Method for investigating underground water environment condition of refuse landfill

Abstract

The invention relates to the field of groundwater environment condition investigation, in particular to a refuse landfill groundwater environment condition investigation method, which comprises the following steps: S1, constructing a refuse landfill hydrogeological conceptual model, and identifying a potential pollution area; s2, drawing an underground water flow field, and determining upstream and downstream of underground water; s3, determining a potential pollution area, collecting underground water monitoring data of each monitoring point in different historical periods, selecting specific pollutants, drawing specific pollutant pollution plumes, and determining the potential pollution area; s4, determining a monitoring point position, a target aquifer and a monitoring index, and constructing an underground water monitoring well; and S5, collecting underground water samples at different time periods and different point locations, and collecting underground water specific pollutant concentration data. Characteristic pollutant pollution plumes are drawn through existing monitoring data, underground water survey well position arrangement is carried out in combination with pollution plume distribution conditions, the underground water pollution distribution conditions of the landfill can be found out, and a thought is provided for underground water survey of the landfill.

Description

Technical Field

[0001] The present invention relates to the technical field of groundwater environmental status investigation, and in particular to a method for investigating the groundwater environmental status of a garbage landfill. Background Art

[0002] Landfills play an important role in my country's waste disposal. Although incineration has gradually become the mainstream method, landfilling still holds a certain market share. Landfill pollution is becoming increasingly prominent, and harmful substances such as heavy metals and organic matter in landfill leachate can also pose a threat to groundwater quality. In recent years, my country has gradually strengthened the supervision and management of domestic waste landfills. To implement my country's groundwater management requirements, support the in-depth fight against pollution, address the problem of unclear groundwater environmental conditions in landfills, and accelerate the filling of gaps in groundwater ecological environmental supervision, my country began to conduct groundwater environmental surveys at a number of landfills in 2022.

[0003] The existing groundwater environmental status survey of landfills usually sets up monitoring points upstream and downstream of the landfill area and on both sides of the landfill perpendicular to the groundwater flow direction. Due to the limitations of the terrain and structures around the landfill, there are certain deficiencies in capturing some contaminated areas, making it impossible to accurately understand the groundwater pollution status. Summary of the Invention

[0004] Based on the above technical problems, this application discloses a method for investigating the groundwater environment status of a landfill, comprising: S1. Construct a hydrogeological conceptual model of the landfill site, collect basic information about the landfill site through data collection and personnel interviews, and identify potential contaminated areas; S2. Draw the groundwater flow field, collect groundwater level data during the wet and dry seasons, and determine the upstream and downstream of the groundwater; S3. Identify potential contaminated areas by collecting groundwater monitoring data from different historical periods and monitoring points, selecting characteristic pollutants, mapping the characteristic pollutant plumes, and identifying potential contaminated areas; S4. Determine the location of monitoring wells. Based on the groundwater flow field during the wet and dry seasons and the distribution of potential contaminated areas, determine the monitoring points, target aquifers, and monitoring indicators through on-site surveys, and then construct groundwater monitoring wells. S5. Carry out groundwater sample collection, collect groundwater samples at different time periods and locations, and collect data on the concentration of characteristic groundwater pollutants; S6. Based on the obtained groundwater survey data, screen the pollutants exceeding the standard, draw the distribution of the pollution plumes of each pollutant, and determine the distribution of groundwater pollution in the landfill; S7. Based on the obtained groundwater characteristic pollutant concentration data, draw the characteristic pollutant pollution plume a; based on the characteristic pollutant monitoring data obtained in S3 and the characteristic pollutant monitoring data obtained in S5, draw the characteristic pollutant pollution plume b, compare the pollution plume a and the pollution plume b, and determine whether the pollution plumes drawn by data from different stages are similar. If they are similar, it indicates that the monitoring points determined by the previous monitoring data and the comprehensive consideration of the groundwater flow field and the distribution of potential pollution areas are reasonable and effectively capture pollutants; otherwise, it means that there may be problems with the layout of the monitoring points and they need to be adjusted and optimized.

