Two-dimensional Electrical Resistivity Tomography Research Articles

Geophysical and Sedimentological Characterization of Oil Sand Deposit in Part of Eastern Dahomey Basin Southwestern Nigeria

Unconventional oil is the group name given to unconventional petroleum deposits such as oil sands and heavy oils. Oil sand, commonly referred to as tar sand or bituminous sand is a sandstone formation impregnated with viscous bitumen. This study utilized the two-dimensional electrical resistivity imaging technique to characterize oil sand and validate its true resistivity value and sedimentological analysis to evaluate the physical properties of the oil sand deposit. The two-dimension electrical resistivity imaging data acquisition was done along seven profiles systematically in a grid format using dipole-dipole electrode configuration and processed using the RES2DINV software. Fresh samples were collected from three points within the study area for grain sizes and textural properties analysis. The result of the 2-D ERI in the study area showed two to three geoelectric layers and the oil sand being the second layer as evident in the 3-D model obtained from the systemic data acquisition procedure. The resistivity obtained for oil sand in the study area range between 2,500 Ωm to 105 Ωm which validates the report of high resistivity value of oil sand in the study area. The sedimentological analysis showed that the sediments in the study area are of medium sand moderately sorted sand grain and leptokurtic to mesokurtic sand suggesting unimodal and bimodal parent source.

Detection of subsurface cavities in the structurally bounded Labe prefecture area, Republic of Guinea using two-dimensional electrical resistivity tomography (ERT)

ABSTRACT This study is conducted within the Gambia River Basin Development Organization Energy Project (OMVG) framework. The construction of a high voltage interconnection network fed by a hydropower station to supply electricity to OMVG Member States was done on stable ground. During the installation pits for the pylons in Labé Prefecture, Republic of Guinea, cavities were discovered in the geological formations during the initial planned route. Structurally, the study area is bounded by two major faults to the east and west of northeast direction. The geomorphology is made up of a central plateau, intermountain depressions, piedmont plains, talwegs, and glacis. Geological investigations were obtained by a geophysical Two-dimensional Electrical Resistivity Tomography (ERT) method. The results show that the synthetic lithological profile from top to base was sandy-clayey soil, hard cuirass, and a layer of gravel followed by a mottled zone comprising an indurated part and an imbibed part just before the source rock. The cavities were observed probably because of the dissolution of certain minerals constituting the weathering crust due to the infiltration, underground waters, and the seasonal variation in the level of the surface watercourses. Geophysical results showed a very good agreement with the visual observations.

Electrical Resistivity Tomography Investigation of Permafrost Conditions in a Thermokarst Site in Fairbanks, Alaska

<abstract> <p>The degradation of permafrost poses severe environmental threats to communities in cold regions. As near-surface permafrost warms, extensive topographic variability is prevalent in the Arctic and Sub-Arctic communities. Geologic hazards such as thermokarst are formed due to varying rates of permafrost degradation, resulting in ground subsidence. This gradual subsidence or abrupt collapse of the earth causes a danger to existing infrastructure and the economic activities of communities in cold regions. Understanding the causes of thermokarst development and its dynamics requires imaging its underground morpho-structures and characterizing the surface and subsurface controls. In this study, we conducted a two-dimensional (2D) electrical resistivity tomography (ERT) survey to characterize the permafrost conditions in a thermokarst prone site located in Fairbanks, Alaska. To increase the reliability in the interpretability of the ERT data, borehole data and the depth-of-investigation (DOI) methods were applied. By using the 2D and three-dimensional (3D) ERT methods, we gained valuable information on the spatial variability of transient processes, such as the movement of freezing and thawing fronts. Resistivity imaging across the site exhibited distinct variations in permafrost conditions, with both low and high resistive anomalies observed along the transects. These anomalies, representing taliks and ice wedges, were characterized by resistivity values ranging from 50 Ωm and above 700 Ωm, respectively. The results from this study showed the effectiveness of ERT to characterize permafrost conditions and thermokarst subsurface morpho-structures. The insights gained from this research contribute to a better understanding of the causes and dynamics of thermokarst, which can be instrumental for engineers in developing feasible remedial measures.</p> </abstract>

