IGRAC has published a case study on 'Groundwater resource management in the St. Bonaventure Township, Lusaka', which was written by researchers of the University of Zambia and the Natural Resources Development College. The study was undertaken to assess impacts of septic tanks, if at all, on the quality of groundwater in the aquifer underlying the St. Bonaventure Township, which is a low-density, high-income settlement located about 10 km south-west of Lusaka.
Groundwater in urban areas
Groundwater is a precious but invisible resource; to assess, monitor, use or protect something which we don’t see is not an easy task. Especially in urban areas, which are characterized by numerous (known and unknown) human impacts on groundwater environment.
Groundwater plays an important role in sustainable development of cities, while the cities are growing rapidly: in 1960, the urban population accounted about 34% of the total global population; the last year it reached 54% and still continues to grow. Demand for groundwater is growing accordingly. So how can we ensure a sustainable use of limited groundwater resources in this situation? How can we prevent (or at least mitigate) depletion, pollution, land subsidence or salinization of groundwater in urban areas?
Sharing experiences and knowledge on groundwater resources management in urban areas is certainly a part of the solution. IGRAC is committed to facilitate this process and to further raise attention about this widely spread problem. As a case study, we intentionally did not select a high-density, low-income urban area. Relatively low-density, high-income settlement in a large city in Africa was chosen, showing that groundwater management might be challenging even in these areas. Therefore, this case study carried out by researchers of the University of Zambia and the Natural Resources Development College is a good example of complexity of groundwater problems in urban areas and a valuable lesson learned.
'Groundwater resource management in the St. Bonaventure Township, Lusaka' presents results of a study that was undertaken in the St. Bonaventure Township – a low-density, high-income settlement located about 10 km south-west of Lusaka. The study was undertaken to assess impacts of septic tanks, if at all, on the quality of groundwater in the aquifer underlying the Township. Selection of the study site was purposive as all households in the Township use septic tanks to dispose of their excreta and wastewater, while boreholes provide sources of water supply to household.
Collection of water samples was done in the dry and wet seasons to determine the effect, if at all, of contrasting levels of saturation in the aquifer and the risk of contamination posed by increased recharge to the groundwater store. Sample analyses for pH, conductivity, total alkalinity, total hardness, nitrate, chloride, sulphate, calcium, magnesium, sodium, potassium, total coliforms and faecal coliforms were done at the Environmental Engineering Laboratory (EEL) in the School of Engineering at the University of Zambia.
Results showed that from the dry season to the rainy season, there were reductions in the average values of conductivity (766 to 714 mg l-1), pH (7.6 to 7.1), total dissolved solids (383.1 to 356.4 mg l-1), sulphate 59.7 to 45.3 mg l-1) , chloride (42.8 to 41.8 mg l-1), nitrate (18.5 to 4.9 mg l-1), and calcium (79.7 to 60.6 mg l-1). On the other hand, average values for total hardness (348.3 mg l-1), total alkalinity (342.8 to 41.3 mg l-1), magnesium (37.5 to 65.3 mg l-), sodium (34.3 to 51.5 mg l-1) and potassium (12.7 to 19.3 mg l-1) recorded increases. Reduction and increase in the values of different parameters could be attributed to phenomena of dilution and leaching of contaminants, respectively, due to varyimg levels of saturation of the aquifer.