Rocky Mountain Arsenal

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Rocky Mountain Arsenal, south entrance. (photo 1960)

The Rocky Mountain Arsenal was a United States chemical weapons manufacturing center located in the Denver Metropolitan Area in Commerce City, Colorado. The site was completed December 1942,[1] operated by the United States Army throughout the later 20th century and was controversial among local residents until its closure in 1992.[citation needed]

Much of the site is now protected as the Rocky Mountain Arsenal National Wildlife Refuge.

Site selection[edit]

The Arsenal's location was selected due to its relative distance from the coasts (and presumably not likely to be attacked), a sufficient labor force to work at the site, weather that was conducive to outdoor work, and the appropriate soil needed for the project. It was also helpful that the location was close to Stapleton airfield, a major transportation hub.[2]

In 1942, the US Army acquired 19,915 acres (80.59 km²) of land on which to manufacture weapons in support of World War II military activities at a cost of $62,415,000. Additionally, some of this land was used for a prisoner of war camp (for German combatants) and later transferred to the city of Denver as Stapleton Airport expanded. A lateral was built off the High Line Canal to supply water to the Arsenal.

Manufacturing operations[edit]

Rocky Mountain Arsenal, south plant. (photo 1970)

Weapons manufactured at RMA included both conventional and chemical munitions, including white phosphorus (M34 grenade), napalm, mustard gas, lewisite, and chlorine gas.[3][4] RMA is also one of the few sites that had a stockpile of Sarin gas (aka nerve agent GB), an organophosphorus compound. The manufacture of these weapons continued until 1969. Rocket fuel to support Air Force operations was also manufactured and stored at RMA. Subsequently, through the 1970s until 1985, RMA was used as a demilitarization site to destroy munitions and chemically related items. Coinciding with these activities, from 1946 to 1982, the Army leased RMA facilities to private industries for the production of pesticides. One of the major lessees, Shell Oil Company, along with Julius Hyman and Company and Colorado Fuel and Iron, had manufacturing and processing capabilities on RMA between 1952 and 1982. The military reserved the right to oust these companies and restart chemical weapon production in the event of a national emergency.

Deep injection well[edit]

RMA contained a deep injection well that was constructed in 1961.[5] It was drilled to a depth of 12,045 feet (3671 m). The well was cased and sealed to a depth of 11,975 feet (3650 m), with the remaining 70 feet (21 m) left as an open hole for the injection of Basin F liquids. For testing purposes, the well was injected with approximately 568,000 US gallons (2150 m³) of city water prior to injecting any waste. The injected fluids had very little potential for reaching the surface or usable groundwater supply since the injection point had 11,900 feet (3630 m) of rock above it and was sealed at the opening. The Army discontinued use of the well in February 1966 because the fluid injection triggered a series of earthquakes in the area.[5][6] The well remained unused until 1985 when the Army permanently sealed the disposal well.

Environmental issues[edit]

Rabbit used to check for leaks at Sarin nerve gas production plant. (photo 1970)

In 1984, the Army began a systematic investigation of site contamination in accordance with the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA), commonly referred to as Superfund. In 1987, the RMA was placed on the National Priorities List (NPL) of Superfund sites. As provided by CERCLA, a Remedial Investigation/Feasibility Study (RI/FS) was conducted to determine the extent of contamination. Since 1985, the mission at RMA has been the remediation of the site.


The primary contaminants include organochloride pesticides, organophosphate pesticides, carbamate insecticides, organic solvents and feedstock chemicals used as raw products or intermediates in the manufacturing process (e.g., chlorinated benzenes), heavy metals, chemical warfare material and their related breakdown products and biological warfare agent such as TX. Additionally, ordnance (including incendiary munitions) was manufactured and tested, and asbestos and polychlorinated biphenyls (PCBs) were used at RMA. Today, it is considered a hazardous waste site according to the Colorado Department of Public and Environmental Health.

Rocky Mountain Arsenal NWR Act[edit]

Mule deer at the Rocky Mountain Arsenal National Wildlife Refuge with Denver, CO in the background. (photo 2009)

In 1986 it was discovered that the absence of human activity had made the area an involuntary park when a winter communal roost of bald eagles, then an endangered species, was discovered on site. The U.S. Fish and Wildlife Service soon realized that more than 330 species of wildlife inhabit the Arsenal including deer, coyotes, white pelicans and owls.

