Soil pollutant migration and early warning simulation method based on geophysics

Abstract

The invention relates to the technical field of soil pollutant migration and early warning, and particularly discloses a geophysical soil pollutant migration and early warning simulation method, which comprises the steps of S1, mounting a geophysical detection equipment component, S2, data acquisition, S3, data processing and S4, data imaging. The induction electromagnetic method is generally used for rapid exploration investigation, stratum conductivity distribution is rapidly obtained, a conductivity abnormal area is found out, and help is provided for subsequent geophysical method construction. The ground penetrating radar is mainly suitable for stratums, underground pipeline positions, underground storage tank positions, shallow waste burying thickness and distribution, underground tank leakage, shallow DNAPL / LNAPL pollution and heavy metal pollution. In an underground pollution survey project, a ground penetrating radar method is mainly used for finding out positions of underground metal, pipelines and electromagnetic wave attenuation, measuring line arrangement and construction are facilitated through a high-density electrical method, and the application range of the high-density electrical method comprises hydrogeological detection, large underground structure detection, underground groove leakage detection and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil pollutant migration and early warning, and in particular relates to a geophysical soil pollutant migration and early warning simulation method. Background Art

[0002] The geophysical workflow includes work method design, site selection, data collection, post-data processing, inference interpretation, geological data feedback, repeated modification of processing parameters and fine processing and inversion. Design of work technology is the primary and crucial link. Only by fully collecting data and fully understanding the geological background of the work area, can we choose the appropriate geophysical method and the observation method of the method itself to achieve satisfactory results. Especially when conducting chemical pollution site investigation, we cannot blindly invest a lot of work and methods without a permissible work site.

[0003] Electrical prospecting is an effective geophysical prospecting method for finding underground structures and hidden faults. High-density electrical prospecting is based on the difference in conductivity between rocks (ores). It is an array prospecting method that infers and interprets the structure of underground geological bodies by observing and studying the distribution patterns and characteristics of artificial electric fields underground, and thus solves geological problems. Compared with the traditional resistivity method, it has the characteristics of high efficiency, rich information and convenient interpretation.

[0004] Electrical prospecting is an effective geophysical exploration method for finding underground structures and hidden faults. The measurement method has developed from conventional resistivity to induced polarization (IP), induction electromagnetic (EM), audio magnetotelluric (AMT), magnetotelluric (MT), and CSAMT. The measurement parameters have developed from single resistivity to multiple parameters such as resistivity, natural potential, polarizability, magnetic susceptibility, and phase. The induction electromagnetic method mainly distinguishes underground strata based on the difference in stratum conductivity. It is suitable for rapid surveys, large-scale preliminary screening surveys, etc. It can quickly obtain the distribution of stratum conductivity and provide a reference for subsequent investigations. The diffusion of pollutants in chemical contaminated sites is often accompanied by changes in the resistivity of the medium, which is manifested as different attenuation of the transmitted signal in the ground penetrating radar record. Therefore, the diffusion range of pollutants and the degree of pollution of the surrounding medium can be estimated based on the attenuation degree and range of the ground penetrating radar signal. The induced polarization method can use the spectral phase data of the stratum to further interpret the polarization phenomenon of the stratum (related to the content of polarizable substances such as clay and metallic minerals), which helps to further clarify the possible sources of abnormal areas in the detection profile.

[0005] In response to this, the inventors proposed a geophysical soil pollutant migration and early warning simulation method. Summary of the invention

[0006] The purpose of the present invention is to provide a geophysical soil pollutant migration and early warning simulation method to solve the problems raised in the above background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A geophysical soil contaminant migration and early warning simulation method comprises the following steps:

[0009] S1. Installing geophysical detection equipment components, including multi-frequency electromagnetic instruments used in induction electromagnetic method, ground penetrating radars used in ground penetrating radar method, high-density electrical method and high-density point method instruments used in induced polarization method;

[0010] S2, data acquisition, obtaining raw data from geophysical exploration equipment components;

[0011] S3, data processing, preprocessing and data conversion of the raw data obtained in step S2 to obtain measurement data;

[0012] S4, data imaging, inverting or imaging the measurement data obtained in step S3 to obtain an interpretation image of the geophysical exploration results.

[0013] Preferably, the data processing in the induction electromagnetic method includes two aspects: data preprocessing and data conversion, wherein the data preprocessing includes:

[0014] Data format conversion: Use the EMexport program provided by the instrument to convert the original EM measurement data .gbf format into .csv format;

[0015] Noise filtering: Use filters to filter the raw data to remove non-geological noise;

[0016] Drift correction to remove errors caused by zero drift and gain drift of the system and instrument;

[0017] GPS correction, correct the spatial position offset between the instrument and GPS.

[0018] Preferably, data conversion is to convert the preprocessed data into certain intermediate parameters, including apparent conductivity and apparent depth data imaging, for obtaining underground electrical distribution information and characterizing the main electrical distribution characteristics of the underground medium.

[0019] Preferably, the depth of electromagnetic detection is related to the skin depth of electromagnetic waves. The detection depth d of the multi-frequency electromagnetic instrument and the skin depth δ have the following relationship:

[0020]

[0021] The smaller the frequency of the electromagnetic waves emitted by the induction electromagnetic method instrument, the greater the skin depth, but the signal amplitude is smaller. As the frequency of the electromagnetic waves increases, the signal amplitude increases and the detection depth decreases.

[0022] Preferably, the data from the ground penetrating radar method is processed using data processing software as follows:

[0023] Preprocessing: distance normalization, time zero adjustment, Dewow to remove DC;

[0024] Gain adjustment: Use compensation gain to enhance deep signal display and highlight the target;

[0025] Data filtering: bandpass filtering, sliding average, background removal;

[0026] Perform profile time-depth conversion based on actual wave speed;

[0027] Three-dimensional data display of ground penetrating radar data.

