Resistivity Anomalies Research Articles

Magnetotelluric imaging of the shallow-seated magma reservoir beneath the Karadağ stratovolcano, Central Anatolia, Turkey

The central Anatolian Volcanic Province encompasses many volcanoes elongated in a northeast-southwest direction. Karadağ is one of the dormant Quaternary stratovolcanoes of the region at the southern end of the province. We acquired broadband magnetotelluric (MT) data in the period range 0.0001–251 s at 124 locations to obtain a three-dimensional electrical resistivity model to identify the associated magmatic-hydrothermal system beneath the Karadağ stratovolcano. The resistivity model provides evidence for low resistivity anomalies that include (1) a near-surface localised low resistivity (~ 20 Ωm) zone situated directly beneath the crater centre that is interpreted to be lacustrine sediments of an extinct crater lake, (2) a shallow low resistivity (~ 10 Ωm) zone of probable hydrothermal alteration in the eastern part of the stratovolcano and (3) a deep and large zone of low resistivity (<10 Ωm) attributed to a shallow-seated magma reservoir at a depth of 3 to 7 km beneath the volcanic edifice. A few hundred meters thick resistive surface layer corresponds to the Karadağ adakitic volcanics (i.e., andesites and dacites), and a resistive basement representing Precambrian to Mesozoic high- and medium-grade metamorphic rocks on the flanks is observed in the resistivity model.

Numerical simulation of deep-hole resistivity anomaly caused by drilling construction in Xinfengjiang geoelectric station

The Xinfengjiang reservoir in Guangdong Province, is one of the large reservoirs that have triggered earthquakes of magnitude greater than 6. Numerous earthquakes have occurred since the impoundment of the reservoir, making it one of the most active seismic zones in south China. In 2015, a set of deep-hole resistivity anomalies was observed in the Heping geoelectric station in Dongyuan county, located near the Xinfengjiang reservoir. After a field investigation, we found that a planned well drilling construction of new measuring channels was being carried out during that corresponding period of time. After careful comparison and analysis on the basis of the collected raw data, we had a reason to believe that drilling construction, rather than the inducement of the Xinfengjiang reservoir, was the main culprit for those unusual georesistivity values. So as to verify the above conjecture, we constructed a series of 3D finite element models based on the geological and hydrological information around Heping station and analyzed the drilling disturbances, respectively. Some significant conclusions were finally drawn according to the precise numerical simulation. This study gives a good example by combining numerical simulation with engineering practice as a way to understand the root cause of georesistivity anomalies in reality.

The Structure of Permafrost in Northern West Siberia: Geophysical Evidence

The permafrost of Arctic West Siberia stores extremely rich resources of hydrocarbon fuels that remain a key energy source and an important element of the global economy. A large amount of natural gas in permafrost is bound in gas hydrates which may become an alternative fuel of the future. Shallow subsurface in the permafrost area of northern West Siberia has been studied by transient electromagnetic (TEM) soundings to estimate the permafrost thickness and to detect faults as channels for fluids and heaving features as possible indicators of gas hydrate accumulations. The shallow transient electromagnetic (sTEM) surveys were conducted in discontinuous and continuous permafrost at two sites in northern West Siberia (the northeastern Yamal Peninsula and the southern Gydan Peninsula), with a focus on the vicinities of lakes and cryogenic landforms (frost mounds). The sTEM method resolves well the heterogeneous permafrost structure, with faults, numerous unfrozen zones (taliks), and frost mounds marked by resistivity and seismic anomalies. Some lakes are located above faults, and their origin may be related to deformation, whereas the frost mounds may mark deep-seated fluid dynamic processes. Local thickening of permafrost may be associated with the presence of gas hydrates. The detected features may trace gas migration pathways and reveal possible sites of gas emission.

