f. e. warren air force base, wyoming · decision for spill site 8 soils, f. e. warren air force...

INTERIM ACTION FOR

SPILL SITE 8, OU14 SOILS FINAL

RECORD OF DECISION

F. E. Warren Air Force Base, Wyoming

May 2009

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INTERIM ACTION FOR SPILL SITE 8, OU14 SOILS FINAL RECORD OF DECISION


Prepared for:

90 MW/EM F. E. Warren Air Force Base, Wyoming

and

Air Force Center for Engineering and the Environment Brooks City-Base, Texas

Prepared by: URS Group, Inc. 8181 East Tufts Avenue Denver, Colorado 80237

May 2009

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Interim Action Record of Decision Spill Site 8 Soils, OU14

F. E. Warren Air Force Base Cheyenne, Wyoming

TABLE OF CONTENTS

LIST OF TABLES ....................................................................................................................... iii

LIST OF FIGURES ..................................................................................................................... iii

LIST OF ABBREVIATIONS AND ACRONYMS ................................................................... iv

1.0 DECLARATION............................................................................................................1-1

1.1 Site Name and Location .......................................................................................... 1-1 1.2 Statement of Basis and Purpose .............................................................................. 1-1 1.3 Assessment of Site .................................................................................................. 1-1 1.4 Selected Remedy ..................................................................................................... 1-1 1.5 Statutory Determinations ........................................................................................ 1-2 1.6 Data Certification Checklist.................................................................................... 1-3 1.7 Authorizing Signatures ........................................................................................... 1-4

2.0 DECISION SUMMARY ...............................................................................................2-1

2.1 Site Name, Location and Brief Description ............................................................ 2-1 2.2 Site History and Enforcement Activities ................................................................ 2-2

2.2.1 F. E. Warren Air Force Base .................................................................... 2-2 2.2.2 Spill Site 8................................................................................................ 2-3

2.3 Community Participation ........................................................................................ 2-4 2.4 Scope and Role of Operable Unit/Response Action ............................................... 2-6 2.5 Site Characteristics.................................................................................................. 2-6

2.5.1 Surface Features....................................................................................... 2-6 2.5.2 Geology.................................................................................................... 2-7 2.5.3 Hydrogeology .......................................................................................... 2-7 2.5.4 Surface Water Hydrology ........................................................................ 2-8 2.5.5 Conceptual Site Model............................................................................. 2-9 2.5.6 Soil Investigations.................................................................................. 2-10 2.5.7 Groundwater Investigations ................................................................... 2-11 2.5.8 Surface Water Investigations ................................................................. 2-11 2.5.9 Nature and Extent of Contamination ..................................................... 2-11

2.6 Current and Potential Future Land and Water Uses ............................................. 2-13 2.6.1 Land Uses............................................................................................... 2-13 2.6.2 Groundwater and Surface Water Uses ................................................... 2-14

2.7 Summary of site risks............................................................................................ 2-14 2.7.1 Summary of Human Health Risk Assessment ....................................... 2-14 2.7.2 Summary of Ecological Risk Assessment ............................................. 2-17

2.8 Remedial Action Objectives ................................................................................. 2-18 2.9 Descriptions of Alternatives ................................................................................. 2-19

2.9.1 Remedy Components ............................................................................. 2-20 Alternative 1 - No Action ..................................................................................... 2-20

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Alternative 2 – Land Use Controls ....................................................................... 2-20 Alternative 3 – Excavation and Offsite Disposal .................................................. 2-24 2.9.2 Expected Outcome of Each Alternative ................................................. 2-25

2.10 Comparative Analysis of Alternatives .................................................................. 2-25 2.10.1 Overall Protection of Human Health and Environment......................... 2-27 2.10.2 Compliance with ARARs ...................................................................... 2-27 2.10.3 Long-Term Effectiveness and Permanence ........................................... 2-28 2.10.4 Reduction of Toxicity, Mobility, or Volume Through Treatment......... 2-28 2.10.5 Short-Term Effectiveness ...................................................................... 2-28 2.10.6 Implementability .................................................................................... 2-28 2.10.7 Cost ........................................................................................................ 2-29 2.10.8 Regulatory Agency Acceptance............................................................. 2-29 2.10.9 Community Acceptance......................................................................... 2-29

2.11 Principal Threat Wastes ........................................................................................ 2-29 2.12 Selected Remedy ................................................................................................... 2-30

2.12.1 Summary of Rationale for Selected Remedy ......................................... 2-30 2.12.2 Description of the Selected Remedy ...................................................... 2-30 2.12.3 Expected Outcomes of Selected Remedy .............................................. 2-31

2.13 Statutory Determination ........................................................................................ 2-31 2.13.1 Protection of Human Health and the Environment ................................ 2-31 2.13.2 Compliance with ARARs ...................................................................... 2-32 2.13.3 Cost-Effectiveness ................................................................................. 2-33 2.13.4 Utilization of Permanent Solutions and Alternative Treatment

Technologies .......................................................................................... 2-34 2.13.5 Preference for Treatment as a Principal Element .................................. 2-34

2.14 Documentation of Significant Changes from Preferred Alternative of Proposed Plan .............................................................................................................................. 2-34

3.0 RESPONSIVENESS SUMMARY ................................................................................3-1

3.1 Stakeholder issues and lead agency responses ........................................................ 3-1 3.2 Technical and Legal Issues ..................................................................................... 3-1

4.0 REFERENCES...............................................................................................................4-1

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LIST OF TABLES

Table No. Title

2-1 Non-Cancer Hazard and Cancer Risk Estimates for Spill Site 8 2-2 Hazard Quotients for Chemicals of Ecological Concern for Spill Site 8 2-3 Spill Site 8 Detailed Alternative Analysis 2-5 Chemical-Specific ARARs 2-6 Location-Specific ARARs 2-7 Action-Specific ARARS

LIST OF FIGURES

Figure No. Title

2-1 F.E. Warren AFB Installation Location Map 2-2 Spill Site 8 Site Map 2-3 Approximate 100-Year Floodplain for Crow Creek at Spill Site 8 2-4 Approximate Extent of Contamination in Soil and Groundwater 2-5 Human Health Conceptual Site Model 2-6 Ecological Conceptual Site Model 2-7 Conceptual Layout of Selected Remedy

Appendix A Summary of Analyte Exceedances in Soil and Groundwater

Appendix B Calculation of Surface Soil Cleanup Level

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LIST OF ABBREVIATIONS AND ACRONYMS

ARAR applicable or relevant and appropriate requirement

BGP Base General Plan

bgs below ground surface

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

CFR Code of Federal Regulations

COC chemical of concern

COPC contaminant of potential concern

COPEC chemical of potential ecological concern

CRP community relations plan

CTE central tendency exposure

DCE dichloroethene or dichloroethylene

EPA United States Environmental Protection Agency

FEW F.E. Warren Air Force Base

FFA Federal Facility Agreement

FS feasibility study

ft/day foot per day

ft/year feet per year

HI hazard index

HQ hazard quotient

IRP Installation Restoration Program

MCL maximum contaminant level

µg/L microgram per liter

mg/L milligram per liter

MNA monitored natural attenuation

NCP National Oil and Hazardous Substances Pollution Contingency Plan

NPL National Priorities List

NPV net present value

O&M operation and maintenance

OU operable unit

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LIST OF ABBREVIATIONS AND ACRONYMS (Continued)

PRG preliminary remediation goal

RAO remedial action objective

RI remedial investigation

RME reasonable maximum exposure

ROD Record of Decision

SARA Superfund Amendments and Reauthorization Act

SDWA Safe Drinking Water Act

SQV sediment quality value

SVOC semivolatile organic compound

TBC to be considered

TRV toxicity reference value

USAF United States Air Force

USC United States Code

VOC volatile organic compound

WDEQ Wyoming Department of Environmental Quality

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1.0 DECLARATION

1.1 SITE NAME AND LOCATION

F. E. Warren Air Force Base (FEW) is located in Laramie County, Wyoming. F. E. Warren was

placed on the National Priorities List (NPL) in February 1990 and was assigned the National

Superfund Database identification number WY5571924179. This Interim Action Record of

Decision (ROD) addresses remedial actions (RAs) for the contaminated soils at Spill Site 8,

Operable Unit 14 (OU14) at FEW. Spill Site 8 is designated as Installation Restoration Program

(IRP) site SS022.

1.2 STATEMENT OF BASIS AND PURPOSE

This decision document presents the selected remedy for contaminated soils at Spill Site 8. The

selected remedy was chosen in accordance with the Comprehensive Environmental Response,

Compensation, and Liability Act (CERCLA), as amended by the Superfund Amendment and

Reauthorization Act (SARA) and, as applicable, the National Oil and Hazardous Substances

Pollution Contingency Plan (NCP). This decision is based on the Administrative Record file for

the site. The U.S. Environmental Protection Agency (EPA) and the State of Wyoming

Department of Environmental Quality (WDEQ) concur with the selected remedy.

1.3 ASSESSMENT OF SITE

The response action selected in this ROD is necessary to protect public health or welfare, or the

environment from actual or threatened releases of hazardous substances into the environment.

1.4 SELECTED REMEDY

The selected remedy for Spill Site 8 soils is excavation and off-site disposal of arsenic

contaminated soil. Soil excavation was selected because it is expected to achieve long-term risk

reduction through removal of contaminated soil. Contaminated groundwater will be evaluated in

a separate feasibility study and record of decision.

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The major components of the selected remedy are:

Excavate soils in the Building 354 Former Storage Area with arsenic concentrations

exceeding the background soil level of 7.5 milligrams per kilogram (mg/kg) to reduce

the potential for arsenic to migrate from soil to groundwater and to reduce potential risk

of direct exposure to surface soils;

Contaminated soil from the excavation will be disposed of at an off-site facility permitted

to receive the soil. The excavation will be backfilled with clean soil.

The Proposed Plan for Spill Site 8 originally included remediation of both soils and

groundwater; however, upon review of the preferred remedy for groundwater, monitored

natural attenuation (MNA), it was determined that the arsenic plume did not meet the

EPA criteria of stability in order to consider MNA as a potential remedy. Therefore, the

remedy for groundwater is being reevaluated and is not carried through in this ROD. A

Final ROD for Spill Site 8 will be completed that selects the groundwater remedy and

incorporates this interim action for soils by reference.

1.5 STATUTORY DETERMINATIONS

The selected remedy for soils at Spill Site 8 is protective of human health and the environment,

complies with Federal and State requirements that are applicable or relevant and appropriate to

the remedial action, is cost-effective, and utilizes permanent solutions to the maximum extent

practicable.

The remedy does not satisfy the statutory preference for treatment as a principal element of the

remedy because it involves excavation and off-site disposal of untreated soil. Although soil will

not be treated, excavation and off-site disposal is an appropriate remedy because it permanently

and significantly reduces the mobility and volume of contaminants at the site. It is an efficient

approach because it permanently removes contaminated soil in the source area in a short

timeframe. Because the impacted area is relatively small, it is also cost-effective.

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1.6 DATA CERTIFICATION CHECKLIST

The following information is included in the Decision Summary section (Section 2.0) of this

ROD. Additional information can be found in the Administrative Record for the site.

Chemicals of concern (COCs) and their respective concentrations (Section 2.5);

Baseline risk presented by the COCs (Section 2.7);

Cleanup levels for COCs and the basis for these levels (Section 2.12);

How source materials constituting principal threats are addressed (Section 2.11);

Current and future land use assumptions and current and future beneficial uses of

groundwater used in the baseline risk assessment and ROD (Section 2.6);

Potential land and groundwater use that will be available to the site as a result of the

selected remedy (Section 2.12.3);

Estimated capital, O&M, and total present worth costs, and the number of years over

which the remedy cost estimates are projected (Table 2-3); and

Key factors leading to the selected remedy (Section 2.10).

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-Interim Action Record ofDecision

Spill Site 8 Soils, OUI4 F. E. Warren Air Force Base

Cheyenne,

AUTHORIZING SIGNATURES

a. The undersigned representative concurs with the Selected Remedy included in this Record of Decision for Spill Site 8 Soils, F. E. Warren Air Force Base, Wyoming.

.. AN~-S-A-F---

Commander, 90th Missile Wing

b. The undersigned representative concurs with the Selected Remedy included in this Record of Decision for Spill Site 8 Soils, F. E. Warren Air Force Base, Wyoming.

CAROL L. CAMPBELL Assistant Regional Administrator Ecosystems Protection and Remediation U. S. Environmental Protection Agency - Region VIII -c. The undersigned representative concurs with the Selected Remedy included in this Record of Decision for Spill Site 8 Soils, F. E. Warren Air Force Base, Wyoming.

JON CORRA Dire r, Wyoming Department of Environmental Quality

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2.0 DECISION SUMMARY

2.1 SITE NAME, LOCATION AND BRIEF DESCRIPTION

F. E. Warren Air Force Base (FEW) is located in Laramie County, on approximately 5,866 acres

adjacent to the western city limits of Cheyenne, Wyoming. The base is bounded by Interstate 25

on the east, Old Happy Jack Road to the south, Military Road on the southwest, Roundtop Road

on the west, and open prairie on the north. The location of FEW is shown on Figure 2-1.

F.E. Warren entered into the USAF’s Installation Restoration Program (IRP) in the late 1980’s

and was placed on the National Priorities List (NPL) in February 1990. F. E. Warren was

assigned the National Superfund Database identification number WY5571924179. In September

1991, the USAF, EPA, and WDEQ signed a Federal Facilities Agreement (FFA) to perform

installation-wide environmental investigations and restoration. The FFA provides the framework

for EPA and WDEQ oversight of continuing remedial investigations at FEW and further

identifies USAF investigation activities and schedules. The FFA was later modified in 1998.

The USAF is the lead agency with support from the EPA and the WDEQ. Based on an

installation-wide remedial investigation (RI), 20 IRP sites were identified and grouped into

operable units (OUs) based on site type, location, and projected response actions. The OUs were

subsequently divided into a system of five investigation zones, designated as Zones A through E,

to facilitate and streamline investigation and cleanup. The delineation of the zones is based on

geographic features (e.g., surface water drainages) and other distinguishing features.

Spill Site 8 is located north-northeast of the confluence of Crow Creek and Diamond Creek in

Zone E (Figure 2-2). The site occupies an area of approximately 18 acres, the majority of which

is open space. Spill Site 8 includes three principal subareas: the Wash Rack Area, the Building

354 Former Storage Area, and the Building 356 Wood Hobby Shops Area. The southern and

western portions of Spill Site 8, including the Wash Rack Area, are located within the 100-year

floodplain of Crow Creek (Figure 2-3).

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2.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES

2.2.1 F. E. Warren Air Force Base

F. E. Warren has served a number of functions since its activation as a military base in the mid

1800s. United States Army outpost Fort D.A. Russell was established at this location in 1867 to

protect railroad workers. Largely due to the influence of Senator Francis E. Warren, Ft. Russell

was selected in 1902 for expansion. To meet the needs of the increased manpower, construction

activity began in 1903. In 1905, Secretary of War William Taft recommended enlargement of

Ft. Russell to a brigade-size post; 150 buildings were erected between 1905 and 1913. These

facilities form a large part of the current National Historic Landmark.

An airfield was located at Ft. Russell in 1919. O'Neil Airfield was the site of transcontinental

reliability test flights, and it was hoped that the post would become an important stop for cross

country flights. By 1920, the Army had abandoned this notion and the airfield was closed.

In honor of Senator Warren and his tremendous impact on the development of Ft. Russell, the

post was renamed Fort Francis E. Warren in 1929. The next major construction episode in the

history of the base occurred during World War II. The area south of Crow Creek was chosen as

the location of a Quartermaster Replacement Center.

In 1947, the property was transferred from the Army to the newly formed USAF and the Base

was assigned to the Air Training Command (ATC). In 1957, FEW was selected as the nation's

first intercontinental ballistic missile complex. The complex consisted of two Launch Control

Centers, each having control of three missiles. In 1959, the first Atlas “D” missiles arrived at the

FEW, and the base was transferred from the jurisdiction of ATC to the Strategic Air Command.

