Final Supplemental Environmental Impact Statement for the Proposed Master Plan Update Development Actions at Seattle-Tacoma International Airport

These letters from the U.S. Environmental Protection Agency (EPA) Region 10 document the agency's review of air quality analyses related to the proposed third parallel runway and Master Plan Update at Seattle-Tacoma International Airport. In a 1997 letter, EPA confirmed that concerns about mobile source emission factors, aircraft operation emissions, and construction emissions had been adequately addressed in the Final Supplemental Environmental Impact Statement, with de minimis thresholds not exceeded under the Clean Air Act. An earlier letter from the mid-1990s outlined EPA's technical recommendations on the air quality modeling protocol, including guidance on screening versus refined analyses, receptor selection, and the need to account for other Port of Seattle projects in the environmental review.

Notes

Two EPA Region 10 letters regarding air quality analysis for Seattle-Tacoma International Airport development. The first (1997) confirms that concerns about the air quality analysis for transportation conformity determination have been adequately addressed in the Final Supplemental EIS. The second (undated, circa 1994) provides comments on the proposed air quality modeling protocol for the Master Plan Update, raising issues about screening vs. refined analysis, receptor selection, dispersion modeling, and cumulative project impacts.

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