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Region 8

Rocky Mountain Arsenal

Rocky Mountain Arsenal site location map Site Type: Federal Facility Final NPL
City: Commerce City
County: Adams
Street Address: 6550 Gateway Road
ZIP Code: 80022
EPA ID: CO5210020769
SSID: 0811
Congressional District: 7

What's New?

Updated September 2012

Emerging Contaminant Sampling – 1,4-dioxane

As part of the 2010 five-year review of the remedy at the Rocky Mountain Arsenal (RMA), EPA requested that the U.S. Army and Shell Chemical Co. sample the groundwater for an "emerging contaminant" called 1,4-dioxane. 1,4-dioxane is an industrial chemical stabilizer that can migrate in groundwater. The agency has become aware that 1,4-dioxane is likely to be present at sites where 1,1,1,-trichloroethane is a contaminant. As a result, 1,4-dioxane is being discovered in groundwater plumes across the nation.

Although 1,1,1,-TCA has been detected occasionally in RMA groundwater, the detections have been very limited in extent and very low in concentration. Still, results from initial sampling at RMA show that 1,4 dioxane is present in groundwater at RMA. As a result, an On-Post and Off-Post sampling effort is underway to determine the extent of 1,4-dioxane both at RMA and in nearby areas.

Section 36 Lime Basins DNAPL Remediation Project

The Lime Basins, located in Section 36 of RMA, were once used for the neutralization of process wastes related to chemical agent, or nerve gas, production. As a result, the Lime Basins contained soil/sludge mixtures with high pH levels and the potential presence of chemical agent. The remedy for the Lime Basins included covering the entire area and encircling it with a slurry wall and dewatering well system to create a barrier between the Lime Basins and the surrounding groundwater. In August 2009, field monitoring of the Lime Basins dewatering wells indicated the potential presence of dense non-aqueous phase liquid (DNAPL). DNAPL is a term used to describe contaminants that are denser than water and tend to sink below the water table when spilled in significant amounts. Subsequent sampling showed that DNAPL was present in two of the wells. In August and September of this year, the Army and Shell Chemical Co. will be drilling eight additional groundwater wells around the Lime Basins in order to identify and remove DNAPL from the area. The Rocky Mountain National Wildlife Refuge and Visitor Center will be closed to all public activities and visitation beginning Monday, August 20 through Friday September 21, 2012 as a safety precaution.

Monitoring for LNAPL at North Plants

Various efforts to recover LNAPL in groundwater beneath the North Plants manufacturing area have occurred since 1993. The most recent effort is a pilot study that began in 2008 and is ongoing.

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Site Description

Burrowing owl
Burrowing owl making the Rocky Mountain Arsenal a summer home

The Rocky Mountain Arsenal (RMA) is nearly 27 square miles, roughly the size of Manhattan. RMA is located at the western edge of the Colorado plains, near the foothills of the Rocky Mountains, ten miles northeast of downtown Denver, Colorado. Characterized by rolling terrain, grasslands, shrublands, wetlands and aquatic habitats, the site supports a variety of plant and wildlife species. To the west and northwest of the site sits Commerce City and the South Platte River. Newer residential developments and the town of Henderson are located to the north, and the neighborhoods of Montbello and Stapleton are to the south. The Denver International Airport is located just to the east.

The U.S. Army established the Rocky Mountain Arsenal (RMA) in 1942 to produce incendiary munitions and chemical warfare agents such as mustard gas used in World War II. Following the war, and through the early 1980s, the Army continued to use these facilities. Private industry was also encouraged to lease facilities at RMA after the war to foster economic growth in the area, offset operational costs and maintain facilities for national security. Under the lease program, Julius Hyman and Company began producing pesticides in 1946.

