Tapping the Coegakop wellfield

Nelson Mandela Bay Municipality has embarked on a series of drought intervention projects designed to ensure future water security. Two of these are currently being constructed by multidisciplinary contractor Stefanutti Stocks, namely the Nooitgedagt/Coega Low Level Scheme: Phase 3, and the Coegakop Biofiltration Water Treatment Works – the latter in consortium with PCI Africa.

The Eastern Cape region has experienced arid conditions for decades. More recently, though, the problem has worsened into an extended drought that poses a threat to the regional economy. In response, emergency water master plans have been developed to mitigate and manage immediate and longerterm scenarios.

One of the key focal points is Port Elizabeth, the province’s largest city and the administrative capital of Nelson Mandela Bay Municipality (NMBM), which extends to include the towns of Despatch and Uitenhage, the latter being one of South Africa’s major automotive manufacturing hubs.

As part of a longer-term response strategy, NMBM appointed Zutari (previously Aurecon South Africa) to develop a Drought Mitigation and Action Plan.

The Water Reconciliation Strategy Study for the Algoa Water Supply Area, published in 2008, identified groundwater as a future water supply option. In 2010, the decision was made to fast-track the viability of groundwater as a potential emergency supply option. In the interim, specific initiatives were approved, including the Nooitgedagt/Coega Low Level Scheme. The third and final phase of the scheme is currently being constructed by Stefanutti Stocks for NMBM. Amatola Water was appointed by the Department of Water and Sanitation (DWS) as the implementing agent. The project started in May 2017 and is scheduled for completion in July 2021.

Nooitgedagt

Situated just north of Port Elizabeth near the Addo Elephant Park, the Nooitgedagt Water Treatment Works (WTW) Phase 3 work entails the treatment capacity being upgraded from 140 Mℓ/day to 210 Mℓ/day. A 45 Mℓ storage reservoir has also been constructed during this phase to accommodate the extra capacity. Additionally, the scope includes some rehabilitation work and cathodic protection of the existing pipe supply system.

Orange River water is delivered to the plant via the Orange-Fish Scheme (Darlington Dam and canals) to the Scheepersvlakte Dam. From there, it flows by gravity pipeline to the Nooitgedagt WTW. Thereafter, the water is treated then gets pumped to the existing 10 Mℓ reservoir, and the newly constructed 45 Mℓ reservoir.

Prime groundwater targets

“Similar to Cape Town’s Day Zero experience, NMBM’s strategy combines the need for greater conservation management with consumer education to lower demand, so we can preserve current resources while developing reserve capacities to meet future drought contingencies and growth projections,” explains project engineer Edzard Verseput, Infrastructure & Engineering: Water & Sanitation, NMBM. Groundwater abstraction is now officially on board and will supplement NMBM’s current consumption of around 300 Mℓ/day.

Like Cape Town, the greater Port Elizabeth area is underlain by Table Mountain sandstone containing extensive artesian aquifers. In Port Elizabeth’s case, geophysical surveying and groundwater exploration drilling began in earnest to map out the region’s Groot WinterhoekAquifer.

Biofiltration: A diagrammatic explanation of the process engineering workflow required to remove the iron and manganese concentrations in the groundwater abstracted at the Coegakop wellfield

A satellite map showing the site for the WTW, the location of the five boreholes feeding the plant, and the downstream Coegakop reservoir. The water then travels to the Motherwell reservoir

In 2012, the Coegakop area, inland from the Coega harbour and Industrial Development Zone, was identified as a potential high-yield zone. The ensuing drilling programme between February 2014 and July 2015 confirmed this.

“The idea of developing a WTW at Coegakop began to germinate,” says Marius van Jaarsveld, technical director, Zutari. “We were subsequently appointed by NMBM for the overall design, project and construction management. Construction of the Coegakop WTW commenced in March 2020.”

Prior to that, there was a long hiatus after the completion of the initial exploration drilling programme in 2015. Then, in April 2018, the next stage commenced with the establishment of the five production boreholes that will feed the future WTW, as well as the construction of their interconnecting raw water pipelines. The final processed water pipeline was also installed and connected to the existing Coegakop reservoir, with all these works completed in September 2019.

Coegakop WTW

“The Nooitgedagt and Coegakop projects both have a key feature in common. Significantly, neither rely on local rainfall for their storage requirements and process outputs,” Verseput continues. “This was an essential stipulation for the city’s emergency water master plans.”

The Coegakop wellfield draws water from sources that have built up over tens of thousands of years. As part of the natural process, and if left unchecked, this groundwater progressively makes its way through a myriad of rock fissures – geological fault lines less than a centimetre thick – until it reaches the ocean at Algoa Bay.

