Longitudinal Conductance Values Research Articles

Multi-Criteria Analysis Method for Aquifer Vulnerability Investigation Using Godt Method at Idi-Ayunre, Ibadan, Southwestern Nigeria

Geophysical investigation involving Vertical Electrical Sounding (VES) Schlumberger array was carried out across Idi-Ayunre, Ibadan, a typical basement complex area having a rock composition of migmatite-gneiss, quartzite, and biotite-hornblende. A total of forty (40) vertical electrical sounding data were acquired with maximum current electrode separation of 100m using resistivity meter and its accessories. The aim of the study was to evaluate the aquifer vulnerability of the study area to contamination. The VES results were both qualitatively and quantitatively interpreted using partial curve matching and were further subjected to computer iteration using WINRESIST. The longitudinal conductance, thickness of layer overlying aquifer and hydraulic conductivity were generated and synthesized to produce the vulnerability map. A GODT multi-criteria model which is an acronym of Groundwater occurrence, Overburden thickness, Depth and Topography developed from the hydrogeologic parameters were evaluated alongside the longitudinal conductance values to determine the aquifer vulnerability of the area and to classify the study area accordingly. The curve type obtained are H and HA. The interpretation revealed three to four geoelectric layers: the topsoil (18.9-178.9Ωm), clayey (9.0-70.6Ωm), fractured basement (31.9-43.1Ωm) and fresh basement (1131-2916Ωm). The longitudinal unit conductance ranges from 0.032-0.93mhos. And from the GODT model derivations, the study area shows 92.5% of high vulnerability rating, 2.5% of low-moderate and 5% of moderate rating; areas with high rating are prone to contamination than areas with low-moderate and moderate rating. Hence, zones of high vulnerability may be not be encouraged for groundwater exploitation and, if need be, constant water quality assessment should be carried out before consumption.

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.

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

Groundwater Potential Evaluation in Parts of Southwestern Nigeria Using Dar-Zarouk Parameters

Dar-Zarouk parameters namely longitudinal conductance, transverse unit resistance, longitudinal resistivity, traverse resistivity, and coefficient of anisotropy, derived from electrical resistivity soundings, were employed in the western and south western portions of Sheet 223 Ilorin NW, Southwestern Nigeria to evaluate the subsurface water prospect. This is aimed at determining the potentiality and vulnerability of groundwater in the area. The longitudinal conductance values obtained range from 0.027 S at VES 3 in the north, indicating the poorest protective capacity, to 26440.95 S at VES 157 in the south, indicating the highest protectivity. Thus, the protective capacity rating of the study area shows very poorly, weak, moderate, good, and excellent ratings at VES stations 10, 12, 9, 2, and 178 respectively. The total transverse resistance range is 8.6 – 32733.87 Ωm2, with the lowest at VES 206 in the southeastern part, indicating high prospects, and the highest at VES 47 in the northern part of the area, indicating poor prospect. The lowest longitudinal resistivity (0.1951 Ωm), indicating high potential as well, occurs at the southern part and while the highest value of 8095.63 Ωm is obtained at the northern part.Furthermore, the coefficient of anisotropy in the area ranges between 0.029 and 5349.78. The south-western boreholes have values that fall between the standard range of 1.39-1.66, indicating that those areas have boreholes with high productivity. In conclusion, most parts of the study area have excellent protective capacities and high potentiality.

