JP2010264399A - Resoiling preventing method after contaminated soil cleaning - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preventing the occurrence of resoiling after once purifying the contaminated soil. <P>SOLUTION: The method for preventing the resoiling after purifying the contaminated soil is a method to prevent the resoiling after purifying the contaminant 40 in soil where a permeable layer 20 is located on or under a low-permeable layer 10. The method comprises the first step of purifying the soil until the concentration of the contaminant 40 in the low-permeable layer 10 and the permeable layer 20 becomes the environment reference value or below and the second step of forming a contaminant decomposition layer 30 including a contaminant decomposing agent to decompose the contaminant 40, or a contaminant adsorption layer 30 including a contaminant adsorbing agent to adsorb the contaminant 40 between the low-permeable layer 10 and the permeable layer 20. The contaminant 40 remaining in the low-permeable layer 10 is decomposed when it passes through the contaminant decomposition layer 30 or the contaminated adsorption layer 30. Resultingly, the contaminant 40 remaining at the low-permeable layer 10 does not flow out into the permeable layer 20. Thus the resoiling of the permeable layer 20 can be inhibited. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for preventing re-contamination after once cleaning soil contaminated with pollutants.

  Conventionally, as a method of purifying soil contaminated with pollutants such as volatile organic compounds (VOC), excavating and transporting contaminated soil, such as chemical injection using Fenton chemicals and groundwater pumping methods In-situ purification methods are known that purify pollutants on the spot (in-situ) without doing so. For example, in the purification method using the above-described Fenton chemical solution, the Fenton chemical solution is injected into the soil of the purification target section, and the soil is purified by decomposing contaminants in the soil by hydroxyl radicals generated by the Fenton reaction. And purification is complete | finished when the density | concentration of the contaminant detected from the observation well installed in the soil of the purification | cleaning area becomes below an environmental standard value (for example, refer patent document 1).

JP 2006-341195 A

  However, even if the concentration of pollutants in the soil falls below the environmental standard value, if the pollutants reach finely permeable layers such as clay and silt layers, the pollutants are completely purified. This is very difficult and contaminants may remain in the impermeable layer. Therefore, even if the soil is once purified, there is a concern that contaminants may flow out from the hardly permeable layer to the permeable layer over time. And when a pollutant flows into a water permeable layer, it is possible that the density | concentration of a pollutant will become more than an environmental standard value again.

  In view of the above points, an object of the present invention is to provide a method for preventing recontamination after once purifying contaminated soil.

  The method for preventing recontamination after purification of contaminated soil according to claim 1 of the present invention is a method for preventing recontamination after purifying contaminants in soil in which the permeable layer is located above or below the hardly permeable layer. The pollutant is decomposed between the hardly permeable layer and the permeable layer, and the first step of purifying the soil until the concentration of the permeable layer and the contaminant in the permeable layer becomes an environmental standard value or less. And a second step of forming a pollutant decomposing layer containing a pollutant decomposing agent or a pollutant adsorbing layer containing a pollutant adsorbing agent that adsorbs the pollutant.

  According to a second aspect of the present invention, in the second step of the first aspect, in the second step of the first aspect, the re-contamination prevention method forms an excavation hole in the permeable layer and extends from the excavation hole to the hardly permeable layer. The pollutant decomposing layer is formed by injecting the pollutant decomposing agent.

  According to a third aspect of the present invention, there is provided a method for preventing recontamination after purification of contaminated soil, wherein in the second step of the first aspect, a drilling hole is formed in the hardly permeable layer, and the hardly permeable layer is formed from the digging hole. The contaminant decomposition layer is formed by injecting the contaminant decomposer below.

  According to a fourth aspect of the present invention, there is provided a method for preventing recontamination after purification of contaminated soil, wherein the pollutant is a volatile organic compound according to any one of the first to third aspects, and the pollutant decomposing agent. It is characterized by using iron powder or peroxysulfate.

  According to claim 5 of the present invention, the method for preventing recontamination after remediation of contaminated soil forms a drill hole in the permeable layer in the second step of claim 1, and extends from the drill hole to the hardly permeable layer. The contaminant adsorbing layer is formed by injecting the contaminant adsorbent into the substrate.

