Valuable aquifers need recharging

I am in awe of the meticulous manner in which this water is being drawn from the earth.

Last week, water was struck at Portland High School, in Mitchell’s Plain, by the Gift of the Givers Foundation.

Dr Gideon Groenewald, hydrologist, geologist and paleontologist, who is supervising the drilling process for the disaster-response NGO, said groundwater is as dependent on constant recharge from good rainfall as a normal surface reservoir.

He said it was important that geohydrologists do careful calculations to not overuse the resource.

“Groundwater is water found beneath the earth’s surface, both in soil and sand pore spaces (called primary aquifers), pore spaces in sandstone and in the fractures of rock formations (called secondary aquifers).

“An aquifer can be seen as a rock that looks like a sponge and the rock has the ability to hold water and then release the water under specific conditions.”

Most of the boreholes are between 150mm and 300mm in diameter and can be up to several kilometres deep.

Dr Groenewald said the drilling process involves the penetration of the rock sequence in the same way as somebody drilling a hole into concrete with a drill tip that is 5m long and 155mm in diameter.

He said in the case of the Cape Flats Aquifer, geologists are careful not to drill too deep because it is, in fact, an in-filled sea channel, and still contains seawater at a certain depth.

“By drilling too deep the boreholes can penetrate the interface between the salt water and fresh water, leading to the contamination of the fresh water upper aquifer with saline water from the deeper aquifers.”

Dr Gideon said it does not matter how many boreholes there are in Cape Town but it did matter how deep people are drilling.

He said the Cape Flats Aquifer seems to consist of three layers of material that can contain water.

“The first, about 15m below the surface, contains sand that is saturated with highly polluted water that is not fit for human consumption without expensive treatment. From about 15m to 40m the Cape Flats is underlain by a marine mud that releases very little water. Below that layer they discovered a highly productive fresh water aquifer that can reach to about 60m, from where the geology is dominated by rocks of the Malmesbury Group that only produces water from linear fractures filled with quartz.

“No saline water was found to a depth of 85m, and the Gift of the Givers Foundation is reluctant to drill deeper than that depth in fear of intersecting the saline layer of water underlying the Cape Flats Aquifer,” said Dr Groenewald.

Earlier this year the foundation pledged the drilling of boreholes, dependent on the state of aquifers in Khayelitsha, Bonnievale, De Doorns, Ceres, Atlantis and Vredendal.

The Gift of the Givers Foundation has now funded itsown borehole drilling rig at a cost of R2.5 million, to expedite the search for water in areas of great need.

Late last month, the organisation got water at Peak View High, in Bridgetown, Athlone.

Ali Sablay, from the foundation’s Cape Town office, said were another three schools lined up for boreholes.

If you would like to support the Gift of the Givers, call Badr Kazi on 083 228 1298, Allauddin Sayed on 083 667 7179 or Muhammad Sooliman on 081 757 9776.