GEOELECTRIC SIGNATURES FROM A LEACHATE PLUME MAPPED FROM A BASEMENT COMPLEX TERRAIN IN AKURE, NIGERIA

In this study, we investigated the implications of a leachate plume within an aquifer system, unravelling the intricate dynamics that govern contaminant transport and dispersion. An integrated approach of geophysical investigations is used to establish the impact of an open-waste disposal site around Aromed, in a part of Akure, in the Precambrian Basement Complex of Southwestern Nigeria. Investigations using eight (8) Vertical Electrical Sounding (VES) and Double-Dipole Resistivity Tomography (ERT) along two (2) traverses were conducted. The geoelectric interpretation and the inverted two-dimensional electrical resistivity tomography (ERT) images provided insights into the underlying geological composition, identifying three distinct units: the topsoil, the weathered column, and the fractured Basement/fresh Basement bedrock. The geoelectric tomography structures in the 2-D interpretation reveal that the dumpsite area exhibits low apparent resistivity estimated to be between 12 to 71 ohm-m in both the topsoil and the weathered column aquiferous zone. These values closely agree with results from the geoelectric sections, which range between 11 - 68 ohm-m, respectively. The relatively low apparent resistivity results are suggestive to be due to the presence of leachate’s chemical composition from the open waste disposal sites, which are suspected to be generated from the dissolution of ions of iron and other conductive minerals producing the leachate plume. The probable leachate depth of migration as revealed by the 2-D tomography structures varies from about <1 – > 14 m beneath the dumpsites. The leachate migration, which is structurally controlled, has a southward flow, majorly in the orientation with the observed structures. The subsurface depression-relief is also attributed to influence the direction of leachate flow. In conclusion, it is suggested that groundwater in the aquiferous zones in the vicinity of the dumpsites have entered a significant pollution level; hence water in the aquifer is not safe for consumption.

Groundwater Investigation Using Electrical Resistivity Imaging Technique in Western Ramadi, Iraq

The two-dimensional electrical resistivity imaging technique was used to examine groundwater in western Ramadi. The survey was performed with a factor (n) and a-spacing values of 6 and 5 m, respectively. The inverse models clearly show the resistivity variation between the anomalous parts of the water table and all the sediments. The vertical extension of the saturation sediments is between 1.5–9.5 m, which is identical to the groundwater level in the three existing wells located in the University of Anbar, with an area of 7 kilometers and an area of 18 kilometers. The extreme thickness of the water saturation layer was determined to be about 10.5 meters. It was concentrated in gypsum and mudstone soils with secondary gypsum and siltstone, considered the upper components of the Injana Formation at the University of Anbar. At 7 Kilometer area which starts from a depth of 1 m to depths of up to 12 m, it is also considered a groundwater reservoir. While 18 Km area is considered to have dry soil and the groundwater in it is far from the surface at 12 m depth.

Numerical modelling of cut-slope stability in the Lesser Himalayan terrain of west-central Nepal

Area development without due consideration of geological factors has led to recurrent slope failures within the Lesser Himalayan Zone thereby rendering socio-economic impacts. This issue is well exemplified by cut-slopes in major highways of Nepal traversing through a diverse range of rocks and soils. The study has focused on addressing the stability challenges posed by highly vulnerable excavated cut-slopes with particular attention given to a debris cut-slope considered as a model for this study is located in the Lesser Himalayan terrain of west-central Nepal. The cut-slope model is analyzed by numerical modellings through both the limit equilibrium method (LEM) and finite element method (FEM). The study further evaluated the underlying causes of these failures to recommend the options for remedial measures. Data acquired from two-dimensional electrical resistivity tomography (2D-ERT), multi-channel analysis of surface waves (MASW), and laboratory testing were integrated into numerical modelling and simulation. The results showed that the lower slope below the natural benching is stable whereas the upper failed slope is unstable due to reduced gravitational loading. In LEM, factors of safety (FoS) range from 0.77 to 0.89 for cut-slope angles of 70° and 60° whereas the FoS in modified slopes (50° and 40°) were slightly greater than 1 which ranged from 1.01 to 1.18 and indicated marginal stability. Application of 25 mm diameter soil nails, each measuring 6 m in length and spaced at 2 m intervals with tensile and plate capacity of 125.6 kN, bond strength of 75.4 kN/m, and 80% of nail length have produced FoS of 1.30 or greater in LEM and FEM which is acceptable values specified by EM 1110-2-1902 and IS 456 2000 for end-of-construction and multistage loadings.

Hydrogeophysical Investigation in Parts of the Eastern Dahomey Basin, Southwestern Nigeria: Implications for Sustainable Groundwater Resources Development and Management

Geoelectrical resistivity measurements were conducted in five locations within the eastern portion of the Dahomey basin for the purpose of subsurface evaluation and detecting saturated zones. The locations are Covenant University (L1), Bells University (L2), Oju-Ore-Ilogbo Road (L3), Obasanjo-Ijagba Road (L4), and Iyana Iyesi (L5). The study was carried out to avert the common challenges of drilling low-yield groundwater boreholes in the area. A total of 30 Vertical Electrical Soundings (VES) and five two-dimensional Electrical Resistivity Tomography (ERT) data sets have been acquired along the study areas. The geoelectrical resistivity results were integrated with the borehole logs to generate the spatial distribution of the subsurface lithologies in the area. The delineated subsurface lithologies include the topsoil (lateritic clay), clayey sand, sandy clay, fine silty sand, coarse sand, and shale/clay units. The fine silty sand and coarse sand units were identified as the two main aquifer units within the area. The depths to the upper aquifer unit in the area include 31.7–96.7 m, 38.5–94.0 m, 30.7–57.5 m, 39.1–63.4 m, and 46.9–57.5 m for locations L1, L2, L3, L4, and L5, respectively. At the same time, the depths to the lower aquifer unit in the area include 43.4–112.7 m, 52.2–108.0 m, 44.2–72.5 m, 53.7–78.5 m, and 63.5–72.9 m for locations L1, L2, L3, L4, and L5, respectively. The estimated hydraulic parameters for both aquifers show they are highly productive with mean porosity, mean hydraulic conductivity, and mean transmissivity of 20–22%, 12.4–17.0 × 10−2 m/s, 1.56–2.18 m2/s for the upper aquifer, and 48–50%, 371–478 × 10−2 m/s, 50.00–62.14 m2/s for the lower aquifer. By focusing on these aquifer systems during exploration, sustainable groundwater resources can be secured, providing relief to homeowners within the study area who might otherwise face the frustration of drilling unproductive and low-yield boreholes. However, it is crucial to consider the presence of sub-vertical faults in the study area, as these faults can significantly impact groundwater development and management. These sub-vertical structural faults may lead to changes in the permeability, hydraulic conductivity, and transmissivity of the delineated aquifers, affecting their productivity across the divide and ultimately influencing the overall water availability in the area. Careful consideration of these geological factors is essential for effective aquifer management and sustainable groundwater utilisation.

Understanding Shallow Basaltic Aquifer System Near West Coast of Maharashtra, India

Two-Dimensional (2D) Electrical Resistivity Tomography (ERT) and geophysical logging and injected tritium tracer studies with hydrogeological tests were carried out at selected location in an area of 5 km2 near the coastal region of Tarapur, Thane district, Maharashtra. The area is in basaltic terrain, overlain by thin cap of alluvium formation and receives an annual rainfall of about 2000 mm. An integrated investigation method was adopted to delineate the subsurface lithological variations, understand the existing aquifer system up to 25 m depth, evaluate aquifer properties, recharge potential and also to monitor the groundwater flow characteristics. The investigation results showed a variable thickness of weathered zone of 1-3 m, existence of two basalt flows, low vertical natural recharge, high transmissivity, high hydraulic conductivity and high groundwater flow rates. The results also depicted that a combination of hydrogeological tests along with resistivity and tracer investigation is an effective tool in mapping and characterizing the shallow potential groundwater aquifer zone in Deccan traps. The integrated study carried out in the coastal area provided detailed subsurface information useful for planning specific water conservation strategies for sustainable groundwater supply. Keywords: Deccan Traps, ERT, Tritium Tracer, Recharge, Groundwater Flow

Using 2D Electrical Resistivity Imaging to Evaluate Soil Investigations in Palm Towers Site of Al-Muthana Airport, Baghdad, Iraq

For engineering site investigations at Al-Muthana Airport land in Baghdad, Iraq, the two-dimensional electrical resistivity imaging method was used. The site investigation is important for figuring out the subsoil profile, weak spots, and groundwater level of possible production sites in the area. Wenner-Schlumberger array was used to survey six electrical resistivity spreads with a total length of 600m, a length of 100m acquired for each survey line, with a distance of 1m between electrodes. The depth of the investigation was 23.5 for each surveyed line. Robust inversion and model techniques showed that the values of resistivities were not all the same in the six inverted models. Based on the inverted models, the depth of the groundwater was found to be between 3 – 4 meters at the first site and about 4.5 meters at the second site, which is 1 m deeper than what was found in the geotechnical investigation report. Further, the top 1-1.5 m of sediments have different components, hardness, and moisture levels. So, the current study stated that this layer should be picked up and compacted before the foundation is built. Far down 1.5m, the layer seems to be wet, so a layer with low permeability must be added around the foundation.

