JP2006082008A - Method for treating contaminated soil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently recover and remove contaminants in a hardly gas permeable-water permeable layer essentially consisting of clay or silt having low water permeability and gas permeability. <P>SOLUTION: In this method for treating the contaminated soil, at first, a well 3 for treatment is piercingly installed in a hardly gas permeable-water permeable layer 2 in contaminated soil 1 which is a hardly water permeable layer and also a hardly gas permeable layer (step 101). After the well 3 for treatment is piercingly installed in the hardly gas permeable-water permeable layer 2, a refrigerant is injected into the well 3 for treatment (step 102). Next, gap water within a treatment region is frozen with the refrigerant, so as to form a dome-shaped rigidity-increased region 21, and then, the treatment region 18 is fused (step 103). Next, water passing or gas passing is performed to the inside of the treatment region 18, so as to recover the contaminants via the well 3 for treatment, or the injection of a chemical is performed via the well 3 for treatment, so as to make the contaminants harmless (step 104). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for treating contaminated soil for detoxifying contaminated soil containing contaminants such as organochlorine compounds.

  Various pollutants such as volatile organochlorine compounds, fuel oils and machine oils, dioxins, or heavy metals such as cadmium, lead, copper, zinc, nickel, and chromium are mixed in the soil of the factory site. Sometimes.

  If the contaminated soil contaminated with such contaminants is left as it is, the contaminants mixed in the soil will diffuse to the surroundings, hindering the lives of the surrounding residents, and if they are released from the soil particles by rainwater In addition, it may cause contamination of groundwater by contaminating water quality. Therefore, the soil contaminated with the above-mentioned pollutants must be cleaned using various methods.

  Various methods have been developed to purify the pollutants in the soil in-situ, including the excavation aeration method and the pumped aeration method, as well as the soil gas suction method and water injection into the contaminated soil. The so-called water washing method that pumps water and treats it on the ground, the so-called bubble entrainment purification method that feeds air and entrains pollutants in the bubbles, the air sparging method that volatilizes harmful substances by introducing air pressure, A wide variety of methods are known, such as a bioremediation method utilizing microbial activity and a chemical solution injection method utilizing a redox reaction.

Japanese Patent Laid-Open No. 11-169837

  Here, aeration, gas suction, bubble entrainment purification, air sparging, chemical solution injection, etc. can all be said to be methods that are expected to be water permeable or air permeable in the contaminated soil, but it is difficult to make clay and silt mainly in the contaminated soil. When the air permeable permeable layer is distributed, since the water permeability and air permeability of the hardly permeable air permeable layer and the like are low, the above-described construction method is hardly applicable.

  The present invention has been made in consideration of the above-described circumstances, and is capable of efficiently recovering and removing the contaminants in the hardly permeable air permeable layer mainly composed of clay and silt having low water permeability and air permeability. It aims at providing the processing method of soil.

  In order to achieve the above object, according to the method for treating contaminated soil according to the present invention, as described in claim 1, contaminants such as volatile organic chlorine compounds, hydrocarbons and heavy metals are present in the hardly permeable layer or the hardly permeable layer. In the method for treating contaminated soil for purifying the contaminated soil contained in the treatment well, a treatment well is inserted into the hardly permeable layer or the hardly permeable layer, a refrigerant is injected into the treatment well, and the refrigerant is used to Forming a dome-like rigidity increasing region so as to surround the processing region by freezing pore water in the processing region surrounding the processing well and applying the expansion pressure of the processing region to the surrounding ground due to the freezing, and the processing After the frozen interstitial water has melted in the region, the pollutant is collected by passing or venting water into the treatment region, or the contaminant is removed by injecting a chemical solution through the treatment well. Nothing It is intended to reduction.

  The method for treating contaminated soil according to the present invention purifies contaminants such as volatile organic chlorine compounds, hydrocarbons and heavy metals contained in a hardly permeable layer or a hardly permeable layer mainly composed of clay and silt. In this invention, first, a processing well is inserted into the hardly water-permeable layer or the hardly air-permeable layer described above.

  Here, the treatment well can be used as a pumping well or a gas suction well after the pretreatment of the present invention is completed. In that case, for example, a water-permeable hole or a gas-permeable hole is formed near the lower end of the well. Provided strainer section.

  Hereinafter, the description will be continued on the assumption that such a strainer portion is provided. Needless to say, if the strainer is not provided in the processing well, a pumping well, a gas suction well, or an injection well may be separately installed.

  If the processing well is installed so as to penetrate into the hardly water-permeable layer or the hardly air-permeable layer, the refrigerant is then injected into the processing well.

