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INSIGHTi
Line 5 Pipeline: Replacement/Tunnel Project
November 9, 2021
The Line 5 Pipeline is a 30-inch, 645-mile pipeline owned by Enbridge carrying up to 540,000 barrels per
day of crude oil and natural gas liquids from Superior, WI, to Sarnia, Ontario (Figure 1). A key segment
of Line 5 is an underwater crossing at the Straits of Mackinac—between Michigan’s upper and lower
peninsulas—where the pipeline runs for approximately four miles across the lakebed. This crossing has
been an environmental concern due to the risk it poses of a “worst case” oil spil into the Great Lakes.
Figure 1. Enbridge Line 5 Pipeline
Source: CRS using data from Platts, and Esri Data & Maps 2019.
Under the terms of various state agreements, Enbridge plans to replace this pipeline segment with a new
one constructed through a tunnel beneath the lakebed—which requires federal approval. Enbridge
continues operating the existing pipeline in the meantime. However, the state of Michigan has ordered
Line 5 to shut down. Whether the pipeline should continue operating in its current configuration, and
whether the federal government should grant a tunnel permit for a replacement crossing, have been the
subject of litigation, federal oversight, and a U.S.-Canada treaty dispute.
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Michigan Easement Challenges
Line 5 was constructed in 1953 as part of a pipeline system linking oil fields in Alberta, Canada, to
refinery markets in the Great Lakes region. (The pipeline currently carries products from both Canadian
and domestic sources.) Enbridge’s predecessor—Lakehead Pipe Line Company—was granted an
easement at the time of construction by the State of Michigan to cross the Straits of Mackinac. In October
2018, Michigan and Enbridge entered an agreement whereby Enbridge would construct a tunnel under the
straits, replace the existing Line 5 segment with a new pipeline segment through the tunnel, and
“permanently deactivate” the old segment. The agreement also provided that the state would be
“expressly confirming Enbridge’s rights to operate the [existing pipeline] under the terms of the Easement
during the construction of the Straits Tunnel and Line 5 Replacement.” The agreement was followed by a
December 11, 2018, state statute creating the Mackinac Straits Corridor Authority, which approved tunnel
construction on December 19, 2018.
On November 13, 2020, under a new gubernatorial administration, state officials notified Enbridge that
the 1953 easement was being revoked on safety grounds, requiring the Line 5 segment across the straits to
cease operating by May 2021. On November 24, 2020, Enbridge filed a chal enge in federal court to the
state’s pipeline safety jurisdiction and shutdown order. In March 2021, the court ordered mediation
between the two parties to resolve the dispute, but as of October 2021, that mediation was reported to be
unsuccessful. The court has not yet ruled on the case. Absent a federal court order, Enbridge continues to
operate the pipeline across the straits.
U.S.-Canada Pipeline Treaty
The Canadian government has ardently supported the continued operation of Line 5. Canada has sought to
intervene though public statements and court filings, citing a 1977 pipeline treaty with the United States
which prohibits a “public authority in the territory of either” from instituting “any measures ... which are
intended to, or which would have the effect of, impeding, diverting, redirecting or interfering with in any
way the transmission of hydrocarbon in transit.” On October 4, 2021, Canada announced that it was
formal y invoking the dispute settlement provision of the treaty regarding Line 5. On November 9, the
White House Deputy Press Secretary stated that “both the U.S. and Canada wil engage constructively” in
Line 5 negotiations and that shutting down the existing pipeline “is something that we’re not going to
do.”
Army Corps Tunnel Permit
In 2020, Enbridge filed a joint application with the U.S. Army Corps of Engineers (Corps) and the
Michigan Department of Environment, Great Lakes, and Energy (EGLE) to build a tunnel below the
lakebed for a new Line 5 pipeline crossing. The Corps has statutory authority over the proposed Line 5
tunnel pursuant to Section 404 of the Clean Water Act (33 U.S.C. §1344), under which the Corps permits
activities that may discharge dredge or fil material into waters of the United States, including wetlands.
(Although Michigan is one of three states that administer their own Section 404 permits, the Corps retains
jurisdiction over certain waters, such as the Straits of Mackinac.) The agency also has authority pursuant
to Section 10 of the Rivers and Harbors Act of 1899 (33 U.S.C. §403), under which the Corps permits
structures and work in or affecting navigable waters.
In carrying out its authorities, the Corps must identify and consider the environmental impacts of the
agency’s proposed actions (e.g., issuing a tunnel permit) pursuant to the National Environmental Policy
Act (NEPA; 42 U.S.C. §§4321 et seq.) among other statutory requirements. On June 23, 2021, the Corps
announced that it would be preparing an Environmental Impact Statement (EIS), to “ensure al potential
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impacts and reasonable alternatives associate d with this project are thoroughly analyzed and wil
ultimately support a decision on the permit application.” The Corps states that its environmental review
“is limited to the proposed crossing of the Straits of Mackinac and adjacent wetlands.” However, it is not
clear to what extent the Corps’ NEPA review may consider the greenhouse gas (GHG) emissions
associated with the fossil fuels passing through pipeline segment, as cal ed for by some advocates. The
agency has not set a deadline to complete the EIS.
On January 29, 2021, EGLE announced that it had approved Enbridge’s application for permits required
to build the tunnel. Although EGLE “acknowledged public concerns about the existing oil pipeline and
affirmed ... that the current pipeline ... poses an unacceptable risk to the Great Lakes,” the agency
concluded that “the proposed tunnel could comply with state environmental laws.” The tunnel project stil
requires approval from the Michigan Public Service Commission, which has ruled that it must consider
GHG emissions caused by products transported by Line 5. The commission’s review is ongoing.
Author Information
Paul W. Parfomak
Specialist in Energy Policy
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff
to congressional committees and Members of Congress. It operates solely at the behest of and under the direction of
Congress. Information in a CRS Report should not be relied upon for purposes other than public understanding of
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