Rocky Mountain Arsenal
This is a National Priorities List (NPL), or "Superfund," hazardous waste site. While the United States Army is the lead agency for remediation of the site, the Colorado Department of Public Health and Environment Remediation Program and the EPA Superfund program provide technical support and input on all remediation-related activities to ensure the objectives of the Superfund program are met.
- North of the former Stapleton Airport and west of Denver International Airport, Adams County.
- Residential and commercial property is located to the north, south and west.
Montbello is located to the south of the RMA, and Commerce City to the west. Reunion is located on the north border of RMA. Brighton is 6 miles north, and Barr Lake State Park is about 5 miles northeast.
The U.S government acquired the Arsenal land in 1942 to manufacture chemical warfare agents, including mustard gas and incendiary munitions, for use in World War II. Following the war and through the early 1980s, the facilities continued to be used by the Army. From 1950 to 1952, the Army constructed the North Plants complex to manufacture the nerve agents VX and GB, (also called sarin). Rocket fuel was blended on-site for the Titan and Delta missile operations.
In an effort to foster economic growth in the area and maintain the facilities for national security, private companies were encouraged to lease facilities beginning in the mid-1940s. Shell Oil Co. leased the property and manufactured agricultural pesticides in the South Plants complex from 1952 through 1982.
Manufacturing and waste disposal practices used during these years resulted in extensive soil, surface water, sediment, groundwater and structures contamination, damage to trees and vegetation, and death to wildlife. Solid and liquid chemical hazardous wastes were disposed of in trenches, burn pits and pooled in open basins covering wide areas. Spills occurred in the central processing areas, storage areas, and out of chemical sewers that existed underground.
Contaminated ground water was first discovered to have migrated off of the Arsenal in the mid-1950s when crop damage and affected livestock was noted on farms north of the Arsenal. At that time, liquid waste disposal methods were employed in an attempt to prevent the chemical contamination from spreading further including lining one of the basins with asphalt, and injection of the waste chemicals into a deep well, but these techniques were ultimately unsuccessful.
The Army and Shell Oil Co. began conducting detailed site investigations in the 1970s to define the extent of contamination. All manufacturing activities ended in 1982.
The Rocky Mountain Arsenal was placed on the National Priorities List of Superfund sites in July 1987.
In 1996, after a lengthy process in which site investigations were conducted and completed, an approach to remedy the chemical contamination at the Arsenal was set forth by the US Army. EPA and the State concurred with the approach.
The remedy selected for the Rocky Mountain Arsenal includes the removal of contaminated soil down to 10’ over much of the contaminated area, and that contaminated overburden is contained in two hazardous waste landfills that remain on the site.
Waste further down than 10’ is left in place in the former areas where the basins, chemical sewers, manufacturing plants, disposal trenches once were.
Some waste disposal pits presented short-term hazards sufficient to preclude their excavation. They have been left in place to excavate, so they have been left in place. All waste that was left in place is now interred beneath large-area engineered covers that prevent any intrusion into the waste that remains below.
Both the landfills and the covers are built to prevent intrusion by humans or animals, and also to prevent further contamination to the groundwater.
At the borders of the RMA and at some places in the site’s interior, contaminated groundwater is pumped from the below the surface and cleaned before reinjection.
In addition to the containment structures, the agreed-upon remedy directs that the entire area is subject to restrictions on land use in perpetuity, including residential development, agricultural use, any potable use of the groundwater, and any consumption of fish or game from the Arsenal. These restrictions must remain in place unless future sampling and scientific investigation determine they can be safely removed.
More than 600 chemicals have been used or manufactured at the arsenal, including:
- Volatile organic compounds (VOCs).
- Heavy metals.
- Diisopropyl methylphosphonate (DIMP), a chemical unique to the Army's manufacture of nerve gas.
The contaminated soils cleanup phase of the process was completed in 2010.
Two Records of Decision (RODs) were signed and describe the required cleanup actions.
Two Records of Decision (RODs) were signed and describe the required cleanup actions.
