Delineating the impact of urbanization on the hydrochemistry and quality of groundwater wells in Aba, Nigeria

Abstract

Groundwater samples from 61 randomly selected tube-wells in densely residential (DR) and sparse residential (SR) parts of Aba, Nigeria were analysed to elucidate the influence of urban land-use on the quality and characterize the hydrochemistry of the groundwater. Twelve water quality indicators: temperature, pH, EC, and TDS (physicochemical), as well as HCO3, Cl, SO4, NO3, Na, K, Ca, and Mg (major ions) were analysed for each well. The results of the analyses were grouped based on the influence of land-use on the wells. The descriptive statistics, Piper, Chadha's, and bivariate scattered plots, as well as index of base ion-exchange, and Friedman nonparametric statistical test were used to delineate and ascertain the significance of the urban impact on the quality of the groundwater wells. The results showed that the groundwater pH is acidic (3.7–5.6), and the mineralization low, with TDS ranging between 6.5 mg/l – 365 mg/l. The statistical mean and standard deviation (x¯±S.D) of the remaining quality indicators were found within the limits set by WHO in all the wells. The Piper and Chadha's plots revealed four dominant water-types with spatial differentiation in the area. Though there are several mixed water-types in the SR area, the Na-HCO3 water-type is dominant and represents the background hydrochemistry of the groundwater in the area. Whereas, Mg, Ca-Cl, water-types predominates in the DR wells. Other dominant water-types found between the SR and DR areas are Na-Cl and Ca-HCO3 types. The rapid compositional change and local alteration in the hydrochemistry of the groundwater were impacted by some identified urban land-use practices, which introduce additional major ions in the groundwater solution. The mixed water-types found in the SR wells were influenced by factors such as the direction of flow and mixing of the groundwater reservoirs impacted by the hydrochemistry of the DR groundwater, which were upstream to the SR wells. The results of indicators such as EC, TDS, Cl, and NO3, when compared showed observable local deterioration moving from wells in the SR to wells in the DR area. This was supported by the Friedman statistical test which revealed statistical significance of some urban practices on the quality of the groundwater. These results highlight the current quality status and harmonize the reports of previous studies which have characterized the hydrochemistry of the groundwater in the study area.