JP6961525B2 - How to evaluate the permeability of the ground - Google Patents

Description

The present invention relates to a method for evaluating the permeability of the ground.

The permeability of the ground is indicated by, for example, the permeability coefficient. The hydraulic conductivity is an index showing the ease of movement of groundwater in the ground. Permeability coefficient may be defined as the volume of groundwater that passes through a unit area in a unit time. Non-Patent Document 1 discloses a typical method for evaluating the hydraulic conductivity of the ground.

The first example is a pumping test. In this test, one pumping well extending in the vertical direction with respect to the ground and at least one observation well provided at a position horizontally separated from the pumping well are provided. That is, at least two wells are provided as wells including the pumping well and the observation well. Next, the amount of water pumped from the pumping well and the amount of decrease in the groundwater level in the observation well are measured. Then, the hydraulic conductivity is obtained by using the amount of pumped water and the amount of decrease in groundwater level.

As a second example, there is a single-hole hydraulic conductivity test. This test uses one well unlike the above pumping test. First, a well is provided in the ground to be evaluated. Next, the water level is lowered by pumping water from the well using a pump or the like. Then, the pumping is stopped. Then, the water level of the well rises to the initial water level again, and the speed of the rise (the speed of water level recovery) is measured. The hydraulic conductivity is obtained by using the speed of water level recovery. For example, examples of the single-hole hydraulic conductivity test include an auger method, a tube method, a piezometer method, and a packer method.

Japanese Geotechnical Society, "Methods and Explanations of Geotechnical Investigation", One of the Two Volumes, Japanese Geotechnical Society, March 25, 2013, pp. 521-614.

The ground may include a water-permeable portion (eg, a sand layer) and a water-impermeable portion (eg, a clay layer). These portions are easily laminated in the vertical direction. Then, the ground may differ in the ease of water passage in the horizontal direction (hereinafter, "horizontal water permeability coefficient") and the ease of water passage in the vertical direction (hereinafter, "vertical water permeability coefficient"). Therefore, in order to evaluate the hydraulic conductivity of a predetermined region in the ground, it is desirable to use the horizontal hydraulic conductivity coefficient and the vertical hydraulic conductivity coefficient. In addition, the hydraulic conductivity may be used in the design of underground structures. In this case, it is desirable to use the average hydraulic conductivity in a certain region rather than the local hydraulic conductivity.

Here, in the above first example, the average hydraulic conductivity in the region sandwiched between the pumping well and the observation well can be obtained. However, since the hydraulic conductivity is the horizontal hydraulic conductivity, it is not possible to evaluate the anisotropy of hydraulic conductivity such as the difference in hydraulic conductivity between the vertical direction and the horizontal direction. Further, in the second example, the horizontal hydraulic conductivity coefficient and the vertical hydraulic conductivity coefficient can be obtained, but these coefficients only indicate the hydraulic conductivity of the local region around the well.

Therefore, the present invention provides a method for evaluating the permeability of the ground, which can comprehensively evaluate the permeability of a two-dimensional region in the ground.

One embodiment of the present invention is a method for evaluating the water permeability of the ground, in which the water level of a first well having a first strainer provided at the lower end and a first impermeable wall extending from the first strainer to the ground is set. The second strainer has a first step of maintaining a measured water level different from the initial water level, a second strainer provided at the lower end, and a second impermeable wall extending from the second strainer to the ground. With respect to the second well provided horizontally separated from the first well so as to overlap with the first strainer, the second step of obtaining the first observation information regarding the water level change of the second well after the start of the first step. The first strainer has a third strainer provided at the lower end and a third impermeable wall extending from the third strainer to the ground so that the third strainer does not overlap with the first strainer and the second strainer in the horizontal direction. Regarding the third well provided horizontally separated from the well, after the start of the first step and in parallel with the second step, with the third step of obtaining the second observation information regarding the water level change of the third well. , The fourth step of obtaining the evaluation value from the first observation information and the second observation information using the evaluation data showing the relationship between the first observation information and the second observation information and the evaluation value for evaluating the water permeability coefficient of the ground. Has.

When the initial water level of the first well is maintained at the measured water level in the first step, the water level of the second well and the water level of the third well change according to the change of the water level. Here, the second strainer of the second well overlaps with the first strainer in the horizontal direction. Then, the movement of water between the second strainer and the first strainer is dominated by the horizontal component. Therefore, the response of the water level in the second well is based on the horizontal permeability (horizontal hydraulic conductivity) in the region between the first well and the second well. On the other hand, the third strainer of the third well does not overlap with the first strainer in the horizontal direction. Then, the movement of water between the third strainer and the first strainer is affected by the vertical component in addition to the horizontal component. Therefore, the response of the water level in the third well is based on the horizontal permeability (horizontal permeability coefficient) and the vertical permeability (vertical permeability coefficient) in the region between the first well and the third well. Therefore, by obtaining the first observation information from the second well in the second step and the second observation information from the third well in the third step, the evaluation value including the influence of the horizontal water permeability coefficient and the vertical water permeability coefficient can be obtained. can get. Then, in the fourth step, the evaluation value is obtained from the first observation information and the second observation information by using the evaluation data showing the relationship between the first observation information and the second observation information and the evaluation value for evaluating the water permeability coefficient of the ground. obtain. Therefore, the permeability of the two-dimensional region in the ground between the first well and the second well and the third well can be comprehensively evaluated.

