Dar-Zarrouk Parameters Research Articles

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

Abstract 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 (<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.

Delineation of sinkhole in evaporite deposits using electrical resistivity survey: a case study of southern Kohat Plateau, Pakistan

Vertical electrical sounding (VES) is a non-destructive geophysical technique which provides fast subsurface lithological investigations and it is widely used in exploration of water, mineral resources, and its characterization. The present study work has been focused on subsurface imaging over evaporite deposits in Bahadarkhel area, Karak, Pakistan where multiple VES points along three profile lines have been acquired using Schlumberger electrode configuration to delineate subsurface lithology and structure of the area. The VES curves have been modeled and interpreted which resulted in true resistivities, depths, and thicknesses of layers. These VES points have been stacked along their respective profile lines for pseudosections and resistivity cross section preparation. Five distinct geoelectrical units have been identified depending upon their true resistivity values. Iso-resistivity 3D surfaces at 30 m and 60 m depths have been generated using the interpreted data which exhibits salt diapiric structure and dissolution of salt at depth by the action of infiltrating water from nearby ephemeral stream. Dar-zarrouk parameter calculations yield transverse resistance, longitudinal conductance, and anisotropy maps which infer that the area is mostly covered with rock salt and the presence of clay beds and calcareous sediments increases the resistivity values.

Spatial behavior of the Dar-Zarrouk parameters for exploration and differentiation of water bodies aquifers in parts of Konkan coast of Maharashtra, India

Demarcation of aquifer boundaries and hydro-geologic characterization can help in proper management and conservation of groundwater resources of a coastal region. The objective of the present study is to identify and delineate the groundwater-bearing zones and protection of freshwater aquifers from saltwater ingress in the northern parts of Sindhudurg district, western Maharashtra, India. A total of 86 vertical electrical soundings (VES) were carried out by Schlumberger electrode arrangement to infer the sub-surface lithology around Kankavali, Vijaydurg, and Malvan. The Dar-Zarrouk parameters were computed to generate the spatial variation maps of transverse resistance (T), longitudinal conductance (S), transverse resistivity (ρt), and longitudinal resistivity (ρl), to decipher the resistivity contrast of fresh water and salt water-bearing formations. The results demonstrate that these parameters provide a better resolution in delineating the seawater intrusion in coastal aquifers. The overburden aquifer protective capacity computed from the longitudinal conductance suggests that 59% of the area has poor aquifer protection, while 23% has weak, 11% has moderate and 7% falls in good protective capacity rating. This parameter reveals the infiltration of contaminants and the health of the aquifer. The electrical anisotropy (λ) value ranges from 0.9 to 5.1, suggesting an increase from SW to NE and also from SE to NW. The fracture porosity (φf) ranges from 10−6 to 0.65, which corroborates with the high and low λ values, reflecting that fracturing is due to anisotropy and significant reserves of groundwater could be exploited in this coastal region.

Vertical Electrical Sounding (VES) for Estimation of Hydraulic Parameters in the Porous Aquifer

Similarities in both water and electric current flows allow the relation of hydraulic and geoelectric parameters of porous aquifers. Based on this assumption and the importance of the hydraulic parameters for groundwater analyses, this study aimed to estimate hydraulic conductivity (K) and transmissivity (T) with vertical electrical sounding (VES) in the porous aquifer at the experimental farm of the University of Brasilia, Brazil. VES is a geophysical technique that provides electrical resistivity (ρ, Ω m) and thickness (h) of the subsurface layers. The ρ and h aquifer data, associated with lithology, water table level (WTL), and groundwater electrical resistivity (ρw, Ω m), allowed the calculation of complementary geoelectric parameters (formation factor, F, and Dar Zarrouk parameters) and the relation with K and T, determined via slug test. VES data allowed the elaboration of geoelectric models, with mean absolute percentage error (MAPE) below 6% compared to field data, and the identification of the aquifer in each VES station. Significant exponential regression models (R2 > 0.5 and p-value < 0.05) showed the possibility of using geoelectric parameters to estimate hydraulic parameters. This study allowed the verification of the applicability of consolidated models and the identification of appropriate empirical relationships for hydrogeological characterization in the Brazilian tropical porous aquifers. The results of this work, besides the rapid sampling and low cost of performing vertical electrical sounding (VES), may justify the use of this geophysical technique for preliminary porous aquifer characterization, especially in regions absent of or with insufficient monitoring wells.