In 1952, Shell Chemical Company acquired Julius Hyman and Company and continued to produce agricultural pesticides on-site until 1982. These activities over time resulted in widespread and significant environmental contamination across the site. Contamination was detected in soil, ditches, stream and lakebed sediments, sewers, groundwater, surface water, biota, structures, and, to a much lesser extent, air. The most highly contaminated sites are concentrated in the central manufacturing, transport and waste disposal areas. The buffer zone along the boundaries or the site proved to be relatively uncontaminated. The principal contaminants included organochlorine pesticides, heavy metals, agent-degradation products and manufacturing by-products, and chlorinated and aromatic solvents.

Some of the most highly contaminated sites included:

Bald eagle pair
Bald eagle pair roosting northeast of the former North Plant's sarin manufacturing facility, looking west with Mt. Evans in the background

South Plants (Central Processing Area, Hex Pit, Buried M-1 Pits, Chemical Sewers): The South Plants complex was built and put into use immediately after RMA was established in 1942. From 1942 through 1945, The Army manufactured mustard and lewisite at South Plants. Mustard and lewisite-filled munitions, as well as bulk product, were stored in the nearby toxic storage yards. Portions of the South Plants manufacturing complex were leased to private industry following World War II, primarily for the production of pesticides. Two major lessees of facilities in South Plants were Julius Hyman and Company (1947-1952) and Shell Chemical Company (1952-1982). The South Tank Farm was constructed as part of the South Plants facility and included 11 storage tank locations that were used for chemical storage.

North Plants: From 1950 to 1952, the Army designed and constructed the North Plants complex to manufacture the nerve agent GB, also called Sarin. One-ton containers of bulk GB and other nerve agent and filled-bombs were stored in the nearby toxic storage yards.

Basins A and F: There are six former disposal basins at RMA. These basins provided for the disposal of contaminated liquid wastes from the chemical manufacturing operations at South Plants and North Plants. Basin A was originally developed as an unlined evaporative basin for disposal of liquid waste from the production of mustard and lewisite. Basins B, C, D, and E were used to hold overflow liquid wastes from preexisting basins. Use of Basin A for liquid disposal was discontinued in 1956 when chemical sewers were constructed to convey waste to Basin F. Basin F was an asphalt-lined evaporation basin constructed by the Army in 1956.

Lime Basins: The former Lime Basins are three unlined basins, each approximately one acre in size, used to treat liquid waste and storm runoff from Army and Shell chemical manufacturing operations at South Plants from 1942 – 1957. Through 1943, wastewater from production of Lewisite was routinely treated with lime prior to discharge to the basins. The lime was used to precipitate metals and reduce arsenic concentration in the wastewater, resulting in a lime sludge that contained high levels of heavy metals, including arsenic. After Lewisite production ceased in November 1943, the Lime Basins continued to receive other liquid waste from South Plants from both Army and Shell production activities, including pesticide production wastewater. These wastes were transported through two chemical sewers that discharged into the south side of the basins. Wastewater from the Lime Basins was subsequently discharged to Basin A. Wastewater disposal to the Lime Basins ceased in January 1957 following the completion of the chemical sewer lines to Basin F.

Complex Army and Shell Disposal Trenches: The Complex Army Trenches are located east of Basin A in central Section 36. The Complex Army Trenches were the primary solid waste disposal area for the Army from the early 1940s through the late 1960s. Those solid wastes included miscellaneous solid chemical waste and potentially contaminated tools and equipment, unwanted containers, rejected incendiaries, empty munitions casing, and rejected munitions. The Complex Army Trenches cover area encompasses approximately 91 acres. Also located in the central area of the site, the Shell Disposal Trenches were used for disposal of liquid and solid wastes associated with Shell insecticide and pesticide manufacturing from 1952 to 1966. The wastes were buried in bulk form and in drums.

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Site Risk

Though nearly 600 different chemicals were associated with activities at RMA, the remedial investigation narrowed its focus to approximately 70. Of these, the principal contaminants are organochlorine pesticides, heavy metals, agent-degradation products and manufacturing by-products, and chlorinated and aromatic solvents. Most of the health risks posed by the site are from aldrin, dieldrin, dibromochloro-propane (DBCP), and arsenic. Aldrin is a pesticide that breaks down to dieldrin. Both chemicals are stored in the body and affect the central nervous system and liver. DBCP is also a pesticide, but it is not stored in the body. DBCP can affect the testes, kidneys, liver, respiratory system, central nervous system and blood cells. Arsenic is a naturally occurring element that can cause cancer in humans.

