Nelson Mandela Bay close to tapping into huge water supply
Coega wells could cover 5%-10% of the metro’s needs
A water-drilling team contracted by the metro came agonisingly close to a mega-strike at Coega on Wednesday.
It is anticipated that the flow from the new Coega artesian well could deliver 150l of water a second – meaning 540m³ an hour or 13,000m³ a day, hydrogeologist Dr Ricky Murray said.
“It’s huge – potentially the biggest yield in Southern Africa and probably in Africa and most parts of the world.
“The whole Coega Industrial Development Zone doesn’t even require half that volume. “We’re very excited,” he said. The monster well is the culmination of extensive work by Murray and geologist Marc Goedhart, who were convinced that the groundwater yield in the area could be substantially improved from the accepted 2.5m-5m a second.
Metro water and sanitation director Barry Martin said a treatment plant was being built at Coega and the water from the new well and four others sunk in the area would be channelled through this plant once it was completed in two years’ time.
“From there, it will go to the Coega Kop Reservoir to be distributed to Motherwell and the Coega Industrial Development Zone.
“Together these wells should cover 5%-10% of the metro’s total water needs, which is substantial when you consider they will not be influenced by rainfall.”
In 2010, the Nelson Mandela Bay municipality contracted Aurecon to look into extra water-supply solutions and the company sub-contracted Murray, who then brought on Goedhart.
They started by relooking at the oil exploration maps of the Uitenhage Artesian Basin compiled in the 1970s by the then Southern Oil Exploration Corporation (Soekor).
The aquifer comprised ancient water that had seeped down from the Grootwinterhoekberge northwest of Uitenhage, Murray said.
“We know from studies done that this seepage travels at 1m per year so it took 20,000 years to get here.
“With this well, we will be intercepting a portion of the aquifer before it flows into Algoa Bay.
“Once the well is established, I will do a yield assessment to see how much we can extract without jeopardising the long-term flow.
“We will not simply mine it. “One of the great benefits is how cheap this water will be compared to desalination, for instance.”
The Soekor study area which they were interested in comprised a layer of young rock on top of a 500-millionyear-old layer of Table Mountain quartzite, he said.
“About 90-million years ago, tectonic forces associated with the fracturing of Gondwana ripped through this quartz layer forming what we know today as the Coega Fault.”
With the help of University of Witwatersrand geologist Prof Edgar Stettler, Murray and Goedhart interrogated the Soekor data further and narrowed their focus to an area west of Coega Kop where the quartzite rose relatively close to the surface.
The area was once covered by the sea and Coega Kop was an island like present-day Jahleel and St Croix islands.
Today, millenia later, located on the eastern rim of Motherwell, the challenge was to find this fault, Murray said.
“We knew it was lying at a near-vertical angle 200m underground.
“It was like looking for a needle in a haystack.”
The different kinds of rock in the area had different densities, however, so through the use of a gravimeter they pinpointed where the quartz rose closest to the surface.
The earth’s crust was constantly charged by lightning strikes and different rocks had different electric conductivity capabilities, he said.
“So we used a magnetelluric machine which measured the different conductivities, mudstone being much more conductive than quartzite, and that allowed us to close in on our target.” With the final resistivity survey, they created their own lightning strikes to check the conductivity capability of the different rock layers, but before they could do so, they had to get the local electrical supply switched off, otherwise they would interfere with the instrument.
“We eventually reached an agreement that they would be off for six hours, which was not really long enough, but it was all we could get,” Murray said.
Developed by a Johannesburg-based company, the resistivity instrument was being used in South America and they had to wait until it became available.
It eventually arrived, and they were all set to go.
The box was locked up in a bakkie at the guesthouse where Murray was staying.
“We woke up to find that the bakkie had been broken into and the thief had cut away all the copper he could from the cabling on the box.
“With our power outage deadline ticking away, we spent precious time piecing the cables together again. But we succeeded.”
With the drill zone narrowed to a few metres, they sank an exploratory well in 2014 and on May 10 hit the jackpot.
“The water exploded out the ground,” Goedhart said.
“It was flowing at up to 4.5 bar, and at six bar when it closed off – that’s three times the pressure of a car tyre.
“It was shooting rocks out the size of a fist.”
The flow was too strong for them to instal a pump and if it had continued it would have flooded Motherwell, so they were forced to plug it.
Before it was plugged, however, they sampled the water and although it contained some irons that would have to be removed, it was fresh and of good quality.
It took five years to finalise tender processes and budget to allow the project to be taken forward, including installation of a production well and the necessary piping and treatment infrastructure.
But last week the team including Environmental Drilling & Remediation Services was back on site and itching to go.
The drill point chosen was just 5m away from the exploration well and at mid-morning on Wednesday, they entered the 200m depth zone where the 2014 strike was made. A stainless steel casing which would not corrode had been grouted into the shaft together with a cement sleeve to avoid the seepage and flooding which occurred before and the pump was ready for immediate installation.
By evening, they had drilled through this zone and, with no sign yet of water, they were forced to call a halt and take stock.
Goedhart said a specially designed camera would be lowered into the shaft on Thursday and after assessing the footage captured they would decide how to proceed.
“One possibility is that the material used to plug the exploration shaft has got in the way, but we will see.”
“We’re five metres away from a mega-strike so it should not be long now.”..