EPA Superfund Record of Decision: Elmendorf Air Force Base EPA ID: AK8570028649 OU 02 Anchorage AK 03/31/1995


                                    EPA/ROD/R10-95/112
                                    1995
EPA Superfund
     Record of Decision:
     ELMENDORF AIR FORCE BASE
     EPA ID: AK8570028649
     OU02
     ANCHORAGE, AK
     03/31/1995

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ELMENDORF AIR FORCE BASE
OPERABIiE 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 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:

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! Containment of seeps using collection systems and subsequent water
treatment and product recycling;

! Extraction of fuel product from the groundwater surface in the shallow
aguifer to minimize further migration;

! Treatment of extracted groundwater and seep water by and 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 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 evalute
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; groundwater
contaminants that will be included in the Base Comprehensive Plan;

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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 aguifer 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 eguivalent 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;

! 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 aguifer to eliminate further
migration;

! Treating the extracted water with an air stripping process to meet
federal, state and local water guality regulations;

! Treating the air emissions from the air stripping process to meet state
and base air emission permit reguirements;

! Disposing of the treated groundwater in accordance with federal, state,
and local regulations and permit reguirements;

! 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 reguirements 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 adeguate protection of
human health and the environment.

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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 upgradient
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.	
LEAD 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.

                                              19 MAY 1995
JOHN S. FAIRFIELD, LT GEN, USAF                 Date
Chairman, HQ PACAF
Environmental Protection Committee
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 31 1995
CHUCK CLARKE                                    Date
Regional Administrator
Region X
U.S. Environmental Protection Agency
STATE OF ALASKA CONCURRENCE WITH 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 State 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

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TABLE OF CONTENTS
                                                                                      Page

      1.0    SITE NAME,  LOCATION AND DESCRIPTION 	1-1

      2.0    ELMENDORF AFB SITE HISTORY AND ENFORCEMENT ACTIVITIES 	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
                  5.1.3  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
             5 .2  ST41 Tank Spill and Sludge Disposal Area 	5-9
                  5.2.1  Geology and Hydrogeology of ST41 	5-16
           5.2.2  Reported Releases at ST41 	5-16
                  5.2.3  Early Actions at ST41 Tank Spill 	5-16
                  5.2.4  Surface Soil/Sediment Contamination at ST41 Tank Spill 	5-18
           5.2.5  Subsurface Soil Contamination at ST41 Tank Spill 	5-22
                  5.2.6  Groundwater Contamination at ST41 Tank Spill 	5-22
                  5.2.7  Surface Water Contamination at ST41 Tank Spill 	5-31
                  5.2.8  ST41 Sludge Disposal Area 	5-31
                  5.2.9  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
                  6.1.2  Risk Characterization 	6-2
                  6.1.3  Risk/Hazard Associated with ST20 	6-6
                  6.1.4  Risk/Hazard Associated with ST41 Tank Spill 	6-9
                  6.1.5  Uncertainties Associated with the Risk Assessment 	6-11
             6. 2  Ecological Risk 	6-11
                        6.2.1     Ecological Evaluation of ST20 	6-13
                        6.2.2     Ecological Evaluation of ST41 	6-13
             6.3  Conclusions 	6-13

      7 . 0    DESCRIPTION OF ALTERNATIVES 	7-1

           7.1  Remedial Action Objectives for ST41 Tank Spill 	7-1

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TABLE OF CONTENTS (Continued)
                                                                                      Page

             7.2  Remedial Alternatives for ST41 Tank Spill 	7-2
                  7.2.1  Free Product,  Surface Water and Seeps 	7-2
                  7.2.2  Alternatives for Groundwater 	7-3
                  7.2.3  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
                  8.1.2  ST41 Source Control 	8-2
             8.2  Primary Balancing Criteria 	8-2
                  8.2.1  ST41 Groundwater 	8-2
                  8.2.2  ST41 Source Control 	8-3
             8.3  Modifying Criteria 	8-4

      9.0    SELECTED REMEDY 	9-1

             9.1  ST20 and ST41 Sludge Disposal Area 	9-1
             9. 2  ST41 Tank Spill 	9-1

      10.0   STATUTORY DETERMINATIONS 	10-1

             10.1  Protection of Human Health and the Environment 	10-1
             10 . 2  Compliance With ARARs 	10-1
                   10.2.1  Action-Specific ARARs 	10-1
                   10.2.2  Chemical-Specific ARARs 	10-2
                   10.2.3  Location-Specific ARARs 	10-3
             10 . 3  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 United in the OU2 Risk Assessment 	6-4

      6-3   Permeability Constituents for Dermal Exposures 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

