Well management methods

Abstract

To provide a well management method that removes PFAS from groundwater and continuously ensures its safety. [Solution] A well management method comprising the steps of: sampling groundwater to be drawn from; conducting a test to confirm the adsorption capacity of PFAS (perfluoroalkyl compounds and polyfluoroalkyl compounds) by an adsorbent; measuring the PFAS concentration of the groundwater collected from an observation well located around the intake well; pumping the groundwater by passing it through the adsorbent inserted into the casing of the intake well; and replacing the adsorbent inserted into the casing of the intake well based on the amount of adsorbent inserted into the casing of the intake well, the PFAS adsorption capacity calculated based on the amount of adsorbent inserted into the casing of the intake well and the results of the adsorption capacity confirmation test, and the cumulative adsorption amount of PFAS estimated based on the amount of groundwater pumped and the PFAS concentration of the groundwater.

Description

[Technical Field]

[0001] This invention relates to a method for managing wells. [Background technology]

[0002] Patent Document 1 describes a method for purifying contaminated soil and contaminated groundwater, characterized by drilling multiple wells in soil contaminated with a chemical substance, installing a purification device containing a purification material in the groundwater of at least one of the multiple wells, forcibly passing the groundwater in the well through the purification material, and transferring the groundwater that has been passed through to the other wells of the multiple wells.

[0003] Patent Document 2 describes a well for pumping groundwater in which a pumping pipe having a submersible pump at its lower end is inserted into a cylindrical casing, and when contaminated groundwater is drawn up through the pumping pipe by the submersible pump, it is purified by an annular filter material installed around the submersible pump and the pumping pipe (particularly Figure 5). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2009-050818 [Patent Document 2] Japanese Patent Publication No. 2000-042537 [Overview of the project] [Problems that the invention aims to solve]

[0005] The problem of pollution caused by compounds known as POPs (persistent organic pollutants) that are released into the environment and remain in soil and groundwater is attracting attention. While many compounds are said to potentially behave as POPs, one group of organofluorine compounds known as PFAS (perfluoroalkyl and polyfluoroalkyl compounds) has been attracting particular attention in recent years.

[0006] PFAS are known to be a cause of environmental problems because they are persistent and remain for a long time. Furthermore, because they are water-soluble surfactants, once released into the environment and diffused into the soil, PFAS continue to contaminate groundwater for a long period, hindering the use of groundwater for domestic or industrial purposes through wells.

[0007] Therefore, methods for remediating groundwater and soil in the environment have been proposed. Patent Document 1 is one example of a proposed method for remediating contaminated soil and contaminated groundwater. However, requests from public institutions to water supply operators regarding PFAS are to position the liquid concentration of PFAS as a target item for water quality management and to manage it appropriately, and do not require the remediation of the soil or groundwater itself in the surrounding environment (for example, the Ministry of Health, Labour and Welfare's notification of March 30, 2020, "Regarding points to note concerning the partial amendment of the Ministerial Ordinance concerning Water Quality Standards, etc." (Yakusei Suihatsu 0330 No. 3)).

[0008] As mentioned earlier, PFAS are persistent and chemically stable substances, making it impossible to detect their presence and concentration in situ. This requires transporting samples to specialized analytical laboratories for analysis such as chromatography. Therefore, even if PFAS contamination of groundwater is confirmed, investigating the extent and manner of its spread to surrounding soil and groundwater is not easy. Such investigations and subsequent soil and groundwater remediation inevitably require large-scale operations. Furthermore, even after such large-scale remediation, there is a risk of re-contamination unless the source of PFAS contamination is removed. For groundwater users who simply desire safe groundwater, this is far from a realistic solution.

[0009] As exemplified in Patent Document 2, purifying only the groundwater that is pumped and used to remove pollutants is considered a practical approach. However, if PFAS is assumed as the pollutant, due to the nature of PFAS, its presence and concentration cannot be detected in situ. Therefore, it is not possible to monitor the quality of the groundwater pumped daily in real time, and even if the filter material breaks through and fails to remove PFAS, this fact cannot be known. Although Patent Document 2 mentions volatile organochlorine compounds (VDCs) as pollutants to be removed, it does not describe how PFAS will be removed from the groundwater and how its safety will be guaranteed, nor does it describe how the equipment for removing PFAS will be maintained. No technical knowledge can be obtained in this regard.