[0028] Preferably, the reflection coefficient Ri of the electromagnetic wave emitted by the ground penetrating radar is expressed as:

[0029]

[0030] Where: ε1, ε2 are the relative dielectric constants of medium 1 and medium 2 respectively. From the above formula, we can know that:

[0031] The larger the absolute value of the reflection coefficient |Ri| is, the stronger the amplitude of the reflected wave generated by the interface is; the smaller the absolute value of the reflection coefficient |Ri| is;

[0032] The weaker the amplitude of the reflected wave generated by the interface, the larger the absolute value of the reflection coefficient |Ri|, the more conducive to detection;

[0033] If the reflection coefficient Ri>0, the reflected wave is in phase with the incident wave; if the reflection coefficient Ri<0, the reflected wave is in anti-phase with the incident wave;

[0034] When the reflection coefficient Ri=0, the electromagnetic wave directly penetrates the interface without reflection; when the reflection coefficient Ri→∞, the electromagnetic wave is totally reflected and cannot penetrate the interface;

[0035] The dielectric constant describes the polarization properties of a medium and reflects the ability of a medium to store charge in an electric field.

[0036] Preferably, the high-density electrical method places all electrodes at each measuring point of the observation profile, and then uses a programmable electrode conversion switch to control each electrode to switch between the measuring electrode and the power supply electrode, uses a microcomputer to quickly and automatically collect data, and obtains a relevant geoelectric section distribution map after processing the measured data; the power supply electrode provides current I to the underground, and the measuring electrode measures the potential difference ΔU between the two electrodes. The apparent resistivity ρs formula is:

[0037]

[0038] Where k is the device coefficient.

[0039] Preferably, the high-density electrical method preprocessing software is Swedish Res2DI nv 5.0.1, and the data distortion points are selected for processing. The processing principle is to conduct field analysis, and the distortion points caused by interference factors are deleted; and the data are modified according to the coordinates of the measuring points. After the individual data processing, the data is merged with the data of the edge gradient device for data inversion processing;

[0040] The inversion processing of the merged data can well display the resistivity changes of the strata, avoid the defects of a single device, and combine the data processed by other methods to infer the spatial distribution of the waste slag landfill area, providing an inversion resistivity model section inference interpretation map for report writing.

[0041] Preferably, the induced polarization method is divided into a DC induced polarization method and an AC induced polarization method; during the charging and discharging process, the additional electric field phenomenon that changes slowly with time due to the electrochemical reaction is called the induced polarization effect. The induced polarization method is based on the differences in the induced polarization effects of different rocks and minerals. By observing and studying the induced polarization effect of the earth, the underground geological conditions are detected; its electrodes are arranged with an intermediate gradient device, a combined profile device, a symmetrical quadrupole device and a dipole-dipole device, and the equipment used is the same as the high-density electrical method.

[0042] Preferably, the geophysical exploration results are interpreted by comprehensive induction electromagnetic conductivity plan map, high-density apparent resistivity inversion profile map, ground penetrating radar profile map, polarizability profile map, geological data and drilling data, taking into account the size and morphological factors of the outliers in the results map, and combining the stratigraphic lithology corresponding to the actual section to interpret the stratigraphic boundaries, faults and rock mass fragmentation and strong weathering, determine the boundaries of the anomalies based on the anomaly shape, range and trend in the results map, and mainly identify the pollution distribution characteristics of the survey area.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The induction electromagnetic method in the present invention is not suitable for detection in an environment with steel mesh paving or nearby metal structure interference, because the secondary field signal strength of the induction electromagnetic method is very small, and metal will have a great impact on the measurement data. The induction electromagnetic method is generally used for rapid survey, rapid acquisition of stratum conductivity distribution, identification of conductivity anomaly areas, and to provide assistance for subsequent geophysical method construction.

[0045] (2) The ground penetrating radar in the present invention is not suitable for testing in environments with excessive terrain undulations and interference from nearby metal structures. If it encounters a thick concrete floor or a steel mesh pavement, its detection depth is severely limited, the data response of the deep strata is weak, and the detection depth is also easily affected by clay and groundwater. Ground penetrating radar is mainly suitable for strata, underground pipeline locations, underground storage tank locations, shallow waste burial thickness and distribution, underground tank leakage, shallow DNAPL / LNAPL pollution, and heavy metal pollution. In underground pollution investigation projects, the ground penetrating radar method is mainly used to identify the location of underground metals, pipelines and electromagnetic wave attenuation, which is convenient for high-density electrical method to lay out survey lines and construction.

[0046] (3) Precautions and limitations for the use of high-density electrical method in the present invention: The survey line should not be laid completely parallel to any underground pipeline or structure; if there is a significant elevation difference on the surface, the elevation of each electrode must be measured; the spacing between survey lines affects the profile depth data; special attention should be paid to space restrictions such as site buildings; the electrode rods must penetrate thick layers of cement concrete (select 0.5-1.2m long electrode rods as needed) or avoid steel mesh. The scope of application of high-density electrical method includes hydrogeological detection, large underground structure detection, underground tank leakage detection, waste burial thickness and distribution detection, suspected pollution and pollution range investigation, soil and groundwater remediation effectiveness evaluation, etc.

