Explanation of Significant Differences for Groundwater Remediation and Revegetation Requirements
Introduction This fact sheet summarizes a significant change in a portion of the remedy for groundwater contamination and revegetation requirements at the Rocky Mountain Arsenal (Arsenal) Federal Facility Site. The proposed changes to the groundwater remediation and revegetation requirements are detailed in the “Explanation of Significant Differences for Groundwater Remediation and Revegetation Requirements, Rocky Mountain Arsenal Federal Facility Site,
February 21, 2006
.” The Explanation of Significant Differences (ESD) and related Arsenal design documents are available for public review and comment (see bottom of fact sheet for locations).
These changes, while necessitating an ESD, do not alter the overall hazardous waste management approach that was selected in the Record of Decision (ROD). The ROD is the official document that describes the Arsenal’s 31 cleanup projects.
What are the significant changes to the remediation project?
Groundwater Requirements The ROD groundwater remedy consists primarily of extraction (removal) and treatment of contaminated groundwater through the continued operation of existing boundary and on-site treatment systems. There are additional areas of extraction and treatment of contaminated groundwater at contaminant sources areas. The Army is proposing to perform additional source treatment in targeted areas to further reduce groundwater contamination. Contaminated groundwater will be extracted from the South Tank Farm Plume (STFP) and the South Plants North Plume (SPNP). The groundwater will be treated at the one of the Arsenal’s on-site wastewater treatment plants and once treated, it will be placed back into the groundwater beyond the original contamination.
The ROD groundwater remedy also includes maintaining water levels or other means of groundwater contamination (plume) control to prevent the South Plants plumes from moving into the
at concentrations exceeding Colorado Basic Standards for Groundwater (CBSGs) in groundwater. The ROD included a provision that groundwater monitoring would be used to demonstrate compliance. A study conducted to evaluate the potential for migration of contaminated groundwater plumes into the
led to the conclusion that contaminated groundwater with concentrations above CBSGs was not migrating into the lakes (USGS 2004). Therefore, the Army is proposing to eliminate the requirement for hydraulic containment, including lake-level maintenance, or other means of plume control, to prevent migration of contaminated groundwater into the lakes.
Revegetation Requirements The ROD soil remedy requires that all sites disturbed during the cleanup will have the surface soil reconditioned and be revegetated (reseeded) with native plants and grasses. Cleanup and support areas completed to date have been revegetated with either temporary or permanent vegetation, and/or have been identified for seeding in accordance with a U.S. Fish and Wildlife Service (Service) management plan titled, “RMA National Wildlife Refuge Habitat Restoration Plan” (USFWS 1999) and annual “Vegetation Management Plan” (TtFW 2005, 2004). All revegetated areas were assessed in June 2005 as part of the Arsenal’s Five-Year Review process. In recognition of the unique status of the Arsenal, in which the Refuge Act of 1992 mandated that the majority of the Arsenal be transferred to the Service for use as a National Wildlife Refuge upon completion of the cleanup, the Army is proposing to clarify the site’s revegetation requirement to require cleanup sites located on property that will be transferred to the Service be reconditioned and seeded in a manner acceptable to the Service. Revegetation will still be completed by the Army; however, responsibility for acceptance of revegetation performance and function after seeding will be independently conducted by the Service.
Summary of the ROD Remedy and the ESD Changes
The table below shows the changes being made to the remedy as compared to what was outlined in the initial remedy. All other aspects of the initial remedy will be implemented as detailed in the 1996 ROD.
Boundary Treatment Systems
No Change. Boundary treatment systems continue to operate in accordance with the ROD.
Basin A Neck Containment System
No Change.The BANCS continues to operate in accordance with the ROD.
Install extraction system in the Section 36 Bedrock Ridge area. Treat extracted water at the BANCS.
Source Treatment/Contaminant Reduction
Addition. Installation of contaminant reduction systems for South Tank Farm Plume and South Plants North Plume. The contaminant reduction system will consist of extraction and treatment of contaminated groundwater in both areas and reinjection of treated water to the respective source area. In addition, groundwater monitoring associated with the contaminant reduction systems will be conducted.
