- 12195 - Delineation of Potentially Contaminated Zones by Electrical Resistivity Method in Aceh Besar, Indonesia Dr. Muhammad Syukri Senior Lecturer Geophysics Section, Department of Physics Faculty of Sciences, Syiah Kuala University, Banda Aceh, Indonesia, e-mail: [email protected]Marwan Ebubakar Lecturer Geophysics Section, Department of Physics Faculty of Sciences, Syiah Kuala University, Banda Aceh, Indonesia, e-mail: [email protected]Dr. Rini Safitri Lecturer Department of Physics Faculty of Sciences, Syiah Kuala University, Banda Aceh, Indonesia, e-mail: [email protected]Dr. Rosli Saad Senior Lecturer Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail:[email protected]ABSTRACT Potentially contaminated zones are identified by the Geophysical Electrical Resistivity Survey method. The occurrences of these zones are governed by some factors like topography, lithology, fractures, faults and weathering condition. The 2D Electrical Resistivity Imaging (2-DERI) was conducted using the pole-dipole configuration in order to delineate potentially contaminated zones in Aceh Besar, Aceh, Indonesia. Interpretations of resistivity results were used to generate the profile configuration consists of low resistivity zone or weathered layer (potentially contaminated zone), and high resistivity zone or hard layer. From the interpretation result the study area is a prospective zone for intrusion of fluid contamination. KEYWORDS: Contaminated, Aceh Besar, pole-dipole, 2-D resistivity, weathered layer.
Transcript
- 12195 -
Delineation of Potentially Contaminated Zones by Electrical Resistivity Method
in Aceh Besar, Indonesia
Dr. Muhammad Syukri Senior Lecturer
Geophysics Section, Department of Physics Faculty of Sciences, Syiah Kuala University, Banda Aceh, Indonesia,
Geophysics Section, School of Physics, 11800 Universiti Sains Malaysia, Penang, Malaysia e-mail:[email protected]
ABSTRACT
Potentially contaminated zones are identified by the Geophysical Electrical Resistivity Survey method. The occurrences of these zones are governed by some factors like topography, lithology, fractures, faults and weathering condition. The 2D Electrical Resistivity Imaging (2-DERI) was conducted using the pole-dipole configuration in order to delineate potentially contaminated zones in Aceh Besar, Aceh, Indonesia. Interpretations of resistivity results were used to generate the profile configuration consists of low resistivity zone or weathered layer (potentially contaminated zone), and high resistivity zone or hard layer. From the interpretation result the study area is a prospective zone for intrusion of fluid contamination.
KEYWORDS: Contaminated, Aceh Besar, pole-dipole, 2-D resistivity, weathered layer.
The geophysical methods are a technique frequently used and most efficiently in the analysis of the potentially contaminated zone. Several investigations have demonstrated the efficiency of electrical resistivity methods for localized the contaminants area (Klefstad, 1975; Bensons et.al., 1997; Kowalska et.al., 2012; Syukri et.al., 2013; Ayolabi et.al., 2013). By this technique, subsurface characteristic is revealed which enhances better understanding of geologic condition and the other factor that influenced the measurement results. In most cases the flow of fluid contaminants in the form of the low resistivity zone are detected nearby, slightly above or penetrate to water table (Stollar and Roux, 1975; Urish, 1983; Mac Farlane et.al., 1983; Akaakpo and Igboekwe, 2011; Saad et.al., 2013; Uchegbulam and Ayolabi, 2014) (Figure 1). In this study we present the results of 2-DERI method application using ABEM SAS 4000 Terrameter system with pole-dipole array. Study area is a region in preparation for waste disposal and located adjacent to the location of settlements. We demonstrate how it is possible to separate potentially contaminated and non–contaminated zones on the base of theoretical calculation of subsurface resistivity.
Figure 1: Conceptual diagram of Potentially Contaminated Zones near a landfill area (Carpenter and Ding, 2012).