A second generation of missiles was developed between 1958 and 1962. Minuteman “B”

missiles were installed in 200 missile silos with 20 launch control sites spread over an area of

8,300 square miles. In 1973, the Minuteman III replaced the Minuteman “B.”

The base was assigned to Air Combat Command in June 1992, and then to Air Force Space

Command in July 1993. At present, the prime mission of FEW is to provide operational,

maintenance, and security support for Peacekeeper and Minuteman III missiles.

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2.2.2 Spill Site 8

The primary features at Spill Site 8 are the Wash Rack Area, the Building 354 Former Storage

Area, and the Building 356 Wood Hobby Shops Area. The Wash Rack Area was reportedly used

as early as 1945 for cleaning vehicles. The primary surface feature in the Wash Rack Area is a

concrete slab with a formed trough along the southern edge that was used to direct water to a

sump in the southwest corner. Subsurface piping was used to convey water away from the sump

toward the low-lying area of Crow Creek. The Building 354 Former Storage Area consists of

Building 354 and a former fenced area, measuring approximately 70- by 100-feet, to the west of

the building. The storage area was reportedly used since at least 1966 to store equipment and

other materials, possibly including drums. The specific equipment and drum contents, if any, are

not known. The fence around the area was subsequently removed in 1976. The Building 356

Wood Hobby Shop Area consists of the area around Building 356 and former Building 357,

which was located just east of Building 356. The area was historically used for vehicle

maintenance and repair activities from at least 1960. The location is currently used for a wood

hobby shop/arts and craft center.

A Supplemental Preliminary Assessment was performed in 2003 to identify sites at F. E. Warren

that required assessment under the IRP. The Supplemental Preliminary Assessment identified

areas of potential concern (AOPCs) that were recommended for additional evaluation, including

limited soil and groundwater sampling and analysis. The AOPCs were consolidated into

separate study areas for further investigation under the Site Inspection process. Study Area 3

consisted of the area that is now designated as Spill Site 8.

A Site Inspection for Spill Site 8 was conducted in 2003 and 2004. The Site Inspection included

limited soil and groundwater sampling to evaluate potential contamination at the site. Several

potential constituents of concern were identified in soil and groundwater at concentrations

exceeding FEW background levels, human health risk-based screening levels in soil, and/or

MCLs in groundwater. The primary constituents of concern were arsenic, which was detected in

soil in the Building 354 Former Storage Area, and polycyclic aromatic hydrocarbons (PAHs),

which were detected in the Wash Rack Area sump and in soil at the discharge pipe outfall near

Crow Creek. Polycyclic aromatic hydrocarbons are organic compounds typically resulting from

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burning of carbon-containing materials. Based on those results, it was recommended that

additional investigation be conducted at Spill Site 8.

An RI for Spill Site 8 was conducted in 2006 to further evaluate the extent of contamination and

to assess the potential risk to human health and the environment. Soil, groundwater, and surface

water sampling were performed to evaluate potential site impacts to those media. Based on the

RI data, the approximate extents of elevated arsenic and PAH concentrations in soil were

delineated. Subsurface soil samples collected at two locations in the Building 354 Former

Storage Area contained arsenic at concentrations exceeding EPA Region 9 Soil Screening Levels

(SSLs) for the protection of groundwater and base background values. A human health risk

assessment performed for the RI concluded that arsenic in surface soil at the Former Storage

Area were within the EPA acceptable target risk range of 1x10-4 and 1x10-6. The approximate

extent of arsenic in groundwater at concentrations above the MCL of 0.01 milligrams per liter

(mg/L) was also delineated downgradient of the Former Storage Area. Groundwater is not

currently used at FEW, and it is not anticipated that it will be used in the future; therefore, a risk

assessment was not conducted for groundwater. However, arsenic is present at concentrations

exceeding the MCL. The results of surface water samples from Crow Creek indicated that the

site is not impacting the creek.

A Feasibility Study (FS) to evaluate remedial alternatives to address the soil and groundwater

contamination was performed in 2007; however, upon review of the preferred remedy included

in the Draft ROD for Spill Site 8, EPA determined that the arsenic plume did not meet the EPA

criteria of stability in order to consider MNA as a proposed remedy. Therefore, the remedy for

groundwater is presently being reevaluated and is not carried through in this ROD. A new FS

will be developed to evaluate additional alternatives for the groundwater at Spill Site 8.

2.3 COMMUNITY PARTICIPATION

The USAF has prepared and implemented a Community Relations Plan (USAF 2001) in

accordance with CERCLA requirements and the Federal Facility Agreement (FFA). The

Community Relations Plan describes community involvement activities that the USAF will

undertake during remedial activities at FEW. The USAF has followed the requirements of the

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Community Relations Plan, including holding public meetings and providing the opportunity for

public comment throughout the cleanup process.

The RI (USAF 2007a), FS (USAF 2007b), other investigative reports, and the Proposed Plan

(USAF 2008a) have been made available to the public and can be found in the Administrative

Record at the following location:

Laramie County Library 2200 Pioneer Avenue Cheyenne, WY 82001 (307) 634-3561

Hours of Operation: 10 am to 9pm (Mon-Thur) 10 am to 6 pm (Fri-Sat)

Restoration Advisory Board (RAB) meetings are held in Cheyenne to update attending

community members on the status of FEW environmental restoration activities and the CERCLA

decision-making process and solicit input from members. The RAB members have been

periodically briefed on Spill Site 8 activities.

A public comment period for the Proposed Plan (USAF 2008a) was held from April 21, 2008

through May 21, 2008. In addition, a public meeting was held on April 22, 2008, to present the

Proposed Plan to the community. At the meeting, representatives from the USAF, the EPA and

the WDEQ answered questions about the site and the remedial alternatives. As described in the

Responsiveness Summary (Section 3), no written comments were received from the public and

no comments were received verbally during the public meetings that would change the remedy

selection process. An official transcript of the public meeting was prepared and placed in the

Administrative Record.

As discussed earlier, the Proposed Plan for Spill Site 8 originally included remediation of both

soils and groundwater, however, upon review of the groundwater preferred remedy (MNA)

included in the draft ROD for Spill Site 8, EPA determined that the arsenic plume did not meet

its criteria of stability in order to consider MNA as a proposed remedy. Therefore, the remedy

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for groundwater is presently being reevaluated and is not carried through in this ROD. A new FS

will be developed to evaluate additional alternatives for the groundwater at Spill Site 8.

2.4 SCOPE AND ROLE OF OPERABLE UNIT/RESPONSE ACTION

Spill Site 8 is associated with operable unit (OU) 14. No response actions have been taken at the

site. The OUs identified at FEW are:

• OU1 – Spill Sites 1 through 7 (Soils);

• OU2 – Spill Sites 2, 4, and 7 (Groundwater); Fire Protection Training Area (FPTA)2 (Groundwater); and Plumes A, B, C, and E (Groundwater);

• OU3 – Landfill 6 (all media);

• OU4 – Acid Dry Wells (all media);

• OU5 – FPTA2 (Soils);

• OU6 – Open Burning/Open Detonation Area (all media);

• OU7 – Firing Ranges (all media);


• OU9 – Landfill 2 (all media; groundwater addressed as part of OU2);

• OU10 – Landfill 7 and FTPA1 (all media);



• OU13 – Plumes A, B, C, and, E (Source Soils).

• OU14 – Spill Site 8

2.5 SITE CHARACTERISTICS

2.5.1 Surface Features

At the Wash Rack Area, the primary surface feature is the wash rack pad (Figure 2-2). The wash

rack pad is a concrete slab with a formed trough along the southern edge that was used to convey

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water to a sump in the southwest corner. Subsurface piping was used to convey the water away

from the sump toward the low-lying area of Crow Creek.

Building 354 is a brick structure approximately 200-feet long by 75-feet wide. A fenced area

located immediately west of Building 354 was noted on historical aerial photographs as a storage

area (Figure 2-2). The fenced area was approximately 70- by 100-feet based on a 1966 aerial

photograph (USAF 2005). The area is now used for vehicle parking.

Building 356 is similar in size and structure as Building 354. The Building 356 auto hobby

shops area consists of the area around Building 356 and former Building 357, which was located

approximately 75 feet east of Building 356 (Figure 2-2). The areas to the east and west of

Building 356 are generally used for vehicle parking.

2.5.2 Geology

The uppermost geologic unit at FEW consists of Quarternary-age alluvial and terrace deposits

composed of sands, silts, and clays. The thickness of these Quaternary deposits varies, but is

typically less than 25 feet (USAF 2003). The Tertiary-age Ogallala Formation, with an

estimated thickness of approximately 300 feet, lies beneath the Quaternary deposits. The

Ogallala Formation consists of a heterogeneous mixture of clay, silt, poorly sorted sand, and

gravel, with occasional hard caliche (calcium-carbonate cemented) layers up to several feet thick

that may create perched aquifers, slow infiltration, and cause drilling and excavation problems.

Soil borings advanced at the site during the SI and RI were shallow, typically less than 20 feet

bgs. Sediments encountered in the soil borings generally consist of clay, silty sand, and sand.

The Wash Rack Area sits on a clayey to gravelly sand terrace alluvium located approximately 12

to 15 feet above the modern stream channel of Crow Creek. The lithology between Building 354

and Building 356 contains thin stringers of poorly-graded to well-graded sands and silty sands

interbedded with clays.

2.5.3 Hydrogeology

Where saturated with groundwater, the Quaternary alluvial and terrace deposits are hydraulically

connected to the underlying Ogallala Formation, and together these units form the High Plains

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Aquifer (USAF 2003). Shallow groundwater at FEW is unconfined and generally within 50 feet

of the surface. This shallow groundwater is hydraulically connected to the surface water regime

and is recharged by, or discharges to, Crow Creek and Diamond Creek at different times of the

year. Groundwater discharge may feed the riparian vegetation, which forms in the low areas

adjacent to the modern stream channels. Some of this groundwater discharge is, therefore, lost to

evapotranspiration from these riparian areas.

Based on groundwater monitoring performed for the Spill Site 8 RI in April 2006, the depth to

groundwater at the site ranged from approximately 8.0 feet below ground surface (bgs) in the

Building 354 area, to 11.7 feet bgs in the Wash Rack Area. Groundwater was detected as

shallow as 3.5 feet bgs in MW-051, approximately 100 feet downgradient of Spill Site 8.

Shallow groundwater flow is primarily from northwest to southeast toward Crow Creek (USAF

2005).

The hydraulic gradient across Spill Site 8, as measured between wells 354-13 and 356-14, was

approximately 0.005 foot/foot (ft/ft). Aquifer tests were not conducted for the SI or RI; however,

a hydraulic conductivity of 8 feet per day (ft/day) was calculated for MW-133 during a basewide

RI conducted in 1988. That well is completed in fine sands and gravels. The hydraulic

conductivity is likely lower in other portions of the site where the lithology contains a higher

content of fine-grain silts and clays. The measured hydraulic conductivity at Spill Site 8 is

generally consistent with those measured in other areas of the Base. Historical aquifer tests

conducted in Zone D, located south of Spill Site 8, resulted in highly variable hydraulic

conductivities ranging from less than 1 foot/day to over 100 feet/day, with a mean of

approximately 3 feet/day for the shallow groundwater zone (USAF 2003).

2.5.4 Surface Water Hydrology

Streamflow at FEW occurs as a result of runoff due to precipitation and snowmelt, and also due

to groundwater discharge during annual dry periods. Crow Creek, which borders Spill Site 8 to

the south and southeast, is the major perennial stream that drains southern areas of the

installation. The Crow Creek drainage area encompasses approximately 217 square miles west

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of FEW. Although Crow Creek is perennial, its tributaries may be intermittent or ephemeral and

may carry very little flow during some drought cycles.

According to the WWQRR, Crow Creek is classified as a 2AB stream that supports game fish

and drinking water. Reservoirs upstream from FEW provide storage that affects the flow

characteristics of Crow Creek. Although sections of Crow Creek west of the base may be

classified as ephemeral, records indicate that Crow Creek flow is perennial within the base itself.

The total drainage area of Crow Creek within the base is approximately 18 square miles as

measured at Station C7 (USAF 2001).

Diamond Creek, the second largest stream entering the base (USAF 1991) joins Crow Creek to

the southwest of Spill Site 8. According to the WWQRR, Diamond Creek is classified as a

Class 3B stream that supports aquatic organisms other than fish. The total drainage area of

Diamond Creek encompasses approximately 10.8 square miles with approximately 0.15 square

miles occurring on the base (USGS 2001). Upstream reservoirs on Diamond Creek probably

affect stream flow characteristics by reducing baseflow and dissipating storm flows.

2.5.5 Conceptual Site Model

Potential contaminant sources at Spill Site 8 include historical releases from the Wash Rack

Area, Building 354 Former Storage Area, and Building 356 Wood Hobby Shops Area.

In the Wash Rack Area, less than 1 cubic foot of sediment was identified and removed from the

sump during the Supplemental Site Inspection. The sediment contained elevated concentrations

of polycyclic aromatic hydrocarbons (PAHs). Contaminants may have been transported to soil

through discharge from the sump piping. Several PAHs were identified at levels exceeding the

2008 EPA Regional Screening values in soil in the vicinity of the drainpipe outfall near Crow

Creek. This suggests that contaminants may have been transported in wash water from the wash

rack sump via the drainpipe (USAF 2005). PAHs generally have a low solubility; therefore, it is

anticipated that the PAHs will not migrate far, either horizontally or vertically, from the outfall.

No PAHs were detected at concentrations above their established MCL values.

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In the Building 354 Storage Area, contaminants may have been transported to soil through

historical spills from drums or other containers. Elevated arsenic concentrations in soils within

the former storage area may be due to natural or anthropogenic sources. Possible anthropogenic

sources in the Building 354 Storage Area may have included the use/storage of arsenical

pesticides and herbicides, wood preservatives, and leaded gasoline. Natural sources of arsenic

include sulfide deposits. Groundwater monitoring results indicate that arsenic levels in

groundwater are generally greatest near the Building 354 Storage Area and decrease

downgradient (southeast). Arsenic in the storage area may have leached from soils to shallow

groundwater (less than 8 feet bgs), where it was transported southeast along the predominant

groundwater flow direction.

In the Building 356 Wood Hobby Shops Area, volatile organic compounds (VOCs) are present

in low concentrations in both surface and subsurface soil. These compounds may have been

released to the ground surface from small spills or incidental releases during historical

automobile servicing and degreasing activities in that area. The relatively low VOC

concentrations do not suggest large releases. The absence of elevated VOC concentrations in

groundwater suggests that VOCs are not migrating from soil to groundwater.

2.5.6 Soil Investigations

Soil samples were collected from the Wash Rack Area, Building 354 Former Storage Area, and

Building 356 Wood Hobby Shops Area during both the SI and RI. Approximately 70 surface

soil samples and 70 subsurface samples were collected to evaluate the nature and extent of soil

contamination at the site. Depending on the investigation, surface soil samples were collected

from between 0 to 2 inches and 0 to 12 inches below ground surface (bgs). Subsurface soil

samples were collected as vertical composites up to 9 feet bgs at the same locations as the

surface soil samples. Samples were analyzed for volatile organic compounds (VOCs),

semivolatile organic compounds (SVOCs), petroleum hydrocarbons, and metals.

In addition to the soil sampling, sediment from the Wash Rack sump was sampled to characterize

the material for removal and disposal.

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2.5.7 Groundwater Investigations

Groundwater samples were collected from approximately 26 locations during the SI and RI to

evaluate the nature and extent of groundwater contamination at the site. Samples were collected

from both temporary and permanent monitoring wells. A phased sampling approach was used

during the RI to optimize the sample locations and analytical parameters. Depending on the

investigation, samples were analyzed for parameters within the following categories: VOCs,

SVOCs, petroleum hydrocarbons, ethylene glycol, and metals.

Water level measurements were collected from each of the wells prior to sampling for use in

generating a shallow groundwater potentiometric surface map to evaluate groundwater flow

directions.