  According to claim 6 of the present invention, the method for preventing recontamination after remediation of contaminated soil forms a drill hole in the hardly permeable layer in the second step of claim 1, and from the drill hole to the hardly permeable layer. The contaminant adsorbing layer is formed by injecting the contaminant adsorbent below.

  According to a seventh aspect of the present invention, there is provided a method for preventing recontamination after purification of contaminated soil, wherein the pollutant is a volatile organic compound according to any one of the first, fifth, and sixth aspects. Activated carbon and / or zeolite is used as the adsorbent.

  According to the method for preventing recontamination after purification of contaminated soil according to the present invention, after the soil is once purified until the concentration of the contaminant becomes equal to or lower than the environmental standard value, the pollutant decomposition layer or between the hardly permeable layer and the permeable layer is used. By forming the pollutant adsorbing layer, the pollutant remaining in the hardly permeable layer is decomposed or adsorbed when passing through the pollutant decomposed layer or pollutant adsorbing layer. The substance does not flow out to the water permeable layer, and it is possible to reliably prevent re-contamination of the water permeable layer.

FIG. 1 is a conceptual diagram for explaining the action of the pollutant decomposition layer or the pollutant adsorption layer formed in the second step of the present embodiment. FIG. 2 is a diagram showing a schematic configuration of an injection apparatus applied in the second step of the present embodiment. FIG. 3 is a diagram showing a procedure for injecting a pollutant decomposing agent or a pollutant adsorbent into soil using the injection apparatus shown in FIG. FIG. 4 is a diagram schematically showing a part of the vicinity of the interface between the hardly permeable layer and the permeable layer after the procedure shown in FIG. 3 is performed. FIG. 5 is a diagram conceptually showing the state of pollutants remaining in the soil and the outflow situation when the soil is purified by a conventional purification method.

  Hereinafter, preferred embodiments of a method for preventing recontamination after purification of contaminated soil according to the present invention will be described in detail with reference to the accompanying drawings.

The soil to be purified in the present embodiment is a soil having a stratum structure in which the permeable layer is located on the hardly permeable layer, and the hardly permeable layer and the permeable layer are contaminated with a contaminant. Here, the impermeable layer is a kind of impermeable layer, which is a stratum that is aquifer but is difficult for groundwater to flow. Specifically, a clay layer having a water permeability of about 10 ⁻¹¹ to 10 ⁻⁹ [cm / sec], a silt layer having a water permeability of about 10 ⁻⁹ to 10 ⁻⁴ [cm / sec], and the like correspond. Further, the water permeable layer is a ground layer that allows water to pass more easily than the hardly water permeable layer, and corresponds to a gravel layer having a water permeability coefficient of about 10 ⁻⁴ or more [cm / sec].

  The contaminants contained in the soil are volatile organic compounds (VOC) such as tetrachloroethylene, trichloroethylene, cis-1,2-dichloroethylene, and benzene, cyanide compounds, and the like. Below, the case where a pollutant is a volatile organic compound is demonstrated.

  In the soil purification method according to the present embodiment, first, in the first step, the soil is purified until the concentration of the hardly permeable layer and the contaminant in the permeable layer in the region to be purified is equal to or lower than the environmental reference value. Next, in the second step, a pollutant decomposition layer or a pollutant adsorption layer described later is formed between the hardly permeable layer and the permeable layer.

  The left diagram in FIG. 1 is a diagram conceptually showing a state in which the pollutant decomposition layer 30 or the pollutant adsorption layer 30 is formed between the hardly permeable layer 10 and the permeable layer 20. Hereinafter, the hardly permeable layer is referred to as “clay / silt layer 10”, and the permeable layer is referred to as “sand gravel layer 20”. As shown in the left diagram of FIG. 1, at the time when the first and second steps described above are completed, the contaminant 40 below the environmental standard value remains in the clay / silt layer 10. When the conventional purification method is performed, these contaminants 40 may flow out to the gravel layer 20 over time, but in this embodiment, the interface between the clay / silt layer 10 and the gravel layer 20 is contaminated. The material decomposition layer 30 or the contaminant adsorption layer 30 is formed. For this reason, when the pollutant decomposition layer 30 is formed, the pollutant 40 remaining in the clay / silt layer 10 is decomposed when passing through the pollutant decomposition layer 30 as shown in the right diagram of FIG. Decomposed by the agent. Further, when the contaminant adsorbing layer 30 is formed, the contaminant 40 remaining in the clay / silt layer 10 is adsorbed by the contaminant adsorbent when passing through the contaminant adsorbing layer 30. This prevents contaminants remaining in the clay / silt layer 10 from flowing out into the gravel layer 20. Hereinafter, the first step and the second step will be described in more detail.

