JP2003033756A - Decontamination method for hardly water-permeable ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination technology useful for remediation of a hardly water-permeable ground in a deep layer which is not sufficiently dealt with by a method of pumping up an underground water or a replacement method. SOLUTION: A suction well 1 that reaches a contaminated area A in the hardly water-permeability ground G2 or penetrates there through is excavated. Then, a plurality of wells 2 for water supply are excavated in such a way that they surround the periphery of the contaminated area A in the ground G2. The water W containing a contaminant decomposing or decomposition promotion agent is supplied to the well 2 for water supply. At the same time, vacuum suction is performed in the suction well 1 while sealing the portion thereof at which the ground G2 is positioned. Thereby, water in the ground G2 is made to flow forcibly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning contaminated ground, and more particularly, it provides a method effective for cleaning poorly permeable ground having a low hydraulic conductivity.

[0002]

2. Description of the Related Art Ground pollution is caused by diffusion of pollutants eluted from pollution sources such as waste mixed in the ground into groundwater. And the water permeability is 10 ⁻² to 10
^-4 cm / sec. As a method for cleaning easily permeable soil consisting of sandy soil with a relatively high groundwater flow rate, a required number of wells are drilled around the pollution source and the contaminated groundwater is pumped. The pumping method is effective. In addition, since the permeability of soil decreases as the amount of silt and clay increases, the groundwater flow becomes extremely slow.If the pollution source is on such a poorly permeable ground, excavate and remove the pollution source and the surrounding ground. The replacement method of backfilling with high quality soil is adopted.

By the way, in recent years, a stratum composed of an alluvial clay layer or a diluvial clay layer, which has been conventionally considered as an impermeable layer, has a deep depth (for example, a depth of about 10 m and a permeability coefficient of 10 ⁻⁴ to 10 ^{−). 5} cm / sec), contamination by VOC (organic chlorine compounds) such as trichlorethylene and tetrachloroethylene has been confirmed, and the existence of such a contamination distribution that penetrates the poorly permeable ground is also understood. ing. This is trichlorethylene, etc.
It is considered that OC has a large specific gravity, so even if it enters from near the surface, it gradually falls into the deep water-impermeable soil. Highly contaminated areas may exist on the soil.

However, since the groundwater flow in such a poorly permeable ground is extremely slow as described above, most of the groundwater pumped by the groundwater pumping method is from the ground of sandy soil. Therefore, it is practically difficult to remove pollutants in the hardly permeable ground.

The method of excavating and removing the pollutant source and the surrounding ground and backfilling with good quality soil is an effective means when the polluted area is at a relatively shallow position in the ground, but when it is at a deep position. It is not realistic to adopt such a construction method. That is, the deeper the contaminated region is, the more excavation amount is required to excavate the contaminated region, and the greater the excavation amount is in the ground area that is not the purification target, which is extremely inefficient. Therefore, conventional methods such as pumping and replacing groundwater cannot sufficiently remove VOCs adsorbed on the above-mentioned impervious soil,
There is a demand for effective pollution control technology for poorly permeable ground.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its technical problem is to contaminate deep-layer hardly permeable ground that cannot be sufficiently dealt with by groundwater pumping or replacement methods. It is to provide a pollution purification technology effective for restoration.

[0007]

The above-mentioned technical problems are as follows.
The present invention can effectively solve the problem. That is, the method for purifying a poorly water-permeable ground according to the invention of claim 1 excavates a required number of suction wells that reach or penetrate into the poorly-permeable ground, and reach the required number of holes to reach or penetrate the hardly-permeable ground. The water supply well is excavated so that a contaminated region in the hardly permeable ground exists between the water supply well and the water supply well containing a pollutant decomposing agent or a pollutant decomposition promoting agent. Is supplied, and the portion of the suction well located in the contaminated region is hermetically sealed and vacuum-sucked to forcefully flow the water in the hardly water-permeable ground.