In the method for evaluating the water permeability of the ground according to one form, in the first step, water is pumped from the first well to maintain the measured water level lower than the initial water level, and the first observation information is the first well. The second observation information is the third converged water level that occurs when the water level of the first well is maintained at the measured water level. It is the second converged water level at which the change in the water level of the well has converged, the evaluation value is the water permeation coefficient ratio which is the ratio of the vertical water permeation coefficient and the horizontal water permeation coefficient in the ground, and the evaluation data is the first convergence with respect to the water permeation coefficient ratio. In the process of showing the relationship between the water level difference between the water level and the second convergent water level, or the difference between the water level change amount of the first convergent water level and the second convergent water level with respect to the water permeation coefficient ratio, and obtaining the evaluation value, the water level difference or the water level change After obtaining the difference in quantity, the water permeation coefficient ratio corresponding to the difference in water level or the difference in the amount of change in water level may be read from the evaluation data. According to this step, as a value for comprehensively evaluating the water permeability of the two-dimensional region, a water permeability coefficient ratio indicating the ratio of the horizontal water permeability coefficient and the vertical water permeability coefficient can be easily obtained.

The method for evaluating the water permeability of the ground according to one form is a fourth having a fourth strainer provided at a position overlapping the third strainer in the horizontal direction and a fourth impermeable wall extending from the fourth strainer to the ground surface. The well may further have a fourth step in which the operation of discharging water through the fourth strainer is performed in parallel with the first step. In this fourth step, water is discharged from the fourth strainer. This water may reach the second and third strainers. Here, there is a difference between the ease of moving water from the fourth strainer to the second strainer and the ease of moving water from the fourth strainer to the third strainer. Specifically, water is more easily reachable by the third strainer that overlaps with the fourth strainer than by the second strainer. Then, it becomes possible to further increase the water level difference between the second and third wells caused by the pumping from the first well. Therefore, the hydraulic conductivity ratio, which is an evaluation value, can be obtained more accurately.

In the method for evaluating the permeability of the ground according to one form, the distance from the first well to the second well may be equal to the distance from the first well to the third well. According to this content, it is possible to easily model the region sandwiched between the first well and the second and third wells. Therefore, evaluation data showing the relationship between the first and second observation information and the evaluation value for evaluating the hydraulic conductivity of the ground can be easily prepared.

According to the present invention, there is provided a method for evaluating the permeability of the ground, which can comprehensively evaluate the permeability of a two-dimensional region in the ground.

FIG. 1 is a perspective view showing an evaluation facility that implements a method for evaluating the permeability of the ground according to the first embodiment. FIG. 2 is a side view showing an evaluation facility that implements a method for evaluating the permeability of the ground according to the first embodiment. FIG. 3 is a graph showing the relationship between the hydraulic conductivity ratio and the water level difference. FIG. 4 is a front view showing the purification system according to the second embodiment. FIG. 5 is a plan view showing a purification system according to the second embodiment. FIG. 6 is a side view showing an evaluation facility that implements a method for evaluating the permeability of the ground according to the first modification. FIG. 7 is a side view showing an evaluation facility that implements a method for evaluating the permeability of the ground according to the second modification. FIG. 8 is a perspective view showing an evaluation facility that implements a method for evaluating the permeability of the ground according to the modified example 3. FIG. 9 is a perspective view showing an evaluation facility that implements a method for evaluating the permeability of the ground according to the modified example 4. FIG. 10 is an example of a graph showing the relationship between the water level response and the change over time. FIG. 11 is a diagram for explaining Experimental Example 1. FIG. 12 is an example of a graph showing the relationship between the hydraulic conductivity ratio and the water level difference.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted.

As shown in FIG. 1, the method according to the embodiment evaluates the permeability of the ground 100. The ground 100 has a laminated structure. The ground 100 has an impermeable layer 101 laminated in the vertical direction D1, an aquifer 102, and an unsaturated layer 103. The impermeable layer 101 is a stratum in which water is difficult to pass through or does not pass through at all because the gaps between particles are small like a clay layer. The aquifer 102 is a highly permeable layer such as a gravel layer or a sand layer, and allows water to pass therethrough. The unsaturated layer 103 is a layer from the ground surface 104 to the aquifer 102.

The method according to the embodiment evaluates the water permeability of the aquifer 102. Permeability is a value indicating the ease with which water in the stratum can pass. For example, the hydraulic conductivity is defined as the volume of groundwater that passes through a unit area in a unit time.

It can be said that the aquifer 102 allows water to pass through as a whole, but when viewed partially, there may be a mixture of areas where water easily passes through and areas where it is difficult for water to pass through. These regions are easy to stack in the vertical direction. Then, the ground 100 has the ease of passing water in the horizontal direction (hereinafter, "horizontal water permeability coefficient (Kh)) and the ease of passing water in the vertical direction (hereinafter," vertical water permeability coefficient (Kv) "). It can be different. Therefore, in order to evaluate the hydraulic conductivity of a predetermined region in the ground 100, the horizontal hydraulic conductivity (Kh) and the vertical hydraulic conductivity (Kv) are used. The method according to the embodiment obtains the horizontal hydraulic conductivity (Kh), the vertical hydraulic conductivity (Kv), and an evaluation value based on these.

