Effects of Urbanization on Groundwater Quality in African Cities: A Case Study of Accra, Ghana

Abstract

Population influx in African cities have caused the emergence of slums. Most urban slum dwellers depend on groundwater sources because of their availability and affordability. Due to the dense living conditions of the slums, wells and boreholes are situated in locations that expose the groundwater to possible contamination. A study was therefore conducted to determine the effects of urbanization on groundwater quality in Accra. A mixed method research design was used whereby interviews were conducted among slum residents in other to acquire information about groundwater usage. Twenty (20) groundwater samples were taken from five (5) slums within the city of Accra for laboratory analysis in order to assess the quality of the water. The coordinates of each sampling location were recorded using GPS. The water samples were analyzed for 27 physiochemical water quality parameters and two (2) microbiological indicators. An analysis of variance (ANOVA) was conducted to assess the difference in water quality parameters between slums. Geostatistical analysis was also conducted to map the extent and distribution of water quality parameters among slums. The results showed that 15 out of 27 water quality parameters were significantly different between slums (p<0.050). Microbiological indicators were also significantly different among slums with p-values such as; E. coli (p=0.0067) and Total coliform (p=0.0003). Four out of the 5 slums were significantly experiencing lead (Pb) poisoning in the groundwater. The mean lead concentrations for these slums were 0.25mg/l, 1.00, 0.25 and 1.5mg/l, respectively for Nima, Chorkor, Jamestown and Pantang. The results were above the WHO lead limit of 0.01mg/l. Chorkor and Sabon Zongo also had salt producing physiochemical parameters which were above the WHO permissible value. The mean values recorded for the salt parameters were 222.50and 462.50mg/l for Ca, 177.50 and 255.00mg/l for Mg, 727.3 and 1063.4mg/l for Cl-, and 270.37, 472.00, 690.16mg/l for Na. Nima, Sabon Zongo and Jamestown were using groundwater that is exposed to high levels of nitrate. The results also show the presence of manganese exceeding WHO value in the groundwater of Nima, Chorkor and Pantang. All the groundwater samples from the 5 slums were bacterially contaminated which is a possible indication of faecal matter presence in the water. A geospatial mapping of water quality parameters showed that slums closer to the sea were high in dissolved ions thereby implying possible salt water intrusion. The mapping also showed that slums closer to major landfills were experiencing more groundwater contamination. The results of the study imply that the environment and location of wells contribute immensely to the quality of groundwater produced. A policy brief and framework have been developed to fill in the gaps for quality assurance in Ghana water policy