[0005] Preferably, the hydrogeological conceptual model in S1 determines the aquifer affected by the landfill, determines the phreatic aquifer for plain-type landfills, and conducts a comprehensive analysis of structural faults and karst development for valley-type landfills to obtain the connection path between the landfill and groundwater.

[0006] Preferably, the potential contaminated areas in S1 are identified by considering the landfill layout, the migration pathways of pollutants, checking for groundwater contamination risks, and collecting monitoring data on characteristic groundwater pollutants in and around the landfill during the wet and dry seasons.

[0007] Preferably, the characteristic pollutants in S3 are selected by excluding other pollution sources, selecting landfill characteristics according to the main types of garbage in the landfill, and determining the characteristic pollutants.

[0008] Preferably, the characteristic pollutant plume in S3 is drawn by ordinary kriging interpolation or spline function interpolation using Arcgis or Surfe software.

[0009] Preferably, the monitoring well locations in S4 are set with control points by obtaining upstream control points, pollution diffusion points and migration paths, with reference to the obtained characteristic pollutant plume.

[0010] Preferably, the groundwater sample in S5 is collected by directly collecting the water sample from the outlet of the water pipeline, allowing the water sample to flow into the groundwater sample bottle. The water sample overflows excessively in the sample bottle to form a convex surface. The bottle cap is tightened, the groundwater sample bottle is turned upside down, and observed for a few seconds to ensure that there are no bubbles in the bottle.

[0011] Compared with the prior art, the technical solution of this application has the following technical effects: The present invention provides a method for investigating the groundwater environment of a landfill site. By preliminarily identifying the distribution of characteristic pollutant plumes through historical monitoring data, the method assists in the layout of groundwater monitoring points and the targeted placement of monitoring wells, thereby better capturing the groundwater pollution situation at the landfill site and providing ideas and reference for investigating the groundwater environment of the landfill site. By collecting groundwater level data over a specific period of time, the groundwater flow field is determined. This data can reflect changes in the groundwater flow field within the landfill and surrounding areas during wet and dry seasons, as well as changes in localized water flow. This provides a good basis for identifying the migration, diffusion, and accumulation of pollutants in groundwater. Compared to conventional methods that rely on a fixed upstream control point and five to six diffusion points, this method offers advantages such as greater targeting, higher accuracy, and lower cost, making it suitable for large-scale deployment.

[0012] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application so that it can be implemented in accordance with the contents of the specification, and to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following is a detailed description of the preferred embodiment of the present application in conjunction with the accompanying drawings.

[0013] Based on the detailed description of the specific embodiments of the present application in conjunction with the accompanying drawings below, those skilled in the art will become more aware of the above and other objects, advantages and features of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without inventive work. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0015] Figure 1 It is a flow chart of the method for investigating the groundwater environment status of a landfill in the present invention. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. In the following description, specific details such as specific configurations and components are provided only to help fully understand the embodiments of the present application. Therefore, it should be clear to those skilled in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present application. In addition, for clarity and brevity, the description of known functions and structures has been omitted in the embodiments.

[0017] It should be understood that references throughout this specification to "one embodiment" or "this embodiment" mean that a particular feature, structure, or characteristic associated with the embodiment is included in at least one embodiment of the present application. Therefore, the appearance of "one embodiment" or "this embodiment" throughout this specification does not necessarily refer to the same embodiment. Furthermore, these particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0018] In addition, the present application may repeat reference numerals and / or letters in different examples. This repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed.

[0019] The term "and / or" in this article is only a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist at the same time. The term " / and" in this article describes another type of association object relationship, indicating that two relationships can exist. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the previous and subsequent associated objects are in an "or" relationship.

[0020] The term "at least one" in this article is merely a description of the association relationship between associated objects, indicating that three relationships may exist. For example, at least one of A and B can mean: A exists alone, A and B exist at the same time, and B exists alone.

[0021] It should also be noted that, in this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include," "comprises," or any other variations thereof are intended to cover non-exclusive inclusion.

