In an important decision released on May 29, 2015, the U.S. Court of Appeals for the Tenth Circuit rejected the Sierra Club and other environmental organizations' most recent objections to the permitting and construction of TransCanada's Gulf Coast pipeline. The case is Sierra Club, et al. v Bostick. The U.S. Army Corps of Engineers issued letters verifying that the Corps Nationwide Permit 12, authorized by the Clean Water Act (CWA), would cover the proposed pipeline. The pipeline has now been constructed and is delivering oil, and covers 485 miles and consists of 2000 water crossings necessitating the use of this permit, which "allows anyone to construct utility lines in U. S. waters 'provided the activity does not result in the loss of greater than ½ acre of U. S. waters for each single and complete project.'" The Court of Appeals noted that the project also required TransCanada to satisfy wetlands mitigation requirements. In challenging the validity of the Nationwide Permit and the verification letters, the plaintiffs argued that the Corps of Engineers violated both the National Environmental Policy Act (NEPA) and the CWA.

With respect to NEPA, the Court of Appeals ruled that this argument had been waived, in particular the alleged risk of oil spills, because it not been raised with the Corps of Engineers during the comment period that was set aside for the submission of such comments. With regard to the CWA, the plaintiffs argued that the Nationwide Permit issued to TransCanada violated the law by authorizing linear projects with substantial environmental impacts and deferring part of the minimal impacts determination to project-level personnel who would be involved in the pipeline project after the Corps of Engineers' permitting initial authorization had been granted. However, the Court of Appeals held that the environmental groups did not show that the permit authorizes linear projects with more-than-minimal impacts, nor that the Corps of Engineers, allowing for Chevron deference, impermissibly construed the CWA by providing for a partial deferral of the minimal-impact analysis.