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.

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.

Integrated Geophysical and Hydrogeochemical Characterization and Assessment of Groundwater Studies in Adum West Area of Benue State,Nigeria

Integration of geophysical and hydrogeochemical methods has been scientifically proven to be useful in vulnerability study and groundwater characterization. Subsurface geoelectric parameters such as resistivity and thickness obtained from geophysical method (Vertical Electrical Sounding VES) was used to determine aquifers vulnerability, longitudinal resistance (ρL) and transverse unit resistance (Rt). Thirty four water samples were collected from groundwater sources for physicochemical analysis.Estimated results from longitudinal conductance (S), (Rt) and (ρL) showed that the values ranges from 0.03 to 2.5mhos, 103.64 to 1964417.8 Ω/m2 and 215.41 to 65731.68 Ω-m respectively. Result from S suggested that 50 % of groundwater is considered to be vulnerable to contamination from the earth surface, while the remaining 50 % is considered to be slightly vulnerable to surface contamination. Further findings obtained from hydrogeochemical analysis such as Gibb’s and Chadba plots revealed that groundwater is highly influenced by rock water interaction,groundwater is classified to be Na+ + HCO3¯, Ca2+ + Mg2++ HCO3¯ , Na+ + Cl¯ and Ca2+ + Mg2+ + Cl¯ water type. Deduction from Soltan classification suggested that groundwater is classified to be of Na+ ˗ HCO3¯ and Na+ ˗ SO4 2¯ water type. Results obtained from Ec and pH suggested that the values were below WHO permissible limit, while result obtained from TDS showed that at some sampling points TDS values were above WHO limit. Based on pH value obtained groundwater within the study area fell within slightly basic to acidic.

HYDROGEOPHYSICAL AND AQUIFER PROTECTIVE CAPACITY OF ABAKALIKI/AFIKPO AREA AND ENVIRONS, SOUTHEASTERN NIGERIA USING GEO-SOUNDING DATA

This work was carried out to evaluate the hydrogeological and geophysical properties of Abakaliki and Afikpo environs. Forty-seven (47) Vertical Electrical Sounding data were acquired with electrode spacing (AB/2) of 500m using Schlumberger electrode configuration. Conventional curve matching techniques were used to interpret the data and obtain initial model parameters. Results of the study showed 3-7 electric layers which indicate multiple aquifer system. QQH, QHK, KHK and QQHK models were the Vertical Sounding curves obtained. The aquiferous layers make up the third and fourth layers. The resistivity of the aquifer varies from 10.74Ωm to 13201Ωm with an average of 1013.58 Ωm. Aquifer depth ranges from 6.2m to 92.5m with an average aquifer depth of 27.07m, while the aquifer thickness varies from 2.3m to 55.87m with an average of 15.61m. Transverse resistance varies from 65.34Ωm2to 7079.14 Ωm2 with an average of 9966.29 Ωm2; and the longitudinal conductance varies from 0.00018Ω-1 to 1.65 Ω-1 with an average of 0.026 Ω-1. From the study, 49% of the study area falls under the poor protective rating while 21% falls under the weak rating with 25% and 5% which makes up the moderate and good ratings respectively. Using the average longitudinal conductance, it is observed that the study area is moderately protected.

Groundwater investigations in the Hattar industrial estate and its vicinity, Haripur district, Pakistan: An integrated approach

The Hattar industrial estate in the Haripur district, Khyber Pakhtunkhwa (KPK), Pakistan, is investigated for the groundwater potential and aquifer vulnerability using vertical electrical sounding (VES) data, borehole logs, and hydrochemical analysis. A total of eight VES points were acquired in the Haripur region using Schlumberger configuration. The interpreted VES models are further constrained by four borehole logs to delineate comprehensive information of the thin lithological layers, subsurface layers configuration, and spatial extent in the area. A quantitative interpretation based on the VES and the borehole data suggests six main subsurface layers: (i) soil cover, (ii) gravel, (iii) clay, (iv) clay with gravel, (v) silty-clay, and (vi) sand with boulder in the study area. A fence diagram is also generated to provide a detailed paleo-depositional model of the subsurface layers. The interpreted VES data is utilized to compute aquifer thickness, longitudinal conductance, and transverse resistance within the study area. The lateral extent and protective capacity for the aquifer were inferred from these measurements. The aquifer thickness is relatively low in the central and eastern parts ranging from 10 m to 11 m. The longitudinal conductance map shows values greater than 2 mhos from the central region to northern one. This is indicative of moderate to good protective capacity for the aquifer and is less vulnerable to infiltration of Hattar industrial polluted fluid. However, the values less than 0.19 mhos in the southwest and east are indicative of weak protective capacity with risk of contamination. The hydrochemical analysis of the surface and subsurface water is carried out at eleven locations to identify the water quality within the study area. The chemical analysis of the water shows the presence of the high concentration of magnesium, bicarbonate, and chlorine away from the World Health Organization (WHO) standard.

