Template revised January 10, 2019.
COMMISSION
AGENDA MEMORANDUM
Item No.
8f
ACTION ITEM
Date of Meeting
November 14, 2023
DATE: November 7, 2023
TO: Stephen P. Metruck, Executive Director
FROM: Keri Stephens, Director, Aviation Facilities & Capital Programs
Eileen Francisco, Director, Aviation Project Management Group
SUBJECT: Tyee Pond Effluent Pipe Replacement (C801173)
Amount of this request:
$2,275,000
Total estimated project cost:
$2,900,000
ACTION REQUESTED
Request Commission authorization for the Executive Director to take all steps necessary to
complete the Tyee Pond Effluent Pipe Replacement project at Seattle-Tacoma International
Airport (SEA). This request is in the amount of $2,275,000 for a total authorization of $2,900,000.
EXECUTIVE SUMMARY
The Tyee Pond stormwater pond and its control structures are a regional detention facility that
the Port of Seattle owns, maintains, and operates. This detention facility is regulated by the
Department of Ecology (DOE) Dam Safety Program. The downstream effluent pipe is over 30
years old and shows signs of damage and deterioration. The pipe must be replaced to ensure
that the detention facility and downstream effluent pipe can function as designed for the next
50 years. Emergency repairs have already been needed and DOE issued a requirement for a
permanent repair to be completed by 2025.
JUSTIFICATION
This project will support the following Century Agenda goals to be the greenest and most energy-
efficient port in North America by meeting or exceeding agency requirements for stormwater
leaving Port-owned or operated facilities.
In December 2021, a pipe assessment was completed that examined the existing pipe
downstream of the repaired section (approximately 382 linear feet). The Pipe Assessment Report
noted joint separation, deformation, and corrosion in the downstream pipe and recommended
replacing the entire pipe. If the pipe completely fails, the hydraulics of Des Moines Creek will be
affected impacting the downstream salmon bearing creek habitat. In the worst-case scenario,
with the detention facility at full capacity, the pipe failure can result in the failure of the Tyee
COMMISSION AGENDA – Action Item No. 8f Page 2 of 4
Meeting Date: November 14, 2023
Template revised June 27, 2019 (Diversity in Contracting).
Pond embankment sending several thousand gallons of stormwater towards downstream
residents adjacent to Des Moines Creek in an uncontrolled fashion.
Diversity in Contracting
The design of this project utilized an existing indefinite delivery indefinite quantity (IDIQ) contract
that has an established WMBE commitment of 10%. The project team will work with Diversity in
Contracting establish the WMBE goal for the major works construction contract.
DETAILS
Tyee Pond is located south of SEA and is located on the east fork of Des Moines Creek flowing
south from Bow Lake. The pond has a capacity of 19.7 acre-ft and is therefore regulated by DOE
Dam Safety program. The pond and effluent pipe were originally constructed in the late 1980’s.
In 2020, emergency repairs were made to a small section of the pipe (approximately 32 linear
feet) that was leaking and causing sinkholes to appear on the pond embankment above the
pipe. DOE accepted the interim repairs but required a permanent repair by 2025.
During project definition the project scope was revised to reflect the actual shorter pipe length,
and a full pipe replacement instead of relining using the cured-in-place pipe method. These
changes resulted in $251,000 in project savings.
The project has completed the environmental permitting requirements with DOE and the U.S.
Army Corps of Engineers. This has led to additional regulatory requirements that has increased
the project cost by $360,000 and delayed construction to the 2024 fish window.
Scope of Work
The project will replace the entire downstream effluent pipe with a 72-inch diameter reinforced
concrete pipe. In addition, two manhole structures will be added to the northern section of the
pipe to provide energy dissipation.
Schedule
Construction start
2024 Quarter 2
In-use date
2024 Quarter 4
This Request
Total Project
Design
$0
$625,000
Construction
$2,275,000
$2,275,000
Total
$2,275,000
$2,900,000
COMMISSION AGENDA – Action Item No. 8f Page 3 of 4
Meeting Date: November 14, 2023
Template revised June 27, 2019 (Diversity in Contracting).
ALTERNATIVES AND IMPLICATIONS CONSIDERED
Alternative 1 – No Improvements
Cost Implications: $0
Pros:
(1) Requires no capital investment.
Cons:
(1) Does not address integrity of Tyee Pond dam required by DOE to perform permanent
repairs by 2025.
(2) Does not address long-term viability of the storm water infrastructure.
(3) Potential to damage downstream salmon bearing creek habitat and residents (and trigger
fines).
This is not the recommended alternative.
Alternative 2 – Utilize the bypass system.
Cost Implications: $702,000
Pros:
(1) Requires less capital investment.
Cons:
(1) Does not address integrity of Tyee Pond dam required by DOE to perform permanent
repairs by 2025.
(2) Does not address long-term viability of the storm water infrastructure.
(3) Potential to damage downstream salmon bearing creek habitat and residents (and trigger
fines).
This is not the recommended alternative.
Alternative 3 – Replace the effluent pipe.
Cost Implications: $2,900,000
Pros:
(1) Permanent solution ensuring Tyee Pond dam integrity.
(2) Offers maximum stormwater flow control from the Tyee Pond.
(3) Doesn’t adversely impact flow to downstream salmon bearing creek.
(4) Fulfills DOE Dam safety regulatory obligations.
Cons:
(1) Requires greater capital investment.
This is the recommended alternative.
COMMISSION AGENDA – Action Item No. 8f Page 4 of 4
Meeting Date: November 14, 2023
Template revised June 27, 2019 (Diversity in Contracting).
FINANCIAL IMPLICATIONS
Cost Estimate/Authorization Summary
Capital
Expense
Total
COST ESTIMATE
Original estimate
$2,791,000
$0
$2,791,000
Previous changes – net
($251,000)
$0
($251,000)
Current change
$360,000
$0
$360,000
Revised estimate
$2,900,000
$0
$2,900,000
AUTHORIZATION
Previous authorizations
$625,000
$0
$625,000
Current request for authorization
$2,275,000
$0
$2,275,000
Total authorizations, including this request
$2,900,000
$0
$2,900,000
Remaining amount to be authorized
$0
$0
$0
Annual Budget Status and Source of Funds
This project CIP #801173 was included in the 2023-2027 capital budget and plan of finance as a
budget of $2,540,000. A budget increase of $360,000 was transferred from the Aeronautical
Allowance (CIP #800753) resulting in a zero-net change to the Aviation capital budget. The
funding sources for this project will be the Airport Development Fund (ADF) and revenue bonds.
Financial Analysis and Summary
Project cost for analysis
$2,900,000.
Business Unit (BU)
Airfield Movement Area.
Effect on business performance
(NOI after depreciation)
NOI after depreciation will increase due to inclusion of
capital (and operating) costs in airline rate base.
IRR/NPV (if relevant)
N/A.
CPE Impact
$0.01 in 2025.
Future Revenues and Expenses (Total cost of ownership)
Operations and maintenance costs are anticipated to be minimal. The pipe will be video
inspected once every 3-5 years.
ATTACHMENTS TO THIS REQUEST
(1) Presentation.
PREVIOUS COMMISSION ACTIONS OR BRIEFINGS
April 26, 2022 – The Commission authorized an additional $390,000 for design.