JP2003033757A - Contaminated soil diffusion prevention method - Google Patents

Abstract

(57) [Summary] [Problem] Practical prevention of the spread of contaminated soil that can relatively easily and at low cost adjust the groundwater level in the underground impermeable wall and prevent the outflow and diffusion of pollutants Provide a method. SOLUTION: An impermeable layer U surrounds a contaminated area I.
The underground impermeable wall 4 is reached, and the contaminated soil is sealed in situ. The culvert type water collecting facility 1 is laid in a ring at a predetermined depth near the inside of the underground impermeable wall 4. By collecting contaminated groundwater in the contaminated area I from the culvert type water collection facility 1, the groundwater level near the underground impermeable wall 4 is locally lowered along the underground impermeable wall 4, and The outside water level sandwiching the water wall 4 is set higher than the inside water level to prevent diffusion of the contaminated groundwater. If necessary, the contaminated groundwater pumped from the culvert type water collecting facility 1 is purified by the treatment plant 2 so as to be infiltrated into the ground in the contaminated area I from the water injection well 3, and by forming a circulation path of the contaminated groundwater, Gradually purify the contaminated soil.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for preventing the spread of contaminated soil by isolating the contaminated soil from the general environment and preventing the spread of the contaminated soil.

[0002]

2. Description of the Related Art As an application regarding the measures for cleaning contaminated soil, for example, Japanese Patent Laid-Open Nos. 9-267082 and 10
For example, those described in JP-A-258266 and JP-A-10-277531 can be cited.

The invention described in Japanese Unexamined Patent Publication No. 9-267082 relates to a method for cleaning soil contaminated with a volatile organic compound, in which a cleaning area using microorganisms is formed in the contaminated area and Purification is achieved by a gas flow circulating in the purification region.

The invention described in Japanese Unexamined Patent Publication No. 10-258266 relates to a method for cleaning soil contaminated by organic waste such as oil in-situ, and a stop for enclosing a contaminated area with a water impermeable layer below and the surrounding area. The water is separated from the water wall, and washing water is supplied under pressure onto the impermeable layer, and the contaminants are taken into the washing water while flowing out to the surface of the earth for recovery.

The invention described in Japanese Patent Application Laid-Open No. 10-277531 relates to a purification method by groundwater circulation that can widely cope with various pollution situations and can reduce costs, and a water injection well surrounding a contaminated area. In addition, the pumping well will be installed so that the injected water will pass through the contaminated area, and the groundwater pumped from the pumping well will be treated by the above-ground pollution treatment equipment and returned to the ground from the water injection well.

On the other hand, according to the guidelines of the Environment Agency issued in February 1999, the basic policy of the in-situ containment policy of pollutants is as follows.

Underground layer thickness 5m or more, permeability coefficient 1.0 ×
There is an impermeable layer of 10 ⁻⁵ cm / sec or less.

The contaminated area is surrounded and closed by a work piece having a water stopping function. Specifically, the steel sheet pile, SMW but water-impervious structure according construction of diaphragm wall (soil mixing wall) are considered, SMW in underground continuous wall width 50cm or more, the permeability is 1.0 × 10 ^{- 6} cm / sec or less. Also, install up to the underground impermeable layer.

When treating groundwater in a contaminated area, a treatment facility removes pollutants to below the environmental standard value and discharges them to the outside.

In order to prevent rainwater and the like from entering, a material having a high water blocking function is laid on the surface. Specifically, it is a double impermeable structure with a combination of impermeable sheet material and improved mixed soil layer.
In addition, when this structure is applied, the treatment by the treatment facility is not necessarily required.

In order to prevent the outflow / diffusion of pollutants outside the planned site, it is desirable to set the groundwater level inside and outside the SMW below the surrounding water level.

[0012]

[Problems to be Solved by the Invention] The above basic policy aims to construct a function at the same level as the impermeable structure of a waste disposal site. It is necessary to adjust the business plan for the occurrence.

Another problem is that there is a great possibility that time and economic constraints will be imposed depending on the installation depth of the SMW.

The impervious function of SMW depends on the construction conditions, and it is difficult to secure the impervious function at the laboratory level.

