PB95-964607
EPA/ROD/R10-95/112
June 1995
EPA Superfund
Record of Decision:
Elmendorf Air Force Base
(OU 2), Greater Anchorage Borough, AK
3/31/1995
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UNITED STATES AIR FORCE
ELMENDORF AIR FORCE BASE, ALASKA
ENVIRONMENTAL RESTORATION PROGRAM
OPERABLE UNIT 2
RECORD OF DECISION
FINAL
MARCH 1995
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ELMENDORF AIR FORCE BASE
OPERABLE UNIT 2
DECLARATION OF THE RECORD OF DECISION
SITE NAME AND LOCATION
Elmendorf Air Force Base (Operable Unit 2)
Southcentral Alaska
STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected final remedial actions for Operable Unit (OU) 2, source
areas ST20 and ST41, at Elmendorf Air Force Base, Alaska, which were chosen in accordance with the
Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), as amended by
the Superfund Amendments and Reauthorization Act of 1986 (SARA), and, to the extent practicable, the
National Oil and Hazardous Substance Pollution Contingency Plan (NCP). The decision is based on the
administrative record. The Administrative Record Index is presented as Attachment A. The remedy was
selected by the U.S. Air Force and the U.S. Environmental Protection Agency (EPA). The State of Alaska
Department of Environmental Conservation (ADEC) concurs with the selected remedy.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from one of the source areas within OU2, the
ST41 Tank Spill, if not addressed by implementing the response actions selected in this Record of Decision
(ROD), may present an imminent and substantial endangerment to public health, welfare, or the environment.
The selected final remedial action incorporates the previously selected interim remedial action for ST41.
DESCRIPTION OF THE SELECTED REMEDY
OU2 consists of three source areas:
ST20 Underground Waste Storage Tank
ST41 Tank Spill (Four Million Gallon Hill)
ST41 Sludge Disposal Area
Although contaminated soil and groundwater were found in the vicinity of ST20 and ST41 Sludge
Disposal Area, it is attributed to upgradient source areas ST48 and ST41 Tank Spill, respectively. No actual or
threatened release of hazardous substances from ST20 or ST41 Sludge Disposal Area were found during the
Remedial Investigation/Feasibility Study. The contaminated media in ST20 will be addressed under the State-
Elmendorf Environmental Restoration Agreement (SERA) program, and the contaminated media in the ST41
Sludge Disposal Area is being addressed under the ST41 Tank Spill remedial action.
Source Area ST41 Tank Spill
The selected remedies address free product, surface water seeps, source control, and groundwater at the
ST41' tank spill source area.
The remedy selected to address free product and surface water seeps is continued operation of the
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interim remedial action, previously selected and documented in an Interim Action ROD which was signed in
September of 1992. The major components of the interim remedial action were as follows:
Containment of seeps using collection systems and subsequent water treatment and product
recycling;
Extraction of fuel product from the groundwater surface in the shallow aquifer to minimize
further migration;
Treatment of extracted groundwater and seep water by an air stripping process to meet federal,
state, and local regulations;
Treatment of the emissions from the air stripping process to meet state regulations and permit
requirements; and
Disposal of the treated groundwater in accordance with federal, state, and local regulations by
discharge to the municipal sewer system.
This final ROD incorporates the interim remedial action, and includes additional remedies for source
control and groundwater remediation. The interim action is intended to achieve free product recovery and to
control the mobilization of contaminants into the shallow groundwater or surface water. The efficiency of the
interim action, specifically with respect to ensuring that wetlands are not adversely impacted, and that all
technically practicable free product is removed, will be evaluated as part of the selected remedy.
The selected remedy for ST41 source control includes the following major components:
Cleaning of the four one million gallon underground storage tanks and filling them with an
inert material;
Excavating, removing, cleaning and disposal/recycling of the piping system;
Removing contaminated soils that may contribute to groundwater contamination and treating in
a pre-approved facility; and
Revegetating the area.
The selected remedy for ST41 groundwater includes the following major components:
Monitoring the groundwater beneath and adjacent to the site to evaluate contaminant migration
and timely reduction of contaminant concentrations by natural attenuation within 21 years.
This will include five-year reviews to assess the protectiveness of the remedial action as long as
contamination remains above unacceptable levels.
Maintaining institutional controls that restrict access to groundwater and groundwater
development at the site as long as hazardous substances remain on the site at levels that
preclude unrestricted use. The specific institutional controls to be implemented and/or
maintained at OU2 are as follows:
1. Development of a site map showing the areas currently and potentially impacted by
groundwater contaminants that will-be included in the Base Comprehensive Plan;
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groundwater contaminants that will be included in the Base Comprehensive Plan;
2. Zoning the affected area for undeveloped outdoor/recreational use only,
3. Continued enforcement of base policy prohibiting installation of groundwater wells (other
than for monitoring purposes) into the shallow aquifer underlying OU2; and
4. Prohibiting unauthorized access to existing water supply and groundwater monitoring wells.
In addition, to ensure long-term integrity of the above land use controls, the Air Force will ensure
that, to the extent that groundwater contamination remains above unacceptable levels, deed restrictions or
equivalent safeguards will be implemented in the event that property containing such contamination is
transferred by the Air Force. The measures taken will include:
Five-year review to assess the protecrJveness of the remedial action;
Periodic evaluation of monitoring results to determine if there is need for further remedial
action.
The contingent remedy for ST41 groundwater includes the following major components:
Extracting groundwater from the shallow aquifer to eliminate further migration;
. Treating the extracted water with an air stripping process to meet federal, state and local
water quality regulations;
Treating the air emissions from the air stripping process to meet state and base air emission
permit requirements; -
Disposing of the treated groundwater in accordance with federal, state, and local regulations
and permit requirements;
Five-year review to assess the protectiveness of the remedial action; and
Monitoring of the effectiveness of the groundwater containment and treatment process until
the benzene concentrations reach the Maximum Contaminant Level (MCL) or groundwater
no longer poses an unacceptable health risk.
STATUTORY DETERMINATIONS
The selected remedies are protective of human health and the environment, comply with Federal
and State requirements that are legally applicable or relevant and appropriate to the remedial actions, and
are. cost-effective. The remedies utilize permanent solutions and alternative treatment (or resource recovery)
technology to the maximum extent practicable, and satisfy the statutory preference for remedies that employ
treatment that reduce toxicity, mobility, or volume as a principal element.
Because the remedies will result in the continued presence of hazardous substances on site above
health-based levels, a review will be conducted within five years of commencement of the remedial action, to
ensure that the remedy continues to provide adequate protection of human health and the environment.
ui
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DECLARATION STATEMENT
The no further action determination for the uncontaminated soil in the vicinity of the ST20
Underground Waste Storage Tank is made based on the RI/FS performed at OU2. No determination for
remedial action is being made for the groundwater and the soil at the groundwater interface in the ST20
area since the contamination is from an apgradient source, ST48, that is being addressed under the SERA
program.
The RI/FS for OU2 determined that the ST41 Sludge Disposal Area was not a source of
contamination to the soil or groundwater in the area. Contaminated soil in this area is attributed to the
ST41 Tank Spill, and remedial measures to address this contamination are identified therein.
IV
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LEAD AGENCY ACCEPTANCE QF THE RECORD OF
ELMENDQRF AIR FORCE BASE. ALASKA
OPERABLE UNIT 2
Signature sheet for the foregoing Record of Decision for the Operable Unit 2 final action at Elmendorf Air
Force Base, Alaska between the United States Air Force and the United States Environmental Protection
Agency, with concurrence by the State of Alaska Department of Environmental Conservation.
9 MAY
, LT GEN, USAF
'ACAF
onmentaJlf rotection Committee
Date
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SUPPORT AGENCY ACCEPTANCE OF THE RECORD OF DECISION
ELMENDORF AIR FORCE BASE. ALASKA
OPERABLE UNIT 2
Signature sheet for the foregoing Record of Decision for the Operable Unit 2 final action at Elmendorf Air
Force Base, Alaska between the United States Air Force and the United States Environmental Protection
Agency, with concurrence by the State of Alaska Department of Environmental Conservation.
MAR 3 1 1995
: CLARKE Date
Regional Administrator
Region X
U.S. Environmental Protection Agency
VI
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STATE OF ALASKA CONCURRENCE WITH THE RECORD OF DECISION
ELMENDORF AIR FORCE
OPERABLE UNIT 2
Signature sheet for the foregoing Record of Decision for the Operable Unit 2 final action at Elmendorf Air
Force Base, Alaska between the United States Air Force and the United States Environmental Protection
Agency, with concurrence by the State of Alaska Department of Environmental Conservation.
MARIANNE G. SEE Date
Acting Regulatory Administrator
Southcentral Regional Office
Alaska Department of Environmental Conservation
vu
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ELMENDORF AIR FORCE BASE
OPERABLE UNIT 2
DECISION SUMMARY
VIII
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TABLE OF CONTENTS
Page
1.0 SITE NAME, LOCATION AND DESCRIPTION M
2.0 ELMENDORF AFB SITE HISTORY AND ENFORCEMENT ACnvmES 2-1
3.0 HIGHLIGHTS OF COMMUNITY PARTICIPATION .3-1
4.0 SCOPE AND ROLE OF THE ELMENDORF OPERABLE UNITS 4-1
5.0 SUMMARY OF OU2 CHARACTERISTICS 5-1
5.1 ST20 Underground Waste Storage Tank 5-1
5.1.1 Geology and Hydrogeology of ST20 5-1
5.1.2 Remedial Actions Taken at ST20 5-1
5.13 Surface Soil/Surface Water/Sediment
Contamination at ST20 , 5-4
5.1.4 Subsurface Soil Contamination at ST20 5-4
5.1.5 Groundwater Contamination at ST20 . ... 5-9
5.1.6 Conclusions 5-9
53. ST41 Tank Spill and Sludge Disposal Area 5-9
52.1 Geology and Hydrogeology of ST41 5-16
522. Reported Releases at ST41 .. 5-16
523 Early Actions at ST41 Tank Spill ; 5-16
52.4 Surface Soil/Sediment Contamination at ST41 Tank Spill 5-18
5.2.5 Subsurface Soil Contamination at ST41 Tank Spill 5-22
52.6 Groundwater Contamination at ST41 Tank Spill 5-22
52.7 Surface Water Contamination at ST41 Tank Spill 5-31
52.8 ST41 Sludge Disposal Area 5-31
52.9 Conclusions 5-33
6.0 SUMMARY OF SITE RISKS 6-1
6.1 Human Health Risk ; 6-1
6.1.1 Identification of Contaminants of Concern 6-1
6.12 Risk Characterization 6-2
6.L3 Risk/Hazard Associated with ST20 6-6
6.L4 Risk/Hazard Associated with ST41 Tank Spill 6-9
6.1.5 Uncertainties Associated with the Risk Assessment 6-11
62 Ecological Risk 6-11
6.2.1 Ecological Evaluation of ST20 6-13
622 Ecological Evaluation of ST41 6-13
63 Conclusions . .... ; 6-13
7.0 DESCRIPTION OF ALTERNATIVES 7-1
7.1 Remedial Action Objectives for ST41 Tank Spill . 7-1
IX
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TABLE OF CONTENTS (Continued)
Page
12 Remedial Alternatives for ST41 Tank Spill 7-2
7.2.1 Free Product, Surface Water and Seeps 7-2
122 Alternatives for Groundwater 7-3
123 Alternatives for Source Control 7-4
8.0 SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES 8-1
8.1 Threshold Criteria , 8-1
8.1.1 ST41 Groundwater 8-1
8.12 ST41 Source Control 8-2
82 Primary Balancing Criteria 8-2
8.2.1 ST41 Groundwater .8-2
8.22 ST41 Source Control 8-3
83 Modifying Criteria 8-4
9.0 SELECTED REMEDY 9-1
9.1 ST20 and ST41 Sludge Disposal Area 9-1
92 ST41 Tank Spill 9-1
10.0 STATUTORY DETERMINATIONS ...;..! .:...10-1
10.1 Protection of Human Health and the Environment 10-1
102 Compliance With ARARs 1 10-1
102.1 Action-Specific ARARs 10-1
1022 Chemical-Specific ARARs ; 10-2
1023 Location-Specific ARARs :. . 10-3
103 Cost Effectiveness 10-3
10.4 Utilization of Permanent Solutions and Alternative
Treatment Technologies to the Maximum Extent Practicable 10-3
11.0 DOCUMENTATION OF SIGNIFICANT CHANGES .. '. 11-1
12.0 REFERENCES 12-1
OPERABLE UNIT 2 RESPONSIVENESS SUMMARY RS-1
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LIST OF TABLES
Page
5-1 History of Source Areas 5-2
5-2 Summary of Constituents Detected in Subsurface Soil at ST20 5-5
5-3 Metals Concentrations of Background Soil . . 5-6
5-4 Summary of Constituents Detected in Groundwater at ST20 . 5-10
5-5 Summary of Constituents Detected in Surface Soil 5-23
and Surface Sediment at ST41 5-21
5-6 Summary of Constituents Detected in Groundwater at ST41 5-24
5-7 Summary of Constituents Detected in Surface Water at ST41 5-32
6-1 Summary of Exposure Scenarios Evaluated for OU2 6-3
6-2 Exposure Parameters Used in the OU2 Risk Assessment 6-4
6-3 Permeability Constituents for Dermal Exposure at OU2 6*5
6-4 ST20 Groundwater Summary of Risk 6-7
6-5 ST41 Groundwater Summary of Risk 6-10
6-6 Summary of ST41 Surface Water Results With
Surface Water Quality Criteria 6-14
XI
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LIST OF FIGURES
Page
1-1 Site Location Map, Elmendorf AFB, Alaska 1-2
1-2 Generalized Hydrogeologic Cross Section Along Ship
Creek . 1-3
4-1 OU2 Contaminant Source Areas, Elmendorf AFB, Alaska 4-2
5-1 Operable Unit 2 Source Area ST20 Location Map 5-3
5-2 Operable Unit 2 Source Area ST20 Location Map Fall
1992 Subsurface Soil Fuel Analytical Results . 5-8
5-3 Operable Unit 2 Source Area ST20 BTEX and TPH
Groundwater Analytical Results, Fall 1990 5-11
5-4 Operable Unit 2 Source Area ST20 BTEX and TPH
Groundwater Analytical Results, Fall 1991 5-12
5-5 Operable Unit 2 Source Area ST20 BTEX and TPH
Groundwater Analytical Results, Spring 1992 5-13
5-6 Operable Unit 2 Source Area ST20 BTEX and TPH
Groundwater Analytical Results, Fall 1992 5-14
5-7 Operable Unit 2 Source Area ST41 Site Location Map 5-15
5-8 Operable Unit 2 Cross Section View Through Tank 603 5-17
5-9 Source Area ST41 IRA Extraction Well and Interceptor
Trench Locations . 5-19
5-10 Source Area ST41 Interim Remedial Action Process
Flow Diagram 5-20
5-11 Source Area ST41 Surface Soil, Subsurface Soil, and Sediment
BTEX and Fuel Analytical Results, Fall 1992 5-21
5-12 Operable Unit 2 Source Area ST41 BTEX and TPH,
Fall 1990 5-27
5-13 Operable Unit 2 Source Area ST41 BTEX and TPH,
Fall 1991 : 5-28
5-14 Operable Unit 2 Source Area ST41 BTEX and TPH,
Spring 1992 5-29
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LIST OF FIGURES (Continued)
Page
5-15 Operable Unk 2 Source Area ST41 BTEX and TPH,
Fall 1992 5-30
6-1 Operable Unk 2 ST20 Groundwater Risks
or Hazards .' 6-8
6-2 Operable Unit 2 ST41 Groundwater Risks
or Hazards 6-12
Mil
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ACRONYMS AND ABBREVIATIONS
ADEC Alaska Department of Environmental Conservation
AFB Air Force Base
ARAR Applicable or Relevant and Appropriate Requirement
AWT Above Water Table
BGS Below Ground Surface
BH Borehole
BTEX Benzene, Toluene, Ethylbenzene, Xylenes
BWT Below Water Table
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act
COC . Contaminant of Concern
COEC Contaminant of Ecological Concern
EPA Environmental Protection Agency
ESD Explanation of Significant Differences
FFA Federal Facility Agreement Under CERCLA Section 120
HEAST Health Effects Assessment Summary Tables
HI Hazard Index
ERA Interim Remedial Action
IRIS Integrated Risk Information System
ERF Installation Restoration Program
LOEL Lowest Observable Effect Level
MCL Maximum Contaminant Level
mgAg Milligrams per Kilogram
MW Monitoring Well
N/A Not Available
NCP National Contingency Plan
NPL National Priorities List
OU Operable Unit
OU2 Operable Unit 2
POL Petroleum, Oil, and Lubricant
POTW Publicly Owned Treatment Works
QA/QC Quality Assurance/Quality Control
RAB Restoration Advisory Board
RAGS Risk Assessment Guidance for Superfund .
RI/FS Remedial Investigation/Feasibility Study
ROD Record of Decision
SARA Superfund Amendments and Reauthorization Act
SDEF Standard Default Exposure Factors
SERA State-Elmendorf Environmental Restoration Agreement
SWQC Surface Water Quality Criteria
TPH Total Petroleum Hydrocarbons
TRC Technical Review Committee
ug/dl Micrograms per Deci-liter
ug/L . Micrograms per Liter
UST Underground Storage Tank
UT Upper Tolerance
XIV
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ELMENDORF AIR FORCE BASE
OPERABLE UNIT 2
DECISION SUMMARY
1.0 SITE NAME, LOCATION, AND DESCRIPTION
Elmendorf Air Force Base (Operable Unit 2)
Southcentral Alaska
Elmendorf Air Force Base (Elmendorf AFB) is the largest United States Air Force installation in
Alaska. The base is a vital aviation link to both Europe and the Far East from the contiguous 48 states.
The primary mission of the base is to provide support for the.air defense and sovereignty of Alaska and
North America. '
Elmendorf AFB is located on 13,095 acres bordered on the south by the city of Anchorage, on the
east by the US Army's Fort Richardson, and on the north and west by the Knik Arm of Cook Inlet (Figure
1-1). The base lies within a large glacially deposited alluvial fan. Local topography is generally flat, with a
slight regional rise to the east. Ship Creek flows along the southern boundary of the base.
Currently, Elmendorf AFB has 6,769 active duty personnel and 10320 dependents. The base
provides a variety of services including 1,588 on-base housing units, 3 elementary schools, day-care facilities, a
hospital, and 3 dental clinics.
