2010-14524. National Oil and Hazardous Substances Pollution Contingency Plan; National Priorities List: Partial Deletion of the Rocky Mountain Arsenal Federal Facility

AGENCY:

Environmental Protection Agency.

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) Region 8 is issuing a Notice of Intent to Delete portions of the On-Post Operable Unit (OU3), specifically the Central and Eastern Surface Areas including surface media and structures (CES), and the surface media of the entire Off-Post Operable Unit (OU4) (OPS) of the Rocky Mountain Arsenal Federal Facility (RMA) from the National Priorities List (NPL) and requests public comment on this proposed action. The NPL, promulgated pursuant to section 105 of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980, as amended, is an appendix of the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). The EPA and the State of Colorado, through the Colorado Department of Public Health and Environment (CDPHE), have determined that all appropriate response actions at these identified parcels under CERCLA, other than operation, maintenance, and five-year reviews, have been completed. However this deletion does not preclude future actions under Superfund.

This partial deletion pertains to the surface media (soil, surface water, sediment) and structures (both former structures that have been demolished and structures retained for future use) within the CES and the surface media of the entire OPS. The rest of the On-Post OU (Figure 1), including groundwater below RMA that is west of E Street, and the groundwater that comprises the Off-Post OU (see Section IV and Figure 1) will remain on the NPL and response activities will continue at those OUs. The groundwater media east of E Street (with the exception of a small area below the northwest corner of Section 6) was previously deleted from the NPL as part of the Internal Parcel Partial Deletion in 2006 (71 FR 43071).

DATES:

Comments must be received by July 19, 2010.

ADDRESSES:

Submit your comments, identified by Docket ID No. EPA-HQ-SFUND-1987-0002, by one of the following methods:

• http://www.regulations.gov: Follow the on-line instructions for submitting comments.
• E-mail: [e-mail].
• Fax: [phone].
• Mail: Ms. Jennifer Chergo, Community Involvement Coordinator (8OC), U.S. EPA, Region 8, 1595 Wynkoop Street, Denver, Colorado, 80202-1129.
• Hand Delivery: 1595 Wynkoop Street, Denver, Colorado, 80202-1129. Such deliveries are only accepted during the Docket's normal hours of operation, and special arrangements should be made for deliveries of boxed information.

Instructions: Direct your comments to Docket ID No. EPA-HQ-SFUND-1987-0002. EPA's policy is that all comments received will be included in the public docket without change and may be made available online at http://www.regulations.gov,, including any personal information provided, unless the comment includes information claimed to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through http://www.regulations.gov or e-mail. The http://www.regulations.gov Web site is an “anonymous access” system, which means EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an e-mail comment directly to EPA without going through http://www.regulations.gov,, your e-mail address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the Internet. If you submit an electronic comment, EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD-ROM you submit. If EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, EPA may not be able to consider your comment. Electronic files should avoid the use of special characters, any form of encryption, and be free of any defects or viruses.

Docket: All documents in the docket are listed in the http://www.regulations.gov index. Although listed in the index, some information is not publicly available, e.g., CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, will be publicly available only in hard copy. Publicly available docket materials are available either electronically in http://www.regulations.gov or in hard copy at:

—EPA's Region 8 Superfund Records Center, 1595 Wynkoop Street, Denver, Colorado, 80202-2466. Hours: 8 a.m. to 4 p.m. by appointment (call 303-312-6473), Monday through Friday, excluding legal holidays; and the

—Joint Administrative Records Document Facility, Rocky Mountain Arsenal, 5650 Havana Street, Building 129, Commerce City, Colorado 80022-1748. Hours: 12 p.m. to 4 p.m., Monday through Friday, excluding legal holidays, or by appointment (call 303-289-0983).

FOR FURTHER INFORMATION CONTACT:

Ms. Jennifer Chergo, Community Involvement Coordinator (8OC), U.S. Environmental Protection Agency, Region 8, 1595 Wynkoop Street, Denver, Colorado, 80202-1129; telephone number: 1-800-227-8917 or 303-312-6601; fax number: 303-312-7110; e-mail address: [e-mail].

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Introduction

II. NPL Deletion Criteria

III. Deletion Procedures

IV. Basis for Intended Partial Site Deletion

I. Introduction

The Environmental Protection Agency (EPA) Region 8 announces its intent to delete the CES and OPS of the RMA Site, Commerce City, Colorado, from the NPL and requests comment on this proposed action. The NPL constitutes Appendix B of 40 CFR part 300 which is the Oil and Hazardous Substances Pollution Contingency Plan (NCP), which EPA promulgated pursuant to section 105 of the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) of 1980, as amended. EPA maintains the NPL as those sites that appear to present a significant risk to public health, welfare, or the environment. Sites on the NPL may be the subject of remedial actions financed by the Hazardous Substance Superfund (Fund). This partial deletion of the RMA Site is proposed in accordance with 40 CFR 300.425(e) and Notice of Policy Change: Partial Deletion of Sites Listed on the National Priorities List (60 FR 55466 (Nov. 1, 1995)). As described in 40 CFR 300.425(e)(3), a portion of a site deleted from the NPL remains eligible for further remedial actions if warranted by future conditions.

EPA will accept comments on the proposal to partially delete this site for thirty (30) days after publication of this document in the Federal Register.

Section II of this document explains the criteria for deleting sites from the NPL. Section III discusses procedures that EPA is using for this action. Section IV discusses the CES and OPS of the RMA Site and demonstrates how they meet the deletion criteria.

II. NPL Deletion Criteria

The NCP establishes the criteria that EPA uses to delete sites from the NPL. In accordance with 40 CFR 300.425(e), sites may be deleted from the NPL where no further response is appropriate. In making such a determination pursuant to 40 CFR 300.425(e), EPA will consider, in consultation with the State, whether any of the following criteria have been met:

i. Responsible parties or other persons have implemented all appropriate response actions required;

ii. All appropriate Fund-financed response under CERCLA has been implemented, and no further response action by responsible parties is appropriate; or

iii. The remedial investigation has shown that the release poses no significant threat to public health or the environment and, therefore, taking of remedial measures is not appropriate.

Pursuant to CERCLA section 121(c) and the NCP, EPA conducts five-year reviews to ensure the continued protectiveness of remedial actions where hazardous substances, pollutants, or contaminants remain at a site above levels that allow for unlimited use and unrestricted exposure. EPA conducts such five-year reviews even if a site is deleted from the NPL. EPA may initiate further action to ensure continued protectiveness at a deleted site if new information becomes available that indicates it is appropriate. Whenever there is a significant release from a site deleted from the NPL, the deleted site may be restored to the NPL without application of the hazard ranking system.

