The United States now produces about as much crude oil as Saudi Arabia does, and enough natural gas to export in large quantities. That's thanks to hydraulic fracturing, a mining practice that involves a rock-cracking pressurised mix of water, sand and chemicals.
Ongoing research by Stanford environmental scientist Rob Jackson attempts to minimise the risks of 'fracking' to underground drinking water sources.
The most recent study by him, published in Environmental Science & Technology, finds that at least 6,900 oil and gas wells in the US were fracked less than a mile (5,280 feet) from the surface, and at least 2,600 wells were fracked at depths shallower than 3,000 feet, some as shallow as 100 feet. This occurs despite many reports that describe fracking as safe for drinking water only if it occurs at least thousands of feet to a mile underground, according to Jackson.
The researchers discovered that at least 2,350 wells less than one mile deep had been fracked using more than 1 million gallons of water each. Shallower high-volume hydraulic fracturing poses a greater potential threat to underground water sources because there is so little separation between the chemicals pumped underground and the drinking water above them.
Read the whole report here .