In the method for cleaning a poorly permeable ground according to the second aspect of the present invention, as a more preferable method in the first aspect, the suction well is excavated so as to reach or penetrate the contaminated region, and the water supply well is The excavation is performed so as to surround the contaminated area.

According to the third aspect of the present invention, there is provided a method for cleaning a poorly water-permeable ground, in which a water supply well reaching or penetrating into a contaminated area of the poorly water-permeable ground is excavated and a first electrode body is provided in the water supply well. Insert, insert a required number of second electrode body reaching or penetrating into the water-impermeable soil so that there is a contaminated area in the water-impermeable soil between the suction well and the water supply Water containing a pollutant decomposer or a pollutant decomposition accelerator is supplied to the well, and the first electrode body is connected to the anode side of the DC power source, and the second electrode body is connected to the cathode of the DC power source. It is connected to the side and a DC voltage is applied between both electrodes to forcibly flow the water in the hardly water-permeable ground.

According to a fourth aspect of the present invention, there is provided a method for cleaning a poorly water-permeable ground as a more preferable method according to the third aspect, wherein one of a water supply well into which the first electrode body is inserted and a second electrode body. Is provided so as to reach or penetrate the contaminated area, and the other is provided so as to surround the perimeter of the contaminated area.

According to the fifth aspect of the present invention, there is provided a method for cleaning a poorly water-permeable ground according to any one of the first to fourth aspects, in which the pollutant decomposing agent is iron colloid, potassium permanganate, stabilized chlorine dioxide, or the like. From a VOC decomposer selected from This VOC decomposing agent directly decomposes VOC (organic chlorine compound) by a reductive dechlorination reaction.

According to a sixth aspect of the present invention, there is provided a method for cleaning a poorly water-permeable ground according to any one of the first to fourth aspects, wherein the pollutant decomposition accelerator is selected from ethanol, methanol and waste sugar condensate. It is composed of a VOC decomposition accelerator. This VOC decomposition promoter activates the activity of the microorganism having the ability to decompose VOC, thereby promoting the decomposition of VOC by the microorganism.

The term "hardly permeable ground" as used herein means a ground having a water permeability coefficient of about 10 ^-4 to 10 ^-5 cm / sec.

[0014]

1 is a vertical cross-sectional view of the ground showing a first preferred embodiment of the method for cleaning a poorly permeable ground according to the present invention, and FIG. 2 shows a plane arrangement of wells in the present embodiment. In the figure, reference numeral G1 in FIG. 1 indicates an easily permeable ground made of sandy soil having relatively high water permeability (for example, about 10 ⁻⁴ cm / sec or more) near the surface layer, and reference numeral G2 indicates this easy permeability. Below the permeable ground G1, for example, in a deep layer with a depth of about 10 m, a hardly permeable ground consisting of alluvial clay layer or diluvial clay layer, reference symbol A is a contaminated area in this hardly permeable ground G2. is there.

In the present embodiment, first, the suction well 1 reaching from the ground surface into the contaminated area A in the hardly water-permeable ground G2.
Is further excavated, and a plurality of water supply wells 2 reaching the inside of the impermeable soil G2 are further excavated so as to surround the contaminated area A. A suction pipe 3 connected to the suction port of the vacuum pump P is inserted into the suction well 1, and a water-permeable ground G1 and a poor water-permeable ground are provided between the outer periphery of the suction pipe 3 and the inner wall of the suction well 1. Sealing is performed by filling the depth of the boundary with G2 with the sealing material 4. Further, to the water supply well 2, a VOC decomposition agent selected from iron colloid, potassium permanganate, stabilized chlorine dioxide, or the like, or a VOC decomposition accelerator selected from ethanol, methanol, waste sugar concentration, or the like is added. The filled water W is filled.

