Not that it really changes anything, but this is downstream of Yellowstone National Park.
Rivers run north to south bro (in the northern hemisphere). Glendrive, Montana is southwest of Williston, a few miles southwest of Williston is where the Yellowstone forks off the Missouri River. It then follows I-94 until it is directly outside the northern boundaries of Yellowstone National Park, at which point if follows Rt. 89 in through the park.
That said, this amount of oil would be incredibly dilute after traveling the hundreds of miles it would take to get to Yellowstone, and from a chemicals of concern standpoint it ain't got shit on your average hot spring.
The Keystone is supposed to be built near/over a major water aquafier, right?
Well sorry Canada, cause F' that pipeline.
The Ogallala, yes, where the majority of the great plains gets it's water from:
This is one of the main points differentiation between current pipeline infrastructure that runs generally along the eastern edges of Kansas, Oklahoma, and somewhere between the eastern edge of Nebraska and the western edge of Iowa. Keystone XL will be the first pipeline to overlay significant portions of the Ogallala. Given that it isn't a very well confined (i.e. encased in non-porous rock) in the upper strata it is also rather prone to having seepage into it.
Another major difference with Keystone XL is that it is intended exclusively or at least primarily for tar sands. Tar sand oils are thicker, require more pressure to push along the pipeline, and are naturally more abrasive due to the suspended solids. This results in an expedited deterioration in the pipeline itself. Supposedly Keystone accounts for this, but seeings how most of the Koch brothers other pipelines leak like sieves because they use the cheapest materials available with consistency, I wouldn't exactly have a ton of faith in that.
The real travesty with Keystone is the government's use of eminent domain to transfer private lands from American citizens into the hands of a Canadian company to ship Canadian oil crude to the gulf for international sale. It has almost zero real value to the American people yet we have the U.S. government acting as the procurement arm for Keystone, all because the Koch brothers own the entire Republican party and a good chunk of Midwest Democrats. It is the very embodiment of government as an agent of private corporations instead of an agent for individual rights and freedoms.