Template revised January 10, 2019.

COMMISSION

AGENDA MEMORANDUM

Item No.

ACTION ITEM

Date of Meeting

December 10, 2024

DATE : November 1, 2024

TO: Stephen P. Metruck, Executive Director

FROM: Sarah Cox, Director Aviation Environment and Sustainability

John Evered, Senior Manager, Aviation Environment and Sustainability

SUBJECT: Authorization of Interlocal Agreement V, Des Moines Creek Basin Plan

Amount of this request:

Total project cost:

$89,304 per year

ACTION REQUESTED

Request Commission authorization for the Executive Director to execute Interlocal Agreement

(ILA) number V with the Cities of Des Moines and SeaTac for continuation of the Des Moines

Creek Basin Plan for a period of 20 years with a financial contribution of $89,304 per year.

EXECUTIVE SUMMARY

The Port, the Cities of Des Moines and SeaTac, and previously King County and the Washington

State Department of Transportation have participated in four prior Interlocal Agreements to

design and permit projects to address drainage, flooding erosion, fish habitat and water quality

issues in Des Moines Creek from a regional, basin-wide approach. During the 4th ILA (executed

April 2004) the Basin Committee completed construction of a Regional Detention Facility (RDF),

High Flow Bypass Pipeline, Habitat Enhancement Basin Plan Restoration Projects, replacement of

a Culvert on Marine View Drive to improve fish passage, and a low flow augmentation project to

provide adequate flow in Des Moines Creek during low flow periods. This ILA also identified

respective jurisdiction operations and maintenance and funding contributions.

The 5th ILA will provide the means to continue to fund Basin restoration activities such as ongoing

operation and maintenance (O&M), replacement and improvement of existing projects including

adaptive management activities, ongoing monitoring of existing projects for permit compliance

and effectiveness, invasive vegetation monitoring and control, education and outreach and a

needs assessment to further address surface water and fish habitat issues within the basin.

JUSTIFICATION

The Basin Plan supports the operation of Seattle Tacoma International Airport and follows the

environmental priorities of the Aviation Environment and Sustainability Program. Completed

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

projects will continue to stabilize the flow regime and reduce erosion in Des Moines Creek from

the airport property and surrounding jurisdictions to the Puget Sound. The regional detention

facility mitigates high flows, and routes base flow away from Des Moines Creek subsequently

lowering in stream erosion. As a result of the Des Moines Creek Basin Detention Standard, the

surface area needed to mitigate new development within the basin is approximately 40% to 60%

less than usually required. Several habitat improvements will continue to be monitored, such as

the placement of large wood and rock in Des Moines Creek that increased channel and habitat

complexity, reduced erosion, and reconnected floodplain-wetland habitats.

The new ILA will also continue to allow for collaboration to solve cross jurisdictional problems

with the other parties, and due to the annual contributions from the Cities of Des Moines and

SeaTac, O&M and replacement costs for facilities on Port property will be lower.

ALTERNATIVES AND IMPLICATIONS CONSIDERED

Alternative 1 – Do not approve the 5

ILA and terminate participation in the Des Moines Creek

Basin Committee.

Cost Implications:

Pros:

(1) No annual requirement for annual contributions.

Cons:

(1) This option would negatively impact local community partnering and increase the Port’s

and other participants costs of individual efforts to protect Des Moines Creek.

(2) This would remove the Port from regional efforts to develop solutions to environmental

issues facing local jurisdictions. The Port would not receive contributions from other

committee members and would have to perform O&M and replacement and

improvement projects on its own.

This is not the recommended alternative.

Alternative 2 – Approve the 5

ILA and continue participation on the Basin Committee

Cost Implications:

Pros:

(1) This option would allow for continued participation in a cooperative effort to mitigate

cross jurisdictional problems.

(2) This is the most cost-effective option to perform required O&M and replacement and

improvement tasks due to contribution from other local jurisdictions.

(3) The flood control and detention facilities governed by the ILA are critical to SEA

stormwater management in addition to the Des Moines Creek basin. The facilities

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

mitigate high flows and route water to Ponds for detention. This ensures that the

facilities are maintained and continue to meet basin plan condition requirements.

Cons:

(1) Required annual contribution.

This is the recommended alternative.

FINANCIAL IMPLICATIONS

Annual Port contributions are calculated based on percent impervious surfaces with the basin;

37.21% by the Port, 46.14% by the City of SeaTac and 16.65% by the city of Des Moines. The

calculation used impervious surface data from a 2017 analysis and excludes approximately 249

acres of STIA’s Industrial Wastewater System that drains directly to the Puget Sound. Annual Port

O&M Fund and Replacement and Improvement Fund contributions will be $22,236 and $66,978

respectively, for a total of $89,304 per year.