  First, in the first step, the soil is purified until the concentration of the contaminant 40 in the clay / silt layer 10 and the gravel layer 20 in the purification target region is equal to or lower than the environmental standard value. As a method of purifying until the pollutant concentration falls below the environmental standard value, the Fenton method in which an oxidizing agent such as Fenton is injected into the soil to decompose the pollutant, the contaminated groundwater is pumped, and the pollutant is separated. Known in-situ purification methods such as a groundwater pumping method to be adsorbed on activated carbon and a biotreatment method using indigenous microorganisms can be applied. Moreover, it is also possible to apply the excavation and carrying-out method of excavating and carrying out contaminated soil and replacing it with non-contaminated soil. In this embodiment mode, a Fenton method is used that can be purified at a lower cost and in a shorter period of time than other methods. The Fenton method decomposes volatile organic compounds in the soil by injecting a Fenton reagent consisting of hydrogen peroxide and catalyst iron ions into the gravel layer 20 and the clay / silt layer 10 using an injection tube. It is a method to do. Specifically, chemical bonds such as carbon-carbon bonds and carbon-chlorine bonds of volatile organic compounds in soil are dissociated by hydroxyl radicals generated by the reaction between hydrogen peroxide water in the Fenton reagent and iron ions. Disassemble.

  The environmental standard is defined in Article 16 of the Basic Environment Law as a standard that is desirable to protect human health and maintain the living environment. The environmental standard value of each pollutant mentioned above is 0.01 mg / l (tetrachloroethylene), 0.03 mg / l (trichloroethylene), 0.04 mg / l (cis-1,2-dichloroethylene), 0.01 mg / l ( Benzene).

  At the stage where the first step is performed, the concentration of contaminants in the clay / silt layer 10 and the gravel layer 20 is reduced to an environmental standard value or less. However, as described above, if only the first step is performed, the contaminant 40 remaining in the clay / silt layer 10 flows out into the gravel layer 20 over time, and the concentration of the contaminant 40 flowing out into the gravel layer is reduced. There is concern that the environmental standard value will be exceeded again. Alternatively, there is a concern that the pollutant 40 flowing out from the clay / silt layer 10 to the gravel layer 20 flows together with the groundwater, so that the pollutant 40 diffuses into the surrounding area. Therefore, in order to prevent the above situation, the second step described below is performed.

  In the second step, as shown in FIG. 1, a pollutant decomposition layer 30 or a pollutant adsorption layer 30 is formed at the interface between the clay / silt layer 10 and the gravel layer 20 in the purification target region.

  The pollutant decomposition layer 30 is a layer capable of decomposing the pollutant 40 over a long period of time, and injecting a pollutant decomposer onto the upper surface of the clay / silt layer 10, that is, the bottom of the gravel layer 20. Formed with. Here, the pollutant decomposing agent refers to either a reducing agent that decomposes the pollutant by reducing the pollutant 40 or an oxidizing agent that decomposes the pollutant by oxidizing the pollutant 40.

  As the reducing agent, iron powder can be used. Iron powder decomposes the above-mentioned volatile organochlorine compounds into harmless hydrocarbons such as ethylene and ethane and chloride ions by a reductive dechlorination reaction. As the oxidizing agent, persulfates such as sodium persulfate and potassium persulfate, or inorganic salts such as permanganate such as potassium permanganate can be used. These oxidizing agents are made stable by oxidative decomposition of volatile organic compounds.

  The pollutant adsorbing layer 30 has a function of adsorbing the pollutant 40 and is formed by injecting a pollutant adsorbing agent on the upper surface of the clay / silt layer 10, that is, on the bottom of the gravel layer 20. Here, the contaminant adsorbent is a porous material having a large number of pores and capable of adsorbing the contaminant 40, and specifically includes activated carbon, zeolite, silica gel, activated alumina, silica and the like. it can. Among these, it is preferable to use activated carbon or zeolite having a large surface area and excellent adsorption performance. These contaminant adsorbents may be used alone or in combination of two or more.

