ANALYSIS OF THE OCCURRENCE OF ELEMENTAL POLLUTANTS IN SHALLOW AQUIFERS USING WATER QUALITY INDEX METHOD: THE CASE OF DAR ES SALAAM, TANZANIA

Abstract

Groundwater is important for drinking purposes especially in urban areas. This is due to the deterioration of surface water quality and increased pollution from poor waste management practices, rapid urbanization growth and industrialization. This study was carried out in unplanned settlements in Dar es Salaam city in order to establish the level of elemental pollutants in shallow aquifer. Water quality index (WQI) was used to assess and delineate the quality of groundwater which generated information for easy interpretation by policy makers and the general public at large. A total of 75 groundwater samples were collected from eight unplanned settlements during wet season (April to June, 2018) and dry season (September to October 2018). Samples were analyzed using standard methods. Average concentrations of eleven physicochemical parameters including TDS, pH, PO₄^2-, NO₃-N, Mg²⁺, Ca²⁺, K⁺, Na⁺, Cl^-, HCO₃^- and SO₄^2- were used to establish WQI. Computed WQI values ranged from 54.46 to 189.5 making two distinctive groups of groundwater i.e. poor and good water quality for drinking. Results showed that 41 and 34 boreholes equivalence of 54.7% and 45.3%, respectively, fall on the category of poor and good water quality for drinking. Results further indicated that based on major ions, most groundwater extracted from boreholes in Dar es Salaam city need prior treatment before it is tapped for human consumption.

 

KEYWORDS:  Correlation coefficient; Drinking Water; Groundwater; hydro geochemistry; Pollution