EXPLANATION OF SIGNIFICANT DIFFERENCES FOR SOUTH PLANTS

BALANCE OF AREAS AND CENTRAL PROCESSING AREA SOIL

REMEDIATION PROJECT

ROCKY MOUNTAIN ARSENAL FEDERAL FACILITY SITE

1.0 INTRODUCTION

1.1 The Rocky Mountain Arsenal

The Rocky Mountain Arsenal (RMA) On-Post Operable Unit 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 (Figure 1). The RMA site is 27 square miles and is currently on the U.S. Environmental

Protection Agency (EPA) National Priority List for environmental cleanup as a result of

contamination released during previous RMA operations.

The On-Post Record of Decision (ROD), which describes the site-wide remedy for 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 ground water contamination. When the site-wide

remediation is complete, most of RMA will become a National Wildlife Refuge, as provided for

in Public Law #102-402.

1.2 Documenting Changes to the ROD

In implementing RODs at many sites throughout the country, the EPA realized that changes will

inevitably occur and has established guidelines for documenting these changes. 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 40 CFR Section 300.435(c)(2)(i), the lead agency is required to publish an

Explanation of Significant Difference (ESD) when significant changes are being considered to a

final remedial action plan as described in a ROD. The lead agency for RMA is the Army.

Regulatory oversight is conducted by the EPA, CDPHE, and the Tri-County Health Department

(TCHD). TCHD oversees local public and environmental issues in Adams, Arapahoe, and

Douglas Counties.

This ESD summarizes modifications to the remedy for South Plants that result from new

information developed by the Army since the ROD was signed. These changes enhance the

effectiveness of the remedy, but do not alter the overall hazardous waste management

approach that was selected in the ROD. Modifications are being made to the South Plants

Central Processing Area (SPCPA) and the South Plants Balance of Areas (SPBA). The

SPCPA is composed of 47 acres and is located in the south central part of RMA. The SPBA is

composed of 378 acres and surrounds the central processing area, The southern portion of the

SPBA is just north of Lake Ladora, Lake Mary, Upper Derby Lake, and Lower Derby Lake,

which is currently prime habitat for wildlife and a potential high use area for the future wildlife

refuge (Figure 2).

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1.3 Circumstances that Led to the South Plants Remedy ESD

This ESD documents the following significant changes to the South Plants remedy:

1) Removal of the requirement for a 1 -foot cover' in the South Plants Balance of Areas

(SPBA) in lieu of 1 -foot of backfill,

2) Removal of the requirement to excavate biota Soi12 from under the 3-foot cover area

of the SPBA, and

3) Enhancement of construction standards for the 4-foot cover over the SPCPA.

Change in the-1-Foot Cover Area: The ROD requires construction of a 1-foot soil cover in part

of the SPBA. Based on design studies conducted in 1999 to more fully characterize the SPBA,

an additional 948 cubic yards of contaminated soil has been identified for excavation, so that

human health exceedance Soi13 will not remain in the SPBA. Because human health

exceedance soil and biota soil will be removed from the SPBA and replaced by clean soil, there

will be no technical reason (i.e., contaminated soil remaining in place) to require a 1 -foot cover.

Change in the 3-Foot Cover Area: The ROD requires the excavation of the top foot of soil from

the 3-foot cover area of the SPBA to remove soil that poses a risk to biota. The ROD also

requires the construction of a 3-foot soil cover in this area and allows the excavated foot of

biota soil to be used as fill material below the 3-foot cover. Because a 3-foot cover will be

constructed, leaving the top foot of biota soil in place in the 3-foot cover area of the SPBA is

consistent with the ROD remedy: biota soil is either covered with a clean soil cover or removed

and placed in a consolidation area (such as Basin A or the SPCPA).