- The Off-Post Record of Decision was finalized in December 1995 and its requirements consist of actions for off-site groundwater and soil.
- The On-Post Record of Decision was signed in June 1996 and describes the cleanup plan for soils, groundwater and structures within the approximately 27-square-mile on-post Operable Unit.
- These field activities began in the fall of 1997 and significant portions of the cleanup have already been accomplished.
- The On-post Record of Decision includes:
- Provisions for a permanent water supply for off-post residents affected by arsenal groundwater contamination.
- Replacement water for South Adams County Water and Sanitation District.
- A medical monitoring program to monitor the success of exposure prevention efforts during the environmental cleanup.
Medical Monitoring Program
- During the development of the remedy for the Arsenal’s contamination, there was a lot of public concern that the cleanup itself might pose a risk to the surrounding residents. A monitoring program was developed to monitor the success of exposure prevention efforts during the environmental cleanup at the Rocky Mountain Arsenal.
- This program was designed to address potential Arsenal-related health concerns of those living in communities surrounding the Rocky Mountain Arsenal, including the southernmost portion of Brighton, Commerce City, Green Valley Ranch, Henderson and Montbello.
During removal of contaminated soil and construction of the remedy containment structures, air monitoring was conducted at multiple sites in the Arsenal’s interior and fence line, and several sites in the surrounding communities. These monitors tested the air for several decades during the cleanup and showed the cleanup was protective of public health. When the cleanup was completed, it was clear that no Arsenal chemicals had been released into the air that exceeded the health-protective levels established for the site since the environmental cleanup began in October 1997.
Air monitoring surveillance continued until the end of July 2009.
- Rates of birth defects in the communities surrounding the arsenal were also monitored and found to be stable and no different than rates for all of Colorado.
- Cancer incidence in the communities near the arsenal was also monitored and found to be varied across location, gender, race and time, and have been determined to not be related to past Arsenal exposure or cleanup activities.
The contaminated groundwater that still exists in and around RMA continues to be actively monitored. Structures that contain the contaminated soil at RMA are also actively monitored, along with surface water and biological resources.
As portions of the cleanup are completed, this property becomes part of the National Wildlife Refuge system and is transferred to the U.S. Department of Interior.
In 2004, 5000 acres along the perimeter of the site were deleted from the National Priorities List of Superfund sites to establish the National Wildlife Refuge.
In 2006, 7,126 additional acres were transferred.
Most of the land areas now belong to the U.S. Fish and Wildlife Service and the Army will retain areas where hazardous wastes are managed, such as the landfill and soil covers.
Site reviews will be conducted every five years to make sure the cleanup remedy is still effective.
The U.S. Fish and Wildlife Service is responsible for managing the Arsenal’s wildlife and habitat.
Natural Resource Damage Assessment
In 2009, the state of Colorado, Shell Oil Co., and the United States Army settled a lawsuit pertaining to damages to the state’s natural resources from past activities at the Rocky Mountain Arsenal that caused extensive contamination of soil and water at the site. The purpose of this Natural Resource Damage Assessment Plan is to document the State Trustees' basis for conducting the damage assessment that provided the basis of the lawsuit and to set forth the proposed approaches for quantifying harm to natural resources and calculating the damages associated with those injuries.
- The settlement amount totaled $27.4M and is to be used for natural resources restoration projects in the South Platte River area.
- Visit the Colorado Attorney General's Colorado Natural Resources Trustees website for more information.
The Assessment Plan
- Enabled the trustees to ensure that the Natural Resource Damage Assessment would be completed in a planned and systematic manner.
- Described the proposed assessment methods so that stakeholders could participate in the assessment process.
- Report Summary: Update of Cancer Incidence in Northeast Denver Residents Living in the Vicinity of the Rocky Mountain Arsenal, 1997-2005 Data Review (May 2010).
- Rocky Mountain Arsenal Medical Monitoring Program: Update of Cancer Incidence in Northeast Denver Residents Living in the Vicinity of the Rocky Mountain Arsenal, 1997-2005 (May 2010).
- Colorado Environmental Health Site Assessment.
Related external website: