AUTHOR: OMALI, AURELIUS OJOINA
DEPARTMENT: GEOLOGICAL SCIENCES
AFFILIATION: NNAMDI AZIKIWE UNIVERSITY, AWKA
Geophysical investigation using Vertical Electrical Sounding (VES) was carried out with a view to determining aquifer types. Groundwater quality in wet and dry seasons was assessed and compared with the standards of the World Health Organization (WHO) and the Standard Organization of Nigeria (SON) to ascertain potability. An evaluation of corrosion and encrustation potentials of groundwater wells was carried out to combat deterioration of groundwater wells. Groundwater yields were determined through pumping test analysis in order to localize yields on the basis of productivity. Geologically, the area is underlain by the crystalline Basement Complex comprising, migmatite, granite gneiss with porphyroblastic gneiss, fine grained biotite gneiss and older granite series. These rocks are overlain uncomformably by Cretaceous sedimentary rocks dominantly composed of feldspathic sandstone and siltstone. Results of Vertical Electrical Soundings (VES) show that the aquifer types in the study area are unconfined aquifers formed within weathered basement and weathered/fractured basement complex rocks. The weathered basement aquifer occurs within 3 – layered and 4 – layered lithologic sections. The sections indicate a 3 – layer A and H – type curves and a 4 – layer AA – type curves. The resistivity of the weathered basement aquifer in the 3 – layer lithologic sections ranges between 6.81Ωm and 166.23Ωm, a depth range of 3.99m to 22.26m and a thickness of between 3.4m and 6.14m while the 4 – layer sections indicate the resistivity varying from316.62Ωm to 750Ωm, a depth ranging from 18m to 25m and a thickness of between 5m and 6.7m. The weathered/fractured aquifer occurs within 4 – layered lithologic sections. The weathered/fractured aquifer shows a 4 – layer AA – type geoelectric model with a resistivity range of 277.6Ωm to 317.5Ωm, a thickness ranging between 3m and 3.7m and a depth varying from 17m to 19.2m. Results obtained from the analyses of groundwater samples reveal that the groundwater in the study area is moderately fresh with the mean total dissolved solids (TDS) recording values of 1015mg/l during the dry season and 1110mg/l during the wet season. The total hardness ranges from 3.36mg/l to 14.5mg/l during the dry season and 24mg/l to 620mg/l during the rainy season. The mean concentrations of measured cations during the dry season, including Mg2+ (2.44mg/l), Ca2+ (12.80mg/l), Na+ (5.45mg/l) and K+ (9.63mg/l) are lower than those recorded during the rainy season with concentrations of Mg2+(3.11mg/l), Ca2+(14.66mg/l), Na+(7.88mg/l) and K+(9.74mg/l). The contents of anions in the groundwater samples recorded Cl- (0.08mg/l), SO42- (0.85mg/l), NO3- (0.09mg/l) and HCO3- (73.17mg/l) during the dry season and a rise in the concentration of Cl- (63.03mg/l), SO42- (4.57mg/l), NO3- (0.18mg/l) and HCO3- (83.73mg/l) during the wet season. The pH of the groundwater samples recorded an average value of 7.7 during the dry season and increased to 8.5 during the wet season. These values indicate alkaline water type. The mean concentration of dissolved oxygen (DO) recorded 5.40mg/l during the dry season and rose to 6.66mg/l during the rainy season. Redox recorded mean values of 383.76mv and 384.20mv during the dry and the wet season respectively. Other Ions recorded mean values of Cu2+ (1.76mg/l), Mn2+ (0.04mg/l), Fe2+ (0.10mg/l), Pb2+ (0.01mg/l), Cd2+ (0.003mg/l) and Cr6+ (0.02mg/l) during the dry season and Cu2+ (0.01mg/l), Mn2+ (0.04mg/l), Fe2+ (0.05mg/l), Pb2+ (0.01mg/l), Cd2+ (0.005mg/l) and Cr6+ (0.02mg/l) during the rainy season. These values are geochemically insignificant. Groundwater characterization using Piper Trilinear Diagrams indicates, Ca2+ – Mg2+- HCO3-, Na+- SO42- – Cl- and Ca2+ – Mg2+ – SO42 – Cl- water types during the wet season and Ca2+ – Mg2+- HCO3- water type during the dry season. The ionic concentrations during the wet season are of the order Ca2+>K+>Na+>Mg2+and HCO3->Cl- >SO42- while the dry season indicates the order of Ca2+>K+>Na+>Mg2+and HCO3- >SO42- >Cl-. Coliform counts in water samples collected from boreholes range between 0 to 20cfu/100ml during the dry season and vary from 0 to 25cfu/100ml during the wet season. The water samples collected from the hand- dug wells recorded a range value of 35 to 1800cfu/100ml during the dry season and 40 – 1800cfu/100ml during the rainy season.Yields of boreholes range from 30m3/day – 130m3/day. High yields were obtained from boreholes located between latitudes 70 48’ N and 70 49’ N and longitudes 60 43’ 45” E and 60 45’E along a NE – SW trending fractures which are in tandem with the dominant lineament trend in the area. Results of corrosion and encrustation potentials of groundwater wells in the study area show that, DO (100%), HCO3- (83%), TDS (57%) and temperature (100%) enhance the corrosion of boreholes while pH (100%) and total carbonate hardness (87%) accelerate encrustation of groundwater wells in the study area.A well developed water supply and sanitation scheme is recommended to ensure adequate water supply and healthy environment.
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Tags: Aquifer Types, Bacteriological Analysis, Bacteriological Parameters, Coliform Bacteria, Confluence City, Corrosion-Encrustation, Electrical Conductivity, Geological Sciences-PhD-2014, Geophysical Investigation, Groundwater Analysis, Groundwater Quality Characterization, Hydrogen Sulphide, Hydrogen Sulphite, Physical Sciences, Redox-MV, Salinity, Schlumberger Array-Electrical Resistivity Survey, Strtugraphic Subdivision, Vertical Electrical Standing, Water Sample Locations