Geoelectrical Resistivity Imaging Research Articles

Application of 2-D and 3-D Geo-electrical Resistivity Tomography and Geotechnical soil Evaluation for Engineering site Investigation: A Case Study of Okerenkoko Primary School, Warri-Southwest, Delta State, Nigeria

In the design of building structures, joint efforts must be decided to resolve the depth to competent layers across the intended site, and periodic subsidence monitoring and deformation assessment of all buildings, specifically high-rise buildings, should be a regular practice, to safeguard the durability of civil engineering structures, to avert the disastrous consequences of structural failure and collapse prevalent of late. It was this extremity that necessitated the adoption of an integrated methodology which employed DC resistivity tomography involving 2-D and 3-D techniques and geotechnical-soil analysis to evaluate subsoil properties for engineering site investigation at Okerenkoko primary school, in Warri-southwest area of Delta State, to adduce the phenomena responsible for the visible cracks/structural failure observed in the school buildings. Rectilinear set of 2-D resistivity data consisting of five (5) parallel and five (5) perpendicular lines were obtained in a 100 x 80 m2 rectangular grid using the Wenner array. Thirteen (13) Schlumberger soundings were also obtained on the site with half-current electrode separation of 200 m. The results brought to light the geological structure beneath the subsurface, which consists of four geoelectric layers identified as top soil, dry/lithified upper sandy layer, wet sand (water-saturated) and peat/clay/sandy clayey soil (highly water-saturated). The deeply-seated peat/clay materials (ρ ≤ 20 Ωm) were delineated in the study area to depths of 17.1 m and 19.8 m from 2-D and 3-D imaging respectively. The dominance of mechanically unstable peat/clay/sandy clay layers beneath the subsurface, which are highly mobile in response to volumetric changes, is responsible for the noticeable cracks/failure/subsidence detected on structures within the study site. The DC resistivity result was validated using geotechnical test of soil samples collected from boreholes covering the first 8.0 m on three of the profiles. Atterberg’s limits of the soil samples revealed plasticity indices of zero for all samples. Thus, the soil samples within the depth analyzed were representatives of sandy soil which does not possess any plasticity and their plasticity index is taken as zero. These findings apparently justify the subsoil conditions defined in the interpretation of 2-D and 3-D resistivity imaging data. 3-D images presented as horizontal depth slices revealed the dominance of very low resistivity materials i.e. peat/clay/sandy clay within the third, fourth and fifth layers at depths ranging from 5.38-8.68 m, 8.68-12.5 m and 12.5-16.9 m respectively. Hence, 3-D tomography amplified the degree of accuracy of the geoelectrical resistivity imaging. Resistivity contour maps of second, third and fourth layers for VES 1 to 13, displayed low resistivity direction predominantly towards the northeastern part of the site, and signifies that rocks within the northeastern part have low resistivity values, which connotes high porosity and establishes the groundwater flow trend in the study area. The methods employed in this study justifiably gave relevant information on the subsurface geology beneath the study site and its suitability for engineering practice. Thus, it is suggested that these methods should be appropriated as major tools for engineering site assessment projects and groundwater future studies.

Application of 2-D Electrical Resistivity Imaging, and Induced Polarization Methods for Delineating Gold Mineralisation at Felda Chiku 3, Kelantan, Malaysia

A geophysical survey has been carried out to assess the distribution of gold minerals at the Felda Chiku 3, Gua Musang district, Kelantan, Peninsular Malaysia. A 2-D geo-electrical resistivity imaging (ERI), combined with Induced Polarization (IP) method, and Oasis Montaj modelling were applied to delineate the potential conductive zones associated with sulphide mineralization. Most Peninsular Malaysia’s gold deposits occur in hydrothermal sulphides as discrete ore formations within the host rocks. A good correlation between the ERI and the IP profiles was observed during the interpretation of the model that successfully identifying the low resistive, and high chargeable sulphide zones, which correspond to the gold mineralization zones. The correlations could be linked to the conductive features at depth ranging from about 25 m - 135 m, trending along N-S directions. The study suggests further geo-electrical investigation to be carried out towards the south-western part of the area as more potential mineralized zones with N-S trends could be found in this region. Further studies would be able to give the extent of the gold deposits in Kelantan and by extension, allow for better informed mineral exploration and drilling operations to mine the gold in the region.