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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
      5-15       Operable Unit 2 Sources Area BTEX and TPH,
                 Fall 1992 	5-30
      6-1        Operable Unit 2 ST20 Groundwater Risks
                 or Hazards 	6-8
      6-2        Operable Unit 2 ST41 Groundwater Risks
                 or Hazards 	6-12

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ACRONYMS AND ABBREVIATIONS
      ADEC     Alaska Department of Environmental Conservation
      AFB      Air Force Base
      ARAR     Applicable or Relevent 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
      COG      Contaminant of Concern
      COEC     Contaminant of Ecological Concern
      EPA      Environmental Protection Agency
      BSD      Explanation of Significant Differences
      FFA      Federal Facility Agreement Under CERCLA Section 120
      HEAST    Health Effects Assessment Summary Tables
      HI       Hazard Index
      IRA      Interim Remedial Action
      IRIS     Integrated Risk Information System
      IRP      Installation Restoration Program
      LOEL     Lowest Observable Effect Level
      MCL      Maximum Contaminant Level
      mg/kg    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      Tatal Petroleum Hydrocarbons
      TRC      Technical Review Committee
      ug/dl    Micrograms per Deci-liter
      ug/L     Micrograms per Liter
      UST      Underground Storage Tank
      UT       Upper Tolerance

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ELMENDORF AIR FORCE EASE
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 10,320 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
unconsolidated deposits. The first of these is poorly sorted glacial sediment (till).
The primary featuree 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 aguifers are present in the vicinity of Elmendorf AFB. The shallow aguifer consists
of either till or outwash deposits, depending on location. The deep confined (artesian)
aguifer consists primarily of sand and gravel. Between the shallow and deep aguifers is a
regional aguitard known as the Bootlegger Cove Formation. This unit consists of
interbedded silt and clay deposits, and ranges from several feet to over fifty feet in
thickness. A generalized cross section showing ther relationship between the shallow
(outwash) aguifer, the Bootlegger Cove Formation, and the deep aguifer is presented in
Figure 1-2. The shallow aguifer 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 aguifer 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 aguifers.

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 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.

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2.0 ELMENDORF RFB SITE HISTORY AND ENFORCEMENT ACTIVITIES

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 II. 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), fire 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 IRP,
the U.S. Air Force identified potential areas of contamination at Elmendorf AFB.
Potential source areas included old landfills, storage and diposal areas, fueling system
leaks, and spill areas.

Elmendorf AFB was proposed for the National Priorities List (NPL) 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, archeological
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.

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, the 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.

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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
guestions and seek public comment.  Representatives from Elmendorf AFB, the EPA, and ADEC
were present at the meeting to answer guestions 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).

4.0   SCOPE AND ROIiE 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:

                     OU1  Landfills (LF05,  LF07,  LF13,  LF59,  OT56)
                     OU2  Tank Spill  Sites  (ST20,  ST41 including the ST41  Slugdge Disposal
                     Area)
             !        OU3  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 (LP02,  LF03, LF04,  SD15,  SD73,  WP14)
             !        OU7  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,  SD30, 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 1995.  OU4 is in the decision making phase, and will be seeking public
comment in April 1995.  RI/FS reports are in progress for OU3, and OU6.  The ROD for OU6
will address cumulative impacts to human health and the environment from all OUs and will

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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, ST20
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.

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.

OU2 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 ST20 Underground Waste Storage Tank

ST20 is located approximately 400 yards west of the north-south runway between 0 and P
Streets, as shown on 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 demolishied 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 Hvdrogeoloav 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,
aguifer testing, and groundwater modeling.

Source area ST20 is underlain by both the shallow water table (unconfined) aguifer and the
artesian (confined) aguifer. The shallow aguifer is made up of outwash plain deposits
which consist of a relatively homogeneous seguence 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 aguifer
communication test performed on Base Well 42 during the ST20 investigation showed that the
Bootlegger Cove formation forms a competent aguitard and that there is no groundwater
interface between the shallow and deeper aguifers 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 aguifer 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.

5.1.2 Removal Actions Taken at ST20

In 1983 the installation prohibited the storage of waste liguids in the tank. In 1986,
following testing for waste characterization, approximately 105,000 gallons of liguid
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 1,300 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.

-------
Table 5-1
      ST20

      1960's

      1960's-1983

      1983

      1983

      1986

      1988

      1990

      1990-1993

      ST41

      1942

      1976

      1983

      1984

      1988

      1989

      1990-1993

      1991

      1993


      1994

      1993-1994
       History of Source Areas

Underground Waste Storage Tank

Tank used to store fuel for a power plant.

Tank used to store liguid waste.

Preliminary Assessment/Site Investigation.

Waste storage ceased.

Tanks emptied/waste disposed.

Two soil borings reveal contamination.

Tanks removed, soil excavated.

