Rocky Mountain Arsenal

IDENTIFICATION: Former U.S. military production facility located near Denver, Colorado

DATE: Established in 1942

Rocky Mountain Arsenal produced, stored, and decommissioned a host of highly toxic and hazardous substances, including chemical weapons, incendiary munitions, and rocket fuels. Shell Chemical Corporation leased part of the facility and manufactured agricultural chemicals there. Both Shell and the U.S. government have participated in a decades-long cleanup program to transform the site into a wildlife refuge.

After the United States officially entered World War II in December, 1941, the military’s urgent need for munitions led to the construction of the Rocky Mountain Arsenal (RMA). In 1942, the U.S. Department of Defense (DOD) selected approximately 43 square kilometers (27 square miles) of prairie and farmland roughly 14.5 kilometers (9 miles) northeast of downtown Denver, Colorado, as the site for the facility, which began production about a year after the country’s entry into the war.

Chemical weapons manufactured at the facility included chlorine, a lung irritant, and mustard, a blister agent. White and other incendiary munitions were also produced. During the war, RMA made 87,000 tons of chemical, intermediate, and toxic products and 155,000 tons of incendiary munitions.

After the war ended, the DOD placed the relatively young arsenal on standby. Rather than allow its chemical production facilities to stand idle during peacetime, it leased portions of the site to commercial interests. Among the lessees was Julius Hyman and Company, which began production at RMA in 1946. Shell Chemical Corporation acquired Hyman in 1952. For the next three decades, Shell used RMA facilities to manufacture pesticides, herbicides, and agricultural chemicals. Shell products made at RMA included the organochlorine pesticides aldrin, dieldrin, and endrin, neurotoxins that proved so persistent in the and so bioaccumulative in the that, decades later, their use was banned by international treaty.

After the United States became involved in the Korean War in 1950, the military reactivated RMA. It began constructing a plant to manufacture a more modern and deadlier class of chemical weapon: the nerve agent. In 1953, the same year hostilities in Korea ended, the new facility began production. It manufactured and filled weapons with the organophosphate designated GB (sarin), one of the most toxic substances ever synthesized. GB production ended in 1957, but munitions-filling operations continued until 1969.

During the late 1950’s and early 1960’s RMA worked on the development of a biological agent called TX (a weaponized form of wheat rust, a fungal disease that attacks crops). In 1959 the arsenal constructed a facility for blending hydrazine and unsymmetrical dimethylhydrazine to produce Aerozine-50, a rocket fuel that was used in lunar missions. During the latter half of the 1960’s RMA activities supported the war effort in Vietnam by manufacturing land mines and white phosphorus incendiary devices. Other wartime operations included emptying existing munitions filled with the chemical warfare agents phosgene and cyanogen chloride so they could be refilled off-site with high explosives.

Environmental Contamination

RMA’s various military and civilian operations generated a vast array of highly hazardous and toxic wastes. More than 750 chemicals were handled or generated at the site, including volatile compounds and heavy metals. Environmental contamination occurred not only from deliberate activities such as burying and using basins for disposal of hazardous liquid wastes but also from unintended releases such as leaks in tanks, pipes, and lines, wind dispersion, and accidental spills that sometimes involved tens of thousands of gallons of chemicals.

In the arsenal’s early days, standard practice was to liquid industrial wastes into centrally located, unlined basins dug into the earth. When farms north of RMA began to complain of crop damage and sickened livestock during the early 1950’s, it became clear that chemical wastes from the disposal basins had percolated through the underlying soil and been carried off-site in groundwater. In 1956, RMA installed a lined evaporative basin covering 37.6 hectares (93 acres). Its lining, a layer of asphalt covered with soil, was intended to keep additional contaminants from reaching the groundwater. However, the wastes discharged to this basin soon degraded the asphalt liner, and by the early 1960’s it had begun to leak. All of RMA’s disposal basins were deadly to waterfowl that mistook them for lakes. The toxic basins were particularly attractive to ducks and geese flying overhead during the colder months, as the chemical wastes did not freeze.

The ongoing problem of effective and safe waste disposal drove RMA to explore alternative technologies. In 1962 a waste disposal well was drilled to a depth of more than 3,600 meters (12,000 feet) at the arsenal. More than 662 million liters (175 million gallons) of treated waste material were eventually disposed of in this deep-injection well. The month after fluid injection began, however, the Denver area began to experience a series of earthquakes that would continue for years. The pumping facilities were shut down in 1966 amid concerns that the pressurized fluid injection was triggering the seismic activity. In 1968, the military decided to dispose of RMA’s stockpile of excess and obsolete chemical munitions by dumping the containerized wastes at sea. Public and congressional concern over this operation’s safety led to its cancellation before it began.