The Utilisation of Electrical Resistivity Imaging (ERI) for Geological Structures Mapping in Rock Mass: A Review

Electrical Resistivity Imaging (ERI) is an in-situ geophysical method widely used in environmental, engineering and hydrogeological explorations due to cost, time, and data coverage efficiency. Traditionally, geotechnical parameters such as discontinuities properties are obtained from rock samples acquired from a borehole. However, it only provides a single information point, costly and time-consuming. Thus, an approach using electrical resistivity to detect the presence of geological structure in a rock mass is an alternative method that can be applied. Discontinuities in rock mass include joints, bedding planes, blasting cracks, fractures, faults, and folds. This paper aims to present the utilisation of geoelectrical resistivity imaging for geological structures mapping in rock mass based on the review from previous research. The Electrical Resistivity Imaging (ERI) method is an effective tool to obtain structural differentiation of geological medium by interpreting 2D and even 3D electrical resistivity models. Electrical Resistivity Imaging (ERI) is an automated data acquisition system, inversion codes, non-invasive and user-friendly. The raw data received from data acquisition was analysed using Res2DINV software. The data inversion was done by applying the robust method and finite element grid to accommodate the steep topography. The data interpretation included numerical modelling to assess the suitability of all used electrode arrays in relation to the geological setting.

Geoelectrical resistivity imaging of shallow oil sands in the Eastern Dahomey Basin (SW Nigeria): Implication for heavy oil exploration and production

The Eastern Dahomey Basin hosts an extensive reserve of oil sands, a significant portion of which is unexplored and located within the southwestern part of Nigeria. Here, we use detailed outcrop mapping and Electrical Resistivity Tomography (ERT) to investigate the physical and geological characteristics of the oil sands and surrounding lithological units within the Eastern Dahomey Basin in SW Nigeria. The oil sands in the studied outcrop belong to the Turonian to Maastrichtian sandstones of the Afowo Formation which is characterized by active bitumen seepage along the length of the outcrop. The ERT results reveal lateral and vertical variability of the overburden and oil sands units in the study area. The oil sands are characterised by two unique geoelectric anomalies. Each of these anomalies has higher resistivity values (>3713 Ωm) compared to the low resistivity values of the topsoil/laterite overburden (160–2790 Ωm) and the underlying clay dominated interval (160–1576 Ωm). Importantly, the oil sands have variable thicknesses of up to 20 m and are located at shallow depths (~1–5 m below ground level). Hence, the oil sands can be exploited using surface mining techniques. This study provides a detailed assessment into the application of a non-invasive geophysical techniques for characterising oil sands near an active seep system, with implications for drawing up exploitation strategies.

Combined geophysical and geotechnical investigation of pavement failure for sustainable construction of Owo-Ikare highway, Southwestern Nigeria

ABSTRACT Very low frequency electromagnetic (VLF-EM) and electrical resistivity methods involving 54 Schlumberger Vertical Electrical Sounding (VES) and 2-D geoelectrical resistivity imaging using dipole-dipole array were utilised along unstable (US) and stable sections (SS) of Owo-Ikare highway to establish causes of its persistent failure. Engineering evaluation of eighteen soil samples from test pits excavated on selected US and SS were investigated. VLF-EM models, geoelectric sections and 2-D resistivity structures revealed existence of conductive subsurface structures, suspected weak zones beneath the US. The road pavement is constructed on poor clayey subgrade with low resistivity values (<100 Ohm-m) which precipitate instability of the highway. Subgrade soils below US have poor geotechnical properties characterized by high moisture content, liquid limit (43.6–63.8% and 20.1–25.2%), plasticity index (13.4–34.4% and 6.5–8.3%), percentage fines (40–67% and 28–30%), A-7-5 to A-7-6 clayey soils, high linear shrinkage (>10%), low compacted density, low CBR, volume changes (Mv) and impervious soils against those of SS. . Thus, deep-weathering, fractured bedrock, uneven bedrock topography with subsurface structures, water-saturated clayey subgrade and unsuitability of the soils for subgrade and subbase road construction are responsible for instability of the road. Replacement of soil beneath the unstable sections and effective drainage enhances its stability.

