AU2021102158A4

AU2021102158A4 - Method for determining morphology and layered characteristic of groundwater contamination plume

Info

Publication number: AU2021102158A4
Application number: AU2021102158A
Authority: AU
Inventors: Huiying Li; Tianxiang Xia
Original assignee: Beijing Municipal Research Institute of Environmental Protection
Current assignee: Beijing Municipal Research Institute of Environmental Protection
Priority date: 2020-06-30
Filing date: 2021-04-23
Publication date: 2021-06-17
Anticipated expiration: 2029-04-23
Also published as: CN111798335B; CN111798335A

Abstract

The present disclosure relates to the technical field of groundwater treatment, and in particular to a method for determining a layered characteristic and a preferential migration path of a groundwater contamination plume. The method includes the following steps: Si: performing contamination identification; S2: identifying a hydrogeological condition; S3: arranging groundwater monitor wells; S4: constructing the monitor wells in layers; S5: washing the monitor wells and collecting samples; S6: detecting the samples; S7: analyzing detection data; and S8: determining a morphology and a layered characteristic of a groundwater contamination plume through the data analysis in step S7. The present disclosure designs a three-dimensional (3D) water quality survey system to perform sampling, monitoring and 3D simulation analysis of water quality data, and achieves the purpose of depicting the layered characteristic of the groundwater contamination plume and accurately identifying the preferential migration path thereof. 17620089_1 (GHMatters) P116159.AU 1/9 E 'iromendlSurve ,rof P1Qt-,' i\tr t 7<t 'oi Uoundxwtter Polluti xX 2 N' 7 " 01401-2040 4841 -20100 2 ~ 0 0 ( 9.7 / _ v. uo 25 tog // 11 61010;;; 01980 U.25' 21 3(MO1 3.4/ rh 4 261 1640 U.2 70 0 1.4-, C0.~ 0.2., Meters FIG.1I 17620153 1 (GHMafters) P116159.AU

Description

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17620153 1 (GHMafters) P116159.AU

METHOD FOR DETERMINING MORPHOLOGY AND LAYERED CHARACTERISTIC OF GROUNDWATER CONTAMINATION PLUME TECHNICAL FIELD The present disclosure relates to the technical field of groundwater investigation and cleanup, and in particular to a method for determining a layered characteristic and a preferential migration path of a groundwater contamination plume. BACKGROUND The existing groundwater quality surveys are conducted based on the assumption of uniform migration and distribution of contaminants in the same aquifer of groundwater. However, in reality, if there are different water-bearing media with different permeability coefficients in the same aquifer, the migration rates of contaminants will vary, leading to the layered distribution of the contamination plume. The contaminants preferentially migrate along the high-permeability water-bearing medium, resulting in a higher migration rate than in other water-bearing media. If risk control is carried out based on a uniform migration rate, the real migration rate will be underestimated, leading to unsatisfactory risk control and even failure. If the high-permeability water-bearing medium is located at the bottom of the aquifer, the contaminants will migrate along the bottom of the aquifer after entering the aquifer. If the downstream monitor well fails to identify the migration path, it will be misled by the contaminant-free upper part of the aquifer and misjudge the contamination situation in the target area. Studies have shown that contaminants with different densities and solubility will migrate along the high-permeability medium. Therefore, to carry out groundwater contamination identification and risk control, it is necessary to identify the layered characteristic and preferential migration path of the groundwater contamination plume. Chinese patent CN104261505A discloses an in-situ remediation system of groundwater. The system includes a vertical impermeable wall along a perimeter of a contaminated area. The vertical impermeable wall has a semi-closed structure. A multi-treatment-unit reaction grid is provided at an opening of the vertical impermeable wall. The multi-treatment-unit reaction grid is provided at a downstream front edge of a groundwater contamination plume, and is perpendicular to a groundwater flow direction. Groundwater monitor wells are respectively provided on the upstream and downstream of the multi-treatment-unit reaction grid to measure changes in a water level and water quality before and after groundwater remediation. Chinese patent CN105254041A discloses an aeration type remediation device and method for contaminated groundwater. The remediation device includes underground wells, an aeration device and an extraction device. The underground wells include a main well and multiple inclined wells. The main well is provided on a ground, the bottom of which is immersed in a contamination plume.

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The inclined wells are provided in a vadose zone. The aeration device includes an aerator, an aeration tube and an aeration head. The aerator is provided on the ground. The aeration tube is connected to the aerator, and extends into a part of the main well immersed in the contamination plume. The aeration head is provided in a part of the aeration tube immersed in the contamination plume, and is drawn out through the inclined well. The extraction device includes an extractor and an extraction tube. The extractor is provided on the ground. One end of the extraction tube is connected to the extractor, and the other end thereof is connected to a sub-extraction tube extending into the inclined well. The aeration device injects air into the contamination plume, and volatile organic compounds (VOCs) in the groundwater enter the vadose zone with the air. The VOCs are pumped off through the extraction device, which effectively eliminates the contaminated gas trapped in the vadose zone during groundwater remediation and improves the remediation efficiency. Chinese patent CN110987525A discloses a well casing device suitable for layered sampling of underground water from a contaminated site. The device includes a groundwater monitor well. An unplasticized polyvinyl chloride (uPVC) well casing is provided in the groundwater monitor well. A length of the uPVC well casing is consistent with a depth of the groundwater monitor well. The uPVC well casing is divided into screened sections and non-screened sections. The screened sections respectively correspond to two aquifers, and a non-screened section corresponds to a confining bed. An annular partition is provided in the uPVC well casing in the confining bed between the upper and lower aquifers. The screened section above the annular partition is provided with an inner casing wall corresponding to the annular partition, so that an upper water sampling chamber is provided between the inner casing wall and an outer casing wall. The techniques disclosed by the patent application documents CN105254041A and CN110987525A can improve the remediation efficiency, but cannot identify the layered characteristic and morphology of the groundwater contamination plume. The present disclosure designs a three-dimensional (3D) water quality survey system based on the identification of a hydrogeological condition for sampling, monitoring and 3D simulation analysis of water quality data. The present disclosure depicts a morphology and a layered characteristic of a groundwater contamination plume and identifies a migration path thereof, providing a scientific and effective basis for fully learning groundwater contaminant migration and developing risk control measures. SUMMARY In order to solve the technical problems existing in the prior art, the present disclosure provides a method for determining a morphology and a layered characteristic of a groundwater