During the early 1970’s RMA commenced on-site disposal operations for mustard and related blister agents, the nerve agent GB, the anticrop agent TX, and explosives. This major undertaking—at the time, the largest of its kind in U.S. Army history—included chemically neutralizing or incinerating extremely dangerous substances. The military had to take extreme precautions to avoid releasing any chemical agents into the atmosphere, where they could be carried off-site into surrounding communities. These demilitarization operations continued into the early 1980’s.

During the mid-1970’s, after crop damage had again been observed north and northwest of RMA, a Colorado Department of Health (CDH) investigation found that off-site groundwater was contaminated with diisopropylmethyl-phosphonate, a of the GB manufacturing process, and dicyclopentadiene, a chemical used by Shell in manufacture. The CDH ordered the Army and Shell to clean up the sources of the contaminants, prevent future releases, and monitor the on- and off-site. Systems to intercept and treat contaminated groundwater were subsequently installed. Follow-up investigations revealed industrial solvents and the pesticides dibromochloropropane and dieldrin in a shallow aquifer. Surface soils across much of the site were found to contain aldrin and dieldrin. Pesticide residues were also found in the tissues of local wildlife.

Site Cleanup

The Army and Shell ended all manufacturing activities at RMA in 1982. In July, 1987, the site became one of the first military installations to be placed on the of Superfund sites. The arsenal’s only mission became cleanup of contaminated soil, surface water, groundwater, and structures, a complex, decades-long undertaking involving both the Army and Shell, as well as federal, state, and local regulatory agencies and a series of legal battles. Shell and the Army ultimately agreed to split the cleanup costs. Citizens’ concerns that potentially hazardous levels of toxic chemicals might be released into the air during operations led to the implementation of a medical program for communities surrounding RMA to provide periodic health checkups for detection and treatment of any illnesses related to chemical releases.

Cleanup of the lined waste basin proved particularly challenging. Nearly 41,640 kiloliters (11 million gallons) of liquid chemical wastes were pumped from it into temporary storage tanks. The remaining sludge, liner, and underlying contaminated soil were to be excavated and air-dried. Shortly after cleanup operations began in 1988, off-site residents and workers north and northwest of RMA complained of noxious odors, headaches, nausea, eye irritation, and rashes. After half a year of trying unsuccessfully to control air emissions, the Army halted excavation activities and capped the remaining materials in place. The liquid wastes were later destroyed by incineration.

In 1986, after a roost of bald eagles was discovered at RMA, the U.S. Fish and Wildlife Service stepped in to manage the site’s wildlife. In 1992 the U.S. Congress designated the site as a national wildlife refuge with the passage of the Rocky Mountain Arsenal National Wildlife Refuge Act. The act specified that the U.S. government must retain title to RMA. The wildlife was preserved and maintained to protect endangered species, while residential or industrial development, agricultural use, consumption of fish or game, and use of groundwater or for drinking purposes were all prohibited. As cleanup has progressed, allowing portions of the site (excluding the underlying groundwater) to be deleted from the NPL, the Army has transferred that land to the Fish and Wildlife Service to establish and expand the wildlife refuge. As of the early 2020s, the refuge covered more than 6,070 hectares (15,000 acres), making it one of the country’s largest urban refuges. The former military facility served as a sanctuary for more than 330 species of animals, including deer, coyotes, foxes, bald eagles, burrowing owls, geese, ducks, badgers, prairie dogs, and a herd of wild bison introduced in 2007. The Army retained possession of waste disposal trenches, landfills, and areas with groundwater treatment systems.

Bibliography

Gascoyne, Stephen. “Slipcovering a Superfund Site.” Bulletin of the Atomic Scientists 49, no. 7 (1993): 33-37.

Hoffecker, John F. Twenty-seven Square Miles: Landscape and History at Rocky Mountain Arsenal National Wildlife Refuge. Denver, Colo.: U.S. Fish and Wildlife Service, 2001.

Konikow, Leonard F., and Douglas W. Thompson. “Groundwater Contamination and Aquifer Reclamation at the Rocky Mountain Arsenal, Colorado.” In Groundwater Contamination, edited by the Commission on Physical Sciences, Mathematics, and Applications of the National Academies. Washington, D.C.: National Academy Press, 1984.

Natural Resource Trustees for the State of Colorado. Natural Resource Damage Assessment Plan for the Rocky Mountain Arsenal, Commerce City, Colorado. Denver: Colorado Department of Public Health and Environment, 2007.

Rocky Mountain Arsenal. History of Rocky Mountain Arsenal, Commerce City, Colorado. Ft. Belvoir, Va.: Defense Technical Information Center, 1980.

"Rocky Mountain Arsenal National Wildlife Refuge." U.S. Fish and Wildlife Service, www.fws.gov/refuge/rocky-mountain-arsenal. Accessed 22 July 2024.

U.S. Fish and Wildlife Service. Rocky Mountain Arsenal National Wildlife Refuge. Washington, D.C.: Author, 2003.