When ExxonMobil's Pegasus pipeline ruptured last month in Mayflower, Ark., it was carrying diluted bitumen, a controversial form of oil from Canada's tar sands region. That was confirmed in a letter an Exxon lawyer wrote to the U.S. Environmental Protection Agency last week.
But the letter contradicts public assertions by company officials that the spilled oil was simply "heavy oil," not tar sands bitumen. It also raises, once again, the question that surfaces after every spill involving oil from Canada: Is it or isn't it diluted bitumen?
Bitumen is a semi-solid form of crude oil found in Canada's vast oil sands region, where it is found with sand, clay and water in formations dating back hundreds of millions of years. Because bitumen is so thick and tarry, producers dilute it with natural gas liquids or light oil so it can flow through pipelines. That creates a type of oil called diluted bitumen, or dilbit.
The letter Exxon sent to the EPA on April 10 was a response to the EPA's request for more information about Wabasca Heavy—the oil that poured out of a 22-foot-long gash on its Pegasus line on March 29. "Can the oil accurately be described as tar sands oil, or a type of diluted bitumen (dilbit)?" the EPA had asked in an April 5 letter to Exxon.
The answer is yes, according to oil producers' definitions of what counts as dilbit, Exxon said. "Canadian producers report their production of Wabasca Heavy as bitumen," wrote Richard Byrne, Exxon's assistant chief attorney of environmental and safety law.
Byrne went on to say that Exxon buys its Wabasca Heavy from Canadian Natural Resources Limited and Cenovus Energy Inc.—two of Canada's biggest oil sands producers. Both companies dilute the bitumen to make it thin enough to meet pipeline specifications, the lawyer wrote.
Other industry groups also describe Wabasca Heavy as dilbit.
A recent report commissioned by the Canadian Energy Pipeline Association, a trade organization, included Wabasca Heavy in a group of eight dilbit samples. And the Battelle Memorial Institute, a private science and technology company in Ohio, counted Wabasca Heavy among seven dilbit samples in a July 2012 study on pipeline corrosion commissioned by the American Petroleum Institute.
Exxon spokesman Alan Jeffers spoke with InsideClimate News about the discrepancy between Exxon's definition of Wabasca Heavy and the definition offered by the Canadian oil producers.
Jeffers said the Alberta government's Energy Resources Conservation Board, an independent agency, told Exxon "that they consider anything from that area bitumen." By contrast, "we consider [Wabasca] heavy crude," not dilbit.
He chalked up the difference to the "varying definitions" and "colloquialisms" associated with the term dilbit.
Jeffers did acknowledge that Wabasca Heavy has similar chemical properties to other types of dilbit, which is crucial when assessing public health dangers and cleanup techniques. "Of course it’s going to have many of the same characteristics, because it's from the same geological time and formation," he said.
But Jeffers also said that when pure Wabasca Heavy crude oil comes out of the ground, it's lighter than "what is traditionally known as bitumen."
In its letter to EPA, Exxon submitted a Material Safety Data Sheet prepared by Cenovus, which said that in terms of chemical composition and density, Wabasca Heavy is the same as four dilbits and two non-dilbit heavy oils. Its list includes Cold Lake, the type of dilbit that spilled out of ruptured Enbridge Inc. pipeline in Marshall, Mich. in 2010. After that spill, the diluents began evaporating and the bitumen sank to the bottom of the Kalamazoo River, where it is still being removed today, almost three years later.
Like the other dilbits, Wabasca Heavy contains bitumen blended with a hydrocarbon diluent, usually natural gas liquids; benzene, a known human carcinogen; and hydrogen sulfide, a corrosive and poisonous chemical compound, according to the Cenovus MSDS. Wabasca Heavy also contains at least eight other hazardous constituents, including N-hexane and naphthalene, according to a separate data sheet that Exxon provided to cleanup workers in Arkansas.
Between 210,000 and 294,000 gallons of Wabasca Heavy crude oil spewed out of the 65-year-old Pegasus pipeline nearly three weeks ago, forcing the evacuation of 22 homes in a Mayflower subdivision.