Total Longitudinal Conductance Research Articles

Application of Electrical Resistivity Sounding Method for Groundwater Exploration in Ugboshi-Afe, Akoko-Edo, Southwestern Nigeria

Schlumberger configuration of Vertical Electrical Sounding (VES) was deplored for groundwater exploration in Ugboshi-Afe study location. A total of nine (9) vertical electrical sounding (VES) locations, spread across the community were occupied to gain insights on the hydrogeological settings within the area. Quantitative computer interpretation of the data yielded three to six geoelectrical layers. The geoelectrical interpretation models were geologically interpreted as: clayey sand/sandy topsoil with resistivity values ranging from 54 Ohm-m to 424 Ohm-m, this is underlain by a relatively high resistivity layer (228-868 Ohm-m) interpreted as lateritic sand, and below this the low resistivity (21.38 Ohm-m – 42.4 Ohm-m) interpreted as clay, then the fractured/weathered geoelectric layer (95Ohm-m to 385Ohm-m), while the fresh basement has resistivity greater than 400 Ohm-m. Several maps such as fractured window thickness map, isoresistivity map of the fractured interval, overburden map were generated to investigate trends that may hold prospects for groundwater exploitation. Furthermore, hydro-resistivity parameters such as Total Transverse Resistance, Total Longitudinal Conductance, Resistivity Reflection Co-efficient and Resistivity Contrast values were calculated for further screening of the study site for groundwater development. The VES1, VES2, VES6 and VES7 locations were concluded as holding prospects for groundwater potentials in the study area.

РЕЗУЛЬТАТЫ ГЛУБИННЫХ МАГНИТОТЕЛЛУРИЧЕСКИХ ИССЛЕДОВАНИЙ В РАЙОНЕ СЛОБОДСКОГО ГЕОДИНАМИЧЕСКОГО УЗЛА (ВОСТОЧНО-ЕВРОПЕЙСКАЯ ПЛАТФОРМА)

The Sloboda Geodynamic Intersection is considered as an area of convergence for major segments, aulacogens, faults, and suture zones of the East European Platform.Between 2020 and 2022, researchers from the Geological Faculty of Lomonosov Moscow State University and the Geoelectromagnetic Research Center (GEMRC IPE RAS) conducted deep magnetotelluric surveys in this region. The surveys were performed along the Pushkiny Gory – Andreapol, Sebezh – Velikiye Luki – Rzhev, and Ostrov – Ostashkov profiles. Through qualitative analysis of the collected data, the dimensionality of the studied medium, the total longitudinal conductance of the sedimentary cover, and the dominant strike direction of conductive structures were assessed. Quantitative interpretation using 1D, 2D, and 3D inversions resulted in geoelectric models comprising a conductive sedimentary cover and a highly resistive basement. Within the depth range of 10–40 km, transcrustal zones of enhanced electrical conductivity were consistently identified, interpreted as the southwest extension of the Ilmen-Ladoga anomaly. These conductivity anomalies are attributed to the deep submergence of heavily tectonized and metamorphosed sedimentary rocks, initially saturated with organic and carbonate matter.

Characterization of groundwater aquifers using hydrogeophysical and hydrogeochemical methods in the eastern Nile River area, Khartoum State, Sudan

The primary goals of this research are to detect the spatial variation of the hydrogeological characteristics and evaluate the groundwater quality in the eastern Nile River, Khartoum state, Sudan, using geophysical and hydrochemical methods. Thirteen Vertical electrical soundings (VES), using Schlumberger configuration, were measured along three profiles to characterize the groundwater aquifer. VES findings denoted that the study area comprises two hydraulically connected aquifers. The upper aquifer of sand has an average thickness of 50 m, and the lower aquifer is composed of sandstone of a thickness of up to 300 m. The results of VES inversion were further used to measure aquifer characteristics, including transverse resistance, longitudinal conductance, hydraulic conductivity, and transmissivity. The detected average values of these parameters were 6690 Ωm2, 1.4 Ω−1, 264 m2/d and 4 m/day, respectively. In addition, regression analysis was performed to suggest local relationships for estimating aquifer characteristics within the study area. On the other hand, total longitudinal conductance was used to predict the protective strength of the hydrogeological columns, ranging from 1.7 to 5.8 Ω−1; as a result, the protective capacity of the aquifer ranged from good to very good, suggesting potable water quality. This result was subsequently confirmed by the groundwater quality index (GWQI) model. Eleven physiochemical parameters analyzed for nine boreholes were used in GWQI estimation to assess groundwater quality in the study area. The primary analysis of the hydrochemical parameters indicated that almost all parameters are below permissible limits prescribed by the World Health Organization (WHO). The computed GWQI varies between 34.8 and 148, and the majority of groundwater samples, precisely 55.5%, are good water types, while 22.2% of the samples are in an excellent quality state. This research concluded that the groundwater aquifer in the study area is ideal for groundwater exploitation. However, applying a detailed geophysical and hydrochemical survey is recommended to reduce the uncertainty of the resulting models.