Surficial deposits in the vicinity of Elmendorf AFB are dominated by two types of unconsblidated
deposits. The first of these is poorly sorted glacial sediment (till). The primary feature of the till material is
the Elmendorf Moraine, expressed topographically as a broad, northeast-to-southwest ridge running through
the mid-portion of the base. The second is glacial outwash sediments. The outwash plain, deposited by
meltwaters moving away from the ice margin, is made up of coarse grained sediments upon which most of
the base facilities are located.
Two aquifers are present in the vicinity of Elmendorf AFB. The shallow aquifer consists of either
till or outwash deposits, depending on location. The deep confined (artesian) aquifer consists primarily of
sand and gravel. Between the shallow and deep aquifers is a regional aquitard known as the Bootlegger
Cove Formation. This unit consists of interbedded silt and day deposits, and ranges from several feet to
over fifty feet in thickness. A generalized cross section showing the relationship between the shallow
(outwash) aquifer, the Bootlegger Cove Formation, and the deep aquifer is presented in Figure 1-2. The
shallow aquifer in the outwash plain ranges from 35 to over 120 feet thick, while the depth to groundwater
ranges from 5 to over 50 feet below ground surface (bgs). The shallow aquifer on the moraine ranges from
1 to 60 feet thick, with the depth to groundwater ranging from 1 to 30 feet bgs. Testing has indicated no
communication between the shallow and deep aquifers.
A groundwater divide roughly coincides with the crest Of the Elmendorf Moraine, with flow
diverging away from the divide and down the flanks of the moraine (generally to the north and south). To
the south of the moraine, the regional flow is to the south and southwest, towards Ship Creek. Flow on the
north side of the moraine is generally to the northwest. Scattered lenses of clayey material in the morainal
till create local areas of confined or semi-confined conditions, and may also locally perch the shallow
groundwater.
1-1
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Fort Richardson
Army Post
Figure 1-1. Site Location Map, Elmendorf AFB, Alaska
1-2
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600 -
400 -
200 -
-JOO -
Knik
Arm
ELEMENDORF
AIR rORCE BASE
(APPROXIMATE)
Elmendorf AFB
Powerplant
.606
400
-200
Chugach
Mountain
Front
»ii... .^T*x-:-:-:-:-:-:-:-:-:-:-:-:---' ~rnV *
-:-:-:-:-:-:-:-:-:-:-:-:-:-:-:-x-----_^r v":_.._-j;
Vertical Exaggeration ± 20X
(Modified From Jacobs Engineering. 1993)
ELMENDORF AFB
LEGEND
Permeable coarsegrained ^^
deposits ^^
Relatively impermeable fine-
grained deposits
Bedrock
^0. Area where Ship Creek may
either be losing water or
gaining water to/from the
shallow aquifer depending
on stream flow.
^--. Ship Creek profile with
^ i diversion dam structure.
Arrows indicate direction of
groundwater movement to
or from the creek.
Figure 1-2. Generalized Hydrogeologic Cross Section Along Ship Creek
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2.0 ELMENDORF AFB SITE HISTORY AND ENFORCEMENT ACTIVmES
The following is a discussion of the history of the Elmendorf AFB site. Information specific to the
OU2 source areas is presented in Section 5.0.
Elmendorf Field was constructed in 1940 as part of a national effort to fortify Alaska in anticipation
of World War n. Military activity at Elmendorf peaked in 1942 during the campaign to retake the'Aleutian
Islands from the Japanese. In 1951, the Army relocated its garrison four miles to the east, and Elmendorf
Field officially became Elmendorf Air Force Base.
In carrying out its defense mission, base operations have generated varying quantities of hazardous
and non-hazardous wastes. The major sources of hazardous wastes include industrial operations (shops), Ore
training and; fuels management. The soils and groundwater at the base have been contaminated from the
storage and handling of fuels and solvents as well as the operation of landfills,
The Air Force developed the Installation Restoration Program (IRP) to address environmental
contamination resulting from past waste disposal practices. The IRP was initiated in 1982 with a records
search to identify past disposal sites containing contaminants that may pose a hazard to human health or the
environment. Under the ERP, the U.S. Air Force identified potential areas of contamination at Elmendorf
AFB. Potential source areas included old landfills, storage and disposal areas, fueling system leaks, and spill
areas. . ;
Elmendorf AFB was proposed for the National Priorities List (NFL) in 1989 and placed on the NPL
in August of 1990. In November 1991, a Federal Facility Agreement (FFA) was negotiated between
Elmendorf, the U.S. Environmental Protection Agency (EPA), and the State of Alaska Department of
Environmental Conservation (ADEC). The FFA established a procedural framework for agency
coordination, and a schedule for all CERCLA activities conducted at the base. The Remedial
Investigation/Feasibility Study (RI/FS) process being followed meets the functional requirements of the
National Environmental Policy Act with regards to protection of wetlands, floodplains, rare and endangered
species, archeologjcal sites, and state historic preservation sites. This final action, the Record of Decision for
Operable Unit 2, is taken in accordance with the FFA and the NCP.
Elmendorf entered into a State-Elmendorf Environmental Restoration Agreement (SERA), similar
to the FFA, in October 1992. The SERA was designed to address remedial actions conducted at petroleum,
oil and lubricant (POL), underground storage tank, and solid waste sources.
2-1
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3.0 HIGHLIGHTS OF COMMUNITY PARTICIPATION
In 1992, Elmendorf AFB assembled a Technical Review Committee (TRC) composed of
representatives from local community councils, federal and state regulatory agencies, and a community at
large member. Quarterly meetings provide Elmendorf AFB an opportunity to brief the TRC on installation
environmental restoration projects and to solicit input from the TRC. Three TRC meetings were held
during preparation of the investigation and feasibility study reports for Operable Unit (OU) 2. In those
meetings, die TRC was informed as to the scope and methodology of the OU2 investigation and proposed
plans for remediation. The TRC is currently transitioning to a Restoration Advisory Board (RAB). Future
community participation will be addressed as part of the RAB.
The Proposed Plan for OU2 was released to the public on June 13,1994. This began a 30 day
public comment period which ended on July 13, 1994. Documents detailing the findings Of the investigation
and evaluation of alternatives were made available to the public at information repositories located at the
following locations: Consortium Library, University of Alaska, Anchorage, Alaska; and Alaska Resources
Library, Bureau of Land Management, Federal Building, Anchorage, Alaska. Notice of the availability of the
proposed plan and of an upcoming public meeting were published in the Anchorage Daily News on June 2,
1994 and in the Sourdough Sentinel on June 10,1994. The public meeting was held June 23,1994 at the
Federal Building, Anchorage, Alaska. The purpose of the meeting was to inform the public of the preferred
alternatives, the alternatives evaluated, answer questions and seek public comment. Representatives from
Elmendorf AFB, the EPA, and ADEC were present at the meeting to answer questions about OU2 and the
alternatives considered.
The public meeting was attended by 26 people. Five oral comments were received during .the
meeting and one written comment was received after the meeting had adjourned. Comments received
covered the following general topics:
Feasibility of biopile technology and natural attenuation in the climate experienced at
Elmendorf AFB and associated cost;
Offsite migration of contaminants through surface water seeps or groundwater flow;
Continued industrial use zoning of the site; and
Risk of the cumulative effects of various contaminants.
Transcripts of the meeting and written comments received during the comment period are included
in the Administrative Record. A responsiveness summary can be found at the end of this Record of
Decision (ROD).
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4.0 SCOPE AND ROLE OF THE ELMENDORF OPERABLE UNITS
The FFA divided the CERCLA study source areas at Elmendorf AFB into the following seven OUs,
on the basis of geographic proximity and similar source characteristics or contaminants:
GUI Landfills (LF05, LF07, LF13, LF59, OT56)
OU2 Tank Spill Sites (ST20, ST41, including the ST41 Slugdge Disposal Area)
OUS Central Containment Area (SD16, SD31, SD52, SS21)
OU4 Northern Containment Area (SD24, SD25, SD28, SD29, FT23, SS10)
OUS Southern Containment Area (ST37)
OU6 Surface Disposal Sites (LF02, LF03, LF04, SD15, SD73, WP14)
OUT Limited Field Investigation (SS19)
In addition to the twenty-five active CERCLA sources, it was agreed between Elmendorf, the EPA
and ADEC that no further action was needed at 12 source areas (SS63, SB30, ST38, SD27, SS42, SD26,
ST40, SS18, ST46, RW17, SS53, and SS22).
The ROD for OU1 was finalized 29 September 1994. The ROD for OUS was finalized and signed
on 2 February 199S. OU4 is in the decision making phase, and will be seeking public comment in April
199S. RI/FS reports are in progress for OUS, and OU6. The ROD for OU6 will address cumulative
impacts to human health and the environment from all OUs and will serve to finalize CERCLA activities at
Elmendorf AFB. .
An additional thirty-nine source areas are not included in any OUs and are being assessed and
remediated under the State-Elmendorf Environmental Restoration Agreement (SERA) established in
October 1992. These sites include petroleum spills, leaking underground storage tanks and former solid
waste landfills. Of the thirty-nine state program sources, fourteen have been approved for no further action.
ST48 (a SERA source area) is of particular importance to OU2, since it is located immediately upgradient
from one of the OU2 source areas, and has a known history of jet fuel line leaks and diesel fuel spills.
OU2, the subject of this ROD, consists of two former underground storage tank sites, $T20 and
ST41, encompassing three source areas:
ST20 Underground Waste Storage Tank;
ST41 Tank Spill; and
ST41 Sludge Disposal Area.
The location of OU2 is depicted on Figure 4-1.
The purpose of this ROD is to document the final remedy at OU2. The selected remedy
incorporates a free product and surface water seep recovery system as an interim remedial action to mitigate
further migration of contaminants to the groundwater. The selected remedy for OU2 is based on the
Administrative Record for the site. The final action for OU2 also includes source control, monitoring, and
institutional controls.
4-1
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Municipality of
Anchorage
Figure 4-1. OU2 Contaminant Source Areas
Elmendorf Air Force Base, Alaska
4-2
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5.0 SUMMARY OF OU2 CHARACTERISTICS
This section is a summary of site conditions, which includes a description of the OU2 source areas, a
discussion of the geologic, hydrogeologic, and surface water environmental characteristics, and the nature and
extent of contaminants of concern.
OTJ2 is located in the central (ST20) and western (ST41) portions of the base (Figure 4-1). Table
5-1 provides a brief summary of milestones, both investigations, and interim actions, performed at OU2.
5.1 ST2Q Underground Waste Storage Tank '
ST20 is located approximately 400 yards west of the north-south runway between O and F Streets, as
shown oh Figure 5-1. The area is flat and covered with pavement and grass. No surface water bodies are
present in this area. ST20 does not contain nor affect any rare or endangered species, floodplains,
archeological sites, state historic preservation sites, or wetlands.
Formerly located at ST20 was a 338,000 gallon reinforced concrete underground storage tank which
served a power plant. After the power plant was demolished in the 1960s, the tank was used to store liquid
wastes including oils, hydraulic fluids and solvents.
Located 160 yards northeast and upgradient of ST20 is a SERA source area, ST48, which has a
known history of jet fuel line leaks and diesel fuel spills. Source Area ST48 is being addressed under the
SERA program.
. 5.1.1 Geology and Hydrogeology of ST20
The geology and hydrogeology was investigated by logging borings drilled in the soil, by surface
geology investigations, and by interpretation of geophysical survey results, aquifer testing, and groundwater
modeling.
Source area ST20 is underlain by both the shallow water table (unconfined) aquifer and the artesian
. (confined) aquifer. The shallow aquifer is made up of outwash plain deposits which consist of a relatively
homogeneous sequence of massive to crudely bedded, poorly sorted sandy gravels and include relatively thin
lenses of sand. These deposits directly overlie the Bootlegger Cove formation. Based on borehole
information, average depth to the Bootlegger Cove formation is 96 feet in the vicinity of ST20. An aquifer
communication test performed on Base Well 42 during the ST20 investigation showed that the Bootlegger
Cove formation forms a competent aquitard and that there is no groundwater interface between the shallow
and deeper aquifers in the vicinity of ST20.
The elevation of the water table at ST20 is approximately 26 feet below ground surface (bgs). The
water levels observed at ST20 indicate that there is not a large seasonal change. Water level measurements
collected during the RI indicate that in the ST20 area groundwater flow direction in the unconfined aquifer is
to the southwest The lack of variability in observed water levels suggests that significant seasonal changes in
gradient will not occur at the ST20 area.
5.12 Removal Actions Taken at ST20
In 1983 the installation prohibited the storage of waste liquids in the tank. In 1986, following testing
5-1
-------
Table 5-1
History of Source Areas
ST20
Underground Waste Storage Tank
1960's Tank used to store fuel for a power plant.
1960V1983 Tank used to store liquid waste.
1983 Preliminary Assessment/Site Investigation.
1983 Waste storage ceased.
1986 . Tanks emptied/waste disposed.
1988 Two soil borings reveal contamination.
1990 Tanks removed, soil excavated.
1990-1993 Remedial Investigation/Feasibility Study
ST41
Tank Spill and Shidge Disposal Area
1942 Fuel tanks constructed.
1976 Oil/water separator installed in southern seep area.
1983 Preliminary Assessment/Site Investigation
1984 Two monitoring wells installed and sampled.
1988 Monitoring wells sampled again.
1989 Small Ham placed in drainage ditch.
1990-1993 Remedial Investigation/Feasibility Study
1991 IRA construction completed, operation began.
1993 IRA operated from October until December, when the IRA was winterized.
1994 IRA restarted in May 1994.
1993-1994 145 gallons of product recovered as of November 1994 from operation of IRA.
5-2
-------
ST48
FUEL SPILL
ST20 UNDERGROUND
STORAGE TANK
(REMOVED)
BASE WELL 42
LEGEND
200 100 0 200
SCALE IN FEET
400
S. HART
MAM BT
CRAWFORD
UMX raoi
G101103B
*CM> nt xo.
FIG5-1
(MTI
2-U-95
CLMCNDORF AIR FORCE BASE
ANCHORAGE. ALASKA
OPERABLE UNIT 2
SOURCE AREA ST20
LOCATION MAP
05-G105-00
FIGURE 5-1
5-3
-------
for waste characterization, approximately 105,000 gallons of liquid waste were removed from the tank and
disposed. In 1990 the base cleaned, excavated and demolished the tank. Although visual inspections
indicated that the tank was structurally sound with no sign of leaks, approximately 1300 cubic yards of
contaminated soil associated with surface spills and tank overflow was removed from around the tank. The
excavated soils, which did not classify as hazardous waste, were treated at the bioremediation pile located on
base.
5.13 Surface Sou/Surface Water/Sediment Contamination at ST20
Because of the extensive removal of surface soil during the excavation of the underground storage
tank at ST20 only one surface soil sample was collected and analyzed at the site in the fall 1990. No
constituents were identified in surface soil at significant concentrations. This sample was located upgradient
of the former UST location. Surface soil, surface water, and sediment contamination were not addressed
during RI activities or the Risk Assessment at ST20.
5.1.4 Subsurface Soil Contamination at ST20
The extent of contamination in subsurface soils was assessed by collecting soil samples for chemical
analyses. The sampling program and laboratory results are discussed in detail in the OU2 RI/FS Report
(U.S. Air Force, 1994) contained in the Administrative Record.
During the fall of 1990, five boreholes were drilled and sampled. These boreholes were
subsequently converted to monitoring wells. In August and September 1992, subsurface soil samples were
collected from 10 additional soil boreholes at ST20. Table 5-2 provides a summary of compounds detected .
in subsurface soils at ST20. In all cases, elevated concentrations occurred at depths greater than 10 feet.
Arsenic was detected in every sample analyzed. The maximum .concentration, 11.1 mg/kg, was
detected in borehole ST20-BH10 at a depth of 25 feet. This was the only sample, out of 63 collected, which
exceeded the background concentration of 9.24 mg/kg. Background soil concentrations used for comparison
with data obtained during the OU2 investigation were taken from the Basewide Background Sampling
Report (U.S. Air Force, 1993), Table 5-3.
Mercury and lead were detected at their highest concentrations in borehole ST20-BH08 at a depth
of 25 feet. Mercury exhibited a concentration of 0.93 mg/kg at this location. This was one of four samples
which exceeded the background concentration of 020 mg/kg (Table 5-3). The other three samples were:
ST20-BH05, 0.21 mg/kg (20 feet); ST20-BH06, 036 mg/kg (15 feet); and ST20-BH08, 032 mg/kg (10 feet).
Lead was detected in all 63 samples analyzed. Its maximum concentration, 193 mg/kg was one of
three subsurface soil samples which exceeded the background concentration of 10.0 mg/kg. Others were:
ST20-BH03, 10.5 mg/kg at 25 feet, and ST20-BH05, 16.9 mg/kg at 25 feet.
Analyses for gasoline and diesel constituents were not performed in 1990. In 1992, gasoline and
diesel were detected in 5 and 4 out of a total of 25 samples, respectively. The maximum concentrations for
both (1,000 mg/kg of gasoline and 610 mg/kg of diesel) were found at a depth of 27 feet in borehole ST20-
BH03. As shown on Figure 5-2, this borehole is located approximately 200 feet away to the northeast,
hydraulically upgradient of ST20 and approximately 100 feet southwest, hydraulically downgradient of ST48.
Figure 5-2 also includes concentrations of all fuel related compounds detected at ST20.
5-4
-------
Table 5-2
Summary of Constituents Detected in
ST20 Subsurface Soil*
' {\mrKWinf
Gasoline
Diesel
Arsenic
Mercury
Lead
> nUDOflumt
ConcamninB
(mj/kg)
1,000
610
11.1
0.93
193
*
SnO-BH03-27(BWT)/F92
ST20-BH03-27(BWT)/F92
ST20-BH10-2S(AWT)/P92
Sr20-BH08-25(AWT)/F92
ST20-BH08-2S(A\VT)/F92
futpuey
5/25
4/25
63/63
13/63
63/63
BKfcjIOQOdr
(s/w
N/A
N/A
924
020
10.0
1 Sampling location identifieis include boring number followed by depth and whether it was above table (AWT) or below (BWT).
The sampling events are also included (Le. Pall 1992 = F92). Information derived from OU 2 RI/FS Report (VS. Air Force, 1994).
2 Background concentrations are 99% upper tolerance limits derived for deep zones, see Table 5-3 of this report (US Air Force,
1993).
N/A Not applicable.