<Evaluation equipment>
Next, the evaluation equipment 1 used in the method according to the embodiment will be described.

As shown in FIG. 2, the evaluation facility 1 includes three wells. The number of wells is not limited to three. The evaluation equipment 1 includes a pumping well 2 (first well), a water level observation well 3 (second well), and a water level observation well 4 (third well).

The pumping well 2 is for changing the state of groundwater in the aquifer 102. Water is pumped from the inside of the pumping well 2 by the pumping pump 6. As a result, the water level of the pumping well 2 drops from the initial water level W2a to the measured water level W2b. Then, during the evaluation, the water level of the pumping well 2 is maintained at the measured water level W2b.

The water level observation well 3 and the water level observation well 4 observe changes in groundwater in the aquifer 102 caused by pumping water from the pumping well 2. Specifically, when water is pumped from the pumping well 2, flows F1 and F2 toward the pumping well 2 are generated. The flows F1 and F2 cause changes in the water levels of the water level observation wells 3 and 4. These changes in the water level of the water level observation well 3 and the water level observation well 4 are affected by the water permeability in the region A existing between the pumping well 2 and the water level observation well 3 and the water level observation well 4. That is, the evaluation method according to the embodiment evaluates the average (planar) permeability of the region A of the aquifer 102 between the pumping well 2, the water level observation well 3, and the water level observation well 4. ..

The pumping well 2 is a shaft that penetrates the unsaturated layer 103 and the aquifer 102 and reaches the impermeable layer 101. The pumping well 2 extends in the vertical direction D1 as an example. The upper end of the pumping well 2 is an opening on the ground surface 104. The lower end of the pumping well 2 reaches directly above the impermeable layer 101. The pumping well 2 has an impermeable wall 2a (first impermeable wall) and a strainer 2b (first strainer). The impermeable wall 2a is a tubular member extending from the ground surface 104 to the lower part of the aquifer 102, and does not take in water from the outside of the tube to the inside and does not discharge water from the inside of the tube to the outside. .. The strainer 2b is attached to the lower end of the impermeable wall 2a. The strainer 2b has a plurality of slits or holes. Therefore, the water flows into the pumping well 2 via the strainer 2b. Then, the pumping well 2 takes in water only at the position where the strainer 2b is provided. That is, the pumping well 2 takes in water in the vicinity of the impermeable layer 101 in the aquifer 102. The strainer 2b has a predetermined length in the vertical direction D1. In the following description, for convenience of explanation, the strainer 2b or the region provided with the slit in the strainer 2b is referred to as a water intake range R2.

The water level observation well 3 has the same configuration as the pumping well 2, and is separated from the pumping well 2 in the horizontal direction D2 by a distance L1. The water level observation well 3 is a vertical shaft extending in the vertical direction to reach the impermeable layer 101, and has an impermeable wall 3a (second impermeable wall) and a strainer 3b (second strainer). Then, the strainer 3b is attached to the lower end of the impermeable wall 3a in the same manner as the pumping well 2. Therefore, the inflow and outflow of water in the water level observation well 3 is performed in the vicinity of the impermeable layer 101. In the following description, for convenience of explanation, the strainer 3b or the region provided with the slit in the strainer 3b is referred to as a drainage range R3. This drainage range R3 overlaps with the water intake range R2 in the horizontal direction D2. The term "overlapping" as used herein means that when the pumping well 2 and the water level observation well 3 are viewed from the side and a virtual horizontal line is drawn, the water intake range R2 and the drainage range R3 overlap on the horizontal line. Therefore, in the term overlapping, the upper end of the intake range R2 and the upper end of the drainage range R3 may or may not coincide with each other. Similarly, the lower end of the water intake range R2 and the lower end of the drainage range R3 may or may not coincide with each other.

The water level observation well 4 has the same configuration as the pumping well 2, and is separated from the pumping well 2 in the horizontal direction D2 by a distance L1. This distance L2 may be the same as the distance L1 in the water level observation well 3, for example. The water level observation well 4 is a vertical shaft extending in the vertical direction, and has an impermeable wall 4a (third impermeable wall) and a strainer 4b (third strainer). Then, the strainer 4b is attached to the lower end of the impermeable wall 4a in the same manner as the pumping well 2. In the following description, for convenience of explanation, the strainer 4b or the region provided with the slit in the strainer 4b is referred to as a drainage range R4.

Here, the strainer 4b of the water level observation well 4 is different in position from the strainers 2b and 3b in the pumping well 2 and the water level observation well 3. Specifically, since the lower end of the water level observation well 4 does not reach the impermeable layer 101, the strainer 4b is arranged at a position separated from the impermeable layer 101 by a predetermined height. Further, the upper end of the strainer 4b is arranged near the upper side of the aquifer 102. That is, the strainer 4b of the water level observation well 4 is arranged above the aquifer 102. Therefore, the drainage range R4 does not overlap with the water intake range R2 in the horizontal direction D2. Further, "non-overlapping" here means that when the pumping well 2 and the water level observation well 4 are viewed from the side and a virtual horizontal line is drawn, the water intake range R2 and the drainage range R4 do not exist on the horizontal line. To say.

<How to evaluate>
Next, a method for evaluating water permeability will be described in detail.

