A. Hydraulic fracturing is a technique used in oil and natural gas production. It releases otherwise irrecoverable resources from certain geological formations by injecting water and additives at high pressure into the ground to create microfractures in the rock. Hydrocarbons can then flow through these fractures into a well. It has become controversial because of concerns that the technique, and well-drilling activity associated with its use, threatens groundwater, surface water, air quality, and other environmental values. Common in Alberta’s oil patch since the 1970s, the practice expanded greatly in this century, triggering gas rushes in British Columbia and Saskatchewan and resistance in several other provinces.

B. First demonstrated in 1947, fracturing has become more powerful and more precise over the decades. In the 1950s, the process employed pumps with less power than a pickup truck to push a few thousand litres of water and sand into the bottom of a vertical well. Today, the power of six train locomotives may be harnessed to drive 50 million litres of water at a time down a hole. Sophisticated additives make the water more slippery, prevent bacterial growth, or prop open the thousands of fissures — up to 3 mm wide and 100 m long — that open in the shattered rock more than a kilometre underground.

C. Fracturing became a game changer in the first decade of the 21st century when it began to be applied on a large scale, including in projects backed by the governments, in combination with another practice known as “horizontal drilling.” Horizontal drilling means that wells no longer go straight down through a layer of gas-bearing shale. Instead, the drill is turned sideways to run for kilometres through the middle of a deposit. Multiple wells drilled this way fan out underground like daisy petals, allowing companies to fracture hundreds of hectares of shale from a single wellpad.

D. Companies that provide hydraulic fracturing services insist that the practice poses no threat to freshwater typically found less than 300 metres below the surface. Thousands of metres and layers of impermeable rock separate that groundwater from petroleum pay zones, leaving little chance that hydro-fracturing a deep shale formation will, by itself, contaminate a water well on the earth’s surface, most assessments suggest. Nonetheless, critics found it troubling that companies were allowed to keep secret the identity of chemicals they mix with water in fracturing fluid.

E. Not given in any of the above paragraphs