Change in the 4-Foot Cover Area: The ROD requires a 4-foot soil cover to be constructed over

the SPCPA. One purpose for the 4-foot cover over the SPCPA is to minimize the infiltration of

water through the cover into underlying contaminated soil. In order to better achieve this goal, the

design and construction of the 4-foot cover will employ new methods that are currently being

tested throughout the Unites States for covers over hazardous waste sites. The new cover design

and construction techniques are being tested at RMA under the Resource Conservation and

Recover Act (RCRA)-Equivalent Cover Demonstration Project (MKC 1998). The 4-foot cover over

the SPCPA will be designed and constructed using the same criteria that were used to build

RCRA-Equivalent cover test plots in order to improve the cover's ability to prevent water from

infiltrating through to the underlying contamination and soil.

I A cover is defined in the ROD as a layer of clean soil that isolates contamination in place, thus preventing exposure

to underlying contamination. Covers also require long term monitoring, inspection, and maintenance to ensure long

term performance (FWEC 1996).

2 Soil the top 0 to 12 inches that poses a potential risk to biota (i.e., small mammals) but not to human health.

3 At RMA, soil posing risk to human health is determined by concentrations of chemicals above action levels

developed in the Record of Decision for the On-Post Operable Unit (FWEC 1996).

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This ESD is being provided for public review as defined in 40 CFR 300.435(c)(2)(i). The ESD and

supporting documentation will become a part of the administrative record for the RMA and is

available to the public at the Joint Administrative Record Document Facility (JARDF) located at

the west gate of RMA on 72 nd Avenue and Quebec Street in Commerce City, Colorado. The

JARDF is open to the public on Monday, Wednesday, and Friday from noon to 4:30 p.m.; on

Tuesday and Thursday from 5:00 p.m. to 9:00 p.m.; and on Saturday from 10:00 a.m. to 4:00 p.m.

The telephone number is 303-289-0143. Although not required, a formal public comment period

is being held for this ESD. Additional information on the submittal of comments is provided in

Section 7.

2.0 BACKGROUND

2.1 Summary of the RIVIA Site History and Contamination Problems

RMA was established in 1942 by the Army to manufacture chemical warfare agents and

munitions for use in World War [I. Following the war and through the early 1980s, the facilities

continued to be used by the Army. Beginning in 1946, some facilities were leased to private

companies to manufacture industrial and agricultural chemicals. Shell Oil Company, the

principal lessee, manufactured pesticides 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 ground water.

The On-Post Operable Unit is one of two operable units at RMA. The On-Post Operable Unit

addresses contamination within the fenced 27 square miles of RMA. The Off-Post Operable

Unit addresses contamination north and northwest of RMA.

The contaminated areas within the On-Post Operable Unit include approximately 3,000 acres of

soil, several areas of ground water contamination, and 798 structures. The most highly

contaminated sites are located in South Plants (the central processing area, Hex Pits, Buried

M-1 Pits, and the chemical sewers), Basins A and F, Lime Basins, and the Army and Shell

trenches. The primary contaminants found in soil and ground water at these sites are

pesticides, solvents, metals, and chemical warfare agent byproducts.

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

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.

Ground water contamination is also present at RMA. The characteristics and locations of the

contamination suggest that the greatest contaminant releases to the ground water 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. The Motor Pool/Rail Yard and North Plants area are other sources of

contaminant releases to the ground water.

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BALANCE OF AREAS AND CENTRAL PROCESSING AREA SOIL

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ROCKY MOUNTAIN ARSENAL FEDERAL FACILITY SITE

Since 1975, the Army and Shell have undertaken several Interim Response Actions and

Remedial Actions at RMA designed to remove threats to the environment, while remaining

consistent with any long-term cleanup. Continuing Interim Response Actions include ground

water intercept and treatment north of RMA; ground water intercept and treatment north of

Basin F; ground water intercept and treatment in the Basin A Neck area; boundary ground

water intercept and treatment operation; remediation of other contamination sources (Motor

Pool and Rail Yard ground water treatment); asbestos removal; removal of chemical process

related equipment; and others.