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17620089_1 (GHMatters) P116159.AU contamination plume. The present disclosure designs a three-dimensional (3D) water quality survey system to perform sampling, monitoring and 3D simulation analysis of water quality data, and achieves the purpose of depicting the layered characteristic of the groundwater contamination plume and accurately identifying a preferential migration path thereof. The present disclosure provides a method for determining a morphology and a layered characteristic of a groundwater contamination plume, including the following steps: Si: performing contamination identification, including identification of a potential contamination source, a potential contaminant, a potential contamination area, a hydrogeological condition and a potential contamination path; S2: identifying the hydrogeological condition; S21: arranging equidistant monitoring points in three rows and three columns for hydrogeological identification in a target area based on a contamination identification result of step Si, and collecting typical geotechnical test samples of different strata at each monitoring point for analysis; S22: identifying a groundwater level through groundwater level monitoring; S23: deriving a permeability coefficient of a target aquifer through an on-site slug test; S24: identifying a groundwater flow direction through water level data of each monitor well acquired in step S22; S3: arranging groundwater monitor wells; S31: horizontal arrangement: setting up groundwater monitor wells at the contamination source and on the upstream, downstream and flanks of groundwater in the potential contamination area; S32: vertical arrangement: arranging groundwater monitor wells in layers with an interval of 3 m when there is one aquifer in a geological layer; setting up groundwater monitor wells in different geological layers separately when there are aquifers in different geological layers, and if a single geological layer has a thickness of greater than 6 m, setting up groundwater monitor wells in layers with an interval of 3 m in the geological layer; S4: constructing the monitor wells in layers; S5: washing the monitor wells and collecting samples; S6: detecting the samples collected in step S5; S7: analyzing detection data acquired in step S6; S71: screening an over-standard indicator, that is, a monitoring indicator exceeding a groundwater quality standard; S72: determining an over-standard characteristic contaminant based on plot contamination identification and potential contamination source analysis;

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S73: characterizing a horizontal concentration distribution of the over-standard characteristic contaminant: analyzing a horizontal distribution of the characteristic contaminant in each layer through an over-standard point symbolization system and a geostatistical spatial analysis system, etc., and identifying spatial distribution characteristics of groundwater contamination in different layers, so as to make a preliminary determination on a layered characteristic of a contamination plume in the aquifer; S74: characterizing a vertical concentration distribution of the over-standard characteristic contaminant in a single monitor well: comparing and analyzing groundwater contamination data in different layers of the single monitor well through data analysis and mapping tools, and identifying a vertical contamination distribution characteristic of the single monitor well; S75: characterizing a three-dimensional (3D) morphology of the contamination plume of the over-standard characteristic contaminant: identifying a 3D distribution characteristic of the groundwater contamination plume by integrating the data of different layers of each monitor well in the target area through a 3D spatial information analysis tool for the contaminant; S8: determining a morphology and a layered characteristic of the groundwater contamination plume through the data analyses in steps S73 to S75, where in step S73, a preliminary determination is made on the layered characteristic of the contamination plume in the aquifer; in step S74, relative positions of the contamination source and the contamination plume are identified, where an area showing a downward trend in the vertical contaminant concentration distribution is one where the contamination source is located, and an area showing an upward trend in the vertical contaminant concentration distribution is one where the contamination plume is located; step S8 specifically includes: identifying locations of the groundwater contamination source and the contamination plume, identifying a typical profile of the groundwater contamination plume, and determining a preferential migration path of the groundwater, based on the 3D simulation of the contamination plume in step S75 combined with preliminary identification results of the horizontal and vertical distributions in steps S73 and S74. Preferably, the S22: deriving a permeability coefficient of a target aquifer through an on-site slug test specifically includes the following sub-steps: SO: putting a water pressure sensor at a certain depth of the well; S02: putting a water level disturbance device into the well and waiting for a water level to stabilize; S03: changing the water level in the well instantly through the disturbance device; S04: recording water level recovery data; and SO5: calculating a permeability coefficient through a chart analysis method;