Geophysical Characterisation of Native Clay Deposits in Some Parts of Niger State, Nigeria

<p class="Abstract">Clay minerals are among the world’s most important and useful industrial minerals. Conductance, transmissivity and corrosity are some physical parameters for determining quality clay. Four (4) clay deposit sites in Kaffin-Koro, Dutse, Dogon-Ruwa and Kushikoko were investigated to evaluate corrosivity, the longitudinal conductance and transmissivity to determine the clay quality. Electrical resistivity method employing Schlumberger electrode array was used to determine the thicknesses and depths of the subsurface strata while Interpex 1xD software was used to interpret the data. Three (3) to four (4) layer earth models were delineated. Kaffin-Koro and Dutse showed three layer models while Dogon-Ruwa and Kushikoko revealed four layers. Moderate clay content was found in Kaffin-Koro in the second layer with longitudinal conductance value of 0.4780 siemens and thickness 0.770m at depth of 1.17m Dogon-Ruwa also had moderate clay content in the third layer with conductance value of 0.237 siemens, depth of 2.43m and thickness 1.76m. Kushikoko had low clay deposit in the second layer with conductance 0.1810 siemens and thickness 2.73 m at 4.37 m while the clay deposit in Dutse appeared to be generally poor as the longitudinal conductance values of the top two layers were less than 0.1 siemens.</p>

Spatial variation of sub-surface heterogenieties within the dyke swarm of Nandurbar region, Maharashtra, India, for groundwater exploration using Inverse Distance Weighted technique

To understand the protective capacity of aquifers, anisotropic nature and fracture geometry of dyke infested terrain in parts of Nandurbar region, Maharashtra, data from 39 vertical electrical soundings using Schlumberger configuration were acquired. Analysis suggests 3–5 layered structure in the study area. Further, the Dar-Zarrouk and other geoelectric indices were computed utilizing resistivity and layer thickness at each station. The Inverse Distance Weighted (IDW) algorithm was used to interpolate data spatially. Longitudinal conductance values suggest that the area has poor to moderate aquifer protective capacity, indicating that weaker zones may be prone to infiltrating contaminants. The high electrical anisotropy (λ) signifies EW and NS oriented dykes, suggesting heterogeneous and anisotropic nature of the subsurface. A direct relationship involving λ and fracture porosity indicate porous medium. The IDW algorithm, used for the first time in this region, provided an accurate and reliable estimate of spatial distribution and the underlying heterogeneities.

Estimation of Dar-Zarrouk parameters and delineation of groundwater potential zones in Karlahi, part of Adamawa Massif, Northeastern Nigeria

Karlahi is largely underlain by granites and migmatites gneiss of the Adamawa Massif. The area lies west of Benue Trough and east of Cameroon volcanic line. The aim of this paper is to determine hydraulic properties of water bearing layer using parameters derived from Dar-Zarrouk equation and characterized them into groundwater potential zones. The resistivity values of the weathered and slightly weathered layers which make up the water bearing layers were added and an average was taken and used as the resistivity of the water bearing formation in computation of Dar-Zarrouk parameters in Karlahi area. The values of resistivity of water bearing formation ranged from 18 to 4963 Ωm with an average resistivity value of 549 Ωm and the thickness of the water bearing formation ranges from 21 to 32 m with an average thickness of 24.5 m. Conductivity values range from 0.000201 to 0.05509 (σ) while the longitudinal conductance range from 0.00483 to 1.2363 Ω-1, the transverse resistance ranges from 407 to 123504.3 Ωm2. The hydraulic conductivity and transmissivity values range from 0.14 to 25.87 m/day and 3.28 to 580.4 m2/day respectively. The longitudinal conductance values in Karlahi area revealed poor to good with an average longitudinal conductance value that is moderate. High transverse resistance values are located in the central and southern part of Karlahi area while low values are located in the eastern part. The spatial distribution map of transmissivity in the area revealed moderate to high transmissivity values in the north central part and a negligible to low transmissivity in southern part, extreme northeastern part. The groundwater potential map of Karlahi area shows negligible to weak potential groundwater zones in SW and SE, moderate potential in the central to northern part of Karlahi area.

