Continued population growth, economic development and climatic change have increased the demand for water supply in South Africa. As a result, most surface water systems have been exhaustively developed, increasing dependency on groundwater, including on meager aquifers during dry spells. This study aims to characterize the hydrogeology of the Pietermaritzburg Formation, a poorly productive aquifer that has been targeted for borehole sitting during drought years though with poor success rate. Pumping test analyses, monthly monitoring of groundwater level, electrical conductivity (EC), pH, water temperature and environmental isotopes (?2H, ?18O) were undertaken in 2018. Analyses of the pumping test data of the pumping well using the Theis and Cooper-Jacob method has returned hydraulic conductivity (K), transmissivity (T) and storativity (S) values of 4.12*10-6 m/day, 1.56*10-4 m2/day and 1.52*10-4, respectively. Analyses of observation well data located west 20 m from the pumping well gave K, T and S values of 1.79*10-7 m/day, 6.95*10-6 m2/day and 2.8*10-10, respectively. A second observation well located 33 m north from the pumping well did not show any water level response to the pumping. Additionally, the rate of water level recovery was very slow both in the pumped well and one of the observation wells. These test results indicate that the investigated aquifer is not only poorly productive but also heterogeneous, compartmentalized in nature and not feasible for sitting water supply wells. Rainfall recharge estimated using the water table fluctuation method (WTF) based on monitored groundwater level data is about 28 mm/a or 3.5% of mean annual precipitation (MAP). The groundwater level, temperature and EC monitoring indicate that as new rainfall recharge reaches the aquifer, the groundwater level and temperatures increases while the EC decreases as a result of salinity reduction because of dilution. Similarly, as the groundwater level declines as a result of prolonged dry seasons, the groundwater temperature drops, while EC increases due to increased salinity. Furthermore, monthly environmental isotope monitoring shows that all the samples plot along the local meteoric water line (LMWL) indicating that groundwater is recharged from local precipitation. The groundwater at the studied site is characterized by Ca-Na-HCO3 hydrochemical facies indicating an early stage of rock-water interaction
Presenter Name
Sphindile
Presenter Surname
Mtshali
Area
Pietermaritzburg Formation, Ukulinga Research Farm
Conference year
2019