Combined application of electrical resistivity tomography and multi-channel analysis of surface waves methods in the tunnel detection: A case study from Kocaeli University Campus Site, Turkey

In this study, two-dimensional electrical resistivity tomography (ERT) and one-dimensional multi-channel surface waves analysis (MASW) methods conducted on the surface were used to examine the location of a creek drainage tunnel constructed for the campus road and its relationship with the surrounding geological units in the Kocaeli University campus site results are presented. As it is known, geophysical studies conducted from the surface are generally applied in terms of feasibility and to determine the geological problems in the route of tunnels before the tunnel construction. Geophysical studies revealing the tunnel and associated underground characteristics in a completed tunnel are very limited. Therefore, this study aims to describe the general character of the tunnel and its surroundings in the subsurface, with measurements made by using surface geophysical methods (ERT and MASW) over the tunnel. In the ERT studies, four different arrays were examined to resolve this problem. These are, respectively; Wenner-alpha, −beta, −gamma and Schlumberger. On the tunnel problem here, a possible model similar to the geological structure dominated by the marl layers in the region was synthetically designed with these arrays. In this study, the effectiveness of all these arrays against the problem was tested. Then, by evaluating the data collected from the field, the appropriate array testing was examined for the real problem. In the context of these studies, the results of the MASW studies conducted between 24 and 46 m of the ERT line were compared with the ERT data to reveal the geological phenomena in the tunnel and its vicinity. The resistivity values (ρ) in the 2D electrical resistivity models obtained from ERT have values of ρ > 80 Ωm in the tunnel section and ρ < 55 Ωm in the materials surrounding the tunnel. The medium-high resistivity values characterize the earthfill layer. In MASW studies, it was revealed that shear wave velocity (Vs) values in the tunnel were lower (<250 m/s) and higher (250 and 500 m/s) in the materials surrounding the tunnel. Deep below the tunnel and in the northeastern part of the field, the ground has relatively higher shear wave velocities (Vs > 400 m/s). Because of the comparison of ERT and MASW results, it was revealed that both methods showed good agreement in terms of tunnel depth and size. While the different sequences used in the ERT study generally provided successful results in identifying the tunnel, different model results were revealed in the surrounding earthfill, weathered and intact marl layers. The MASW results, on the other hand, gave more successful results than expected in determining the location of the tunnel. Because of the comparison of both methods, it has been shown that the use of the ERT and MASW methods together can provide more effective results in examining the location of buried tunnels and their relationship with the surrounding geological units.

Use of geoelectrical resistivity method for detecting near-surface groundwater potential zones at Riyadh city, Saudi Arabia

Six profiles of the two-dimensional multi-channel electrical resistivity tomography (ERT) were conducted at the northwest part of Riyadh city using the SYSCAL Pro system with a dipole–dipole configuration to detect the near-surface water-bearing potential zones. The ERT field measurements use a series of regularly placed electrodes to measure the electrical resistivity along the profile. The results of the inverse models are displayed as cross-sections of the true resistivity distribution of the subsurface with depth along with each profile. The two-dimensional (2-D) inversion results of the electrical resistivity data indicate three geoelectric zones; 1st zone of low resistivity values (<100 Ω.m), representing two groundwater-bearing potential zones from top to bottom as follows; the 1st one extends downwards to 10- and 15-meters depth, while the 2nd zone spreads between 15- and 30-meters depth, 2nd zone with resistivities ranging from 100 to 1000 Ω.m, which represent the highly fractures limestone; the 3rd zone with resistivities greater than 1000 Ω.m reflecting compacted limestone rocks. It is noticed also some of the low resistivity pockets are isolated through the subsurface geoelectrical cross-section indicating the presence of voids and/or cavities. Based on these results, the investigated area is considered as one of the promising zones for groundwater supply in Riyadh city and its future urbanization expansion projects. This can be accessed by drilling wells down to a depth of 50 m for groundwater extraction.

