Superfund Record of Decision Dover Air Force Base (FT 03) Dover DE


                                    EPA/ROD/R03-97/177
                                    1997
EPA Superfund
     Record of Decision:
     DOVER AIR FORCE BASE
     EPA ID: DE8570024010
     OU09
     DOVER, DE
     09/30/1997

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                                                   EPA/541/R-97/177


                               INSTALLATION RESTORATION PROGRAM

                          RECORD OF DECISION FOR NATURAL ATTENUATION OF
                            GROUNDWATER AND NO FURTHER ACTION FOR SOIL
                                  FOR FIRE TRAINING AREA 3  (FT03),
                               WITHIN THE EAST MANAGEMENT UNIT AT
                                 DOVER AIR FORCE BASE, DELAWARE

                                           AUGUST 1997
                                            Submitted to
                                    436th Airlift Wing, CES/CEV
                             Dover Air Force Base, Delaware 19902-6600
                                            Submitted by
                            HAZARDOUS WASTE REMEDIAL ACTIONS PROGRAM
                     Environmental Restoration and Waste Management Programs
                                   Oak Ridge, Tennessee 37831-7606
                                             managed by
                                LOCKHEED MARTIN ENERGY SYSTEMS, INC.
                                               for the
                                     U.S. Department of Energy
                                 Under Contract DE-AC05-840R21400

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CONTENTS

LIST OF FIGURES iii

LIST OF TABLES iii

ACRONYMS iv

1. DECLARATION OF SELECTED REMEDY 1
1.1 SITE NAME AND LOCATION 1
1. 2 STATEMENT OF BASIS AND PURPOSE 1
1. 3 ASSESSMENT OF THE SITE 1
1.4 DESCRIPTION OF THE SELECTED REMEDY 2
1. 5 STATUTORY DETERMINATIONS 2

2 . DECISION SUMMARY 4
2 .1 INTRODUCTION 4
2 . 2 PUBLIC PARTICIPATION 5
2 . 3 SITE BACKGROUND 5
2 . 4 SUMMARY OF SITE RISKS 9
2 . 5 REMEDIAL ACTION OBJECTIVE 13
2 . 6 SUMMARY OF ALTERNATIVES 13
2.6.1 Alternative 1-No Action 15
2.6.2 Alternative 2-In Situ Remediation of Groundwater Using Natural Attenuation 15

2.6.3 Alternative 3-In Situ Remediation Using Density-Driven Convection 17
2.6.4 Alternative 4-In Situ Remediation Using Permeable Reactive Barrier Walls 20
2.6.5 Alternative 5-Ex Situ Remediation Groundwater Using Air Stripping 21
2 . 7 SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES 23
2.7.1 Overall Protection of Human Health and the Environment 23
2.7.2 Compliance with ARARs 24
2.7.3 Long-Term Effectiveness and Permanence 24
2.7.4 Reduction of Toxicity, Mobility, and Volume 24
2.7.5 Short-Term Effectiveness 35
2.7.6 Implementability 35
2.7.7 Cost 36
2.7.8 Regulatory Acceptance 36
2.7.9 Community Acceptance 36
2.8 SELECTED REMEDY 36
2.8.1 Performance Standard for the Selected Remedy 38
STATUTORY DETERMINATION 39
GLOSSARY A-l

RESPONSIVENESS SUMMARY B-l

TIME CALCULATIONS FOR NATURAL ATTENUATION C-l

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                                           LIST OF FIGURES
Figure 1 Location of Dover Air Force Base	
Figure 2 Management Units and Areas of Investigation, Dover Air Force Base.
Figure 3 Previous Sampling Locations at Fire Training Area 3 (FT03)	
Figure 4 EMU Monitoring Points, Dover Air Force Base 	
. .6
. .7
.10
.18
                                           LIST OF TABLES
Table 1. Hypothetical Future Commercial/Industrial Scenario for Groundwater.
Table 2. Summary of Contaminants Detected During the RI in FT03 Groundwater.
Table 3. Comparative Analysis of Alternatives for FT03 	
Table 4. Summary of Comparative Analysis of Alternatives for FT03	
Table 5. Summary of Potential ARARs 	
Table 6. Action Alternative Cost Summary for FT03 	
.11
.12
.25
.31
.32
.37
                                           ACRONYMS
1,2-DCE    1,2-Dichloroethene
ARAR       Applicable or relevant and appropriate requirements
AS         Air sparging
AWQC       Ambient Water Quality Criteria
bgs        Below ground surface
BRA        Baseline Risk Assessment
BTEX       Benzene, toluene, ethylbenzene, and xylene
CERCLA     Comprehensive Environmental Response, Compensation, and Liability Act of 1980
Cfm        Cubic feet per minute
COG        Contaminant of concern
DAFB       Dover Air Force Base
DDC        Density-driven convection
DNREC      State of Delaware Department of Natural Resources and Environmental Control
EMU        East Management Unit
ER-L       Effects Range-Low
FFS        Focused Feasibility Study
FS         Feasibility Study
ft.        Feet or foot
ft 2       Square feet
FT03       Fire Training Area 3
FTA        Fire training area
GAG        Granular activated carbon
gal        Gallon
gpm        gallons per minute
HI         Hazard Index
IRP        Installation Restoration Program
Ibs/day    Pounds per day
LECR       Lifetime excess cancer risk
MCL        Maximum Contaminant Level
NCP        National Oil and Hazardous Substances Pollution Contingency Plan
O&M        Operations and maintenance
OWS        Oil/water separator
PCB        Polychlorinated biphenyl
PCE        Tetrachloroethene
PP         Proposed Plan
psig       Pounds per square inch-gauge
RAO        Remedial action objective
RI         Remedial Investigation
ROD        Record of Decision
SARA       Superfumd Amendments and Reauthorization Act of 1986
SDWA       Safe Drinking Water Act
SVE        Soil vapor extraction
SVOC       Semivolatile organic compound
TCE        Trichloroethene
TPH        Total petroleum hydrocarbon

