8f. Memo

Tyee Pond Effluent Pipe Replacement

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 
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.
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. 
This project will support the following Century Agenda goals to be the greenest and most energyefficient
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

Template revised January 10, 2019.

             COMMISSION AGENDA – Action Item No. 8f                                   Page 2 of 4 
Meeting Date: November 14, 2023 
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. 
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. 
Construction start                                2024 Quarter 2 
In-use date                                       2024 Quarter 4 
Cost Breakdown                                     This Request           Total Project 
Design                                                           $0               $625,000 
Construction                                             $2,275,000             $2,275,000 
Total                                                         $2,275,000              $2,900,000 

Template revised June 27, 2019 (Diversity in Contracting).

[Annotation] Mathews, Stuart
Is it really worth having this as an alternative, since it is in now way viable? I get we like to have 3 alternatives, but we try to avoid alternatives that are not viable, and as we are under a requirement by DOE to make the repair, we don't have a choice to not do the improvements. I would just go with two alternatives in this case. 
[Annotation] Bornhorst, Heather
@Mathews, Stuart We have this debate quite a lot but we are always told to include the no action.
[Annotation] Cox, Sarah
Does item #3 in Alternative 2 not apply here?
[Annotation] Bornhorst, Heather
@Cox, Sarah Comment addressed
COMMISSION AGENDA – Action Item No. 8f                                   Page 3 of 4 
Meeting Date: November 14, 2023 
Alternative 1 – No Improvements 
Cost Implications: $0 
(1) Requires no capital investment. 
(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
This is not the recommended alternative. 
Alternative 2 – Utilize the bypass system. 
Cost Implications: $702,000 
(1) Requires less capital investment. 
(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
This is not the recommended alternative. 
Alternative 3 – Replace the effluent pipe. 
Cost Implications: $2,900,000 
(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. 
(1) Requires greater capital investment. 
This is the recommended alternative. 

Template revised June 27, 2019 (Diversity in Contracting).

[Annotation] Jason Olson
Do we mention anywhere what this deduction was?
[Annotation] Bornhorst, Heather
The notebook approval included these changes - change in pipe length (shorter) and change from relining to replacing.  We did not discuss this in the memo.
[Annotation] Olson, Jason
Yes, but might be worth a mention in the memo somewhere just in case someone asks. We do mention the $360K above, so I get why we can't combine. 
[Annotation] Nguyen, Hanh
Is there a signed IC form for the budget increase?
COMMISSION AGENDA – Action Item No. 8f                                   Page 4 of 4 
Meeting Date: November 14, 2023 
Cost Estimate/Authorization Summary              Capital        Expense           Total 
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 
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 will increase due to inclusion of
(NOI after depreciation)             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. 
(1)   Presentation. 
April 26, 2022 – The Commission authorized an additional $390,000 for design. 

Template revised June 27, 2019 (Diversity in Contracting).


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