JP2002273403A - Purification method of contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a purification method in which only a part in which contaminated soil exists is selected, the region of execution of purification works is specified either in the planar direction or in the depth direction and an iron powder is mixed only into the contaminated soil of a necessary part. SOLUTION: In this purification method, the soil contaminated with an organic chlorine-based compound is purified by mixing the contaminated soil and the iron powder with the use of an auger 1, a specified contaminated underground soil layer is made to be the object of purification, a space between the ground surface of the region of purification object and the layer of contaminated ground is dug while ejecting air from a digging drill, subsequently, the whole region of contaminated soil layer is dug likewise while ejecting the iron powder from the digging drill 4, thereafter, the mixed soil of the contaminated soil and the iron powder is confined in the original position by pulling out a digging shaft while reversing the same and the contaminated soil is thus made harmless.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for purifying soil contaminated with organochlorine compounds using iron powder.
The present invention relates to a method for purifying contaminated soil that can economically purify only a soil layer that needs to be purified at an original position where the degree of contamination varies in the depth direction of the contaminated soil with high working efficiency.

[0002]

2. Description of the Related Art A technique of using iron powder for purifying soil contaminated with an organic chlorine compound at a site of a semiconductor factory or a metal processing factory has already been proposed in, for example, Japanese Patent Application Laid-Open No. 11-235577. The method for detoxifying soil according to the publication includes dichloromethane, carbon tetrachloride, 1,
2-dichloroethane, 1,1,1-trichloroethane,
1,1,2-trichloroethane, trichloroethylene,
When purifying soil contaminated with volatile organic chlorine-based compounds such as tetrachloroethylene and 1,3-dichloropropene and PCBs and organic chlorine-based compounds such as dioxins, these organic chlorine-based compounds are removed using iron powder. It is decomposed and made harmless by the action of dechlorination or dehydrochlorination.

[0003] In the case of in-situ treatment, a method of spraying iron powder into the ground by using a high-pressure medium such as air or water, and a method of using a civil engineering machine used for ground improvement work to add iron to soil. A method of mechanically excavating and mixing the powder has been suggested. It is also suggested that iron powder be mixed with all soil to be purified in a mixing ratio of iron powder to contaminated soil in a range of 0.1% by weight to 10% by weight.

By the way, even in a contaminated area such as the above-mentioned semiconductor factory or metal processing factory, the degree of contamination at a position in the depth direction greatly varies depending on the components of the soil. In detail, when the upper part of the contaminated ground is soil such as sand and gravel, chlorine-based compounds, which are pollutants leaking to the surface of the ground, flow down into the ground due to rainwater, etc.
Over time, the gravel layer has often been naturally purified.

On the other hand, when a silt layer or a silt mixed layer is present in the formation, the degree of contamination increases, and it has been found by boring surveys that a very high concentration of contamination zone exists. Further, such a polluted zone is particularly remarkable in a groundwater area, and it is considered that pollutants that have flowed down by rainwater stay in such a groundwater area.

[0006] Furthermore, even in an area far away from the actual source of contamination, a certain depth under the ground may be highly contaminated. In such a case, it is considered that the contaminant that has flowed down by rainwater or the like in the contaminated area as described above was diffused or moved by the groundwater, and in particular, the contaminant was more diffused in a direction viewed as the downstream side of the groundwater. However, in such a place, the actual contaminated soil is only the groundwater zone at a certain depth below the ground, and the portion above it is not much contaminated.

[0007]

SUMMARY OF THE INVENTION In view of the present situation of the above-mentioned contaminated area or contaminated stratum, the present invention selects only a portion where contaminated soil actually exists, and can reliably and quickly purify the contaminated soil with iron powder. Providing a purification method,
In particular, it is intended to provide a more economical and efficient purification method in which the construction area of the purification work is specified both in the horizontal direction and in the depth direction, and iron powder is mixed only in the contaminated soil at a necessary portion.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method for purifying soil contaminated with an organochlorine compound by mixing the contaminated soil with iron powder using an auger. Drilling is performed for the specified contaminated soil layer from the surface of the area to be purified to the contaminated layer while discharging air from the auger drilling drill, and then the entire area of the contaminated soil layer is similarly discharged with iron powder from the drilling drill. This is a purification method characterized in that contaminated soil and a mixture of iron powder are confined in the original position by excavating while excavating and then pulling out while reversing the excavation axis to detoxify contaminants. Further, in such a purification method, after excavating the entire contaminated soil layer while discharging iron powder from a drill, the contaminated soil and the iron powder may be further stirred by rotating up and down the drilling axis. it can. Further, the purification method of the present invention further includes excavation for discharging and mixing the iron powder into the contaminated soil layer by the auger, and alternately repeats the rows of the construction area and the non-construction area when viewed on the construction ground surface. Maintain the strength of the purification ground by constructing with an interval of about 2m to 5m apart, or by constructing with a mutual interval of about 2m to 5m each in the construction area each time viewed from the construction ground. It is characterized by doing.
The purification method of the present invention is characterized in that the amount of iron powder to be mixed is made variable according to the degree of soil contamination or the amount of water in the purification layer.

