Rocky Mountain Arsenal

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Rocky Mountain Arsenal

The Rocky Mountain Arsenal (RMA), a few miles northeast of Denver, was originally constructed and operated by the Chemical Corps of the United States Army. Beginning in 1942, the arsenal was the main site at which the Chemical Corps manufactured chemical weapons such as mustard gas, nerve gas, and phosgene. The Army eventually leased part of the 27 mi2 (70 km2) plot of land to the Shell Oil Company which produced DDT, dieldrin, chlordane , parathion, aldrin, and other pesticides at the site.

The presence of a chemical weapons plant has long been a source of concern for many Coloradans. In 1968, for example, a group of Denver-area residents complained that nerve gas was being stored in an open pit directly beneath one of the flight paths into Denver's Stapleton International Airport.

Indeed, the Army was well aware of the hazard posed by its RMA products. In 1961, it found that wastes from manufacturing processes were seeping into the ground, contaminating groundwater and endangering crops in the area. The Army's solution was to institute a new method of waste disposal. In September 1961, engineers drilled a deep well 12,045 ft (3,654 m) into the earth. The lowest 75 ft (23 m) of the well was located in a highly fractured layer of rock. The Army's plan was to dump its chemical wastes into this deep well. The unexpressed principle seemed to be out of sight, out of mind.

Fluids were first injected under pressure into the well on March 8, 1962, and pressure-injection continued over the next six months at the rate of 5.5 million gal (21 million l) per month. After a delay of about a year, wastes were once more injected at the rate of 2 million gal (7.5 million l) per month from August 1964 to February 1966. This practice was then terminated.

The reason for ending this method of waste disposal was the discovery that earthquakes had begun to occur in the Denver area at about the same time that the Army had started using its deep injection well . Seismologists found that the pattern of the earthquakes in the region between 1962 and 1966 closely matched the pattern of waste injection in the wells . When large volumes of wastes were injected into the well, many earthquakes occurred. When injection stopped, the number decreased. Scientists believe that the liquid wastes pumped into the injection well lubricated the joints between rock layers, making it easier for them to slide back and forth, creating earthquakes.

Earthquakes are hardly a new phenomenon for residents of Colorado. Situated high in the Rocky Mountains, they experience dozens each year although most are minor earthquakes. However, the suggestion that the Army's activity at RMA might be increasing the risk of earthquakes became a matter of great concern. The proximity of RMA to Denver raised the possibility of a major disaster in one of the West's largest metropolitan areas.

Faced with this possibility, the Army decided to stop using its injection well on February 20, 1966. Earthquakes continued to occur at an abnormally high rate, however, for at least another five years. Scientists hope that liquids in the well will eventually diffuse through the earth, reducing the risk of further major earthquakes.

In 1992 Congress announced plans to convert the arsenal to a wildlife refuge . The land around RMA had been so badly poisoned that humans essentially abandoned the area for many years. The absence of humans, however, made it possible for a number of species of wildlife to flourish.

On October 16, 1996, the U.S. Army announced its plans for the clean-up of the Rocky Mountain Arsenal. That plan dealt with three areas of environmental concern: water, structures, and soil . The Army declared its intent to continue its program of treating water supplies and groundwater on the site and to provide safe drinking water to neighboring off-site communities. It outlined plans to demolish all existing buildings for which no future use had been designated. These buildings along with all other contaminated materials were scheduled for disposal in new on-site capped landfills.

The most extensive clean-up efforts were to be focused on soil that had been contaminated by activities at the Arsenal. Any unexploded weapons were scheduled for removal and off-site detonation. Contaminated soils and other materials were to be buried in new waste landfills. These landfills were designed to consist of leak-proof barriers with 6 in (15 cm) concrete barrier caps and underground barrier walls to protect wildlife from their contents. Existing trenches and sewers are to be surrounded by barrier walls, covered with concrete barrier caps, and/or plugged with concrete caps, all to protect wildlife from their contents.

In addition to these physical plans, the Army announced plans for three other on-going activities at the Arsenal: (1) the discontinuation of any additional hazardous waste disposal activities at the Arsenal; (2) on-going medical monitoring at adjacent communities during the period of clean-up; and (3) monitoring and control of emissions and odors from the site during clean-up.

Clean-up activities at RMA are being directed by the U.S. Army under the supervision of the Environmental Protection Agency . In 2001, there were 31 environmental clean-up projects proposed, and 26 were underway. The Shell Chemical Company is also participating in the study of environmental problems at RMA and in efforts to deal with those problems. Until the clean-up process has been completed, the former RMA site is being managed as a wildlife refuge by the U.S. Department of the Interior's Fish and Wildlife Service . At the conclusion of the process, the refuge will become a National Wildlife Refuge .

[David E. Newton ]



"Aresenal Update." Defense Cleanup 12 no. 10 (March 9, 2001): 78.

Breen, B. "From Superfund Site to Wildlife Refuge." Garbage 4 (May-June 1992): 22.

Gascoyne, S. "From Toxic Site to Wildlife Refuge; If Approved an Ambitious Plan Would Transform a Former Chemical-Weapons Arsenal near Denver." The Christian Science Monitor (September 12, 1991): 10.

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Rocky Mountain Arsenal

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