III. Deletion Procedures

The following procedures apply to the deletion of the CES and OPS of the RMA Site:

(1) EPA consulted with the State before developing this Notice of Intent for Partial Deletion.

(2) EPA has provided the State 30 working days for review of this notice prior to publication of it today.

(3) In accordance with the criteria discussed above, EPA has determined that no further response is appropriate.

(4) The State of Colorado, through the CDPHE, has concurred with the deletion of the CES and OPS of the RMA Federal Facility Site, from the NPL.

(5) Concurrently, with the publication of this Notice of Intent for Partial Deletion in the Federal Register, a notice is being published in a major local newspaper, the Denver Post. The newspaper announces the 30-day public comment period concerning the Notice of Intent for Partial Deletion of the Site from the NPL.

(6) The EPA placed copies of documents supporting the proposed partial deletion in the deletion docket and made these items available for public inspection and copying at the Site information repositories identified above.

If comments are received within the 30-day comment period on this document, EPA will evaluate and respond accordingly to the comments before making a final decision to delete the CES and OPS. If necessary, EPA will prepare a Responsiveness Summary to address any significant public comments received. After the public comment period, if EPA determines it is still appropriate to delete the CES and OPS of the RMA Site, the Regional Administrator will publish a final Notice of Partial Deletion in the Federal Register. Public notices, public submissions and copies of the Responsiveness Summary, if prepared, will be made available to interested parties and included in the site information repositories listed above.

Deletion of a portion of a site from the NPL does not itself create, alter, or revoke any individual's rights or obligations. Deletion of a portion of a site from the NPL does not in any way alter EPA's right to take enforcement actions, as appropriate. The NPL is designed primarily for informational purposes and to assist EPA management. Section 300.425(e)(3) of the NCP states that the deletion of a site from the NPL does not preclude eligibility for future response actions, should future conditions warrant such actions.

IV. Basis for Intended Partial Deletion

The following information provides EPA's rationale for deleting the CES and OPS of the RMA Federal Facility from the NPL.

Site Background and History

The Rocky Mountain Arsenal Federal Facility (RMA), EPA ID No. CO5210020769, is located in Commerce City—approximately eight miles northeast of downtown Denver—in Adams County, Colorado. RMA was established in 1942 by the U.S. Army 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 U.S. Army. Beginning in 1946, some facilities were leased to private companies to manufacture industrial and agricultural chemicals. Shell Oil Company, the principal lessee, manufactured pesticides at the site from 1952 to 1982. Common industrial and waste disposal practices resulted in contamination of structures, soil, surface water, and groundwater. As a result of this contamination, RMA was proposed to the NPL, excluding the Basin F surface impoundment, on October 15, 1984, (49 FR 40320). On July 22, 1987, RMA was finalized on the NPL and expanded to include Basin F (52 FR 27620 and 52 FR 27643).

RMA is located at the western edge of the Colorado Plains, consisting of a rolling terrain characterized by grasslands, shrublands, wetlands, aquatic habitats, and extensive weedy areas. Regional surface drainage is northwest into the South Platte River which eventually joins the North Platte River in Nebraska. The RMA Site consists of 30 OUs (numbers 0 through 29) including 24 Interim Response Actions (IRA) conducted between October 1985 and June 1996 as part of the On-Post (OU 3) remediation and 4 IRAs completed in 1993 for remediation of the Off-Post (OU 4). The IRAs were conducted to prevent or minimize further migration of groundwater contaminants and eliminate potential releases from source areas through isolation or destruction of the contaminants. Each of the OUs is described below.

OU 00: South Adams County—Installation of temporary granular activated carbon filters (GAC) at the South Adams County plant to address trichloroethene in the potable water supply (1986).

OU 01: Klein Water Treatment Plant—Groundwater treatment plant constructed on RMA property (Section 33) to treat off-post contaminant plumes along the western boundary of RMA (1989).

OU 02: Chemical Sales—Remedial investigation of off-post groundwater plumes which resulted in identification of the Chemical Sales Company Superfund Site located upgradient (south) of RMA (1990).

OU 03: On-Post—Addresses soil and groundwater contamination within the fenced 27 square miles of RMA proper (ongoing). OUs 6 through 29 contributed to remediation of the On-Post OU and were completed prior to or integrated into the On-Post OU as part of the 1996 On-Post ROD.

OU 04: Off-Post—Addresses contamination north and northwest of the RMA proper site. OUs 00 through 02 and OU 5 contributed to remediation of the Off-Post OU and were completed prior to or integrated into the Off-Post OU as part of the 1995 ROD.

OU 05: Off-Post Groundwater Intercept and Treatment System IRA—Treatment plant constructed to address contaminant plumes that had migrated off post prior to installation of the boundary treatment systems (1993).

OU 06: North Boundary Groundwater Treatment System IRA—Recharge trenches were added along the entire length of the North Boundary Treatment System slurry wall and operational improvements were made to the existing system (1993).

OU 07: Basin F Groundwater Treatment System IRA—Extraction of contaminated groundwater migrating from the Basin F area for treatment at the Basin A Neck Treatment System (1990).

OU 08: Abandoned Well Closure IRA—Old or deteriorating farm wells and unused on-post wells were grouted closed (1990).

OU 09: Basin A Neck Groundwater Treatment System IRA—Groundwater treatment plant constructed to treat contaminant plumes migrating through paleochannels from the Basin A area (1990).

OU 10: Basin F Liquids & Sludges IRA—Containment of 600,000 cubic yards of Basin F sludges/soil in a lined, 16-acre storage area with a leachate collection system (1989).

OU 11: Building 1727 Sump IRA—Treatment of liquid in the Building 1727 Sump with activated alumina and GAC to remove contaminants (1989).

OU 12: Hydrazine IRA—The hydrazine facility was demolished and the debris disposed at an off-site hazardous waste landfill. The area was regraded and revegetated (1992).

OU 13: Fugitive Dust Suppression IRA—Reapplication of a dust suppressant was applied to Basin A (1991).

OU 14: Sanitary Sewer IRA—Sanitary sewer manholes were plugged to eliminate potential transport of contaminated groundwater that may have entered the sewer system through cracks or loose connections (1992).

OU 15: Asbestos IRA—Continuation of the Army's survey and removal of friable asbestos from on-post structures (1996).