* Limited to compounds of potential concern identified by following procedures consistent with EPA Region X Supplemental Risk
Assessment Guidance for Superfund (EPA,1991c).
5-5
-------
Table 5-3
Metals Concentration of Background Soil
Metal
Arsenic
Barium
Berylliu
m
Cadmiu
m
Chromiu
m
Lead
Mangane
se
Depth
Range
Surface
Root
zone
Deep
Surface
Root
zone
Deep
Surface
Root
zone
Deep
Surface
Root
zone
Deep
Surface
Root
zone
Deep
Surface
Root
zone
Deep
Surface
Root
zone
Deep
Concentrations1
Minimum
3.90
4.70
3.50
77.3
43.4
37.1
0.12
0.29
0.09
0.17
0.93
0.96
9.6
19.0
18.5
4.30
4.10
3.00
67.8
193.5
' 375.0
Mean
7.20
6.87
5.46
113.8
103.3
54.5
0.37
0.41
0.28
1.07
1.62
1.63
19.6
31.8
31.6
6.93
5.65
5.30
319.9
489.4
518.3
' Maximum
13.10
9.60
8.35
154.0
171.3
823
0.62
0.55
0.48
1.95
1.90
2.70
343
45.3
80.9
11.10
7:00
9.10
738.0
74Z5
; 640.0
Standard
Deviation
2.54
1.28
1.18
24.9
31.4
12.7
0.15
0.08
0.11
0.55
0.26
0.44
8.1
6.4
13.9
1.80
0.89
1.48
197.0
136.2
58.6
Number of
Case*
14
14
21
14
14
21
14
14
21
14
14
21
14
14
21
14
14
21
14
14
21
Number of
Ndrt
Detects
0
0
0
0
0
0
3
0
3
2
0
0
0
0
0
0
0
0
0
0
0
>
99% Upper
Tolerance2
(rag/kg) SoJt
-
16.18
11.40
9.24
201.7
2143
95.0
0.91
0.70
0.63
3.01
153
3.03
48.4
54.4
76.1
13.3
8.78
10.0
1,015.7
9703
705.8
Upper 99%
Confidence
Limit for the
Mean
9.0
7.78
6.12
131.4
125.5
61.5
0.47
0.46
034
1.46
1.80
1.87
25.5
36.3
393
8.2
6.28
6.12
459.4
585.8
550.6
Number
of Point*
above UT
Level
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
-------
Table 5-3
(continued)
Metal
Mercury
Nickel
Thallium
Vanadiu
m
Depth
Range
-
Surface
Root
zone
Deep
Surface
Root
zone
Deep
Surface
Root
zone.
Deep
Surface
Root
zone
Deep
Concentrations'
(nag/kg)
Minimum
0.050
0.040
0.040
1.3
11.0
17.6
0.105
0.085
0.060
21.5
46.9
33.2
Mean
,
0.029
0.075
0.088
13.0
29.6
34.6
0.133
0.101
0.092
53.4
60.0
44.3
Maximum
0.150
0.220
0.165
31.7
44.5
73.1
0.280
0.115
0.190
83.1
76.6
59.9
Standard
Deviation
0.029
0.044
0.036
10.1
8.8
11.4
NA
NA
NA
18.5
8.8
6.7
Number of
Cases
14
14
21
14
14
21
14
14
21
14
14
21
Number of
Non
Detect*
.
0
0
0
2
0
0
13
14
20
0
0
0
-
99% Upper
Tolerance*
, (mg/k|)$pj|
0.19
0.23
0.20
48.5
60.6
71.1
NA
NA
NA
118.6
93.1
65.8
Upper 99%
Confidence
Limit for the
Mean
0.11
0.11
0.11
20.1
35.8
40.9
NA
NA
NA
66.5
66.3
48.0
Number
of Points
above UT
Level
0
1
0
0
0
1
NA
NA
NA
0
0
0
-
1 Assumes non-detected values are equal to one half of the detection limit.
2 Upper tolerance limit for the 99th peroenlilc with a 95% confidence percentile.
UT Upper Tolerance
-------
I
ST48
FUEL SPILL
STJO UNOERCmUNO
STOWGC TANK
(REMOVED)
LEGEND
aow BHTCTIOM
OM»V K1ECTOS OT fUCL MOATED
COMPOUNDS Mi SHOm
BASE *EU 4J 0 100
SCALE IN FEET
STJO-BMOJ
("08)
Clociel Outwoih/Alluvium
(Well Graded Grovels/Sands) LJ
^""E:
tUneOea
joo-
MOBUONTA1. SCAU
Bootleqqer Cove Formation
(Ooy/SHl)
r- 200
- 180
- 160
- '««>
- '20
- 100
- BO
- 60
I- 40
S. HART
MMU CMC.
UAOC mow
ST20_C
ACAO ru NO.
nos-2
MIC
2-14-95
ELMENDORF .AIR FORCE BASE
ANCHORAGE. ALASKA
SOURCE AREA ST20
OPERABLE UNIT 2
FALL 1992
SUBSURFACE SOIL
FUEL ANALYTICAL RESULTS
won
05-C105-00
WBTTJE
FIGURE 5-2
5-8
-------
5.1.5 Groundwater Contamination at ST20
As part of RI activities, monitoring wells were installed and sampled to evaluate the nature and
extent of groundwater contamination and to confirm or deny the presence of free-phase petroleum product
at the ST20 source area. A network of 5 monitoring wells, installed in 1990, was supplemented with 7
additional monitoring wells installed in 1992. In addition to sampling these 12 monitoring wells, samples
were collected from 3 monitoring wells located upgradient at source area ST48. The investigation
determined that no free product is present on the water table in the vicinity of ST20. Table 5-4 summarizes
compounds detected at significant1 concentrations in the groundwater. Risk and/or hazard associated with
the maximum concentration detected is provided as a screening tool. A detailed discussion of site risks is
provided in Section 6.0.
Benzene, arsenic, beryllium, chromium, manganese, nickel, lead, thallium and vanadium were found
at elevated concentrations in die groundwater underlying the OU2 source area. The maximum
concentrations of all but benzene were detected in monitoring wells B2MW and B4MW, located hydraulically
upgradient from ST20. These monitoring wells were installed in 1992 as part of the investigation at SERA
source area ST48.
Figures 5-3 through 5-6 provide concentrations of fuel-related compounds detected at ST20.
Benzene was detected in 14 of 40 samples analyzed during the RI. Although the maximum concentration
detected was 440 ug/L at well ST20-02 in fall 1991, a concentration of 400 ug/L was detected at well ST20-
01, 200 feet upgradient, during the previous sampling event in 1990. Well ST20-01 was installed upgradient
of the ST20 source area to provide background groundwater quality data.
Analysis for other fuel-related compounds, ethylbenzene, toluene, xylene, and total petroleum
hydrocarbons (TPH) also revealed high concentrations upgradient of ST20. The maximum'concentration of
ethylbenzene, 210 ug/L, was detected in monitoring well ST20-03 in fall 1991; however, a concentration of
200 ug/L was detected in upgradient well ST20-01 in fall 1990. Toluene, xylene, and TPH were all detected
at their maximum concentrations in well ST20-01: xylene and TPH in fall 1990, and toluene in fall 1992.
5.1.6 Conclusions
Data collected over time indicates that groundwater quality has been impacted by an upgradient
source. Subsurface soil contamination was primarily isolated to the vadose zone suggesting that .
contamination was transported to this point by flowing groundwater. It appears that contamination
underlying source area ST20 is the result of releases that occurred upgradient, at source area ST48.
5.2 ST41 Tank Spill and Sludge Disposal Area
ST41, known as "four million gallon hill", was originally constructed as the "War Emergency Fuel
Storage" facility in 1942. It is situated about one-half mile east of the Knik Arm of Cook Inlet at the west
end of the Elmendorf Moraine (Figure 4-1). ST41 covers approximately 20 acres and is comprised of two
source areas. The first consists of four 1,000,000-gallon aviation gasoline underground storage tanks and
associated piping. A second is a 1-acre sludge disposal area suspected at the western edge of ST41. A site
map is provided as Figure 5-7.
No rare or endangered species were found in the ST41 area. There are also no floodplains,
archeological sites, or state preservation sites at ST41. A small, one-acre palustrine wetland is located
approximately 200 feet to the northwest of ST41 in a utility corridor (see Figure 5-7).
5-9
-------
Table 5-4
Summary of Constituents Detected in Groundwater at ST20*
Compound
Benzene
Ethyl benzene
'Toluene
Xyiene
Trichloroethene
Chloroform
Bis(2-ethyhexyl)phthalate
4-Methyl 2-Pentnanone
Nitrate
Total Petroleum Hydrocarbons
1,2-Dibromoethane
Arsenic
Barium
Beryllium
Chromium
Mercury . .
Manganese
Nickel
Lead .
thallium
Cadmium
Vanadium
^faBimimi
(vefr)
440
210
252
1000
2.0
25
180
29
220,000
44,000
0.064
180
2500
83
570
1-0
32,400
1200
600
230
9
990
*
ST2(M)2/F91
ST20-03/F91
ST20-01/F91
srawo/F9i
sraMB/Fw
ST20-04/P92
ST20-01/F91
ST20-03/F92
ST204J4/P91
ST2(M)4/P91
B3MW/F92
B2MW/F92
B4BW/S92
B4MW/S92
B4MW/S92
B2MW/F92
. B4MW/S92
B4MW/F92
B2MW/F92
B2MW/F92
SraMM/F91
B2MW/S92
l!kl I|IK IM^
14/40
15/40
12/40
20/40
3/40
10/40
9/26
1/26
19/33
20/35
7/24
24/33
23/33
2/33
15/33
1/33
33/33
20/33
29/33
1/33
2/33
17/33
RBfc/Haand?
3.0E-04
50ug/L cannot be quantified using EPA's uptake Biokenetic Model.
HI Hazard Index .
N/A No toxicity data available, therefore no risk was calculated.
.Limited to compounds of potential concern identified by following procedures consistent with EPA Region X Supplemental Risk
Assessment Guidance for Superfund (EPA,1991c)
5-10
-------
ST48
FUEL SPILL
I
ST20 UNDERGROUND
STORAGE TANK
(REMOVED)
BASE WELL 42
LEGEND
200 100 0 200
|J ^
SCALE IN FEET
400
ocitcno «LO> ocncnoN iwi
S.HART
PKOl Old
JUL
G1011038
*CM> ru Ma
PIC5-3
2-U-95
ELMENDORF AIR FORCE BASE
ANCHORAGE. ALASKA
OPERABLE UNIT 2
SOURCE AREA ST20
BTEX AND TPH
GROUNOWATER
ANALYTICAL RESULTS
FALL 1990
05-G105-00
FIGURE 5-3
5-11
-------
<>0
ft \ \& O!
ST20-04^& \\ ?
?:< ^° \\ T
it 1 . \ \ *
T20-01
iW
89
>IO
960
N
4
-ST20 UNDERGROUND
STORAGE TANK
(REMOVED)
BASE WELL 42
LEGEND
one «0sn«T
a - i
T .
c - cnnuouiM
i - IOUL nuMn
imomi. nuccim
or OMUOMIDI io»
200 100 0 200
«* L
SCALE IN FEET
S. HART
PKCU CNC.
JML
iuoc nnu
G10110JG
HG5-4
DA If
2-14-95
400
ELMENDORF AIR FORCE BASE
ANCHORAGE, ALASKA
OPERABLE UNIT 2
SOURCE AREA ST20
- BTEX AND TPH
GROUNOWATER
ANALYTICAL RESULTS
FALL f991
05-G105-00
FIGURE 5-4
5-12
-------
ST48
FUEL SPILL
ST20 UNDERGROUND
STORAGE TANK
(REMOVED)
BASE WELL 42
LEGEND
xuo «a rafti
200 100 0 200
«* L
SCALE IN FEET
4OO
PM. (XCCTOi
or aaMM>mi\o>
S. HART
ORMM IT
JML
UHX FHOM
G101103B
ELMENOORF AIR FORCE BASE
ANCHORAGE. ALASKA
OPERABLE UNIT 2
SOURCE AREA ST20
BTEX AND TPH
GROUNDWATER
ANALYTICAL RESULTS
SPRING 1992
FIGURE t-S
5-13
-------
34UW
ST20-MW-08
r - 1.5 ..
r - 1.1
X - 3.0
ST20-03
- it
ST4B
w
i
B36ME1- SPILL"
MD
ST20 UNDERGROUND
STORAGE TANK
(REMOVED)
BASE WELL 42
LEGEND
0*0 MOSHBCT
200 100 0 200
=5
SCALE IN FEET
400
UTO UCMTOmC «u
T
C - C
i - tout, nuw
TM . TOTW. Tinorui
0 NO IIKIIUII
OWCTIW
mm ao.
S. HART
PHOJltXG.
JML
G101103G
ACMI ru NO
FIG5-6
ELMENDORF AIR FORCE BASE
ANCHORAGE. ALASKA
OPERABLE UNIT 2
SOURCE AREA ST20
BTEX AND TPH
GROUNOWATER
ANALYTICAL RESULTS
' FALL 1992
Mil
2-H-95 05-G105-00
FIGURE 5-6
5-14
-------
s*
(-«
IA
POWER CABLE UTILITY CORRIDOR
PCL osraeuncN UNIS
GROUNOMHR IMP
GROUNDWATCR DIVIDE
(DASHED WHERE INFERRED)
FROM PORT OF ANCHORAGE
ELUENDORF AIR FORCE BASE
ANCHORAGE. ALASKA
.OPERABLE UNIT 2
SOURCE AREA ST41
SITE LOCATION MAP
-------
5.2.1 Geology and Hydrogeology at ST41
The geology of the ST41 area, as defined by numerous borings drilled in the vicinity, is dominated by
glacial till of the northeast-southwest trending Elmendorf moraine and the underlying Bootlegger Cove
Formation. The geologic and hydrogeologic characteristics of ST41 share little similarity to the ST20 area.
Morainal deposits at ST41 make up the upper ten to twenty feet of the subsurface soil through most
of the ST41 area. These morainal soils are composed of a heterogeneous mixture of interbedded sands, silts
and days. This lithologic assortment is typically associated with low aquifer yield, due to the fine-grained
nature of the material and subsequent limitations in lateral conductivity. A cross section through ST41,
depicting the relationship between the moraine and Bootlegger Cove soils, is provided as Figure 5-8. The
cross-sectional trace is provided on Figure 5-9. Till deposits range in thickness from zero to over twenty feet,
overlying the Bootlegger Cove Formation which is up to 60 feet thick in the vicinity of OU2. In the northern
portion of the cross section, a slightly coarser-grained interval of soil is encountered, referred to as the "cover
sand", which also overlies the Bootlegger Cove Formation. The presence of irregular, interbedded lenses of
fine-grained material in both the till and the cover sand at ST41 are responsible for the relatively low
hydraulic conductivities in this area.
Only the shallow, unconfined aquifer was encountered during the RI at ST41. A groundwater divide,
primarily the result of the topography of the Elmendorf Moraine, causes groundwater in the shallow aquifer
to flow to the northwest on the northern side of the moraine, and to the southeast on the southern side. The
groundwater flow in this area is also locally, influenced by the irregular surface of the Bootlegger Cove
Formation. The depth to the shallow groundwater varies across the site; the average depth to groundwater is
15 feet below ground surface, this groundwater level is above the bottom of the tanks. The thickness of the
saturated interval averages 13 feet. .
Groundwater emerges as surface water seeps and springs along the north and south slopes of the hill
as a result of the relatively steep topography and the fine-grained nature of the till material. Approximately
200 feet to the northwest of ST41, located within a utility corridor, is a small wetland area which
encompasses approximately one acre. No portion of this wetland is designated on the National Wetlands
Inventory map produced in 1979, and as such, this is an undelineated wetland area. The surface
manifestation of the wetland area is reportedly a result of the excavation of the man-made utility corridor.
The seeps and springs are included as contaminant treatment areas in the Elmendorf natural resource
assessment.
522 Reported Releases at ST41
One report stated that a 60,000-gallon aviation gasoline spill occurred at ST41 in the mid-1960s.
Approximately 33,000 gallons of JP-4 fuel were spilled in 1964, with 16,000 gallons reportedly recovered.
Several hundred thousand gallons of JP-4 fuel were also reported to have spilled between 1975 and 1984.
523 Early Actions at ST41 Tank Spill
An underground oil/water separator was installed in the hill directly north of Loop Road and south
of the tanks in 1976. This piece of equipment was intended to collect free phase product and water before it
seeped out of the hill and into the roadside drainage ditch.
In 1989, a small dam was constructed in the drainage ditch along the north side of Loop Road to
prevent migration of fuel product and contaminated seep water off the site.
Tests performed late in 1990 indicated that piping used to distribute fuel to and from the tanks was
5-16
-------
Q
L£C£M2
OAOS
BUUIWIC
280'
2601
§ 240' -|
3
| "o- H
180- 1
160'
140'
120' -
GROUND SURFACE
IRA EXTRACTION
WELL EW-2
-FLOATING FUEL
PRODUCT
C'
ST41-BH-05
LOOP ROAD-^ SEEP AHEA
IRA EXTRACTION
TRENCH ET-J
SEEP AREA
UOMTOIhNG 1CLL
MRCHOLC
IICVADON
M rCCI ABOVt
WAN HA LE«l
r 280"
260'
h 240'
2201
200' '
160-
SYMBOLS
IOIAI ocpm IN rui or
MOMIOAHC WU. OR BOREHOLE
CZO.OOC CONIACt
OA9CO «H(RC urtesto
CRAWFORD
""WtflllO
FIC5-8.
"?6/ia/93
ELUENDORF AIR FORCE BASE
ANCHORAGE. ALASKA
OPERABLE UNIT 2
CROSS SECTIONAL VIEW
THROUGH TANK 603
05-0105-00
5-8
-------
leaking. The piping and tanks were drained of fuel and taken out of service in early 1991. The piping and
tanks associated with ST41 are depicted on Figure 5-7.
In 1992, the Air Force implemented an Interim Remedial Action (IRA) to remove free product
floating on the groundwater, and to intercept contaminated water prior to being discharged from seeps on
both the north and south sides of the source area. This action was supported by both EPA and ADEC and
documented in an Interim ROD signed in September of 1992. The Interim ROD was subject to a public
rr.Tnmp.nf period and a public meeting was held to address community questions and concerns regarding the
proposed system. These comments and the resulting responses are documented in a responsiveness summary
attached to the Interim ROD, which is part of the Administrative Record for this site.