2D Geo-electrical Resistivity Imaging of Clay Deposit in Agbonmwoba Village, Edo State, Nigeria

This study involves delineation of clay deposits in Agbonmwoba village area of Obaretin town, Edo state using 2D geo-electrical resistivity tomography technique to image the extent and economic quantity of the deposit, in order to appraise its commercial viability. The Wenner-Schlumberger electrode configuration was employed in five different locations within the study area, and a total of ten (10) Wenner-Schlumberger soundings were acquired in the area with a spread length of 200m along each traverse. The field data was inverted using the Earth Imager 2D inversion software program. Low resistivity geologic formations (ρ &lt; 50 Ωm) were interpreted as clay formations using knowledge of regional geology of the area as reported from previous studies. Along traverses 1, 2 and 8 sampled at old Sapele road Ekiosa clay deposits was imaged at depth of 8.9-15m at lateral spread of 30m and 70m in TR1, 8.9-17.9m in TR2 and 4m in TR8. In traverses 3 and 4 sampled along Presco road in Obaretin, clay deposits were imaged at 8.9m from the surface in TR3 and 8.9-10m in TR4 at lateral spread of 70m and 100m respectively. Traverses 5, 6 and 7 were sampled at Agbonmwoba primary school, and clay deposit was imaged at 17.9-21m in TR5 at lateral spread of 80-90m, clayey sand was imaged at 7.5m (&lt; 8.9m) and sand deposit was imaged at 24.0m (&lt; 26.8m) which underlies clay. In TR6, clay deposit was imaged at 8.9m from the surface and in TR7, clay deposits were imaged in layers at profound depths &gt;30m at lateral spreads of 20-80m and 130-160m respectively. In TR8 clay deposit was imaged at 4m from the surface. In TR9 clay deposit was imaged at 8.9-17.9m at lateral spread of 90-110m and in TR10 clay deposit was imaged at 17.9-20m at lateral spread of 40m and 100-120m respectively. This results show that clay deposits imaged along traverses 1, 2, 4, 5, 9, and 10 are located at proximal depths within the subsurface and this implies that the subsurface geology distribution along these profiles is slightly homogenous in lithology, and clay deposits along these traverses are exploitable, while clay deposits along traverses 3, 6 and 8 are found at the surface (0-8.9 m) as thin clay deposits and therefore not commercially viable for exploitation. Clay deposits imaged in traverse 7 was relatively massive in size (subsurface distribution) and was observed at profound depth of 26.8-35.7m (&gt; 30m), which makes it commercially viable for exploitation compared with other traverses. The results was correlated with borehole lithologic section drilled along TR5 in the area and both sections agreed in lithologic sequence with respect to depth. Thus, 2D resistivity imaging gives a better vertical and lateral view of subsurface layers than geo-electric sections computed from 1D models, because of its ability to give a continuous record of subsurface formations at greater depth. Keywords: Electrical resistivity tomography (ERT), Clay deposit, Wenner-Schlumberger configuration, 2D resistivity pseudosection. DOI: 10.7176/JEES/10-10-06 Publication date: October 31 st 2020

Integration of 2D geoelectrical resistivity imaging and boreholes as rapid tools for geotechnical characterization of construction sites: A case study of New Akhmim city, Sohag, Egypt