OU 16: M-1 Settling Basins IRA—The objective was to treat the M-1 Settling Basins sludge using in situ vitrification (ISV). However, due to technology complications with the ISV, implementation of the IRA was suspended (1991).

OU 17: CERCLA Wastewater Treatment Plant IRA—Facility constructed to treat wastewater generated by investigative activities and implementation of response actions (1992).

OU 18: Motorpool IRA—An extraction well system was constructed to remove a trichlorethene plume emanating from the Motorpool area for treatment at the Irondale Containment System (1990). A soil vapor extraction system was operated in 1991 to remove volatile contaminants from the soil.

OU 19: Rail Classification Yard IRA—An extraction well system was constructed to remove a dibromochloropropane plume emanating from the Rail Yard area for treatment at the Irondale Containment System (1991).

OU 20: Lime Settling Basins IRA—A soil cover was constructed over the Lime Settling Basins to minimize infiltration of precipitation through the basin waste (1993).

OU 21: South Tank Farm Plume IRA—Continued monitoring of groundwater plumes to assess if additional action was necessary (1994).

OU 22: Army Trenches IRA—Continued monitoring of groundwater plumes to assess if additional action was necessary (1994).

OU 23: Shell Trenches IRA—A slurry wall was constructed to isolate the trenches from surrounding groundwater and a soil cover placed over the trenches to minimize infiltration of precipitation through the trench waste (1994).

OU 24: Northwest Boundary Containment System IRA—Additional extraction, reinjection, and monitoring wells were installed to increase treatment capacity (1993).

OU 25: Basin F Liquid (SQI) IRA—Incineration of 11 million gallons of basin liquids and decontamination waters (1995).

OU 26: Chemical Process-Related Activities IRA—Decontamination and disposal of process related equipment and piping for both agent and non-agent manufacturing processes in the North Plants and South Plant facilities (1996).

OU 27: Underground Storage Tank IRA—Content characterization, deactivation, excavation, decontamination, and removal of underground storage tanks (1995).

OU 28: Waste Management IRA—Temporary management of hazardous waste in storage at RMA or generated by the response actions, and not addressed by another IRA (1996).

OU 29: Polychlorinated Biphenyls (PCB) IRA—Inventory and remediate PCB-contaminated structures and soil (1996).

The original On-Post Operable Unit (OU 3) encompassed 27 square miles (16,990 acres) and was bounded by 56th Avenue and the former Stapleton International Airport on the south, Buckley Road and Denver International Airport on the east, Quebec Parkway and Commerce City on the west, Colorado Highway 2 and the Off-Post OU on the northwest, and 96th Avenue and the Off-Post OU on the north (Figure 1). In the 1980s, it was observed that over 300 species of wildlife, including bald eagles, utilize much of the natural environment that remains at RMA. In recognition of these unique urban wildlife resources at RMA, President George H.W. Bush signed the 1992 Rocky Mountain Arsenal National Wildlife Refuge Act (Public Law 102-402). Most of the RMA On-Post OU, including the CES, is designated to become part of a National Wildlife Refuge upon completion of the site-wide remedy.

Between 2003 and 2006, EPA conducted four partial deletions from the On-Post OU consisting of 13,406 acres of surface media so that property transfer could be expedited. Of the property deleted to date, 917 acres were sold to Commerce City for commercial development, 12 acres were transferred to South Adams County Water and Sanitation District for the Klein Treatment Facility, 126 acres were transferred to local governments for road-widening, and 12,188 acres have been transferred to the National Wildlife Refuge. Another 163 acres were retained by the Army, primarily for water treatment systems. While EPA has not conducted any partial deletions for the Off-Post OU, EPA did issue a Ready for Reuse (RfR) Determination in September 2009 for a portion of the Shell Oil Company property (approximately 294 acres) that is within or adjacent to the Off-Post OU. EPA's determination indicated that the Shell RfR Property “is ready for use for any purpose allowed under local land use and zoning laws.” While there has been no redevelopment/reuse of the Shell RfR Property thus far, the area around the Shell RfR Property and Off-Post OU has undergone primarily residential development in recent years.

The proposed partial deletion for the OPS includes the entire surface media of the Off-Post OU (OU 4) without exclusions. Of the 3,584 acres (5.6 square miles) of the On-Post OU (OU 3) that remain on the NPL, the proposed partial deletion for the CES includes 2,500 acres (3.9 square miles) of surface media (soil, surface water, and sediment), as shown in Figure 1, and structures (both former structures that have been demolished and structures retained for future use) within the On-Post OU. The entire CES proposed for partial deletion will be transferred from the Army to the U.S. Fish and Wildlife Service (USFWS) for expansion of the RMA National Wildlife Refuge. The portions of the On-Post OU not proposed for deletion, also shown in Figure 1, include the following:

• Cover areas (Hazardous Waste Landfill (HWL), Enhanced Hazardous Waste Landfill (ELF), Basin F, and Integrated Cover System (ICS)) including drainages;
• Three areas of groundwater treatment (Railyard Extraction and Treatment System, Lime Basins Mass Removal System, and the South Tank Farm Mass Removal System);
• Three laydown areas (areas used to stage equipment and construction materials or conduct support activities during remedy implementation); and
• Two structures: The CERCLA Wastewater Treatment Facility and the Landfill Wastewater Treatment System (LWTS).

The following information provides EPA's rationale for deletion of the CES and OPS of the RMA Site from the NPL:

Remedial Investigation/Feasibility Study (RI/FS) and Selected Remedy

On-Post OU (OU 3). Prior to the selection of remedial alternatives for the On-Post OU, an RI/FS was conducted to provide information on the type and extent of contamination, human and ecological risks, and feasibility of remedial actions suitable for application at RMA. The RI, completed in January 1992, studied five environmental media at the RMA Site, including soils, water, structures, air, and biota. The RI identified approximately 3,000 acres of contaminated soil, 15 groundwater plumes, and 798 structures. The FS was finalized in October 1995 for the On-Post OU.

