The 1996 Environmental Impact Statement (EIS) by Landrum & Brown. This will give you an idea of what to expect from the upcoming EIS (if it is determined to be necessary.)
Sea-Tac Airport Final EIS, Feb. 1996, Vol. 1 of 7
Sea-Tac Airport Final EIS, Feb. 1996, Vol. 2 of 7
Sea-Tac Airport Final EIS, Feb. 1996, Vol. 3 of 7
Sea-Tac Airport Final EIS, Feb. 1996, Vol. 4 of 7
Sea-Tac Airport Final EIS, Feb. 1996, Vol. 5 of 7