Donbas conductivity anomaly in the Karpinsky Swell

Donbas Foldbelt (DF) and Karpinsky Swell (KS) are contiguous parts of a system of elongated sedimentary basins forming lineament from Poland through Pripyat Trough in Belarus, the Dnieper-Donets Basin (DDB) and DF in Ukraine, KS in Russia, across the Caspian Sea, through Mangyshlak in Turanian plate in Asia. In DF, the Mesozoic-Cenozoic sediments were raised, and subsequent erosion exposed the Carboniferous coal-bearing strata. In contrast to DF, the Paleozoic rocks in KS are covered by 1—3 km thick sediments of Mesozoic-Cenozoic age; productive structures of the earlier age cannot be confidently studied in KS by geological methods. So, geophysical methods are the promising approach for the KS deep structure studies. This work is devoted to electromagnetic (EM) studies of the electrical conductivity of rocks by the methods of magnetic variation profiling (MVP) and magnetotelluric sounding (MTS). Previously [Rokityansky, Tereshyn, 2022], we described the results of the EM research on DF in detail. MVP reveals the intense Donbas electrical Conductivity Anomaly (DCA) running along the main anticline of the folded Donbas. DCA parameters: maximum possible depth of the anomalous currents center h=18±2 km. Frequency response maximum Т0≈3600 s yields the total longitudinal conductance G=(8±2)∙108 S∙m. 70 MTS at periods 0.1—3000 s yield two conductive stripes, with the upper edge varying from 0.3 to 5 km. The stripes are parallel to the DCA axis and are considered as part of DCA. A very large value of G suggests that the anomalous body extends to some considerable depth. The DCA axis spatially coincides with an intense (up to 90 mW/m2) deep heat flow anomaly. Thus, the nature of the DCA lower part can be a partial melting. Theoretical estimates show that intense anomalous fields of geomagnetic variations arise over highly elongated conductors. Therefore, there is reason to expect that the anomaly continues eastward. We found two MTS profiles crossing the Karpinsky swell, and under both profiles strong conductivity anomalies are clearly seen. We re-interpreted original data and presented parameters of all 3 anomalies in an identical style. The main conclusion: the anomaly parameters on the three profiles are approximately the same, and one can assume with a high probability the existence of a single anomaly of electrical conductivity in the Donbas and Karpinsky Swell with a common length of more than 500 km and longitudinal conductance G≈8×108 S×m.

Leachate delineation and aquifer vulnerability assessment using geo-electric imaging in a major dumpsite around Calabar Flank, Southern Nigeria.

A near-surface resistivity investigation was undertaken to investigate soil contamination and aquifer vulnerability due to leachate percolation in a major dumpsite in Calabar. The study was undertaken using 2-D electrical resistivity tomography (ERT) and vertical electrical sounding. Ten traverse lines were created within and outside the dumpsite and geo-electric measurement was conducted using dipole-dipole and Schlumberger electrode configurations. Interpretation of the measured data was carried out using DIPROWIN and WinResist program. 2-D resistivity structures were produced, showing four resistivity layers. Conductive layers with a resistivity of less than 14Ωm were delineated as leachate infiltrated and soil-contaminated zones. The study has shown that leachate has spread across all the survey lines except the two control stations outside the dumpsite. The investigation has further revealed that leachate has percolated the subsurface up to 25m in the area. Subsequently, twenty vertical electrical soundings were carried out to evaluate aquifer protective capacity/vulnerability in the area. The interpretation shows the area is underlain by four to five geo-electric layers. Total longitudinal conductance values were calculated. Two VES points (14 and 19), representing 10% of the sounding points, showed a weak protective capacity rating; eight VES points (1, 7, 9, 11, 12, 13, and 18), representing 35% of the soundings, showed a moderate protective capacity rating; ten VES points (2, 3, 4, 5, 6, 8, 10, 15, 16, 17, and 20), representing 55% of the total soundings, showed a good protective capacity rating. Three (3) hand-dug wells were sampled with the view to obtaining the groundwater and leachate flow direction within the dump vicinity. An electric water level recorder was used to determine the static water level (SWL) of the three wells, and the leachate flow direction was determined to be north-easterly.

