EPA Superfund Record of Decision Amendment · EPA Superfund Record of Decision Amendment: ROCKY...

EPA/AMD/R08-03/137

2003

EPA Superfund

Record of Decision Amendment:

ROCKY MOUNTAIN ARSENAL (USARMY)

EPA ID: CO5210020769

OU 03

ADAMS COUNTY, CO

04/15/2003

AMENDMENT TO THE RECORD OF DECISION FOR THE ON-POST OPERABLE

UNIT, ROCKY MOUNTAIN ARSENAL FEDERAL FACILITY SITE

HEX PIT REMEDIATION

Final

Prepared by:

Foster Wheeler Environmental Corporation

Prepared for:

Rocky Mountain Arsenal Remediation Venture Office

Department of the Army

Shell Oil Company

U.S. Fish and Wildlife Service

This document is the property of Rocky Mountain Arsenal Remediation Venture Office and was prepared by Foster Wheeler

Environmental Corporation. It is provided on the condition that it will neither be reproduced, copied, or issued to a third party; will be used solely for the intended purpose; and will be used solely for the execution or review of the engineering, remediation, and/or construction of

the subject project.

DEPARTMENT OF THE ARMYBASE REALIGNMENT AND CLOSURE

ROCKY MOUNTAIN ARSENAL7200 QUEBEC STREET, BUILDING 111

COMMERCE CITY, CO 80022-1748

DAIM-BO-A-RM-RE 17 April 2003

MEMORANDUM FOR U.S. Environmental Protection Agency, (Mr. Kerry Guy), Region VIII, Mail Code 8HWM-FF, 999-18th Street, Suite 300, Denver, Colorado 80202-2405

SUBJECT: Final Record of Decision (ROD) Amendment for the Hex Pit Site

1. Enclosed is the Final Record of Decision (ROD) Amendment for the Hex Pit Site. Comments received on the Draft ROD Amendment from the Regulatory Agencies have been incorporated. Responses to comments are also enclosed.

2. If you have any questions, please contact Ms. Lorri Harper at 303-289-0411.

Encl BRUCE M. HUENEFELDRMA Committee Coordinator

CF:Rocky Mountain Arsenal, (DAIM-BO-A-RM-CL/Major M. Weslyn Erickson),

Chief Counsel, Commerce City, Colorado 80022-1748 (wo/encl)Pacific Western Technologies, Ltd, (Mr. James Bush), 605 Parfet Street, Suite 200,

Lakewood, Colorado 80215 (w/encl)Shell Oil Company, (Mr. Roger B. Shakely), P.O. Box 538,

Commerce City, Colorado 80037 (wo/encl)Washington Group, (Mr. Mark Thomson), P.O. Box 1717,

Commerce City, Colorado 80022 (wo/encl)Holme Roberts and Owens, (Mr. Thomas F. Cope), 1700 Lincoln Street, Suite 4100,

Denver, Colorado 80203 (wo/encl)U.S. Fish and Wildlife Service, (Mr. Tom Jackson), Rocky Mountain Arsenal,

Commerce City, Colorado 80022-1748 (wo/encl)Tri-County Department Environmental Health Division, (Mr. Rick Kinshella),

4201 East 72nd Avenue, Commerce City, Colorado 80222-1488 (wo/encl) Rocky Mountain Arsenal, (DAIM-BO-A-RM-D/Document Tracking Center),

Commerce City, Colorado 80022-1748 (wo/encl)

Rocky Mountain Arsenal Hex Pit ROD AmendmentHex Pit Remediation Revision 0

WBS 2.04.19.02 April 9, 2003

Hex Pit ROD Amendment.doc i

CONTENTS

Section Page

DECLARATION ...........................................................................................................................................1

DECISION SUMMARY ................................................................................................................................1

1.0 INTRODUCTION .............................................................................................................................1

2.0 SITE HISTORY, CONTAMINATION AND SELECTED REMEDY....................................................22.1 RMA Operational History ............................................................................................................22.2 Hex Pit History and Contamination Summary ...............................................................................32.3 Summary of the Selected Remedy from the On-Post ROD .............................................................42.4 Summary of the Selected Remedy for the Hex Pit from the On-Post ROD .......................................42.5 Site Evaluation and Technology Selection .....................................................................................52.6 Remedial Design and Implementation ...........................................................................................7

3.0 BASIS FOR THE AMENDMENT .....................................................................................................83.1 Contingent Remedy .....................................................................................................................9

4.0 REMEDY DESCRIPTION ................................................................................................................94.1 Remedial Action Objectives .........................................................................................................94.2 Description of Alternatives ......................................................................................................... 10

4.2.1 Alternative 1: No Additional Action (RCRA-Equivalent Cover). .............................................. 114.2.2 Alternative 2: Vertical Barrier; RCRA-Equivalent Cover ........................................................ 124.2.3 Alternative 3: Excavate; On-Post Landfill .............................................................................. 124.2.4 Alternative 4: Excavate; Off-Post Incineration ......................................................................... 13

5.0 COMPARATIVE ANALYSIS OF ALTERNATIVES ....................................................................... 145.1 Overall Protection of Human Health and the Environment ........................................................... 145.2 Compliance with ARARs ........................................................................................................... 155.3 Long-Term Effectiveness and Permanence .................................................................................. 155.4 Reduction in Toxicity, Mobility and Volume (TMV) ................................................................... 155.5 Short-Term Effectiveness ........................................................................................................... 165.6 Implementability ....................................................................................................................... 165.7 Cost .......................................................................................................................................... 175.8 State Acceptance ........................................................................................................................ 175.9 Community Acceptance ............................................................................................................. 18

6.0 SELECTED REMEDY .................................................................................................................... 18

7.0 SUPPORT AGENCY COMMENTS ................................................................................................. 19

8.0 STATUTORY DETERMINATIONS ................................................................................................ 20

9.0 COMMUNITY PARTICIPATION COMPLIANCE .......................................................................... 219.1 Overview .................................................................................................................................. 219.2 Background on Community Involvement .................................................................................... 229.3 Summary of Comments ............................................................................................................. 23


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Hex Pit ROD Amendment.doc ii

9.4 Responses to Comments ............................................................................................................. 239.5 Remaining Concerns .................................................................................................................. 289.6 Community Relations Activitie s ................................................................................................. 28

10.0 REFERENCES ................................................................................................................................ 29

APPENDICES

Appendix A ROD Dispute Resolution Agreement pertaining to Hex Pit

TABLES

2.5-1 Hex Pit Contaminants of Concern and Site Evaluation Criteria

5.0-1 Comparative Analysis of Alternatives - Hex Pit Remediation

6.0-1 Cost Estimate Summary for the Hex Pit Selected Remedy

8.0-1 Location-Specific ARARs

8.0-2 Chemical-Specific ARARs

8.0-3 Action-Specific ARARs

9.6-1 Community Involvement Activities Conducted at RMA Pertinent to the Hex Pit Remediation

FIGURES

1.0-1 Hex Pit Location Reference

2.5-1 Hex Pit Characterization Boundaries


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ACRONYMS

ARAR Applicable or Relevant and Appropriate Requirement

BANCS Basin A Neck Containment System

bcy bank cubic yard(s)

CDPHE Colorado Department of Public Health and Environment

CERCLA Comprehensive Environmental Response, Compensation and Liability Act

CFR Code of Federal Regulations

COC Contaminant of Concern

EPA U. S. Environmental Protection Agency

FFA Federal Facility Agreement

HCl Hydrochloric acid

HWL Hazardous Waste Landfill

IRA Interim Response Action

ISTD In Situ Thermal Destruction

JARDF Joint Administrative Record Document Facility

NCP National Contingency Plan

O&M Operations and Maintenance

OU Operable Unit

PCDD/Fs Polychlorinated dibenzo dioxins and furans

ppm part(s) per million

PRG Preliminary Remediation Goal

RAB Restoration Advisory Board

RAO Remedial Action Objective

RCRA Resource Conservation and Recovery Act

RMA Rocky Mountain Arsenal

ROD Record of Decision

RVO Remediation Venture Office

SEC Site Evaluation Criteria

TCHD Tri-County Health Department

TMV Toxicity, Mobility and Volume

USFWS U. S. Fish and Wildlife Service


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WBS 2.04.19.02 April 9, 2003

Hex Pit ROD Amendment.doc D-1

DECLARATION

SITE NAME AND LOCATION

Rocky Mountain Arsenal Federal Facility Site Operable Unit 03: On-PostCommerce City, Adams County, Colorado

STATEMENT OF BASIS AND PURPOSE

This decision document amends the remedy decision for the Hex Pit project of the Rocky Mountain Arsenal (RMA) Federal Facility Site. The RMA is located in southern Adams County east of Commerce City, Colorado. The Hex Pit project is located near the north boundary of the South Plants Central Processing Area in Section 1 of the RMA. The original remedy decision is documented in the Record of Decision (ROD) for the On-PostOperable Unit (OU) (FWENC 1996). The ROD was signed June 11, 1996 and is currently being implemented for the remainder of the 25.5 square miles of the OU. A change in the ROD-selected remedy for the Hex Pit was necessitated due to the failure of the innovative treatment process during implementation. The technology was selected based on the administrative record for the site and was chosen in accordance with the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA), as amended by the Superfund Amendments and Reauthorization Act of 1986, and, to the extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan. This amendment does not change the selected remedy for groundwater, structures or soil at RMA other than the Hex Pit project.

The U.S. Environmental Protection Agency and the State of Colorado concur on the selected remedy documented in this ROD Amendment.

ASSESSMENT OF SITE

The Hex Pit was used between 1950 and 1952 to dispose of waste resulting from the production of hexachlorocyclopentadiene (Hex, also known as HCCPD and CL6CP). Hex was an intermediate process chemical used in the production of pesticides. The residual waste from the production process was a tarry, chlorinated organic, resinous material often referred to as Hex bottoms or Hex residue. The material was buried in drums and in bulk and the pit was covered with several feet of soil. Subsequent to disposal activities at the site, Shell constructed a tank storage structure, Building 571B, over the southern part of the Hex Pit.

Design characterization of the Hex Pit was performed in 1997 and 1999 to identify the boundaries of the pit, refine the volume estimate, and to determine concentrations of contaminants of concern (COCs). Waste material was encountered in an area approximately 45 feet by 94 feet at depths ranging from 2 to 8 feet below ground surface and was primarily mixed with soil, although several substantial pockets of tarry residue exist within the boundaries. During demolition of the foundation of Building 571B, conducted as part of the South Plants


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Structures Demolition and Removal Project, Hex waste and remnants of drums were discovered in the soil at depths down to approximately 12 feet. The waste was located in an area south and southwest of the Hex Pit boundary as determined by the design characterization in April 1999. Based on this new discovery, the Hex Pit boundary was extended to encompass the additional contaminated area and drums. Additional soil borings were used to visually identify the extent of the Hex Pit waste. The final Hex Pit configuration resulted in an area approximately 110 feet long, varying from 45 to 96 feet in width, with a total area of approximately 5,410 square feet and a total volume of 2,005 bank cubic yards. Chemical sampling results from the design characterization confirmed concentrations of Hex were well above the site evaluation criteria (SEC) established in the ROD, requiring remediation to protect human health. Concentrations of the COCs, aldrin, dieldrin , carbon tetrachloride and chlordane were also detected at levels greater than the SEC.

Actual or threatened releases of hazardous substances from this site, if not addressed by implementing the response action selected in this ROD amendment, may present an imminent and substantial endangerment to public health, welfare, or the environment.

RATIONALE FOR REMEDY CHANGE

The ROD required use of an innovative thermal treatment for the Hex Pit material. The specific technology was selected in accordance with ROD and dispute resolution requirements through a technology screening process. The technology evaluation, completed in September 1998, evaluated 12 different technologies and included a preliminary screening and subsequent comparative analysis to identify a recommended innovative thermal technology for remediating the Hex Pit. Based on the comparative evaluation, In Situ Thermal Desorption (ISTD) was selected as the most technically appropriate technology for Hex Pit remediation.

A bench-scale treatability test of the ISTD technology was performed in 1999 on contaminated soil samples collected from the Hex Pit. The treatability test results, along with a conceptual design and cost estimate for ISTD remediation, were presented in the Hex Pit Treatability Study Report (ENSR 2000). Concentrations of Flex, aldrin, dieldrin, endrin, isodrin and chlordane were detected above the SEC and were identified as project COCs. The bench-scale treatability testing demonstrated that ISTD was capable of achieving destruction/removalefficiencies in excess of 99 percent.

The final design for the Hex Pit was completed in March 2001 (TerraTherm 2001). The design involved placing 266 evenly spaced heating wells within the Hex Pit waste and soil. The heating wells used electricity to heat the Hex Pit waste and soil to over 600°F and destroy the contamination in situ. Offgasses produced from the waste destruction were captured by a vacuum system applied to collection wells and treated through an air treatment system to meet emission requirements. Construction of the ISTD system started in October 2001 and field implementation of the process began in March 2002. As the soil and waste became heated, the contaminants were being destroyed as planned, releasing the chlorine present in the waste. When the chlorine came in contact with water from the surrounding soil, hydrochloric acid (HCl) vapor was formed.


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The ISTD design anticipated that the HCl formed would be adequately neutralized by the higher pH of the surrounding soil; however, this did not occur. As a result, the HCl vapor was drawn into the vacuum wells, piping and process equipment. This vapor, as it condensed in the treatment train began to corrode the piping, wells and other process equipment. This resulted in failure of key portions of the ISTD process equipment and forced a shutdown of the system.

Assessment of the system indicated that the presence of HCl condensate and the corrosion rate of the HCl for the system materials were greater than anticipated during design resulting in the failure (EMTEC 2002). To continue the ISTD remedy would have required replacement of system wells, piping and process equipment with a material that could resist HCl corrosion. The Material Failure Assessment Report (TerraTherm 2002) indicated that replacement of the system components would have represented a significant cost increase, provided that a suitable material could be identified. A pilot study was recommended to confirm the applicability of replacement materials and the efficacy of redesign. Costs for redesign would be equal to or more than the initial design costs due to the necessity of completing treatability and pilot studies to determine suitable system materials. Construction costs would also be significantly higher based on the expected increased cost of corrosion-resistant materials required for the ISTD system. The added design and construction costs, along with similar operating costs for implementing the revised ISTD system, would result in a project cost increase greater than the plus 50 percent accuracy provided in the ROD, and potentially impact implementation of the South Plants cover.

DESCRIPTION OF SELECTED REMEDY

The selected remedy for the Hex Pit is excavation and disposal in the on-post landfill. This alternative includes excavation of approximately 2,005 bank cubic yards of contaminated soil and waste material from the Hex Pit with disposal in the on-post Hazardous Waste Landfill (HWL). Excavation will be completed to a minimum depth of 10 feet across the 5,410 square foot area of the Hex Pit. Additional excavation, if necessary, will continue based on visual evidence of Hex Pit waste beyond the design boundary. If the waste extends below the groundwater table, three horizontal wells are in place to dewater the site and allow additional excavation (these wells will be appropriately abandoned at the end of the project in accordance with approved well abandonment procedures). The limit of excavation depth will be 1 foot above the practical limit of dewatering, currentlyestimated at 15 feet below ground surface. Air emissions and odor controls, developed during remedial design to meet regulatory requirements, will be applied during excavation, transportation and placement of waste in the HWL. After excavation, the site will be backfilled using on-post borrow material. A Resource Conservation and Recovery Act (RCRA) equivalent cover will be constructed over the entire central South Plants area, including the Hex Pit, during 2004-2005.

STATUTORY DETERMINATIONS

The new, selected remedy for the Hex Pit satisfies the requirements of CERCLA Section 121 and is protective of human health and the environment, complies with federal and state requirements that are legally applicable or relevant and appropriate to the remedial action, is


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cost effective and uses a permanent solution through proper disposal and containment of the wastes in the on-postHWL. The remedy selected in this ROD Amendment does not satisfy the statutory preference for treatment as a principal element of the remedy for the following reasons: (1) the treatment remedy that was originally selected failed, and (2) Alternative 4 (Off-site Incineration) is not cost effective and is not supported by the community.

The Hex Pit is located within the South Plants cover area. This area will be retained by the Army and assessed every 5 years, as part of site-wide 5-year reviews, to ensure that the overall remedy continues to provide adequate protection of human health and the environment and complies with applicable regulations. In addition, site-wideinstitutional controls identified in the RMA FFA are included as requirements in the ROD. These requirements restrict future land use and prohibit certain activities such as agriculture, use of on-post groundwater as a drinkingsource, and consumption of fish and game taken at RMA.


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SIGNATURES

For U.S. Environmental Protection Agency

Max H. DodsonAssistant Regional AdministratorOffice of Ecosystems Protection and Remediation

For U.S. Army

Charles T. ScharmannProgram Manager for Rocky Mountain Arsenal

For State of Colorado

Howard Roitman Director, Hazardous Materials and Waste Management Division and Acting Director, Environmental Programs


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Shell Oil CompanyP.O. Box 2463

Houston, TX 77252-2463United States of America

March 24, 2003

Mr. Charlie ScharmannProgram Manager, Rocky Mountain ArsenalBuilding lllCommerce City, CO 80022

Dear Mr. Scharmann:

Re: Hex Pit Remediation, WBS 2.04.19.02

Amendment to the Record of Decision for the On-Post Operable Unit, Rocky MountainArsenal Federal Facility Site

Hex Pit Site Remediation

The original remedy decision for the Hex Pit Site is documented in the Record of Decision (ROD) for the On-PostOperable Unit (FWENC 1996). The ROD was signed June 11, 1996 and is currently being implemented. The remedy change presented in the amendment was necessitated due to the failure of the treatment process during implementation of the ROD-selected remedy for the Hex Pit.