[0009]

1 to 6 show an embodiment of the present invention.
It will be explained by. FIG. 1 shows a state in which a normal single-axis earth auger or a three-axis earth auger 1 is used, and the excavation axis is set on a construction pile core. In this case, for example, the excavating shaft 2 of the triaxial earth auger 1
In this way, a required amount of iron powder for purifying contaminated soil can be discharged from the drill 4 at the tip thereof at a required time. Earth Auger 1
Is of a type capable of excavating while appropriately discharging air or water from the end of the drill 4.

FIG. 2 shows the distance to the top end of the soil to be purified by the earth auger 1, that is, the non-contaminated soil layer L _1.
Is drilled, and the drilling up to this position is usually performed while blowing air from the end of the drill 4. In this case, for example, in a place where the groundwater below the groundwater layer is contaminated by the groundwater, since the iron powder is mixed only with the contaminated soil layer, ordinary excavation is performed up to the purification work position.

[0011] Figure 3 shows a drilling state of the contaminated soil layer L ₂ to be actually clean. By conventional drilling shown in FIG. 2, and drilling the L ₁ moiety is a non-contaminated soil layer while discharging air from the end of drilling the drill 4, followed with injection of iron powder to the discharge air, further pollution the excavation depth of L _2, which corresponds to the soil layer. In this case, the excavating speed of the excavating shaft 2 is, for example, a pitch of 10 to 30 cm, and drills holes at a speed of about 50 cm per minute.

FIG. 4 shows a process of repeating the stirring as necessary after the injection of the required amount of iron powder into the contaminated soil which needs to be purified in the state of FIG. Such agitation step, for example by drilling shaft 2 only by about 3m vertical movement while rotating, it is not necessary to move the excavation drill 4 portions over the entire area over the implanted depth L ₂ of the iron powder.

FIG. 5 shows a state in which the excavating shaft 2 of the earth auger 1 is pulled up after the injection of the iron powder for purification and the mixing and stirring are completed. It is. This also helps to prevent the spread of contaminated soil mixed with iron powder to non-contaminated parts. A cleaning necessary part soil layer in the same figure. In this way, over from the position lowered by the depth L ₁ from the surface to the construction depth L _2, iron powder mixing zone 5 is construction.

FIG. 6 shows an example using a triaxial earth auger.
Area H for mixing iron powder_nAnd the flat construction area distribution of
Various aspects of the procedure for performing the excavation work are shown. Figure
In 6 (A), the so-called semi-wrap method
H₁, H₂, H₃, H₄Excavate in the order of ……
First row L₁To construct. Excavation in this case is natural
And the discharge mixing of the iron powder
Is only the soil layer that needs purification. Next, the first column L₁From
a second row L at a position separated by a distance of α₂And H_nTo H
_{n + 1}, H_{n + 2}In the same manner as in the first column in the order of
Excavation and discharge mixing of iron powder are performed repeatedly.
You.

[0015] In this case, in the first row L _1, for example, the construction area of the H ₁ and H ₂ are partially overlapping each other, the area of the overlapping portion is small, a single drilling By the mixing process, the cleaning operation proceeds by the width of the substantially three-axis excavation shaft. And, when the construction of the second column L _2, since it is construction apart by a first row L ₁ and the distance α as shown in the drawing, the soil in the contaminated layer of the ground corresponding to the distance α is the non-construction zone Purification is performed by the iron powder mixed in the required area for purification in the construction area or the row of the construction area.

The construction procedure shown in FIG. 6 (B) shows a state where the rows L ₁ and L ₂ corresponding to the _first and _second rows are constructed by the complete wrapping method. In this case, in each excavation process, the two excavation axes on both sides of the three axes are consequently overlapped with each other, and the construction speed is considerably reduced, but the excavation direction (vertical direction) The construction accuracy is greatly improved, and there is an advantage that the ground strength in the non-construction area is more reliably maintained.

The construction procedure shown in FIG. 6C is based on a so-called single system, and the construction areas H _{1 to} H _n are separated from each other by a distance α. Then, similarly to the above, soil contamination in the contaminated layer in the non-construction area is purified by iron powder mixed with the contaminated soil in the construction area, but an extremely high construction speed can be obtained. Further, since the amount of iron powder mixed can be increased or decreased within a certain range, soil contaminants in the non-construction area can be sufficiently decomposed and made harmless by the iron powder mixed in the construction area.