The role of electrons during the martensitic phase transformation in NiTi-based shape memory alloys

Nickel-titanium (Ni50Ti50)-based alloys are the most important representatives of the class of shape memory alloys. However, the role of electrons in this transformation leading to the shape memory effect is not yet overall understood. Here we show how the alloy composition affects resistivity, Hall coefficient and Seebeck coefficient as well as Terahertz reflectance during the martensitic phase transformation. Remarkably, the charge carrier density obtained by Hall measurements is reduced by almost one order of magnitude in the martensitic phase compared to the austenitic phase, and its reduction starts well before the actual transformation. This reduction of the charge carrier concentration is also seen in the obtained Terahertz spectra. Together with this reduction of the charge carrier density, the charge carrier mobility increases at the phase transformation. This means that neither additional scattering events nor altered electron-phonon coupling play a dominant role for the interpretation of the anomaly in the electrical resistivity. We further utilize these transport data to deduce the electronic entropy contribution to this phase transformation and compare it to the total entropy contribution obtained by heat capacity measurements. The electronic entropy contribution directly scales with the martensitic start temperature and reaches over 30% of the total entropy contribution for compositions close to equiatomic Ni50Ti50. The experimental data points towards a partly transfer of electron density from the free electron gas (austenite) to the bonding (martensite). We interpret this in terms of a formation of a charge density wave phase that would fit to both findings, the strong reduction of charge carriers, as well as the high electronic entropy contribution to this phase transformation.

Athermal ω Phase and Lattice Modulation in Binary Zr-Nb Alloys.

To further explore the potential of Zr-based alloys as a biomaterial that will not interfere with magnetic resonance imaging (MRI), the microstructural characteristics of Zr-xat.% Nb alloys (10 ≤ x ≤ 18), particularly the athermal ω phase and lattice modulation, were investigated by conducting electrical resistivity and magnetic susceptibility measurements and transmission electron microscopy observations. The 10 Nb alloy and 12 Nb alloys had a positive temperature coefficient of electrical resistivity. The athermal ω phase existed in 10 Nb and 12 Nb alloys at room temperature. Alternatively, the 14 Nb and 18 Nb alloys had an anomalous negative temperature coefficient of the resistivity. The selected area diffraction pattern of the 14 Nb alloy revealed the co-occurrence of ω phase diffraction and diffuse satellites. These diffuse satellites were represented by gβ + q when the zone axis was [001] or [113], but not [110]. These results imply that these diffuse satellites appeared because the transverse waves consistent with the propagation and displacement vectors were q = <ζ ζ¯ 0>* for the ζ~1/2 and <110> directions. It is possible that the resistivity anomaly was caused by the formation of the athermal ω phase and transverse wave. Moreover, control of the athermal ω-phase transformation and occurrence of lattice modulation led to reduced magnetic susceptibility, superior deformation properties, and a low Young’s modulus in the Zr-Nb alloys. Thus, Zr-Nb alloys are promising MRI-compatible metallic biomaterials.

Strain-relaxation induced transverse resistivity anomaly in epitaxial films through lithography engineering

The exotic transverse resistivity in magnetic materials has received intense research because of possible new emergent physics. Here, we report the strain-relaxation induced transverse resistivity anomaly in Mn2CoAl epitaxial films through lithography engineering. The anomalous Hall resistivity decreases from 0.48 to 0.17 μΩ cm at 10 K when the widths of the Hall bar decreases from 40 to 1 μm, and the temperature dependence of reverses for the 1.4 μm deep-etched samples. Importantly, Hall resistivity anomalies appear in the 1 μm-wide and 1.4 μm-wide deep-etched Hall bar samples, which can be well explained by the two-channel transport mechanism. We believe that these observations can be attributed to the strain relaxation effect when the Hall bar width is narrowed to around 1 μm. Our work shows that the induced strain relaxation can possibly lead to the alternation of the materials’ electronic structure, and the size effect should be considered when the sample size is reduced to about 1 μm.