It is difficult to set the groundwater level in the contaminated area to a uniform steady water level, and it is also difficult to link it to the groundwater level of the surrounding ground. And so on.

The inventions described in the above-mentioned JP-A-9-267082 and JP-A-10-258266 are:
It is intended for specific pollutants and cannot be applied to various pollutants.

In the case of the invention described in Japanese Patent Application Laid-Open No. 10-277531, various kinds of pollution can be dealt with depending on the performance of the ground-based pollution control device. However, in the arrangement of the water injection well and the pumping well, the groundwater circulation path is provided. Is difficult to secure, and pollutants may spread to the surrounding area.

Further, the inventions described in the above publications do not satisfy the above basic policy of the measure for confining pollutants in the original position and are insufficient as an alternative method.

In order to prevent the outflow / diffusion of pollutants to the outside of the planned site, the invention of the present application, in order to prevent the outflow / diffusion of the pollutants, can be performed relatively easily and at low cost to determine the groundwater level in the underground water barrier. It is intended to provide a practical method for preventing the spread of contaminated soil, which can be adjusted to prevent the outflow and spread of pollutants.

[0020]

The method for preventing the spread of contaminated soil according to claim 1 of the present application constructs an underground water barrier to surround a contaminated area, and installs a water collecting facility near the underground water barrier. By arranging and collecting or pumping water from the water collection facility, the groundwater level near the underground impermeable wall is locally lowered and adjusted so that the water level is lower than the water level outside the underground impermeable wall. It is characterized by that.

In the present invention, by collecting or pumping water from the water collection facility, the groundwater level decreases near the water collection facility. However, by arranging this water collection facility near the underground water barrier,
From a local point of view, the water level inside the underground impermeable wall, that is, on the contaminated area side can be made lower than the water level outside the underground impermeable wall, that is, outside the contaminated area. The basic policy of the in-situ pollutant containment policy in the guidelines of the Environment Agency will be satisfied, and the outflow and diffusion of pollutants outside the planned site can be prevented.

That is, in order to lower the water level in the entire contaminated area, the amount of pumped water required is large, and the groundwater level adjustment and maintenance are very costly, whereas in the present invention, the water level can be lowered locally. Since all that is required is a significant reduction in cost when viewed as a total.

As the underground impermeable wall, SMW underground continuous wall,
If a steel sheet pile wall or any other continuous underground wall that can be expected to block water can be used, and if it is constructed so as to reach the impermeable layer, the above basic policy will also be satisfied, but the conditions are allowed. In this case, it may be possible to reduce the construction cost of the underground impermeable wall by making it above the impermeable layer.

As the water collection facility, in addition to conventional water collection wells (pumping wells), underdrain type water collection facilities laid at a predetermined depth in the ground are conceivable.

[0025] A second aspect of the present invention is the method for preventing the spread of contaminated soil according to the first aspect, in which the contaminated groundwater collected or pumped from the water collecting facility is purified and then permeated into the contaminated area again.

In this case, after the contaminated groundwater pumped up from the water collection facility is purified, it is returned to the ground in the contaminated area, and the groundwater flows from the infiltration facility where the water level is high to the water collection facility where the water level is lowered. As a result, a circulation route for contaminated groundwater is formed, and the contaminated soil can be gradually purified while taking in pollutants from the contaminated soil.

The purification treatment of the pumped-up contaminated groundwater is carried out by various treatments which have been conventionally known, for example, in one step or in a multistage manner depending on the kind of the pollutant, by a treatment plant or the like provided near the water collection facility. It can be done in stages.

As means for infiltrating the purified contaminated water into the contaminated area, water injection wells, infiltration trenches, or underdrain type infiltration facilities laid in the ground are conceivable.
In the case of a seepage trench or underdrain type seepage facility, it may be possible to construct it in a ring or net form so that it can penetrate the entire contaminated area. Even in that case, basically, it will be built inside the water collection facility whose purpose is to lower the water level near the underground water barrier.

A third aspect of the present invention is the method for preventing the spread of contaminated soil according to the first or second aspect, wherein the water collecting facility is annularly arranged at a predetermined depth in the ground inside the underground impermeable wall. This is limited to the case of a type of water collection facility.