[0010] This invention has been made in view of the above circumstances, and its purpose is to provide a well management method that can remove PFAS from groundwater and continuously ensure its safety. [Means for solving the problem]

[0011] The invention disclosed in this application, which aims to solve the above-mentioned problems, has various aspects, and a summary of some of the most representative aspects is as follows.

[0012] (1) A well management method comprising the steps of: sampling groundwater to be drawn from; conducting a test to confirm the adsorption capacity of PFAS (perfluoroalkyl compounds and polyfluoroalkyl compounds) by an adsorbent; measuring the PFAS concentration of the groundwater collected from an observation well located around the intake well; pumping the groundwater by passing it through the adsorbent inserted into the casing of the intake well; and replacing the adsorbent inserted into the casing of the intake well based on the amount of adsorbent inserted into the casing of the intake well, the PFAS adsorption capacity calculated based on the amount of adsorbent inserted into the casing of the intake well and the results of the adsorption capacity confirmation test, and the cumulative adsorption amount of PFAS estimated based on the amount of groundwater pumped and the PFAS concentration of the groundwater.

[0013] (2) A well management method in which the step of measuring the PFAS concentration of the groundwater in (1) is performed repeatedly, either periodically or irregularly.

[0014] (3) A method for managing wells in which, in (1) or (2), multiple observation wells are provided, and the PFAS concentration of the groundwater is determined by using the groundwater with the highest concentration among the groundwater samples taken from the multiple observation wells.

[0015] (4) A method for managing wells in which, in (1) or (2), a plurality of observation wells are provided, and the PFAS concentration of the groundwater is taken from the observation well located upstream of the intake well in the flow of the groundwater, among the plurality of observation wells.

[0016] (5)(4) A well management method in which the direction of groundwater flow is estimated based on the groundwater changes in a plurality of observation wells. [Brief explanation of the drawing]

[0017] [Figure 1] This figure schematically shows a cross-section of the soil in which a well managed by a well management method according to a preferred embodiment of the present invention is installed. [Figure 2]It is a schematic diagram showing a state where an adsorbent is inserted into the casing of a water intake well. [Figure 3] It is a flowchart showing an example of the procedure of a well management method according to a preferred embodiment of the present invention. [Figure 4] It is an example of an adsorption isotherm obtained by an adsorption capacity confirmation test. [Figure 5] It is a plan view showing an example of the positional relationship of an observation well 2 provided around a water intake well 1.

Embodiments for Carrying Out the Invention

[0018] FIG. 1 is a diagram schematically showing a cross-section of the soil in which a well managed by the well management method according to a preferred embodiment of the present invention is installed.

[0019] Although the soil has fine differences depending on its topography, as a general structure, it is considered that as it goes from the ground surface to the underground, it forms layers in the order of the unsaturated zone VZ, the saturated zone SZ, the impervious layer or the semi-impervious layer AC. The height of the ground surface is the ground surface height GL, and the height of the surface of the saturated zone SZ coincides with the groundwater level depth WL, which is the surface where the groundwater becomes atmospheric pressure. In the unsaturated zone VZ, there are voids between the particles constituting the soil, and interstitial water and air are mixed. In the saturated zone SZ, the space between the particles constituting the soil is filled with interstitial water.

[0020] In the saturated zone SZ, a groundwater flow corresponding to the underground topography occurs. For example, when the surface of the impervious layer or the semi-impervious layer AC is not horizontal, such as having an inclination, the groundwater inside the saturated zone SZ forms a flow according to the shape of the impervious layer or the semi-impervious layer AC. In FIG. 1, such a groundwater flow is indicated by an arrow F.