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USAGE U.S. Army Corp of Engineers
USAF U.S. Air Force
USEPA U.S. Environmental Protection Agency
USGS U.S. Geological Survey
UST Underground storage tank
VOC Volatile organic compound
Ig/L Micrograms per Liter

1. DECLARATION OF SELECTED REMEDY

1.1 SITE NAME AND LOCATION

Fire Training Area 3 (FT03), East Management Unit (EMU), Dover Air Force Base (DAFB),
Kent County, Delaware.

1.2 STATEMENT OF BASIS AND PURPOSE

This record of decision (ROD) presents the selected remedial action for groundwater at FT03,
which was chosen in accordance with the reguirements of the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980 (CERCLA), as amended and, to the extent
practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40
Code of Federal Regulations Part 300. The U.S. Air Force (USAF), the lead agency, as the
owner/operator of the base, prepared this decision based on the Administrative Record for the
site. The U.S. Environmental Protection Agency (USEPA) Region III and the State of Delaware
Department of Natural Resources and Environmental Control (DNREC) provided support.

The state of Delaware concurs with the selected remedy. The Information Repository for the
Administrative Record contains the information supporting this remedial action decision and is
at the Dover Public Library, Dover, Delaware.

1.3 ASSESSMENT OF THE SITE

DAFB identified soil and groundwater contamination related to the activities that occurred in
and around the FT03 site. FT03 is the location of two former fire training areas (FTA). The
older of the two former FTAs was located between the circular parking pad and Pipe Elm
Branch. Before construction of the newer FTA between the older area and the parking pad in
1970, the site of the older FTA was backfilled and graded. The original surface of the older FTA
is now buried approximately 6 to 8 feet (ft.) below ground surface (bgs). The newer, former
FTA was located directly adjacent to the parking pad and included dumpsters that were ignited
during training exercises.

Remediation of the newer FTA was completed in 1992. The dumpsters, soil, and gravel near
the parking pad were removed and the site was covered with a clay cap. An underground storage
tank (UST) and an oil/water separator (OWS) (Site OT56) were also removed during the remediation
activities. No further action needs to be conducted on the soils at the older former FTA.

Early environmental investigations identified oil and grease and several volatile organic
compounds (VOCs), including vinyl chloride, in groundwater. Of the VOCs detected,
concentrations of 1,2-dichloroethene (1,2-DCE) and vinyl chloride each egualed or exceeded
their maximum contaminant levels (MCLs) once. Fuel-related compounds (i.e., benzene,
ethylbenzene, and toluene) were also detected, but only benzene was detected at a concentration
above its MCL. The fuel compounds and VOCs, migrating towards the older FTA, are likely
related to the former UST at the newer, now remediated FTA. No other contaminants are a
concern. The remedial action for the soil at the newer FTA site has already been completed.
Subseguent findings from pre-remediation soil sampling and RI investigations indicate that
contaminant concentrations have been reduced to below action levels for both the older and
newer FTAs.

A Baseline Risk Assessment (BRA) was conducted for FT03. The total lifetime excess
cancer risks (LECRs) associated with exposure to FT03 groundwater under the hypothetical
future commercial/industrial use scenario is 1E-04. The estimated Hazard Index (HI) for
hypothetical future commercial/industrial exposure to groundwater is three. The HI is the
criterion used to evaluate the noncarcinogenic effects. Because the HI is above 1, it is

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appropriate to consider risk-reducing action at this site. The risks associated with FT03
groundwater are due to vinyl chloride, arsenic, and manganese. Remaining soil contaminants do
not appear to be a human health or ecological risk based on the RI BRA; therefore, a ROD for
No Further Action of the soil at FT03 has been previously selected.

Actual or threatened releases of hazardous substances from this site, if not addressed by
implementing the response action selected in this ROD, may present an imminent and substantial
endangerment to public health, welfare, or the environment.

1.4 DESCRIPTION OF THE SELECTED REMEDY

The selected remedy consists of in situ remediation of groundwater using natural attenuation,
institutional controls consisting of continuation of the restrictions on using on-base
groundwater from the Columbia Aguifer, and performance of groundwater monitoring. Final
evaluation of the performance of this remedy of contaminated groundwater beneath the site and
compliance with applicable or relevant and appropriate reguirements (ARARs) will occur in the
final basewide ROD.

1.5 STATUTORY DETERMINATIONS

The selected remedial action satisfies the remedial selection process reguirements of
CERCLA and NCP. As reguired under CERCLA, the selected remedy provides the best balance
of trade-offs among the nine evaluation criteria. The selected action provides protection of
human health and the environment, complies with federal and state reguirements that are legally
applicable or relevant and appropriate to the action, and is cost effective. This remedy uses
permanent solutions and alternative treatment technology to the maximum extent practicable and
satisfies the statutory preference for remedies that use treatments that reduce toxicity,
mobility, or volume as a principal element.

