Residents of the central Arkansas town of Mayflower were preparing for a calm Easter weekend when their plans unexpectedly changed. On Friday, March 29, the Exxon Pegasus pipeline burst, flooding this tiny Little Rock suburb with as much as 200,000 gallons of tar sands crude. Many residents say they didn’t even know about the pipeline, which carries Canadian petroleum from Illinois to Texas.

"We could see oil running down the road like a river," a Mayflower resident told TV station KTHV. A week later, 22 homes remain evacuated, while cleanup efforts have been complicated by bad weather and the unique characteristics of tar sands crude.

As the Natural Resources Defense Council’s Anthony Swift explains, “[T]he Pegasus line was carrying Wabasca Heavy diluted bitumen — a toxic climate mix of heavy tar sands bitumen and volatile petrochemical diluents,” like benzene, a toxic and carcinogenic solvent that helps keep the bitumen in liquid form. At room temperatures, undiluted bitumen is a solid (asphalt is mostly bitumen).

Once this mixture is exposed to air, the solvents begin to outgas, creating toxic fumes that are a danger to wildlife and human health. And if the thick slurry makes it to a waterway, problems compound fast. Unlike light crude, tar sands crude sinks, rendering conventional clean-up approaches — skimmers, vacuums, and floating booms — irrelevant.

Bad news for lakes

Unfortunately, Mayflower sits at the edge of Lake Conway, a 6,700-acre state-owned reservoir that’s a popular fishing destination in the area. Independent reporting from the group Tar Sands Blockade purports to show that Lake Conway has been impacted, though official reports continue to insist that the lake is oil-free. Media access to the spill zone has been hampered, apparently at ExxonMobil’s request. Nearby, state agencies are monitoring Lake Maumelle, the primary drinking water source for the region’s 400,000 residents.  

In 2010, a Michigan pipeline failure showed regulators and emergency response crews how hard it is to resolve a tar sands crude spill in water. Over the course of a day, nearly a million gallons of Canadian tar sands crude poured from a ruptured pipeline owned by Canada’s Enbridge Energy into the Kalamazoo River, contaminating nearly 40 miles of waterway and prompting a state of emergency to protect Lake Michigan. To date, cleanup costs for the Enbridge spill have hit nearly $800 million. Just last month, the EPA ordered the company to resume dredging the river to try to clear it of sunken “dilbit” (diluted bitumen).

Obama decision on Keystone XL expected this summer

The Mayflower spill comes at an especially sensitive time for the Canadian tar sands project, as President Obama is expected to approve or reject TransCanada’s plan for an expanded Keystone XL pipeline project this summer. The 1,600-mile-long pipeline would move up to 1.3 million barrels per day from Canada’s Alberta Tar Sands, through the middle of America, to refineries along the Gulf Coast of Texas.

Along the way, the pipeline would pass through a number of environmentally sensitive areas, including Nebraska’s Ogallala Aquifer, one of the world’s largest underground freshwater reservoirs. A vast geological formation supplying drinking water to homes, businesses, ranches and farms in eight states, the condition of Ogallala water isn’t an abstract consideration for the millions of people who live in the Great Plains.

A report prepared by Nebraska’s Department of Environmental Quality asserts that any Keystone XL spills along the aquifer would result in a local, not regional, impact, but other analysts aren’t so sure. According to, the study only modeled a generic spill situation totaling 42,000 gallons. Real world spill scenarios, including last week’s Arkansas spill, often exceed that number by many times. Aside from the Pegasus spill in Arkansas and the 2010 Enbridge spill, in 2011 another ExxonMobil pipeline leaked more than 60,000 gallons into Montana’s Yellowstone River.

In an interesting twist of fate, just days before its Pegasus line ruptured in Arkansas, ExxonMobil was hit with a $1.7 million fine for having inadequate emergency procedures in that 2011 spill. And while supporters of the Keystone XL project argue that the Canadian tar sands crude will get to southern refineries with or without the pipeline — by truck or train if need be — lately trains aren’t showing themselves as great transport options, either.

On March 27, a mile-long freight train carrying Canadian tar sands crude derailed in Minnesota, spilling as much as 30,000 gallons, while a week later, 400 barrels broke free when a Canadian Pacific freight train in northwest Ontario, Canada, derailed. Cleanup efforts for both continue.

In Mayflower, residents wait to hear when they can return to their homes, wondering whether their community will forever be known as the site of the Pegasus oil spill. The public comment period on the Keystone XL project ends April 22, and a final decision on the pipeline’s future is expected within months.

Related stories on MNN and TreeHugger:

Pipeline spills call attention to Keystone XL
From Michigan to Arkansas, a series of recent oil spills have raised doubts about the proposed Keystone XL oil pipeline.