Horizontal Resistivity Profiles Research Articles

APPLICATION OF ELECTRICAL RESISTIVITY METHOD FOR SAFETY EVALUATION OF ASEJIRE DAM IBADAN, SOUTHWESTERN NIGERIA

Dam construction provides economic importance to the environs through, water supply and flood control. Post-construction investigation is however necessary for maintenance stability to avoid irreversible environmental changes. In view of this, horizontal resistivity profiling and vertical electrical sounding (VES) were conducted along the embankments and the downstream of Asejire dam to determine its integrity. The methods used were horizontal resistivity profiling and vertical electrical soundings conducted along the embankments and the downstream. Thirty-one VES and Dipole-Dipole Profiling were occupied along the embankments and downstream using Resistivity meter at 20 m intervals for both the VES and Dipole-Dipole. The Dipole-Dipole data were inverted into 2-D Resistivity Images using DIPPRO™ 4.0 Inversion Software while the VES data were quantitatively interpreted using the partial curve matching technique and Winresist 1.0 Version Software. Results of dipole-dipole image and geo-electric section identified three geo-electric layers; comprising topsoil presumably clayey sand and laterites with resistivity and thickness between 59-760m and 0.7-5.2m respectively. The second layer is weathered layer attributed with clay/clayey sand having resistivity and thickness 18-766m and 3.1-36.7 m. The third layer suspected to be fresh bedrock with resistivity range 121-3672m and 18-766 m thick. The Dipole-Dipole results displayed resistivity less than 500m in the first layer with structural evidence of discontinuous observables, but the underlying sequences displayed no indicative of structural weakness. This significant features play a major role in seepage processes from the dam, therefore lithological composition obtained from these results shows the dam has a good integrity.

Investigation of Dam Integrity from Electrical Resistivity Methods: A Case of Erelu Dam, Southwestern Nigeria

DOI:10.17014/ijog.8.2.265-274Erelu dam is geologically within the Precambrian Basement Complex of southwestern Nigeria, which serves a principal source of water supply to an increasing population; currently at about 779,318. In an attempt to investigate the integrity of the dam, horizontal resistivity profiling (HRP) of dipole-dipole and Schlumberger’s vertical electrical sounding (VES) approaches were explored to delineate the lithologic layers, facies, and geologic structures in the subsurface of the dam. The HRP revealed changes in subsurface conductivity that depicts lateritic hard pan and saturated rock blankets at shallow depth. The vertical geo-electric section delineated predominant four lithologic units. The regolith is 7 m thick and constitutes the vertical rock fill impervious cores of the dam, which is underlained by saprolitic and fresh bedrock. The region of weathered rock depression coincided the shallow saturated anomalous zone and showed surface manifestation of fractured or unconsolidated terrain within the embankment. The fracture serves as conduit for seepage which could be responsible for possible loss in the reservoir water and increases its susceptibility to failure. It is recommended to keep monitoring the seepage with reservoir levels, by periodical geophysical and geotechnical measurements for the two (dry and wet) seasons.

Apport De La Prospection Géoelectrique (Tomographie Et Trainé Éléctrique) À L’étude Des Tourmalinites Stanniferes d’Achmmache (Maroc Central)

The Achemmache region is located in the East of El Hammam district, in the Eastern part of the Northern Hercynian Central Morocco; Tin concentrations, economically exploitable, have been recognized in brecciated tourmaline structures of Late Visean, and generally oriented E-W. Therefore, they contrast with other tourmaline oriented NE-SW which proved barren. In order to keep the horizontal and vertical continuity as well as the dip and extension of mineralized structures in the sector, a geophysical survey by Horizontal Electrical resistivity (TE) prospecting and Electrical Tomography was performed in the region. The TE1 profile was performed in the West Zone where the mineralized structures outcrop; it allows highlighting four positive anomalies, while the TE2 profile was carried out in Eastern zone of the sector where the mineralized structures are largely hidden. It can also bring out only two rather distant positive anomalies. These anomalies correspond to mineralized structures of tourmaline. While a duplicate executing of TE1 and TE2, mineralized structures show that some resistant ones have different dips, while some others are subvertical. The TM1 profile was carried out at the same location of electrical TE1 profile in order to confirm the tourmaline structures. The TM1 shows from the NW to the SE an alternation of resistant levels with the relatively conductive levels. The resistive levels are correlated with tourmaline structures identified by the horizontal electrical resistivity. The structures dips show a good correlation between the electrical tomography results and these obtained by the horizontal electrical resistivity profiles with duplicate mode. The study of thin sections and polished sections of the SCA110 and SCA8 core drilling, carried out by BRPM, allowed to recognize, at the mineralized zones, a paragenesis composed of gangue minerals such as quartz, calcite, tourmaline metallic minerals, sulphides and oxides such as magnetite and cassiterite.

