JP2004122049A - Purification method of soil and ground water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a purification method of soil and ground water which allow soil and ground water to be efficiently purified by injecting water or chemicals to the soil and ground water at the original position and allows the injected water or the chemicals to be recovered from underground without leaking the injected water and chemicals to the outside of an object region to be treated. <P>SOLUTION: Three pumping wells or more (white circle) are arranged for one injection well (black circle) so as to surround the injection well. Then, the water or the chemicals is injected into the soil and the ground water from the injection well and the ground water is pumped from the respective pumping wells. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for in situ physicochemical purification of soil and groundwater contaminated by chemicals. The purification method of the present invention is suitably used, for example, for purification of soil and groundwater contaminated with an organic chlorine compound.
[0002]
[Prior art]
In recent years, contamination by various chemical substances in soil and groundwater has become evident, and measures have been urgently taken. In particular, organochlorine compounds such as trichloroethylene and tetrachloroethylene, which are widely used as cleaning agents in various factories and cleaning shops, are suspected to be carcinogenic substances, so it is necessary to take immediate measures against contamination by these organochlorine compounds. There is.
[0003]
Conventional methods for treating soil and groundwater contaminated with organochlorine compounds include a decomposition method in which contaminated soil is excavated and mixed with a decomposer, and a pump and pump that pumps up contaminated groundwater to perform aeration and activated carbon adsorption.・ Treatment method has been mainly used.
[0004]
However, the decomposition treatment method in which soil is excavated and mixed with a decomposing agent requires a large-scale construction for excavation, and the required cost is enormous. In addition, in the case of the excavation method, when there is a building or the like on the contaminated soil, it is necessary to remove the building or the like, so that purification is often difficult. In the pump-and-treat method, in which treatment is performed after pumping groundwater, it often takes several years or more to complete purification, and it is strongly desired to shorten the purification period.
[0005]
On the other hand, in order to solve the above problems, a method of purifying soil and groundwater by injecting water or a chemical into the soil and groundwater in situ without excavation has been proposed (for example, Patent Documents 1 and 2). In these purification methods, water is usually used for washing and removing contaminant chemicals, and chemicals are used for decomposing or immobilizing (insolubilizing) contaminant chemicals. Oxidizing agents such as permanganate and persulfate are often used as agents used for decomposing polluting chemicals. Water or chemicals are usually injected into an aquifer, which is an underground layer through which groundwater flows in soil.
[0006]
[Patent Document 1]
JP 2000-42537 A [Patent Document 2]
JP 2000-51834 A
[Problems to be solved by the invention]
However, in the method of injecting the drug in situ into soil and groundwater, it is not preferable to leave the injected drug in the aquifer because the drug itself is often toxic to species. . In addition, in the method of injecting water into soil and groundwater in situ, since the injected water contains pollutant chemicals, it is not preferable to leak this water out of the treatment target area.
[0008]
The present invention has been made in view of the circumstances described above, and by injecting water or a chemical into soil and groundwater in situ, it is possible to efficiently purify the soil and groundwater, and at the same time, to inject the injected water or chemical. It is an object of the present invention to provide a method for purifying soil and groundwater that can be recovered from the underground without leaking out of the treatment target area.
[0009]
[Means for Solving the Problems]
The present inventors have studied an optimal system configuration that can achieve the above-described object from a hydraulic viewpoint. As a result, at least three pumping wells are arranged around the injection well so as to surround the injection well, and the amount of water or chemical injected from the well into the groundwater and soil, and the amount of groundwater pumped from the pumping well. It has been found that by appropriately controlling the amount of water and chemicals, the groundwater and soil in the treatment target area can be efficiently purified, and the injected water or chemical can be reliably recovered.
[0010]
The present invention has been made on the basis of the above-described findings, and in purifying soil and groundwater by injecting water or chemicals in situ into soil and groundwater contaminated with chemical substances, one injection well is used. Soil and groundwater, wherein three or more pumping wells are arranged so as to surround the injection well, and water or a chemical is injected from the injection well into soil and groundwater, and groundwater is pumped from each of the pumping wells. To provide a purification method.