2.5.8 Surface Water Investigations

A basewide surface water risk assessment, conducted in 2002, established that Crow Creek does

not pose an unacceptable risk to human health (USAF 2002). Samples for the basewide surface

water risk assessment were collected from 20 locations on Crow Creek, including one location

(C3.4) downstream of Spill Site 8.

During the RI, surface water samples were collected from four locations on Crow Creek (C3,

C3.4, C3.42, and C3.5) upstream, adjacent to, and at the downstream edge of the site to evaluate

if overland runoff and groundwater discharge from the site are resulting in exceedances of Class

2AB surface water standards in Crow Creek.

2.5.9 Nature and Extent of Contamination

The extent of contamination in soil at Spill Site 8 was evaluated in the RI based on site

concentrations exceeding FEW background concentrations, EPA Region 9 residential soil PRGs,

and EPA Region 9 SSLs. The extent of contamination in groundwater was evaluated based on

site concentrations exceeding background and MCLs. Summaries of analytes exceeding PRGs,

SSLs, and MCLs are included in Appendix A.

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2.5.9.1 Soil

In the Building 354 Former Storage Area, arsenic was detected in surface and subsurface soil at

concentrations above regional background (7.5 mg/kg), the residential soil PRG (0.39 mg/kg),

and the SSL (0.29 mg/kg). Maximum arsenic concentrations of 68 mg/kg were detected in

surface soil (location 354-02), and 112 mg/kg in subsurface soil (location 354-12). The area

where arsenic concentrations exceed background (7.5 mg/kg) is approximately 3,000 square feet

(Figure 2-4). The vertical extent of SSL exceedances is estimated to be approximately 4 to 8 feet

bgs based on subsurface soil sampling results. The source of the elevated arsenic concentrations

in soil is uncertain. Possible activities that may have led to elevated arsenic levels include the

use/storage of arsenical pesticides and herbicides, wood preservatives, and leaded gasoline.

In the Wash Rack Area, PAHs were detected in soil at concentrations exceeding PRGs. The

most widespread and frequently detected PAH was benzo(a)pyrene, which was detected above

the PRG of 0.062 mg/kg for direct exposure and the SSL for migration to groundwater of 0.31

mg/kg. The maximum detected benzo(a)pyrene concentration in soil was 1.3 mg/kg. Based on

the SI and RI results, the area of exceedances is generally located in the floodplain of Crow

Creek and occupies an area of approximately 3,200 square feet (Figure 2-4). The vertical extent

of elevated PAH concentrations is relatively shallow, extending approximately 1 to 2 feet below

ground surface (bgs). In the Building 356 area, no analytes were detected at concentrations or

frequencies suggesting site-related contamination sources. Some VOCs were detected at low

concentrations in soil, possibly from historical vehicle maintenance activities, but those

detections were below PRGs and SSLs.

2.5.9.2 Groundwater

Based on the RI results, a groundwater plume containing elevated arsenic concentrations was

identified in shallow groundwater at Spill Site 8. The extent of arsenic in groundwater was

evaluated based on site concentrations exceeding FEW background levels and the arsenic MCL

(0.01 mg/L). The plume consists of two lobes, both originating in the vicinity of the Building

354 Former Storage Area (Figure 2-4). The larger of the plume lobes extends approximately 750

feet downgradient (southeast). The highest arsenic concentration detected in groundwater was

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0.045 mg/L. The vertical extent of the plume appears to be limited to the shallow groundwater

zone, between approximately 16 and 30 feet bgs.

Benzene was the only other constituent detected above an MCL (i.e., 5 micrograms per liter

[µg/L]) during the RI. It was detected at a maximum concentration of 9.9 µg/L in one well (354

14). The well was resampled one month later and the concentration was 5.3 µg/L (USAF

2007a). Benzene was not detected in temporary monitoring wells subsequently installed

upgradient and downgradient of 354-14, indicating that the presence of benzene was an isolated

occurrence with limited lateral extent (USAF 2007a). Based on these results, the benzene in

groundwater was not further investigated.

General water quality parameters (e.g., pH, temperature, specific conductance, turbidity,

dissolved oxygen, and oxidation-reduction potential) were measured in the field while collecting

samples from permanent monitoring wells. Shallow groundwater pH values were generally

neutral, ranging from approximately 6.5 to 7.0. Specific conductance values, a general indicator

of total dissolved solids content, were highly variable, ranging from approximately 380 to 1,680

microsiemens per centimeters (µS/cm).

2.5.9.3 Surface Water

No metals were detected above reporting limits in surface water samples collected from Crow

Creek during the RI. In addition, PAHs were not detected in surface water or sediment during

the basewide surface water risk assessment. These results indicate that potential overland flow

and/or groundwater discharge from Spill Site 8 to surface water are not resulting in exceedances

of the Class 2AB criteria in Crow Creek.

2.6 CURRENT AND POTENTIAL FUTURE LAND AND WATER USES

2.6.1 Land Uses

Current land use at Spill Site 8 includes commercial and recreational uses, as well as occasional

utility and grounds maintenance. According to the FEW General Plan (USAF 2006), planned

future land use at Spill Site 8 is generally similar to current use. The southern portion of the site

is within the 100-year floodplain of Crow Creek (Figure 2-3); therefore, future residential

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development in that area is unlikely. Current/future office workers are assumed to work in

buildings in the Spill Site 8 area, outside of the flood plain.

2.6.2 Groundwater and Surface Water Uses

The Wyoming Department of Environmental Quality (WDEQ) has not formally classified

shallow groundwater underlying FEW for a specific use, but groundwater is generally suitable

for domestic and agricultural uses. Groundwater is not currently used at FEW and it is not

anticipated that it will be used in the future. The City of Cheyenne, Board of Public Utilities

supplies and satisfies FEW’s water requirements and it is anticipated that it will continue to meet

the installation’s future water needs. Crow Creek defines the southern and southeastern

boundaries of Spill Site 8. Crow Creek is classified as a 2AB stream that supports game fish and

drinking water uses.

2.7 SUMMARY OF SITE RISKS

A baseline human health risk assessment and ecological risk assessment were conducted as part

of the Spill Site 8 RI (USAF 2007a). The risk assessments were based on human health and

ecological conceptual site models developed for the site (Figure 2-5 and Figure 2-6). A baseline

risk assessment is a scientific procedure that uses facts and assumptions to estimate the potential

for adverse effects on humans, plants, or animals from exposure to chemicals, assuming no

cleanup occurs. A risk assessment is used to evaluate if a site requires cleanup.

The response action selected in this ROD is necessary to protect the public health or welfare or

the environment from actual or threatened releases of hazardous substances into the

environment. The response action selected is based on the results of the Spill Site 8 risk

assessment (USAF 2007a) and guidelines presented in A Guide to Preparing Superfund

Proposed Plans, Records of Decision, and Other Remedy Selection Decision Documents (EPA

1999).

2.7.1 Summary of Human Health Risk Assessment

Based on current and potential future land-use scenarios, potential receptors identified for Spill

Site 8 (Figure 2-5) include:

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Hypothetical future on-site resident;

Current/future on-site office workers;

Current/future on-site utility workers;

Current/future on-site recreational visitors.

These scenarios were evaluated in the human health risk assessment. The hypothetical future on

site residential scenario was evaluated for risk management purposes only. Future residential

land use at Spill Site 8 is not anticipated according to the FEW General Plan (USAF 2006). The

hypothetical residential scenario was evaluated to assess if institutional controls are needed or, if

there is a change in future land use, whether a remedy may need to be reevaluated.

Cancer and noncancer risk estimates based on the human health risk assessment are summarized

in Table 2-1. For carcinogenic constituents, excess cancer risks greater than 10-4 require actions

to reduce the risk. Cancer risks of 10-4 to 10-6 are considered acceptable but may require risk

management. Cancer risks less than 10-6 allow for unrestricted use of the site and do not require

remedial actions. For non-carcinogenic constituents, a hazard index of less than 1 indicates no

adverse health effects are expected. A hazard index greater than 1 indicates a potential health

effect may exist. All risk at SS8 were within the EPA target risk range of 10-4 to 10-6 and below

the HI of 1 for noncancer risk.

In the Building 354 Former Storage area, it was concluded that direct contact with contaminated

surface soil could pose cancer risks greater than 1x10-6 to potential receptors but is within the

EPA target risk range. The potential receptors and their associated cancer risks are:

• Hypothetical future residents (1x10-4),

• Office workers (2x10-5),

• Utility workers (1x10-7), and

• Recreational visitors (6x10-6).

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Arsenic in surface soil is the cancer risk driver for the Building 354 area. Direct contact with

surface soil does not pose a threat of non-cancer effects.

In the Building 356 area, the potential receptors and their associated cancer risks are:





The combination of inhalation of VOCs in indoor air plus direct contact with surface soil is

responsible for the cumulative cancer risk of 2x10-6 for hypothetical future residents. The VOCs

in indoor air are based on low level VOC detections in surface soil, as discussed in Section

2.5.9.1. The cancer risks for exposure to surface soil and indoor air individually are less than or

equal to 10-6, and the non-cancer risk hazard indices are less than 1, for both media (Table 2-1).

Visitors to the Building 356 Wood Hobby Shop may be exposed to contaminated surface soil

and/or indoor air. Potential exposure routes for visitors are designated as “Current/Future

Community Service Visitors” on the human health conceptual site model (Figure 2-5). Visitor

exposure is expected to occur only occasionally. Therefore, visitors were only evaluated

qualitatively in the risk assessment. Because the potential risk for office workers, who are on

site for an estimated 250 days per year, is less than 10-6 (i.e., 3x10-7), it is concluded that the

potential risk for occasional visitors is less than 10-6 as well.

In the Wash Rack Area, the potential receptors and their associated cancer risks are:




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The noncancer hazard index values for the hypothetical future residents, office workers, utility

workers, and recreational users were below the noncancer hazard threshold of 1.

A basewide surface water risk assessment was conducted in 2002 (USAF 2002). Based on that

risk assessment, it was concluded that sediments, surface water, and fish in Crow Creek do not

pose an unacceptable threat to human health. A summary of the non-cancer and cancer risk

estimates is provided in Table 2-1.

2.7.2 Summary of Ecological Risk Assessment

Hazard quotients (HQs) for chemicals of ecological concern (COECs) are summarized in Table

2-2. HQs provide a line-of-evidence for interpreting potential ecological risks. They do not

provide definitive measure of risk, but do provide an indication of potential risk. In general, a

HQ less than 1.0 suggests no risk. A HQ greater than 1.0 suggests a potential risk, but the

uncertainties associated with the risk must be further considered and evaluated. Uncertainties,

such as uptake factors, exposure concentrations, toxicity data extrapolation, and bioavailability,

are qualitatively evaluated and factored into the risk estimate.

The ecological habitats at Spill Site 8 are primarily disturbed grasses with riparian habitat

bordering Crow Creek along the west and south edges of the site. Ecological receptors may

include invertebrates, plants, herbivores, invertivores, and carnivores (Figure 2-6). Potentially

complete exposure routes to these receptors include direct contact with contaminated soils,

ingestion of contaminated soils, or ingestion of prey or other organisms that have been in contact

with contaminants. Contaminants in surface soil (i.e., upper 2-inches of soil) may be available to

receptors through direct contact or ingestion. If contaminants are present in subsurface soil (i.e.,

up to 4 feet bgs), they may be available to burrowing organisms through direct contact and

ingestion.

Based on the ecological risk assessment for the Building 354 area, terrestrial receptors exposed

to soil at Building 354 do not appear to be at unacceptable risk from thallium or from the other

COECs (i.e., arsenic, lead, selenium, and silver). HQs greater than 1.0 were identified for all the

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COECs; however, most of the HQs were less than 3, with the exception of thallium (HQ>10).

When compared to background, the thallium concentrations detected in the Building 354 are not

likely site related. The risk from the other COECs is likely overestimated because a large

percentage of the assumed exposure area has no viable ecological habitat due to the presence of

buildings and gravel parking/driving areas. No ecological risk drivers are identified for Building

354, and no further action is indicated.

Based on the ecological risk assessment for the Building 356 area, given the small size of the

exposure area and the disturbed nature of the habitat, it is unlikely that risk from any of the

COECs (i.e., copper, lead, mercury, selenium, thallium, and zinc) is ecologically significant at a

population level at FEW. Because thallium concentrations in surface and subsurface soils at

Building 356 are not higher than background, thallium concentrations in surface and subsurface

soils at Building 356 likely are not site-related, and there is no site-related risk. The other

COECs at Building 356, except for copper, have hazard quotients (HQs) lower than 4.0 and the

combination of the uncertainties tends to overestimate risk; therefore, risk from these COECs

(i.e., lead, mercury, selenium, and zinc) is reduced.

Based on the ecological risk assessment for the Wash Rack Area, given the small size of the

exposure area (1.4 acres), it is unlikely that risk from lead and mercury and other COECs (i.e.,

selenium, silver, thallium, zinc, bis[2-ethylhexyl] phthalate, and di-n-butyl phthalate)is

ecologically significant at a population level at FEW. Because thallium concentrations in surface

and subsurface soils at the Wash Rack are not higher than background, the thallium

concentrations in soils at the Wash Rack likely are not site-related, and there is no site-related

risk. Other COECs for the Wash Rack, except for lead and mercury, have HQs lower than 4.0

and the combination of the uncertainties tends to overestimate risk; therefore, risk from these

COECs (i.e., selenium, silver, zinc, bis[2-ethylhexyl] phthalate, and di-n-butyl phthalate) is not

believed to be significant.

2.8 REMEDIAL ACTION OBJECTIVES

Remedial Action Objectives (RAOs) are site-specific cleanup objectives that have been

established based on the nature and extent of contamination, potential for human and

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environmental exposure, and applicable or relevant and appropriate requirements (ARARs).

Remedial Action Objectives provide the basis for selecting appropriate response actions and

remedial technologies, and for developing alternatives. The following RAOs have been

identified for Spill Site 8:

• Reduce the potential for arsenic to migrate from soil to groundwater in the

Building 354 Former Storage Area;

• Reduce the potential for exposure to arsenic-contaminated surface soils in the

Building 354 Former Storage Area; and

• Restore groundwater to beneficial use, where restoration means reducing arsenic

concentrations in groundwater to the MCL of 0.01 mg/L. (Not addressed in this

action)

Remedial action objectives for PAHs in soil are not proposed. The calculated risks for the PAH

contaminated soils for all pathways are well within the EPA target risk range of 10-4 to 10-6.

Three sample locations slightly exceeded the EPA SSL for migration to groundwater of

0.31mg/kg using the September 2008 tables. However, as indicated in the RI, PAHs are very

stable in the environment and are not expected to migrate laterally or vertically into the

grounwater.

2.9 DESCRIPTIONS OF ALTERNATIVES

The following remedial alternatives for soils at Spill Site 8 were developed and compared as

described in the FS (USAF 2007b). Groundwater remedies were also evaluated in the FS

however, as discussed earlier, alternatives for cleaning up the contaminated groundwater must be

reevaluated and are therefore not discussed here. Two of the originally evaluated alternatives, 3

and 4, were combination remedies for both soils and groundwater. Both included excavation and

off- site disposal of the soils. Therefore, alternative 4 will not be discussed further in this ROD

and alternative 3 will be reduced to the soils portion only. It should be noted that soil

containment was identified as a potential alternative for soils but was screened out due to the

difficulty in implementation and the high maintenance cost.

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Alternative 1 - No Action;

Alternative 2 – Land Use Controls (LUCs);

Alternative 3 – Excavation and offsite disposal

The primary components of these alternatives are presented below. A detailed analysis for each

alternative is summarized in Table 2-3.

2.9.1 Remedy Components

Alternative 1 - No Action

Regulations governing the Superfund program require that a “no action” alternative be evaluated

to establish a baseline for comparison. The primary components of Alternative 1 include:

No further action will be taken regarding contaminants in soil;

No LUCs, such as administrative or engineering controls, would be implemented; and

No long-term monitoring would be implemented.

