WINDSOR, Ontario — Assumption Park gives residents of this city lovely views of the Ambassador Bridge and the Detroit skyline. Lately they’ve been treated to another sight: a three-story pile of petroleum coke covering an entire city block on the other side of the Detroit River.  
Detroit’s ever-growing black mountain is the unloved, unwanted and long overlooked byproduct of Canada’s oil sands boom.
And no one knows quite what to do about it, except Koch Carbon, which owns it.