Empirical Study of the Groundwater Protection Potential and Water Quality Using the Electrical Resistivity Method and a PG990 Spectrometer Around Obafemi Awolowo University Dumpsite Southwestern Nigeria

Groundwater plays a very important and fundamental part in human existence because of its essential role in living systems. The study aimed at carrying out an empirical study into groundwater protective potential and water quality around Obafemi Awolowo University solid waste facility and AbaGboro Community. This was achieved by using the electrical resistivity method to delineate the subsurface inhomogeneity around the dumpsite facility and also using the PG990 Atomic Absorption Spectrometer for metal analysis of water quality. The Schlumberger electrode array arrangement was engaged in the survey. A total of twelve vertical electrical soundings (VES) data was collected within the Obafemi Awolowo University dumpsite. The water samples were collected at two locations within the AbaGboro community which was 4.5 Km from the dumpsite to determine its quality. The results of the VES revealed the depth, resistivity, and thickness. The observed resistivity and the thickness values were further used in determining the groundwater protective potential, by calculating the Dar-Zarrouk parameters which showed that 91.7% of the study area is within poor/weak protective potential. The result from the water analysis of the hand-dug bore holes of the two different locations in the AbaGboro Community showed the presence of heavy metal concentrations as Pb, As, Mn, Cd, Zn, Cr and Co. Therefore, periodic assessment of water quality should always be carried out because we cannot anticipate when the groundwater will be contaminated due to relatively poor/weak groundwater protective potential.

Geophysical Assessment of Seawater Intrusion into Coastal Aquifers of Bela Plain, Pakistan

Seawater intrusion is a major challenge in many coastal areas all around the world, mainly caused by over-exploitation of freshwater resources, climate change, and sea-level rise. Consequently, seawater intrusion reaches several kilometers inland, thus making the freshwater resources polluted and unsuitable for human use. Conventionally, the fresh-saline water interface is delineated by the number of laboratory tests obtained from boreholes. However, such tests suffer from efficiency in terms of data coverage, time, and cost. Hence, this work introduces Dar-Zarrouk (D-Z) parameters, namely transverse resistance (Tr), longitudinal conductance (Sc), and longitudinal resistivity (ρL) computed from non-invasive vertical electrical sounding (VES). Two-dimensional (2D) imaging of D-Z parameters provides a clear distinction of fresh-saline aquifers. Such techniques remove ambiguities in the resistivity interpretation caused by overlapping of fresh and saline aquifers during the process of suppression and equivalence. This study was carried out by 45 VES along five profiles in the coastal area of Bela Plain, Pakistan. D-Z parameters delineate fresh, brackish, and saline aquifers with a wide range of values such as freshwater with Tr > 2000 Ωm2, Sc < 3 mho, and ρL > 20 Ωm; saline water with Tr < 1000 Ωm2, Sc > 25 mho, and ρL < 5 Ωm; and brackish water with Tr between 1000–2000 Ωm2, Sc from 3 to 25 mho, and ρL between 5–20 Ωm. The D-Z results were validated by the physicochemical analysis using 13 water samples and local hydrogeological setting. The obtained results propose that D-Z parameters can be used as a powerful tool to demarcate the fresh-saline aquifer interface with more confidence than other traditional techniques. This geophysical approach can reduce the expensive number of borehole tests, and hence contributes to the future planning and development of freshwater resources in the coastal areas.