Geo-electrical Evaluation of the Effects of Waste Dump Sites on Groundwater in Eneka, Rivers State, Nigeria

This study aims at investigating the effects of waste dumps on the groundwater in Eneka using resistivity method. Two dump sites and a dump-free site were investigated in the area. The investigation involved seven horizontal resistivity profiling and four vertical electrical soundings. The result of the investigation revealed that the surrounding soil and water in the waste dumpsites have been contaminated to depths below 20 meters which is within the aquifer system of the area. This was evident in the attendant low resistivity values of 0.04 ohm.m 60.07 ohm.m around the dumpsites relative to the high resistivity values greater than 500 ohm.m in the dump free areas. The results of the investigation are serious considering the negative implications on public health and the ecosystem of the area if not checked, monitored and managed.

Estimation of depth to fresh–salt water interface and its implications for sustainable groundwater resource management: a case study of the Coastal strip of Dar es Salaam, Tanzania

Dar es Salaam City is highly depending on groundwater resources since 1997. The resulting overexploitation is entailing the risk of seawater intrusion. This problem has been systematically investigated for the first time, and appears to be wide-spread. Determining the depth of the fresh–salt water interface was deemed crucial in the view of sustainable exploitation of the Dar es Salaam quaternary coastal aquifer system. Vertical electrical soundings (VES) and horizontal resistivity profiles have shown a decrease of resistivity with depth and toward the coastline. Cross sections have shown the presence of salt water in the aquifer near the coastline, and the boundary between fresh and saline waters is mapped. The surface prospection resistivity data showed comparable results as reflected in hydrochemical/lithological cross sections and resistivity well logs. Salt water was found mostly in the area within 2 km of the coastline, and the depth to the interface in this zone is ranging from 1.3 to 20 m. Away from the coastline, the interface (if present) is at greater depth. VES executed at Kurasini (4 km from the sea) showed the fresh–salt water interface at a greater depth (43 m).

Evaluation of the impact of asbestos wastes on soils in Emene-Enugu, Southeastern Nigeria.

This study investigated the impacts of asbestos wastes on soils in Emene-Enugu, southeastern Nigeria, generated by the activities of a major asbestos products manufacturing company in southeastern Nigeria. The methods of investigation included vertical electrical sounding (VES), 2-D horizontal resistivity profiling (HRP), induced polarization (IP) survey, chemical analysis of plant tissues and standard penetration tests of soil samples. The 2-D HRP and IP identified six closed waste pits alongside the two active pits. The VES revealed four geoelectrical layers in the area: from bottom to top; the inferred lithologies included dark shale, clay, gravel and recent sands. The geochemical data results revealed that Cd concentration of the soils of the waste pits is above the contaminated land exposure assessment soil guideline value for residential and allotment land uses. The geochemical pollution indices classified the soils as "unpolluted" to "extremely polluted". Bioconcentration factor of Pb in plant tissues was found to be above recommended limits of 0.045. The geotechnical parameters indices revealed that the soils varied from "very soft" to "stiff" and "very loose" to "medium". Soils of the active pits have very low strength and bearing capacity while closed pits have high strength and bearing capacity. It may be safe, therefore, to conclude that as the wastes are completely turned into soils, they will assume geotechnical properties similar to those of natural soils.

Groundwater potential evaluation of a part of Gidan Kwano campus of The Federal University of Technology, Minna, central Nigeria using geoelectric methods

Groundwater potential evaluation of Gidan Kwano campus of the Federal University of Technology, Minna, Central part of Nigeria was undertaken using Vertical electrical Sounding (VES) to provide information about the subsurface lithology and structures with the aim of evaluating its groundwater potential. A total of 48 VES was made along eight profiles with six sounding stations per profile within an area of about 10km2, using the Schlumberger array configuration. A combination of VES, Horizontal Resistivity Profile and Sounding – Profiling produced a subsurface geological appraisal of the study area. The results of the interpretations of VES data were used to produce the Isopach map of depth to Basement and the Fracture map of the study area. The results and the surface geologic map were found to be closely correlated. Fractures located within the study area coincide with the direction of stream flow suggesting that the drainage system is structurally controlled. The VES curves reveal that the area is generally characterized by three geoelectric layers. The top soil layers thickness ranges from 0.2m to 7.4m. The weathered layer has an average thickness of 0.3m to 58.8m. The mean depth to bedrock was computed as 35m. Out of the 48 VES made, 8 VES stations have been selected as priority locations for the development of groundwater resources. The study area has a very high potential for groundwater development. Despite all the limitations of the VES technique, it has been found to be reliable for groundwater exploration in the Basement Complex terrain particularly when the Schlumberger Configuration and combined with computer - aided interpretation for the survey data.Keywords: Vertical Electrical Sounding (VES), Horizontal Resistivity Profiling (HRP), Sounding-Profiling (Pseudosection), Groundwater Potential.

