JP2004138531A - Underground pollutant exploration method and underground pollution distribution monitoring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an underground pollutant exploration method and an underground pollution distribution monitoring method capable of acquiring a tomographic video of the ground by a borehole underground radar, and acquiring quickly and accurately the distribution position, the concentration or the like of an underground pollutant from the tomographic video. <P>SOLUTION: This underground pollution distribution monitoring method has a procedure for forming boreholes 11, 12 under the ground, a procedure for radiating an electromagnetic wave into the underground from a transmission means 2 arranged in the borehole, a procedure for receiving the electromagnetic wave radiated from the transmission means by a reception means 3 arranged in the borehole, a procedure for operating the tomographic video including the underground pollutant distribution by a received signal by the reception means, and a procedure for monitoring the pollutant distribution following the elapse of time by the change with time of the tomographic video. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an underground pollutant detection method and an underground pollutant detection method for exploring the presence or absence of soil and groundwater contamination by pollutants, the concentration and position of underground pollutants, and monitoring the distribution of underground pollutants. It relates to a distribution monitoring method.
[0002]
[Prior art]
Conventionally, the following method has been used for the underground pollution survey for investigating the pollution of soil and groundwater by pollutants such as heavy metals and volatile organic compounds. These include methods of collecting and analyzing soil samples on the ground surface, methods of drilling a survey hole from the ground surface and sampling and analyzing soil gas, and methods of performing radar exploration from the ground surface. If the location of the contaminated area on the ground surface could be determined, drilling was performed based on the ground surface position, a soil sample was collected and analyzed, and the state of contamination underground was investigated.
[0003]
Furthermore, in order to investigate the concentration and distribution of contamination underground, it was necessary to drill a number of boreholes and collect and analyze soil and groundwater samples from each borehole. From these analyses, the concentration and distribution of pollutants throughout the underground survey area are inferred.
[0004]
When the concentration and location of pollutants are determined, the next step is to pump and aerate, pump and decompose, inject, pump and aerate (decompose) water, contaminate soil, and contaminated groundwater. Pollution purification treatment such as detoxification by injection is performed. When performing the pollution purification process, it is necessary to monitor how the pollution state changes with the purification process and confirm the effectiveness of the pollution purification process. In this case, the pollution state was monitored by a method basically similar to the underground pollution survey described above.
[0005]
[Problems to be solved by the invention]
As described above, underground pollution surveys and monitoring of the state of pollution have mainly been performed by boring, collecting samples from the boreholes, and analyzing the samples. Therefore, in order to accurately investigate the concentration and the position of the pollutant, it is necessary to drill a large number of boring holes, and there has been a problem that the cost and time for the investigation are significantly increased. In addition, excavating a large number of boreholes has a problem that the polluted state is affected and accurate measurement of the polluted state becomes extremely difficult.
[0006]
Furthermore, it is difficult to accurately determine the concentration and depth position of the contaminant by a method of detecting the state of contamination by radar from the ground surface, and it was only possible to grasp the position of the contaminated point on the ground surface. In order to ascertain the exact state of the contamination, it was necessary to drill a borehole, collect a sample, and analyze it from the surface position of the pollutant determined by radar survey from the surface.
[0007]
Therefore, the present invention obtains an underground tomographic image by tomography (tomography) using a so-called borehole underground radar in order to detect underground pollutants or monitor underground pollution distribution, and obtains an underground image from the tomographic image. An object of the present invention is to provide an underground pollutant exploration method and an underground pollution distribution monitoring method capable of quickly and accurately obtaining the distribution position and concentration of pollutants.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an underground pollutant detection method of the present invention includes a step of forming a boring hole in the underground, a step of radiating electromagnetic waves from transmitting means disposed in the boring hole to the underground, By a receiving means arranged in the hole, a procedure of receiving electromagnetic waves radiated from the transmitting means, a procedure of calculating an underground tomographic image by a received signal of the receiving means, and Exploring the concentration and position.
[0009]
In the underground pollutant detection method, it is preferable that the tomographic image is calculated based on a transmission characteristic between a transmission signal and a reception signal of an electromagnetic wave.
[0010]
Further, the method of monitoring the distribution of underground pollution according to the present invention includes the steps of forming a boring hole in the underground, the step of radiating electromagnetic waves from the transmitting means disposed in the boring hole to the underground, and disposing the electromagnetic wave in the boring hole. Receiving means for receiving an electromagnetic wave radiated from the transmitting means; receiving signal from the receiving means for calculating a tomographic image including a distribution of contaminants underground; and a temporal change in the tomographic image. To monitor the distribution of pollutants with time.
[0011]
In the underground contamination distribution monitoring method, it is preferable that the tomographic image is calculated based on a transmission characteristic between a transmission signal and a reception signal of an electromagnetic wave.
