I really don't think this will do much in terms of damaging water, like not at all. Oil used to seep into rivers in Pennsylvania and other places all the time (this is actually what snake oil was). And being a new pipeline wont have issues any time soon. Also water in this area is likely drawn from the Ogallala aquifer and its doubtful much oil would even seem into it if there was a catastrophic leak. This is allmy reckoning though, could be wrong. I just know crude is a lot less dangerous than, say, surfactants that might leak on the surface if a frack job isn't properly managed.

Also think why pipelines are built. It is because they are more efficient over time. They cost less in transport costs over it's lifetime for the amount of oil compared to truck or rail. This means LESS emmissions, less resource use, and better for the environment.

The biggest issue in my mind is breaking Native American treaties. Though the natives in my opinion would be best served by them making a deal to get royalties from the pipeline and ensuring concessions to not disturb their gravesites. This would be best for the economic welfare and heritage for them.