Geo-hydraulic evaluation of aquifers of the Upper Imo River Basin, Southeastern Nigeria using Dar-Zarrouk parameters

Aquifer geo-hydraulic evaluation of the Upper Imo River Basin, Southeastern Nigeria, was carried out to estimate aquifer parameters from surface resistivity data. Forty (40) vertical electrical sounding data were acquired with the ABEM™ Terrameter SAS 4000 using the Schlumberger array with a maximum current electrode separation of 1000 m. Seven (7) parametric soundings were carried out close to the location of existing boreholes with pumping test data to geologically constrain the predictive process. The vertical electrical sounding data were processed using a combination of curve matching and computer modeling using the OFFIX™ Software. Aquifer resistivity of the study area ranged between 136 and 4640 Ωm. The depth to water table varies between 23.6 and 94.5 m, while the aquifer thickness varies between 1.7and 126.2 m with Ibeku and environs having the thinnest aquifers. Estimates of the Dar-Zarrouk parameters revealed that the transverse resistance varies between 534.8 and 196,092 Ωm2, while the longitudinal conductance ranged between 0.001737 and 0.7211 Ω−1. Estimates of the geo-hydraulic parameters using Dar-Zarrouk parameters calibrated with local geology revealed that aquifer hydraulic conductivity ranges from 1.902 to 42.85 m/day and 0.4195 to 5.339 m/day for the areas underlain by the Benin and Ameki Formations, respectively. Similarly, aquifer transmissivity values on the other hand ranged between 71.97 and 1810.91 m2/day and 1.448 and 424.985 m2/day for the Benin and Ameki Formations, respectively. The range of aquifer hydraulic parameters interpreted in the study area revealed that the groundwater potentials of the area vary from fair to good with the areas underlain by the Benin Formation having higher groundwater potentials.

Assessment of Groundwater Resources in Coastal Areas of Pakistan for Sustainable Water Quality Management Using Joint Geophysical and Geochemical Approach: A Case Study

Delineation of fresh/saline groundwater is essential for sustainable water quality management, especially in the coastal areas all around the globe. Seawater intrusion causes substantial degradation in quality of freshwater resources in the coastal areas. The main reason for saltwater intrusion is the changing environment in terms of sea-level rise, climate change, and over-extraction of freshwater resources to meet the growing demands. In this study, an integrated approach of geophysical and geochemical methods was used to assess saltwater intrusion in the coastal areas of Bela Plain, Pakistan. The inverted electrical resistivity computed from 50 vertical electrical sounding (VES) constrained the subsurface into five layers and two aquifers through 3D imaging, such as silty clay and sandy clay containing saline water, and sand, sandy gravel, and gravel containing freshwater. However, the narrow range of resistivity values shows an overlap of saline/fresh groundwater. Such ambiguity in the resistivity interpretation was removed by Dar-Zarrouk (D-Z) parameters. D-Z parameters, namely transverse unit resistance (Tr), longitudinal unit conductance (Sc), and longitudinal resistivity (ρL) estimated from VES, marked a clear distinction between saline and fresh aquifers with a wide range of values. The geochemical method was performed using 20 water samples for the main cations (K+, Ca2+ Na+, and Mg2+), anions (SO42−, HCO3−, Cl−, and NO3−), and other parameters (TDS, EC, and pH). Fresh/saline aquifers revealed by D-Z parameters are in good agreement with those delineated by physicochemical parameters and local hydrogeological conditions. This study delineates seawater intrusion of about 13–42 km from Sonmiani Bay in the Arabian Sea towards the inlands of Bela Plain. Therefore, it is expected that this investigation will be helpful in future planning for the management and exploitation of freshwater resources in the study area. Our study suggests that D-Z parameters can be used as the most inexpensive alternative to the traditional geotechnical and environmental tests for the demarcation of fresh/saline groundwater with a large coverage in any coastal or contaminated area under a homogeneous or heterogeneous setting.

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.

