TagMiller Creek(254)

This technical document describes a mixing zone analysis for stormwater discharge from the 3rd Runway North at Sea-Tac Airport into Miller Creek, designated as Basin SDW-1. The analysis uses design storm modeling with various rainfall scenarios (2-year/2-hour, 2-year/72-hour, and 3-year/72-hour events) to calculate effluent flow rates for both acute and chronic water quality criteria. Stormwater from the basin's approximately 128 acres of pervious and impervious area is routed through a detention pond before discharge, with outflow rates determined by a storage-discharge rating curve.

This document is a fact sheet accompanying an NPDES (National Pollutant Discharge Elimination System) permit issued to the Port of Seattle for Seattle-Tacoma International Airport, governing how the airport manages and discharges treated industrial wastewater and stormwater. It covers discharge locations into Puget Sound, Des Moines Creek, Miller Creek, and the City of SeaTac storm sewer system, and establishes effluent limitations and monitoring requirements. The permit addresses water quality standards, pollution prevention plans, and compliance schedules to protect surrounding waterways from airport-related contaminants.

Draft map AR035006 showing restrictive covenants on the west side of Seattle-Tacoma International Airport (northern section). Features include Relocated Miller Creek, Lora Lake, Miller Creek/Lora Lake/Vacca Farm Wetland and Floodplain Mitigation Area, Miller Creek Mitigation Area, Toe of Fill boundaries, Relocated S. 154th Place, and multiple 60-foot ROW designations (30 feet each side from center

Attachment G table detailing wetland acreage impacts and mitigation credits by wetland function for in-basin and Auburn sites, related to the Sea-Tac Airport or associated project. Functions covered include Resident/Anadromous Fish (8.6 acres impacted), Passerine Birds (14.9 acres), Waterfowl (1.9 acres), Amphibians (9.8 acres), Small Mammals (13.2 acres), Exports Organic Matter (10.9 acres), Ground Water

AR 035003. Attachment F table comparing wetland mitigation projects — Vacca Farm, Miller Creek Buffer, Tyee Golf Course, and Auburn Wetland — against Society of Wetland Scientists (SWS) criteria including reinstatement of driving ecological processes, restoration integrated into the landscape, restores a persistent resilient system, results in historic wetland conditions, and performance standards based on

Exhibit AR034998-AR035000, Attachment E: Summary table of compensatory mitigation (on-site and off-site) for watershed, wetland, and stream impacts at Seattle-Tacoma International Airport related to third runway embankment and South 154th Street relocation. Details on-site permanent impacts including filling approximately 980 linear feet of Miller Creek channel, filling 8,500 cy of Miller Creek floodplain, and filling

Attachment D table summarizing wetland mitigation credit for Seattle-Tacoma International Airport Master Plan Update improvements. Documents in-basin mitigation (102.27 acres, 29.80 credit) and out-of-basin mitigation (65.38 acres, 42.91 credit) for a total of 167.65 mitigation acres and 72.71 total credit. In-basin mitigation includes wetland restoration at Vacca Farm (credit ratio 1:1), wetland enhancement at Vacca

Attachment C summarizing proposed mitigation actions to avoid and minimize wetland impacts for a runway project at Sea-Tac Airport area. Document details mitigation requirements and actions for Miller Creek, Des Moines Creek, Category II and III wetlands (Wetlands 3, 4, 5, 8, 9, 18, 37, 44, 52, A1, and Borrow Area wetlands B1, B4–B10, B15a,

Three bar charts showing 7-day low flow occurrences modeled using 1994 HSPF (Hydrological Simulation Program Fortran) for the period 1949-1995. Charts cover Miller Creek, Des Moines Creek, and Walker Creek, displaying occurrence counts (0-4) by date ranging from summer through winter months (June through December). AR034949-AR034951. Related to stormwater hydrology and low flow analysis for

This section of the Sea-Tac Airport Master Plan Update Environmental Impact Statement examines how proposed airport expansion alternatives would affect water quality and hydrology in the surrounding area, particularly Miller Creek and Des Moines Creek. The analysis finds that increased impervious surfaces would raise stormwater runoff volumes and peak flow rates, potentially causing downstream flooding and erosion, but that required detention storage facilities and mitigation measures would largely prevent significant water quality degradation. Both creeks, while classified as Class AA extraordinary waters, already show some pollution from urban stormwater runoff, though deeper regional groundwater used for drinking remains unaffected.