[0021] Because PFAS is water-soluble, it diffuses through the soil via groundwater flow F. Therefore, if a source of PFAS contamination exists, the PFAS will be carried by groundwater flow F and contaminate water drawn from wells located far away. Such sources of contamination may exist on the surface, for example, and as shown by arrow P1 in the figure, they may infiltrate into the soil during rainfall and contaminate groundwater in the saturated zone SZ. Alternatively, PFAS that has infiltrated into the soil in the past may accumulate deep underground and, as shown by arrow P2 in the figure, continue to contaminate groundwater via groundwater flow F.

[0022] In addition, an intake well 1 and an observation well 2 located around intake well 1 are provided. Both intake well 1 and observation well 2 are drilled to a depth greater than the groundwater level WL, reaching the saturation zone SZ. Furthermore, casings 10 and 20 are provided on the sides of intake well 1 and observation well 2 to prevent soil collapse from blocking the wells. The lower part of casings 10 and 20 serves as a strainer, preventing soil particles from entering the well while allowing groundwater to be drawn into the well.

[0023] Inside the casing 10 of the intake well 1, an intake pipe 11 is inserted deeper than the groundwater level WL, and an intake pump 12, located at the tip of the intake pipe 11, pumps groundwater up to the surface for intake. Adsorbent 13 is inserted inside the casing 10, and groundwater that flows into the casing 10 after passing through the strainer of the casing 10 of the intake well 1 passes through the adsorbent 13 to be purified, and is then pumped up by the intake pump 12 and taken out to the surface through the intake pipe 11.

[0024] In the intake well 1, the adsorbent 13 can be inserted into the casing 10 in front of, behind, or both of the intake pump 12. Figure 2 is a schematic diagram showing the adsorbent 13 inserted into the casing 10 of the intake well 1. In this figure, a part of the inside of the intake well 1 is shown in cross-section for easier understanding. In the figure, (a) is an example where the adsorbent 13 is placed in front of the intake pump 12, and (b) is an example where the adsorbent 13 is placed behind the intake pump.

[0025] In example (a), the adsorbent 13 is inserted around the intake pipe 11 and intake pump 12 inside the casing 10 of the intake well 1. Groundwater flowing into the casing 10 after passing through the strainer 14 located at the bottom of the casing 10 passes through the adsorbent 13 to reach the intake pump 12 and is pumped up to the surface. In example (b), the adsorbent 13 is inserted inside the intake pipe 11 inside the casing 10 of the intake well 1. Groundwater flowing into the casing 10 after passing through the strainer 14 located at the bottom of the casing 10 passes through the adsorbent 13 when it is pumped up to the surface by the intake pump 12.

[0026] Here, the adsorbent 13 is used to adsorb and remove PFAS dissolved in groundwater, and specifically may be an ion exchange resin, activated carbon, zeolite, or a combination thereof. Furthermore, the adsorbent 13 may be filled with ion exchange resin or the like inside an appropriate cartridge to facilitate its replacement. The dimensions and shape of the cartridge are designed to match the dimensions of the casing 10 and intake pipe 11 of the intake well 1.

[0027] Returning to Figure 1, observation well 2 is provided to sample groundwater passing through the saturation zone SZ periodically or irregularly, and does not necessarily require a permanent pumping mechanism. Of course, like intake well 1, it may be equipped with a pumping mechanism consisting of an intake pipe and an intake pump, or an intake hose may be inserted into the casing 20 as needed to collect groundwater as appropriate.

[0028] As mentioned above, purified groundwater is pumped up from intake well 1 after passing through the adsorbent 13. During this process, PFAS contained in the groundwater flowing into intake well 1 is adsorbed onto the adsorbent 13 and gradually accumulates. At this time, the maximum amount of substance (adsorbate) that the adsorbent 13 (adsorbent medium) can adsorb is the amount of adsorption at the equilibrium state where the adsorbate is adsorbed and detached from the adsorbent medium (equilibrium adsorption amount). This equilibrium adsorption amount is known to depend on the concentration of the adsorbate, and the relationship between the equilibrium adsorption amount and the concentration of the adsorbate is generally known as the adsorption isotherm.

