Missouri River Water Management News

Missouri River Water Management News Releases are available on the Northwestern Division website.RSS Feed

Halligan Water Supply Project Final Environmental Impact Statement published

Published Oct. 23, 2023
Updated: Oct. 23, 2023

The U.S. Army Corps of Engineers, Omaha District has published the Final Environmental Impact Statement for the proposed City of Fort Collins Halligan Water Supply Project. The Final Conceptual Mitigation Plan and its state approved Fish and Wildlife Mitigation and Enhancement Plan are included in the EIS as appendices.

The Halligan Water Supply Project would require excavation and the discharge of dredged or fill material into the North Fork of the Cache la Poudre River and adjacent wetlands and therefore would require authorization by USACE under Section 404 of the Clean Water Act. USACE is neither a proponent nor an opponent of the proposed project and is required to evaluate the proposed project under the National Environmental Policy Act process.

Comments received during the public comment period for the Draft EIS published November 22, 2019, were considered as part of the Final EIS. The purpose of the Final EIS is to provide decision-makers and the public with information pertaining to the Halligan Project, disclose environmental impacts of the alternatives, and identify mitigation measures to reduce impacts. It also provides information for local and state agencies having jurisdictional responsibility for affected resources.

The U.S. Environmental Protection Agency Region VIII, U.S. Fish and Wildlife Service, U.S. Forest Service, Bureau of Land Management, Colorado Department of Natural Resources, Colorado Department of Public Health and Environment, and Larimer County participated as cooperating agencies in the development of the Final EIS.

Fort Collins proposes to enlarge the existing Halligan Reservoir located on the North Fork of the Cache la Poudre River, approximately 25 miles northwest of Fort Collins. The Draft EIS stated that the reservoir would be enlarged by raising the existing Halligan Dam by 25.4 feet. However, subsequent development of a conceptual design for enlargement of Halligan Dam highlighted several challenges involved in modifying and enlarging the existing dam to meet requirements of the Rules and Regulations for Dam Safety and Dam Construction of the Colorado Department of Natural Resources, Division of Water Resources, Office of the State Engineer. As a result, Fort Collins has modified its Proposed Action in the Final EIS with the modification being referred to as “Fort Collins’ Modified Proposed Action.”

Fort Collins’ Modified Proposed Action would enlarge Halligan Reservoir by constructing a replacement dam 26 feet higher than the existing dam and approximately 200 feet downstream of the existing dam. This modified dam placement addresses the dam safety challenges and allows the existing dam to act as a coffer dam during construction, which would improve Fort Collins’ ability to manage water and sediment during construction while reducing the need to lower reservoir water levels during construction.

The modified dam placement would not affect Fort Collins’ purpose and need. It would increase the reservoir surface area from 253 acres to 391 acres and the reservoir capacity from about 6,400 acre-feet to about 14,600 acre-feet to provide an additional 7,900 acre-feet of annual firm yield per year to meet Fort Collins’ projected water demands for the year 2065. Upon completing the new dam, Fort Collins would either partially or fully remove the existing dam. The modified dam placement would not change how the Halligan Project is operated or the associated indirect effects on hydrology-related resources but would slightly change the construction footprint and associated direct effects on land-based resources. Those effects of the modified dam placement are evaluated in the Final EIS.

Halligan Reservoir would continue to be filled with direct flows from the North Fork of the Cache la Poudre River under the Fort Collins’ Modified Proposed Action. Releases would be made to the river downstream of the dam and would flow through Seaman Reservoir to the confluence with the Cache la Poudre River. From there, water would be exchanged up to Fort Collins’ intake or to the Munroe Canal intake and delivered to Fort Collins’ water treatment facility through the Pleasant Valley Pipeline. 

The Modified Proposed Action would maintain a minimum flow of five cubic feet per second in the North Fork of the Cache la Poudre River from May 1 to September 30, release a minimum of three cubic feet per second the remainder of the year, and forego all diversions to the enlarged Halligan Reservoir for the three days that coincide with the forecasted peak runoff flow event for the river.

The Final EIS also evaluates the effects of several alternatives to Fort Collins’ Modified Proposed Action, including the No-Action Alternative, the Expanded Glade Alternative, the Gravel Pits Alternative, and the Agricultural Reservoirs Alternative.

The decision on whether to issue a permit for the Halligan Water Supply Project will be based on the Final EIS evaluation of probable and cumulative impacts of the proposed project and its alternatives with consideration to public interest. The decision will reflect the national concern for both protection and use of important resources. The benefits that may reasonably be expected to accrue from the proposal must be balanced against reasonably foreseeable detriments. USACE will not make a permit decision until the City of Fort Collins has submitted an application for a State of Colorado Water Quality Certification under Section 401 of the Clean Water Act and until the Colorado Department of Public Health and Environment has evaluated it.

The Halligan Water Supply Project Final EIS is available for viewing or downloading at:  http://www.nwo.usace.army.mil/Missions/Regulatory-Program/Colorado/EIS-Halligan/

Printed copies of the Halligan Water Supply Project Final EIS are available for viewing at the following libraries and offices:

  • Colorado State University Morgan Library, 1201 Center Ave., Fort Collins, Colorado 80523
  • Poudre River Public Library District-Old Town Library, 201 Peterson St., Fort Collins, Colorado 80524
  • Poudre River Public Library-Harmony Library, 4616 S. Shields St., Fort Collins, Colorado 80526
  • University of Northern Colorado, James A. Michener Library, 14th Ave. and 20th St., Greeley, Colorado 80639
  • U.S. Army Corps of Engineers, Denver Regulatory Office, 9307 S. Wadsworth Blvd., Littleton, Colorado 80128

Questions about the Final EIS or permit process can be directed to Cody Wheeler at 720-922-3846, or via email at cody.s.wheeler@usace.army.mil.

They can also be mailed to:

Attn: Cody Wheeler
U.S. Army Corps of Engineers, Denver Regulatory Office
9307 S. Wadsworth Blvd.
Littleton, Colorado 80128

Release no. 23-035