Media Affected Contaminants Source of Contamination
soil, surface water and groundwater aldrin, dieldrin, dibromochloro-propane (DBCP), arsenic nerve agent and pesticide manufacturing

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Cleanup Progress

Excavation of Basin F cover soil
Excavation of Basin F cover soil from Borrow Area 4, looking northwest

In 1984, the Army began a systematic investigation of site contamination in accordance with the Comprehensive Environmental Response Compensation and Liability Act (CERCLA) of 1980, and as a result, the site was placed on the National Priorities List (NPL) in 1987. The NPL is a list of the nation's most hazardous sites, commonly referred to as Superfund sites. As required by CERCLA, the Army conducted a Remedial Investigation/Feasibility Study (RI/FS) to determine the nature and extent of contamination and to develop and evaluate remedial alternatives.

In the late 1980s, the Army, EPA and Shell signed the Federal Facility Agreement (FFA), which specified the process by which decisions will be made for the cleanup of RMA and established certain cleanup goals. The FFA provided a framework under which the parties agreed to conduct Interim Response Actions (IRA) on specific contamination problems in advance of the final cleanup plan.

The remedial investigation and subsequent investigations identified contamination in soils, ditches, stream and lakebed sediments, natural depressions and manmade basins, sewers, groundwater, surface water biota and structures. The most highly contaminated sites were located at South Plants (i.e., Central Processing Area, Hex Pit, Buried M-1 Pits, Chemical Sewers), Basins A and F, Lime Basins, and the Army and Shell trenches (all described above).

RMA was divided into two operable units (OUs) for administration purposes. The On-Post OU encompasses the fenced 27 square miles of RMA proper. The Off-Post OU encompasses the contamination north and northwest of RMA.

The FFA requirements and the CERCLA remedial investigation/feasibility study/risk assessment process ultimately led to the signing of two Records of Decision (RODs). The Off-Post ROD (focused on contamination to the north of the Arsenal property) was signed December 19, 1995 and the On-Post ROD (focused on the contamination on the Arsenal property) was signed June 11, 1996. The RODs provide the framework, purpose, and overall rationale for the remediation actions selected for the site. The Army, EPA, and the Colorado Department of Public Health and Environment (CDPHE) signed both RODs. The U.S. Fish and Wildlife Service (USFWS) and Shell concurred with the On-Post ROD.

For the On-Post area, the goal of the remedial action was to implement remedies that eliminated, reduced or controlled current or future exposure to contaminated soil or structures; to reduce contaminant migration into the groundwater, and to prevent contaminated groundwater from migrating off post. The Off-Post remedy focused on addressing groundwater contamination north and northwest of RMA.

Nearly 200 sites with varying degrees of contamination were delineated across RMA in the remedial investigation and subsequent investigations. These sites were combined into groups containing similar contaminant types and distributions. Overall, the contaminated areas within the On-Post Operable Unit include approximately 3,000 acres of soil, 15 groundwater plumes and 798 remaining structures. The complex effort to complete the various cleanup projects and meet the requirements set forth in the RODs would take 17 years and cost nearly $2 billion. The environmental remediation at RMA required close cooperation and between the Army, Shell, EPA, the state, Tri-County and various community members and leaders, particularly those who participated regularly in the Regional Advisory Board.

The following is a description of some of the significant cleanup projects that occurred at RMA.


The selected remedy in the On-Post ROD for groundwater included continued operation of the three RMA boundary groundwater containment and treatment systems, the North Boundary Containment System, the Northwest Boundary Containment System and the Irondale Containment System. These systems and the on-post groundwater systems (Basin A Neck, North of Basin F, Motor Pool, and Rail Yard) will continue to operate until shut-off criteria specified in the ROD are met. Other significant components of the On-Post Groundwater remedy included installing a new extraction system in the area of RMA near South Plants and maintaining water levels in the three lakes on site.

