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Record of Decision
for Site 4 - Old Landfill
Marine Corps Base (MCB)
Quantico, Virginia
Naval Facilities Engineering Command Washington
October 2007
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TABLE OF CONTENTS
SECTION PAGE NO. ACRONYMS AND ABBREVIATIONS
........................................................................................................
iv 1.0
DECLARATION............................................................................................................................1-1
1.1 SITE NAME AND
LOCATION......................................................................................1-1
1.2 STATEMENT OF BASIS AND PURPOSE
..................................................................1-1
1.3 ASSESSMENT OF
SITE..............................................................................................1-1
1.4 DESCRIPTION OF SELECTED
REMEDY..................................................................1-2
1.5 STATUTORY DETERMINATIONS
..............................................................................1-4
1.6 ROD DATA CERTIFICATION
CHECKLIST.................................................................1-4
1.7 AUTHORIZING SIGNATURE
......................................................................................1-5
2.0 DECISION SUMMARY
.................................................................................................................2-1
2.1 SITE NAME, LOCATION, AND
DESCRIPTION..........................................................2-1
2.2 SITE HISTORY AND ENFORCEMENT
ACTIVITIES..................................................2-2
2.2.1 Site
History...................................................................................................................2-2
2.2.2 Previous Investigations and Enforcement
Actions.......................................................2-2
2.3 COMMUNITY PARTICIPATION
..................................................................................2-6
2.4 SCOPE AND ROLE OF RESPONSE ACTION
...........................................................2-6 2.5
SITE CHARACTERISTICS
..........................................................................................2-8
2.5.1 Physical
Setting............................................................................................................2-8
2.5.2 Conceptual Site Model
.................................................................................................2-9
2.5.3 Sampling
Strategy......................................................................................................2-10
2.5.4 Nature and Extent of
Contamination..........................................................................2-11
2.6 CURRENT AND POTENTIAL FUTURE LAND AND RESOURCE
USES.................2-12 2.7 SUMMARY OF CONTAMINANT FATE AND
TRANSPORT MODELING.................2-13 2.8 SUMMARY OF SITE
RISKS......................................................................................2-14
2.8.1 Direct Exposure – Human Health
Risks.....................................................................2-15
2.8.2 Indirect Exposure – Human Health and Ecological
Risks..........................................2-19 2.8.3
Conclusions of Site
Risks...........................................................................................2-21
2.9 REMEDIAL ACTION
OBJECTIVES...........................................................................2-21
2.10 DESCRIPTION OF ALTERNATIVES
........................................................................2-23
2.10.1 Description of Remedy Components
.........................................................................2-23
2.10.2 Common Elements and Distinguishing Features of Each
Alternative .......................2-27 2.10.3 Expected Outcomes of
Each Alternative
...................................................................2-28
2.11 SUMMARY OF COMPARATIVE ANALYSIS OF
ALTERNATIVES...........................2-28 2.11.1 Overall
Protection of Human Health and the Environment
........................................2-28 2.11.2 Compliance with
Applicable or Relevant and Appropriate Requirements (ARARs) ..2-29
2.11.3 Long-Term Effectiveness and
Permanence...............................................................2-30
2.11.4 Reduction of Toxicity, Mobility, or Volume through Treatment
..................................2-31 2.11.5 Short-Term
Effectiveness...........................................................................................2-31
2.11.6 Implementability
.........................................................................................................2-32
2.11.7 Cost
............................................................................................................................2-33
2.11.8 State Acceptance
.......................................................................................................2-33
2.11.9 Community Acceptance
.............................................................................................2-33
2.12 PRINCIPAL THREAT
WASTES.................................................................................2-33
2.13 SELECTED
REMEDY................................................................................................2-33
2.13.1 Summary of the Rationale for the Selected
Remedy.................................................2-33 2.13.2
Description of the Selected
Remedy..........................................................................2-34
2.13.3 Summary of the Estimated Remedy Costs
................................................................2-36
2.13.4 Expected Outcomes of the Selected Remedy
...........................................................2-36
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TABLE OF CONTENTS
SECTION PAGE NO. 2.14 STATUTORY DETERMINATIONS
............................................................................2-37
2.14.1 Protection of Human Health and the Environment
....................................................2-37 2.14.2
Compliance with
ARARs............................................................................................2-38
2.14.3 Cost-Effectiveness
.....................................................................................................2-38
2.14.4 Utilization of Permanent Solutions and Alternative Treatment
(or Resource Recovery) Technologies to the Maximum Extent
Practicable ...................................2-38 2.14.5
Preference for Treatment as a Principal
Element......................................................2-40
2.14.6 Five-Year Review Requirement
.................................................................................2-40
2.15 DOCUMENTATION OF SIGNIFICANT
CHANGES...................................................2-40 3.0
RESPONSIVENESS SUMMARY
.................................................................................................3-1
3.1
OVERVIEW..................................................................................................................3-1
3.2 BACKGROUND ON COMMUNITY
INVOLVEMENT...................................................3-2
REFERENCES..........................................................................................................................................
R-1 APPENDICES A GLOSSARY
TABLES
NUMBER 2-1 Summary of Positive Results - 2006 Remedial
Investigation Data 2-2 Summary of Positive Results - 2006 Remedial
Investigation and Historical Groundwater Data 2-3 Summary of COCs
for Groundwater 2-4 Toxicity Data Summary 2-5 Risk Characterization
Summary - Carcinogens 2-6 Risk Characterization Summary -
Noncarcinogens 2-7 ARARs and TBC Criteria 2-8 Summary of Evaluation
of Groundwater Alternatives 2-9 Capital Cost Details for Selected
Remedy, Alternative 3: In-Situ Bioremediation: ORC Treatment 2-10
Annual Cost Details for Selected Remedy, Alternative 3: In-Situ
Bioremediation: ORC Treatment 2-11 Present Worth Costs for Selected
Remedy, Alternative 3: In-Situ Bioremediation: ORC
Treatment
ii
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FIGURES
NUMBER 2-1 Vicinity Map 2-2 Installation Map, Basewide Site Map
2-3 Site Layout 2-4 Conceptual Site Model 2-5 RI Sampling
Locations
iii
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ACRONYMS AND ABBREVIATIONS
µg/dL microgram per deciliter
µg/L microgram per liter
AICUZ Air Installation Compatible Use Zone
ARAR applicable or relevant and appropriate requirement
BAF sediment to invertebrate bioaccumulation factor
bgs below ground surface
BSAF sediment to fish bioaccumulation factor
BTAG Biological Technical Assistance Group
CDI chronic daily intake
CERCLA Comprehensive Environmental Response, Compensation, and
Liability Act
CERCLIS CERCLA Information System
CFR Code of Federal Regulations
CNS central nervous system
COC chemical of concern
COPC chemical of potential concern
CS Confirmation Study
CSF cancer slope factor
CSM conceptual site model
DON Department of the Navy
DRMO Defense Reutilization and Marketing Office
ECTran Excel-Crystal Ball
EE/CA Engineering Evaluation/Cost Analysis
EPA United States Environmental Protection Agency
ESD Explanation of Significant Differences
FFA Federal Facilities Agreement
FFS Focused Feasibility Study
FS Feasibility Study
ft/day feet per day
ft/ft foot per foot
GI gastrointestinal
GIS Geographic Information System
gpm gallons per minute
HASP health and safety plan
HEAST Health Effects Assessment Summary Table
HHRA human health risk assessment
iv
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HI hazard index
HQ hazard quotient
IAS Initial Assessment Study
IEUBK Integrated Exposure Uptake Biokinetic
ILCR Incremental Lifetime cancer risk
IR Installation Restoration
IRA Interim Remedial Action
IRIS Integrated Risk Information System
LTM Long-Term Monitoring
LUC land use control
MCAF Marine Corps Air Facility
MCB Marine Corps Base
MCL Maximum Contaminant Level
mg/kg milligrams per kilogram
msl mean sea level
NA not applicable/available
NAVFAC Naval Facilities Engineering Command
NCEA National Center for Environmental Assessment
NCP National Oil and Hazardous Substances Pollution Contingency
Plan
NEESA Naval Energy and Environment Support Activity
NOV Notice of Violation
NPDES National Pollutant Discharge Elimination System
NPL National Priorities List
O&M operation and maintenance
OSHA Occupational Safety and Health Administration
OSWER Office of Solid Waste and Emergency Response
OU Operable Unit
PAH polynuclear aromatic hydrocarbon
PCB polychlorinated biphenyl
PRG preliminary remediation goal
QPMT Quantico Project Managers Team
RAGS Risk Assessment Guidance for Superfund
RAO remedial action objective
RBC risk-based concentration
RCRA Resource, Conservation, and Recovery Act
RF&P Richmond, Fredricksburg, and Potomac
RfD reference dose
v
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RfDo oral reference dose
RFA RCRA Facility Assessment
RI Remedial Investigation
RME reasonable maximum exposure
ROD Record of Decision
SARA Superfund Amendments and Reauthorization Act
STP Sewage Treatment Plant
SVOC semivolatile organic compound
SWMU Solid Waste Management Unit
TAL Target Analyte List
TCL Target Compound List
UCL upper confidence limit
USFWS U.S. Fish and Wildlife Service
VAC Virginia Administrative Code
VDEQ Virginia Department of Environmental Quality
VOC volatile organic compound
VPDES Virginia Pollutant Discharge Elimination System
WQC water quality criteria
vi
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1.0 DECLARATION
1.1 SITE NAME AND LOCATION
Site 4 – Old Landfill
Marine Corps Base
Quantico, Virginia
CERCLIS ID No. VA1170024722
1.2 STATEMENT OF BASIS AND PURPOSE
This decision document presents the Selected Remedy for Site 4
(Old Landfill) at the Marine Corps Base
(MCB) Quantico, Virginia. The Selected Remedy was chosen in
accordance with the Comprehensive
Environmental Response, Compensation, and Liability Act
(CERCLA), as amended by the Superfund
Amendments and Reauthorization Act (SARA), and, to the extent
practicable, the National Oil and
Hazardous Substances Pollution Contingency Plan (NCP). This
decision is based on the Administrative
Record for this site.