Remedial Investigation/Feasibility Study

Tank Spill and Sludge Disposal Area

Fuel tanks constructed.

Oil/water separater installed in southern seep area.

Preliminary Assessment/Site Investigation

Two monitoring wells installed and sampled.

Monitoring wells sampled again.

Small dam placed in drainage ditch.

Remedial Investigation/Feasibility Study

IRA construction completed, operation began.

IRA operated from October until December, when the IRA was
winterized.

IRA restarted in May 1994.

145 gallons of product recovered as of November 1994 from operation
of IRA.

-------
-------
Table 5-2
Summary of Constituents Detected in
ST20 Subsurface Soil*

Compound Maximum Locationl Frequency Background2
Concentration (mg/kg)
(mg/kg)

Gasoline 1,000 ST20-BH03-27(BWT)/F92 5/25 N/A

Diesel 610 ST20-BH03-27(BWT)/F92 4/25 N/A

Arsenic 11.1 ST20-BH10-25(AWT)/F92 63/63 9.24

Mercury 0.93 ST20-BH08-25(AWT)/F92 13/63 0.20

Lead 19.3 ST20-BH08-25(AWT)/F92 63/63 10.0

1 Sampling location identifiers include boring number followed by depth and whether it was above
table (AWT) or below (BWT). The sampling events are also included (i.e. Fall 1992 = F92).
Information derived from OU 2 RI/FS Report (U.S. Air Force, 1994).

2 Background concentrations are 99% upper tolerance limits derived for deep zones, see Table 5-3 of
this report (U.S. 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) .
-------
Metals Concentration of Background Soil
99% Upper
Non
above UT
Level
Deep
14
14
21
Chromium Surface
Root
zone
Deep

Lead
14
14
21
14
14
21
48.4
54.4
76.1
14
14
21
-------
Table 5-3
(Continued)
Mercury

Deep

Nickel

Deep

Thallium
Deep
Depth
Range
Surface
Root
zone
Surface
Root
zone
14
21
14
14
21
14
14
21
Number of

Detects
-------

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 significant 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 the 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 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 guality 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 release that
occurred upgradient, at source area ST48.
-------
Table 5-4
Summary of Constituents Detected in Groundwater at ST20*
Frequency
Benzene
Ethylbenzene
Toluene
Xylene
Trichloroethene
Chloroform
Bis ( 2-ethyhexyl ) phthalate
4-Methyl 2-Pentnanone
Nitrate 220
Total Petroleum Hydrocarbons 44
1 , 2-Dibromoethane 0
Arsenic
Barium
Beryllium
Chromium
Mercury
Manganese 32
Nickel
Lead
Thallium
Cadmium
Vanadium
440
210
252
1000
2.0
2 5
180
29
,000
,000
.064
180
2500
8.3
570
1.0
, 400
1200
600
230
9
990
ST20-02/F91
ST20-03/F91
ST20-01/F91
ST20-03/F91
ST20-05/F90
ST20-04/F92
ST20-01/F91
ST20-03/F92
ST20-04/F91
ST20-04/F91
B3MW/F92
B2MW/F92
B4BW/S92
B4MW/S92
B4MW/S92
B2MW/F92
B4MW/S92
B4MW/F92
B2MW/F92
B2MW/F92
ST20-04/F91
B2MW/S92
3.0E-04
<1.0 HI
<1.0 HI
<1.0 HI
2.8E-05
3.1E-05
3.1E-05
N/A
2. 6 HI
N/A
9.5E-05
3.7E-03/16.4 HI
<1.0 HI
4.2E-04
3.7 HI
N/A
192.6 HI
1.6 HI
Yes 3
78.8 HI
<1.0 HI
3. 9 HI
1 Location is monitoring well number followed by the sampling event, (i.e. Fall 1991 = F91).
HI Hazard Index
N/A No toxicity data available, therefore no risk was calculated.
-------

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).

5.2.1 Geology and Hvdrogeoloav at ST41

The geology of the ST41 area, as defined by numerous borings drilled in the vicinity, is
dominated by glacial till of the northest-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 clays. This lithologic assortment is typically
associated with low aguifer yeild, due to the fine-grained nature of the material and
subseguent 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 aguifer 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 aguifer 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
the wetland is designated on the National Wetlands Inventory map produced in 1979, and as
-------
such, this is an underlineated 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.

5.2.2 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.

