Quality assessment of groundwater in an agricultural belt in eastern Nigeria using a Water Quality Index

Abstract

The physico-chemical and microbial analyses of fifteen hand-dug wells (HDWs) and six boreholes (BHs) in the  Ezeagu and Uzo-uwani Local Governments Areas (LGAs) of Enugu State in south-eastern Nigeria were conducted  to evaluate their water quality for potability. Samples were collected from 15 HDWs and 6 BHs. A total of 126 water samples were collected over two years covering the dry, early rainy and rainy seasons. There was a high correlation between electrical conductivity (EC) and the alkali and earth alkali metals at 95% confidence level as follows: EC and total dissolved solids (TDS) (r² = 0.904), EC and NO₃− (r² = 0.520), EC and K⁺ (r² = 0.540) for hand-dug wells; EC and TDS (r² = 0.730), EC and Ca²⁺ (r² = 0.697), EC and Na+ (r² = 0.721), EC and Mg²⁺ (r² = 0.637), EC and Cl− (r² = 0.717) for boreholes. The Water Quality Index (WQI) was calculated using the weighted arithmetic index method. The WQI  ranged from 58.26 ± 14.22 to 84.74 ± 3.03 and 48.70 ± 8.43 to 57.29 ± 5.81 for hand-dug well and borehole water samples, respectively. There were significant seasonal and spatial differences (p < 0.05) in some parameters, as  well as high coliform bacteria counts, biochemical oxygen demand (BOD), chemical oxygen demand (COD) and low  dissolved oxygen (DO). The obtained WQI values indicate pollution levels that make this groundwater unsuitable for human drinking water.