Due to the increasing in the population density, the restriction of the agricultural areas and the scarcity of building's lands and their highly costs in Egypt, especially in Sohag province which led the officials and decision-markers to search for alternatives in the desert places to solve this problems. Therefore, New Akhmim area was proposed as a new site for constructing a new city. The main aim of this research is to delineate the engineering characteristic of the soil, identify of the bedrock depth and determine the subsurface structures and lithology of the investigated site. Great effort should be done to determine the depth to competent layer (bedrock) within the proposed site and correlate the results with the available boreholes. Complementary geophysical tool was implemented for the engineering designs in order to ensure stability of building construction and evade the shocking effects of building collapse later. Thus, electrical resistivity tomography (ERT) was undertaken on the present site for monitoring these subsurface engineering issues. The field geometry was made up of eight profiles using Wenner configuration. The data of the 2D resistivity tomography along these profiles with smallest electrode separation of 5 m were interpreted using Res2dinv software. The subsurface is characterized by three different resistivity zones, which were interpreted as gravel intercalated with coarse sands at the top, sand beneath it and shale beneath the sand layer. The ERT results were in consistent with the results of ten engineering boreholes drilling in the study area. The presence of shale was correlated to the cause of chronic differential settlements of some engineering structures like slickensides due to drying and wetting within the area. No serious structural features were detected as faults, karstification phenomena or caving. So the area is valid for construction proposes.

Investigating the near surface leachate movement in an open dumpsite using surficial ERT method

Geoelectrical resistivity imaging technique was conducted at Abule-egba open dumpsite, Lagos with intentions to monitor the movement of the contaminant leachate within the near surface. The two survey traverses (T1 and T2) of 2D electrical resistivity tomography were conducted using Wenner array configuration with minimum electrode spacing of 1 metre and maximum data levels of seven. The inversion models revealed the two delineated geoelectrical layers which are sandy-clay and sand units. The leachate fluids has the resistivity values of 5.75 – 10.4 Ωm at depth range of 2.5 – 4.0 metres along T1 and T2 moving from NW to the SE section. The leachate fluids are capable of polluting shallow groundwater aquifer within the study area and the residents are advised to drill deeper in the subsurface for clean and portable groundwater resources.

Investigating groundwater pollution at an open dumpsite using 2D geoelectrical resistivity imaging and vertical electrical sounding

Geoelectrical resistivity survey has been conducted within the Kurata dump site in Ota, south-western Nigeria. This present study focuses on the use of 2D resistivity imaging and Vertical Electrical Sounding to delineate conductive leachate point and degree of movement within the subsurface for conceivable groundwater pollution. The 2D resistivity survey was carried out using the ABEM Terrameter (SAS 1000/4000) System with multiple-gradient array electrode configuration. The Vertical Electrical Sounding was conducted using the schlumberger electrode configuration. One 2-D imaging profile of length 100m and one Vertical Electrical Sounding of length 200m were acquired on the established traverse. The resistivity data was inverted utilizing RES2DINV and WinResist to obtain the inverse model resistivity distribution. The 2D inverse resistivity models of the subsurface showed that the study site has a multi-layered aquifer system, four geoelectrical layers were inferred from the resistivity imaging and they are lateritic clay, clayey sand, sandy clay and coarse sand units. There is one aquifer system about 13 m which is highly polluted. The unpolluted aquifer system is localized around 19 m with inverted resistivity range 498Ωm – 685Ωm in the traverse. Also there might be conceivable sullying of deep groundwater system in the long term if appropriate moderation procedures are not thought about at the area.

2D and 3D subsurface geo-electrical resistivity imaging of contaminant plume from cassava processing mill in Uzebba Area of Edo North, Edo State, Nigeria

Electrical Resistivity Tomography (ERT) was used to map and detect the subsurface contaminant plumes from the cassava effluents in the various cassavas processing mill in the study area. The result from the 3D resistivity images showed clearly the distribution of the plumes from all the profile lines in the surveyed area. From the results it is evident that at a depth of 2.5m-21.9m with resistivity values between 6.2Ωm-13.1Ωm the plumes were observed. The results thus point out the need for environmental Education and proper management/location of cassava processing mill by the relevant agencies of Government.Keywords: Geo-electrical, Contaminant Plume, Cassava effluent, Imaging, Mill

3-D subsurface geoelectrical resistivity imaging of contaminant plume from cassava processing mill in Ozalla Area of Edo North, Nigeria

Electrical Resistivity Tomography (ERT) was used to map and detect the subsurface contaminant plumes from the cassava effluents in the various cassavas processing mill in Ozalla Area of Edo North, Edo State, Nigeria. The result from the 3D resistivity images shows clearly the distribution of the plumes from all the profile lines in the surveyed area. From the results it is evident that at a depth of 2.5 m - 21.9 m with resistivity values between 6.2 Ωm -13.1 Ωm the plumes were observed. The results thus point out the need for environmental Education and proper management/ location of cassava processing sites by the relevant agencies of Government.Keywords: Geoelectrical, Mill, Contaminant Plume, Cassava effluent, Imaging

