Hydrogeological and hydrochemical investigation of the Durban Metropolitan District, Eastern South Africa.
Ndlovu, Minenhle Siphesihle.
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Population and economic growth within the Durban Metropolitan region in eastern South Africa has increased the demand for water supply. This ever-increasing demand means that all available water supply sources including groundwater will be looked at, particularly in urban and peri-urban areas. However, the state of the groundwater resource in the region is poorly understood. This study aims to contribute towards improved understanding of the state of groundwater resources in the Metropolitan District through an integrated hydrogeological, hydrochemical and environmental isotope investigations. Results of hydrogeological and hydrogeochemical characterization identified at least five hydrostratigraphic units of varying hydraulic and hydrochemical characteristics. 1) The weathered and fractured Granitic basement aquifers of the Mapumulo Group and Oribi Gorge Suite characterized by average borehole yield and transmissivity (T) of 1.2 l/s and 3.9 m2/day, respectively, with hydrochemical facies of Ca-Mg-HCO3. 2) The fractured Natal Group sandstone, characterized by average borehole yield and hydraulic conductivity (K) of 5.6 l/s and 2.8 m/day, respectively with Na-Mg-HCO3-Cl as dominant water type; 3) The fractured aquifers of the Dwyka Group diamictite and tillite are characterized by average borehole yield of 0.4 l/s and T of 1.3 m2/day and Na-Cl-HCO3 as the dominant water type; 4) The Vryheid Formation, which is part of the Ecca Group, is characterized by a mean borehole yield of 2.5 l/s, T of 4.9 m2/day, K of 0.17 m/day and Na-Cl-HCO3 water type; 5) The intergranular primary aquifers of the Maputaland Group which consists the Bluff, Berea Formations and recent alluvium and estuarine deposits (locally called harbour beds Formation) have average borehole yield of 14.8 l/s and transmissivity of up to 406 m2/day with a mainly Na-Cl-HCO3 hydrochemical signature. The region receives mean annual precipitation (MAP) of 935 mm/yr of which 9.2% infiltrates to recharge the various aquifers. Environmental isotope information (2H, 18O and 3H) indicated that groundwater recharge is of modern precipitation. Groundwater tritium values of 37.4 and 92 TU are measured around the Bul Bul Drive and Bisasar Road Landfill sites, respectively, indicating groundwater contamination from landfill leachate leakage. Based on the main hydrogeological, hydrogeochemical and environmental isotope findings, a regional hydrogeological conceptual model is developed that characterizes the hydrogeological and hydrochemical conditions of the Durban Metropolitan region.