Groundwater potential and quality assessments of a coastal environment: a case study of the location of Federal University of Technology Ikot Abasi (FUTIA), Akwa Ibom State, Nigeria

Abstract

The economic, residential, agricultural, educational, and social relevance of groundwater to coastal residents provoked the selection of FUTIA and its surroundings, located along the Okpobo River and Atlantic Ocean shorelines, for integrated geo-electrical and hydrochemical investigations. The main thrust of this research was to better understand the potentiality, vulnerability, and agronomic implications of using groundwater for home, industrial, and irrigation purposes, which would lead to better planning, management, and conservation of the resource. By applying vertical electrical method involving 1-D and 2-D techniques, potentially prolific surficial (< 30 m depth) and moderately deep (> 30 m depth $\le$ 200 m) aquifers were delineated. The study area is fraught with surficial unconfined aquifers drilled to follow the depths of the preexisting productive but vulnerable aquifers near them. The untapped semi-confined to confined aquifers for depths > 30 m and less than 200 m were viewed to have less susceptibility to contaminations due to the presence of overlying argillaceous units concealing them. In all, groundwater yield index (GWYI) was observed to range from $1.389\times {10}^{5}$ to$1.860\times {10}^{8}\Omega {m}^{2}$, while the values of longitudinal unit conductance (S) characterized the aquifers to be poor $\left(S<\text{0.10 }{\Omega }^{-1}\right)$ and weak $\left(S:\text{0.10 -0.19 }{\Omega }^{-1}\right)$ with the exception of VES 17 (V17) and VES 20 (V20) delineated as having good $\left(S=1.42{\Omega }^{-1}\right)$ and moderate $\left(S=\text{0.206 }{\Omega }^{-1}\right)$ protections respectively. Geochemical analysis, which showed some elevated concentration above WHO standard indicated the order of relative abundance of light cations to be $N{a}^{+}$>$C{a}^{2+}$>$M{g}^{2+}$>${K}^{+}$; heavy metals as $C{r}^{2+}$>$M{n}^{2+}= C{u}^{2+}$> $F{e}^{2+}$>$P{b}^{2+}$>$C{d}^{2+}$>$N{i}^{2+}$ and the anions in as $HC{O}_{3}^{-}$>$S{O}_{4}^{-2}$> $C{l}^{-}$>${F}^{-}$. Results also revealed that the area is more abundant in anions due to charge balance error (CBE) found to be equal to -50%. The results of Irrigation water evaluation (IWE) and irrigation water quality indices (IWQI), indicated that none of the groundwater analyzed was suitable for irrigation of all plants (no restriction class of IWQI) in the survey area. However, water with moderate and low restriction categorizations were recommended for use in irrigation of plants with moderate salt tolerance and sensitive salt-resistant crops, respectively due to high Soil sodicity. With the characterization of groundwater parameters and potential maps, graphs and charts pregnant with information on aquifer peripheral covering layers, which advises on vulnerability; potential capacity of aquifer and geochemical and agronomic information, stakeholders can assure the survival of coastal fauna and flora as well as appropriate planning and management for long-term water supply for domestic, industrial, agriculture and social uses under recurring, demanding, and harsh climatic circumstances at a low cost.