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Appendix D: Environmental Evaluation of Year 2020 Impacts and a Forecast Greater Than the New Forecast

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This appendix from Seattle-Tacoma International Airport's Final Supplemental Environmental Impact Statement evaluates potential environmental impacts through the year 2020 under three scenarios, including the new Port forecast and cases where aviation demand grows 10% faster than projected. Key findings indicate that noise impacts are expected to remain below current levels in all scenarios, with 'With Project' improvements producing roughly 53% of current noise conditions by 2020. The analysis also examines air quality, enplanement levels, and aircraft operations across both Do-Nothing and preferred alternatives to guide long-term airport planning.

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Appendix D of the Seattle-Tacoma International Airport Final Supplemental Environmental Impact Statement (FSEIS), prepared by the Port of Seattle and FAA, extrapolating environmental impacts to year 2020 under three test cases: Case 1 (new Port forecast extended to 2020), Case 2 (aviation demand 10% greater than new forecast, Do-Nothing and With Project both accommodate demand), and Case 3 (demand 10% greater, Do-Nothing constrained at 2010 levels). Analysis covers aircraft operations, enplanements, noise and land use impacts, and air quality/emissions inventory along International Blvd for Alternative 3 (North Unit Terminal) and Alternative 1 (Do-Nothing). References FAA Order 5050.4A, Clean Air Act Conformity (40 CFR Part 51.857), and 1996 Sea-Tac Master Plan Update targeting 19 million annual enplanements.

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