Indonesian Review of Physics (IRiP) p-ISSN: 2621-3761 | e-ISSN: 2621-2889 Vol.4, No.2, December 2021, pp. 55 - 60 DOI: 10.12928/irip.v4i2.4020 http://journal2.uad.ac.id/index.php/irip Email: irip@mpfis.uad.ac.id 55 Application of Self-Potential Method to Observe Groundwater Flow in Tanjungpura University Area, Pontianak Muhardi*, Kaharudin, and Mathaliul Anwar Department of Geophysics, Universitas Tanjungpura, Indonesia Email: muhardi@physics.untan.ac.id Article Info ABSTRACT Article History Received: Apr 27, 2021 Revised: Dec 28, 2021 Accepted: Dec 28, 2021 The study aims to observe groundwater flow in the Tanjungpura University area, Pontianak, West Kalimantan. Data collection applied three lines have a length of 65 m, a distance between the lines is 5 m, and a space between the porous pots is 5 m. Each line has 12 points to measure the self-potential value. The results showed that the variation of the self-potential value before the correction was -9.98 mV to 17.24 mV, while after correction, it was -10.52 mV to 16.92 mV. The self-potential distribution shows that the relatively high potential value is in the south, while the low is in the north. The distribution of self-potential values in the study location is caused by groundwater movement, which flows north. In addition, groundwater also flows to the south, especially at 20-30 m from the base station. Thus, the low self-potential value in the north can be used as a reference to identify groundwater accumulation to explore raw water in the study location. This is an open-access article under the CC–BY-SA license. Keywords: Groundwater Self-potential Pontianak To cite this article: M. Muhardi, K. Kaharudin, and M. Anwar, “Application of Self-Potential Method to Observe Groundwater Flow in Tanjungpura University Area, Pontianak,” Indones. Rev. Phys., vol. 4, no. 2, pp. 55–60, 2021, doi: 10.12928/irip.v4i2.4020. I. Introduction The groundwater has a significant role because its use is needed in everyday life. It can be found at different depths, and it depends on local geological conditions [1]. Even though its availability is abundant in the aquifer layer, information about groundwater presence is needed so that it can be used optimally. One of the information required by society for groundwater utilization is groundwater flow so that its existence can be identified. Groundwater is water that comes from layers of soil or rocks. It has an essential role in living things, including maintaining the balance of nature, maintaining the availability of raw water for domestic and industrial purposes. The aquifer layer contains alternative raw water that can be used for the community’s daily needs. As the population increases, the amount of water demand also increases. The need for clean water in Pontianak, especially at the Tanjungpura University area, is provided by Perusahaan Daerah Air Minum (PDAM). However, the availability of water managed by PDAM has a few obstacles in the dry season. The water quality sometimes decreases, for example, a change in taste to be more brackish and even salty. Therefore, it is necessary to provide information about alternative raw water sources to solve these problems. Geophysical methods have been conducted to investigate the condition and presence of groundwater. For example, groundwater conditions in coastal areas are generally carried out to determine the effect of intrusion on its presence [2]. Both unconfined and confined aquifers exist that store and stream groundwater [3][4]. So that information can be used as a reference for exploiting groundwater in domestic and industrial. One of the methods in geophysics that can be used to analyze subsurface conditions is self-potential [5]. The self-potential method is a passive method that utilizes self-potential that occurs under the earth’s surface. This method has been used to identify groundwater movement [6][7], seawater intrusion [8][9], leachate distribution [10], soil movement [11][12], monitoring contaminant [13], underground river flow [14], and water leakage through dams [15]. Self-potential on the surface is caused by the presence of electrochemical and mechanical activities [16]. This method’s use is relatively more uncomplicated [17] because the costs required are http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526275227&1&& http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526650381&1&& http://journal2.uad.ac.id/index.php/irip http://creativecommons.org/licenses/by-sa/4.0/ http://creativecommons.org/licenses/by-sa/4.0/ Indonesian Review of Physics (IRiP) Vol.4, No.2, December 2021, pp. 55 - 60 56 Muhardi, et al. Application of Self-Potential Method to Observe Groundwater …. p-ISSN: 2621-3761 e-ISSN: 2621-2889 relatively cheap. This method’s working principle measures the static stress on the earth’s surface by using two porous pots (porous electrodes) [18] connected to a multimeter. The purpose of using a porous pot is to eliminate the effect of electrode polarization during measurements [17]. This method is considered very responsive for identifying conductive objects, for example, metal minerals [19]. Based on the description above, it is necessary to determine the distribution of potential values and groundwater flow around the area of Tanjungpura University, Pontianak using the SP method. II. Theory Self-potential (spontaneous potential) occurs below the earth’s surface caused by electrochemical or mechanical activity. One of the factors that control these two activities is subsurface water. The potential is also related to the weathering of sulfide mineral bodies, mineral density of various rocks at geological contact, material organisms’ bioelectric activity, corrosion, temperature, and pressure gradient in subsurface fluids. The types of self-potential anomalies and their sources, as shown in Table 1. Table 1. The types of self-potential anomalies and their sources [16] Source Type of anomaly ▪ Sulphide ore bodies ▪ Graphite ore bodies ▪ Magnetic and other electronically conducting minerals ▪ Coal ▪ Manganese Negative [ hundreds of mV ] ▪ Quartz vein ▪ Pegmatites Positive [ tens of mV ] ▪ Fluid streaming, geochemical reaction, etc Positive/negative [ ≤ 100 mV ] ▪ Bioelectric (plants, tree) Negative [ ≤ 300 mV ] ▪ Groundwater movement Positive/negative [ up to hundreds of mV ] ▪ Topography Negative [ up to 2 V ] Four mechanisms can produce self-potential, namely as follows : a. Electrokinetic potential (streaming potential) Electrokinetic potential occurs when something moves, namely fluid (electrolyte solution) in the pores of rock. The moving fluid will produce a difference in hydrostatic pressure so that it will produce an electric potential difference which is expressed in the following equation (1) [16]. 𝛿𝑉 = 𝜇𝐶𝐸 𝛿𝑃 4𝜋𝜂 (1) Where 𝛿𝑉 is the electric potential difference, is the dielectric constant, 𝜇 is the electrolyte resistivity, 𝐶𝐸 is the electrofiltration coupling coefficient, 𝛿𝑃 is the difference in hydrostatic pressure, and 𝜂 is the dynamic viscosity of the electrolyte. Streaming potential can cause high anomaly values to the topography so that higher areas generally have more negative potential values. For an example of the self- potential anomaly produced by pumping from a well as shown in Figure 1. b. Diffusion potential (liquid junction) Diffusion potential will arise when two metal electrodes are inserted into two solutions of different concentrations. In rocks, variations in electrolyte concentrations produce a diffusion potential when there is a difference in the movement of anions and cations. c. Nerst potential Nerst potential can be found in the clay layer with a negative charge when two identical electrodes are inserted into a homogeneous electrolyte with different concentrations. In the solution, there is no difference in potential. However, at other electrodes, there is a potential difference. d. Mineralization potential Mineralization potential occurs when two metals as different electrodes are inserted into a homogeneous solution. There is a potential difference between these electrodes, which is known as electrolytic contact potential. It occurs with both the streaming and the diffusion potential. Figure 1. Example of the self-potential anomaly produced by pumping from a well [16] III. Method The study was conducted in the area of Tanjungpura University, Pontianak City, which is at coordinates 0003’08.60”S - 0003’14.10”S and 109020’56.50’’E - 109021’05.40”E. The potential value measurement applied three lines (L1, L2, L3) with a length of 65 m each. The design and measurement locations are shown in Figure 2. http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526275227&1&& http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526650381&1&& Indonesian Review of Physics (IRiP) Vol.4, No.2, December 2021, pp. 55 - 60 57 Muhardi, et al. Application of Self-Potential Method to Observe Groundwater …. p-ISSN: 2621-3761 e-ISSN: 