On June 11, 1996, the Army, EPA, and the State of Colorado signed the “Record of Decision for the On-Post Operable Unit” (On-Post ROD). The On-Post ROD formally established the cleanup approach to be taken and specified individual remedial actions to be implemented for soil, structures, and groundwater. In general, the remedial action objectives were to prevent or limit potential exposure of humans and biota and any further contamination of the surface water, groundwater, or air due to releases from the soils, sediments, and structures at the On-Post OU. The overall remedy for the On-Post OU includes extraction and treatment of the contaminated groundwater plumes, demolition of 750 structures with no designated future use, excavation and disposal of soil and demolition debris with a cumulative contamination concentration presenting an excess cancer risk to human health of greater than 1x10⁻⁴ or a Hazard Index greater than 1.0 for non-cancer risks (collectively referred to as human health exceedance (HHE) soils), as well as munitions debris, in two state-of-the-art hazardous waste landfills to be built within the On-Post OU; and excavation and consolidation of debris and soil presenting a risk to biota (biota soil) in the Basin A, South Plants, and Basin F project areas. The excavated HHE soil areas were backfilled with on-post borrow material and revegetated. The On-Post ROD also requires continued use restrictions for the CES that restrict “current and future land use, specifies that the U.S. government shall retain ownership of RMA, and prohibits certain activities such as agriculture, use of on-post groundwater as a drinking source, and consumption of fish and game taken at RMA.”

Multiple changes to the On-Post ROD have been made during implementation of the remedy over the past 14 years through Explanations of Significant Differences (ESD) and two ROD Amendments. With regard to the CES, there are 13 ESDs which document changes in the project boundaries, volumes of soil excavated, and associated costs for each of the implementation projects. These changes have included significant increases in excavated HHE soils at the Section 35 Soil project and excavated biota soils at the Munitions (Testing) Soil project. Of note, any contaminated soils to be contained under soil covers at the North Plants, Secondary Basins, and South Plants Balance of Areas projects were excavated based on additional sampling efforts and the 1- and 2-foot soil cover requirements were eliminated. These boundary, volume, and cover changes have resulted in an estimated increase of $123.5 million for the combined individual projects while the overall On-Post RMA remedy cost has remained unchanged at $2.2 billion.

Off-Post OU (OU 4). The Off-Post OU followed the same investigative process and an RI for the Off-Post study area that evaluated groundwater, soil, surface water, sediment, air and biota was completed in 1988 with an addendum issued in 1992. The RI identified two plume groups encompassing 590 acres in the Off-Post area and wind-deposited contamination in surface soils immediately north of the On-Post boundary in the southeast portion of Section 14 and the southwest portion of Section 13. The Off-Post Endangerment Assessment/Feasibility Study (EA/FS) was issued in 1992 and the Off-Post ROD was signed by the Army, EPA, and the State of Colorado on December 19, 1995. The Off-Post remedy includes extraction and treatment of the contaminated groundwater plumes, and closure of poorly constructed wells that could be acting as migration pathways. For settlement purposes, though the health risks present in the soils were within EPA's acceptable cancer risk range (less than 1 x 10⁻⁴) for residential use, Shell agreed to revegetate approximately 160 acres of soil to enhance the degradation of low-level pesticide residues. The Off-Post ROD also required institutional controls to prevent the use of groundwater exceeding remediation goals. There have been no remedy modifications related to the OPS.

Post-RODs Investigations

On-Post OU (OU 3). Since the signing of the On-Post ROD on June 11, 1996, three main studies have been conducted that are relevant to the deletion of the On-Post CES. These include the “Summary and Evaluation of Potential Ordnance/Explosives and Recovered Chemical Warfare Materiel Hazards at the Rocky Mountain Arsenal” completed in 2002 (Summary Team), the “EPA Denver Front Range Dioxin Study” completed in 2001, and a two-part Residual Ecological Risk (RER) Assessment that was completed in 2003. Each of these on-post investigations is described below:

Summary and Evaluation of Potential Ordnance/Explosives and Recovered Chemical Warfare Materiel Hazards at the Rocky Mountain Arsenal (2002). This effort was conducted in response to the unexpected discovery of ten M139 bomblets as part of the Miscellaneous Structures Demolition and Removal Project—Phase I in the Section 36 Boneyard (central portion of the RMA Site). Using state-of-the-art computer imaging, mapping technology, and software capability which had not existed previously, a comprehensive RMA-wide evaluation for the potential presence of ordnance and explosives as well as recovered chemical warfare materiel hazards was completed. The evaluation identified six additional areas for remedial action, all in the CES, and concluded that the future discovery of additional sites with ordnance/explosives or recovered chemical warfare materiel hazards is highly unlikely. Remediation of four of the Summary Team sites (BT29-1, BT29-2, BT30-01, and BT32-11) was completed in 2004 and is documented in the Construction Completion Report (CCR) for the Burial Trenches Soil Remediation Project, Part II. Remediation of the fifth Summary Team site (ESA-4a) was completed in 2008 and is documented in the CCR for the Munitions (Testing) Soil Remediation Project, Part II. Remediation of the sixth Summary Team site (CSA-2c) was completed in 2008 and is documented in the Munitions (Testing) Soil Remediation Project, Part III.

Dioxin Study. In 2001, EPA conducted a four-part Denver Front Range Dioxin Study which determined that the concentration of dioxins at most of the RMA Site, including the CES, was not statistically different from values observed in open space and agricultural areas within the Denver Front Range area. Therefore, there is no significant health risk from dioxin in soils to future Refuge workers, volunteers, or visitors.

RER Assessment. As required by the ROD, a RER assessment was completed in 2003 addressing both terrestrial and aquatic health risks. The Terrestrial Residual Ecological Risk Assessment was completed in 2002. This report concluded that no significant excess terrestrial residual risks will remain after the ROD-required cleanup actions for soil, including additional areas of excavation and tilling identified as part of remedial design refinement as required by the ROD, are completed. The Aquatic Residual Risk Assessment was completed in 2003. The Assessment presented an evaluation of risks to the great blue heron, shorebirds and waterbirds and concluded that there are no significant risks to aquatic birds in the South Lakes beyond those already identified for remediation in the ROD.

Off-Post OU (OU 4) Indoor Air Evaluation. Since the signing of the Off-Post ROD in 1995, one study has been conducted for the Off-Post OU. Based on EPA guidance issued in 2002 and 2003, EPA conducted an indoor air evaluation of volatile organic compounds for the entire Off-Post OU using the Johnson and Ettinger Model (GW-SCREEN) as implemented by EPA. Estimated indoor air concentrations and potential cancer and non-cancer risks were calculated for theoretical inhalation exposure to vapors emanating from groundwater at a depth that varies from less than 5 feet to 27.5 feet. Where the depth to groundwater was less than 11 feet, slab on grade foundations were assumed; otherwise, the future residential scenario assumed the residences would be constructed with basements. The result of the assessment indicated that modeled concentrations were below human health risk criteria, that no further evaluation of the vapor intrusion pathway was warranted, and that there was no need to implement intrusion controls in buildings overlying the groundwater plumes in the Off-Post OU.

