The whole tarsands oil tankers blowing up a whole town phenomenon is, so far, restricted to Canada, but Casselton, ND has had at least two close calls, once with spectacular effect:
https://www.youtube.com/watch?v=2ai08xm7T20
The Alberta Clipper line 67 exploded once in November 2007 near Clearbrook, MN killing two pipeline workers. PHMSA later fined Enbridge $2.4 million for safety violations connected to the incident.
Both modes of transport for tarsands should be avoided, and there is no good route through Northern MN wetlands and rivers. The forecast for climate change based on models where the tarsands are fully exploited show this region making an awkward and fiery transition from forests and wetlands to savanna.
Keystone's threat to the Oglala aquifer is based on studies of the 1979 spill site in MN. It is a shame that the study can't protect this area from more crude going through the leaky pipes here, but at least it has helped slow Keystone related carbon emissions.