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17620089_1 (GHMatters) P116159.AU where, during the test, in order to obtain a maximum initial change in the water level of the test well, a dynamic water level change is recorded before a certain amount of water is injected or extracted from the well until the end of the test; a relationship curve between the water level H and time is drawn, and the permeability coefficient K of the aquifer is calculated. Preferably, in the horizontal arrangement in step S31, in order to determine a contamination source and a contamination boundary of a plot, monitor wells are further arranged on upstream and downstream boundaries of the groundwater of the plot. Preferably, the S73: characterizing a horizontal concentration distribution of the over-standard characteristic contaminant specifically includes the following sub-steps: drawing horizontal contaminant distributions at different depths of a screen in the monitor well; distinguishing over-standard and non-over-standard samples with different colors; distinguishing over-standard levels with different symbols; preliminarily identifying a contamination plume direction and range based on the groundwater flow direction; and marking monitor wells at the contamination source, a centerline of the contamination plume and a boundary of the contamination plume. Preferably, the S74: characterizing a vertical concentration distribution of the over-standard characteristic contaminant specifically includes the following sub-steps: drawing a histogram of the vertical concentration distribution of the contaminant in the monitor well at the contamination source; and drawing a histogram of the vertical concentration distribution of the contaminant in the monitor well at the centerline of the contamination plume. Preferably, the S75: characterizing a 3D morphology of the contamination plume of the over-standard characteristic contaminant specifically includes the following sub-steps: drawing a 3D distribution map of the groundwater contamination plume; intercepting a horizontal profile of the groundwater contamination plume of different layers according to a layered arrangement principle of the monitor wells; intercepting a migration profile of the contamination plume according to an existing determination on the centerline of the contamination plume; and analyzing a migration path and trend of the contamination plume according to a contaminant nature and a stratum characteristic. Preferably, step S8 specifically includes: identifying locations of the groundwater contamination source and the contamination plume, identifying a typical profile of the groundwater contamination plume, and determining a preferential migration path of the groundwater, based on

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17620089_1 (GHMatters) P116159.AU the 3D simulation of the contamination plume in step S75 combined with preliminary identification results of the horizontal and vertical distributions in steps S73 and S74. Preferably, the potential contamination path includes: a contaminant migrates from a surface to deep soil; the contaminant infiltrated into the deep soil migrates to the groundwater; the contaminant entering the groundwater migrates downstream along with the flow of the groundwater, causing the groundwater contamination plume to further spread and contaminate soil in a saturation zone and a surrounding plot; the contaminant in the contaminated groundwater migrates downstream along with the flow of the groundwater, causing the groundwater contamination plume to spread to a target plot and contaminate soil in a saturation zone. Preferably, in step S21, typical geotechnical test samples of different strata are collected at each sampling point to analyze an aquifer status, a lithologic characteristic of a vadose zone and groundwater recharge, runoff and drainage conditions in the area; the aquifer status and the lithologic characteristic of the vadose zone in the area include lithology and hydraulic conductivity of the aquifer and lithology and thickness of the vadose zone; the groundwater recharge, runoff and drainage conditions in the area include groundwater depth, groundwater recharge source, drainage outlet, groundwater flow direction and permeability coefficient. Preferably, in S5, after washing the monitor wells, non-volatile organic compounds (non-VOCs) are collected; after the collection of the non-VOCs is completed, a sampling flow rate is reduced to 150-350 ml/min to collect VOCs. Compared with the prior art, the present disclosure has the following beneficial effects: The present disclosure designs a 3D water quality survey system based on the identification of a hydrogeological condition to perform sampling, monitoring and 3D simulation analysis of water quality data, and achieves the purpose of depicting the layered characteristic of the groundwater contamination plume and accurately identifying the preferential migration path thereof. The present disclosure can be used to effectively evaluate the preferential migration channel of the groundwater contaminant, so as to provide a basis for reasonably evaluating the migration rate of the contaminant. A contamination plume that migrates along the bottom of the aquifer cannot be monitored by means of conventional monitor well arrangement. To solve this problem, the present disclosure adjusts the monitor well arrangement according to the layered characteristic of the contamination plume, and fully evaluates the groundwater contamination range. The present disclosure can accurately identify the layered characteristic and migration path of the contaminant profile for an area requiring remediation or risk control, so as to make the remediation or risk control more targeted and effective. In summary, the present disclosure can provide a scientific and effective basis for groundwater contamination identification and risk control measures.

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17620089_1 (GHMatters) P116159.AU

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows detected concentrations and over-standard concentrations of benzene in groundwater. FIG. 2 shows detected concentrations and over-standard concentrations of tetrahydrofuran in the groundwater. FIG. 3 shows a vertical distribution of benzene in the groundwater in Area A according to Embodiment 1. FIG. 4 a vertical distribution of tetrahydrofuran in the groundwater in Area A according to Embodiment 1. FIG. 5 shows 5-8 m concentrations of the characteristic contaminant tetrahydrofuran. FIG. 6 shows 9-12 m concentrations of the characteristic contaminant tetrahydrofuran. FIG. 7 shows 13-15 m concentrations of the characteristic contaminant tetrahydrofuran. FIG. 8 shows 16-20 m concentrations of the characteristic contaminant tetrahydrofuran. FIG. 9 shows a preferential migration path of contaminated groundwater. DETAILED DESCRIPTION The specific implementations of the present disclosure are described in detail below with reference to the accompanying drawings. Embodiment 1 1. Contamination identification (1) Potential contamination sources Potential contamination sources of a survey plot included a production workshop, a wastewater treatment station and a drying workshop. The spillage and leakage of a raw solvent, production wastewater and a waste liquid in the production workshop and the drying workshop caused the infiltration and migration of a contaminant, resulting in soil and groundwater contamination in an area. Aging cracks at the bottom of the wastewater treatment station and a wastewater pond caused contaminants to infiltrate and migrate to soil and groundwater. A hydrogeological analysis showed that in the survey plot, Area A was located in the upstream of Area B and Area C. The aquifer of the plot had good permeability and fluidity, and the migration of contaminated groundwater in the upstream of the plot to the downstream might lead to the contamination of the groundwater and soil in the aquifer. (2) Potential contaminants According to the process and the identification of raw and auxiliary materials, it was preliminarily determined that the contaminants in the plot included benzene series, chlorinated hydrocarbons, phenol, aniline, total petroleum hydrocarbons (TPH), heavy metals and methyl