Shell Oil Company concurs with this Amendment to the Record of Decision for the On-Post Operable Unit, Hex Pit Site Remediation. This Amendment calls for excavation and disposal of the Hex Pit in the on-site HazardousWaste Landfill.

Roxanne Decyk Sr. Vice PresidentCorporate Affairs and Human Resources

United States Department of the Interior

FISH AND WILDLIFE SERVICE

Rocky Mountain Arcena1 National Wildlife Refuge

Building 111

Commerce City, Colorado 80022-1748

Telephone (303) 289-0232 Fax (303) 289-0579

March 6, 2003

Mr. Charlie ScharmannProgram Manager, Rocky Mountain Arsenal Bldg. 111Commerce City, CO 80022-1748

On behalf of the United States Fish and Wildlife Service (Service), I am pleased to endorse and support the signing of this On Post Record of Decision Amendment for the remediation of the Hex Pit Site at Rocky Mountain Arsenal. The Service concurs that the selected remedy for this site is the best choice considering all alternatives and looks forward to the completion of this work.

Sincerely,

Dean Rundle Refuge Manager

Tri-County Health DepartmentServing Adams, Arapahoe and Douglas Counties

IIi

Richard L. Vogt, M.D.

Executive Director

March 12, 2003

Mr. Charles ScharmannOffice of the Program Manager Rocky Mountain ArsenalAMXRM-E, Building 111Commerce City, CO 80022-1748

Amendment to the Record of Decision for the On-Post Operable Unit

Hex Pit Soil Remediation

Rocky Mountain Arsenal

Dear Mr. Scharmann:

Tri-County Health Department (TCHD) has reviewed the Amendment to the Record of Decision for the On-PostOperable Unit related to Hex Pit Soil Remediation Project. TCHD concurs with the selected remedy, Excavate:On-Post Landfill. This concurrence is based on our review of the Revised Proposed Plan, attendance at the October 10, 2002 public meeting, and our review and participation in the preparation of the ROD Amendment.

TCHD will continue to provide input to the RVO regarding the Hex Pit project as the revised remedy moves through the remedial design and implementation process.

Sincerely,

TRI-COUNTY HEALTH DEPARTMENT

Kenneth L. Conright, R.E.H.S., R.H.S.P. Environmental Health Manager.

cc: Dr. Vogt, TCHD Joan Sowinski, CDPHELaura Williams, EPA Roger Shakely, ShellBruce Wilson, TCHD Dean Rundle, USFWSCraig Tessmer, Adams County RMA File


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Hex Pit ROD Amendment.doc 1

DECISION SUMMARY

1.0 INTRODUCTION

This Amendment documents the change to the remedy for the Hex Pit project of the Rocky Mountain Arsenal(RMA) Federal Facility Site. The RMA On-Post Operable Unit (OU) is a federally owned facility located in southern Adams County, Colorado, approximately 10 miles northeast of downtown Denver, directly north of the former Stapleton International Airport and west of Denver International Airport. The RMA On-Post OU site is 25.5 square miles 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 Hex Pit is located near the north boundary of the South Plants Central Processing Area in Section 1 of RMA (Figure 1.0-1).

The Record of Decision (ROD) (FWENC 1996), which describes the remedy for the entire On-Post-OU of RMA, was signed by the U.S. Army, the EPA, and the Colorado Department of Public Health and Environment (CDPHE) on June 11, 1996. The selected remedy includes 31 cleanup projects for soil, structures, and treatment of groundwater contamination. Implementation of the remedy for the remainder of the OU is currently underway and will continue through approximately 2011. As the site-wide remediation is completed, most of the On-PostOU of RMA will become a National Wildlife Refuge, as provided for in Public Law #102-402.

The Army is the lead agency for RMA and is issuing this ROD Amendment as part of its responsibilities under Section 117 of the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA), as amended by the Superfund Amendment and Reauthorization Act of 1986, and pursuant to the National Contingency Plan (NCP), 40 Code of Federal Regulations (CFR) Section 300.435(c)(2)(ii). Regulatory oversight is conducted by the EPA, CDPHE, and the Tri-County Health Department (TCHD). The TCHDoversees local public and environmental issues in Adams, Arapahoe, and Douglas Counties.

The selected remedy in the 1996 ROD for the Hex Pit project included treatment of the contaminated pit material using an innovative thermal technology. The specific technology, In Situ Thermal Desorption (ISTD), was selected in accordance with the ROD and additional criteria identified in the ROD Dispute Resolution Agreement (PMRMA 1996). Implementation of the ISTD was started in March 2002; however, the system failed shortly after startup due to excess hydrochloric acid (HCl) formation resulting in corrosion of the treatment train and partial system failure. Continuing with the ISTD remedy would require replacement of system wells, piping and process equipment with a material that could resist HCl corrosion. Costs for redesign would be equal to or more than the initial design costs due to the necessity of completing treatability and pilot studies to determine suitable system materials. Construction costs would also be significantly higher based on the expected increased cost of corrosion-resistant materials required for the ISTD system. The added design and construction costs, along with similar operating costs for implementing the revised ISTD system, would result in a


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project cost increase greater than the plus 50 percent accuracy provided in the ROD and potentially impact implementation of the South Plants cover. This Amendment summarizes information regarding the Hex Pit from documents in the Administrative Record and remedy files, which were used as the basis to select the new remedial alternative.

This Amendment will become part of the Administrative Record as required by the NCP, 40 CFR 300.825(a)(2). The Administrative Record is available to the public at the Joint Administrative Record Document Facility (JARDF) that is located on the RMA in Building 129, Room 2024. The JARDF is open Monday through Friday between Noon and 4 pm or by appointment. The telephone number for the JARDF is 303-289-0136 or

1-800-862-0754.

2.0 SITE HISTORY, CONTAMINATION AND SELECTED REMEDY

2.1 RMA Operational History

The RMA was established in 1942 by the Army to manufacture chemical warfare agents and agent-filledmunitions and to produce incendiary munitions for use in World War II. Initial facility building activities included construction of the South Plants manufacturing complex, extension of railway systems onto RMA, construction of a railway classification yard and service and maintenance facilities, modifications to preexisting irrigation reservoirs and construction of a new reservoir to supply South Plants with process cooling water, and construction of three seepage ponds in a large earthen depression in Section 36. Prior to 1942, the area was largely undeveloped ranchland and farmland. Following the war and through the early 1980s, the facilities continued to be used by the Army. Beginning in 1946, parts of the South Plants facilities were leased to private companies to manufacture-industrial and agricultural chemicals. Shell, the principal lessee, manufactured pesticides from 1952 to 1982 at the site. Common industrial and waste disposal practices used during these years resulted in contamination of structures, soil, surface water, and groundwater.

The On-Post OU is one of two operable units at RMA. The Off-Post OU addresses contamination north and northwest of RMA. The On-Post OU addresses contamination within the fenced 27 square miles of RMA. In January 2003, a 1.5 square mile area of the On-Post OU was determined to meet cleanup requirements and is no longer part of the NPL site. Implementation of the remedy for the remaining 25.5 square miles is ongoing and is scheduled for completion in 2011.

The contaminated areas within the On-Post OU include approximate ly 3,000 acres of soil, 15 groundwater plumes, and 798 structures. The most highly contaminated areas identified are in South Plants (the central processing area, Hex Pit, Buried M-1 Pits, and the chemical sewers), Basins A and F, Lime Basins, and the Armyand Shell disposal trenches. The primary contaminants found in soil and groundwater at these sites are pesticides, solvents, metals, and chemical warfare agent by products.

The sites with the highest levels and/or the greatest variety of contaminants are located in the central manufacturing, transport, and waste disposal areas. The highest contaminant


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concentrations tend to occur in- soil within five feet of the ground surface, although exceptions are noted, particularly at sites where burial trenches, disposal basins, or manufacturing complexes are located.

The characteristics and locations of the groundwater plumes suggest that the greatest contaminant releases to the groundwater have occurred from Basin A and the Lime Settling Basins, the South Plants chemical sewer, the South Plants tank farm and production area, the Army and Shell trenches in Section 36, and the former Basin F. Plumes flowing from the Motor Pool/Rail Yard and North Plants area have been other sources of contaminant releases to the ground water.

2.2 Hex Pit History and Contamination Summary

The Hex Pit is located within the South Plants near the north boundary of the Central Processing Area in Section 1 of RMA. The Hex Pit was used between 1950 and 1952 to dispose of waste resulting from the production of hexachlorocyclopentadiene (Hex, also known as HCCPD and CL6CP). Hex was an intermediate process chemical used in the production of pesticides. The residual waste from the production process was a tarry material often referred to as Hex bottoms or Hex residue. These Hex bottoms are chlorinated organic, resinous materials that are relatively insoluble in water. The Hex bottoms were buried in drums and in bulk and the pit was covered with several feet of soil. Subsequent to disposal activities at the site, Shell constructed a tank storage structure, Building 571B, over the southern part of the Hex Pit.

During the Remedial Investigation conducted for the Hex Pit in 1985, one soil boring was located at the Hex Pit; however, the boring was only drilled to a depth of 1.2 feet due to the presence of water in the soil. One sample was collected at the 0 to 1-ft depth but later determined that the sample had not entered the pit. The surface sample collected contained detectable levels of contaminants of concern (COCs) including hex, aldrin, dieldrin, endrin and isodrin. At RMA, a risk assessment called the Integrated Endangerment Assessment/Risk Characterization (FWENC 1994) was performed and used as the baseline risk assessment for the ROD. The ROD contains a complete description of the risk assessment performed for the on-post operable unit, including the Hex Pit.

The available historical record and results of the risk assessment for the Hex Pit waste material allowed the investigation to conclude that high concentrations of contaminants existed within the buried material. It was also considered likely that containerized material could be encountered. As a result, the ROD identified the Hex Pit as a principal threat site. The Hex Pit was identified as approximately 110 feet, by 81 feet by 10 feet deep resulting in an estimated volume of 3,300 bank cubic yards.

An investigation (“Investigation of the Hex Pit as a Possible Source of Groundwater Contamination at the RMA” MKE 1989) was conducted to assess if the Hex Pit was a source of groundwater contamination and whether an IRA should be implemented. The results of the investigation indicated that low-level concentrations of some Hex Pit contaminants were present in groundwater. However, because these contaminants were present both upgradient and downgradient of the pit, the Hex Pit could not be identified as a definite source. If the Hex Pit is


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assumed to be a source of groundwater contamination, the concentrations of Hex Pit contaminants accounted for approximately 0.01 percent of the total concentration of organic compounds present in groundwater (MKE 1989). In addition, the relative insolubility of the Hex compounds and the typical separation between the waste and groundwater reduce the potential for release of these compounds to groundwater.

The majority of the groundwater contamination in South Plants, including the Hex Pit area, migrates northward under Basin A in Section 36 and is treated at the Basin A Neck Containment System (BANCS), which was installed in 1990. Downgradient of the BANCS, groundwater migrates toward the Northwest and North Boundary Containment Systems where it is treated. These systems were installed in 1984 and 1981, respectively.

2.3 Summary of the Selected Remedy from the On-Post ROD

The overall remedy required by the 1996 ROD for the On-Post OU includes:

• Intercept and treatment of contaminated groundwater at the three existing on-site treatment plants.

• Construction of a new RCRA- and TSCA-compliant hazardous waste landfill (HWL) on-post.

• Demolition of structures with no designated future use and disposal of the debris in either the new, on-post HWL or the Basin A consolidation area, depending upon the degree of contamination.

• The contaminated soil at RMA is addressed primarily through containment in the on-post HWL or 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 become part of the future wildlife refuge.

• For South Plants, excavation of principal threat and human health exceedance soil and disposal in the on-post HWL. Excavation of soil posing a risk to biota outside the Central Processing Area for use as backfill or gradefill under the Central Processing Area soil cover. Construction of soil covers over the South Plants area.

2.4 Summary of the Selected Remedy for the Hex Pit from the. On-Post ROD

During the RI/FS, the Hex Pit was identified as approximate ly 110 feet by 81 feet with a maximum depth of 10 feet, resulting in an estimated total volume of waste and contaminated soil of 3,300 bank cubic yards. Of the total, 1,000 bank cubic yards (bcy) were considered highly contaminated principal threat materia l comprised of actual pit waste material. The remaining 2,300 bcy was contaminated soil within the project boundary.

The Hex Pit remedy included in the ROD is stated as follows:

Treatment of approximately 1,000 bank cubic yards (bcy) of principal threat material using an innovative thermal technology. The remaining 2,300 bcy are excavated and disposed in


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the on-post hazardous waste landfill. Remediation activities are conducted using vapor-and odor-suppressionmeasures as required. Treatability testing will be performed during remedial design to verify the effectiveness of the innovative thermal process and establish operating parameters for the design of the full-scale operation. The innovative thermal technology must meet the treatability study technology evaluation criteria described in the dispute resolution agreement (PMRMA 1996). Solidification/stabilization will become the selected remedy if all evaluation criteria for the innovative thermal technology are not met. Treatability testing for solidification will be performed to verify the effectiveness of the solidification process and determine appropriate solidification/stabilization agents. Treatability testing and technology evaluation will be conducted in accordance with EPA guidance (OS WER-EPA 1989) and EPA’s “Guide for Conducting Treatability Studies under CERCLA” (EPA 1992).

The remediation goals and standards for innovative thermal technology as stated in Table 9.5-1 of the ROD are as follows:

• Standard: Design to achieve 90% or greater destruction of contaminants.

• Standard: Landfill all treatment residuals and untreated material in the on-post hazardous waste landfill.

The specific thermal technology was selected using criteria detailed in the ROD Dispute Resolution Agreement (PMRMA 1996). A copy of the section of the ROD Dispute Resolution Agreement pertaining to the Hex Pit is included in Appendix A. The ROD Dispute Resolution Agreement identified three tasks to be completed for technology selection: design data collection, technology evaluation, and a treatability study. The technology evaluation criteria included a remediation goal of destruction and removal efficiency greater than 90 percent, groundwater monitoring for an in situ technology, and a remediation cost to not exceed the cost for excavation and off-site incineration. The selected technology would be applied to the contaminated material found in the Hex Pit, based on visual observation, with the remaining soil excavated and disposed in the on-post HWL in accordance with the ROD.

2.5 Site Evaluation and Technology Selection

In August of 1997, a field investigation was initiated to collect design data and refine previous estimates of the Hex Pit boundaries (RVO 1998). This investigation included a geophysical survey of the area, collection of samples from three paired boreholes to define the Hex Pit boundary, collection of three soil samples from within the pit, and odor emission tests. The results of this investigation indicated the pit to be approximately 42 feet wide and 95 feet long with the southern boundary ending somewhere beneath building 571B. Samples taken from inside the newly defined pit boundary contained concentrations of Hex ranging from 13,000 parts per million (ppm) to 160,000 ppm. The locations of these samples are shown on Figure 2.5-1 and a summary of analytical results is presented on Table 2.5-1. Tests were conducted to evaluate the odor potential of the Hex Pit waste. Although the odor was described as unpleasant, the measured odor concentrations were not particularly high.


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Following the initial field investigation, the technology evaluation for selection of the specific innovative thermal treatment process was conducted in two phases. First, a list of thermal technologies that were capable of treatingthe hex waste was developed. These 12 technologies were screened using three preliminary evaluation criteria: destruction and removal efficiency, cost, and general implementability. Technologies retained after the preliminary screening step were then comparatively evaluated using the characteristics of effectiveness, implementability and cost. Consequently, ISTD was selected as the most appropriate thermal technology for treating the Hex Pit waste. A discussion of the technology evaluation is presented in the Innovative Thermal Technology Evaluation Report for the Hex Pit Site at the Rocky Mountain Arsenal (CDPHE et al. 1998). This report was provided to the public for formal review and comment.

Additional design characterization of the Hex Pit was performed in 1999 to further identify the boundaries of the pit, refine the volume estimate, and determine concentrations of COCs. Complete results of the site characterization are presented in the Site Characterization Report (ENSR 1999). A total of 51 borings were drilled within and around the perimeter of the Hex Pit to visually identify the lateral and vertical boundaries of the pit. Waste material was encountered in an area approximately 45 feet by 94 feet at depths ranging from 2 to 8 feet below ground surface and was primarily mixed with soil, although several substantial pockets of tarry residue were identified within the project boundaries. The volume estimate from the ROD was refined based on the site characterization results and estimated to be 1,567 total bcy.

Chemical sampling results from composite waste samples collected during the design characterization confirmed that concentrations of Hex were well above the site evaluation criteria (SEC) established in the ROD. The SEC are risk-based criteria used to evaluate soil COC concentrations and determine where remedial actions are warranted. Concentrations of aldrin, dieldrin and chlordane were also detected at levels greater than the SEC. A summary of the Hex Pit characterization results along with the ROD SEC are presented on Table 2.5-1.

A bench-scale treatability test of the ISTD technology was performed in 1999 on contaminated soil samples collected from the Hex Pit. The purpose of the treatability test was to gather data regarding the feasibility ofachieving the site-specific cleanup goals established in the ROD, and to gather data on the potential offgas stream for use in the design of the emission control system. The treatability test results, along with a conceptual design and cost estimate for ISTD remediation, were presented in the Hex Pit Treatability Study Report (ENSR 2000). Additional characterization of soil/waste samples was performed and results are summarized in Table 2.5-1. In addition to Hex, concentrations of aldrin, dieldrin, endrin, isodrin and chlordane were detected, at levels greater than the SEC. Some volatile organic compounds were also detected although the concentrations were below the SEC. Based on contaminant concentrations present the Hex Pit remains designated as a principal threat site. The COCs identified for the project were Hex, aldrin, dieldrin, endrin, isodrin and chlordane. The bench-scaletreatability testing demonstrated that ISTD was capable of achieving destruction/removal efficiencies greater than 99 percent for all COCs and would eliminate the need to excavate and landfill the treated Hex Pit waste and soil. Evaluation of the offgas from the bench testing indicated that the full-scale


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remediation would require an air quality control system to address emissions of organic (hydrocarbon) compounds and acid gases.