Other On-Post groundwater remedies included installing slurry walls around the Complex Army Disposal Trenches and the Lime Basins to create a barrier between the contamination in those areas and the groundwater surrounding them. In addition, the South Tank Farm and Lime Basins Mass Removal Project was a short-term (2006-2010) effort to extract and treat contaminated groundwater from the South Tank Farm Plume and the Lime Basins areas. Attempts to recover LNAPL from groundwater beneath North Plants have been ongoing since it was first identified there in 1993.

The selected remedy in the Off-Post ROD for groundwater included continued operation of the RMA boundary groundwater containment and treatment systems as well as an off-post intercept and treatment system, long-term surface and groundwater monitoring, providing alternative water supplies to south Adams County, and the implementation of institutional controls intended to prevent future use of contaminated groundwater.


Overall, the objective in the On-Post ROD for soils was to eliminate human and wildlife exposure to contaminated soils and chemical agent, prevent migration of contaminants from On-Post soils to Off-Post via windblown dust or other means, and prevent human and wildlife contact with physical hazards such as unexploded ordnance. To contain contaminated soils and debris on-site, two landfills and a number of consolidation areas were created with uniquely protective caps and covers.

View a map of the 2012 Soil Remediation Project Status, June 22, 2012

Basin A Consolidation Area: Work performed to prepare Basin A for on-site waste consolidation included constructing a foundation layer to prevent contact of waste hauling and placement equipment with potential UXO in the basin. The Basin A Consolidation Area was available for waste consolidation in 1998 and operations continued through 2004. Approximately 2.6 million cubic yards of contaminated waste and gradefill material was consolidated in Basin A until it was filled to capacity, closed and covered. Basin A was completed in 2009.

The Hazardous Waste Landfill (HWL) and the Enhanced Hazardous Waste Landfill (ELF): The HWL is a double lined landfill constructed to hold approximately 1.2 million cubic yards of material consisting of soil, buried debris and building debris which presented a potential risk to human health. The enhanced or triple-lined landfill (ELF) was constructed south of the HWL and is comprised of two waste containment cells. Both ELF cells were constructed similar to the double lined cells at the HWL with multiple layers of clay and plastic liners, but with an additional layer for enhancement.

Both the HWL and the ELF were designed to meet state 1,000-year siting criteria. Design elements include a landfill-cell bottom located a minimum of 20 feet above the groundwater, a water storage layer designed with increased thickness to account for erosional soil loss during the 1,000-year period, a rock-amended vegetative soil layer designed to withstand a 1,000-year storm event, and surface waste controls and drainage features designed for the 1,000-year storm event. The HWL began accepting wastes in 1999 and filled to capacity and closed in 2009. The triple-lined ELF began accepting waste in 2006 and filled to capacity and closed in 2008.

Excavation of cover soil for Integrated Cover System
Excavation of cover soil for the construction of the Integrated Cover System, looking northwest
O&M RCRA-equivalent cover, September 2010
Operations and Maintenance RCRA-equivalent cover, September 2010
Basin F cover, September 2010
Basin F cover, September 2010

Integrated Cover System: An Integrated Cover System was applied to the Basin A, Basin F, South Plants Balance of Areas and Central Processing Area, Complex Army Disposal Trenches, Shell Disposal Trenches and Lime Basins, approximately 730 acres total. These covers are referred to as Resource Conservation and Recovery Act (RCRA) -equivalent covers. These RCRA-equivalent covers are designed to ensure that no precipitation migrates through the contaminated waste consolidated below. Specifically, RMA RCRA-equivalent covers are evapotranspiration covers with a capillary barrier, which were demonstrated to allow no greater range of infiltration through the cap than the range of infiltration that would pass through an EPA-approved RCRA cap. Construction materials included soil and crushed concrete stockpiled on the former Stapleton airport property.