Next, when the vacuum pump P is driven, the inside of the closed space 1a by the seal material 4 in the suction well 1 is vacuumed. This closed space 1a is a water-impermeable ground G2.
Since it is located inside, a groundwater pressure gradient is generated in the water-impermeable ground G2, and the groundwater in this water-impermeable ground G2 is forcibly moved toward the closed space 1a. Along with this, the water W added with the VOC decomposition agent or the VOC decomposition accelerator in each water supply well 2 becomes less permeable to the ground G2.
It penetrates in from around the contaminated area A. Also,
Since this groundwater flow WF is induced in the direction of converging from the periphery of the contaminated area A, the groundwater flow WF can be purified while preventing VOC from spreading underground.

When water W containing a VOC decomposing agent is used, for example, iron colloid as a VOC decomposing agent has an average particle size of φ0.5 μm and is used when the voids between soil particles are larger than this. You can Then, such a VOC decomposing agent reductively dechlorinates VOC pollutants such as trichlorethylene and tetrachloroethylene adsorbed on the soil particles in the process of passing through the soil particle gaps in the contaminated area A of the hardly water-permeable ground G2. Is decomposed by this, and the purification of pollution is performed by this.

When water W containing a VOC decomposition accelerator is used, this VOC decomposition accelerator is used as a poorly permeable ground G.
In the process of passing through the soil particle gap in the contaminated area A of 2, the decomposition activity and growth of the decomposition microorganisms (microorganisms capable of decomposing organic chlorine compounds) existing in the ground are promoted. Therefore, the indirect decomposition of VOCs by utilizing microorganisms is promoted, thereby purifying the pollution.

FIG. 3 is a sectional view of the ground showing a second preferred embodiment of the method for cleaning a poorly water-permeable ground according to the present invention, FIG. 4 is a plan view, and reference numeral G1 is the same as FIG. 1 above. Permeable ground consisting of sandy soil near the surface layer, reference sign G2 is a poorly permeable ground composed of deep alluvial clay layer or diluvial clay layer, reference sign A is a contaminated area in this poorly permeable ground G2. is there.

In this embodiment, first, a water supply well 5 is excavated from the ground surface toward a contaminated area A in the hardly water-permeable ground G2, and an iron pipe 6 as a first electrode body is inserted into the water supply well 5. Then, the periphery thereof is filled with sand or gravel 7 and the like, and between the outer circumference of the iron pipe 6 and the inner wall of the water supply well 5,
Sealing is performed by filling the depth of the boundary between the easily water-permeable ground G1 and the hardly water-permeable ground G2 with the sealing material 4. It is preferable that the iron pipe 6 has a large number of small holes formed in a portion below the height at which it is sealed by the sealing material 4. In the space 4a sealed by the sealing material 4 in the water supply well 5, a VOC decomposer selected from iron colloid, potassium permanganate, stabilized chlorine dioxide, or the like, or ethanol, methanol, or V selected from waste sugar
Water W containing an OC decomposition accelerator is filled.

On the other hand, a plurality of iron bars 8 as the second electrode body are inserted around the contaminated area A in the hardly water-permeable ground G2 so as to surround the contaminated area A. The iron pipe 6 and the iron rod 8 are electrically connected to the DC power supply V via a conductor 9. In this case, the iron pipe 6 is connected to the anode of the DC power supply V, and each iron rod 8 is connected to the cathode of the DC power supply V.

It is preferable that the iron pipe 6 has a large number of small holes at a portion below the height at which it is sealed by the sealing material 4, that is, a portion to be inserted into the water impermeable ground G2.
Further, the iron pipe 6 and the iron rod 8 have a height in the easily water-permeable ground G1 previously covered with an electrically insulating synthetic resin tube or the like, so that the electric current flows between the iron pipe 6 and the iron rod 8. Does not short circuit the easily permeable ground G1.

In this state, when the DC power source V is driven and a DC voltage is applied to the iron pipe 6 in the water supply well 5 and the iron rod 8 around it, the iron pipe 6 serving as an anode is formed in the impermeable ground G2.
From the (water supply well 5) side toward the iron rod 8 side which becomes the cathode,
The groundwater flow WF due to the electroosmosis phenomenon is induced, that is, the groundwater in the hardly permeable ground G2 is forcibly moved. Then, along with this, the water W to which the VOC decomposition agent or the VOC decomposition accelerator in the water supply well 5 is added becomes the water-impermeable ground G2.
Permeates from the inside of the contaminated area A toward the surrounding area.