Geo-electrical modeling of leachate contamination at a major waste disposal site in south-eastern Nigeria

The contamination of aquifers due to the leaching of organic and inorganic waste materials deposited in landfills and open dumpsites leads to serious degradation of the environment. To determine the extent of leaching and to assess the migration of the leachate into the surrounding aquifer, vertical electrical sounding (VES) and electrical resistivity tomography (ERT) surveys were carried out along a heavily contaminated waste disposal site in South-eastern Nigeria. The results obtained from the vertical electrical soundings show that the area comprises three subsurface layers, and that the aquifer lies between the second and third layer. Computation of longitudinal conductance values shows that the overall protective capacity of the aquifer is weak; hence, the capacity for leachate contamination within the aquifer is higher. Models obtained from the electrical resistivity tomography surveys indicate the direction of the leachate plumes and also show the extent of leachate percolation into the aquifer. On the electrical resistivity tomography models, the locations of anomalous low resistivity zones indicate the presence of leachate. The results show that the leachate is moving rapidly towards the aquifer and this will create serious environmental degradation to valuable water resources in the area, thereby affecting health of humans and livestock within this heavily populated zone. Further, the results from the resistivity surveys confirm that the resistivity technique is a powerful tool for delineating the presence of leachate plumes and for indicating to what extent the leachate has infiltrated into the surrounding aquifer.

Investigation of Groundwater Potential using Electrical Resistivity Method and Hydraulic Parameters in Lam Apeng, Aceh Besar, Indonesia.

Lam Apeng is a village with a majority of people living as farmers, which causes the need of water for agriculture is increasing. The water demand in this area continues to increase as the population increases, for various purposes. The objective of this study is to determine the distribution of the groundwater layer using the electrical resistivity method and to determine groundwater potential using hydraulic parameters. This research is conducted using 2 measurement line with a length of each line is 112 meters and distances of each electrode is 2 meters. The data invert using Res2Dinv software to obtain 2D subsurface lithology subsurface. At line 1, the aquifer (sand) layer is located in the second layer with a rock resistivity value of 12 Ωm - 18.6 Ωm at a depth of 8 m - 18 m. At line 2, the aquifer (sand) layer is also located in the second layer with a resistivity value of 4.6 Ωm - 18 Ωm at a depth of 5 m – 12 m. Based on the interpretation of the two measurement lines, it can be concluded that the type of aquifer in the research site is a semi unconfined aquifer. In this study, hydraulic parameters (hydraulic conductivity, longitudinal conductance, transverse resistance, and transmissivity) was calculated based on the resistivity value and the thickness of the aquifer layer. The average resistivity of the aquifer layer used is 15.3 Ωm and 11.3 Ωm, respectively for line 1 and line 2, indicating that the aquifer was moderately corrosive. Longitudinal conductance values are 0.65 Ω-1 and 0.62 Ω-1 which indicated moderate protective capacity. The transmissivity values are 6.78 m2/dayand 4.77 m2/day, which indicates that the designation in this area is low and the groundwater potential is local or only for personal consumption.

Identification of potential groundwater locations using geophysical data and fuzzy gamma operator model in Imo, Southeastern Nigeria

Groundwater is among the most important resources of water supply of the worldwide population. The objective of this research is to select the most suitable drilling location of new groundwater wells, with a decision-making tool using geographic information system (GIS). The optimum location was evaluated based on the hydro-geoelectrical parameter derived from vertical electrical sounding (VES) including longitudinal conductance, aquifer thickness, aquifer resistivity, transmissivity, formation factor, and porosity. The analysis of the VES data revealed that the porosity values range from 1.8 to 21%, the formation factor values vary between 0.0355 and 0.14, the transmissivity values range from 3.4 to 6 m2/day, the longitudinal conductance values vary from 3 to 4.6 Ω−1, the aquifer thickness values range from 4.1 to 8.5 m, the aquifer resistivity varies between 0.7 and 40 Ω m. Hydro-geoelectrical data were integrated into GIS to precisely determine the best location for groundwater wells. Fuzzy liner membership was used to standardize the criteria layers; then, these layers were combined using fuzzy gamma overlay to produce the suitability map. The study area was classified into four classes: excluded, low suitability, moderate suitability, and high suitability. It is recommended that this method should be adopted by different governmental agencies involved in water resources management in Nigeria.