Хавчуу Ам Ордын Судалгаанд Геофизикийн Аргуудыг Хэрэглэсэн Байдал

When comparing the exploration results thus far from Khavchuu with those of known mineralisation and mineral deposits in the region. The occurrence of north to north-east trending, low angle, thrust faults which also coincide with resistivity and chargeability highs, magnetic lows, As anomalies and positive Au chip samples, issimilar to that observed and documented at Boroo. The resistivity anomalies generated have been interpreted as being associated with an area of silicification or quartz veining and from the dipole-dipole results these seem to occur as shallowly dipping structures similar to those hosting the Boroo mineralisation. The chargeability highs could be interpreted as regions of sulphide mineralisation and coincide with many of the anomalous areas again as with Boroo, although in the southern area the near surface chargeability low becomes a chargeability high with depth suggesting a degree of sulphide destruction during weathering in the upper regions. Magnetic lows could be interpreted again as zones of weathering and associated destruction of magnetite in granites or sulphides in mineralised regions. Assuming that any mineralisation at Khavchuu will exhibit a similar refractory component, this broad weathering could be of significant economic importance.

Imaging the heat source of the Kangding high-temperature geothermal system on the Xianshuihe fault by magnetotelluric survey

The Kangding geothermal field along the Xianshuihe fault is a typical high-temperature geothermal system with an enormous capacity for geothermal power generation. The Xianshuihe fault is a major active sinistral strike-slip fault in eastern Tibet Plateau, where the fault splits into three parallel branches near Kangding. We collected data from 17 magnetotelluric stations in the Kangding geothermal system. After data processing, the dimensionality of the subsurface structure was qualitatively estimated using the phase tensor. The electrical resistivity model inverted with ModEM shows the Kangding geothermal system from the surface to a depth of 20 km, which correlates closely with the near-surface geology. The synthetic tests confirmed that the main resistivity anomalies identified in the electrical resistivity model were robust. There are several significant low resistivity anomalies of less than 10 Ωm beneath the Kangding geothermal system. The cap rock and liquid-dominated reservoir can be interpreted as shallow conductive zones. The conductors beneath the Kangding geothermal field at a depth of 10 km are interpreted as an underlying zone of partial melt, which provides fluids and heat for the geothermal system. The partial melt fractions are in the range of 4–19%, confirming that there is a magmatic heat source beneath the Kangding geothermal system.

Detecting resistivity and induced polarization anomalies of galena veins in the presence of highly chargeable and conductive geological units at Daryan barite deposit in Iran

Assessment of resistivity and induced polarization (IP) data for metallic sulfide ore explorations is considered a routine task in the mining industry. The success in these surveys would be challenging if the sulfide ore lies within conductive and chargeable geological units. In this study, the resistivity and IP data of the Daryan area in northwestern Iran were examined for the detection of high-grade galena veins hosted by the Kahar Formation, a complex geological formation with several conductive and chargeable geological units. To facilitate the geophysical interpretations, a simple approach was adopted to solve the problem, and it was shown that a combination of correct geophysical modeling and approximate clustering of physical properties can help to check and revise (if necessary) the geological model or geophysical interpretations. In the Daryan area, the barite mineralization had high resistivity and low IP anomalies. More importantly, it was found that the highest IP and the lowest resistivity values were not the responses of galena mineralization but the graphite-rich shale. Thus, in complicated situations, the data should be treated and interpreted carefully because the “rules of thumb” may not work. This fact highlighted that prioritization of anomalies based on geophysical models alone is not an appropriate strategy in mineral exploration, and the interpretations must always be evaluated with geology. Moreover, it was discussed that both volume concentration and style of conductive minerals can be vital for creating elusive electrical responses, thus caution should be taken while interpreting electrical models in areas with complicated geology.