[0022] Example 1 This embodiment mainly describes a method for investigating the groundwater environment status of a landfill. Figure 1 Shown, including: S1. Construct a hydrogeological conceptual model of the landfill site, collect basic information about the landfill site through data collection and personnel interviews, and identify potential contaminated areas; S2. Draw the groundwater flow field, collect groundwater level data during the wet and dry seasons, and determine the upstream and downstream of the groundwater; S3. Identify potential contaminated areas by collecting groundwater monitoring data from different historical periods and monitoring points, selecting characteristic pollutants, mapping the characteristic pollutant plumes, and identifying potential contaminated areas; S4. Determine the location of monitoring wells. Based on the groundwater flow field during the wet and dry seasons and the distribution of potential contaminated areas, determine the monitoring points, target aquifers, and monitoring indicators through on-site surveys, and then construct groundwater monitoring wells. S5. Carry out groundwater sample collection, collect groundwater samples at different time periods and locations, and collect data on the concentration of characteristic groundwater pollutants; S6. Based on the obtained groundwater survey data, screen the pollutants exceeding the standard, draw the distribution of the pollution plumes of each pollutant, and determine the distribution of groundwater pollution in the landfill; S7. Based on the obtained groundwater characteristic pollutant concentration data, draw the characteristic pollutant pollution plume a; based on the characteristic pollutant monitoring data obtained in S3 and the characteristic pollutant monitoring data obtained in S5, draw the characteristic pollutant pollution plume b, compare the pollution plume a and the pollution plume b, and determine whether the pollution plumes drawn by data from different stages are similar. If they are similar, it indicates that the monitoring points determined by the previous monitoring data and the comprehensive consideration of the groundwater flow field and the distribution of potential pollution areas are reasonable and effectively capture pollutants; otherwise, it means that there may be problems with the layout of the monitoring points and they need to be adjusted and optimized.

[0023] Furthermore, the hydrogeological conceptual model in S1 determines the aquifer affected by the landfill, determines the phreatic aquifer for plain-type landfills, and conducts a comprehensive analysis of structural faults and karst development for valley-type landfills to obtain the connection path between the landfill and groundwater.

[0024] Furthermore, the identification of potential contaminated areas in S1 is carried out by considering the plan layout of the landfill and the migration pathways of pollutants, checking the risk of groundwater contamination, and collecting monitoring data of characteristic groundwater pollutants in and around the landfill during the wet and dry seasons.

[0025] Furthermore, the characteristic pollutants in S3 are selected by excluding other pollution sources, selecting landfill characteristics according to the main types of garbage in the landfill, and determining the characteristic pollutants.

[0026] Furthermore, the characteristic pollutant plume in S3 is drawn by using the ordinary kriging interpolation method or the spline function interpolation method using Arcgis or Surfe software.

[0027] Furthermore, the monitoring well locations in S4 are set with control points by obtaining upstream control points, pollution diffusion points and migration paths, with reference to the obtained characteristic pollutant plumes.

[0028] Furthermore, the groundwater sample in S5 is collected by directly collecting the water sample from the outlet of the water pipeline, allowing the water sample to flow into the groundwater sample bottle. The water sample overflows excessively in the sample bottle to form a convex surface. The bottle cap is tightened, and the groundwater sample bottle is turned upside down and observed for a few seconds to ensure that there are no bubbles in the bottle.

[0029] This embodiment describes in detail that this application uses historical monitoring data to draw characteristic pollutant plumes, assisting in the precise layout of monitoring wells, which can more effectively capture the groundwater pollution situation in the landfill. At the same time, the groundwater level data during the flood season and the dry season are collected to draw the flow field, which can clearly reflect the changes in the groundwater flow field in and around the landfill at different times, and provide a basis for analyzing the migration, diffusion and enrichment of pollutants. Compared with the conventional fixed point layout method, it is more targeted, more accurate and less costly, and provides a scientific and effective idea and reference for the investigation of the groundwater environmental status of landfills and even other industrial pollution sites.

