Geohydraulic and vulnerability assessment of tropically weathered and fractured gneissic aquifers using combined electrical resistivity and geostatistical methods

Sustainable potable groundwater supplied by aquifers depends on the protective capacity of the strata overlying the aquifer zones and their thicknesses, as well as the nature of the aquifers and the conduit systems. The poor overburden development of the Araromi area of Akungba-Akoko, in the crystalline basement of southwestern Nigeria, restricts most aquifers to shallow depths. Hence, there is a need to investigate the groundwater quality of the tropically weathered and fractured gneissic aquifers in the area. A combined electrical resistivity tomography (ERT) and Schlumberger vertical electrical sounding (VES) technique were employed to assess the groundwater-yielding potential and vulnerability of the aquifer units. The measured geoelectric parameters (i.e., resistivity and thickness values) at the respective VES surveyed stations were used to compute the geohydraulic parameters, such as aquifer resistivity (\({\rho }_{o}\)), hydraulic conductivity (K), transmissivity (T), porosity (\(\phi\)), permeability (\({\Psi }\)), hydraulic resistance (\({\text{K}}_{R}\)), and longitudinal conductance (S). In addition, regression analysis was employed to establish the correlations between the K and other geohydraulic parameters to achieve the objectives of this study. The subsurface lithostratigraphic units of the studied site were delineated as the motley topsoil, weathered layers, partially weathered/fractured bedrock units, and the fresh bedrock, based on the ERT and the A, H, AK, HA, and KQ curve models. The K model regression-assisted analysis showed that the \({\rho }_{o}\), T, \(\phi\), \({\Psi }\), and S contributed about 81.7%, 3.31%. 96.6%, 100%, and 11.63%, respectively, of the determined K values for the study area. The results, except T and S, have strong high positive correlations with the K of the aquifer units; hence, accounted for the recorded high percentages. The aquifer units in the area were classified as low to moderate groundwater-yielding potential due to the thin overburden, with an average depth of <4 m. However, the deep-weathered and fractured aquifer zones with depths ranging from about 39–55 m could supply high groundwater yield for sustainable exploitation. The estimated S values, i.e., 0.0226–0.1926 mho, for aquifer protective capacity ratings rated the aquifer units in the area as poor/weak to moderately high with extremely high to high aquifer vulnerability index, based on the estimated low Log \({\text{K}}_{R}\) of about 0.01–1.77 years. Hence, intended wells/boreholes in the study area and its environs, as well as any environments with similar geohydraulic and vulnerability characteristics, should be properly constructed to adequately prevent surface and subsurface infiltrating contaminants.

Integrated studies to investigate paleochannel aquifer in Dan Chang District, Suphan Buri Province, Western Thailand

Climate change is currently causing droughts in many parts of Thailand, especially in Dan Chang District, Suphan Buri Province where many areas are outside irrigation coverage and deep groundwater explorations are less successful due to groundwater shortages. Therefore, there is a need to explore other shallow groundwater (i.e. less than 15 m deep) resources to relieve the drought problems in the communities. This work uses integrated studies of remote sensing, geology and geophysics to identify the location of a paleochannel that contains shallow groundwater resources in the Nong Makha Mong Subdistrict, Dan Chang District, Suphan Buri Province. Potential sites were selected using preliminary remote sensing analysis along with field surveys. A high-resolution topography map from aerial photos was generated and 2D resistivity imaging surveys were conducted at the selected sites to delineate the location of the paleochannel. The drilled wells prove the success of the integrated study to identify the shallow groundwater in the paleochannel at a depth of 3 to 15 m with a groundwater yield of 4 m3/h. The sediments from the borehole suggest that a combination of alluvial deposits and fluvial sediments. Due to the relative lower cost of drilling shallow wells, this work could be used as a pilot project for local communities to explore shallow groundwater aquifers in paleochannels in areas that face a severe drought crisis and have very little deep groundwater potential.

Geohydraulic and vulnerability assessment of tropically weathered and fractured gneissic aquifers using combined electrical resistivity and geostatistical methods