2.2 Summary of the Selected On-Post Remedy

Under the on-post-cleanup plans, contaminated ground water will be intercepted and treated at

the three existing onsite treatment plants, Structures with no designated future use will be

demolished and the debris placed in either the new, on-post hazardous waste landfill or the Basin

A consolidation area, depending upon the degree of contamination. The contaminated soil at

RMA will be addressed primarily through containment in an on-post hazardous waste landfill 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 wildlife refuge.

2.3 Summary of the South Plants Remedy

South Plants was a manufacturing area for mustard-based chemical warfare agent and

pesticides. The southern portion of the SPBA is just north of Lake Ladora, Lake Mary, Upper

Derby Lake, and Lower Derby Lake, which is currently prime habitat for wildlife and a potential

high use area for the future wildlife refuge (Figure 2).

South Plants was previously characterized during the Remedial Investigation initiated in 1984. A

summary of the information collected during the Remedial Investigation/Feasibility Study process

can be found in the Remedial Investigation Summary Report prepared by Ebasco Services

Incorporated in 1992 and in the Detailed Analysis of Alternatives Report prepared by Foster

Wheeler Environmental Corporation in 1995. Risk-based analysis of data collected during the

Remedial Investigation resulted in designation of human health exceedance and biota soil in

South Plants. The ROD also defined a potential chemical agent soil contamination area, based

on site history.

Remedial Actions and Interim Response Actions in South Plants have included the removal of

friable asbestos, removal of polychlorinated biphenyls (PCBs) associated with electrical

transformers, removal of agent-related chemical process equipment and piping, removal of

underground storage tanks and above-ground storage tanks, and plugging of the sanitary and

chemical sewers.

The ROD identifies the following major actions for the South Plants remedy:

" Demolition of structures.

" Removal of floor slabs and foundations in soil excavation areas. Slabs that are not in

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excavation areas are to be left in place and cracked to prevent ponding of water.

" Collection of two composite samples per acre in the SPBA prior to placing the 1 -foot

cover to verify that the soil under the 1 -foot soil cover does not exceed human health

criteria. If the residual soil is found to exceed these levels, the 3-foot cover will be

extended over these areas or the exceedance soil will be excavated and landfilled.

" Screening during excavation of potentially agent-contaminated soil followed by

treatment (if necessary) and landfilling.

" Excavation of human health exceedance soil (to a maximum depth of 5 feet in the

SPCPA and to a maximum depth of 10 feet in the SPBA) and disposal in the onsite

hazardous waste landfill.

" Excavation of the top foot of soil from the entire SPBA because it presents a risk to

biota.

" Backfill of human health exceedance soil excavations with biota soil or clean soil.

" Placement of fill that may consist of biota soil under the SPCPA soil cover.

" Construction of a 4-foot soil cover with a biota barrier over the SPCPA.

" Construction of a 3-foot soil cover over the area of the SPBA immediately surrounding

the SPCPA.

" Construction of a 1 -foot soil cover over former biota exceedance areas around the

periphery of the SPBA.

" Revegetation consistent with ROD requirements for covers.

" Institutional controls consistent with ROD requirements for covers.

" Long-term maintenance of the 1-, 3-, and 4-foot covers.

" Long-term ground water monitoring. 0

Currently, many structures in South Plants have been demolished as required by the ROD, and

only foundations remain. Underground utilities exist but are no longer energized. Overhead

electric lines and utility poles have been removed. Railroad tracks and ties throughout the South

Plants area have been removed.

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3. 0 MODIFICATIONS TO THE ROD REMEDY

3.1 Change to the 1 -Foot Soil Cover Area of the SPBA

Table 1 summarizes the ROD-prescribed requirements for the 1 -foot soil cover area of the

SPBA and shows the changes to those requirements. As shown in the table, the primary

change to this area is the deletion of the 1 -foot cover and replaced with 1 -foot of backfill. The

table also shows enhancements that were made to other aspects of the ROD-prescribed

remedy for this area to ensure the overall remedy is equally protective as the remedy

prescribed in the ROD.