  Next, as an example of the second step, by using iron powder as a reducing agent as a pollutant decomposing agent, a slurry in which iron powder is dispersed in water is injected into the interface between the clay / silt layer 10 and the gravel layer 20. The case where the pollutant decomposition layer 30 is formed will be described. Hereinafter, a slurry in which iron powder is dispersed in water is referred to as “iron powder dispersion solution”. The iron powder used in the present embodiment includes particles whose particle size is larger than the particle size of the clay / silt layer 10. Therefore, the iron powder injected into the interface between the clay / silt layer 10 and the gravel layer 20 remains on the upper surface of the clay / silt layer 10 and functions as a wall that separates the clay / silt layer 10 and the gravel layer 20.

  As a method of injecting the iron powder dispersion solution into the interface between the clay / silt layer 10 and the gravel layer 20, a known injection method using an injection tube can be applied. FIG. 2 is a diagram showing a schematic configuration of an injection device when a double pipe strainer method is applied as an example of the injection method, and FIG. 3 injects an iron powder dispersion solution using the injection device shown in FIG. It is a figure which shows the procedure to do.

  The injection device illustrated in FIG. 2 includes an iron powder dispersion solution mixer 51 that mixes and stirs iron powder and water, a flash agent A liquid mixer 52A that mixes and stirs the flash A liquid, and a flashing agent. A mixer 52 </ b> B for an instantaneous setting agent B that mixes and stirs B liquid, and a double tube rod 55 having an outer tube 53 and an inner tube 54. Here, the instantaneous setting agent prevents the iron powder dispersion solution from diffusing outside the injection range when the iron powder dispersion solution is injected into the gravel layer 20, and limits the injection range of the iron powder dispersion solution. It is a solidified material. This instantaneous setting agent is injected into the gravel layer 20 by mixing, for example, an instantaneous setting agent A liquid consisting of sodium silicate and water and an instantaneous setting agent B liquid consisting of a water glass material and water.

  The iron powder dispersion solution mixer 51 and the instantaneous setting agent A liquid mixer 52 </ b> A are connected to the outer tube 53 of the double tube rod 55 via an injection hose 56. The injection hose 56 is provided with a switching valve 56 a, and when the switching valve 56 a is switched, either one of the iron powder dispersion solution and the instantaneous setting agent A liquid is sent to the outer pipe 53 by the liquid feeding pump 58. Further, the mixer for B liquid B 52 B is connected to the inner pipe 54 of the double tube rod 55 through the injection hose 57, and the B liquid B is sent to the inner pipe 53 by the liquid feed pump 59. The injection hoses 56 and 57 are provided with flow meters 61 and 62 for measuring the respective flow rates flowing through the hoses and the pressure at the time of liquid feeding.

  The double tube rod 55 is supported by a boring machine (not shown), and a blade portion (not shown) for excavating the soil to form the injection hole 63 is attached to the tip of the double tube rod 55. Further, a discharge port for discharging the fluid flowing through the outer tube 53 to the outside and a discharge port for discharging the fluid flowing through the inner tube 54 to the outside (both not shown) are provided at the tip of the double tube rod 55. Is provided.

  Hereinafter, the procedure for forming the pollutant decomposition layer 30 will be described with reference to FIG. First, as shown in FIG. 3 (1), the gravel layer 20 is excavated to the position where the clay / silt layer 10 is reached using the double pipe rod 55 and a boring machine that supports the rod 55, and the gravel layer 20 is formed. The excavation hole 63 is formed. Next, as shown in FIG. 3 (2), the double tube rod 55 used for drilling is used as it is as an injection tube, the liquid feed pumps 58 and 59 are driven, and the instantaneous setting agent A liquid is supplied to the outer tube 53 Then, the instantaneous setting agent B liquid is sent to the inner tube 54, discharged from the discharge port, and mixed in the soil. As shown in FIG. 3 (2), the injection position of the instantaneous setting agent 64 is a position that is a predetermined height above the upper surface of the clay / silt layer 10. Next, the switching valve 56a is switched, and the iron powder dispersion solution 65 is sent to the outer pipe 53 by the liquid feed pump 58. As shown in FIG. 3 (3), the instantaneous setting agent 64 and the upper surface of the clay / silt layer 10 In between, the iron powder dispersion solution 65 is injected. The above (2) and (3) are defined as one step, and this step is repeated until a predetermined layer thickness is obtained as shown in (4) of FIG.