During the execution of the treatability test, process vapor samples were collected and analyzed for project COCs and potential oxidation by-products including hydrogen chloride and polychlorinated dibenzo dioxins and furans (PCDD/Fs). The results of the PCDD/F analyses conducted indicated that detectable levels of PCDD/F congeners were present within the test samples before and after treatment. However, test results indicated that concentrations of PCDD/F congeners in the samples were reduced by approximately 95 percent as a result of the treatment. Therefore, the decision was made to proceed with the ISTD technology for treating the Hex Pit waste.

Subsequent to the design site characterization, Building 571B was demolished as part of the South Plants Structures Demolition and Removal Project. During the removal of the foundation, Hex waste and remnants of drums were discovered in the soil at depths down to approximately 12 feet. The waste was located in an area south and southwest of the Hex Pit boundary as determined by the design characterization in April 1999. Based on this new discovery, the Hex Pit boundary was extended to encompass the additional contaminated area and drums. Additional soil borings were used to visually identify the extent of the Hex Pit waste. The final Hex Pit configuration resulted in an area approximately 110 feet long, varying from 45 to 96 feet in width, with a total area of approximately 5,410 square feet. The total volume of contaminated waste/soil at the Hex Pit was estimated to be 2,005 bcy. Of this total, approximately 833 cubic yards were identified as Hex Pit waste with the balance (1,172 cubic yards) being soil interlayered with the waste material.

Figure 2.5-1 illustrates the project boundary determined during site characterization efforts. The locations of the visually identified contaminated and uncontaminated soil borings collected near the edges of the Hex Pit are shown on the figure and form the basis for determining the project boundary. Soils immediately adjacent to the Hex Pit are part of the South Plants Central Processing Area project and are addressed as part of the South Plants remedy.

2.6 Remedial Design and Implementation

The final design for the Hex Pit was completed in March 2001 (TerraTherm 2001). The design involved placing 266 evenly spaced heating wells within the Hex Pit waste and soil. The configuration of the heating wells was designed to treat the entire Hex Pit waste and soil volume of 2,005 cubic yards, rather than just the pit waste volume. The heating wells used electricity to heat the Hex Pit waste and soil to over 600°F and destroy the contamination in-situ. Offgasses produced from the waste destruction were captured by a vacuum system appliedto collection wells and treated through an air treatment system to meet emission requirements. After completion of the ISTD treatment, soil samples would be collected to determine whether treatment goals had been met. In the event that the ISTD treatment did not achieve the HHE criteria listed in the ROD, the treated Hex Pit waste and soil would be excavated and disposed in the on-post HWL. After completion of the Hex Pit remedy, the entire Hex Pit area would be covered with a protective soil and vegetative cover (RCRA-equivalent cover) as part of the South Plants remedy.


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Cost for implementation of the ISTD treatment was estimated at $3.1 million based on the final design. Together with design costs of approximately $1 million, the total ISTD project cost was estimated at $4.1 million. The design schedule estimated a construction start date in July 2001 with completion of the treatment in January 2002; however, this schedule was delayed approximately three months during bid review and contract negotiations. The implementation schedule was designed to provide for completion of the Hex Pit project prior to construction of the South Plants soil cover, scheduled to begin in November 2002, to avoid potential delays to the South Plants project.

3.0 BASIS FOR THE AMENDMENT

Construction of the ISTD system started in October 2001 and field implementation of the process began in March 2002. As the soil and waste became heated, the contaminants were being destroyed as planned, releasing the chlorine present in the waste. When the chlorine came in contact with water from the surrounding soil; I-ICIvapor was formed.

The ISTD design anticipated that the HCl vapor formed would be neutralized by the higher pH of the surrounding soil; however, this did not occur. As a result, the HCl vapor was drawn into the vacuum wells, piping and process equipment. This vapor, as it condensed, began to corrode the piping, wells and other process equipment, which caused failure of key portions of the ISTD process equipment and forced a shutdown of the system.

Assessment of the system indicated that the presence of HCl condensate and the corrosion rate of the HCl for the system materials were greater than anticipated during design resulting in the failure (EMTEC 2002). To continuethe ISTD remedy would require replacement of system wells, piping and process equipment with a material that could resist HCl corrosion. The Material Failure Assessment Report (TerraTherm 2002) indicated that replacement of the system components would have represented a significant cost increase, provided that a suitable material could be identified. A pilot study was recommended to confirm the applicability of replacement materials and the efficacy of a redesign. Redesign and construction would include the following elements:

• treatability study to identify suitable material for system construction

• redesign of entire system

• pilot study to confirm suitability of materials and determine appropriate system operating parameters

• ISTD construction including removal of previous ISTD wells, installation of new wells and installation or

retrofitting of aboveground piping and system components

• implementation of ISTD treatment

Costs for redesign would likely be equal to or more than the initial design costs due to the necessity of completing treatability and pilot studies to determine suitable system materials. Construction costs would also be significantly higher based on the expected increased cost of corrosion-resistant materials required for the ISTD system. At thetime of system shutdown,


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project costs (design and implementation) had exceeded $3.2 million. The added design-and construction costs along with similar operating costs for implementing the revised ISTD system would increase the total project cost over $7 million, resulting in a project cost increase of greater than 70 percent which is greater than the plus 50 percent accuracy provided in the ROD.

In addition, proceeding with redesign and reconstruction was estimated to take 18-24 months and thereby impactthe adjacent South Plants project by delaying cover construction. Also, because access to the HWL is required in the event that the treatment did not meet the required remediation goals, the delay to the Hex Pit project would cause a delay in closure of the HWL. Delaying the South Plants cover construction and keeping the HWL open and operating for the additional time would further increase costs to the overall RMA remediation program. With the expected cost increase well above the plus 50 percent threshold and the significant schedule impacts to the overall RMA remediation efforts, a reevaluation of remedial actions for the Hex Pit project was necessary.

3.1 Contingent Remedy

The ROD specifies that if the innovative thermal treatment selected for Hex Pit remediation failed to meet the technology evaluation criteria included in the ROD Dispute Resolution Agreement (Appendix A), then the contingent remedy would be solidification/stabilization. After ISTD failure, the Army began looking at the site conditions and contingent remedy requirements to plan for implementation of the contingent remedy. However, a review of the new Hex Pit information gained during the site characterization, treatability study and ISTD implementation indicated potential problems not identified at the time of the ROD. The very tarry nature of the waste would create material handling difficulties during the solidification/stabilization process. Also, concerns were identified related to the ability of available solidification/stabilization reagents to reduce the mobility of the Hex Pit contaminants due to high concentrations of organic COCs. Potential vendors were contacted to identify reagents capable of reducing the contaminant mobility. No potential reagents or solidification/stabilizationmixtures were identified that would effectively reduce the mobility of the Hex Pit waste. The material handling difficulties and lack of an effective solidification/stabilization mixture resulted in a determination that solidification/stabilization was not implementable and a reevaluation of remedial actions for the Hex Pit project was necessary.

4.0 REMEDY DESCRIPTION

4.1 Remedial Action Objectives

Section 7.4.2 of the 1996 ROD identified the Remedial Action Objectives (RAOs) for the soil medium (which includes the Hex Pit) as follows:

Human Health


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• Prevent ingestion of, inhalation of, or dermal contact with soil or sediments containing COCs at concentrations that generate risks in excess of 1 x 10

-4 (carcinogenic) or a hazard index greater than 1.0

(noncarcinogenic) based on the lowest calculated reasonable maximum exposure (5th

percentile) preliminary pollutant values (which generally represent the on-site biological worker population).

• Prevent inhalation of COC vapors emanating from soil or sediments in excess of acceptable levels, as established in the Human Health Risk Characterization.

• Prevent migration of COCs from soil or sediment that may result in off-post groundwater, surface water or windblown particulate contamination in excess of off-post remediation goals.

• Prevent contact with physical hazards such as unexploded ordnance.

• Prevent ingestion of, inhalation of, or dermal contact with acute chemical agent hazards.

Ecological Protection

• Ensure that biota are not exposed to COCs in surface water, due to migration from soil or sediment, at concentrations capable of causing acute or chronic toxicity via direct exposure of bioaccumulation.

• Ensure that biota are not exposed to COCs in soil and sediments at toxic concentrations via directexposure or bioaccumulation.

There are no changes to the RAOs resulting from this ROD Amendment, and the level of protection of human health and the environment remains the same. In addition, no changes to the future land use of RMA are anticipated as a result of this ROD Amendment.

4.2 Description of Alternatives

Based on the historical Hex Pit information and new information obtained since the ROD was signed, four alternatives were evaluated for remediation of the Hex Pit. Because the innovative thermal technology selected in accordance with the ROD failed during implementation, it was not included in this evaluation. In addition, due to the inability to identify a viable reagent for the ROD contingent remedy (solidification/stabilization), it was also not considered as an alternative.

In addition to the NCP requirement to consider a no-action alternative (which serves as a point of departure from other alternatives under consideration), three other remedial alternatives were considered, including the following:

Alternative 1 – No additional action specifically for the Hex Pit. The Hex Pit waste and soil are contained beneath a RCRA-equivalent cover as part of the larger South Plants project.


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Alternative 2 – Construct a vertical barrier keyed into competent bedrock to isolate the Hex Pit. The Hex Pit waste and soil is contained beneath the South Plants RCRA-equivalent cover.

Alternative 3 – Contaminated soil and Hex Pit material are excavated and disposed in the on-post HWL. Air emissions and odors are controlled during excavation and landfilling activities. The excavation is backfilled and contained beneath the South Plants RCRA-equivalent cover.

Alternative 4 - Contaminated soil and Hex Pit material are excavated and transported to an approved,RCRA-permitted hazardous waste incineration/landfill facility for treatment and disposal. Air emissions and odors are controlled during excavation and landfilling activities. The excavation is backfilled and contained beneath the South Plants RCRA-equivalent cover.

All remedy components presented in the ROD for groundwater and structures are unaffected by this ROD Amendment. No impacts are expected on any other ROD-designated soil projects outside of the Hex Pit for Alternatives 1, 2 and 4. Alternative 3 may impact the HWL as Hex Pit material is to be transported directly to and disposed at the HWL. The Hex Pit is located within the South Plants cover area. This area will be retained by the Army and assessed every 5 years, as part of site-wide 5-year reviews, to ensure that the overall remedy continues to provide adequate protection of human health and the environment and complies with applicable regulations. In addition, site-wide institutional controls identified in the RMA FFA are included as requirements in the ROD. These requirements restrict future land use and prohibit certain activities such as agriculture, use of on-postgroundwater as a drinking source, and consumption of fish and game taken at RMA.

4.2.1 Alternative 1: No Additional Action (RCRA-Equivalent Cover)

The evaluation of a no-action alternative is generally required to establish a baseline for comparison of remedial alternatives. Under this alternative, no action specific to the Hex Pit material would be taken, i.e., all of the Hex Pit material would remain in place with no toxicity, volume or mobility reduction of COCs. However, since the Hex Pit is located within South Plants, the site would be contained beneath the South Plants RCRA-equivalentcover. Ten to 14 feet of gradefill material would be placed over the site followed by construction of the cover. Existing heater wells constructed for the ISTD would be left in place beneath the cover. Three existing horizontal wells used for dewatering during the original remedy would be abandoned in place in accordance with approved well abandonment procedures. Key applicable or relevant and appropriate requirements (ARARs) relating to this remedy are those regulations pertaining to particulate and odor emissions, stormwater/erosion control andgroundwater monitoring. Complete ARARs pertinent to constructing a soil cover barrier are included in the ROD, Table A-16. Although there is no action taken specific to the Hex Pit, implementation of this remedy achieves RAOs since the waste is contained beneath the South Plants RCRA-equivalent cover. Five-year site reviews and groundwater compliance monitoring are conducted to assess potential migration of contaminants from the Hex Pit.


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The estimated cost for implementing this alternative includes an estimated capital cost of $16,800 and estimated annual operations and maintenance (O&M) cost of $2420. The total estimated present worth long-termmonitoring cost is $70,000. These costs include installation of groundwater monitoring wells and the groundwatersampling and analysis costs to assess any migration of the waste left in place. This cost does not reflect leachate generation study costs that might be necessary to assess the mobility of the waste contaminants. Costs for abandonment of the three existing dewatering wells is estimated at $50,000. Implementation for design and construction of this alternative would take approximately 12 months.

4.2.2 Alternative 2: Vertical Barrier; RCRA-Equivalent Cover

A vertical barrier is constructed around the perimeter of the. Hex Pit boundary with the barrier keyed into competent bedrock to prevent groundwater movement into the pit waste. No intrusive activities or treatment relating to Hex Pit material occur during implementation of this remedy and the Hex Pit material remains in place with no reduction in COC toxicity or volume; however, the mobility of COCs is reduced as a result of containment within the vertical barrier. After construction of the vertical barrier is completed, the South Plants RCRA-equivalent cover would be constructed over the Hex Pit as described under Alternative 1. Existing heater wells constructed for the ISTD would be left in place beneath the cover. Three existing horizontal wells used for dewatering during the original remedy would be abandoned in place in accordance with approved well abandonment procedures. Key ARARs relating to this remedy are those regulations pertaining to particulate and odor emissions, stormwater/erosion control, waste management/on-post disposal and groundwater monitoring. Complete ARARs pertinent to constructing a vertical barrier are included in the ROD, Table A-18.Implementation of this remedy achieves RAOs through containment of the waste within the vertical barrier and beneath the South Plants RCRA-equivalent cover.

The estimated cost for implementing this alternative includes an estimated capital cost of $930,000 and estimated annual O&M costs of $2,420. The total estimated present worth cost is $1,000,000. These costs include long-termgroundwater monitoring costs. Implementation for design and construction of this alternative would take approximately 14 months. Compatibility testing of groundwater with selected vertical barrier materials would be completed during design.

4.2.3 Alternative 3: Excavate; On-Post Landfill

The Hex Pit waste material, existing ISTD wells and surrounding soil within the project boundary would be excavated and transported to the on-post HWL for disposal. Excavation would be completed to a depth of 10 feet across the 5,410 square foot area for a total volume of 2,005 bcy as shown in Figure 2.5-1. Addition excavation, if necessary, would continue based on visual evidence of Hex Pit waste beyond the design boundary. Dewatering of some of the excavated material may be required (depending on the groundwater level during field activities) to ensure that the excavated material meets the on-post HWL waste acceptance criteria pertaining to the prohibition of free liquids in waste to be disposed. Air emissions and odor controls, developed during remedial design to meet regulatory requirements, would be applied


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during excavation, transportation and placement of waste in the HWL. If the waste extends below the groundwater table, three existing horizontal wells are in place to dewater and allow additional excavation (these wells will be abandoned at the end of the project in accordance with approved well abandonment procedures). The excavation depth would be one foot above the practical limit of dewatering, currently estimated at 15 feet be lowground surface. The excavation would be backfilled using on-post borrow material and subsequently contained beneath the South Plants RCRA-equivalent cover. Implementation of this remedy would result in no COC reductions in toxicity and volume of waste. All RAOs are met through containment of contaminated material in the on-post HWL. The COC mobility is reduced through containment of Hex Pit material in the HWL. Key ARARs relating to this remedy are those regulations pertaining to particulate and odor emissions,stormwater/erosion control and waste management/on-post disposal.

One of the issues identified for this alternative was whether the Hex Pit waste would meet waste acceptance requirements for the existing on-post HWL. Although the Hex Pit was considered in the liner, and waste compatibility evaluations and demonstrations conducted in support of the HWL design and siting, additional compatibility testing was conducted in support of this alternative. During development of the remedial alternatives for the Revised Proposed Plan, a leachate characterization analysis was performed to specifically assess compatibility of the Hex Pit waste in the HWL. Hex Pit waste samples were collected and a representative leachate was generated. The leachate characteristics were compared with the compatibility and acceptance criteria established for the HWL. This comparison verified the compatibility of the Hex Pit leachate with the HWL liner and other wastes (RVO 2003). Also, due to the relatively small volume of waste associated with the Hex Pit project, the existing on-post HWL has sufficient capacity to accept the waste.

The estimated present worth cost for implementing this alternative includes an estimated capital cost of $920,000 with no annual O&M cost. Implementation for design and construction of this alternative would take approximately 12 months.

4.2.4 Alternative 4: Excavate; Off-Post Incineration

The 2,005 bcy of Hex Pit material and surrounding soil within the project boundary would be excavated and transported to an off-post RCRA-permitted hazardous waste incinerator. Treatment residuals would be disposed in a permitted off-post RCRA hazardous waste landfill. Existing ISTD wells would be removed, sized and subsequently disposed in the on-post HWL. In addition, three existing horizontal wells are in place, should dewatering be required during excavation (these wells will be abandoned at the end of the project in accordance with approved well abandonment procedures). Air emissions and odor controls would be applied during excavation.

The excavation would be backfilled using on-post borrow material and then contained beneath the South Plants RCRA-equivalent cover. Key ARARs relating to this remedy are those regulations pertaining to particulate and odor emissions, stormwater/erosion control and waste management/treatment/off-post disposal. Complete ARARs pertinent to incineration are


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included in the ROD, Table A-21. Implementation of this remedy results in COC toxicity, volume and mobility reduction and achieves RAOs through treatment of contaminated material.