As previously stated, the purpose of the IRA is to remove floating free product and to intercept and
treat contaminated water flowing from surface water seeps. Figure 5-9 presents the layout of the system.
There is one extraction well which is used for product recovery on the north side of the site. Another well is
located on the south side of the site and on the top of the bill directly north of Loop Road. This well
intercepts a surface water seep. There are three extraction trenches which were constructed to intercept
surface water seeps. One trench is located on the north side of the hill, and intercepts groundwater which
was flowing into seeps leaching to the wetland area. Two extraction trenches were constructed at the south
side of the site to mitigate seeps which were visually offensive.
Figure 5-10 presents a general flow diagram of the IRA. The fuel/water mixture enters the system
(located in Building 31-600) and flows into a gravity driven oil/water separator. Free product is recovered
and transferred to a holding tank for recycling. Contaminated water flows into an air stripper which uses
forced air to volatize or evaporate contaminants into the air. Treated water is transferred into holding tanks,
tested, and discharged into base sewer system or re-treated. Air discharge from the system is treated by a
carbon filter and then discharged.
Construction of the IRA was completed in late October 1993. A two-month operation period was
performed to ensure all equipment was operating properly. The system was shut down and winterized in late
December 1993. During this initial start-up period approximately 70 gallons of product were recovered, and
65,000 gallons of water was processed. IRA operation was restarted on 16 May 1994. As of November 1994,
approximately 145 gallons of product has been recovered and a total of 141,800 gallons of contaminated
water has been treated. The volume of product recovered has been less than anticipated: This low recovery
rate is due to the fine-grained nature of the subsurface soils. .
During construction of the IRA, a substantial volume of soil was removed during the excavation of
the trenches and installation of recovery wells. Much of the soil removed was contaminated with fuel
constituents. The fuel contamination is believed to be associated with former line leaks at the site.
Approximately five hundred yards of soil was removed. Of that total, 350 yards of contaminated soil was
transported to the base biopile for treatment.
A study aimed at evaluating and improving the efficiency of the IRA system is currently underway.
The efficiency study will include a component specific evaluation. System modification may include rlianging
pump types, pumping rates, or discontinuing one or more of the five extraction components. Prior to
modification, recommendations will be presented in an OU2 Treatability Study Report, to be reviewed and
approved by all parties. Depending upon the scope of the modifications required, an Explanation of
Significant Differences (ESD) or an amendment to the ROD will be necessary'
5.2.4 Surface Soil/Sediment Contamination at ST41 Tank Spill
The nature and extent of surface soil and sediment contamination was determined by sampling
surface soil at three locations, and sediment at eleven locations. Analytical results for'fuel related
5-18
-------
IRA TREATMENT SYSTEM x
X
X
GEOPHYSICS
GRID AREA
UNDERGROUND
P0\ o
ARE
CROSS-SECTION UNE
FOR HGURE 5-8
GROUNDWATER DIVIDE
(DASHED WHERE INFERRED)
ET-1 AEW-1
EXTRACTION WELL LOCATION
INTERCEPTOR TRENCH LOCATION
CROUNDWATER SEEP
41 -oT] *ELLS \«HERE FREE PRODUCT
' HAS SEEN HISTORICALLr DETECTED
SCALE IN FEET
Figure 5-9. Source Area ST41 IRA Extraction Well and Interceptor
Trench Locations, Elmendorf AFB, Alaska
5-19
-------
t) Contaminated groundwoter li e>trocted by
containment trenches end wellt.
2) Contaminated fuel and water miiituro la
seperoled In an all/water separator. Fuel l<
o
-1
£JME
(SUBMERSIBLE)
amp.
(SUBMERSIBLE)
&TRACI10H *"' '' nmurnof) wni l» ^~.
\
f
, IRKHQ
/M SUBHE
i_J
NORTH HTtRCEPT.OR. TKPfCH
\_
f
(V
1 PUMP
A| 1 THEHCH PUMP -
/V I SUBMERSIBLE
SOOTH IhTtRCEPTOR TRENCH il
j~« ^
olr stripper (J). trays.
from th
VENDOR PACKAGE
v=J CRAvrrr aow
"1,
\ 1
\
-a
5LUOOC
PUMP
M
RECOVERfJ
I
?-
D FUEL
PRODUCT PUMP
H >
VENDOR PACKAGE
1 >
TSO FACIUTY JAMJ TO TSD FACILITY
J) Contaminated water If distributed uniformly over a
' series of perforated talnteit eteel troye. The voter
droplets ore expoeed to olr forced upward through the
Thl» process elrlpe the volatile organic compound!
TO ATUOSPHERC
aaoKB
5) Vapors from the olr
itrlpper are filtered
through activated carbon
hire the volatile
organic compound* ore
adsorbed to the carbon
and treated emissions
are discharged to the
atmosphere In accordance
with all air permit
requirement*.
Z>0
THENCH PUMP
suaufHSiait
TO STORAGE
4) The treated water li discharged Into holding tanks
for testing. Following letting, the treated water le
hauled* and discharged Into the wastewoter sewer In
compliance with the Elmendorf wostewater discharge
permit.
SOtfTH MTtBCEPTOR TRENCH I?
NOTES:
ORMO - DEFENSE REUTIUZATION AND
UAHKETINC OFFICE
Figure 5-10. Source Area ST41 Interim Remedial Action
Process Flow Diagram, Elmendorf AFB, Alaska
-------
ST41-SE-05
O.H - caoas
- «.«
A
ST41-SC-06
- muor
xST41
AV-ST41
m ".on
ST41-8H-11
0.001 - rotuof (to)
ROAO «M> S1RCC1
8ULDWC
ST41-BH-10
ST41-UW38
BORtHOll COUPtinO *3
UCMIORINC Mil.
I. ItC POSTED VALUES ARE
SAIUUS COUCCIEO ABOVC THC
WA1CR IABU.
2. 0.001 - rouxHC in)
CONCCNIRADON KPIH
mg/Vg II.
J - PRE5CN1 8IUM CCTCCKON LWII
C - CMXCOCO CAUBHAIWN RANK
ST41-SE-OI
- ana
n - ana
irj - oaaaf
- fimuounr
aaM - ratunr
r - num
ST41-MW37A- cr>
ELUENOORF AIR FORCE BASE
ANCHORAGE. ALASKA
SOURCE AREA ST41
SURFACE SOL. SUBSURFACE
SOL. AND SEOIUENI
BTEX 'AND FUEL
ANALYTICAL RESULTS. FALL 1992
-------
compounds detected during this effort are presented on Figure 5-11. Sample locations are identified by the
prefix "SS" for surface soils, "SE* for sediments, and "SB" for subsurface soils.
Three constituents were identified in surface soils at ST41 at concentrations of potential concern:
arsenic, diesel, and gasoline. Arsenic was detected at a maximum concentration of 16.1 mg/kg; gasoline at
2,000 mg/kg, and diesel at 3,600 mg/kg (Table 5-5). All of these maximum concentrations were detected at
surface soil sampling location ST41-SS-03 in fall 1992.
Nine constituents were identified in sediment at ST41 at concentrations of potential concern; these
compounds are presented in Table 5-5. Three of these were found to occur at significantly elevated levels;
lead, diesel, and gasoline. The maximum concentration of lead was detected at 118 mg/kg; diesel at 71,000
mg/kg; and gasoline at 1,800 mg/kg. Each of these concentrations occurred at location ST41-SE-09 in fall
1992.
5.2.5 Subsurface Soil Contamination at ST41 Tank Spill
Subsurface soil samples were collected to determine the nature and extent of subsurface soil
contamination. These samples were collected from a network of soil borings drilled and sampled in 1992.
Some of these borings were completed as monitoring wells to complement the existing'network of
monitoring wells. Five constituents with significant concentrations were identified for subsurface soils at
ST41: pentachlorophenol, diesel, gasoline, mercury, and lead (Table 5-5).
Lead was detected at a maximum concentration of 363 mg/kg at location ST41-BH03-17 in fall 1992
(this corresponds to borehole number ST41-BH03 at a depth of 17 feet). Diesel and gasoline were detected
at their maximum concentrations of 33 mg/kg and 170 mg/kg, respectively at location ST41-SB07-2Q in fall
1992. This soil sample was collected below the water table. Analytical results for fuel-related compounds
during the 1992 effort are presented in Figure 5-11.
The RI effort did not investigate the presence of contamination in the upper 10 feet of soil with the
exception of surface soil sampling. Results from Tracer Testing performed in late 1990 indicated that the
major source of contamination was leaking joints and couplings in piping associated with the fuel storage
tanks. Although, subsurface soil contamination is present at ST41, indications are that the contamination is
limited to the areas where piping leaks may have occurred (see Figure 5-7). Since the groundwater table is
above the bottom of the tanks, and the tanks have not leaked, residual soil contamination is not expected to
exist below the tanks.
Contamination in a smear zone, the result of seasonal fluctuations b the groundwater table, is
apparent at ST41-16. At this location, seasonal occurrence of free product suggests that during periods of
seasonal water table depression, the floating product phase adheres to the soil matrix as residual soil
contamination. Due to the shallow depth to groundwater, and the close relationship between soil and
groundwater contamination, disturbance of contaminated soil around piping during a removal action may
cause a temporary increase or decrease in dissolved phase concentrations in groundwater, as steady state
conditions are re-established.
5.2.6 Groundwater Contamination at ST41 Tank Spill
The nature and extent of groundwater contamination at ST41 was investigated by installing a
network of monitoring wells and collecting samples for ground water quality analyses. As previously
discussed, a groundwater divide transects the area and groundwater flows to the north and the south across
the ST41 site. Of the 32 monitoring wells at the source area, four have a history of free-phase petroleum
product floating on the water table, ST41-07, ST41-16, ST41-19, and ST41-28. As expected, groundwater
5-22
-------
Table 5-5
Summary of Constituents Detected in Surface Soil
and Surface Sediment at ST41*
Compound
Maximum
Concentration
(mg/kg)
Location1
Surface Soil
Arsenic3
Diesel3
Gasoline3
16.1
3,600
2,000
ST41-SO-03/F92
ST41-SO-03/F92
ST41-SO-03/F92
Frequency
Background2
(mg/kg)
3/3
1/2
2/2
16.18
N/A
N/A
Subsurface Soil
Mercury3
Lead3
Pentachlorophenol
Diesel3
Gasoline3
1.0
363
0.57
33.0
170.0
ST41-BH01-35/F92
ST41-BH03-17/F92
ST41-BH01-35-FR/P92
ST41-BH07-20(BWT)/F92
ST41-BH07-20(BWT)/F92
30/73
30/73
4/65
20/62
.3/62
0.20
10.0
N/A
N/A
N/A
Surface Sediment
2-Methylnaphthalene
Benzo(a)anthracene
Chrysene
Benzo(b)fluoranthene
Benzp(k)fluoranthene
Benzo(a)pyrene
Diesel3
Gasoline3
Lead3
56.0
024
0.25
0.19
0.19
0.21
71,000
1,800
118
ST41-SE-09/F92
ST41-SE-01/F92
ST41-SE-01/F92
ST41-SE-01/F92
ST41-SE-01/F92
ST41-SE-01/F92
ST41-SE-09/P92
ST41-SE-09/F92
ST41-SE-09/F92
5/11
1/11
1/H
1/11
1/11
3/11
6/11
5/11
11/11
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
133
1 Sampling location identifiers include boring number followed by depth and whether it was above the water table or below. The
sampling events are also included (Le., Fall 1992 = F92). Information derived from OU2 RI/FS Report (US. Air Force, 1994).
2 Background concentrations are 99% upper tolerance limits for deep zones, see Table 5-3 of this report (U.S. Air Force, 1993).
3 Constituents identified as Contaminants of Concern (COCs) as outlined in the OU2 RI/FS Report (U.S. Air Force, 1994).
N/A Not applicable
* Limited to compounds of potential concern identified by following procedures consistent with EPA Region X Supplemental Risk
Assessment Guidance for Superfund (EPA,1991c)
5-23
-------
Table 5-6
Summary of Constituents Detected in Groundwater at ST41*
Compound
Maximum
Concentration
te/L)
Areas Without Five Product
1,1,2,2-Teirachloroethane
Benzene1
Ethylbenzene1
Toluene1
Total Xylenes1
2-Methylnaphthalene
4-Methylphenol
Naphalene
Bis(2-elhlhotyl)ph(halatc'
Chloroform
Total Petroleum Hydrocarbons
Nitrate
Antimony
Arsenic'
Beryllium1
Cadmium
Lead
Manganese1
Nickel
0.8
1,100
3,800
960
4,200
13
6
23
29
3.0
9,400
90,400
20
76
4.0
9.0
65
29,100
440
LooUoo2
ftrcquency
Wrt/Hwanl3
ST41-W8/F91
ST41-W7/P91
ST41-19/F92
ST41-07/F91
ST41-19/F92
ST41-19/F91
ST41-19/F91
ST41-19/F92
ST41-22/F92
ST41-MW37B/FW
ST41-25/F92
ST41-10/P92
ST41-02/F91
ST41-22/S92
ST4MO/FV1
ST41-04/P91
ST41-W8/S92
ST41 -25/592
ST41-W8/S92
3/93
18/94
23/94
16/94
22/94
4/89
3/89
6/89
17/89
2/93
30/93
30/93
1/93
46/93
3/93
10/93
84/93
. 93/93
55/93
iSxlO'06
7.4X10'04
3.1 HI
<1H1
1.2 HI
N/A
N/A
<1.0HI
4.2X10-06
2JxlO-06
N/A
1.6 HI
<1.0 HI
1.6X10'03
6.9 HI
2AtlO'M
<1.0 HI
173.0 HI
<1.0 HI
-------
Table 5-6
(continued)
CnoinouDd
: :i- !' '- ' '
Vanadium
Chromium " .
Barium
Thallium1
Melhlene chloride
Trichlorofluoromethane
Ethylene dibromide
Area* Wilb A History of Free Product
Benzene
Ethylbenzene
Toluene
Total xylenes
Bis(2-ehtylhexyl)phthalate
Maxinunxi
'.:'; Coooealntion
' i 0**<)
660
350
1900
180
3,800
2.0
180
30,000
4,700
20,000
26,000
150,000
Location2
ST41-W8/S92
ST41-W8/592
ST4MO/F91
ST41-16/F92
ST41-W7/S92
ST41-18/S92
ST41-35/S92
ST4M6/S92
ST41-16/F92
ST41-16/F92
ST41-16/S92
ST41-28/F91
Frequency
44/93
52/93
77/93
1/93
14/93
3/93
8/53
All
All
All
All
All
Rak/HazanJ3
3.3 HI
2.2 HI
<1.0 HI
61.6 HI
N/A
N/A
N/A
2.0xlO'02
5.0 HI
13.6 HI
5.9 HI
2.6xlO'02
fc!
1 Constituents identified as Contaminants of Concern (COCs) as outlined in the OU2 RI/FS (U.S. Air Force, 1994).
2 Location is monitoring well number followed by the sampling event, (i.e. Fall 1991 = F91)
3 Risk/Hazard associated with residential scenario using exposure parameters provided in Table -6-2 of this document.
HI-Hazard Index
N/A- No toxicity data available, therefore no risk was calculated.
* Limited to compounds of potential concern identified by following procedures consistent with EPA Region X Supplement Risk Assessment Guidance for Superfund (EPA, 1991c).
-------
quality monitoring has revealed the highest levels of fuel-related compounds at these 4 wells. Table 5-6
presents a summary of the significant constituents identified in the groundwater at ST41. For fuel related
compounds, the maximum concentrations at ST41 were consistently detected in free product areas.
Maximum results for these constituents are provided for both areas without free product, and areas with a
history of free product (Table 5-6).
The highest levels of fuel-related compounds, not associated with free product areas, we're found b
wells ST41-W7 and ST41-2S. Figures 5-12 through 5-15 present maximum concentrations of fuel-related
apounds detected, by well, over the four different sampling events.
The evaluation of metals in groundwater at ST41 included a statistical comparison of results to
background data, and a comparison between total and dissolved metals results. Both total and dissolved
analytical results for arsenic and lead were found to be at levels statistically indistinguishable from
groundwater data collected by the USGS in the Anchorage Bowl area used as background data for ST41
(U.S. Air Force, 1994). Arsenic and lead have traditionally been detected at elevated levels throughout the
base, in both contaminated and uncontaminated areas. Total metals concentrations in groundwater were
consistently higher than dissolved metals results. This is likely the result of instrument detection of inorganic
constituents adsorbed onto paniculate matter in the groundwater. The dissolved analyses are run on less
turbid, filtered samples, which are more representative of water used for consumption in the Anchorage
Bowl area. In addition, there were no identifiable base activities which would result in a source of elevated
concentrations of arsenic or manganese.
Elevated concentrations of arsenic, lead, and manganese were consistently detected in the total
recoverable metals samples taken at ST41. Arsenic was detected in a total metals sample from monitoring
well ST41-16 at a maximum concentration of 180 ug/L in fall 1992. Lead, was detected in a total metals
sample from monitoring well ST41-27 at a maximum concentration of 56 ug/L in fall 1992. Thallium was
also detected at an elevated level of 180 ug/L; however, it was detected only twice out of 122 samples.
Manganese was detected in every sample. The maximum concentration, 29,100 ug/L, occurred in
well ST41-25 in spring 1992. Manganese, like arsenic, has traditionally been detected at elevated levels in
other contaminated and uncontaminated areas of the base. At ST41, elevated levels of manganese appear to
coincide with areas where high organics are present. Manganese commonly plays the role as electron
acceptor during natural breakdown processes associated with organic compounds, specifically hydrocarbon
chains associated with petroleum products. High concentrations of manganese may be an indicator that
natural attenuation is taking place at ST41. The Air Force conducted a study in June 1994 to investigate the
efficiency of natural attenuation in degrading fuel contamination at ST41. The results of this study showed
that conditions for natural attenuation are present based on geochemical evidence and modeling results.
Specifically, this investigation suggests that natural attenuation was occurring at ST41 based on the following:
The correlation between areas with depleted oxygen, sulfate, and nitrate/nitrite with areas
of elevated BTEX;
The correlation between areas with elevated ferrous iron and methane with areas of
elevated BTEX; and
The correlation between areas with a low reduction/oxidation potential with areas of
elevated BTEX.
The study concluded that the groundwater at ST41 is capable of assimilating BTEX concentrations in excess
of 30,000«g/L.