Because the remedy will result in the continued presence of hazardous substances on the site
above action levels, a review will be conducted within 5 years of commencement of the remedial
action to ensure the remedy continues to provide adeguate protection of human health and the
environment in accordance with NCP Section 300.430 (f) (4) (ii). This 5-year review will be
performed as part of a basewide monitoring program.

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                                  2. DECISION SUMMARY

2.1 INTRODUCTION

   DAFB recently completed a draft Feasibility Study  (FS) and a technical assessment of natural
attenuation processes at DAFB that addressed contaminated groundwater in the immediate
vicinity of FT03. FT03 is located along the eastern boundary of DAFB, Delaware, and is the
location of two former fire training areas.

   The Draft Feasibility Study, East Management Unit, Dover Air Force Base  (Dames & Moore
May 1997)  was undertaken as part of the USAF's Installation Restoration Program (IRP). The
basis for the FS was the Draft Final Basewide Remedial Investigation  (RI), East and North
Management Units, Dover Air Force Base report (Dames & Moore August 1995), which
characterized contamination and evaluated potential risks to public health and the environment.
This was supplemented by two administrative reports titled Hydrogeologic and Water-Quality
Data for the East Management Unit of Dover Air Force Base, 1995-96 and Assessment of
Natural Attenuation of Contamination from Three Source Areas in the East Management Unit,
Dover Air Force Base, both prepared by the U.S.  Geological Survey  (USGS), Baltimore,
Maryland,  in February and March 1997, respectively.

   Early environmental investigations identified oil and grease and several VOCs,  including
vinyl chloride, in groundwater. Of the VOCs detected, concentrations of 1,2-DCE and vinyl
chloride each egualed or exceeded their MCLs once. Fuel-related compounds (i.e., benzene,
ethylbenzene, and toluene) were also detected, but only benzene was detected at a concentration
above its MCL. The fuel compounds are likely related to the former USTs at the newer, now
remediated FTA. The solvents likely originated from the older, buried FTA.

   This ROD addresses the source of hazardous substances present in FT03 groundwater that
was evaluated in the RI and FS. Also, this ROD summarizes the FS, describes the remedial
alternatives that were evaluated, identifies the remedial alternative selected by DAFB and
USEPA, and explains the reasons for this selection. The State of Delaware concurs with the
remedy selected in this ROD. The remedial action for the site soil has already been completed
and subseguent findings from post-remediation soil sampling indicates that contaminant
concentrations have been reduced to below action levels. Remaining soil contaminants do not
appear to be a human health or ecological risk based on the RI BRA (Draft Final RI Report,
August 1995); therefore, a ROD for No Further Action of the soil at FT03 has been
recommended.

   As an aid to the reader, a glossary of the technical terms used in this ROD is provided at
the end of the summary.

2.2 PUBLIC PARTICIPATION

   DAFB offered opportunities for public input and community participation during the RI/FS
and Proposed Plan (PP) for FT03 in the EMU. The PP was made available to the public in the
Administrative Record. Documents composing the Information Repository for the
Administrative Record for the site are available at the Dover Public Library, Dover., Delaware.
The notice of availability for the PP was published in the local newspaper and the base
newspaper. A public comment period was held from Monday, June 16, 1997, until Wednesday,
July 15, 1997. The public comment period was not extended as there were no reguests for an
extension. No written comments were received from the public, and no public meeting was
reguested. These community participation activities fulfill the reguirements of Section
113(k)(2)(B)(I-v) and 117(a)(2) of CERCLA.

   Comments submitted by the USEPA and DNREC consisted of editorial changes and clarification of
some issues; however, the editing and clarification did not result in any significant change to
the preferred alternative presented in the PP.

2.3 SITE BACKGROUND

   DAFB is located in Kent County, Delaware, 3.5 miles southeast of the city of Dover
(Figure 1) and is bounded on the southwest by the St. Jones River. DAFB comprises
approximately 4,000 acres of land, including annexes, easements, and leased property (Figure 2).

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DAFB is relatively flat, with elevations ranging from approximately 10 to 30 ft. above mean sea
level. The surrounding area is primarily cropland and wetlands.

DAFB began operation in December 1941. Since then, various military services have
operated out of DAFB. The current host organization is the 436th Airlift Wing. Its mission is to
provide global airlift capability, including transport of cargo, troops, eguipment, and relief
supplies.

DAFB is the U.S. East Coast home terminal for the C-5 Galaxy aircraft. The base also serves
as the joint services port mortuary, designed to accept casualties in the event of war. The C-5
Galaxy, a cargo transport plane, is the largest aircraft in the USAF, and DAFB is one of the few
military bases at which hangars and runways are designed to accommodate these planes.

The portion of DAFB addressed in this RODCIRP Site FT03C is located within the EMU,
one of four management units into which the base has been divided (Figure 2). FT03 is one of
several associated areas identified in the EMU. FT03 is the site of two former FTAs. The older
of the two former FTAs was located between the circular parking pad and Pipe Elm Branch.
Before construction of the newer FTA between the older area and the parking pad in 1970, the
site of the older FTA was backfilled and graded. The original surface of the older FTA is now
buried approximately 6 to 8 ft. bgs. The newer, former FTA was located directly adjacent to the
parking pad and included dumpsters that were ignited during training exercises.