Estimation of Aquifer Protective Capacity, Soil Corrosivity and Dar-Zarrouk Parameters in Kaura Area of Kaduna State, Nigeria

This study presents an estimation of aquifer protective capacity, soil corrosivity and Dar-Zarrouk parameters for Kaura area of Kaduna State in northern Nigeria. Electrical resistivity sounding data and borehole pumping test data obtained from 20 locations within the LGA were obtained and used for this study. The geoelectric data exhibited curve types generally consisting of H, HA, KH or K-A-H types from which five-layer lithology were delineated across the entire study area. Well yield varies from 16 – 400 litres/min, pumping rate ranges from 16 to 140 l/min, drawdown varies from 1 – 22m, while specific capacity ranged from 1 – 95 litres/min. The aquifer protective capacity characterization was based on values of longitudinal unit conductance of the overburden, and 35% of the locations showed good protective capacity, while the remaining 65% exhibited moderate protective capacity. From the soil corrosivity evaluation, the upper soil layers were classified as moderately corrosive at one location, four locations were marked as slightly corrosive, while the remaining locations were found to be practically non-corrosive. Based on thicknesses and resistivities of the overburden layers, Dar-Zarrouk parameters were determined. The reflection coefficient ranged from 0.29 to 0.92, resistivity contrast occurred between 0.35 to 25.38, while the coefficient of anisotropy ranged from 0.70 to 3.84 with mean value of 1.57. Values above 1.0 are generally considered high and they occurred more toward the western part of the area than the middle and eastern parts. Both the longitudinal unit conductance map and coefficient of anisotropy map were generated for the area.

Estimation of Aquifer Protective Capacity, Soil Corrosivity and Dar-Zarrouk Parameters in Kaura Area of Kaduna State, Nigeria

This study presents an estimation of aquifer protective capacity, soil corrosivity and Dar-Zarrouk parameters for Kaura area of Kaduna State in northern Nigeria. Electrical resistivity sounding data and borehole pumping test data obtained from 20 locations within the LGA were obtained and used for this study. The geoelectric data exhibited curve types generally consisting of H, HA, KH or K-A-H types from which five-layer lithology were delineated across the entire study area. Well yield varies from 16 – 400 litres/min, pumping rate ranges from 16 to 140 l/min, drawdown varies from 1 – 22m, while specific capacity ranged from 1 – 95 litres/min. The aquifer protective capacity characterization was based on values of longitudinal unit conductance of the overburden, and 35% of the locations showed good protective capacity, while the remaining 65% exhibited moderate protective capacity. From the soil corrosivity evaluation, the upper soil layers were classified as moderately corrosive at one location, four locations were marked as slightly corrosive, while the remaining locations were found to be practically non-corrosive. Based on thicknesses and resistivities of the overburden layers, Dar-Zarrouk parameters were determined. The reflection coefficient ranged from 0.29 to 0.92, resistivity contrast occurred between 0.35 to 25.38, while the coefficient of anisotropy ranged from 0.70 to 3.84 with mean value of 1.57. Values above 1.0 are generally considered high and they occurred more toward the western part of the area than the middle and eastern parts. Both the longitudinal unit conductance map and coefficient of anisotropy map were generated for the area.

Delineation of Groundwater Potential Zones using Integrated Approach in Semi-Arid Hard Rock Terrain, Kanavi Halla Sub-Basin, Belagavi District, Karnataka