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17620089_1 (GHMatters) P116159.AU tert-butyl ether (MTBE). (3) Potential contamination areas The potential contamination areas included the production workshop, the wastewater treatment station, the wastewater pond, materials and finished products warehouses and production wastewater discharge ditches. (4) Hydrogeological conditions There were a soil layer (0-3 m), a silty sand layer (3-6.5 m), a fine sand layer (6.5-10.0 m), a medium sand layer (10.0-20.0 m) and the bottom of the aquifer (20 m) in a buried depth from the ground. (5) Potential contamination paths i. Due to infiltration, contaminants on the surface migrate to the deep soil. ii. The contaminants infiltrated into the deep soil migrate to the groundwater. iii. The contaminants entering the groundwater migrate downstream with the flow of groundwater, making a groundwater contamination plume further spread and soil in a saturation zone contaminated. 2. Identification of hydrogeological conditions (1) Arrangement plan According to the previous data and analysis results of the plot, the actual soil layer changes and distribution of the plot were obtained, and equidistant monitoring points were arranged in three rows and three columns for formation exploration and lithology analysis. Typical geotechnical test samples of different strata were collected at each point for lithology analysis. The hydrogeological identification needs to derive the hydrogeological conditions in and around the plot. (1) Aquifer status and lithologic characteristic of a vadose zone in the area, including the lithology, structure, water yield and hydraulic conductivity of the aquifer, the lithology and thickness of the vadose zone, etc. (2) Groundwater recharge, runoff and drainage conditions in the area, including groundwater depth, groundwater recharge source, drainage outlet, groundwater flow direction and permeability coefficient, etc. The geotechnical sampling points were designed to collect undisturbed soil samples and obtain relevant geotechnical parameters of typical strata. The locations and sampling depths of geotechnical test samples collected through soil holes depended on actual conditions, and at least one soil sample was collected from each soil layer by each soil hole. After the geotechnical samples were collected, the soil holes were filled with bentonite to prevent artificial "skylights" from being formed to cause vertical leakage of contaminants. The geotechnical test samples were sent for a laboratory analysis in accordance with the Code for Investigation of Geotechnical Engineering

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(GB50021-2009). (2) Slug test Slug test is a method of instantaneously injecting or extracting a certain amount of water from a well, and observing the change in the water level of the well to obtain the permeability coefficient of the aquifer near the well. It is described below in terms offield test process and data processing. The field test process is summarized as five steps: (1) Put a water pressure sensor at a certain depth of the well. (2) Put a water level disturbance device into the well and wait for the water level to stabilize. (3) Change the water level in the well instantly through the disturbance device. (4) Record water level recovery data. (5) Calculate the permeability coefficient through a chart analysis method. During the test, in order to obtain a maximum initial change in the water level of the test well, a dynamic water level change is recorded before a certain amount of water is injected or extracted from the well until the end of the test; a relationship curve between the water level H and time is drawn, and the permeability coefficient K of the aquifer is calculated. 3. Arrangement of groundwater monitor wells 3.1 Horizontal arrangement According to the Technical Guidelinesfor Soil EnvironmentalInvestigation and Assessment of Construction Land (Announcement No. 72 of 2017) released by the Ministry of Ecology and Environment of the People's Republic of China, in a detailed investigation stage, no less than 1 groundwater sampling point should be arranged for every 6400 m2 of a potential contamination area screened based on contamination identification and preliminary investigation. The groundwater contamination investigation was mainly to investigate and analyze whether there was groundwater contamination in the plot and the extent and scope of groundwater contamination. According to the potential contamination of the plot and the occurrence and flow direction of groundwater in the plot, groundwater monitor wells were arranged at the contamination source and on the upstream, downstream and flanks of the groundwater in the potential contamination area. In order to determine the contamination source and contamination boundary of the plot, monitor wells were further arranged on upstream and downstream boundaries of the groundwater of the plot. 3.2 Vertical arrangement Groundwater monitor wells were arranged in layers with an interval of 3 m when the aquifer was in the same geological layer. Groundwater monitor wells were arranged in different geological layers when there were