The Rocky Mountain Arsenal National Wildlife Refuge Act was passed in October 1992 and signed by then President George H. W. Bush. It stipulates that the majority of the site will become a National Wildlife Refuge under the jurisdiction of the Fish and Wildlife Service when the environmental restoration is completed. The Act also provides that to the extent possible, parts of the Arsenal are to be managed as a Refuge in the interim. Finally, the Act provides for the transfer of some Arsenal land for road expansion around the perimeter of the Arsenal and 915 acres (3.70 km²) to be sold for development and annexation by Commerce City.

Developments since 2004[edit]

Although comprising 17,056 acres (69.02 km²) at the beginning of remediation in 1997, 5,976 acres (24.18 km²) of the RMA have been determined to meet cleanup requirements and are no longer part of the National Priorities List. Of that, approximately 4,927 acres (19.94 km²) were transferred by the Department of Army to the USFWS in April 2004 and another 917 acres (3.71 km²), located in the southwest corner of the site, were sold to Commerce City in June 2004. Also, in 2004, approximately 129 acres (0.52 km²), located at the boundaries, were transferred to local jurisdictions and to the U.S. Army Reserve Center for road improvement projects. An additional 7,200 acres (29 km2) was transferred to the USFWS in October 2006, making the Rocky Mountain Arsenal Wildlife Refuge one of the largest urban refuges in the United States. At that time the refuge comprised 12,500 acres (51 km2) and is home to more than 330 species of animals. Implementation of the remedy for the estimated 11,080 acres (44.84 km²) remaining is ongoing and is scheduled for completion in 2011.

As of September 2010 clean-up was considered as complete and the remaining portions of land were transferred over to the U.S. Fish and Wildlife Service bring the total to 15,000 acres. The two remaining sites on the property that are retained by the Army are the South Plants location due to historical use and the North Plant location which is now a landfill containing the remains of various buildings used in the North and South Plant locations.

As of May 21, 2011 the official Visitor Center was opened with an exhibit about the site's history ranging from the homesteading era to its current use as a National Wildlife Refuge (

Public use[edit]

Congruent with the outline of the June 1996 USFWS Comprehensive Management Plan, RMA will be available for public use through both community outreach and educational programs (as provided by the Visitor Access Plan and the USFWS). This public availability will be implemented while simultaneously supporting the remediation effort and the USFWS activities.

Dick's Sporting Goods Park[edit]

In April 2007 Dick's Sporting Goods Park, a soccer-specific stadium, was opened on part of the former Rocky Mountain Arsenal land that was transferred to Commerce City. The new venue hosts the Colorado Rapids of Major League Soccer.


A small herd of wild bison was introduced to the refuge in March 2007 as part of the USFWS Bison Project. The animals were transferred from the National Bison Range in Montana [1].


  1. ^ "History of Rocky Mountain Arsenal" (PDF). Rocky Mountain Arsenal Information Center. May 1980. Retrieved 2015-07-09. 
  2. ^ "Site History". Rocky Mountain Arsenal. Rocky Mountain Arsenal Remediation Venture Office. Archived from the original on 2013-02-26. 
  3. ^ "A Brief History of Rocky Mountain Arsenal" (PDF). RMA Fact Sheets. Rocky Mountain Arsenal Remediation Venture Office. Archived from the original (PDF) on 2013-02-17. 
  4. ^ Shannon, Brian (1997). "ARSENAL Base Clean-Up". ICE Case Studies. American University. Archived from the original on 2015-07-09. Retrieved 2015-07-09. 
  5. ^ a b "Deep Injection Well Fact Sheet". RMA Fact Sheets. Rocky Mountain Arsenal Remediation Venture Office. Archived from the original on 2013-11-08. 
  6. ^ "Colorado Earthquake History". Earthquake Hazards Program. United States Geological Survey. 2015-01-14. Archived from the original on 2015-07-09. Retrieved 2015-07-09. 

External links[edit]

Coordinates: 39°49′42″N 104°51′31″W / 39.828258°N 104.858740°W / 39.828258; -104.858740