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Update on the City of Cape Town’s New Water Programme

Umvoto Africa continued as the principal hydrogeological consultants for the groundwater components of the City of Cape Town‘s New Water Programme (CCT NWP) under engineering consultants Zutari and iX engineers, which was implemented to diversify bulk water supply and improve long-term water security and resilience of the City. The CCT NWP groundwater projects target the major fractured Nardouw and Peninsula Aquifers of the Table Mountain Group (TMG), and the primary Cape Flats and Atlantis Aquifers.

The end of 2021 came with the great news that Zutari, with Umvoto as its groundwater specialist, were appointed for a 5 year contract by the CCT’s Water and Sanitation Department to continue with the refurbishment, development and commissioning of the Atlantis Water Resource Management Scheme (AWRMS), Cape Flats Aquifer (CFA) Management Scheme and TMG Aquifer wellfields.

Throughout 2021 each individual project made the following progress:

TMG

Exploratory drilling, in combination with focused mapping and geophysical surveys, continued in 2021 across various TMG target site areas throughout the Eikenhof-Nuweberg and Theewaterskloof areas. In addition, the Nardouw Aquifer monitoring network within Steenbras Wellfield was expanded through an array of nine shallow (50 metres deep) core boreholes, specifically targeting important potentially groundwater-dependent ecosystems such as wetlands, and structural features such as hydrotects.

Throughout 2021 a further three Nardouw Aquifer production boreholes were commissioned and added to the existing operating production boreholes commissioned during late 2020 – this now amounts to a total of seven commissioned and operating Nardouw Aquifer production boreholes (H1A1, H1A2, H1A3b, H1A4b, H8A2, H8A11 and H8A13) producing ~100-175 litres per second (l/s) or ~9-15 million litres per day (Ml/day) into Upper Steenbras Dam from Steenbras Wellfield. For the 200 days from mid-April to early November ~2 million m3 of groundwater was abstracted during wellfield commissioning and testing, and pumped into Upper Steenbras Dam (~6.5% of the total upper dam’s storage of 31.77 million m3) at an average of ~10 Ml/day.

Deep drilling at the four deep planned Peninsula Aquifer production boreholes hit new strides throughout 2021, and the H8A9 borehole achieved its target completion at a final depth of 1002 m within the Peninsula Formation (with a tested yield of 15 l/s). Two further boreholes (H8A5 and H8A10) are also currently ~1000 m deep within the Peninsula Formation, whereas the H8A4 borehole has been drilled and cased to the Pakhuis Formation at a depth of 736 m – H8A5 and H8A10 are planned to be deepened to 1100 m, whereas H8A4 is planned to be deepened to 1000 m during 2022. Drilling of the >1000 m deep wide diameter exploration/production boreholes into the deeply confined Peninsula Aquifer required a combination of drilling technologies, while simultaneously overcoming and mitigating a host of environmental constraints and geological/hydrogeological factors in a safe, yet productive manner. The full Steenbras Wellfield will therefore be complete towards the end of 2022 once all Peninsula Aquifer production boreholes are commissioned (in addition to the commissioning of one more completed Nardouw Aquifer production borehole), and the full wellfield has been tested.

Numerous construction, geological and environmental challenges were overcome by combined planning, continual adaptation and mitigations initiated between Umvoto and the drilling contractor (SA Rock Drills), engineering consultant (Zutari), client (CCT) and specialists. This truly innovative and integrated approach has set the standard for large-scale, deep aquifer, bulk water supply wellfield developments in South Africa. In addition, the Peninsula Aquifer production holes are likely the deepest wide diameter municipal water supply boreholes in South Africa. The extensive knowledge gained stands to assist with future deep aquifer wellfield developments across the country and the continent.

CFA

Umvoto continued with the development and monitoring of the Cape Flats Aquifer (CFA) as part of the CCT NWP in 2021. This saw the drilling of additional production boreholes, reaching a total of 72 production boreholes and 268 boreholes overall (including monitoring, exploration and injection boreholes). The first CFA wellfield, Strandfontein West, is planned to be commissioned in early 2022, with construction of the water treatment plant currently being completed. Strandfontein West will supply 5 Ml/d of water directly into the potable distribution network.

Additional work included the ongoing environmental conservation officer (ECO) inspections to ensure that environmental management procedures were followed throughout borehole drilling/testing and construction processes relating to borehole chambers, water reticulation pipelines and water treatment plants. Monthly and quarterly monitoring of climate, wetlands, groundwater levels and water quality continued throughout the year, building on the baseline data collected over the last 4 years.

Highlights from 2021 include the commissioning of 2 injection boreholes for the managed aquifer recharge (MAR) component of the scheme and the large-scale contaminants of emerging concern (CEC) sampling and analysis monitoring campaign. This campaign included 32 monitoring sites for the CFA, consisting of both surface and groundwater, forming one of the largest CEC studies for a municipal groundwater scheme in South Africa.

AWRMS

The AWRMS refurbishment proceeded with continued success in 2021 as part of the CCT NWP. The drilling and testing campaign continued in full force with three new exploration boreholes being drilled across the Atlantis Aquifer to further investigate the geological and hydrogeological conditions in the upper reaches of the aquifer, as well as the area between the Silwerstroom and Witzands Wellfields. This was coupled by an extensive ground based 2D electrical resistivity tomography (ERT) survey program totalling ~10 km of subsurface profiles, which complimented the findings of the drilling and provided new insights into the basement topography of the Atlantis Aquifer. Furthermore, ten production boreholes underwent 72-hour test-pumping with yields of up to ~28 l/s. This means that all new production boreholes have undergone successful test pumping in accordance with (and exceeding) the South African National Standard (SANS) 10299-4:2003.

Nine of these new production boreholes were equipped with string work, and the remainder are to be completed in the coming years – including the installation of modern submersible pumps and real-time telemetry monitoring equipment. The wellfields are therefore almost ready to be commissioned with the new production boreholes of improved design. To protect the boreholes and prevent vandalism, durable and robust borehole cages were also installed to protect the boreholes from unwanted vandalism. Cleaning and upgrading of some of the interconnected MAR basins is also planned to further improve the quality of the water captured for MAR.

The monitoring network has continued to expand with a total of ~150 monitoring points, including re-introduction of far-field monitoring. Both surface and groundwater are subject to a variety of water quality, water level, and flow monitoring on a combination of monthly, quarterly or biannual basis. CECs were also introduced into the extensive monitoring programme to assess the transportation and fate of many potentially recalcitrant chemicals within the AWRMS. The data collected are complex, and it is invaluable in improving the understanding of the aquifer system and updating our numerical model from steady state to transient, as planned. The monitoring network will be continually revised, adapted and updated as knowledge of the dynamic system improves.

Our team of ECOs have done their due diligence in overseeing the completion of the reverse flow pipeline (which will provide water from Atlantis to Melkbos), the Silwerstroom pump line, the construction of 2 x 5 Ml tanks that offer storage for the future wellfield operation, a new waste basin for the Witzands Softening Plant, and construction of the slabs and cages around each production borehole, amongst the drilling and testing carried out across the aquifer.

All the efforts over the last ~4 years have formed the basis for the culmination of an integrated water use licence application (IWULA). Overall, the components of the AWRMS refurbishment and restoration require a combination of Section 21 (a), (c), (e), (f), (i) and (j) water use authorisations.

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