WASHINGTON — The Sierra Club and other environmental groups Monday requested more time to comment on the Keystone XL pipeline project in the wake of the Mayflower oil spill.

The State Department needs to learn exactly what went wrong with the Pegasus pipeline in Arkansas before deciding the fate of the Keystone project, said Sierra Club executive director Michael Brune.

"The State Department needs answers to exactly what went wrong with the Pegasus pipeline, why Exxon couldn’t shut down the pipeline immediately, and how the administration can assure Americans that the Keystone XL pipeline – at nearly 10 times the size – would be safe. The short answer is, it wouldn’t," Brune said.

The Sierra Club, National Wildlife Federation, Natural Resources Defense Council, League of Conservation Voters and 350.org sent a letter to the State Department seeking to extend the public comment period on its environmental assessment of the Keystone pipeline from 45 days to at least 120 days.

The Keystone XL pipeline would carry tar sands crude from Canada to Gulf Coast refiners. The Pegasus pipeline carries a similar grade of crude along an 850-mile stretch between Illinois and Texas.

Environmental groups have strongly opposed the Keystone pipeline plan, which is now under review by the State Department. They want the additional comment time to be used to answer specific questions about tar sands pipeline safety raised by the failure and spill of the ExxonMobil Pegasus pipeline in Mayflower.

About 5,000 barrels of oil spilled when the pipeline ruptured March 29, forcing the evacuation of nearly two dozen homes in the Northwoods neighborhood of Mayflower, about 25 miles northwest of Little Rock.

The Environmental Protection Agency has categorized the incident as a "major spill" because it was greater than 250 gallons.

The Arkansas congressional delegation has supported the Keystone pipeline in large measure because the steel pipe would come from Welspun Tubular in Little Rock.

Reps. Tim Griffin, R-Little Rock, Steve Womack, R-Rogers, and Rick Crawford, R-Jonesboro, have co-sponsored legislation to speed approval of the Keystone pipeline by lifting a requirement for presidential approval of the plan.

The House Energy and Commerce Committee will hold a hearing Wednesday on the legislation that was introduced by Rep. Lee Terry, R-Neb.

Griffin, whose district includes Mayflower, said Mayflower oil spill has not changed his view on Keystone. While there are risks, pipelines are the safest available way to transport oil, he said.

"Do you want to put it in trucks running up and down the highway? It’s not safer," he said during a recent interview on KARN radio.

Griffin said he wants to make sure all the pipelines are safe and that the families affected the spill in Mayflower are made whole.

"We need to make this right for them," he said.