Characterisation and temporal variability assessment of groundwater quality in Petauke Town, Eastern Province

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Mbewe, Solomon
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The study was aimed at contributing to the provision of good quality groundwater supply in Petauke District. It comprised collection and analysis of 50 groundwater samples from boreholes in the dry and wet season in Petauke Town. Water exit points were sterilised before collection of samples. Physical properties were assessed on-site using potable pH and conductivity meters, whereas samples for chemical and microbiological analysis were collected in sterilised bottles and transported to the Environmental Engineering Laboratory at the University of Zambia for analysis. In the laboratory, the numbers of total and faecal coliforms were determined using the membrane filtration technique whereas for chemical analysis, samples were analysed for major ion chemistry using the standard methods after APHA (1998). The quality of analytical data was evaluated by computing the ionic balances for all the samples.Furthermore, data for the major ions (Ca2+, Mg2+, Na+, K+, SO42-, Cl-, CaCO3 2-,HCO3 2-) were plotted on the Piper diagram so as to understand the evolution of hydro-chemical parameters of groundwater in the town. Groundwater classification was done after WHO (2006) whereas temporal variability of water quality between the dry and wet season was assessed using the ANOVA. The suitability of water for drinking was assessed by comparing the data obtained in the field and laboratory analysis to the WHO (2008) and ZABS (2008) limits. Parameters with values above the limits were identified as groundwater contaminants in the town.The study revealed that groundwater in the town was characterised by low pH (6.17),high iron (2.63 mg/l) and high bicarbonate content (609.6 mg/l), high total hardness (as 598 mgCaCO3/l) and the abundance of major ions were in the order of Ca > Mg >Na> K = HCO3 > Cl >SO4. Hydrochemical facies identified were Ca-HCO3 and Ca (Mg) HCO3 type. Fifty eight percent of groundwater was hard, 26% was moderately hard, 14% was very hard and only 2% was soft. Observed values of most of the parameters fell within the ZABS and WHO guidelines for drinking water except for nitrate (10%), total colifoms (72%), faecal coliforms (56%), pH (28%), iron (24%) and total hardness (58%). The ANOVA showed that there was no significant seasonal variation in groundwater quality. Groundwater contaminants in the town were found to be total and faecal coliforms, nitrate, pH, iron and total hardness. Groundwater in Petauke Town belongs to the CaHCO3 and Ca (Mg) HCO3 group and is hard. Most of the boreholes (75%) were microbiologically contaminated. There was no seasonal variability in groundwater quality and most of the parameters fell within the WHO/ZABS guidelines for drinking water except total and faecal coliforms, total hardness, turbidity, nitrates, nitrites pH and iron which were identified as contaminants. The over-abundance of carbonates, iron and calcium are naturally caused whereas microbiological pollution and excess nitrates are caused by anthropogenic activities. To prevent the effects of water pollution on human health, there is need for effective groundwater monitoring and chlorination of boreholes.
Aquifers-Zambia , Groundwater Management , Groundwater