Applying of High-Resolution Geophysical Techniques for Drainage Investigations at El-Basateen Cemetery Area, Cairo, Egypt

Due to the collapse of some cemetery in Basateen area, South of Cairo, this paper presents the application of geoelectrical resistivity sounding and imaging, as well as ground penetrating radar techniques for outlining the reasons and the presence of draining water and groundwater at the investigated area. A Vertical Electrical Sounding (VES) survey was performed at 3 points through the studied site to investigate the vertical extent of the subsurface sequence and the saturation levels. A total of 9 Dipole-Dipole imaging profiles were surveyed to determine the lateral distribution of saturation of drain water and infiltrated groundwater, and a total of 6 GPR profiles with 100- and 200- MHz antennae were surveyed to evaluate and determine the depth and the degree of saturation of the subsurface layer/s. The qualitative and quantitative interpretation of the acquired VES's and dipole-dipole imaging profiles showing easily the levels of saturations at the studied site. From the interpretation of GPR profiles, it was possible to locate and determine the saturated zones and the level of the groundwater through the area. The radar signals are penetrated enough and enabled the identification of the subsurface reflectors. The results of GPR, VES's and Resistivity imaging showed a good agreement. The integrated interpretations were verified by local geology and information from several bores. Also, the study was supported by a chemical analysis from the drain water and Ein El-Seera spring (close to studied site), to determine the main source of the drain and infiltrated water at the studied site.

Geoelectrical characterisation of basement aquifers: the case of Iberekodo, southwestern Nigeria

Basement aquifers, which occur within the weathered and fractured zones of crystalline bedrocks, are important groundwater resources in tropical and subtropical regions. The development of basement aquifers is complex owing to their high spatial variability. Geophysical techniques are used to obtain information about the hydrologic characteristics of the weathered and fractured zones of the crystalline basement rocks, which relates to the occurrence of groundwater in the zones. The spatial distributions of these hydrologic characteristics are then used to map the spatial variability of the basement aquifers. Thus, knowledge of the spatial variability of basement aquifers is useful in siting wells and boreholes for optimal and perennial yield. Geoelectrical resistivity is one of the most widely used geophysical methods for assessing the spatial variability of the weathered and fractured zones in groundwater exploration efforts in basement complex terrains. The presented study focuses on combining vertical electrical sounding with two-dimensional (2D) geoelectrical resistivity imaging to characterise the weathered and fractured zones in a crystalline basement complex terrain in southwestern Nigeria. The basement aquifer was delineated, and the nature, extent and spatial variability of the delineated basement aquifer were assessed based on the spatial variability of the weathered and fractured zones. The study shows that a multiple-gradient array for 2D resistivity imaging is sensitive to vertical and near-surface stratigraphic features, which have hydrological implications. The integration of resistivity sounding with 2D geoelectrical resistivity imaging is efficient and enhances near-surface characterisation in basement complex terrain.

Assessment of soil salinity using electrical resistivity imaging and induced polarization methods

2D imaging involving geoelectrical resistivity and time domain induced polarization has been used to assess the spatial variability of the physical properties of subsurface soil in Covenant University Farm, southwestern Nigeria. Apparent resistivity and chargeability of the induced polarization effect were concurrently measured along six traverses using Wenner array. The observed data were processed to produced 2D inverse models of the subsoil resistivity and chargeability. Soil samples were also collected and analysed for conductivity and salinity levels. The results show that the salinity level in the soil is within the range for normal soil and therefore healthy for plant growth. The inverse model sections were integrated with the laboratory test to qualitatively assess the salinity, degree of compaction, and thickness of the soil in the farm. Other petrophysical properties such as clay volume, moisture content and organic matter which are related to soil conductivity were also inferred. The study demonstrates that geoelectrical resistivity imaging can be a useful tool for effectively assessing the variations of soil condition in large tracts of land for precision agriculture. Key words: Soil salinity, 2D imaging, geoelectrical resistivity, induced polarization, precision farming.

