Umatilla Army Depot sits on roughly 20,000 acres near Hermiston, Oregon and has stored conventional munitions and chemical warfare agents since 1941. Wastewater from explosive washout operations was discharged into two unlined lagoons between the 1950s and 1965, contaminating soil and groundwater. The site was added to the National Priorities List in July 1987 and is divided into ten operable units to tackle different contamination problems across the property.
Contaminants include explosive compounds such as HMX, RDX, and TNT found in lagoon soils and groundwater. Metals including arsenic, lead, cadmium, chromium, and others are present mainly in soils and debris from deactivation furnace areas. Nitrate and nitrite compounds appear in sludge, liquid waste, and sediment. Pesticide residues including DDT compounds have been detected in soils at miscellaneous areas. A sitewide PFAS (per- and polyfluoroalkyl substances) operable unit has been designated, with remedial investigation expected to begin between October and December 2027.
The U.S. Army is responsible for remediation, with EPA overseeing cleanup as the lead regulatory agency. Completed actions include solidification and stabilization of contaminated soils, bioremediation of explosives-contaminated soils, and demolition of structures. A groundwater treatment system using granular activated carbon addresses a 350-acre explosives-contaminated plume. Lagoon groundwater cleanup moved into operation and maintenance after completion in January 1999. Work in the A.D.A. area is scheduled to finish in December 2025, with additional estimated work starting between October and December 2027.
An EPA assessment shows that human exposure is not currently under control, meaning unsafe contamination levels have been detected and people could reasonably be exposed. Groundwater migration is under control and is not spreading unacceptably. Physical construction is not yet complete across the entire site. The depot closed in August 2012 under the Base Realignment and Closure program. The site does not yet meet criteria for sitewide readiness for anticipated reuse. The most recent five-year review was completed in September 2024. Sources also note a fifth Five-Year Review was completed in 2023, both of which are available for public review.
Community members can access site documents at the Hermiston Public Library, the Umatilla Chemical Depot BRAC Environmental Coordinator office, or the EPA Region 10 Oregon Operations Office in Portland. For questions about the site or five-year review reports, contact the Oregon Department of Environmental Quality. The EPA Remedial Project Manager is also available.