[0047] (4) The attenuation curve of the secondary electric field of the underground medium after power failure measured by the induced polarization method in the present invention is different from the stable primary electric field measured by the high-density electrical method. The secondary field data is greatly affected by the electromagnetic coupling phenomenon and the electrode polarization effect. In addition, the secondary voltage data is small, and the data quality is more obviously affected by noise. Therefore, the grounding of the electrode must be good during the construction of the induced polarization method, and the electrode cannot contact the metal; when encountering a cement concrete hardening environment, a large diameter drill rod is required to drill through the hardened layer to facilitate the layout of the non-polarized electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A flow chart of a geophysical soil pollutant migration and early warning simulation method of the present invention;

[0049] Figure 2 This is a schematic diagram of the trajectory of the induction electromagnetic method in the second embodiment of the present invention;

[0050] Figure 3It is a conductivity contour plane diagram of f=63025Hz using the induction electromagnetic method in the second embodiment of the present invention;

[0051] Figure 4 It is a conductivity contour plane diagram of f=18025Hz using the induction electromagnetic method in the second embodiment of the present invention;

[0052] Figure 5 It is a conductivity contour plane diagram of f=5325Hz using the induction electromagnetic method in the second embodiment of the present invention;

[0053] Figure 6 It is a plane diagram of conductivity contour lines of f=1525Hz using the induction electromagnetic method in the second embodiment of the present invention;

[0054] Figure 7 This is a result diagram of the induction electromagnetic method zoning in the second embodiment of the present invention;

[0055] Figure 8 This is a cross-sectional view of the GPR-L1 ground penetrating radar in Embodiment 3 of the present invention;

[0056] Fig. 9 This is a cross-sectional view of the GPR-L2 ground penetrating radar in Embodiment 3 of the present invention;

[0057] Fig.10 This is a cross-sectional view of the GPR-L20 ground penetrating radar in the third embodiment of the present invention;

[0058] Fig.11 This is a cross-sectional view of the GPR-L21 ground penetrating radar in Embodiment 3 of the present invention;

[0059] Fig.12 It is a plan view of the anomaly delineation result of the ground penetrating radar in the third embodiment of the present invention;

[0060] Fig.13 This is the actual material map detected by the high-density electrical method BJ-L1 in the fourth embodiment of the present invention;

[0061] Fig.14 This is a diagram of the inversion and interpretation results of the high-density electrical method BJ-L1 survey line in the fourth embodiment of the present invention;

[0062] Fig.15 This is a diagram of the inversion and interpretation results of the high-density electrical method NH-L11 survey line in the fourth embodiment of the present invention;

[0063] Fig.16 It is a map of actual material detected in the investigation area of ​​induced polarization method in the fifth embodiment of the present invention;

[0064] Fig.17 This is a diagram of the inversion and interpretation results of the JD-L1 survey line using the induced polarization method in Example 5 of the present invention;

[0065] Fig.18 This is a diagram of the inversion and interpretation results of the JD-L2 survey line using the induced polarization method in Example 5 of the present invention. DETAILED DESCRIPTION

[0066] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0067] Embodiment 1:

[0068] See also Figures 1 to 18 As shown, a geophysical soil contaminant migration and early warning simulation method includes the following steps:

[0069] S1. Installing geophysical detection equipment components, including the GEM-2 multi-frequency electromagnetic instrument used in the induction electromagnetic method, the Geopro-10 ground penetrating radar used in the ground penetrating radar method, and the GD-20 high-density point method instrument used in the high-density electrical method and the induced polarization method;

[0070] S2, data acquisition, obtaining raw data from geophysical exploration equipment components;

[0071] S3, data processing, preprocessing and data conversion of the raw data obtained in step S2 to obtain measurement data;

[0072] S4, data imaging, inverting or imaging the measurement data obtained in step S3 to obtain an interpretation image of the geophysical exploration results.

[0073] Specifically, the data processing in the induction electromagnetic method includes two aspects: data preprocessing and data conversion, wherein the data preprocessing includes:

[0074] Data format conversion: Use the EMexport program provided by the instrument to convert the original EM measurement data .gbf format into .csv format;

[0075] Noise filtering: Use filters to filter the raw data to remove non-geological noise;

[0076] Drift correction to remove errors caused by zero drift and gain drift of the system and instrument;

[0077] GPS correction, correct the spatial position offset between the instrument and GPS.

[0078] Specifically, data conversion is to convert the preprocessed data into certain intermediate parameters, including apparent conductivity and apparent depth data imaging, which is used to obtain underground electrical distribution information and characterize the main electrical distribution characteristics of the underground medium.

[0079] Specifically, the depth of electromagnetic detection is related to the skin depth of electromagnetic waves. The relationship between the detection depth d of the multi-frequency electromagnetic instrument and the skin depth δ is as follows:

[0080]

[0081] The smaller the frequency of the electromagnetic wave emitted by the induction electromagnetic method instrument, the greater the skin depth, but the signal amplitude is smaller. As the frequency of the electromagnetic wave increases, the signal amplitude increases and the detection depth decreases. In low conductivity areas (<50Ms / m), the choice of frequency is mainly based on the signal level, and reliable measurement data has been obtained; in low conductivity areas (>200Ms / m), the choice of frequency is mainly based on the detection depth.

[0082] Specifically, the data from the ground penetrating radar method is processed using data processing software as follows:

[0083] Preprocessing: distance normalization, time zero adjustment, Dewow to remove DC;

[0084] Gain adjustment: Use compensation gain to enhance deep signal display and highlight the target;

[0085] Data filtering: bandpass filtering, sliding average, background removal;

[0086] Perform profile time-depth conversion based on actual wave speed;

[0087] Three-dimensional data display of ground penetrating radar data.

