Abstract
A total of sixteen Vertical Electrical Sounding (VES) surveys and five physicochemical analyses were carried out in selected locations within the Yenagoa Metropolis, in Bayelsa State, Nigeria, to delineate the concentration of ferruginous minerals in freshwater aquifers in the area. For the geophysical survey, the Schlumberger electrode configuration was employed. The resulting data obtained was processed and interpreted using Excel suite, IPI2WIN resistivity, Surfer-11 and Rockworks software. The results revealed four to six geologic layers across the area, and were used to generate geoelectric maps which showed that in most part of the study area, there were uneven distributions of shallow aquifers (4 – 10m), and uneven layers of clay and sandy-silt at varying depths up to 20m. The physicochemical analysis of raw water samples collected from five boreholes located in close proximity to the VES sounding locations were analysed for physical and chemical parameters. Physical parameters tested include colour, conductivity, turbidity, and temperature. Chemical parameters analysed are pH, Dissolved Oxygen (DO), Total Dissolved Solids (TDS) Alkalinity, Total Iron, Carbonate, Chloride, Sulphate, and heavy metals such as copper, chromium, nickel, cadmium, manganese, zinc and lead. The pH was determined using a Mettler Toledo (GmbH 8603 Schwerzenbach) pH meter by direct measurement. An analogue mercury thermometer was used for temperature measurements and a Hach 2100A turbidimeter for turbidity determination. Also, the concentrations of Zinc, Lead, and Copper in the water samples were obtained using the flame atomic absorption spectrophotometer. It was observed that the values SO42- , Cl-, Na2+, Mg2+, Ca2+, F- have values below World Health Organization (WHO) standard in all boreholes tested while Mn2+, NH3, PO3−and Fe2+, K+, and Cu2+ have values above WHO standard in some boreholes. The pH values all showed that the water was slightly basic as the values all exceeded the neutral limit 7, with only station showing slightly elevated pH value 9, suggesting the presence of iron bacteria. F-, K+, Fe2+ and Mn2+ have values that exceeded the WHO standard. The results from Physicochemical and geophysical analysis suggest that at depths of 20 – 45m, the concentration of ferruginous minerals is high especially towards the north eastern section of the study area and so drilling should be made to approximate depths of 50 – 80m for minimal iron contamination in the aquifers.
Highlights
The importance of water as a useful natural resource goes beyond the fact of being essential for the survival of mankind and for the survival of the natural environment
It was observed that the values SO42, Cl, Na2+, Mg2+, Ca2+, F- are below World Health Organization (WHO) [30] standard in all boreholes tested while Mn2+,NH3, PO3−and Fe2+, K+, and Cu2+ have values above WHO [30] standard in some boreholes
The pH values shown in table 3.2a and 3.2b, all showed that the water was slightly basic as the values all exceeded
Summary
The importance of water as a useful natural resource goes beyond the fact of being essential for the survival of mankind and for the survival of the natural environment. Due to the fact that groundwater moves slowly through underground mediums and by the action of natural flushing of aquifers, when areas are contaminated, they commonly remain so for decades or longer The presence of these dissolved minerals in groundwater is a result of weathering and interaction with the geologic formation which may affect human health (Freeze and Cherry 1979; Domenico and Schwartz 1990; Kortatsi, 2007; Aghazadeh and Mogaddam 2010). The Niger Delta region is blessed with large quantity of groundwater from shallow aquifer, but the region is still challenged by water inadequacy due to the commercialization of available potable water, making it unavailable to indigent people This is a major issue as most groundwater aquifers found in Bayelsa state contain high concentration of dissolved iron and other heavy metals. This study, focuses on the need for accurate characterization of the subsurface for a better understanding of the groundwater architecture and how it is affected by the iron concentration of the area to aid plan for the future development of boreholes and wells in this region
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