HomeMy WebLinkAboutMemo - Mail Packet - 11/16/2021 - Memorandum From Eileen Dornfest Re: Halligan Water Supply Project - Quarterly Report And Preferred Dam Concepts
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700 Wood Street
PO Box 580
Fort Collins, CO 80522
970.212.2900
V/TDD 711
utilities@fcgov.com
fcgov.com/utilities
M E M O R A N D U M
DATE: November. 8, 2021
TO: Mayor Arndt and Councilmembers
FROM: Eileen Dornfest, Special Projects Manager
THROUGH: Kelly DiMartino, Interim City Manager
Theresa Connor, Interim Utilities Executive Director
RE: Halligan Water Supply Project: Quarterly Report and Preferred Dam Concepts
The purpose of this memo and attachment is to provide the following information about the Halligan Water
Supply Project (Halligan Project or Project):
1. A quarterly update on the Project.
2. An update on the dam selection for the enlarged Halligan Reservoir.
BOTTOM LINE
Staff continue to lead the Halligan Project through design and several required state and federal
permitting processes. A quarterly Project update is attached. The permitting schedule continues to drive
the overall Project schedule.
After additional evaluation of two viable dam concepts for an enlarged Halligan Reservoir, the Adjacent
Dam Concept has been selected as the preferred concept for the enlarged Halligan Reservoir Dam. Future
Project planning and design will incorporate this concept.
BACKGROUND
The existing Halligan Dam is a concrete arch dam that was constructed in 1909. Preliminary design
activities began for the Halligan Water Supply Project in 2020. Analyses conducted at that time revealed
two viable dam concepts for enlarging the reservoir to create the additional water storage needed to
two dam concepts are:
The Existing Dam Concept, which would include significantly modifying the existing Halligan
Dam to meet current regulations and hold up to the increased scrutiny given to dam design
following the 2017 Oroville Dam spillway failure.
The Adjacent Dam Concept, which would entail building a replacement dam immediately
downstream of and adjacent to the current dam.
Preliminary analyses indicated the two dam concepts are similar in cost given the information available at
the early stage of design.
Preliminary analyses also indicated that the Adjacent Dam Concept could provide several benefits over
the Existing Dam Concept, including those related to reductions in construction risk and improvements in
long-term operational efficiency and maintenance access, among others. Information about these two dam
concepts was presented to City Council in the last quarterly Project update, dated August 2, 2021.
HALLIGAN DAM CONCEPT SELECTION
To ensure the project not only meets the needs of water customers but also
minimizes impacts on the environment, the Project team has evaluated a variety of details related to the
two dam concepts. These evaluations have included the following:
Subsurface conditions at the location of both proposed dam locations, including evaluations of
geotechnical, geological and groundwater conditions.
Investigations into the structural integrity of the existing Halligan Dam.
Verifications of concept-level construction cost estimates for both dam concepts.
Evaluation of environmental impacts for both dam concepts, with a focus on impacts to wetlands
the Halligan Project from the U.S. Army Corps of Engineers.
Potential permitting and legal implications of either dam concept.
Outreach to Project stakeholders about the two dam concepts, including outreach to local
landowners, environmental groups, the Fort Collins Water Commission, and regulating agencies
and cooperating agencies in the Halligan Project permitting process.
After a thorough evaluation of the two viable dam concepts, the Project team has selected the Adjacent
Dam Concept as the preferred concept. Given the information gained to date, the Existing and Adjacent
Dam Concepts are similar in cost and environmental impact. No negative design or permitting impacts
have been identified to deter the City from proceeding with the Adjacent Dam Concept. Furthermore,
feedback received from Project stakeholders has ranged from general questions of interest to neutral or
positive feedback.
The Adjacent Dam Concept will provide the following benefits to the City:
Incorporation of modern construction techniques and materials.
Improved long-term functionality and increased efficiency for operations.
Improved maintenance access and possible reduction in long-term maintenance costs.
Reduced construction risk:
o Increased ability to manage water and sediment during construction.
o Reduction of uncertainties and design/construction challenges inherent in enlarging a
112-year-old-dam.
Reduced impacts to reservoir operations during construction.
NEXT STEPS
Design activities over the next six months will focus on advancing the Adjacent Dam Concept to a 30%
level of design. After 30% design is complete, an updated Project cost estimate will be developed and
shared with City Council in 2022.
If there are any questions about this update or the Halligan Water Supply Project, please contact Eileen
Dornfest at 970-416-4296 or edornfest@fcgov.com.
Attachments:
Attachment 1: Q4 Quarterly Report
CC: Water Commission
Lance Smith, Utilities Finance Director
Donnie Dustin, Water Resources Manager
Liesel Hans, Interim Deputy Director - Water Resources & Treatment Operations
Mark Kempton Interim Deputy Director - Water Resources & Treatment Operations