Crews are still working to clean up residual oil left from a 2010 oil spill in southern Michigan that occurred when Line 6B of the Lakehead system ruptured.
Canadian pipeline company Enbridge raised its spill volume from 19,500 barrels to 20,082 barrels, though that figure is much less than the 28,000 barrel estimate used by the U.S. Environmental Protection Agency.
Any penalties are tied to the volume of oil spilled.
Carl Weimer, executive director of watchdog group Pipeline Safety Trust, told InsideClimate News that Enbridge should work to come up with a "better number."
"I am always suspicious when the original number sticks around so long, because penalties for Clean Water Act violations are based on how much goes into the water," he said.
The National Transportation Safety Board is examining the section of pipe taken from the site of the spill. The final NTSB report is expected this summer. The company could be fined as much as $1,100 per barrel of oil spilled.