Mapping and Delineation of Hard Rock Aquifers in Parts of the South-western Nigeria Basement Complex Using Integrated Geophysical Techniques

Abstract: An integrated geophysical survey involving three different techniques; namely, VLF-EM, Seismic Refraction and Vertical Electrical Sounding (VES) has been carried out in parts of Eruwa, Ibarapa East LGA, Oyo State with a view of determining the structural characteristics of the subsurface geology and identifying suitable sites where viable borehole could be sited to reduce the problem associated with acute shortage of groundwater in the area. The area lies within the crystalline basement rock terrain of South-Western Nigeria and bounded by Latitude 7° 32' 59"N and Longitude 3° 25' 59"E. The VES results reveal that the area is made up of four major lithologic layers with the topmost layer being majorly laterites, the second layer being sandy clay, the third is weathered basement, while the fourth layer is fractured basement. The aquifer in the study area is mostly confined with curve responses of HA- and HKH-types. The 2-D pseudosection also showed that the fresh basement is very extensive laterally with undulating topography. The result of VLF-EM revealed high-amplitude anomalies. These anomalies are indicative of high conductive zones within the basement bedrock of the study area. The results of the seismic inversion reveals three lithologic layers; namely, the topmost layer / topsoil which is sandy (moderately loose) with an average velocity of 500 m/s, the middle layer can be sandy clay/laterite/caked clay with an average velocity of 1,149.33 m/s and the third layer can be said to be the beginning of the weathered/fresh basement with a velocity of 2,719 m/s. In conclusion, the three geophysical techniques have shown that the area is a hard-rock terrain with complicated geology with aquifers confined and the water bearing formation with low total longitudinal conductance. Keywords: Basement terrain, Granitic masses, Aquifer, Topography, Curve types.

EVALUATION OF AQUIFER PROTECTIVE CAPACITY USING ELECTRICAL RESISTIVITY METHOD IN LAMBATA, KWALI AREA COUNCIL, ABUJA

This study evaluated the aquifer protective capacity of Lambata in Kwali area council of Abuja, using electrical resistivity method. The obtained data were interpreted manually by partial curve matching and the obtained results were iterated using WINREIST software. The first layer is the topsoil whose resistivity range from 127.7 to 562.4 Ωm and its thickness range from 0.7 to 1.6 m. The second layer is laterite and its resistivity range from 302.3 to 937.6 Ωm, the thickness of the second layer range from 3.7 to 13.3 m. The third layer is a clay formation whose resistivity range from 46.7 to 88.8 Ωm and its thickness range from 6.6 to 27.9 m. The fourth layer is a weather/ fractured basement, this layer is the aquifer and it is confined by the overlying clay formation. Its resistivity range from 59.0 to 870.2 Ωm, while its thickness range from 6.0 to 28.5 m. The fifth layer is the fresh basement whose resistivity range from 1038.5 to 4992.5 Ωm. The total longitudinal conductance values of the overburden in the study area range from 0.00143 to 0.410334 mΩ-1. The average aquifer thickness in the study area is 16.60 m. The aquifer protective capacity is about 93.3% moderate and 6.7% weak. The aquifer protective capacity of the study area is fairly good but not sufficient to protect the groundwater in the area from pollution. We therefore strongly suggest that there should be proper environmental and waste monitoring management in the study area to safeguard the groundwater