Groundwater quality in the deeper aquifer is protected by the presence of a competent aquitard, the
5-26
-------
CONCCNIRAT10N ABOVE RSC/AKAH
CONCCNIDAnOH BUO« R9C/AHAR
e - auaoa.
- IO.UCMC
c -
> - KVUNC
IPH . I01A1 PCntCUUU HYOROOSBOXS
GROUNDWATER OMOE
(DASHED WHERE INFERRED)
CONCXNIIUnCNS w wgA
eus MIS rau PROOUC'
Z.' _' iJ MAS BUN MStMCAiir ocnctco
ELMENOORF AIR FORCE BASE
ANCHORAGE, ALASKA
OPERABLE UNIT 2
SOURCE AREA ST41
BTEX AND TPH
FALL 1990
-------
ST4I-W7°
t - MO
T - IS
MOMTORMGIKU
CONCENTRATION AMVC HOC/MM
CONCENTRATION etiow aac/utat
CKOUNDWATEK DIVIDE
(DASHED WHERE INFERRED)
a ' BOUCNC
i - taut*
c
« - nuxt
IPH . TOM. Pcmauiw
CQNCtNTRAIXMS M «A
gT4jIjg] WUS WCK FRU PMOUCt
HAS KCH HS10MCAU.Y OC1TCTCD
ST4I-W-B
im - too
ELUENOORF AIR FORCE BASE
ANCHORAGE. ALASKA
OPERABLE UNIT 2
SOURCE AREA ST41
BTEX AND TPH
FALL 1991
-------
j':'<5lu\. /*
I - 100 X. /
»-» ^vj d
mu t IAM V/
UONIKMING icu
CONUNIRAnON ABOVC RaC/M)Afl
CONCCNIRAnaH BCUW R9C/AHM
xST41-07] /ST4I_,8
'r-'n /
c - 4i J
t - HO O
GROUNOWATER OMDE
(DASHED WHERE INFERRED)
im - IOIAI Ptmaxuu HIWOCXIOONS
eiK CONCCNIRATIONS M
0ST4I-2S o
U.« - UO °CIil w B
O ' - n SI4I-W-8
ST41-21
ELMENOORf AIR rORCE BASE
ANCHORAGE. ALASKA
OPERABLE UNIT 2
SOURCE AREA ST41
BTEX AND TPH
SPRING 1992
-------
ST41-08
im - 1.100
VOMTOIMG KU.
CONCCNlRAnoN MOX R8C/ARAR
CONCtlimAlKM 8tlO» IOC/AHA*
1 - TOIUCNC
C - tTHYlKNICW
- unite
IPH - IOIM. PtlHOUUU MHBBOCAS90NJ
GROUNOWATER DIVIDE
Gnu coMCCHmAnoxs w
rsf4i~ial w
Lr'_'_ ?J HA
S OCCN MStOKICAUT OCIICTCO
: am ooNcuimAnaNs inno ran
WU.S ST41-11 AM) Jt4l-y»M AM FOR
ix WAV
CLMENDORF AIR FORCE BASE
ANCHORAGE. ALASKA
OPERABLE UNIT 2
SOURCE AREA ST41
BTEX AND TPH
FALL 1992
-------
Bootlegger Cove formation, therefore groundwater quality in the deeper aquifer has not been monitored at
ST41. The potential for possible hydrologic communication between the shallow and deep aquifers has been
investigated as part of several previous investigations at different locations on base. A pumping test was
conducted in 1992 at ST20 to determine if the shallow aquifer was impacted by high volume pumping of the
deep aquifer. The results of these tests indicated that the Bootlegger Cove, formation provides protection of
the deep aquifer.
The potential for migration of contaminants in groundwater at ST41 was estimated using several
factors including groundwater flow, retardation, and degradation. Because of the groundwater divide that
transects the site, separate groundwater flow rates were calculated for each side of the divide. Slug test and
porosity data indicate that the travel time required for groundwater to flow a distance of 750 feet to the
northwest across ST41 would be on the order of 40 years. To flow the same distance to the southwest would
require about 35 years. These low flow rates contribute to the effectiveness of naturally attenuating
processes for contaminant reduction at the site.
52.7 Surface Water Contamination at ST41 Tank Spill
Surface water at ST41 was sampled at a location on the north side of the site in 1990 and 1991.
During RI activities in 1992, ten additional surface water sampling locations were selected based on an
ecological survey. Table 5-7 presents a summary of the significant constituents identified for surface water at
ST41.
Organic compounds chosen with elevated concentrations include benzene, ethylbenzene, toluene,
total xylenes, diesels, gasoline, and 1^-Dichloroethane. Inorganic constituents with elevated concentrations
include arsenic, lead, manganese, and thallium
The maximum recorded concentrations of benzene, toluene, ethylbenzene, total xylenes, and 1,2-
dichloroethane were each detected at sampling location ST41-SW-02. Diesel, gasoline, arsenic, and lead
maxima were detected at sampling location ST41-SW-09. Manganese and thallium maxima were detected at
sampling locations ST41-SW-10 and ST41-SW-04, respectively.
The IRA was designed in part to mitigate the seeps where these contaminants were detected.
Extraction trenches were installed to intercept groundwater seeps. The IRA will continue to operate as
necessary to prevent adverse impact to the environment at ST41. It is possible that contaminated
groundwater may also impact downgradient surface water at ST41, since there is close interaction between
the groundwater, seeps, and wetland (surface water) areas. However, since groundwater samples from wells
located between the areas of contaminated groundwater and the wetlands have not shown elevated levels of
contamination, it is apparent that groundwater contamination is not currently impacting these sensitive areas.
S2& ST41 Sludge Disposal Area
Site ST41 also consists of a suspected one-acre tank sludge disposal area located adjacent to the
storage tanks. A map dated 1953 suggested this area was used for sludge disposal. The base conducted a
historical record search and a field investigation consisting of geophysical surveys and subsurface soil
sampling to determine the presence or absence of disposed sludge. The investigation did not find any
evidence of actual sludge disposal at ST41 and no contamination was found; therefore, a no further action
determination was made, and the ST41 sludge disposal area is not included in the following sections of this
Record of Decision. .
5-31
-------
Table 5-7
Summary of Constituents Detected in Surface Water at ST41*
Compound .
Benzene2
Toluene2
Ethylbenzene2
Total Xylenes2
1,2-Dichloroethane
Arsenic^
Manganese2
Lead
Thallium2
Diesel2
Gasoline2
JMEiQDlfiQltt
Concentration
**8/L)
1,500
380
4,200
2,900
33
63
9,700
41
440
12,000,000
59,000,000
Location1
ST41-SW-03/S93
ST41-SW-03/S93
ST41-SW-03/S93
ST41-SW-03/S93
ST41-SW-05/S93
ST41-SW-09/F92
ST41-SW-10/F92
ST41-SW-09/F92
ST4-SW-04/F92
ST4-SW-09/F92
ST41-SW-09/F92
Frequency '
4/11
5/11
4/11
5/11
2/11
3/11
11/11
4/11
1/11
3/11
3/11
1 Location is sample number followed by the sampling event, (Le., Fall 1991 = F91). Information derived bom OU2 RJ/FS Report
(VS. Air Force, 1994). .
2 Constituents identified is Contaminants of Concern (COCs) as outlined in the OU 2 RI/FS Report (VS. Air Force, 1994).
* Limited to compounds of potential concern identified by following procedures consistent with EPA Region X Supplemental Risk
Assessment Guidance for Superfund (EPA,1991c)
5-32
-------
523 Conclusions
Soil contamination appears to be associated with leaking valves and fittings around piping at ST41.
A seasonal smear zone of contamination has been identified in the southern portion of ST41, and a free
phase occurrence of floating product is present on the water table in the northern portion of the site. High
concentrations of fuel-related groundwater contamination, limited to the surficial aquifer and within
approximately 500 feet of the former fuel storage tanks, are generally associated with areas where free phase
petroleum product is floating on the water table. Several hundred feet separate the wetland area from areas
with historical free product.
Migration of contaminants in the groundwater at ST41 is expected to be substantially retarded by the
fine-grained nature of the subsurface soils, and the resultant low groundwater velocity. The low hydraulic
conductivity associated with the aquifer in this vicinity contributed to difficulties in well development during
the field season due to poor aquifer yield. The fine-grained nature of the soils, coupled with a lack of
subsurface homogeneity, is likely the result of the poor recovery of free phase product by the IRA system to
date. This is due to slow product recharge at the extraction points, and a reduced radius of recovery
influence, and results in a high water to product recovery ratio. However, the interbedded clays and silts in
the soils at ST41 will act to retard vertical, dissolved-phase contaminant migration.
Surface water seeps which have previously indicated contamination have been mitigated by the
trench collection system installed as part of the IRA. The substantial quantity of contaminated soil removed
during the construction of the IRA should also reduce the potential for continued seep contamination, due to
elimination of the soil as a continuing source. Operation of the IRA system is included as part of the final
remedy outlined in this ROD. The system will continue to operate until it is both no longer technically
practicable to recover free product and discontinuation will not result in adverse impact to the wetlands.
Operation should continue until such time that it can be determined that long-term monitoring for natural
attenuation of the contamination indicates that continued operation of the IRA is not necessary to prevent
degradation of the environment. As stated above, it is possible that contaminated groundwater may also
impact downgradient surface water at ST41, due to the dose interaction between these hydraulic systems.
However, since groundwater samples from wells located between the areas of contaminated groundwater and
the wetlands have not shown elevated levels of contamination, it is apparent that groundwater contamination
is not currently impacting the wetlands.
While the floating product at ST41 represents a continuing source for future groundwater
contamination, the occurrence of product was accounted for in the natural attenuation study. This study
concluded that natural attenuation of all contamination at ST41, including that contributed by the free phase
product, should occur successfully. .
5-33
-------
(This page intentionally left blank.]
-------
6.0 SUMMARY OF SITE RISKS
This chapter summarizes the Baseline Risk Assessment for OU2, which forms the basis for taking
remedial action and. indicates exposure pathways that need to be addressed through remedial action. It
indicates what risks could exist if no action were taken at a source area, and includes a discussion of both
human health and ecological risks.
6.1 Human Health Risk
A human health risk assessment begins with the identification of COCs (contaminants of concern) at
the site. The next step is the identification of exposure pathways for those chemicals to human receptors in
an exposure assessment. To estimate the risk to receptors, measures of the toxicity of the COC as delivered
by the particular exposure pathways are combined mathematically with conservative estimates of the
concentrations of the COCs. With this is factored a specific duration of exposure, as determined in the
toxicity assessment. Characterization of risk follows these general steps. The following general EPA
guidance was used to conduct the risk assessment:
Risk Assessment Guidance for Superfund Volume 1 - Human Health Evaluation Manual
(Part A) Interim Final (EPA, 1989);
Risk Assessment Guidance for Superfund (RAGS) Volume 1 - Human Health Evaluation
Manual (Part B, Development of Risk-based Preliminary Remediation Goals), Interim,
Office of Solid Waste Emergency Response (EPA, 1991a);
Risk Assessment Guidance for Superfund (RAGS) Volume 1 - Human Health Evaluation
manual. Supplemental Guidance: Standard Default Exposure Factors (SDEF), Interim
Final (EPA, 1991b);
EPA Region X, Supplemental Risk Assessment Guidance for Superfund (EPA, 1991c); and
Guidance for Data Useability hi Risk Assessment (Part A) Final EPA Publication No.
9285.7-09A (EPA, 1992a).
6JIJ. Identification of Contaminants of Concern
The contaminants of concern for OU2 were identified using the screening method suggested in the
supplemental guidance for Superfund Risk Assessments in EPA Region X (EPA, 1991c). This method,
called the "risk-based screening approach", compares the highest concentrations of each chemical detected at
a site to a risk-based screening concentration. Screening concentrations were chosen, using a residential
scenario, for the ingestion of soils and sediments, and for the ingestion of water and inhalation of its vapors
during showering. Possible COCs were -identified based on the results from the analysis of soil, surface
water and groundwater samples at OU2. .
A chemical was eliminated if the maximum concentration resulted in a cancer risk less than l.OE-06
(one in a million) in water, and l.OE-07 in soil (the threshold was lowered ten-fold to take into account the
multiple exposure pathways for soil-borne contaminants). For non-cancer risks, a chemical was eliminated in
soil or groundwater if the maximum concentration resulted in a hazard quotient (HQ) of 0.1 or less. The
HQ is the sum of all ratios of. the concentration in the medium, to the highest concentration estimated not to
cause a noticeable effect with chronic exposure, summed across all pathways for the chemical Chemicals
were also eliminated.if their presence could not be attributed to the source of contamination. 'COCs specific
6-1
-------
lo ST20 and ST41 are described in subsequent sections below.
(J 2 Risk Characterization
The human health risk evaluation used both the exposure concentrations and the toricity data to
determine a Hazard Index (HI) for potential noncarcinogenic effects and a cancer risk probability for
potential carcinogenic contaminants. In general, an HI of less than or equal to 1 indicates that even the
most sensitive individual is not likely to experience adverse health effects. The cancer risk level is the
additional chance that an exposed individual will develop cancer over the course of a lifetime. It is expressed
a& a probability such as l.OE-06 (one in one million). According to the National Contingency Plan, the EPA
target risk range for excess lifetime cancer risk for a Superfund site is between l.OE-04 and l.OE-06.
The human health risk assessment performed at OU2 is based on two hypothetical exposure
scenarios: a future residential land use scenario and a future commercial/industrial land use scenario. EPA
Region X guidance requires risk under the conditions of exposure of residential land use to be evaluated
even if residential development is unlikely. It should be noted that direct contact with groundwater
underlying and immediately downgradient from ST20 and ST41, which is a required element in the future
land use scenario, is highly unlikely to occur. Chronic exposures to contaminated media are not currently
occurring at OU2. The risk assessment'was performed for exposure to groundwater at both ST20 and ST41.
Exposure to the contaminated soil identified at ST41 is unlikely due to the depth to contamination (greater
than ten feet). There is no surface water at ST20, and significant surface soil contamination was not
detected. Exposure to contaminated surface water, sediment and surface soil at ST41 was not considered.
The IRA eliminated the completed pathway for surface water exposure. In addition, the current and future
land use, and the fact that the contamination detected in sediment and surface- soil was located on a steep
embankment, make exposure highly unlikely. . ...
Future exposures at ST41 are likely to be equivalent to current exposures because there are no plans
for further developing the area, which is zoned for undeveloped recreational use. However, to evaluate the
possibility that any future development may result in unacceptable risk or hazard as a result of contaminants
present in groundwater, it was assumed in the risk assessment that contact with groundwater will occur under
the conditions of exposure of residential use, as required by EPA Region X. This is a conservative
assumption because residential use of this area is highly unlikely due to the site physiography and geology.
At ST41, contaminated surface water and sediment locations are on a steep embankment directly
north of Loop Road. Substantial amounts of contaminated sediment and soil were removed during the
construction of the IRA, and since the area sustains only infrequent recreational use, contact with
contaminated surface water, sediment or surface soil is extremely unlikely and would be limited to dermal
exposure. The aquifer at ST41 is also of sufficiently poor quality (low yield) that it would not likely support
a residential well. Furthermore, restrictions applied as part of the remedy at OU2 would not allow the
contaminated aquifer to be used to supply groundwater for use at the base.
Risk as a result of exposure to contaminants in groundwater underlying ST41 and ST20 are also
quantified assuming commercial/industrial land use. Contact with groundwater under the conditions of
exposure of a commercial/ industrial scenario are equally unlikely because the contaminated aquifer is not
allowed to be used to supply groundwater for either residential or commercial/industrial use (Elmendorf
AFB Policy, 1994). Furthermore, based upon the poor yield of the aquifer at ST41, it is unrealistic to expect
it would be suitable for recreational or commercial use. It was assumed only to provide a comparison with
risks and hazards estimated under the conditions of exposure of a residential land-use scenario. The
exposure pathways evaluated for each exposure scenario are listed in Table 6-1. Risks were calculated using
exposure point concentrations equal to the highest concentrations detected. Exposure parameters are
provided in Tables 6-2 and 6-3.
6-2
-------
Table 6-1
Summary of Exposure Scenarios Evaluated for OU2
Scenario
Future Residential
Future Commercial/
Industrial
Description
-''''" *'::V:" ;'.:'>".
Individual resides in the source
area as it now exists; use of
groundwater from the under-
lying aquifer for domestic
purposes.
Individual works in area;
occasionally uses groundwater
from the underlying aquifer
for consumption only.
Matrix
Groundwater
Groundwater
Pathways
Ingestion inhalation
dermal contact.
Ingestion
Exposure
Concentrations
Analytical groundwater
data from monitoring
wells.
Analytical groundwater
data from monitoring
wells.
-------
Table 6-2
Exposure Parameters Used in OU2 Risk Assessment
Ingectiooof Cbemkafcin
rouDowaicr:
Ingestion rate (L/day)
Exposure frequency (days/yrs)
Exposure duration (yrs)
Body weight (kg)
Averaging time (days)
Noncarcinogens
Carcinogens
Inhalation of Chemie*lt ifl GltmAdinA
Maximum chemical concentration in
air
Inhalation rate (L/hr)
Exposure frequency (days/yr)
Exposure duration (yrs)
Exposure time (his/day)
Showering time (his)
Fraction volatilized (unities:)
Flow rate (L/hr)
Volume air (L)
Body weight (kg)
Averaging time (days)
Noncarcinogens
Carcinogen
tafentURMB
2
350
30
70
10950
25550
_-,_...
Average
1.4
275
9
70
3285
25550
cfWb3e Showering:
Site/Chemical-Specific
600
350
30
0.24
0.08
0.75
1800
9800
70
10950
25550
Site/Chemical-Specific
600
275
9
0.24
0.08
0.75
1800
9800
70
3285
25550
Commeitxil/
tatatrrtRMB
1.0
250
25
70
9125
25550
-
Dermal Absorption of Chemicals in Oiouudmler While Showering:
Maximum chemical concentration in
water (mg/L)
Surface area contacted (cm2)
Permeability constant4 (cm/hr)
Exposure' frequency (days/yr)
Exposure duration (yrs)
Exposure time (hrs/day)
Showering time (his)
Fraction volatilized (unitless)
Flow rate (L/hr)
Volume air (L)
Conversion factor for water (L/cm3 )
Body weight (kg)
Averaging time (days)
Noncarcinogens
Carcinogen
Site/Chemical-Specific
20000
Chemical-Specific
350
30
.017
0.08
0.75
1800
9800
0.001
70
. 10950
25550
Site/Chemical-Specific
20000
Chemical-Specific
275
9
0.12
0.08
0.75
1800
9800
0.0001
70
3285
25550
RME = Reasonable Maximum Exposure
L/day= Liters per day
6-4
-------
Table 6-3
Permeability Constants for Dermal Exposure at OU2
Analyte
U-Trichlorocthane
1,1^2-Tetrachloroethane
1,1-Dichloroetbane
1,1-Dichloroetheoe
1,2-Trichlorobenzene
1,2-Dibromoe thane
2-Methylnaphthalcne*
4-Methyl-2-Pentanone*
Antimony*
Arsenic
Barium*
Benzene
Benzo(a)pyrene
Beryllium .