Methane Occurrence and Quantification in a Very Shallow Water Environment: A Multidisciplinary Approach

AbstractIn the last decades, geological degassing in shallow marine environments has been recognized as a significant contributor to atmospheric methane, hence to the global‐warming potential. Especially in shallow water environments, a proper assessment of the distribution, quantification and migration pathways of methane within the sediments is fundamental to help forecasting the amount that could leak and eventually reach the atmosphere. Traditionally, velocity anomalies from seismic data are the ones used to assess the occurrence of gas and its concentration. However, in shallow‐waters (&lt;30 m), the post‐critical conditions make the near‐surface velocity estimation from P‐wave reflections extremely challenging, requiring an integrated approach. Here, we propose an original joint analysis of seismic data and geophysical logs, together with information from drilling reports, with the aim of characterizing and quantifying the gas along two crossing multichannel seismic profiles in the Northern Adriatic Sea, a very shallow marine basin where methane occurrence within the sedimentary succession is widespread. We estimated the gas distribution from resistivity anomalies, which are correlated with the seismic response associated with the presence of gas through the signal frequency content. Our results show a different concentration pattern in the two seismic profiles, revealing that gas is both diffuse ad concentrated in local accumulations, in agreement with the gas‐related features already identified on the seismic data. Gas concentration appears to be locally associated to the tectonic features identified in the area, indicating that faults act as preferential conduits for gas migration, locally reaching the seafloor and seeping in the water column.

Alloying-driven transition between ferromagnetism and antiferromagnetism in UTGe compounds: UCo1−xIrxGe

The evolution of magnetic properties of isostructural and isoelectronic solid solutions of the superconducting itinerant $5f$-electron ferromagnet (FM) UCoGe with antiferromagnet (AFM) UIrGe was studied by magnetization, AC susceptibility, specific heat, and electrical resistivity measurements of a series of $\mathrm{U}{\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x}\mathrm{Ge}$ compounds in polycrystalline and single-crystalline form at various temperatures and magnetic fields. Both the weak FM and superconductivity in UCoGe were found to have vanished already for very low Ir substitution for Co $(x=0.02)$. The AFM of UIrGe is gradually suppressed. This is documented by a rapid decrease in both N\'eel temperature and the critical field of the metamagnetic transition with decreasing Ir concentration, which both tend to vanish just above $x=0.8$. The section of the $T\text{\ensuremath{-}}x$ phase diagram in the range $0.02\ensuremath{\le}x\ensuremath{\le}0.8$ is dominated by a correlated paramagnetic phase (CPM) exhibiting very broad bumps in temperature dependencies of $b$-axis magnetization and specific heat developing with increasing $x$. For $x\ensuremath{\ge}0.24$, wide peaks appear in the $c$-axis thermomagnetic curves due to AFM correlations which may eventually lead to frozen incoherent spin configurations at low temperatures. The CPM is also accompanied by specific electrical resistivity anomalies. The $T\text{\ensuremath{-}}x$ phase diagram determined for the $\mathrm{U}{\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x}\mathrm{Ge}$ compounds contrasts with the behavior of the related $\mathrm{U}{\mathrm{Rh}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x}\mathrm{Ge}$ system, which was reported to exhibit an extended concentration range of stable FM in Rh-rich compounds and a discontinuous transformation between the FM and AFM phases at a critical Rh-Ir concentration. The striking difference is tentatively attributed to (a) the instability of tiny U moment in the weak itinerant FM UCoGe induced by substitutional disorder at already very low Ir doping, (b) the rather stable U moment in URhGe formed by much less delocalized $5f$ electrons assisted by weakly varying lattice parameters of $\mathrm{U}{\mathrm{Rh}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x}\mathrm{Ge}$ compounds.

