Geoelectric Assessment of Ground Water Prospects and Vulnerability of Overburdened Aquifer in Oleh Delta State, Nigeria

Geoelectric Assessment of Ground Water Prospects and Vulnerability of Overburdened Aquifer in Oleh Delta State, Nigeria

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 14, Number 3 (2019) pp. 806-820 © Research India Publications. http://www.ripublication.com Geoelectric Assessment of Ground Water Prospects and Vulnerability of Overburdened Aquifer in Oleh Delta State, Nigeria *Dr. Julius Otutu Oseji and Dr. James Chucks Egbai *Department of Physics, Faculty of Science, Delta State University, Abraka, Nigeria. Abstract To achieve this, a geophysical study is necessary in Oleh. Vertical Electrical Sounding using Schlumberger arrangement Hence the study was carried out not only to reveal the depth, was carried out in Oleh Community not only to assess the thickness of the aquifer and the lithological set up at Oleh groundwater potential but determine the vulnerability of the Community but evaluate the aquifer protective capacity of the overburdened aquifer and hence establish areas having high overlying formations and determine areas boreholes could be potential for appreciable and sustainable groundwater supply. sited for potable and sustainable water supply. Fourteen (14) stations were established and surveyed using a maximum current electrode separation of 300.00 m. The field LOCATION OF THE STUDY AREA (OLEH) data obtained was first analyzed by curve matching before computer iteration. The result showed that apart from the Oleh is located in Isoko South Local Government Area of 0 1 11 locations in VES 5, 6, 7 and 11 that has shallow aquifer and Delta State, Nigeria. It lies between Latitudes 05 26 16 E 0 1 11 0 1 11 0 1 may be easily contaminated; boreholes could be sited in every to 05 29 55 E and Longitudes 06 11 11 N to 06 13 11 other location to a depth of 35.00 m at the 4th layer for potable 54 N. Oleh is the headquarter of Isoko South Local and sustainable water supply. The analysis of the borehole Government Area and is one of the administrative units in water at Oleh revealed that values for acidity, alkalinity, Isoko region of Delta State with several primary, secondary hardness, turbidity and conductivity in the groundwater is schools and many private school. The Faculties of Law and within the safe standard values for drinkable water apart from Engineering of the Delta State University is also in Oleh. being slightly acidic. This acidity is associated with the gas Groundwater resources in Oleh are particularly used for flaring in the study area. The overburden protective capacity domestic purposes. The increase in population also leads to a was evaluated using Longitudinal Conductivity of Protecting geometrical demand for portable water. Therefore an layers and this showed that apart from VES 4 obtained from evaluation of the aquifer protective capacity and groundwater Ogbemudia Road in Oleh that is weakly protected, every other sustainability is very important at Oleh. locations are poorly protected hence in the event of pollution, groundwater in Oleh is easily contaminated. LOCAL GEOLOGY OF OLEH Keywords: Groundwater; Vertical Electrical Sounding; Oleh is in the sedimentary region of the Niger-Delta Basin. Aquifer; protective capacity; Oleh The geologic sequence of the Niger-Delta consist of three lithostratigraphic units (Benin, Agbada and Akata formations) INTRODUCTION overlain by quaternary deposit [13]. Groundwater is the water that is located below the earth’s The Benin formation is the youngest formation that fills the surface. It is found in vast quantities filling the spaces Niger- Delta area and extends from the West towards the between grains of soil or rock. In the time past, the indigenes Southwest and beyond the coast line. It consists of coarse of Oleh depend on the local hand-dug wells for domestic and grained sand and locally fine to medium grained sand that is agriculture water needs, with the exploration for groundwater poorly sorted. The predominant formation is the sandy unit using modern technologies, portable water has grown to be with fragment of wood [2]. Underlining the Benin formation the choice for domestic and industrial usage. is the Agbada formation. This is the major oil and natural gas bearing facies in the basin. It crops out between Ogwuashi and The increase in population and urbanization at Oleh resulted Asaba known as Ogwuashi/Asaba formation. It is made up of to a corresponding reduction in the quality of groundwater due sandy units with thickness greater than that of the Benin to the movement of leachet to the aquifer or other formation [2]. Anthropogegenic interference [1]. Most wells drilled close to dumpsite areas have been abandoned due to contamination of Below the Agbada formation is the Akata formation. It leachate from waste disposal site and the infiltration of comprised of shale turbidities