Response Actions

Remedial Action for the CES of the On-Post (OU 3)

Surface media: The surface media of the CES consists of soil, sediment, and surface water within approximately 3.9 square miles (2,500 acres) in the central and eastern portions of the RMA On-Post OU. Areas with similar contamination were combined into individual projects based upon evidence gathered during the RI. This resulted in 18 separate soil/sediment cleanup projects within the CES including portions of Sections 1, 2, 3, 4, 6, 10, 19, 20, 23, 24, 25, 26, 29, 30, 31, 32, 34, 35, and 36. Completion of these 18 remediation projects is documented in individual project CCRs. The following is a brief summary of these projects and the soil contamination that was remediated within the CES.

• The Basin F/Basin F Exterior Soil Remediation Project included the excavation of soil from three pesticide-contaminated sites within Section 26 of the CES (NCSA-4a, 4b, and 5c). HHE soil was excavated from all three sites and disposed in the HWL. Biota risk soil was excavated from two of these sites (NCSA-4a and NCSA-4b) and consolidated in Basins A and F. This work, completed in 2008, is documented in two CCRs: Basin F/Basin F Exterior Remediation Project—Part 1 and Basin F/Basin F Exterior Remediation Project—Part 1, Phase 2.
• The Burial Trenches Soil Remediation Project included the excavation of soil from six chromium- and lead-contaminated soil sites within Sections 29, 30, 31, and 32 of the CES (BT29-1, BT29-2, BT30-1, BT32-10, BT32-11, ESA-2c). All six sites contained ordnance and explosives, munitions debris and related soil, as well as asbestos-containing material, general construction-related debris and trash that was excavated and disposed in the HWL. This work, completed in 2004, is documented in the CCRs for the Burial Trenches Soil Remediation Project—Part I and Part II.
• A portion of the Complex (Army) Disposal Trenches Subgrade Construction Project is located within Section 36 of the CES. This project consisted of surface grading to provide permanent stormwater drainage off of the adjacent RCRA-Equivalent Cover. No contaminated soils were identified in Section 36 for excavation as part of the Complex Trenches Subgrade Project. The grading, completed in 2008, is documented in the CCR for the Complex (Army) Disposal Trenches Remediation Project, Subgrade Construction.
• The Corrective Action Management Unit (CAMU) Soil Remediation Project included the excavation of soil from one site (site “CAMU”) within Sections 23, 24, 25, and 26 in the CES. This site consisted of pesticide-contaminated, biota risk soils and miscellaneous debris that was excavated and consolidated in Basin A. This work, completed in 2000, is documented in CCRs for the CAMU Soils Remediation Project, and the CAMU Soils Remediation Completion and Support Project.
• The Existing (Sanitary) Landfills (ESL) Remediation Project included the excavation of contaminated soil from four sites within the CES: one site in Section 1 (P1 soil site adjacent to SSA-4) and three sites in Section 36 (CSA-1d, CSA-2d, and P1 soil site adjacent to CSA-1d). As documented in the CCR for the Section 1 Existing (Sanitary) Landfills Remediation Project, completed in 2006, biota risk soil was excavated from the P1 soil site adjacent to SSA-4 and consolidated in Basin A. As documented in the CCR for the Section 36 ESL Project, completed in 2004, HHE soil, biota risk soil, and trash and debris were excavated from site CSA-1d and disposed in the HWL; munitions debris was excavated from site CSA-2d and disposed in the HWL; and additional biota risk soil was excavated from the P1 soil site adjacent to CSA-1d and consolidated in Basin A.
• The Miscellaneous Northern Tier Soil Remediation Project included the excavation of one site in Section 25 of the CES (NPSA-4) that contained HHE soil contaminated with chloroacetic acid. As documented in the CCR for the Miscellaneous Northern Tier Soil Remediation Project, completed in 2006, HHE soil was excavated and disposed in the HWL and biota risk soil was excavated and consolidated in Basin A.
• The Miscellaneous RMA Structures Demolition and Removal Project included the excavation of two sites in Section 25 of the CES (BA9A Parcel 3 and 25CC-3). As documented in the CCR for the Miscellaneous RMA Structures Demolition and Removal Project—Phase III, completed in 2009, ACM-contaminated soil, trash, debris, and munitions debris was excavated from the two sites and disposed in the Enhanced Hazardous Waste Landfill (ELF). Some of the ACM-contaminated soil was also disposed off-site at a permitted, CERCLA off-site rule approved landfill.
• The Miscellaneous Southern Tier Soil Remediation Project included excavation of three sites within the CES (SSA-2a, SSA-2b, and a P1 soil site adjacent to SSA-2a) where former process water and wastewater ditches in Sections 1 and 2 contained HHE and biota risk soils contaminated with aldrin, dieldrin, and heavy metals. This work, completed in 2006, is documented in the CCR for the Miscellaneous Southern Tier Soil Remediation Project. A subsequent project, the Sand Creek Lateral Project, involved excavation of additional contaminated soil from two of the Miscellaneous Southern Tier Soil Remediation sites including site SSA-2b located in Section 1 and site SSA-2a located in Section 2. As documented in the CCR for the Sand Creek Lateral Project, completed in 2008, additional HHE soil was excavated from these two sites and disposed in the HWL and ELF, and biota risk soil was excavated and consolidated in Basin A.
• The Munitions (Testing) Soil Remediation Project included 11 sites within Sections 19, 20, 25, 29, 30, 31, and 32 of the CES (BT32-10, CSA-2c, ESA-1b, ESA-1c, ESA-1d, ESA-4a, ESA-4b, MT29-1, MT-DREZ, BA 9A Parcel 2, and BA10 Burn Area). As documented in the CCRs for the Munitions (Testing) Soil Remediation Project, Parts I, II, III, and IV, completed in 2009, munitions debris and related soil, asbestos-containing material, mercury-contaminated biota risk soil, and miscellaneous debris were excavated from all these sites and disposed in the HWL and the ELF. Biota risk soil and miscellaneous debris was excavated and consolidated in Basin A.
• The North Plants Structures Demolition and Removal Project included seven soil remediation sites in Section 25 of the CES (NPSA-1, NPSA-3, NPSA-5, NPSA-6, NPSA-8c, NPSA-9f, and a P1 soil site associated with NPSA-1). HHE soil, biota risk soil, a chemical sewer system, and a sanitary sewer system were present in the North Plants area where the nerve agent GB, also called Sarin, was manufactured. As documented in the CCR for the North Plants Structure Demolition and Removal Project, completed in 2004, HHE soil and chemical sewers were excavated from three remedy sites within the CES (NPSA-1, 5 and 6) and disposed in the HWL. Over 6,000 linear feet of sanitary sewer line was removed from the North Plants manufacturing area and also disposed in the HWL. In addition, biota risk soil and miscellaneous debris was excavated from six remedy sites within the CES (NPSA-3, 5, 6, 8c, 9f and the P1 soil site associated with NPSA-1) and consolidated in Basin A.
