A typical groundwater storage assessment in the Tugela area, South Africa

Water storage assessment is an important component of feasibility studies for prospective mining areas. As required by national mineral resources and environmental Acts, this may include assessment of both exploitable and sustainable storage; the former relates to the amount of groundwater stored within the exploitable aquifer depth and the latter is defined as the groundwater that can be sustainably extracted without producing unacceptable environmental and economic problems. A simplified method is proposed to assess the groundwater storage in a typical mine area, Tugela in South Africa. In the area, five aquifers (Natal Group, Coastal plain deposits, Basement aquifer, Ecca Group and Dwyka Group) have better harvest potential compared with others on the basis of borehole yield. The study area was divided into four subareas (A, B, C and F) based on proposed mining boundaries. Both exploitable and sustainable groundwater storage were estimated. The estimated exploitable groundwater storage for subareas A, B, C and F are 20.66, 5.78, 43.12, 36.90 Mm³, respectively, on the basis of current median exploitation depths of each aquifer or geological formation. The calculated sustainable groundwater storage for subareas A, B, C and F are 3.31, 0.89, 6.67 and 6.01 Mm³, respectively, with a total of 16.88 Mm³. Groundwater recharge of the subareas was also estimated for subareas A, B, C and F as 31.92, 11.44, 43.38 and 29.78 Mm³/annum, respectively, with a total of 116.53 Mm³/annum. The assessment method can be applied to other areas with similar hydrogeological settings with the available datasets.