[0029] Therefore, when a target concentration is set for groundwater to be considered purified and PFAS removed, if an amount of PFAS exceeding the equilibrium adsorption amount at that target value is adsorbed by the adsorbent 13, it becomes impossible to reduce the PFAS concentration in the water to below the target value using that adsorbent 13. This is what is known as breakthrough, and when this happens, the adsorbent 13 must be replaced with a new one.

[0030] From the above discussion, it can be seen that if the equilibrium adsorption amount at the target concentration of the adsorbent 13 and the total amount of PFAS adsorbed and accumulated on the adsorbent 13 as pumped groundwater passes through can be estimated, then, since the amount of adsorbent 13 installed in the intake well 1 is known, it is possible to estimate whether or not the adsorbent 13 has broken through. The well management method according to this embodiment utilizes this fact to rationally manage the adsorbent 13 so that it does not break through without having to monitor the PFAS concentration of the pumped groundwater one by one.

[0031] Figure 3 is a flowchart showing an example of the procedure for managing a well according to this embodiment. The following describes each step of the well management method according to this embodiment in accordance with this flowchart.

[0032] <Step 1> (ST1) A water intake well 1 and an observation well 2 will be installed. While at least one observation well 2 is sufficient, it is desirable to install multiple observation wells surrounding the water intake well 1, as will be described later. Furthermore, the observation wells 2 will be located near the water intake well 1, specifically at a distance of several meters to several tens of meters from the water intake well 1.

[0033] <Step 2> (ST2) The groundwater to be drawn will be sampled, and a test will be conducted to confirm the adsorption capacity of PFAS by the adsorbent 13. This sampling is usually performed using observation well 2. If multiple observation wells 2 are provided, any one of them may be used. Note that intake well 1 is not suitable for this sampling because it is not possible to draw untreated groundwater that has not passed through the adsorbent 13 once it is installed. However, groundwater collected during the installation of intake well 1 may be used.

[0034] As already explained, the relationship between equilibrium adsorption and adsorbate concentration is generally represented by an adsorption isotherm. However, the adsorbate adsorbed by the adsorbent 13 is not necessarily limited to PFAS, but also includes other dissolved ions. Therefore, the adsorption isotherm for PFAS is not necessarily constant and is thought to vary depending on the type and concentration of other dissolved ions contained in the groundwater, and differs depending on the properties of the groundwater, making it difficult to prepare in advance. On the other hand, the type and concentration of dissolved ions other than PFAS contained in the groundwater are largely determined by the location from which the groundwater is pumped and the surrounding soil. Therefore, for groundwater taken from a specific intake well 1, the adsorption isotherm for PFAS relative to the adsorbent 13 used is determined for groundwater sampled from around the intake location, and this is considered to be almost constant and hardly change.

[0035] The adsorption capacity confirmation test determines the adsorption isotherm for PFAS adsorbed by adsorbent 13 in sampled groundwater. Figure 4 shows an example of an adsorption isotherm obtained by the adsorption capacity confirmation test. By adding different amounts of adsorbent to multiple groundwater samples and measuring the concentration of PFAS in the groundwater after reaching equilibrium (equilibrium concentration), the amount of PFAS adsorbed per unit weight of the adsorbent at that equilibrium concentration (equilibrium adsorption amount) can be determined from the difference between the PFAS concentration before adsorption and the amount of adsorbent added (dry weight), and furthermore, an adsorption isotherm showing the relationship between the two can be obtained from multiple measurement results. There are no particular restrictions on the units of equilibrium concentration and equilibrium adsorption amount, but in Figure 4, ng / L and ng / mg-dry (dry weight) are used, respectively. In addition, it is generally known that the obtained adsorption isotherm becomes a straight line when the equilibrium concentration is plotted on a logarithmic scale, as shown in the figure, in the region of low equilibrium concentration. The black diamond marks in the figure show examples of measured values. The PFAS concentration of each sample is measured by analysis by a specialized analytical institution.

[0036] Once such adsorption isotherms are determined, the target concentration of PFAS to be achieved after removing PFAS from groundwater is ρ d Therefore, the equilibrium adsorption amount m shown by the adsorbent at that time. d This can be obtained.