Alternative 2 – Land Use Controls

Land use controls (LUCs), also known as Institutional Controls, are administrative, engineering,

and/or physical measures to protect human health and the environment by controlling access and

exposure to contaminants left in place at the site. LUCs are made part of the Base General Plan

(BGP) and are kept in place until unrestricted use and unlimited exposure are allowed.

For Alternative 2, LUCs would be implemented for the arsenic contaminated soil area in the

Building 354 Former Storage Area to reduce the potential for human exposure.

The general components of the LUCs alternative include:

Restrictions on access to or movement of arsenic-contaminated soil. For estimating

purposes, it is assumed that LUCs for the contaminated soil area would be in place for

approximately 30 years.

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The USAF is required to notify EPA and WDEQ prior to any transfer or sale of the

property, or if the land use in the affected area is modified.

The USAF is responsible for implementing, monitoring, maintaining, enforcing, and

reporting on LUCs. Because this alternative does not allow unrestricted use and unlimited

exposure, this alternative would be subject to review not less than every five years.

Specific objectives and implementation actions for LUCs at Spill Site 8 are described below.

A. Land Use Control Objectives:

A.1 Restrict access to or use of arsenic-contaminated soil in the Building 354 Former Storage Area, and restrict movement of the soil offsite or to other parts of FEW.

B. LUC Implementation Actions: To meet the LUC objectives, the following actions and

restrictions shall be implemented and maintained at Spill Site 8:

B.1 Employ USAF administrative procedures to track all development activity at FEW

that requires excavation so that no project violates use restrictions for Spill Site 8.

Existing procedures are included in Air Force Instruction (AFI) 32-1021, Planning and

Programming of Facility Projects, and work request procedures under AFI 32-1001,

Operations Management, or their equivalents as they may be amended. AFIs and

procedures require coordination with and prior approval by environmental personnel if a

proposed project is located on or near an Environmental Restoration Program site. Base

personnel would verify locations of potentially contaminated sites via the available

information (maps, documents, databases, GIS, etc.). The USAF will ensure that these or

equivalent instructions, processes, and/or requirements will be complied with for all

proposed construction or surface soil disturbing activities.

B.2 Update the BGP. The BGP implements “zoning-like” requirements at FEW. The

BGP is one of the first and primary documents to be reviewed when installation

personnel are proposing projects on the installation. AFI 32-7062 requires this

comprehensive planning document for the establishment and maintenance of

administrative and physical controls. The BGP resides in the office of the Base

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Community Planner. The USAF will develop a detailed map to be included in the BGP

showing the extent of soil and/or groundwater contamination associated with Spill Site 8.

This information as well as LUCs, boundaries, and expected durations will be added to

the existing LUC section of the BGP within 90 days of ROD signature. This section

includes a comprehensive listing and map of all LUCs on the installation. The USAF may

change the BGP and agrees to notify the EPA and the WDEQ at least 30 days prior to a

change that addresses or affects LUCs at Spill Site 8.

The following restrictions will be incorporated into the BGP and cross-referenced to this

map:

B.2.1 No disturbance of the arsenic-contaminated soil area, except for

environmental remediation or testing purposes, until concentrations of arsenic in

the soil are at such levels to allow for unrestricted use and exposure.

B.2.2 No movement of contaminated soil to other parts of FEW, and restrict

offsite movement of contaminated soil to treatment and/or disposal only.

B.3 The USAF shall not modify or terminate LUCs or modify land use within the

affected areas without approval by EPA and WDEQ. The USAF shall seek prior

concurrence before any anticipated action that may disrupt the effectiveness of the LUCs.

B.3.1 For proposed land use changes which do not include transfer of the

property, the USAF will notify the EPA and the WDEQ at least 45 days in

advance of any anticipated Base proposal inconsistent with the use restriction and

assumptions described herein, any anticipated action which may disrupt the

effectiveness of the LUCs, or any action which may alter or negate the need for

the LUCs.

B.3.2 The USAF will provide notice to the EPA and the WDEQ at least 6 months

prior to any transfer or sale of property at Spill Site 8 affected by the above

restrictions so that the EPA and the WDEQ can be involved in discussions to

document that appropriate provisions are included in the transfer terms or

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conveyance documents to maintain effective LUCs. If it is not possible for the

facility to notify the EPA and the WDEQ at least 6 months prior to any transfer or

sale, then the facility will notify the EPA and the WDEQ as soon as possible but

no later than 60 days prior to the transfer or sale of any property subject to LUCs.

In addition to the land transfer notice and discussion provisions above, the USAF

further agrees to provide the EPA and the WDEQ with similar notice, within the

same time frames, as to federal to federal transfer of property. The USAF shall

provide a copy of the executed deed to the EPA and the WDEQ. The USAF will

provide similar notification as to leases, in addition to transfers by deed.

B.4 The USAF will conduct periodic monitoring of the LUCs (at least annually). The

USAF shall provide notice to the EPA and the WDEQ within 10 business days if it

discovers any activity that is inconsistent with the LUC requirements, objectives or

controls, or any action that may interfere with the effectiveness of the LUCs. The USAF

shall include in such notice a list of corrective actions taken or planned to address such

deficiency or failure.

B.5 The USAF will fully comply with and be accountable for the LUCs identified herein

and will timely submit to the EPA and the WDEQ an annual monitoring report (AMR) on

the status of the LUCs, including the operation, maintenance, and monitoring of LUCs,

and how any LUC deficiency or inconsistent use has been addressed.

B.5.1 The LUC AMR shall be filed in the Administrative Record and Information

Repository.

B.5.2 The LUC AMR is not subject to approval and/or revision by the EPA and

the WDEQ and will be provided to each for informational purposes only.

B.6 The USAF is responsible for implementing (to the degree controls are not already in

place), monitoring, maintaining, enforcing, and reporting on the identified LUCs. If the

USAF determines that it cannot meet specific LUC requirements, it is understood that the

remedy may be reconsidered and that additional measures may be required for the

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protection of human health and the environment. The USAF shall obtain the concurrence

of the EPA and the WDEQ prior to modifying or terminating any LUCs, Objectives, or

LUC Implementation Actions.

Alternative 3 – Excavation and Offsite Disposal

Alternative 3, the selected remedy for the site, involves excavation of contaminated soil in a

portion of the Former Storage Area adjacent to Building 354. LUCs for soil would not be

required because the contaminated soil would be excavated and removed.

The primary components of Alternative 3 include:

Excavation of surface and subsurface soils with arsenic concentrations exceeding the

regional background value of 7.5 mg/kg. This encompasses an area of approximately

3000 square feet. The depth of soil excavation is estimated to be approximately 6 to 8

feet below ground surface, resulting in the removal of approximately 600 cubic yards of

soil. The actual lateral and vertical extent of excavation will be determined during the

remedial design phase. The excavated soil will be disposed of at an offsite disposal

facility permitted to receive the soil, and the excavation will be backfilled with soil that

has been verified to be clean. Samples for Toxicity Characteristic Leaching Procedure

(TCLP) analysis were not collected during previous investigations to determine if the soil

is considered hazardous or non-hazardous. However, based on the total arsenic

concentrations and the estimated volume of soil to be removed, it is unlikely that the

excavated soil would be classified as a hazardous waste. A TCLP analysis will be

performed on soil from the site during the remedial design phase or prior to soil disposal.

For estimating purposes it was assumed that 10% of the soil will be disposed as

hazardous and 90% will be non-hazardous.

Excavation of Spill Site 8 soils that exceed 7.5 mg/kg will also reduce the potential risk

for direct contact to surface soils (i.e., upper 2 inches of soil) that exceed acceptable

levels.

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2.9.2 Expected Outcome of Each Alternative

Alternatives 1 will not meet the objectives of reducing the potential for migration of arsenic in

soils to groundwater or reduce potential for direct exposure to contaminated soils. Although

Alternative 2 will not meet the objective of reducing potential migration to groundwater, it does

reduce the direct exposure to contaminated soils. Alternative 3 will reduce the potential for

future migration of arsenic from soil to groundwater and exposure to contaminated soils in the

Building 354 Former Storage Area.

2.10 COMPARATIVE ANALYSIS OF ALTERNATIVES

The remedial alternatives were evaluated using criteria given in EPA guidance (EPA 1988) and

in the NCP [40 CFR 300.430(f)(5)(i)] to determine which would be most protective of human

health and the environment, cost effective, and easiest to implement. The alternative method

selection and screening process is described in the Spill Site 8 FS (USAF 2007b).

To comply with the NCP, evaluation criteria must be applied to all remedial alternatives. These

criteria, as described in Guidance for Conducting RI/FSs Under CERCLA (EPA 1988) and the

NCP [40 CFR 300.430(f)(5)(i)] fall into three categories: threshold criteria, balancing criteria

and modifying criteria. The following table summarizes the nine criteria within these broad

categories:

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EVALUATION CRITERIA FOR SUPERFUND REMEDIAL ALTERNATIVES

Thre

shol

d C

riter

ia –

Crit

eria

mus

t be

met

befo

re a

n al

tern

ativ

eca

n be

con

side

red

as a

rem

edy

Overall Protection of Human Health and the Environment determines whether an alternative eliminates, reduces, or controls threats to public health and the environment through institutional controls, engineering controls, or treatment.

Compliance with ARARs evaluates whether the alternative meets federal and state environmental statutes, regulations, and other requirements that pertain to the site, or whether a waiver is justified.

Bal

anci

ng C

riter

ia –

Rel

ativ

e tra

deof

fs b

etw

een

diff

eren

t cr

iteria

are

eva

luat

ed

Long-Term Effectiveness and Permanence considers the ability of an alternative to maintain protection of human health and environment over time. Reduction of Toxicity, Mobility, or Volume of Contaminants Through Treatment evaluates an alternative’s use of treatment to reduce the harmful effects of principal contaminants, their ability to move in the environment, and the amount of contamination present. Short-term Effectiveness considers the length of time needed to implement an alternative and the risks the alternative poses to workers, residents, and the environment during implementation. Implementability considers the technical and administrative feasibility of implementing the alternative, including factors such as the relative availability of goods and services. Costs includes estimated capital and annual operations and maintenance costs, as well as present worth cost. Present worth cost is the total cost of an alternative over time in terms of today’s dollar value. Cost estimates are expected to be accurate within a range of +50 to –30 percent.

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State/Support Agency Acceptance considers whether the State agrees with or opposes the preferred alternative. WDEQ reviews and comments upon all important documents throughout the process.

Community Acceptance considers whether the local community agrees with or opposes the preferred alternative. Comments received on the Proposed Plan are an important indicator of community acceptance.

These criteria were applied to the evaluations of the four alternatives for Spill Site 8, as

described in the FS (USAF 2007b). The preferred alternative provides the best balance of

tradeoffs among the alternatives with respect to the evaluation criteria. The USAF expects the

preferred alternative will satisfy the statutory requirements in CERCLA Section 121(b) that the

selected alternatives:

Be protective of human health and the environment,

Comply with ARARs,

Be cost-effective,

However, the remedy does not satisfy the statutory preference for treatment as a principal

element of the remedy because it involves excavation and off-site disposal of untreated soil.

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Although soil will not be treated, excavation and off-site disposal is an appropriate remedy

because it permanently and significantly reduces the mobility and volume of contaminants at the

site. It is an efficient approach because it permanently removes contaminated soil in the source

area in a short timeframe. Because the impacted area is relatively small, it is also cost-effective.

The comparative analysis for selection of the preferred cleanup method for Spill Site 8 is

discussed in the following sections.

2.10.1 Overall Protection of Human Health and Environment

Alternative 1, No Action, would not be protective of human health and the environment under

current conditions. This alternative allows potential exposure to arsenic-contaminated soils and

further contamination of groundwater and thus is not protective.

Alternative 2, LUCs, would provide minimal protection by restricting access to contaminated

soil but is not protective because it does not reduce the potential for further contamination of

groundwater via migration from soils.

Alternative 3, Excavation and off-site disposal, would provide protection because it involves

removal of contaminated soil that serves as a potential source (i.e., contaminant loading) of

arsenic to groundwater that could present a risk to human health.

2.10.2 Compliance with ARARs

The chemical, location, and action-specific Applicable or Relevant and Appropriate

Requirements (ARARs) for the site are summarized in Tables 2-5 through 2-7. The principal

chemical-specific ARAR for the site is the arsenic MCL of 0.01 mg/L; in this case, the potential

for arsenic in soils to migrate to groundwater causing groundwater levels to exceed the MCL.

Alternative 1 and Alternative 2 would not comply with ARARs.

Alternative 3 would comply with potential action- and location-specific ARARs.

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2.10.3 Long-Term Effectiveness and Permanence

Alternative 1 does not provide long-term effectiveness because untreated arsenic contamination

remains in soil.

Alterative 2 provides long-term effectiveness by implementing controls to restrict access to and

use of contaminated soil. However, this alternative does not address the continued source of

arsenic from the soils to groundwater.

Alternative 3 would provide the greatest long-term effectiveness because this alternative

involves removal of contaminated soil that is a potential future source of arsenic to groundwater.

2.10.4 Reduction of Toxicity, Mobility, or Volume Through Treatment

None of the alternatives provide a reduction in arsenic toxicity, volume and mobility through

treatment. Alternative 3 would reduce the mobility of arsenic because the contaminated soil

would be removed, thereby reducing the potential for leaching of arsenic from soil to

groundwater. The volume of contaminated soil would not be reduced, but would be moved to an

off-site location (landfill).

2.10.5 Short-Term Effectiveness

Alternatives 1 and 2 would have the least short-term impacts to the community, workers, or the

environment because they do not involve construction of an active treatment system.

Alternative 3 would have the greatest impacts due to excavation of the contaminated soil.

Additional incremental risk to on-site workers and the community may occur during excavation

and transport of the excavated soil.

2.10.6 Implementability

Alternative 1 is most easily implemented because it does not involve any actions.

Alternative 2 is also easy to implement, but is slightly more difficult than Alternative 1 because

of the administrative effort required to maintain LUCs in the FEW General Plan.

Alternative 3 is moderately difficult to implement because of the excavation process.

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2.10.7 Cost

Alternative 1, No Action, would have no associated capital or O&M costs.

Alternative 2, LUCs, was the next lowest O&M costs; no capital costs would be incurred. O&M

costs would include: (1) periodic updates of the administrative controls in the FEW General

Plan, (2) providing updates to the Restoration Advisory Board, and (3) 5-year reviews.

Alternative 3, Excavation and off-site disposal has the highest capital cost. There are no O&M

cost associated with this alternative.

2.10.8 Regulatory Agency Acceptance

Alternative 3, Excavation and Off-site Disposal, is the preferred alternative for Spill Site 8 soils.

Both EPA and WDEQ support this alternative.

2.10.9 Community Acceptance

The public comment period on the Proposed Plan was held from April 21 through May 21, 2008,

and a public meeting was held on April 22, 2008. No written or verbal comments were received

during the public comment period. No verbal comments that would change the selected remedy

were received during the public meeting.

The Proposed Plan for Spill Site 8 originally included remediation of both soils and groundwater;

however, upon review of the preferred remedy for groundwater (MNA), it was determined that

the arsenic plume did not meet the EPA criteria of stability in order to consider MNA as a

potential remedy. Therefore, the remedy for groundwater is presently being reevaluated and is

not carried through in this ROD. A final ROD for Spill Site 8 will be completed that selects the

groundwater remedy.

2.11 PRINCIPAL THREAT WASTES

The NCP establishes an expectation that treatment will be used to address the principal threats

(i.e., source material that is highly toxic and/or highly mobile) posed by a site wherever

practicable. There are no principal threat wastes at Spill Site 8 as arsenic in soils is not

considered highly toxic or highly mobile.

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2.12 SELECTED REMEDY

2.12.1 Summary of Rationale for Selected Remedy

The selected remedy for addressing contaminated soil at Spill Site 8, OU14 is Alternative 3,

Excavation and Off-site Disposal. A conceptual layout of the selected remedy is shown on

Figure 2-7.