Integrated groundwater potentials studies, aquifer hydraulic characterisation and vulnerability investigations of parts of Ndokwa, Niger Delta Basin, Nigeria

Field geological and geophysical (Vertical Electrical Sounding VES) survey data were used in investigating groundwater potentials, aquifer characteristics and vulnerability in parts of Ndokwa area, Niger Delta, Nigeria. Data from twenty-one (21) representative VES survey points using Schlumberger configuration were acquired, processed and interpreted. Pumping test data and litho-log data from existing boreholes in the area were used to constrain interpretation and correlation of the VES results. The results revealed five to six geo-electric layers/units across the study area. The subsurface lithology is predominantly sandstone intercalated, in some cases, with clay, sandy clay, and clayey sand. Results also revealed the average depth to aquifer as 71.91 m (10.33–173.97 m); average aquifer thickness as 42.52 m (4.7–149.7 m) and average aquifer resistivity value as 1289 Ωm (470.84–2697.7 Ωm). Average overburden thickness was estimated to be 28.53 m (4.28–62.44 m). Aquifer characteristics derived from the VES results gave average calculated aquifer transmissivity value as 1162.31 m2/day (129.54–4181.31 m2/day), and average calculated aquifer hydraulic conductivity as 27.28 m/day (25.69–28.92 m/day). Longitudinal conductance values range of 0.006–0.137 were recorded from geo-electric field survey data in the area, indicating dominance of sand and sparse distribution of clay; and suggesting that the Aquifer Protective Capacity APC of the overburden above the aquifers in the study area is mostly poor to weak and prone to contamination from infiltration. The DRASTIC model was applied to ascertain the DRASTIC Index and compute aquifer vulnerability distribution of the area; and it revealed that the study area is characterised by low – moderate – high vulnerability at different locations. Topsoil corrosivity studies showed that topsoil in the area is practically non-corrosive to slightly corrosive. The results of this study have implications for groundwater resources development and management in the study area.

Delineation of Saline Water Intrusion Lateral Extent Using Hydro-chemically and Geo-electrically Derived CRS - Model Parameters - A Case Study of Eastern Dahomey Basin, Nigeria

This study was another attempt to map the subsurface lateral extent of saline water intrusions into aquifers at the eastern part of Dahomey basin, Nigeria. The study comprised geo-electric sounding method consisting of 108 vertical electrical soundings (VES) data acquired using Schlumberger array technique and hydro-chemical analysis of 61 water samples. The geoelectric survey results was presented as average longitudinal Conductance and average longitudinal Resistivity maps. The longitudinal conductance values vary from moderate to high (20 - 180 mhos) in the costal areas, while lower values (lesser than 10 mhos) were recorded in the mainlands. Conversely the average longitudinal resistivity values were low to moderate (0.26 - 41.7 ohm-m) in the coastal areas and in few places such Agbabu, Legbogbo and Sabomi in the mainland, while higher values (more than 60 ohm-m) were obtained from the mainlands. The hydro-chemical analysis results was presented as equivalent Salinity map; its values range from 25.8 mg/l (Ode-Irele) to 2808 mg/l (Asisa), high values were obtained from Ugbo, Ugbonla, Odonla, Idogun and Ayetoro area in the southeastern part of the study area and likewise at Agbabu in the north central part of the study area. The results were synthesized using CRS-model. The final CRS-model map showed that the saline water intrusion extended to 35 % of the total area which covers; most part of the coastal area and Agbabu in the mainland.