South Plants Balance of Areas and Central Processing Area Soil Remediation Project: Contaminated soil and chemical sewers from previous manufacturing, storage and spills of chemicals in the South Plants area were excavated and taken to the Hazardous Waste Landfill and the Basin A consolidation area. The area was recontoured and the project was completed in 2003.

Basin F/Basin F Cover: Basin F was a 93 acre, asphalt-lined evaporation pond constructed in 1956 to store waste byproducts from Arsenal manufacturing operations. In 1988 the liquid waste was drained from Basin F and transferred to three holding tanks and two double-lined ponds. From 1993 to 1995, approximately 11 million gallons of hazardous waste liquid and approximately 800,000 gallons of rinse water from the holding tanks and ponds were incinerated in a submerged quench incinerator on site. The remaining solids in Basin F were consolidated and contained in an approved 15-acre dome-shaped, double lined and covered waste pile, known as the Basin F waste pile. The Basin F waste pile consisted of contaminated soil dredged from and beneath the Basin F disposal basin. In 2006 and 2007, the waste pile was excavated and taken to the Enhanced Triple-Lined Landfill.

Munitions Testing Soil Remediation: This involved locating UXO at RMA and excavating and transporting it off-site for detonation or other demilitarization process This was performed using a geophysical survey to locate UXO and also at sites known to have had activities associated with UXO, the RMA demolition range, Munitions test site, surface burn site, and burial trenches/target characterization and recovery. In addition leftover munitions debris and contaminated soil in the area of UXO was removed and taken to the on-site landfills.

Miscellaneous structures demolition: Altogether, remediation included demolition of 46 above ground and below ground structures, removal of asbestos containing material and miscellaneous debris piles, closure of the Irondale pipeline, backfilling and revegetation.

Today, all ROD-required cleanup for contaminated soils is complete. Certain activities are ongoing, including annual monitoring of land use controls, continual groundwater monitoring and treatment, and landfill cover and wastewater treatment system (LWTS) inspections. The LWTS was designed and constructed to process wastewater associated with the operations of the HWL and ELF. The LWTS effluent meets state standard and discharges to First Creek. First Creek is a tributary to the Upper South Platte River. Monitoring reports are produced quarterly.

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Community Involvement

Community involvement plays an important role in the Superfund process. EPA uses a number of different tools and resources to promote effective, on-going, meaningful community involvement. The goals of the Superfund community involvement program are to:

  • Keep communities affected by sites informed throughout the cleanup process.
  • Provide opportunities for communities to comment and offer their input about site cleanup plans.
  • Facilitate the resolution of community issues tied to a site.

In the 1950s, residents living north and northwest of the site began to be concerned about RMA when crop damage was noticed on nearby farms. The Army began to study the groundwater flowing off the site and detected contamination. In the 1960s, the Army disposed of liquid chemical waste from the Basin F project into a 12,045-foot deep injection well after the Basin F liner began to leak. Some community members and geoscientists believed that the Army's deep injection well might have caused earthquakes in the Denver area. Although this was never proven, the Army stopped using the well in 1966 and sealed it in 1985.

In the mid 1980s, community interest peaked again with the Army's initiation of 14 Interim Remedial Actions (IRAs) for air, soil, water and structures. These response actions focused on immediate cleanup needs while the site was undergoing extensive study.

In the late 1980s, one of the site's 14 IRAs generated strong community interest, concern and involvement. The Basin F IRA involved the transfer of 4 million gallons of Basin F liquid to three 1.3 million gallon holding tanks and approximately 6.5 million gallons to a double-lined holding pond. The project also removed 600,000 cubic yards of sludge, soil, and liner material from in and under Basin F and placed it in the Basin F Wastepile. The project encountered several obstacles including heavy rainfall. The excess rainfall increased the volume of the Basin F liquid and raised the need for a second double-lined holding pond. Once the liquid was drained from the holding basin, the method used to dry the sludge so that it could be placed into the waste pile created strong odors resulting in community concern and frustration. Several public meetings were held. Air purifiers were distributed to affected residents to alleviate odors. Local and federal government agencies studied the odors and determined there were no acute health impacts to residents.