Table 1: Changes to the 1 -Foot Cover Area of the SPBA

ROD-Presgribed Remedy Modification

Demolition of structures, and cracking remaining slabs and Enhancement. All structures will be demolished and all

foundations to prevent ponding of water. foundations and slabs will be removed.

Collection of two composite samples per acre prior to placing Enhancement. An enhanced sampling program was

the 1 -foot cover to verify that the soil under the 1 -foot soil conducted during the design phase of the project that

cover does not exceed human health criteria. included 200 samples in addition to the required 2 samples

per acre (for a total of more than 600 samples in 208 acres).

Excavation and landfill of human health exceedance soil. Enhancement. Excavation of all ROD-defined human health

exceedance soil and excavation of any additional human

health exceedance soil identified during the enhanced

sampling program. All human health exceedance soil will be

disposed in the on-post hazardous waste landfill.

Excavation of all ROD-defined blota soil. No Change. All ROD-defined biota soil will be excavated and

consolidated in the SPCPA.

Backfill of human health exceedance soil excavations with Enhancement. Only clean soil will be used to backfill

biota soil. excavations in the 1-foot cover area of SPBA.

Construction of a 1 -foot soil cover. Reduction. A 1 -foot soil cover will not be constructed, but 1

foot of clean soil will be back-filled following biota soil

excavation.

Revegetation standards consistent with ROD requirements for Reduction. Vegetation standards consistent with refuge

cover systems. policy will be used.

Institutional controls consistent with ROD requirements for Reduction. Institutional controls for a noncover area will be

covers systems (e.g., delineation and access control). implemented (e.g,, controlled access via roads and trails).

Long-term ground water monitoring. No Change. The same long-term ground water monitoring

program will be implemented.

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3.2 Change to the 3-Foot Soil Cover Area of the SPBA

Table 2 summarizes the ROD-prescribed requirements for the 3-foot soil cover area of the

SPBA and shows the removal of the requirement to excavate biota soil from under the 3-foot

cover area.

Table 2: Changes to the 3-Foot Cover Area of the SPBA

ROD-Prescribed Remedy Modification

Demolition of structures, removal of foundations and slabs in No Change. All structures will be demolished; foundations

excavation areas, and cracking remaining slabs and and slabs will be removed in excavation areas and cracked in

foundations to prevent ponding or water in non-excavation non-excavation areas.

areas.

Excavation and landfill of human health exceedance soil. No Change. Excavation of all ROD-deflned human health

exceedance soil and disposal in the on-post hazardous waste

landfill.

Excavation of all ROD-defined biota soil. Reduction. Not all soil posing a potential risk to biota will be

excavated, however, the biota soil will be covered with a 3-

foot cover as required by the ROD.

Backfill of human health exceedance soil excavations with No Change. Biota soil can be used to backfill human health

biota soil. exceedance excavations in the 3-foot cover area of SPBA.

Construction of a 3-foot soil cover. Enhancement. The cover will be designed and constructed

using concepts derived from the RCRA-Equivalent Cover

Demonstration Project at RIVIA. Also, the initial constructed

cover thickness will be increased to 3.25 feet to allow for

erosion and will be constructed of soil from the clear borrow

areas.

Revegetation standards consistent with ROD requirements for No Change. The same revegetation standards will be used.

covers systems.

Institutional controls consistent with ROD requirements for No Change. Institutional controls for a cover area will be

covers (e.g., markers delineating the extent of the cover and implemented (e.g., markers delineating the extent of the

access control). cover and access control).

Long-term ground water monitoring. No Change. The same long-term ground water monitoring

program will be implemented.