5.2.3 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 eguipment 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 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 and 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 comment period and a public meeting was
held to address community guestions 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 hill 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 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 changing 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 (BSD) 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 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 consitiuents 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 36.3 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 detected at their maximum concentrations of 33 mg/kg and 170 mg/kg,
respectively at location ST41-SB07-20 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 in the groundwater
table, is apparent as 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 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 guality 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).
-------
Table 5-5
Summary of Constituents Detected in Surface Soil
and Surface Sediment at ST41*
impound

Surface Soil
ArsenicS
DieselS
GasolineS
Maximum
Concentration
(mg/kg)

16.1
3,600
2,000
Locationl
Freguency
Subsurface Soil

MercuryS 1. 0
LeadS 36.3
Pentachlorophenol 0.57
DieselS 33.0
GasolineS 170.0

Surface Sediment
ST41-SO-03/F92
ST41-SO-03/F92
ST41-SO-03/F92
3/3
1/2
2/2
Background2
(mg/kg)
16.18
N/A
N/A
ST41-BH01-35/F92 30/73 0.20
ST41-BH03-17/F92 30/73 10.0
ST41-BH01-35-FR/F92 4/65 N/A
ST41-BH07-20(BWT)/F92 20/62 N/A
ST41-BH07-20(BWT)/F92 3/62 N/A
56.0
0.24
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/F92
ST41-SE-09/F92
ST41-SE-09/F92
5/11
1/11
1/11
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
13.3
2-Methylnaphthalene
Benzo(a)anthracene
Chrysene
Benzo(b)fluoranthene
Benzo(k)fluoranthene
Benzo(a)pyrene
DieselS
GasolineS
LeadS
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 (i.e., Fall
1992 = F92). Information derived from OU2 RI/FS Report (U.S. 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 Supplement Risk Assessment Guidance for Superfund (EPA, 1991c)
-------
Table 5-6
Summary of Constituents Detected in Groundwater at ST41*

Compound Maximum Location2 Frequency Risk/HazardS
Concentration
(Ug/L)

Area Without Free Product
1,1,2,2-Tetrachloroethane
Benzenel
Ethylbenzenel
Toluenel
Total Xylenesl
2-Methylnaphthalene
4-Methylphenol
Naphalene
Bis(2-ethlhexyl)phthalatel
Chloroform
Total Petroleum Hydrocarbons
Nitrate
Antimony
Arsenicl
Berylliuml
Cadmium
Lead
Manganesel
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
ST41-W8/F91
ST41-W7/F91
ST41-19/F92
ST41-07/F91
ST41-19/F92
ST41-19/F91
ST41-19/F91
ST41-19/F92
ST41-22/F92
ST41-MW37B/F92
ST41-25/F92
ST41-10/F92
ST41-02/F91
ST41-22/S92
ST41-10/F91
ST41-04/F91
ST41-W8/S92
ST41-25/S92
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
2.5x10-06
7.4x10-04
3.1 HI
<1 HI
1.2 HI
N/A
N/A
<1.0 HI
4.2x10-06
2.5x10-06
N/A
1.6 HI
<1.0 HI
1.6x10-03
6.9 HI
2.5x10-04
<1.0 HI
173.0 HI
<1.0 HI
-------
Table 5-6
(continued)

Compound
Maximum Location2
Concentration
(Ug/L)
Frequency Risk/HazardS
Vanadium

Chromium

Barium

Thalliuml

Methlene chloride

Trichlorofluoromethane

Ethylene dibromide

Areas With A History of Free Product

Benzene

Ethylbenzene

Toluene

Total xylenes

Bis (2-ethylhexyl)phthalate 150,000

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).
660
350
1900
180
3,800
2.0
180
: Product
30,000
4,700
20,000
26,000
150,000
ST41-W8/S92
ST41-W8/S92
ST41-10/F91
ST41-16/F92
ST41-W7/S92
ST41-18/S92
ST41-35/S92

ST41-16/S92
ST41-16/F92
ST41-16/F92
ST41-16/S92
ST41-28/F91
44/93
52/93
77/93
1/93
14/93
3/93
8/53

ALL
ALL
ALL
ALL
ALL
3.3 HI
2.2 HI
<1.0 HI
61.6 HI
N/A
N/A
N/A

2.0x10-02
5.0 HI
13.6 HI
5.9 HI
2.6x10-02
-------
The highest levels of fuel-related compounds, not associated with free products areas,
were found in wells ST41-W7 and ST41-25. Figures 5-12 through 5-15 present maximum
concentrations of fuel-related compounds 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 particulate 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 ug/L.

Groundwater quality in the deeper aguifer is protected by the presence of a competent
aguitard, the Bootlegger Cove formation, therefore groundwater guality 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.