  When injecting the refrigerant, if the intrusion position is a saturated layer, groundwater flows from the strainer part. First, an airtight cap is attached to the head of the treatment well, and the airtight cap is inserted airtightly. The air is pressed into the treatment well through the pneumatic pipe, and the flowing groundwater is pushed back to the surrounding ground through the strainer.

  Next, in this state, the refrigerant is fed through the refrigerant pipe that is similarly installed in the airtight cap. At this time, the compressor connected to the pneumatic feed pipe is appropriately controlled so that the fed refrigerant does not flow out from the strainer portion to the surrounding ground.

  By injecting the coolant into the treatment well in this manner, the pore water in the treatment area surrounding the treatment well is frozen and the expansion pressure of the treatment area due to the freezing is applied to the surrounding ground to increase the dome-like rigidity. The region is formed so as to surround the processing region.

  That is, by injecting a refrigerant into the treatment well, the treatment area composed of a hardly permeable layer or a hardly permeable layer surrounding the treatment well by the refrigerant, in other words, the pore water in the hardly permeable layer to be purified is frozen. Then, the entire treatment region is expanded by the volume expansion due to the freezing, and the expansion pressure is applied to the surrounding ground surrounding the treatment region.

  In this way, since the surrounding ground subjected to such expansion pressure is also composed of a hardly permeable layer or a hardly permeable layer mainly composed of clay or silt, the surrounding ground is pushed out by pore water and the skeletal structure of the soil particles. Changes to become a dome-shaped rigidity increasing region with improved rigidity.

  In such a state, the surrounding earth pressure is mainly borne by the rigidity increasing region and hardly reaches the inner processing region.

  Therefore, after the treatment area is melted, the gap in the treatment area expanded by volume expansion does not shrink to the original size at least immediately after melting, and is protected from the surrounding earth pressure by the dome-like rigidity increasing area. The magnitude | size will be hold | maintained for a fixed period, and the water permeability and air permeability of the process area | region which consist of a hardly water-permeable layer or a hardly air-permeable layer improve markedly.

  Next, in such a state, the pollutant is made harmless by collecting or polluting the pollutant through the treatment well by performing water flow or ventilation in the treatment area, or by injecting the chemical solution through the treatment well. To do.

  In addition, as described above, when a treatment well is not provided with a strainer part and a pumping well, a gas suction well, or an injection well is separately installed, pumping or gas suction is performed through the pumping well or the gas suction well. Alternatively, the chemical solution may be injected through an injection well.

  In injecting the coolant into the treatment well, any injection method may be used as long as the dome-shaped rigidity increasing region is formed so as to surround the treatment well by the coolant. When the refrigerant is injected in a plurality of stages so that the horizontal cross-sectional area of the frozen processing region increases from the top to the bottom, the dome-like rigidity increasing region can be reliably formed. It becomes possible.

  As a specific shape in which the horizontal cross-sectional area increases from the top to the bottom, a cone shape, a bell shape, a dome shape, or the like can be considered.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a method for treating contaminated soil according to the present invention will be described with reference to the accompanying drawings. Note that components that are substantially the same as those of the prior art are assigned the same reference numerals, and descriptions thereof are omitted.

  The method for treating contaminated soil according to this embodiment purifies contaminants such as volatile organic chlorine compounds, hydrocarbons, and heavy metals contained in a hardly permeable layer or a hardly permeable layer mainly composed of clay and silt. FIG. 1 is a flowchart showing a procedure for carrying out a contaminated soil treatment method according to the present embodiment.

  As can be seen from FIG. 2, in order to treat a pollutant using the contaminated soil treatment method according to the present embodiment, first, as shown in FIG. 2, the contaminated soil 1 is both a hardly permeable layer and a hardly permeable layer. The processing well 3 is installed so as to penetrate into the hardly permeable air permeable layer 2 (step 101).

  Here, the processing well 3 is provided with a strainer portion 5 in which a water permeable hole 4 also serving as a gas permeable hole is formed in the vicinity of the lower end.

  If the processing well 3 is installed so as to penetrate the hardly air-permeable permeable layer 2, next, a coolant such as liquid nitrogen is injected into the processing well 3 (step 102).

  Here, since groundwater flows into the processing well 3 from the strainer section 5, when injecting the refrigerant, first, the airtight cap 6 is attached to the head of the processing well 3, and the airtight cap is attached. The air is pressed into the treatment well 3 through the pneumatic feed pipe 7 which is airtightly inserted into the ground, and the groundwater flowing in is pushed back to the surrounding ground through the strainer section 5.

  Next, in this state, the refrigerant is fed into the airtight cap 6 through the refrigerant pipe 8 that is also installed in an airtight manner. At this time, it is desirable to appropriately control a compressor (not shown) connected to the pneumatic feed pipe 7 so that the fed refrigerant does not flow out from the strainer portion 5 to the surrounding ground.