The estimated present worth cost for implementing this alternative includes an estimated capital cost of $3,350,000 with no annual O&M cost. Implementation for design and construction of this alternative would take approximately 14 months.

5.0 COMPARATIVE ANALYSIS OF ALTERNATIVES

The NCP identifies nine criteria to be used in the evaluation of remedial alternatives (EPA 1990). The evaluation consists of an assessment of individual alternatives against each of the nine criteria and a comparative analysis that focuses on the relative performance of each alternative against each other. The criteria are grouped into three categories. The first two criteria, overall protection of human health and the environment and compliance with ARARs, are considered “threshold criteria” that must be met by each alternative to be eligible for selection. The next group of criteria are considered “balancing criteria” because they are used to achieve the best overall solution. These criteria include long-term effectiveness and permanence; reduction of toxicity, mobility, or volume through treatment; short-term effectiveness; implementability; and cost. The final two criteria, state acceptance and community acceptance, are modifying criteria and are used to evaluate the feasibility of implementing an alternative in terms of its acceptance by Regulatory Agencies and the community.

This section of the ROD Amendment provides an evaluation of each alternative against the nine criteria, noting how it compares to the other alternatives under consideration. This evaluation provides the basis for determining which Hex Pit alternative provides the best balance with respect to the statutory balancing criteria in Section 121 of CERCLA and in Section 300.430 of the NCP. For purposes of comparison, Table 5.0-1 provides a side-by-sidesummary of the evaluation of the four alternatives.

5.1 Overall Protection of Human Health and the Environment

Overall protection of human health and the environment assesses whether each alternative provides adequate protection of human health and describes how risks posed through each exposure pathway are eliminated, reduced, or controlled, through treatment, engineering controls, and/or institutional controls.

All of the alternatives evaluated achieve RAOs and provide protection of human health and the environment through in-place containment or by removal and treatment/disposal in appropriate facilities. Alternative 1, the No Additional Action alternative, is also expected to provide adequate protection because the area is contained beneath the South Plants RCRA-equivalent cover thereby interrupting the exposure pathway for humans and biota. There would be a potential impact to groundwater quality if the groundwater table rises and contacts the waste. Therefore, this alternative is the least protective alternative under consideration. Alternative 2 provides somewhat better protection because of the addition of a vertical barrier around the


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project boundary. Both Alternative 1 and Alternative 2 rely on long-term cover maintenance to ensure protectiveness. In addition, groundwater is captured and treated at the RMA facilities thereby achieving groundwater RAOs and providing protection for human health and the environment. Alternatives 3 and 4 are more protective than Alternatives 1 and 2 because the Hex Pit waste and contaminated soil are removed and contained in the on-site HWL or treated off-site through incineration.

5.2 Compliance with ARARs

Section 121(d) of CERCLA and the NCP, 40 CFR 300.430(f)(l)(ii)(B), require that remedial actions at CERCLA sites at least attain legally applicable or relevant and appropriate Federal and State requirements, standards, criteria, and limitations, collectively referred tows ARARs, unless such ARARs are waived under CERCLA section 121(d)(4). All of the alternatives being evaluated comply with Federal and State ARARs and comply with the location-, chemical-, and action-specific ARARs listed in the ROD, which remain unchanged for the implementation of any of the proposed alternatives.

5.3 Long-Term Effectiveness and Permanence

Long-term effectiveness and permanence refers to expected residual risk and the ability of a remedy to maintain reliable protection of human health and the environment over time, once clean-up levels have been met. This criterion includes the consideration of residual risk that will remain onsite following rernediation and the adequacy and reliability of controls.

All of the alternatives achieve long-term effectiveness; however, there is moderate residual risk associated with Alternative 1. Concentrations of Hex and organochlorine pesticides posing a principal threat in the soil are left in place, leaving the potential for future groundwater contamination. Alternative 2 has decreased risk due to the addition of the vertical barrier. In addition, RAOs are met through the presence of groundwater pump and treat systems downgradient from the Hex Pit. Under these two alternatives, site reviews are conducted and soil and groundwater monitoring is required. Alternative 1, and to a lesser extent Alternative 2, are subject to uncertainties concerning groundwater contamination and would provide the least long-term effectiveness and permanence.

Residual risk is minimized or eliminated with implementation of Alternatives 3 and 4 since all of the Hex Pit material volume, approximately 2,005 bcy, is removed and is either disposed in the on-post HWL (Alternative 3) or treated off-site by incineration with the treated residue disposed in a RCRA-permitted landfill (Alternative 4). There is a high degree of confidence in the effectiveness of engineering controls for both off-site incineration and on-site landfilling. Alternative 4 eliminates long-term risk since the COCs associated with the Hex Pit material are irreversibly destroyed.

5.4 Reduction in Toxicity, Mobility and Volume (TMV)

Reduction of toxicity, mobility or volume through treatment refers to the anticipated performance of the treatment technologies that maybe included as part of the remedy.


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Alternatives 1, 2 and 3 result in no reduction in toxicity or volume and no resulting treatment residuals are generated since treatment of the waste does not occur. Under Alternatives 1 and 2, the Hex Pit material remains in place with mobility reduced through containment beneath the South Plants RCRA-equivalent cover. For Alternative 1, there would be a potential increase in mobility and impact to groundwater quality if the groundwater table rises and contacts the waste. Alternative 2 mitigates this risk through installation of a vertical barrier around the Hex Pit; however, since no groundwater extraction is included inside the barrier, the possibility exists for a reverse gradient to be created that would potentially force contamination through the barrier.

Alternative 3 provides a significant reduction in mobility through removal of waste and soil from the Hex Pit and containment in the on-post HWL. Alternative 4 permanently eliminates TMV of COCs since incineration of the Hex Pit material results in the irreversible destruction of COCs.

5.5 Short-Term Effectiveness

Short-term effectiveness addresses the period of time needed to implement the remedy and any adverse impacts that may be posed to workers, the community and the environment during construction and operation of the remedy until cleanup levels are achieved. Alternatives 1 and 2 entail little, if any short-term risks to workers and the community, as there are no intrusive activities into the Hex Pit materia l. Alternative 2 has slightly higher risks during installation of the vertical barrier; however, the barrier is installed outside the extent of the waste material so risks are still minimal.

Short-term risks for on-site workers associated with Alternatives 3 and 4 are higher due to excavation and material handling of highly contaminated materials that include potential vapor-or odor-causing contaminants. These risks are minimized through the implementation of administrative and engineered controls and the use of personal protective equipment. Risks to the public would be minimal due to the size and duration of the excavation and the presence of emission controls; however, short-term risks to the public for Alternative 4 could be somewhat higher due to the potential of accidents during transportation of waste material from RMA to an approved incineration facility.

5.6 Implementability

Implementability addresses the technical and administrative feasibility of a remedy from design through construction and operation. Factors such as availability of services, administrative feasibility, and coordination with other government entities are also considered. All of the alternatives are technically and administratively feasible and rely on readily available equipment, techniques and on- or off-site treatment/disposal facilities.

Alternative 2 would require evaluation of the groundwater characteristics to ensure selection of a compatible vertical barrier material. Alternative 3 required the evaluation of waste compatibility with the HWL liner. The evaluation was performed in July 2002 and indicated that the leachate produced would not compromise the integrity of the HWL clay liner (RVO


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2003). In addition, HWL waste acceptance criteria will be met with regard to free liquids. Dewatering will be conducted depending on the level of the groundwater table during implementation. Dewatering wells installed for this purpose during ISTD implementation are still in place and will be used to lower the groundwater table when necessary.

Three off-site hazardous waste incinerators were provided the material characteristics and analytical information for the Hex Pit waste. These facilities confirmed that they could successfully treat and subsequently dispose of treated Hex Pit material residue, therefore Alternative 4 is implementable with a high degree of certainty. Air and odor emissions controls are required for Alternatives 3 and 4 during excavation, and at the HWL for Alternative 3. These controls are available and have been successfully used at RMA during previous soil excavation projects.

As a part of the larger RMA cleanup, the schedule for conducting the Hex Pit remedy can directly affect the schedule of other implementation projects. The primary impact is to the construction of the South Plants cover. If Hex Pit remedy implementation extends into the South Plants cover construction period, then the South Plants cover design would need to be modified to leave the Hex Pit area uncovered until completion of the Hex Pit remedy. Since all the Alternatives have 12- to 14-month implementation times, there is minimal impact expected to the South Plants schedule. However, Alternative 2 would result in moderate impact to the South Plants schedule if additional compatibility testing were required beyond the estimated design time frame of 10 months.

5.7 Cost

Alternative 1 cost is significantly lower than the other three alternatives since it involves no additional action specific to the Hex Pit other than long-term groundwater monitoring and closure of the horizontal wells. This cost does not include operation and maintenance costs for groundwater extraction and treatment at the RMA groundwater treatment systems. Costs associated with Alternatives 2 and 3 are roughly equivalent and somewhathigher than Alternative 1, but are still considered low to moderate. Costs for the treatment alternative, Alternative 4, are significantly higher than for Alternative 2 or 3.

Cost uncertainty for Alternative 2 is minimal and is associated with compatib ility of the vertical barrier with the surrounding groundwater. Cost uncertainties for Alternatives 3 and 4 are moderate and are related to air and odor emission control, potential dewatering costs, and the potential need for more intensive materials handlingresulting from excavation of drums/debris.

5.8 State Acceptance

The state (CDPHE) has expressed its support for Alternatives 3 and 4, with a preference for Alternative 3. The state does not support Alternatives 1 or 2 because the Hex Pit waste is left in place and might not provide adequate long-term protection of the groundwater. The state prefers Alternative 3 because it is consistent with the site-wide remedy, the short-term risks are minimized on site and for the community, while the long-termprotection for disposal in the HWL is better then covering the waste in place and it is cost-effective.


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5.9 Community Acceptance

Oral comments received during presentations to the public indicate that the community, in general, supports the preferred alternative, Alternative 3, of removing the Hex Pit waste with on-site landfill disposal rather than leaving the waste in place or transporting it off site for incineration. Alternative 1 was not preferred because the Hex Pit waste would not be directly addressed. Alternative 4 was not preferred due to concerns over safety during transportation of the Hex Pit waste through the community to an off-site incineration facility. While Alternatives 2 and 3 were both considered acceptable, there was an indicated preference toward Alternative 3. However, the commenters expressed specific concerns related to odor control, design review by the public and landfill compatibility for Alternative 3. Community involvement and responses to the community’s specific comments are provided in Section 9.

6.0 SELECTED REMEDY

Based on the comparative analysis presented in Section 5, the selected remedial alternative for cleanup of the Hex Pit is Alternative 3: Excavate; On-Post Landfill. This is the same alternative presented as the preferred alternative in the proposed plan issued in September 2002. This alternative includes excavation of contaminated soil and waste material from the Hex Pit with disposal in the on-site HWL. Air emissions and odor controls, developed during remedial design to meet regulatory requirements, will be applied during excavation, transportation and placement of waste in the HWL. Excavation will be completed to a minimum depth of 10 feet across the 5,410 square foot area as shown in Figure 2.5-1. Additional excavation, if necessary, will continue based on visual evidence of Hex Pit waste beyond the design boundary. Dewatering of some of the excavated material may be required (depending on the groundwater level during field activities) to ensure that the excavated material meets the on-post HWL waste acceptance criteria pertaining to the prohibition of free liquids in waste to be disposed. If the waste extends below the groundwater table, three existing horizontal wells are in place to dewater and allow additiona l excavation (these wells will be abandoned at the end of the project in accordance with approved well abandonment procedures). The limit of excavation depth will be one foot above the practical limit of dewatering, currently estimated at 15 feet below ground surface.

This alternative was selected over the other alternatives because it provides substantial risk reduction through containment of waste material in the on-post HWL within a reasonable time frame and at a lower cost than the treatment alternative. The selected alternative meets RAOs by containing the Hex Pit material in the HWL, thereby preventing future exposure to or migration of contaminants. In addition, the project area will be contained beneath the South Plants RCRA-equivalent cover following excavation of contaminated soil and waste. The Army will maintain control over the cover area and perform long-term maintenance activities. The selected remedy, in conjunction with the RCRA-equivalent cover, will allow management of the area consistent with the anticipated future land use of the surrounding site as a wildlife refuge.

The estimated cost for the selected alternative is $920,000. A summary of the estimated cost elements is provided in Table 6.0-1. The information in this cost estimate summary table is


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based on the best available information regarding the anticipated scope of the project and site experience for other soil remediation projects completed at RMA. Changes in the cost elements are likely to occur as a result of new information and data collected during remedial design. This is an order of magnitude engineering cost estimate and is expected to be within plus 50 to minus 30 percent of the actual project cost.

7.0 SUPPORT AGENCY COMMENTS

A draft ROD Amendment was provided to the Regulatory Agencies (EPA, CDPHE and TCHD) for review and comment. A summary of the major comments submitted by each agency is provided below. Comments received from the agencies have been incorporated into the final ROD Amendment.

The main comments received from EPA were concerning the statutory basis for the amendment and the technical basis used to delineate the Hex Pit extent of excavation. The EPA requested additional detail on the cost basis for why a ROD amendment was necessary. Because the cost increase to continue implementing the ISTD treatment was greater than the 50 percent order of magnitude, a reevaluation (ROD amendment) was necessary. The EPA also requested additional detail on the basis for the area and volume designated for excavation for the Hex Pit. The comment was concerned with providing a solid discussion of the visual basis for identifying Hex Pit waste to provide the basis for remedial design and implementation. Additional comments from EPA included that the amendment needed more detail on the Hex Pit leachate compatibility study for HWL disposal and clarification of COCs for the Hex Pit waste.

The CDPHE commented that the ROD Amendment required additional documentation for the basis of eliminating the contingent remedy (solidification/stabilization), particularly concerning the evaluation of potential solidification/stabilization agents. The comment requested that the discussion be expanded to clarify the decision to eliminate the contingent remedy due to its inability to reduce the mobility of the Hex Pit waste through solidification/stabilization. The CDPHE also requested more detail for the Hex Pit leachate compatibility study including a summary of the data that demonstrate the Hex Pit material and leachate meet the waste acceptancerequirements for the on-post HWL.

Major comments received from TCHD were concerned with documentation of the Hex Pit volume basis and conclusions regarding odor control requirements. The TCHD requested that additional detail be provided to describe how the Hex Pit project boundary was extended beyond the ROD boundaries yet the volume of contaminated waste was reduced from the ROD total of 3,300 bank cubic yards to a design total of 2,005 bank cubic yards. The TCHD also commented that the ROD Amendment should not exclude any odor control strategies and that the conclusions regarding the specific odor control methods or requirements should be determined during the design.


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8.0 STATUTORY DETERMINATIONS

Based on the information available at this time, the Army, in consultation with EPA, believes the selected alternative provides the best balance of tradeoffs with respect to the balancing and modifying criteria. The selected alternative satisfies the requirements of CERCLA Section 121 and is protective of human health and the environment, complies with federal and state requirements that are legally applicable or relevant and appropriate to the remedial action, uses a permanent solution through proper disposal and containment of the wastes in the on-post HWL, and is cost effective. The remedy selected in this ROD Amendment does not satisfy the statutory preference for treatment as a principal element of the remedy for the following reasons: (1) the treatment that was originally selected failed, and (2) Alternative 4 is not cost effective and is not supported by the community. The state concurs on the selection of Alternative 3 for remediation of the Hex Pit.

Protection of Human Health and the Environment

The selected remedy protects human health and the environment by removing the contaminated material from the Hex Pit, thereby reducing the associated risks to below acceptable levels. The contaminated material will be contained in the on-post HWL, eliminating exposure pathways and significantly reducing mobilit y to other media. There are moderate short-term risks to on-site workers associated with vapor and odor emissions that cannot be completely eliminated, although the risks are minimized by engineering and administrative controls. These engineering and administrative controls minimize any risks from vapor and odor emissions to the adjacent community.

Compliance with ARARs

The selected remedy complies with all location-, chemical-, and action-specific ARARs that are pertinent to Hex Pit remediation at RMA. These ARARs, developed in compliance with Section 121(d) of CERCLA, are presented in Tables 8.0-1, 8.0-2 and 8.0-3.

Utilization of Permanent Solutions and Alternative Treatment Technologies to the Maximum Extent Practicable and Preference for Treatment as a Principal Element of the Remedy

The remedy selected in this ROD Amendment represents the maximum extent to which permanent solutions and treatment technologies can be practicably used at the Hex Pit. Of the alternatives that are protective of human health and the environment and comply with ARARs, the selected remedy provides the best balance of tradeoffs for long-term effectiveness and permanence; reduction in toxicity, mobility, or volume; short-term effectiveness and implementability. Also considered were the statutory preference for treatment as a principal element and State and community acceptance.

Of the alternatives considered, all of the alternatives would achieve long-term effectiveness, however, there is a continued risk to groundwater associa ted with Alternative 1. Since potential short-term risks could be addressed for all alternatives, the short-term effectiveness criterion was not a decisive factor in the selection decision. Alternative 4 would use treatment to reduce


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toxicity, mobility and volume, but at a significantly higher cost than the other alternatives, and Alternative 4 was not supported by the community. Since both the selected alternative and Alternative 2 have similar costs, are implementable and have similar short-term effectiveness, the major tradeoffs that provide the basis for this decision are the reduction of mobility, and more certain long-term effectiveness and permanence achieved by excavation of the material and containment in the HWL.