The first step S1 is carried out. In the first step S1, the water level of the pumping well 2 is maintained at a measured water level W2b different from the initial water level W2a. Specifically, by pumping water from the pumping well 2, the measured water level W2b is maintained lower than the initial water level W2a. The water level may be defined as, for example, the depth from the ground surface 104 to the water surface WL. In the first step S1, the pump 6 is used to continuously pump the water in the pumping well 2. For example, the amount of pumped water is about 10 liters per minute.

The second step S2 is carried out. This second step S2 is performed in parallel with the first step S1. That is, the second step S2 is performed in a state where the water level of the pumping well 2 is maintained at the measured water level W2b after a predetermined time has elapsed from the start of the first step S1 (until it converges to the measured water level). According to the second step S2, the convergent water level W3b (first convergent water level) as the first observation information is obtained. The convergent water level W3b is a convergence of changes in the water level of the water level observation well 3 that occurs when the water level of the pumping well 2 is maintained at the measured water level W2b.

Further, the third step S3 is carried out. This third step S3 is also performed in parallel with the first step S1. That is, the third step S3 is performed in a state where the water level of the pumping well 2 is maintained at the measured water level W2b after a predetermined time has elapsed from the start of the first step S1 (until it converges to the measured water level). According to the third step S3, the convergent water level W4b (second convergent water level) as the second observation information is obtained. The convergent water level W4b is a convergence of changes in the water level of the water level observation well 4 that occurs when the water level of the pumping well 2 is maintained at the measured water level W2b.

Next, the fourth step S4 is carried out. In the fourth step S4, the convergent water level W3b and the convergent water level W4b are used to obtain a value for evaluating the water permeability. For example, the values for evaluating water permeability include the above-mentioned horizontal water permeability coefficient (Kh) and vertical water permeability coefficient (Kv). Further, the vertical horizontal hydraulic conductivity ratio (simply also referred to as “water permeability coefficient ratio (Kh / Kv)”), which is these ratios, may be used as a value for evaluating the hydraulic conductivity.

First, the difference between the convergent water level W3b and the convergent water level W4b (water level difference WD) or the difference between the water level changed from the initial water level to the convergent water level W3b and the water level changed to the convergent water level W4b (difference in the amount of water level change) is obtained. Next, the water level difference WD (or the difference in the amount of water level change) is converted into the hydraulic conductivity ratio (Kh / Kv). For this conversion, a graph as shown in FIG. 3 may be used. The graph shown in FIG. 3 is obtained by modeling the characteristics of the region A to be evaluated and performing a simulation using the model. In the graph G1, the horizontal axis represents the hydraulic conductivity ratio (Kh / Kv). The vertical axis shows the water level difference WD. For example, when the water level difference WD is 15 centimeters. According to the graph G1, it can be seen that the hydraulic conductivity ratio (Kh / Kv) corresponding to the water level difference WD (15 cm) is about 4.3. Therefore, according to the fourth step S4, the hydraulic conductivity ratio (Kh / Kv) can be obtained from the water level difference WD (or the difference in the amount of water level change).

As described above, according to the evaluation method according to the embodiment, when the initial water level W2a of the pumping well 2 is maintained at the measured water level W2b in the first step S1, the water level of the water level observation well 3 and the water level of the water level observation well 3 are determined according to the change in the water level. The water level of the water level observation well 4 changes. Here, the strainer 3b of the water level observation well 3 overlaps with the strainer 2b in the horizontal direction D2. Then, the movement of groundwater (flow F1) between the strainer 2b and the strainer 3b is dominated by the horizontal component. Therefore, the response of the water level in the water level observation well 3 is based on the permeability (horizontal permeability coefficient (Kh)) in the horizontal direction D2 in the region A between the pumping well 2 and the water level observation well 3. On the other hand, the strainer 4b of the water level observation well 4 does not overlap with the strainers 2b and 3b in the horizontal direction D2. Then, the movement of groundwater (flow F2) between the strainer 4b and the strainer 2b is affected by the vertical component in addition to the horizontal component. Therefore, the response of the water level in the water level observation well 4 is the permeability (horizontal permeability coefficient) in the horizontal direction D2 and the permeability (vertical permeability coefficient (vertical permeability coefficient)) in the horizontal direction D2 in the region A between the pumping well 2 and the water level observation well 4. Based on Kv)). Therefore, by obtaining the convergent water level W3b from the water level observation well 3 in the second step S2 and the convergent water level W4b from the water level observation well 4 in the third step S3, the horizontal water permeation coefficient (Kh) and the vertical water permeation coefficient (Kv) are obtained. An evaluation value including the influence of is obtained. Then, in the fourth step S4, evaluation data (see FIG. 3) showing the relationship between the convergent water level W3b and the convergent water level W4b and the hydraulic conductivity ratio (Kh / Kv), which is an evaluation value for evaluating the hydraulic conductivity of the ground 100, is used. Then, the evaluation values are obtained from the convergent water level W3b and the convergent water level W4b. Therefore, the permeability of the two-dimensional region A in the ground 100 between the pumping well 2, the water level observation well 3 and the water level observation well 4 can be comprehensively evaluated.