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3.3 Change to the 4-Foot Cover

Table 3 summarizes the ROD-prescribed requirements for the 4-foot soil cover over the SPCPA

and shows the enhanced, RCRA-Equivalent, construction methods that will be used to construct

this cover,

Table 3: Changes to the 4-Foot Cover Area of the SPCPA

ROD-Prescribed Remedy Modification

Demolition of structures, removal of foundations and slabs in No Change. All structures will be demolished; foundations

excavation areas, and cracking slabs and foundations to and slabs will be removed in excavation areas and cracked in

prevent ponding or water in non-excavation areas. non-excavation areas.

Excavation and landfill of human health exceedance soil to a No Change. All ROD-defined human health exceedance soil

maximum depth of 5 feet. will be excavated to a depth of 5 feet and disposed in the onpost hazardous waste landfill.

Backfill of human health exceedance soil excavations with No Change. Blota soil will be used to backfill human health

biota soil. exceedance excavations in the 4-foot cover area of SPCPA.

Consolidation of biota soil excavated from the SPBA and No Change. Biota soil will be used as fill under the 4-foot

placement as fill under the 4-foot cover. cover.

Construction of a 4-foot soil cover. Enhancement. The cover will be designed and constructed

to meet the same criteria as that used for the RCRAEquivalent Cover Demonstration Project at RIVIA. Also, the

initial constructed cover thickness will be increased to 4.5-feet

thick to allow for erosion and will be constructed using soil

from the borrow areas.

Revegetation standards consistent with ROD requirements for No Change. The same revegetation standards will be used,

cover systems. consistent with refuge policy.

Institutional controls consistent with refuge policies for a cover No Change. Institutional controls for a cover area will be

area (e.g., markers delineating the extent of the cover and implemented (e.g., markers delineating the extent of the

access control). cover and access control).

Long term ground water monitoring. No Change. The same long-term ground water monitoring

program will be implemented.

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4.0 BASIS FOR THE ESD

4.1 Basis for the Change to the 1 -Foot Soil Cover Area of the SPBA

As part of the South Plants remediation project, the ROD requires additional characterization of

the 1 -foot cover area by requiring the collection of two samples per acre to verify that soil left

after excavation does not exceed human health criteria. Since the 1 -foot cover area lies

outside the more contaminated central processing area, the potential for remaining

contamination above that already identified and reported during the Remedial

Investigation/Feasibility Study is expected to be minimal. While the ROD-required sampling

would indicate whether human health exceedance soil was removed from the top foot, it would

not verify this at depth. Therefore, after consulting with the regulatory agencies (EPA, CDPHE,

and TCHD) the Army developed an enhanced sampling program to more fully characterize the

I -foot cover area at depth. This resulted in significantly more samples than originally required

by the ROD. The enhanced sampling program was implemented during the summer of 1999

and based on the sample results, there is no technical reason to retain the 1 -foot cover

requirement. Long term maintenance requirements for the 1-foot cover area may be eliminated

and the protectiveness of the remedy is not compromised. The elimination of the 1 -foot cover

will also result in a long term cost savings, and will allow transfer of this area to Department of

the Interior for inclusion as part of the wildlife refuge, Details of the enhanced sampling

program are described below.

Sample locations for the enhanced sampling program were selected based upon site history,

historical sampling data collected during the Remedial Investigation, proposed locations of

future use features, and boundaries of excavation sites. Additional samples were placed where

fewer samples had been collected in the past, and where exceedances or near-exceedances

were identified outside of excavation areas. Samples were placed along proposed locations for

a possible future tram route, trails, and at the boundary of the 3-foot cover area and the 1 -foot

cover in the SPBA. Samples were also placed around ROD-identified excavation areas to

verify that the planned excavation would be sufficient to remove the human health exceedance

soil. Discrete samples were collected at various depths at all of these locations.

Additional samples were placed in areas of SPBA that still had a relatively low sample density.