FT03 is two to three acres and located in the northeast portion of DAFB, east of the N/S
runway. The site is situated approximately 800 ft. from the installation boundary and 400 ft.
south of IRP Site ST58. It is mainly flat, with a gentle slope to the north and east, and is
located in a maintained grass-turf area is likely used by grazers and insect-hunting birds.
Surface water runoff flows overland to the north, where it is collected by a drainage ditch and
ultimately discharges to the Pipe Elm Branch of Little River.

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streams. Thus, there was no support for a migration pathway from FT03 to the sediment. Metals
detected in surface water could not be attributed solely to the sediment.

The 1989 investigation indicated that fuel-related compounds [i.e., benzene, toluene,
ethylbenzene, and xylenes (BTEX)], TPH, and lead in soils were highest within the area of the
then-active FTA pit. A second deeper zone of elevated lead and TPH concentrations was within
the estimated boundary of the older FTA. Detected compounds included BTEX, chlorinated
solvents, and several pesticides. The two zones of soil contamination appeared to be separated
by a subsurface clay layer. Chlorinated solvents [e.g., vinyl chloride and tetrachloroethene
(PCE)] were detected in groundwater beneath and downgradient of the site. The presence of
contaminants in the upper and lower portions of the Columbia Aguifer and downgradient of the
suspected source area was evidence that contaminants in the saturated zone were migrating both
vertically and laterally in the direction of groundwater flow. The contaminant concentrations
found in groundwater relative to the concentrations found in soils, suggested that the clay zone
beneath FT03 may retard the migration of contaminants in the unsaturated zone.

These investigations led to a Focused Feasibility Study (FFS) and subseguent remedial
activities for the contaminated soil and structures at the site. Based on the FFS, a ROD was
signed in September 1990. Remediation began in March 1992 and was completed in October
1992. The remedial action included removal and disposal of approximately 1,000 tons of
contaminated soil and structures (i.e., OWS, piping, UST, and dumpsters), and installation of a
clay cap and soil cover over the newer FTA. Confirmatory sampling and analysis indicated that
compounds remaining in the soil were below action levels.

The RL conducted from February 1993 to May 1994, detected BTEX, TPH, and lead in soil,
but their levels have been reduced to below action levels because of earlier remedial actions.
In groundwater, several VOCs and semivolatile organic compounds (SVOCs) were detected
immediately downgradient of the former UST. Benzene exceeded its MCL. At the older FTA, vinyl
chloride exceeded its MCL and 1,2-DCE egualed its MCL at the newer FTA. Table 1 provides a
summary of the contaminants and their concentrations detected during the RI. The extent of VOCs
near the older FTA appeared limited, as no VOCs were detected at a downgradient well pair.

Pesticides and polychlorinated biphenyls (PCBs) were detected in soil and groundwater at the
site; however, their concentrations were below action levels for soil and water (Table 1).
Aroclor 1260 was the only PCB detected in two soil samples. The low concentrations of pesticides
in soil and groundwater are generally attributed to the widespread use of these compounds across
the base and surrounding farmlands.

The only SVOC detected above its MCL was bis(2-ethylhexyl)phthalate, but this compound
was also detected in laboratory blanks and is thus considered a laboratory artifact. Several
metals were detected above their respective MCL or the base-specific background
concentrations. Table 1 provides a summary of the contaminants and their concentrations
detected during the RI.

Six soil borings and 15 monitoring wells have, been installed during the investigation of
FT03. Figure 3 illustrates the FT03 and sampling locations. The estimated size of the FT03
source area is 28,000 ft.

2.4 SUMMARY OF SITE RISKS

The purpose of the BRA (Draft Final RI Report, August 1995) is to determine whether
exposure to site-related contaminants could adversely affect human health and the environment.
The focus of the BRA is on the possible human health and environmental effects that could occur
under current or potential future use conditions if the contamination is not remediated. The
risk is expressed as LECR for carcinogens and as HI for noncarcinogens. For example, an LECR of
1E-06 represents one additional case of cancer in one million exposed population, whereas an HI
above one presents a likelihood of noncarcinogenic health effects in exposed populations. The
USEPA has established the target risk range of 1E-04 to 1E-06 for LECR. Risks greater than 1E-
04 generally warrant an action under CERCLA. An HI greater than one indicates a possibility of
adverse noncancer health effects based on exposure to multiple contaminants or pathways.

The uncertainty with noncancerous health toxicity values is a factor of 10, so HI values
greater than one for any potable purposes may not necessarily reguire an action under CERCLA in
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order to be protective of human health. It is considered very unlikely that the Columbia Aquifer
would be used by the base. To ensure the Columbia Aquifer would not be used, institutional
controls for restrictions of the qroundwater use at FT03 would be implemented as part of the
selected alternative. The restriction would be applicable for all future scenarios, includinq
residential, recreational, and commercial/industrial.

The RI/FS focused on the collection of data to determine the extent of contamination in the
vicinity of FT03. Groundwater contained several contaminants of concern (COCs):
VOCS: 1,2-DCE
Benzene
Ethylbenzene
Vinyl chloride
Metals:
Arsenic
Cobalt
Manqanese
Maqnesium
SVOCS: 2-Methylnaphthalene
Bis(2-ethylhexyl)phthalate
Pesticides:
Dieldrin
Endosulfan II
Ensdosulfan sulfate
Endrin aldehyde
Endrin ketone
A summary of the COCs and their concentrations in qroundwater is qiven in Table 1. The
detected concentrations of twelve (12) contaminants in qroundwater exceeded their respective
MCLs or base-specific backqround concentrations in at least one of the samples collected durinq
the RI in the vicinity of the source area. The source area for qroundwater contamination is in
close proximity to the base boundary and the qroundwater discharqe point is to a drainaqe ditch
connected to Pipe Elm Branch of Little River; hence, the potential exists for the future
off-base miqration of contaminants with qroundwater.