As described in relation to claim 1, as the water collecting facility, it is possible to use a conventional water collecting well or a trench, but the water collecting facility is uniform along the underground water barrier. In order to lower the water level, a large number of water collection wells are required, and the depth of excavation also increases in the case of trenches, whereas in the case of underdrain type water collection facilities, comparison is made according to the target water level. It can be constructed at any desired depth, and by making it continuous in a ring shape, it is possible to reduce the water level almost uniformly along the underground impermeable wall.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows an embodiment of the present invention, in which an underground water barrier 4 is constructed so as to surround a contaminated area I. This underground impermeable wall 4 reaches the impermeable layer U, and basically the underground impermeable wall 4 and the impermeable layer U form a closed space, which is a structure that can confine the contaminated soil in its original position. ing.

A culvert type water collecting facility 1 is laid in a ring shape at a predetermined depth near the inside of the underground water shielding wall 4, and the culvert type water collecting facility 1 is provided.
The contaminated groundwater in the contaminated area I is collected from the above, and is pumped to the ground if necessary, so that the groundwater level decreases toward the underdrain type water collecting facility 1 in a curved or curved manner. Therefore, it is possible to adjust the water level inside the underground water shield wall 4 close to the underdrain type water collection facility 1 to be lower than the groundwater level outside the contaminated area O according to the amount of collected water or the amount of pumped water.

For example, the water permeability is 1.0 × 10 ^-6 cm /
Even when an SMW continuous underground wall of less than a second is used as the underground impermeable wall 4, the quality actually varies.
Even if it is slightly permeable, if the water level on the contaminated area I side is higher than the water level on the O side outside the contaminated area, the contaminated groundwater may diffuse to O outside the contaminated area. Since the water level is lower than the water level outside the contaminated area on the O side, the effect of preventing the diffusion of contaminated groundwater becomes more reliable. This means that even when a steel sheet pile wall or the like is used for the underground impermeable wall 4,
The same applies when complete impermeability cannot be expected.

When pumping water from the underdrain type water collecting facility 1, for example, a human hole or a collecting cell may be provided at an arbitrary position in the continuous direction, and the water can be pumped from there. The part can also be used for water quality monitoring.

The pumped-up contaminated groundwater is treated in the treatment plant 2 and then permeates into the ground from a water collection facility installed at a predetermined position inside the underdrain type water collection facility 1. In the figure, a single water injection well 3 is shown in the center of the contaminated area I.
The water injection wells 3 may be provided at a plurality of locations, or a water injection trench or an underdrain water injection facility having a configuration similar to or similar to that of the underdrain water collection facility 1 described above may be used. However, in principle, the water injection position of the water injection facility should be located above the water injection position of the water collection facility.

In this case, regarding the groundwater level, the water level in the one part of the underdrain type water collecting facility where the water collection or pumping is performed is the lowest, and the water level is highest in the three water injection wells for returning the treated water to the ground again. There is.

Therefore, by adjusting the depth of the underdrain type water collection facility 1 and the amount of collected or pumped water, the depth of the water injection well 3, the amount of permeation of treated water, etc., the contaminated area near the underground impermeable wall 4 The groundwater level in I can be set to be equal to or lower than the groundwater level in O outside the contaminated area, whereby diffusion of pollution can be prevented.

On the other hand, a circulation route of contaminated groundwater is formed between the underdrain type water collection facility 1, the treatment plant 2 and the water injection well 3. By repeating this circulation, pollutants in the soil are gradually removed, You can purify contaminated groundwater. In addition, the surplus treated water having a low pollution level and the pollutants removed after being treated in the treatment plant 2 can be carried out and disposed of outside the region depending on conditions.

Further, the surface of the contaminated area I is to be provided with a surface water-blocking work 5 for preventing rainwater from penetrating into the ground if necessary. As for this surface impermeable work, those indicated by the guidelines and the like can be used.