[0037] <Step 3> (ST3) The PFAS concentration of groundwater sampled from observation wells 2 located around intake well 1 is measured. This measurement is also performed by a specialized analytical institution. If only one observation well 2 is installed, the PFAS concentration of the groundwater obtained from that observation well 2 is used. In contrast, Figure 5 shows an example where multiple observation wells 2 are installed.

[0038] Figure 5 is a plan view showing an example of the positional relationship of observation wells 2 installed around intake well 1. Here, four observation wells 2 are installed surrounding intake well 1. The reason for installing multiple observation wells 2 in this way is that the direction of groundwater flow F (see Figure 1) cannot be immediately determined, and depending on the position of the observation wells 2 relative to intake well 1, the PFAS concentration of groundwater obtained from observation wells 2 may not necessarily match the PFAS concentration of groundwater taken from intake well 1.

[0039] At this time, several methods can be considered for measuring and determining the PFAS concentration of groundwater. The first method is to use the groundwater with the highest concentration among those collected from multiple observation wells 2 as the PFAS concentration of the groundwater. All collected groundwater samples are measured for PFAS concentration. This is because if the replacement management of the adsorbent 13 is carried out according to the groundwater sample with the highest PFAS concentration among those obtained from around the intake well 1, management on the safe side will be carried out regardless of the direction of the groundwater flow F, thus preventing the adsorbent 13 from breaking through unnoticed.

[0040] The second method involves using the PFAS concentration of the groundwater from one of the multiple observation wells 2, specifically the one located upstream of the intake well 1 in the groundwater flow. In this case, it is not necessary to take groundwater samples from all of the multiple observation wells 2 and measure them, but the direction of the groundwater flow underground must be known. This direction of groundwater flow can be estimated based on the groundwater levels in the multiple observation wells 2.

[0041] In other words, the groundwater level corresponds to the underground topography, mainly the shape of the impermeable or low-permeability layer AC, and the water flows from areas with higher water levels to areas with lower water levels. Therefore, by measuring the groundwater levels in multiple observation wells 2, it can be estimated that the well with the highest groundwater level is located upstream of the intake well 1 in the groundwater flow.

[0042] For multiple observation wells 2, if a significant difference in groundwater levels can be observed, the second method described above can be used; otherwise, the first method described above can be used.

[0043] Furthermore, the measurement of PFAS concentrations in groundwater in Step 3 is performed repeatedly, either regularly or irregularly. Regularly, this is done, for example, every few weeks to several months. This is because the concentration may gradually decrease as PFAS flows out from the source of contamination, or it may increase due to the emergence of a new source of contamination. Irregularly, this is done when external factors that cause fluctuations in the PFAS concentration of groundwater flowing into the vicinity of intake well 1 are observed. For example, after heavy rain, there is concern about the inflow of new PFAS into the groundwater from the source of contamination, and in the event of civil engineering work involving excavation of the ground or a major earthquake occurring nearby, there is a possibility of fluctuations in groundwater flow, so additional measurements may be performed in addition to the regular measurements.

[0044] <Step 4> (ST4) Groundwater is pumped by passing it through an adsorbent 13 inserted into the casing 10 of the intake well 1. Since the pumped groundwater is purified, it can be used directly as domestic or industrial water, and it is also advisable to store it in a storage tank so that purified water can be taken out as needed. At this time, the amount of water pumped should be monitored using appropriate measuring instruments such as a flow meter.

[0045] <Step 5> (ST5) The cumulative adsorption amount of PFAS is estimated based on the pumping volume of groundwater and the PFAS concentration in the groundwater. Here, taking a conservative approach, we assume that the entire amount of PFAS contained in the groundwater is adsorbed by the adsorbent 13, and the cumulative adsorption amount M c It is estimated by the following formula.

number

[0046] Here, the period from when the PFAS concentration in groundwater is measured to when the PFAS concentration in groundwater is measured next is called an interval, and if we sequentially number them as 1, 2, 3, ···, n and call the k-th interval the interval k, then ρ k is the PFAS concentration in groundwater (interval PFAS concentration) in the k-th interval (i.e., measured at the start of the k-th interval), and V k is the pumping volume in the k-th interval (interval pumping volume).