In short, from the amount of water pumped from the pumping well 2 and the water level difference WD (or the difference in the amount of water level change) between the water level observation well 3 and the water level observation well 4, the ground 100 between the pumping well 2 and the water level observation wells 3 and 4 The average horizontal water permeability coefficient (Kh) and vertical water permeability coefficient (Kv) are estimated (4th step S4). From this estimation, the hydraulic conductivity ratio (Kh / Kv) can be obtained. Since the entire groundwater of the aquifer 102 to be evaluated is made to flow (flows F1 and F2) by pumping from the pumping well 2 (first step S1), the average horizontal permeability of the entire aquifer 102 is permeated. It is possible to estimate the coefficient (Kh) and the vertical hydraulic conductivity (Kv).

In other words, the method according to the embodiment is not a local hydraulic conductivity as in the conventional single-hole hydraulic conductivity test, but a simple average hydraulic conductivity ratio (Kh / Kv) of the entire aquifer 102. It can be measured with equipment. Further, in order to evaluate the average permeability, it is necessary to generate horizontal and vertical flows of groundwater, but the method according to the embodiment can easily generate such flows. Further, the method according to the embodiment does not require a packer and can be easily measured. Moreover, in the method according to the embodiment, since the excavation depth of the observation well is shallower than that of the conventional test method in which a plurality of observation wells are provided, the boring extension can be shortened.

Further, as a value for comprehensively evaluating the water permeability of the two-dimensional region, a water permeability coefficient ratio indicating the ratio between the horizontal water permeability coefficient and the vertical water permeability coefficient can be easily obtained.

<Second Embodiment>
The hydraulic conductivity ratio obtained by the evaluation method according to the embodiment may be used, for example, in the design of a groundwater purification system. 4 and 5 are diagrams showing the configuration of the groundwater purification system 20. The purification system 20 economically forms a purification wall using microbial decomposition in a short period of time, and purifies contaminated groundwater reliably and quickly.

The purification system 20 is installed on a water-impervious material and a water-impervious material provided so as to divide a plurality of wells installed in the ground into two or more in the depth direction for one groundwater layer. A pump capable of controlling the water supply direction up and down and an activator injection pump for adding an activator that activates microorganisms to a plurality of wells are provided. The plurality of wells are installed in the ground so that the parallel direction is substantially perpendicular to the direction of the groundwater flow. The pump installed in one of the plurality of wells and the pump installed in the other well adjacent to one of the plurality of wells are controlled so that the water supply directions are opposite to each other.

According to this purification system 20, the pumps installed in the adjacent wells are controlled so that the water supply directions are opposite to each other so that the adjacent wells are substantially perpendicular to the flow of contaminated groundwater. Horizontal flow occurs. Therefore, it is possible to reduce the promotion of diffusion of contaminated groundwater to the periphery. In addition, the groundwater to which the activator is added moves quickly in the direction perpendicular to the flow of the contaminated groundwater, and the activator can be diffused uniformly. Furthermore, by adding the activator while operating the pump, the concentration of the activator in the groundwater can be kept close to a constant state, so that microbial decomposition at a high decomposition rate becomes possible at an early stage.

The purification system 20 purifies volatile organic chlorine compounds. The purification system 20 is installed on the ground 100 near the boundary of the predetermined site 33. The purification system 20 has a plurality of wells 23, sand 27, impermeable material 29, pump 21, pipe 13, and activator injection pump 15.

The plurality of wells 23 are vertically installed in the ground 100 at predetermined intervals. At this time, the surface including the plurality of wells 23 is set to be substantially perpendicular to the flow direction of the contaminated groundwater 39 shown by the arrow G in FIG. The plurality of wells 23 include wells 23a and 23b. Wells 23a and 23b are arranged alternately.

The impermeable material 29 is provided so as to divide the well 23 into two or more in the depth direction with respect to the aquifer 102 which is a sand layer having groundwater.

The pump 21 is provided on the impermeable material 29. The pump 21 can control the water supply direction up and down. Of the plurality of wells 23, the pump 21 installed in the well 23a and the pump 21 installed in the well 23b adjacent to the well 23a are controlled so that the water supply directions are opposite to each other. The pump 21 installed in the well 23a is controlled to send water upward. Further, the pump 21 installed in the well 23b is controlled to send water downward. At this time, the pumps 21 installed in the plurality of wells 23a are controlled so as to supply water upward. Further, the pumps 21 installed in the plurality of wells 23b are controlled so as to supply water downward.

One end of the pipe 13 is connected to the well 23 and the other end is connected to the activator injection pump 15. The activator injection pump 15 is installed on the ground 100. The activator injection pump 15 adds an activator that activates anaerobic microorganisms to the well 23 via a pipe 13. The flow rate of the activator injection pump 15 is 1/100 or less of the flow rate of the pump 21 installed in the well 23, preferably about 1/1000. As the activator, for example, lactic acid, glucose, ethanol, glycerol, acetic acid, butyric acid, propionic acid, formic acid, sorbitol, oligolactic acid, shoe cloth, polylactic acid, soybean oil, emulsion oil and the like are used.

The activator added to the well 23 is mixed with the groundwater of the well 23. The activator concentration becomes uniform by the water supply of the pump 21. When the operation of the activator injection pump 15 is restarted and the activator is added to the groundwater in the well 23 from the activator injection pump 15, the addition is made so that the concentration of the activator in the groundwater becomes a predetermined control value. The amount of activator to be used is adjusted.