ADDITIONAL BACKGROUND

The following activities are planned to be accomplished under the direction of the Basin

Committee during ILA V:

1. Ongoing project O&M including routine operation and maintenance activities, permit

compliance actions, optimization of Project operations to maximize environmental

benefits, and response to emergency conditions. O&M activities will include but not be

limited to maintenance and operation of constructed structures, maintenance and

replanting of wetland plantings, maintenance and replanting of streamside vegetation,

bank protection activities, maintenance of aquatic habitat structures, preparation and

implementation of emergency action plans, and control of wildlife hazards in the vicinity

of the projects.

2. Capital Replacement and Improvement Activities consisting of minor and major

maintenance in response to ageing and unforeseen circumstances impacting constructed

projects. This may include but is not limited to repairs to the RDF pond spillway and flow

control structures, repairs and/or replacement of the bypass pipe and structure, habitat

structure repair and/or replacement, in-stream sediment management, replacement or

planting of vegetation associated with habitat restoration projects, and weir replacement.

Capital replacement and improvement is also intended to adaptively manage projects to

meet design goals and optimize overall project performance in response to unforeseen

changing of conditions such as modified basin hydrology, physical site changes, climate

change, regulatory changes and unanticipated aquatic habitat stressors.

3. Project monitoring will document compliance with permitting conditions, support O&M,

address any ongoing O&M issues, quantify effectiveness of the projects in meeting

hydrologic and engineering design goals, and serve as the basis for any changes proposed

to the projects as a result of adaptive management. Project monitoring may also include

monitoring and inspection of flow control structures, hydraulic conveyance systems,

arsenic containment cap, vegetation, RDF berms and damn structures, wildlife, aviation

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

wildlife hazards and controls, stream flow, wetland fluctuations, groundwater stream

banks, and habitat structures.

4. Invasive vegetation monitoring and control will reduce the spread of harmful species with

the potential to outcompete native plants in areas where stream restoration projects

have been implemented. Nonnative plants will be removed and replaced with native

plants in the Des Moines Creek stream corridor.

5. Education and outreach may be performed to support local stewardship activities for the

purpose of educating community members about aquatic habitat within Des Moines

Creek and restoration activities completed by the Committee. The Committee may

provide resources to non-profit and local watershed or environmental groups for

watershed activities that support Committee goals.

6. A basin needs assessment will continue the evaluation of quality and quantity of habitat

and water quality conditions in Des Moines Creek needed to continue preservation and

protection of aquatic life. New projects may be identified that build upon the Basin Plan

restoration projects already implemented to further the Committee’s commitment to Des

Moines Creek Basin improvement.

7. Ongoing management of an O&M fund to collect and manage funds necessary to pay for

the operation of projects and normal maintenance activities.

8. Ongoing management of a replacement and improvement fund to collect and manage

funds to pay for any required replacements or improvements deemed necessary as a

result of monitoring or adaptive management.

ATTACHMENTS TO THIS REQUEST

(1) Interlocal Agreement V, Des Moines Creek Basin Plan Restoration Projects

(2) Presentation slides

PREVIOUS COMMISSION ACTIONS OR BRIEFINGS

April 13, 2004, the Commission authorized the Chief Executive Officer to execute Interlocal

Agreement IV with the Cities of Des Moines and SeaTac, King County and Washington

Department of Transportation to implement the Basin Plan, construct a suite of projects

and designate the Port of Seattle as project manager for the Regional Detention Facility.

The cost to the Port was $11,983,000. The agreement was signed by all parties on June

11, 2004.

November 28, 2000, the Commission authorized the Chief Executive Officer to execute an

Interlocal Agreement III between the Port of Seattle, King County, and the Cities of SeaTac

and Des Moines. The Port’s share of the costs was $170,000, which was included in the

2001 operating budget. The agreement was signed July 30, 2001.

February 24, 1998, the Commission authorized execution of Interlocal Agreement II to

prepare a Preliminary Design Report. The Port’s share of the costs was $78,000, funded

by the Airport Development Fund. The agreement was signed by all four jurisdictions on

June 17, 1998.

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December 10, 2024

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

January 15, 1997, by Executive approval, the Managing Director of Aviation signed an

amendment to Interlocal Agreement I to include an additional task to develop pilot

projects and continue the program.

October 2, 1995, by Executive approval, Interlocal Agreement I with the Cities of Des Moines

and SeaTac and King County was authorized to prepare a Basin Plan for the Des Moines

Creek. The Port’s share of the costs was $80,000 which was included in the 1995 and 1996

expense budgets. It was signed by all four jurisdictions on January 16, 1996.