[0088] Specifically, the reflection coefficient Ri of the electromagnetic wave emitted by the ground penetrating radar is expressed as:

[0089]

[0090] Where: ε1, ε2 are the relative dielectric constants of medium 1 and medium 2 respectively. From the above formula, we can know that:

[0091] The larger the absolute value of the reflection coefficient |Ri| is, the stronger the amplitude of the reflected wave generated by the interface is; the smaller the absolute value of the reflection coefficient |Ri| is;

[0092] The weaker the amplitude of the reflected wave generated by the interface, the larger the absolute value of the reflection coefficient |Ri|, the more conducive to detection;

[0093] If the reflection coefficient Ri>0, the reflected wave is in phase with the incident wave; if the reflection coefficient Ri<0, the reflected wave is in anti-phase with the incident wave;

[0094] When the reflection coefficient Ri=0, the electromagnetic wave directly penetrates the interface without reflection; when the reflection coefficient Ri→∞, the electromagnetic wave is totally reflected and cannot penetrate the interface (such as when the antenna is located above the manhole cover);

[0095] The dielectric constant describes the polarization properties of a medium and reflects the ability of a medium to store charge in an electric field.

[0096] Specifically, the high-density electrical method places all electrodes (dozens to hundreds) at each measuring point of the observation profile, and then uses a programmable electrode conversion switch to control each electrode to switch between the measuring electrode and the power supply electrode, and uses a microcomputer to quickly and automatically collect data. After processing the measured data, the relevant geoelectric section distribution map can be obtained; the power supply electrode provides current I to the underground, and the measuring electrode measures the potential difference ΔU between the two electrodes. The apparent resistivity ρs formula is:

[0097]

[0098] Where k is the device coefficient. There are many measurement devices for high-density electrical method, such as Wenner device, Wenner-Schlumberger array, dipole, Schlumberger device, edge gradient, etc. Different devices have different running pole methods and device coefficients.

[0099] Specifically, the high-density electrical method preprocessing software is Swedish Res2D I nv 5.0.1, and the data distortion points are selected for processing. The processing principle is to conduct field analysis, and the distortion points caused by interference factors are deleted; and the data are modified according to the coordinates of the measuring points. After the individual data are processed, the data are merged with the data of the edge gradient device for data inversion processing;

[0100] The inversion processing of the merged data can well display the resistivity changes of the strata, avoid the defects of a single device, and combine the data processed by other methods to infer the spatial distribution of the waste slag landfill area, providing an inversion resistivity model section inference interpretation map for report writing.

[0101] Specifically, the induced polarization method is divided into direct current induced polarization method and alternating current induced polarization method; during the charging and discharging process, the additional electric field phenomenon that changes slowly with time due to the electrochemical reaction is called the induced polarization effect. The induced polarization method is based on the difference in induced polarization effects of different rocks and minerals. By observing and studying the induced polarization effect of the earth, the underground geological conditions are detected; its electrode arrangement includes an intermediate gradient device, a combined profile device, a symmetrical quadrupole device and a dipole-dipole device, and the equipment used is the same as the high-density electrical method.

[0102] Specifically, the geophysical exploration results are interpreted by comprehensive induction electromagnetic conductivity plan map, high-density apparent resistivity inversion profile map, ground penetrating radar profile map, polarizability profile map, geological data and drilling data, taking into account the size and morphological factors of the outliers in the results map, and combining the stratigraphic lithology corresponding to the actual section to interpret the stratigraphic boundaries, faults and the fragmentation and strong weathering of the rock mass, and determine the boundaries of the anomalies based on the anomaly shape, range and trend in the results map, mainly to identify the pollution distribution characteristics of the investigation area.

[0103] Embodiment 2:

[0104] Induction electromagnetic method explained:

[0105] The instrument used for the induction electromagnetic method is the GEM-2 multi-frequency electromagnetic instrument. The transmitting and receiving coils of the GEM-2 are fixed in a device that looks like a snowboard with a strap. The housing containing all the electronic components can be embedded in the snowboard. The handheld computer (PDA) is connected to the housing via Bluetooth and used as a user interface and display.

[0106] Assemble and turn on the instrument on site, adjust the parameters, and wait for the instrument to make a "beeping" sound, indicating that the instrument's high-precision GPS real-time positioning has been connected, then you can carry out the measurement work normally; when people carry the instrument, put the metal objects on their bodies aside, and then walk at a row and column spacing of 2 to 5m, at a speed of about 0.7 to 1.5m / s, record 5 readings per second, and conduct grid detection of the area within the geophysical exploration range; after the measurement task is completed, pause and save the data, and transmit the data after returning.

[0107] The setting of acquisition frequency is the key to setting measurement parameters. The detection of the phosphate land area by induction electromagnetic method was set at 63025Hz, 18325Hz, 5325Hz and 1525Hz. According to the skin depth calculation formula, the depth corresponding to this frequency is shown in Table 1.

[0108] Serial number Frequency (Hz) Depth(m) 1 63025 0～1.0 2 18325 1.0～2.0 3 5325 2.0～3.5 4 1525 3.5～7

[0109] Table 1

[0110] Figure 2The track of the on-site personnel carrying the instrument was measured with a row spacing of 2*2, a walking speed of about 0.7~1.5m / s, and 5 readings per second. The phosphate plot area was grid-surfaced. Due to the large number of metal-containing buildings in the survey area, the spatial position between the instrument and the GPS was offset. The conductivity plane maps at different depths were drawn according to different detection frequencies, see Figure 3 , Figure 4 , Figure 5 and Figure 6 .

[0111] The coordinate projection system of the GEM-2 multi-frequency electromagnetic instrument equipment is UTM-WGS84. In order to keep the coordinate projection system of all measurement data the same, the coordinate data recorded by the GEM-2 multi-frequency electromagnetic instrument GPS are converted to the National 2000 coordinate system, with a central meridian of 120° and a Gauss projection 3° zone.