[0030] Based on Example 1, this implementation describes in detail a method for investigating the groundwater environmental status of a landfill. This method involves identifying the distribution of characteristic pollutant plumes based on preliminary groundwater monitoring data at the landfill and conducting targeted groundwater monitoring well deployment. The method is applicable to investigating the groundwater pollution status of industrial contaminated sites such as landfills and hazardous waste landfills. Taking the investigation of the groundwater environment status of a landfill in Jiangsu Province as an example, how to use the method of the present invention to investigate the groundwater environment status of the landfill is specifically explained. The specific implementation steps are as follows: S1. Constructing a conceptual hydrogeological model of the landfill S1-1. Basic information of landfill (1) The landfill was put into use in 1990, covering an area of more than 50 mu. It was designed mainly for the landfill of domestic waste and was closed as of 2010. Before closure, the landfill area was approximately 42 mu, with a depth of 5 to 6 meters.

[0031] (2) The landfill layers are as follows from top to bottom: ① plain fill: light grayish yellow to light grayish brown, mainly composed of silty clay mixed with a small amount of gravel, with a thickness of 0.40 to 0.80 m and an average of 0.54 m; ②-1 silty clay: light brownish gray, plastic, with a thickness of 0.80 to 1.50 m and an average of 1.20 m; the bottom of the layer is buried at a depth of 1.40 to 2.30 m and an average of 1.74 m; ②-2 silt: light gray, slightly to medium dense, with a thickness of 4.60 to 5.90 m and an average of 5.14 m and a bottom of 6.20 to 7.30 m and an average of 6.82 m. ②-3 layer of silty clay: light gray, partially silty silty clay, thickness 13.80-17.10m, average 15.08m, layer bottom burial depth 17.50-21.30m, average 19.64m; ②-4 layer of silty clay interbedded with silt: light gray, interbedded with a thin layer of silt, this layer is spread throughout the site and has not been exposed.

[0032] (3) The groundwater in the landfill is primarily pore water, distributed primarily in the ②-2 silt soil, with a depth of 1.4 to 2.5 m. It receives replenishment from atmospheric precipitation and surface water, and is discharged through evaporation and into surface rivers. The terrain in the area is flat, and under natural conditions, runoff is weak.

[0033] S1-2. Potentially contaminated areas Identify potential leakage points, leachate treatment areas, leachate outlets, and potential contaminated areas in the landfill through data collection, personnel interviews, and on-site surveys.

[0034] S1-3. Aquifers susceptible to pollution According to the landfill depth range and site hydrogeological conditions, the aquifer susceptible to pollution is determined to be the ②-2 layer of phreatic aquifer.

[0035] S2. Draw the groundwater flow field Collect multi-year groundwater level data in the area where the landfill is located, screen and classify the valid data according to the flood season and dry season, draw the multi-year groundwater flow fields in the flood season and dry season respectively, determine the upstream and downstream and hydraulic gradients, and analyze the migration pathways of pollutants and areas prone to enrichment.

[0036] S3. Identify potential contaminated areas S3-1. Selection of characteristic pollutants Based on the landfill type and historical monitoring data, characteristic pollutants representing the landfill's pollution were selected. There are no other industrial enterprises near the landfill, and leachate monitoring results indicate that oxygen consumption and nitrite nitrogen concentrations reached 167 mg / L and 15.3 mg / L, respectively. These pollutants have also been detected historically at monitoring wells surrounding the landfill. Therefore, in this example, oxygen consumption and nitrite nitrogen were selected as representative monitoring indicators for the landfill's characteristic pollutants.

[0037] S3-2. Determination of potential contamination plumes Based on the collected historical groundwater monitoring data, the groundwater monitoring data of the target monitoring layer being the phreatic aquifer were screened out, the historical monitoring data of oxygen consumption and nitrite nitrogen were selected, and the Surfer software was used to draw the characteristic pollutant pollution plume.