Since the portions of the surfaces of the iron pipe 6 and the iron rod 8 in the easily water-permeable ground G1 are insulated, the electric current is not short-circuited through the easily water-permeable ground G1, and the slightly water-permeable ground G2. Forced groundwater flow WF due to electro-osmosis in S.R. If each iron rod 8 is inserted along a cylindrical surface centered on the iron pipe 6, the distance between the iron pipe 6 and each iron rod 8 becomes equal, so that the electric current between the iron pipe 6 and each iron rod 8 and, by extension, this The groundwater flow WF due to is also almost uniform.

Therefore, as explained above, the VOC
When water W containing a decomposing agent is used, the water-impermeable ground G
Decomposing microorganisms existing in the ground when water W containing a VOC decomposition accelerator is used by decomposing VOC pollutants by a reductive dechlorination in the process of passing through the soil particle gaps in the second pollution area A. By promoting VOC decomposition by
Purification of pollution is performed.

In this embodiment, the groundwater flow WF due to the electroosmosis phenomenon is assumed to be generated from the contaminated area A toward the surrounding area. However, in the case where the underground diffusion of VOCs becomes a problem, FIG. And, contrary to FIG. 4, the water supply well 5 is
Excavation is performed so as to surround the contaminated region A, the iron pipe 6 connected to the anode of the DC power source V is inserted, and the iron rod 8 connected to the cathode is inserted into the contaminated region A in the hardly water-permeable ground G2. By doing this, the groundwater flow W due to the electroosmosis phenomenon
Since F is generated in the direction of converging from the periphery of the contaminated area A, it is possible to purify the VOC while preventing the underground diffusion.

Further, in each of the above-mentioned embodiments,
In each of the above explanations, it is assumed that the hardly water-permeable ground G2 is located at a deep depth, but the method of the present invention is of course applicable regardless of the depth of the contaminated area A of the hardly water-permeable ground G2. is there. In addition, the present invention is particularly effective as a pollution remediation means for poorly permeable ground in which the groundwater infiltration rate is extremely slow, and thus the pollution remediation that depends only on the groundwater flow due to the pumping of groundwater cannot be expected, as in the above-described respective embodiments. However, it can also be applied to the purification of the ground consisting of sandy soil or sandy clay.

[0028]

According to the method of purifying a poorly permeable ground according to the first aspect of the present invention, a remarkable water flow is caused by the vacuum suction of the suction well into the hardly permeable ground where the groundwater flow is usually extremely slow. Since the water containing the pollutant decomposing agent or the pollutant decomposition promoting agent is supplied from the water supply well to the contaminated area of the poorly permeable ground, It is effective as a pollution purification means for difficult-to-permeable soil that cannot be expected to be purified only by the flow, and is also effective as a purification method for deep-permeable, difficult-to-permeable soil that is difficult to clean by substituting good quality soil. .

According to the method for purifying poorly permeable ground according to the second aspect of the present invention, the pollutant decomposing agent or the pollutant decomposition accelerating agent is added from the water supply well existing so as to surround the perimeter of the contaminated area. Since the water moves toward the inside of the contaminated area, it is possible to purify the contamination while preventing the diffusion of the contaminants.

According to the method of purifying a poorly permeable ground according to the third aspect of the invention, a remarkable water flow is forcibly caused by electroosmosis in the hardly permeable ground where the groundwater flow is usually extremely slow, As a result, water containing a pollutant decomposing agent or a pollutant decomposition accelerator is supplied from the water supply well to the contaminated area of the poorly permeable ground.Therefore, purification of pollution that depends only on the groundwater flow by pumping groundwater It is effective as a pollution purification means for difficult-to-permeable soil that cannot be expected, and is also effective as a pollution-cleaning means for deeply permeable soil that is difficult to clean by replacement with good quality soil.