[0112] from Figure 3 It can be seen that there is an obvious steep conductivity gradient zone at 40mS / m and 75mS / m, and combined with the on-site situation, it is speculated that it is the boundary of the suspected pollution area. The suspected pollution area is distributed on the west side of the investigation area, resulting in higher conductivity on the west side of the investigation area; the conductivity on the east side is lower, and it is speculated that the near-surface pollution is lighter;

[0113] from Figure 4 It can be seen that there are obvious steep conductivity gradient zones at 40mS / m and 75mS / m, and combined with the on-site conditions, it is speculated that they are the boundaries of the suspected contaminated areas. The suspected contaminated area is distributed on the west side of the investigation area, resulting in higher conductivity on the west side of the investigation area; the conductivity on the east side is lower, and it is speculated that the near-surface pollution is lighter. The resistivity of 1m and 2m is basically close. It is speculated that it is caused by the steel bars in the cement near the surface and the pollutants below. Among them, the three anomalies of 75mS / m are speculated to be related to pollution or underground landfill.

[0114] from Figure 5 It can be seen that there are obvious steep conductivity gradient zones at 40mS / m and 75mS / m, and combined with the on-site situation, it is speculated that it is the boundary of the suspected pollution area. The suspected pollution area is basically in the whole area, and the heavy pollution area is located in the north and south of the survey area. The suspected abnormal area in the middle has always existed and its range has narrowed with the increase of depth. It is speculated that it is caused by the accumulation of pollution near the surface;

[0115] from Figure 6It can be seen that there are obvious steep conductivity gradient zones at 40mS / m and 75mS / m, and combined with the on-site situation, it is speculated that it is the boundary of the suspected pollution area. The suspected pollution area is basically located on the north and south sides of the survey area. The north side is close to the retaining wall, which may cause anomalies. The south side is close to the river bank and is speculated to be caused by deep silty soil. The sporadic distribution of pollution in the middle of this depth is speculated to be caused by the lower pollution content compared with the surrounding area.

[0116] By calculating the conductivity difference ratio of different frequencies to the highest frequency, the formula is as follows:

[0117]

[0118] We can see that the conductivity changes little within 2m, and the conductivity on the east and south edges at a depth of 3.5m increases rapidly. Perhaps it is related to the shallow high resistance zone. At a depth of 7m, the conductivity abnormal change rate increases. The middle part is basically decreasing. Only a few areas have increased conductivity.

[0119] From the above, we can see that the entire measurement area is divided into several small blocks, mainly into high conductivity change rate blocks, indicating that there is a large change rate with depth. As the main area of ​​groundwater movement. It is speculated that groundwater flows to the northeast and southeast. The two areas in the middle with small conductivity changes may be high conductivity enrichment areas, which may be related to pollution enrichment.

[0120] Embodiment three:

[0121] Ground Penetrating Radar Method Explained:

[0122] The results of ground penetrating radar mainly reflect the distribution of electrical properties (dielectric constant) of underground media. As long as there are electrical differences in underground media, the corresponding reflected waves can be found in the radar image profile to identify the reflected wave characteristics of various strata. In terms of detecting pollutants in chemical contaminated sites, it is usually presented as the attenuation of the transmitted signal. Therefore, the diffusion range of pollutants and the degree of pollution of the surrounding medium can be estimated based on the attenuation degree and range of the ground penetrating radar signal.

[0123] A total of 21 ground penetrating radar detection profiles were deployed in the survey area, such as Figure 8 As shown in the figure, the radar profile shows that the main radar anomalies in the survey area are basically around 1m in depth. The results are analyzed as follows:

[0124] The GPR-L1 survey line is located at the boundary of the survey area, below the suspended pipeline, and runs from southwest to northeast. Fig. 9 The overall analysis of the profile data results is as follows: near the profile mileage of 25.58m, the event axis is hyperbolic, which is presumed to be an underground pipeline.

[0125] The GPR-L2 survey line is located in the southwest of the survey area. The front end of the profile passes through the fiberglass tank area and is laid out from southwest to northeast. The overall analysis of the profile data results is as follows: Near the profile mileage of 14.40m, the phase axis is hyperbolic, which is speculated to be an underground pipeline. Near the profile mileage of 19.34m, the phase axis is hyperbolic, which is speculated to be an underground pipeline.

[0126] The surveying work of GPR-L3~GPR-L19 lines is the same as above and will not be repeated here.

[0127] The GPR-L20 survey line is located in the middle of the survey area and runs from northwest to southeast. Fig.10 The profile has no abnormalities and can be used as a comparison for abnormal profiles.

[0128] The GPR-L21 survey line is located in the middle of the survey area and runs from northwest to southeast. Fig.11 The profile has no abnormalities and can be used as a comparison for abnormal profiles.

[0129] Fig.12 It can be seen that the suspected contaminated areas are basically concentrated on the west side, which corresponds well to the shallow anomalies in the EM results. It is speculated that it may be caused by acidic substances formed by the decomposition of shallow pollution.

[0130] As can be seen from the above, based on the above-mentioned ground penetrating radar profile results, the pipeline anomalies of each survey line are projected onto the map and connected. The shallow weak signal suspected pollution area is projected onto the map. The main shallow pollution area is located on the west side of the survey area. It basically conforms to the results of all work.

[0131] Embodiment 4:

[0132] High-density electrical method explanation:

[0133] A high-density resistivity profile was laid upstream of the survey area. Fig.13 The survey line has a point spacing of 2m, a profile length of 98m, a starting point of a small number, such as BJ-1, and a terminal point of a large number, such as BJ-50. The terrain rises slowly from the small end to the large end of the survey line, with a height difference of about 1.5m. There is a steep slope of about 1m at the mileage of 44m.