  That is, the air pressure in the upper space in the processing well 3 is adjusted so that the groundwater pushed back does not flow again from the strainer unit 5 and the injected refrigerant does not flow out of the strainer unit 5.

  In this way, the refrigerant can be recovered in a subsequent process without causing the refrigerant to flow out to the surrounding ground. Note that if the refrigerant itself does not cause any problem in the surrounding ground itself, whether or not to perform the above-described control may be determined according to the necessity of recovery.

  FIG. 3 is a diagram showing a state of injecting the refrigerant.

  As can be seen from the figure, in this embodiment, the refrigerant is injected in a plurality of stages. That is, first, as shown in FIG. 6A, the coolant 11 is injected into the processing well 3 from a coolant tank (not shown) so that the coolant injection amount is slightly lower than the groundwater level. The primary frozen region 12 is formed by freezing the pore water in the hardly permeable air permeable layer 2 surrounding the well 3.

  Next, as shown in FIG. 2B, once the liquid level of the refrigerant 11 is lowered, the interstitial water in the hardly permeable air permeable layer 2 spreading near the bottom in the primary freezing region 12 is frozen to 2 Next freezing regions 13 are formed, and these are designated as new freezing regions 14.

  Next, as shown in FIG. 3C, the liquid level of the refrigerant 11 is raised again to the vicinity of the groundwater, so that the interstitial water in the hardly permeable air permeable layer 2 spreading around the freezing region 14 is frozen to form the tertiary. Freezing regions 15 are formed, and these are used as new freezing regions 16.

  Next, as shown in FIG. 4 (d), by temporarily lowering the liquid level of the refrigerant 11, the interstitial water in the hardly permeable air permeable layer 2 spreading near the bottom in the freezing region 16 is frozen and quaternary frozen. Regions 17 are formed and these are designated as new frozen regions 18.

  In this way, the above-described procedure is repeated as necessary so that the treatment area to be purified of contaminants is frozen into a dome shape or a bell shape. In the present embodiment, the frozen area 18 is a processing area 18.

  In this way, when the coolant 11 is injected into the processing well 3 to freeze the interstitial water in the processing region 18 composed of the hardly permeable air-permeable layer surrounding the processing well 3, as shown in FIG. By the volume expansion, the entire processing region 18 can be expanded, and the expansion pressure can be applied to the surrounding ground surrounding the processing region 18.

  And the surrounding ground which is the hardly air permeable permeation layer which has received the expansion pressure from the dome-shaped or bell-shaped processing region 18 has a dome-shaped structure in which pore water is pushed out and the skeletal structure of the soil particles is changed to improve rigidity. It becomes the rigidity increasing region 21.

  If the dome-like rigidity increasing region 21 is formed in this way, the processing region 18 is melted (step 103). The refrigerant is collected at an appropriate time.

  In this way, the soil particle gap in the treatment region 18 is larger than the original size due to volume expansion due to freezing, and the water permeability and gas permeability are greatly improved. In addition, the peripheral earth pressure is mainly borne by the rigidity increasing region 21 and hardly reaches the inner processing region 18.

  Therefore, after the processing region 18 melts, the soil particle gap in the processing region 18 expanded by volume expansion does not shrink to the original size at least immediately after melting, and the dome-shaped rigidity increasing region 21 surrounds the surrounding soil. The size is maintained for a certain period in a form that is protected from pressure.

  Next, in such a state, by passing water or ventilating the processing region 18, the contaminated groundwater or contaminated gas containing the pollutant is recovered through the processing well 3, or through the processing well 3. By injecting the chemical solution, the pollutant is rendered harmless (step 104).

  Here, in the case where the water permeability and air permeability of the rigidity increasing region 21 are significantly reduced with the change in the skeleton structure of the soil particles, a water injection well or an air injection well is provided at the lower end thereof. What is necessary is just to penetrate and arrange | position in this rigidity increase area | region so that a strainer part may be located in the dome-shaped rigidity increase area | region 21. FIG.

  As described above, according to the method for treating contaminated soil according to the present embodiment, the treatment area 18 in the hardly permeable air permeable layer 2 containing the pollutant is frozen in a dome shape or a bell shape to surround it. Since the rigidity increasing region 21 is formed in the processing region 18 and then the processing region 18 is melted, the water permeability and gas permeability of the processing region 18 can be greatly improved. It becomes possible to purify the inside of the processing region 18 by using the pollutant purification method.

  Moreover, according to the processing method of the contaminated soil which concerns on this embodiment, in the freezing process of the process area | region 18, by repeating raising and lowering the liquid level of a refrigerant | coolant, the rigidity increase area | region 21 can be formed in a dome shape or a bell shape. It becomes possible.