Continued operation of the CERCLA Wastewater Treatment Plant to support remediation activities
No Change. The CWTP will be used to treat extracted groundwater for contaminant reduction.
No Change.Groundwater monitoring will be conducted under a long-term groundwater monitoring program to ensure continued compliance with objectives established for contaminant migration and the lack of changed groundwater conditions in the future.
Delete the requirement for hydraulic containment, including lake-level maintenance, or other means of plume control, to prevent migration of contaminated groundwater into the lakes.
Remedy components for all sites include reconditioning the surface soil and revegetating areas disturbed during remediation with locally adapted perennial vegetation.
Clarification. Sites will be reconditioned and seeded in a manner acceptable to the USFWS consistent with the USFWS management plan and annual “Vegetation Management Plan.” For areas disturbed during the remedy, the USFWS will certify, in writing, to the EPA that the site has been revegetated or has a USFWS-approved revegetation plan that is being implemented, and that the USFWS is satisfied that the site's habitat is being or will be restored to achieve the statutory purposes of the Refuge.
Cost The addition of this source groundwater extraction and treatment remedy results in a cost increase compared to the ROD-estimated cost. The baseline estimated cost for implementation of the groundwater remedy is $180 million based on cost estimates presented in the ROD (FWENC 1996). The baseline estimate represents original ROD estimated costs reorganized to reflect implementation project descriptions in the Remediation Design and Implementation Schedule (PMRMA 2004). The estimated design cost for implementation of the additional groundwater extraction and treatment is $ 5.8 million, including capital construction costs and operation costs for the treatment facility. This represents a 3 percent increase from the ROD-estimated cost and is not considered a significant change. Major cost elements for the additional extraction and treatment are installation of extraction/recharge wells, treatment system modifications, additional groundwater monitoring costs and treatment system operational costs.
Site History The Arsenal is located in
, approximately 10 miles northeast of downtown
. The Arsenal now encompasses 11,000 acres and is currently on the U.S. Environmental Protection Agency (EPA) National Priorities List for environmental cleanup as a result of contamination released during previous RMA operations. The On-Post ROD, which describes the site-wide remedy for the Arsenal, was signed by the U.S. Army, EPA and the State of
with concurrence from Shell Oil Company (Shell) and the U.S. Fish and Wildlife Service on
June 11, 1996
. The selected remedy includes 31 different cleanup plans for soils, structures and the treatment of groundwater contaminants.
The Arsenal was established in 1942 by the U.S. Army to manufacture chemical warfare agents and incendiary munitions for use as a deterrent in World War II. Following the war and through the early 1980s, the facilities continued to be used by the U.S. Army. Beginning in 1946, some facilities were leased to private companies to manufacture industrial and agricultural chemicals. Shell, the principal lessee, manufactured pesticides from 1952 to 1982. Common industrial and waste disposal practices used during these years resulted in contamination of structures, soil, surface water, and groundwater.
Currently, the Arsenal is undergoing an extensive environmental cleanup of the site’s soil, structures and groundwater. Once cleanup is complete, the Arsenal’s vast open spaces will constitute one of the nation’s largest, urban wildlife refuges. In April 2004, 5,000 acres of Arsenal land were transferred from the U.S. Army to the U.S. Fish and Wildlife Service marking the official establishment of the Rocky Mountain Arsenal National Wildlife Refuge. In all, 15,000 acres will be transferred to the U.S. Fish and Wildlife Service by the time cleanup is complete in 2011. The site now provides sanctuary for nearly 330 species of animals, including deer, coyotes, bald eagles and white pelicans.
Operable Units The On-Post Operable Unit is one of two operable units at RMA. The On-Post Operable Unit addresses contamination within the boundaries of the Arsenal. The Off-Post Operable Unit addresses contamination north and northwest of the Arsenal.
The overall remedy required by the 1996 Record of Decision (ROD) for the On-Post Operable Unit (OU) includes:
· Interception and treatment of contaminated groundwater at the three existing on-site treatment plants.
· Construction of a new Resource Conservation and Recovery Act and Toxic Substances Control Act-compliant Hazardous Waste Landfill on-post.
· Demolition of structures with no designated future use and disposal of the debris in either the HWL or Basin A, depending upon the degree of contamination.
