For many countries, including South Africa, natural gas offers a way to reduce their dependence on declining and increasingly expensive oil imports. However, one of the techniques for extracting the gas, fracking, remains highly controversial, and there are question marks over the environmental safety of the process. There are also allegations of information quashing against the United States' Environmental Protection Agency.
South Africa has been split over the question of whether to frack, with one side saying that it would increase the country's energy independence, boost industry and job creation and reduce the cost of power. The other side, led by residents and lobbyists such as the Treasure the Karoo Action Group, say that it will damage the ground water and biodiversity of the already water-scarce region, which is one of the most biologically diverse in the world, and that it is not a more environmentally friendly way of producing power.
Fracking is one aspect of natural gas extraction: wells are drilled using a mixture of oil-based lubricants, and the rock formations are then "fractured" using a combination of water and specific chemicals to break the rock open so the gas can be collected.
The most recent study, published by scientists from Duke University, the University of Rochester and California State Polytechnic University, finds that, while there were not increased concentrations of salts, metals or radioactivity in the drinking wells, meaning that it had not been contaminated by the fracking chemicals, "home owners living less than one kilometre from gas wells have drinking water contaminated by stray gasses".
They analysed 141 drinking wells across northern Pennsylvania, home to the Marcellus Shale Formation which extends into southern New York. With estimated reserves of 489-trillion cubic feet of natural gas, it has substantially more than South Africa's 390-trillion cubic feet, according to the United States' Energy Information Administration.
"Methane was detected in 82% of drinking water samples, with average concentration six times higher for homes less than one kilometre from gas wells … propane was detected in 10 water wells, all within approximately one kilometre," the authors write.
"Ultimately, we need to understand why, in some cases, shale gas extraction contaminates groundwater and how to keep it from happening elsewhere."
This builds on work published in 2011 by Duke University researchers, which also found increased levels of hydrocarbons (which include methane and propane) in nearby drinking water. However, the university said at the time that: "Little research has been conducted on the health effects of drinking methane contaminated water."
Last year, Cabinet lifted its moratorium on shale gas exploration, saying that South Africa was an energy-poor country that needed to explore the possibility of natural gas.