The Department of the Navy (DON) and United States Environmental
Protection Agency (EPA) jointly
selected the remedy, and the Virginia Department of
Environmental Quality (VDEQ) concurs with the
Selected Remedy.
This Record of Decision (ROD) also addresses hazardous waste
activities conducted at Solid Waste
Management Units (SWMUs) B-08 (Building 669) and L-03 [Defense
Reutilization and Marketing Office
(DRMO) Scrapyard], which were located within the boundaries of
Site 4. Site 4 and these two SWMUs
were designated as Operable Unit (OU) 4 in the MCB Quantico
Federal Facilities Agreement (FFA)(1). By
signing the Installation Restoration (IR) Program Consensus
Agreement No. 7(2), the Quantico Project
Managers Team (QPMT) recognized that all documents pertaining to
Site 4 serve to address and close
out the entire OU, not just Site 4. Consequently, the decisions
presented in this document for Site 4
actually apply to OU 4.
1.3 ASSESSMENT OF SITE
The response action selected in this ROD is necessary to protect
the public health or welfare or the
environment from actual or threatened releases of hazardous
substances into the environment.
1-1
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1.4 DESCRIPTION OF SELECTED REMEDY
Site 4 is one of the 226 sites included in the MCB Quantico IR
Program. Separate investigations and
assessments are being conducted for most of these sites in
accordance with CERCLA. However, as
stated in Section 1.2, this ROD applies to Site 4, SWMU B-08,
and SWMU L-03, which comprise OU4.
This ROD, which addresses the site as a source area, consists of
the final remedial actions to be taken
regarding on-site contamination (in landfill waste, soil, and
groundwater) at Site 4. Off-site contamination
that is present in the Quantico Embayment as a result of
historical releases from Site 4 is being
addressed under a broader watershed study (Site 99 – Quantico
Embayment). Therefore, this ROD does
not include remedial alternatives for the Quantico
Embayment.
The remedial actions in this ROD address the measures necessary
to ensure that remedial/removal
actions previously conducted at the site continue to be
protective of human health and the environment,
and thereby become components of the final remedy for Site 4.
The remedial actions in this ROD also
address the potential threat of the migration of on-site
contaminants (via groundwater discharge) from
Site 4 to the Quantico Embayment.
Previous remedial/removal actions, whose components need to be
incorporated in the final remedy for
Site 4, include the following: an Interim Remedial Action (IRA)
that was completed at Site 4 in 1997 and a
2005 action that addressed landfill waste encountered during a
CERCLA non-time-critical soil removal
action at a nearby IR Program site, Site 32 (Pesticide Control
Building). The following paragraphs
describe the previous remedial/removal actions and the need for
the Selected Remedy that is being
addressed in this ROD.
In 1997, an IRA was completed at Site 4 to address potential
risks associated with exposure to landfill
waste, soil, surface water, and sediment. The IRA was conducted
in accordance with a ROD(3). The IRA
included removal of soil/sediment from a drainage ditch, removal
of solid waste material and sediment
from the shoreline of the Quantico Embayment (part of the
Potomac River), installation of a fence,
installation of a geotextile separation layer and placement of a
soil barrier layer, and construction of
erosion protection on the river bank adjacent to the landfill.
The barrier layers and fencing were installed
on and around a majority of the site. As discussed in this ROD,
future exposure to contaminated media
(beneath the barrier layers) and damage to the barrier layers
need to be prevented via institutional
controls.
During recent site investigations (1999 post-IRA activities for
Site 4 and a 2005 CERCLA non-time-critical
removal action conducted at Site 32), some landfill waste was
discovered outside the existing fence at
Site 4. The waste encountered in 2005 was completely removed and
the excavated area was restored.
1-2
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The waste encountered in 1999 was not removed but was found to
be covered with at least 2 feet of
clean soil, which acts as a soil barrier layer. Institutional
controls are necessary to prevent human
exposure to the remaining wastes not covered by a geotextile
barrier layer.
With the intent of providing alternatives to the DON for
selecting a permanent remedy for Site 4, a
Feasibility Study (FS) Report(4) was prepared to address on-site
contamination at Site 4, including the
areas where waste was more recently discovered. As part of
alternatives for a permanent remedy for Site
4, the FS evaluated the adequacy of the components of the
previous remedial/removal actions for
protection of human health and the environment. Furthermore, the
FS evaluated the migration of on-site
contaminants via groundwater discharge to the Quantico
Embayment.
The Selected Remedy for Site 4 is institutional controls that
maintain the components of the previous
remedial/removal actions and restrict the use of land and
groundwater beneath the site and long-term
groundwater monitoring. The Selected Remedy, in conjunction with
the previously implemented
remedial/removal actions, will achieve substantial and long-term
risk reduction through a combination of
containment, prohibition of land and groundwater uses that would
cause unacceptable risk to human
health, and monitoring to provide data to confirm that migration
of groundwater contaminants does not
adversely affect the environment. Site reviews would also be
conducted. The Selected Remedy includes
the following major components:
• Fencing - Maintenance of the existing fence that was placed
around a majority of the site to prevent
disturbance of the barrier layers installed during the 1997 IRA.
Because of the railroad right-of-way
and the need to maintain access to the airfield via the access
road at the landfill, it is not considered
to be feasible to install fencing around sections of the site
where waste was encountered in 1999 and
2005.
• Institutional controls - Controls will be put in place to
prohibit residential development, intrusive
activities (e.g., excavation) in areas where landfill
waste/contamination is present, and the use of
contaminated groundwater beneath the landfill as long as
concentrations of hazardous substances in
the soil and groundwater are at such levels that prevent
unrestricted use and unlimited exposure.
• Monitoring - Long-term monitoring of groundwater at Site 4
will be conducted to confirm that future
migration of on-site contaminants does not adversely impact
human and ecological receptors
indirectly exposed to landfill contaminants in the Quantico
Embayment. Although not included in this
ROD, monitoring in the Embayment will be conducted as part of
remedial actions at Site 99.
1-3
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1.5 STATUTORY DETERMINATIONS
The Selected Remedy attains the mandates of CERCLA Section 121
and, to the extent practicable, the
regulatory requirements of the NCP. The Selected Remedy, in
conjunction with the IRA, is protective of
human health and the environment, complies with federal and
state requirements that are applicable or
relevant and appropriate to the remedial action, is cost
effective, and utilizes permanent solutions and
alternative treatment (or resource recovery) technologies to the
maximum extent practicable. This
remedy is also consistent with the EPA directive for the
application of the presumptive remedy approach
for CERCLA municipal landfill sites(5).
The DON’s decision not to treat landfill waste and groundwater
will not result in unacceptable risks to
human health or the environment because of the current and
future land use assumptions. Based on the
risk assessments completed for the site, the only potential
unacceptable risks to human health and the
environment were for hypothetical future residents. These risks
will be addressed by implementing
institutional controls to prohibit residential development at
the site. Direct exposure to landfill waste left in
place is not anticipated because a geotextile separation layer
and soil barrier layer were installed over a
majority of the waste. The waste that is not covered by the
barrier layers is buried beneath at least 2 feet
of soil, which is consistent with the thickness of the soil
barrier layer installed during the IRA. Therefore,
the soil covering this waste would prevent typical exposures.
Treatment of groundwater is not necessary
to provide adequate protection of human health and the
environment. Fate and transport modeling
conducted for the FS showed that the leaching, discharge,
partitioning, and bioconcentration of on-site
landfill contaminants via the natural discharge of groundwater
would not adversely impact human and
ecological receptors exposed to surface water and sediment in
the Quantico Embayment. Additionally,
restoration of groundwater beneath the landfill is not required
because the landfill is not within the area of
attainment as defined by EPA. The area of attainment does not
include areas where wastes are left in
place. Groundwater contamination does not extend beyond the
landfill boundary, which is the Quantico
Embayment.
