A simple question about finding water provided the seed.
The result was a project with branches in cutting-edge science and old-fashioned volunteerism.
“I was having a conversation with one of our computer support people and he was asking about how to find water,” said Susan J. Webb, University of the Witwatersrand, Johannesburg, South Africa.
“He told me about Dayspring (Children’s Village), which he had been volunteering at for a number of years, and how their water had been drying up and sometimes they had to send the children away as they had no water.”
Dayspring Children’s Village was established by the Rev. Charles and Wendy Paine to equal education opportunities and care for the disadvantaged. It was birthed in the 1980s during apartheid and was one of the few integrated boarding schools of its time.
Wanting to learn more about the applications of geology and geophysics in groundwater exploration and monitoring, Webb was intrigued.
Upon visiting the school about two years ago, “The first thing that struck me was a large stand of trees on the property,” she said. “I had been hearing about the work ‘Working for Water’ (a government-funded program) had been doing, clearing out non-indigenous trees and bringing back surface water.
“I immediately thought maybe the trees were part of the problem,” she said. “These are the huge blue gum, eucalyptus trees that are from Australia.”
Having spotted the possible root of the problem, Webb and her colleagues and students went to work.
“We are lucky to have a large amount of equipment and lots of enthusiastic students,” Webb said. “The main method we used was resistivity, and David Ngobeni used this in his master’s project.”
Specifically, he used a novel application of time-lapse resistivity.
“In addition we used magnetics – both methods discovered an unknown pipe,” she said. “The magnetic work was done by (AAPG member) Obone Sepato as part of his honors project.
“We also used refraction seismic as part of several honors projects, and the first 4-D gravity survey in the country,” she said. “We also tried Ground Penetrating Radar GPR to delineate the tree roots.
“It was novel in that we are able to apply a lot of techniques – you wouldn’t ever be able to do that on a commercial scale,” she added.
The group also did some hydrology studies.
“We were able to run the isotopes at Itemba labs and found that the near surface aquifer (the one that runs out and that they depend on) is readily recharged, but the deeper aquifer has old water – no indication of deuterium, therefore the water is old. That is a significant result for the region.
“In addition the resistivity data partially mapped the near-surface aquifer – we need to see a little deeper – a geological contact and fractures within the lithologies, which are likely to be hosting the water,” she continued. “The current borehole appears to be at the intersection of a contact between the metamorphosed shales and the pyroxene rich sills.
“The time-lapse resistivity indicates a measureable change in water content for a significant distance away from the blue gum trees – however, we need to probe slightly deeper to be sure of this importance,” she said.
“We found an old pipe that may be the source of the contamination in the second borehole, as that is likely to be caused in the near surface.”
The school is close to Johannesburg, where the university is located, allowing fairly frequent day trips to continue the research. The school has begun clearing the trees and results are promising, she said.
Besides the benefits to the school, the project has had positive side effects at the university as well.
“We have been able to examine the hydrology of two very different aquifers,” she said, “document the variations in resistivity in the near surface throughout the seasons and its relationship with the trees, and develop techniques for using 4-D gravity.
“The biggest difference has been the number of students we have been able to involve,” she said. “Many students become interested in the project because of the humanitarian aspect, and we are able to take a large number of volunteers out to work on the project for short periods of time as it is only a short drive away. Several of these students have become interested in geophysics because of this experience.
“We have had a number of honors projects (similar to U.S. undergraduate research projects) and a master’s project hosted at Dayspring,” Webb said.
“Over the course of the project we were able to involve well over 30 students directly in the geophysics – many of who had never heard of geophysics, as a lot of our students come from a physics background,” she said.
“We even had participation from an overseas student and a number of staff members.”