Abstract Water scarcity has become a major problem especially in arid and semi-arid regions due to insufficient rainfall throughout the globe. This has led in serious search for groundwater resources. Kanavi Halla Sub Basin (KHSB) of Ghataprabha River basin drained by Ghataprabha River, Belagavi District of Karnataka state in India has been considered for present study. Electrical resistivity survey was carried out at selected sites using Schlumberger method with four electrode configuration. A total of 22 Vertical Electrical Sounding (VES) were conducted throughout KHSB and representative of different litho units were considered. Data obtained were then interpreted using curve matching technique with IPI2Win software. The interpreted graphs show three to six layers. The various interpreted curve types are of AAK-type, HA-type, A- type, KH-type, HAA-type, KQH-type, AK-type, K-type, HQH-type, H-type and AKQH-type. From the results it shows that the maximum number of curves are associated with A type which refers to hard rock terrain, whereas curve associated with H type indicates water potential site. The expected subsurface strata are interpreted on the basis of observed bore well drilling data. Borewell log reveals soil formation followed by moderately weathered formation, weathered jointed formation, jointed formation, hard formation from top to bottom. Further deep, the formation is devoid of joints and fractures. Therefore, the weathered, jointed formation may be interpreted as water bearing zone. 2-D geo-electric section has been drawn using IPI2WIN over eight selected trends to understand the geometry of the aquifer formed. The investigation was meant to characterize the aquifer in KHSB along with the risk assessment for contaminants through seepage in terms of protective capacity with the help of Dar-Zarrouk (D-Z) parameters such as longitudinal unit conductance (S), longitudinal resitivity (ρl), transverse unit resistance (T), transverse resistivity (ρt), Electrical anisotropy(λ) and root mean square resistivity (ρm). These were evaluated to know the aquifer conditions in order to demarcate the freshwater bearing zones. South eastern part of KHSB might be contaminated and 30% of the area is weak to poor capacity protective zone for contaminants. The work adequately highlights the practical use of geophysical techniques, combination of geo-electrical modelling, D-Z parameters, borehole log in the groundwater resource assessment process. This technique is highly recommended for the area with similar geological setup.

Geoelectrical investigation of groundwater potential and vulnerability of Oraifite, Anambra State, Nigeria

Electrical resistivity survey employing vertical electrical sounding was carried out in Oraifite, Southeastern Nigeria, involving a total of twenty soundings across, in order to assess the groundwater potential and the aquifer vulnerability in Oraifite. The field data were interpreted using the WINRESIST software, and the resulting geoelectric curves give the resistivities, depths and thicknesses of each geoelectrical layer. Dar Zarrouk parameters and aquifer transmissivity were computed using the values of aquifer resistivity and thickness. From the results, variations of the computed parameters were observed. Aquifer resistivity ranges from 420.1 to 27,585.8 Ωm having an average value of 4906.3 Ωm, while its thickness varies from 13.4 to 93. 9 m. Longitudinal conductance varies from 0.0015 to 0.2136 Ω−1, transverse resistance ranges from 29,388.88 to 1,158,604.0 Ωm2, while the transmissivity varies from 1.1692 to 123.7905m2/day. The contour maps reveal the distributions of these parameters, which help in delineating zones with different layer characteristics. The result from this study can be a reference for decision making in the abstraction and management of groundwater repositories.

Vertical electrical sounding in the investigation of subsurface gravel deposits in arid environments—a case study, El-Salhayia plain, West Ismailia area, Egypt

The vertical electrical sounding (VES) is a common geophysical technique which depends mainly on the clear difference in the electrical resistivity between the causative body and the hosting sediments. These conditions could be achieved in the arid environmental zone of Egypt. The VES technique has been tested and used in the El-Salhayia plain in order to locate the subsurface accumulations of dry gravels. Twenty soundings have been measured in the plain by using the Schlumberger array. Interpretation of the VES curves showed that they are of 3-layer K-type where the dry gravel bodies represent the middle layer and occurred as lenses that gave high electrical resistivity relative to the hosting dry sand sediments. The estimation of the transverse resistance (i.e., one of the Dar-Zarrouk parameters) of the expected subsurface gravel layer detected three promising sites for quarrying operations in the El-Salhayia plain, where the depths and thicknesses of the gravel deposits could be estimated. The grain size analysis of some drilling samples from four available water wells in the study area confirmed the occurrence of gravel deposits with different sizes (i.e., granules and pebbles). Accordingly, the vertical electrical sounding technique can be highly recommended as an effective tool for gravel prospecting in similar conditions.