Geoelectric investigation to delineate groundwater potential and recharge zones in Suki river basin, north Maharashtra

Suki river basin of Raver sub-division is located towards the northeastern part of Jalgaon district in Maharashtra State. The existing land use pattern of the region clearly shows that more than 60% of the area is utilized for agricultural sector. Groundwater is the major source of irrigation and domestic purposes. To assess the overall water resources development of Raver area for better environment in future, investigation was carried out with the help of geophysical indicators. Vertical electrical sounding studies were conducted at 17 stations in the study area using Wenner configuration. The study was aimed at characterizing the aquifer in the area as well as assessing its potential risk to contaminant seepage in terms of protective capacity of the overburden rock materials using Dar-Zarrouk (D-Z) parameters, viz., the transverse resistance (T), longitudinal conductance (S), transverse resistivity (ρ t ) and longitudinal resistivity (ρ l ). These were computed to generate the resistivity regime of freshwater-bearing formations and its movement. The central-western part of the study area reflects very good to good protective capacity rating as can be seen from the high longitudinal conductance values. The low value of the protective capacity in the eastern part is making the aquifer system in the area highly vulnerable to surface contamination. This indicates that the ground water quality may have been deteriorated in the area and borehole water samples should be randomly sampled for contaminant loads based on this analysis.

Application of geoelectrical and chemical methods for groundwater assessment in Isheri-North, Ogun state, Nigeria

Geoelectrical investigation and chemical analyses were carried out at Isheri North area of Ogun State in order to assess the groundwater quality at shallow depth and its deep potential zone for groundwater development. The study area has been selected for investigation due to infiltration of the polluted Ogun River. Forty-three (43) Schlumberger Vertical Electrical Soundings (VES) and chemical analyses of water samples from one hand dug well and two shallow boreholes in the study area were carried out. Four to five geoelectric layers which correspond to top soil, clayey sand, sandy clay, clay and sand were delineated. The longitudinal conductance values (0.02 - 0.106mhos) of the topsoil in the area reveal its poor to weak protective capacity, thus exposing the underlying clayey sand to contamination as reflected from its resistivity values ranging from 4.8-15.1m. This low resistivity zone at shallow depth (3 – 26m), occasioned by infiltration, was further ascertained by high values of conductivity, turbidity, total hardness, TDS, Cl, Fe, and Mn ions in the analyzed water samples taken at depth ranges from 9 – 16m. The results of the analyzed water samples from this shallow zone are beyond international standards for drinking water. The underlying clay resistivity values ranged between 1.9 - 6.1m and thickness varied from 50.8 - 100.5m. This acts as the seal for the underlying aquifer (sand layer). The resistivity of the sand layer varied from 91.7-159m with a depth interval of 101.7-109.4m and 73.4-82.3m in VES 1 and VES 14 respectively. This constitutes the deep aquifer units in the study area. The longitudinal conductance values of the overburden above the profound aquifer units varied between 10.5-33.0 mhos and are indicative of very good to excellent protective capacity rating. Thus, the underlying deep aquifer units are well protected from being contaminated.Keywords: Electrical Resistivity, Groundwater, Aquifer, Geoelectric Section

Geoelectric Sounding for Evaluating Soil Corrosivity and the Vulnerability of Porous Media Aquifers in Parts of the Chad Basin Fadama Floodplain, Northeastern Nigeria

A geoelectrical survey was carried out in parts of the Chad Basin Fadama Floodplain as a means of evaluating both the soil corrosivity and protective capacity. One hundred and six Schlumberger Vertical Electrical Sounding data were collected at the corners of a 225 x 225 m square grid network. Topsoil resistivity and topsoil longitudinal unit conductance maps were generated from the first and second order geoelectric parameters respectively. Areas considered as high corrosivity are the north central, southwestern, southern and northern parts with (r<180w-m). Part of the study area characterized by materials of poor to weak protective capacity has longitudinal conductance values of less than 0.1 and (0.1 - 0.19) mhos respectively. Values between (0.2 - 0.79 mhos - sandy clay cover) and (0.8 - 4.9 mhos - clay cover) correspond to moderate and good protective capacity respectively. It can thus be concluded that the flanks of the floodplain underlain by appreciable clayey topsoil thickness columns are susceptible to corrosion tendency. These same flanks are characterized by materials of moderate to good protective capacity and serve as sealing potential for the underlying hydrogeological system in the area.