs transport process, wherein the Stone model is used to define the relative permeability function, and the Parker model is used to define the capillary pressure function;

[0115] The expression of the Stone model is as follows:

[0116]

[0117]

[0118]

[0119] S w +S g +S n =1

[0120] where k rg , k rw , k rn are the relative permeabilities of the gas, water and NAPL phases, respectively, S w , S g , S n are the saturations of the water, gas and NAPL phases, respectively, S wr , S gr , S nr are the residual saturations of the water, gas and NAPL phases, respectively, and f is a fitting parameter.

[0121] The Parker model is expressed as follows:

[0122]

[0123]

[0124]

[0125]

[0126]

[0127] where S we is the effective saturation of the water phase, S le is the effective saturation of the liquid phase, S m is the residual saturation of the liquid phase, P cgn is the gas-DNAPL capillary pressure, P cgw is the gas-water capillary pressure, a gn is the inverse of the gas-DNAPL entry pressure, a nw is the inverse of the DNAPL-water entry pressure, m and f are fitting parameters, S n , S w are the saturations of the NAPL and water phases, respectively, and g is the acceleration due to gravity.

[0128] The T2VOC module ignores dynamic dispersion of the fluid, only simulates molecular diffusion in the gas phase, and describes mass transfer in all phases by convection, assumes that the fluid phase of each element is in a local chemical equilibrium state, and therefore the interphase mass transfer between all phases can be described by the equilibrium partition relationship, and the water in the NAPL phase is ignored, and the related mechanisms of NAPL interphase mass transfer include evaporation state NAPL, dissolved state NAPL and gas-liquid mass transfer.

[0129] Another technical solution to achieve the object of the application is a DNAPLs pollution analysis system in a typical groundwater system, characterized in that it comprises:

[0130] An information collection module for collecting DNAPLs pollution research area information;

[0131] A typical groundwater system construction module that determines the DNAPLs pollution research area range based on the DNAPLs pollution research area information, generalizes the characteristics affecting the DNAPLs pollution distribution, judges the groundwater flow direction and flow state and determines the initial conditions, boundary conditions, recharge conditions and discharge conditions of the groundwater, and constructs a typical groundwater system model;

[0132] A DNAPLs pollution model construction module that identifies the DNAPLs pollutant properties, DNAPLs pollution sources, DNAPLs pollution release mechanisms and DNAPLs pollution source area structure based on the typical groundwater system model, determines the migration path and migration and transformation mechanism of the DNAPLs pollutant in the typical groundwater system, and constructs a DNAPLs pollution model in the typical groundwater system;

[0133] A DNAPLs pollution analysis module that uses a numerical model of DNAPLs migration to analyze DNAPLs pollution based on the DNAPLs pollution model in the typical groundwater system;

[0134] The output end of the information collection module is connected to the input end of the typical groundwater system construction module, the output end of the typical groundwater system construction module is connected to the input end of the DNAPLs pollution model construction module, and the output end of the DNAPLs pollution model construction module is connected to the input end of the analysis module.

[0135] The analysis method of DNAPLs pollution in the typical groundwater system is to carry out DNAPLs pollution research by taking the typical groundwater system composed of the aeration zone, the pore phreatic aquifer, the pore confined aquifer and the bedrock weathered fissure medium as a whole framework, that is, to study DNAPLs pollution by taking different structural layers of the groundwater system as a whole, to establish a DNAPLs pollution model in the actual and complex groundwater system, so that the established DNAPLs pollution model in the groundwater system is consistent with the actual DNAPLs pollution in the groundwater system, and can provide a scientific basis for pollution responsibility identification for the relevant departments, and can provide strong support for subsequent scientific monitoring and treatment and prevention of DNAPLs contaminated groundwater, which has important significance for guaranteeing the safety of groundwater resources and environment and realizing the sustainable development of human society, and solves the problem that the conceptual model established by the current research on DNAPLs pollution in the groundwater system is often quite different from the overall accuracy of the actual DNAPLs pollution in the groundwater system.

[0136] The technical means disclosed in the scheme of the present application is not limited to the technical means disclosed in the above technical means, but also includes technical solutions composed of equivalent replacement of the above technical features. The unfinished matters of the present application belong to the common knowledge of those skilled in the art.