GEOELECTRIC STUDY OF GROUNDWATER REPOSITORY IN PARTS OF AKWA IBOM STATE, SOUTHERN NIGERIA

Geoelectric survey employing Vertical Electrical Sounding (VES) was carried out in order to assess the groundwater repositories. A total of seven soundings were obtained with their layer resistivity, thickness and depth within the maximum electrode separation. The geoelectric parameters obtained were used to estimate the Dar-Zarrouk parameters (longitudinal conductance and transverse resistance), hydraulic conductivity and transmissivity. The result shows the aquifer resistivity ranging from 77.14 to 784.76 Ωm, with thickness ranging from 28.78 to 80.04 m. The longitudinal conductance have values ranging from 0.071 to 0.825 Ω-1 while the values of hydraulic conductivity and transmissivity range from 1.087 to 5.881 m/day and 60.180 to 374.031 𝑚2/day respectively. The contour maps generated show the variation of these parameters across the subsurface, and areas with poor protective capacity were delineated. The results also delineate the groundwater potential of the study area as moderate, while the corrosivity rating indicates non-corrosive and slightly corrosive.

Aquifer vulnerability using geophysical and physiochemical methods in parts of Ethiope West Local Government Area of Delta State, Nigeria

Supply of potable water in Oghara communities in particular and parts of Ethiope West Local Government Area of Delta State in general is inadequate as a result of increasing population and development activities in the area. This can be resolved and sustained if groundwater resources are effectively managed. This study was carried out to determine the aquifer vulnerability and groundwater quality using geophysical and physiochemical methods in parts of Ethiope West Local Government Area, Delta State. Thirty vertical electrical soundings and four dipole–dipole profiling were administered using Abem Terrameter SAS 1000 AB. The field data were curve matched and iterated using WinResist and Dipro software. The aquiferous zone was found in the fourth layer with resistivity ranging from 159 Ωm to 100234 Ωm, thickness ranging from 12 m to 156 m, and depth ranging from 32 m to 162 m except VES 25, whose aquifer is in the third layer. The dipole–dipole resistivity structure shows low resistivity values along areas where waste dump was sited with resistivity ranging from 300 Ωm to 630 Ωm. This finding suggests that the leachate from the dumpsite is affecting the characteristics possessed by the subsurface close to it. The first order geoelectric and Dar-Zarrouk parameter study of aquifer protective capacity revealed a protection capacity value less than 0.1 for VESs 1–18 and 20–30, while VES 19 revealed a value of 0.24. Thus, Oghara communities are extremely unprotected, and the aquifer is prone to contamination. The physiochemical analysis carried out indicates that groundwater is slightly acidic with a pH value ranging from 5.40 to 6.40 when compared with the WHO permissible limit. The groundwater flow direction is depicted from the east to the west; this will assist policy planners to decide where dumpsites and companies generating waste could be sited to preserve groundwater potential.

Geoinformatics and geophysical survey-based estimation of best groundwater potential sites through surface and subsurface indicators

Groundwater is the most important natural resource around the world which needs new and advanced technologies for control and monitoring. This investigation was to check the groundwater potential zones by integrated techniques of geoinformatics and geophysical investigation through a vertical electrical sounding in Rawalakot, Azad Kashmir, Pakistan. The study area being a sedimentary basin, sandstone is the major rock type with good porosity and permeability. Satellite data were used to generate different thematic maps such as slope percent, lineament density, land use/cover, drainage density, geology, roughness index, curvature, topographic wetness index, and rainfall. Subsequently suitable rank and weightage was assinged for final weight overlay analysis to identify the groundwater potential zones. Final potential map was generated with good, moderate, and poor zones. This analysis revealed that 92.60% of the area is categorized to be having good to moderate groundwater potential. Then, an electrical resistivity survey was done by vertical electrical sounding (VES) using Schlumberger electrode configuration, at 32 locations to check the subsurface condition. The predominant curve types were Q type, A type, H type, and K type. The apparent resistivity was calculated at 20-m, 40-m, and 60-m depths. Dar-Zarrouk parameters were calculated to identify the subsurface aquifers and protective capacity rating. Integrating the outcome of GIS and geophysical studies, the region with good groundwater potential was delineated with more accuracy.