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17620089_1 (GHMatters) P116159.AU aquifers in different geological layers. When a single geological layer had a thickness of greater than 6 m, the groundwater monitor wells were arranged in layers with an interval of 3 m in the geological layer. 4. Construction of monitor wells in layers 1) Drill to 0.5 m below the bottom of a first aquifer by cable tool drilling based on the stratum structure of the plot, and drive a casing as the drilling progresses to prevent a borehole from collapsing. 2) Measure an actual depth of the borehole with a measuring tape before construction, and connect and fix a connecting tube to a fixed-depth groundwater sampling probe. 3) Place the connected fixed-depth groundwater sampling probe to a designed sampling depth, and fill quartz sand into a gap between the probe and the casing through a tremie pipe, where a filling thickness of the quartz sand is about 1.5 m. After 30 cm thick quartz sand is added, the casing is withdrawn by 30 cm; this process is repeated until the corresponding depth, so as to prevent the casing and the connecting tube from being locked and withdrawn together due to too much quartz sand. 4) Put a sealing material into the borehole through the tremie pipe to a design depth. The casing is withdrawn for about 30 cm before the sealing material is added; this process is repeated until the design depth so as to prevent the casing and connecting tube from being locked and withdrawn together due to the expansion of the sealing material. 5) Repeat steps 2), 3) and 4) until all fixed-depth groundwater sampling probes are placed. 6) Add the sealing material to a distance of 30 cm from a surface opening. While the sealing material is added, water is added to make the sealing material expanded. 7) Mount a well casing in the borehole and pour cement slurry into a pad. 8) Cover the well casing by a cap that is connected to the connecting tube. 5. Washing and sampling of monitor wells 1) Wash the wells at 1 L/min for 30 min according to the aquifer characteristics of the plot in 48 h after the well is constructed, and finish when reaching 5 times the volume of the well casing. 2) Transfer a groundwater sample in the fixed-depth sampling probe at the designed depth to a corresponding sample jar through a variable-frequency low-flow sampling device at 400 mL/min. In order to avoid cross-contamination, a special silicone tube of a peristaltic pump in the variable-frequency low-flow sampling device is not reused. 3) Record an initial water level, a washing flow rate and time during the washing and sampling processes to calculate a washing volume (3-5 times of well casing volume); monitor changes in water quality indicators during the washing process, and collect non-VOCs after satisfying washing

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17620089_1 (GHMatters) P116159.AU requirements (dissolved oxygen (DO) 10%; temperature (T) 0.1; pH 0.1; oxidation-reduction potential (ORP) 10 mv); then reduce a sampling flow rate to 150-350 ml/min to collect VOCs. Specifically, the sampling includes the following steps: a) Check a water level gauge and calibrate a portable water quality monitor. b) Prepare a sample jar, a protective agent and a sampling record book as required. c) Wash a sampling pump and a sampling tube, and collect a sample according to a quality control plan. d) Record a meteorological parameter on the day of sampling, put the water level gauge into the monitor well, and measure an initial water level. e) Place the sampling pump slowly in the monitor well, so that a suction port of the pump is located 1.0 m below a water surface; put a water level gauge with scale marks, together the sampling pump, to measure a depth of the pump in the groundwater. f) Calculate a theoretical well washing volume, connect an extraction tube, connect a control power supply of the sampling pump, start the sampling pump, adjust an operating condition of the sampling pump by adjusting a voltage value so that a lift of the sampling pump is greater than the water level, and collect an effluent of the pump through a bucket. g) Measure a groundwater level every 2 min, and if the groundwater level drops no more than cm, gradually increase an extraction rate under the prerequisite that the groundwater level drops no more than 10 cm. h) Measure water quality parameters at regular intervals. The washing can end when the parameters meet the following conditions: (1) pH variation range: 0.1; (2) Temperature variation range: 3%; (3) Electrical conductivity variation range: ±3%; (4) ORP variation range: 10 mV; (5) DO variation range: 10% (or DO < 2.0 mg/L, with a variation range of 0.2 mg/L); (6) Turbidity > 10 nephelometric turbidity units (NTUs), with a variation range of 10%; 5 NTUs < turbidity < 10 NTUs, with a variation range of 1.0 NTUs; or the measured turbidity is less than 5 NTUs for three consecutive times. (7) The washing volume reaches 3-5 times a theoretical washing volume, but the various water quality parameters do not meet the requirements. i) Reduce the sampling flow rate to no more than 500 ml/min, and place a VOCs sample jar at a water outlet of the sampling tube to collect VOCs; cover and tighten ajar cap with a Teflon gasket when the sample jar is full and a convex liquid surface is presented, label, and place the sample jar in a sample storage box. j) Collect non-VOCs samples to analyze other groundwater indicators according to corresponding technical requirements.