Because the Selected Remedy will result in hazardous substances,
pollutants, or contaminants remaining
on site at concentrations greater than levels that allow for
unlimited use and unrestricted exposure, a
statutory review will be conducted every 5 years after
initiation of the remedial action to ensure that the
remedy is, or will be, protective of human health and the
environment.
1.6 ROD DATA CERTIFICATION CHECKLIST
The following information is included in the Decision Summary
section of this ROD. Additional
information can be found in the Administrative Record for this
site.
1-4
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2.0 DECISION SUMMARY
2.1 SITE NAME, LOCATION, AND DESCRIPTION
The MCB is located in Quantico, Virginia, approximately 35 miles
south of Washington, D.C. and 75 miles
north of Richmond, Virginia (Figure 2-1). The facility covers
more than 59,000 acres in southern Prince
William County, northern Stafford County, and eastern Fauquier
County. The facility is bounded to the
north by Cedar Run and Virginia State Route 646; to the east by
the Potomac River; to the south by Tank
Creek, Aquia Creek, and Virginia State Route 610; and to the
west by Dorrells Run and Virginia State
Route 612 (Figure 2-2). The EPA CERCLA Information System
(CERCLIS) identification number for
MCB Quantico is VA1170024722.
The DON [specifically the Naval Facilities Engineering Command
(NAVFAC) Washington] is the lead
agency for site activities at MCB Quantico. The EPA is the lead
regulatory agency, and VDEQ is the
support agency. Clean-up funds are provided by the Department of
Defense.
Site 4 (Old Landfill) is a 24-acre landfill located along the
banks of the Potomac River in the Mainside
area of MCB Quantico (Figure 2-2). The area of the Potomac River
adjacent to Site 4 is known as the
Quantico Embayment. The site boundaries, which are presented in
Figure 2-3, were identified using
historical aerial photographs that illustrated intrusive
activities or cleared areas during landfill operations.
The site is bounded on the east by the Quantico Embayment and on
the south by IR Site 96 (Old Landfill
Southern Wetlands). The Marine Corps Air Facility (MCAF) Turner
airfield is located immediately south of
Site 96. Based on information gathered during post-IRA
activities, the northern and western boundaries
of the site were redefined when landfill waste was encountered
during construction activities near the
Richmond, Fredricksburg, and Potomac (RF&P) Railroad tracks
and soil removal activities at IR Site 32
(Pesticide Control Building). The RF&P Subdivision is part
of CSX Transportation. The northern
boundary of the site overlaps with the boundaries of Site 32.
Figure 2-3 illustrates the locations where
landfill waste was found outside of the existing fence that was
installed as part of the 1997 IRA.
Two other IR Program sites, SWMUs L-03 (DRMO Scrapyard) and B-08
(Building 669), were located
within the boundaries of Site 4 (see Figure 2-3). A constructed
wetland (also referred to as the unnamed
tributary), bisects the northern and southern portions of Site
4.
2-1
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2.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES
2.2.1 Site History
Landfill operations began in the northern portion of the site in
the early 1920s near the railroad tracks and
continued to expand eastward until 1971 when another municipal
landfill was opened at the Base.
Operations at Site 4 have extended the original shoreline an
additional 600 to 1,200 feet eastward to
create a new Quantico Embayment bank, which consists of
artificial fill. After 1966, operations extended
to the area south of the unnamed tributary (near Site 96). The
landfill received material from all Base
activities east of U.S. Highway 1, including the hospital and
the airfield. Wastes reportedly disposed at
Site 4 include municipal refuse, construction debris, paints and
thinners, transformers, dielectric fluids,
waste oils, batteries, and compressors. Wastes were burned prior
to burial until the mid-1960s. The
estimated volume of fill material is 281,000 cubic yards.
Concurrent to and after landfill operations ceased, a portion of
the site was also used as a DRMO
scrapyard (SWMU L-03) and transformer storage area (SWMU B-08)
from the 1950s until 1979. Items
stored at the SWMUs included drums containing waste fuels and
solvents, transformers, and out of
service military vehicles. Electrical transformers were stored
in the eastern portion of SWMU L-03 and at
SWMU B-08. Transformers were opened and drained to recover the
copper wire and steel casings.
Consequently, transformer oil, possibly containing
polychlorinated biphenyls (PCBs), was released onto
the ground surface along the eastern boundary of SWMU L-03
within an area of approximately 50 feet by
375 feet. SWMU B-08, located northeast of SWMU L-03, was
approximately 60 feet by 110 feet. No
information exists concerning quantities of chemicals released
at these SWMUs. A removal action for
PCB-contaminated soil was conducted at SWMUs L-03 and B-08 in
1990. During this removal action,
contaminated soil with PCB concentrations greater than 10
milligrams per kilogram (mg/kg) was
excavated and disposed off site(6).
In June 1980, a pipeline adjacent to the railroad tracks 266
feet southwest of Epperson Avenue ruptured
and approximately 100,000 gallons of diesel fuel spilled onto
the ground surface at the landfill. The
pipeline was repaired, the spill was contained, and the fuel was
cleaned up to the extent possible. The
pipeline is currently in use.
2.2.2 Previous Investigations and Enforcement Actions
The environmental investigations and related
regulatory/enforcement activities that pertain to Site 4 are
listed below and summarized in the remainder of this
subsection:
2-2
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• Initial Assessment Study (IAS)(7)
• Resource, Conservation, and Recovery Act (RCRA) Facility
Assessment (RFA)(8)
• Confirmation Study (CS)(9)
• EPA review of aerial photography(10)
• Preliminary Remedial Investigation (RI)(11)
• VDEQ issues a Notice of Violation (NOV) (June 1993) and DON’s
response action
• Focused Feasibility Study (FFS)(12)
• United States Fish and Wildlife Service (USFWS) ecological
studies for Site 4 pertaining to the
evaluation of receptors present in the Quantico
Embayment(13)(14)
• IRA(15)
• Discovery of waste outside the existing fence near the western
boundary in 1998 followed by soil
borings to determine the extent of the waste in 1999
• RI(16)
• Post-IRA activities and evaluation of remedial alternatives
for Site 99, Quantico Embayment(17)(18)
• Discovery of waste outside the existing fence near the
northern boundary of the landfill during a 2005
CERCLA non-time-critical removal action for soil contaminated
with pesticides at Site 32
Site 4 was one of 17 sites at MCB Quantico that were initially
identified as potential sources of
contamination during the IAS. Early studies that were used to
characterize landfill operations at the site
included the RFA, Confirmation Study, EPA review of aerial
photography, and preliminary RI.
The Naval Energy and Environment Support Activity (NEESA)
completed an IAS for MCB Quantico in
1984. The IAS identified 17 sites of potential concern,
including Site 4 (Old Landfill). Because of the
potential to contaminate surface water and groundwater, Site 4
was recommended for further study.
2-3
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Site 4 was identified as a separate site from the DRMO Scrapyard
(SWMU B-08), which was also
recommended for further study in the IAS.
A CS at Site 4 and SWMU B-08 was completed in 1988. Elevated
levels (greater than 10 mg/kg) of
PCBs were detected in the surface soil at Site 4 and SWMU B-08.
The CS recommended that an RI be
conducted at Site 4. The preliminary RI began in 1991. A removal
action for contaminated soil with PCB
concentrations greater than 10 mg/kg was completed at the SWMUs
B-08 and L-03 in 1990.
The VDEQ issued an NOV in June 1993 for Site 4. The NOV noted
discharge of chemicals to state
waters without authority of a National Pollutant Discharge
Elimination System (NPDES) permit, thereby
violating water quality standards for surface water and
groundwater and causing environmental damage
(i.e., PCBs were detected in fish tissue samples collected from
the Quantico Embayment). In response to
the NOV, the DON initiated immediate measures to mitigate
overland transport of contaminated soil and
sediment from Site 4. These actions consisted of the
installation of silt fences to prevent contaminated
sediment from migrating from the western side of the site and
scarifying the asphalt pavement to make
the area more permeable.
MCB Quantico was placed on the National Priorities List (NPL) in
May 1994.
An Engineering Evaluation/Cost Analysis (EE/CA) was conducted in
1994 in preparation for a CERCLA
non-time-critical removal action at Site 4. In 1995, the EE/CA
was converted to a FFS, which addressed
soil, surface water, and sediment at Site 4. Additional
groundwater samples were collected in 1994 to
support the FFS. The data collected in 1994 in conjunction with
previous data (from the IAS, CS, and the
preliminary RI) indicated that no distinguishable groundwater
plume was present. Low levels of
inorganics and organics had been detected sporadically
throughout the site, and no new chemicals were
detected in the groundwater in 1994. Moreover, the detected
groundwater concentrations in 1994 were
consistent with groundwater concentrations observed during the
preliminary RI. This FFS was used to
support the 1997 IRA.
