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Huge ancient freshwater aquifer under seabed

Posted by: Saving Water SA (Cape Town, South Africa) – partnered with Water Rhapsody conservation systems – 10 May 2010

A marine research company has proposed a R1.8-billion project to solve the water crisis in Nelson Mandela Bay by tapping ancient water from a huge freshwater source under the seabed.

Dramatic geologic formations are displayed in the Cape Fold Belt - the folded sedimentary sequence of rocks in the south-western corner of South Africa.

In a recent presentation to the Development Bank of SA, Deep Water Research (DWR) from Cape Town said the aquifer – situated 60km off Port Elizabeth – “is larger than the Breede River Dam”. Sucked out hot from at least a kilometre beneath the floor of the sea, the supply would be “very long term and consistent”, it said.

Local experts have raised questions about the proposal, however, pinpointing the need for a comprehensive impact assessment and the need to balance the certainty of finding water in the volumes described against the funds spent searching for it. The security of the resource, the threat of seawater contamination and the geological ramifications should be taken into account, they argued.

In a presentation to the bank at its Midrand headquarters, Hugh Lloyd, a director of DWR, said there were large volumes of fresh water off the South African coast.

“A programme to explore and develop this resource on the coast, where our water resources are diminishing rapidly, has been initiated by DWR.”

The aquifers were revealed during years of oil and gas exploration, he explained. “An exploration well off Port Elizabeth intersected a potentially abundant supply of potable water.

“This resource alone has the potential to be an order of magnitude larger than the Breede River Dam. Such aquifer water resources have potential major advantages over dams as the water is not polluted, doesn’t evaporate, the supply is very long term and consistent, and it can become productive far sooner than a dam.”

The water in this and other aquifers comes from rain that has fallen for millenia on the sponge-like Cape Fold Belt. The belt includes various inland ranges as well as coastal mountains like the Groendal (near Uitenhage), Van Stadens and Tsitsikamma, and also outcrops in central Port Elizabeth. This rain sinks into fractured sandstone and quartzite and seeps gradually down through cracks in the Table Mountain group rock to the coast.

It emerges in local landmarks like the Uitenhage springs, and was the catalyst for the establishment of the old Swartkops spa baths. It, however, also flows out beneath the seabed.

With South Africa now gripped in a severe, long-term water crisis, DWR had created a programme to explore and develop this submarine resource, Lloyd said. Programme milestones include the development of “a concept hydro-geological model together with broad-based engineering and economics”, and a memorandum of agreement with the Water and Environmental Affairs Department to explore for water along the entire South African coast.

The company had also gained access to data compiled by the Department of Geosciences and the national Petroleum Agency, he said.

“The department has written a letter of intent to DWR to purchase 130 million cubic metres a year from DWR in the Eastern Cape.”

DWR had further reached an agreement with the world’s leading companies in the field of oil and water exploration and sea spring water, he said. Including the Port Elizabeth site, there are at least five possible sites worth exploring off the country’s south and east coast as well as others off the Western Cape and Namibia.

“Each project comprises a well farm and facilities delivering 50 million cubic metres of water a year.”

Lloyd said the capital cost for each extraction project would be R1.855-billion, and it would take about 2½ years to get each project up and supplying water.

Preliminary financial analyses of the project generally indicate “it is very robust and viable”.

“It has the potential of being repeated many times both in Southern Africa and world-wide.”

Wilderness Foundation director Andrew Muir – a former Herald Citizen of the Year, who has raised concerns about unregulated drilling – said a strategic environmental assessment was needed to consider the full costs and benefits of the project. The assessment would need to include the laying of the site-to-shore pipeline, the effect on geology and marine ecology, and the energy consumption of such a huge drilling operation.

“We support any initiative to try to find an alternative water source, but the full picture must be carefully considered.

“I do not know about any projects like this world-wide. Would the proposed extraction be sustainable? What will happen environmentally and geologically if we take this water out?”

Retired senior geologist Dr Russel Shone said he was unaware of any successful project of this kind anywhere else in the world.

Table mountain group rock was very hard and it was doubtful the fractures would collapse if the water was sucked out of them, he said. The water in the fractures could be as much as 400 million years old.

But even if a large slab of this rock was pinpointed, it would be very hard to determine how much water it held, he said.

“The table mountain group rock is the sponge. By using seismic data and bouncing shock waves they can determine how much of this rock there is and how far down it is.

“But the water is in the cracks in the sponge – and just how fractured is that particular rock? It would be very hard to say. It’s the great enigma of this geology.

“It sounds to me like these guys are flying a kite.”

Consideration needed to be given to the motivation and benefits behind the project, he said.

“Drillers drill holes and they get paid even if nothing is found.

“We must ask if the project is economically feasible – that’s the cost of looking for the water and then, even if it is found, of drilling for it in difficult marine conditions. Water is a basic human need. It’s not like petroleum, where costs can be recouped when it is sold.”

Even if fresh water was found, there was a danger that as it was extracted, it would be replaced by seawater, he said.

“There is a chance that this salinity can then leak out of the fracture at another point.”

Lloyd said “some private funding” was already available for the project and the hope was that the government would now buy into the project through either the Industrial Development Corporation or Development Bank of South Africa, both of which had been approached. “The next step will be to speak to Nelson Mandela Bay Municipality.”

Pressed on how sure he was of achieving supply, he said DWR had a “borehole core”, obtained from years of exploration in the area for oil and gas.

“This core tells us the volume of the fractures – and PE looks very good. What we still need to know is whether the fractures are wide enough to get the flow rate we need.”

There would be no danger of seawater seeping into the aquifer because fresh water was lighter than seawater and it naturally pushed the seawater out, he said.

– Guy Rogers
Source: Weekend Post

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