  Therefore, the rigidity increasing region 21 becomes an arch structure and supports the earth pressure acting from the periphery, and as a result, the surrounding earth pressure does not act on the internal treatment region 18, and thus the gap becomes the original size after melting. It does not shrink, and it is possible to reliably maintain a state where water permeability and air permeability are improved.

  In the present embodiment, when the water permeability and the air permeability become difficult due to the significant decrease in the water permeability and air permeability of the rigidity increasing region 21, the water injection well or the air injection well is subsequently replaced with the rigidity increasing region. However, instead of this, such a water injection well or an air injection well may be installed together with the processing well 3 in advance.

  In such a case, the water injection well or the air injection well can be used as a well for injecting a refrigerant, like the treatment well.

  That is, for example, in the case of purifying contaminants by washing with water, two treatment wells 31a and 31b are spaced apart from each other in the hardly permeable air permeable layer 2 as shown in FIG. The air-permeable permeable layer 2 is frozen to form the treatment region 32 and the rigidity increasing region 33, and then one treatment well 31a may be a pumping well and the other treatment well 31b may be a water injection well.

  Although not particularly mentioned in the present embodiment, a water-permeable material (air-permeable material) composed of gravel, crushed stone, or the like may be filled in the depth direction so as to surround the processing well 3.

  According to such a configuration, even if the hardly permeable and water-permeable portion remains in the processing region 18, the contaminated groundwater and the contaminated gas remaining in the entire processing region 18 are reliably recovered from the strainer portion 5 through the water-permeable material. It becomes possible. In addition, it is desirable that the upper end of the water-permeable material is sealed in a water-tight and air-tight manner using bentonite, mortar, or the like so that the gap between the water-permeable materials does not communicate with the ground.

  In this embodiment, the freezing region is formed in a dome shape or a bell shape while raising and lowering the height of the refrigerant. Instead of this, the freezing region is frozen while discontinuously decreasing the height of the refrigerant. A region may be formed. In such a case, for example, it is conceivable to gradually reduce the refrigerant in three stages.

  Even in such a configuration, the frozen region can be formed in a dome shape or a bell shape.

  In the present embodiment and the modification, the refrigerant is injected in a plurality of stages. However, the refrigerant is injected in a plurality of stages. In other words, the refrigerant is continuously injected without injecting the refrigerant discontinuously. If the freezing region can be formed in a dome shape or a bell shape by lowering to a low level, it is not always necessary to inject the refrigerant in a plurality of stages.

  In the present embodiment, the strainer portion 5 is formed in the processing well 3 so that it can be used as a pumping well or a suction well in a purification operation performed in a later process. In the case where it is difficult to push back in place, instead of such a configuration, a holeless refrigerant injection pipe having an outer diameter substantially equal to or smaller than the inner diameter of the processing well 3 is separately prepared, and the refrigerant injection pipe May be inserted into the processing well 3, and then the refrigerant may be injected into the refrigerant injection pipe. In such a configuration, the refrigerant is indirectly injected into the processing well 3.

The flowchart which showed the implementation procedure of the processing method of the contaminated soil which concerns on this embodiment. The figure which showed the processing system which implements the processing method of the contaminated soil which concerns on this embodiment. The figure which showed the procedure in which a hardly air permeable permeation layer is frozen by the processing method of the contaminated soil which concerns on this embodiment. The figure which showed the relationship between the process area | region 18 and the rigidity increase area | region 21. FIG. The schematic sectional drawing which concerns on a modification.

Explanation of symbols

1 Contaminated soil 2 Difficult-permeable permeable layer (Refractory permeable layer, Difficult-permeable layer)
3 treatment well 18 treatment area 21 rigidity increase area

Claims (2)

In the method for treating contaminated soil for purifying contaminated soil containing contaminants such as volatile organic chlorine compounds, hydrocarbons, heavy metals, etc. in the hardly permeable layer or hardly permeable layer,
A treatment well is inserted into the hardly water-permeable layer or the hardly air-permeable layer, a refrigerant is injected into the treatment well, and the pore water in the treatment region surrounding the treatment well is frozen by the refrigerant and the frozen By applying the expansion pressure of the treatment area to the surrounding ground, a dome-like rigidity increasing area is formed so as to surround the treatment area, and after the frozen pore water is melted in the treatment area, A method for treating contaminated soil, comprising collecting the pollutant by passing water or aeration, or detoxifying the pollutant by injecting a chemical solution through the treatment well. 2. The treatment of contaminated soil according to claim 1, wherein when the pore water in the treatment area is frozen, the refrigerant is injected in a plurality of stages so that a horizontal cross-sectional area of the frozen treatment area increases from above to below. Method.

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