The BRA, performed as part of the base-wide RI, considered hypothetical future qroundwater
use from the Columbia Aquifer under the commercial/industrial scenario. Details concerninq the
selection of the COCs and the evaluation of the human health risks may be reviewed in the Draft
Final RI, Volumes III and IV, Auqust 1995.

The total LECRs for the hypothetical commercial/industrial exposure to qroundwater is 1E-
04. Vinyl chloride and arsenic are the primary contributors to the LECR. HI for qroundwater is
3E+00. Manqanese is the primary contributor to the HI for qroundwater. The resultinq risk
exposures are presented in Table 2.

Table 1. Hypothetical Future Commercial/Industrial
Scenario for Groundwater
Pathway
Inqestion
Inhalation
Total
Hazard Index
3E+00
3E-01
3E+00
LECR
1E-04
2E-05
1E-04
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Table 2. Summary of Contaminants Detected During the RI in FT03 Groundwater
Analyte
Volatile organic compounds
Highest
concentration
(Ig/L)
Number
of hits
Number of
samples
Benzene
1,2-Dichloroethene
Ethylbenzene
Vinyl chloride
Semivolatile organic compounds
2-Methylnaphthalene
Bis(2-ethylhexyl)phthalate
PCBs/Pesticides
Dieldrin
Endosulfan II
Endosulfan sulfate
Endrin aldehyde
Endrin ketone
Metals (Total)
Arsenic
Beryllium
Cadmium
Chromium
Cobalt
Lead
Magnesium
Manganese
Nickel
Maximum
contaminant
levels
(Ig/L)
150.0
70
380
21.0
8.0
24.0
0.024
0.002
0.003
0.016
0.002
46.4
6.3
37.3
303
35.6
88.6
23,800
1910
121
1
2
1
1
1
1
4
2
1
1
1
4
3
2
6
3
4
6
6
3
8
8
8
8
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
5
70
700
2

50
4
5
100
10.4*
15
18,300*
1,440*
100
*DAFB-specific background concentrations (Ig/L) for dissolved metals
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2.5 REMEDIAL ACTION OBJECTIVE

Remedial action objectives (RAOs) are media-specific goals to be reached during site
remediation that are protective of human health. These objectives are typically achieved by
preventing exposure and reducing contaminant levels (Guidance for Conducting Remedial
Investigations and Feasibility Studies Under CERCLA, Interim Final, USEPA, October 1988).

The RAO for FT03 is the reduction of contaminant concentrations in groundwater to the Safe
Drinking Water Act (SDWA) MCLs or Delaware's DNREC regulatory levels. The selected
acceptable contaminant levels are MCLs. For COCs that do not have an MCL, the DAFB-
specific background level will be used. The area to be remediated is defined as the area of
attainment. The area of attainment defines the area over which cleanup levels will be achieved
in the groundwater. It encompasses the area outside the boundary of any waste remaining in place
and up to the boundary of the contaminant plume. Cleanup levels are to be achieved throughout
the area of attainment. Within the area of attainment, the goal of the remedial action for
groundwater is to reduce the concentrations of COCs below their MCLs.

DAFB does not use the Columbia Aguifer for two primary reasons: (1) the aguifer cannot meet
the residential and industrial demand and (2) the water guality is less desirable than that of
the deeper aguifer. Land-use restrictions will remain in place because DAFB is one of the few
airports capable of servicing the C-5 Galaxy aircraft; therefore, it very likely will remain a
USAF base in the distant future. These institutional controls help minimize exposure to site
contaminants.

The potential off-base migration of groundwater contaminants to areas not under DAFB land-
use restrictions is another route of exposure. In this case, the objective is to prevent
unacceptable levels of contaminants from migrating off-base by achieving the remedial action
objective within the area of attainment.

The selected acceptable contaminant levels are MCLs, which are available for most of the
COCs, including the primary contributors to the total LECR in groundwater, vinyl chloride (2 Ig
/L)and arsenic (50 Ig/L). For manganese, the primary contributor to the HI risk, which does
not have an MCL, the DAFB-specific background level is used (1,440 Ig/L-dissolved).

2.6 SUMMARY OF ALTERNATIVES

General response actions are the steps that could be taken to achieve the RAOs for the
groundwater at FT03. Based on results of the initial screening of the response action
technologies presented in the FS and the selection of representative process options, the
following six technologies are considered to be applicable:

• No Action

• Institutional Controls
- Land-use restrictions
- Groundwater-use restrictions
- Groundwater monitoring

• In situ Groundwater Treatment
- Natural attenuation
- Density-driven convection
- Permeable reactive barrier wall

• Groundwater Collection
- Vertical groundwater extraction wells

• Ex situ Groundwater Treatment
- Metals pretreatmnent
- Air stripping

• Groundwater Disposal
- Surface water discharge
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These technologies are combined to form five distinct alternatives that have varying degrees
of success at achieving the RAOs for FT03. The five alternatives and features of each
technology are summarized as follows.