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17620089_1 (GHMatters) P116159.AU k) Disassemble the corresponding sampling equipment, cover the well tightly, and properly collect and dispose of waste generated during the sampling process. 6. Data analysis and contamination identification 6.1 Screening of over-standard indicators Monitoring indicators were screened based on a groundwater quality standard. There were 60 test samples for TPH, 81 test samples for MTBE and 82 test samples for the remaining VOCs indicators. There were 76 test indicators, among which 44 were detected and 22 exceeded the standard. The over-standard rates of 1,3,5-trimethylbenzene, bromobenzene, benzene, styrene, m-xylene and p-xylene, toluene, TPH (C1 5 -C 2 8 ), TPH (C-C), acetone, tetrahydrofuran, carbon disulfide, 1,2-dichloroethane, 1,1,2-trichloroethane, cis-1,2-dichloroethylene, dichloromethane, vinyl chloride, trichloroethylene, chlorobenzene, trichloromethane, monobromide dichloromethane, MTBE and acetonitrile were 3.66%, 1.22%, 43.90%, 1.22%, 1.22%, 12.20%, 13.33%, 40.00%, 6.10%, 53.66%, 2.44%, 1.22%, 1.22%, 1.22%, 6.10%, 2.44 %, 3.66%, 15.85%, 7.32%, 2.44%, 6.17% and 1.22%, respectively. The maximum detected concentration of benzene was 20100 pg/L, which was 166.5 times higher than the standard. The maximum detected concentration of tetrahydrofuran was 760000 pg/L, which was 1265.67 times higher than the standard. The maximum detected concentration of chlorobenzene was 4200 pg/L, which was 6 times higher than the standard. The maximum detected concentration of TPH (C 6 -C 9) was 797000 pg/L, which was 1593 times higher than the standard. 6.2 Horizontal distribution The horizontal concentration distribution of the over-standard indicator was characterized as follows: Draw horizontal contaminant distributions at different depths of a screen in the monitor well. Distinguish over-standard and non-over-standard samples with different colors. Distinguish over-standard levels with different symbols. Preliminarily identify a contamination plume direction and range based on the groundwater flow direction. Mark monitor wells at the contamination source, a centerline of the contamination plume and a boundary of the contamination plume. The detected and over-standard points of benzene series were mainly distributed in the north and west of Area A (see FIG. 1). The over-standard indicators were benzene, toluene, m-xylene and p-xylene. The maximum detected concentration of benzene was 20100 pg/L at Point A4, where the sampling depth was 8 m. The second detected concentration of benzene was 4840 pg/L at Point A17, where the sampling depth was 6.5 m. These points were located in the production area of Area A, corresponding to an Odyssey drying workshop, etc. The

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17620089_1 (GHMatters) P116159.AU maximum detected concentration of toluene was 306000 pg/L at Point A24, where the sampling depth was 7 m, followed by 183000 pg/L at Point A4, where the sampling depth was 8 m. These points were located in the west of Area A, corresponding to the vicinity of the Odyssey drying workshop and the wastewater pond, etc. There was one over-standard point of m-xylene and p-xylene, with a detected concentration of 323 pg/L at Point A24, where the sampling depth was 7 m. This point was located on the west of Area A, corresponding to the vicinity of the wastewater pond. The benzene series might come from production materials, intermediate products and drying processes. In petroleum hydrocarbons, TPH (C6 -C 9 ) and TPH (C1 5 -C 2 8 ) exceeded the standard. The over-standard points of TPH (C-C 9) were found in most of Area A (see FIGS. 1 and 2). The maximum detected concentration was 797000 pg/L at Point A24, where the sampling depth was 7 m, corresponding to the vicinity of the Odyssey wastewater pond. Other detected concentrations were 300000 pg/L, 122000 pg/L and 70100 pg/L at Points A4, A17 and A37, where the sampling depths were 8 m, 6.5 m and 6.5 m, respectively. These points were located on the west and north of Area A, corresponding to the Odyssey drying workshop and Warehouse 1, etc. The sampling depths were concentrated in the upper part of the aquifer. The over-standard points of TPH (C1 5 -C 2 8 ) were Points Al and A4. The maximum detected concentration was 2950 pg/L at Point A4, where the sampling depth was 8 m, followed by 1610 pg/L at Point A1, where the sampling depth was 8 m. The over-standard points of chlorobenzene were concentrated in the west and north of Area A, with a maximum over-standard ratio of 6. The maximum detected concentration of chlorobenzene was 4200 pg/L at Point A4, where the sampling depth was 8 m, corresponding to the Odyssey drying workshop. Other detected concentrations are 3260 pg/L, 1930 pg/L and 1410 pg/L at Points A37, A24 and A17, where the sampling depths were 6.5 m, 7 m, and 10.5 m respectively, corresponding to vicinity of Odyssey Warehouse 1 and the wastewater pond. The chlorobenzene was concentrated in the upper part of the aquifer in depth. The over-standard points of chlorinated hydrocarbons were concentrated at Points A4, A30, and A37 in Area A, corresponding to the drying workshop, Warehouse 3 and Warehouse 1, etc. The over-standard indicators were 1,2-dichloroethane,1,1,2-trichloroethane,cis-1,2-dichloroethylene,dichloromethane,vinylchloride, trichloroethylene, trichloromethane and monobromide dichloromethane, among which trichloromethane had the largest over-standard ratio. There were three over-standard points of trichloromethane, which were A4, A17 and A24 located in Area A. The maximum detected concentration was 426000 pg/L at Point A4, where the sampling depth was 8 m, corresponding to the Odyssey drying workshop, followed by 9920 pg/L and 318 pg/L at Points A17 and A24, where the sampling depths were respectively 6.5 m and 7 m, corresponding to the vicinity of the Odyssey