[0038] S4. Determination of monitoring wells S4-1. Determination of monitoring well location The location of the monitoring wells is determined based on the obtained oxygen consumption and the distribution of the nitrite nitrogen pollution plume. If there is an available monitoring well at the center of the pollution plume, it will be used as the well location for this investigation. Otherwise, a monitoring well will be arranged at the center of the potential pollution plume. According to the size of the characteristic pollution plume, for areas with a larger distribution range of the pollution plume, the wells will be appropriately arranged in the middle area of the pollution plume according to the changes in the concentration gradient of the pollution plume to control the size of the pollution plume and capture the distribution of pollutants. According to the distribution of the groundwater flow field in S2, groundwater monitoring wells are arranged in some areas that are prone to enrichment of pollution. In addition, for the upstream and diffusion areas of the landfill, additional well locations are arranged according to the Technical Guidelines for Investigation and Assessment of Groundwater Environmental Status of Landfills. In this embodiment, 9 groundwater sampling points are arranged.

[0039] S4-2, well depth The target aquifer for groundwater monitoring this time is the ②-2 layer of phreatic aquifer. The well depth is set to 8m, the screen tube position is set to -1m to -7.5m, the bottom 0.5m is a sedimentation tube, and the construction of the monitoring well meets the requirements of the "Groundwater Monitoring Well Construction Specifications".

[0040] S4-3. Monitoring indicators According to the requirements, the monitoring indicators include pH, chloride, sulfate, total hardness, total dissolved solids, iron, manganese, copper, zinc, volatile phenols, anionic surfactants, oxygen consumption, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, fluoride, cyanide, mercury, arsenic, selenium, cadmium, chromium (hexavalent), lead, benzene, DDT, p,p'-DDT, hexachlorobenzene, chloroform, dichlorobromomethane, bromoform, carbon tetrachloride, vinyl chloride, chlorobenzene, benzene, toluene, ethylbenzene, xylene, styrene, benzo(a)pyrene, fecal coliform, and total coliform.

[0041] S4-4. Monitoring Well Construction Groundwater monitoring wells are constructed in accordance with the requirements of the "Groundwater Monitoring Well Construction Specifications".

[0042] S5. Groundwater sample collection Low-flow technology was used for well washing and groundwater sampling. Water samples were collected directly from the outlet of the water pipeline and allowed to flow into the groundwater sample bottle. The water sample overflowed excessively in the sample bottle, forming a convex surface. The bottle cap was tightened, and the groundwater sample bottle was turned upside down and observed for a few seconds to ensure that there were no bubbles in the bottle. When collecting water samples, the sampling port depth was set at about 1.0 m below the water surface. Groundwater sample collection was completed within 2 h, and the water outlet flow rate was 30 mL / min.

[0043] S6. Groundwater Survey Data Analysis Based on the acquired groundwater survey data, pollutants exceeding standards were screened, the distribution of each pollutant plume was mapped, and the distribution of groundwater contamination at the landfill site was determined. In this example, eight groundwater sampling points were deployed, and the monitoring period was September 2022, with a total of eight groundwater samples collected. The test results showed that ammonia nitrogen, volatile phenols, oxygen consumption, nitrite, sulfide, and E. coli exceeded the Class IV water limits in the Groundwater Quality Standard (GB / T14848-2017).

[0044] S7. Evaluation of the effectiveness of point layout: the oxygen consumption concentration data obtained in S6 were selected to draw the characteristic pollutant pollution plume a; based on the oxygen consumption concentration data obtained in S3 and the oxygen consumption concentration data obtained in S5, the characteristic pollutant pollution plume b was drawn. By comparing the pollution plume a and the pollution plume b, it was found that the point layout of this groundwater survey was highly targeted, low-cost, and had good advantages and universality.

[0045] This example, through steps such as constructing a hydrogeological conceptual model and mapping groundwater flow fields, accurately identifies potential contaminated areas and characteristic pollutants. Monitoring wells are then rationally deployed, and water samples collected and analyzed to identify multiple pollutants exceeding standards and clearly define the distribution of contamination. Evaluation of the effectiveness of this point-based deployment demonstrates the method's high targetedness and low cost, effectively assessing the status of groundwater contamination at landfills. This provides a key basis for subsequent pollution control and environmental regulation, and is highly valuable for groundwater environmental surveys at landfills.