Donbas geoelectrical structure

The Donbas was formed as the result of Late Devonian rifting of the East European craton. During the Carboniferous, the subsidence of the basin and sedimentation were at their maximum, and a 15-kilometer stratum of Carboniferous deposits formed in the Donbas. The total thickness of the deposits reaches more than 20 km. The next important event was folding, which occurred in the Late Triassic — Early Jurassic and Late Cretaceous — Early Tertiary. The inversion lifted the upper part of the folded Donbas and subsequent erosion exposed the Carboniferous coal-bearing strata on the surface of the earth. Deep electrical conductivity was studied by the methods of magnetovariational profiling (MVP) and magnetotelluric sounding (MTS). The first large survey (13 long-period MTS sites and 32 MTS points) was carried out in 1986; in 1988 another 30 MTS were performed. In 2012-2013, a profile of 15 MVP-MTS sites was made with modern instruments that allow obtaining more accurate results. The data interpretation yields the following conclusions. The intense Donbass electrical conductivity anomaly (DAE) runs along the main anticline of the folded Donbass. In the northwest, it continues in the DDD, in the southeast — on the Karpinsky swell. DAE parameters obtained by the MVP method: Based on the frequency response of the anomalous field, the total longitudinal conductance G = (8±2)×108S×m was estimated. Profile graphs of the anomalous field of geomagnetic variations give an estimate of the maximum possible depth of the anomalous currents center hmax.c.curr, which depends on the variations period. For DAE at the maximum frequency response Т0≈3600 s, it turns out to be equal to hmax.c.curr=18±2 km. The upper edge of the anomaly is estimated from MTS data. Most of the available 70 MTS ρк curves begin at periods of 0.1—1 s from approximately the same level of 15 Ohm·m±half an order of magnitude. This means that in the Donbass, the rocks of the upper approximately half-kilometer layer have, as a rule, electrical resistivity in the range of 5—50 Ohm·m. Deeper, the resistivity can increase to hundreds and thousands of Ohm·m or decrease to units or fractions of Ohm·m. An analysis of the MTS by area showed that objects of low resistance (LRO) are located in two conductive bands, the upper edge of which varies from 0.3 to 5 km. The bands are parallel to the DAE axis and can be considered as some part of the anomaly. A very large value of G leads to the assumption that the anomalous body extends to a considerable depth. When compared with the data of other geophysical methods, it turned out that the DAE spatially coincides with an intense (up to 90 mW/m2) linear anomaly of the deep heat flow. This fact suggests that the nature of the DAE lower part can be a partial melting of fluid-enriched heated local rocks or intrusion of mantle magma. The obtained geoelectric results support the idea of the modern tectonic activation in Donbas.

GEOELECTRICAL EVALUATION FOR GROUNDWATER ASSESSMENT AT OWAN EAST LOCAL GOVERNMENT AREA OF EDO STATE, SOUTHERN NIGERIA, USING SCHLUMBERGER ARRAY

Geoelectrical investigation was carried out in Otuo Community of Edo State, Southern Nigeria, with the aim of delineating the best aquifer bearing zone, and as well the vertical and lateral variation of subsurface lithology with depth and distance respectively. Schlumberger electrode configuration was employed in obtaining four (4) VES data. In determining the capacity bearing rating and groundwater potential of the area, the Dar Zarruk Parameters were tools used in characterizing the aquifer viz: Resistivity Contrast (RC), Resistivity Reflection Coefficient (RRC), Total Transverse Resistance (T) and Total Longitudinal Conductance (S). From the results obtained, VES 3 is the showed high potential source for groundwater compared to other VES points. It has the highest T value of 73,050.27 Ωm2 (showing a very good transmissivity of the layer), RC (3.045) and RRC (0.500), however, all parameters fell within good prospect for groundwater development. VES 1, 2 and 4 having values of 4787.22, 4003.95 and 28106.1005 (ohm-m2) respectively. The results obtained also show that VES 3 had the highest fracture thickness of 61.26 m meaning it has the highest groundwater potential, since VES 1, 2 and 4 having values of 22.02 m, 27.34 m, 48.91 m respectively.

A Further Application of Coefficient of Anisotropy and Reflection Coefficient as Indices in Delineating Groundwater Potential in Basement Complex of Ado Ekiti, Southwestern Nigeria

One index might not be enough in geophysical investigation of underground water potentials in basement terrain, there is a need to look into other indices for an improved investigation, the combination of some indices will lead credence to the result hence this work is a further application of coefficient of anisotropy, reflection coefficient and fracture coefficient on spatial distribution of underground water in Ado Ekiti basement complex. This work examined the thickness of aquifer, its resistivity spread and other hydro geological parameters such as total longitudinal conductance, total transverse resistances, coefficient of Anisotropy, reflection coefficient and fracture contract to determine water potentials in the study area. Resistivity and thickness are linearly related for high productive Aquifer formation, thus these indices generated from thickness and resistivity have been examined in other to determine the porosity and permeability and hence transmissivity of the aquiferous zone in the study area. Aquifer resistivity ranges from 7.7Ωm to 545Ωm in weather zone and between 9.5Ωm to 1902.6Ωm in fracture zone these values are within productive range in basement complex environment. Shallow basement of less water potential have been found in part of North west and north east of the study area, total transverse resistance also discovered low porosity at Aiyedun quarters, Elemi housing Estate and Ita Eku these are hard rock zone, this area has also been identified through their coefficient of anisotropy as low or none productive zone the coefficient of anisotropy is higher than 1.5. Area of promising water bearing zone are with the North west, west, south west and south east of the study area.

