The Mackinac Straits Corridor Authority voted Dec. 12 to direct staff to prepare and submit correspondence to the U.S. Army Corps of Engineers about the supplemental draft environmental impact statement that added analysis of a horizontal directional drilling alternative.

Devin Sullivan, the Authority’s special assistant, told members the Michigan Supreme Court granted leave to hear appeals of the Michigan Public Service Commission order that approved Enbridge’s application to construct a replacement segment of Line 5 within the tunnel. "The appellants filed their briefs on November 14. This week, the party submitted a stipulated motion to extend the remaining briefing schedule," Sullivan said, adding that, "assuming those motions are granted, the appellee’s briefs will be due on December 22. Appellant’s reply briefs, and any amicus briefs will be due 01/23/2026, and responses to the amicus briefs will be due 02/13/2026."

At the same meeting, Michael Belligan of the Michigan Department of Transportation briefed the board on the Army Corps’ supplemental draft EIS. "The supplemental draft EIS was released on 11/13/2025," Belligan said, and the Corps "added analysis of the horizontal directional drilling method or installation alternative," which the Corps had previously dismissed as technically infeasible. He said the Corps was processing additional public comments and that a final EIS is "expected to be completed sometime in spring 2026, with the record of decision coming 30 days later."

Board members expressed concern that the horizontal directional drilling alternative departs from what the Authority’s enabling statutes and tunnel agreements contemplate. "From my perspective, the lack of secondary containment for horizontal directional drilling … would suggest that we at least bring those things to the attention of the Corps," Chairman Novak said during discussion. Sullivan and other members noted the tunnel agreement requires coordination only for permits specific to the tunnel and not for pipeline permits governed by the MPSC order; Sullivan said that legal distinction informed the board’s approach.

The board voted to direct staff to prepare correspondence that "identifies the departure from what is currently contemplated in both the statutory and contractual agreement with Enbridge and horizontal directional drilling," and asked that staff move quickly given the timing of Corps actions. Sullivan was directed to draft the comment for submission.

Separately, the board reviewed state permitting timelines reported by MDOT and EGLE staff and heard from Enbridge’s government-relations representative, Anna Mooney, who described the supplemental EIS as "very narrow in scope to this alternative" and said Enbridge continues to work with regulators. MDOT and Enbridge officials said EGLE’s processes and the Corps’ schedule will determine when formal decisions are issued.

The Authority did not adopt a legal position on the line-replacement appeals beyond directing staff to prepare the Corps correspondence and to track the Michigan Supreme Court briefing schedule. The board said the forthcoming correspondence will formally register the Authority’s concerns with the Corps’ supplemental analysis and the potential need to revisit statutory and contractual frameworks if HDD were to be authorized.