Bis(2-Ethylhexyl)phthalate
Bromomethane
Cadmium
Carbon Tetrachloride
Chloroform
Chloromethane
Chromium
Copper*
Dichlorodifluoromethane
Ethylbenzene-
Hexachlorobutadienc
Manganese*
Mercury
Meihylene chloride
Naphthalene
Nickel
Nitrate
Petroleum hydrocarbons*
Polychlorinatcd biphcnyts
Tetrachloroethene
Thallium*
Toluene
Trichloroethene
Trichlorofluoromethane
Vanadium*
Vinyl chloride
Xylene
Zinc
. Permeability Constants
1.7&02
9.0B-03
8.9E-03
1.6E-02
l.OE-01 ' .
3.0E-03
\SEr03
l.SB-03
1J&03
3^&04 .
l^E-03
1.1B-01
liE+00
3JB-04
33E-02
3SEM
3.2E-04
2aE-02 .
13&4J1
4^&03
2.0E-03
UE-03
12E-02
l.OE+00
l^E-01 .
l.SE-03
1.0E40
4JE-03
6.9E-02
l.OE-03
15E-03
13E-C3
l.OE-i-00
7.9&03
1.5E-03
l.OE+00
23E41
1.7E02
UE-03
73E-03
8.0E-02
6.0E-W
* PCs were not available for these contaminants, therefor the PC for water (13-03) was used.
6-5
-------
The following sections summarize human health risks associated with exposure to site contaminants
and provide potential remedial action criteria.
6.13 Risk/Hazard Associated with ST20
Data generated from subsurface soil sampling indicated that contamination was present at a depth
greater than 10 feet below ground surface. Since routine excavation in the area to repair and install
underground utilities would not be conducted at a depth greater than 10 feet, no pathway to potential
receptors exist when these activities are performed. In addition, while a risk was identified at ST20 in the
groundwater, this risk was based on the highly conservative residential scenario, and is based primarily on
constituents emanating from an upgradient source. Under a more reasonable industrial scenario, the cause
of elevated risk is limited to manganese concentrations, which are at levels similar to those found in other
contaminated and uncontaminated areas on base, and within the Anchorage BowL
'The risk assessment performed for groundwater at ST20 determined that exposure would result in
an unacceptable risk to.human health. Several COCs posed a risk of greater than 1 in 10,000. Also, other
COCs had hazard indices greater than one. Table 6-4 provides a summary of maximum unacceptable site
risk/hazard associated with each COC at the site for both the residential and commercial/industrial exposure
scenarios. Maximum unacceptable risk/hazard occurs at upgradient monitoring wells B2MW and B4MW for
all of the COCs listed except benzene.
Benzene is the only organic COC identified at ST20. The maximum concentration at monitoring
well ST20-02, in the fall of 1991, was 440 ug/L. The associated risk calculated using the residential exposure
scenario was determined to be 3.0E-04. When the commercial/industrial exposure parameters were applied,
the calculated risk dropped to a level of 5.9E-05. In addition, data generated during the Ri indicate that the
source of the benzene contamination is upgradient of the former ST20 underground storage tank (UST). A
concentration of 400 ug/L in monitoring well ST20-01, which is approximately 200 feet upgradient of the
former UST, was detected However, data collected in 1990 was not used in the risk assessment because it
did not meet the quality assurance/quality control (QA/QC) requirements for assessing risk.
Figure 6-1 depicts the unacceptable risk/hazard for each COC at ST20. The greatest risk occurs to
the northeast of the former UST location, and is due to metals contamination. Lead occurrences over 50
ug/I are plotted on Figure 6-1. Lead risks were calculated using EPA's Biokenetic Uptake Model. EPA has
determined that a blood-lead level of 10 to 15 micrograms of lead per deci-liter of blood (ug/dl) represents a
level of concern. It is generally accepted that if no more than 5% of exposed children are estimated to have
blood lead levels of 10 ug/dl, there will be no significant health risk due to lead. The lead level in one well,
ST20-MW10, marginally exceeded the EPA lead uptake/biokenetic model for children; Lead results used in
the risk calculations are for total lead, and are likely indicative of instrument detection of lead adsorbed onto
paniculate matter in the groundwater. When dissolved lead is considered, lead levels fall within an
acceptable range. Source Area ST48 (under investigation as part of the SERA program), located in the
vicinity of monitoring wells B2MW and B4MW, is the suspected, source of this contamination.
When the commercial/industrial scenario is applied, the carcinogenic risk is within an acceptable
range. Only the non-carcinogenic hazard is above acceptable levels. The cause of this risk at ST20 is limited
to elevated levels of manganese in the groundwater. The elevated manganese concentrations were detected
in samples from wells ST20-01, ST20-02, and ST20-03, with hazard indices of 7.2, 6.1 and 12.7, respectively.
It should be noted that manganese has been found at similar levels throughout the base in both
contaminated and uncontaminated areas, .and at other locations within the Anchorage Bowl, and that the
levels detected are within the range anticipated for manganese in glacial soils (U.S. Air Force, 1994).
In summary, groundwater at ST20 would pose an unacceptable risk/hazard to human health;
however, the source of contamination appears to be due to fuel releases at the upgradient site ST48. ST48 is
6-6
-------
Table 6-4
ST20 Groundwater
Summary of Risk
Gpfnpound
Benzene
Nitrate
Arsenic
Beryllium
Chromium
Lead
Nickel
Manganese
Thallium
Vanadium
Maximum
Concentratioa
toto
440
150,000
180
S3
570
600
1200
32,400
230
970
Loafioo*
ST20-02/F91
ST20-04/F91
B2MW/F92
B4MW/S92
B4MW/S92
B2MW/F92
B4MW/S92
B4MW/S92
B2MW/F92
B4MW/F92
Residential
Risk/Hazard2
3.0B-04
2.6 HI
3.7E-03/16.4 HI
4.2E-04
3.7 HI
Yes*
1.6 HI
192.6 HI
78.8 HI
3.9 HI
50 /ig/L cannot be quantified using EPA's uptake
Biokinectic Model.
-------
-B4MW
* *
T ..
IJT-OJ fl« HC/
3.7C-04 (to H)
mmuai «jr-o»/» jr-0*
.
tOHWUI ItC-M
i< ii i M
AMLUUH7U NMt> Mr
BMSE WEUL 42
3STW STREET
n n
LEGEND
ROAD AND STREET
BUILONC
GfiOUNOWATER .WOMTORINC «ELL
PBINOPAl OK£CHO« Of CROUNDWATER Flow
RESOCHTW./COWUCRCIAL-INIXJSTRIA1. COMPOUND
RISK OR HAZARD
LEAD DATA RtPORTCO IN ug/L
tXPOSURE TO t£AO >9Ou9/l Wia "tSULT IN TOXC EFFTCTS.
TOXIC EFFtCTS FSOM L£AO >JOugA CANNOT BE OUANTTFCO
USINC EPA-S UPTAKE/8KXINCTC MODa.
200 100 0 200
5
SCALE IN FEET
400
PROJ. MCR.
S. HART
PROJ. EMC.
DRAWN BY
MITZEL
MADE FROU
204-CR
ACAO FILE NO.
RG6-1
DATT
3-15-95
ELMENDORF AIR FORCE BASE
ANCHORAGE. ALASKA
OPERABLE UNIT 2
ST20
GROUNDWATER
RISKS OR HAZARDS
PROJ. NO. r
05-G105-00
JFIGURE MO.
I riGURC 6-1
6-8
-------
currently being addressed under the SERA program, and a Corrective Action Plan is due in 1995.
6.1.4 Risk/Hazard Associated with ST41 Tank Spill
The risk assessment at ST41 was performed for groundwater only. Exposure to the contaminated
soil identified at ST41 is unlikely due to the depth to contamination (greater than ten feet). Contaminated
surface water and sediment locations are located on a steep embankment directly north of Loop Road.
Exposure to contaminated surface water, sediment and surface soil at ST41 was not considered because the
IRA eliminated the completed pathway for surface water exposure, and removed substantial amounts of
contaminated sediment and soil during construction. Since the area sustains only infrequent recreational use,
and because of the location of the contamination on a steep embankment, contact with contaminated surface
water, sediment or soil was deemed unlikely, thereby negating the need for calculating risks for these media.
The risk assessment determined that exposure to contaminated groundwater at ST41 would pose an
unacceptable risk to human health (greater than 1 in 10,000). Furthermore, the HI is greater than 1. Table
6-5 provides a comparison of risks associated with the residential and commercial/industrial exposure
scenarios for maximum concentrations of all COCs detected. In cases where the maximum risk/hazard
occurs in a free product area, the highest risk/hazard calculated for wells without free product is also
provided. The COCs exhibiting an unacceptable risk/hazard using residential exposure parameters are
BTEX (benzene, toluene, ethylbenzene, xylenes), arsenic, beryllium, manganese, and thallium
Risk/hazard associated with arsenic under the residential scenario is 1.6E-03/6.9 HI. This drops to
4.6E-04/2.5 HI when a commercial/industrial scenario is examined. Manganese at the highest exposure
point concentration exhibits a residential HI of 173.9. Using commercial/industrial exposure parameters the
hazard index drops to 56.9. Although risks were calculated for these constituents, the statistical evaluation of
arsenic concluded that the arsenic concentrations detected were not statistically different from results from
data collected by the USGS in the Anchorage Bowl area which were used for background comparison (U.S.
Air Force, 1994). In addition, the elevated manganese concentrations can be attributed to the occurrence of
biological activity associated with natural attenuation which has been shown to be occurring at ST41.
Manganese, along with dissolved oxygen, nitrate/nitrite, sulfate, and other ionic species play an important
role in the reduction/oxidation reactions which occur during active biodegradation of petroleum compounds
see Section 5.2.6). There is no anthropogenic source for these metals at ST41.
Although the risk assessment determined thalKnm and beryllium to be COCs with a residential
risk/hazard of.61.6 and 2JE-04, respectively, they were only detected 1 and 3 times out of 93 samples
analyzed. Due to the sporadic nature, thallium and beryllium are not considered to pose an unacceptable
risk at ST41.
When excluding areas where free phase petroleum product has been found floating on the water
table, the maximum risk associated with benzene was determined to be 2.4E-04. When a
commercial/industrial scenario is applied risk drops to less than l.OE-06. The maximum concentration of
benzene detected within the free product plume was 30,000 ug/L. When this concentration was input as an
exposure point concentration, a residential risk of 2.0E-02, and a commercial/industrial risk of 3.0E-03 were
calculated. .
In addition to evaluating risk at ST4L, selection of the final remedy must take into account that
groundwater must be remediated to comply with federal drinking water standards (Maximum Contaminant
Levels, MCLs). The MCLs for ST41 COCs are provided for reference in Table 6-5. In areas historically
free of product, the COCs which exceeded primary MCLs for drinking water include: benzene, ethylbenzene,
and thallium. .In areas where fuel product has been historically present, all COCs with MCLs exceeded the
MCLs.
6-9
-------
Table 6-5
ST41 Groundwater Summary of Risk
OooxfOooA
Areas Without Re* Product
Benzene
. Ethylbenzene
Xyiene
Arsenic
Beryllium
Manganese
Thallium
Maabmm
fc»/D
' l^rr'^fl1
y.yfrt^tfrf
Bi^/Hntnt
f^nfnfirtat/yiktHgif&^P
Rcfe/Hamd
' i-
1,100
3300
4,200
76
4.0
29,100
61.6 HI
ST41-07/F91
ST41-19/F92
ST41-19/F92
ST41-22/S92
ST41-10/P91
ST41-25/S92
ST41-16/F92
7.4&04
3.1 HI
um
l^E-03/6.9 HI
25E-04
173.9 HI
61^
1.1&O4
-------
When applying residential exposure point concentrations to wells containing free product, toluene,
ethylbenzene, and xylene are found to have His of 13.6, 5.0, and 5.9 respectively. This is an unacceptable
hazard to human health. However, in the commercial/industrial scenario, the HI of toluene drops to 1.2 and
the His of ethylbenzene and xylene are < 1.0, which is within the acceptable range.
Figure 6-2 highlights1 maximum risk, by well, associated with exposure to fuel-related compounds in
groundwater. Unacceptable site risk/hazard (>1.0E-04 or >1.0 HI) are only found at wells within the free-
. product plume under the commercial/industrial scenario. In the residential scenario, only one location
outside the free-product plume, ST41-W-7, exhibits an unacceptable risk, 2.4E-04 resulting from elevated
benzene concentrations.
6.1.5 Uncertainties Associated With the Risk Assessment
Health risk assessment methodology has inherent uncertainty associated with how accurately the
calculated risk estimates represent the actual risk. The effects of the assumptions and the uncertainty factors
may not be known. Usually, the effect is difficult to quantify numerically (e.g^ in terms of an error bar). As
a result, the effect is discussed qualitatively. Some of the assumptions and uncertainty factors associated with
the baseline risk assessment include the following.
The assessment used the EPA Region X residential land use scenario, -which assumes
consumption and domestic use of contaminated groundwater and is therefore highly
conservative (may overestimate risk);
The assessment used predominantly EPA Region X default exposure assumptions, which .are
typically based on 90th to 95th percentile values and are therefore highly conservative (may
overestimate risk);
Existing concentrations are assumed to be the concentrations anticipated in the future, such
that no reduction through natural degradation and attenuation over time occurs (may
overestimate risk);
No increase through additional contamination is assumed (may underestimate risk); and
. Potential degradation products of existing organic constituents are not considered (may
overestimate or underestimate risk).
Free product is expected to diminish at ST41.
62 Ecological Risk
An ecological risk assessment was conducted at ST41. Ecological evaluation of ST20 was not
undertaken, as described below. The ecological risk assessment conducted at ST41 consisted of an ecological
screening evaluation involving identification and characterization of the biological resources at risk,
development of the ecological conceptual site model, identification of the contaminants of ecological concern
(COECs), discussion of the potential lexicological effects of the selected COECs, selection of assessment end
points, initial quantification of toxicity and risk characterization, and discussion of future data needs for
biological diversity assessments and/or population studies, that would be conducted if deemed necessary.
The ecological risk assessment was conducted in accordance with the following guidance documents:
Risk Assessment Guidance for Superfund Volume 1 - Human Health Evaluation Manual
(EPA, 1989);
67!!
-------
Mmsraui. COUPOUND
f»SK OR HUAKO
41-MW36
CKOUNDWATEK DMOE
(DASHED WHERE INFERRED) -^ SM1 ,5
~i51 *"'
-------
General Guidance for Ecological Risk Assessment at Air Force Installations (Mitre
Corporation, 1990); and the
Framework for Ecological Risk Assessment (EPA, 1992b).
6.2.1 Ecological Evaluation of ST20
No sensitive ecological areas are present at ST20. ST20 is located in an industrial area where
ground cover consists of buildings, pavement, and mowed grass. Because of its location in a developed area
of the base, use of the area by plants and animals is limited; and, therefore no ecological risk assessment was
conducted specifically for ST20.
622 Ecological Evaluation of ST41
Based on calculated ecological quotients, frequency of detection, and detected concentrations, the
COECs at ST41, in approximate order of decreasing concern, are diesel-range hydrocarbons, gasoline-range
hydrocarbons, PCP, mercury, 2-methymaphthalene, naphthalene, benzo(a)pyrene, aluminum, and lead. The
maximum concentrations of each constituent were used to calculate ecological risk; therefore, the ecological
risk assessment was based on the most contaminated surface water detected at ST41. This contamination
was not detected in the wetlands area northwest of the site. As a result, the exposures calculated are
conservative with respect to the impact on ecological resources in the wetland area. Even though the
ecological risk was calculated using conservative assumptions, minimal risk was identified. This is primarily
the result of contaminant occurrences being limited to very small, localized areas.
In addition to ecological risk, compliance with State of Alaska surface water quality criteria (SWQC)
are also considered as part of the ecological assessment. These SWQC standards are presented with the
COCs identified at ST41 in Table 6-6. Attainment of these standards is currently being achieved through the
operation of the IRA. la general, localized wood frog and shrew populations at the ST41 area are most
likely to be at risk from ingestion of COECs. Wood frogs and small mammal populations may also be at
risk from inhalation of and dermal contact with gasoline-range hydrocarbons and diesel-range hydrocarbons.
Wood frog tadpoles may be at risk from exposure to lead and other contaminants in surface water and
sediment. Because of their small home range size, individuals of these species living in contaminated areas
may be frequently exposed. .
Passerine bird populations may also be at risk from ingestion of COECs at ST41. However, this
exposure is expected to be limited because elevated concentrations of most contaminants appear to be
confined to small areas, and the home range of most individual passerine birds is expected to include, but
not be limited to, portions or all of the ST41 area.
Since the IRA at ST41 eliminates the primary ecological exposure pathway by intercepting the
surface water seeps that discharge into wetlands, the environmental risk assessment did not identify
significant ecological impacts warranting any additional action.
63 Conclusions
Actual or threatened releases of hazardous substances from this site, if not addressed by
implementing the response action selected in this Record of Decision, may present an imminent threat and
substantial endangerment to public health, welfare, or the environment.
6-13
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Table 6-6
Summary of ST41 Surface Water Results With
Surface Water Quality Criteria*
Compound
Benzene2
Toluene2
Ethylbenzene2
Total xylenes2
1,2-Dichloroetnane
Arsenic2
Manganese
Lead
Thallium2
Diesel2
Gasoline2
Mirrimnm
Concentration
$lg/L)
1,500
380
4,200
2,900
33
63
9,700
41
440
12,000,000
59,000,000
Location1
ST41-SW-03/S93
ST41-SW-03/S93
ST41-SW-03/S93
ST41-SW-03/S93
ST41-SW-05/S93
ST41-SW-09/F92
ST41-SW-10/F92
ST41-SW-09/F92
ST4-SW-04/F92
ST4-SW-09/F92.
