Updates
December 17, 2012: Montana approves pipeline to nowhere.
Montana on Monday approved easements to let the Keystone XL pipeline cross state-owned land, including the Missouri and Yellowstone rivers.
The Land Board, chaired by Gov. Brian Schweitzer, running his last meeting before leaving office, sold the package of 50-year easements to TransCanada for $741,000. The board also finalized approval for land leases for the completion of the Montana-Alberta Tie Line.
Original Post
Unless there is "twinning," no Bakken oil is going to go in that heavy oil sands pipeline. Just saying.
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Added later: The most definitive layperson's description of the Keystone XL mentions a single pipeline; there is no mention of "twinning." But this is a layperson's description; without technical details I do not know if there will be two pipelines. I am quite sure that in the original plans there was no "second" pipeline for light sweet crude. So, we'll see. I am still looking for a source to answer the question.
Added later: In addition, a cursory review of the description of the pipeline provided by TransCanada says nothing about a second pipeline to carry light sweet Bakken crude oil, including the official document describing the pipeline.
Added later: In addition, a landowner in Texas recently sued to stop the construction of the pipeline across his Texas property because the easement permit was for a crude oil pipeline, not a bitumen pipeline. The court stopped construction for a short period, but then allowed construction to continue. There was no mention of a second pipeline.
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A reader provides these links regarding the Keystone: I see no reference to a dual pipe.
Here is the Seeking Alpha article on the Bakken on ramp, http://seekingalpha.com/article/321263-the-bakken-oilfield-transcanada-keystone-xl-project-may-bypass-federal-reviewTransCanada documents related to the on ramp aka the Bakken Marketlink, http://www.transcanada.com/search_results.html?q=Bakken+on-ramp&x=0&y=0If the link is not live by the time you get it, use “Marketlink” at the TransCanada website search engine, you will find 8 documents including the note from Governor Brian Schweitzer and Senator Max Baucus.Links to good route maps at TransCanada’s web site, http://www.transcanada.com/5730.htmlKeystoneXL project e-mail address, http://www.transcanada.com/5736.html