In August 1997, the IRA for Site 4 was initiated to mitigate
risks associated with soil, surface water, and
sediment. The IRA included the following tasks:
• Removal and off-site disposal of soil/sediment contaminated
with PCBs at concentrations greater
than 10 mg/kg from the former drainage channel shown on Figure
2-3.
• Demolition and removal of four on-site buildings.
2-4
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• Excavation and placement on the landfill of solid waste from
along the shoreline and from the
Quantico Embayment (material that had been exposed as a result
of erosion of the landfill).
• Regrading of the landfill.
• Installation of a barrier layer over a majority of the site.
The barrier layer consisted of a non-woven
geotextile separation membrane placed on top of the regraded
waste and a 2-foot soil layer
(18 inches of compacted common fill and 6 inches of compacted
topsoil). The geotextile membrane
was installed to keep the landfill waste separate from the
common fill layer. The barrier layer was
installed to eliminate/minimize the potential for direct contact
with the waste. Grass was then planted
over the surface.
• Construction of wetlands in the southern portion of the site
in the unnamed tributary that bisects the
site (shown on Figure 2-3). The wetlands were planted to replace
wetlands destroyed or impacted by
the implementation of the IRA.
• Construction of erosion protection (shoreline revetment) along
the river bank adjacent to the landfill.
• Installation of a chain-link fence around a majority of the
landfill.
Additional information on the IRA is contained in the Site 4 IRA
Report(15). The barrier layer and fence
installed during the IRA encompasses a majority of the landfill.
During the planning stages of the IRA, the
planning team, which consisted of the DON and regulatory
agencies, decided that the barrier layers and
the fence would not be installed past the airfield access road
in the western portion of the site and
Epperson Avenue, which is located in the northern portion of the
site. Although not documented in the
associated reports or meeting minutes, it is likely that this
specific decision was made by reviewing
historical aerial photographs for the site and concluding that
minimal amounts of landfill waste were likely
present in areas of the site north of Epperson Avenue and west
of the airfield access road.
Subsequent to the IRA, small amounts of waste were discovered
outside the existing fence in 1999 and
2005. Buried waste discovered outside the existing fence
consisted of domestic refuse (plastic, plastic
bags, ash, wood, etc.) and, as such, it is similar to the
majority of the waste deposited in the landfill. In
1999, excavation during utility work in an area west of the
landfill (between the access road and the
railroad tracks) uncovered landfill waste outside of the
existing fence. Additional soil borings were
installed in this area as part of RI activities in 1999 to
reevaluate the western boundary and to
characterize the contamination in this area. Buried waste was
encountered between 2 and 4 feet below
ground surface (bgs) in two areas outside the fence, as
illustrated on Figure 2-3. During a 2005 CERCLA
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non-time-critical removal action for soil contaminated with
pesticides at Site 32, landfill waste was
encountered north of Epperson Avenue (Figure 2-3). The DON
decided to remove all of that waste,
dispose of it in an appropriate landfill, and restore the
excavated area. An EE/CA and Action
Memorandum were prepared for the Site 32 soil removal
action.
RI activities were conducted at the site from June 1997 to
January 1999. Groundwater, soil, and seep
samples were collected to evaluate post-IRA site conditions.
Additional borings were also advanced to
refine the western boundary, as previously discussed. Direct
exposure to on-site contamination was
evaluated in the RI report. Indirect exposure to on-site
contamination (after migration to the Quantico
Embayment) was addressed in the FS Report.
2.3 COMMUNITY PARTICIPATION
The RI Report, FS Report, and Proposed Plan for Site 4 at MCB
Quantico, Virginia were made available
to the public. The RI Report was made available in April 2000.
The FS Report was made available in
October 2005. The Proposed Plan was made available in April
2007. These documents can be found in
the Administrative Record and the information repositories
maintained at the Chinn Park Regional Library
in Prince William, Virginia, the John Musante Porter Memorial
Library in Stafford, Virginia, and the Natural
Resources and Environmental Affairs Branch at MCB Quantico. The
notice of availability of these
documents was published in the Potomac News and Manassas Journal
Messenger on April 4, 2007 and
The Free Lance Star on April 6, 2007. A public comment period
was held from April 18 to May 7, 2007.
In addition, a public meeting was held on April 18, 2007 to
present the Proposed Plan to the public. At
this meeting, representatives of the DON, EPA, and VDEQ were
prepared to answer questions about
environmental concerns at the site and potential remedial
alternatives. However, no one from the public
attended the meeting, and no verbal or written comments have
been received from the public.
2.4 SCOPE AND ROLE OF RESPONSE ACTION
This ROD addresses the final remedial actions to be taken
regarding on-site contamination (landfill waste
contaminated soil, and groundwater) at OU 4, which consists of
Site 4, SWMU B-08, and SWMU L-03.
The scope of the proposed action is limited to contamination
present within the site boundaries and the
future potential migration of on-site contamination to the
Quantico Embayment. As identified in Section
1.0, remedial actions for off-site contamination in the Quantico
Embayment resulting from historical
releases at these sites are being addressed under a broader
watershed study (identified as Site 99,
Quantico Embayment).
There are five OUs identified at MCB Quantico as noted in
Appendix A to the FFA(1). RODs have
previously been issued for OU 1 (Pesticide Burial Area), OU 2
(Arsenic Burial Area), OU 3 (Former Rifle
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Range), and OU 6 (Old Batch Plant). It should be noted that the
list of OUs is not sequential, as there is
no OU 5 identified in the FFA.
Also, RODs are currently being prepared for the following
sites:
• Sites 8 (Camp Barrett Disposal Area, 9 (Camp Goettege Disposal
Area), 10 (Camp Upshur Disposal
Area), 21 (Smith Lake Road Cleared Area), 32 (Pesticide Control
Building), 33 (The Basic School
Northwest Training Area), 34 (Building 4 Accumulation Area), and
98 (Golf Course Maintenance
Area)
• Site 95 (Building 2101 Paint Booth Sump)
• Site 96 (Old Landfill Southern Wetlands) and 99 (Quantico
Embayment)
• Site 100 (Chopawamsic Creek)
• SWMU M-13 (Building 2113 Underground Tank Loading/Unloading
Area)
The following are the components of the overall site cleanup
plan for Site 4 (activities addressed under
this ROD are in bold face):
• IRA (completed in 1997)
• Maintenance of site fence and soil barrier layers (layers
installed as part of the 1997 IRA for Site 4 and the soil removal
action at Site 32)
• Implementation of land use controls (LUCs)
• Implementation of a monitoring program and site reviews
In order for the components of these previous actions to remain
effective as part of a permanent remedy
for the site, additional controls at Site 4 are needed to
prevent future exposure to on-site contamination,
to avoid damage to the barrier layers (installed in 1997 and
2005), and to address other media of concern
not addressed in the 1997 IRA (waste found outside the existing
site fence and groundwater). With the
intent of providing alternatives for selecting a permanent
remedy for Site 4, an FS Report was prepared to
address the entire Site 4 area, including the areas where waste
was discovered after the IRA was
completed. As part of alternatives for a permanent remedy, the
FS evaluated the adequacy of the
components of the previous remedial/removal actions with respect
to the protection of human health and
the environment. Fate and transport modeling also was conducted
in the FS to address the migration of
contaminants in on-site media to the Quantico Embayment. This
ROD presents the Selected Remedy
that will prevent unacceptable risks (from direct and indirect
exposure) to on-site contaminants.
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2.5 SITE CHARACTERISTICS
2.5.1 Physical Setting
Site 4 consists of an area of approximately 24 acres and is
currently an unused, regraded, grass-covered
open field. Prior to the 1997 IRA and barrier layer
construction, the landfill surface was level to slightly
sloping and ranged in elevation from approximately 20 feet above
mean seal level (msl) to approximately
10 feet above msl along the Quantico Embayment. The 100-year
flood plain has been established by the
U.S. Army Corps of Engineers to be 9.5 feet above msl. During
the 1997 IRA, the site was significantly
regraded, and all structures were removed. Currently, the
surface of Site 4 slopes gently from 23 feet msl
along the western access road to 6 feet msl along the Quantico
Embayment (Figure 2-3). A portion of the
shoreline has been covered with riprap revetment to prevent
further erosion. Except along the
Embayment, chain-link fencing has been installed around a
majority of the landfill.
The Site 4 shoreline abuts the Quantico Embayment over a
distance of 1,500 feet. The original shoreline
was adjacent to the railroad tracks. Landfill operations
extended the shoreline between 600 and
1,200 feet east from the original locations. Local surface water
near Site 4 discharges into the Quantico
Embayment. Before the IRA, on-site surface water discharge
occurred from the unnamed tributary that
bisects the site and an intermittent drainage channel that
originated near SWMU L-03 (DRMO
Scrapyard). Currently, on-site surface drainage consists
primarily of the unnamed tributary. During the
IRA, a wetland was constructed in the area of the unnamed
tributary to replace wetlands destroyed or
impacted by implementation of the IRA. A storm sewer outfall
discharges to the constructed wetland. No
apparent channels direct surface water runoff from the
northeastern portion of the landfill to the
Embayment; however, any runoff from this area is likely to flow
directly into the Embayment or otherwise
percolate into the vegetated soil along the bank of the
Embayment.