A multiparametric approach for rejuvenation of the Gaurikund geothermal spring system in the Northwest Himalayan region

The Gaurikund town falls on the way of the famous trekking route to Kedarnath that faced the wrath of the 2013 flood disaster. This fateful event severed more than 5000 casualties, demolished several infrastructures, and shifted the course of Gaurikund spring from its original position. Nevertheless, the Gaurikund geothermal spring system located in the Himalayan Geothermal Belt of the Garhwal region is preeminent for religious beliefs, balneotherapeutic values and a gateway to delve within the geothermal and hydrological characteristics of the area. In this perspective, restoration of Gaurikund geothermal spring system becomes a necessity. A multiparametric approach comprising geospatial, geology, hydrochemistry and geophysics has been used to study and justify these aspects at Gaurikund. The geological studies infer that the geothermal spring gets recharged by the steep, southerly dipping joints in granite gneiss. Subsequently, the deep percolated water heats up due to the high geothermal gradient and then emerge along the Vaikrita Thrust and its sympathetic minor fault-thrust system by advection. Moreover, four spring outlets are inventoried, with discharge varying from 7.46 to 95.54 L/min. The normal emissivity model uses the pre and post-disaster satellite data and generates maximum kinetic temperature images, showing a positive correlation between land surface temperature and spring discharge. Two-dimensional Electrical Resistivity Tomography (Schlumberger, Wenner and Gradient configurations) survey revealed two low resistivity zones proximal to the geothermal spring on the right bank of the Mandakini river. The engineering interventions carried out by bank protection and construction of small gully plugs in the catchment area is recommended along Gaurikund-Sonprayag section on the right bank of Mandakini river.

Electrical resistivity application for road failure assessment at an industrial hub in Ogun State, Nigeria

This paper employs the geophysical surveying technique of two-dimensional electrical resistivity imaging (2D ERI) for gaining insights into the causes of incessant road failures being encountered at an industrial hub, along Idiroko Road, in Ota, Ogun State, Nigeria. These utilises occupation of three traverses, each of 100 m for the 2D ERI, constituting a control of a stable road portion, and a stable and unstable portions of a crucial turning along the dual carriage highway of Idiroko Road in Ota. The obtained 2D ERI measurements were rendered to the processing of the RES2DINV software for the derivation of the 2D resistivity inverse model. Results show that the portions of the roads that are stable exhibited higher values of apparent resistivity compared to portions exhibiting frequent road failures. Ensuing sub-surface layer characterisations by the 2D ERI revealed geo-electrical layers exhibiting permeable soil formations that allow water to percolate in the stable portion of the road while the unstable portion depicted presence of water in an impermeable soil formation. These engender recommendations for road construction durability issues that can culminate into system of sustainable road network at the studied industrial hub location in Ogun State, Nigeria.

Evidence from the Vredefort Granophyre Dikes points to crustal relaxation following basin-size impact cratering

The timescale of the modification stage of basin-sized impact structures is not well understood. Owing to ca. 10 km of erosion since its formation, the Vredefort impact structure, South Africa, is an ideal testing ground for deciphering post-impact modification. Here, we present geophysical and geochemical evidence from the Vredefort Granophyre Dikes, which were derived from the - now eroded - Vredefort impact melt sheet. The dikes have been studied mostly in terms of their composition, while the timing and duration of their emplacement remain controversial. We examined the modern depth extent of five dikes, with three from the inner crystalline core of the central uplift, and two from the boundary between the core and the supracrustal collar of the central uplift, using two-dimensional electrical resistivity tomography. We found that the core dikes terminate near the present erosion surface (i.e., <5 m depth). In contrast, the dikes at the core-collar boundary extend to a depth ≥ 9 m. These observations suggest that the core dikes are exposed near their lowermost terminus. In addition, we obtained bulk geochemical composition of the dikes, finding that the andesitic composition phase is present in the core-collar dikes that is not found in the core dikes. The presence of this phase indicates the episodic emplacement of impact melt into subvertical crater floor fractures.We conclude that the dike formation was protracted and occurred over a time span of at least 104 years. The sequential formation of the Vredefort Granophyre Dikes points to horizontal extension of crust below the impact melt sheet above a kinematic velocity discontinuity, a crustal instability resulting from the dynamic collapse of the transient cavity.