These samples were placed using a grid system. The sampling area was divided into one-half

acre grid areas. Grid areas that did not have existing remedial investigation samples or newly

identified samples were selected for collection of composite samples. The composite samples

were collected from 12 inches to 18 inches below the ground surface at the grid locations.

Figure 3 shows the location of samples collected during the enhanced sampling program.

The resulting sampling plan called for over 600 sample locations throughout the 1 -foot cover area,

approximately 200 samples more than required by the ROD. Depending on the site history in the

vicinity of a specific sample location, samples were analyzed for a combination of pesticides,

metals, and volatile organic compounds.

The results of the enhanced sampling program are described in the South Plants Balance of

Areas Sample Results Report prepared by Foster Wheeler Environmental Corporation in March

2000. Of the approximately 600 samples collected during the enhanced sampling program, only 3

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human health exceedances were identified. Furthermore, the three exceedances are located

beneath two human health exceedance soil areas that were already identified for excavation by

the ROD and were easily incorporated into the design as areas of additional excavation. During

the Remedial Investigation of the SPBA, 1,111 samples were collected resulting in 39 human

health exceedances. Therefore, there is now a data set of over 1,700 samples in the 208 acres

area that resulted in 42 exceedances. No evidence of previously undetected contaminant source

areas was identified.

Two additional enhancements to the ROD-prescribed remedy will be implemented in the 1 -foot

cover area. All structure foundations and floor slabs will be removed rather than leaving some in

place and cracking them, and only clean soil will be used to backfill the deeper human health

exceedance excavations rather than using biota soil as backfill. Therefore, because human

health exceedance soil and biota soil are to be removed from the entire 1 -foot area of the SPBA,

there is no technical reason to retain the requirement for a cover.

4.2 Basis for the Change in the 3-Foot Soil Cover Area of the SPBA

The ROD requires excavation of the top 1 -foot of soil from the 3-foot cover area to remove

potential risk to biota. After the 1 -foot of biota soil is removed, the ROD requires placement of

a 3-foot cover. However, the ROD also allows biota soil to be used as fill under the 3-foot

cover.

The change in this ESD removes the requirement to excavate the top 1 -foot of biota soil from

under the 3-foot cover system. A portion of the existing biota soil will be left undisturbed rather

than excavated and used as fill in other sections of the South Plants cover areas. Any biota

removed will be consolidated into the SPCPA. A cover constructed of 3-feet of clean soil will be

placed over the biota soil. This final disposition of biota soil in the 3-foot cover area of the SPBA

is consistent with the ROD remedy: biota soil is either covered with clean soil or removed and

placed in a consolidation area (such as Basin A or the SPCPA). This change results in a more

cost effective remedy while maintaining the same level of protection required by the ROD (i.e,,

biota soil that is left in place is contained under a long term-c6ver). Long-term maintenance

requirements remain unchanged.

4.3 Basis for the Change to the 4-Foot Cover

The ROD requires construction of a 4-foot soil cover over the SPCPA after human health

exceedance soil has been excavated to a maximum depth of 5 feet. The ROD also requires

that the cover provide long-term protectiveness by being designed and constructed to minimize

the infiltration of water through the cover into remaining contamination and the underlying soil.

To meet this objective, the latest technology for minimizing infiltration through covers will be

employed for the 4-foot cover over the SPCPA, by using the same design and construction

methods that were used for the ongoing RCRA-Equivalent Cover Demonstration Project at

RIVIA.

RCRA-equivalent soil covers use an evapotranspirative soil layer in conjunction with native

vegetation to obtain levels of performance equal to RCRA hazardous waste landfill covers. In

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April 1998, the Army designed and constructed four RCRA-equivalent cover test plots at RMA,

to determine if these alternative covers could provide a level of performance equal to that

provided by a traditional RCRA hazardous waste cover system (typically constructed using

compacted clay and geosynthetic membranes). The RCRA-equivalent cover test plots are

allowed to develop a full stand of native vegetation for three years, and following successful

establishment, each test cover is monitored to determine if it can meet strict standards for

minimal infiltration of water (i.e. a standard of 1.3 millimeters per year). Successful test plots

will be considered "RCRA-equivalent." Successful cover designs from the field test can then be

used as the RCRA-equivalent cover design at sites were the ROD specifically requires the

placement of RCRA-equivalent covers (such as at the Former Basin F site), and additionally, in

the SPCPA.