[0011]
In the present invention, the water or the chemical injected from the injection well comes into contact with the contaminated soil and the groundwater, thereby cleaning and removing, decomposing, fixing, and the like the contaminant chemicals, thereby purifying the soil and the groundwater. In this case, in the present invention, groundwater is pumped from three or more pumping wells surrounding the injection well while water or chemical is injected from the injection well, so that the water or chemical is directed from the injection well to each of the surrounding pumping wells. It spreads around the injection well together with the flowing groundwater, and the groundwater and soil within the treatment target area are efficiently purified. Further, the water or the chemical injected from the injection well can be collected together with the groundwater from each pumping well, so that the injected water or the chemical can be prevented from leaking out of the treatment target area.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail. The substances to be purified in the present invention are soil and groundwater contaminated by chemical substances, and the polluting chemical substances are mainly organic halogen compounds such as cis-1,2-dichloroethylene, trichloroethylene, and tetrachloroethylene. However, in addition to contamination by oils, dioxins, aromatic compounds, etc. other than VOCs (volatile organic compounds), water or chemicals are injected in situ to decompose, wash, fix, etc. polluting chemicals The present invention is applicable to the purification of soil and groundwater.
[0013]
In the present invention, three or more pumping wells are arranged for one injection well so as to surround the injection well. That is, three or more pumping wells may be arranged so as to surround one injection well, and there is no other limitation on the arrangement of the injection well and the pumping well. Then, water or chemicals are injected from the injection well into the soil and groundwater, and groundwater is pumped from each pumping well. The underground layer for injecting water or chemicals and for pumping groundwater is usually an aquifer in which groundwater flows in the above-described soil.
[0014]
FIG. 1 shows an arrangement example of the injection well and the pumping well in the present invention. In FIG. 1, an injection well is indicated by ●, and a pumping well is indicated by ○. 1A shows an example in which one injection well is surrounded by three pumping wells, FIG. 1B shows an example in which one injection well is surrounded by four pumping wells, and FIG. An example in which a well is surrounded by six pumping wells, and (d) shows an example in which six injection wells are arranged and a total of 12 pumping wells are arranged so that each injection well is surrounded by four pumping wells. It is. In the example of (d), some pumping wells are also used to surround two or more injection wells. Among these, particularly preferred are the cases of (b) and (d), in which one injection well is surrounded by four pumping wells, in that the range of influence of the drug can be widened and the cost of drilling wells can be increased. is there.
[0015]
FIG. 2 shows an example of the arrangement of an injection well and a pumping well that does not fall into the category of the present invention and cannot obtain the effects of the present invention. In FIG. 2, the injection well is indicated by ●, and the pumping well is indicated by ○. (E) is an example in which one injection well and one pumping well are opposed to each other, (f) is an example in which three injection wells and three pumping wells are opposed to each other, and (g) is one. (H) is an example in which only one injection well is arranged. In the examples of (e) and (f), the injected water or chemical does not spread around the injection well, in the example of (g), the injected water or chemical leaks out of the treatment target area, and in the example of (h), the injected water or chemical does not spread. The spread of the water or chemicals is slow, and the water or chemicals leak out of the area to be treated.
[0016]
In the present invention, when a chemical is injected into soil and groundwater, it is preferable to use an oxidizing agent as the chemical and oxidatively decompose contaminant chemicals. There is no limitation on the type of the oxidizing agent.For example, it is conceivable to use permanganate.However, when permanganate is used, manganese dioxide can be generated as a reaction product to block the aquifer. That permanganate has high reactivity with organic matter in soil and increases drug consumption; manganese is a substance whose concentration is regulated by the Water Quality Standards of the Water Supply Law, etc. In the present invention, it is particularly suitable to use persulfate or a persulfate as an oxidizing agent, since is higher in toxicity to aquatic organisms than a persulfate. As the persulfate, for example, potassium persulfate, sodium persulfate and the like can be used. The concentration of the injected oxidant in groundwater varies depending on the type of pollutant chemicals and soil properties, but it is generally 10 mg / L or more, especially 50 mg / L or more at the end of the reaction zone (end of the purification range). desirable.
[0017]
The amount of the drug injected from the injection well and the distance between the injection well and the pumping well are adjusted so that the hydraulic residence time of the drug in the reaction region is 2 hours or more, more preferably 12 hours or more. Further, the ratio of the pumping amount to the injection amount may be determined within a range in which there is no leakage of the medicine out of the treatment target area and the diffusion of the medicine occurs efficiently between equal to several times. The injection amount and the pumping amount can be determined by a simulation calculation using, for example, a basic flow equation (continuous equation) of groundwater. In this case, as the parameters used for the above-described simulation calculation, the permeability, the stratum structure, the direction of groundwater flow, the velocity, and the like of the aquifer to be purified are used.
[0018]
The concentration of the drug injected from the injection well (drug concentration in the drug solution) differs depending on the concentration and type of the contaminating chemical substance, and is usually determined by the result of a treatability test using contaminated water at the site. The range is preferably from 100 to 50,000 mg / L, and more preferably from 100 to 50,000 mg / L in consideration of storage of the drug solution. It is also possible to store and inject the drug as a solution in a tank, but if the purification is performed over a long period of time, store it as a solid, create a solution using an automatic drug dissolution device, etc., and continuously inject it. It is also possible.