Application of geoelectrical resistivity imaging and VLF-EM for subsurface characterization in a sedimentary terrain, Southwestern Nigeria

Geoelectrical resistivity imaging and very-low frequency electromagnetic (VLF-EM) geophysical techniques were integrated to characterize the subsurface as part of preliminary investigations for groundwater resource assessment, development, and management in a sedimentary terrain, southwestern Nigeria. Six parallel 2D geoelectrical resistivity field data were collected using Wenner array; the VLF-EM data were equally collected along the same traverses. In addition, four vertical electrical soundings (VES) were conducted on the site using Schlumberger array to provide layering information. The plots of filtered in-phase and quadrature components of the VLF-EM data as well as their corresponding Fraser and Karous-Hjelt pseudo-sections are presented. The observed apparent resistivity data for the 2D traverses were inverted to produce 2D inverse model resistivity and then collated to 3D data set, which was inverted to obtain 3D inverse model resistivity of the subsurface. Iso-resistivity surfaces for 750, 1,000, and 1,500 Ωm extracted from the 3D inverse model show the 3D distribution of these resistivities. High-resistivity layer at depth range of 10.2–16.4 m and thickness ranging from 11.0 to 21.0, which overly the aquifer unit, delineated in the VES and 2D/3D resistivity models could not be distinctly discriminated in the Fraser and Karous-Hjelt pseudo-sections of the VLF-EM data. However, some conductive linear anomalies thought to be fissures or joints, which could serve as the main conduit path for groundwater recharge, were delineated in the Fraser and Karous-Hjelt pseudo sections. Thus, the use of geoelectrical resistivity or VLF-EM technique alone is inadequate to characterize the subsurface features in the study site; consequently, the integration of 2D and 3D resistivity imaging with VLF-EM technique enhanced the degree of reliability of the subsurface characterization in the study site.

Effectiveness of 3D geoelectrical resistivity imaging using parallel 2D profiles

Acquisition geometry for 3D geoelectrical resistivity imaging in which apparent resistivity data of a set of parallel 2D profiles are collated to 3D data set was evaluated. A set of parallel 2D apparent resistivity data were generated over two model structures. The models, horst and trough structures, simulates the geological environment of a weathered profile and refuse dump site in a crystalline basement complex, respectively. The apparent resistivity data were generated for Wenner-alpha (WA), Wenner-beta (WB), Wenner-Schlumberger (WSC), dipole-dipole (DDP), pole-dipole (PDP), and pole-pole (PP) arrays with minimum electrode separations (a = 2, 4, 5 and 10 m ) and inter-line spacing (L = a, 2a, 2.5a, 4a, 5a and 10a). The 2D apparent resistivity data for each of the arrays were collated to 3D data set and inverted using a full 3D inversion code. The 3D imaging capability and resolution of the arrays for the set of parallel 2D profiles are presented. Grid orientation effects, which decrease with decreasing inter-line spacing, are observed in the inversion images. Inter-line spacing of not greater than four times the minimum electrode separation gives reasonable inverse models. The resolution of the inverse models can be greatly improved if the 3D data set is built by collating sets of orthogonal 2D profiles. Key words: Acquisition geometry, parallel 2D profiles, 3D surveys, geoelectrical resistivity, 3D imaging, inversion.

Anomaly effects of orthogonal paired-arrays for 3D geoelectrical resistivity imaging

A series of 2D apparent resistivity data were generated over two synthetic models representing different geological or environmental conditions commonly associated with geophysical applications for hydrogeological, environmental and engineering investigations. The apparent resistivity data were generated for the following arrays: Wenner-alpha (WA), Wenner-beta (WB), Wenner–Schlumberger (WSC), dipole–dipole (DDP), pole–dipole (PDP) and pole–pole (PP) arrays, which were paired such that apparent resistivity data for 2D profiles in a parallel direction are obtained with a particular array type and those in a perpendicular direction are observed with a different array type. The 2D apparent resistivity data for the orthogonal paired-arrays were then collated to 3D data sets. The effectiveness and efficiency of the orthogonal paired-arrays in 3D geoelectrical resistivity imaging were evaluated by determining the mean absolute anomaly effects of the electrode configurations on the synthetic models. The results show that DDP–PDP, DDP–PP, DDP–WSC, PDP–PP, DDP–WB, PDP–WB and WB–WSC orthogonal paired-arrays produced higher anomaly effects on the synthetic models. This indicates that DDP–PDP, DDP–PP, DDP–WSC, PDP–PP, DDP–WB, PDP–WB and WB–WSC orthogonal paired-arrays are more sensitive to 3D features of the geologic models than the other orthogonal paired-arrays investigated.