While the testing of the RCRA-equivalent cover test plots will not be complete for two years,

rigorous modeling and preliminary monitoring data from the ongoing field study suggests that

the covers will meet the strict standards for minimal infiltration of water. On this initial basis, the

Army has chosen to design and construct the cover over the SPCPA to a minimum thickness of

4.5 feet, using the same specifications and quality control principles that were used for the

successful RCRA-equivalent cover test plot.

5.0 SUPPORT AGENCY COMMENTS

The EPA, CDPHE, and TCHD have reviewed and concurred with this ESD. Comments from

these agencies have been incorporated into the document.

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6.0 STATUTORY DETERMINATIONS

Considering the changes described in this ESD and the new information, the Army, EPA and

CDPHE believe that the remedy remains 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.

Signatures

For U.S. Environmental Protection Agency

Date

Max H. Dodson

Assistant Regional Administrator

Office of Ecosystems Protection and Remediation

For U.S. Army

Date

Charles T. Scharmann

Program Manager for Rocky Mountain Arsenal

For State of Colorado

V\ Date kk- k1o -- Crzj

Howard Roitman

Director, Hazardous Materials and Waste Management Division

7.0 PUBLIC PARTICIPATION COMPLIANCE

The Army published a public notice in the Rocky Mountain News and Denver Post on April 6,

2000, making the Draft South Plants ESD available for public review and comment. A

presentation regarding the ESD was made to the Restoration Advisory Board (RAB) on March

2, 2000. The RAB is a community group that is open to the public and meets monthly to receive

information and provide input on remedial activities being conducted at the RMA. The public

comment period was closed on May 8, 2000. No comments from the public were received. The

requirements set out in the National Contingency Plan, Section 300.435(c)(2)(ii), have been

met. This ESD and all documents that support the changes and clarifications are part of the

Administrative Record and available at the Joint Administrative Record Document Facility

(JARDF) and the EPA Region 8 Superfund Record Center.

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EXPLANATION OF SIGNIFICANT DIFFERENCES FOR SOUTH PLANTS

BALANCE OF AREAS AND CENTRAL PROCESSING AREA SOIL

REMEDIATION PROJECT

ROCKY MOUNTAIN ARSENAL FEDERAL FACILITY SITE

8.0 REFERENCES

Ebasco Services Incorporated. 1992. Remedial Investigation Summary Report. Final. Rocky

Mountain Arsenal. Commerce City, Colorado. January.

Foster Wheeler Environmental Corporation (FWEC). 1996. Record of Decision for the On-Post

Operable Unit. Rocky Mountain Arsenal, Commerce City, Colorado. June.

FWEC. 1995. Detailed Analysis of Alternatives Report. Final. Rocky Mountain Arsenal.

Commerce City, Colorado. October.

FWEC. 1999. South Plants Balance of Areas Sample Results Report. Rocky Mountain

Arsenal. Commerce City, Colorado.

Morrison Knudsen Corporation (MKC). 1998. RCRA-Equivalent Cover Demonstration Project,

Final Design Package. Rocky Mountain Arsenal. Commerce City, Colorado. January.

U.S. Environmental Protection Agency (EPA). 1999. A Guide to Preparing Superfund Proposed

Plans, Records of Decision, and Other Remedy Selection Decision Documents. EPA 540-R98-031. Washington D.C. July.

EPA. 1989. Federal Facility Agreement Pursuant to CERCLA Section 120. Docket No. CERCLA

Vill-89-13. Rocky Mountain Arsenal. Commerce City, Colorado. February 17.

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