5.2.7 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, toluene, total
xylenes, diesels, gasoline, and 1,2-Dichloroethane. Inorganic contituents 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.
-------
Table 5-7
Compound

Benzene2

Toluene2

Ethylbenzene2

Total Xylenes2
Summary of Constituents Detected in Surface Water at ST41*

Maximum Locationl Frequency
Concentration
(Ug/L)
1,500

380

4,200

2,900
1,2-Dichloroethane 33
Arsenic2

Manganese2

Lead

Thallium2

Diesel2

Gasoline2
63

9,700

440

12,000,000

59,000,000
ST41-SW-03/S93 4/11

ST41-SW-03/S93 5/11

ST41-SW-03/S93 4/11

ST41-SW-03/S93 5/11

ST41-SW-05/S93 2/11

ST41-SW-09/F92 3/11

ST41-SW-10/F92 11/11

ST41-SW-09/F92 4/11

ST4-SW-04/F92 1/11

ST4-SW-09/F92 3/11

ST41-SW-09/F92 3/11
1 Location is sample number followed by the sampling event, (i.e., Fall 1991 = F91).
Information derived from OU2 RI/FS Report (U.S. Air Force, 1994).

2 Constituents identified as Contaminants of Concern (COCs) as outlined in the OU 2 RI/FS
Report (U.S. 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)
-------
5.2.8 ST41 Sludge Disposal Area

Site ST41 also consists of 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.

5.2.9 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 is present on the water table in
the northern portion of the site. High concentrations of fuel-related groundwater
contamination, limited to the surficial aguifer 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 contaminations 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 aguifer in this
vicinity contributed to difficulties in well development during the field season due to
poor aguifer 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 guantity 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 close 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.
-------
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 COG 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 in Risk Assessment (Part A) Final EPA
Publication No. 9285.7-09A (EPA, 1992a).

6.1.1 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 guotient (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 to ST20 and ST41 are described in subsequent
sections below.

6.1.2 Risk Characterization

The human health risk evaluation used both the exposure concentrations and the toxicity
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 as
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-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 exposures 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 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 yeild) 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 conataminated 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 scecario
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.
-------
Table 6-1
Scenario
Future Residential
Future Commercial/
Industrial
Summary of Exposure Scenarios Evaluated for OU2

Description Matrix
Pathways
Individual resides in the source Groundwater
area as it now exists; use of
groundwater from the under-
lying aguifer for domestic
purposes.

Individual works in area; Groundwater
occasionally uses groundwater
from the underlying aguifer
for consumption only.
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
Ingestion of Chemicals in
Groundwater:
Residential RME
Residential
Average
Commercial/
Industrial RME
Ingestion rate (L/day)
Exposure frequency (days/yrs)
Exposure duration (yrs)
Body weight (kg)
Averaging time (days)
Noncarcinogens
Carcinogens
2
350
30
70

10950
25550
1.4
275
9
70

3285
25550
1.0
250
25
70

9125
25550
Inhalation of Chemicals in Groundwater While Showering:
Maximum chemical concentration in
air
Inhalation rate (L/hr)
Exposure frequency (days/yr)
Exposure duration (yrs)
Exposure time (hrs/day)
Showering time (hrs)
Fraction volatilized (unitless)
Flow rate (L/hr)
Volume air (L)
Body weight (kg)
Averaging time (days)
Noncarcinogens
Carcinogen
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
Dermal Absorption of Chemicals in Groundwater 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 (hrs)
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
-------
Table 6-3
Permeability Constants for Dermal Exposure at OU2
Analyte
Permeability Constants
1,1-Trichloroethane
1,1,2, 2-Tetrachloroethane
1,1-Dichloroethane
1,1-Dichloroethene
1, 2-Trichlorobenzene
1, 2-Dibromoethane
2-Me thylnaphthalene *
4-Methyl-2-Pentanone*
Antimony*
Arsenic
Barium
Benzene
Benzo(a)pyrene
Beryllium
Bis (2-Ethylhexyl)phthalate
Bromomethane
Cadmium
Carbon Tetrachloride
Chloroform
Chioromethane
Chromium
Copper*
Dichlorodifluoromethane
Ethylbenzene
Hexachlorobutadiene
Manganese*
Mercury
Methylene chloride
Naphthalene
Nickel
Nitrate
Petroleum hydrocarbons*
Polychlorinated biphenyis
Tetrachloroethene
Thallium*
Toluene
Trichloroethene
Trichlorofluoromethane
Vanadium*
Vinyl chloride
Xylene
Zinc
1.7E-02
9.0E-03
8.9E-03
1.6E-02
l.OE-01
3.0E-03
1.5E-03
1.5E-03
1.5E-03
3.2E-04
1.5E-03
1.1E-01
1.2E+00
3.2E-04
3.3E-02
3.5E-03
3.2E-04
2.2E-02
1.3E-01
4.2E-03
2.0E-03
1.5E-03
1.2E-02
l.OE+00
1.2E-01
1.5E-03
l.OE-03
4.5E-03
6.9E-02
l.OE-03
1.5E-03
1.5E-03
l.OE+00
7.9E-03
1.5E-03
l.OE+00
2.3E-01
1.7E-02
1.5E-03
7.3E-03
8.0E-02
6.0E-04
PCs were not available for these contaminants, therefor the PC for water (1.5-03) was
used.
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The following sections summarize human risks associated with exposure to site contaminants
and provide potential remedial action criteria.