[0134] The data collection process of high-density electrical method is to determine the survey line position, RTK measurement of electrode position coordinates, high-density cable and electrode layout, and data collection according to the field survey.

[0135] Fig.14This is the inversion and interpretation result of the high-density electrical method background survey line. The survey line is located upstream along the groundwater direction, about 3km away from the survey area and about 200m away from the Macha River. It does not contain LNAPL pollution; the area is artificially planted with trees and has a large clay content. According to the high-density electrical resistivity inversion results, geological data of the survey area, and surface grounding conditions, a comprehensive factor analysis was conducted. The resistivity of the survey line is divided into two layers as a whole. The shallow resistivity is higher, with a resistivity value of about 20 to 57Ω·m, which is speculated to be plain fill; the deep resistivity is lower, with a resistivity value of about 8.6 to 20Ω·m, which is speculated to be silty clay and filled with groundwater, so it is in a low-resistance state.

[0136] Fig.15 The inversion and interpretation results of the high-density electrical method NH-L11 survey line. The NH-L11 survey line is located on the factory road at mileage 6-14m, and on hardened land at mileage 14-75m; borehole SW002 is located at mileage 31m of the survey line.

[0137] The soil in borehole SW002 at a depth of 5.5m showed excessive pollution of chlorobenzene, and the groundwater exceeded the standard for oxygen consumption, ammonia nitrogen, total dissolved solids, total hardness, fluoride, chloride, sulfate, chlorobenzene, sulfide, nitrobenzene, 2-chlorophenol, arsenic, nickel, total phosphorus, aniline, and C6-C9. The resistivity profile of the high-density electrical method NH-L10 line was between 8.6 and 57Ω·m at a mileage of 30m, with a resistivity of 10.6 to 5m, and a resistivity of less than 8.6Ω·m in the low-resistance abnormal area between 5 and 2m. It is inferred that the excessive pollution of soil and groundwater detection indicators is caused by the diffusion of pollutants from nearby. From the resistivity profile of NH-L11 survey line, it can be seen that there are 7 obvious low-resistance anomalies with mileage 3-8m and elevation 8-3m, mileage 18-30m and elevation 8.5-2.5m, mileage 34-38m and elevation 9-4.5m, mileage 40-48m and elevation 9--3m, mileage 47-55m and elevation 9-6m, mileage 57-60m and elevation 9-7m, mileage 63-67m and elevation 9.5-4m, and the resistivity is less than 5Ω·m. It is speculated that these 7 low-resistance anomaly areas are polluted areas.

[0138] From the above, we can see that the interpretation results of the high-density electrical method NH-L11 survey line correspond well to the borehole SW002, which shows that the results of high-density electrical detection are credible and reliable.

[0139] Embodiment five:

[0140] Explanation of the induced polarization method:

[0141] Two induced polarization profiles were set up in the survey area. Fig.16The JD-L1 survey line has a point spacing of 4m and a profile length of 68m; the JD-L2 survey line has a point spacing of 3m and a profile length of 63m; the starting point of the survey line is a small point number, such as L1-1;

[0142] The end point of the survey line is a large point number, such as L1-18. The survey area is flat with almost no elevation difference. The red dots in the figure are the locations of the measuring electrodes of the induced polarization method. The point number of the measuring electrode is line number minus electrode number.

[0143] A total of 18 detection indicators exceeded the standard in the survey area, namely oxygen consumption, ammonia nitrogen, total dissolved solids, total hardness, fluoride, chloride, sulfate, chlorobenzene, sulfide, nitrobenzene, 2-chlorophenol, arsenic, nickel, cobalt, total phosphorus, aniline, and petroleum hydrocarbons (C6-C9, C10-C40), including inorganic and organic pollutants. Since inorganic pollutants carry a certain charge, they dissolve in water to reduce their resistivity and increase their polarizability, thus forming a local low-resistance and high-polarization anomaly. In addition, after some organic pollutants infiltrate into the water body, they degrade under natural conditions and decompose into charged particles, which reduces the resistivity of the water body and increases its polarizability. The petroleum hydrocarbons in the aeration zone undergo a series of redox electrochemical reactions, which makes the area where they are located have low resistance and high polarization characteristics relative to the surrounding medium, which may also correspond to the low-resistance and high-polarization anomaly.

[0144] The groundwater mineralization in the survey area is relatively high. According to the groundwater survey data in the survey area, the total dissolved solid content is between 1690 and 8360 mg / L, and the groundwater conductivity is relatively high. The previous high-density electrical detection results also show that the resistivity of the plots in the survey area is relatively low, which is not conducive to the data collection of the induced polarization method. A layer of steel mesh is laid under the hardened plots in the survey area, which causes the induced polarization method data of the survey lines JD-L1 and JD-L2 to reflect that the average apparent polarization rate of the site is mainly distributed between 0.3% and 15%, and the overall quality of the induced polarization method data is poor.

[0145] Fig.17 This is the inversion and interpretation results of the JD-L1 survey line using the induced polarization method. The JD-L1 survey line is located in the northeast of the survey area, close to the blue production workshop. The metal structure of the workshop may affect the quality of the induced polarization data. The surface of the survey line is covered with a thin layer of soil, and the bottom is the old hardened ground.