ST41-SW-09/F92
Atato Surface
Water Quality
Criteria
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7.0 DESCRIPTION OF ALTERNATIVES
A feasibility study (FS) was performed as part of the OU2 RI/FS process. The Feasibility Study
recommended that OU2, source area ST41 be considered for remedial action because of the potential risk
from unrestricted industrial use of groundwater containing dissolved contaminants, the exceedance by
groundwater constituents of Primary MCLs established under the Safe Drinking Water Act, and the presence
of free phase petroleum product floating on the water, table. The Baseline Risk Assessment concluded that
the greatest risks at ST41 are associated with benzene in the shallow groundwater. This section of the
Record of Decision describes the remedial alternatives proposed in the FS. For more details, the OU2 FS
should be referenced (U.S. Air Force, 1994).
7.1 Remedial Action Objectives for ST41 Tank Spilt
Remedial action objectives were developed to specify actions necessary to protect human health and
the environment. These objectives define the contaminants of concern, exposure routes and receptors, and
remediation goals, which are defined as an acceptable contaminant level for each exposure route. Remedial
action objectives were developed based on assumptions made during the RI/FS and decision making process
including:
The primary contributor to unacceptable risk is the presence of free phase petroleum
product floating on the water table;
The potential for migration of contaminants to downgradient receptors is low due to the
fine-grained nature of the subsurface soils;
Soils contaminated with fuel-related constituents in the vicinity of the piping around ST41
may be contributing to groundwater contamination; and
< Fuel has leaked from valve fittings, valve pits, and cracks in the piping system and not from
the underground, storage tanks.
Specific remedial action objectives are:
Prevent ingestion and contact with groundwater containing contaminants in concentrations
in excess of background or MCLs, whichever is greater;
Prevent use for aquaculture, or if aquaculture use is proposed in the future, treat water to
an acceptable level;
Prevent contaminated seep water (surface water) from entering wetlands;
Reduce further migration of contaminants due to free phase product currently on water
table, and any residual product that may exist in piping and underground tanks;
Prevent migration of contaminants found in soil that would result in groundwater
contamination in excess of MCLs or health-based levels; and
Attain residual contaminant levels which would restore groundwater as a potential source of
drinking water.
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Compliance with aO action-, chemical-, and location-specific ARARs (defined in Section 10,
Statutory Determinations).
Final remediation goals for groundwater include prevention of ingesdon or direct contact with
groundwater containing contaminants in concentrations hi excess of background or federal drinking
water standards (Primary MCLs): .
, MCL (u/L)
Benzene 5.0
Ethylbenzene 700.0
Toluene 1,000.0
Xylene 10,000.0
Final remediation goals for surface water and seeps include compliance with location and chemical
specific ARARs. The location specific goal is avoidance of long and short-term adverse impacts
associated with destruction or modification of the wetlands area. The chemical specific goal includes
compliance with state surface water quality criteria (SWQCs, see Table 6-6):
Contaminant State SWOC
Benzene 10
Ethylbenzene 10
Toluene 10
State water quality standards for each constituent are based on total aromatic hydrocarbon
concentrations.
If aquaculture use is proposed in the future, the water used will be treated to acceptable aquaculture
levels.
12 Remedial Alternatives for ST41 Tank Spill
To attain remedial action objectives for free-phase petroleum product floating on the water table,
surface water seeps, contaminated groundwater, and source control at ST41, a wide range of possible
alternatives were evaluated in the feasibility study. Four alternatives addressing groundwater contamination
and three for source control were considered for implementation and presented in the Proposed Plan. Each
of these alternatives is described in the following sections. The alternative for addressing free product,
surface water and seeps is also discussed. All costs are based upon a 10% discount rate over the life of the
alternative. Actual costs may vary by +100% to -50%.
12.1 Free Product, Surface Water and Seeps
Inherent to each alternative except the no-action alternative, is the continued operation of the IRA
until such point that all technically practicable product is recovered, discontinuation would not be deleterious
to surface water (wetlands) or seeps, and it can be established that natural attenuation will effectively address
any remaining free product or dissolved phase constituents in groundwater through long term monitoring.
Operation of the IRA would be anticipated as long as it is necessary to prevent adverse impact to the
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environment. The alternatives for groundwater do not include the cost of continued operation of the IRA
specifically for product, surface water, or seep mitigation. The original estimated cost for operation and
maintenance of the IRA was $27,500 annually. Actual 1994 costs approximate $85,000 for operation between
16 May and 31 December 1994.
122 Alternatives for Groundwater
Alternative G-I: No Action
Capital Costs: $0.0
Average Annual Costs: $0
Total Present Worth Costs: $0
Time to Complete Cleanup: Not Applicable
Evaluation of this alternative is required by CERCLA to use as a baseline reflecting current
conditions without any cleanup. This alternative is used for comparison with each of the alternatives. While
natural processes should degrade and reduce the concentrations of benzene at ST41 to acceptable levels, this
alternative does not include any long term monitoring to ensure the effective cleanup time. Although this
alternative does not include the continuing operation of the IRA, costs for discontinuing its operation are not
included. There are no costs associated with this alternative.
. Alternative G-II: Natural Attenuation with Institutional Controls, Long Term Monitoring for Groundwater
Capital Costs: $1^00 .
Average Annual Costs: $79,000
Total Present Worth Costs: $713,700 (based on a 10% discount rate per year)
Estimated Time to Complete Cleanup: 21 years
This alternative includes long term monitoring to ensure naturally occurring physical, chemical and
biological processes continue to degrade and reduce the concentrations of contaminants. The exact rates of
attenuation and degradation are unknown at this site. Contaminants dissolved in groundwater are known to
degrade, however the degradation rate .depends on environmental factors and the contaminant species.
Conservative estimates based on modeling show that benzene concentrations will be reduced below the
maximum contaminant level (MCL) of 5 ug/L in approximately 21 years. Benzene is used since this
constituent is expected to be the most difficult to reduce to MCLs. Monitoring of water and soil is necessary
to assess the rate of attenuation/degradation.
The long term monitoring program provides information on the degradation rates and will monitor .
plume migration. The plume is'not predicted to escape the existing monitoring well network. The purpose
of the monitoring is to ensure that the plume does not migrate to potential receptors, and to verify whether
natural attenuation is occurring. If monitoring indicates a longer time period for groundwater recovery is
required, the EPA and ADEC will reevaluate the need for additional remedial action. The continued
operation of the IRA, considered as the alternative for free product, surface water, and seeps, will contribute
to source removal.
. Institutional controls are also included as part of this alternative. Elmendorf AFB has implemented
a base policy prohibiting the use of the shallow aquifer as a drinking water or aquaculture supply source.
Alternative G-IH: Limited Collection and Treatment of Groundwater, Natural Attenuation with Long-Term
Monitoring
Capital Costs: $1,500
Average Annual Costs: $250,000
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Total Present Worth Costs: $2,998,000 (based on a 10% discount rate per year)
Estimated Time to Complete Cleanup: 21 years
In this alternative the IRA recovery and treatment system will be operated after the free-product is
removed from the site and continued until the groundwater contaminant concentrations upgradient of the
IRA system are lowered to MCLs or acceptable risk levels. The primary purpose of the IRA shifts from a
free product recovery system to a groundwater recovery and treatment system after the all technically
practicable free product is removed. Conservative estimates indicate that the benzene contaminated
groundwater within reach of IRA system will achieve MCLs in 17 years.
The estimated time to complete the cleanup of the entire site is 21 years since natural attenuation is
the only cleanup mechanism for groundwater downgradient of the IRA system. The long term monitoring
program and institutional controls have the same goals as alternative G-EL
Alternative G-IV: Complete Groundwater Collection and Treatment, Long Term Monitoring and
Institutional Controls
Capital Costs: $218,000
Average Annual Costs: $254,000
Total Present Worth Costs: $2,981,000
Estimated Time to Complete Cleanup: 17 years
This alternative involves adding groundwater recovery wells and/or trenches to the existing IRA
system. The entire contamination plume at ST41 would be captured and treated until the groundwater
concentrations reach MCLs, or acceptable, risk levels are attained. Conservative estimates based on modeling
indicate that the site will be cleaned up in 17 years. The long term monitoring program and institutional
controls proposed for this alternative have the same goals as Alternative G-II.
7.2.3 Alternatives for Source Control
The piping associated with the underground storage tanks along with the residual soil contamination
around the piping are a probable continuing source for groundwater contamination. Abandonment of the
underground storage tanks is required in accordance with State underground storage tank regulations.
Three alternatives are presented for abandonment of the underground storage tanks and associated
piping as described below: .
Alternative S-I: No Action .
Average Annual Costs: $0.0 .
Total Present Worth Costs: $0.0
Time to Complete Cleanup: Not Applicable
Evaluation of this alternative is required by CERCLA. This alternative is used for comparison with
each of the alternatives. This alternative leaves the existing tanks, piping, and soil in-place as they are today.
Alternative S-II: In-Place Tank Abandonment and Piping Removal
Capital Costs: $1,160,000
Total Present Worth Costs: $1,160,000
Time to Complete Cleanup: Less than one year
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This alternative involves the cleaning of all four tanks and filling them with an inert material such as
sand or gravel. Tank sludges will be disposed of in a facility consistent with the off-site disposal rule for
CERCLA-derived waste. Contaminated rinse water will also be disposed in a pre-approved manner, possibly
being treated in the IRA system, if appropriate. This alternative also includes the excavation and removal of
the piping system associated with the tanks. Contaminated soil associated with the piping system would be
addressed by removal of all soil shown to contain teachable concentrations of fuel-related constituents.
Treatment and/or disposal of an unknown volume of contaminated soil will be in accordance with all
applicable state and federal regulations, including 18 ACC 78310, and the off-site disposal rule for
CERCLA-derived waste. Petroleum contaminated soil resulting from leaks in the UST system may be
transported offsite, subjected to low-grade thermal treatment, and then recycled as road material.
Alternative S-III: Complete Tank and Piping Removal
Capital Costs: $3,785,000
Total Present Worth Costs: $3,785,000
Time to Complete Cleanup: Less than one year
This alternative involves the cleaning, demolition and disposal of all four tanks. It also includes the
excavation, removal and disposal of the piping system associated with the tanks, and the removal of an
unknown quantity of contaminated soil. All wastes generated during tank and piping cleaning and removal
will be disposed of and treated in a pre-approved manner in accordance with applicable, state and federal
regulations.
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8.0 SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES
In accordance with federal regulations, the four groundwater alternatives and three alternatives for
source control were evaluated based on the nine criteria presented in the National Contingency Plan. The
results of this analysis are discussed in this section. The nine criteria used to evaluate the remedial
alternatives and identify a preferred alternative are as follows:
Overall protection of human health and the environment;
Compliance with ARARs;
Long-term effectiveness and permanence;
Reduction of toxicity, mobility, and volume through treatment;
Short-term effectiveness;
Implementability;
Cost;
State Acceptance; and
Community Acceptance.
The following analysis briefly reviews and compares each of the alternatives for groundwater and
source control with the evaluation criteria. The alternatives for surface water and seeps were subjected to a
similar evaluation in the selection of the interim action remedy at ST41. This comparative process is
incorporated into the ERA Record of Decision, which is.part of the Administrative Record for OU2.
8.1 Threshold Criteria
Overall protection of human health and the environment and compliance with ARARs are threshold
requirements which must be met by each alternative for the alternative to be evaluated further.
8.1.1 ST41 Groundwater
Overall protection of human health and the environment Alternative G-n, G-ffl and G-IV provide
adequate protection of human health and the environment by reducing contaminant levels to below MCLs.
The MCL for benzene will be achieved in 21 years or less with Alternatives G-n and G-ffl and in 17 years
or less with Alternative G-IV. Alternatives G-n, G-m and Q-IV will reduce contaminant levels to below the
MCL before the contamination can migrate beyond the existing ST41 monitoring well network. This is based
on the assumed rate of groundwater migration, no new contaminant .loading, and continued operation of the
IRA as necessary. The institutional controls (i.e., base policy prohibiting the development of the shallow
aquifer as a drinking water or aquaculture supply source) combined with the unlikelihood of development of
the site for future residential or commercial activities prevents future exposure to the contaminated
groundwater. Current exposure risk is minimal because no drinking water or industrial water supply wells
exist at ST41.
Alternative G-I does not address remediation of the affected groundwater and seeps. Since this
alternative does not meet the threshold criteria requiring protection of human health and the environment,
or compliance with ARARs, it is eliminated from further evaluation.
Compliance with Applicable or Relevant and Appropriate Requirements (ARARs). Alternatives G-
II, G-IH and G-IV are expected to meet chemical specific and location specific ARARs, given the estimated
cleanup time frames. Chemical specific ARARs include compliance with federal drinking water standards
for the groundwater, and removal of soil with leachable POL contamination. Location specific ARARs
include avoidance of long and short-term adverse impacts associated with destruction or modification of the
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wetlands area. Action-specific ARARs related to air and waste management associated with the IRA would
bo be met for alternatives G-ri, G-m, and G-IV.
i.1 J ST41 Source Control
Overall protection of human health and the environment Alternative S-n involves tank
abandonment in place. It also includes removal of the piping system and removal of the contaminated soil
associated with the piping system. The contaminated soil will be treated and disposed of in a manner
consistent with applicable state and federal regulations. These measures are protective of human health and
the environment.
Alternative S-ffl accomplishes the same goals as S-U except that the four tanks are also removed
and disposed of in accordance with State and federal regulations. Tank removal may result in habitat
destruction, increased erosion and aquifer disruption, due to extremely large tank sizes and corresponding
excavations (one million gallons, each).
Alternative S-I does not involve any action to provide protection of human health and the
environment. Alternative S-I does not meet the threshold requirement and therefore does not warrant
further evaluation.
Compliance with Applicable or Relevant and Appropriate Requirements (ARARs). Alternatives
S-Q and S-ffl comply with all chemical- and action-specific ARARs. Chemical-specific ARARs include
compliance with state requirements for removal of soil with leachable POL contamination. Action-specific
ARARs include state and federal regulations pertaining to waste management. Location-specific ARARs
include protection of wetlands. Alternative S-n complies with location-specific ARARs. Alternative S-ffl
may result in alteration of the wetland environment due to the extremely large size of the tanks which would
be removed.
8.2 Primary Balancing Criteria
The following subsections discuss the primary balancing criteria used in the comparison of ST41
remedial alternatives.
8.2.1 ST41 Groundwater
Long-Term effectiveness. Alternatives G-II, G-ffl and G-IV combined with the IRA, reduce
contaminant concentrations to levels which result in attainment of MCLs in the long term. Once MCLs are
achieved and sources are removed, no risks will remain at OU2.
Reduction in toxicity, mobility, or volume of contaminants through treatment Alternatives G-II,
G-ffl and G-FV reduce the toxicity, mobility and volume of contamination through treatment. Each
alternative includes active removal and reuse/recycling of free product, as well as removal of contaminated
seepwater associated with the continued operation of the IRA. Alternative G-II combined with the
treatment of groundwater associated with the IRA, reduces contaminant concentrations to acceptable levels
within the same approximate time frames as Alternatives G-lll and G-IV.
Short-term effectiveness. Alternatives G-III and G-IV provide greater short term effectiveness in
lowering contaminant levels than Alternative G-II because the scale of the groundwater extraction and
treatment associated with these alternatives more rapidly decreases contaminant levels in groundwater.
Alternatives G-II and G-III however, do not present increased risk to workers, surrounding communities or
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the local environment, whereas alternative G-IV may result in some minimal environmental impacts from the
construction and operation of the additional collection system; and daily workers may be exposed to short-
term health risks through contact with air and groundwater. The monitoring of groundwater and institutional
controls during attainment of MCLs proposed under alternatives G-II, G-ffl and G-IV provide a short-term
effective measure by which human health and the environment would be protected.
Implementability. Alternative G-II can be implemented the most easily since the IRA and a
network of groundwater monitoring wells are already in place. A long-term monitoring plan is all that is
required to periodically assess the existing monitoring well network. Alternative G-IQ can also be
implemented with ease since in addition to the long term monitoring program proposed, continued operation
and maintenance.of the IRA system for groundwater and product removal requires no major system
modification. Alternative G-IV requires the installation of additional groundwater recovery wells and/or
. trenches and possible IRA system upgrades in order to implement this alternative. Alternative G-IV is the
most labor intensive of the alternatives to implement since it involves installing recovery wells and trenches
and increasing or modifying the treatment facility. .
Cost Alternative G-H with a total projected present worth cost of $713,700, is the least expensive
alternative. Alternatives G-DI and G-IV, with projected costs of $2,998,000 and $2,981,000 respectively,
essentially cost the same. Present worth for each alternative was based on a discount rate of 10%, applied
over the life of the alternative. Actual project cost may be +100% to -50% of the estimated cost
Alternatives G-ffl and G-IV are approximately 4 times more expensive than Alternative G-II. These costs
are higher due to the annual operation and maintenance required to maintain active treatment systems.
8.2.2 ST41 Source Control
Long-Term effectiveness. Both Alternatives S-n and S-ffl provide for long term effectiveness and
permanence. S-H removes the piping and associated soil with teachable contaminants, and prevents the
underground tanks remaining in the ground from being a continuing source of contamination. S-IH
accomplishes the same goal by removing the tanks and piping system completely, in addition to removing
associated contaminated soiL
Reduction in toxidty, mobility, or volume of contaminants through treatment Both alternatives
S-n and S-m involve treatment Alternative S-K will reduce the toxicity, mobility and volume of
contamination by cleaning the tanks, removing the piping system, and removing any soil associated with the
piping system with teachable contaminants for offsite disposal and treatment.
Alternate S-m will reduce the toxicity, mobility and volume of contamination by removing the
underground storage tanks, the piping system and the contaminated soil associated with the piping system for
offsite disposal and treatment.
Short-term effectiveness. Alternative S-n provides short-term effectiveness. Minimal environmental
impacts may include dust production and habitat disruption during the excavation and removal of the piping
system. Alternative S-ffl will involve human health and environmental impacts. Increased dust production
during excavation of the tanks and piping systems will affect both the workers and base personnel The
extensive excavation will also result in habitat destruction, increased erosion and aquifer disruption.
Implementability. Alternative S-II is easier to implement than alternative S-m, however the
equipment, materials and skilled workers necessary to implement both of the alternatives are available.
Alternatives S-II and S-III will both require confined space entry permits for tank cleaning.
