## 2 Materials and Methods
### Two-Dimensional Resistivity Description and Data Acquisition  
The SuperSting R8/IP multielectrode resistivity provides apparent resistivity, induced polarization, and battery voltage. The measurement range is \(\pm\)10 V, and the max measuring resolution is 30 nV, depending on the voltage level. The internal transmitter is 200 W and the external 15 kW. The output current ranges from 1 to 2000 mA continuous, and it can be measured with high accuracy. The output voltage is 800 V, and the actual electrode voltage depends on the ground resistivity and transmitted current. There are eight input channels. The input gain ranges automatically and always uses the receiver's full dynamic range. The input impedance is more than 50 M\(\Omega\). The system calibration is conducted digitally by the microprocessor, based on the correction values stored in the memory. The supported configurations in manual mode are resistance, Wenner, Schlumberger, pole-dipole, dipole-dipole, and pole-pole, and any configuration can be programmed in automatic mode. Figure 4: Base map showing the locations of the 2-D resistivity tomography profiles and EM38-MK2 at the study area. The operating system is stored in a reprogrammable memory. For each measurement, full-resolution readings of the mean value and error are stored along with the user-entered coordinates and time of the day. The displayed and stored data in the memory are apparent resistivity (Ohm-m), current intensity (mA), and measured voltage (mV) for each measurement. In addition, the data can also be realtime displayed on an Android device with bright color, transmitter/receiver plot, IP curves, and contact resistance measurements. The internal SuperSting memory in the resistivity mode can store more than 79,000 measurements and can store more than 26,000 measurements in the combined resistivity/induced polarization mode. The RS-232C channel is available to dump the data from the instrument to a Windows-type computer based on the user command. The operating time of the SuperSting R8/IP depends on survey conditions and the used battery size. The internal circuitry in the auto mode can adjust the current to save energy. The operating temperature ranges from \(-5\) to \(+50\)\({}^{\circ}\)C.  
The resistivity method depends on the injection of the electrical current (I) into the ground by using two current electrodes A (source) and B (sink), and two potential electrodes M and N, computing the resulting potential differences (AV) as illustrated in Figure 5. Increasing the electrode spacing results in a deep depth of investigation, where the electric current passes through the investigated subsurface targets. By considering the subsurface structure, the depth of investigation represents about 20% to 40% of the spacing of the current electrodes [33]. The following Equations (1) and (2) give the apparent electrical resistivity of the subsurface  
\[\rho_{a}=\frac{V_{MN}}{I}\ G \tag{1}\]  
where \(G\) is the Geometrical Factor and is given by  
\[G=\frac{2\pi}{1/d_{1}-1/d_{2}-1/d_{3}-1/d_{4}} \tag{2}\]  
where \(d_{1}\), \(d_{2}\), \(d_{3}\), and \(d_{4}\) are the distances of the potential electrodes M and N from the current electrodes (A and B), see Figure 5.  
For more details about resistivity and survey deployment basics, refer to [PERSON] and [PERSON] [34] and [PERSON] [35]. In this study, the 2D electrical resistivity measurements were carried out using the SuperSting R8/IP 8 multielectrode channel resistivity and IP imaging system with 112 electrodes at one-meter spacing manufactured by AGI Advanced Geosciences, Inc., Austin, TX, USA (Figure 3A). A combination of dipole-dipole, Wenner-Schulumberger, and pole-dipole configurations at each transect of the conducted ten 2-D resistivity profiles was implemented and merged during the processing of the interpretation of resistivity data for each transect. Figure 5: Schematic diagram illustrating the basic concept of electrical resistivity measurement. The coordinates of the conducted 2-D profiles were measured using the GPS system.