An alternative methodology for the analysis of electrical resistivity data from a soil gas study

The aim of this paper is to present an alternative method for the analysis of resistivity data. The methodology was developed during a study to evaluate if electrical resistivity can be used as a tool for analysing subsurface gas dynamics and gas emissions from landfills. The main assumption of this study was that variations in time of resistivity data correspond to variations in the relative amount of gas and water in the soil pores. Field measurements of electrical resistivity, static chamber gas flux and weather data were collected at a landfill in Helsingborg, Sweden. The resistivity survey arrangement consisted of nine lines each with 21 electrodes in an investigation area of 16 x20 m. The ABEM Lund Imaging System provided vertical and horizontal resistivity profiles every second hour. The data were inverted in Res3Dinv using L-1-norm-based optimization method with a standard least-squares formulation. Each horizontal soil layer was then represented as a linear interpolated raster model. Different areas underneath the gas flux measurement points were defined in the resistivity model of the uppermost soil layer, and the vertical extension of the zones could be followed at greater depths in deeper layer models. The average resistivity values of the defined areas were calculated and plotted on a time axis, to provide graphs of the variation in resistivity with time in a specific section of the ground. Residual variation of resistivity was calculated by subtracting the resistivity variations caused by the diurnal temperature variations from the measured resistivity data. The resulting residual resistivity graphs were compared with field data of soil moisture, precipitation, soil temperature and methane flux. The results of the study were qualitative, but promising indications of relationships between electrical resistivity and variations in the relative amount of gas and water in the soil pores were found. Even though more research and better data quality is necessary for verification of the results presented here, we conclude that this alternative methodology of working with resistivity data seems to be a valuable and flexible tool for this application.

Investigation of Corrosion of Buried Oil Pipeline by the Electrical Geophysical Methods

The delineation of possible areas of corrosion along an underground oil pipeline in Ubeji, Delta State, Nigeria was investigated using the horizontal electrical resistivity profiling technique and the Spontaneous Potential geophysical method. The resistivity and self potential values of the soil along the pipeline were obtained using the R-plus resistivity meter. The results show that areas of low resistivity, having values between 98.0 and 116.0 Ohm-m, coincide with areas of high negative spontaneous potential values, in the range -31.0 to -52 mV. The low apparent resistivity and high negative spontaneous potential values are indications that the soil is very corrosive and there is the possibility of the pipeline failure and oil spillage around these hot spots in the future. These methods applied in the study are quick, economic and efficient for detecting likely anodic hot spots along buried pipelines which need to be protected. Routine electrical geophysical investigations along buried oil pipelines should be undertaken for the early detection and prevention of pipeline failure with its attendant environmental, human and economic consequences.

The appraisal of a proposed barite quarry in Akpet Area, Cross River State, from resistivity investigation

Electrical resistivity survey was done at a site at Akpet area, Cross River State to evaluate the subsurface for barite mineralization. Both vertical electrical sounding (VES) and horizontal resistivity profiling (HRP) were performed in conjunction with surface geological mapping in the area. In both VES and HRP, the Schlumberger electrode array was adopted and measured resistivity data interpreted using conventional curve matching techniques and iterative computer modelling. Results show that three (3) zones designated A, B and C with barite mineralization occur within a depth of 5m in the subsurface at the project site. The combined high specific gravity of 4.4 g/cc and high BaSO4 (>92%) show that the barite of the study area are of high quality. The practical recovery of over 8 tons of barite at the project site shortly after this report which revealed the occurrence of large deposit of barite in the area; show that the applicability of the resistivity method in the search of barite and other minerals alike is very reliable. KEY WORDS: Barite, resistivity, subsurface, recovery. Global Journal of Geological Sciences Vol.2(2) 2004: 171-175

A model for the resistivity structure of LNAPL plumes and their environs in sandy sediments