and small amount of silt and contaminants through the soil [12]). The vulnerability of clay. The Akata unit is formed from being over pressured and groundwater depends on the depth of the aquifer and the type not properly dehydrated with deficient oxygen and abundant of soil on the subsurface of the study area [11]. Therefore, a plant remains [5] better knowledge of the underground water formation and The Niger Delta sequence thus consists mainly of marine characteristics is important so as to ascertain whether the clays overlain by continental gravel and sand formations. groundwater is prone to contamination or not [11] 806 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 14, Number 3 (2019) pp. 806-820 © Research India Publications. http://www.ripublication.com Figure 1: Base Map of the Study Area (Oleh) Showing Locations of Vertical Electrical Soundings METHOD in the current electrodes spacing results in a deeper penetration of the electric field and a different apparent Groundwater investigation at Oleh Community was carried resistivity values obtained. The apparent resistivity out with the following materials: ABEM SAS 1000 measurements gave information about resistivity of a medium Terrameter, Current and Potential electrodes made of steel whose volume is proportional to the electrode spacing. rods, Measuring tapes, Hammers, Cables with crocodile clips, Resistivity is affected more by the water content and quality Global Positioning System (GPS) and Recording sheet of than the actual rock material in porous formations. The graph papers. The Schlumberger Arrangement of the Vertical of half current electrode spacing (AB/2) in the x-axis and Electrical Sounding with maximum current electrode spacing apparent resistivity values obtained from the field in the y-axis of 300.00 m was used for depth penetration in order to were plotted on a log-log graph and curve matched with investigate the groundwater potential and the protective standard curves to obtain the values of the resistivity and capacity of aquifer at the subsurface. The field procedure is thickness of the subsurface layers [8; 17; 16] Using the the expansion of the current electrodes successively while the Winresist software, the values obtained were iterated until the potential electrodes remain fixed until when the voltage curve and layer parameter with minimum root mean square readings on the terrameter fall below the reading accuracy, error is displayed [15] as shown in Figures (2 - 14). then a new potential electrode distance that is five times less than the current electrode distance is established and the Based on the knowledge of the local geology, resistivity survey continued till the end of the prospect [6]. An increase values and type of curves obtained, geological interpretations 807 International Journal of Applied Engineering Research ISSN 0973-4562 Volume 14, Number 3 (2019) pp. 806-820 © Research India Publications. http://www.ripublication.com were made in terms of the type of soil that can sustain in table 2.The portion where conductance is greater than 10 appreciable water for borehole and well and presented in table mhos is classified as excellent protective capacity, if the 1.The aquifer protective capacity characterization is based on conductance is between 5 and 10 mhos it has very good protective capacity and when the conductance ranged between the values of the summation of the thickness H hhT 21 .... 0.7 to 4.9 mhos the protection capacity is good and between and the average of the resistivity of the protecting layers 0.2 to 0.69 mhos, the aquifer is moderately protected. The zone which has conductance values of 0.1 to 0.19 mhos is R . The longitudinal conductivity of the protecting n weakly protected while areas with less than 0.1 mhos is considered as poor aquifer protective capacity [7; 1]. layers were obtained with the equation H T and presented R Table 1: Geoelectric parameter and lithologic delineation of the VES at Oleh Resistivity Thickness Depth to bottom VES Layers ( m ) ( m ) ( m ) Lithology Type of Curves 1 126.00 0.30 0.30 Top Soil (Clayey Sand) 2 6687.30 0.60 1.00 Coarse Grained Sand 1 3 305.00 3.10 4.10 Clayey Sand KHK 4 4123.80 11.50 15.60 Coarse Grained Sand ρ1<ρ2>ρ3<ρ4>ρ5 5 1610.30 …….. ……. Medium Grained Sand 1 410.60 0.70 0.70 Top Soil (Clayey Sand) 2 922.00 0.40 1.10 Fine Grained Sand 3 2055.20 0.70 1,80 Medium Grained Sand 4 147.90 5.30 7.20 Clayey Sand AHA 2 5 1401.70 27.70 34.90 Fine Grained Sand ρ1<ρ2<ρ3>ρ4<ρ5<ρ6<ρ7 6 3314.60 51.50 86.40 Coarse Grained Sand 7 4519.30 ……. …… Coarse Grained Sand 1 61.00 0.60 0.60 Top Soil (Clay) 2 126.10 0.20 2.70 Clayey Sand KHA 4 3 25.90 7.90 10.50 Clay ρ1<ρ2>ρ3<ρ4 4 10636.40 ……. ….. Coarse Grained Sand 1 256.60 1.10 1.10 Top Soil (Clayey Sand) 2 159.30 0.60 1.60 Clayey Sand QHA 5 3 6.30 1.10 2.80 Clay ρ1>ρ2>ρ3>ρ4<ρ5 4 576.30 3.80 6.60 Fine grained sand 5 87101.40 …….

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