6.1.3 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 area 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 COG at the site for
both the residential and commercial/industrial exposure scenarios. Maximum unacceptable
risk/hazard occurs at upgradient monitoring wels B2MW and B4MW for all of the COCs listed
excepth benzene.

Benzene is the only organic COG 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 guality assurance/guality control
(QA/QC) reguirements for assessing risk.

Figure 6-1 depicts the unacceptable risk/hazard for each COG 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/L 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 absorbed onto particulate 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, ST20-01,
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 and 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 currently being addressed under the SERA program, and a Corrective
Action Plan is due in 1995.

-------
Table 6-4
ST20 Groundwater
Summary of Risk
Compound
Benzene
Nitrate
Arsenic
Beryllium
Chromium
Lead
Nickel
Manganese
Thallium
Vanadium
Maximum
Concentration
(Ug/L)
440
150,000
180
8.3
570
600
1200
32,400
230
970
Locationl
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
3.0E-04
2.6 HI
3.7E-03/16.4 HI
4.2E-04
3.7 HI
YES3
1.6 HI
192.6 HI
78.8 HI
3.9 HI
Commercial/Ind
Risk/Hazard
4.6E-05
<1.0 HI
1.1E-03 5.9 HI
1.2 E-04
1.1 HI
YES3
<1.0 HI]
63.4 HI
28.1 HI
1.4 HI
1 Location is monitoring well number followed by the sampling event, (i.e., Fall 1991 =
F91) .

2 Risk/Hazard for each scenario were calculated using maximum concentrated provided for
exposure point concentration and other exposure parameters provided in Table 9 of this
document.
3 Exposure to lead levels greater than 50 jlg/L will result in toxic effects to human
health. Toxic effects from lead concentration >50 y.g/L cannot be quantified using
EPA's uptake Biokinectic Model.
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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 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 infreguent
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, exylenes) , 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 occuring 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 thallium and beryllium to COCs with a residential
risk/hazard of 61.6 and 2.5E-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 ST41, 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.
-------
Table 6-5
Compound
ST41 Groundwater Summary of Risk
Maximum Locationl
Concentration
(Ug/L)
Residential2 Commercial/Industrial2
Risk/Hazard Risk/Hazard
Areas Without Free Product
Benzene 1,100 ST41-07/F91

Ethylbenzene 3,800 ST41-19/F92

Xylene 4,200 ST41-19/F92

Arsenic 76 ST41-22/S92

Beryllium 4.0 ST41-10/F91

Manganese 29,100 ST41-25/S92

Thallium 61.6 HI ST41-16/F92

Areas With A History of Free Product

Benzene 30,000 ST41-16/S92

Ethylbenzene 4,700 ST41-16/F92

Toluene 20,000 ST41-16/F92

Xylene 26,000 ST41-16/S92

Bis(2-ethylhexyl)phthalate 150,000 ST41-28/F91
HI
7.4E-04

3.1 HI

1.2 HI

1.6E-03/6.9 HI

2.5E-04

173.9 HI

61.6

2.0E-02

5.0 HI

13.6 HI

5.9 HI

2.6E-02/217 HI
1.1E-04

<1 HI

4.6E-04/2.5 HI

6.0E-05

56.9 HI

22.0 HI

3.0E-03

4.0 HI

1.2 HI

<1 HI

7.3E-03/73.4
1 Location is monitoring well number followed by the sampling event, (i.e., Fall 1991 =
F91) .

2 Risk/Hazard for each scenario were calculated using maximum concentrated for exposure
point concentration and other exposure provided in Table 6-2 of this document.
-------
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 highlights 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, ST42-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
guantify numerically (e.g., in terms of an error bar). As a result, the effect is
discussed gualitatively. 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.

6.2 Ecologies 1 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 toxicological effects of the selected COECs, selection of
assessment end points, initial guantification 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);

! 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.

6.2.2 Ecological Evaluation of ST41

Based on calculated ecological guotients, freguency 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-methylnaphthalene,
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 guality
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. In 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 freguently 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.

