It's unclear (to me at least). The Standing Rock Sioux are saying they've found " burials rock piles called cairns and other sites of historic significance to Native Americans". At least some of those sites are on private land (another can of worms). But all of the sites have been found pretty recently. Like after the pipeline was approved to go through the area. The Sioux are also claiming the energy company has destroyed even more sacred stuff they just found, while the company is claiming it's destroyed nothing of historical significance. The Sioux might be right, but the timing is a little fishy to me.
There has also been the claim made in Federal Court that the Army Corps of Engineers didn't follow proper procedures when they approved the pipeline's plans.
Growing up dog sledding in Alaska I have spent many a day cruising down the Trans-Alaska pipeline and seen just exactly how much the wilderness is disrupted by this kind of thing. (not all that much) It seems to me if there was a legitimate attempt to solve the problem, a mile wide run of land could be found that didn't disturb sacred sites. I'm kinda getting the feeling that this is an attempt to stop any further exploiting of energy reserves in that part of the US, and is using a publicly sympathetic face.
I could be wrong though.
From my experience, they generally employ archeologists while they are building a pipeline (or any other major earth-moving project) to preserve anything they find of "historical" significance. Not only did my cousin do that for the Missouri DOT for several years, but when Enbridge built the pipeline through the farmland of the Aurora Sportsmen's Club, they found what they call a "Garbage Pit" of an early homesteader. When they finished laying the pipeline through our land (of which they paid us a huge chunk of money.*) They gave us all the "stuff"
% they had dug-up, which we proceeded to donate to the Waterman Historical Society. Which then acted as if we had discovered King Tut's Tomb for them. It apparently give the bluehairs a year's+ worth of fodder for their meetings. (They did lots of research and discovered the family that had a homestead right near there, I was sent voluminous e-mails regarding the research of the "finds", to include things like what years Sears, Roebuck, and Co. had sold that china pattern(s) and all kinds of other info on the various bits of detritus).
So if anything of any significance were to be found, the digging would stop and either a) the site excavated archeologically or b) bypassed (Hence the 300' construction right of way, in case they need to deviate a bit from the original line, plus move equipment and materials during the construction.
*- Anyway. When word first got out, they weren't going to go through our farmland, they were going to go through a neighboring farm. That Owner said "Hell No." So Enbridge approached us and ask if they could make a slight jog that would go through our land (pretty much across the entire thing diagonally), oh, and by the way, here's a giant pile of money. We took the money and ran. They paid for the right of way, plus the loss of a year's harvest on 100 acres (roughly) of land that couldn't be farmed that year. By the following year, the only way you could tell there was a pipeline under our land was by the funny looking poles near the northwest and southeast corners. Our neighbor was (and still is) pissed once he found out how much money we got for doing jack-*expletive deleted*it.
%- It literally was bits of broken dishes, bits of cloth, animal bones, glass, and the usual crap that people throw in the trash when there was no further use/re-use for it. The old ladies of the town were beyond giddy with the "find". The old men were happy, because the old ladies were out of the house and running all over to do research on every bit and scrap of crap we gave the Historical Society. Things like that and holding a fundraiser to repair the first and to-date only new police cruiser the town had ever purchased went a long to endearing the club to the town.