· The contaminated soil at the Arsenal is addressed primarily through containment in the on-post HWL, under caps/covers, or through treatment, depending upon the type and degree of contamination. Areas that have caps or covers require long-term maintenance and will be retained by the Army. These areas will not be a part of the Rocky Mountain Arsenal National Wildlife Refuge.
· The Basin A disposal area is used for consolidating structural debris from other Arsenal contaminated areas and soil that poses a risk to wildlife, known as biota soil. Once all of the waste is received, a wildlife barrier and soil cover will be placed over Basin A.
Site Contamination The contaminated areas within the On-Post Operable Unit include approximately 3,000 acres of soil, 15 groundwater plumes and 798 structures. The most highly contaminated sites were identified in South Plants (i.e., Central Processing Area, Hex Pit, Buried M-1 Pits, Chemical Sewers), Basins A and F, the Lime Basins, and the U.S. Army and Shell Trenches. The primary contaminants found in the soil and/or groundwater at these areas is pesticides, solvents, heavy metals and chemical agent by-products. Most of these contaminated areas have been cleaned up or are in the process of being cleaned up.
The areas showing the highest concentrations and/or the greatest variety of contaminants are located in the central manufacturing, transport and waste disposal areas. The highest contaminant concentrations tend to occur in soil within about five feet of the ground surface, though the higher contamination is also found at greater depths particularly where burial trenches, disposal basins or manufacturing complexes are located.
Groundwater contaminant plumes predominantly consist of organic compounds, arsenic, fluoride and chloride. The overall concentrations and configurations of the plumes suggest that the greatest contaminant releases to the unconfined flow system have occurred from Basin A, the Lime Settling Basins, the South Plants Chemical Sewers, the South Plants Tank Farm and Production Area, the U.S. Army and Shell Trenches in Section 36, and the former Basin F. Plumes flowing from the Motor Pool, Rail Yard and North Plants areas are other sources of contaminant releases to the unconfined flow system.
Public Participation A public notice was published beginning on February 24, 2006 in the Denver Post, Rocky Mountain News, Brighton Blade, Commerce City Beacon and Commerce City Gateway newspapers announcing the document’s public comment period, how to provide comments and where the document is available for review. Comments should be directed to Ms. Peggy Machamer, Rocky Mountain Arsenal, Building 111,
. Comments can also be e-mailed to email@example.com or faxed to 303-289-0582.
A presentation explaining the ESD will be provided to the Arsenal’s Restoration Advisory Board (RAB) on
March 30, 2006
. The meeting is open to the public. The RAB is a community group that meets regularly to receive information and provide input on the cleanup. The public comment period will close on
March 24, 2006
. Upon completion of the comment period, the Army, in consultation with the EPA and the State of
, will evaluate each comment and any significant new data received before issuing a final report documenting the groundwater remediation and revegetation requirements.
This ESD and all documents that support the changes and clarifications are part of the Administrative Record and are available at the Joint Administrative Records and Document Facility (JARDF) and the EPA Region 8 Superfund Records Center. The JARDF can be reached at 303-289-0362. Hours of operation are Monday through Friday
or by appointment. EPA’s
can be reached at 303-312-6473. Hours of operation are Monday through Friday from
Affirmation of Statutory Determinations Considering the new information presented in this ESD, the Army, in consultation with EPA and CDPHE, believes that the groundwater remedy and the soil remedy, with the modifications described, satisfy the requirements of CERCLA Section 121 and are protective of public health and the environment, comply with federal and state requirements that are legally applicable or relevant and appropriate to the remedial action, use a permanent solution through extraction and treatment of contaminated groundwater, and are cost effective.
For more information, please contact:
•Remediation Venture Public Relations Office
Rocky Mountain Arsenal Building 111
Rocky Mountain Arsenal Web site and Community Information Line www.rma.army.mil / 303-289-0136
Environmental Protection Agency
Remedial Project Manager
•Colorado Department of Public Health & Environment
State Project Officer
•Joint Administrative Record and Document Facility (JARDF)
Rocky Mountain Arsenal, Building 129
or by appointment (303) 289-0362
999 18th Street