Soil excavation was selected because it is expected to achieve long-term risk reduction and will

reduce the potential for future migration of arsenic from soil to groundwater. Excavation of

contaminated soil is an appropriate part of the selected remedy because it permanently reduces

the volume and potential for further contaminant migration at the site. Other potential

remediation technologies, such as soil containment and LUCs, do not result in a permanent

reduction in contaminant volume at the site, and in the case of LUCs, do not result in a reduction

in contaminant migration. Under this alternative, contaminated soil in a portion of the Former

Storage Area adjacent to Building 354 will be excavated, disposed off site, and the excavation

backfilled with clean soil. Based on the range of total arsenic concentrations detected in soil in

the proposed excavation area (i.e., 60 to 112 mg/kg), and considering that the majority of the

excavated soil will contain less than approximately 100 mg/kg, it is unlikely that the excavated

soil will be classified as a hazardous waste. However, for estimating purposes, it was assumed

that 10% of the material will require disposal as hazardous waste.

2.12.2 Description of the Selected Remedy

Alternative 3 involves excavation of contaminated soil in a portion of the Former Storage Area

adjacent to Building 354. LUCs for soil are not required because the contaminated soil will be

excavated and removed.

The primary components of the remedy include:

Excavate soils in the Building 354 Former Storage Area with arsenic concentrations

exceeding the soil screening level of 7.5 milligrams per kilogram (mg/kg) to reduce the

potential for arsenic to migrate from soil to groundwater and to reduce potential risk of

direct exposure to surface soils. This encompasses an area of approximately 3000 square.

The depth of soil excavation is estimated to be approximately 4 to 8 feet below ground

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surface, resulting in the removal of approximately 670 to 890 cubic yards of soil. The

actual lateral and vertical extent of excavation will be determined during the remedial

design phase. The excavated soil will be disposed of at an offsite disposal facility

permitted to receive the soil, and the excavation will be backfilled with clean fill soil.

2.12.3 Expected Outcomes of Selected Remedy

Soil excavation was selected because it is expected to achieve long-term reductions in the

potential for contaminant migration to groundwater through removal of the contaminated soil.

2.13 STATUTORY DETERMINATION

Based on the information available at this time, the USAF, EPA, and WDEQ believe the

preferred alternative, Alternative 3: Excavation and off-site disposal, meets the threshold criteria

and provides the best balance of tradeoffs among the alternatives with respect to the balancing

and modifying criteria. Alternative 3 will be protective of human health and the environment,

will comply with ARARs, will reduce contaminant mobility, and will provide a cost-effective

long-term solution.

Under CERCLA §121 and the NCP, the lead agency must select remedies that are protective of

human health and the environment, comply with ARARs (unless a statutory waiver is justified),

are cost effective, and utilize permanent solutions and alternative treatment technologies or

resource recovery technologies to the maximum extent practicable. In addition, CERCLA

includes a preference for remedies that employ treatment that permanently and significantly

would reduce the volume, toxicity, or mobility of hazardous wastes as a principal element and a

bias against off-site disposal of untreated wastes. The following sections discuss how the

Selected Remedy meets these statutory requirements.

2.13.1 Protection of Human Health and the Environment

This alternative would provide protection to human health and the environment through removal

of contaminated soil. The baseline risk assessment results indicate that contaminated surface soil

presents an unacceptable risk to human health. Contaminated soil will be removed, thereby

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reducing the potential for exposure and the potential for future infiltration of arsenic to shallow

groundwater.

2.13.2 Compliance with ARARs

This alternative will comply with potential action- and location-specific ARARs. Soil exceeding

the residential PRG (0.39 mg/kg) will remain on the site; however, it was established during the

RI that the regional background arsenic concentration (7.5 mg/kg) naturally exceeds the PRG.

Chemical-Specific ARARs

Chemical-specific federal ARARs include the following:

• None

Chemical-specific Wyoming State ARARs include the following:

• Wyoming Environmental Quality Act/Wyoming Air Quality Standards and Regulations. Provide air emission standards for various chemicals and compounds, including fugitive emissions.

• Wyoming Hazardous Waste Rules and Regulations. Identify and list hazardous wastes.

Action-Specific ARARs

Action-specific federal ARARs include the following:

• Clean Water Act, 33 U.S. Code (USC) 1251 et seq. Provides criteria and chemical standards for discharge of pollutants into waters of the United States. Sets requirements for the control of stormwater runoff.

• Clean Air Act, 40 CFR Part 50. Establishes standards for ambient air quality to protect public health and welfare, which will be applicable only if air emissions are present.

The principal action-specific Wyoming State ARARs include the following:

• Wyoming Environmental Quality Act. Provides requirements for discharge into waters or emission of air contaminants, which will be applicable only if air emissions are present.

• Wyoming Water Quality Rules and Regulations. Provide regulations for discharges to waters of the state, including both surface and ground waters.

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• Wyoming Air Quality Standards and Regulations. Provide standards for control of emissions, including particulates and odors. Include requirements for construction, modification, and operation, which will be applicable only if air emissions are present.

• Wyoming Hazardous Waste Rules and Regulations. Provide standards for hazardous waste generators, transporters, and interim status standards for owners or operators of hazardous waste treatment, storage, and disposal facilities that also apply to short-term storage of hazardous waste.

• Wyoming Solid Waste Management Rules and Regulations. Prohibit dumping of nonhazardous solid waste (i.e., trash) on the site.

Location-Specific ARARs

Location-specific federal ARARs include the following:

• Clean Water Act – Dredge and Fill Regulations • Endangered Species Act • Fish and Wildlife Coordination Act • Migratory Bird Treaty Act • National Historic Preservation Act • Archaeological and Historical Data Preservation Act • Archaeological Resources Protection Act (1979)

In addition to the site-specific ARARs listed above, the USAF will comply with applicable laws

related to transportation, treatment, and disposal activities related to FEW waste materials.

2.13.3 Cost-Effectiveness

In the lead agency’s judgment, the selected remedy is cost-effective and represents a reasonable

value for the money to be spent. In making this determination, the following definition was

used: “A remedy shall be cost-effective if its costs are proportional to its overall effectiveness.”

(NCP §300.430(f)(1)(ii)(D)). This was accomplished by evaluating the “overall effectiveness”

of those alternatives that satisfied the threshold criteria (i.e., were both protective of human

health and the environment and ARAR-compliant). Overall effectiveness was evaluated by

assessing three of the five balancing criteria in combination (long-term effectiveness and

permanence; reduction in toxicity, mobility, and volume through treatment; and short-term

effectiveness). Overall effectiveness was then compared to costs to determine cost-effectiveness.

The relationship of the overall effectiveness of this remedial alternative was determined to be

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proportional to its costs and hence this alternative represents a reasonable value for the money to

be spent.

The capital cost of Alternative 3 is estimated to be $400,000. This includes excavation and off

site disposal of soil, backfilling with clean soil, and confirmation soil sampling. There are no

O&M costs associated with this alternative.

2.13.4 Utilization of Permanent Solutions and Alternative Treatment Technologies

The selected remedy represents the maximum extent to which permanent solutions and treatment

technologies can be utilized in a practicable manner. The selected remedy removes arsenic

contaminated soils from the Building 354 Former Storage Area. The selected remedy provides

the best balance of trade-offs in terms of the five balancing criteria and two modifying criteria.

2.13.5 Preference for Treatment as a Principal Element

The remedy does not satisfy the statutory preference for treatment as a principal element of the

remedy because it involves excavation and off-site disposal of untreated soil.

Although soil will not be treated, excavation and off-site disposal is an appropriate remedy

because it permanently and significantly reduces the mobility and volume of contaminants at the

site. It is an efficient approach because it permanently removes contaminated soil in the source

area in a short timeframe. Because the impacted area is relatively small, it is also cost-effective.

2.14 DOCUMENTATION OF SIGNIFICANT CHANGES FROM PREFERRED ALTERNATIVE OF PROPOSED PLAN

The Proposed Plan for the ROD was released for public comment on April 21, 2008. The

preferred alternative identified in the Proposed Plan was Alternative 3, Excavation and

Groundwater MNA. However, upon review of the preferred remedy for groundwater (MNA)

included in the draft ROD for Spill Site 8, it was determined that the arsenic plume did not meet

the EPA criteria of stability in order to consider MNA as a potential remedy. Therefore, the

remedy for groundwater at Spill Site 8 is presently being reevaluated and was not carried through

in this ROD. A Final ROD for Spill Site 8 will be completed that selects the groundwater

remedy. This change does not affect the originally selected remedy for the soils which was

determined to be protective of human health and the environment. No written or verbal

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comments were received from the public during the comment period that would change the

remedy selection process.

This ROD also includes an RAO that was added after the Proposed Plan was released to the

public. That RAO, to reduce the potential for arsenic to migrate from soil to groundwater in the

Building 354 area (Section 2.8), addresses subsurface soils with arsenic concentrations

exceeding the SSL. Removal of subsurface soils that may be impacting shallow groundwater

was included in the description of the selected remedy in the Proposed Plan, but an RAO

specifically addressing that action was not stated. Therefore, the addition of that RAO in this

ROD is intended to clarify the scope of the remedial action and does not change the selected

remedy.

The screening levels used during the completion of the remedial investigation and easibility

study were based on the 2004 EPA Region 9 Preliminary Remediation Goals as adopted by

WDEQ. In September 2008 EPA published a new set of screening tables which resulted in

lower screening values for arsenic and PAHs. Therefore, this ROD reflects the most recent

screening values resulting in different levels of cleanup as those indicated in the Proposed Plan.

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3.0 RESPONSIVENESS SUMMARY

3.1 STAKEHOLDER ISSUES AND LEAD AGENCY RESPONSES

In accordance with NCP §300.430(f)(3), a public comment period on the Proposed Plan for the

Spill Site 8 remedy was held from April 21, 2008 to May 21, 2008. At the time of the public

comment period, the USAF had identified the preferred alternative for the remedy at Spill Site 8,

with EPA and WDEQ concurrence. A public meeting was held on April 22, 2008 to present the

preferred alternative. No written or verbal comments were received during the public comment

period. Because no community comments or new information was provided that alters any of

the assumptions or conclusions used in developing the preferred alternative, the preferred

alternative is the selected remedy without any changes.

3.2 TECHNICAL AND LEGAL ISSUES

No technical and legal issues have been identified.

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4.0 REFERENCES

U.S. Air Force (USAF). 1991. Remedial Investigation for F.E. Warren Air Force Base,

Wyoming. Administrative Report for the Installation Restoration Program.

USAF. 2001. Community Relations Plan. F. E. Warren Air Force Base, Cheyenne, Wyoming.

November.

USAF. 2002. Surface Water Risk Assessment, F.E. Warren Air Force Base, Cheyenne,

Wyoming. Final.

USAF. 2003. Final Zone D Groundwater Remedial Investigation Report. F. E. Warren Air

Force Base, Cheyenne, Wyoming. October.

USAF. 2005. Final Phase II Supplemental Site Inspection Report Addendum for Study Area 3.

F. E. Warren Air Force Base, Wyoming. June.

USAF. 2006. F. E. Warren Air Force Base General Plan. July.

USAF. 2007a. Final Spill Site 8 Remedial Investigation Report, F. E. Warren Air Force Base,

Wyoming. February.

USAF. 2007b. Final Spill Site 8 Feasibility Study Report. F. E. Warren Air Force Base,

Wyoming. Final. October.

USAF. 2008a. Proposed Plan for Spill Site 8, F. E. Warren Air Force Base, Wyoming. March.

USAF. 2008b. U.S. Air Force, Environmental Restoration Program Information Management

System (ERPIMS) database.

U. S. Environmental Protection Agency. (USEPA). 1988. Guidance for Conducting Remedial

Investigations and Feasibility Studies Under CERCLA. Interim Final. October.

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USEPA. 1999. A Guide to Preparing Superfund Proposed Plans, Records of Decision, and

Other Remedy Selection Decision Documents. EPA 540-R-98-031, OSWER 9200.1-23P. July.

USEPA. 2002. Guidance on Surface Soil Cleanup at Superfund Sites: Applying Cleanup Levels.

Draft. Prepared by Industrial Economics, Inc and New Fields for Office of Emergency and

Remedial Response. January 31.

United States Geological Survey (USGS). 2001. Water Resources Data, Wyoming: Water-Data

Report WY-00-1.

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TABLES

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Table 2-1 Non-Cancer Hazard and Cancer Risk Estimates

Spill Site 8, F. E. Warren AFB

Receptor Exposure Medium Hazard Index Cancer Risk

Area CT RME CT RME

Building 354 Surface Soil 0.03 0.1 1E-06 2E-05

Indoor Air -- -- 8E-09 4E-10

Office Total 0.03 0.1 1E-06 2E-05(1)

Worker Building 356 Surface Soil 0.01 0.03 2E-08 1E-07

Indoor Air 0.2(2) 1(2) 1E-07(2) 6E-09(2)

Total 0.3 1 2E-08 3E-07

Wash Rack Surface Soil 0.01 0.03 1E-07 1E-06

Indoor Air -- -- -- --

Total 0.01 0.03 1E-07 1E-06

Utility Building 354 Combined Soil 0.3 1 5E-07 9E-07

Worker Building 356 Combined Soil 0.1 0.3 2E-09 6E-09

Wash Rack Combined Soil 0.1 0.3 9E-09 3E-08

Recreational Building 354 Surface Soil 0.003 0.03 1E-07 6E-06(1)

User Building 356 Surface Soil 0.0009 0.01 2E-09 7E-08


Building 354 Surface Soil 0.2 0.6 6E-06 1E-04

Indoor Air -- -- 6E-09 6E-08

Total 0.2 0.6 6E-06(1) 1E-04(1)

Child/Adult Building 356 Surface Soil 0.07 0.2 7E-08 1E-06

Resident Indoor Air 5(2) 7(2) 9E-08(2) 8E-07(2)

Total 5(3) 7(3) 2E-07 2E-06(4)


Indoor Air -- -- -- --

Total 0.07 0.2 5E-07 9E-06(5)

CT - Central tendency exposure condition RME - Reasonable maximum exposure condition (1) Cancer risk driver (CR > 1E-06) is arsenic (direct contact with soil) (2) Recalculated using a more realistic depth of contamination for TCE and trimethylbezene hot spots (3) Non-cancer risk drivers (HI > 1) are 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzene (4) There are no cancer risk drivers (CR > 1E-06). Benzo(a)pyrene in surface soil (CR =1E-06) and TCE in indoor air (CR = 8E-07) account for the RME cancer risk. (5) Cancer risk drivers (CR > 1E-06) are benzo(a)pyrene, and dibenzo(a,h)anthracene (direct contact with soil)

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Table 2-2

Hazard Quotients for Chemicals of Ecological Concern

Spill Site 8, F. E. Warren AFB, Wyoming

Building 354

Surface Soil Background

(mg/kg)

Subsurface Soil Background

(mg/kg)

Surface Soil Max.

(mg/kg)

Subsurface Soil Max.

(mg/kg) Avian Invertivore Mammalian Invertivore

Plants Soil Invertebrates (American Robin) (Deer Mouse) COECs Surface Soil Subsurface Soil Surface Soil Subsurface Soil Surface Soil Subsurface Soil Surface Soil Subsurface Soil

Arsenic 7.5 (3.2)(1) 7.5 (7.2)(1) 68 112 1.2 2.0 1.2 Lead 26.8 16.6 139 202 1.6 1.2 Selenium 0.27 1 1 1.4 1.5 1.6 Silver 0.45 0.75 0.078 1.4 2.2 Thallium 2.3 1.5 0.58 7.2 1.2 10 1.1 1.9 17

Building 356


(mg/kg)


(mg/kg)

Surface Soil Max.

(mg/kg)


(mg/kg) Avian Invertivore Mammalian Invertivore

Plants Soil Invertebrates (American Robin) (Deer Mouse) COECs Surface Soil Subsurface Soil Surface Soil Subsurface Soil Surface Soil Subsurface Soil Surface Soil Subsurface Soil

Copper 11.9 12.8 17.6 777 1.3 1.1 7.6 1.3 Lead 26.8 16.6 118 316 2.3 3.3 Mercury 0.056 0.061 0.09 0.42 1.5 Selenium 0.27 1 0.73 0.61 1.5 1.2 Thallium 2.3 1.5 7.4 4.2 7.5 7.5 13 12 Zinc 152 50.1 48.5 140 1.3

Wash Rack


(mg/kg)


(mg/kg)

Surface Soil Max.