  The above steps (1) to (4) are performed over the entire area to be purified. The injection interval (interval between adjacent injection holes 63) may be set as appropriate, but in this embodiment, the iron powder dispersion solution is injected at an injection interval of 0.5 to 2.0 m. If the injection interval is too wide, there is a possibility that the effect of decomposing the pollutants cannot be sufficiently obtained. On the other hand, when the injection interval is too narrow, the density of the iron powder in the pollutant decomposition layer 30 becomes higher than necessary, which causes an increase in cost.

  FIG. 4 is a diagram schematically showing a part of the vicinity of the interface between the clay / silt layer 10 and the gravel layer 20 after the above steps (1) to (4) are performed over the entire region to be purified. is there. By performing the above steps, as shown in FIG. 4, a pollutant decomposition layer 30 having a bottom of the gravel layer 20 of about 1.5 m to 2 m is constructed.

  Although the case where the pollutant decomposition layer 30 is formed has been described in the above example, the same method as described above is performed when the pollutant adsorption layer 30 is formed instead of the pollutant decomposition layer 30. That is, a slurry in which one or more porous materials such as activated carbon and zeolite are dispersed in water is used for the clay / silt layer by the procedure shown in FIG. 3 using the injection device shown in FIG. By injecting into the interface between 10 and the gravel layer 20, the contaminant adsorbing layer 30 can be constructed.

  As described above, according to the method for preventing recontamination after purification of contaminated soil according to the present embodiment, after the soil is once purified until the concentration of the contaminant 40 is equal to or lower than the environmental standard value, the clay / silt layer 10 and By forming the pollutant decomposition layer 30 made of a reducing agent or an oxidant between the gravel layer 20 and the contaminant 40 remaining in the clay / silt layer 10 passes through the pollutant decomposition layer 30. Since it is decomposed, it is possible to prevent contaminants from flowing out into the gravel layer 20. As a result, it is possible to prevent a situation in which the pollutant 40 flowing out from the clay / silt layer 10 to the gravel layer 20 again exceeds the environmental standard value, and the pollutant 40 flows together with the groundwater. Can be prevented from spreading to the surrounding area.

  Further, according to the method for preventing recontamination after purification of contaminated soil according to the present embodiment, the excavation hole 63 is formed in the gravel layer 20 in the second step, and the excavation hole 63 is reduced onto the clay / silt layer 10. Since the contaminant decomposition layer 30 is formed by injecting the agent or the oxidizing agent, the contaminant decomposition layer 30 can be formed by a low-cost and simple method.

  Furthermore, according to the method for preventing re-contamination after purification of contaminated soil according to the present embodiment, iron powder is used as a pollutant decomposing agent (reducing agent) for decomposing volatile organic compounds, so that the pollutant decomposing layer 30 has a long period of time. Since the pollutant is decomposed over a long period of time, the outflow of the pollutant to the gravel layer 20 can be reliably prevented.

  In the above embodiment, only the example using the iron powder as the reducing agent as the pollutant decomposing agent that decomposes the volatile organic compound has been described. However, the present invention is not limited to this and is an oxidizing agent. Even in the case where the pollutant decomposition layer 30 is formed by injecting peroxysulfate, the pollutant is decomposed over a long period of time as in the above embodiment, and the outflow of the pollutant to the gravel layer 20 is ensured. Can be prevented.