A common feature of groundwater flow in the aquifer 102 is that the horizontal permeability is greater than the vertical permeability. In the purification system 20, by operating the pump 21, the flows F3, F4, and F5 of FIG. 1 are generated in the ground 100. Therefore, in the design of the purification system 20, the horizontal hydraulic conductivity (Kh), the vertical hydraulic conductivity (Kv) and the hydraulic conductivity ratio (Kh / Kv) are used in order to preferably estimate the flows F3, F4 and F5. .. In the method according to the first embodiment, the average hydraulic conductivity ratio (Kh / Kv) of the region sandwiched between the pair of wells 23 can be preferably obtained. Therefore, the method according to the first embodiment can provide design parameters suitable for the design of the purification system 20.

The groundwater moves in the direction perpendicular to the flow direction of the contaminated groundwater 39 shown in FIG. 2 (the direction indicated by the arrow G), and the activator uniformly diffuses into the ground 100 around the well 23. As shown in FIG. 2, the portion where the activator is diffused functions as a purification wall 25. The VOC in the contaminated groundwater 39 that has flowed into the purification wall 25 is decomposed by the action of anaerobic microorganisms activated by the activator while passing through the purification wall 25, and flows out from the purification wall 25 as purified groundwater 39A. do.

Although the embodiment of the present invention has been described above, the embodiment is not limited to the above embodiment and may be implemented in various forms.

<Modification example 1>
In the evaluation method according to the first embodiment, the state of groundwater in the aquifer 102 was changed by pumping groundwater from the pumping well 2. For example, as in the evaluation equipment 1A shown in FIG. 6, the state of groundwater in the aquifer 102 may be changed by injecting water from the water injection pump 6A into the water injection well 2A (first step). In this case, the measured water level W2c is higher than the initial water level W2a. Even with such a configuration, the state of groundwater in the aquifer 102 changes, and flows F6 and F7 are generated. Therefore, changes in the water level (convergent water levels W3c, W4c) occur in the water level observation well 3 and the water level observation well 4. As a result, as in the first embodiment, the water permeability of the two-dimensional region in the ground 100 can be comprehensively evaluated.

<Modification 2>
In order to change the state of the groundwater in the aquifer 102, the groundwater was pumped in the first embodiment and water was injected in the modified example 1. For example, using the evaluation equipment 1B shown in FIG. 7, pumping and water injection may be performed at the same time in the first step S1. The evaluation facility 1B has a pumping well 2B and a pumping well 2D provided in parallel with the water injection well 2C (fourth well). Here, the strainer 2b of the pumping well 2B overlaps with the strainer 3b of the water level observation well 3. On the other hand, the strainer 2c (fourth strainer) of the water injection well 2C overlaps with the strainer 4b of the water level observation well 4. Then, the pumping from the pumping well 2 and the water injection from the water injection well 2C are performed in parallel. First, the convergent water level W3b of the water level observation well 3 is easily affected by pumping (the water level is easily lowered) and is not easily affected by water injection (the water level is not easily raised). On the other hand, the convergent water level W4b of the water level observation well 4 is not easily affected by pumping (the water level is not easily lowered) and is easily affected by water injection (the water level is easily raised). Then, by performing the pumping and water injection in the first step S1 in parallel, the difference between the water level of the water level observation well 3 and the water level of the water level observation well 4 (water level difference WD) or the difference in the amount of water level change is expanded. Can be done. Therefore, it is possible to obtain an evaluation value that more preferably shows water permeability.

<Modification example 3>
For example, as shown in FIG. 8, in the evaluation method according to the third modification, measurement may be performed using one or more sets of well sets 10A and 10B. Each well set 10A and 10B has a water level observation well 3 and a water level observation well 4. The position of the strainer 3b possessed by the water level observation well 3 of the well set 10A is the same as the position of the strainer 3b possessed by the water level observation well 3 of the well set 10B. Similarly, the position of the strainer 4b of the water level observation well 4 of the well set 10A is the same as the position of the strainer 4b of the water level observation well 4 of the well set 10B. The well sets 10A and 10B have different distances from the pumping well 2. For example, the well set 10A has distances L1 and L2 from the pumping well 2 of 7.5 meters. Further, the well set 10B has a distance L3 and L4 from the pumping well 2 of 3.5 meters. If the distance from the pumping well 2 is different, the water level difference WD may also be different. For example, the closer to the pumping well 2, the larger the water level difference WD tends to be. Then, the water level difference WD is obtained in the well set 10A, and the water level difference WD is obtained in the well set 10B. Then, based on these water level difference WDs, two hydraulic conductivity ratios (Kh / Kv) are obtained. Therefore, a more reliable hydraulic conductivity ratio (Kh / Kv) can be obtained. In this evaluation, the difference in the amount of change in the water level may be used instead of the water level difference WD.

<Modification example 4>
In the first embodiment, the water level observation well 3 is provided so as to be adjacent to the water level observation well 4. For example, as shown in FIG. 9, the observation well 5A may have a double tube structure. The observation well 5A has an inner pipe 3A (second well) and an outer pipe 4A (third well). The inner pipe 3A has a strainer 3b corresponding to the second well and provided at a position overlapping the strainer 2b of the pumping well 2. The outer tube 4A has an inner diameter larger than the diameter of the inner tube 3A. The outer pipe 4A covers from the upper end to the middle of the inner pipe 3A. That is, the outer tube 4A is shorter than the inner tube 3A. Further, the outer pipe 4A has a strainer 4b corresponding to the third well and provided at a position not overlapping with the strainer 2b of the pumping well 2. According to this configuration, one hole for the observation well 5A is sufficient. Therefore, the evaluation equipment 1D can be easily prepared.

