• Environmental epidemiology
• HEALTH IMPACT ASSESSMENT
• HEALTH POLICY

Over the past decade, there has been a surge in drilling for natural gas and oil in shale rock. Natural gas and oil extraction using high-volume, slickwater hydraulic fracturing from clustered multiwell pads using long, directionally drilled laterals (known by its popular name ‘fracking’), is an unconventional extraction process that is currently the focus of controversy. The process involves the injection of millions of gallons of water, chemical additives, and a proppant (sand and/or silica) at high pressure into a wellbore in order to create small fractures in the rock formations to allow natural gas (or oil) to be released. But for the lack of effective technology, this source of energy would have been tapped long ago.

While there are some positive aspects of high-volume hydraulic fracturing (eg, reduction in the dependence on foreign oil and gas; becoming a net exporter of natural gas and oil; possible reduction in unemployment in areas where wells are drilled), there are serious concerns including its impact on climate change and the potential harm to the environment and human health.

The process of drilling, extracting and transporting oil and gas is a dirty, messy and polluting process if not done correctly, cleanly and carefully. Well venting, flaring and burning gas on release account for the largest sources of air emissions. Volatile organic compounds and diesel particulate matter, for example, result in elevated air pollution concentrations that exceed US Environmental Protection Agency (EPA) guidelines for both carcinogenic and non-carcinogenic health risks.1 Truck traffic and diesel truck exhaust contribute to airborne emissions of fugitive dust and high benzene concentrations.

The structural integrity of wells can and does fail over time; for example, cement cracks and steel casing barriers corrode.2 Wells have blowouts, spills are common, and methane is …