At present, Uitenhage taps into this water, which naturally flows to the surface at a local artesian spring. Around 6 Mℓ is processed daily to meet part of the town’s potable requirements. Based on the groundwater data collected at Coegakop, the peak output capacity for the new WTW has been determined at 20 Mℓ/day. ‘At this point we’re aiming for 17 Mℓ/day,” says Verseput, which ties into the DWS water use licence abstraction figure of 26 Mℓ/day.

A major portion of the funding for the final WTW phase, which amounts to some R212 million, is being provided by National Treasury through Cogta as Municipal Disaster Recovery Grant funding. The Stefanutti Stocks PCI Consortium has been appointed as the main contractor. The contract has an intensive construction programme schedule running over a 25-month timeframe, or the equivalent of some 730 days. Stefanutti Stocks mobilised on-site on 5 June 2020.

“PCI Africa will be responsible for the mechanical, electrical, control and instrumentation component, with Stefanutti Stocks responsible for the construction of the integrated process control and administration building, as well as all related concrete structures. Externally, that includes the construction of the settling ponds,” explains John Woodburn, contracts director, Stefanutti Stocks Coastal.

Provision has been made for the appointment of 100 emerging micro enterprises. In addition, employment opportunities will be created for local unskilled and semi-skilled labour drawn from the nearby Motherwell community.

The WTW building features an integrated design to maximise security and minimise vandalism. The build’s windows on the upper level are screened by honeycombed brickwork, while the glazed sections of the roof are recessed

Biofiltration needed

The groundwater sourced from the wellfield contains high concentrations of dissolved iron (>7.5 mg/ℓ) and manganese (>2.5 mg/ℓ), which rules out the use of conventional chemical water purification, as is the case for Nooitgedagt. In the case of the Coegakop WTW, proprietary biofiltration technologies will be employed.

Nooitgedagt/Coega Low Level Scheme: Phase 3

Nooitgedagt expansion: the new settling tanks with sludge hoppers and flocculation channel

Zutari’s team is responsible for the process design and this will become the second of its kind built in South Africa. The first is a 10 Mℓ biofiltration plant in Hermanus, Western Cape, which was also designed by Zutari.

The upside is that the biological process costs will be cheaper. The cost per kilolitre of water will also be a lot less since it’s being sourced straight out of the ground. Aside from the iron and manganese elements, the water is pristine and characterised by low levels of salinity.

Coegakop’s production boreholes, which were completed during a previous phase, telescope down to an internal diameter of 300 mm and feature lined stainless-steel casings. Drilled to a depth of between 200 m and 300 m, the water abstraction rate is regulated by purposedesigned stainless-steel pumps. Being artesian systems, the water naturally travels up the borehole at a pressure of 6 bar and over, so the energy needs to be contained.

Aside from water purification, there are no additional bulk transfer costs since the treated water goes straight to the existing Coegakop reservoir approximately 650 m away. From there, pipelines supply Motherwell, the Coega IDZ and an expanding consumer zone.

Integrated process building design

Since the operators at Coegakop will be stationed there on a constant 24/7 basis, the WTW was designed to ensure maximum security for the occupants. To achieve this, the process and administration components are housed in one secure, self-contained building. A rainwater harvesting system has also been included in the design, which will flush the ablutions.

“The process and administration building forms the largest component and will entail intricate work, especially when installing the filtration systems,” says Andre van der Merwe, project manager, Stefanutti Stocks.

The borehole chamber buildings feature an innovative modular design. A section of the wall and roof will be constructed using removable precast panels. This will enable a drilling rig to be moved into position to work on the borehole, when required. Thereafter, everything can be closed up again. The balance of the chamber building is reinforced concrete.

The WTW design makes provision for extensions to the filtration works on either side of the filter banks. Thanks to the modular layout, units can be added either side of the treatment plant.

A design partnership from day one

To bring the Coegakop project to this point, 10 design workshops have been held jointly by Zutari, NMBM, and the Stefanutti Stocks PCI Consortium. To perfect the models, Zutari’s use of virtual (VR) and augmented reality (AR) software proved invaluable during the simulation and interrogation of the plant setup. This was the core of a technical paper that was presented at the 2018 IMESA Conference held in Port Elizabeth. Zutari also plans to use AR and VR to train the operators ahead of the plant’s opening, so that they can hit the ground running.

The numbers still need to be verified. However, once the plant is fully operational, NMBM is confident that Coegakop will supply the lowest cost per kilolitre of water within the NMBM water supply system - far lower, for example, than going the desalination route.

The exploration borehole network drilled to date extends north all the way from Coegakop to just past Uitenhage. Here, intermittent monitoring sites have been established. Some of the exploration boreholes at Coegakop will also be equipped with level sensors linked to a Scada system. Overall, this will determine how abstraction rates affect the overall aquifer. The data will also prove invaluable for the DWS in monitoring water use in terms of the licensed aquifer abstraction.

In the meantime, the project team is forging ahead to meet the Coegakop WTW’s targeted completion date in August 2022.