• The Residual Ecological Risk Soil Project included excavation or tilling with sampling of biota risk soil from 18 remedy sites within Sections 1, 2, 24, 26, 35, and 36 (1CN-2, 1WC-1, 2NW-4, 6NW-3, 24SW-1, 26NW-5, 26SE-6, 26SW-1, 26WC-2, 35NC-7, 35SW-2, 35SW-3, 35WC-4, 36EC-1, 36NE-3, 36NW-4, Ditch 2d backfill, Basin F Area 1) and 8 Borrow Areas within Sections 1, 6, 23, 24, 25, 26, 30, 31, 35, and 36 (Borrow Areas 3, 4, 5, 6, 7, 8, 9 and 11) of the CES. These soils were contaminated with low levels of pesticides, primarily aldrin and dieldrin, which presented a residual health risk to biota. As documented in the CCRs for the Residual Ecological Risk Soil Remediation Project—Part 1 and Part 2, completed in 2009, soil at the 18 RER sites was either excavated and consolidated in Basin A, Basin F, or in South Plants, or tilled to an 18 inch depth with follow-up sampling. Biota risk soil was removed from the eight borrow areas and used as daily cover in the HWL, ELF, and Basin A consolidation area, as well as gradefill at depths at least two feet below final grade in areas that will remain in Army control.
• The Sanitary and Chemical Sewer Plugging Project consists of two project phases that were conducted independently of each other. Phase I included plugging manholes associated with sanitary sewer lines in Sections 2, 24, 25, 26, and 35 of the CES. These sewer lines potentially served as conduits for the transport of contaminated groundwater and, therefore, the ROD required that the manholes be plugged with grout. As documented in the CCR for this project, completed in 1998, 62 sanitary sewer manholes in the CES were plugged. Subsequent to this plugging project, 37 of the plugged manholes were excavated as part of implementation of soil remediation projects.
• The Sanitary Sewer Manhole Plugging Project—Phase II included plugging additional manholes in Sections 3, 4 and 35 of the CES. As documented in the CCR for this project, completed in 2009, 21 sanitary sewer manholes in the CES were plugged with grout. There are three manholes in Section 35 which will remain open to support an existing future use structure.
• The Secondary Basins Soil Remediation Project included the excavation of soil from six pesticide-contaminated sites within Section 26 of the CES including two former liquid disposal basins (NCSA-2a and -2b), one ditch (NCSA-2d) between the two basins, and adjacent surface soil areas (NCSA-4b, Surface Soil site, P1 Soil Area). As documented in the CCR for the Secondary Basins Soil Remediation Project, completed in 2004, HHE soil was excavated from four of these sites NCSA-2a, -2b, -2d, and the Surface Soil site and disposed in the HWL. Biota risk soil and miscellaneous debris were excavated from all six sites and consolidated in Basin A. In 2009, additional HHE soil was excavated from the ditch (NCSA-2d) and disposed in the ELF. This additional excavation is documented in the CCR for the Secondary Basins Soil Remediation Project, NCSA-2d (Basin F Drainage Ditch) Contingent Soil Volume (CSV) (NCSA-2d CSV Project).
• The Section 26 Human Health Exceedance and Biota Exceedance Soil Removal Project included the excavation of soil from one pesticide-contaminated site (NCSA-4b) within Section 26 of the CES. As documented in the CCR for the Section 26 Human Health Exceedance and Biota Exceedance Soils Removal Project, completed in 2000, HHE soil was excavated from this site and disposed in the HWL, and the biota risk soil was excavated and either consolidated in Basin A or used as daily cover in the HWL. In 2003, additional contaminated soil was excavated at this site where low level biota risk soil was identified. The additional excavation is documented in an Addendum to the Section 26 Human Health Exceedance and Biota Exceedance Soils Removal Project CCR.
• The Section 35 Soil Remediation Project included excavation of soil from nine sites within the CES that were contaminated by liquid waste from a former retention/detention basin including a basin located in Section 35 (NCSA-5b), former process water and wastewater ditches in Sections 2 and 35 (NCSA-1c, NCSA-5a, NCSA-5c, NCSA-5d, NCSA-6a), and areas surrounding the ditches (Surficial Biota, Surficial P1, Additional Surficial P1). As documented in the CCR for the Section 35 Soil Remediation Project, completed in 2004, HHE soil, chemical sewers, and associated debris were excavated and disposed in the HWL, and biota risk soil was excavated and consolidated in Basin A. A subsequent project, the Sand Creek Lateral Project, included additional work at three sites within Section 35 of the CES including two of the Section 35 Soil Remediation sites (NCSA-5b and -5c) and a section of sanitary sewer (NCSA-8a). As documented in the CCR for the Sand Creek Lateral Project, completed in 2008, HHE soil was excavated from NCSA-5b and -5c and disposed in the HWL and the ELF, and biota risk soil was excavated and consolidated in Basin A. The sanitary sewer (NCSA-8a) was removed and consolidated in Basin A.
• The Section 36 Balance of Areas Soil Remediation Project included the excavation of soil from six sites within Section 36 of the CES (CSA-1d, -2b, -3, -4, P1 East, and P1 North). As documented in CCRs for the Section 36 Balance of Areas Soil Remediation Project (Parts 1 and 2), completed in 2009, HHE soil, munitions debris, chemical sewers and associated debris from two sites (CSA-3 and -4) were excavated and disposed in the HWL. Biota risk soil and miscellaneous debris from four sites (CSA-1d and -2b, P1 East and P1 North) were excavated and disposed in Basin A. Part 2 of the project also included grading in Sections 31 and 36 to construct permanent stormwater drainages off of the adjacent Complex (Army) Trenches RCRA-Equivalent Cover and the Shell Disposal Trenches 2-Foot Cover.
• The South Plants Balance of Areas and Central Processing Area Soil Remediation Project included 16 remedy sites located in Sections 1 and 2 of the CES (SPSA-2b, -2e, -4a, -4b, -5b, -6, -7a, -7b, -7c, -8a, -8b, -8c, -9a, -9b, -10, and a P1 soil area outside of Borrow Area 11) which contained chemical sewers, HHE and biota risk soils contaminated with pesticides, chloroacetic acid, volatile organic compounds, metals, and mercury, as well as the potential for chemical warfare agents, munitions debris and unexploded ordnance. As documented in the CCRs for the South Plants Balance of Areas and Central Processing Area Soil Remediation Project—Phase 1 and Phase 2, completed in 2009, HHE soil, chemical sewers, and associated debris, and munitions debris from 12 of the sites (SPSA-2b, -2e, -4a, -4b, -5b, -6, -7c, -8a, -8b, -9a, -9b, -10) were excavated and disposed in the HWL. Biota risk soil was excavated from all of the sites excluding SPSA-10 and consolidated under the South Plants Covers or in Basin A. Structural debris from foundation demolition was consolidated within the South Plants soil cover areas.