[0019]
If the pumped groundwater contains pollutant chemicals and a sufficient amount of oxidant remains in the groundwater, decomposition will proceed even if it is left standing for an appropriate period after pumping, and the pollution Although the substances are decomposed, even if the contaminated chemicals contained in the pumped groundwater are decomposed by performing at least one treatment such as aeration treatment, ultraviolet irradiation treatment, and ozone addition treatment on the pumped groundwater. Good. The groundwater treated in this way can be discharged into rivers or sewage.However, a method of adding a chemical to a part or all of this groundwater so as to have a predetermined concentration and re-injecting the same is cost-effective. It is also very effective in terms of system. That is, in the present invention, after adding a chemical to a part or all of the groundwater pumped from the pumping well, the groundwater to which the chemical has been added can be injected again into the soil and the groundwater from the injection well, whereby the unreacted chemical can be obtained. It is possible to reduce the cost by effectively utilizing the groundwater and reusing the pumped groundwater.
[0020]
Groundwater often has a reducing atmosphere, and the groundwater often contains divalent iron ions. When this divalent iron ion comes into contact with air by pumping or is oxidized by an oxidizing agent, it turns into iron oxide and precipitates. In this case, in order to reuse the pumped ground water as water for injection, it is appropriate to remove suspended substances such as iron oxide and fine soil by filtering or coagulating sedimentation.
[0021]
【Example】
Hereinafter, examples performed using the present invention will be described. Note that this example does not limit the scope of the present invention.
[0022]
Using the method of the present invention as a means for purifying soil and groundwater contaminated with trichloroethylene (TCE), a purification test was conducted on site. The area to be purified is a 10m x 10m square, a system that injects oxidant from one injection well located in the center and pumps groundwater from a total of four pumping wells located in four corners. did. In addition, an observation well was installed downstream of the groundwater flow direction and outside the purification target area to confirm whether or not the oxidant had flowed out of the target area.
[0023]
When a simulation was performed using a groundwater flow analysis program (Mod Flow), the result of particle tracking (a method of calculating the recovery rate assuming that the injected substance is particles) showed that the injection flow rate from the injection well was 1 m ³ / hr. On the other hand, a flow rate of 1 m ³ / hr from each pumping well, that is, a total flow rate of 4 m ³ / hr was determined to be optimal. The concentration of the oxidizing agent to be injected was set to 1500 mg / L based on the result of the treatability test using the contaminated groundwater at the site.
[0024]
As a result, the TCE concentration in the groundwater before the purification treatment was 5.2 mg / L, and the TCE concentration in the groundwater three months after the start of the purification treatment was 0.03 mg / L. No oxidizing agent was detected in the observation well during the purification period. Further, the simulation results are shown in reference drawings. According to the reference drawing, it can be seen that TCE in the processing target area is decomposed, and that the oxidizing agent has not leaked out of the processing target area. From the above results, it was confirmed that according to the present invention, soil and groundwater contaminated with chemical substances can be efficiently and safely purified in a short period of time.
[0025]
【The invention's effect】
As described above, according to the present invention, by injecting water or a chemical in situ into soil and groundwater, soil and groundwater can be efficiently purified, and the injected water or chemical can be removed from the treatment target area. Can be recovered from underground without leaking to the underground. Therefore, according to the present invention, soil and groundwater contaminated with chemical substances can be efficiently and safely purified in a short period of time.
[Brief description of the drawings]
FIG. 1 is a diagram showing an arrangement example of an injection well and a pumping well according to the present invention.
FIG. 2 is a diagram showing an example of arrangement of an injection well and a pumping well which does not fall within the scope of the present invention.
[Explanation of symbols]
● Injection well ○ Pumping well

Claims (4)

In order to purify soil and groundwater by injecting water or chemicals in situ into soil and groundwater contaminated with chemical substances, three or more pumping wells are placed around one injection well in order to purify the soil and groundwater. And a step of injecting water or a chemical into soil and groundwater from the injection well and pumping groundwater from each of the pumping wells. The soil and groundwater according to claim 1, wherein after adding a chemical to a part or all of the groundwater pumped from the pumping well, the groundwater to which the chemical is added is again injected into the soil and the groundwater from the injection well. Purification method. 3. The method according to claim 1, wherein the chemical is an oxidizing agent. The method according to claim 3, wherein the oxidizing agent is persulfuric acid or persulfate.

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