Claims

1. A method for analyzing DNAPLs contamination in typical groundwater systems, characterized in that, Includes the following steps: S1, collect information on the research area of ​​DNAPLs pollution; S2. Based on the information of the DNAPLs pollutant study area, determine the generalized characteristics of the DNAPLs pollution distribution influencing the study area, determine the groundwater flow direction and flow pattern, and determine the initial conditions, boundary conditions, recharge conditions and discharge conditions of the groundwater, and construct a typical groundwater system model. S3. Based on a typical groundwater system model, identify the properties of DNAPLs pollutants, sources of DNAPLs pollution, release mechanisms of DNAPLs pollution, and structure of DNAPLs pollution source areas. Determine the migration pathways and transformation mechanisms of DNAPLs pollutants in a typical groundwater system and construct a DNAPLs pollution model in a typical groundwater system. S4. Based on the DNAPLs pollution model in a typical groundwater system, the DNAPLs pollution was analyzed using a numerical model of DNAPLs migration. The structure of the typical groundwater system includes a heterogeneous porous medium vadose zone, an unconfined aquifer, a confined aquifer, and bedrock weathering and fracture medium; Among them, the vadose zone of heterogeneous porous media is also called the unsaturated zone; The migration pathways of the DNAPLs contaminants in typical groundwater systems: Under the combined effects of gravity, capillary pressure and viscosity, DNAPLs pollutants leak from the surface into the underground environment and can continuously migrate downwards in water, from unsaturated zones to saturated aquifers, and finally to the bottom bedrock. The steps for constructing the DNAPLs pollution model in the typical groundwater system are as follows: By treating different structural layers in the groundwater system as a whole, we can clarify the multi-coupling process of DNAPLs pollutants in different structural layers and establish a DNAPLs pollution model for typical groundwater systems based on the migration paths and transformation mechanisms of DNAPLs pollutants in typical groundwater systems. For multiphase flow simulation, capillary pressure and relative permeability are important factors that determine fluid transport and distribution in groundwater systems. The Stone model and the Parker model are used as constitutive models to simulate the DNAPLs transport process. The Stone model is used to define the relative permeability function, and the Parker model is used to define the capillary pressure function. The Stone model expression is as follows: S w +S g +S n =1 Where, k rg k rw k rn The relative permeabilities of the gas phase, aqueous phase, and NAPL phase are S, respectively. w S g S n S represents the saturation of the aqueous phase, gas phase, and NAPL phase, respectively. wr S gr S nr These represent the residual saturation of the aqueous phase, gas phase, and NAPL phase, respectively, and f is the fitting parameter; The Parker model expression is as follows: Where, S we It is the effective saturation of the aqueous phase, S le It is the effective saturation of the liquid phase, S m It is the residual saturation of the liquid phase, P cgn It is the gas-phase DNAPL capillary pressure, P cgw It is the gas-water capillary pressure, α gn It is the reciprocal of the gas-DNAPL inlet pressure, α nw It is the reciprocal of the DNAPL-water inlet pressure, where m and f are fitting parameters, and S n S w , where are the saturation levels of the NAPL phase and the aqueous phase, respectively, and g is the acceleration due to gravity.

2. The method for analyzing DNAPLs contamination in a typical groundwater system according to claim 1, characterized in that, The information on the DNAPLs contamination study area includes geological information, hydrogeological information, hydrometeorological information, borehole information, and water level information of the DNAPLs contamination study area; Among them, the hydrogeological information uses three-dimensional geostatistical methods to accurately characterize the heterogeneity of the medium, and performs geostatistical analysis and simulates the distribution of spatial classification variables through transition probability and Markov chain methods.

3. The method for analyzing DNAPLs contamination in a typical groundwater system according to claim 1, characterized in that, The characteristics affecting the distribution of DNAPLs contamination include media type, aquifer type, aquifer spatial distribution, and spatial distribution of relative aquifer continuity and tendency.

4. The method for analyzing DNAPLs contamination in a typical groundwater system according to claim 1, characterized in that, The migration and transformation mechanisms of DNAPLs pollutants in typical groundwater systems are the mechanisms that affect the migration and transformation processes of DNAPLs in soil-groundwater systems, including physical, chemical, and biological mechanisms, among which different mechanisms can be coupled.