Characterization of the Dynamics of Leachate Contamination Plumes in the Surroundings of the Hulene-B Waste Dump in Maputo, Mozambique

The contamination of areas around solid urban waste dumps is a global challenge for the maintenance of environmental quality in large urban centres in developing countries. This study applied a geophysical method (electrical resistivity) to identify leachate contamination plumes in the subsoil and groundwater, as well as to describe their temporal dynamics (2020 and 2021) in the surroundings of the Hulene-B waste dump, Maputo, Mozambique. Eight 400 m electrical resistivity profiles were performed, four profiles in January 2020 and four profiles in May 2021 overlapped, and the data were inverted with RES2D software. The electrical resistivity models predominantly indicate an E-W movement of large contamination plumes that are successively diluted with saturated media and groundwater, creating zones of less resistive anomalies (&lt;4.2–8.5 Ω·m) possibly contaminated at the two analysed seasons, between 2020–2021. The thickness of the contamination plumes was higher in summer (2020) for profiles 1 and 2, and we associate it with the production and migration mechanisms of leachate that are intense in the hot and rainy season. Southwest of the dump, profile 4b showed the propagation of anomalous areas on the surface and at depth, which are associated with the production of leachate resulting from the continuous decomposition of waste that is continuously deposited in a new area southwest of the dump, thus generating a slow and continuous migration of leachate at depth, mainly in winter (2021). The spatial distribution of contamination plumes during both seasons was reduced significantly farther away from the waste deposit, revealing the attenuating effect of groundwater and lithological substrate (Profile 3).

Assessment of landslides in Bosnia and Herzegovina and Serbia: A Geoscientists Without Borders project

A severe storm caused floods and landslides in the Balkan region in May 2014. In response to the disaster, geophysical and geotechnical surveys were organized as a Geoscientists Without Borders (GWB) project of SEG. It took place in eight landslide-prone areas in Serbia and Bosnia and Herzegovina in three phases in 2015 and 2016. The seismic and electric resistivity surveys were conducted, and the results were interpreted in conjunction with the geotechnical inspection. The surveys identified the size of a potential landslide layer by the S-wave velocity distribution and, in particular high-risk locations, by electric resistivity anomalies. This interpretation enhanced the geotechnical observation. From the result, several countermeasures were recommended to suit the budgetary restrictions of local governments. Among them, the survey results in the Lopare locality have been presented as an example. The project was organized by the Association of Geophysicists and Environmentalists of Serbia involving many scientists, engineers, students, government staff, and local communities. As well as technical achievements, the significance of the project included providing students with opportunities to have practical experience of geophysical surveys and to learn outside the classroom and bringing together participants from different racial, political, religious, and educational backgrounds. All were made aware of the importance of humanitarian expert work. We have assessed the effectiveness of the GWB project using the guidelines of the Organization for Economic Co-operation and Development, Development Assistance Committee. One important outcome of the assessment was that such a volunteer geoscientific survey cannot stand alone. It would be more effective if incorporated in overall recovery and prevention programs.

Integrated Geoelectrical Resistivity Method for Environmental Assessment of Landfill Leachate Pollution and Aquifer Vulnerability Studies

Leachate plumes from landfills are a major source of pollution in Nigeria, especially in urban areas. Assessing leachate contamination in the subsoil is considered a complex process that needs detailed field measurement to accurately define the extent of contamination. To ascertain the extent of pollution of the subsoil and groundwater sources which were reportedly contaminated by leachate plumes from an old dumpsite located in Osubi town, an integrated geo-electrical method involving 1-D vertical electrical sounding (VES) and 2-D, 3-D ERT techniques were employed. Orthogonal set of 2-D apparent resistivity data was collected in a 100 × 50 m2 rectangular grid around the dumpsite, using the Wenner array. Two years later, three (3) 2-D resistivity imaging profiles were also recorded in time-lapse mode at the dumpsite to monitor the possible effects of attenuation on the leachate over time. Ten (10) VES data were also acquired and used along with the 2-D imaging data. 2-D apparent resistivity data were inverted with Dipprowin software program. The orthogonal set of 2-D lines of apparent resistivity was merged into 3-D data and inverted with RES3DINV program to create a 3-D subsurface resistivity model. Geological models observed from 2-D and 3-D resistivity inversion revealed low resistivity values in the order ρ Ω·m which is indicative of leachate plumes in the saturation zone (pore water). The 2-D resistivity-depth sections imaged low resistivity leachate plumes at the near surface (ant within the first, second and third layers at depth ranging from 0.00 - 2.50 m, 2.50 - 5.38 m and 5.38 - 8.68 m respectively. Thus, leachate contamination clearly increased with depth beyond the depth of first and second aquifers in the area which implies that available groundwater for domestic use is already contaminated with leachate from the dumpsite. Leachate contaminant-depth map estimated for the second geoelectric layers for VES 2, 3, 4, 7, 8, 9, and 10 shows that the second layer has been invaded completely by leachate contamination up to 6.5 m depth. 2-D apparent resistivity data acquired two years after show lower resistivity anomalies of the leachate plume caused by time-lapse attenuation effect on the observed resistivity of the leachate. This indicates that the leachate plume has become more conductive and toxic to the environment. The Longitudinal conductance map of the area shows that the aquifer protective capacity of this area is weak (0.1 - 0.19 Mho) thus, aquifers in the area are prone to pollution from the dumpsite. The three techniques used in this study (2-D, 3-D ERT and 1-D VES) fitly provided crucial information on the degree of contamination caused by the landfill leachate plume. Therefore, it is advisable to implement an environmental remediation and leachate management program.