• Alternative 1-No Action. This alternative involves no activities to reduce
contamination or to monitor site conditions. Institutional controls (e.g., restriction of
groundwater use by DAFB) are already in place and are likely to remain so in the future.
These controls, however, do not apply beyond the base boundary.

• Alternative 2-In Situ Remediation of Groundwater Using Natural Attenuation.
This alternative relies on passive treatment of contaminated groundwater through natural
physical, chemical, and biochemical processes. These processes, particularly
biodegradation processes, result in the reduction of groundwater contaminant
concentrations at reasonably predicted rates. Institutional controls consisting of
continuation of the restrictions on using the Columbia Aguifer and performance of
groundwater monitoring are also included.

• Alternative 3-In Situ Remediation of Groundwater Using Density-Driven
Convection. Density-driven convection is an in situ groundwater treatment technology
that specifically addresses source-area contamination. The distal end of the plume is
addressed by natural attenuation. Institutional controls consisting of continuation of the
restrictions on using the Columbia Aguifer and performance of groundwater monitoring
are also included.

• Alternative 4-In Situ Remediation of Groundwater Using Permeable Reactive
Barrier Walls. Groundwater in the source area is treated in situ using a permeable wall
of reactive iron filings. The distal end of the plume is addressed by natural attenuation.
Institutional controls consisting of continuation of the restrictions on using the
Columbia Aguifer and performance of groundwater monitoring are also included.

• Alternative 5-Ex Situ Remediation of Groundwater Using Air Stripping.
Groundwater is removed from the source areas using extraction wells. The extracted
water undergoes metals pretreatment and is then processed through an air stripper. The
treated water is subseguently discharged to an on-base stream: Pipe Elm Branch. The
distal end of the plume is addressed by natural attenuation. Institutional controls
consisting of continuation of the restrictions on using the Columbia Aguifer and
performance of groundwater monitoring are also included.

These remedial alternatives are described in the following subsections. In addition, the
capital, annual operation and maintenance (O&M), and present worth costs of each alternative
are provided.

2.6.1 Alternative 1-No Action

Alternative 1, the No Action alternative, is considered in the range of alternatives to serve
as a baseline or to address sites that do not reguire active remediation. The NCP and CERCLA
guidance reguire that the No Action alternative be evaluated. This alternative assumes that no
remedial action will occur and that the site would be left in its present condition. No efforts
are undertaken to reduce groundwater contaminants. Any changes to the site would be a direct
result of natural processes, and no monitoring would be conducted to document changes in
contaminant levels. Existing land-use restriction in place at DAFB will continue to be enforced
to prohibit the unauthorized extraction and use of groundwater from the Columbia Aguifer. This
action will prevent human exposure to the groundwater, thereby averting a public health risk at
DAFB. This alternative does not comply with the chemical-specific ARARs of the SDWA MCLs and
success at meeting the RAOs must be determined (See Table 5). No cost is associated with this
alternative.

Alternative 1

Cost Category Cost ($)

Capital 0
Annual Operations and 0
-------
Maintenance
Present Worth
2.6.2 Alternative 2-In Situ Remediation of Groundwater Using Natural Attenuation

Alternative 2, in situ remediation of groundwater using natural attenuation, relies on
passive treatment of contaminated groundwater through natural physical, chemical, and
biochemical processes. USGS conducted an extensive natural attenuation study of the EMU sites
(USGS, 1997) and concluded that none of the COCs were currently migrating past the base boundary
above MCL concentrations in either groundwater or surface water. In addition, the COCs are not
predicted to migrate off-base in the future. Nonetheless, groundwater monitoring will be
employed to demonstrate that natural attenuation is effectively reducing contaminant
concentrations and preventing their off-base migration at levels above the RAO concentrations
over the long term. Natural attenuation processes, particularly biodegradation processes, result
in the reduction of groundwater contaminant concentrations at reasonably predicted rates.

Based on the aguifer characteristics and findings from the RI Report and the Natural
Attenuation Study, the USGS reasoned that most of the attenuation is the result of
biodegradation. The estimated time needed for biodegradation of chlorinated aliphatic
hydrocarbons [e.g., vinyl chloride, 1,2-DCE] to decrease concentrations by one order of
magnitude ranges from 0.1 to 3.7 years; the time needed for biodegradation to decrease
concentrations by two orders of magnitude ranges from approximately 0.3 to 7.4 years. Using
the longest flow path from Landfill 13 (west of FT03) to Pipe Elm Branch, approximately 3000
ft. long, the groundwater travel times are somewhere between 8 and 180 years from recharge to
discharge. Given theses conditions, the USGS then reasoned that biodegradation can decrease
concentrations to near or below the detection level in the long flow path. In the short flow
path, it was concluded that although biodegradation can decrease concentrations, it would only
do so by an order of magnitude. A table is included at the end of this summary which shows the
comparison of remediation times for natural attenuation of groundwater versus the calculated
groundwater travel times. The results showed that for short travel paths (i.e., 100 ft. at FT03)
and high flow velocities (i.e., 376 ft./year), natural attenuation processes are insufficient to
decrease concentrations by one order of magnitude. In a couple of cases, the intermediate flow
path of 1500 ft. and a high flow velocity was not satisfactory to decrease concentrations of TCE
by one order of magnitude. It should be noted that the initial concentration of a specific
contaminant will dictate cause for concern that groundwater will discharge to a surface water
body and pose a risk to human health or the environment. Potential concerns for FT03 are
described in the following paragraphs.