2621-2889 Figure 2. Survey design at the study location This measurement applies a fixed base configuration using two electrodes (porous pots). The fixed base configuration has the advantage that looping is not required in measurement and the data processing is simpler. The measuring point’s potential is measured by one porous pot at the reference point (base station), and another porous pot moves along the measurement path at a fixed distance. The reference point in the mineralized zone measurement is an area not included in the mineralized zone being measured. The cable required in this configuration is relatively long because one electrode is fixed at the reference point and one of the other electrodes is measured at the farthest. An illustration of the potential measurement with a fixed base configuration and the spot axis’s schematic is shown in Figure 3. Data acquisition in the field is conducted using two methods: time and position functions. The data based on the time function is used to make corrections to the data based on the position function. This reference point is outside the survey target area and used to collect the database. This rover measurement is conducted along the measurement line with the planned distance. Each line’s potential value distribution is then plotted over an area to observe the groundwater flow in the study location. Figure 3. a) Illustration of potential measurement by fixed base configuration [20]; b) schematic of porous spot [18] IV. Results and Discussion As a function of time, the data acquisition process is conducted outside the target survey area. It is used as a place for collecting the self-potential database. The results of the self-potential variation based on the time function are shown in Figure 4. Measurements were conducted during the data acquisition process in the field at 11.54 am - 01.30 pm. This data is obtained every two minutes, assuming that it can correct the potential value obtained based on the position function. The variation of the potential value during measurement is 3.72 - 6.94 mV. The data acquisition process as a function of the position is conducted in 3 lines. The line length is 65 m, the distance between the lines is 5 m, and the space between the porous pots is 5 m. Each line is conducted at 12 points to measure the potential value. Figure 5 shows the results of the potential measurements on the three lines. The potential value on line 1 is -10.52 mV to 18.24 mV, on line 2 is -3.92 mV to 12.10 mV, and on line 3 is -7.74 mV to 2.92 mV. Figure 4. Self-potential base on daily variation a) b) http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526275227&1&& http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526650381&1&& Indonesian Review of Physics (IRiP) Vol.4, No.2, December 2021, pp. 55 - 60 58 Muhardi, et al. Application of Self-Potential Method to Observe Groundwater …. p-ISSN: 2621-3761 e-ISSN: 2621-2889 Figure 6 shows the distribution of self-potential values at the study location. This distribution is obtained by combining the self-potential values on the three lines. Based on the isopotential contour map, the variation before correction is -9.98 mV to 17.24 mV, while after correction is -10.52 mV to 16.92 mV. The interpretation process is based on the distribution of self-potential values that have been corrected for daily variations. In general, the self- potential distribution pattern shows that the relatively high potential value is in the south (shown in white to red), while the relatively low potential value is in the north (purple to blue). The distribution of self-potential values in the study location is thought to be caused by groundwater flow movement [16]. The self-potential distribution with a value of ≤ 100 mV is a value caused by fluid movement [5][21]. Figure 7 shows the groundwater flow below the surface. A black arrow symbol indicates groundwater flow prediction. The arrow’s length indicates the flow velocity based on qualitative interpretation [6]. The groundwater flows from high potential to low potential [14]. The low potential value indicates groundwater distribution to the area [22]. In general, groundwater is thought to flow to the north. In addition, groundwater also flows to the south of the study location, especially at 20-30 m from the base station. Thus, the low self-potential value in the north (purple to blue) can be used as a reference to identify groundwater accumulation to explore raw water in