The remedy selected in this ROD Amendment does not satisfy the statutory preference for treatment as a principal element of the remedy for the following reasons: (1) the treatment that was originally selected failed, and (2) Alternative 4 is not cost effective and is not supported by the community. The remedy selected in this ROD Amendment provides for excavation, proper disposal and permanent containment of the wastes in the on-postHWL. The area of the excavation will then be capped.

Cost Effectiveness

Cost effectiveness is assessed by evaluating three of the five balancing criteria to determine overall effectiveness: long-term effectiveness and permanence; reduction of toxicity, mobility, or volume through treatment; and short-term effectiveness. Overall effectiveness is then compared to cost to determine if the remedy is cost effective.

Proportional to cost, the selected remedy provides the best overall effectiveness of the alternatives considered. The selected remedy will achieve the RAOs for the contaminated material and permanently reduce mobility of contaminants. The remedy makes use of proven technology that will be protective over the long term and minimize or mitigate short-term impacts during remediation.

Five-Year Review Requirements

The Hex Pit is located within the South Plants cover area. This area will be retained by the Army and assessed every 5 years, as part of site-wide 5-year reviews, to ensure that the overall remedy continues to provide adequate protection of human health and the environment and complies with applicable regulations. In addition, site-wideinstitutional controls identified in the RMA FFA are included as requirements in the ROD. These requirements restrict future land use and prohibit certain activities such as agriculture, use of on-post groundwater as a drinking source, and consumption of fish and game taken at RMA.

9.0 COMMUNITY PARTICIPATION COMPLIANCE

9.1 Overview

The selected remedy in the 1996 ROD for the Hex Pit included treatment of the contaminated pit material using an innovative thermal technology. An innovative technology, ISTD, was selected in accordance with the ROD requirements after evaluation of technologies that were capable of treating the hex waste. During the evaluation process, the public was invited to provide comments on the technology evaluations at several public meetings. Following


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completion of the evaluation, a technology evaluation report identifying the selected innovative technology as ISTD was distributed for public comment.

During the design process, public comment periods were also provided at the 30 percent and the 95 percent design phases. Public availability presentations were made to the RAB on May 4, 2000, September 7, 2000, and January 4, 2001. No comments were received from the public on the design prior to finalization.

Implementation of the ISTD treatment was started in March 2002. However, the system failed shortly after startup due to excess HCl formation resulting in corrosion of the treatment train and partial system failure. A preliminary assessment of the ISTD system, system failure, and feasibility of continuing the treatment technology required a new evaluation of cleanup alternatives.

The community in general seemed to support the preferred alternative of removing the Hex Pit waste with on-sitelandfill disposal rather than leaving the waste in place or transporting it off site for incineration. However, concerns relating to the ability to control emissions and odors during excavation and the compatibility of the waste for landfill disposal were expressed.

9.2 Background on Community Involvement

In accordance with CERCLA Section 117 and the NCP, 40 CFR 300.435(c)(2)(ii), the Army issued a Revised Proposed Plan for public comment describing the changes in the preferred remedy for the Hex Pit. The Revised Proposed Plan and supporting information were made available at the JARDF, which is located on RMA in Building 129, Room 2024. Legal notice of availability of the Revised Proposed Plan and the public comment period was published in The Denver Post on September 22, 2002.

The Army conducted a public meeting on October 10, 2002 to present the information regarding the Hex Pit remediation and the Revised Proposed Plan. A public comment period of 30 days was provided to receive written comments on the Revised Proposed Plan. In response to a request received at the public meeting, the public comment period was extended to 60 days and closed on November 22, 2002. Comments received at the public meeting are summarized with responses in Section 9.4. No written comments were received from the general public.

In addition to the JARDF and public meetings, the Army regularly provides information to the public regarding cleanup activities at RMA through Restoration Advisory Board (RAB) meetings. This board serves as the primary forum through which neighboring communities can receive and share information as well as provide input to the parties involved in the RMA’s cleanup. Established in April 1994 by the Department of Defense, the RAB is comprised of community members, elected officials, governmental agencies and the Remediation Venture Office (RVO) (U.S. Army, Shell Oil Company and the U.S. Fish and Wildlife Service). These entities work together to review remediation designs and discuss cleanup issues of interest to the community. The goal of the RMA’s RAB is to encourage community participation by discussing and exchanging information regarding the final environmental cleanup of RMA. The RAB has been involved in the Hex Pit remediation project through review of the treatability


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study reports and design documents. These documents are available for public review at the JARDF. For more information concerning the RAB, contact the RMA Public Affairs Office at (303) 289-0136.

Prior to issuing the Revised Proposed Plan, the Army provided a discussion of the ISTD failure and the remedial alternatives being considered for the Hex Pit and solicited input from the RAB on these alternatives. Preliminary comments received from the RAB indicated that their preferred alternative was on-post landfilling. Comments from both the RAB meeting and the October 10, 2002 public comment meeting were considered before finalizing selection of the remedy for the Hex Pit.

9.3 Summary of Comments

The public meeting for the Revised Proposed Plan for the Hex Pit was held on October 10, 2002. The Army provided a presentation on the Hex Pit remedial alternatives evaluation and the new preferred alternative. Questions and comments followed the presentation. A court reporter recorded the meeting and provided a transcript, which is available in the JARDF. The following section summarizes individual comments from the public meeting transcript. The commentor’s name is indicated followed by the comment and response. Specific concerns expressed at the public meeting were related to odor control, design review by the public and landfill compatibility. No written comments were received from the public during the public comment period. The selected remedy was chosen after careful consideration of public comments received on the Revised Proposed Plan for this ROD Amendment.

9.4 Responses to Comments

Mr. Union: Mr. Union affiliated himself with the Commerce City Beacon. He asked if the taxpayers paid for the Hex Pit remedy that had failed.

Response: The subcontractor that completed the design, construction and brief operation of the ISTD treatment system was paid for the actual work that they performed. The project was paid for by the Army and Shell.

Mr. Russell: Mr. Russell asked for consideration to provide the 60 percent Hex Pit design for public review, rather than just the 30 percent and 95 percent designs, to provide for adequate public review.

Response: The NCP requires that the final (100 percent) design be made available to the public (by publishing a notice of availability in local newspapers) and the conduct of a public meeting discussing the design, if requested. However, the RVO is aware of the public sensitivity to remediation design elements, particularly related to emission and odor control, and acknowledges Mr. Russell’s desire to review and comment on all stages of the Hex Pit design. Therefore, the RVO routinely provides both the 30 percent and 95 percent design packages for all RMA projects to the public for review and comment as well as presenting these designs at the RAB public meetings. This allows the public to provide input early in the design process (30 percent phase) and assess if their concerns have been adequately addressed (95 percent phase) before the


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design is finalized. The RVO will continue to provide pertinent design information throughout the design process at RAB public meetings.

Mr. Mulqueen: Mr. Mulqueen expressed concern that air issues were not part of the Amendment. He later expressed concern again that the waste is volatile and has odor potential and this issue is not addressed in the Amendment but rather will be addressed in design. Specifically, he wanted more detail as to what air control and monitoring measures would be used. He understood air issues would be part of the design but thought they should be addressed as part of the Amendment to allow for comment as part of the remedy selection.

Response: The RVO understands that air and odor emissions potential are critical concerns of the community. The Revised Proposed Plan for the Hex Pit identified these issues as potential short-term risks during excavation requiring appropriate controls to mitigate the risk. Emission and odor controls are identified in the ROD Amendment as ARARs, and are presented on Table 8.0-3. To meet these requirements, control measures will be developed during remedial design - when emission and odor control testing can best be performed. This allows exploration of all available control methods in conjunction with the specific excavation strategy to select the best controls for the project. The control measures will be selected specifically for the Hex Pit excavation and will be designed to prevent off-site releases. In addition, the design will include monitoring requirements consistent with the site-wide air and odor monitoring plans to assist in controlling emissions and adjusting project operations to minimize air impacts from remediation. The design, including the specific control measures to be implemented, will be made available for pubic review and comment before being finalized. Public reviews will be conducted at both the 30 percent and 95 percent design stages.

Mr. Mulqueen: Is the proposed disposal location the triple -lined landfill?

Response: No. Consistent with the ROD, the disposal site is the existing on-site, double -lined landfill. The triple -lined landfill that will be constructed at RMA is to be used for disposal of waste from the Basin F Wastepile and the Section 36 Lime Settling Basins.

Mr. Mulqueen: Commented on the paint filter test and volatility of the waste relative to acceptance at the landfill.

Response: All waste disposed in the HWL must be capable of passing the paint filter test. This test provides an indication of free liquids in the waste, which are prohibited from disposal in the HWL. Characterization of the Hex Pit indicates that the waste does pass the paint filter test. Visually wet materials are not necessarily an indication of the presence of free liquids or landfill unacceptability. However, if visually wet materials are encountered during excavation, the acceptability of the waste for disposal in the HWL will be determined using the paint filter test. Although the constituents of the Hex Pit waste are considered semi-volatile, this characteristic does not impact the paint filter test. Emission and odor concerns related to the volatility of the waste will be addressed during design as discussed in the response to the first comment.

Ms. Jaquith: Ms. Jaquith requested clarification on the corrosive potential of the Hex Pit waste with respect to the landfill liner and compatibility with other materials that will be in the landfill


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in contact with the waste. Ms. Jaquith also asked what would happen if the waste is heated at some point.

Response: During development of the remedial alternatives for the Revised Proposed Plan, a leachate characterization analysis was performed to specifically assess compatibility of the Hex Pit waste in the HWL. Hex Pit waste samples were collected and a representative leachate was generated. The leachate characteristics were compared with the compatibility and acceptance criteria established for the HWL. This comparison verified compatibility of the Hex Pit leachate with the liner and other wastes (RVO 2003).

The Hex Pit waste in its current solid form does not have the high corrosive potential that the vapor exhibited during the ISTD operation. Analytical results of the Hex Pit soil during the compatibility study indicated pH in the neutral to slightly acidic range. The highly corrosive environment is created when the waste is heated, begins to break down, and produces large amounts of chlorine that react with water to form hydrochloric acid. The ISTD process was designed to achieve minimum temperatures of 600°F throughout the soil and waste. This target temperature was based on the boiling point of Hex (about 460°F) to ensure that all the waste was treated. There are no mechanisms through which the landfill could be heated to reach these temperatures.

Ms. Fischer: Ms. Fischer asked whether payment had been made for the failed ISTD treatment.

Response: The subcontractor that completed the design, construction and brief operation of the ISTD treatment system was paid for the work they performed. It is important to note that innovative technologies are generally less proven and have a higher potential to fail. The ISTD technology was selected as the best approach to successfully treat the Hex Pit material.

Ms. Fischer: Will the underground equipment from the ISTD project be disposed with the Hex Pit waste and if so, will the equipment corrode due to contact with the Hex Pit waste?

Response: All heater and heater/vacuum wells installed during ISTD operation will be removed and disposed in the HWL along with the Hex Pit waste. Because the metal will remain in contact with the waste, some additional corrosion, in the form of rust, might occur. However, the result of this corrosion does not present any waste compatibility or liner compatibility problems for the HWL.

Mr. Mulqueen: Requested that the results of the compatibility testing for the landfill liner be made available.

Response: The results of the HWL compatibility testing performed by the RVO are summarized in the Hex Pit Leachate Investigation Summary Report. This report is available in the JARDF as supporting documentation for the ROD Amendment and a copy can be requested by calling the JARDF at 303-289-0136 or 1-800-862-0754.

Ms. Jaquith: What was the concern with selecting the alternative involving the vertical groundwater barrier?


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Response: This alternative included construction of a vertical barrier around the perimeter of the Hex Pit boundary followed by containment of the Hex Pit beneath the South Plants RCRA-equivalent cover. The Hex Pit material would remain in place while the vertical barrier and RCRA-equivalent cover would serve to prevent groundwater movement into the waste. Review of this alternative against the selected alternative (excavation and landfill), determined that the selected alternative provides a better balance of tradeoffs because containment of the waste in the on-site landfill provides a higher degree of long-term effectiveness and reduction of mobility.

Ms. Jaquith: Commented that she appreciated the fact that the RVO was considering the long-term protection of the groundwater supply in the remedial alternatives evaluation for the Hex Pit.

Response: The RVO remains committed to implementing a remedy for the Hex Pit that provides long-termprotection of human health and the environment.

Ms. Jaquith and Ms. Fischer: The public comment period should be extended to 30 days after the public meeting or 30 days after all requested information has been submitted to the public.

Response: The public comment period was initially set at 30 days following the public notice of availability for the Revised Proposed Plan, which was published September 22, 2002, closing on October 25, 2002. The comment period was extended an additional 30 days and closed November 22, 2002.

Mr. Union: Do we know if the groundwater has been contaminated by Hex Pit material in the past and if so, how has the contaminated groundwater been dealt with?

Response: An investigation (“Investigation of the Hex Pit as a Possible Source of Groundwater Contamination at the RMA” [MKE 1989]) was conducted to assess if the Hex Pit was a source of groundwater contamination and whether an IRA should be implemented. The results of the investigation indicated that low-level concentrations of some Hex Pit contaminants were present in groundwater. However, because these contaminants were present both upgradient and downgradient of the pit, the Hex Pit could not be identified as a definite source. If the Hex Pit is assumed to be a source of groundwater contamination, the concentrations of Hex Pit contaminants accounted for approximately 0.01 percent of the total concentration of organic compounds present in groundwater (MKE 1989). In addition, the relative insolubility of the Hex compounds and the typical separation between the waste and groundwater reduce the potential for release of these compounds to groundwater.

The majority of the groundwater contamination in South Plants, including the Hex Pit area, migrates northward under Basin A in Section 36 and is treated at the Basin A Neck Containment System (BANCS), which was installed in 1990. Downgradient of the BANCS, groundwater migrates toward the Northwest and North Boundary Containment Systems where it is treated. These systems were installed in 1984 and 1981, respectively.

Mr. Mulqueen: Would like information regarding cost estimate detail related to the cost of excavation and landfilling versus the cost of leaving in place and dealing with groundwater contamination.


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Response: Groundwater monitoring and treatment costs were not included in the cost estimate because the Hex Pit is contained in the larger South Plants Central Processing Area. Groundwater monitoring for South Plants is included in the overall remedy, and the much larger groundwater plume flowing from South Plants is already treated at the existing treatment facilities. Therefore, the cost impact related to groundwater contamination-fromthe Hex Pit cannot be individually assessed and is expected to be minimal.

Mr. Mulqueen: Would like to see the Hex Pit waste fully characterized.

Response: The Hex Pit waste was characterized during the treatability study phase of the remedial design for the ISTD treatment. Three separate characterization efforts were completed during the remedial design and treatability study. Analyses of the Hex Pit waste were completed for volatile organic compounds, OCPs, metals including arsenic, lead and mercury, dioxins and also for soil/waste physical characteristics. The complete results of the design characterization are presented in the Hex Pit Site Characterization Report and the Hex Pit Treatability Study Report. Both reports are available in the JARDF and a copy of each can be requested by calling 303-289-0136 or 1-800-862-0754.

Mr. Jaquith: Had Coors been contacted to see if they could make ceramic casings for heating rods that would be less affected by corrosion?

Response: Coors was not contacted to pursue the use of ceramics as an option. Although ceramic and glass are well known for their corrosion-resistant properties, use of ceramic well casings for the ISTD system would not eliminate the corrosion problems. In addition to corrosion of the well casings and heater rods, the entire above ground treatment system, including the thermal oxidizer, was subject to heavy corrosion. The significantly increased cost to replace the entire system with ceramic or other components necessitated a reevaluation of cleanup alternatives.

City Government Comments

During the public comment period, comments were received from the City and County of Denver, Department ofEnvironmental Health. Their comments included concerns about air and odor emissions during remediation, preventing off-site releases, monitoring during remediation, and communication between the RVO and the Regulatory Agencies, including the Denver Department of Environmental Health, on odor and emission releases.

Response: The RVO understands that air and odor emissions potential are critical concerns of the community. The Revised Proposed Plan for the Hex Pit identified these issues as potential short-term risks during excavation requiring appropriate controls to mitigate the risk. Emission and odor controls are identified in the ROD Amendment as ARARs and are presented on Table 8.0-3. To meet these requirements, control measures will be developed during remedial design when emission and odor control testing can best be performed. This allows exploration of all available control methods in conjunction with the specific excavation strategy to select the best controls for the project. The control measures will be selected specifically for the Hex Pit excavation and will be designed to prevent off-site releases. In addition, the design will include


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monitoring requirements consistent with the site-wide air and odor monitoring plans to assist in controlling emissions and adjusting project operations to minimize air impacts from remediation. The RVO will continue to provide information consistent with current practice to the Denver Department of Environmental Health concerning remediation activities, monitoring results and potential releases to ensure that all concerns are appropriately addressed.

9.5 Remaining Concerns

All concerns and issues raised at the Revised Proposed Plan public meeting or during the public comment period for the Revised Proposed Plan were addressed in the Revised Proposed Plan and this ROD Amendment. Based on the comments received, the RVO is aware that air and odor emissions potential are critical concerns for the community. Emission and odor controls are identified in the ROD Amendment as ARARs. To meet these requirements, control measures will be developed during remedial design when emission and odor control testing can best be performed. This allows exploration of all available control methods in conjunction with the specific excavation strategy to select the best controls for the project. The control measures will be selected specifically for the Hex Pit excavation and will be designed to prevent off-site releases. In addition, the design will include monitoring requirements consistent with the site-wide air and odor monitoring plans to assist in controlling emissions and adjusting project operations to minimize air impacts from remediation. The design, including the specific control measures to be implemented, will be made available for pubic review and comment before being finalized. Public reviews will be conducted at both the 30 percent and 95 percent design stages. Based on the written and verbal comments received, no changes to the remedy selection as it was identified in the RevisedProposed Plan were necessary.

