FINAL ENVIRONMENTAL ASSESSMENT Ennis Big Sky Airport Improvements AIP # 3-30-0090-019-2017 Madison County, Montana October 2019 TABLE OF CONTENTS ENNIS BIG SKY AIRPORT ENVIRONMENTAL ASSESSMENT TABLE OF CONTENTS Table of Contents ......................................................................................................................... i List of Tables ............................................................................................................................ vii List of Figures ........................................................................................................................... vii Acronyms ................................................................................................................................ viii 1. BACKGROUND AND PROPOSED ACTION ......................................................................... 1-1 1.1 Background .................................................................................................................................................................... 1-1 1.1.1 Airport Location .............................................................................................................................................. 1-1 1.1.2 Airport History ................................................................................................................................................ 1-1 1.1.3 Existing Facilities at EKS ............................................................................................................................. 1-3 1.1.4 Airport Classification and Use ................................................................................................................... 1-7 1.1.5 14 CFR Part 77 Airspace at EKS ................................................................................................................ 1-7 1.1.6 Previous Airport Planning .......................................................................................................................... 1-8 1.1.6.1 2018 Master Plan Update/Alternative Development and Evaluation Study ...... 1-8 1.2 Current and Forecasted Aviation Activity at EKS .......................................................................................... 1-9 1.2.1 Types of Aircraft Using EKS ....................................................................................................................... 1-9 1.2.2 Current Aviation Activity at EKS ............................................................................................................ 1-11 1.2.2.1 Current Operational Baseline ................................................................................................ 1-11 1.2.3 Forecasted Annual Operations ............................................................................................................... 1-12 1.2.4 Critical Aircraft Determination Based on Forecasting .................................................................. 1-13 1.3 Proposed Action ....................................................................................................................................................... 1-14 1.4 Implementation of the Proposed Action ......................................................................................................... 1-19 2. PURPOSE AND NEED .......................................................................................................... 2-1 2.1 Purpose of the Proposed Action ........................................................................................................................... 2-1 2.2 Need for the Proposed Action ................................................................................................................................ 2-1 2.2.1 Need for Land Acquisition ......................................................................................................................... 2-1 2.2.2 Need to Reconstruct, Extend, and Widen Runway 16/34 ............................................................ 2-2 2.2.2.1 Need for Additional Runway Length ..................................................................................... 2-2 2.2.2.2 Need for Increased Runway Width ........................................................................................ 2-4 2.2.2.3 Need for Modifying Runway Grades ..................................................................................... 2-4 2.2.2.4 Need for Increasing the Strength of the Runway Pavement ....................................... 2-5 2.2.3 Need to Relocate and Construct an Extension to the Partial Parallel Taxiway to a Full-Length Parallel Taxiway ......................................................................................... 2-6 2.2.4 Need to Remove Airport Buildings ......................................................................................................... 2-8 2.2.5 Need to Reconstruct the South Apron ................................................................................................... 2-8 2.2.6 Need to Extend Taxilane C, Construct a Portion of Taxilane D, and Construct Hangars ......................................................................................................................................... 2-8 2.2.7 Need to Relocate NAVAIDS, AWOS III/P, and Relocate/Rehabilitate Electrical Vault ...... 2-9 2.2.8 Need to Relocate Self-Service Fuel Dispensing Unit ........................................................................ 2-9 2.2.9 Need to Remove Obstructions to 14 CFR Part 77 Airspace ........................................................ 2-10 2.2.10 Need to Amend Instrument Approach and Departure Procedures ....................................... 2-10 2.2.11 Need to Install Wildlife Animal Fencing ............................................................................................ 2-11 2.3 Requested Federal Actions .................................................................................................................................... 2-11 3. ALTERNATIVES CONSIDERED............................................................................................. 3-1 3.1 No Action Alternative ................................................................................................................................................ 3-1 i TABLE OF CONTENTS ENNIS BIG SKY AIRPORT ENVIRONMENTAL ASSESSMENT 3.2 Airport Relocation ...................................................................................................................................................... 3-1 3.3 Airport Improvement Alternatives Initially Considered ............................................................................ 3-2 3.3.1 Alternative #2 – Extend Runway North Meeting FAA Runway Grade Criteria .................... 3-4 3.3.2 Alternative #4 – Rotate Runway and Extend North Meeting FAA Runway Grade Criteria .................................................................................................................................................. 3-4 3.3.3 Alternative #5 – Extend Runway to the South Meeting FAA Runway Grade Criteria ........ 3-5 3.3.4 Alternative #6 – Extend Runway to the North with Non-Standard Grade ............................. 3-5 3.3.4.1 Alternative #6A – Extend Runway to the North with 1.9% Maximum Grade ..... 3-5 3.3.4.2 Alternative #6B – Extend Runway to the North with 1.5% Maximum Grade ..... 3-5 3.3.4.3 Alternative #6C – Extend Runway to the North with 1.3% Maximum Grade ...... 3-6 3.4 Alternatives Eliminated from Consideration ................................................................................................... 3-6 3.5 Alternatives Carried Forward for Analysis ...................................................................................................... 3-9 3.5.1 No Action Alternative ................................................................................................................................. 3-10 3.5.2 Alternative #6B – Extend Runway North with 1.5% Maximum Grade (Proposed Action) .......................................................................................................................... 3-13 4. AFFECTED ENVIRONMENT ................................................................................................. 4-1 4.1 Introduction .................................................................................................................................................................. 4-1 4.2 Air Quality ...................................................................................................................................................................... 4-1 4.2.1 Background ....................................................................................................................................................... 4-1 4.2.2 Ambient Air Quality ....................................................................................................................................... 4-2 4.3 Coastal Resources ....................................................................................................................................................... 4-2 4.4 Land Use .......................................................................................................................................................................... 4-3 4.4.1 Existing Land Uses at and Near the Airport .......................................................................................