<Modification 5>
When the temporal response of the water level is used as the evaluation value, the second step S2 may be started at the same time as (or immediately after the start) of the first step S1. In the second step S2, the time when pumping from the pumping well 2 is started is set to zero, and the relationship between the elapsed time from the start time and the water level in the water level observation well 3 (water level response: first observation information) is obtained. Further, in the third step S3, the relationship between the elapsed time and the water level in the water level observation well 4 (water level response: second observation information) is obtained. Next, in the fourth step S4, an evaluation value for evaluating the water permeability is obtained by utilizing the relationship with the water level in the water level observation well 3 and the relationship with the water level in the water level observation well 4. Specifically, the slope of the water level change (time change rate of the water level) is obtained from a graph (see FIG. 10) that plots the change over time of the water level, and the water permeation coefficient is calculated from the slope. Further, the water permeation coefficient ratio is calculated from the time change rate of the water level (graph G4) observed in the second observation well and the time change rate of the water level (graph G5) observed in the third observation well. In the fourth modification, the permeability in the region between the pumping well 2 and the water level observation wells 3 and 4 is obtained by the water level response. Therefore, as in the first embodiment, the permeability of the two-dimensional region in the ground can be comprehensively evaluated.

<Experimental example>
As Experimental Example 1, a single-hole hydraulic conductivity test was performed as a comparative example. Further, as Experimental Example 2, a test based on the method for evaluating the water permeability according to the above-mentioned Modified Example 3 was conducted. The ground 100 to be evaluated is shown in FIG. The ground 100 includes an impermeable layer 101, an aquifer 102, and an unsaturated layer 103. The thickness of the aquifer 102 is 4.5 meters. The thickness of the aquifer 102 is the water level of the groundwater before pumping and water injection. The thickness of the unsaturated layer 103 is 6 meters. Experimental Examples 1 and 2 were carried out on such a ground 100 to obtain a hydraulic conductivity ratio (Kh / Kv), respectively. Then, the hydraulic conductivity ratios (Kh / Kv) obtained in Experimental Examples 1 and 2 were compared. As a result, the results of the test (Experimental Example 2) based on the method according to the embodiment have less variation in the evaluation values than the results of Experimental Example 1 according to the comparative example, and the overall average evaluation value of the aquifer 102 is small. It was found that (water permeability coefficient ratio (Kh / Kv)) was obtained. Hereinafter, Experimental Examples 1 and 2 will be specifically described.

<Experimental example 1>
In Experimental Example 1, two water permeability tests by the piezometer method and the tube method were performed four times each. The hydraulic conductivity ratio (Kh / Kv) was obtained at four different positions in the aquifer 102. At the four positions, position A1 has a depth of 7 to 7.5 meters from the ground surface 104, and position A2 has a depth of 9 to 9.7 meters from the ground surface 104. Further, the positions B1 and B2 are separated from the positions A1 and A2 by 8.3 meters (length LA) in the horizontal direction, respectively. The position B1 has a depth of 8 to 8.5 meters from the ground surface 104, and the position B2 has a depth of 9 to 9.5 meters from the ground surface 104.

As a result, the hydraulic conductivity ratio (Kh / Kv) was 100 at position B1, 0.81 at position B2, 0.04 at position A1, and 4 at position A2. From these results, it was found that the hydraulic conductivity ratios obtained by the single-hole hydraulic conductivity test vary greatly. This was considered to indicate local permeability inside the aquifer 102. That is, it is a reasonable result as an evaluation of water permeability in a local region. However, it was considered difficult to utilize these results as an indication of the average permeability of the region containing positions A1, A2, B1 and B2.

<Experimental example 2>
In Experimental Example 2, the evaluation equipment 1C shown in the modified example 3 was used. The strainer 3b of the water level observation well 3 was placed in an area of 9 to 10.5 meters from the ground surface 104. The strainer 4b of the water level observation well 4 was arranged in an area of 6 to 8 meters from the ground surface 104. The well set 10A was provided at a position 7.5 meters away from the pumping well 2. The well set 10B was provided at a position 3.5 meters away from the pumping well 2.

Then, 13.25 liters of groundwater per minute was pumped from the pumping well 2 (first step S1).

In the well set 10A, the initial water level W3a of the water level observation well 3 was the reference point -4.701 meters, and the convergent water level W3b was the reference point -5.486 meters (second step S2). On the other hand, the initial water level W4a of the water level observation well 4 was the reference point -4.692 meters, and the convergent water level W4b was the reference point -5.402 meters (third step S3). As a result, the difference in the amount of change in the water level in the well set 10A was 7.5 cm. The difference in the amount of change in the water level difference was read as the hydraulic conductivity ratio (Kh / Kv) using the graph prepared in advance shown in FIG. The horizontal axis of FIG. 12 is the hydraulic conductivity ratio (Kh / Kv), and the vertical axis is the water level difference WD (difference in the amount of water level decrease). The graph G2 is an estimation line of the water level difference WD (difference in water level decrease) -permeability coefficient ratio at a position 7.5 meters away from the pumping well 2. According to the graph G2, it was found that the water level difference WD (difference in the amount of water level decrease) (7.5 cm) corresponds to the hydraulic conductivity ratio (3.5).