Preliminary Assessment of the Soil Foundation Characteristics Utilizing the 2D Resistivity Imaging and Down-Hole Seismic Refraction Techniques: A Case Study in Tenth of Ramadan City, Egypt

Two-dimensional electrical resistivity imaging and seismic refraction, in the form of down-hole survey, were applied to delineate the subsurface section and elastic moduli and identify geotechnical characteristics of subsurface materials in the 10th of Ramadan industrial area, Cairo, Egypt. The results of four 2-D profiles of electrical resistivity, in the form of dipole–dipole and Wenner configurations, revealed that the subsurface section contains two main geo-electrical layers; the first is made of sand, some silt, and gravels, reflecting low resistivity values ranging from 25 to 65.5 ohm m. This layer is overlying a high resistivity layer (65.5 to135 ohm m), corresponding to medium to coarse sand, with gravel and calcareous materials. It is worth noting that that the down-hole technique was used to measure velocities of P and S waves in order to derive the low strain dynamic elastic properties, such as Poisson’s ratio, Shear modulus, stress ratio, concentration index, N-value, and the ultimate and allowable bearing capacities of the subsurface soil, down to an approximate depth of 30 m in the borehole at the site. In addition, the Vs30 value was calculated and revealed that the soil is categorized as a NEHRP class (D). Furthermore, the results of geotechnical parameters and elastic moduli were found to be realistic and sensible for the purposes of engineering constructions and imply that the soil in the study area is characterized by fairly to moderately competent quality. A new empirical correlation is proposed between the obtained Vs and resistivity values, where Vs = 1.0302 ρ + 172.74.

Coupled geophysical and geochemical approach to detect the factors affecting the groundwater salinity in coastal aquifer at the area between Ras Sudr and Ras Matarma area, South Sinai, Egypt

The integration of geophysical and hydrochemical approaches successfully reflects the hydrogeological vulnerability of the arid coastal aquifer in the study area. Both techniques defined the high and low groundwater potentialities regarding water quality and quantity and delineated the fresh/saline water interface.The groundwater exploration comprises 36 transient electromagnetic (TEM) sounding and 4 Two-dimensional electrical resistivity imaging (2DERI) lines. The inversion of both geophysical methods reveals four consequent subsurface layers; 1) the surficial unsaturated alluvial sand deposits layer has a resistivity range of 50–538 Ωm, and thickness <10 m, 2) the partially saturated alluvial sand, 3) the saturated alluvial sand and silt with fresh/brackish groundwater, and 4) the lower saturated alluvial sand and gravel layer with saline groundwater and clay sheet intercalations. The third water-bearing layer acts as a thin fresh/brackish groundwater lense of a moderate resistivity (0.8–55 Ωm) floating over deeper saline groundwater with a very low resistivity range (0.8–5.8 Ωm).The relatively moderate to higher resistivity of the fresh/brackish groundwater zone recorded in the eastern side at the downstream portion of the study area indicates promising subsurface recharge. The thickness of this zone ranges from 4 to 24 m (Groundwater Group I; 507 ≤ TDS ≤3920 mg/L & Groundwater Group II; 4031 ≤ TDS ≤4717 mg/L). While the lower resistivity values characterize the northern and southern portions of higher groundwater salinity (Group III; 5144 TDS 6771 mg/L & Group IV 7452 TDS 27573 mg/L), suggesting mixing with deeper saline/seawater and intercalations of clay sheets. Regarding water quality, it is recommended to excavate the groundwater only for the freshwater/brackish zone to avoid up conning of deep saline groundwater. Finally, flash floods are the primary source of groundwater in this vulnerable area. With a recent intensive expansion of groundwater excavation, a continual monitoring program or groundwater modelling is highly recommended.

Integrated TEM and 2DERI techniques to delineate groundwater bearing zones in fractured carbonate rocks at the upstream portion of wadi Halazeen, Northwestern Coast, Egypt