For FT03, concentrations of vinyl chloride (21 Ig/L) in groundwater may be sufficiently
high that natural attenuation could be ineffective to meet the remedial objective of 2 Ig/L.
This assumes the worst case of a short flow path of 100 ft. to a surface water body, a high flow
velocity of 376 ft./year, and the highest contaminant concentration detected in the RI. However,
because of the relatively low levels of vinyl chloride present at this site, it is expected that
the vinyl chloride will naturally attenuate by dilution to MCLs within a relatively short
distance. The estimated remediation time through natural attenuation processes for FT03
groundwater ranges from less than 1 year to 4 years. Soil remediation has been accomplished
through a previous removal action.

The RI and Natural Attenuation Study showed that concentrations of aliphatic and aromatic
hydrocarbons (i.e., fuel-related components) are greatest near the spill sites and least
downgradient. No fuel-related hydrocarbons were detected in the surface water samples
collected in 1995 and 1996. In general, the USGS concluded that redox conditions measured at
the sites are favorable for biodegradation of these compounds. One could then hypothesize that
fuel-related hydrocarbons are being successfully biodegraded prior to discharge to the surface
water bodies.

The proposed monitoring network is illustrated in Figure 4 and consists of two groundwater
wells. To the extent possible, existing wells were selected for monitoring. At FT03, the well
within the source area (MW19) and a new well at the base boundary (well POC1) are proposed
for monitoring to confirm the predicted decrease in concentrations at MW19 and to observe that
contaminant levels are below MCs at the base boundary. Well points and monitoring locations
illustrated on Figure 4 and not specified for use at this site, are planned for use in other
-------
nearby site monitoring programs. Groundwater samples will be collected using dedicated pumps
installed in each of the monitoring wells. During the Remedial Design for this site, the base
will develop, with DNREC and EPA review and approval, an "Operation and Maintenance" plan,
which will detail the monitoring wells, sampling parameters, freguency and performance
standards necessary to support the natural attenuation decision both prior to and after the
issuance of the final base-wide ROD.

This alternative is considered capable of complying with the chemical-specific (e.g., MCLs)
and action-specific (e.g., long-term monitoring) ARARs (see Table 5). In addition to monitoring,
institutional controls such as land-use and groundwater-use restrictions that prohibit the use
of the contaminated aguifer will remain in place. This action will prevent human exposure to the
groundwater, thereby averting a public health risk.

Alternative 2

Cost Category Cost ($)

Capital 4,200
Annual Operations and 7,300
Maintenance
Present Worth 35,000
2.6.3 Alternative 3-In Situ Remediation Using Density-Driven Convection

This alternative includes the in situ treatment of groundwater using density-driven
convection (DDC) over the source areas of contamination. The DDC process is a recently developed
in situ method for removal of VOCs from the saturated zone. The DDC process involves injection
of air into the bottom of a well screened at both the top and the bottom. The injected air
bubbles rise upward in the well and create a turbulent, frothing action inside of the wellbore.
The rising air bubbles strip contaminants from the water and increase the dissolved oxygen
content of the water. The rising bubbles create a frictional drag, which produces a positive
hydraulic head (i.e., greater than static aguifer head) at the bottom of the well. Thus, the
frictional drag acts as a groundwater pump, sucking contaminated water from the surrounding
aguifer through the bottom well screen, and pushing the water through the wellbore and out of
the top well screen. Aerated water discharged through the top well screen then infiltrates back
down to the water table, while the discharged air bubbles travel through the vadose zone and are
captured by soil vapor extraction (SVE) wells. The designed air injection pressures range from
12 to 16 pounds per sguare inch - gauge (psig) with an injection flow rate of 20 cubic feet per
minute (cfm) for DDC wells.

The DDC wells are assumed to have a diameter of 8 in. and will be installed to the bottom of
the Columbia Aguifer at an average depth of 45 ft. bgs. The DDC wells will have a dual well
screen. The bottom screen will be 15 ft. long and anchored at the bottom of the well. The
bottom screen will be connected to a 5-ft. section of well casing to which the upper screen will
be connected. The upper screen will be 15 ft. long and will straddle the water table. The well
packing of the two screened intervals will be separated by a bentonite seal. Before completion
of the well, a "tee" with a capped 3-ft. horizontal extension will be installed 3 ft. below
grade to facilitate air piping. The wells will be completed with a flush-mount manhole and
concrete cap.

The DDC wells will be operated by injecting air into the wells with a blower or compressor.
Based on the estimated number of DDC wells, one air compressor unit will be used at FT03.
The compressor station can service 4 to 15 DDC wells. For costing purposes, the air compressor
is assumed to have a 5-horse power motor producing 36 cfm at 16 psig. The air compressor unit
will have a control panel and will be located within a weatherproofed shed. The control panel
will have pressure controls, flow rate indicators, and control valves for each sparging line.

The DDC system will operate in tandem with an SVE system to capture volatile
contaminants stripped from the saturated zone. SVE wells are constructed of slotted screen pipe
surrounded by gravel or sand pack; a vacuum-tight seal at the ground surface will prevent short
circuiting of air. The SVE wells are connected to a vacuum pump by air-handling piping. The
vacuum pump produces a lateral air flow through the soil that picks up and carries gaseous-phase
-------
contaminants that are located in the interstitial soil pore spaces of the vadose zone. An
air/liquid separator is used to remove liquids before enterinq the vacuum blower. An offqas
carbon adsorption treatment system is included to remove extracted VOCs before atmosphere
discharqe of the qas stream.