(mg/kg)


(mg/kg) Avian Herbivore Avian Invertivore Mammalian Invertivore

Plants Soil Invertebrates (Horned Lark) (American Robin) (Deer Mouse) COECs Surface Soil Subsurface Soil Surface Soil Subsurface Soil Surface Soil Subsurface Soil Surface Soil Subsurface Soil Surface Soil Subsurface Soil

Lead 26.8 16.6 285 39 1.2 4.4 Mercury 0.056 0.061 1.7 0.11 2.9 5.4 Selenium 0.27 1 1.1 0.63 1.7 1.3 Silver 0.45 0.75 2 0.15 3.5 Thallium 2.3 1.5 4.9 7.2 7.8 11 1.2 13 19 Zinc 152 50.1 213 41 2.0 bis(2-ethylhexyl) phthalate 0(2) 0(2) 0.47 ND(0.03) 2.8 Di-n-butyl phthalate 0(2) 0(2) 0.19 ND(0.04) 1.7

LOAEL -- lowest observed adverse effect level LOEC -- lowest observed effect concentration

Notes: (1) The indicated arsenic values represent the regional arsenic background concentration of 7.5 mg/kg, and the historical F. E. Warren AFB background concentrations of 3.2 mg/kg (surface soil) and 7.2 mg/kg (subsurface soil). (2) The background concentration for organic compounds is assumed to be zero.

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Table 2-3

SUMMARY OF DETAILED ANALYSIS OF REMEDIAL ALTERNATIVES

Remedial Alternatives Overall Protection of Human Health and

Environment

Compliance with ARARs

Long-Term Effectivenessand Permanence

Reduction of Toxicity, Mobility, and Volume through Treatment Short-Term Effectiveness Implementability Cost

ALTERNATIVE 1 — Does not protect human Does not comply with all potential Does not provide long-term effectiveness Toxicity, mobility, and volume of No additional risk to site workers and Very easy to implement. No monitoring of No Action health and the

environment. Potential for migration to groundwater and risk to exposure to soils would remain. Arsenic concentrations in

chemical-, action-, and location-specific ARARs.

because untreated arsenic contamination remains in soil at concentrations exceeding migration to groundwater standards and risk-based concentrations.

arsenic are not reduced by active treatment.

the environment because there is no construction.

effectiveness is possible. $0

ALTERNATIVE 2 — Does not comply with all potential Provides minimal long-term effectiveness by Toxicity, mobility, and volume of Implementation would not result in Easy to implement technically and Capital Land Use Controls Provides minimal

protection to human health and the environment by restricting access to and use of contaminated soil. . Would not be effective in preventing migration of contaminated soil from the site through erosion by wind or surface water.

chemical-, action-, and location-specific ARARs. .

implementing Land Use Controls to limit or prevent use of groundwater and managing risk posed by the remaining arsenic. Controls contained in the General Plan are a long term and reliable management control to provide protection because they are required for all major installations and are enforceable by the Installation Commander. Administrative activities and periodic monitoring of access control measures are required.

arsenic are not reduced by active treatment.

additional risk to workers or the environment because there is no construction. However, contaminants in soil would still be susceptible to migration from the site due to natural processes (e.g., wind and runoff) and may pose additional risk to receptors. For estimating purposes, it is assumed that Land Use Controls will be in effect for 150 years, the estimated time frame, based on modeling, for MNA to reduce arsenic concentrations in groundwater to MCLs.

administratively. FEW administrative requirements include modifying the General Plan. Reliable management control that includes administrative monitoring and review on an annual basis. Minimal coordination activities with USEPA and WDEQ. No groundwater monitoring proposed to monitor effectiveness. Site access controls (i.e., fencing) would require occasional maintenance.

$5,000

Total O&M $445,000

Present Value $110,000

ALTERNATIVE 3 — Protects human health and Complies with potential action- and Soil removal would eliminate a source of Removal of contaminated soil results in Minimal additional risk to site workers Moderately easy to implement. Soil contamination Capital Excavation and off-site disposal the environment through

source removal of contaminated soil. No unacceptable short-term or cross media impacts are expected.

location-specific ARARs. contaminant exposure for human receptors and a potential source of contaminant leaching to groundwater.

a reduction of arsenic mobility. Toxicity and volume are not reduced because contaminated soil is disposed of at off-site landfill.

and the environment during excavation of contaminated soil. That additional risk could be mitigated with the proper personal protective equipment (PPE). Excavated soil will be transported off site; therefore additional incremental risk is incurred during transportation and off site disposal.

is shallow (less than 8 feet bgs) and excavation to that depth is relatively easy.

$149,000

Present Value $149,000

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Table 2-5

CHEMICAL-SPECIFIC APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS (ARARs)

Standard, Requirement, Criteria, or Limitation Citations Description

Applicable/Relevant and Appropriate Comments

STATE OF WYOMING WYOMING ENVIRONMENTAL QUALITY ACT

W.S. 35-11-101 to 35-11-1428

--

--

--

Article 2, W.S. 35-11-201 to 35-11-212

Addresses discharge or emission of air contaminants, including particulates

Yes/NA Compliance with state air quality numeric and other substantive requirements identified as ARARs satisfies all requirements of this provision.

Article 3, W.S. 35-11-301

Prohibits certain acts without a permit Yes/NA Compliance with state water quality substantive requirements identified as ARARs satisfies all requirements of this provision (permits are only required for off-site actions; all FS alternatives are on-site actions).

WYOMING HAZARDOUS WASTE RULES AND REGULATIONS

Chapter 1 Overview and Definitions Yes/NA If hazardous waste is generated, this chapter would apply. Applicable as necessary to implement other substantive requirements.

Chapter 2 Identification and Listing of Hazardous Waste

Yes/NA If hazardous waste is generated, this chapter would apply. Applicable in identifying listed or characteristic hazardous waste subject to other substantive requirements.

Notes: ARARs = Applicable or relevant and appropriate requirements FS = Feasibility Study MCL = Maximum Contaminant Level MCLG = Maximum Contaminant Level Goal mg/L = milligrams per liter NA = Not applicable W.S. = Wyoming Statute

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Sheet 1 of 2

Table 2-6

LOCATION-SPECIFIC APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS (ARARs)

Standard, Requirement, Criteria, or

Limitation

Citation

Description

Applicable/ Relevant and Appropriate

Comments

FEDERAL ENDANGERED SPECIES ACT 16 USC 1531-

1543; 50 CFR Parts 17, 402

Requires that federal agencies ensure that any action authorized, funded, or carried out by the agency is not likely to jeopardize the continued existence of any threatened or endangered species or destroy or adversely modify critical habitat.

Yes/NA Several listed or proposed endangered and/or threatened species have been observed. The Colorado butterfly plant is proposed for listing as a threatened species and has been observed in riparian habitat along Crow and Diamond Creeks. In addition, the Preble’s meadow jumping mouse, a threatened species, has been captured along Crow Creek. The potential effects on endangered/threatened species or their habitat will depend on the alternative selected and locations considered for the preferred alternative. The USAF will consult with the USFWS to ensure that the remedial action meets the substantive requirements of the Endangered Species Act with respect to any identified listed or proposed endangered or threatened species.

FISH AND WILDLIFE COORDINATION ACT

16 USC 661 et seq.

Requires development of measures to prevent, mitigate, or compensate for project-related losses to fish and wildlife if an action will result in the control or structural modification of a natural stream or body of water.

No/No The USAF will consult with the USFWS and Wyoming Fish and Game Department to develop measures to prevent, mitigate, or compensate for project-related losses to fish and wildlife.

MIGRATORY BIRD TREATY ACT 16 USC 703-712 Provides protection for migratory bird species (includes geese, ducks, raptors, many passerines). Prohibits killing or taking of bird or any part, nest, or egg of any such bird.

Yes/NA Applicable to any alternative that could impact migratory birds present in area. Will be addressed during coordination with USFWS.

NATIONAL HISTORIC PRESERVATION ACT

16 USC 470 et seq.; 36 CFR Part 63, Part 65, Part 800

Requires federal agencies to take into account the effect any federal undertaking may have on any historic properties included in or eligible for the National Register of Historic Places.

Yes/NA The Base Historic Preservation Officer will determine whether any remedial action alternatives (e.g., drilling borings, installing trenches, constructing wetlands) will affect historic properties and coordinate that determination with the State Historic Preservation Officer.

ARCHEOLOGICAL AND HISTORICAL DATA PRESERVATION ACT

14 USC 469 – 469 c-1.

Establishes procedures to provide for preservation of historical and archeological data that might be destroyed through alteration of terrain as a result of a federal construction project or a federally licensed activity program.

Yes/NA The Base Historic Preservation Officer will determine whether any remedial action alternatives (e.g., drilling borings, installing trenches, constructing wetlands) will potentially destroy historical and/or archaeological data and if so, USAF will take measures to ensure it is evaluated and preserved.

ARCHEOLOGICAL RESOURCES PROTECTION ACT (1979)

16 USC 470 aa – 470 ll

Provides requirements for any excavation or removal of archeological resources from public or Indian lands.

Yes/NA Although permits are not required for this on-site remedial action, the Base Historic Preservation Officer will determine whether any remedial action alternatives will necessitate excavation or removal of archaeological resources and, if so, USAF will comply with substantive requirements for excavation, removal, and preservation.

3727.pdf3728.pdf

Sheet 2 of 2

Table 2-6 LOCATION-SPECIFIC APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS (ARARs)

Standard, Requirement, Criteria, or

Limitation

Citation

Description

Applicable/ Relevant and Appropriate

Comments

EXECUTIVE ORDER ON FLOODPLAIN MANAGEMENT

Exec. Order No. 11988

Requires federal agencies to evaluate the potential effects of actions they may take in a floodplain to avoid, to the extent possible, the adverse impacts associated with direct and indirect development of a floodplain.

No/No (TBC)

Based on a memorandum from the Deputy Assistant Secretary of the Air Force (Environment, Safety, and Occupancy Health), dated 24 August 1999 entitled “Findings of No Practicable Alternatives (FONPAs) and CERCLA Installation Restoration Program (IRP) Activities”, this Executive Order is to be viewed as “to be considered”, not an ARAR, for Air Force IRP actions under CERCLA. The USAF will comply with the substantive requirements of this Executive Order and document compliance with the substantive requirements in the administrative record. This will include documentation in the Record of Decision that there are no practicable alternatives and that all practicable measures will be taken to minimize harm, if construction in floodplains is included as part of the selected remedial action alternative.

EXECUTIVE ORDER ON PROTECTION OF WETLANDS

Exec. Order No. 11990

Requires federal agencies to avoid, to the extent possible, the adverse impacts associated with the destruction or loss of wetlands and to avoid support of new construction in wetlands if a practicable alternative exists.

No/No (TBC)

Based on a memorandum from the Deputy Assistant Secretary of the Air Force (Environment, Safety, and Occupational Health) dated 24 August 1999 entitled “Findings of No Practicable Alternatives (FONPAs) and CERCLA Installation Restoration Program (IRP) Activities”, this Executive Order is to be viewed as “to be considered”, not an ARAR, for Air Force IRP actions under CERCLA. The Air Force will comply with the substantive requirements of this Executive Order and document compliance with the substantive requirements in the administrative record. This will include documentation in the Record of Decision that there are no practicable alternatives and that all practicable measures will be taken to minimize harm, if construction in wetlands is included as part of the selected remedial action alternative.

Notes: ARARs = Applicable or relevant and appropriate requirements CERCLA = Comprehensive Environmental Restoration, Compensation and Liability Act CFR = Code of Federal Regulations USEPA = United States Environmental Protection Agency NA = Not applicable TBC = To be considered USAF = U.S. Air Force USC = U.S. Code USFWS = U.S. Fish and Wildlife Service

3727.pdf3728.pdf

Sheet 1 of 1

Table 2-7 ACTION-SPECIFIC APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS (ARARs)

Requirement, Criteria,

or Limitation

Citations

Description Applicable/Relevant

and Appropriate

Comments

FEDERAL CLEAN WATER ACT 33 USC Sec. 1251-1376 -- -- -- NPDES Storm Water Regulations 40 CFR 122 Establishes requirements for discharge of

storm water. Yes/NA Storm water runoff may occur from the site, making substantive requirements

applicable. Criteria and Standards for the National Pollutant Discharge Elimination System

40 CFR 125 Provides discharge criteria, chemical standards, and permit forms for existing industrial operations.

Yes/NA Although permits are not required, substantive provisions are applicable to remedial actions that cause discharge to waters of the U.S.

CLEAN AIR ACT 42 USC Sec. 7401-7642 -- -- -- National Primary and Secondary Ambient Air Quality Standards

40 CFR Part 50 Establishes standards for ambient air quality to protect public health and welfare (including standards for particulate matter and lead)

Yes/NA Emissions from remedial action will be subject to NAAQS unless state standards are more stringent.

STATE OF WYOMING WYOMING ENVIRONMENTAL QUALITY ACT Article 2, W.S. 35-11-

201 to 35-11-212 Discharge or emission of air contaminants Yes/NA Compliance with state air quality numeric and other substantive requirements

identified as ARARs satisfies all requirements of this provision. Article 3, W.S. 35-11-

301 Prohibits certain acts without a permit. Yes/NA Compliance with state water quality substantive requirements (permits are not

required) identified as ARARs satisfies all requirements of this provision. WYOMING AIR QUALITY STANDARDS AND REGULATIONS

Chapter 1, Section 5 Abnormal conditions and equipment malfunctions

Yes/NA Primarily applicable during construction and any maintenance of remedial action alternative.

Chapter 2, Section 11 (a), (c)

Odors Yes/NA Applicable if any alternative creates odors. No monitoring is required.

Chapter 3, Section 2 Control of particulate emissions, including fugitive dust

Yes/NA Primarily applicable during construction and maintenance of remedial action alternative.

Chapter 6, Section 2 (c) (v) and (j)

Requirements for construction, modification, and operations

Yes/NA Although permits are not required, substantive requirements apply.

WYOMING HAZARDOUS WASTE RULES AND REGULATIONS

Chapter 1 Overview and Definitions Yes/NA If hazardous waste is generated, this chapter would apply. Applicable as necessary to implement other substantive requirements.

Chapter 8 Standards for Generators of Hazardous Waste Yes/NA If hazardous waste is generated, this chapter would apply. Chapter 9 Standards for Transporters of Hazardous

Waste Yes/NA If hazardous waste is transported, this chapter would apply.

Chapter 11, Sections 4(g), 5, 6, 9(b) and (e), 10, 11 (except (h)(iii) and (k), 24, 31

Interim Status Standards for Owners and Operators of Hazardous Waste Treatment, Storage, and Disposal Facilities

Yes/NA If hazardous waste is generated, these provisions would apply. Chapter 8, Section 3(e) refers to these requirements for a generator that accumulates hazardous waste on site for 90 days or less.

Chapter 13 Land Disposal Restrictions Yes/NA If hazardous waste is generated, these provisions would apply. WYOMING SOLID WASTE MANAGEMENT RULES AND REGULATIONS

Chapter 1, Section 1(h) General Provisions – Prohibited Acts. Yes/NA Applicable to all alternatives. Prohibits open dumping of garbage or trash generated during construction or maintenance activities.