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17620089_1 (GHMatters) P116159.AU wastewater pond, etc. The trichloromethane was concentrated in the upper part of the aquifer in depth. There was one over-standard point of trichloroethylene, namely A37, corresponding to the vicinity of Odyssey Warehouse 1. The detected concentration was 20400 pg/L, with an over-standard ratio of 96. The sampling depth was 10.5 m, and the trichloromethane was concentrated in the middle of the aquifer. The over-standard points of tetrahydrofuran were round in most of Area A (FIG. 2). The maximum over-standard ratio of most points were greater than 10. The maximum detected concentration was 760000 pg/L at Point A4, where the sampling depth was 8 m, followed by those at Points AW2, A24, Al, AW13 and AW11. All these points were located in the western production area of Area A, corresponding to the Odyssey drying workshop, Workshop 1, Workshop 2, the wastewater pond and the wastewater treatment station, etc. The detected concentrations were 647000 pg/L, 361000 pg/L, 295000 pg/L, 284000 pg/L and 260000 pg/L, and the sampling depths were 10 m, 7 m, 8 m, 18 m and 16.5 m. The tetrahydrofuran at the points in the production area was mostly distributed in the upper part of the aquifer, and the tetrahydrofuran at other areas was mostly distributed at the bottom of the aquifer. There was one over-standard point of carbon disulfide, namely A4, corresponding to the drying workshop of Odyssey. The detected concentration was 22300 pg/L and the sampling depth was 8 m. There is one over-standard point of styrene, namely SWGY357-1, corresponding to the vicinity of the Odyssey workshop. The detected concentration was 40.2 pg/L and the sampling depth was 20 m. There were two over-standard points of acetone, namely A4 and A17, corresponding to the vicinity of the Odyssey drying workshop. The maximum detected concentration was 2770000 pg/L at Point A4, where the sampling depth was 8 m, followed by 129000 pg/L at Point A17, where the sampling depth was 6.5 m. The over-standard points of MTBE were scattered, and their concentrations had little difference. The maximum detected concentration was 61.2 pg/L at Point AW14, where the sampling depth was 11.5 m, followed by 50 pg/L at Point AW2, where the sampling depth was 7 m. 6.3 Vertical distribution Draw a histogram of the vertical concentration distribution of the contaminant in the monitor well at the contamination source. Draw a histogram of the vertical concentration distribution of the contaminant in the monitor well at the centerline of the contamination plume. Draw a 3D distribution map of the groundwater contamination plume. Intercept a horizontal profile of the groundwater contamination plume of different layers

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17620089_1 (GHMatters) P116159.AU according to a layered arrangement principle of the monitor wells. Intercept a migration profile of the contamination plume according to an existing determination on the centerline of the contamination plume. Analyze a migration path and trend of the contamination plume according to a contaminant nature and a stratum characteristic. The vertical over-standard distribution of benzene is shown in FIG. 3. The benzene concentration at the over-standard points changed vertically. The benzene was distributed more in the aquifer, reaching the lower part of the aquifer. The distribution concentration of benzene in Area A was generally larger in the upper part of the aquifer and smaller in the lower part of the aquifer, and the maximum concentration was generally distributed in the upper part of the aquifer. The vertical over-standard point of trichloromethane was A4, which had a depth of 8 m. Trichloromethane was concentrated in the upper part of the aquifer, and no over-standard sign was seen below the upper part of the aquifer. The vertical over-standard point of trichloroethylene was A37, which had a depth of 10.5 m. Trichloroethylene was concentrated in the middle of the aquifer, and no over-standard sign was seen at the upper part and bottom of the aquifer. The vertical over-standard distribution of tetrahydrofuran is shown in FIG. 4. The tetrahydrofuran was distributed more in the aquifer, reaching the lower part of the aquifer. The distribution concentration of tetrahydrofuran in Area A was generally larger in the upper part of the aquifer and smaller in the lower part of the aquifer, and the maximum concentration was generally distributed in the upper part of the aquifer. The concentration distribution of the characteristic contaminant tetrahydrofuran is shown in FIGS. 5 to 8. A preliminary determination was made on the layered characteristic of the contamination plume in the aquifer. Relative positions of the contamination source and the contamination plume were identified, where an area showing a downward trend in the vertical contaminant concentration distribution was one where the contamination source was located, and an area showing an upward trend in the vertical contaminant concentration distribution was one where the contamination plume was located. Based on the 3D simulation of the contamination plume combined with preliminary identification results of the horizontal and vertical distributions, the locations of the groundwater contamination source and the contamination plume was identified, a typical profile of the groundwater contamination plume was identified, and a preferential migration path of the groundwater was determined. The preferential migration path of the contaminated groundwater as shown in FIG. 9 was derived by analyzing the above detection data. The foregoing is merely illustrative of the preferred examples of the present disclosure and is

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17620089_1 (GHMatters) P116159.AU not intended to limit the present disclosure, and various changes and modifications may be made by those skilled in the art. Any modifications, equivalent substitutions and improvements made within the spirit and scope of the present disclosure should fall within the protection scope of the present disclosure. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

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Claims

What is claimed is: 1. A method for determining a morphology and a layered characteristic of a groundwater contamination plume, comprising the following steps: Si: performing contamination identification, comprising identification of a potential contamination source, a potential contaminant, a potential contamination area, a hydrogeological condition and a potential contamination path;

S2: identifying the hydrogeological condition; S21: arranging equidistant monitoring points in three rows and three columns for hydrogeological identification in a target area based on a contamination identification result of step Si, and collecting typical geotechnical test samples of different strata at each monitoring point for analysis; S22: identifying a groundwater level through groundwater level monitoring; S23: deriving a permeability coefficient of a target aquifer through an on-site slug test; S24: identifying a groundwater flow direction through water level data of each monitor well acquired in step S22; S3: arranging groundwater monitor wells; S31: horizontal arrangement: setting up groundwater monitor wells at the contamination source and on the upstream, downstream and flanks of groundwater in the potential contamination area;