In the early to mid 1990s, RMA had to decide how best to destroy the Basin F liquid waste being stored in holding tanks. After community outreach and input including a series of public meetings and weekend workshops, the Army, Shell and the USFWS along with EPA, CDPHE and the Tri-County Health Department decided to incinerate the liquid waste by means of the submerged quench incinerator. The incinerator began processing the Basin F liquid in 1993.

Community involvement continued throughout the 1990s. Through public meetings, publications, videos, and other communication tools, the community was encouraged to be involved in the decision making process that would ultimately lead to the ROD. The ROD outlines RMA's final environmental cleanup plans. The RMA Restoration Advisory Board (RAB) and Site Specific Advisory Board (SSAB) were comprised of community members and were formed with the purpose of informing and answering community questions about the ROD as well as listening to concerns and receiving input from the community. The Department of Defense recognized the RAB as the official RMA citizen advisory group. The RAB was comprised of community members from the affected neighboring areas, Shell, the Army and regulatory agencies. The final board meeting was held in November 2011.

The ROD also stipulated a Medical Monitoring Advisory Group (MMAG) be formed to evaluate information concerning exposure pathways from the cleanup, to identify and recommend appropriate public health actions and to communicate this information to the community. The state of Colorado formed the MMAG in December 1995 according to the ROD's provision and in response to citizen concerns that public health protections play a key role in RMA's cleanup program. The MMAG, comprised of community members from the affected neighboring areas, Shell, USFWS and regulatory agencies, focused on human health monitoring, environmental monitoring, emergency preparedness, and public involvement and education. The MMAG developed recommendations to monitor for any impact on community health during the environmental cleanup, and ensure information about the cleanup and the program is available to the communities. As part of the MMAG's recommendations, the group called for the creation of a Medical Monitoring Program Citizen Advisory Board (CAB). The CAB served as a communication link to the communities.

In 2000, another surge of public interest occurred with the recovery of 10 sarin- (nerve gas) filled bomblets. The bomblets were recovered in an old scrap yard area located in the central portion of the site. Because of RMA's proximity to neighboring communities and downtown Denver, there was high media and public interest about the bomblets and the disposal option selected. Over the course of several months, experts from the federal and state governments, including high-ranking Army officials, Colorado Governor Bill Owens, Senator Wayne Allard and Representative Diana DeGette, worked together to determine the best destruction method for the bomblets that would be protective of the community, RMA workers and the environment. A variety of community outreach tools were implemented including:

  • Communicating with elected officials and the media (at times, on a daily basis).
  • Distributing door-to-door information bulletins (in English and Spanish)
  • Providing 5,000 flyers to local businesses for distribution.
  • Recording seven automated pre-recorded phone messages with critical updates that reached more than 31,000 neighbors.
  • Providing email updates to nearly 300 residents.
  • Updating RMA's website daily.
  • Hosting five off-site public meetings (with an interpreter available for the Spanish-speaking community) to explain the destruction options and to provide a forum for community input.
  • Establishing a community information hotline for residents to receive more information or to talk to an RMA representative.

The Community Involvement Plan (CIP) was most recently revised in 2007. The revised CIP was based on interviews with more than 50 residents. The CIP contains information on the specific ways to keep the community informed about cleanup actions at RMA.

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EPA places a high priority on land reuse as part of its Superfund response program mission. The agency tries to select cleanup options that encourage and support future use of a site. EPA uses two fundamental methods to facilitate reuse of Superfund sites:

  • Exploring future uses before the cleanup remedy is implemented, an approach that gives the Agency the best chance of designing cleanup remedies to support the likely future use of a site.
  • Working with landowners and communities to remove barriers not considered necessary for the protection of human health or the environment at those sites where remedies are already in place.

One option for reuse is the siting of clean and renewable energy projects on contaminated (or formerly contaminated) lands. As part of this effort, EPA is evaluating the potential for energy projects on these properties and working with landowners and communities to identify ways to remove barriers to such projects.