the study location. Figure 5. The measurement result of self-potential; Line 1 (top), Line 2 (middle), and Line 3 (bottom) Figure 6. Self-potential distribution; before daily variation corection (top) ; and after daily variation corection (bottom) http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526275227&1&& http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526650381&1&& Indonesian Review of Physics (IRiP) Vol.4, No.2, December 2021, pp. 55 - 60 59 Muhardi, et al. Application of Self-Potential Method to Observe Groundwater …. p-ISSN: 2621-3761 e-ISSN: 2621-2889 Figure 7. Prediction of subsurface groundwater flow V. Conclusion Based on the results of this study, it can be concluded that the variation in the self-potential value before correction is -9.98 mV to 17.24 mV, while after correction, it is -10.52 mV to 16.92 mV. The self-potential distribution shows that the relatively high potential value is in the south, while the low is in the north. The distribution of self- potential values in the study location is caused by groundwater movement, which flows north. In addition, groundwater also flows to the south, especially at 20-30 m from the base station. Thus, the low self-potential value in the north can be used as a reference to identify groundwater accumulation to explore raw water in the study location. VI. Acknowledgment The authors would like to thank the Laboratory of Geophysics and GIS, Faculty of Mathematics and Natural Science, Tanjungpura University, for facilitating the study and lending the self-potential equipment. References [1] R. Rustadi, G. A. Pauzi, and O. Taufik, “Investigasi Geologi dan Geolistrik Untuk Menafsirkan Keberadaan Air Tanah Dangkal di Ambarawa, Lampung [Geological and Geoelectrical Investigations to Interpret the Existence of Shallow Groundwater in Ambarawa, Lampung],” J. Teor. dan Apl. Fis., vol. 06, no. 01, pp. 109–114, 2018, doi: 10.23960%2Fjtaf.v6i1.1832 [2] M. Muhardi, F. Faurizal, and W. Widodo, “Analisis Pengaruh Intrusi Air Laut terhadap Keberadaan Air Tanah di Desa Nusapati, Kabupaten Mempawah Menggunakan Metode Geolistrik Resistivitas [Analysis of the Effect of Seawater Intrusion on the Presence of Groundwater in Nusapati Village, Mempawah Regency Using the Geoelectrical Resistivity Method],” Indones. J. Appl. Phys., vol. 10, no. 2, pp. 89–96, 2020, [Online]. Available: https://jurnal.uns.ac.id/ijap/article/view/38125. [3] D. Darsono, “Identifikasi Akuifer Dangkal dan Akuifer Dalam dengan Metode Geolistrik (Kasus : di Kecamatan Masaran) [Identification of Shallow Aquifers and Deep Aquifers with Geoelectrical Methods (Case: in Masaran District)],” Indones. J. Appl. Phys., vol. 1, no. 1, pp. 40– 49, 2016, doi: 10.13057/ijap.v6i01.1798. [4] M. Muhardi, R. Perdhana, and N. Nasharuddin, “Identifikasi Keberadaan Air Tanah Menggunakan Metode Geolistrik Resistivitas Konfigurasi Schlumberger (Studi Kasus: Desa Clapar Kabupaten Banjarnegara) [Identification of Groundwater Presence Using the Geoelectrical Resistivity Method of Schlumberger Configuration (Case Study: Clapar Village, Banjarnegara Regency)],” Prism. Fis., vol. 7, no. 3, pp. 331–336, 2019, doi: 10.26418/pf.v7i3.39441. [5] M. Arisalwadi, R. S. Cahyani, A. R. Septiana, Rahmania, and F. D. Sastrawan, “Aplikasi Metode Self-Potential untuk Pemetaan Bawah Permukaan di Area Kampus ITK [Application of Self-Potential Method for Subsurface Mapping in ITK Campus Area],” Indones. Phys. Rev., vol. 3, no. 3, pp. 124–131, 2020, doi: 10.29303/ipr.v3i3.65. [6] M. M. Nordiana, A. T. Olugbenga, M. A. Saharudin, S. Nabila, and N. El Hidayah Ismail, “The Application of 2- D Resistivity and Self Potential (SP) Methods in Determining the Water Flow,” J. Phys. Conf. Ser., vol. 995, pp. 1–9, 2018, doi: 10.1088/1742- 6596/995/1/012077. [7] H. Siswoyo, S. Harganto, F. S. H. Kusuma, R. Hisbulloh, and A. B. Pratama, “Investigation of Groundwater Potential on Agricultural Land in Bono Village, Pakel District, Tulungagung Regency by Using Self-Potential Method,” Din. Rekayasa, vol. 14, no. 2, pp. 112–118, 2018, doi: 10.20884/1.dr.2018.14.2.219. [8] M. T. Graham, D. J. MacAllister, J. Vinogradov, M. D. Jackson, and a. P. Butler, “Self-Potential as a Predictor of Seawater Intrusion in Coastal Groundwater Boreholes,” Water Resour. Res., vol. 54, pp. 1–17, 2018, doi: 10.1029/2018WR022972. [9] M. Muslim, A. Azwar, and M. Muhardi, “Identifikasi Sebaran Intrusi Air Laut di Sekitar Area Pelabuhan Internasional Kijing, Kabupaten Mempawah