Seattle Wellfield Modeling & Analysis (26-026-S)

The City of Seattle is seeking proposals for Seattle Wellfield Modeling & Analysis (26-026-S) . Proposals are due no later than 1:00 pm on Monday, April 27, 2026 . All questions are to be submitted through the e-procurement portal at https://procurement.opengov.com/portal/seattle no later than 5:00 pm on Friday, April 10, 2026 .

Seattle Public Utilities (SPU) is seeking a consultant to support groundwater modeling and technical analysis for water‑right permitting of the Seattle Wellfield, as well as the design of required mitigation project. Since 1985, SPU and the former Seattle Water Department have worked towards completing the Riverton and Boulevard Park Wellfields, now collectively called the Seattle Wellfield, located north of SeaTac International Airport. SPU has operated the wellfield intermittently since the late 1990s under temporary permits, mostly recently in 2015. The wells were originally pursued to provide peaking supply to meet high summer demands. The wells are also useful in other situations and times of the year: supplementing the surface supplies during drought conditions which helps ensure instream flows and maintaining supply to the southwest part of the SPU regional distribution system in the event of a transmission emergency.

The Seattle Wellfield pumps water from an aquifer that is a known source of water for Miller Creek and potentially also a source for Des Moines Creek and the Green River. Under current Washington State case law, Seattle must mitigate for impacts to local water bodies. SPU pumped the wells for three months during a water shortage in 2015 and collected groundwater level data during and after that pumping. This data along with subsurface information published by U.S. Geological Survey was used to build a groundwater model intended to simulate the effect of pumping the wells on the aquifer, Miller Creek, Des Moines Creek, and the Green Rivers.

Based on previous analysis, SPU must develop a mitigation plan to obtain permanent groundwater right. The current conceptual mitigation project would commit Seattle to metering dechlorinated water into Miller Creek from one of SPU’s transmission lines to offset the impacts of pumping. Additional modeling is needed to assess potential impacts to Des Moines Creek and non-tidal reaches of the Green River which are located further away from the project wellfield. Mitigation plans to these water bodies have not been developed as they are subject to the extent of potential impacts.

A draft Report of Examination (ROE) in support of the Seattle Wellfield development was submitted to the Washington State Department of Ecology (Ecology) in 2020 under the Cost Reimbursement program. The ROE was shared with Tribal Nations, including the Muckleshoot Indian Tribe (MIT). Ecology and the MIT have provided comments to the draft ROE that require additional modeling analysis.