Cost Alternative S-III, at $3,785,000, is 3 times as expensive as Alternative S-II, at $1,160,000.
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83 Modifying Criteria
State acceptance. The State of Alaska concurs with the Air Force and EPA in the selection of the
final remedial alternative for OU2. The State of Alaska has been involved with the development and review
of the RI/FS, Proposed Plan and Record of Decision. This includes selection of Alternative G-E for
groundwater remediation and Alternative S-H for source control The State of Alaska also concurs with the
Air Force and EPA in the selection of Alternative G-IV as a contingent alternative for the remediation of
groundwater.
Public Acceptance. Based on the comments received from the public and the support given by the
Technical Review Committee (TRC), the public supports the selection of the Air Force's preferred
alternative. A Responsiveness Summary, which addresses questions and comments received during the public
comment period, is attached to this Record of Decision.
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9.0 SELECTED REMEDY
Under CERCLA Section 121, selected remedies must be protective of human health and the
environment, comply with ARARs, be cost effective, and use permanent solutions and alternative treatment
technologies or resource recovery technologies to the maximum extent practicable. In addition, CERCLA
includes a preference for remedies that use treatments which significantly and permanently reduce the
volume,' toxicity or mobility of hazardous wastes as their principal element. The following subsections discuss
how the remedy for OU2 meets these statutory requirements.
9.1 ST20 and ST41 Sludge Disposal Area
No further action is required for uncontaminated soils in and around the ST20 source area; This-
determination does not extend to fuel contaminated groundwater and soil at the groundwater interface
underlying ST20, since the contamination is attributed to a separate source area, ST48, that is being
addressed under the SERA program. Any remedial actions that may be necessary to address the
contamination will be evaluated and implemented under, the SERA program.
The presence of the ST41 Sludge Disposal Area could not be verified. Contamination in the soil
found in the area thought to contain the ST41 source is attributable to leaks in the tank system. Remedial
measures to address this contamination are included as part of the ST41 Tank Spill remedy; specifically,
maintenance of institutional controls to restrict access as long as hazardous substances remain in the soils
that preclude unrestricted use.
92 ST41 Tank Spill
. The selected remedy is Alternative G-n for groundwater remediation and Alternative S-II for source
control Alternative G-IV as a contingent alternative for the remediation of groundwater. Surface water
seeps and free product will be addressed through continued operation of the IRA as necessary.
The selected remedy, Alternative G-n, for ST41 groundwater includes the following major
components:
Continuing the operation of the IRA free-product recovery system until all technically
practicable free product has been recovered to mitigate this continuing source of
contamination;
Continuing the operation of the IRA system in place for seep mitigation until it can be
determined that SWQCs will be met by the seep water. In addition, long term monitoring
must show that natural attenuation will continue to be protective of the wetlands in the .
area;
Monitoring the groundwater beneath and adjacent to the site to evaluate contaminant
migration and timely reduction of contaminant concentrations by natural attenuation within
21 years. This will include five-year reviews to assess the protectiveness of the remedial
action as long as contamination remains above unacceptable levels. Monitoring will be
conducted in accordance with the long term monitoring plan schedule set forth in the
Remedial Design/Remedial Action Statement of Work; and
Maintaining institutional controls that restrict access to groundwater and contaminated
surface and subsurface soils, as well as groundwater development at the site, as long as
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hazardous substances remain on the site at levels that preclude unrestricted use. The
specific institutional controls to be implemented and/or maintained at OU2 are as follows:
1. Development of a site map showing the areas currently and potentially impacted by
groundwater contaminants that will be included in the Base Comprehensive Plan;
2. Zoning the affected area for industrial use only, excluding the development of commercial
aquaculture;
3. Continued enforcement of base policy prohibiting installation of groundwater wells (other
than for monitoring purposes) into the shallow aquifer underlying OU2 at Elmendorf AFB;
and
4. Prohibiting unauthorized access to existing water supply and groundwater monitoring wells..
In addition, to ensure long-term integrity of the above land use controls, the Air Force will ensure
that, to the extent that groundwater contamination remains above unacceptable levels, deed restrictions or
equivalent safeguards will be implemented in the event that property containing such contamination is
transferred by the Air Force. The measures taken will include:
Five-year review to assess the protectiveness of the remedial action; and
Periodic evaluation of monitoring results to determine if there is need for further remedial
action.
The contingent remedy, Alternative G-FV, for ST41 groundwater includes the following major
components:
Continuing the operation of the IRA free-product recovery system until all technically
practicable free product has been recovered to mitigate this continuing source of
contamination;
Extracting groundwater from the shallow aquifer to eliminate further migration;
Treating the extracted water with an air stripping process to meet federal, state and local
water quality regulations;
Treating the air emissions from the air stripping process as needed to meet substantive state
and base air emission permit requirements;
Disposing of the treated groundwater in accordance with federal, state, and local regulations
and substantive permit requirements;
Five-year review to assess the protectiveness of the remedial action; and
Monitoring of the effectiveness of the groundwater containment and treatment process until
the concentrations reach the MCL and groundwater no longer poses an unacceptable risk.
The contingent remedy will be implemented if the Air Force, in consultation with the State and
EPA, evaluate the effectiveness of the selected remedy and determine:
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Long-term monitoring of groundwatei1 at ST41 indicates that natural attenuation is not
occurring at an acceptable rate, such that concentrations of contaminants will not meet
regulatory standards within an acceptable period of time. An estimated timeframe of 21
years will be used to evaluate natural attenuation.
The selected remedy, Alternative S-II, for ST41 source control includes the following major
components:.
Cleaning of the four one million gallon underground storage tanks, disposal of the residuals
according to applicable statutes, and filling them with an inert material such as sand or
gravel Abandoning the tanks in situ reduces the potential adverse human health and
environmental risks associated with removing tanks of this size;
Excavating, removing and disposal/recycling of the piping system;
Removal of contaminated soil associated with the piping which contains leachable
concentrations of fuel-related contaminants, and offsite disposal and low thermal treatment
of those soils; and
Revegetating the area.
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10.0 STATUTORY DETERMINATIONS
The selected remedy meets the statutory requirements of'Section 121 of CERCLA, as amended by
SARA. The selected remedy also meets, to the extent practicable, the NCP. The evaluation criteria are
discussed below.
10.1 Protection of Human Health and the Environment
The selected remedies, Alternatives G-EI and S-II, protect human health and the environment by
eliminating the source of the groundwater contamination and reducing the concentrations of contaminants in
the groundwater below acceptable risk levels. Benzene is the primary contaminant at source area ST41
which posed an unacceptable risk requiring remedial action. The source of the benzene contamination will
be removed by the continued operation of the free product recovery system for approximately five years.
Natural attenuation will' degrade the dissolved benzene and other contaminants of concern in groundwater
into carbon dioxide and water.
. The contingent alternative, G-FV, will be implemented if long term monitoring indicates that natural
attenuation and the operation of the IRA until all technically practicable free product has been removed are
not providing adequate protection of human health and the environment. Alternative G-FV protects human
health and the environment by removing contaminated groundwater from the ground, treating it to publicly
owned treatment works (POTW) standards and then discharging the treated groundwater to the sanitary
sewer, or other acceptable disposal method.
The risk to human health at OU2 occurs if someone were to drink the contaminated groundwater
daily over a thirty year period. Low hydraulic conductivity values for the shallow aquifer in the vicinity of
source area ST41 make it a poor raw water source for domestic or industrial uses and reduces the likelihood
that the contaminant plume will migrate beyond the existing monitoring well network during the remedial
action. Long term monitoring will be used to monitor plume migration, the reduction in contaminant
concentration, and the reduction in free floating product. Institutional controls in the form of base policy
prohibiting the use of the shallow aquifer reduces this risk. The risk is also reduced by the fact that source
area ST41 is located in a part of the base which is adjacent to an active runway and is zoned for industrial
use only. Additional risk reduction is realized by abandoning the tanks in situ, removing the piping system
and removing grossly contaminated soils due to possible line leaks. The five year review of the remedial
action will allow the EPA and ADEC the opportunity to improve upon the remedial action, if necessary.
102 Compliance with ARARs
The selected remedies are expected to comply with all applicable or relevant and appropriate
requirements (ARARs) of federal, State of Alaska, and Municipality of Anchorage environmental and public
health laws. This includes compliance with all action-, chemical-, and location-specific ARARs listed below.
102.1 Action-Specific ARARs
To the extent hazardous waste, as defined by the Resource Conservation and Recovery Act,
42 U.S.C. sec. 6901 et. seq., is extracted from the groundwater and to the extent air
emissions result from operations of and air stripper, the selected remedies will comply with
the requirements of 40 CFR 264 Subparts AA & BB. Spent carbon from the carbon
adsorption unit and filters which may be used in conjunction with the remedies and/or
residual materials from the pretreatment system will be stored and disposed of or recycled
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at a RCRA approved facility in accordance with EPA policy for offsite disposal of CERCLA
waste.
Air emissions from the air stripper will meet ambient air quality criteria established by the
State of Alaska Air Quality regulations (18 AAC 50).
Processed wastewater will be discharged into the Anchorage municipal wastewater system in
accordance with 40 CFR 403.5 and the Anchorage Water and Wastewater Utility
requirements of 100 ppb for BTEX and 10 ppm for TPH.
To the extent wastewater will be discharged into the waters of the United States, such
discharge will comply with the substantive requirements of 40 CFR Part 125 and the Alaska
Wastewater Disposal regulations set forth in 18 AAC 72 and 18 AAC 70.
To the extent the selected remedies result hi the removal of petroleum contaminated soil
the contaminated soil will be handled and treated consistent with the requirements of 18
AAC 78310.
10.2.2 Chemical-Specific ARAKs
Primary MCLs established under the Safe Drinking Water Act are relevant and appropriate
requirements for groundwater that is a potential drinking water source:
Contaminant MCL (ug/L)
Benzene 5.0
Ethyibenzene 700.0
Toluene 1,000.0
Xylene 10,000.0
Alaska surface water quality criteria, established under the State of Alaska Water Quality Standards,
are relevant and appropriate requirements for surface water that can be used for growth and
propagation of fish, shellfish, and other aquatic life or wildlife (see Table 6-6):
Contaminant State SWOC (ug/L)'
Benzene 10
Ethyibenzene 10
Toluene 10
State water quality standards for each constituent are based on total aromatic hydrocarbon
concentrations.
The selected remedies will meet Alaska Oil Pollution Regulation 18 AAC 75310 (1994)
pertaining to surface and groundwater cleanup of petroleum related benzene.
The selected remedy will meet. Alaska Underground Storage Tank Regulation 18 AAC
78315 (1994) for the cleanup guidelines for underground storage tank contaminated soil.
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10.2.3 Location-Specific ARARs
Executive Order 11990 and 40 CFR Part 6, Appendix A, require that Federal Agencies conduct
activities to avoid, to the extent possible, the long and short-term adverse impacts associated with the
destruction or modification of wetlands.
10 3 Cost-Effectiveness
The selected remedy, Alternative G-n, is cost-effective because it has been determined to provide
overall effectiveness proportionate to its costs and duration to achieve the remediation goals. The contingent
remedy, Alternative G-FV, is the most cost-effective of the remaining alternatives.
10.4 Utilization of Permanent Solutions and Alternative Treatment Technologies to the.
Maximum Extent Practicable
The U.S. Air Force, the State of Alaska, and EPA have determined that the selected remedies
represent the maximum extent to which permanent solutions and treatment technologies can be used in a
cost-effective manner at the OU2 site. Of those alternatives that are protective of human health and the
environment and comply with ARARs, the U.S. Air Force! the State of Alaska, and the EPA, the selected
remedies provide the best balance of tradeoffs in terms-of long-term effectiveness and permanence, reduction
in tenacity, mobility, or volume achieved through treatment, short-term effectiveness, implementability, cost
(as discussed in the preceding section), and the statutory preference for treatment as a principal element and
considering State and community acceptance. . .
The most decisive factors in the selection decision were long-term effectiveness, implementability,
and cost-effectiveness. Alternatives G-n and S-n and the contingent alternative G-IV provide the best
options for cost-effective and practical remediation of OU2. Alternative G-IV would in principle reduce the
concentrations of benzene in the aquifer more quickly; however, given the ease of implementation and cost-
effectiveness of alternative G-n, alternative G-IV was selected as the contingent alternative.
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11.0 DOCUMENTATION OF SIGNIFICANT CHANGES
The selected remedy was the preferred alternative presented in the Proposed Plan. No changes have
been made.
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12.0 REFERENCES
Alaska State Oil Pollution Regulation. 18 AAC 75327, 1994.
Alaska State Water Quality Standards. 18 AAC Chapter 80, 1991.
Alaska State Underground Storage Tank Regulation. 18 AAC 78.315, 1994.
Mitre, Corporation, "General Guidance for Ecological Risk Assessment at Air Force Installations,"
DeSesso, John M., and Price, Fred T, December 1990.
U.S. Air Force (CH2M Hill). Elmendorf Air Force Base. Alaska. Basewide Background Sampling Report.
February 1993. .
U.S. Air Force (Jacobs Engineering Group, Inc.). Elmendorf Air Force Base. Alaska.
Restoration Program. Operable Unit 2 Remedial Investigation /Feasibility Study. March 1994.
U.S. Environmental Protection Agency (USEPA). Risk Assessment QMl^?lnflr ^VT Superf""d
Volume 1: Human Health Evaluation Manual Part A. USWER Directive 9285.701 a. December
1989.
U.S. Environmental Protection Agency (USEPA). Risk Assessment finiHyi^. for Superfund Vnlnme 1:
Human H^fllth Evaluation Manual (Part B. Development of Risk-bas,e«fl Preliminary Remediation
Goals). Interim, Office of Solid Waste and Emergency Response Directive 92857.7-Olb, December
1991a.
U.S. Environmental Protection Agency (USEPA), Risk- Assessment Guidance for Superfund Volume 1:
Human Health Evaluation Manual. Supplemental Guidance: Standard Default Exposure Factors.
Interim Final, Office of Solid Waste and Emergency Response Directive 9285.6-03, March 1991b.
U.S. Environmental Protection Agency (USEPA). Environmental Protection Agency. Region X.
Supplemental Risk Assessment Guidance for Superfund. August 1991c.
U.S. Environmental Protection Agency (USEPA). Quality Criteria for Water. 1991d.
U.S. Environmental Protection Agency (USEPA). Guidance for Data Usability in Risk Assessment (Part Al
Final, 9285.7-09A, 1992a.
U.S. Environmental Protection Agency (USEPA). Framework for Ecological Risk Assessment. EPA 630R-
92-001, February 1992b.
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ELMENDORF AIR FORCE BASE
OPERABLE UNIT 2
RESPONSIVENESS SUMMARY
The Proposed Plan for OU2 was issued to the public on June 13; 1994. This began a puoiic
comment period that ended on July 13, 1994. In order to encourage public comment,'the U.S. Air Force
inserted pre-addressed, written comment forms in distributed copies of the Proposed Plan. In addition
comment forms were also distributed at the June 23,1994 public meeting held at the Federal Building in
Anchorage to receive comments on the Proposed Plan.
The public meeting was attended by twenty six people, including nine community members. Oral
comments were received from two people: one representative from Physicians for Social Responsibility and
one citizen representing Cleannaire Alaska.
Following the public meeting and prior to the conclusion of the public comment period, written
comments were submitted by one individual.
All comments received are documented in the administrative record file for the site. A transcript of
the public meeting is available for public review at the site information repositories. The repositories are
located at the Bureau of Land Management's Alaska Resources Library and the University of Alaska at
Anchorage's Consortium Library.
Public comments, relevant to OU2 and/or the environmental restoration program at Elmendorf, are
presented below and have been paraphrased for greater clarity.
COMMENTS AND RESPONSES
Public Comment: There was a concern that biopile technology and natural attenuation remediation
may not work in this climate.
USAF Response: A study by the UJS. Army Corps of Engineer's Cold Regions Research and
Engineering Laboratory indicates that biopile technology will work in this climate. ADEC has observed a
number of bioremediation projects in the Anchorage area which have been effective at remediating
petroleum contaminated sites. Some bioremediation projects in the Anchorage area have achieved ADEC
Level A cleanup standards for petroleum contaminated soils. Level A cleanup standards equate to restoring
the formerly contaminated soil to a point where the soil can be reused without any restrictions, limitations or
potential harmful effects to human health and the environment.
The Air Force Center for Environmental Excellence and the EPA's Kerr Laboratory are
cooperatively conducting a treatability study to validate the natural attenuation at OU2. If the ongoing
treatability study does not validate the feasibility of natural attenuation then a more active remedial action
will be implemented.
Public Comment: There was a concern about migration of the contaminant plumes either through
surface seeps or groundwater Dow.
USAF Response: The rates of migration are tracked and are well documented in the remedial
investigation report. The site data indicate that the contaminated groundwater should not migrate beyond
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the existing monitoring weU network in the immediate vicinity of source area ST41. The interim remedial
action free product recovery system has been successful in mitigating the release of contaminated
groundwater and free floating petroleum product via seeps.
Public Comment: There was a concern that the Proposed Plan assumed that the sites would always
be zoned for industrial use only.
USAF Response: Institutional controls in the form of the base prohibiting the use of shallow
groundwater for a drinking water source and the base comprehensive plan which zones the source area ST41
as an industrial use area due to its proximity to an active runway will insure that the risks to exposure to the
contaminated groundwater is minimized for as long as the Air Force owns the property. Should the base be
closed through the base realignment and closure process all remedial actions for contaminated property will
be in place prior to title conveyance. If additional deed restrictions are required at the time of conveyance
they will be negotiated at that time. . .
Public Comment: There was a concern that the risks from the cumulative effects of various
contaminants were not being addressed. ;
USAF Response: While the cumulative effects of some contaminants are not known, the risk
assessment performed in the remedial investigation is very conservative in its assumptions. The fact that
there is no current exposure pathway is in itself protective of human health. The ongoing remedial
investigation for OU6 will look at the cumulative risks associated with all of the OUs on Elmendorf AFB.
Public Comment: A vendor offered his services for carbon disposal and offered supportive narrative
for in situ bioremediation technologies although he noted that the costs associated with bioremediation in
Alaska seem to exceed like costs in the contiguous 48 by some 65-75% based on his observations.
USAF Response: The comment is noted. No response necessary.
Public Comment: A written comment was submitted from an individual concurring with the selected
remedies.
USAF Response: The comment is noted. No response necessary.
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