  In addition, according to the method for preventing recontamination after purification of contaminated soil according to the present embodiment, after the soil is once purified until the concentration of the contaminant 40 becomes equal to or less than the environmental standard value, the clay / silt layer 10 and the gravel layer 20 When the pollutant adsorbing layer 30 made of a pollutant adsorbent such as activated carbon or zeolite is formed in between, the contaminant 40 remaining in the clay / silt layer 10 passes through the pollutant adsorbing layer 30. Since it is adsorbed by the contaminant adsorbent, it is possible to prevent the contaminant from flowing out into the gravel layer 20. As a result, it is possible to prevent a situation in which the pollutant 40 flowing out from the clay / silt layer 10 to the gravel layer 20 again exceeds the environmental standard value, and the pollutant 40 flows together with the groundwater. Can be prevented from spreading to the surrounding area.

  Further, according to the method for preventing recontamination after purification of contaminated soil according to the present embodiment, in the second step, the excavation hole 63 is formed in the gravel layer 20, and the activated carbon is formed on the clay / silt layer 10 from the excavation hole 63. Since the pollutant adsorbing layer 30 is formed by injecting a pollutant adsorbent such as zeolite or zeolite, the pollutant adsorbing layer 30 can be formed by a low-cost and simple method.

  In the above embodiment, a method for preventing recontamination of soil having a stratum structure in which a water permeable layer (sand gravel layer 220) is located on a hardly water permeable layer (clay / silt layer 10) has been described. The application object of the present invention is not limited to this, and the present invention can also be applied to soil having a stratum structure in which the water permeable layer is located under the hardly permeable layer. In this case as well, the soil is purified in the first step until the concentration of the contaminants in the poorly permeable layer and the permeable layer is equal to or lower than the environmental standard value, as in the above embodiment. Next, in the second step, an excavation hole is formed in the hardly permeable layer using the double pipe rod 55 described above, and the above-mentioned pollutant is formed from the excavation hole below the hardly permeable layer using the method shown in FIG. By injecting the decomposing agent or the contaminant adsorbent, the contaminant decomposing layer 30 or the contaminant adsorbing layer 30 is formed at the interface between the hardly permeable layer and the permeable layer.

DESCRIPTION OF SYMBOLS 10 Clay, silt layer 20 Gravel layer 30 Contaminant decomposition layer or contaminant adsorbing layer 40 Contaminant 51 Mixer for iron powder dispersion solution 52A Mixer for instantaneous setting agent A liquid 52B Mixer for instantaneous setting agent B liquid 53 Outer pipe 54 Inner pipe 55 Double pipe rod 56, 57 Injection hose 58, 59 Liquid feed pump 61, 62 Flow meter 63 Drilling hole 64 Quick setting agent 65 Iron powder dispersion solution

Claims (7)

A method for preventing re-contamination after purifying contaminants in soil where the permeable layer is located above or below the hardly permeable layer,
A first step of purifying the soil until the concentration of contaminants in the hardly permeable layer and the permeable layer is equal to or lower than an environmental standard value;
A pollutant decomposing layer containing a pollutant decomposing agent that decomposes the pollutant or a pollutant adsorbing layer containing a pollutant adsorbing agent that adsorbs the pollutant is formed between the hardly permeable layer and the water permeable layer. Process,
A method for preventing recontamination after purification of contaminated soil, comprising:   In the second step, the pollutant decomposition layer is formed by forming a drilling hole in the permeable layer and injecting the pollutant decomposition agent from the drilling hole onto the hardly permeable layer. Item 2. A method for preventing recontamination after purification of contaminated soil according to item 1.   In the second step, the pollutant decomposition layer is formed by forming an excavation hole in the hardly permeable layer and injecting the contaminant decomposition agent from the excavation hole under the hardly permeable layer. The method for preventing recontamination after purification of contaminated soil according to claim 1.   The pollutant is a volatile organic compound, and iron powder or peroxysulfate is used as the pollutant decomposing agent. Pollution prevention method.   In the second step, the pollutant adsorption layer is formed by forming a drill hole in the water permeable layer and injecting the contaminant adsorbent from the drill hole onto the hardly permeable layer. Item 2. A method for preventing recontamination after purification of contaminated soil according to item 1.   In the second step, the pollutant adsorbing layer is formed by forming a drilling hole in the hardly permeable layer and injecting the contaminant adsorbent from the drilling hole under the hardly permeable layer. The method for preventing recontamination after purification of contaminated soil according to claim 1.   The pollutant is a volatile organic compound, and activated carbon and / or zeolite is used as the pollutant adsorbent. 7. Pollution prevention method.

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