9.6 Community Relations Activities

Table 9.6-1 includes a list of community relations activities related to the Hex Pit during site characterization, ISTD design and development of this ROD Amendment.


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10.0 REFERENCES

CDPHE et al. (Colorado Department of Public Health and Environment, Tri-County Health Department, U.S. Environmental Protection Agency)1998 (Sept.) Innovative Thermal Technology Evaluation Report for the Hex Pit Site at the Rocky

Mountain Arsenal.

EMTEC (Rocky Mountain Engineering and Materials Technology, Inc.) 2002 (July 8) Hex Pit Soil Remediation Failure Evaluation.

ENSR (ENSR Corporation)2000 (Feb.) Hex Pit Treatability Study Report. Final.

1999 (Aug.) Hex Pit Site Characterization Report. Final.

EPA (U.S. Environmental Protection Agency)1999 (July) A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other

Remedy Selection Decision Documents. EPA 540-R-98-031.

1992 (Oct.) Guide for Conducting Treatability Studies Under CERCLA. Final. EPA 540-R-92-071a.

1990 (Mar. 8) National Oil and Hazardous Substances Pollution Contingency Plan. Final Rule. 40 CFR Part 300. Federal Register 55 (46): 8666-8865.

EPA et al. (U.S. Environmental Protection Agency, U.S. Department of Army, U.S. Department of Interior,Agency for Toxic Substance and Disease Registry)1989 (Feb. 17) Federal Facility Agreement Pursuant to CERCLA Section 120. Docket No. CERCLA

VIII-89-13.

FWENC (Foster Wheeler Environmental Corporation)1996 (June 11) Record of Decision for the On-Post Operable Unit, Version 3.1.

1994 (July) Integrated Endangerment Assessment/Risk Characterization, Final, Version 4.2.

MKE (MK-Environmental Services)1989 (Aug.) Investigation of the Hex Pit as a Possible Source of Groundwater Contamination at the

RMA

OSWER-EPA (Office of Solid Waste and Emergency Response, U.S. EPA)1989 (July) Guidance on Preparing Superfund Decision Documents. OSWER/9355.3-02.

PMRMA (Program Manager for Rocky Mountain Arsenal)2002 (Sept. 22) Revised Proposed Plan for the Rocky Mountain Arsenal On-Post Operable Unit, Hex Pit

Site.

1996 (June 10) On-Post Operable Unit Record of Decision Dispute Resolution Agreement.


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RVO (Remediation Venture Office)2003 (Mar. 13) Hex Pit Leachate Investigation Summary Report.

1998 (Feb. 1 8) Hex Pit Design Data Collection Sampling Report.

TerraTherm (TerraTherm, Inc.)2002 (Apr.) Hex Pit Remediation/Material Failure Assessment Report.

2001 (Mar.) Hex Pit Remediation - Final (100%) Design Package.

2000a (Dec.) Hex Pit Remediation - 95 Percent Design Analysis Addendum.

2000b (July) Hex Pit Remediation – 95 Percent Design Report.

2000c (Apr.) Hex Pit Remediation – 30 Percent Design Report.

TABLES

Table 2.5-1 Hex Pit Contaminants of Concern and Site Evaluation Criteria

COC

1997 Design Data Collection

Maximum

Concentration

(µg/g)

1999 Site Characterization

Maximum

Concentration

(µg/g)

1999 Treatability Study Maximum

Concentration

(µg/g)

ROD SiteEvaluation

Criteria (µg/g)

Hex 160,000 9,000 21,000 1,100

Aldrin 590 ND 320 71

Chlordane 27 1,500 3,600 55

Dieldrin 1,300 2,200 5,600 41

Endrin ND ND 280 230

Isodrin 23 ND 200 52

Benzene 0.13 ND 10 1,040

Carbon Tetrachloride 51 21 34 30

Chloroform 40 10 30 370

Methylene Chloride 2.6 14 0.7 2,300

Tetrachloroethylene 72 25 51 410

ND = nondetect

Table 5.0-1 Comparative Analysis of Alternatives - Hex Pit Remediation Page 1 of 2

CRITERIA ALTERNATIVE 1: NO ALTERNATIVE 2: ALTERNATIVE 3: ALTERNATIVE 4:

ADDITIONAL ACTION VERTICAL BARRIER EXCAVATE; ON-POST OFF-POST

(RCRA-EQUIVALENT WITH RCRA- LANDFILL INCINERATION

COVER) EQUIVALENT COVER

Overall Protection of Protective. Exposure Protective. Exposure Protective. Exposure Protective. Exposure

Human Health and the prevented by covering prevented by containing prevented by containing prevented by off-site

Environment waste in place. Impacts to waste in place. Impacts to waste in the HWL. Impacts treatment (destruction) of

groundwater reduced by groundwater are reduced to groundwater are waste and subsequent

the RCRA-equivalent through both vertical (GW minimized through disposal of residuals in an

cover over the site. barrier) and horizontal removal and containment off-site hazardous waste

Potential impact if (RCRA-equivalent cover) in the HWL. landfill. Groundwater

groundwater rises into containment. Groundwater impacts eliminated

waste. Groundwater treated treated at existing treatment through removal.

at existing treatment facilities.

facilities.

Compliance with ARARs Complies with action -, Complies with action -, Complies with action -. Complies with action -,

chemical-, and location - chemical-, and location - chemical-. and location= chemical-, and location -

specific ARARs. specific ARARs. specific ARARs. specific ARARs.

Long-Term Effectiveness Moderate residual risk. Moderate-Minimal residual Minimal residual risk. No residual risk. Relies on

and Permanence Relies on containment risk. Relies on containment Relies on disposal in HWL destructive treatment as

beneath RCRA -equivalent from vertical barrier and to prevent migration and permanent solution to

cover to reduce migration RCRA-equivalent cover to exposure. prevent migration and

and exposure. reduce migration and exposure.

Groundwater treated at exposure. Groundwater

existing treatment treated at existing treatment

facilities. facilities.

Reduction of Toxicity, Mobility reduced through Mobility reduced through Mobility significantly TMV permanently

Mobility, or Volume soil cover. Mobility vertical and horizontal reduced throug h eliminated for incinerated

(TMV) through increases if groundwater containment. No reduction containment in HWL. No material. Residual ash

Treatment rises into waste. No in toxicity or volume. reduction in toxicity or disposed in off post

reduction in toxicity or volume. landfill.

volume.

Short-Term Effectiveness Minimal short -term risk. Minimal short -term risk. Moderate short-term risk Moderate short-term risk

No intrusive activity or Waste and surrounding soils from excavation and due to excavation and

contaminated material are not disturbed as vertical material handling of waste material handling of waste

handling. Waste is left in barrier is installed outside of (odors. air emissions. (odors, air emissions.

place and covered with the Hex Pit footprint. Waste groundwater dewatering. groundwater dewatering,

RCRA-equivalent cover. is left in place and covered etc.), and the subsequent etc.), and off -site material

No air/odor impacts. with RCRA -equivalent on-site transport and handling during

cover. No anticipated disposal at HWL. Risks transportation and

air/odor impacts during manageable through treatment. Risks

barrier installation. adequate odor/emission manageable through

control and material adequate odor/emission

handling procedures. control and material

handling procedures.

Implementability Implementable. No Implementable. Readily Implementable. HWL Implementable. Proven

implementation required available technology. available to accept and available technology.

beyond abandonment of Verification of barrier to material. Air and odor Existing wells to be

existing wells and RCRA - groundwater compatibility emissions control required segregated from Hex Pit

equivalent cover. Long - required. L ong-term during excavation and waste and disposed at on-

term groundwater groundwater monitoring landfilling. Implementation post HWL. Air and odor

monitoring required. required. Implementation time is 12 months. emissions control required.

Implementation time is 12 time is 14 months. Implementation time is 14

months. months.

Table 5.0-1 Comparative Analysis of Alternatives - Hex Pit Remediation Page 2 of 2

CRITERIA ALTERNATIVE 1: NO ALTERNATIVE 2: ALTERNATIVE 3: ALTERNATIVE 4:

ADDITIONAL ACTION VERTICAL BARRIER EXCAVATE: ON-POST OFF-POST

(RCRA-EQUIVALENT WITH RCRA- LANDFILL INCINERATION

COVER) EQUIVALENT COVER

Cost Minimal. Long-term Low to moderate. Estimated Low to moderate. High. Estimated cost is

monitoring cost estimated cost is $1.000,000 (includes Estimated cost is $3,380,000.

at $70,000 (cost does not long-term groundwater $920,000.

include leachate generation monitoring cost).

study costs that might be

necessary to assess the

mobility of the waste

contaminants). Cost to

close horizontal wells

estimated at $50,000.

State Acceptance Not acceptable. Hex Pit Not acceptable. Hex Pit Preferred. Better long- Acceptable. Provides

waste is left in place and waste is left in place and term protection than permanent, destructive

might not provide might not provide adequate . containment in place. treatment. Short-term

adequate long-term long-term protection of the Short-term risks are risks to community are

protection of the groundwater minimized on site and higher during

groundwater eliminated for the transportation for off-post

community. incineration.

Community Acceptance Less preferred. More Preferred. Concerns Most Preferred due to Less preferred. Concern

Community prefers to were related to possibility of containment in HWL. over transportation of

address Hex Pit directly groundwater contamination Concerns were related to highly contaminated waste

rather than indirectly resulting from leaving t he odor control, design review through the community.

through South Plants cover waste in place. and landfill compatibility.

and groundwater

treatment/monitoring.

Table 6.0-1 Cost Estimate Summary for the Hex Pit Selected Remedy

Capital Cost

Description Cost

Design $ 416,000

Procurement $ 16,000

Submittals $ 40,000

Mobilization/Demobilization $ 12,000

Excavation $ 215,000

Odor Control $ 48,000

Health and Safety $ 33,000

Project Management and Support $ 140,000

Total Capital Cost $ 920,000

Annual Operation and Maintenance Costs $ 0

(See Note 1)

Total Project Cost $ 920,000

Note 1: There are no O&M costs associated with the selected remedy. O&M costs for the soil cover are included as part of the South Plants p roject cost. O&M costs for groundwater extraction and treatment are

included as part of the site-wide treatment system operations cost.

Table 8.0-1 Hex Pit Remediation Location-Specific ARARs and TBCs Page 1 of 1

Item Citation Requirement

Endanger ed Species Act 16 USC Section 1531 The requirements for the Endanger ed Species Act are embodied in§ 44.2 (c) of the RMA FFA. Specifically, wildlife habitat shall be

preserved and managed as necessary to protect endangered species

of wildlife to the extent required by the Act, migratory birds to the

extent required by the Migratory Bird Treaty Act, and bald eagles to the extent required by the Bald and Golden Eagle Protection

Act. (NOTE: The cited acts are not ARARs, but independently

apply to remedial activities).

National Wildlife Refuge System

Administration Act16 USC 668dd

50 CFR 25

The National Wildlife Refuge Administration Act prohibits the

taking or possessing of any fish, bird, mammal or other wildvertebrate or invertebrate animals or part or nest or egg thereof

within any such area; or entering, using or otherwise occupying

any such area for any purpose; unless such activities are performed

by persons authorized to manage such area or unless such activities are permitted. (NOTE: NWRSAA is an independently applicable

regulatory requirement, not an ARAR).

Table 8.0-2 Hex Pit Remediation Chemical-Specific ARARs and TBCs Page 1 of 1


National Ambient Air Quality 40 CFR 50 Sources cannot cause or contribute to an exceedance of a national

Standards ambient air quality standard.

Colorado Ambient Air Quality 5 CCR 1001 -5, Regulation 3 Sources cannot cause or contribute to an exceedance of a national

Standards

5 CCR 1001 -14

or ambient air quality standard as follows:

• Lead -1.5 µg/m3 (Max. arithmetic mean avg. over calendar quarter)

• TSP -75 & 260 µg/m3 (primary standard -annual

(geometric), 24 -hr)• PM -150 & 50 µg/m3 (24 -hr average concentration &

annual arithmetic mean, respectively)

Colorado Standards for Control 5 CCR 1001 -10 Regulation The standards for hazardous air pollutants are not to be exceeded.of Hazardous Air Pollutants 8, Part C, Section 1

Table 8.0-3 Hex Pit Remediation Action-Specific ARARs and TBCs Page 1 of 4


Worker Protection

Health and Safety Protection 29 CFR Part 1910 29 CFR Part 1910 provides guidelines for workers engaged in activities

requiring protective health and safety measures regulated by OSHA.

Requirements provided in 29 CFR 1910.120 apply specifically to the

handling of hazardous waste/materials at controlled hazardous waste sites.

Note: OSHA regulations are independently applicable regulatoryrequirements, not ARARs.

Health and Safety Protection 29 CFR 1910.120 (b) to (j) Provides guidelines for workers involved in hazardous waste operations and

emergency response actions on sites regulated under RCRA and CERCLA.

Specific provisions include the following:

• Health and safety program participation required by on-site workers

• Site characterization and analysis

• Site control

• On-site training

• Medical surveillance

• Engineering controls

• Work practices

• Personal protective equipment

• Emergency response plan

• Drum handling

• Sanitation

• Air monitoring

Worker Exposure ACGIH 1991-1992 [TBC] Chemical-specific worker exposure guidelines established by OSHA,

NIOSH 1990 [TBC]ACGIH, and NIOSH.

Aldrin

29 CFR 1910.10004 ACGIH-TWA = 0.25 mg/m 3 (skin)

NIOSH-REL = 0.25 mg/m3 (skin)

OSHA-PEL = 0.25 mg/m 3 (8- hr TWA) (skin)

Chlordane

ACGIH-TWA=0.5 mg/ m3 (skin)

NIOSH-REL=0.5 mg/ m3 (skin)

OSHA-PEL=0.5 mg/ m3 (8-hr TWA)(skin)

Dieldrin

ACGIH-TWA=0.25 mg/m3 (skin)

NIOSH-REL=0.25 mg/m3

OSHA-PEL=0.25 mg/m3 (skin)

Endrin

ACGIH-4WA=0.1 mg/m 3 (skin)

NIOSH-REL=0.1 mg/m 3 (10-hr TWA) (skin)

OSHA-PEL=0.1 mg/m3 (8-hr TWA) (skin)

Hexachlorocyclopentadiene (HCCPD)

ACGIH-TWA=0.01 ppm, 0.11 mg/m3

OSHA PEL=0.01 ppm, 0.1 mg/m 3

NIOSH-REL=0.01 ppm, 0.013 mg/m3

Hydrogen Chloride

ACGIH-Ceiling=5 ppm, 7.5 mg/m3

NIOSH-Ceiling=5 ppm, 7 mg/m3

OSHA-Ceiling= 5 ppm, 7 mg/m3



Air/Odor Emission

Particulate Emissions During 5 CCR 1001-3, Regulation 1, Colorado air pollution regulations require owners or operators of sources that

Excavation Section III (D) (h) (iii) emit fugitive particulates to minimize emissions through use of all available

5 CCR 1001-5, Regulation 3 methods to reduce, prevent, and control emissions. In addition, no off-site

transport of particulate matter is allowed.

5 CCR 1001-2, Section II Estimated air emissions from the proposed remedial activity per Colorado

APEN requirements.

Emission of hazardous air 5 CCR 1001-10, Regulation 8 Emission of certain hazardous air pollutants is controlled by NESHAPs.

pollutants Remedial activities could cause volatilization of some organic and/or metal

40 CFR Part 61 contaminants.

42 USC Section 7412 • Emissions to the atmosphere from mercury shall not exceed 1,600

grams/24-hr. period

Odor emissions 5 CCR 1001-4, Regulation 2 Colorado odor emission regulations require that no person shall allow

emission of odorous air contaminants that result in detectable odors that are

measured at the fenceline in excess of the following limits:

1. For residential and commercial areas—odors detected after the odorous

air has been diluted with seven more volumes of odor- free air.

2. For all other land use areas—odors detected after the odorous air has

been diluted with 15 more volumes of odor- free air.

Volatile organic chemical 5 CCR 1001-9, Regulation 7 VOC regulations apply to ozone nonattainment areas. The air quality control

emissions Subparst III and IV area for RMA is currently nonattainment for ozone. Storage and transfer of

VOCs and petroleum liquids are controlled by these requirements.

Disposal of VOCs is regulated for all areas, including ozone nonattainment.

The regulations control the disposal of VOCs by evaporation or spilling

unless reasonable available control technologies are utilized.

Air emissions from diesel- 5 CCR 1001-15, Regulation 12 Applies to motor vehicles intended, designed and manufactured primarily for

powered vehicles associated use in carrying passengers or cargo on roads, streets, and highways, and state

with excavation and backfill

operation

as follows:

1. No person shall emit or cause to be emitted into the atmosphere from

any diesel-powered motor vehicle weighing 7,500 pounds and less,

empty weight, any air contaminant, for a period greater than 5

consecutive seconds, which is of such a shade or density as to obscure

an observer’s vision to a degree in excess of 40% opacity.

2. No person shall emit or cause to be emitted into the atmosphere from

any diesel-powered motor vehicle weighing more than 7,500 pounds,

empty weight, any air contaminant, for a period greater than 5

consecutive seconds, which is of such a shade or density as to obscure

an observer’s vision to a degree in excess of 35% opacity, with the

exception of subpart “C.”

3. Any diesel-powered motor vehicle exceeding these requirements shall be

exempt for a period of 10 minutes if the emissions are a direct result of a

cold engine startup and provided the vehicle is in a stationary position.