GENERAL GEOLOGY
The regional geology of Aceh Besar Quadrangle has been mapped by Bennet et al., (1981) (Figure 2). The lithology of Aceh Besar (Blang Bintang area) is dominated by Lam Tuba volcanic, composed of andesitic to dacitic volcanics, pumiceous breccia, tuffs, agglomerate and ash flows which intruded of the Seulimeum formation composed of tuffaceous and calcareous sandstones, conglomerates and minor mudstones. From upstream of the town of Jantho to downstream of the town of Indrapuri, the Pleistocene coarse-grained partly volcanic sands and gravels form a prominent
Vol. 20 [2015], Bund. 22 12197 terrace surface on either side of the Krueng Aceh. These older terrace deposits may attain a thickness of up to 75 m. The alluvium near the coast of the city of Banda Aceh extends to a depth of more than 200 m below ground level becoming thinner upstream (Bennet et al., 1981). The study area is located at Blang Bintang, near Krueng Raya mount, Aceh Besar. It forms a topographic depression, occupied by alluvial flat and low, flat-topped hills within the Barisan Range, a rugged mountain range that runs along the entire western edge of the island of Sumatra. Following closely the crest of the Barisan range is a continuous system of axial valleys, including the Krueng Tangse valleys, which marks the outcrop of the main fault line of the Sumatran fault system. This is essentially a right lateral fracture system (Katili and Hehuwat, 1967; Page et al., 1979). The topographic morphology of the Krueng Raya is subdued because the rocks are strongly fractured and altered (Nordiana et.al., 2014). Figure 2 shows the location of the study area.
Figure 2: Location map of study area at Blang Bintang, Aceh Besar, Indonesia
(Google Earth, 2015).
METHODOLOGY
2-D resistivity survey lines L1-L8 were conducted around the study area using pole-dipole array with minimum electrode spacing of 5 m for a maximum total spread length of 400 m. Terrameter ABEM SAS4000 system was used to collect the data with ES10-64C selector. 2-D resistivity data was modeled using Res2Dinv software. A least-squares inversion of the resistivity data was conducted using a finite element mesh with surface topography to generate a 2-D model of resistivity versus depth/elevation. Field resistivity structures of 2-D resistivity data was processed using RES2Dinv software (Loke and Barker, 1996) for inverse interpretation and surfer software for
Vol. 20 [2015], Bund. 22 12198 gridding, contouring and final presentation. Data was interpreted in term of relation to lateral variations of resistivity of rocks at subsurface.
RESULTS AND DISCUSSION
Figure 3-10 show the result of the inverse model resistivity of L1-L8 respectively. Generally, the study areas are divided into two main layer, low resistivity zone (alluvium with resistivity value of <20 Ohm-m) and high resistivity zone (hard layer with resistivity value of >20 Ohm-m). The low resistivity zones were delineated in the profiles interpreted as potentially contaminated zone which is permeable layer so that easier to permeation by contaminant fluid. The difference in elevation between the plan landfills and the residential area will facilitate the flow of contaminant fluids into residential area. This fact causes the groundwater in the study area would be potentially contaminated, and this low resistivity zone will be a preferential migration pathway for fluid contaminants.
Figure 3: Inverted Section of L1 Resistivity Profile.
Figure 4: Inverted Section of L2 Resistivity Profile.
Figure 9: Inverted Section of L7 Resistivity Profile.
Figure 10: Inverted Section of L8 Resistivity Profile.
CONCLUSION
The study was conducted to delineate potentially contaminated zones using 2-DERI. Overall, the study area is divided into two main layers, low and high resistivity zone. Alluvium (calyey) layer which is the conductive zone can be interpreted as contamination area. The efficiency of 2-DERI delineated the boundary of permeable layer characterization of potentially contaminated zone was confirmed, correlating the area of low resistivity.
ACKNOWLEDGEMENTS
Thanking to the Ministry of Education and Culture, Indonesia for financial support in the scheme of Decentralized Research Competitive Grants Program 2015. Special thanks are extended to the technical staffs of the geophysics laboratory and geophysics postgraduate students, School of Physics, Universiti Sains Malaysia and geophysics students, Faculty of Sciences and Faculty of Engineering, Syiah Kuala University for their assistance during the data acquisition.
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