6.3 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.
-------
Table 6-6
Summary of ST41 Surface Water Results With
Surface Water Quality Criteria*
Compound Maximum
Concentration
(Ug/L)
Benzene2
Toluene2
Ethylbenzene2
Total xylenes2
1, 2-Dichloroethane
Arsenic2
Manganese2
Lead
Thallium2
Diesel2
Gasoline2
1,500
380
4,200
2,900
33
63
9,700
41
440
12,000,000
59,000,000
Locationl

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
Alaska Surface
Water Quality
Criteria (ug/L)

lOa

lOa
15b

15b
1 Location is sample number followed by the sampling event, (i.e., Fall 1991 = F91).

2 Constituents identified as Contaminants of Concern (COCs) as outlined in the OU 2 RI/FS
(U.S. Air Force, 1994).

a Based on total aromatic hydrocarbons.

b Based on total hydrocarbons.

* Limited to compounds of potential concern identified by following procedures consistent
with EPA Region X Supplement Risk Assessment Guidance for Superfund (EPA, 1991c).

** Substances shall not individually or in combination exceed 0.01 times the lowest
measured 96 hour LC50 for lifestages of species identified by the department as being
the most sensitive, biologically important to the location, or exceed criteria cited
in the State of Alaska Water Quality Standards (18 AAC Ch.80, 1995).

NC No criteria for this exposure.

N/A Not available.

LOEL - Lowest Observable Effect Level
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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. The section of the Record of
Decision describes the remedial alternatives 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 Spill

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 aguaculture, 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.

! Compliance with all action-, chemical-, and location-specific ARARs
(defined in Section 10, Statutory Determinations).
-------
Final remediation goals for groundwater include prevention of ingestion or direct contact
with groundwater containing contaminants in concentrations in excess of background or
federal drinking water standards (Primary MCLs):

Contaminant MCL (ug/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 (ug/L)*

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.

7.2 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 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%.

7.2.1 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 natrual 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 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.
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7.2.2
Alternatives for Groundwater
Alternative G-I: No Action
Capital Costs:
Average Annual Costs:
Total Present Worth Costs:
Time to Complete Cleanup:
$0.0
$0
$0
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:
for Groundwater
Natural Attenuation with Institutional Controls, Long Term Monitoring
Capital Costs:
Average Annual Costs:
Total Present Worth Costs:
Estimated Time to Complete Cleanup:
$1,500
$79,000
$713,700 (based on a 10% discount rate per year)
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-III: Limited Collection and Treatment of Groundwater, Natural Attenuation
with Long-Term Monitoring
Capital Costs:
Average Annual Costs:
Total Present Worth Costs:
Estimated Time to Complete Cleanup:
$1,500
$250,000
$2,998,000 (based on 10% discount rate per year)
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 natrual
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-II.

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 reguired 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 reguired 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: $1,160,00
Total Present Worth Costs: $1,160,000
Time to Complete Cleanup: Less than one year

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 leachable concentrations
of fuel-related constituents. Treatment and/or disposal of and unknown volume of
contaminated soil will be in accordance with all applicable state and federal regulations,
including 18 ACC 78.310, 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 guantity 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.

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 IRA 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 reguirements 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-II, G-III 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-II and G-III and in 17 years or less with Alternative G-IV. Alternatives
G-II, G-III and G-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 prevent 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 effected 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-III 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 wetlands area.
Action-specific ARARs related to air and waste management associated with the IRA would
also be met for alternatives G-II, G-III, and G-IV.

8.1.2 ST41 Source Control

Overall protection of human health and the environment. Alternative S-II 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-III accomplishes the same goals as S-II 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 (ARAs). Alternatives
S-II and S-III 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-II complies with location-specific ARARs. Alternative S-III may result in alteration of
the wetland environment due to the extremely large size of the tanks which would be
removed.
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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-III 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-III and G-IV 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 contaminated concentrations to acceptable
levels within the same approximate time frames as Alternatives G-III 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 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-III 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 reguired to periodically assess the existing monitoring well network.
Alternative G-III 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 reguires no major system modification. Alternative G-IV
reguires 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-II, with a total projected present worth cost of $713,700, is the
least expensive alternative. Alternatives G-III and G-IV, with projected costs of
$2,998,000 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-III and G-IV are
approximately 4 times more expensive than Alternative G-II. These costs are higher due to
the annual operation and maintenance reguired to maintain active treatment systems.

8.2.2 ST41 Source Control

Long-Term effectiveness. Both Alternatives S-II and S-III provide for long term
effectiveness and permanence. S-II removes the piping and associated soil with leachable
-------
contaminants, and prevents the underground tanks remaining in the ground from being a
continuing source of contamination. S-III accomplishes the same goal be removing the
tanks and piping system completely, in addition to removing associated contaminated soil.

Reduction in toxicity, mobility, or volume of contaminations through treatment. Both
alternatives S-II and S-III involve treatment. Alternative S-II 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 leachable contaminants for
offsite disposal and treatment.