4. These standards shall apply to motor vehicl es intended, designed, and

manufactured primarily for travel or use in transporting persons,

property, auxiliary equipment, and/or cargo over roads, streets, and

highways.

NOTE: A diesel vehicle does not include the following: vehicles registered

pursuant to 42 -3-123(11) or 42-3-128, CRS; off-the-road diesel-powered

vehicles or heavy construction equipment.



Visibility Protectio n 40 CFR 51.300-307 Remediation activities must be conducted in a manner that does not cause

adverse impacts on visibility. Visibility impairment interferes with the

40 CFR 52.26-29 management, protection, preservation or enjoyment of federal Class I areas.

Smoke and opacity 5 CCR 1001-3. Regulation 1, Remediation activities must be conducted in a manner that will not allow or

Section 11.A.(2) cause emission into the atmosphere of any pollutant that is in excess of the

applicable opacity standard.

Stormwater Management

Discharge of stormwater to 40 CFR Part 122-125 Stormwater runoff, snow melt runoff, and surface runoff and drainage

on-post surface water associated with industrial activity (as defined in 40 CFR 122) from RMA

remedial actions that disturb 5 acres or more and that discharge to surface

waters must be conducted in compliance with the stormwater management

regulations.

Wastewater Management

Discharge of liquid wastes 40 CFR Part 122 Any wastewater generated during remedial activities will be routed to the

and wastewater 40 CFR Part 125 on-post CERCLA Wastewater Treatment Facility if it is not hazardous waste

40 CFR Part 129 and will not interrupt the existing treatment system. If wastewater is routed to

the on-post treatment plant, it must be treated in accordance with NPDES

40 CFR Part 262.

requirements.

6 CCR 1007-3, Part 262 Wastewater that is determined to be a hazardous waste must be treated in

accordance with the provisions of RCRA.

Waste Characterization

Solid waste determination 40 CFR 260, 260.30-.31, 261.2, A solid waste is any discarded material not excluded by a variance granted

261.4 under 40 CFR 260.30 and.260.31. Discarded material includes abandoned,

6 CCR 1007-3 260, 260.30,

260.31, 261.2, 261.4

recycled, and waste-like materials.

Solid waste classification 6 CCR 1007-2, Section I Wastes that do not meet the criteria for hazardous wastes are classified as

solid wastes. Colorado solid waste rules contain five solid waste categories:

industrial wastes, community wastes, commercial wastes, special wastes, and

inert material.

Waste Management

Determination of Hazardous 40 CFR 262.11 Wastes generated during excavation activities must be characterized and

waste 6 CCR 1007-3 evaluated according to the following method to determine whether the waste is

Section 262.11 hazardous:

40 CFR Part 261 • Determine whether the waste is identified in 40 CFR 261.4.

6 CCR 1007-3, Part 261 • Determine whether the waste is listed under 40 CFR 261.

• Determine whether the waste is identified in 40 CFR 261 by testing the

waste according to specified test methods or by applying knowledge of

the hazardous characteristics of the waste in light o f the materials or the

rocess used.

Treatment, storage, or 40 CFR Part 264. If remediation of waste/soil at RMA generates hazardous wastes, the wastes

disposal of RCRA hazardous 6 CCR 1007-3, Part 264 must be treated, stored, or disposed in accordance with substantive

waste requirements of RCRA regulations.

40 CFR Part 268,

6 CCR 1007-3, Part 268

40 CFR 264.171-173 Requirements for managing containers used to store hazardous wastes

6 CCR 1007-3,

Section 264.171-173

40 CFR 264.16 (a) (1) Requirements for personnel training

6 CCR 1007-3,

Section 264.16 (a) (1)

40 CFR 264.52 (a) Requirements for preparing contingency plan

6 CCR 1007-3,

Section 264.52 (a)


Item Citation R e q u i r e m e n t

Treatment. storage and 40 CFR 268.45 Hazardous debris must be treated using specific technologies to extract.

disposal of hazardous debris destroy. or immobilize hazardous constituents on o r in the debris. In certain

6 CCR 1007-3, cases after treatment, the debris may no longer be subject to RCRA subtitle C

Section 268.45 regulation.

Corrective Action 40 CFR 264, Subpart S The CAMU regulations allow for exceptions from otherwise g enerally

Management Units 6 CCR 1007-3, Part 264, applicable LDRs and minimum technology requirements for remediation

Subpart S wastes managed at CAMUs. These regulations provide flexibility and allow

for expedition of remedial decisions in the ma nagement of remediation

wastes. One or more CAMUs may be designated at a facility. Placement of

hazardous remediation wastes into or within the CAMU does not constitute

land disposal of hazardous wastes, so the LDRs are not triggered.

Temporary Units (TU) 6 CCR 1007-3, Design, operating or closure standards for temporary tanks and container

Section 264.553 storage areas may be replaced by alternative requirements. The TU must be

40 CFR 264.553 located within the facility boundary, used only for treatment/storage of

remediation waste, and will be limited to one year of operation with a one-year

extension upon approval by the regulatory authority.

On-Post Transportation 5 CCR 1001-15, Regulation 12 All on-post shipments of hazardous waste may be required to meet the

5 CCR 1001-4, Regulation 2 provisions of 5 CCR 1001, 40 CFR Parts 52 and 81, and AR 50-6 including,

5 CCR 1001-3, Regulation 1 but not limited to the following:

Section III (D)(2) 1. Transportation of wastes in diesel-powered vehicles may be subject to

state opacity and visibility standards.

5 CCR 1001-5, Regulation 3 2. Loading, unloading, or transportation of wastes may cause odors or

emissions from contaminants that exceed state odor limits.

3. Transportation on unpaved roadways may be subject to state requirements

to reduce particulate emissions resulting from the use of the roadway.

4. This regulation describes procedures to be followed during the

transportation of Chemical Surety Materials.

Noise Abatement Colorado Revised Statue, The Colorado noise Abatement Statute provides that:

Section 25-12-103 1. Applicable activities shall be conducted in a manner so any noise

produced is not objectionable due to intermittence, beat frequency, or

shrillness. Noise is defined to be a public nuisance if sound levels

radiating from a property line at a distance of twenty-five feet or more

exceed the sound levels established for the specified time periods and

zones.

7:00 a.m. to 7:00 p.m. to

Zone next 7:00 p.m, next 7:00 a.m.

Residential 55 db(A) 50 db(A)

Commercial 60 db(A) 55 db(A)

Light Industrial 70 db(A) 65 db(A)

Industrial 80 db(A) 75 db(A)

2. In the hours between 7:00 a.m. and the next 7:00 p.m., the noise levels

permitted in Requirement 1 (above) may be increased by 10 decibels for a

period not to exceed 15 minutes in any one-hour period.

3. Periodic, impulsive, or shrill noises shall be considered a public nuisance

when such noises are at a sound level of 5 decibels less than those listed in

Requirement 1 (above).

4. Construction projects shall be subject to the maximum permissible noise

levels specified for industrial zones for the period within which

construction is to be completed pursuant to any applicable construction

permit issued by proper authority or, if no time limitation is imposed, for a

reasonable period of time for completion of the project.

5. For the purpose of this article, measurements with sound level meters shall

be made when the wind velocity at the time and place of such

measurement is not more than 5 miles per hour.

6. In all sound level measurements, consideration shall be given to the effect

of the ambient noise level created by the encompassing noise of the

environment from all sources at the time and place of such sound level

measurements.

Table 9.6-1 Community Involvement Activities Conducted at RMA Page 1 of 1 Pertinent to the Hex Pit Remediation

Public Comment Period or

Date of Public Meeting Document Provided or Topic Discussed

4/13/98 Public Availability Session on the Hex Pit, RAB meeting, Discussion on Hex Pit history, site

characterization, and technology selection process

4/20/98, 5/18/98 Public Availability Sessions on the Hex Pit, EPA forum at Kearney Middle School,

Discussion on Hex Pit history, site characterization, and technology selection process

10/1/98 to 11/12/98 Innovative Thermal Technology Evaluation Report for the Hex Pit Site at the Rocky

Mountain Arsenal (CDPHE et al. 1998)

4/25/00 to 5/25/00 Hex Pit Soil Remediation 30 Percent Design (TerraTherm 2000c)

8/2/00 to 9/4/00 Hex Pit Soil Remediation 95 Percent Design (TerraTherm 2000b)

12/29/00 to 1/29/01 Addendum to Hex Pit Soil Remediation 95 Percent Design (TerraTherm 2000a)

5/23/02 RAB meeting, discussion on remedial alternatives being considered for Hex Pit following

ISTD failure

9/22/02 to 11/22/02Revised Proposed Plan for the Rocky Mountain Arsenal On-Post Operable Unit, Hex Pit Site

(PMRMA 2002)

10/10/02 Public Meeting for the Revised Proposed Plan for the Rocky Mountain Arsenal On-Post

Operable Unit, Hex Pit Site

FIGURES

APPENDIX A

ROD Dispute Resolution Agreement

Hex Pit Dispute Resolution Agreement

The EPA and CDPHE disputed the selected remedy of solidification presented in the draft ROD. The following pages are copied from the 1996 On -Post Operable Unit Record of Decision Dispute Resolution Agreement and include discussion of the dispute resolution and the technology evaluation criteria to be used in selecting the treatment technology for the Hex Pit.

2

CDPHE Dispute 1 - Air Emissions

EPA Dispute 12 - CDPHE Disputes by Reference

Dispute:

The State disputes the ROD text identifying the air emissions remediation goals

that apply to the excavation of soil. EPA supports the CDPHE dispute by reference.

Resolution:

This dispute was resolved pursuant to the incorporation of additional text into

Table 9.5-1 (Remediation Goals and Standards) of the ROD. A component of this text

indicates that the Parties will control air emissions as necessary to attain

criteria that will be established via an air pathways analysis program that will

ensure that the remedial action will be-protective of human health and the

environment and minimize nuisance odors. This text will clarify the air emissions

remediation goals and standards for all remedies.

Additionally, agreement was reached that each remedial design or work plan will

contain language describing an expedited process (with a goal of not more than 36

hours) to be followed for quick resolution to any party’s concerns regarding

remediation work practices related to air emissions. Each remedial design or work

plan will identify the site-specific air emission criteria to be used as

operational parameters and the necessary contingency plans in the event the

criteria are exceeded. This expedited dispute process is intended to evaluate

changes to work practices on an immediate basis and implement changes. The

expedited dispute resolution process will, to the extent practicable, be consistent

with the dispute resolution process in the Federal Facility Agreement (FFA). In

that the FFA specifies that the remedial designs and work plans are disputable

documents, the incorporation of air emissions criteria and expedited dispute

process into designs and plans can be ensured by all Parties.

EPA Dispute 2 - Hex Pit Remedy

CDPHE Dispute 2 - Hex Pit Remedy

Dispute:

The EPA and State dispute the Hex Pit remedy (solidification) presented in the ROD

Resolution:

This dispute was resolved pursuant to the selection of the “innovative thermal”

technology as the selected remedy in the ROD subject to meeting the technology

evaluation criteria as

3

determined by the design treatability study and evaluation, and the incorporation

of all necessary text modifications into the ROD that support the selection of this

remedy. The following specific responsibilities and requirements incorporated into

this dispute resolution agreement are:

- The technical evaluation criteria attached (encl 1), are to be used as the

basis for performing the additional design data collection, the design

treatability study, and the technology design evaluation. Agreement was

reached that the innovative treatment technology would be applied to the

actual buried material (volume estimated at approximately 1000 cubic yards

and to be refined by the additional design data and during excavation). The

remaining soil volume will be disposed in the on-post hazardous waste

landfill. Remaining soil may also be utilized to implement the innovative

technology.

- The total remedy cost for implementation of the innovative thermal

technology shall not exceed the total remedy cost for off-post incineration.

Costs will be determined for each technology on a consistent basis.

- The EPA and State, as the lead advocates of the innovative thermal

technology, shall take the lead role in addressing all concerns related to

the selection of an innovative technology, subject to agreement by the EPA

and State on the particular innovative treatment technology selected for

treatability study. The Army shall remain neutral on the selection of the

innovative technology, however, the Army remains committed to the successful

remediation of this site using the selected technology.

- The EPA and State, as the lead advocates of the innovative thermal

technology, shall be responsible to the extent practicable and appropriate

for the preparation and defense, in coordination with the Army, of

justifications and responses for all subject audits (e.g. GAO, AAA, and

Congressional) related to the selection of the innovative technology.

- The contracting documentation shall include the necessary bonding (up to

two-times the estimated treatment cost) and indemnification or warranty

clauses to ensure successful project completion. The contract for

implementation of the innovative technology shall be a fixed price/turn key

bid. The treatment contract shall contain the necessary provisions that

reflect the risk, uncertainties, innovation, implementability, and cost

technologies. The provisions shall be applied on a consistent basis for each

technology.

4

- In the event that the selected innovative technology is not implementable

as determined by the technology evaluation, a solidification technology will

be selected and undergo treatability testing to verify its effectiveness.

- The process for evaluating the selected technology will be in accordance

with EPA OSWER Directive 9355.3-02 and EPA Final Guidance for Conducting

Treatability Studies under CERCLA (EPA/540/R-92/071a).

CDPHE Dispute 5 – Dioxin

EPA Dispute 12 - CDPHE Disputes by Reference

Dispute:

The State disputes the ROD text describing how the potential risk to Dioxin will be

evaluated. EPA supports the CDPHE dispute by reference.

Resolution:

This dispute was resolved pursuant to the incorporation of additional text into the

ROD. This text describes how the evaluation of contaminants (e.g. dioxin) will be

evaluated by the combined efforts of technical working groups or subcommittees as a

part of the demonstration that the remedy is protective of human health and the

environment. Evaluations would be performed as required and at a minimum as part of

the 5 year review.

The Federal Facility Agreement (FFA) specifies that the RMA Committee has the

responsibility on a daily basis for the design and implementation of response

actions in accordance with the terms of the ROD and the FFA and in that regard the

R.MA Committee has begun to take action to address dioxin and is responsible for

continued evaluation of this issue.

CDPHE Dispute 6 - RCRA Equivalency

EPA Dispute 7 - RCRA-Equivalent Cap

Dispute:

The EPA and the State dispute the ROD text identifying the remediation goals for

RCRA equivalent caps. The inclusion of the requirement for a comparative analysis

and field demonstration as part of the cap design is required as a remediation

goal. The CDPHE believe that the field demonstration should include a parallel

field demonstration for a RCRA cap and the equivalent cap.

Hex Pit Technology Evaluation Criteria

The following process to evaluate an innovative thermal technology has been agreed upon to support the selection of the this remedy for the Hex Pit. The design data collection and treatability study results would be used to determine the effectiveness,

implementability and cost of the ROD selected remedy. The selected technology would be applied to the contaminated material found in the site, based on visual observation, with the remaining soil excavated and disposed in the on-posthazardous waste landfill. The following outlines the process for evaluating the selected technology:

Selected Technology in the ROD: Innovative Thermal

Design Data Collection

• Begin within 3 months of the finalization of the ROD

• Prepare technical plan

• Refine extent of contamination- refine estimate of 700-1,000 yd3 of buried contaminated material- remaining 2,300-2,600 yd3 is expected to be below principal threat exceedance levels

• Representative sample for treatability study

• Sample characterization

• Odor/volatile emissions characterization

• Analytical method development if necessary

Treatability Study

• Identify specific innovative technology

• Prepare technical plan

• Conduct treatability study for innovative technology

• $ 100,000 budget for innovative thermal technology treatability study

• Confirm full-scale implementability

• Determine material handling requirements

Technology Evaluation

• Evaluation against treatability study goals

– Remediation goal for innovative thermal technology is greater than 90% DRE– 100% reduction in mobility after disposal in landfill for an ex situ treatment– groundwater monitoring based on contaminants identified in the site characterization will be used to determine

the effectiveness of an in situ thermal treatment– Waiver may be required for thermal technology implementation if DRE<99.99% – Develop detailed cost estimate for technology implementation

– Cost for implementation of the innovative thermal technology must not exceed the total remedy cost for off-postincineration as determined for each technology on a consistent basis.

– Prepare technical report for treatability testing and technology evaluation results

• The design data collection, treatability study and technology evaluation will be completed within 12-18 months if consistent with the overall remediation schedule. The treatability study and technology evaluation will be conducted in accordance with EPA guidance.

The innovative thermal technology must meet the treatability study technology evaluation criteria as described above. Solidification/stabilization will become the selected remedy if all evaluation criteria for the innovative thermal technology are not met. A similar treatability testing and technology evaluation process would then be completed for the solidification

technology.

9617302-5/5-A-a

Responses to Regulatory Agency

Comments on the Draft Record of Decision AmendmentHex Pit Site Remediation

Rocky Mountain Arsenal

Page 1 of 3

Responses To Environmental Protection Agency

Comments on the Draft Record of Decision Amendment


General Comments

1. This draft record of decision (ROD) amendment describes the remedy change for the Hex Pit site as part of the On-Post Operable Unit. Because the original ROD was titled, “Record of Decision for the On-PostOperable Unit,” the ROD Amendment should include “On-Post Operable Unit” in the title.

Response: The title has been changed to “Amendment to the Record of Decision for the On-PostOperable Unit, Rocky Mountain Arsenal Federal Facility Site, Hex Pit Site Remediation”.

2. Contaminants of concern (COCs) are mentioned in several places, but they are never explicitly and completely identified. For example, the second paragraph on page D-1 (continuing on page D-2) states, “Chemical sampling results from the design characterization confirmed concentrations of Hex [hexachlorocyclopentadiene] were well above the site evaluation criteria (SEC) established in the ROD. The COCs aldrin, dieldrin, endrin, and chlordane were also detected at levels greater than the SEC.” From this discussion it is unclear that hexachlorocyclopentadiene and isodrin are COCs. The document should explicitly identify the COCs for the site.

