US Department of Justice
EPA claims the automaker used software that allowed diesel vehicles to emit more pollution on the road than they do in emissions tests.
2010 pipeline rupture sent three-million litres of crude oil into the Kalamazoo River and a tributary creek.
Federal lawsuit alleges the German automaker intentionally tampered with the vehicles sold in the US.
Officials say the releases, between 2006 and 2009, emitted hydrogen cyanide, sulfur dioxide, nitrogen oxides and mercury.