Frequency domain electromagnetic and electrical resistivity geophysical investigation of tar sands deposits in the Ijebu Waterside area, Eastern Dahomey Basin, southwestern Nigeria

The use of electromagnetic conductivity and electrical resistivity geophysical techniques has been employed in this study to investigate the occurrence, thickness, and spatial distribution of bitumen deposit around Makun-Omi in the Ijebu Waterside area of southwestern Nigeria. Subsurface apparent conductivity distribution data obtained using Geonic 34-3 equipment along fifteen traverses which sounded from different depths of 7.5, 15, 30 and 60 m at inter-coil separation of 10, 20 and 40 m in vertical and horizontal coupling modes and ground resistivity distribution measurements, obtained using Geopulse Tiger Allied resistivity meter at fourteen Vertical Electrical Sounding (VES) stations, were processed and employed to characterize the subsurface in terms of tar sands distribution. The conductivity and resistivity distribution in the form of a 3D earth model, iso-depth maps, 2D sections generated from the processed conductivity and resistivity data indicate relatively low conductivity &lt;20 mS/m and high resistivity &gt;1300 Ωm values around tar/bitumen impregnated sands which mostly occurred in the southern part of the study area. Clearly defined conductivity and resistivity anomalies which delineate the lateral and vertical occurrence of tar impregnated sands underscore the efficacy of integrating electromagnetic and electrical resistivity geophysical techniques to identify occurrence of economic deposits of tar sands in parts of southwestern Nigeria.

The geophysical signature of a continental intraplate volcanic system: From surface to mantle source

The structure of continental intraplate volcanic systems — which occur far from tectonic boundaries, unlike the majority of Earth's volcanism — is enigmatic and not fully understood, as are the underlying mechanisms responsible, due in part to a lack of high-resolution geophysical data. Central Mongolia contains Quaternary–Neogene aged alkaline basalt flows and volcanic cones, thousands of kilometres from active tectonic margins, in addition to an abundance of geochemical and petrological data — making this a natural laboratory to study intraplate volcanism. Using a recently collected, high-resolution, multi-scale, magnetotelluric dataset acquired across central Mongolia, we generate and analyze electrical resistivity models of the structure beneath the Tariat and Chuluut volcanic zones with the goal of imaging the volcanic system from surface to mantle source. The models reveal narrow, subvertical, lower resistivity anomalies in the middle-upper crust that are conspicuously located beneath surface expressions of volcanism. The lower crust (depths of 25–50 km) is characterized by the widespread distribution of isolated low-resistivity zones. A local low-resistivity zone is imaged in the mantle (depths of 60–90 km) above a broad, homogenous, doming low-resistivity feature. Considering the available evidence, we propose that the low-resistivity anomalies in the middle-upper crust are the remnant signatures of past transient magma pathways (or collection of pathways), caused by metasomatic alteration during the ascent of hot magmatic fluids. The lower crustal anomalies are interpreted to be domains of saline fluids in a thermally perturbed lower crust. In the mantle, the low-resistivity structure is explained by a broad mantle upwelling and thermal anomaly with a local zone of low-percent partial melt — the source for intraplate volcanism. The geophysical images are consistent with geochemical and petrological evidence from erupted lavas that indicates a single common mantle source region, limited crustal contamination, and rapid direct ascent, making crustal magma storage unlikely. Thus the geophysical models show remarkable and unique translithospheric images of a continental intraplate volcanic system, from surface to mantle source, with the results relevant to other continental regions.

