Men wearing protective clothing survey cleanup efforts March 30, 2013 where an underground crude oil pipeline ruptured in the Northwood subdivision in Mayflower, Arkansas. (Rick McFarland/Arkansas Democrat-Gazette/Via Reuters)

Exxon Mobil said that one of its pipelines leaked “a few thousand” barrels of Canadian heavy crude oil near Mayflower, Ark., prompting the evacuation of 22 homes and reinforcing concerns many critics have raised about the Keystone XL pipeline that is awaiting State Department approval.

The pipeline breach took place late Friday, Exxon said, in the 20-inch diameter, 95,000-barrel-a-day Pegasus pipeline, which originates in Patoka, Ill., and carries crude oil to the Texas Gulf Coast, the country’s main refining center. Mayflower is about 25 miles north of Little Rock.

By Sunday afternoon, the company had deployed 15 vacuum trucks and 33 storage tanks to start cleaning up and temporarily store about 12,000 barrels of oil and water that had been recovered, the company said. Crews were steam-cleaning oil from property, Exxon Mobil said, while some fought in rainy weather to keep the oil from reaching nearby Lake Conway through storm drains.

The pipeline, which was built in the 1940s and was recently expanded, was carrying low-quality Wabasca Heavy crude oil from Alberta, Exxon Mobil spokesman Alan T. Jeffers said. According to the Crude Monitor Web site, Wabasca Heavy is a blend of oil produced in the Athabasca region, where the oil sands are located.

An existing Keystone pipeline carries crude oil that comes from the oil sands deposits in Alberta to Patoka through Exxon Mobil’s lines. Jeffers said he did not know if this batch of crude oil came from the Keystone line.

Many critics of the Keystone XL pipeline say that corrosion risks are greater in pipelines carrying low-quality bitumen-laden crude from the oil sands. They have urged President Obama to reject the Keystone XL permit application.

“This latest pipeline incident is a troubling reminder that oil companies still have not proven that they can safely transport Canadian tar sands oil across the United States without creating risks to our citizens and our environment,” said Rep. Edward J. Markey (Mass.), the ranking Democrat on the House Natural Resources Committee.

TransCanada, owner of the Keystone system, has said that the new pipeline would be far safer than any other part of the nation’s 2.6 million miles of oil, gas and chemical pipelines.

The Environmental Protection Agency declared the Arkansas leak a “major spill,” a label put on any spill of 250 barrels or more. Exxon Mobil said it was preparing for a spill of up to 10,000 barrels, but that the estimate would probably end up being lower than that.

The company and other responders were battling to keep the crude oil, which gushed into yards and ran down residential streets in a Mayflower neighborhood, from leaking into Lake Conway, a popular recreation and game-fishing spot. Cleanup crews have deployed 3,600 feet of boom near the lake as a precaution, and as of Sunday afternoon no oil had reached the lake, Jeffers said.

He added that dikes had been built to prevent runoff into the lake, but heavy rains were making that difficult, and runoff from storm drains into the lake was a concern.

Several residents posted Facebook photographs and online videos of the oil pooling in yards and streets.

Allen Dodson, a Faulkner County judge and one of three unified incident commanders responding to the spill, said in an interview that oil mostly affected five or six yards and that the “smell had gone down dramatically.”

Jeffers said that the company received phone calls from people in the area at the same time its pipeline monitors in Houston noticed a drop in pressure in the line. The pipeline is buried about two feet deep in the Mayflower area, he said. Exxon Mobil said responders were on the scene within half an hour. Approximately 120 Exxon Mobil workers are responding to the incident in addition to federal, state and local officials and workers.

Exxon Mobil said that fumes from the oil spill posed a risk in “high pooling areas,” where oil could be seen on the ground and where crews were working with safety equipment.

The company said the cause of the spill is under investigation.

The Arkansas spill came just four days after the Transportation Department’s Pipeline and Hazardous Materials Safety Administration proposed fining Exxon Mobil $1.7 million for a July 2011 spill in Montana’s Yellowstone River. In that incident, Exxon Mobil’s 12-inch Silvertip Pipeline spilled 1,509 barrels of crude oil into the Yellowstone River near Laurel, Mont., during flooding.

The agency is alleging that Ex­xon Mobil did not properly address known seasonal flooding risks to the safety of its pipeline, including erosion of riverbeds that could leave pipelines exposed to damage from debris flowing downstream. The agency also said Exxon Mobil did not implement measures that would have mitigated a spill into a waterway. 

Exxon Mobil has contended that the unusually large fine — possibly the result of a doubling of civil penalties under the Pipeline Safety, Regulatory Certainty and Job Creation Act of 2011 signed into law last year by Obama — contradicted a report that said the company took “reasonable precautions.” The new ceiling is $2 million. The company said it spent about $100 million cleaning up damage from the spill.

The Arkansas incident also comes just a few days after a Canadian Pacific Railroad train carrying oil sands crude — a mixture of heavy bitumen and lighter dilutents — from Alberta to Chicago derailed near Parkers Prairie, Minn., spilling about 357 barrels.

That accident drew attention because the State Department’s new environmental impact statement on the Keystone XL said that if the pipeline were blocked, oil sands crude would still be able to reach markets via railroads, which carry more than 1 million barrels a day of oil in the United States. Supporters of the pipeline say that shipping oil by pipeline would be safer and more fuel efficient than doing so by rail.