The increasing reliance on groundwater as supplementary water resource for the decreasing rainfall in the Northwestern Coastal Zone of Egypt (NWC) makes groundwater exploration and aquifers characterization in that area of particular importance. A representative locality for the conditions under which groundwater occurs in NWC is the upstream portion of Wadi Halazeen, which lies some 37 km to the west of Mersa Matruh city. In the present work, integrated Transient electromagnetic (1DTEM) and two-dimensional electrical resistivity imaging (2DERI) has been conducted to explore and characterize the groundwater of Miocene aquifer in the upstream portion of Wadi Halazeen. A total of 25 TEM soundings along with 5 normal and reciprocal profiles of 2DERI were measured. The lithological data of the borehole has been used to parameterize the inversion of the geophysical data. In order to maximize the reliability of the inversion results, the acquired data is subjected to some processing such as smoothing, editing and removing depending on TEM sounding significance plus computing reciprocal error of 2DERI measurements. The inversion results of both geophysical methods indicated that the geoelectrical succession consists of five layers along with the surface weathered layer (Dolomitic limestone, Sandy limestone, limestone, marly limestone and clay). The results indicated also that facies change is a common feature characterizes most of the layers. This feature controls groundwater occurrence within the fifth layer where the lithological composition of this layer changes from fractured limestone to marly limestone to marl and clay. Groundwater exists in a channel-like zone of fractured limestone and marly limestone which extends from south to north in the study area. Generally, the groundwater salinity of the study area and neighboring groundwater wells tapping the fractured Miocene aquifer are range between 2900 and 4268 ppm, while the groundwater of DRC5 well which lays in the watershed area has a relatively lower salinity value (1482 ppm) where it receives large recharge related to annual precipitations and surface runoff water than area of outside basin boundary divides. Integration of the results of 1DTEM and 2DERI delivered plausible information about the groundwater occurrence in fractured carbonate rocks.

Offline Electrode(s) Effect on Two-Dimensional Electrical Resistivity Tomography Survey: Qualitative and Quantitative Assessment

Offline Electrode(s) Effect on Two-Dimensional Electrical Resistivity Tomography Survey: Qualitative and Quantitative Assessment

Groundwater resources exploration of Harrat Khaybar area, northwest Saudi Arabia, using electrical resistivity tomography

Two-dimensional (2D) electrical resistivity tomography (ERT) survey has been conducted in the Harrat Khaybar volcanic field, northeast of Al Madinah Al Munawwarah, Saudi Arabia, to assess the presence of groundwater resources. For this purpose, eleven ERT profiles were generated at six sites oriented north–south and east–west at various lengths between 590 m and 890 m. The ERT data were collected using the Syscal Pro multinode resistivity imaging system with a dipole–dipole array and 5 m of electrode separation. Then, these data have been processed using RES2DINV software to get 2D geoelectric cross-sections. The interpreted 2D geoelectric cross-sections clarified that the Harrat Khaybar occupied by sheets of lava flows underlain by alluvial deposits of gravelly sand and clay. These deposits rest on a Precambrian crystalline rock configuration that has the potential to provide groundwater to the region. Promising water-bearing formations were detected within sub-basaltic alluvial sediments and basaltic flows as well. Moreover, the reported water table in the area has 47 m depth in average with thickness varies between 6 and 200 m. These results correlate well with those of previous hydrogeological studies conducted in Harrat Khaybar. These results are very important for the residents in Harat Khaybar, where enables them to benefit from the groundwater resources in the area for domestic and agricultural purposes.

Solution of Collinearity Problem in Two-Dimensional Electrical Resistivity Tomography using Wenner Array

Two-dimensional electrical resistivity tomography (2-D ERT) is one of the most common geophysical tools employed to satisfy the ever-growing need for obtaining subsurface information. Most of the conventional electrode arrays used for 2-D ERT survey are built with the theoretical assumption that the survey lines are straight to guarantee four collinear electrodes at every point of measurement. However, due to surface constraint associated with most survey areas, it is rarely possible to conduct a two-dimensional resistivity survey on a straight line. Therefore, 2-D ERT survey conducted on a surface constraint field requires shifting one or more electrodes off the survey line, which contrasts with the underlying assumption. Consequently, the result might be prone to false anomalies. Thus, this study aimed to device a new approach that could mitigate the false anomalies posed by non-collinearity of electrodes in 2-D ERT result. In view of this, ABEM Terrameter SAS4000 using Wenner array configuration was adopted for the survey. The data was acquired with all electrodes inline and one or more electrodes offline at stepwise distances, respectively. Based on the result obtained, the new approach mitigates the offline electrodes effect, as the inverse resistivity tomograms resolves the geometries of the true model reasonably well. More so, it has high R-value &gt;90% which is an indication of proximity to the true model. Hence, it is concluded that the new approach is effective in mitigating offline electrode effect on a 2-D ERT result.