S32: vertical arrangement: arranging groundwater monitor wells in layers with an interval of 3 m when there is one aquifer in a geological layer; setting up groundwater monitor wells in different geological layers separately when there are aquifers in different geological layers, and if a single geological layer has a thickness of greater than 6 m, setting up groundwater monitor wells in layers with an interval of 3 m in the geological layer; S4: constructing the monitor wells in layers; S5: washing the monitor wells and collecting samples; S6: detecting the samples collected in step S5; S7: analyzing detection data acquired in step S6; S71: screening an over-standard indicator, that is, a monitoring indicator exceeding a groundwater quality standard; S72: determining an over-standard characteristic contaminant based on plot contamination

identification and potential contamination source analysis; S73: characterizing a horizontal concentration distribution of the over-standard characteristic contaminant, so as to make a preliminary determination on a layered characteristic of a contamination plume in the aquifer;

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S74: characterizing a vertical concentration distribution of the over-standard characteristic contaminant in a single monitor well: comparing and analyzing groundwater contamination data in different layers of the single monitor well through data analysis and mapping tools, and identifying a vertical contamination distribution characteristic of the single monitor well, so as to identify relative positions of the contamination source and the contamination plume, wherein an area showing a downward trend in the vertical contaminant concentration distribution is one where the contamination source is located, and an area showing an upward trend in the vertical contaminant concentration distribution is one where the contamination plume is located; S75: characterizing a three-dimensional (3D) morphology of the contamination plume of the over-standard characteristic contaminant: identifying a 3D distribution characteristic of the groundwater contamination plume by integrating the data of different layers of each monitor well in the target area through a 3D spatial information analysis tool for the contaminant; S8: determining a morphology and a layered characteristic of the groundwater contamination plume through the data analyses in steps S73 to S75.
2. The method for determining a morphology and a layered characteristic of a groundwater contamination plume according to claim 1, wherein the S22: deriving a permeability coefficient of a target aquifer through an on-site slug test specifically comprises the following sub-steps: SO: putting a water pressure sensor at a certain depth of the well; S02: putting a water level disturbance device into the well and waiting for a water level to stabilize; S03: changing the water level in the well instantly through the disturbance device; S04: recording water level recovery data; and S05: calculating a permeability coefficient through a chart analysis method; wherein, during the test, in order to obtain a maximum initial change in the water level of the test well, a dynamic water level change is recorded before a certain amount of water is injected or extracted from the well until the end of the test; a relationship curve between the water level H and time is drawn, and the permeability coefficient K of the aquifer is calculated; wherein in the horizontal arrangement in step S31, in order to determine a contamination source and a contamination boundary of a plot, monitor wells are further arranged on upstream and downstream boundaries of the groundwater of the plot.
3. The method for determining a morphology and a layered characteristic of a groundwater contamination plume according to claim 1, wherein the S73: characterizing a horizontal concentration distribution of the over-standard characteristic contaminant specifically comprises the following sub-steps:

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17620089_1 (GHMatters) P116159.AU drawing horizontal contaminant distributions at different depths of a screen in the monitor well; distinguishing over-standard and non-over-standard samples with different colors; distinguishing over-standard levels with different symbols; preliminarily identifying a contamination plume direction and range based on the groundwater flow direction; and marking monitor wells at the contamination source, a centerline of the contamination plume and a boundary of the contamination plume; wherein the S74: characterizing a vertical concentration distribution of the over-standard characteristic contaminant specifically comprises the following sub-steps: drawing a histogram of the vertical concentration distribution of the contaminant in the monitor well at the contamination source; and drawing a histogram of the vertical concentration distribution of the contaminant in the monitor well at the centerline of the contamination plume; wherein the S75: characterizing a 3D morphology of the contamination plume of the over-standard characteristic contaminant specifically comprises the following sub-steps: drawing a 3D distribution map of the groundwater contamination plume; intercepting a horizontal profile of the groundwater contamination plume of different layers according to a layered arrangement principle of the monitor wells; intercepting a migration profile of the contamination plume according to an existing determination on the centerline of the contamination plume; and analyzing a migration path and trend of the contamination plume according to a contaminant nature and a stratum characteristic; wherein step S8 specifically comprises: identifying locations of the groundwater contamination source and the contamination plume, identifying a typical profile of the groundwater contamination plume, and determining a preferential migration path of the groundwater, based on the 3D simulation of the contamination plume in step S75 combined with preliminary identification results of the horizontal and vertical distributions in steps S73 and S74.
4. The method for determining a morphology and a layered characteristic of a groundwater contamination plume according to claim 1, wherein the potential contamination path comprises: a contaminant migrates from a surface to deep soil; the contaminant infiltrated into the deep soil migrates to the groundwater; the contaminant entering the groundwater migrates downstream along with the flow of the groundwater, causing the groundwater contamination plume to further spread and contaminate soil in a saturation zone and a surrounding plot; the contaminant in the contaminated groundwater migrates downstream along with the flow of the groundwater, causing

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17620089_1 (GHMatters) P116159.AU the groundwater contamination plume to spread to a target plot and contaminate soil in a saturation zone.
5. The method for determining a morphology and a layered characteristic of a groundwater contamination plume according to claim 1, wherein in step S21, typical geotechnical test samples of different strata are collected at each sampling point to analyze an aquifer status, a lithologic characteristic of a vadose zone and groundwater recharge, runoff and drainage conditions in the area; the aquifer status and the lithologic characteristic of the vadose zone in the area comprise lithology and hydraulic conductivity of the aquifer and lithology and thickness of the vadose zone; the groundwater recharge, runoff and drainage conditions in the area comprise groundwater depth, groundwater recharge source, drainage outlet, groundwater flow direction and permeability coefficient.

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