Background
The U.S. Army Corps of Engineers (USACE), Detroit District, is reviewing an application pursuant to Section 10 of the Rivers and Harbors Act of 1899 and Section 404 of the Clean Water Act for a Department of the Army (DA) permit by Enbridge Energy, Limited Partnership (Enbridge) (File LRE-2010-00463-56-A19) to construct a tunnel (the Line 5 Tunnel Project) that would house a replacement segment of Enbridge's Line 5 pipeline crossing the Straits of Mackinac (Straits) in Lake Michigan (see Figure 1). The primary Federal involvement associated with the proposed action is the discharge of dredged or fill material into waters of the United States, and the construction of structures and/or work that may affect navigable waters. Based on the potential impacts of the proposed project, the USACE intends to prepare an Environmental Impact Statement (EIS) in compliance with the National Environmental Policy Act (NEPA) to render a final decision on the permit application. The USACE is also preparing an Ethnographic/ Traditional Cultural Landscape Study as part of the EIS and its responsibilities under Section 106 of the National Historic Preservation Act.
Purpose and Need
The purpose of the project is to provide safe transportation of light crude oil, light synthetic crude oil, light sweet crude oil, and natural gas liquids (NGLs) between Enbridge’s existing North Straits Facility and Mackinaw Station, and to approximately maintain the existing capacity of the Line 5 pipeline while minimizing environmental risks.
Proposed Action
Applicant's Preferred Alternative: Construction of a 21-foot-diameter tunnel approximately 3.6 miles long, in bedrock underneath the lakebed of the Straits of Mackinac.
The applicant has proposed to decommission the existing Dual Pipelines in-place as part of the proposed project.
Project Plans
Click here for latest project plans
Description of the Line 5 Tunnel Project
The proposed Line 5 Tunnel Project is located within Mackinac County in Michigan’s Upper Peninsula and Emmet County within Michigan’s Lower Peninsula and includes subsurface crossing of the Straits. Line 5 currently crosses the Straits via two, 20-inch-diameter pipes that rest on or are anchored to the lakebed of the Straits (referred to as the “Line 5 Dual Pipelines” or “Dual Pipelines”). Enbridge is proposing to construct a tunnel underneath the lakebed of the Straits. This tunnel would house a new 30-inch pipeline for light crude oil, light synthetic crude oil, light sweet crude oil, and natural gas liquids, replacing the existing, dual pipelines crossing the Straits.
The proposed tunnel would cross below the lakebed of the Straits, connecting Point La Barbe in Michigan’s Upper Peninsula to McGulpin Point in Michigan’s Lower Peninsula in Mackinac and Emmet Counties, respectively. The distance between these two land points is approximately 3.6 miles and represents the shortest distance between Michigan’s Upper and Lower Peninsulas. The tunnel would extend as near as practicable to Enbridge’s existing Line 5 North Straits Facility located on the north side of the Straits to an opening point as near as practicable to Enbridge’s existing Line 5 Mackinaw Station located on the south side of the Straits.
Figure 3 shows the overall location of the proposed Project, including the location of the existing Dual Pipelines crossing of the Straits, the location of the existing North Straits and Mackinaw Station facilities (also referred to as the North Site and South Site, respectively), the location of the proposed Line 5 Tunnel crossing, and construction footprints associated with construction and operations of the proposed Project.
Figures 4a, 4b, 5a, and 5b provide additional detail on activities proposed at the South and North sites including proposed temporary disturbance areas and proposed facilities necessary for tunnel operations.
The construction area would be covered in gravel fill. Proposed activities within the temporary disturbance areas include construction equipment staging areas and sediment and stormwater ponds. Activities at the South Site would include additional temporary facilities such as a project construction office building, parking for construction workers, a power substation and generator, spoil storage and management areas, a slurry and water treatment plant for treatment of excavated materials during tunnel construction, and a mechanic shop. Approximately 4,461 cubic yards of general fill would be discharged into 1.53 acres of wetlands.
In addition, one water intake structure for construction of the tunnel would be installed near the south shore of the Straits. The intake structure would be marked with a surface buoy. The offshore intake structure would be removed upon completion of tunnel construction. Treated water would be released into the Straits. Two outfalls would discharge stormwater or treated construction process water into the Straits from the shoreline, with one on the North Site and one on the South Site. Areas of temporary disturbance would be revegetated following construction. Figures 4a, 4b, 5a and 5b show the construction footprints for construction and the proposed post-construction site layout for the South and North Sites, respectively.
The tunnel would be constructed using a tunnel-boring machine. Except for the entrance points on either side of the Straits, the tunnel would be constructed entirely within the bedrock at depths between 60 feet and 370 feet beneath the lakebed of the Straits.
Note: A bank cubic yard (BCY) is a volumetric measurement of soil or material that is in its natural state in the ground. It is equivalent to 27 cubic feet (3 feet by 3 feet by 3 feet). When excavated and loaded loosely into a truck, the original one BCY of material expands to approximately 1.25 cubic yards.
Tunnel construction activities would result in removal of a total of approximately 532,000 bank cubic yards, which includes 431,000 bank cubic yards between the ordinary high water marks beneath the lakebed. The material would be transported to offsite disposal sites.
A shallow launch portal approximately 400 feet long, 40 to 60 feet wide, and up to 50 to 80 feet deep would be constructed within the southern work area (McGulpin Point) and would serve as the entry point for the tunnel-boring machine. A circular shaft 65 feet in diameter and 80 feet deep would be constructed in uplands at the tunnel-boring machine exit point in the northern work area (Point La Barbe).
Once complete, the proposed tunnel’s inside diameter would be approximately 21 feet. Pre-cast concrete segmental lining would be installed as the tunnel is constructed, and the space outside the tunnel’s concrete lining would be filled with low-permeability grout. The new 30-inch pipeline would be installed within the tunnel and connected to the existing portions of the Line 5 pipeline. Upon completion, Enbridge proposes to decommission the existing submerged Line 5 dual pipelines crossing the Straits by purging, cleaning, and abandoning in place. Permanent facilities would include parking, stormwater ponds, and outfall structures on both the South and North sides; an infiltration basin, portal building, and an operations building on the South Side, and a ventilation building on the North Side (see Figures 4b and 5b).
Portions of the project over which USACE has regulatory jurisdiction include the structures and work associated with tunnel construction under the Straits of Mackinac, the water intake structure in the Straits of Mackinac, and the discharge of fill material into wetlands. Anticipated direct detrimental impacts to wetlands include 1.53 acres of disturbance.
Reasonable Alternatives
USACE is reviewing the environmental impacts of the proposed project and reasonable alternatives to the project. Alternatives considered in detail in the USACE's Environmental Impact Statement are described below.
No Action Alternative: USACE denial of Enbridge's permit. Under the No Action Alternative, the existing Dual Pipelines could continue operations with the average annual transport of approximately 540,000 barrels per day (bpd) of NGLs including propane, as well as light crude oil.
Existing Dual Pipelines Engineered Gravel/Rock Protective Cover Alternative: Placement of an engineered gravel/rock protective cover over the existing Dual Pipelines as an alternative to the Applicant's Preferred Alternative.
Decommissioning sub-alternatives considered in USACE's EIS include: removal of the segment along the lakebed, removal of the segment between the ordinary high water marks, or removal of the entire Dual Pipeline segment including terrestrial portions. The decommissioning sub-alternatives are considered in conjunction with the Applicant's proposed construction of a new pipeline segment in the tunnel.