[0046] The above are only preferred embodiments of the present invention, which do not limit the scope of protection of the present invention. For those skilled in the art, the present invention can be modified and varied in various ways. Any changes, modifications, replacements, integrations and parameter changes to these embodiments through conventional substitutions or that can achieve the same functions without departing from the principles and spirit of the present invention fall within the scope of protection of the present invention.

Claims

1. A method for investigating the groundwater environment of a landfill, characterized in that: Here are the steps: S1. Construct a hydrogeological conceptual model of the landfill site, collect basic information about the landfill site through data collection and personnel interviews, and identify potential contaminated areas; S2. Draw the groundwater flow field, collect groundwater level data during the wet and dry seasons, and determine the upstream and downstream of the groundwater; S3. Identify potential contaminated areas by collecting groundwater monitoring data from different historical periods and monitoring points, selecting characteristic pollutants, mapping the characteristic pollutant plumes, and identifying potential contaminated areas; S4. Determine the location of monitoring wells. Based on the groundwater flow field during the wet and dry seasons and the distribution of potential contaminated areas, determine the monitoring points, target aquifers, and monitoring indicators through on-site surveys, and then construct groundwater monitoring wells. S5. Carry out groundwater sample collection, collect groundwater samples at different time periods and locations, and collect data on the concentration of characteristic groundwater pollutants; S6. Based on the obtained groundwater survey data, screen the pollutants exceeding the standard, draw the distribution of the pollution plumes of each pollutant, and determine the distribution of groundwater pollution in the landfill; S7. Draw the characteristic pollutant pollution plume a based on the obtained groundwater characteristic pollutant concentration data; draw the characteristic pollutant pollution plume b based on the characteristic pollutant monitoring data obtained in S3 and the characteristic pollutant monitoring data obtained in S5, and compare the pollution plume a and the pollution plume b to determine whether the pollution plumes drawn by data from different stages are similar. If they are similar, it indicates that the monitoring points determined by the previous monitoring data and the comprehensive consideration of the groundwater flow field and the distribution of potential pollution areas are reasonable and effectively capture pollutants; otherwise, it means that there may be problems with the layout of the monitoring points and they need to be adjusted and optimized.

2. The method for investigating the groundwater environment of a landfill according to claim 1, characterized in that: The hydrogeological conceptual model in S1 determines the aquifer affected by the landfill, determines the phreatic aquifer for plain-type landfills, and conducts a comprehensive analysis of structural faults and karst development for valley-type landfills to obtain the connection path between the landfill and groundwater.

3. The method for investigating the groundwater environment of a landfill according to claim 1, wherein: The identification of potential contaminated areas in S1 is carried out by considering the layout of the landfill and the migration path of pollutants, checking the groundwater pollution risk, and collecting monitoring data of characteristic groundwater pollutants in and around the landfill during the flood season and the dry season.

4. The method for investigating the groundwater environment of a landfill according to claim 1, wherein: The characteristic pollutants in S3 are selected by excluding other pollution sources, selecting landfill characteristics according to the main types of garbage in the landfill, and determining the characteristic pollutants.

5. The method for investigating the groundwater environment of a landfill according to claim 1, wherein: The characteristic pollutant plume in S3 is drawn by ordinary kriging interpolation or spline function interpolation using Arcgis or Surfe software.

6. The method for investigating the groundwater environment of a landfill according to claim 1, wherein: The monitoring well locations in S4 are set with control points by obtaining upstream control points, pollution diffusion points and migration paths, with reference to the obtained characteristic pollutant plumes.

7. The method for investigating the groundwater environment of a landfill according to claim 1, characterized in that: The groundwater sample in S5 is collected by directly collecting the water sample from the outlet of the water pipeline, allowing the water sample to flow into the groundwater sample bottle. The water sample overflows excessively in the sample bottle to form a convex surface. The bottle cap is tightened, and the groundwater sample bottle is turned upside down and observed for a few seconds to ensure that there are no bubbles in the bottle.

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