Notes
This report analyzes the timing and volume of discharges to local receiving streams and wetlands during low-flow periods from Seattle-Tacoma International Airport, considering improvements from the Port of Seattle’s Master Plan Update. It evaluates hydrologic impacts of the proposed third runway embankment on Miller, Walker, and Des Moines Creeks, and presents a Flow Impact Offset Facility Plan to mitigate low-streamflow impacts by detaining excess stormwater runoff during winter for release during annual low-flow periods. The plan was submitted in response to a Water Quality Certification condition issued by the Washington State Department of Ecology.