Notes: ARARs = Applicable or relevant and appropriate requirements Sec. = Section CFR = Code of Federal Regulations USAF = U.S. Air Force USEPA = U.S. Environmental Protection Agency USC = U.S. Code NA = Not applicable WDEQ = Wyoming Department of Environmental Quality NAAQC = National Ambient Air Quality Standards NPDES = National Pollutant Discharge Elimination System

W.S. = Wyoming Statute

3727.pdf3728.pdf

FIGURES

3727.pdf3728.pdf

PLUME C

PLUME BPLUME A

ZONE D

PLUME E

ZONE C

ZONE E

LF-5a

WCAZONE B

ZONE A

SS7

SPILL SITE 8

FiringRange

LF6

LF4bLF2a

LF4a

LF7a

LF3

LF7b

LF2b

LF2c

LF5b

PLUME C

PLUME BPLUME A

ZONE D

PLUME E

ZONE C

ZONE E

LF-5a

WCAZONE B

ZONE A

SS7

SPILL SITE 8

FiringRange

LF6

LF4bLF2a

LF4a

LF7a

LF3

LF7b

LF2b

LF2c

LF5b

NOTES:1. Horizontal Datum: Wyoming State Plane, East Zone, NAD83, Feet2. Vertical Datum: NAVD88, Feet

.

Uta

hMontana

Idah

o

Colorado

W y o m i n g

Neb

rask

aS

outh

Dak

ota

F. E. Warren AFB

Cheyenne

!̂.

§̈¦90

§̈¦80

§̈¦25

2_1_SS8_Site.mxd LEDJuly 2008LAST REVISION DATE DR BYFILE NAME

Installation Location MapF.E Warren Air Force Base

SPILL SITE 8 RECORD OF DECISIONF. E. WARREN AIR FORCE BASE, WYOMING

Figure 2-1.

EXPLANATIONBuilding

IRP SiteExcavated (fully/partially)

Waste Co-location Area (WCA)

Paved RoadUnpaved Road

Existing Permeable Reactive Barrier

Investigation/Remediation ZoneBoundary

Interpreted TCE Concentrationsof 2001 - 2004 (µg/L)

5

1015

25

50100

400

1000

0 1,000 2,000 3,000 4,000500Feet

Proj

ects

08\S

S8_

RO

D\2

_1_S

S8_

Site

.mxd

1 inch equals 2,000 feet

Installation RestorationProgramTrichloroetheneMicrograms per literSpill Site 7Landfill

=

====

IRP

TCEµg/LSS7LF

3727.pdf3728.pdf

SS7

SPILL SITE 8

MISSILE DRIVE

S. C

REE

K D

RIV

E

S. FRONTIER DRIVE

CROW CREEK

DIAMOND CREEK

Building 354

Building 356

Wash Rack

Former StorageArea (Approximate)

FormerBuilding357

LF7b

SS7

SPILL SITE 8

MISSILE DRIVE

S. C

REE

K D

RIV

E

S. FRONTIER DRIVE

CROW CREEK

DIAMOND CREEK

Building 354

Building 356

Wash Rack


FormerBuilding357

LF7b


.

2_2_SS8_site_map.mxd LEDJuly 2008LAST REVISION DATE DR BYFILE NAME

Spill Site 8 - Site Map


Figure 2-2.

EXPLANATIONIRP Zone

IRP Site

Excavated (fully/partially)

Paved Road

Unpaved Road

Existing Permeable Reactive Barrier0 200 400 600 800100

Feet

Pro

ject

s08\

SS

8_R

OD

\2_2

_SS

8_si

te_m

ap.m

xd

1 inch equals 400 feet

3727.pdf3728.pdf

SS7

SPILL SITE 8

MISSILE DRIVE

S. C

RE

EK D

RIV

E

S. FRONTIER DRIVE

CROW CREEK

DIAMOND CREEK

Building 354

Building 356

Wash Rack


LF7b

SS7

SPILL SITE 8

MISSILE DRIVE

S. C

RE

EK D

RIV

E

S. FRONTIER DRIVE

CROW CREEK

DIAMOND CREEK

Building 354

Building 356

Wash Rack


LF7b


.2_3_FloodPlain.mxd LEDJuly 2008

LAST REVISION DATE DR BYFILE NAME

Approximate100-Year Floodplainfor Crow Creekat Spill Site 8


Figure 2-3.

EXPLANATIONBuilding

IRP Site

Excavated (fully/partially)

Waste Co-location Area (WCA)

Paved Road

Unpaved Road

Existing Permeable Reactive Barrier

100-Year Floodplain

0 200 400 600 800100Feet

Pro

ject

s08\

SS

8_R

OD

\2_3

_Flo

odPl

ain.

mxd

1 inch equals 400 feet

3727.pdf3728.pdf

!C

!C

!C

!C

!C!C

!C

!C

!C

SPILL SITE 8

S. C

REE

K D

RIV

E

S. F

RONT

IER

ROAD

Wash Rack

BUIL

DING

354

BUIL

DING

356

FORM

ERBU

ILD

ING

357

Approximate

Groundwater

Flow Direction

Approximate Extent ofArsenic Exceeding MCL

ApproximateArea Exceeding

Backgroundfor Arsenic

ApproximateArea ExceedingBenzo(a)pyreneSoil ScreeningLevel (SSL)

MW-051

356-14

354-14

354-12

354-13

354-11

354-13M

0.01

0.01

0.01

Proposed Well

Proposed Well!C

!C

!C

!C

!C!C

!C

!C

!C

SPILL SITE 8

S. C

REE

K D

RIV

E

S. F

RONT

IER

ROAD

Wash Rack

BUIL

DING

354

BUIL

DING

356

FORM

ERBU

ILD

ING

357

Approximate

Groundwater

Flow Direction

Approximate Extent ofArsenic Exceeding MCL

ApproximateArea Exceeding

Backgroundfor Arsenic

ApproximateArea ExceedingBenzo(a)pyreneSoil ScreeningLevel (SSL)

MW-051

356-14

354-14

354-12

354-13

354-11

354-13M

0.01

0.01

0.01

Proposed Well

Proposed Well

0 150 30075Feet

Proj

ects

09/S

S8_

Soi

l_R

OD

/2_4

_SS8

_Ext

_soi

l_gw

Rev

01.m

xd

1 inch = 150 feet

NOTES:1. Horizontal Datum: Wyoming State Plane, East Zone, NAD83, Feet2. Vertical Datum: NAVD88, Feet 2_4_SS8_Ext_soil_gwRev01.mxd LEDApril 2009


Approximate Extent ofContamination inSoil and Groundwater


Figure 2-4..EXPLANATION!C Existing Monitoring Well

SS8 Former Storage Area

IRP SiteExcavated (fully/partially)

Building


Approximate extent of arsenic exceeding MCL (0.01 mg/L)

Inferred extent of arsenic exceeding MCL (0.01 mg/L)

Milligrams per literLandfill

==

mg/LLF

Approximate Groundwater Flow Direction

3727.pdf3728.pdf

Figure 2-5Human Health Conceptual Site Model

Spill Site 8 F.E. Warren Air Force Base, Wyoming

Human Receptors

UpgradientSources

PotentialSite-Related

Sources MediaTransport

Mechanism MediaTransport


Mechanism Exposure Media Exposure Route Cur

rent

/Fut

ure

Offi

ce W

orke

rsC

urre

nt/F

utur

e C

omm

unity

Se

rvic

e Vi

sito

rs(1

)C

urre

nt/F

utur

e U

tility

Wor

kers

Cur

rent

/Fut

ure

Rec

reat

iona

l Vi

sito

rs

Hyp

othe

tical

Fu

ture

Res

iden

ts

Volatilization/Dust Generation Air Air Inhalation C C C C C

Ingestion C C C C CDirect Contact C C C C C

Ingestion I I C I IDirect Contact I I C I I

Inhalation I I C I I

Volatilization Vapor Intrusion Indoor Air Inhalation C C I I C

Runoff Leaching

Ingestion I I N I IDirect Contact I I N I I

Inhalation I I N I IWash Rack

Drainage Pipeline(3)

Discharge

Ingestion I I I N(2) N(2)

Direct Contact I I I N(2) N(2)

Ingestion I I I N(2) N(2)

Direct Contact I I I N(2) N(2)

C - Exposure pathway potentially complete, quantifiableN- Exposure pathway potentially complete, but negligible, not quantified

I - Exposure pathway incomplete

(2)Crow Creek found to not pose an unacceptable risk in the Final Surface Water Risk Assessment (USAF 2002). Not evaluated further in this risk assessment.

(4)FEW has a catch and release policy for fish in Crow Creek.(5) Groundwater exposure pathways are considered to be incomplete because there is not current or future planned human use of groundwater at SS08.

I(4) N(2)Ingestion I I I

Crow Creek(2) Partitioning

Groundwater Groundwater

Crow Creek

Groundwater

Subsurface Soil in a Trench or

Foundation

Creek Water

Creek Sediment

(3)The Wash Rack drainage pipeline may have been blocked, restricting flow to Crow Creek (Draft Phase II Supplemental Site Inspection Report Addendum for Study Area 3. F.E. Warren Air Force Base, Wyoming [USAF 2005]); exposure pathway shown as a broken line.

(1)The more highly exposed office workers in the community service building will be evaluated in the risk assessment. Therefore, risk to community service visitors will be evaluated qualitatively in the risk assessment.

Percolation Subsurface Soil Excavation

Creek Fish

Historical Releases and Leaks from Wash Rack,

Building 354, and Building 356

SurfaceSoilSurface Soil Surface Soil

W:\Projects\22238003_FEW_SS8\Sub_00\6.0_Proj_Deliv\ROD\Draft\Fig2-5 HHRA CSM Page 1 of 13727.pdf3728.pdf

Figure 2-6Ecological Conceptual Site Model

Spill Site 8 F.E. Warren AFB, Wyoming

T e r r e s t r i a lE c o l o g i c a l R e c e p t o r s

A q u a t i c

PotentialUpgradient

Sources

PotentialSite-Related

Sources MediaTransport



Mechanism Exposure Media Exposure Route Plan

ts Soil

Inve

rteb

rate

s

Herb

ivor

es

Inve

rtiti

vore

s

Carn

ivor

es

Inve

rteb

rate

s

Fish

Volatilization/Dust Generation Air Air Inhalation NQ NQ NQ NQ NQ NA NA

Ingestion NA NQ C6 C6 C6 I IDirect Contact C6 C6 NQ NQ NQ I I

Uptake Food/Prey Organisms

Food/Prey Organisms Ingestion NA NQ C3 C4 C5 I I

Ingestion NA NQ C C C I IDirect Contact C C NQ NQ NQ I I

Leaching

RunoffIngestion NQ NQ I I I I I

Direct Contact NQ NQ I I I I IWash Rack

Drainage Pipeline1

Discharge1

Ingestion NE NE NE NE NE NE NEDirect Contact NE NE NE NE NE NE NE

Ingestion NE NE NE NE NE NE NEDirect Contact NE NE NE NE NE NE NE

Notes: C - Exposure pathway potentially Complete, quantifiable

I - Exposure pathway Incomplete, not quantified

(3) Ingestion of plants NQ - Exposure potentially complete, but Not Quantifiable

(4) Ingestion of insects and soil invertebrates NA - Exposure pathway Not Applicable, not logical, not quantified

(5) Ingestion of small mammals(6) The proposed surface soil excavation will result in removal of arsenic concentrations exceeding 60 mg/kg.

Crow Creek2 Partitioning

Historic Releases and Leaks from Building 354, Building 356, and Wash

Rack

Leaching, Infiltration

SurfaceSoilSurface Soil Surface Soil

Subsurface Soil

Creek Water

Creek Sediment

NE - Exposure potentially complete but Not Evaluated based on results of the Final Surface Water Risk Assessment (USAF 2002)

Crow Creek2

(1) The Wash Rack drainage pipeline may have been blocked, restricting flow to Crow Creek (USAF 2005); exposure pathway shown as a broken line.(2) Crow Creek found to not pose an unacceptable risk in the Final Surface Water Risk Assessment (USAF 2002); exposure pathway shown as a dashed line.

Subsurface Soil

Groundwater Groundwater Groundwater

W:\Projects\22238003_FEW_SS8\Sub_00\6.0_Proj_Deliv\ROD\Draft\Fig2-6_ERA CSM Sheet 1 of 13727.pdf3728.pdf

#*

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REEK

DRI

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Former Storage Area (Approximate)

354T1-041.11.3

354T1-113.24.0

354T1-071.73.8

354T1-101.22.3

354T1-053.71.9

354T1-123.53.2

354T1-086.72.9

354-145.61.5 (2.5 - 4')

354T1-032.21.2

354-132.32.2 (2.5 - 4')

354T1-012.61.3

354T1-021.62.3

354-085.42.1 (2.5 - 4')3.1 (5.5 - 7')2.6 (8 - 9')

354-102.63.1 (2.5 - 4')5.8 (5.5 - 7')1.9 (8 - 9')

354-045.14.7 (2 - 4')

354-073.6 M (0 - 1')8.0 M (2.5 - 4')7.9 (5 - 9')

354-0910 M (0 - 1')6.4 (2.5 - 4')

354-0317 (0 - 1')1.2 (4 - 9')

354-067.08.1 (2.5 - 4')

354-0268 (0 - 1')91 (2 - 4')

354-1260 M (0 - 1')112 (2.5 - 4')

354-014.9 (0 - 1')16 (2 - 4')

354-057.5

6.2 (2.5 - 4')

354T1-092.13.6

354T1-062.66.4

354-112.4

2.9 (2.5 - 4')

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Former Storage Area (Approximate)

354T1-041.11.3

354T1-113.24.0

354T1-071.73.8

354T1-101.22.3

354T1-053.71.9

354T1-123.53.2

354T1-086.72.9

354-145.61.5 (2.5 - 4')

354T1-032.21.2

354-132.32.2 (2.5 - 4')

354T1-012.61.3

354T1-021.62.3

354-085.42.1 (2.5 - 4')3.1 (5.5 - 7')2.6 (8 - 9')

354-102.63.1 (2.5 - 4')5.8 (5.5 - 7')1.9 (8 - 9')

354-045.14.7 (2 - 4')

354-073.6 M (0 - 1')8.0 M (2.5 - 4')7.9 (5 - 9')

354-0910 M (0 - 1')6.4 (2.5 - 4')

354-0317 (0 - 1')1.2 (4 - 9')

354-067.08.1 (2.5 - 4')

354-0268 (0 - 1')91 (2 - 4')

354-1260 M (0 - 1')112 (2.5 - 4')

354-014.9 (0 - 1')16 (2 - 4')

354-057.5

6.2 (2.5 - 4')

354T1-092.13.6

354T1-062.66.4

354-112.4

2.9 (2.5 - 4')

C3


.SS8_B354_Remedy_Rev01.mxd LEDApril 2009


Conceptual Layout ofSelected Remedy


Figure 2-7.

EXPLANATION

!<Tier 1 Soil Location Only andConcentration in mg/kg

A Tier 1 Groundwater Location Only

!ATier 1 Soil and Groundwater Locationand Concentration in mg/kg

!CMonitoring Well - Verification Samplingand Concentration in mg/kg

!<Phase I/II SI Sample Locationand Concentration in mg/kg

#*Surface Water Sampling Location -To Be Sampled

#*Surface Water Sampling Location -Not Sampled

Building


Approximate Excavation Depths:0-2'

0-6'

0-8' 0 30 60 90 12015Feet

Pro

ject

s09\

SS

8_S

oil_

RO

D\S

S8_

B35

4_R

emed

y_R

ev01

.mxd

1 inch = 80 feet

ArsenicEPA Regional SSL 0.29 mg/kgBackground 7.5 mg/kg

354-102126

Surface Soil Concentration in mg/kg (exceedances ofbackground/criteria are in red)Subsurface Soil Concentration in mg/kg (exceedances ofbackground/criteria are in red)

ND Non Detect at Reporting Limit M A matrix effect was present F The analyte was positively identified but the associated numerical value is below the reporting limit.