[0146] According to the inversion results of the induced polarization method, the geological data of the survey area, the drilling data, and the surface conditions, a comprehensive factor analysis was conducted. From the resistivity profile of the JD-L1 survey line, it can be seen that it is divided into three layers according to the size of the resistivity value, and the resistivity distribution is continuous; the high-resistance area (>20Ω·m) in the shallow red area is inferred to be cement concrete or surface plain fill, the medium-resistivity area (5Ω·m><20Ω·m) in the yellow to light blue area is inferred to be silty clay, and the low-resistivity area (<5Ω·m) in the blue area is inferred to be a reflection of the polluted area. From the polarization profile of the JD-L1 survey line, it can be seen that it is divided into two layers according to the size of the polarizability value, and the polarizability distribution is continuous; the low-polarizability area (<1.8%) in the shallow green to yellow area is inferred to be cement concrete or surface plain fill, and the high-polarizability area (>1.8%) in the deep red area is inferred to be a reflection of silty clay and polluted areas. The resistivity and polarizability profiles of JD-L1 are interpreted as a comprehensive survey line. It is found that there is an obvious low-resistance anomaly and high-polarization anomaly area at a distance of 10-56m and an elevation of 5-0m. The resistivity is less than 5Ω·m and the polarizability is greater than 1.8%. It is speculated that this abnormal area is a polluted area.

[0147] Fig.18 This is the inversion and interpretation result of JD-L2 survey line using induced polarization method. JD-L2 survey line is located in the southeast direction of the survey area, close to the boundary of the survey area. The surface of the survey line is covered with a thin layer of soil, and the bottom is the old hardened ground. The small end of the survey line is close to the blue production workshop. The metal structure of the workshop affects the data quality of the survey line mileage 0-15m. Borehole SW006 is located at the survey line mileage 7.5m, and borehole SW005 is located at the survey line mileage 48m.

[0148] According to the inversion results of the induced polarization method, the geological data of the survey area, the drilling data, and the surface conditions, a comprehensive factor analysis was conducted. It can be seen from the resistivity profile of the JD-L2 survey line that it is divided into three layers according to the size of the resistivity value, and the resistivity distribution is continuous; the high-resistance area (>20Ω·m) in the shallow red area is inferred to be cement concrete or surface fill, the medium-resistivity area (5Ω·m><20Ω·m) in the yellow to light blue area is inferred to be silty clay, and the low-resistivity area (<5Ω·m) in the blue area is inferred to be the reaction of the contaminated area. It can be seen from the polarization profile of the JD-L2 survey line that the entire profile is basically a high polarizability area, and only the local polarizability value is less than 1.8%. The metal foundation structure affects the flow direction of the power supply current, resulting in an increase in the resistance on the deep left side of the survey line; according to the groundwater detection results of SW006, the detection index here exceeds the standard, so it is inferred that the deep left side is also a contaminated area. There is an obvious low-resistance anomaly and high-polarization anomaly area at mileage 28-33m and elevation 6-2.5m, with a resistivity less than 5Ω·m and a polarization greater than 1.8%. It is speculated that this abnormal area is a polluted area.

[0149] As can be seen from the above, the induction electromagnetic method is not suitable for detection in an environment with steel mesh paving or nearby metal structure interference, because the secondary field signal intensity of the induction electromagnetic method is very small, and metal will have a great impact on the measurement data. The induction electromagnetic method is generally used for rapid investigation, rapid acquisition of stratum conductivity distribution, identification of conductivity anomaly areas, and to provide assistance for subsequent geophysical method construction.

[0150] Ground penetrating radar is not suitable for field measurements in environments with large terrain fluctuations and interference from nearby metal structures. If it encounters thick concrete floors or steel mesh pavements, its detection depth is severely limited, the data response of deep strata is weak, and the detection depth is also easily affected by clay and groundwater. Ground penetrating radar is mainly suitable for strata, underground pipeline locations, underground storage tank locations, shallow waste burial thickness and distribution, underground tank leakage, shallow DNAPL / LNAPL pollution, and heavy metal pollution. In underground pollution investigation projects, ground penetrating radar is mainly used to identify the location of underground metals, pipelines, and electromagnetic wave attenuation, which is convenient for high-density electrical method to lay out survey lines and construction.

[0151] Precautions and limitations for using high-density electrical method: The survey line should not be laid completely parallel to any underground pipeline or structure; if there is a significant elevation difference on the surface, the elevation of each electrode must be measured; the spacing between survey lines affects the profile depth data; special attention should be paid to space restrictions such as site buildings; the electrode rods must penetrate thick layers of cement concrete (select 0.5-1.2m long electrode rods as needed) or avoid steel mesh. The scope of application of high-density electrical method includes hydrogeological detection, large underground structure detection, underground tank leakage detection, waste burial thickness and distribution detection, suspected pollution and pollution range investigation, soil and groundwater remediation effectiveness evaluation, etc.

[0152] The attenuation curve of the secondary electric field of the underground medium after power failure measured by the induced polarization method is different from the stable primary electric field measured by the high-density electrical method. The secondary field data is greatly affected by the electromagnetic coupling phenomenon and the electrode polarization effect. In addition, the secondary voltage data is small, and the data quality is more obviously affected by noise. Therefore, the grounding of the electrode must be good during the construction of the induced polarization method, and the electrode cannot contact the metal; when encountering a cement concrete hardening environment, a large diameter drill rod is required to drill through the hardened layer to facilitate the layout of the non-polarized electrode.

[0153] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A geophysical soil contaminant migration and early warning simulation method, characterized in that: The following steps are involved: S1. Installing geophysical detection equipment components, including multi-frequency electromagnetic instruments used in induction electromagnetic method, ground penetrating radars used in ground penetrating radar method, high-density electrical method and high-density point method instruments used in induced polarization method; S2, data acquisition, obtaining raw data from geophysical exploration equipment components; S3, data processing, preprocessing and data conversion of the raw data obtained in step S2 to obtain measurement data; S4, data imaging, inverting or imaging the measurement data obtained in step S3 to obtain an interpretation image of the geophysical exploration results.