menggunakan Metode Resistivitas [Identification of the Distribution of Seawater Intrusion Around the Kijing International Port Area, Mempawah Regency using the Resistivity Method],” J. Fis., vol. 11, no. 1, pp. 19–26, 2021, doi: 10.15294/jf.v11i1.29138. [10] S. Rosid, R. N. Koesnodo, and P. Nuridianto, “Estimasi Aliran Air Lindi TPA Bantar Gebang Bekasi Menggunakan Metoda SP,” J. Fis. Unnes, vol. 1, no. 2, pp. 54–59, 2012, doi: 10.15294/jf.v1i2.1640. http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526275227&1&& http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526650381&1&& https://jurnal.fmipa.unila.ac.id/jtaf/article/view/1832 https://jurnal.uns.ac.id/ijap/article/view/38125 https://doi.org/10.13057/ijap.v6i01.1798 https://doi.org/10.26418/pf.v7i3.39441 https://doi.org/10.29303/ipr.v3i3.65 https://doi.org/10.1088/1742-6596/995/1/012077 https://doi.org/10.1088/1742-6596/995/1/012077 https://doi.org/10.20884/1.dr.2018.14.2.219 https://doi.org/10.1029/2018WR022972 https://journal.unnes.ac.id/nju/index.php/jf/article/view/29138 https://journal.unnes.ac.id/nju/index.php/jf/article/view/1640 Indonesian Review of Physics (IRiP) Vol.4, No.2, December 2021, pp. 55 - 60 60 Muhardi, et al. Application of Self-Potential Method to Observe Groundwater …. p-ISSN: 2621-3761 e-ISSN: 2621-2889 [11] B. Santoso, S. Subagio, M. U. Hasanah, and H. Suwarga, “Investigation Estimating of Land Movement Using Methods of Electrical Resistivity Tomography and Self- Potential in Pasanggrahan Baru Area, South Sumedang,” J. Geol. dan Sumberd. Miner., vol. 21, no. 1, pp. 33–44, 2020, doi: 10.33332/jgsm.geologi.v21i1.497. [12] B. Santoso, Setianto, I. H. Mohammad, and Risdiana, “Investigasi Gerakan Tanah dan Akuifer menggunakan Metode Electrical Resistivity Tomography di Sekitar Lereng BGG-Jatinangor,” J. Ilmu dan Inov. Fis., vol. 2, no. 1, pp. 45–52, 2018, doi: 10.24198/jiif.v2i1.15392. [13] P. Soupios and M. Karaoulis, “Application of Self- Potantial (SP) Method for Monitoring Contaminants Movement,” 8th Congr. Balk. Geophys. Soc., pp. 1–5, 2015, doi: 10.3997/2214-4609.201414147. [14] M. F. Hasan, A. Susilo, and Sunaryo, “Identification of Underground River Flow Pattern Using Self Potential (SP) and Resistivity Methods for Drought Mitigation at Druju, Sumbermanjing Wetan, Indonesia,” Disaster Adv., vol. 11, no. 5, pp. 25–31, 2018. [15] L. D. Thanh, N. C. Thai, N. M. Hung, N. C. Thang, and L. T. T. Huong, “Self-Potential Method for Detection of Water Leakage Through Dams,” Earth Sci. Malaysia, vol. 4, no. 2, pp. 152–155, 2020, doi: 10.26480/esmy.02.2020.152.155. [16] J. M. Reynolds, An Introduction to Applied and Environmental Geophysics. England: John Wiley & Sons Ltd, 1997. [17] W. M. Telford, L. P. Geldart, and R. E. Sheriff, Applied Geophysics, Second Edi. New York: Cambridge University Press, 1990, doi: 10.1017/CBO9781139167932. [18] S. B. Cabusson, A. Finizola, and N. Grobbe, “A practical Approach for Self-Potential Data Acquisition, Processing, and Visualization,” Interpretation, vol. 9, no. 1, pp. 1–21, 2021, doi: 10.1190/INT-2020-0012.1. [19] M. E. Everett, Near-Surface Applied Geophysics. New York: Cambridge University Press, 2013, doi: 10.1017/CBO9781139088435. [20] M. Dentith and S. Mudge, Geophysics for the Mineral Exploration Geoscientist. New York: Cambridge University Press, 2014, doi: 10.1017/CBO9781139024358. [21] L. O. Hutabarat, Fajriani, and R. A. Putra, “Identifikasi Pola Sebaran Air Tanah di Gampong Lengkong melalui Anomali Self-Potential [Identification of Groundwater Distribution Patterns in Lengkong Village through Self- Potential Anomalies],” J. Hadron, vol. 2, no. 2, pp. 43–48, 2020, doi: 10.33059/jh.v2i2.2626. [22] M. F. R. Hasan, T. W. Swastika, N. Martina, and L. S. Wulandari, “Identification of Groundwater Distribution Using Self Potential Method,” Appl. Res. Civ. Eng. Environ., vol. 1, no. 1, pp. 16–23, 2019, doi: 10.32722/arcee.v1i01.1953. http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526275227&1&& http://issn.pdii.lipi.go.id/issn.cgi?daftar&1526650381&1&& https://doi.org/10.33332/jgsm.geologi.v21i1.497 https://doi.org/10.24198/jiif.v2i1.15392 https://doi.org/10.3997/2214-4609.201414147 https://doi.org/10.26480/esmy.02.2020.152.155 https://doi.org/10.1017/CBO9781139167932 https://doi.org/10.1190/INT-2020-0012.1 https://doi.org/10.1017/CBO9781139088435 https://doi.org/10.1017/CBO9781139024358 https://ejurnalunsam.id/index.php/jh/article/view/2626 https://doi.org/10.32722/arcee.v1i01.1953