3727.pdf3728.pdf

APPENDIX A SUMMARY OF ANALYTE EXCEEDANCES

IN SOIL AND GROUNDWATER

3727.pdf3728.pdf

Table A-1Summary of Exceedances in Soil - Wash Rack Area

Spill Site 8 Site Inspection and Remedial Investigation

Sample Sample DepthLocation Date Method Type (feet bgs) Parameter Result PRG(1) SSL(2) Background(3) UnitsWR-06 8/26/2003 SW8270 N 0 - 1 Benzo(a)pyrene 1.3 0.062 8.0 NA mg/kgWR-12 11/9/2004 SW8270C N 0 - 1 Benzo(a)pyrene 0.76 0.062 8.0 NA mg/kg

WRT1-05 5/16/2006 BNASIM N 0 - 0.16 Benzo(a)pyrene 0.063 M 0.062 8.0 NA mg/kgWRT1-05 5/16/2006 BNASIM FD 0 - 0.16 Benzo(a)pyrene 0.130 J 0.062 8.0 NA mg/kgWRT1-08 5/16/2006 BNASIM N 0 - 0.16 Benzo(a)pyrene 0.073 0.062 8.0 NA mg/kg

WR-04 8/22/2003 SW6010 N 2.5 - 4 Thallium 7.2 5.2 3.6 1.5 mg/kg

Notes:bgs Below ground surfaceFD Field duplicate

mg/kg Milligrams per kilogramN Normal environmental sample

NA Not Applicable(1) PRG = U.S. Environmental Protection Agency, Region IX, Residential Soil Preliminary Remediation Goal.(2) SSL = U.S. Environmental Protection Agency, Region IX, Soil Screening Level.(3) Background is based on maximum of typical range in Western U.S., as reported in Element Concentrations in Soils and Other Surficial Materials of the

Conterminous United States , USGS Professional Paper 1270. 1984.

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Table A-2Summary of Exceedances in Soil - Building 354


Sample Sample DepthLocation Date Method Type (feet bgs) Parameter Result PRG(1) SSL(2) Background(3) Units354-01 8/20/2003 SW7060 N 0 - 1 Arsenic 4.9 0.39 29.0 7.5 mg/kg354-02 8/20/2003 SW7060 N 0 - 1 Arsenic 68.4 0.39 29.0 7.5 mg/kg354-03 8/20/2003 SW7060 N 0 - 1 Arsenic 17.1 0.39 29.0 7.5 mg/kg354-04 8/20/2003 SW7060 N 0 - 1 Arsenic 5.1 0.39 29.0 7.5 mg/kg354-05 11/8/2004 SW6010B N 0 - 1 Arsenic 7.5 0.39 29.0 7.5 mg/kg354-07 11/5/2004 SW6010B N 0 - 1 Arsenic 3.6 0.39 29.0 7.5 mg/kg354-08 11/4/2004 SW6010B N 0 - 1 Arsenic 5.4 0.39 29.0 7.5 mg/kg354-09 11/5/2004 SW6010B N 0 - 1 Arsenic 9.9 0.39 29.0 7.5 mg/kg354-12 11/5/2004 SW6010B N 0 - 1 Arsenic 60.4 0.39 29.0 7.5 mg/kg354-14 11/8/2004 SW6010B N 0 - 1 Arsenic 5.6 0.39 29.0 7.5 mg/kg

354T1-05 5/17/2006 SW6020 N 0 - 0.16 Arsenic 3.7 0.39 29.0 7.5 mg/kg354T1-08 5/17/2006 SW6020 N 0 - 0.16 Arsenic 6.7 0.39 29.0 7.5 mg/kg354T1-11 5/17/2006 SW6020 N 0 - 0.16 Arsenic 3.2 0.39 29.0 7.5 mg/kg354T1-12 5/17/2006 SW6020 N 0 - 0.16 Arsenic 3.5 0.39 29.0 7.5 mg/kg

354-01 8/20/2003 SW7060 N 2 - 4 Arsenic 16.0 0.39 29.0 7.5 mg/kg354-01 8/20/2003 SW6010 N 2 - 4 Thallium 7.2 5.2 3.6 1.5 mg/kg354-02 8/20/2003 SW7060 N 2 - 4 Arsenic 91.2 0.39 29.0 7.5 mg/kg354-06 11/8/2004 SW6010B N 2.5 - 4 Arsenic 8.1 0.39 29.0 7.5 mg/kg354-07 11/5/2004 SW6010B N 5 - 9 Arsenic 7.9 0.39 29.0 7.5 mg/kg354-07 11/5/2004 SW6010B N 2.5 - 4 Arsenic 8.0 0.39 29.0 7.5 mg/kg354-12 11/5/2004 SW6010B N 2.5 - 4 Arsenic 112 M 0.39 29.0 7.5 mg/kg


mg/kg Milligrams per kilogramN Normal environmental sample(1) PRG = U.S. Environmental Protection Agency, Region IX, Residential Soil Preliminary Remediation Goal.(2) SSL = U.S. Environmental Protection Agency, Region IX, Soil Screening Level.(3) Background is based on maximum of typical range in Western U.S., as reported in Element Concentrations in Soils and Other Surficial Materials of the



Table A-3Summary of Exceedances in Soil - Building 356 Area


Sample Sample DepthLocation Date Method Type (feet bgs) Parameter Result PRG(1) SSL(2) Background(3) Units356-12 8/21/2003 SW6010 N 9 - 10 Thallium 7.4 5.2 3.6 1.5 mg/kg


mg/kg Milligrams per kilogramN Normal environmental sample

NA Not Applicable(1) PRG = U.S. Environmental Protection Agency, Region IX, Residential Soil Preliminary Remediation Goal.(2) SSL = U.S. Environmental Protection Agency, Region IX, Soil Screening Level.(3) Background is based on maximum of typical range in Western U.S., as reported in Element Concentrations in Soils and Other Surficial Materials of the



APPENDIX B CALCULATION OF SURFACE SOIL

CLEANUP LEVEL

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Surface Soil Cleanup Level Evaluation for Spill Site 8


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This evaluation summarizes the methodology used to determine a proposed cleanup level for arsenic in surface soil at Spill Site 8. Spill Site 8 includes three primary subareas: the Wash Rack Area, the Building 354 Former Storage Area, and the Building 356 Wood Hobby Shops area. A human health risk assessment performed for the Spill Site 8 Remedial Investigation (RI) concluded that arsenic in surface soil (i.e., the upper 2 inches) at the Former Storage Area could pose a risk greater than 1x10-6 to potential receptors. The U.S. Environmental Protection Agency (EPA) Region 9 Preliminary Remediation Goal (PRG) for arsenic in soil is 0.39 milligrams per kilogram (mg/kg), which is lower than the regional background concentration of 7.5 mg/kg. Therefore, the objective of this evaluation is to identify a cleanup level for arsenic in surface soil such that removal of soil exceeding that level will result in an average remaining arsenic concentration equal to or less than the regional background concentration (i.e., 7.5 mg/kg).

METHODOLOGY The data set used for the evaluation includes arsenic concentrations measured in 26 surface soil samples collected from the Former Storage Area during the Site Inspection (SI) and the RI (USAF 2005 and USAF 2007). An iterative elimination method was used to identify which soil sample locations would need to be removed (i.e., excavated) so that the average remaining site concentration equals or is less than the regional background for arsenic (i.e., 7.5 mg/kg). This approach follows the iterative method described in the EPA draft guidance Guidance on Surface Soil Cleanup at Superfund Sites: Applying Cleanup Levels (USEPA 2002) and Schulz and Griffin (2001).

Four historical surface soil sample locations in the Former Storage Area contained arsenic concentrations exceeding regional background. The four locations and their corresponding arsenic concentrations are 354-02 (68 mg/kg), 354-03 (17 mg/kg), 354-09 (10 mg/kg), and 354-12 (60 mg/kg). The area encompassing these locations (i.e., the area exceeding background) is shown on Figure B-1. To evaluate how much of this area would need to be removed to reduce the average remaining arsenic concentration to background, the following procedure was followed:

1. Order the data set of arsenic concentrations in descending order (highest to lowest).

2. Replace the highest arsenic concentration with the regional background value (7.5 mg/kg) to simulate removal of the soil at that location and replacement with clean soil backfill containing the background concentration of arsenic.

3. Calculate the 95% UCL for the revised data set using ProUCL. The 95% UCL represents the “new” average remaining arsenic concentrations for the exposure area.

4. Compare the 95% UCL with the regional background arsenic concentration (7.5 mg/kg).

5. If the 95% UCL is greater than the regional background concentration, then repeat steps 1 through 4 for the next highest arsenic concentration. If the 95% UCL is less than the regional background concentration, then the proposed cleanup level is approximated by the concentration that resulted in the 95% UCL being less than background.

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Surface Soil Cleanup Level Evaluation for Spill Site 8


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RESULTS As highlighted in Tables B-1 and B-2, removal of surface soil around sample locations 354-02 (68 mg/kg) and 354-12 (60 mg/kg) results in an average residual arsenic concentration of approximately 5.9 mg/kg. This value is below the regional background concentration of 7.5 mg/kg. Therefore, removing surface soils with an arsenic concentration of approximately 60 mg/kg or greater would achieve the objective of reducing average site concentrations at or below background levels. This encompasses an area centered on and within approximately 10 feet of former sample location 354-2 and existing well 354-12.

REFERENCES Schulz, T.W. and S. Griffin. 2001. Practical Methods for Meeting Remediation Goals at Hazardous Waste Sites. Prepared by Risk Analysis 21(1): 43-52.

United States Air Force (USAF). 2005. Final Phase II Supplemental Site Inspection Report Addendum for Study Area 3. F.E. Warren Air Force Base, Wyoming. June.

USAF. 2007. Final Remedial Investigation Report for Spill Site 8. F.E. Warren Air Force Base, Wyoming. February.

U.S. Environmental Protection Agency (USEPA). 2002. Guidance on Surface Soil Cleanup at Superfund Sites: Applying Cleanup Levels. Draft. Prepared by Industrial Economics, Inc and New Fields for Office of Emergency and Remedial Response. January 31.

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Tables and Figure

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Table B-1Summary Statistics for Potential Surface Soil Removal

Spill Site 8 - Building 354 Former Storage AreaF.E. Warren AFB, Wyoming

Assume: Soil excavation and backfill with clean soil (i.e. arsenic concentration in backfill = 7.5 mg/kg)Goodness-of-Fit

TestAnalysis Round Soil Type Area Analyte

Group Analyte Exclude Locations Unit No. of Samples

Detection Rate Mean Std Dev Min Max Distribution Method of UCL Calculation Assessed

95% UCL1 (1) Surface (2) 354 Metals ARSENIC -- mg/kg 26 100% 9.02 16.69 1.1 68.4 Non-parameteric 99% Chebyshev (Mean, Sd) UCL 41.592 (1) Surface (2) 354 Metals ARSENIC MW-354-02 mg/kg 26 100% 6.68 11.49 1.1 60.44 Lognormal 95% H-UCL 8.703 (1) Surface (2) 354 Metals ARSENIC MW-354-02, MW-354-12 mg/kg 26 100% 4.64 3.48 1.1 17.1 Gamma 95% Approximate Gamma UCL 5.884 (1) Surface (2) 354 Metals ARSENIC MW-354-02, MW-354-12, MW-354-03 mg/kg 26 100% 4.27 2.47 1.1 9.95 Gamma 95% Approximate Gamma UCL 5.265 (1) Surface (2) 354 Metals ARSENIC MW-354-02, MW-354-12, MW-354-03, MW-354-09 mg/kg 26 100% 4.18 2.28 1.1 7.53 Gamma 95% Approximate Gamma UCL 5.11

Summary Statistics Upper Confidence Limit (UCL)

(4) References:USEPA (2002). Calculating Upper Confidence Limits for Exposure Point Concentrations at Hazardous Waste Sites. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Report No. OSWER 9285.6-10.Singh, A., Singh, A. K., and Maichle, R. (2004). ProUCL Version 3.0 User Guide. Office of Research and Development, U.S. Environmental Protection Agency, Report No. EPA/600/R04/079.

(3) The distributional assumption from (2) is used to select the appropriate UCL calculation method. For normal distribution, the UCL is based on the t-statistics. For lognormal distribution, gamma distribution, and non-parametric assumption, the UCL is based on the recommendations from USEPA (2002) and Singh (2004).

(2) Goodness-of-Fit Test at 5% significance level is used to test for distributional assumption.

Notes:(1) The duplicate result is not used in this analysis.


Table B-2Building 354 Former Storage Area - Arsenic Concentrations (mg/kg)

Soil Cleanup Level Calculation Dataset

LOCIDAnalysis Round 1

Analysis Round 2

Analysis Round 3

Analysis Round 4

Analysis Round 5

354T1-04 1.1 1.1 1.1 1.1 1.1354T1-10 1.2 1.2 1.2 1.2 1.2354T1-02 1.6 1.6 1.6 1.6 1.6354T1-07 1.7 1.7 1.7 1.7 1.7354T1-09 2.1 2.1 2.1 2.1 2.1354T1-03 2.2 2.2 2.2 2.2 2.2MW-354-13 2.3 2.3 2.3 2.3 2.3MW-354-11 2.42 2.42 2.42 2.42 2.42MW-354-10 2.58 2.58 2.58 2.58 2.58354T1-01 2.6 2.6 2.6 2.6 2.6354T1-06 2.6 2.6 2.6 2.6 2.6354T1-11 3.2 3.2 3.2 3.2 3.2354T1-12 3.5 3.5 3.5 3.5 3.5MW-354-07 3.62 3.62 3.62 3.62 3.62354T1-05 3.7 3.7 3.7 3.7 3.7MW-354-01 4.9 4.9 4.9 4.9 4.9MW-354-04 5.1 5.1 5.1 5.1 5.1MW-354-08 5.37 5.37 5.37 5.37 5.37MW-354-14 5.58 5.58 5.58 5.58 5.58354T1-08 6.7 6.7 6.7 6.7 6.7MW-354-06 6.99 6.99 6.99 6.99 6.99MW-354-05 7.53 7.53 7.53 7.53 7.53MW-354-09 9.95 9.95 9.95 9.95 7.5MW-354-03 17.1 17.1 17.1 7.5 7.5MW-354-12 60.44 60.44 7.5 7.5 7.5MW-354-02 68.4 7.5 7.5 7.5 7.5

Notes:1) Values in yellow indicate concentrations "removed" and replaced with background concentration (7.5 mg/kg).

2) "Analysis Round" corresponds to interation of removing the highest concentrationand replacing it with the background concentration. See Table B-1 for UCL calculation.

Arsenic Concentration (mg/kg)


Response to EPA comments Dated January 12, 2009 on the Spill Site 8 Draft Interim ROD for Soils

Comment: Section 2.9.1 Remedy Components – Alternative 2 – Land Use Controls, Page 2-21, second paragraph, second sentence. Please remove.

Response: The sentence was removed as suggested. Comment: Section 2.9.1 Remedy Components – Alternative 2 – Land Use Controls, Page 2-22, B.2 – please add BGP to your acronym list.

Response: Base General Plan (BGP) has been added to the acronym list. Comment: Section 2.9.2 Expected Outcome of Each Alternative – Page 2-25, this paragraph needs to be rewritten to reflect that Alternative 2 does not meet the objective of reducing potential for migration however, it does reduce direct exposure to contaminated soils.

Response: This paragraph has been rewritten as suggested. Comment: Section 2.10.4 Reduction of Toxicity, Mobility, or Volume Through Treatment – Page 2-29, please add Alternative 3 to this list because none of the alternatives provide reduction in arsenic toxicity, volume, and mobility “through treatment”.

Response: This paragraph has been rewritten as suggested. Comment: Section 2.13.2 Compliance with ARARs – Page 2-33, Chemical-Specific ARARs – Chemical specific federal ARARs, 1st bullet – should be removed, not applicable to this “Soils” ROD. Also, please remove the 2nd bullet under Chemical-specific Wyoming ARARs, not applicable to this ROD.

Response: The two bullets were removed from this section as suggested. Comment: Section 2.13.2 Compliance with ARARs – Page 2-34, Location-Specific ARARs – Principal location-specific state ARARs 1st bullet should be removed. Again, not applicable to this “soils” ROD.

Response: This bullet was removed as suggested. Comment: Additionally, all of the ARARs tables should be updated to match the new text.

Response: The ARARS tables have been updated to reflect the changes made in the text.

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