According to the method of cleaning a poorly water-permeable ground according to the invention of claim 4, a pollutant decomposer or a pollutant decomposition agent is provided between the electrode body provided in the contaminated region and the electrode body surrounding the periphery of the electrode body. Since the water containing the pollutant decomposition accelerator flows radially by electroosmosis, the pollution can be efficiently purified.

According to the method for purifying hardly water permeable soil according to the fifth aspect of the present invention, since the VOC decomposer is used in the treated water, reductive dechlorination is carried out in the process of forced flow in the contaminated area of the hardly water permeable soil. Since VOCs are decomposed by the reaction, VOC contamination represented by trichlorethylene and the like can be effectively restored.

According to the method for purifying poorly permeable ground according to the sixth aspect of the invention, since the VOC decomposition accelerating agent that promotes the activity and growth of the VOC decomposing microorganisms is used in the treated water, trichlorethylene can be decomposed by the VOCs by the microorganisms. It is possible to effectively repair VOC contamination represented by the above.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of the ground showing a preferred first embodiment of a method for cleaning a poorly water-permeable ground according to the present invention.

FIG. 2 is a diagram showing a planar arrangement of a suction well and a water supply well in FIG.

FIG. 3 is a vertical cross-sectional view of the ground showing a second preferred embodiment of the method for cleaning a poorly water-permeable ground according to the present invention.

FIG. 4 is a diagram showing a plane arrangement of a water supply well, an iron pipe, and an iron bar in FIG.

[Explanation of symbols]

1 suction well 1a closed space 2,5 Water well 3 suction pipe 4 Seal material 6 Iron tube (first electrode body) 8 Iron bar (second electrode body) A contaminated area G1 easily permeable ground G2 Hardly permeable ground V DC power supply P vacuum pump W treated water

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) E02D 3/10 105 F term (reference) 2D043 DA04 EB06 4D004 AA41 AB06 AC07 CA18 CA37 CC11 CC20

Claims (6)

[Claims] 1. A required number of suction wells reaching or penetrating into the water-impermeable ground are excavated, and a required number of water supply wells reaching or penetrating into the water-impermeable ground are provided between the suction wells. The excavation is performed so that there is a contaminated area in the hardly water-permeable ground, and water containing a pollutant decomposing agent or a pollutant decomposition accelerator is supplied to the water supply well, and the difficulty in the suction well is increased. A method for cleaning a contaminated ground, characterized in that the water in the hardly water-permeable ground is forced to flow by hermetically sealing a portion located in the water-permeable ground and vacuum suction. 2. The pollution according to claim 1, wherein the suction well is drilled to reach or penetrate the contaminated area, and the water supply well is drilled to surround the perimeter of the contaminated area. Ground purification method. 3. A water supply well reaching or penetrating into a contaminated area of the water-impermeable ground is excavated, and a first electrode body is inserted into the water-supply well to reach or penetrate the water-impermeable ground. Insert a required number of second electrode bodies so that there is a contaminated region in the hardly water-permeable ground between the suction well, and a pollutant decomposer or pollutant decomposition accelerator in the water supply well. The contained water is supplied, and the first electrode body is connected to the anode side of the DC power supply, and the second electrode body is connected to the cathode side of the DC power supply to apply a DC voltage between both electrodes. Therefore, the contaminated ground purification method is characterized in that the water in the hardly water-permeable ground is forced to flow. 4. One of the water supply well into which the first electrode body is inserted and the second electrode body are provided so as to reach or penetrate the contaminated region, and the other surrounds the periphery of the contaminated region. The contaminated ground purification method according to claim 3, wherein the method is provided as follows. 5. The difficulty according to claim 1, wherein the pollutant decomposer is a VOC decomposer selected from iron colloid, potassium permanganate, stabilized chlorine dioxide and the like. Method for cleaning permeable ground. 6. The hardly water-permeable ground according to any one of claims 1 to 4, wherein the pollutant decomposition accelerator is a VOC decomposition accelerator selected from ethanol, methanol, and waste sugar concentrate. Purification method.