# Groundwater Detection Using the Pseudo-3D Resistivity Method: A History of Case Studies
## 3 Case Studies
### Groundwater Exploration Cases
#### 3.2.2 Groundwater Survey in Huarong County with Geophysical Methods  
The Huarong groundwater survey is located in the seat of the government of Huarong County. Huarong County is a county in the west of Yueyang City, Hunan Province, located in the north of Dongting Lake (Figure 2). The survey area boundary is mainly composed of rivers and lakes accumulation plain landforms, and most of the landforms are flat except for local ridges and hills. The topography is high in the northwest and low in the southeast. The previous geological survey shows that the exposed strata in the Huarong mineral water plant are simple, mainly the Baishajing Formation of Middle Pleistocene of the Quaternary and the first to fifth members of the Lengjiaxi Group of the Pre-Sinian. We have carried out the combined profiling method, resistivity sounding method, CSAMT and pseudo-3D resistivity method on the Huarong survey (in Figure 8). Since the fault development depth in this area is not large, the stratum electrical properties are not very different, and the 2D resistivity sounding exploration response ability is limited. As a result, there will be a certain degree of error in judging the position of the stratigraphic contact surface. Therefore, the pseudo-3D resistivity method is added for exploration, and it is the main basis for later drilling. A total of six survey profiles were completed in this pseudo-3D resistivity array, named as profiles L1, L2, L3, L4, L5, and L6. Figure 8: Geophysical prospecting arrays in the Huarong Survey Area. **(a)** Pseudo-3D arrays. **(b)** The combined profiling method, resistivity sounding method, and CSAMT arrays (the black cross-shaped measuring points are the combined profiling and resistivity sounding points, and the red circles are the CSAMT measuring points. The black cross-shaped measuring points are the pseudo-3D resistivity point). The profile L1 is 570 m long. The distance between two consecutive points is 30 m. The total number of measuring points is 19, and the azimuth angle is 57 degrees. In Figure 9, it is speculated that there is a NW-trending fault passing near the No. 255 measuring point. The electrical sounding results at this location obviously show an abnormal response of shallow low resistance, and that the resistivity increases significantly to 400 \(\Omega\) m at a depth of about 100 m. Therefore, it is speculated that there is a good water-conducting fracture in this part, and that there is a contact surface between the muddy and sandy strata, so it is speculated that there should be a good aquifer there. In the later period, the No. ZK03 verification hole is arranged near the No. 255 measuring point. The verification results show that the slate with high argillaceous composition is mainly at a depth shallower than 100 m, and that the sandy composition was increased below 100 m, which is an obvious shale at the contact surface. Fractures develop in the sandy stratum below the contact surface. Judging from the water output, the water exposed by the hole is mainly confined water, and the water tends to flow out from the surface of the borehole pipe. The later pumping test shows that the water output of this hole is about 410 tons, which is very high, and that the verification results are in good agreement with the inferred results. Figure 9: The resistivity sounding and pseudo\(-\)3D resistivity inversion results of L1 survey profile. (**a**) Resistivity sounding result. (**b**) Pseudo\(-\)3D resistivity result (the value of the median line in the figure is the base 10 logarithm of the resistivity. The blue lines indicate the locations of boreholes). The profile L2 is 640 m long. The distance between consecutive points are 40 m. The total number of measuring points is 16, and the azimuth angle is 105 degrees. In Figure 10, between No. 160 and No. 240 of profile L2, it is speculated that the F2 fault passes through.