Text Size
Increase text size
Increase text size

Rocky Mountain Arsenal

This site is one of the "Superfund" hazardous waste sites in Colorado. A site qualifies for the National Priorities List (NPL or Superfund list) when the U.S. Environmental Protection Agency (EPA) determines there is a release or threatened release of hazardous substances that may endanger public health, welfare or the environment. The US Army is the lead agency for the Rocky Mountain Arsenal remediation because the site is a federally-owned facility.




**NEW**  Rocky Mountain Arsenal Recovery Plan Final Complete Proposals 




The Rocky Mountain Arsenal (the Arsenal) is located north of the former Stapleton Airport and west of Denver International Airport. Residential and commercial property are located to the south and west, with residential, commercial and agricultural land to the north. Henderson is 4 miles to the northwest, 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 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. During the 1950s and into the 1960s, obsolete and deteriorating munitions were destroyed onsite. From 1950 to 1952, the Army constructed the North Plants complex to manufacture the nerve agent GB, also called Sarin. Rocket fuel was blended onsite 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 Company manufactured agricultural pesticides in the South Plants complex from 1952 through 1982.


Manufacturing and waste disposal practices used during these years resulted in soil, surface water, sediment, ground water and structures contamination. Solid and liquid wastes were disposed of in trenches, burn pits and unlined basins. Contaminated ground water was first discovered north of the Arsenal in the mid-1950s, when crop damage was noted on farms. New liquid waste disposal methods were employed to try to prevent further contamination, including a lined basin called Basin F and deep well injection, but these were unsuccessful. The Army and Shell Oil Company began conducting detailed site investigations in the 1970s to define the extent of contamination. All manufacturing activities ended in 1982.


Fourteen interim response actions were undertaken to solve immediate environmental problems while the final cleanup solutions were being determined. They included systems to capture and treat contaminated ground water before it flows off the site. Another system north of the Arsenal treats contaminated water that has already moved offsite. Other interim response actions included removal and treatment of 10.5 million gallons of Basin F liquids, closure of a well more than two miles deep, and removal of 76,000 drums of hazardous salts.


Environmental laws and regulations govern the Arsenal cleanup activities. A federal law called the Comprehensive Environmental Response and Liability Act, commonly known as Superfund, establishes procedures that must be followed during environmental cleanup programs. The Rocky Mountain Arsenal was placed on the National Priorities List of Superfund sites in July 1987. Some Arsenal cleanup activities are governed by another federal environmental law called the Resource Conservation and Recovery Act (RCRA). The Colorado Department of Public Health and Environment (the Department) has been delegated authority to oversee compliance with this law in Colorado.


More than 600 chemicals have been used or manufactured at the Arsenal, including volatile organic compounds (VOCs), heavy metals, pesticides, and diisopropyl methylphosphonate (DIMP), a chemical unique to the Army's manufacture of nerve gas. Four chemicals (aldrin, dieldrin, dibromochloropropane and arsenic) cause most of the potential human health risks.



The potential human exposure pathways include ingestion, skin absorption and inhalation from contaminated soils, ground water and air. Current potential exposure is greatly reduced through site access and institutional controls, an alternate drinking water supply for neighboring residents whose wells have been affected by Arsenal contaminants, and careful planning of the cleanup project. Public access to the site is strictly controlled and workers follow prudent health and safety procedures. Colorado State University and the Colorado Department of Public Health and Environment have conducted health investigations in the communities around the Arsenal.


Contamination was detected in soil, ditches, stream and lakebed sediments, sewers, ground water, surface water, wildlife and structures. The contaminated areas onsite included approximately 3000 acres of soil, 15 groundwater plumes and 798 structures. The most highly contaminated sites are concentrated in the central six sections, or square miles, of the Arsenal where the former manufacturing and disposal areas are located. The primary contaminants found in soil and groundwater in these areas are organochlorine pesticides, solvents, metals, and chemical warfare agent by-products. In addition, contamination has been detected in some wildlife.


The portion of the Rocky Mountain Arsenal cleanup that will require the movement and disturbance of contaminated material is nearly complete. The contaminated soils cleanup phase of the process is expected to be complete by early 2008.

The purpose of this Natural Resource Damage Assessment Plan is to document the State Trustees' basis for conducting a damage assessment, and to set forth the proposed approaches for quantifying harm to natural resources and calculating damages associated with those injuries. The Assessment Plan enables the Trustees to ensure that the Natural Resource Damage Assessment will be completed in a planned and systematic manner and at a reasonable cost. The Plan describes the proposed assessment methods so that stakeholders can participate in the assessment process.



Assessment Plan


The U.S. Army has the lead role in remediation of the two Arsenal Operable Units, off-post and on-post. Shell Oil Company shares in the costs and implementation of the cleanup actions. The EPA, Colorado Department of Public Health and Environment and Tri-County Health Department provide regulatory oversight. 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. A Record of Decision for the on-post operable unit cleanup 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 and a medical monitoring program to monitor the success of exposure prevention efforts during the environmental cleanup. Other cleanup actions include:



  • Construct double and triple lined on-post hazardous waste landfills.

  • Excavate, solidify and dispose of 26,000 cubic yards of buried M-1 Pit waste in the landfill.

  • Excavate and dispose of 600,000 cubic yards Basin F waste pile contaminated soil in the triple-lined landfill.