Alternate S-III 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-II 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-III will involve human health
and environmental impacts. Increased dust production during excavation of the tanks and
piping systems will effect both the workers and base personnel. The extensive excavation
will also result in habitat destruction, increased erosion and aguifer disruption.

Implementability. Alternative S-II is easier to implement than alternative S-III, however
the eguipment, materials and skilled workers necessary to implement both of the
alternatives are available. Alternatives S-II and S-III will both reguire 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.

8. 3 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-II for groundwater remediation and Alternative S-II for source
control. The Statte 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 guestions and
comments received during the public comment period, is attached to this Record of
Decision.

9. 0 SEIiECTED 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 reguirements.
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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.

9.2 ST41 Tank Spill

The selected remedy is Alternative G-II 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-II, 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 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 aguaculture;
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3. Continued enforcement of base policy prohibiting installation of groundwater wells
(other than for monitoring purposes) into the shallow aguifer underlying OU2 at
Elmendorf AFB; and

4. Prohibiting unauthorized access to existing water supply and groundwater monitoring
wells.

! 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-IV, 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 aguifer to eliminate further
migration;

! Treating the extracted water with an air stripping process to meet federal,
state and local water guality regulations;

! Treating the air emissions from the air stripping process as needed to meet
substantive state and base air emission permit reguirements;

! Disposing of the treated groundwater in accordance with federal, state, and
local regulations and substantive permit reguirements;

! 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:

! Long-term monitoring of groundwater at ST41 indicates that natural
attenuation is not occuring 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.
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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.

10.0 STATUTORY DETERMINATIONS

The selected remedy meets the statutory reguirements 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-II 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 reguiring
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-IV, 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 adeguate protection of human health and
the environment. Alternative G-IV 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 aguifer 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 aguifer 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
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the remedial action will allow the EPA and ADEC the opportunity to improve upon the
remedial action, if necessary.

10.2 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.

10.2.1 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
qroundwater 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 filter 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 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 in the removal of petroleum
contaminated soil the contaminated soil will be handled and treated with
the requirements of 18 AAC 78.310.

10.2.2 Chemical-Specific ARARs

! 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
Ethylbenzene 700.0
Toluene 1,000.0
Xylene 10,000.0
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Alaska surface water quality criteria, established under the State of Alaska Water Quality
Standards, are relevent and appropriate requirements for surface water that can be used
for qrowth and propaqation of fish, shellfish, and other aquatic life or wildlife (see
Table 6-6):

Contaminant State SWOC (uq/L)*

Benzene 10
Ethylbenzene 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 Requlation 18 AAC 75.310 (1994)
pertaininq to surface and qroundwater cleanup of petroleum related benzene.

* The selected remedy will meet. Alaska Underqround Storaqe Tank Requlation 18 AAC 78.315
(1994) for the cleanup quidelines for underqround storaqe tank contaminated soil.

10.2.3 Location-Specific ARARs

Executive Order 11990 and 40 CFR Part 6, Appendix A, require that Federal Aqencies conduct
activities to avoid, to the extent possible, the lonq and short-term adverse impacts
associated with the destruction or modification of wetlands.

10.3 Cost-Effectiveness

The selected remedy, Alternative G-II, is cost-effective because it has been determined to
provide overall effectiveness proportionate to its costs and duration to achieve the
remediation qoals. The continqent remedy, Alternative G-IV, is the most cost-effective of
the remaininq 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 solution and treatment
technoloqies 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 lonq-term effectiveness and permanence,
reduction in toxicity, mobility, or volume achieved throuqh treatment, short-term
effectiveness, implementability, cost (as discussed in the precedinq section), and the
statutory preference for treatment as a principal element and considerinq State and
community acceptance.

The most decisive factors in the selection decision were lonq-term effectiveness,
implementability, and cost-effectiveness. Alternatives G-II and S-II and the continqent
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, qiven the ease of implementation and cost-effectiveness of
alternative G-II, alternative G-IV was selected as the continqent 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 75.327, 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
Environmental Restoration Program. Operable Unit 2 Remedial Investigation/Feasibility
Study, March 1994.

U.S. Environmental Protection Agency (USEPA) . Risk Assessment Guidance for Superfund
(RAGS), Volume 1: Human Health Evaluation Manual Part A, USWER Directive 9285.701 a.
December 1989.

U.S. Environmental Protection Agency (USEPA). Risk Assessment Guidance for Superfund
Volume 1: Human Health Evaluation Manual (Part B. Development of Risk-based 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 A) , 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
OPERABIiE UNIT 2
RESPONSIVE SUMMARY

The Proposed Plan for OU2 was issued to the public on June 13, 1994. This began a public
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 U.S. 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 eguate 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 flow.

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 the existing monitoring well 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.
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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 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 reguired 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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