It is probable that access to the site for most terrestrial
animals is limited by the existing fence; however,
access from the Quantico Embayment is possible. It is also
likely that shore-dwelling mammals, upland
birds, and waterfowl make use of the site for feeding on
vegetation and soil invertebrates.
Three types of materials were encountered during subsurface
investigations at the site. These materials
consist of fill material associated with landfill operations,
river deposits, and the Potomac Group. The fill
material was observed to be approximately 2 to 13 feet thick and
generally thickens toward the south and
east, towards the Quantico Embayment. Fill material consists of
concrete, glass, and wood fragments in
a silt/sand/clay matrix. Cans and garbage bags were also
encountered. The river deposits encountered
beneath the fill material consist primarily of alluvium and
river terrace deposits that are sand, silt, and
organic clay interlayered with peat deposits. Outside and
adjacent to the northern portion of the site,
terrace deposits consisting of gravel, sand, silt, and clay
mixtures were encountered. A distinct cohesive,
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dense sand with silt, clay, and gravel was encountered at depths
ranging from 50 to 66 feet bgs. This
material is believed to be part of the Potomac Group. A 4- to
12-foot-thick hard clay layer, ranging from
40 to 61 feet bgs, was also encountered at the top of the
Potomac Group. This clay layer dips to the east
approximately 1 degree across the site and may act as a
confining unit between the river deposits and
the Potomac Group.
The upper aquifer at Site 4 consists of river deposits, as
previously defined. Groundwater levels in the
upper aquifer generally varied from 3 to 20 feet bgs depending
on the season and amount of precipitation
that had occurred in the area. Because the site is located next
to the Quantico Embayment, shallow
groundwater underneath the site generally flows southeast toward
and discharges into the Embayment.
However, within the river terrace deposits, there is an upward
vertical gradient near the Embayment.
Groundwater from the deeper part of the shallow aquifer also
discharges to the Embayment because of
this vertical gradient. The groundwater of the Potomac Group is
likely flowing eastward in the direction of
the dip. The vertical gradient between the river terrace
deposits and the Potomac Group is generally
upward. Therefore, it is a reasonable assumption that
groundwater from the Potomac Group also
discharges to the Embayment.
The hydraulic gradient across the site ranges from 0.01 to 0.003
foot per foot (ft/ft) with an average of
0.005 ft/ft and generally increases near the Quantico Embayment.
Based on slug test data, the average
hydraulic conductivity of the landfill material is 35.48 feet
per day (ft/day)(12). The average hydraulic
conductivity of the shallow material upgradient of the landfill
is 10.47 ft/day. The average hydraulic
conductivity for the natural material underlying the fill
materials in the landfill is 0.36 ft/day.
Site 4 is bound to the north and west by industrialized portions
of MCB Quantico. Site 32 and the
Mainside Sewage Treatment Plant (STP) border the site to the
north, and the western edge of the site is
bound by the railroad tracks, closed steam generation plant,
barracks, and several office buildings. The
southern edge of the site is surrounded partially by wetlands
and barracks utilized by airfield personnel.
The Quantico Embayment forms the eastern site boundary. The site
is currently an unused, grass-
covered open field. There are no areas of archeological or
historical importance at Site 4.
2.5.2 Conceptual Site Model
Figure 2-4 is the conceptual site model (CSM) for Site 4. The
CSM graphically integrates information
regarding the physical characteristics of the site, exposed
populations, sources of contamination, and
contaminant mobility (fate and transport) to identify potential
exposure routes and receptors evaluated in
the human health risk and ecological risk assessments. A
well-defined CSM allows for a better
understanding of the risks at a site and aids in the
identification of the potential need for remediation. The
waste buried in or deposited at the landfill is the primary
source of contamination.
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Human receptors under the current land use and reasonably
anticipated future land use scenarios include
off-site or base recreational users and adult or adolescent
trespassers. Residential use of the site with
use of shallow groundwater as a source of drinking water is not
a reasonably anticipated future land use.
However, in the human health risk assessment, hypothetical
future residential use of the site was
evaluated for completeness and decision-making purposes (i.e.,
to determine whether unrestricted land
use was appropriate or LUCs would be needed).
Current and potential future land use and resource uses are
discussed in Section 2.6. Potential risks to
human health and ecological receptors are discussed in Section
2.8.
2.5.3 Sampling Strategy
The waste buried in the landfill and contaminated soil are the
current sources of on-site contamination at
Site 4. Contaminated soil removed during the 1990 removal action
and 1997 IRA are no longer sources
of contamination. This section discusses the sampling conducted
following completion of the IRA.
Samples collected prior to the IRA were discussed in detail in
the IRA ROD(3). This section also does not
discuss the sampling that has been conducted in the Quantico
Embayment because the evaluation of the
Embayment is outside the scope of this ROD and is being
addressed as part of another IR site, Site 99.
Between June 1997 and January 1999, an RI was conducted to fill
perceived data gaps that remained
after the 1997 IRA, to evaluate site conditions following the
IRA, and to collect sufficient data that would
support selection of a final remedy for the site. The RI
sampling locations are shown on Figure 2-5.
Three rounds of groundwater samples were collected during the RI
to assess the nature and extent of
groundwater contamination following completion of the IRA. The
first and second rounds
(September/October 1997 and February 1998) included the sampling
of five upgradient wells and 11 site-
related wells. The third round (January 1999) included the
sampling of three monitoring wells that had
been installed in December 1998. All groundwater samples were
analyzed for Target Compound List
(TCL) volatile organic compounds (VOCs), semivolatile organic
compounds (SVOCs), and
pesticides/PCBs and Target Analyte List (TAL) metals.
One upgradient subsurface soil sample was collected in September
1997 for comparison purposes. The
sample was collected from a depth of 14 to 21 feet bgs and
analyzed for TCL VOCs, SVOCs, and
pesticides/PCBs and TAL metals. To define the extent of the
western and northern landfill boundary, 20
hand auger soil borings were installed in 1999 between the fence
and the railroad tracks and on the
northern side of Epperson Avenue. Two surface soil samples were
also collected in 1999 along the
northeastern edge of the landfill. Soil samples collected in
1999 were analyzed for TCL VOCs, SVOCs,
and pesticides/PCBs and cyanide.
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2.5.4 Nature and Extent of Contamination
This section summarizes the nature and extent of on-site
contamination (soil and groundwater) at Site 4.
An emphasis is placed on data collected after the 1997 IRA was
completed. Groundwater data collected
after the 1997 IRA is more representative of current groundwater
conditions at the site. Soil data
collected prior to the IRA was discussed in detail in the IRA
ROD(3).
Soil within the landfill has been the subject of various actions
as mentioned in Section 2.2.2. During the
first removal action in 1990 and subsequent IRA in 1997,
PCB-contaminated soil was removed and
disposed off site, and therefore some of the soil data collected
prior to the IRA are no longer considered
to be representative of the current soil characteristics in the
landfill. During the IRA, soil and sediment
from the unnamed tributary and a portion of the Quantico
Embayment near the shoreline were excavated
and placed in the landfill under the barrier layers installed
during the IRA. These data (along with the
remainder of the undisturbed areas of the landfill) represent
current on-site contamination present in the
landfill. Table 2-1 presents a summary of the occurrence and
distribution of chemicals that are currently
present in the soil at the landfill.
In order to evaluate the presence of landfill waste outside the
existing fence and to characterize
associated contamination, 20 hand auger soil borings were
advanced in 1999 in the western portion of
the site between the access road and the railroad tracks and in
the northern portion of the site north of
Epperson Avenue near Site 32. Based on the results of this field
effort, the horizontal extent of the waste
material in the landfill was considered to have been defined.
The actual thickness of the landfill waste
outside the existing fence was not determined because the soil
borings were advanced using a hand
auger. At some locations, the auger could not be advanced deeper
because of refusal. In 1999, no
waste was observed in the borings north of Epperson Avenue.
However, buried waste was encountered
between 2 to 4 feet bgs in two small areas outside the existing
fence in the western portion of the site, as
illustrated on Figure 2-3. The waste encountered did not
encroach onto the railroad right-of- way. The
small areas of waste west of the airfield access road in the
western portion of the site are considered to
represent the edges of the landfill, where waste is sporadic and
scattered. As summarized in Table 2-2,
the wastes encountered were inert materials (domestic refuse,
such as glass, plastic, wood, etc.),
sporadically interspersed with layers of ash.
During the RI, groundwater samples were collected from five
upgradient wells (MW013, MW018, MW19A,
MW022, and MW023) to determine the groundwater concentrations
prior to entering the landfill area.