Structures: All but one of the 750 ROD-identified “no future use” structures within the On-Post OU have been demolished. The remaining ROD structure is the CERCLA Wastewater Treatment Facility in Section 36, which was constructed to treat remedy-generated wastewater. The CERCLA facility currently treats groundwater from the Groundwater Mass Removal Project and is excluded from this proposed partial deletion. One other structure, the LWTS facility, built as part of the remedy to treat wastewater from the on-post landfills, is being decommissioned and is also excluded from this proposed partial deletion.

Demolition and removal of structures within the CES was accomplished by several projects. The remedial action for structures included demolition of the structures and foundations; removal and disposal of debris, substations, roads and parking areas; removal and disposal or recycling of underground storage tanks, structural steel and other metal components; backfilling and grading; and revegetation of the excavated areas. The demolition of most structures is documented in the following project CCRs.

(1) South Plants Structure Demolition and Removal Project Phase 1 and Phase 2 (2002);

(2) South Plants Balance of Areas and the Central Processing Area Soil Remediation Project Phase 2 (2009);

(3) North Plant Structure Demolition and Removal Project (2004); and

(4) Miscellaneous RMA Structure Demolition and Removal Projects—Phases I, II and III (2009).

Groundwater: The proposed partial deletion of the CES does not include groundwater; however, the following groundwater remedy projects are or were located within the CES footprint of the RMA Site. The Section 36 Bedrock Ridge Groundwater Plume Extraction System, constructed in 2008, is an ongoing project which extracts contaminated groundwater flowing from the Basin A and South Plants areas for treatment at the Basin A Neck Groundwater Treatment System. The North of Basin F IRA intercept system was permanently shut down in 2004 due to declining flows, biofouling, declining well capacity, and decreasing contaminant concentrations. The Confined Flow System Well Closure project, completed in 2000, included the closure of 15 wells in the CES which extended into the deeper, confined-low aquifer.

In addition, the portion of the On-Post OU that currently remains on the NPL includes several groundwater remedy components that are not within the proposed CES deletion area and will remain part of the NPL site. These include:

• The Rail Yard Treatment System, located in Section 3, is an ongoing project which treats contaminated groundwater associated with the Rail Yard.
• The Lime Basins and South Tank Farm Groundwater Mass Removal extraction systems, located in Section 36 and Section 1 respectively, are part of an ongoing project that extracts contaminated groundwater for treatment at the CERCLA Wastewater Treatment Facility.
• The CERCLA Wastewater Treatment Facility, located in Section 35, is an ongoing project which treats contaminated groundwater from the Lime Basins and South Tank Farm areas as part of the Groundwater Mass Removal Project.

Use of the groundwater and surface water for potable purposes from the entire original On-Post OU, including the CES, is prohibited by the FFA and On-Post ROD. The FFA and On-Post ROD also prohibit residential development, agricultural activities, and hunting and fishing for consumptive purposes throughout the original On-Post OU. These restrictions will continue to be prohibited even after the CES is transferred to the U.S. Department of Interior and are enforced by the Army through an “Interim Rocky Mountain Arsenal Institutional Control Plan” approved in 2003 and revised in 2006 and 2008.

Remedial Action for the OPS of the Off-Post (OU 4)

Soil: The Off-Post OU of the RMA Site is located directly north and northwest of the On-Post OU. To date, none of the Off-Post OU has been deleted. As agreed in the Off-Post ROD, though the health risks present in the soils were within EPA's acceptable cancer risk range for residential use (less than 1 × 10⁻⁴), Shell completed tilling and seeding of approximately 160 acres in Sections 13 and 14 of the OPS for settlement purposes to enhance the degradation of low-level pesticide residues. This activity is documented in the “Final Inspection/Implementation Report for the Off-Post Tillage Task” completed in 1997.

Groundwater: The proposed partial deletion of the OPS does not include groundwater; however, the following groundwater remedy components are or were within the OPS footprint of the RMA Site. The Off-Post Groundwater Intercept and Treatment System (OGITS), constructed in 1993, is an ongoing project that treats contaminated groundwater plumes that flow off-post to the north and northwest of RMA. The Off-Post Well Abandonment project, completed in 1999, included the closure of 7 wells in the Off-Post OU that extended into the deeper, confined flow aquifer. Institutional controls to prevent the use of groundwater exceeding remediation goals as well as deed restrictions on the Shell Property have been in place since 1996.

Cleanup Goals

Cleanup goals for the On-Post OU were established based upon a scenario for potential contaminant exposure incurred by a biological worker, e.g., a wildlife biologist working in the field, in consideration of the anticipated future land use of the On-Post OU as a National Wildlife Refuge. Soils and structures with a cumulative contamination concentration presenting an excess cancer risk to human health of greater than 1 × 10⁻⁴ or a Hazard Index greater than 1.0 for non-cancer risks were identified for excavation/demolition and on-site disposal. To confirm that the ROD-delineated soil contamination areas and depths met remedial action objectives, the On-Post ROD provided for excavation of an additional 150,000 cy of soil beyond that estimated in the selected remedy. For the entire On-Post OU, this volume was identified using 1,014 confirmatory samples as well as visual observations (e.g., for staining, debris, and odors). For the CES, more than 100 samples were collected and roughly 22,000 cy of additional soil was excavated.

Operation and Maintenance (O&M)

No O&M is required for any of the proposed CES and OPS partial deletion areas. However, the Army is responsible for O&M of the On-Post internal groundwater treatment facilities, and Off-Post OGITS until contaminant concentrations are below remedial action levels, as well as continued maintenance of groundwater wells for long-term groundwater monitoring. Long-term access to groundwater wells within the On-Post OU is delineated in Public Law 102-402 and the “Interim Rocky Mountain Arsenal Institutional Control Plan.” Long-term access to the groundwater wells in the Off-Post OU is provided through a license agreement between the Army and Shell.