CORRECT DETERMINATION OF INTEGRAL CONDUCTIVITY IN SOLVING INCORRECT INVERSE PROBLEMS OF ELECTROMAGNEIC LOGGING

The paper suggests and investigates a problem statement of well-logging inverse problem that is based on the integral conductivity parameter to describe a geoelectric section. Approach was introduced for a layered cylindrical model with radially heterogeneous continuous distribution of electric properties that parametrize the problem with a function of total longitudinal conductivity. The results of hydrodynamic modeling for oil/fresh water- and brine-based drilling muds were used to study multiple propagation resistivity tool signal equivalency for two classes of models with continuous and piece-wise constant conductivity distribution. Physically based algorithm enabling one to convert one model class to the other, preserving the signal equivalency was proposed. It was demonstrated that the radial models with different radial conductivity distribution and similar integral conductivity curves are equivalent. This fact lays a rationale of using the integral conductivity parameters along with conductivity while inversion. The integral conductivity parameter can be used to build the functionals, whose minimization improves algorithm stability and enables determining functional parameters in hydrodynamic filtration models.

GEOPHYSICAL EVALUATION OF SUBSURFACE PROTECTIVE CAPACITY AND GROUNDWATER PROSPECT IN A TYPICAL SEDIMENTARY ZONE, EASTERN DAHOMEY BASIN USING ELECTRICAL RESISTIVITY TECHNIQUE

Subsurface protective capacity evaluation is important in groundwater prospecting. With the aid of Dar-Zarrouk parameters which show direct relationship with contaminants infiltration time and transmissivity, joint interpretation of vertical electrical sounding (VES) and 2-D resistivity imaging were employed to evaluate overburden protective capacity and groundwater potentials at Mowe in Obafemi-Owode LGA, southwest Nigeria. Total longitudinal conductance S, total transverse resistance T, longitudinal resistivity ρL and transverse resistivity ρT were computed. Sand/clayey sand was delineated at 70% of the area either as confined aquifers (78%) or unconfined aquifers (22%). S values in 87% of locations has moderate protective rating (0.2071 – 0.5630), one location has good protective rating (0.7736), others have weak protective ratings (0.1053 – 0.1814). The entire area is characterized by low overburden thickness H (7.9 – 25.6 m), which agrees with a correlation coefficient of 0.58 between S and H. T values is in the range 235 – 2046 Ωm2 with high values indicating high transmissivity zones, suggesting high probability of pollutant contamination of aquifer, also agreeing with moderate correlation coefficient of 0.69 between T and H. The study area was grouped into three regions on the cross plot of T versus S: low S and high T – poor protection and high contaminant transmission; moderate/good S and low T – good protection with low contaminants transmission; moderate/low S and low T – weak protective capacity and poor transmissivity. Excellent correlation (0.99) exists between ρL and ρT, with ρT slightly higher than ρL, and low ρL signifying the presence of conductive clayey materials in the overburden.

Application of logistic regression analysis in prediction of groundwater vulnerability in gold mining environment: a case of Ilesa gold mining area, southwestern, Nigeria.

Reports of environmental problems occasioned from gold mining activities had prompted the groundwater vulnerability prediction/assessment of the study area. This was with a view to identifying factors responsible for the probability of groundwater contamination as well as developing empirical (LR) model and map that predict the probability of occurrence of contaminant(s) with respect to threshold level in the groundwater resources in the study area. In order to achieve the objectives of the study, logistic regression was applied to independent variables obtained from results of the analysis of remote sensing and geophysical data on one hand and dependent variables obtained from analysis of water samples on the other hand. The results of the analysis obtained from water chemistry established that all the physio-chemical parameters and major metallic ions are within the permissible limit. However, zinc concentration (Zn), being the only dependent variable that had two categorical outcomes, was the contaminant utilized for the study. Similarly, only five (5) independent (predictive) variables, which are percent clay in soil, drainage, slope, unsaturated zone thickness, and total longitudinal conductance, were established to have good correlation and statistically significant with the dependent variable, the contaminant, and thus utilized in logistic regression model development. The quantitative assessment of the developed model established that the overall model prediction accuracy was 85.7% suggesting that the model had a very good fit. The probability prediction model was also accurate and reliable with percentage reliability established to be 90%. In conclusion, it is evident from the results obtained from the study that since the model developed was assessed to be accurate and reliable, the model, and hence the technique, can be replicated in another area of similar geologic condition.