Several metals and VOCs were detected in these upgradient wells.
Groundwater samples were also
collected from 11 site-related wells (MW002, MW012, MW01A,
MW04A, MW11A, MW14A, MW16A,
MW17A, MW20A, MW024, and MW025) in 1997 and 1998. In December
1998, three additional
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monitoring wells were installed. Well MW026 was installed
adjacent to an existing well cluster (MW01A
and MW16A) to assess contamination above the confining unit in
this area. One additional well cluster
(MW027/MW028) was installed within the site fence at the
northern limit of the landfill to assess
groundwater in the northern portion of the landfill. Table 2-3
summarizes the data collected during the
most recent sampling rounds (1998 and 1999) for the site-related
wells in comparison to the upgradient
wells and EPA Region III risk-based concentrations(19) (RBCs).
As shown on Table 2-3, TCL VOCs,
SVOCs, and pesticides/PCBs were either infrequently detected (in
either one or two samples) or detected
at low concentrations in the site-related monitoring wells. The
only VOCs that were detected at
concentrations greater than their RBCs were 1,4-dichlorobenzene
[3.9 micrograms per liter (µg/L) at
MW-11A] and benzene (1.6 µg/L at MW-2 and 2.3 µg/L at MW-11A).
None of the SVOCs were detected
at concentrations greater than their RBCs. The only pesticides
that were detected at concentrations
greater than their RBCs were 4,4-DDD (1.4 µg/L) and dieldrin
(0.26 µg/L) both at MW-27. Several metals
were detected in site-related monitoring wells at greater
concentrations than in upgradient monitoring
wells. The only metals that were detected at concentrations
greater than their RBCs were arsenic (eight
locations at concentrations ranging from 1 to 17 µg/), iron
(nine locations at concentrations ranging from
11,600 to 105,000 µg/L), and manganese (six locations at
concentrations ranging from 874 to
4,070 µg/L). Arsenic was the only chemical detected at
concentrations greater than the federal Maximum
Contaminant Level (MCL) of 10 µg/L (13 µg/L at MW-12 and 17 µg/L
at MW-25). This indicates that
organic contamination is not widespread but only exists at
localized areas beneath the landfill. However,
much of the groundwater beneath the landfill is contaminated
with metals. A discussion of the relevance
of exceedances of RBCs to site risks is provided in Section 2.8.
Groundwater contamination does not
extend beyond the landfill boundary, which is the Quantico
Embayment. Groundwater discharges to the
Quantico Embayment or possibly through seeps on the shore. A
discussion of the fate and transport of
chemicals detected in groundwater is provided in Section 2.7.
The groundwater is beneath the landfill,
currently is not used, and is not expected to be used in the
future as a drinking water source.
2.6 CURRENT AND POTENTIAL FUTURE LAND AND RESOURCE USES
This section of the ROD discusses the current and reasonably
anticipated future land uses and current
and potential beneficial groundwater uses at Site 4. This
section forms the basis for reasonable exposure
assessment assumptions and risk characterization
conclusions.
Site 4 is currently a vacant, unused open field. The site is not
used for any specific purpose, and it is
expected to remain unused in the future. There are no plans for
residential development of the site. In
fact, as long as the MCAF uses the land near Site 4 as an
airfield, land use scenarios at Site 4 are limited
because the majority of Site 4 lies within the “clear zone” for
the airfield. As identified under the DON's
Air Installation Compatible Use Zones (AICUZ) Program(23), any
use within "clear zones" is limited to
agricultural only. The placement of structures, buildings, or
above-ground utilities is typically prohibited.
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Groundwater beneath the landfill currently is not used for any
purpose. The DON has no plans to use this
groundwater in the future.
Although it is not expected that the site area would be
developed for residential use in the future,
hypothetical residential use was evaluated in the baseline human
health risk assessment during the RI.
Impacts to the natural resources adjoining the site (i.e., the
Quantico Embayment) were evaluated in the
FS.
Beneficial uses of surface water (i.e., Quantico Embayment)
include the following: recreational uses
(e.g., swimming and boating); the propagation and growth of a
balanced population of aquatic life,
including game fish that may be expected to be present;
wildlife; and the production of edible and
marketable natural resources (e.g., fish and shellfish).
2.7 SUMMARY OF CONTAMINANT FATE AND TRANSPORT MODELING
Contaminants left in place at Site 4 are expected to eventually
migrate to the Quantico Embayment. This
section briefly describes the fate and transport modeling, which
was included in the FS Report. The
modeling was conducted to predict chemical concentrations in the
Quantico Embayment (surface water,
sediment, and fish) that would result from the leaching,
discharging, partitioning, and uptake of
contaminants present in the on-site media (landfill soil,
groundwater, or seeps), assuming that no
additional remedial actions are taken at the site.
The following modeling/fate and transport evaluations, which
were approved by the EPA Las Vegas
Laboratory, were performed in the FS:
• Groundwater modeling – Lateral groundwater transport was
estimated using the Excel-Crystal Ball
(ECTran) Program(31) (a one-dimensional analytical transport
simulator) and the maximum chemical
concentrations detected in the groundwater samples collected
from the landfill monitoring wells in
1998 and 1999. As discussed in the FS Report, these
concentrations were used because they are
considered to be the most representative of current groundwater
conditions at the site. Because of
the many uncertainties inherent with the use of modeling,
several model simulations (e.g., runs) were
performed by varying the input assumptions (i.e., hydraulic
gradient, hydraulic conductivity,
partitioning coefficients, etc.). The range of predicted
concentrations for surface water and sediment
in the Quantico Embayment based on the groundwater modeling are
provided in Table 2-4.
• Soil source modeling – Because there are various chemicals
that have been detected in the landfill
soil but not in the groundwater for the site, soil source
modeling was performed to evaluate whether
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chemicals present in soil could leach into the groundwater and
migrate to the Quantico Embayment at
concentrations of concern. The ECTran program was used to
predict chemical concentrations in the
Embayment. The size, shape, and thickness of the contaminated
soils were estimated using site-
specific data obtained during historical site investigations.
Maximum concentrations of chemicals
detected in the landfill soil samples were initially used in the
modeling effort. For certain chemicals,
the average chemical concentrations were used to evaluate the
uncertainty associated with the use of
the maximum concentration. Predicted concentrations for surface
water and sediment in the
Embayment based on the soil source modeling are contained in
Table 2-5.
• Landfill seep evaluation – To determine whether chemicals
detected in the landfill seeps could
accumulate in the Quantico Embayment sediment at concentrations
of concern to ecological
receptors, a simple partitioning model was used to estimate the
migration of seep chemicals to
surface water and sediment. Maximum detected chemical
concentrations in the seep samples
collected from the site were used for the evaluation. For
conservative purposes, no dilution of seep
water by surface water in the Embayment or constructed wetland
was assumed to occur. In reality,
significant dilution in the Embayment is anticipated. Table 2-6
presents the predicted Embayment
sediment concentrations based on the seep data.
• Fish uptake evaluation – A simple uptake model was used to
estimate the chemical concentrations in
fish resulting from predicted Embayment sediment concentrations.
The maximum sediment
concentration estimated by the groundwater modeling, soil source
modeling, or landfill seep
evaluation was used. Sediment to fish bioaccumulation factors
(BSAFs) were used to predict fish
tissue concentrations for pesticides. However, because these
values are not available for inorganics
(metals), sediment to invertebrate bioaccumulation factors
(BAFs) were used to predict inorganic
chemical concentrations in the fish. The predicted fish
concentrations are provided in Table 2-7.
The surface water, sediment, and fish concentrations predicted
by the aforementioned models were then
compared to human health and ecological criteria to determine
whether the concentrations would pose an
unacceptable risk to human and ecological receptors. The results
of this comparison are summarized in
the next section (Section 2.8, Summary of Site Risks) under the
indirect exposure discussions.
2.8 SUMMARY OF SITE RISKS
This section includes a summary of the potential human health
and ecological risks for exposure to on-
site media at Site 4 assuming that no additional actions are
taken to mitigate risks. Risk assessments
provide the basis for taking additional action and identify the
contaminants and exposure pathways that
need to be addressed by a remedial action.
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Although the risk assessments evaluated all COPCs (i.e., those
chemicals present at concentrations
greater than risk-based screening levels), this section of the
ROD places emphasis on those exposure
pathways and chemicals that are likely to pose a threat (i.e.,
COCs). COCs are a subset of the COPCs
identified in the risk assessments. No specific information is
provided for chemicals and media that do
not pose an unacceptable risk. Specific details of the risk
assessments, including all chemicals and
media addressed, can be found in the FFS, RI, and FS
Reports.