Five-Year Review

Pursuant to CERCLA Section 121(c) and § 300.430(f)(4)(ii) of the NCP, the next five-year review will be completed in 2011 to ensure the continued protectiveness of remedial actions where hazardous substances, pollutants, or contaminants remain at a site above levels that allow for unlimited use and unrestricted exposure. Because the CES and OPS are subject to restrictions on land and water use, they will be included in future, RMA-wide five-year reviews.

Two site-wide, five-year reviews have been conducted to date including the Five-Year Review Report completed in January 2001 and the Five-Year Review Report completed in December 2007. The 2005 Five-Year Review identified 13 issues requiring followup actions, none of which affected the protection of human health or the environment for the Off-Post or On-Post OUs. Seven of these actions were related to improving reporting and coordination, and clarification of remedy requirements. Other issues concerned the incomplete capture of groundwater at the Bedrock Ridge Extraction System, operating problems of the primary sump system in Cell 2 of the Basin F Wastepile, modification of the OGITS extraction system, the discovery of fuel contamination in the groundwater below the North Plants area, and updating portions of the groundwater treatment systems including site-specific treatment criteria known as Practical Quantitation Limits (PQLs), and updating monitoring well networks. None of the issues impacted the CES or OPS, though actions regarding the groundwater monitoring networks may indirectly affect small portions of the CES and OPS.

All but three of the followup actions have been completed. Modification of the OGITS extraction system has been completed and the start-up data is being reviewed. A pilot study for assessing the North Plants Fuel Release has been approved and is ongoing. The PQL study was initiated in 2009 and submittals from laboratories are under review.

A fourth extraction well was installed at the Bedrock Ridge Extraction System and, in 2008, was determined to be adequately capturing the groundwater plume. The Basin F Wastepile Remediation Project, completed in 2009, included the excavation of the Wastepile and the liner system, and disposed the waste in the ELF, thereby eliminating any continuing concerns regarding the sump system.

Community Involvement

Public participation activities have been satisfied as required in CERCLA Section 113(k), 42 U.S.C. 9613(k) and CERCLA Section 117, 42 U.S.C. 9617. Since 1988, each of the parties involved with the Arsenal cleanup has made extensive efforts to ensure that the public is kept informed on all aspects of the cleanup program. More than 100 fact sheets about topics ranging from historical information to site remediation have been developed and made available to the public. Upon completion of the 30 calendar day public comment period for this proposed partial deletion of the RMA Site, EPA Region 8, in consultation with the State and the Army, will evaluate each comment and any significant new data received before issuing a final decision concerning the proposed partial deletion.

CES of the On-Post (OU 3): Following the release and distribution of the draft Detailed Analysis of Alternatives report for the On-Post OU (a second phase of the FS), the Army held an open house for about 1,000 community members. The open house provided opportunity for individual discussion and understanding of the various technologies being evaluated for cleanup of the On-Post RMA Site. The Proposed Plan for the On-Post OU was issued for public review from October 16, 1995, through January 19, 1996. A public meeting was held on November 18, 1995, attended by approximately 50 members of the public, to obtain public comment on the Proposed Plan. Minimal comments were received on the alternatives presented for the projects in the Central Area of the On-Post OU. Specifically, the comments requested that the health and safety of nearby communities be protected from air emissions during excavation and demolition activities and that potential dioxin contamination of the entire RMA Site be evaluated.

The designs for the each of the 29 remediation projects within the CES (18 soil remediation projects and 11 structure demolition projects) were provided to the public for a thirty calendar day review and comment period at both the 30 percent and 95 percent design completion stages (45 separate public comment periods). Most designs were also presented for discussion at the RMA Restoration Advisory Board which is composed of community stakeholders, regulatory agencies, the Army, Shell Oil Company, and USFWS. No written comments regarding the excavation/demolition approach or the proposed health and safety controls for each project were received.

OPS of the Off-Post (OU 4): An expanded Community Relations outreach was implemented to ensure community members had the opportunity to comment on the Proposed Plan for the Off-Post OU. In January 1993, all documents supporting an expected Proposed Plan were made available for public review in local libraries. A direct mailing to more than 1200 local citizens was made. The RI, RI Addendum, EA/FS, and Proposed Plan for the Off-Post OU were issued for public review on March 21, 1993, and was extended until June 21, 1993. On April 28, 1993, a public meeting was held to obtain public comment of the Proposed Plan. Comments received focused on requests for expanded groundwater treatment, incorporation of a surface soil remedy, and concerns over the selection of a DIMP cleanup standard.

The Draft Final ROD (1993) was revised in consideration of comments received from the city and county governments, environmental action groups and private citizens. Settlement discussions involving municipalities, local health departments, special districts, and citizen groups were held from late 1994 until April 1, 1995, to discuss the final remedies for both the On-Post and Off-Post OUs.

Determination That the Criteria for Deletion Have Been Met

EPA, with concurrence from the State of Colorado, dated March 22, 2010, has determined that all appropriate CERCLA response actions have been completed for the CES and OPS of the RMA Site to protect public health and the environment and that no further response action by responsible parties is required. Based on the extensive investigations and risk assessment performed for the CES and the OPS of the RMA Site, there are no further response actions planned or scheduled for these areas.

There are no known hazardous substances remaining in the CES above health-based levels with respect to anticipated uses of and access to the site which are identified in the FFA, On-Post ROD, and Public Law 102-402. Similarly, no known hazardous substances remain in the OPS above health-based levels with respect to anticipated uses of and access to the site which are limited through deed restrictions. As a result, all completion requirements for the CES and OPS have been achieved as outlined in OSWER Directive 9320.2-09A-P and the NCP. Therefore, EPA proposes to delete the CES and OPS portions of the RMA Site from the NPL.

List of Subjects in 40 CFR Part 300

• Environmental protection
• Air pollution control
• Chemicals
• Hazardous waste
• Hazardous substances
• Intergovernmental relations
• Penalties
• Reporting and recordkeeping requirements
• Superfund
• Water pollution control
• Water supply

Authority: 33 U.S.C. 1321(c)(2); 42 U.S.C. 9601-9657; E.O. 12777, 56 FR 54757, 3 CFR, 1991 Comp., p.351; E.O. 12580, 52 FR 2923, 3 CFR, 1987 Comp., p.193.

Dated: June 10, 2010.

Carol Rushin,

Deputy Regional Administrator, Region 8.