Investigating groundwater corrosion and overburden protective capacity in a low latitude crystalline basement complex of southwestern Nigeria

ABSTRACT The total longitudinal conductance S obtained from the interpretations of vertical electrical soundings data acquired near 40 well bores was calibrated using total dissolved solids (measured in situ) in the sampled wells’ groundwater to determine the overburden protective capacity and groundwater corrosion in a crystalline basement complex of Ogbomoso North, southwestern Nigeria. The acidity (pH) and electrical conductivity (EC) were also measured. Groundwater corrosiveness was determined using the Langelier saturation index (LSI) and the aggressive index (AI). The computed S of predominantly H-, KH-, QH-, HA- and HKH- types resistivity curve was 0.037995– 1.10878 mhos. The TDS, pH and EC of the water samples measured 36–747 ppm, 6.15–9.3 and 74–1491 μS/cm, respectively. The regression equation of the TDS-based S calibration curve indicates a strong positive correlation (R2 = 0.8932) and revealed the overburden protective capacity ranged from excellent to good, fair and poor. The computed LSI and AI were −3.61 to 1.2 and 7.8–12.8, respectively. The high values of both LSI (0.2–1.2) and AI (11.2–12.8) in the southwestern part suggest groundwater there is strongly corrosive, while low values of −3.6 to −1.2 and 7.8–10.2 in the northwestern and southeastern parts indicate non-corrosive groundwater.

Geo-electrical Resistivity Evaluation of Groundwater Potential at University Of Benin Ugbowo Campus, Benin-City, Edo State of Nigeria, Using the Schlumberger Array

Geo-electrical resistivity survey was conducted in part of the University of Benin, Benin-City, Ovia Northeast of Edo State, Nigeria, with a view to establishing the most dependable aquifer bearing zone and the lateral and vertical variation of subsurface lithology with distance and depth respectively. In this study, the schlumberger electrode configuration was employed for the acquisition of VES data in the field. A total of 6 VES stations were engaged within the study area. A, H and HK resistivity curve types were identified, reflecting facies or lithological variations in the area. Three patterns of geo-electrical resistivity curves obtained using IP2WIN software can be associated with different rock formations in the study area. Dar Zarruk Parameters were tools used for aquifer characterization in determining the groundwater potential of the area and capacity bearing rating, viz: Total transverse resistance (T) and Total longitudinal conductance (S), Resistivity Contrast (RC) and Resistivity Reflection Coefficient (RRC). Results obtained shows that VES 1 (coordinate N6o 23’56.69’’, E5o 37’ 32.83’’) with four layers and an A curve type is the most potential source for groundwater compared to other VES points. It is a sandy clay layer of resistivity 198Ωm, with thickness to infinity and well confined at the top by a laterite layer. VES 1 has the highest Total Traverse Resistance 690310 Ωm2 (showing a very good transmmitivity of the layer), Resistivity Contrast (0.01) and Resistivity Reflection Coefficient (0.90), all parameters falling within good prospect for groundwater development, but has a Total Longitudinal Conductance (S) value of 0.002 mho which shows that VES 1 has a poor bearing capacity. In summary, the results of the geo-electrical resistivity survey conducted at the Vice Chancellor’s Lodge area of University of Benin using Schlumberger Array, revealed the most dependable aquifer bearing zone and the lateral and vertical variation of subsurface lithology with distance and depth respectively. Keywords: Geo-electrical Resistivity, Aquifer, Subsurface Lithology, Benin-City

