Updated: 7:20 p.m. | Posted: 2:43 p.m.
Federal Railroad Administration officials are investigating what may have caused two separate freight train derailments in Wisconsin over the weekend.
A 25-car derailment near Alma, Wis., on Saturday morning spilled about 20,000 gallons of ethanol into the Mississippi River. BNSF Railway spokesperson Amy McBeth said no environmental impacts have been observed near the site of the crash, although the company continues to monitor the river.
A study by the Massachusetts Department of Environmental Protection warned that ethanol was very flammable and appeared to contribute to oxygen depletion when present in high quantities in water. A spokesperson for the Minnesota Pollution Control Agency said the state is aware of the situation and is monitoring the Minnesota side of the river for possible environmental impacts.
The tracks near Alma are expected to reopen sometime on Monday night, McBeth said.
Another 13 cars carrying crude oil derailed on Sunday afternoon in Watertown, Wis., spilling about 500 gallons of crude oil and leading to the evacuation of 35 nearby families.
In a statement Monday evening, Canadian Pacific officials said people have been allowed to return home. CP said "monitors have not detected any level of volatile organic compounds in residential neighborhoods. That air monitoring will continue as a precaution as recovery operations continue."
A temporary track at the site opened at 6:15 p.m. Monday to trains moving at a slower speed. All trains in the area will operate at reduced speeds for the time being, Canadian Pacific said.
The railway company also says it will work with state and federal agencies to remove, clean and replace contaminated soil.
Much of the spilled crude oil at the site of the derailment was immediately siphoned up and contained, according to Canadian Pacific spokesperson Andy Cummings.
As the amount of oil from the Bakken formation in North Dakota increased in recent years, the prospect of a large spill in a populated area has caused some communities to consider tightening safety requirements.
The derailments come as the federal government seeks to institute new guidelines governing train safety. That effort is currently being challenged in court by both oil industry groups and environmentalists.
Jared Margolis, staff attorney for the Center for Biological Diversity, said the proposed federal rules don't go far enough.
"We're in a situation where we're moving more and more oil and ethanol by rail, but we don't have regulations that guarantee that we're not going to have accidents, and when accidents do occur, that we're not going to have large spills like you saw this weekend," Margolis said.
Railroad industry officials have said some of the new requirements, such as new electronic brakes, are too costly.
Wisconsin was the scene of 20 derailments in 2014, according to data from the Federal Railroad Administration. There were 45 reported derailments in Minnesota last year.