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.

Groundwater Potential Assessment Using Geoelectrical Data: A Case Study Of Phuket Island, Thailand

Groundwater is the dominant source of water supply on Phuket island, Thailand. The water demand on Phuket has been increasing due to rapid urbanization and population growth. A scarcity of freshwater and over-extraction of groundwater may shortly become severe problems for Phuket. Geoelectrical data obtained by Vertical Electric Sounding (VES) were employed in this study to estimate the Dar Zarrouk parameters of the study area. Twenty-four VES stations were set up using Schlumberger configuration with a 1.0 m minimum spacing. The lithology layers from 24 unpublished borehole data indicating each subsurface layer were validated with the resistivity data obtained from VES. The geoelectric profiles gave a maximum of three layers with varying resistivities and thicknesses across each VES station. Two parameters (longitudinal conductance and transverse resistance) of the Dar Zarrouk model were calculated from VES data to generate the thematic maps in a GIS environment, thus the groundwater potential in Phuket Island was represented as a single map by using the weighted overlay technique in ArcGIS, based on both longitudinal conductance and transverse resistance. The groundwater potentials were classified into three potential levels (low, medium, and high). The results reveal that the highest groundwater potential areas are isolated and in specific locations, while the majority of area has medium level groundwater potential. Finally, the low potential zones are in the flank and the top parts of the study area.

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.

Hydrogeological appraisal of basement and sedimentary terrain in Ogun state using Geoelectrical methods

The coverage of the groundwater potential was estimated using the geometry calculator, the potential groundwater zones were validated using geophysical surveyed points of some selected locations in Abeokuta and Ewekoro. Generally, the result of the study shows that the higher the aquifer thickness and depth the better the groundwater potential. In the basement part of the study area (Abeokuta), the Northwestern region is characterized by increase in overburden thickness (28.1 m at VES-9), weathered layer resistivity (546 Ω m at VES-7) and longitudinal conductance unit (0.193 S at VES-3 and 0.218 S at VES-7), reflecting high aquifer potentials. In this regard, the Northeastern part of the study area can be categorized as good groundwater potential; moving towards the Southwestern part from the northern, groundwater potentiality changes from good to moderate while the Southwestern/ central part is categorized as area with poor groundwater potential. In the Sedimentary part of the study area (Ewekoro), the northcentral region is characterized by increase in overburden thickness (93 m at VES-10), longitudinal conductance unit (3.644 S at VES-6), reflecting high aquifer potentials. In this regard, the northcentral part of the study area can be categorized as good groundwater potential; moving towards the northeastern part of the study area, groundwater potentiality changes from good to moderate while the southwestern part is categorized as area with poor groundwater potential. The area showed very good protective capacity at VES’s 2, 3, 4, 5, 7 and 8; making 60% of the VES stations. Good protective capacity is observed at VES 1 and 6, making 15% of the VES stations in the town. The excellent protective capacity is observed at VES 9 and 10; making 15% of the study area.

EVALUATION Of GROUNDWATER VULNERABILITY IN FRACTURED AQUIFER USING GEOELECTRIC LAYER SUSCEPTIBILITY INDEX AT OJU, SOUTHERN BENUE TROUGH NIGERIA

A combination of geoelectric and hydrogeologic concept was used in the assessment of groundwater vulnerability in fractured aquifers of Oju and environs. The study area is underlain by the sediments of the Asu River Group, Southern Benue Trough Nigeria. A total of twenty-seven (27) Vertical Electrical Sounding (VES) was carried out within the study area. Geoelectric parameters (layer, resistivity and thickness) of the overlying layers across the study area were determined and used to evaluate the vulnerability of the underlying aquifers. Three charts were compared using geo-electrically derived models; LC (Longitudinal Conductance), GLSI (geoelectric layer susceptibility indexing) and GOD (groundwater occurrence, overlying lithology and depth to the aquifer. Results obtained from LC revealed that the study area fell within the moderate category, GLSI showed that aquifer vulnerability were categorize within negligible to low category and GOD fell within low to moderate category. On the average, groundwater within the study area is considered moderate vulnerable to groundwater contamination.