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Delineation of potentially contaminated zones by electrical resistivity method in Aceh Besar, Indonesia
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.
... The survey area is close to the Krueng Raya mount and the Ie Se'uem hotspring. The tectonic setting of the area 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[11];[12]. The crest of the Barisan Range is a continuous system of axial valleys, including the Kr. ...
The objective of a geomagnetic survey is to investigate subsurface characteristic of geology, especially the weathered zone on the basis of the anomalies in the earth's magnetic field resulting from the magnetic properties of the underlying rocks. The magnetic properties of rocks called as magnetic intensity is extremely variable depending on the type of rock and the environment of the region. The result of the research shows that the local magnetic intensity varies of -697 nT and 484 nT in the study area 1 and about -697 nT and 103 nT in the study area 2 whichare indicative of weathered zones. The weathered zones were interpreted by highly magnetic contrast. The total magnetic anomaly of Blang Bintang, Aceh Besar (Indonesia) shows higher magnetic anomalies over the eastern part (area 1) and low magnetic anomalies in the western part (area 2) of the study area, which indicate the presence of weathered zonedue to the presence of sediments such as clay, gravel and schist within the zone. The study has shown that magnetic method could be used as an efficient tool for delineating weathered zone in a study area.
Leachate originating from open refuse dumpsite systems can be delineated through an integration of qualitative and quantitative methods. This study was designed to examine extent of leachate and pollution from one of the numerous open refuse dumpsites in Lagos metropolis. Qualitative assessment was determined using electrical resistivity tomography (ERT), vertical electrical sounding (VES) and induced polarization geophysical methods. Both ERT and VES methods revealed persistent low resistivity (1 - 20 Ωm) of leachate to the depth above 35 m. The two methods were projected to produce 3-D view of the site which shows a NW-SE flow pattern of the leachate and possibly, the groundwater. IP values observed over the polluted zone was −2.9 - 8 ms, indicating a sandy layer. Quantitative assessment was
achieved by analysis of geochemical substances in the water samples taken from wells and boreholes in the precinct of the dumpsite. Here, we examine the macroelements, salts (sulphates, nitrates and chlorides), heavy metals, radioactive metals contents and physical parameters of the water samples. The analyses reveal the presence of these substances in the water and their strong correlations justified the provenance as the same. As part of the quantitative evaluation, physical parameters (pH, TDS, DO, salinity, total hardness, turbidity, electrical conductivity EC and temperature) of the water samples were also determined. The samples pH plotted in the acidic domain unsuitable for human consumption. Leachate flow direction was generated from the decreasing concentration of measured parameters (geochemical elements and physicals properties) in NW-SE direction which agrees with similar flow pattern deduced from ERT results.
The electric resistivity method has been used to delineate shallow zones of ground-water contamination resulting from solid waste disposal sites. Application of this method to sites located in alluvial deposits in Iowa revealed that the degree of success of the method was directly related to the degree of contamination. A detailed investigation of the interrelationship between electric resistivity, material variation, and water quality was conducted in the alluvial deposits of the Skunk River at Ames, Iowa.
One of the primary problems in field investigations of ground-water pollution is locating the contaminant plume. Drilling of sampling holes on a hit-or-miss basis is both time-consuming and expensive. Under many subsurface conditions, surface electrical resistivity profiling can quickly and cheaply locate the general position of the plume and identify areas most feasible for sampling and monitoring. Many contaminants contain an ionic concentration considerably higher than the background level of native ground water. When such a contaminant is introduced into an aquifer, the electrical resistivity of the saturated soil is reduced. Surface electrical resistivity profiling across a suspected area can identify this reduced resistivity zone as an anomaly. The sensitivity of the method depends on relative uniformity of geology and topography as well as minimal extraneous electrical interferences. It is also essential that the “A” spacing used in the profiling procedure be carefully selected. If the resistivity contrast between contaminated and uncontaminated ground water is high, detection of at least the central part of the plume is likely within expected geologic variation. The method has been successfully used in the location of plumes from contaminants including brine, uranium reprocessing liquid wastes and landfill leachate in glacial deposits of New England.