Sustainable potable groundwater supplied by aquifers depends on the protective capacity of the strata overlying the aquifer zones and their thicknesses, as well as the nature of the aquifers and the conduit systems. The poor overburden development of the Araromi area of Akungba-Akoko, in the crystalline basement of southwestern Nigeria, restricts most aquifers to shallow depths. Hence, there is a need to investigate the groundwater quality of the tropically weathered and fractured gneissic aquifers in the area. A combined electrical resistivity tomography (ERT) and Schlumberger vertical electrical sounding (VES) technique were employed to assess the groundwater-yielding potential and vulnerability of the aquifer units. The measured geoelectric parameters (i.e., resistivity and thickness values) at the respective VES surveyed stations were used to compute the geohydraulic parameters, such as aquifer resistivity (\({\rho }_{o}\)), hydraulic conductivity (K), transmissivity (T), porosity (\(\phi\)), permeability (\({\Psi }\)), hydraulic resistance (\({\text{K}}_{R}\)), and longitudinal conductance (S). In addition, regression analysis was employed to establish the correlations between the K and other geohydraulic parameters to achieve the objectives of this study. The subsurface lithostratigraphic units of the studied site were delineated as the motley topsoil, weathered layers, partially weathered/fractured bedrock units, and the fresh bedrock, based on the ERT and the A, H, AK, HA, and KQ curve models. The K model regression-assisted analysis showed that the \({\rho }_{o}\), T, \(\phi\), \({\Psi }\), and S contributed about 81.7%, 3.31%. 96.6%, 100%, and 11.63%, respectively, of the determined K values for the study area. The results, except T and S, have strong high positive correlations with the K of the aquifer units; hence, accounted for the recorded high percentages. The aquifer units in the area were classified as low to moderate groundwater-yielding potential due to the thin overburden, with an average depth of <4 m. However, the deep-weathered and fractured aquifer zones with depths ranging from about 39–55 m could supply high groundwater yield for sustainable exploitation. The estimated S values, i.e., 0.0226–0.1926 mho, for aquifer protective capacity ratings rated the aquifer units in the area as poor/weak to moderately high with extremely high to high aquifer vulnerability index, based on the estimated low Log \({\text{K}}_{R}\) of about 0.01–1.77 years. Hence, intended wells/boreholes in the study area and its environs, as well as any environments with similar geohydraulic and vulnerability characteristics, should be properly constructed to adequately prevent surface and subsurface infiltrating contaminants.

Intrinsic Parametric Approach to Groundwater Vulnerability Assessment: A Case Study of Ijero Mining Site, Ijero-Ekiti.

The research was conducted to unravel the aquifer protective capacity and groundwater yield of the environment of a mining site at Ijero-Ekiti, Nigeria. The electrical resistivity method was employed and data gotten were used in combining the conventional longitudinal conductance and a new approach that indexes the resistivity and thickness considering some layers which could be protective and have low resistivity like clay material. The area is characterized by the Nigeria Basement Complex consisting of Precambrian rocks, made up of the migmatite gneiss, amphibole schist, quartzite, calc gneiss, schist biotite gneiss, biotite-schist, epidiorite, pegmatite and granite. A total of 9 points were sounded with maximum current electrode separation of 50 – 80 m. The sounding data were interpreted with the aid of partial curve-matching and computer iteration. Result of the interpretation of the geophysical data shows that the area is composed of variable subsurface layering that ranges from three to four layers. Groundwater potential zones were delineated based on the geo-electrical data. The study reveals that VES 1, 3, 4, 5 and 8 have high to medium groundwater potential. However, VES 2, 6 and 9 are characterized by low groundwater potential. The distinct aquifer protective zones identified in the study area using longitudinal conductance and geoelectric layer susceptibility indexing are poor and weak. The study has been able to detect the groundwater yield and the protective capacity of the overburden in the northeastern part of Ijero-Ekiti where a mining site is located using electrical method. Geochemical analysis of water and soil samples from the area is recommended to understand the right treatment required for some of the groundwater sources for drinking.

Electrical Resistivity Tomography And Induced Polarization Study For Groundwater Exploration In The Agricultural Development Areas of Brunei Darussalam

Electrical Resistivity Tomography (ERT) and Induced Polarization (IP) study was carried out for groundwater exploration at eight agricultural development areas in Brunei Darussalam. The study was undertaken to meet the growing demands of water supply in the Brunei agricultural sector, particularly for paddy field irrigation. A total of nineteen survey lines with survey lengths of up to 800 m and investigation depths of up to 150 m below ground level were conducted to delineate subsurface geological structures, formations and aquifer zones in the study area. Aquifer zones with resistivity values ranging from 1 to 100 ohm-m and chargeability values of less than 1 mV/V were detected in all surveyed locations. New groundwater well drilling was conducted at two of the surveyed sites based on interpretations of 2D resistivity and chargeability inversion models. Water well drilling encountered aquifer zones, which were primarily in sandy layers. Hydraulic tests revealed groundwater yields of 4.3 and 288 m³/day. Estimated transmissivity values of the aquifer units based on pumping tests are 0.53 and 109 m²/day, while their hydraulic conductivity values are 0.05 and 2.75 m/day. Estimated parameters of the aquifer units indicate weak to moderate groundwater yield for withdrawal and distribution for irrigation purposes at the investigated sites. The present study helped decision-makers take suitable measures for placing future irrigation wells and achieve significant groundwater exploration results in the study area.