[0012]
In addition, in the underground contamination distribution monitoring method, it is preferable that the method further includes a step of calculating a difference between the tomographic image at a first time and the tomographic image at a second time after the first time.
[0013]
In the above-mentioned underground pollution distribution monitoring method, it is preferable to monitor a change in the distribution of pollutants while performing a pollution purification process.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of an underground pollutant detection method and an underground pollution distribution monitoring method of the present invention. Boring holes 11 and 12 are excavated at predetermined intervals in the ground 10 in a region where underground pollutants are detected or underground pollution distribution is monitored. A transmitting antenna 2 and a receiving antenna 3 are arranged in these bore holes 11 and 12.
[0015]
The borehole radar tomography apparatus 1 receives the electromagnetic wave radiated from the transmitting antenna 2 by the receiving antenna 3, measures the transmission characteristics of the electromagnetic wave between the boring holes 11 and 12, and forms the ground between the boring holes 11 and 12. This is a device for analyzing the structure. The structure of the ground between the boring holes 11 and 12 can be output as a tomographic image so that it can be easily recognized visually.
[0016]
As the electromagnetic wave radiated from the transmission antenna 2, a continuous wave of several MHz to several hundred MHz, a pulse wave, or the like is used. When searching for and monitoring contaminants on the ground, notable electromagnetic characteristics include the dielectric constant (complex permittivity) and conductivity of the ground, and the electromagnetic wave propagation velocity and electromagnetic wave attenuation rate depending on them. For example, many organic salts such as trichloroethylene have a relative dielectric constant of about 2, which is significantly different from the relative dielectric constant of water of 81. Further, these organic salts are almost insulating materials, and have a large difference in conductivity from groundwater or ground containing electrolyte.
[0017]
That is, when the contaminant is an organic salt, the conductivity of the contaminated portion 4 becomes smaller than that of the other portions. On the other hand, when the contaminant is a nitrate nitrogen compound such as nitrate or nitrite or a heavy metal salt, the conductivity of the contaminated portion 4 is higher than the other portions. Also, when the contaminant is a mixture of various substances, the transfer characteristic of a plurality of frequencies or a wide band of frequencies is measured by using the fact that the complex permittivity shows frequency dependence (dielectric dispersion), and thereby, It is possible to accurately measure the state of contamination.
[0018]
Due to these facts, the contaminated portion 4 contaminated with organic salts and the other ground portion cause a detectable difference in the dielectric constant and conductivity of the ground. By calculating and displaying a tomographic image showing the structure of the ground 10 between the boring holes 11 and 12 based on the propagation speed and attenuation rate of the electromagnetic wave, an image clearly showing the contaminated portion 4 as shown in FIG. 1 can be obtained. become. By exploring or monitoring underground pollutants from this tomographic image, these exploration or monitoring can be performed very easily as compared with the conventional method of excavating many boreholes and collecting samples. That is, the time and cost for exploration or monitoring can be significantly reduced.
[0019]
Actually, in order to obtain a tomographic image of the ground by the borehole radar tomography apparatus 1, the transmitting antenna 2 and the receiving antenna 3 are sequentially changed to a plurality of positions as shown in FIG. The transfer characteristic of the electromagnetic wave of is measured. The tomographic image in the vertical plane between the boring holes 11 and 12 can be obtained from the data of the transfer characteristics. A calculation method for obtaining a tomographic image of the ground from the transfer characteristics such as the propagation speed and the attenuation rate of the electromagnetic wave is called an inverse analysis algorithm and is known.
[0020]
In FIG. 1, a tomographic image in a vertical plane is obtained by the transmitting antenna 2 and the receiving antenna 3 in the boring holes 11 and 12, but if a plurality of such sets of boring holes are excavated, A tomographic image in the horizontal plane can also be obtained. For example, as shown in FIG. 2, by excavating the boring holes 11a, 11b, 12a and 12b in addition to the boring holes 11 and 12, and measuring the transmission characteristics of the electromagnetic wave between these boring holes. A tomographic image in a horizontal plane can be obtained.
[0021]
Further, in FIG. 1, the transmission characteristics of the electromagnetic wave transmitted from the boring hole 11 to the boring hole 12 are measured to obtain a tomographic image. However, the transmitting antenna 2 and the receiving antenna 3 are arranged in the same boring hole. It is also possible to obtain a tomographic image based on the transmission characteristics of the electromagnetic wave reflected from the ground.
[0022]
FIG. 3 is a diagram showing an outline of monitoring the underground pollution distribution while performing the pollution purification process when the position of the contaminated portion 4 of the ground 10 is found. If the contaminated part 4 of the ground 10 due to the contaminant is confirmed, the contaminant must be removed by performing a purification process on the contaminated part 4 as the next step. As shown in FIG. 3, an extraction well is drilled so as to reach the contaminated part 4, and soil gas and groundwater containing contaminants are pumped up. Then, the soil gas and the groundwater are processed by the pollution purification device 5 to remove the pollutants. Groundwater or the like purified by removing pollutants is returned to the ground 10 again.
