Spatial Variation in Groundwater Geochemistry and Water Quality Index in Port Harcourt, Rivers State, Nigeria

Abstract

The aim of this work is to convert the complex chemical quality data of groundwater in Port Harcourt area into a Water Quality Index, WQI, determine the operating geochemical processes and produce a map reflecting the spatial distribution of the water quality. Results of the physicochemical analysis of the groundwater from 71 boreholes show that 21% of the boreholes are low in pH indicating acidic water. Elevated electrical conductivity values in some of the water samples suggest pollution by seawater. Iron concentration is above the World Health Organization guide value in 9% of the boreholes studied, with maximum value up to 0.62mg/L. A high coliform count in 9% of the wells poses a potential health risk. The water is generally classified as soft and fresh water based on its hardness and TDS. Concentrations of major ions are: Ca>Mg>Na>K =HCO3>Cl>SO4>NO3 in the order of abundance. Ca-Mg-HCO3 and Ca-Mg-SO4-Cl are the dominant hydrogeochemical facies. Interpretation of the hydrogeochemical data suggests that ion exchange; reverse ion exchange and silicate weathering are the prevailing hydrochemical processes responsible for groundwater chemistry. Hydrochemical indices (Mg/Ca, Cl/HCO3, and Cation Exchange Values, (CEV) generally indicate low-salt inland water, with minimal marine influence. Using the weighted arithmetic mean method of the Water Quality Index Scheme, the groundwater is classified into five groups: Excellent (59%), Good (30%), Poor (11%), Very poor (4%) and Unsuitable (6%) with respect to human consumption. The general trend on the WII map reveals that water quality decreases southwestwards suggesting a possible influence of the sea water.