Enbridge in May issued a proposal to the Michigan Public Service Commission to replace more than 200 miles of Line 6B, part of the oil pipeline system transporting so-called tar sands oil from Canada. Line 6B ruptured in 2010, spilling roughly 20,000 barrels of tar sands into Michigan rivers and streams.
Enbridge plans for the Line 6B overhaul include efforts to double the amount of crude oil transports to 500,000 barrels per day.
Beth Wallace, community outreach coordinator for the National Wildlife Federation, told Michigan Public Radio that tar sands oil left pipeline walls vulnerable.
"In order for them to transport it in its raw form, which it almost is equivalent to holding a chunk of clay, they have to dilute it with this liquid gas condensate and pump it at very high pressures, which heats the line as well," she said. "It's like sandblasting a line."
Enbridge spokesman Joe Martucci, however, said "no factual data or technical studies" support those claims.
U.S. regulators are examining the section of the ruptured line to determine the cause of the accident.