[0023]
While performing the above-described contamination purification processing, the borehole radar tomography apparatus 1 outputs the structure of the ground between the boring holes 11 and 12 as a tomographic image as in FIG. 1 and changes in the tomographic image with time. To track. At this time, it is preferable to calculate and display a difference image ΔP = P2−P1 between the tomographic image P1 at the time T1 and the tomographic image P2 at the time T2 after the time T1.
[0024]
Since the difference image ΔP indicates a change in the ground component or the structure between the time T1 and the time T2, it is possible to selectively extract only the influence of the pollution purification processing. That is, an image component that does not change due to a fixed structure or the like in the ground can be eliminated, and the effect of the pollution purification processing can be more clearly monitored.
[0025]
In this way, a change in the size of the range of the contaminated portion 4 and a change in the concentration of the contaminant can be grasped very quickly. That is, the contamination state can be monitored almost in real time. Therefore, it is possible to quickly and accurately grasp and evaluate the effectiveness of the purification method of the pollution purification device 5 and the operation state. As a result, an accurate and effective purification method can be adopted, thereby shortening the construction period and significantly reducing the cost of the pollution purification treatment.
[0026]
【The invention's effect】
The present invention is configured as described above, and has the following effects.
[0027]
Transmitters and receivers placed in the borehole obtain an underground tomographic image from the transmission characteristics of electromagnetic waves, and use this tomographic image to search for underground contaminants. It is extremely easy to search for underground pollutants as compared to a method of taking a sample. That is, it has become possible to significantly reduce the time and cost for exploration.
[0028]
Transmitters and receivers located in the borehole obtain a tomographic image of the underground from the transmission characteristics of electromagnetic waves, and monitor the distribution of underground contamination from the tomographic image. It is possible to accurately grasp, and quickly and accurately grasp and evaluate the effectiveness of the pollution purification method and the operation status of the pollution purification device. As a result, an accurate and effective purification method can be adopted, thereby shortening the construction period and significantly reducing the cost of the pollution purification treatment.
[0029]
Since the difference between the tomographic image at the first time and the tomographic image at the second time is calculated, only the effect of the contamination purification process can be selectively extracted. That is, an image component that does not change due to a fixed structure or the like in the ground can be eliminated, and the effect of the pollution purification processing can be more clearly monitored.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of an underground pollutant detection method and an underground pollution distribution monitoring method of the present invention.
FIG. 2 is a diagram illustrating an example of an arrangement in a horizontal plane of a boring hole for obtaining a tomographic image in a horizontal plane.
FIG. 3 is a diagram showing an outline of monitoring a distribution of underground pollution while performing a pollution purification process.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Borehole radar tomography apparatus 2 ... Transmitting antenna 3 ... Receiving antenna 4 ... Contaminated part 5 ... Contamination purification apparatus 10 ... Ground 11, 12 ... Boring hole

Claims (6)

A procedure for forming a borehole (11, 12) in the basement;
Radiating an electromagnetic wave to the underground from the transmitting means (1) arranged in the boring holes (11, 12);
Receiving electromagnetic waves radiated from the transmitting means (1) by receiving means (2) arranged in the boring holes (11, 12);
Calculating a tomographic image of the underground based on the signal received by the receiving means (2);
Searching for the concentration and position of the pollutant using the tomographic image. An underground pollutant detection method according to claim 1,
The underground pollutant detection method, wherein the tomographic image is calculated based on a transmission characteristic between a transmission signal and a reception signal of an electromagnetic wave. A procedure for forming a borehole (11, 12) in the basement;
Radiating an electromagnetic wave to the underground from the transmitting means (1) arranged in the boring holes (11, 12);
Receiving electromagnetic waves radiated from the transmitting means (1) by receiving means (2) arranged in the boring holes (11, 12);
Calculating a tomographic image including a distribution of contaminants underground by a reception signal of the receiving means (2);
Monitoring the distribution of pollutants over time based on the temporal change of the tomographic image. An underground pollution distribution monitoring method according to claim 3,
The underground contamination distribution monitoring method, wherein the tomographic image is calculated based on a transmission characteristic between a transmission signal and a reception signal of an electromagnetic wave. An underground pollution distribution monitoring method according to any one of claims 3 and 4,
A step of calculating a difference (ΔP) between the tomographic image (P1) at a first time (T1) and the tomographic image (P2) at a second time (T2) after the first time. Underground pollution distribution monitoring method. An underground pollution distribution monitoring method according to any one of claims 3 to 5,
An underground pollution distribution monitoring method that monitors changes in the distribution of pollutants while performing pollution purification processing.

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