GEOELECTRICAL INVESTIGATION OF GROUNDWATER QUALITY THROUGH ESTIMATES OF TOTAL DISSOLVED SOLIDS AND ELECTRICAL CONDUCTIVITY IN PARTS OF AKWA IBOM STATE, SOUTHERN NIGERIA

This paper presents the results of a geophysical investigation of groundwater quality in parts of Akwa Ibom State, Southern Nigeria. A total of 11 vertical electrical soundings (VES) was carried out in the study area using the Schlumberger electrode configuration. The results of the interpretation show that the area comprises 4 geoelectric layers. The third layer constitutes the major economic hydrogeological unit in the area and has resistivity of between 50.3 Ωm and 2088.9 Ωm and thickness of between 36.8 m and 149.0m respectively. The groundwater quality was assessed through estimates of the electrical conductivity and total dissolved solids in water. The conductivity ranges from 74.5 to 604.4µS/cm with an average value of 244.0µS/cm while the TDS values range from 47.7 to 386.8 ppm with an average value of 156.1 ppm. Based on these values, which are within the permissible limits, the water is considered to be fresh and suitable for drinking and other domestic/agricultural usages. The results show excellent correlation between the estimated TDS and the Dar-zarrouk parameters (longitudinal conductance and transverse resistance) on one hand and the aquifer bulk resistivity on the hand which demonstrate the ease of deriving TDS from surface resistivity data.

Hydrogeophysical assessment and protective capacity of groundwater resources in parts of Ezza and Ikwo areas, southeastern Nigeria

Geoelectrical investigations were carried to determine the aquifer potentials and protective capacity of Ezza and Ikwo areas, Ebonyi State, Southeastern Nigeria. A total of thirty-five (35) Vertical Electrical Sounding survey was conducted using the Schlumberger configuration to evaluate the character of the aquifers in the studied locations. Geoelectric sections derived from the modeling of the sounding data reveal 4 to 7 subsurface layers. The Vertical Electrical Sounding curves obtained were QH, QHK, QHKH, QQH, KHK, QHAK, and QQHK. The third and fourth layers constitute the aquiferous zones. The aquifer resistivity ranges from 11.7 to 814 Ωm, while the aquifer thickness and depth range from 99.2 to 3.4 m and 8.7 to 105.8 m respectively. The Dar Zarrouk (longitudinal conductance and transverse resistance) parameters were determined from the results. The longitudinal conductivity ranges from 0.004975 to 2.9573 mhos, whereas the transverse resistance ranges from 70.1 to 17,161.6 Ωm2. Furthermore, the aquifer potentials of the study area were shown to differ with aquifer size, structure and characteristics are influenced by the underlying geology generally. From the study, it was concluded that the western axis of the study area underlying the Ebonyi Formation has a higher aquifer potential compared to the eastern axis underlying the Abakaliki Formation. This is supported by the geology of the area with the Abakaliki Formation dominated by shales that have very low permeability, while the Ebonyi Formation consists of shales with alternations of sandstone which supports good aquifer conditions. The study area has a moderate aquifer protective capacity.

GEOELECTRIC STUDY OF GROUNDWATER REPOSITORY IN PARTS OF AKWA IBOM STATE, SOUTHERN NIGERIA

Geoelectric survey employing Vertical Electrical Sounding (VES) was carried out in order to assess the groundwater repositories. A total of seven soundings were obtained with their layer resistivity, thickness and depth within the maximum electrode separation. The geoelectric parameters obtained were used to estimate the Dar-Zarrouk parameters (longitudinal conductance and transverse resistance), hydraulic conductivity and transmissivity. The result shows the aquifer resistivity ranging from 77.14 to 784.76 Ωm, with thickness ranging from 28.78 to 80.04 m. The longitudinal conductance have values ranging from 0.071 to 0.825 Ω-1 while the values of hydraulic conductivity and transmissivity range from 1.087 to 5.881 m/day and 60.180 to 374.031 𝑚2/day respectively. The contour maps generated show the variation of these parameters across the subsurface, and areas with poor protective capacity were delineated. The results also delineate the groundwater potential of the study area as moderate, while the corrosivity rating indicates non-corrosive and slightly corrosive.