Geophysical site characterization investigations at fuel spill sites have been generally guided by a working hypothesis which assumes that the light non-aqueous phase liquids (LNAPL) are a fully saturating phase of intrinsically very high electrical resistivity. Using observations from other related sciences, and contrary geophysical observations, a different model is developed which treats these spills as dynamic, changing systems dominated by surprisingly low resistivities. The major geophysical response of a mature or established spill of this type is due to an anomalously low resistivity zone in the lower vadose zone and upper portion of the aquifer. This zone is produced by a high total dissolved solids (TDS) leachate which is aperiodically flushed down from the volume of intimately mixed hydrocarbon, water, oxygen and soil near the base of the vadose zone where microbial activity is a maximum. This leachate is a result of acidification by organic and carbonic acids of the water-filled capillaries in the heterogeneous mixing zone at the free/residual product level, and is produced by the leaching and etching of the native mineral grains and grain coatings. This conductive inorganic plume is generally coincident with the uppermost part of the anaerobic dissolved hydrocarbon plume as defined by hydrochemical studies, but is thin and most concentrated at the top of the aquifer. It has been best detected and mapped by virtue of the amplitude shadow it causes on ground penetrating radar (GPR) profiles, and more recently by direct measurement using vertical resistivity probes (VRP) with readings every 5.08 cm from the surface to more than 7.5 m in depth. Other surface electrical geophysical methods (VES, electromagnetic method (EM), and multi-spaced horizontal resistivity profiling) can define this zone only if conditions are optimal. The conductive zone has been known for some years by hydrochemists and hydrogeologists, especially at sites where water samples are collected from short screens at multi-level wells.

Determination of potential groundwater sites using geological and geophysical techniques in the Cross River State, southeastern Nigeria

Radar images, aerial photographs, geoelectrical studies (vertical electrical sounding, VES and horizontal resistivity profiling, HRP), geological logs based on exploratory drilling and the local surfacial geology have been employed for groundwater investigations in the Cross River Sate, southeastern Nigeria. Results from the study show that areas with high lineament frequency and a thick regolith should be targeted for groundwater investigation within the crystalline basement complex terrains, whereas in the sedimentary areas the target areas are determined by the lithology and stratigraphical sequence. Using the results of this study there is an increase in the number of successful boreholes drilled in the area from 35% to 92%. It is also observed that remotely sensed, geoelectric and exploratory drilling data are adequate for delineating the surface and near-subsurface hydrogeology of the area.

A Study of Acid Mine Drainage Using Earth Resistivity Measurements

AbstractA resistivity survey was conducted in a reclaimed mine spoils disposal site near Wheatland, Indiana to study the ground‐water contamination. Due to the high conductivity of the acidic leachate from coal refuse, it was possible to detect the valleys in which this material was dumped (gob valleys) by using the horizontal resistivity profiling technique. The thickness of the gob valleys and information about the stratigraphy of the site were obtained by using the vertical electrical sounding (VES) technique. The VES data for sounding points located near monitoring wells, together with the chemical analyses of water samples taken from these wells, were used to obtain an empirical relationship between the inferred earth resistivity and the amount of Total Dissolved Solids (TDS) in the ground water. The horizontal resistivity profiling data and the VES data at a 30‐ft electrode spacing were contoured. The resulting isoresistivity map, together with the empirical relationship, can be used to predict the approximate TDS concentration at a depth of approximately 30 ft at any point on the Wheatland site.

RESISTIVITY, SELF‐POTENTIAL, AND INDUCED‐POLARIZATION SURVEYS OF A VAPOR‐DOMINATED GEOTHERMAL SYSTEM

The Mud Volcano area in Yellowstone National Park provides an example of a vapor‐dominated geothermal system. A test well drilled to a depth of about 347 ft penetrated the vapor‐dominated reservoir at a depth of less than 300 ft. Subsequently, 16 vertical electrical soundings (VES) of the Schlumberger type were made along a 3.7‐mile traverse to evaluate the electrical resistivity distribution within this geothermal field. Interpretation of the VES curves by computer modeling indicates that the vapor‐dominated layer has a resistivity of about 75–130 ohm‐m and that its lateral extent is about 1 mile. It is characteristically overlain by a low‐resistivity layer of about 2–6.5 ohm‐m, and it is laterally confined by a layer of about 30 ohm‐m. This 30‐ohm‐m layer, which probably represents hot water circulating in low‐porosity rocks, also underlies most of the survey at an average depth of about 1000 ft. Horizontal resistivity profiles, measured with two electrode spacings of an AMN array, qualitatively corroborate the sounding interpretation. The profiling data delineate the southeast boundary of the geothermal field as a distinct transition from low to high apparent resistivities. The northwest boundary is less distinctly defined because of the presence of thick lake deposits of low resistivities. A broad positive self‐potential anomaly is observed over the geothermal field, and it is interpretable in terms of the circulation of the thermal waters. Induced‐polarization anomalies were obtained at the northwest boundary and near the southeast boundary of the vapor‐dominated field. These anomalies probably are caused by relatively high concentrations of pyrite.