Tracing subsurface migration of contaminants from an abandoned municipal landfill

This paper aims at determining of inorganic leachate contamination for a capped unsanitary landfill in the absence of hydrogeological data. The 2D geoelectrical resistivity imaging, soil physicochemical characterization, and surface water analysis were used to determine contamination load and extent of selective heavy metal contamination underneath the landfill. The positions of the contaminated subsoil and groundwater were successfully delineated in terms of low resistivity leachate plumes of Zn > Pb > Cr > Cu. Taking into consideration poor physical and chemical characteristics of the local soil, these metals first seem to be attenuated naturally at near surface then remobilize unavoidably due to the soil acidic environment (pH 4.2-6.18) which in turn, may allow an easy washing of these metals in contact with the shallow groundwater table during the periodic fluctuation of the Kelang River. These heavy metals are believed to have originated from hazardous industrial waste that might have been illegally dumped at the site.

Electrical Resistivity of Subsurface: Field and Laboratory Assessment

The objective of this paper is to study the electrical resistivity complexity between field and laboratory measurement, in order to improve the effectiveness of data interpretation for geophysical ground resistivity survey. The geological outcrop in Penang, Malaysia with an obvious layering contact was chosen as the study site. Two dimensional geoelectrical resistivity imaging were used in this study to maps the resistivity distribution of subsurface,whereas few subsurface sample were obtained for laboratory advance. In this study, resistivity of samples in original conditions is measured in laboratory by using time domain low-voltage technique, particularly for granite core sample and soil resistivity measuring set for soil sample. The experimentation results from both schemes are studied, analyzed, calibrated and verified, including basis and correlation, degree of tolerance and characteristics of substance. Consequently, the significant different between both schemes is explained comprehensively within this paper.

Anomaly effects of arrays for 3d geoelectrical resistivity imaging using orthogonal or parallel 2d profiles

The effectiveness of using a net of orthogonal or parallel sets of two-dimensional (2D) profiles for three-dimensional (3D) geoelectrical resistivity imaging has been evaluated. A series of 2D apparent resistivity data were generated over two synthetic models which represent geological or environmental conditions for a typical weathered profile and waste dump site, respectively, commonly associated with geophysical applications for hydrogeological, environmental and engineering investigations. Several minimum electrode separations and inter-line spacing were used to generate the apparent resistivity data for each electrode array with a view to determining the optimum inter-line spacing relative to the minimum electrode separation. The 2D apparent resistivity data for each array were collated to 3D data sets. The effectiveness and efficiency of the arrays in 3D geoelectrical resistivity imaging were evaluated by determining the mean absolute anomaly effects of the electrodes arrays on the synthetic models. The anomaly effects observed in dipole-dipole (DDP), pole-dipole (PDP) and Wenner-Schlumberger (WSC) arrays were generally larger than that observed in other arrays considered. The least anomaly effect on the synthetic models was observed in pole-pole (PP) array. This indicates that DDP, PDP and WSC arrays are more sensitive to 3D features. In all the arrays, the anomaly effects observed in the data set generated using the conventional square grids were slightly larger than those from parallel or orthogonal 2D profiles. This slight increase is attributed to the increased data density and is insignificant when compared with those of parallel and orthogonal 2D profiles. Hence, the use of parallel or orthogonal 2D profiles for 3D geoelectrical resistivity survey is effective. Key words: Anomaly effects, orthogonal/parallel 2D profiles, 3D surveys, geoelectrical resistivity imaging, measurement effectiveness