Groundwater Development Of The Table Mountain Group Aquifers As Part Of The City Of Cape Town's New Water Programme

The original City of Cape Town (CCT) Table Mountain Group (TMG) Aquifer Feasibility Study and Pilot Project was initiated in 2002, the purpose being to evaluate the feasibility of augmenting the CCT's bulk water supply using groundwater from the TMG (specifically the fractured Peninsula and Nardouw Aquifers). CCT TMG groundwater exploration/development was fast tracked under the "New Water Programme" (NWP; from 2017-present) as a result of two interrelated water scarcity/demand factors, namely periodic drought (including the major 2015-2017 1:590-year event) and rapid urban growth. Initial NWP TMG groundwater development (including additional exploration via detailed geological mapping and heliborne geophysics) has occurred in the vicinity of the CCT-operated Steenbras Dam, in the form of a minimum 15-20 Ml/day wellfield scheme. The planned "Steenbras Wellfield" targets both TMG aquifers along the Steenbras-Brandvlei Megafault Zone on the southeastern limb of the Steenbras Syncline (which regionally occurs within the high groundwater potential Cape Fold Belt Syntaxis). Current drilling activities have included ultra-deep (up to 975 m depth, representing the deepest groundwater-specific boreholes outside of mining/resource activities in South Africa), wide diameter abstraction (using rotary air percussion, reverse circulation and hydraulic/water hammer techniques) and core exploratory boreholes into both TMG aquifers. Tested abstraction borehole yields range between 10-70 l/s, while artesian-discovery core holes into the Peninsula Aquifer from Steenbras towards Theewaterskloof Dam have surface pressures and flows of up to 800 kPa and 4 l/s respectively (from BQ-sized holes intersecting water strikes between 840-910 m). Further CCT TMG groundwater exploration and wellfield scheme development (potential total combined supply of ~50-150 hm3/a or ~140-400 Ml/day) is planned along major TMG structures within the Grabouw-Eikenhof and Theewaterskloof basins, Wemmershoek, Voelvlei, Berg River and the CCT South Peninsula region. This has, and will continue to include, monitoring of surface/groundwater-dependent ecosystems as a geo-ethical approach to minimise ecological/environmental impact.