[0018]

EXAMPLE An experimental example of an iron powder discharge mixing area corresponding to the above-mentioned contaminated soil layer is as follows. In this experimental example, since the experimental purification area was a so-called volcanic zone, the contaminated soil layer was deep, and the relationship between the geology in the depth direction and the contaminated layer was as follows. By boring survey, the soil quality up to a depth of 64 m and the pollution degree of the collected soil were measured. As a result, up to about 14 m from the surface of the ground, the gravel layer and the gravel-mixed sand layer are in alternating layers, with little contamination between them. The stratum from 15m to 52m depth has three layers of silt or silt mixed with clay of about 0.8m to 1.0m in between. About 52 m or less forms a groundwater layer. The depth corresponding to the groundwater layer is 52 m or more.
At 64 m, strata such as tuff sand, medium welded tuff, volcanic ash sand, and clay mixed with gravel are repeated.

On the other hand, the soil contamination status is about 16
m, the pollution is rapidly progressing, and the degree of contamination is particularly remarkable from a depth of about 53 m to about 63 m.
3-64 m proved not to be particularly contaminated. Therefore, at the time of this trial purification work, about 13m depth
Up to the depth of about 13m
From to a depth of about 52m is applying a process shown in FIG. 3, during this period of iron powder discharge amount, and that the unit excavated soil 1 m ³ per 20kg injection, also up to the 64m from a depth of about 52m step shown in FIG. 3 excavated by, it was decided to iron powder discharge amount during a unit excavating the soil 1 m ³ per 200 kg. In addition, using a triaxial earth auger, and according to the construction procedure of FIG. 6 (C), it was determined that the construction interval was α = 3 m.

[0020]

According to the present invention, when the depth of the underground contaminated layer differs depending on the construction site conditions, purification work can be performed only on the contaminated soil layer, and furthermore, according to the contamination concentration or soil environment. As a result, an optimum purification work can be performed, and an extremely economical and quick purification work can be performed. In addition, by providing the non-excavation area, there is an effect that various other works can be performed on the ground surface of the purification work area immediately after the completion of the purification work.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state in which an auger excavation axis is set at the time of purification work.

Figure 2 is a drilling situation illustration of uncontaminated soil layer L _1.

3 is a drilling situation illustration of contaminated soil layer L _2.

FIG. 4 is an explanatory view of a stirring step.

FIG. 5 is an explanatory diagram of a purification excavation end situation.

FIG. 6 is an explanatory diagram showing a planar distribution example of an excavation work area.

[Explanation of symbols]

Reference Signs List 1 earth auger 2 drill axis 4 drill drill L ₁ non-contaminated soil layer L ₂ contaminated soil layer H _n purification work area

Continued on the front page (72) Inventor Nobuo Hamamoto 3-1-2 Iwamotocho, Chiyoda-ku, Tokyo F-term (reference) in the Tokyo branch of Seiko Kogyo Co., Ltd. 4D004 AA41 AB06 CA34 CA45 CA47 CB24 CC11

Claims (6)

[Claims] 1. A method of purifying soil contaminated with an organochlorine compound by mixing the contaminated soil and iron powder using an auger, and targeting a specific underground contaminated soil layer, Drilling is performed from the surface of the area to be cleaned to the contaminated layer while discharging air from the auger drill, and then the entire depth of the contaminated soil layer is also drilled while discharging iron powder from the drill and then drilling. A purification method characterized in that by removing the shaft while reversing the shaft, the mixed soil of excavated contaminated soil and iron powder is sealed in its original position to detoxify the pollutants. 2. The method according to claim 1, wherein after excavating the entire depth of the contaminated soil layer while discharging iron powder from the excavation drill, the excavated contaminated soil and the iron are moved up and down while rotating the excavation shaft. A purification method characterized by employing a step of further stirring the powder. 3. The excavation for discharging and mixing the iron powder into the contaminated soil layer by the auger is performed by alternately repeating the rows of the construction area and the non-construction zone when viewed on the construction ground surface. The purification method according to claim 1 or 2, wherein the construction is performed with an interval of about 2 m to 5 m apart to maintain the proof strength of the purification ground. 4. The excavation for discharging and mixing the iron powder into the contaminated soil layer by the auger is performed by setting a distance between each of the construction areas at each time of about 2 m to 5 m as viewed on the construction ground. The purification method according to claim 1 or 2, wherein the proof strength of the purification ground is maintained by doing. 5. The purification method according to claim 1, wherein the auger for excavation is a triaxial earth auger. 6. The purification method according to claim 1, wherein the amount of iron powder discharged into the contaminated soil layer can be freely changed according to the excavation depth.