Urban landfills investigation for leachate assessment using electrical resistivity imaging in Johor, Malaysia

The use of the electrical resistivity imaging (ERI) approach has expanded dramatically in engineering applications over the years due to the efficiency of the technique in terms of time, expense, and data coverage. The assessment was carried out using ERI to assess the landfill leachate's pollution level at Simpang Renggam, Johor, Malaysia. The ERI survey was carried out in the research region, utilizing the ABEM Terrameter LS 2 equipment using the Schlumberger electrode configuration. Besides, seven (7) parameters of leachate characterization such as Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD5), Suspended Solid (SS), Power of Hydrogen (pH), Ammonia Hydrogen (NH3-N), Turbidity and Biodegradability Ratio (BOD5/COD) were also performed to identify and evaluate the current leachate condition of the landfill. Furthermore, the study, which involves the measurement of the apparent resistivity of the subsurface materials were able to determine the existence of chemical pollutants in the soil at 1.5 m to 4.0 m depth, with special reference to the chemically apparent resistivity linked with the low resistivity anomalies of 1 – 10 Ωm. Based on the investigations conducted, the physiochemical and microbial analysis of the Simpang Renggam leachate site was found to be 1633 mg/L (Chemical Oxygen Demand), 137.41 mg/L (Biological Oxygen Demand), 359.8 mg/L (Suspended Solid), 7.61 (Power of Hydrogen), 385.29 (Ammonia Hydrogen), 117.65 (Turbidity) and 0.07 (Biodegradability Ratio) which shows that all of the parameter's value exceeded the value as stated in the local standard which is Environmental Quality Act (1974) except for the pH value which is within the range value as stated in the standard. The leachate from dumps was thought to arise due to system failures in accepting and managing trash, which was exacerbated by the recent high rains. In hindsight, the ERI result was practical for identifying leachate and, therefore, can benefit the authorities in immediate action to halt the extensive water disturbance at the research region.

Delineation of necroleachate pathways using electrical resistivity tomography (ERT): Case study on a cemetery in Brazil

Cemeteries can be considered as potential sources of soil and groundwater contamination in burial sites where there is no collection and treatment system for necroleachate, an effluent rich in organic matter and inorganic elements produced during the decomposition of corpses. Brazilian cemeteries are mostly located in the interior of cities, where collective or family deposits with the absence of necroleachate collection devices predominates. The tropical climate, the recurrence, and the distribution of corpses, combined with soil permeability, are decisive elements in the percolation and distribution of necroleachate in the subsurface. An important tool for the diagnosis and evaluation of organic and inorganic contamination in soil and shallow aquifers is geophysics, through research methods related to the contrast of physical properties in the presence of this type of contaminant. This research consists of a geophysical investigation in a medium-sized cemetery in the southeastern Brazil, using the DC resistivity method using three different electrodes arrays: Wenner, Schlumberger and Dipole-Dipole. Additionally, results were combined with the history of burials in the 5 years prior to the geophysical study. The 2D inversion models confirm the presence of low resistivity anomalies related to the presence of ionic compounds. 3D visualization models with results of the three acquisition arrays are compared to the amount of burial by compartmentalized areas of the cemetery, which clearly reveals a relationship of areas with high and recent recurrence of burials and areas of low resistivity in depth. The results do not present significant differences between arrays, with similarities in terms of location and dimension of the most significant areas of low resistivity.