RESISTIVITY TYPE CURVES OVER OUTCROPPING VERTICAL DYKE—II *

AbstractThe theoretical horizontal resistivity profiles Over an outcropping vertical dyke with two‐electrode and Schlumberger electrode systems are discussed. The two‐electrode array seems very useful in locating the highly conducting thick or thin vein, while the Schlumberger (gradient) array is suited to detect the conducting vein of low and moderately high resistivity contrast and as well as the resistive vein of all widths and resistivity contrasts. Besides, the inline gradient array has a distinction of establishing a clue to evaluate the resistivity contrast of the vein.

RESISTIVITY TYPE CURVES OVER OUTCROPPING VERTICAL DYKE—I *

AbstractThe theoretical horizontal resistivity profiles over an outcropping vertical dyke for various parameters‐electrode spacing, vein‐width and resistivity contrast—with inline alpha, beta and gamma‐Wenner electrode systems are described. The resistivity profiles present a most bewildering variety of shapes as compared to those in resistivity soundings. The analysis of type curves suggests suitable electrode configuration for detection of wide, moderately wide, and thin veins. The negative apparent resistivity values on the gamma anomalies for resistive vein over certain vein‐widths of higher positive values of resistivity reflection factor contradict the concept of apparent resistivity hitherto held.

Geoelectrical and Seismic Refraction Investigations Near San Jose, Californiaa

ABSTRACTThe geoelectrical resistivity method, in conjunction with a few seismic refraction profiles, is used to locate permeable strata for the artificial recharge of ground water. Both Schlumberger and Wenner electrode configurations are used in carrying out the resistivity measurements. Possibilities and limitations in the interpretations of some sounding curves are discussed. An attempt to interpret (horizontal) resistivity profiles in terms of theoretical profiles over hemispherical sinks is included.The results of the seismic refraction profiles seem to show that, within the depth of interest, the alluvial strata lack a good elastic differentiation. On the other hand, the resistivity measurements have indicated the presence of buried stream channels. The discovery of one such channel is confirmed by later drilling and a good correlation is shown between geoelectrical predictions and geologic findings. It is shown that the construction of isoresistivity maps can greatly contribute to the successful performance and interpretation of electrical soundings.

To: “Theoretical Horizontal Resistivity Profiles Over Hemispherical Sinks,” by Kenneth L. Cook and Russell L. Gray, GEOPHYSICS, v. 26, n. 3, p. 342–354

Corrections to “Theoretical Horizontal Resistivity Profiles Over Hemispherical Sinks,” by Kenneth L. Cook and Russell L. Gray, Geophysics, v. 26, n. 3, p. 342–354; also published as special reprint, including complete album of curves, pages 1–48 (June, 1961).

VELA UNIFORM RESEARCH PROGRAM IN SEISMOLOGY

Corrections to “Theoretical Horizontal Resistivity Profiles Over Hemispherical Sinks,” by Kenneth L. Cook and Russell L. Gray, Geophysics, v. 26, n. 3, p. 342-354; also published as special reprint, including complete album of curves, pages 1-48 (June, 1961).

THEORETICAL HORIZONTAL RESISTIVITY PROFILES OVER HEMISPHERICAL SINKS

An album of 40 sets (about 200 different curves) of theoretical horizontal resistivity profiles over and near outcropping hemispherical sinks shows the effects of sink diameter, reflection factor k, and distance of the traverse from the center of the sink upon the magnitude and shape of the apparent resistivity curves. Curves for sink diameters of 16a, 8a, 6a, 4a, 2a, a, and 0.5a, and reflection factors k of ±0.8, ±0.6, ±0.4, and ±0.2 are included. The values of apparent resistivity for both the Lee and Wenner configurations were computed using a digital computer. In general, the larger the sink, the larger the magnitude of the apparent resistivity anomaly up to a sink diameter of about 8a, for which the apparent resistivity over the central part of the sink is essentially equal to the resistivity of the sink, irrespective of the reflection factor. For sink diameters equal to the electrode separation a, large apparent resistivity anomalies result from “pseudo‐focusing” effects. The major peaks of the apparent resistivity curves, which lie outside the edges of the sink for negative reflection factors and inside for positive reflection factors, can be used to detect the edges of the sinks. The album of curves provides a general utility for the qualitative interpretation of apparent resistivity anomalies over features other than hemispherical sinks, such as faults (for large sinks), dikes, grabens, and similar features.