Modeling of groundwater yield by the electrical method case of the Triassic sandstone aquifer (Tataouine South-Eastern Tunisia)

The method of electrical resistivity has proven very effective in the evaluation of groundwater. This specialized technique uses Dar-Zarrouk (D-Z) parameters in the estimation of longitudinal unit conductance, transverse unit resistance, and longitudinal resistivity to examine the groundwater level, to distinguish the fresh, brackish, and saline water interface, and to assess the storage capacity of groundwater in the Triassic sandstone aquifer system in the Tataouine region (South-Eastern Tunisia). In this context, 23 vertical electrical soundings (VESs) were carried out in the Tataouine region using the Schlumberger configuration with a current electrode with a maximum spacing of the current electrodes (AB) of 500–600 m. The results indicate that the study area consists of three types of aquifers: (i) silt/clay saline water (&lt;20 Ωm), (ii) a mixture of sand and clay freshwater (20–40 Ωm), and (iii) sand freshwater (40–200 Ωm). These sand freshwater aquifers are characterized by low longitudinal unit conductance (0–2.8 S), high values of transverse unit resistance (more than 9,000 Ωm2), and longitudinal resistivity (more than 35 Ωm) and are mainly concentrated in the north, south, and south-west regions of the study area. It should also be noted that the coefficient of anisotropy (λ) overlaps and does not clearly differentiate the characteristics of the aquifers of fresh, brackish, and saline water. An interpretation of VESs can also determine the storage capacity of groundwater by determining yield index values. Groundwater supply for the entire study area was classified as low yield, with a percentage of 13% and a maximum of 31% of the study area and 56% of moderate yield. Lastly, the real data from the drilling confirm all these results presented previously. The findings suggest that D-Z parameters are useful for making a distinction of various aquifer zones.

Groundwater Yield Modeling in the Floodplain of Hadejia, Northwestern Nigeria

This paper proposed a model explaining variation of shallow groundwater yield and dynamic level with respect to river location in the floodplain of Hadejia, along Hadejia River Basin of Jigawa State, Northwestern Nigeria. To achieve the aim, six transects were established within one km2 of floodplain and were oriented perpendicular to the river channel. Three tube wells were sampled and positioned along each transect at regular intervals making a total of 18 wells. Pumping test, which was repeated four times at 15 minutes interval in both morning and evening hours was used to measure groundwater yield. Multivariate statistical tools such as analysis of variance, Pearson product moment correlation, and cluster analysis were used, respectively, to test the research hypothesis and to classify sampling points into similar groups based on groundwater yield. Results show that the average yield of wells for evening hours recorded a higher yield of 3.3 L/s (55.93%) than the yield in the morning hours of 2.6 L/s (44.07%). Further, the 2-way ANOVA at 5% level of significance showed no significant difference in the groundwater yield related to relative location of wells in morning (p value, 0.30>0.05) and evening (p value, 0.21>0.05) hours. The results of ANOVA revealed no statistically significant difference between the points. It suggests that the adopted model can be applied in other similar sedimentary basins with a view to validating it. A decision support system is recommended among the strategies to improve groundwater resources management in the area.

Hydrogeophysical Investigation of Groundwater Systems in Otukpo, Benue State, North-Central Nigeria

Hydrogeophysical investigation of groundwater systems in Otukpo, Benue State, Nigeria has been carried out using vertical electrical sounding (VES) technique to delineate the groundwater potentials across the study area. Ten (10) vertical electrical soundings were carried out during the geophysical survey using the Schlumberger configuration of electrical resistivity method with maximum current and potential electrode spacing of 600 meters and 80 meters respectively. The VES data was qualitatively and quantitatively interpreted using the conventional curve matching and computer iteration methods. The result of qualitative interpretation depicts that the VES curves obtained within the study area are mainly the QH and KQH which are typically indicative of a sedimentary terrain. The results of the quantitative interpretation reveal that the resistivity values from shallow subsurface to the depth of about 500 m of the VES stations ranges from 3 Ωm to 1250 Ωm. The VES results also show that the study is characterized by seven (7) different inferred lithological layers namely; topsoil, sand/silt, laterite, clay, shale, sandstone and the basement rock. The result also reveals that the depth to water-saturated unit ranges from 450 to 500 meters within the study area. Two distinguished aquifer types were obtained within the area namely; unconfined and confined aquifers. The findings reveal that the future borehole drillers should target the confined aquifers situated between the depths of 450meters to 500 meters beneath the surface for sustainable groundwater yield across the study area.