[0047] <Step 6> (ST6) Based on the amount of adsorbent 13 inserted into the casing 10 of production well 1, the PFAS adsorption capacity calculated from the results of the adsorption capacity confirmation test, the pumping volume of the pumped groundwater, and the cumulative adsorbed amount of PFAS estimated based on the PFAS concentration in the groundwater, determine whether it is necessary to replace the adsorbent 13 inserted into the casing 10 of production well 1. Here, regarding the amount of adsorbent 13, since the space for the adsorbent 13 that can be installed is determined based on the dimensions and shape of production well 1, etc., its amount (dry weight) is also determined and is known.

[0048] The PFAS adsorption capacity M of the adsorbent 13 a is the equilibrium adsorption amount m obtained by the adsorption capacity confirmation test in Step 2 d and, from the dry weight W of the adsorbent 13,

Equation

[0049] The cumulative adsorbed amount M c is considered to cause breakthrough when it exceeds the adsorption capacity M a , so using a safety factor α (for example, 1.2),

Equation

[0050] <Step 7> (ST7) If it is determined that the adsorbent 13 needs to be replaced, the pumping from the intake well 1 will be stopped, and the adsorbent 13 inserted inside the casing 10 of the intake well 1 will be replaced with a new one. After the adsorbent 13 is replaced, the cumulative adsorption amount M c Reset to 0, and then again check the interval PFAS concentration ρ for each interval k. k and section pumping volume V k We will continue the measurements.

[0051] Furthermore, since the replaced used adsorbent 13 is waste containing PFAS, the PFAS will be detoxified by decomposition treatment in a heat treatment furnace or other means before proper disposal.

[0052] According to the well management method described above, it is possible to continuously ensure the safety of groundwater pumped from intake well 1 without the need to measure its PFAS concentration in situ, and to replace the adsorbent 13 at the appropriate time without wasting its adsorption capacity, thereby achieving rational and economical well management.

[0053] The specific examples used in the above description of embodiments are merely examples of how the invention can be implemented, and are not intended to limit the details of their arrangement or the equipment used. Depending on the specific circumstances in which the invention is implemented, implementers may modify or change them, and the description herein does not preclude such application. [Explanation of Symbols]

[0054] 1 Intake well, 2 Observation well, 10 Casing, 11 Intake pipe, 12 Intake pump, 13 Adsorbent, 14 Strainer, 20 Casing, VZ Unsaturated zone, SZ Saturated zone, AC Impermeable or low-permeability layer, GL Ground surface height, WL Groundwater level depth, F Groundwater flow.

Claims

1. The steps include sampling the groundwater to be drawn and conducting a test to confirm the adsorption capacity of PFAS (perfluoroalkyl compounds and polyfluoroalkyl compounds) using an adsorbent, The steps include measuring the PFAS concentration of the groundwater collected from observation wells located around the intake well, The steps include: pumping up groundwater by passing it through the adsorbent inserted into the casing of the intake well; Based on the amount of adsorbent inserted into the casing of the intake well, the adsorption capacity of PFAS calculated based on the results of the adsorption capacity confirmation test, and the cumulative adsorption amount of PFAS estimated based on the amount of groundwater pumped and the PFAS concentration of the groundwater, the adsorbent inserted into the casing of the intake well is replaced. Methods for managing wells.

2. The step of measuring the PFAS concentration in the groundwater is performed repeatedly, either periodically or irregularly. The method for managing a well according to claim 1.

3. Multiple observation wells are provided, and the PFAS concentration of the groundwater is determined by using the groundwater sample with the highest concentration taken from the multiple observation wells. A method for managing a well according to claim 1 or 2.

4. Multiple observation wells are provided, and the PFAS concentration of the groundwater is measured from the observation well located upstream of the intake well in the groundwater flow. A method for managing a well according to claim 1 or 2.

5. The direction of the groundwater flow is estimated based on the groundwater levels in multiple observation wells. The method for managing a well according to claim 4.

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