Mountain Home Air Force Base

Overview

Mountain Home Air Force Base covers about 9 square miles southwest of Mountain Home, Idaho. Decades of aircraft maintenance, industrial work, and waste disposal since 1943 left soil and groundwater contaminated with petroleum products, solvents, pesticides, and waste oils. EPA added the site to the National Priorities List in August 1990. The Air Force, EPA Region 10, and the Idaho Department of Environmental Quality signed a Federal Facility Agreement in January 1992 to coordinate cleanup. The base remains an active military installation housing roughly 7,500 service members and their families.

The site is divided into multiple operable units, each targeting a specific contaminated area. Key contaminants include benzene, trichloroethene, tetrachloroethene, chloroform, xylenes, toluene, cadmium, chromium, lead, mercury, and asbestos. These are found in soil, soil gas, and groundwater at the fire training pit, the base wells area, and the asbestos landfill. A sitewide investigation for per- and polyfluoroalkyl substances (PFAS) is also in progress. The base draws its drinking water from a regional aquifer roughly 375 feet below ground.

Cleanup methods in use or completed include capped landfills with institutional controls, soil vapor extraction to pull volatile organic compounds (VOCs) out of soil and perched groundwater, chemical oxidation, bioremediation, multi-phase extraction, and free product recovery. Remedy construction is complete at two operable units. The fire training pit and base wells area have active remedial work underway. The asbestos landfill had its investigation completed in September 2024, with remedial design and construction planned between 2026 and 2027. The oil water separator area requires no further action under a 2020 decision. The most recent five-year review, completed in September 2021, found that cleanup actions protect public health and the environment in the short term. However, long-term protectiveness depends on continued attention to VOC vapors in the bedrock. Groundwater migration has not yet been confirmed as stabilized.

Institutional controls currently restrict access to contaminated areas, and EPA assessments indicate human exposure is under control at this time. The site is estimated to be ready for anticipated reuse between September and November 2028. Community members can review key documents at the Mountain Home Public Library or at the 366th Civil Engineering Squadron Environmental Flight office on base. Inquiries can be directed to the EPA Remedial Project Manager or the Community Involvement Coordinator.