In October 1992, the U.S. Congress enacted a bill, the Rocky Mountain Arsenal National Wildlife Refuge Act of 1992 (Refuge Act). The bill designated approximately 16,000 acres of RMA as one of the nation's largest urban wildlife refuges. The bill allows the transfer of responsibility from the Army to the USFWS once the cleanup process is complete. To date, EPA has deleted from the NPL more than 15,000 acres of land at the Rocky Mountain Arsenal because all required cleanup activities have been completed. Of that, more than 12,000 acres have been transferred from the Department of Defense to the USFWS to become part of the National Wildlife Refuge System.

Land Deletions from the National Priorities List (Superfund sites)

  • Selected Perimeter and Surface Area Deletion: In 2004, EPA deleted approximately 5,000 acres of Rocky Mountain Arsenal land from the National Priorities List because all required cleanup activities in this area were complete. This land was then transferred from the U.S. Army to the U.S. Fish and Wildlife Service to create the Rocky Mountain Arsenal Wildlife Refuge.
  • Western Tier Parcel Deletion: In 2004, EPA also deleted nearly 1,000 acres of Rocky Mountain Arsenal land from the National Priorities List because all required cleanup activities were complete in this area. This land was then transferred from the U.S. Army to Commerce City to become the Prairie Gateway development.
  • Internal Parcel Deletion: In 2006, EPA deleted more than 7,000 acres of Rocky Mountain Arsenal land from the National Priorities List because all required cleanup activities were complete in this area. This land was then transferred from the U.S. Army to the U.S. Fish and Wildlife Service to augment the Rocky Mountain Arsenal National Wildlife Refuge.
  • Central and Eastern Surface Areas (CES) and Off-Post Operable Units (OPS): In 2010, EPA deleted 2,500 acres of land within the RMA boundary and all of the area just north of the boundary (Off-Post) from the National Priorities List because all required cleanup activities were complete in this area.

On September 30, 2009, EPA determined that the property owned by the Shell Oil Company, north of the Rocky Mountain Arsenal and within the Off Post Operable Unit, was ready for reuse. EPA and the state of Colorado agreed on the Ready for Reuse determination, indicating the surface of the property was ready for reuse for any purpose allowed under local land use and zoning laws. However, groundwater at the property remains restricted. There continues to be a prohibition against construction of alluvial wells as well as use of deeper groundwater until groundwater standards are met. The site also was selected as a Return to Use demonstration project(PDF, 2 pp, 667 K, about PDF) in 2010, in recognition of how EPA’s partnership with the Army, the Colorado Department of Public Health and Environment, the Fish and Wildlife Service, and Shell Oil has led to the creation of nearly 14,700 acres of National Wildlife Refuge land just 10 miles from downtown Denver.

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Land Use Controls and Other Institutional Controls

Land use controls are the most common type of institutional control (IC). ICs are administrative or legal controls that help reduce the likelihood for human exposure to contamination. ICs can also help protect the integrity of the remedy. Examples of ICs are:

  • Zoning ordinances.
  • Environmental covenants.
  • Deed notices.
  • Well-drilling restrictions.
  • Building permits.
  • Informational advisories.

The majority of RMA was designated as a National Wildlife Refuge per the Rocky Mountain Arsenal National Wildlife Refuge Act of 1992 (Refuge Act). As components of the remedy have been completed and the certain portions of RMA land deleted from the NPL (See above section), those lands have been transferred to the U.S. Fish and Wildlife Service to oversee as part of the Refuge. Refuge property must be managed in accordance the FFA, On-Post ROD and Refuge Act. On-Post land restrictions include prohibitions on the construction of basements (without further study), use of water on the site as a source of potable water, hunting and fishing for consumptive use, and residential, industrial and agricultural use. The FFA ICs also require preservation and management of wildlife habitat to protect endangered species, migratory birds and bald eagles.