The same work was carried out for the well set 10B. In the well set 10B, the initial water level W3a of the water level observation well 3 was the reference point -4.709 meters, and the convergent water level W3b was the reference point -5.474 meters (second step S2). On the other hand, the initial water level W4a of the water level observation well 4 was the reference point -4.601 meters, and the convergent water level W4b was the reference point -5.207 meters (third step S3). As a result, the difference in the amount of change in the water level in the well set 10B was 15.9 cm. According to the graph G3, it was found that the difference in the amount of change in the water level difference (15.9 cm) corresponds to the hydraulic conductivity ratio (3.7).

As described above, according to the evaluation method according to Experimental Example 2 (the present embodiment), it was found that the variation was small and the average hydraulic conductivity ratio of the entire aquifer 102 could be obtained.

1, 1A, 1B, 1C, 1D ... Evaluation equipment, 2, 2B ... Pumping well (1st well), 2A, 2C ... Water injection well (4th well), 2D ... Pumping well, 2a ... Impermeable wall (No. 1) 1 Impermeable wall), 2b ... Strainer (1st strainer), 2c ... Strainer (4th strainer), 3 ... Water level observation well (2nd well), 3a ... Impermeable wall (2nd impermeable wall), 3b ... Strainer (2nd strainer), 4 ... Water level observation well (3rd well), 4a ... Impermeable wall (3rd impermeable wall), 4b ... Strainer (3rd strainer), 5A ... Observation well, 6 ... Pumping pump, 13 ... Pipe, 15 ... Activator injection pump, 20 ... Purification system, 21 ... Pump, 23, 23a, 23b ... Well, 27 ... Sand, 29 ... Impermeable material, 25 ... Purification wall, 33 ... Site, 39A ... Groundwater , 39 ... Contaminated groundwater, 10A, 10B ... Well set, 100 ... Ground, 101 ... Impermeable layer, 102 ... Water zone, 103 ... Unsaturated layer, 104 ... Ground surface, D1 ... Vertical direction, D2 ... Horizontal direction, R2 ... Intake range, R3, R4 ... Drainage range, WL ... Water surface, W2a ... Initial water level, W2b, W2c ... Measured water level, W3b, W3c ... Convergent water level (first convergent water level), W4b, W4c ... Convergent water level (second) Convergent water level), WD ... Water level difference.

Claims (4)

It is a method to evaluate the permeability of the ground.
A first step of maintaining the water level of a first well having a first strainer provided at the lower end and a first impermeable wall extending from the first strainer to the ground at a measured water level different from the initial water level.
It has a second strainer provided at the lower end and a second impermeable wall extending from the second strainer to the ground, and from the first well so that the second strainer overlaps with the first strainer in the horizontal direction. Regarding the second wells provided at horizontal intervals, the second step of obtaining the first observation information regarding the water level change of the second well after the start of the first step, and the second step.
It has a third strainer provided at the lower end and a third impermeable wall extending from the third strainer to the ground so that the third strainer does not overlap with the first strainer and the second strainer in the horizontal direction. Regarding the third well provided horizontally separated from the first well, the second observation information regarding the water level change of the third well after the start of the first step and in parallel with the second step. The third step to obtain
The evaluation value is obtained from the first observation information and the second observation information by using the first observation information and the evaluation data showing the relationship between the second observation information and the evaluation value for evaluating the water permeability coefficient of the ground. A method for evaluating the water permeability of the ground having the fourth step. In the first step, water is pumped from the first well to maintain the measured water level lower than the initial water level.
The first observation information is the first convergent water level at which the change in the water level of the second well that occurs when the water level of the first well is maintained at the measured water level has converged.
The second observation information is the second convergent water level at which the change in the water level of the third well that occurs when the water level of the first well is maintained at the measured water level has converged.
The evaluation value is a hydraulic conductivity ratio, which is a ratio of the vertical hydraulic conductivity to the horizontal hydraulic conductivity in the ground.
The evaluation data is the relationship between the water level difference between the first convergent water level and the second convergent water level with respect to the water permeation coefficient ratio, or the amount of change in the water level between the first convergent water level and the second convergent water level with respect to the water permeation coefficient ratio. Show the relationship of the difference,
The step according to claim 1, wherein in the step of obtaining the evaluation value, after obtaining the difference in the water level or the difference in the amount of change in the water level, the ratio of the hydraulic conductivity corresponding to the difference in the water level or the difference in the amount of change in the water level is read from the evaluation data. How to evaluate the permeability of the ground. In a fourth well having a fourth strainer provided at a position overlapping the third strainer in the horizontal direction and a fourth impermeable wall extending from the fourth strainer to the ground surface, water is supplied through the fourth strainer. The method for evaluating the water permeability of the ground according to claim 1 or 2, further comprising a fourth step of performing the discharging operation in parallel with the first step. The method for evaluating the permeability of the ground according to any one of claims 1 to 3, wherein the distance from the first well to the second well is equal to the distance from the first well to the third well. ..

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