Response: The text has been modified to clearly identify the Hex Pit COCs.

3. The ROD Amendment states in Section 3.1 that the waste was discovered to a depth of 12 feet and that the selected remedy will apply to the entire site volume. However, because it is not explicitly stated in the description of Alternative 3 (Section 5.2.3) that the waste will be excavated to a depth of 12 feet, the depth to which the waste will be excavated is unclear. The ROD Amendment should explicitly identify the excavation criteria for the remedy. (i.e., performance evaluation based on visual observations or a specific depth). If a depth is specified rather than a performance evaluation as the excavation criteria, and the possibility exists that waste will be left in place, this should also be discussed in the ROD Amendment.

In addition to the excavation criteria, other criteria, such as disposal requirements, should be identified for the remedy, as applicable.

Response: Section 5.2.3 has been modified to describe the extent of excavation and the basis for the Hex Pit remediation. Excavation will be to a depth of 10 feet across the site continuing if visual evidence of Hex Pit waste extends deeper.

4. The ROD Amendment discusses the issue of compatibility of the Hex Pit waste for the hazardous waste landfill (HWL) in Sections 5.2.3 and 6.6. However, these discussions do not present an accurate picture of why the Hex Pit waste can be disposed into the HWL. These

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sections should be revised to more clearly describe why the Hex Pit waste can be disposed into the HWL and should indicate that the leachate characterization results confirmed the liner compatibility test results conducted during the initial design of the landfill.

Response: The text has been revised to provide more detail on the leachate characterization and HWL liner compatibility.

Specific Comments

1. Declaration, Assessment of Site, Page D-l. The declaration provides a summary of the ROD Amendment and the assessment describes the historical disposal activities in the first paragraph. However, this paragraph does not state that the Hex Pit material was disposed of in bulk. This section should be revised to indicate that the Hex Pit material was disposed in bulk, as well as in drums.

Response: Comment incorporated.

2. Declaration, Rationale for Remedy Change, Page D-2, Paragraph 1. This paragraph discusses the design, construction, and implementation of the Hex Pit in situ thermal destruction (ISTD) project. However, the verb tense and sequence of activities serve to confuse the description, which is the prelude to the rationale for remedy change. This paragraph should be revised to present a clear understanding of the design, construction, and implementation of the Hex Pit ISTD remedy so that the rationale for remedy change is apparent.

Response: This section has been reorganized for clarity.

3. Section 3.1, Page 5, Paragraph 2. This section discusses an August 1997 investigation and states that samples taken from inside the boundary of the Hex Pit contained concentrations of hex as high as 160,000 parts per million (ppm). However, this investigation is not referenced and the concentrations are not consistent with Table 3.1-1. This investigation should be referenced and this paragraph and Table 3.1-1should show concentrations of hex that are consistent with one another.

Response: A reference for this investigation has been added and the results have been added to the text discussion and Table 3.1-1.

4. Section 4.0, Page 8. This section describes the scope and role of the response action and the last sentence in the first paragraph indicates that an alternate remedy was selected. It is unclear that the alternate remedy selected is the remedy described in this ROD Amendment. In addition, the last sentence in the second paragraph indicates that the ROD Amendment will be the final response action for the Hex Pit Site, which is not correct. The section should be revised to make clear that the “alternate” remedy is the remedy described in this ROD Amendment and that the final response action is the selected remedy described in this ROD Amendment.

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5. Section 7.0, Page 16. This section describes the selected remedy and states that the selected alternative is expected to allow the property to be used for the anticipated future land use as a wildlife refuge. However, the fact that this site will be within a soil cover area, maintained by the Army in perpetuity is not mentioned. This section should be revised to include this concept.


6. Section 7.0, Page 17, Paragraph 2. This paragraph states that the selected remedy will comply with all applicable or relevant and appropriate requirements (ARARs) in Appendix A of the ROD. However, Appendix A in the ROD includes an extensive list of ARARs (FWENC 1996). It is unclear which ARARs apply to the hex pit site, and therefore, it is unclear how compliance with ARARs can be assured. Compliance with those key ARARs that are specifically applicable to the hex pit and to the selected remedy should be discussed.

Response: The ARARs specific to the selected remedy for the Hex Pit have been added to the document.

Tables

7. Table 3.1-1., This table presents the Hex Pit COCs and SEC. However, the concentrations of hex in the table are not consistent with the concentrations discussed in Section 3.1. The concentrations of hex in the table and the text should be consistent.

Response: The table has been revised to be consistent with the text.

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Responses To Colorado Department of Public Health and Environment



Gene ral Comments

The draft addresses most of the guidance components listed in Chapter 7 of EPA 540-R-98-031 A Guide to Preparing Superfund Plans, Records of Decision, and Other. Remedy Selection Decision Documents dated July 1999. There may be one component that is missing in the document and that is a statement that the amended remedy satisfies CERCLA 121. Please check that this statement is made under Section 8.0 Statutory Determinations. A summary statement similar to the following is suggested.

Based on, information currently available, the Army believes the preferred alternative meets the threshold criteria and provides the best balance of tradeoffs among the other alternatives with respect to the balancing and modifying criteria. The Army expects the preferred alternative to satisfy the following statutory requirements of CERCL 121(b): (1) be protective of human health and the environment; (2) comply with ARARs; (3) be cost-effective; (4) utilize permanent solutions and alternative treatment technologies or resource recovery technologies to the maximum extent practicable; and (5) satisfy the preference for treatment as a principal element or explain why the preference for treatment will not be met.

CDPHE acknowledges that the above five requirements are discussed in Section 8 of the draft with the exception of the preference for treatment. A discussion of the five-year review requirement appears to have been substituted for the preference for treatment discussion in the draft. Some discussion of how the preferred alternative addresses the fifth requirement should be included.

Another component that requires further discussion is the side-by-side comparison of the contingent remedy with the amended remedy. Although briefly discussed in Section 3.3 Contingent Remedy, it seems appropriate for a ROD amendment that some discussion of the nine evaluation criteria and reference to supporting documentation be included. The original selected remedy, ISTD, is clearly eliminated from comparison because of implementation failure; however, this is not as obvious for the contingency remedy. The reasons for its dismissal need more discussion. Descriptions of the contingent remedy could be made in Section 5.2 and the comparison of the nine evaluation criteria could be made in Section 6.0 as well as in Table 6.0-2. This is further discussed under the specific comments that follow.

Although the draft for Section 10.0 Responsiveness Summary did not contain responses to public comments, it is acknowledged that this package was received on February 12, 2003, and that comments are due by close of business February 25, 2003. The Department cannot concur with the final draft until this package has been reviewed and RVO responses to any Department comments have been resolved.

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Response : This summary statement is made in the Declaration and in Section 7 with additional discussion concerning the individual elements in Section 8. A paragraph has been added to Section 8 to discuss why the selected remedy does not meet the preference for treatment. Also, a reference to CERCLA has been added to the summary statement in Section 7 and in the Declaration.

The ROD Amendment does not include the contingent remedy, solidification/ stabilization, in the alternative comparison because it was eliminated as a possible remedy prior to generating the ROD Amendment. The discussion in Section 3.3 has been modified to clearly identify that the contingent remedy was reviewed and eliminated by the RVO in conjunction with the Regulatory Agencies prior to deve lopingnew remedy alternatives.

Specific Comments

Page D-3, First Paragraph. CDPHE recommends that either the text be modified or an additional sentence be added to emphasize the general lack of confidence among the regulatory agencies that a feasible redesign was possible for such a corrosive environment. As written, the text appears to emphasize that elimination of the ISTD remedy was based on cost. This comment also applies to the fourth paragraph of Section 3.2, page 7.

Response: The text has been modified to emphasize this point.

Page D-3, Second Paragraph. This paragraph is either out of place, incomplete, or needs additional support.

Response: This paragraph was moved to the Assessment of Site section where it belongs.

Page D-3, Third Paragraph. The text in this paragraph is somewhat unclear, and the reference to permanence should be avoided. CDPHE recommends the RVO consider rewriting the second sentence to state, “The selected remedy represents a long-term solution that utilizes containment as a principal element to reduce toxicity, mobility, or volume of contaminants, consistent with the overall ROD remedy that utilizes a combination of treatment and containment as the principal remedial elements.”

Response: This paragraph, and the statutory discussion in Section 8, have been revised to indicate that the statutory preference for treatment is not met at this site, and the reasons for not meeting this preference are given.

Page 5, Second Paragraph. Is there a reference for the August 1997 field investigation?

Response: This reference has been added.

Page 5, Fourth Paragraph. Some of the information in this paragraph seems to repeat information from the second paragraph on page 5 (for example pit size and chemical

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concentrations). Did the design characterization work discussed in this paragraph utilize data from the field investigation or did it independently confirm the data with new data?

Response: The design characterization provided a more detailed site investigation to determine the Hex Pitsite boundaries and COC concentrations for design. The text has been modified to indicate that this effort was to “further” define the boundaries.

Page 7, First Paragraph. The third sentence states that the soil was heated to over 500 °F to destroy waste in-situ.The Revised Proposed Plan for the Rocky Mountain Arsenal On-Post Operable Unit states on pages 6 and 7 that soil temperature was heated to over 600 °F and that contaminants were being destroyed. Please correct this discrepancy.

Response: The text was corrected to indicate 600 °F.

Page 7, Section 3.3. The discussion regarding the contingent remedy (stabilization/solidification, or S/S) appears to adequately reflect the discussions within the working group: The text, however, indicates that S/S waseliminated, in part, due to “unknowns associated with identifying an effective S/S mixture due to high concentrations of organic COCs.” CDPHE recalls that the regulatory agencies had requested the RVO investigate whether or not reagents were available that could be used effectively as S/S admixtures for the Hex waste. The text should confirm that such an investigation was performed and should describe how the RVO arrived at the decision that no reagents are available to achieve the desired objectives, particularly in terms of reducing the mobility of the contaminants. In addition, CDPHE recalls that the working group considered both in-situ and ex-situ S/S in the comparative analysis of alternatives. It is unclear why these alternatives are no longer included in Table 6.0-2. Although CDPHE acknowledges it is unlikely that either of these alternatives would be selected, it seems appropriate, for completeness, to include both in-situ and ex-situ S/S in the comparative analysis.

Response: The text has been modified to include additional discussion concerning the evaluation of potential solidification/stabilization mixtures for the Hex Pit contingent remedy. Because the contingent remedy was eliminated prior to development of the ROD Amendment, it is not included in the alternative evaluation. See also response to the general comments.

Page 8, Section 4.0. The language in this section appears to repeat previously stated information. The intent or purpose of this section is unclear.

Response: This section, although repeating some information, is included to provide the reader with a discussion of the scope of the Hex Pit remediation in relation to the overall RMA remediation and the 1996 ROD. This section mirrors text provided in the 1996 ROD.

Page 9. Section 5.2, Second Paragraph, second line. Change “...four other remedial alternatives...” to “...five other remedial alternatives...” to clarify that there are five other alternatives (if in-situ and ex-situ S/S are included) in addition to the no action alternative.

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Response: This text was not modified since solidification/stabilization has not been added to the ROD Amendment. See also response to the general comments.

Page 10, Second Paragraph, fifth line. The RMA Federal Facilities Agreement (FFA) should be referenced in Section 11.0 References. It is unclear whether the reference listed in Section 11.0 under EPA et al (U.S. Environmental Protection Agency et al) 1989 (Feb. 17) is the same document as that cited in the text.

Response: A citation has been added to the text for this reference.

Page 11, Section 5.2.3, Second Paragraph. CDPHE recommends additional language regarding the implementation and the results of the Hex Pit leachate investigation. A few sentences should be devoted to describing the Hex Pit Leachate Investigation Summary Report. A summary of the data supporting the argument that the hex pit material and leachate meet the waste acceptance requirements for the on-post hazardous waste landfill should be included. Also please mention how hex pit waste would be handled under this alternative in the event that portions of it could not meet waste acceptance requirements.

Response: This section has been modified to include additional discussion pertaining to the Hex Pit Leachate Investigation Summary Report. Specifics concerning material handling for waste acceptance will be included in the design.

Page 15, Section 6.8, First Paragraph, Third Sentence. Please provide the complete reference for the Revised Proposed Plan and include the reference in Section 11.0 References.

Response: This reference has been added.

Page 16, Section 6.9. Please provide the dates for public comment.

Response: Dates for the public comment period are provided in Section 9, Community Participation Compliance.

Table 3.1-1 Hex Pit Contaminants of Concern and Site Evaluation Criteria . A footnote should be added to explain the meaning of the double dash in the table.

Response: This designation indicates nondetect for that COC. The table has been modified to show ND rather than the double dash and a note has been added to the table defining the ND entry.

Table 6.0-2 Comparative Analysis of Alternatives – Hex Pit Remediation. The criteria components “State Acceptance” and “Community Acceptance” should be added to the table.

Response: The modifying criteria have been added to the table.

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Figure 1 .0-1. Although this figure is OK for general reference, another figure with appropriate scale should be provided to show more detail such as roads and landmarks in relation to the Hex Pit location.

Response: A figure has been added to show the location and configuration of the Hex Pit site boundary.

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Responses To Colorado Department of Public Health and Environment

Comments on the Draft Record of Decision Amendment Responsiveness Summary


Specific Comments

Page 21 Response to Mr. Union’s question. The response references the MK-Environmental Services, 1989 report. Does the information presented in the fifth sentence, regarding the 0.01 percent contribution, and in the seventh sentence, regarding the risk from groundwater not considered to be significant, come from the 1989 report or are these statements derived from some other information?

Response: This information is taken directly from the conclusions of the 1989 groundwater report. A citation has been added to the response to clarify the source of the statement.

Page 22 Response to Mr. Mulqueen’s comment. CDPHE does not agree that there is no impact to groundwater from the Hex Pit waste. Although the MK-Environmental Services report mentioned in the previous comment concluded that the Hex Pit was not an active primary source, it could not conclude that there was no impact.

Response: This response has been modified to be consistent with the 1989 report and the previous comment response.

Page 22 Response to Mr. Jaquith’s question. This question was not answered. Was Coors contacted? In addition the answer is misleading because, if there are ceramic casings, they could be placed in a borehole without damage as is normally done with PVC casing. Also it would be helpful to explain to Mr. Jaquith that the system failure was due to corrosion of the above ground treatment equipment and not the heating rods. Ceramic heating rods, if they exist, would not solve the problem.

Response: This response has been revised to be more responsive and provide the information as suggested in the comment.

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Responses To Tri-County Health Department



GENERAL COMMENT

1. Hex Pit Volume

Section 2.3 indicates that the estimated ROD volume was 3300 cubic yards. The last two paragraphs of Section 3.1 describe how the Hex Pit site boundary was extended during the site evaluation to encompass additional contaminated area and drums, yet the volume of contaminated waste was reduced to 2005 bcy. For clarity, TCHD recommends that additional discussion be included in Section 3.1 clarifying how the volume was reduced from 3300 cy to 2005 when the Hex Pit boundary was expanded.

Response: The first paragraph of Section 3.1 indicates that the ROD volume of 3,300 bcy was based on a site area of 1,000 square yards. The second and fourth paragraphs describe how the site boundary changed from the ROD area to a smaller area based on site characterization. The last two paragraphs are describing an increase in the site area and volume compared to the area and volume determined during the site characterization (paragraphs 2 and 4) rather than an increase from the ROD area and volume. The text has been modified to clarify these volume modifications through the design process.

SPECIFIC COMMENTS

2. DECLARATION Statement of Basis and Purpose

TCHD recommends that the last sentence in this section be modified to indicate where the Letters of Concurrence are included in the document.

Response: This statement has been removed from the document. The letters of concurrence will be attached to the ROD Amendment to illustrate support for the selected remedy; however, discussion of the letters has been removed since concurrence is not required for approval of the Amendment.

3. DECLARATION Rational for Remedy Selection

The last paragraph of this section seems out of place. Please clarify.

Response: This paragraph was moved to the Assessment of Site section where it belongs.

4. Section 2.1 RMA Operational History

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The fifth paragraph of this section states that significant groundwater contamination occurred as a result of releases from the Lime Settling Basins. Is this correct?

Response: The Lime Basins were identified in the FS and 1996 ROD as a significant groundwater contamination source.

5. Section 3.1 Site Evaluation and Technology Selection

In the first full paragraph on page 5, the 1997 field investigation is discussed. The last two sentences discuss odor testing conducted during the field investigation. Based on the 1997 testing, the RVO concludes that “odor control can be accomplished without the rigorous control devices projected in the ROD cost estimates”. TCHD believes that the level of odor control should be determined during remedial design. Conclusions regarding the level of odor control seem inappropriate for the ROD Amendment. Since the 1997 odor test results were never reviewed by the agencies contemplating an excavation scenario, TCHD recommends that the last two sentences of the paragraph be reworded to simply present a summary of the odor test results and leave conclusions regarding odor control to the design.

Response: This section has been modified to eliminate the statement regarding odor control as projected in the ROD.

6. Section 6.6 Implementability

TCHD recommends that the second to last sentence in the first full paragraph on page 15 be reworded as follows:

Air and odor emissions controls are required for Alternatives 3 and 4 during excavation, and at the HWL for Alternative 3.


7. Section 10.0 Responsiveness Summary

Since comments were received from the City and County of Denver, the last sentence of the first paragraph of the “Public Comment” section could be clarified by rewording as follows:

No written comments were received from the public during the public comment period.


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