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Exhibit 206: Issues Related to Ecology’s Section 401 Water Quality Certification Review of the Proposed Sea-Tac Airport Expansion

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Sea-Tac Airport
Third Runway
PCHB
Box 08

This document outlines the Washington State Department of Ecology's Section 401 Water Quality Certification review process for the proposed Sea-Tac Airport expansion, detailing the legal standards and unresolved environmental issues involved. Ecology was required to determine whether the expansion would meet state water quality standards by assessing direct, indirect, and cumulative impacts on wetlands, stormwater, and streamflow, while coordinating with federal Clean Water Act permit requirements under Sections 401 and 402. As of October 2000, key aquatic resource protection issues—including stormwater management, wetland mitigation, and streamflow augmentation—remained unresolved pending additional information from the Port of Seattle.

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Exhibit 206 (AR 018548–018550), dated January 21, 2001, is a staff presentation document from Washington State Department of Ecology (Ecology) addressing Section 401 Water Quality Certification review of the proposed Sea-Tac Airport third-runway expansion by Port Of Seattle. Document covers: ‘reasonable assurance’ standard under Clean Water Act Section 401, interaction of CWA Sections 401 and 402 (NPDES), antidegradation requirements, beneficial uses, numeric and narrative water quality criteria, stormwater plan, streamflow augmentation plan, wetland impacts and mitigation, clean fill material standards, and direct/indirect/cumulative impact determination. References Ecology’s Water Quality Program, Shorelands and Environmental Assistance Program, and Ecology’s draft Stormwater Management Manual Section 1.9.8. Filed in PCHB (Pollution Control Hearings Board) proceeding related to the third-runway EIS.

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