Environment - Fracking health risks: Drilling into the unknown

What are they sending down there? (Image: Ralph Wilson/AP)

Many fear that by-products of shale fracking – cracking the rock to release its gas – will harm their health. New Scientist examines the evidence

Read more: "Frack responsibly and risks – and quakes – are small"

YOU could call it a fracking mess. Fracturing deep shale deposits by injecting them with water, sand and chemicals at high pressure - with the aim of releasing the gas they hold - is causing concern worldwide. In New York State, officials seeking to lift a 2010 moratorium on fracking are sifting through 40,000 public comments on a proposal to regulate the process. Even by the famously opinionated standards of the Empire State, it's an unprecedented response.

Fracking has taken off in a big way in the north-east US in the past few years, particularly in the huge Marcellus Shale formation, which sits beneath New York, Pennsylvania and other Appalachian states (see map). By 2035, US shale gas production is likely to more than double, according to government projections. While that should be good for the climate, providing a cleaner alternative to coal, the dash for gas has triggered its own environmental controversies. Concerns about tainted drinking water lead the way.

See interactive graphic: "The shale gas boom"

So far, evidence that fracking poses serious risks to human health or the environment - beyond the pollution associated with fossil fuel extraction - is scant. But studies are few and hard to interpret, and feelings are running high: neighbours of new fracking operations complain of problems like breathing difficulties, nausea and headaches. "When the public is confused, the public is angry," says Bernard Goldstein, an environmental toxicologist at the University of Pittsburgh, Pennsylvania.

These concerns could even bring the shale gas bandwagon to a halt. "If action is not taken to reduce the environmental impact ... there is a real risk of serious environmental consequences causing a loss of public confidence that could delay or stop this activity," advisers to US energy secretary Steven Chu concluded late last year.

Officials in New York State are expected to decide on how to proceed by the end of the year. Their deliberations will be watched across the globe. Many nations have shale deposits that could hugely increase natural gas production, but opposition to their exploitation is growing. Lawmakers in France and Bulgaria have voted to ban fracking, and in the UK, small earthquakes triggered by fracking have caused alarm (see "Frack responsibly and the risks - and quakes - are small").

In fact, fracking has been around for decades. Traditionally, water was pumped into vertical wells to liberate shallower reserves of "tight gas" trapped in rocks like sandstone. What has changed is the introduction of technology that allows multiple wells to be drilled from the same pad, then run horizontally over thousands of metres through deep shale beds. The amount of water pumped into these wells is far greater than in tight-gas fracking (see diagram).

The technology was first deployed in Texas in the early 2000s, to little public complaint. It was a different story when production started to take off in Appalachia, where people are not used to oil and gas exploration.

The water used in fracking contains sand, to hold new cracks open, plus small quantities of chemical additives. Their identity is often kept secret by drilling companies, but they may include lubricants like mineral oil, ethylene glycol to prevent scale build-up, and glutaraldehyde to inhibit bacterial growth. Between 10 and 40 per cent of the water flows straight back up the well pipe within a couple of weeks. Once the flowback slows, gas can be collected, along with a small amount of "produced water".

Fracking fluid may be harmful. In addition to the additives, it can pick up toxic salts and volatile organic compounds such as benzene, xylene and phenols from the rock. Geologists say this mixture is unlikely to percolate up through a couple of thousand metres of impermeable rock to reach the shallow groundwater used for drinking. Indeed, the clearest evidence of groundwater pollution comes from a much shallower tight-gas frack. In December, the US Environmental Protection Agency (EPA) reported that groundwater near Pavillion, Wyoming, was contaminated with chemicals including fracking additives. In this case, some fracking had occurred just 372 metres down, within the aquifer from which local people draw their water.

The EPA is now working on a national study of the potential effects on groundwater. It should have initial results by the year's end.

One way fracking water - and methane - could enter groundwater is if the vertical well casing is breached. Methane is not toxic, but it can explode.

Last year, researchers led by Rob Jackson of Duke University in Durham, North Carolina, analysed water from drinking wells above the Marcellus Shale. They found that wells within 1 kilometre of a shale-gas drilling site contained 17 times as much methane as those further away (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1100682108). However, the team found no fracking chemicals or salts from the shale, and whether the methane came from the fracked zone or from shallower deposits is in dispute.

Even if groundwater is untainted, the contaminated fracking water must be safely disposed of. In Texas, it has been injected even further below ground, into wells left over from previous drilling. This has caused most of the earthquakes linked to fracking - which still tend to be too small to cause harm. In Appalachia few such deep wells are available. Instead, large companies are recycling their water for future fracks, while smaller operators are faced with expensive water treatment. "There's never been an injection earthquake to my knowledge that has caused damage or injury," says Mark Zoback, a geophysicist at Stanford University in California.

Environmental scientists remain worried about illegal discharges and accidents. "You just know there's going to be spillage and contamination," says William Schlesinger, president of the Cary Institute of Ecosystem Studies in Millbrook, New York.

Although the water has caused most concern, many of the ailments blamed on fracking seem more consistent with air pollution. In unpublished work, John Adgate of the Colorado School of Public Health in Denver found that airborne volatile organic compounds spike during the initial flowback period. Could this harm human health? "That's the $64,000 question, and there's not good data," says Adgate.

This lack of data could come to haunt the industry, says Goldstein. In the absence of any studies linking health to actual human exposures to pollution, he argues, fracking will get blamed for clusters of disease - whether or not it is justified. "There will be media attention, lawsuits, and there will be declines in property values," he says. "Industry is piling up problems for the long run, and so is government."

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