5. The method for analyzing DNAPLs contamination in a typical groundwater system according to claim 1, characterized in that, The numerical model for DNAPLs transport utilizes the T2VOC module in the TOUGH2 algorithm to calculate volatile organic compounds. The T2VOC module assumes the presence of air, water, and organic chemicals, distributed in any one or more of the gas, aqueous, and NAPL phases. The gas, aqueous, and NAPL phases are uniformly represented as the β phase. The mass balance equation for DNAPLs transport is: Where t is time, φ is porosity, and S β It is the saturation level occupied by the β phase, ρ β It is the density of the β phase, X β κ V is the mass fraction of component κ in the β phase. n It is an arbitrary flow region, Γ n It is the surface area, k is the absolute permeability, k rβ It is the relative permeability of the β phase, μ β It is the dynamic viscosity of the β phase, P β q is the fluid pressure in the β phase, g is the gravitational acceleration, n is the normal vector per unit area, and q is the fluid pressure in the β phase. κ It is the rate at which heat is generated per unit volume, and the pressure P. β and saturation S β Defined by the capillary pressure function and the relative permeability function respectively, they are called the relative permeability-water content constitutive relations, i.e., constitutive models.

6. A DNAPLs contamination system in a typical groundwater system, characterized in that, include: The information collection module is used to collect information on the DNAPLs contamination study area; A typical groundwater system construction module, based on the information of the DNAPLs pollutant study area, determines the scope of the DNAPLs pollutant study area, generalizes the characteristics affecting the distribution of DNAPLs pollution, determines the groundwater flow direction and flow pattern, and determines the initial conditions, boundary conditions, recharge conditions and discharge conditions of the groundwater, and constructs a typical groundwater system model; The DNAPLs pollution model construction module, based on a typical groundwater system model, identifies the properties of DNAPLs pollutants, sources of DNAPLs pollution, release mechanisms of DNAPLs pollution, and structure of DNAPLs pollution source areas. It also determines the migration paths and transformation mechanisms of DNAPLs pollutants in a typical groundwater system and constructs a DNAPLs pollution model for a typical groundwater system. The DNAPLs pollution analysis module analyzes DNAPLs pollution based on a DNAPLs pollution model in a typical groundwater system and uses a numerical model of DNAPLs migration. The output of the information collection module is connected to the input of the typical groundwater system construction module, the output of the typical groundwater system construction module is connected to the input of the DNAPLs pollution model construction module, and the output of the DNAPLs pollution model construction module is connected to the input of the analysis module. The structure of the typical groundwater system includes a heterogeneous porous medium vadose zone, an unconfined aquifer, a confined aquifer, and bedrock weathering fracture medium. Among them, the vadose zone of heterogeneous porous media is also called the unsaturated zone; The migration pathways of the DNAPLs contaminants in typical groundwater systems: Under the combined effects of gravity, capillary pressure and viscosity, DNAPLs pollutants leak from the surface into the underground environment and can continuously migrate downwards in water, from unsaturated zones to saturated aquifers, and finally to the bottom bedrock. The steps for constructing the DNAPLs pollution model in the typical groundwater system are as follows: By treating different structural layers in the groundwater system as a whole, we can clarify the multi-coupling process of DNAPLs pollutants in different structural layers and establish a DNAPLs pollution model for typical groundwater systems based on the migration paths and transformation mechanisms of DNAPLs pollutants in typical groundwater systems. For multiphase flow simulation, capillary pressure and relative permeability are important factors that determine fluid transport and distribution in groundwater systems. The Stone model and the Parker model are used as constitutive models to simulate the DNAPLs transport process. The Stone model is used to define the relative permeability function, and the Parker model is used to define the capillary pressure function. The Stone model expression is as follows: S w +S g +S n =1 Where, k rg k rw k rn The relative permeabilities of the gas phase, aqueous phase, and NAPL phase are S, respectively. w S g S n S represents the saturation of the aqueous phase, gas phase, and NAPL phase, respectively. wr S gr S nr These represent the residual saturation of the aqueous phase, gas phase, and NAPL phase, respectively, and f is the fitting parameter; The Parker model expression is as follows: Where, S we It is the effective saturation of the aqueous phase, S le It is the effective saturation of the liquid phase, S m It is the residual saturation of the liquid phase, P cgn It is the gas-phase DNAPL capillary pressure, P cgw It is the gas-water capillary pressure, α gn It is the reciprocal of the gas-DNAPL inlet pressure, α nw It is the reciprocal of the DNAPL-water inlet pressure, where m and f are fitting parameters, and S n S w , where are the saturation levels of the NAPL phase and the aqueous phase, respectively, and g is the acceleration due to gravity.

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