2 (a) to 2 (d) show a concrete example of the underdrain type water collection facility 3. As shown in FIG. In the water collection facility 3 of FIG. 2 (a), a perforated pipe 11 such as a hard vinyl chloride pipe having a water permeation hole is used as a core material, and a single-grain crushed stone 12 is laid around the perforated pipe 11 to secure a water permeation area. Further, a suction preventive material 13 made of a non-woven fabric or the like is wound around it to prevent clogging or the like due to infiltration of soil particles. Although this type has good water permeability for collecting water from the ground, it tends to increase the installation cost.

In the water collection facility 3 of FIG. 2 (b), instead of the crushed stone 12 of FIG. 2 (a), a fiber drainage material 14 is wound around the perforated pipe 11 and a suction prevention material 13 is provided around it. It has a rolled structure. The water permeability is inferior to that of Fig. 2 (a), but the cost can be reduced. As the commercially available fiber drainage material 14, for example, there is a porous material (trade name: hemitalone) in which mutual nodes of fibers are fusion-molded and integrated.

In the water collection facility 3 of FIG. 2 (c), the suction preventive material 13 is wound around the single-grain crushed stone 12 without using a perforated pipe to form a continuous underdrain. Although the cost is the lowest, it is inferior in terms of water permeability to the ones shown in Figs. 2 (a) and 2 (b).

In the water collection facility 3 of FIG. 2 (d), a drainage material 14 made of fiber is used instead of the crushed stone 12 of FIG. 2 (c), and a suction prevention material 13 is wound around it.

[0044]

According to the present invention, when a water collecting facility for collecting or pumping contaminated groundwater is arranged in the vicinity of an underground impermeable wall constructed so as to surround a contaminated area, when viewed locally, Inside the underground water barrier, that is, the water level on the contaminated area side,
It is possible to lower the water level outside the underground impermeable wall, that is, outside the contaminated area, thereby preventing the outflow and diffusion of pollutants outside the contaminated area.

Since it is only necessary to locally lower the water level, the required amount of collected water or pumped water is small, and the cost required for maintenance can be reduced.

Since the required amount of water collected and pumped is small,
It is possible to prevent ground subsidence due to a decrease in groundwater level.

By continuously connecting the underdrain type water collecting facility in claim 3 in a ring shape, it is possible to form a groundwater flow with little deviation, and to make the water level near the underground impermeable wall uniform and to keep it outside the contaminated area. By preventing the diffusion of pollutants into water and forming a circulation route of sewage and groundwater between the sewage treatment facility and the water injection facility, the purification effect of contaminated soil can be obtained.

By infiltrating the purified water into the ground again, it is possible to prevent the ground subsidence due to the lowering of the groundwater level.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an embodiment of the present invention.

2 (a) to (d) are cross-sectional views showing an example of the form of an underdrain type water collection facility used in claim 3;

[Explanation of symbols]

I ... contaminated area, O ... outside contaminated area, U ... impermeable layer, W ... groundwater level, 1 ... underdrain type water collection facility, 2 ... treatment plant, 3 ...
Water injection well, 4 ... Underground water barrier, 5 ... Surface water barrier, 11 ... Perforated pipe, 12 ... Crushed stone, 13 ... Suction prevention material, 14 ... Fiber drainage material

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasushi Sudo             Kashima-ken, 1-2-7 Moto-Akasaka, Minato-ku, Tokyo             Inside the corporation F term (reference) 2D049 EA01 EA14                 4D004 AA41 CA40

Claims (3)

[Claims] 1. A ground impervious wall is constructed so as to surround a contaminated area, and a water collection facility is arranged near the ground water impermeable wall to collect or pump water from the water collection facility. A method for preventing the spread of contaminated soil, which comprises locally lowering the groundwater level in the vicinity of a medium impermeable wall so that the water level is lower than the water level outside the underground impermeable wall. 2. The method for preventing the spread of contaminated soil according to claim 1, wherein the contaminated groundwater collected or pumped from the water collection facility is purified and then permeated into the contaminated area again. 3. The contaminated soil diffusion according to claim 1 or 2, wherein the water collection facility is an underdrain type water collection facility that is annularly arranged inside the underground impermeable wall at a predetermined depth in the ground. Prevention method.