Groundwater Recharge and Aquifer Transmissivity of Crystalline Basement Terrain

It is known that substantial groundwater bearing zones can develop within the weathered and fractured units of impermeable crystalline rocks if there is a good and recurrent source of recharge. On account of this, eighty-two geo-electric soundings were carried out to determine the degree and extent of weathering and bedrock fracturing; and in addition, twenty-one single –well (constant discharge) pumping tests were also conducted for the estimation of the transmissivity of the water-bearing zones across the various bedrock terrains of Ibarapa areas of southwestern Nigeria. Weathering development was found to be more pronounced in areas underlain by amphibolite and gneisses bedrocks with a regolith thickness range of 4.4 - 47.5m (av.18.41 m) as compared to the relatively shallower soil horizon range of 2.4 - 23.6 m (av. 12.03 m) that developed upon light coloured rocks of migmatite and granites. The recharge potentials as inferred from the total longitudinal conductance indicated that there is likelihood of better water infiltration in areas underlain by migmatite and granites with 0.02 – 0.60 mhos. The discharging areas underlain by amphibolite and gneisses with higher conductance of 0.01 – 1.42 mhos were characterized by thicker and finer grained overburden unit and more numerous bedrock fractures that sustain reliable groundwater yield. Only one-third of the boreholes were sustainable with transmissivities of 7.75 – 0.50 m 2 /day; these prolific boreholes were mostly within amphibolite and gneisses terrains. Change in the drawdowns during pumping was between 1.7 and 14m, while the groundwater yield was between 93.58 and 32.78 m 3 /day. Keywords: Groundwater recharge, transmissivity, sustainable yield DOI : 10.7176/JEES/9-10-13 Publication date :October 31 st 2019

Groundwater Vulnerability Assessment using Electrical Resistivity Method in the Northern part of Ado-Ekiti, Southwestern Nigeria

Over the years, the demand for clean and safe water has skyrocketed globally in response to rising population. Since groundwater is a more reliable source of potable water, assessment of aquifer vulnerability becomes a necessity. This research therefore aimed at delineating geo-electric parameters inform of layer resistivity and thickness, towards generating a second order geo-electric section. This study employed the use of electrical resistivity method to evaluate the vulnerability of aquifers to contamination in the northern part of Ado-Ekiti, southwestern Nigeria. Forty Vertical Electrical Sounding (VES) locations were studied using the Schlumberger array with current electrodes spacing (AB/2) of 150m. ABEM SAS 300 Resistivity Meter was useful for collecting the VES data which were presented as VES curves and quantitatively interpreted through partial curve matching and Computer Assisted 1-D forward modeling using the WinResist software. Geo-electric section along five (5) traverses, iso-resistivity map of the weathered layer and an isopach map showing the depth to aquifer were generated. Seven (7) different types of VES curves were identified, namely A, H, K, KA, HA, QA and KH types. The four geo-electric layers delineated include the topsoil (resistivity values between 29 – 1176 Ωm; thickness from 0.5 – 4.4 m), lateritic layer (resistivity values between 138– 3787 Ωm; thickness between 1.0 – 63.6m), weathered layer (resistivity values between 6 – 298 Ωm; thickness between 0.7 – 17.8 m), and fresh basement (resistivity values between 331 – 7479 Ωm). The total longitudinal unit conductance (S) values obtained range from 0.009 to 2.972 mhos. This suggests that most parts (northern, central, western and eastern portions of the area) have medium to high protective capacity rating; except the eastern portion. Therefore, most parts (80%) of the study area appear to be less vulnerable to contamination.

Geoelectrical exploration for groundwater in crystalline basement rocks of Gbongudu community, Ibadan, Southwestern Nigeria

Gbongudu community, Ibadan underlain by crystalline rocks of Basement Complex of Southwestern Nigeria has need for alternative water supply due to inadequacies of surface water supply and common occurrences of low yield or dry boreholes coupled with rapid development within the community. Geophysical investigation involving electrical resistivity was carried out with the aim of evaluating the groundwater potential of the community. Thirty-three (33) Vertical Electrical Soundings were acquired across the community adopting Schlumberger electrode configuration with current electrode separation (AB) varying from 2 to 200 m. The acquired field data were interpreted using partial curve matching with suitable auxiliary chart and “RESIST” resistivity sounding interpretation software was also used for iteration. The results revealed two to five geo-electric layers, namely, topsoil, clayey soil, lateritic clay, weathered layer, fractured unit and fresh basement. The weathered and the fractured units form the aquiferous zones in the area investigated. Thematic maps of geoelectric and Dar-Zarrouk parameters produced from the interpreted VES data are aquifer unit (weathered layer) thickness map, aquifer unit (weathered layer) resistivity map, overburden thickness map, basement resistivity map, basement topography map, reflection coefficient map, total longitudinal conductance map, total transverse resistance map and electrical anisotropy (coefficient of anisotropy) map. The thematic maps were combined to form a single component which gives the groundwater potential map of the study area. The groundwater potential map was used to classify the study area into poor, low and good aquifer potential zones. The study reveals that the weathered and fractured zone that occur in the southeastern part of the study area constitute the water bearing zone which can be regarded as good groundwater potential. This study has provided evidence on the hydrogeologic framework and subsurface nature of main aquifer units in the area.KEY WORDS: Groundwater exploration, RESIST, Dar-Zarrouk parameters, Electrical anisotropy, Borehole drilling.

