As a non-American that isn't familiar with the country's regulatory framework for things like this, I'm wondering: who's the regulator tasked with reviewing and approving infrastructure like pipelines?
From what I can gather, USACE is responsible for the planning/design, but I'm genuinely curious how something like this wouldn't have arisen as part of the regulatory process. Even if this particular site hadn't been discovered during the planning stages of the pipeline or at the time of the (presumed) approval by the regulator, is it not typical for the construction firm or owner/operator to be required to engage a third party to complete archaeological digs along, and adjacent to, the proposed route?