It is often presented as a cross-sectional equivalent image. Physical units often use resistivity (ohm-m) to represent different levels of color with different tones.
Induction electromagnetic works
The main method of induction electromagnetic method (EM) is frequency domain electromagnetic method (FDEM), which generates an induced magnetic field in the formation through the instantaneous current of the coil, and calculates the apparent conductivity of the material by recording the phase difference of the secondary magnetic field. In a fixed case, the two-dimensional tangent plane distribution of the conductivity of the material at a specific depth can be delineated
It is often presented in the form of a cut plane equivalent image or a single point measurement, depicting the difference in surface electrical distribution, and the conductivity of the physical unit (mS/m), representing different heights and values in different shades
Results – Background Areay
The background area is located approximately 250 meters upstream of the field.
The area size is about 40m*170m
Red frame line is the background EM measurement area
The middle yellow line is the background ERT line
Background EM results show that the overall level of conductivity in the background region is mainly below 20mS/m, that is, the purple region in the figure.
The background ERT results indicate that the resistivity distribution is between about 30 ohm.m and 300 ohm.m. There is no extremely high or very low resistivity anomaly in the area. Based on this, if the results in the plant area are extremely low resistance (<2 ohm.m), it is highly likely to be caused by heavy metal pollution.
Areas 1, 3 are the house and construction, and the high conductivity that appears above area 2 is also caused by housing, so these interference items are first excluded. Areas 2, 4, and 5 are the main pollution potential areas, and the area surrounded by the areas 3, 4, and 5 also has a very high pollution potential. This area is complicated by other buildings due to its large number of constructions. Subsequent further determination of the location and distribution of the pollution by ERT. According to the results in the figure, the high-conductivity anomalies appearing in the suspect area are over 200mS/m, even exceeding 250mS/m.。
The distribution range of the resistivity of the test line ERT1~ERT3 is basically consistent with the background value, and it is speculated that the result of the line is no abnormal pollution area. At the beginning of the ERT4~5 line, there is a very low anomaly area, the resistivity is about 2 ohm.m, and its depth is 6~7 meters, which is presumed to be a high concentration pollution anomaly area. There are three suspicious low-resistance anomalies in ERT6. The resistivity is not very low as ERT4~5. It is speculated that the pollutants are not concentrated in the bottom of the line, but are mapped from the side to the line profile, or The concentration of pollutants here is low. The three line detection lines of ERT7~ERT9 are located in the high pollution area, and the results show a high degree of agreement with the EM results. The main heavy metal pollution potential is located in the middle of the line ERT7 and ERT8. Corresponding areas, from ERT7 to ERT9, the degree of pollution gradually diminished. Compared with the second half of the line, there are different degrees of light pollution potential at the front end of the three lines, and there is a serious pollution trend within about 13 meters.
The front end of the two lines of ERT10~11 is a medium pollution potential area, which coincides with the front end of ERT4 and ERT5 in this pollution potential area. In the 0-64m of ERT10, the depth is about 7m and the ERT11 is 0-44m, and the depth is about 4m, which is the pollution potential. ERT12 is a line across moderately and heavily polluted areas. It has a light heavy metal pollution potential in the range of about 66-84m and a depth of about 8-18m. It is in the range of 112m to 168m and the depth is about 8m. There is a serious pollution potential. ERT13 is located in the heavily polluted area, and there is a significant low-resistance anomaly area, which is about 42-80m in the horizontal distance and about 6m in the depth of the line.
Advantages of geophysical methods
The plane distribution range of the abnormal value of the measurement area is determined by the inductive electromagnetic method, and the distribution range of the abnormal value of the measurement area in the vertical direction is determined by the high-density resistivity method. The two methods are closely matched to obtain the geological body in the space of the measurement area. Characteristic parameter
The traditional way of investigating is to estimate the possible distribution through limited borehole sampling, and to estimate the extent and depth of the pollution distribution through the correlation of the results between the points; the geophysical prospecting is non-destructive. The method of measuring the landfill and stratum structure under the ground, in addition to the characteristics of no drilling, can also obtain continuous profile data through a wide range of measurements.
Geophysical methods investigate contaminated sites, no holes are exposed, prevent further spread of pollution, environmental protection, and no secondary pollution.
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