Application of square array configuration and electrical resistivity tomography for characterization of the recharge area of a karst aquifer: A case study from Menekşe karst plateau (Kocaeli, Turkey)

Groundwater recharge characteristics of a karst plateau which plays an important role in the recharge of a regionally important highly productive karst aquifer was revealed by combined application of Electrical Resistivity Tomography (ERT) and Square Array Configuration methods. A forward model of targeted karst features and geological structures constructed prior to ERT survey enabled a more comprehensive and more reliable interpretation of the real data. The transition between the anomalies resulted from different structures were sharp and the artifacts were distinct in the inverted sections of the synthetic data whereas a smoother transition was observed between different types of anomalies in the real data and the artifacts were harder to be distinguished from the anomalies related to the real subsurface structures. The air-filled karst shafts and caves inside the Triassic aged marbles resulted in high resistivity anomalies approximately between 3000 and 6000 Ωm. On the other hand, clay rich soil zones and water bearing fissure networks led to low resistivity anomalies ranged between 100 and 400 Ωm. ERT survey detected various well karstified fast recharge zones and indicated that the network of karstified zones dipped through northeast (NE). The method also pointed out that nonkarstified fissure networks and thick layers (10–15 m) of clay rich soil zones leading to a lagged recharge existed some regions in the plateau. Square Array Configuration survey signified that dominant fracture zones existed in SW-NE and NW-SE directions and indicated that the faults and fractures in the region (SE-NW and SW-NE oriented) extended deep inside the karst aquifer. Overall evaluation of ERT and Square Array Configuration results enabled the determination of fast and slow recharge zone distribution throughout the karst plateau and thus, distinguished the highly sensitive regions in karst plateau for groundwater contamination. Finally, this study showed that combined application of Square Array Configuration and ERT surveys could successivley characterize groundwater recharge in a complex karst terrain and could constitute a supportive method for revealing the spatial vulnerability differences of a karst region to groundwater contamination.

AQUIFER VULNERABILITY EVALUATION IN SOUTHWESTERN NIGERIA FROM AHP-GODT MODEL USING GEO-ELECTRICAL DERIVED PARAMETERS

&lt;em&gt;The study aimed to determine the exposure levels of the subsurface aquiferous layers, owing to the alarming rate of contamination of the groundwater within 8.150 &lt;sup&gt;0&lt;/sup&gt;N - 8.156 &lt;sup&gt;0&lt;/sup&gt;N and 4.244 &lt;sup&gt;0&lt;/sup&gt;E - 4.248 &lt;sup&gt;0&lt;/sup&gt;E. Thus, aquifers' overlying layers, resistivity, and thickness anomalies were determined to generate an aquifer vulnerability map. A multi-criteria decision method of estimated Groundwater confinement, Overlying strata, Depth to Aquifer, and Topography index approach was implemented. Schlumberger's Vertical Electrical Sounding technique was implemented to acquire 30 Vertical Electrical Sounding points under a maximum half-current electrode separation (AB/2) of 65 m. IP2Win geophysical software packages were used to analyze the varying layer resistivity, depth, thickness, and also the sounding curves of the study area. The 2D model revealed a maximum of four geo-electric layers. The layers' resistivity and thickness ranges are clayey silt topsoil (52.5-1104 Ωm; 0.5-9.59 m), weathered layer (10.3-804 Ωm; 0.6-12.1 m), fractured basement (5.5-50832 Ωm; 6.7-18.1 m) and fresh basement (8.3-27348 Ωm; infinity m). On the Groundwater Overlying Strata Depth to Aquifer and Topography model scale, the area is generally characterized by the moderate vulnerability. Implying here is that aquifers have a moderate protective capacity in which the overlying strata above the aquifer are mostly impermeable layers (clay and silt) of high thickness and low porosity.&lt;/em&gt;