Hawaii Marine Corps Base - Aircraft Maintenance Hangar Environmental Assessment Report (Revised Draft)

Key Chapter Title List

1. Executive Summary (including Proposed Action, Purpose and Need, Evaluation of Alternatives, Summary of Environmental Resource Assessment, Potential Environmental Impacts and Mitigation Measures, Public Participation)
2. Purpose and Need for the Proposed Action (including Project Background, VR-51 Squadron Mission, Scope of Environmental Analysis, Relevant Laws and Regulations, Public and Agency Participation, Required Permits)
3. Description of the Proposed Action and Alternatives (including Screening Factors, Alternatives to be Analyzed, Alternatives Not Considered for Detailed Analysis, Best Management Practices and Protective Measures)
4. Affected Environment and Environmental Consequences (including Air Quality, Water Resources, Biological Resources, Natural Hazards and Resilience, Cultural Resources, Infrastructure, Hazardous Materials and Waste, Noise)
5. Cumulative Impact Analysis (including Cumulative Effects for Each Resource Area)
6. Summary and Conclusions of Impacts for the Proposed Action and Alternatives
7. Consistency with Federal Policies and Executive Orders
8. List of Consulting and Coordinating Agencies
9. List of Report Preparers
10. References
11. Appendices (including Public Comments and Responses, NHPA Section 106 Consultation, ESA Section 7 Consultation, CZMA Coordination, Air Emissions Calculations, Noise Study)

Document Introduction

This report is a revised draft Environmental Assessment prepared in accordance with the National Environmental Policy Act (NEPA) and its implementing regulations, the Chief of Naval Operations Instruction 5090.1, and Marine Corps Order 5090.2, Volume 12. The core subject of the report is to assess the potential environmental impacts of constructing a new dedicated maintenance hangar and associated aircraft parking apron for the U.S. Naval Air Reserve VR-51 Squadron's C-40A aircraft within the Marine Corps Base Hawaii (MCBH) Kaneohe Bay area. Although the VR-51 Squadron completed its transition from C-20G to C-40A aircraft in 2019, this assessment not only covers the impacts of C-40A operations but focuses more on the direct and indirect environmental consequences that may arise from the construction of the new hangar and related infrastructure itself.

The report first clarifies the project's necessity: the currently used Hangar 104 has insufficient clear height to accommodate the C-40A for maintenance and storm protection, forcing the squadron to frequently conduct long-distance flights to other bases for maintenance, resulting in operational inefficiencies and increased costs. Therefore, the report establishes strict geographic and functional screening criteria and, based on these, proposes two action alternatives (the "Preferred Alternative" to rebuild on the site of Hangar 104 and a new construction alternative in the "Green Area") along with a "No Action" alternative for comparative analysis. The assessed resource areas are comprehensive, covering eight key aspects: air quality, water resources, biological resources, natural hazards and resilience, cultural resources, infrastructure, noise, and hazardous materials and waste. Areas considered to have negligible impacts, such as geology, land use, airspace, transportation, and socioeconomics, were not analyzed in detail.

In the environmental impact analysis section, the report systematically evaluates the "Affected Environment" and "Environmental Consequences" for each resource area under the two action alternatives. The overall conclusion indicates that the environmental impacts of both action alternatives are "below significant levels" in most areas. For example, construction period emissions are below regulatory thresholds; impacts on water resources are manageable through the implementation of Best Management Practices and Low Impact Development techniques; through the integration of a series of stringent protective measures (such as specific lighting standards, bird collision avoidance design, construction timing restrictions, etc.) and following informal consultation with the U.S. Fish and Wildlife Service, impacts on species listed under the Endangered Species Act are considered negligible or extremely unlikely to occur. However, regarding cultural resources, if construction proceeds on the site of Hangar 104 (the Preferred Alternative), it would result in an "adverse effect" due to the demolition of this historic structure, which is a contributing element to the "Kaneohe Bay Naval Air Station Aviation Historic District," and due to impacts on the viewshed of the adjacent "National Historic Landmark" district. The Navy is currently consulting with the State Historic Preservation Officer and other relevant parties, intending to develop and implement mitigation measures (such as preparing a Historic Structure Report, developing a digital interactive application, etc.) through a Memorandum of Agreement to reduce the impact to below significant levels. The conclusion of the Noise Study appendix notes that although the noise from a single C-40A flight is higher than that of the former C-20G, the total number of operations has not increased, resulting in a negligible impact on the cumulative noise environment.

Finally, through cumulative impact analysis, the report considers this project within the broader context of concurrent and future military construction projects at MCBH (such as the establishment of MQ-9 and KC-130J squadrons, barracks modernization, wastewater treatment plant upgrades, the arrival of the 3rd Marine Littoral Regiment, etc.). It concludes that the addition of this project will not lead to significant cumulative adverse impacts. Synthesizing all analyses, the report finds that implementing either action alternative would not result in significant adverse environmental impacts, providing the basis for issuing a subsequent "Finding of No Significant Impact." This revised draft will be open for an additional 30-day public comment period from March 8 to April 7, 2025.