Ross Dam Low Level outlet Project

The City of Seattle is seeking qualifications for Ross Dam Low Level outlet Project . Qualifications are due no later than 11:59 pm on Friday, October 10, 2025 . All questions are to be submitted through the e-procurement portal at https://procurement.opengov.com/portal/seattle no later than 11:59 pm on Friday, September 19, 2025 .

The Ross low-level outlets (LLOs) are a critical dam safety component of Ross Dam. They enable released from the lower portion of the reservoir and are not currently fully accessible for maintenance and inspection. Under the Federal Energy Regulatory Commission’s (FERC) Dam Safety regulations, the LLOs must be inspected, tested, and maintained to ensure safe and reliable operation.

The LLOs convey water through two 72-inch-diameter steel penstocks also referred to as outlet conduits or bypass penstocks that are located in an approximately 350 feet long by 28 feet wide rock blasted tunnel. Portions of the tunnel and penstocks sit below the level of Diablo Lake which causes the tunnel to fill with water over time. The tunnel was designed to operate dry, but it is currently flooded. The water in the tunnel exceeds pollutant standards established under Washington administrative code (WAC) and cannot be discharged without treatment and approval from the Department of Ecology.

In approximately 2014, City Light obtained a National Pollutant Discharge Elimination System (NPDES) permit authorizing the discharge of treated water from the tunnel using electro-coagulation as the treatment method. In 2023, Water Tectonics was contracted to perform this work and the divers found that the material and conditions were vastly different than expected. During the project, divers discovered that the material and conditions in the tunnel differed significantly from expectations, as documented in Exhibit A: Water Tectonics Summary Report. The area contained woody debris which was removed, and the contaminated sediment was thicker and more solidified than anticipated. Exhibit B: Discharge Monitoring Reports September – November 2023. The work concluded when the weather window closed; the floors of the first three bays (Bays 7-9, approximately. 100 feet) were hydrovacuumed. The remaining tunnel bays were not completed, and Bays 7-9 will require reevaluation to confirm their condition.

The goal of this project is to return the Ross LLO tunnel to its designed state, by dewatering the tunnel and ensuring contaminants are not released into Diablo Lake

The project site along the downstream side of City Light’s Ross Dam on the Skagit River in Whatcom County, approximately 130 miles northeast of Seattle. The site is located in the North Cascades Recreational Area, part of the National Park System. This is a remote site and accessible only by boat.