  • Excavate and dispose of more than one million cubic yards of contaminated soil from various locations on the Arsenal into the landfill.

  • Excavate and dispose of 165,000 cubic yards of former Basin F Principal Threat waste in the triple-lined landfill.

  • Excavate and dispose of 8000 cubic yards of Hex Pit waste in the triple-lined landfill.

  • Destroy offsite (or detonate onsite if unstable) any identified unexploded ordnance. Excavate and dispose of unexploded ordnance debris and associated soil in the landfill.

  • Install slurry walls and RCRA-equivalent soil covers for the Army Complex and Shell disposal trenches and the Lime Basins where contamination will be left in place.

  • Construct a RCRA-equivalent soil cover over the former Basin F site. Construct soil covers over Basin A, South Plants Central Processing Area, Secondary Basins, North Plants, South Plants Balance of Areas and Section 36 Balance of Areas.

  • Excavate 1.5 million cubic yards of soil that may pose a risk to wildlife for use as fill under the covers or in the Basin A Consolidation Area.

  • Monitor excavated soil associated with chemical agent manufacturing and treat, if necessary.



  • Continue operation of existing on-post Arsenal groundwater treatment systems until water quality goals are achieved. The off-post groundwater treatment system will continue to operate under Off-post Record of Decision requirements.

  • Install a new groundwater treatment system in the northeast corner of Section 36.

  • Treat NDMA (N-nitrosodimethylamine) contamination in groundwater at the North Boundary Containment system to achieve water quality goals.



  • Demolish approximately 530 structures and 250 electrical substations and salvage metals where appropriate.

  • Dispose of demolition debris with significant contamination, polychlorinated biphenyls, or from chemical agent production areas in the on-post hazardous waste landfill.

  • Dispose of some less contaminated structural debris in the Basin A Consolidation Area.



  • Restrict Arsenal land use and access. The 1992 Rocky Mountain Arsenal National Wildlife Refuge Act and the Federal Facility Agreement restrict future land use and prohibit certain activities such as agriculture, residential development, use of on-post groundwater as a drinking source, and consumption of fish and game taken at the Arsenal. Long-term management will include access restriction for soil covers and landfills to ensure integrity of the containment systems.

  • Refine areas of soil and lake sediments requiring cleanup action for protection of wildlife.


As portions of the cleanup are completed, this property becomes part of the National Wildlife Refuge system and is transferred to the US 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. Eventually, most of the land area will belong to the US 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 US Fish and Wildlife Service is responsible for managing Arsenal wildlife and habitat.

The Rocky Mountain Arsenal On-post Record of Decision directed that a medical monitoring program be instituted that would respond effectively to Arsenal-related health concerns of the surrounding communities during the soil cleanup. The medical monitoring program served the communities of Commerce City, Montbello, Henderson and Green Valley Ranch.


The Record of Decision also directed that a Medical Monitoring Advisory Group (the Advisory Group) be formed to recommend appropriate program components. The Advisory Group, formed in 1995, consisted of a diverse panel of community members, physicians, nurses, scientists, state and local health officials and representatives from the EPA, Army, Shell and the US Fish and Wildlife Service. The Advisory Group focused program recommendations on four key performance areas: baseline health assessment and human health monitoring, environmental monitoring, emergency preparedness and public involvement and education.


The Advisory Group completed its work in October 1998 and submitted a final report to the Colorado Department of Public Health and Environment consisting of twelve recommendations. The Department formally accepted all twelve recommendations developed by the Advisory Group and began program implementation. These recommendations included systematic evaluation of air quality data and its public health significance, a process for selecting appropriate public health actions, systems to track birth defects and cancer rates in the neighborhoods around the Arsenal, improvements to the Arsenal air and odor monitoring programs, improvements to emergency response programs, health professional education and public involvement and education.


The Advisory Group recommended that citizen involvement continue during program implementation. A Citizen Advisory Board (the Advisory Board) was formed in 1999. The Advisory Board meets annually and is responsible for making recommendations to improve the program.


If you would like more information about the Rocky Mountain Arsenal or the medical monitoring program, contact Warren Smith at 303-692-3373.

The Medical Monitoring Program was developed to monitor the success of exposure prevention efforts during the environmental cleanup at the Rocky Mountain Arsenal. The 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.


Monitoring Results

Results of the air monitoring show the cleanup was protective of public health and show that no chemical exceeded the health protective levels established for the site since the environmental cleanup began in October 1997. In fact, the chemical readings were significantly below the health protective standards.  Odor measurements were also below the state standard. Eight permanent air monitoring stations on the Rocky Mountain Arsenal and two in the adjacent neighborhoods regularly tested air quality for more than 27 chemicals of concern. Air monitoring locations were chosen to measure air quality close to the cleanup, along the Arsenal fence line, and in the adjacent community. The contaminated soil remediation ended in 2008; the air monitoring surveillance continued until the end of July 2009.  


Rates of birth defects in the communities surrounding the Arsenal were found to be stable and similar to rates for all of Colorado. Statistical elevations in cancer incidence in the communities near the Arsenal varied across location, gender, race and time and are not likely to be related to cleanup activities.



Susan Newton

State Project Manager 


888-569-1831 Ext. 3321 (Toll-free)


Warren Smith

State Community Involvement Coordinator


888-569-1831 Ext. 3373 (Toll-free)


Jennifer Chirgo

EPA Community Involvement