Off-Post land deleted from the NPL carries institutional controls defined in the Off-Post Rod. That includes a deed restriction on drilling new alluvial wells and using groundwater for potable purposes until such groundwater meets groundwater remediation standards established in the ROD. The primary mechanism for implementing the institutional controls is a well notification program developed in conjunction with the state engineer’s office.

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Five-Year Reviews

EPA or the lead agency conducts five-year reviews following the start of a Superfund cleanup when contamination is left on the site. These reviews are repeated every five years. We use these reviews to determine:

  • How the remedy is working.
  • If the remedy remains protective of human health and the environment.

The third and most recent five-year review report documents a thorough review of the remedy chosen for Rocky Mountain Arsenal from April 2005 through March 2010. Federal law requires that this type of review be conducted every five years to ensure it remains protective of human health and the environment. The report provides background about the site history and contamination; description of the remedial actions taken; progress since the last five year review; criteria for the current assessment; and still unresolved issues with recommendations and follow-up actions. Overall, the 2012 report concluded that the remedy being implemented at the Rocky Mountain Arsenal is expected to be protective of human health and the environment upon remedy completion, and in the interim, exposure pathways that could result in unacceptable risks are being controlled. The report does identify specific issues to be addressed and recommendations and follow up actions. You may view the 2010 five-year review report in the Site Documents section below, or by contacting one of the representatives or visiting one of the information repositories listed in the Contacts section.

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Site Documents

You will need Adobe Reader to view some of the files on this page. See EPA’s About PDF page to learn moreReturn to Use Initiative: 2010 Demonstration Project (PDF), updated December 2011(2 pp, 667 K)

2010 Five-Year Review Report, September 2011

Notice of Deletion, September 13, 2010

Responsiveness Summary to public comments submitted on Notice of Deletion, August 2010

Ready for Reuse Determination for the Shell Property, September 2009

Community Involvement Plan, January 2008

Records of Decision and related Decision Documents

Note: All of the dioxin soils reports can be found in this FTP folder.

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Greg Hargreaves
Remedial Project Manager
U.S. Environmental Protection Agency, Region 8
1595 Wynkoop Street (EPR-F)
Denver, CO 80202-1129
800-227-8917 ext. 312-6661 (toll free Region 8 only)

Cynthia Peterson
Community Involvement Coordinator
U.S. Environmental Protection Agency, Region 8
1595 Wynkoop Street (8OC)
Denver, Colorado 80202-1129
800-227-8917 ext. 312-6879 (toll free Region 8 only)


Susan Newton
State Project Officer
Colorado Department of Public Health and Environment
4300 Cherry Creek Drive South
Denver, CO 80246-1530
888-569-1831 ext. 3321 (toll free)

Warren Smith
State Community Relations Manager
Colorado Department of Public Health and Environment
4300 Cherry Creek Drive South
Denver, CO 80246-1530
888-569-1831 ext. 3373 (toll free)

Site Information Repositories:

Joint Administrative Records and Design Facility
Building 129, 6550 Gateway Road
Commerce City, CO 80022
12 p.m.–4 p.m. weekdays

Colorado Department of Public Health and Environment
HMWMD Records Center
4300 Cherry Creek Drive South
Denver, Colorado 80246-1530
888-569-1831 ext. 3331 (toll free)
303-759-5355 FAX
By appointment only

EPA Superfund Records Center
1595 Wynkoop Street
Denver, CO 80202-1129
To request copies of administrative record documents call:
800-227-8917 ext. 312-7273 (toll free Region 8 only)

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Photo/Video Gallery

Click on a thumbnail below to view the full size image.

Coyote (with prairie dog in its mouth) crossing the equipment parking area for the Integrated Cover System project, looking northwest
Coyote pup frolicking in the former Secondary Basins area of the project, looking northwest
Thousands of migrating Canada geese in a temporary wildlife pond southwest of the former Basin F impoundment
American avocet in Lower Derby Lake
Snowy egret in Lower Derby Lake

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U.S. Army Rocky Mountain Arsenal Website

Rocky Mountain Arsenal site at the Colorado Department of Public Health and Environment Exit

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