Electrical conductivity anomalies in the contact zones of Archean and Proterozoic geobloks on the Ukrainian and Baltic Shields

Kirovograd (KA) and Ladoga (LA) anomalies of the crustal electrical conductivity are located in the Sarmatian and Fennoscandinavian domains of the East European Craton. In the paper the main attention is paid to the areas of anomalies, which are juxtaposed with the regional linear zones of Archean (AR) and Proterozoic (PR) geoblocks junction. For Fennoscandia, the analysis is based on data from the latest magnetotelluric (MTS) and magnetovariational (MVP) studies with emphasis on the anomalous fields of horizontal components of geomagnetic variations (tensor M). Comparison of the geoelectric parameters of the KA and LA reveals the prominent features of their similarities and differences. Both anomalies consist of two quasi-parallel conductors “А” and “Б”, distant one from another on 50—100 km. The main conductors “A” are located within megablocks of the PR age. They were detected by the anomalous behavior of geomagnetic variations (MVP method) and have a maximum frequency response of the MVP parameters (induction vectors and tensor M) at the periods T 0 » 1 ¸ 2 thousand seconds, which gives the estimates of the total longitudinal conductance G » (1—3)×10 8 S×m for both KA and LA anomalies. Subparallel conductors “Б” produce extremal responses at higher frequencies ( T 0 » 100 ¸ 300 s) and are less conductive ( G » (0,4—2)×10 7 S×m). Conductor “Б” directly marks the AR-PR border, which passes through regional faults: the Yanisyarvinsky on the Baltic Shield and the Krivorozhsko-Kremenchugsky on the Ukrainian Shield. Recent studies reveal the existence of Baryatinska anomaly of electrical conductivity on the western slope of the Voronezh massif which can be considered as the northern continuation of the КА up to 54,5° of northern latitude. The southern extension of the LA is the Ilmenska anomaly at the 58° of northern latitude, apparently running to 56° and having a branch, probably, extending up to the Baryatinska anomaly. These data give rise the hypotheses of the Trans-European submeridional chain of electrical conductivity anomalies (TECAE), stretching from the northern end of the Gulf of Bothnia to the Black Sea. We present geophysical materials supporting this assumption, with the most solid one being the general spatial coincidence of the TECAE with the gradient zones of the transcraton permanent magnetic field anomalies (PMFA), where the positive PMFA are located east of the electrical conductivity anomalies, and the negative ones are west of them.

Investigation of the Aquifer Protective Capacity and Groundwater Quality around Some Open Dumpsites in Sapele Delta State, Nigeria

Aquifer protective capacity and groundwater quality investigations around some open dumpsites were conducted along New Road Sapele, Delta State. Nine Schlumberger arrangements of vertical electrical soundings (VES) were carried out with a maximum electrode separation of 500 m, and obtained data were interpreted by partial curve matching and computer iteration using Win Resist software. 2D survey using nine dipole-dipole stations was also utilized to give resistivity map of the dumpsites, while standard laboratory methods were used to analyze the groundwater. The study shows four to five geoelectric sections. The aquifer is within the third, fourth, and fifth layers at a depth of 30 m. The overburden protective capacity from the total longitudinal unit conductance indicates that VES 1 and 5 are adequately protected with protective capacity of 0.7 to 0.9 mhos, VES 2, 3, 6, and 7 are moderately protected with conductance values of 0.2 to 0.69 mhos, VES 4 is weakly protected with values of 0.12 mhos, and VES 8 and 9 are poorly protected with values of 0.003 to 0.004 mhos. In the 2D imaging, VES 4, 8, and 9 show contaminant presence to the depth of 20 m while VES 3, 6, and 7 show contamination to a depth of 50 m. However, the aquifer shows good transmissivity, an indication that if it is contaminated, the contaminants will circulate the aquifer at a high rate. The groundwater flows in the northeast (NE) direction, thereby recharging river Ethiope. The study also shows the presence of lead (0.01 mg/l), nickel (0.02 mg/l), and cadmium (0.03 mg/l), which made it unsafe for drinking and use in other life-related activities. Groundwater should hence be sourced from a depth of about 45–50 m in order to tap from the uncontaminated aquifer.