Information on the risks associated with direct exposure to
landfill soil and waste is not highlighted in this
ROD because these risks were addressed in the Site 4 IRA ROD,
which described the remedial activities
conducted during the 1997 IRA. Risk evaluations conducted for
exposure to landfill soil have been limited
since the completion of the IRA ROD because the barrier layers
installed over a majority of the site during
the IRA serve to restrict exposure. No evaluation of ecological
risks has been completed for direct
exposure to soil. However, potential risks from exposure to soil
samples collected prior to the IRA were
addressed in the FFS Report to justify installation of the
barrier layers during the IRA. Waste and soil at
the site (underneath and outside of the limits of the barrier
layers) is primarily contaminated with PCBs,
polynuclear aromatic hydrocarbons (PAHs), pesticides, and
inorganics (refer to Table 2-1). Although it is
not covered by the barrier layers, the small amount of waste
outside the limits of the layers is covered by
at least 2 feet of soil, which adequately restricts human and
environmental exposure.
In general, direct exposure to on-site contamination at Site 4
was evaluated in the RI Report. A summary
of the risks associated with these exposures are discussed in
Sections 2.8.1 (human health) and 2.8.2
(ecological). Indirect exposure to on-site contamination (after
migration to the Quantico Embayment
occurs) was addressed in the FS Report. A summary of risks
associated with indirect exposures is
provided in Sections 2.8.3.
2.8.1 Direct Exposure – Human Health Risks
Direct exposure to groundwater at Site 4 was evaluated in the
baseline human health risk assessment
(HHRA) contained in the RI Report. The risk assessment for
groundwater was conducted using the 1997
and 1998 groundwater data only. When the results of the 1999
groundwater sampling became available,
the risk assessment was not revised because a comparison of the
1999 groundwater data to EPA Region
III RBCs indicated that no additional COCs would be identified.
In addition, the 1999 data indicated that
there would still be unacceptable risks from exposure to
contaminated groundwater
Identification of Chemicals of Concern
Table 2-8 presents the COCs and exposure point concentrations
for each COC at Site 4. Aluminum,
arsenic, barium, iron, and manganese were selected as COCs for
groundwater. These chemicals pose
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unacceptable risks to hypothetical future residents.
Additionally, arsenic was present in the groundwater
samples from three monitoring wells (MW012, MW014, and MW025) at
concentrations greater than the
federal MCL (10 µg/L).
The exposure point concentration is the concentration that was
used to estimate the exposure and risk
from each COC. Table 2-8 also includes the concentration range
for each COC in groundwater, the
frequency of detection, the exposure point concentration, and
how the exposure point concentration was
derived. The exposure point concentration is the lower of the 95
percent upper confidence limit (UCL) of
the arithmetic mean and the maximum detected concentration.
Exposure Assessment
The exposure assessment defines and evaluates the type and
magnitude of human exposure to the
chemicals present at or migrating from a site. The exposure
assessment is designed to depict the
physical setting of the site, identify potentially exposed
populations, and estimate chemical intakes under
the identified exposure scenarios. Actual or potential exposures
are based on the most likely pathways of
contaminant release and transport, as well as human activity
patterns. A complete exposure pathway
has three components: a source of chemicals that can be released
into the environment, a route of
contaminant transport through an environmental medium, and an
exposure or contact point for a human
receptor.
The compilation of contaminant sources, likely exposure
pathways, and receptors at Site 4 is depicted in
the CSM, which was presented on Figure 2-4. Potential receptors
exposed to on-site media include the
following: current and future adult trespassers, current and
future adolescent trespassers, and
hypothetical future residents. Future residential use is not a
reasonably anticipated land use but was
evaluated to identify whether unrestricted land use could be
permitted. Major assumptions about
exposure frequency (days/year), exposure duration (years), and
other exposure factors (e.g., body
surface area for dermal exposure, ingestion rates) that were
included in the HHRA can be found in the RI
Report.
In accordance with the IRA ROD, excavation activities are
prohibited in the landfill. However,
construction workers could be exposed to landfill contaminants
on the outskirts of the site while
conducting maintenance activities for the underground utilities
located near the railroad tracks and along
Epperson Avenue. A construction worker scenario was not
evaluated in the HHRA because the exposure
duration would be limited to brief durations and proper
precautions would be taken to reduce potential
exposure. Although this scenario was not evaluated in the HHRA,
the remedy selected in this ROD will
need to address exposure to the landfill waste that is left in
place at the site.
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Toxicity Assessment
Tables 2-9 (carcinogenic) and 2-10 (noncarcinogenic) provide
toxicity data for COCs in groundwater.
Carcinogenic toxicity data is only available for arsenic, which
is a known human carcinogen. The
remaining COCs for groundwater (aluminum, barium, iron, and
manganese) are not classifiable as human
carcinogens, and there are no cancer slope factors (CSFs)
available for these chemicals. However, all
COCs have reference doses (RfDs) indicating their potential for
adverse noncarcinogenic effects in
humans.
Tables 2-9 and 2-10 do not contain toxicity data for the
inhalation route of exposure since this route of
exposure is not applicable when VOCs are not COCs for
groundwater.
Risk Characterization
Methodology
For carcinogens, risks are generally expressed as the
incremental probability of an individual developing
cancer over a lifetime of exposure to the carcinogen. An
incremental lifetime cancer risk (ILCR) is
calculated from the following equation:
ILCR = CDI x CSF
Where: ILCR = a unitless probability (e.g., 2.5E-05) of an
individual developing cancer
CDI = chronic daily intake averaged over 70 years
(mg/kg/day)
CSF = cancer slope factor, expressed as (mg/kg/day)-1
These risks are probabilities that are usually expressed in
scientific notation (e.g., 1E-06). An ILCR of
1E-06 indicates that an individual experiencing the reasonable
maximum exposure estimate has a 1 in
1,000,000 chance of developing cancer as a result of
site-related exposure. This is referred to as an
“increased lifetime cancer risk” because it would be in addition
to the risks of cancer individuals face from
other causes such as smoking or exposure to too much sun. The
chance of an individual developing
cancer from all other causes has been estimated to be as high as
one in three. The EPA generally
acceptable risk range for site-related exposure is 1E-04 to
1E-06 or an excess lifetime cancer risk of 1 in
10,000 to 1 in 1,000,000.
The potential for noncarcinogenic effects is evaluated by
comparing an exposure level over a specified
time period (e.g., lifetime) with an RfD derived for a similar
exposure period. An RfD represents a level
that an individual may be exposed to that is not expected to
cause any deleterious effect. The ratio of
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exposure to toxicity is called a hazard quotient (HQ). An HQ
less than 1.0 indicates that a receptor’s
dose of a single contaminant is less than the RfD and that toxic
noncarcinogenic effects from that
chemical are unlikely. The hazard index (HI) is generated by
adding the HQs for all COCs that affect the
same target organ (e.g., liver) or that act through the same
mechanisms of action within a medium or
across all media to which a given individual may reasonably be
exposed. An HI less than 1.0 indicates
that, based on the sum of all HQs from different contaminants
and exposure routes, toxic
noncarcinogenic effects from all contaminants are unlikely. An
HI greater than 1.0 indicates that site-
related exposures may present a risk to human health.
The HQ is calculated as follows:
Noncancer HQ = CDI/RfD
Where: CDI = chronic daily intake (mg/kg/day)
RfD = reference dose (mg/kg/day)
CDI and RfD are expressed in the same units and represent the
same exposure period (i.e., chronic,
subchronic, or short term).
Carcinogenic Risks
If no clean-up action is taken, hypothetical future residents
would have an unacceptable increased
probability of developing cancer as a result of the direct
ingestion of site-related groundwater
contaminated with arsenic. Table 2-11 summarizes the risk
estimates for the hypothetical future
residential scenario. As indicated previously, arsenic is the
only carcinogenic COC for groundwater.
Total ILCRs associated with direct exposure to groundwater are
2.6E-04 for a future child resident and
4.4E-04 for a future adult resident. Although dermal contact
with groundwater is not a significant (i.e.,
greater than 1E-04) exposure pathway, the risks for direct
ingestion are significant.
Noncarcinogenic Risks
If no clean-up action is taken, hypothetical future residents
may also develop adverse deleterious effects
as a result of direct ingestion of site-related groundwater
contaminated with aluminum, arsenic, iron, and
manganese. Barium is an additional COC for the future child
resident. A summary of the
noncarcinogenic risks for hypothetical residents is provided in
Table 2-12. An HI of 31 was calculated for
the future child resident, and the HI for the future adult
resident is 14. The groundwater COCs
contributing the most to these unacceptable risks are iron,
manganese, and arsenic.
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Uncertainty Analysis
The main sources of uncertainty inherent in the Site 4 HHRA
are:
• Residential Land Use – Groundwater at Site 4 is not expected
to be used as a drinking water source.
The site is currently used as a military base and the future use
of the site is expected to remain the
same. It is unlikely that this area would be rezoned residential
and developed for residential use
because the site is located with the "clear zone" for the
airfield. Additionally, the fact that the site has
been landfilled is also a limiting factor for future
development. A hypothetical residential scenario was
evaluated only for the purposes of evaluating unrestricted land
use.