2. A geophysical soil contaminant migration and early warning simulation method according to claim 1, characterized in that: The data processing in the induction electromagnetic method includes two aspects: data preprocessing and data conversion, wherein the data preprocessing includes: Data format conversion: Use the EMexport program provided by the instrument to convert the original EM measurement data .gbf format into .csv format; Noise filtering: Use filters to filter the raw data to remove non-geological noise; Drift correction to remove errors caused by zero drift and gain drift of the system and instrument; GPS correction, correct the spatial position offset between the instrument and GPS.

3. A geophysical soil contaminant migration and early warning simulation method according to claim 2, characterized in that: Data conversion is the process of converting preprocessed data into certain intermediate parameters, including apparent conductivity and apparent depth data imaging, which is used to obtain underground electrical distribution information and characterize the main electrical distribution characteristics of underground media.

4. A geophysical soil contaminant migration and early warning simulation method according to claim 1, characterized in that: The depth of electromagnetic detection is related to the skin depth of electromagnetic waves. The relationship between the detection depth d of the multi-frequency electromagnetic instrument and the skin depth δ is as follows: The smaller the frequency of the electromagnetic waves emitted by the induction electromagnetic method instrument, the greater the skin depth, but the signal amplitude is smaller. As the frequency of the electromagnetic waves increases, the signal amplitude increases and the detection depth decreases.

5. The geophysical soil contaminant migration and early warning simulation method according to claim 1, characterized in that: The data from the ground penetrating radar method are processed using data processing software as follows: Preprocessing: distance normalization, time zero adjustment, Dewow to remove DC; Gain adjustment: Use compensation gain to enhance deep signal display and highlight the target; Data filtering: bandpass filtering, sliding average, background removal; Perform profile time-depth conversion based on actual wave speed; Three-dimensional data display of ground penetrating radar data.

6. A geophysical soil contaminant migration and early warning simulation method according to claim 1, characterized in that: The expression of reflection coefficient Ri of electromagnetic wave emitted by ground penetrating radar is: Where: ε1, ε2 are the relative dielectric constants of medium 1 and medium 2 respectively. From the above formula, we can know that: The larger the absolute value of the reflection coefficient |Ri| is, the stronger the amplitude of the reflected wave generated by the interface is; the smaller the absolute value of the reflection coefficient |Ri| is; The weaker the amplitude of the reflected wave generated by the interface, the larger the absolute value of the reflection coefficient |Ri|, the more conducive to detection; If the reflection coefficient Ri>0, the reflected wave is in phase with the incident wave; if the reflection coefficient Ri<0, the reflected wave is in anti-phase with the incident wave; When the reflection coefficient Ri=0, the electromagnetic wave directly penetrates the interface without reflection; when the reflection coefficient Ri→∞, the electromagnetic wave is totally reflected and cannot penetrate the interface; The dielectric constant describes the polarization properties of a medium and reflects the ability of a medium to store charge in an electric field.

7. A geophysical soil contaminant migration and early warning simulation method according to claim 1, characterized in that: The high-density electrical method places all electrodes at each measuring point of the observation profile, and then uses a programmable electrode conversion switch to control each electrode to switch between the measuring electrode and the power supply electrode, uses a microcomputer to quickly and automatically collect data, and obtains the relevant geoelectric section distribution map after processing the measured data; the power supply electrode provides current I to the underground, and the measuring electrode measures the potential difference ΔU between the two electrodes. The apparent resistivity ρs formula is: Where k is the device coefficient.

8. The geophysical soil contaminant migration and early warning simulation method according to claim 1, characterized in that: The high-density electrical method pretreatment, the processing software is Swedish Res2DInv 5.0.1, choose to process the data distortion points. The processing principle is to conduct field analysis. For the distortion points caused by interference factors, delete them. And modify the data according to the coordinates of the measuring points. After processing the data separately, merge the data of Wens and edge gradient devices to perform data inversion processing. The inversion processing of the merged data can well display the resistivity changes of the strata, avoid the defects of a single device, and combine the data processed by other methods to infer the spatial distribution of the waste slag landfill area, providing an inversion resistivity model section inference interpretation map for report writing.

9. A geophysical soil contaminant migration and early warning simulation method according to claim 1, characterized in that: The induced polarization method is divided into direct current induced polarization method and alternating current induced polarization method. During the charging and discharging process, the additional electric field phenomenon that changes slowly with time due to the electrochemical reaction is called induced polarization effect. The induced polarization method is based on the difference in induced polarization effect of different rocks and minerals. It detects underground geological conditions by observing and studying the induced polarization effect of the earth. The electrode arrangement includes an intermediate gradient device, a combined profile device, a symmetrical quadrupole device and a dipole-dipole device, and the equipment used is the same as that of the high-density electrical method.

10. A geophysical soil contaminant migration and early warning simulation method according to claim 1, characterized in that: The geophysical exploration results are interpreted based on the comprehensive induction electromagnetic conductivity plan map, high-density apparent resistivity inversion profile map, ground penetrating radar profile map, polarizability profile map, geological data and drilling data. The size and morphological factors of the outliers in the results map are considered, and combined with the stratigraphic lithology corresponding to the actual section, the stratigraphic boundaries, faults and rock mass fragmentation and strong weathering are interpreted. The boundaries of the anomalies are determined based on the anomaly shape, range and trend in the results map, mainly to identify the pollution distribution characteristics of the investigation area.

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