• Iron Toxicity – Incidental ingestion of iron was the main
contributor to unacceptable noncarcinogenic
risks for future residents exposed to groundwater. Currently no
toxicity values for iron are published
in the EPA Integrated Risk Information System (IRIS) or in EPA
Health Effects Assessment Summary
Tables (HEAST). The oral RfD used to evaluate exposures to iron
was obtained from the EPA
Region 3 RBC Tables. This value is based on an allowable daily
intake and not on an adverse effect
level. In addition, iron is considered an essential nutrient.
Consequently, the adverse health effects
associated with this chemical may be overestimated.
2.8.2 Indirect Exposure – Human Health and Ecological Risks
Indirect exposures to on-site landfill contaminants that migrate
to the Quantico Embayment were
evaluated in the FS Report. As identified in Section 2.7 of this
report, modeling was conducted to
estimate contaminant concentrations in the Embayment, and the
predicted concentrations were
compared to human health and ecological risk-based criteria to
qualitatively assess potential risks to
human health and the environment. A summary of the results of
the qualitative risk evaluation are
provided in this subsection.
Groundwater Modeling
A summary of the results of the groundwater modeling was
presented in Table 2-4. None of the predicted
concentrations for surface water and sediment in the Quantico
Embayment were greater than the human
health criteria. However, predicted concentrations for a few
chemicals (dieldrin, iron, and manganese for
surface water and dieldrin for sediment) were greater than
ecological screening criteria. These
exceedances are not considered to be significant for the
following reasons:
• Predicted concentrations of iron and manganese in surface
water are considered to be
overestimated. Oxidation and precipitation reactions were not
considered in the transport model.
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Because the predicted concentrations were similar to the
screening criteria (on the same order of
magnitude), the predicted concentrations are expected to be less
than the screening criteria, if
oxidation and precipitation reactions were taken into
consideration.
• Predicted groundwater concentrations at discharge for iron and
manganese are similar to the existing
groundwater concentrations detected in wells located upgradient
of Site 4. Therefore, the landfill is
not the source of these chemicals.
• Predicted concentrations of dieldrin in surface water and
sediment are overestimated. This chemical
was only detected in one of the monitoring wells sampled in 1998
and 1999. If the average
concentration of dieldrin in the groundwater were used, the
predicted concentrations are expected to
be less than the screening criteria.
Therefore, the FS concluded that the future discharge of
existing contaminated groundwater to the
Embayment is not expected to result in adverse human health or
ecological impacts.
Soil Source Modeling
Table 2-5 summarizes the results of the soil source modeling.
When the maximum detected
concentration of soil in the landfill is used, predicted
concentrations for a few chemicals
[bis(2-chlorethyl)ether, copper, iron, and silver in surface
water] were greater than human health and/or
ecological screening criteria. However, these exceedances are
not considered problematic because
predicted concentrations based on the average soil concentration
are less than the screening criteria.
Because the average soil concentration is considered to be a
better representation of the soil
concentration across the entire landfill, the future leaching
and discharge of landfill soil contaminants to
groundwater and the Embayment is not expected to result in
adverse human health or ecological impacts.
Landfill Seep Evaluation
A summary of the landfill seep evaluation was provided in Table
2-6. Even with the conservative
assumption that seep water is not diluted by water in the
constructed wetland and Quantico Embayment,
all predicted sediment concentrations are less than ecological
screening criteria. Therefore, this
qualitative evaluation of potential ecological risks indicates
that the discharge of seeps to the constructed
wetland and the Embayment would not adversely impact aquatic
receptors that live in the sediment.
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Uptake and Bioconcentration Evaluations
Quantitative evaluations of uptake and bioconcentration of
landfill chemicals by benthic invertebrates,
fish, other aquatic animals, and humans using the predicted
Quantico Embayment sediment
concentrations presented in Table 2-7 was also conducted in the
FS Report. Terrestrial food chain
modeling was performed to determine whether the predicted
sediment concentrations have the potential
to cause a risk to piscivorous wildlife that consume fish that
may have accumulated chemicals from the
sediment in the Quantico Embayment. The raccoon and great blue
heron were chosen to represent
surrogate species for piscivorous mammals and birds.
Additionally, predicted fish tissue concentrations
resulting from the food chain modeling were used to estimate the
potential risks associated with human
consumption of fish.
Potential risks associated with uptake and bioconcentration of
landfill chemicals by benthic invertebrates,
fish, other aquatic animals, and humans are considered to be
negligible. All HQs for ecological and
human receptors were less than 1.0, and ILCRs for human
receptors were within the EPA target cancer
risk range of 1E-04 to 1E-06. Because no COCs were identified
for these evaluations, a detailed
description of the risk evaluation is not provided in this ROD.
Specific risk information for the evaluations
can be found in the FS Report.
2.8.3 Conclusions of Site Risks
The response action selected in this ROD is necessary to protect
the public health or welfare or the
environment from the unacceptable risks associated with 1)
direct contact with landfill waste and soil
contaminated with PCBs, PAHs, pesticides, and inorganics and 2)
direct ingestion (i.e., potable use) of
groundwater beneath the landfill contaminated with aluminum,
arsenic, barium, iron, and manganese.
These risks are not a concern under current land use because 1)
the waste and soil at the site are
covered by barrier layers or at least 2 feet of soil and 2)
groundwater beneath the landfill is not currently
used or anticipated to be used in the future as a drinking water
source.
2.9 REMEDIAL ACTION OBJECTIVES
Remedial action objectives (RAOs) provide a general description
of what the cleanup will accomplish.
These goals typically serve as the design basis for many of the
remedial alternatives that are discussed in
the next section. The RAOs provide a basis for evaluating
clean-up options for the site and an
understanding of how the risks identified in the previous
section will be addressed by the response action.
Based on the potential exposure pathways, receptors of concern,
and potential future land use scenarios,
the RAOs for Site 4 are as follows:
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• Prevention of human exposure to contaminated groundwater (as
long as it poses an unacceptable
risk), soil, and buried waste through ingestion, dermal contact,
and inhalation
• Minimization of the erosion of contaminated soil into the
Quantico Embayment
• Monitoring the potential migration of contaminated groundwater
to the Quantico Embayment
Preliminary remediation goals (PRGs) have not been established
for soil/buried waste at Site 4 because
direct contact with this material has been eliminated/reduced
through the implementation of the IRA.
Waste found outside the existing fence during a 2005 removal
action at Site 32 was removed. Although
some of the waste found outside the existing fence after the
implementation of the IRA (during 1999
Site 4 activities) is not covered by the barrier layers, it is
covered with at least 2 feet of soil. This 2-foot
layer of soil minimizes direct contact with this waste in the
same manner that the barrier layers minimize
direct contact with the buried waste inside the existing fence.
Any exposure that could occur as a result
of construction (e.g., utility maintenance) is expected to be
insignificant and of short duration. Moreover,
any excavation in these areas outside the fence would be either
under or in close proximity to the airfield
access road, and consequently the facility would need to be
notified. If such an excavation occurs,
health-and-safety based restrictions would be needed to protect
the health and safety of the workers who
would engage in the excavation.
Groundwater PRGs based on protection of human and ecological
receptors exposed to surface water,
sediment, and fish in the Quantico Embayment are currently being
developed as part of a Long-Term
Monitoring (LTM) Plan for groundwater. Migration of current
groundwater contaminants to the Quantico
Embayment was estimated using fate and transport modeling (as
discussed in Sections 2.7 and 2.8).
Maximum and average concentrations in the groundwater were used
as the input to predict the
concentrations in the Embayment’s surface water, sediment, and
fish. Although the modeling concluded
that the contaminants present in the soil, groundwater, and
seeps at the site would not adversely affect
potential human or ecological receptors in the Embayment,
contaminants have been detected in the
sediment in the Embayment at concentrations greater than
risk-based screening criteria. Because there
are inherent uncertainties in the contaminant levels in the
landfill and the fate and transport modeling,
PRGs will be developed for groundwater.
Although PRGs for groundwater were presented in the FS Report,
these values were set at the maximum
detected groundwater concentration for each detected chemical.
However, based on the results from the
fate and transport modeling, groundwater concentrations could
increase without posing unacceptable
risks to the Quantico Embayment. As a result, risk-based PRGs
are considered to be more appropriate
for this site. Therefore, risk-based PRGs will be developed in
the LTM Plan and will be back-calculated
using the fate and transport modeling used in the FS Report.
This will be accomplished by replacing the
predicted (modeled) concentrations in the Quantico Embayment
with concentrations that would not pose
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unacceptable risks to potential receptors and running the model
backwards. The result would be on-site
concentrations that would not pose unacceptable risks in the
Quantico Embayment.
EPA does not require restoration of groundwater in areas where
waste is left in place. Chemical
concentrations in the groundwater may reach levels that would
allow for unrestricted use over time
because of natural processes. Unrestricted use of groundwater
would be attained when concentrations
of chemicals meet acceptable levels based on drinking water
standards and health advisor