Based on the formation permeability and thickness, the vendor that offers this technoloqy
Wasatch Environmental) estimated that the effective radius of influence for sinqle DDC wells
will be 50 ft. This radius of influence was used to determine the location and the number of the
wells that will be required to remediate the source areas. The radius of influence for an SVE
well is estimated to be 45 ft. based on the air sparqinq (AS)/SVE treatability study conducted
at WP21 in the West Manaqement Unit (Extended Aquifer Air Sparqinq/Soil Vapor Extraction
Treatability Study for Site SS59 (WP21), Dover Air Force Base, EA Enqineerinq, Science and
Technoloqy, 1994). SVE wells were spaced approximately 80 ft. apart, allowinq for some
overlap and providinq full coveraqe. Based on the spacinq requirements, FT03 is estimated to
need six DDC wells and nine SVE wells.

Usinq the results of the AS/SVE treatability study at WP21, the extraction vacuum pressures
and flow rates are assumed to be 50 to 70 in. water column pressure and 25 to 30 cfm,
respectively. For FT03 SVE wells, an estimated one vapor extraction station will be used. The
extraction station will receive and treat vapors from nine vapor extraction wells. The
extraction station will consist of a knock-out pot, a vacuum pump, and a vapor phase carbon
adsorption unit to treat VOC-contaminated vapors. The knock-out pot will be located between the
extraction wells and the vacuum pump and will separate entrained water in the extracted qas
stream. Water qenerated in each knock-out pot will be piped to a 55-qal liquid phase carbon
adsorption unit. Liquid phase qranular activated carbon (GAG) treatment units will be used to
reduce the level of the orqanics to levels that comply with discharqe requirements (see Table
5). Followinq treatment, the treated water will be discharqed into surface drainaqe that flows
into Pipe Elm Branch.

Vapor from the knock-out pot will be treated in vapor-phase carbon adsorption units where
orqanic contaminants will be removed. The air flow at each station will be split into two
parallel streams, each of which will be treated usinq a 150-lb canister of GAG. For the one SVE
station, two carbon canisters will be required. Initially (i.e., the first year of operation),
the carbon canisters will have to be replaced about every 6 months. Each extraction station will
be located within a weatherproofed shed. Durinq subsequent years of operation, the carbon
consumption rate will be proqressively less as the contaminant extraction ratio, decline.

The SVE system will require periodic monitorinq. For costinq purposes, 10 air samples are
assumed to be collected and analyzed the first month durinq startup. The first month's samples
will be collected both upstream and downstream of the vapor-phase GAG units weekly.
Thereafter, one air sample/month will be collected to track the proqress and efficiency of
remediation. In addition, the emissions from the SVE station will be monitored semiannually to
ensure that it is in compliance with standards (see Table 5).

A field pilot test of the DDC system will be necessary before final desiqn of the remediation
action. The study will be used for system desiqn and modelinq of contaminant removal rates.
Selected test wells will be installed to evaluate field responses to applied air pressures,
identify the locations of clay lenses, confirm the radius of influence of the vapor extraction
wells, determine the radius of influence of the DDC wells, and determine optimum operatinq
conditions. The system addresses the source area at the site. The distal ends of the plume will
be allowed to attenuate naturally.

Groundwater monitorinq will be performed to track the lonq-term proqress and effectiveness
of qroundwater remediation and to monitor contaminant miqration. One new monitorinq well
will be installed at FT03. The well, in addition to the one existinq well, will be used to
monitor plume miqration. Samples will be collected and analyzed from the two wells semiannually.
All qroundwater samples will be tested for all COCs. The actual frequency, duration, and
analytical parameters may chanqe, dependinq on the lonq-term results of samplinq. For costinq
purposes, monitorinq is assumed to occur for 5 years.

Alternative 3
-------
Cost Category Cost ($)
Capital 160,000
Annual Operations and 19,000
Maintenance
Present Worth 210,000

This alternative is considered capable of complying with the chemical-specific (e.g.,
emissions and MCLs) and action-specific (e.g., active land treatment and long-term monitoring)
ARARs (see Table 5). In addition to monitoring, institutional controls such as land-use and
groundwater-use restrictions that prohibit the use of the contaminated aguifer will remain in
place. This action will prevent human exposure to the groundwater, thereby averting a public
health risk.

2.6.4 Alternative 4-In Situ Remediation Using Permeable Reactive Barrier Walls

Alternative 4 is the in situ treatment of groundwater using permeable reactive barrier
walls. For FT03, this alternative includes the construction of a 300-ft.-long trench containing
2,000 cubic yards of reactive iron filings to capture and channel the contaminated plume through
the reactive wall where the contaminants will be degraded. The capture was modeled using the
two-dimensional groundwater model TWODAN.

The base-wide RI report indicates that the water table is located at a depth of
approximately 10 to 12 ft. bgs in this portion of the site. The reactive metal walls will be
installed using a one-pass trenching tool. The width and thickness of the permeable barrier wall
will be determined based on the results of a treatability study. The treatability study will be
performed to determine the residence time reguired of the contaminated groundwater within the
reactive wall. The study will consist of bench-scale tests that will use samples of the
contaminated groundwater and pass them over the reactive metal to measure the contaminant
degradation and, thus, determine residence time reguirements. Based on the known groundwater
velocity at the wall, the residence time will determine wall thickness.

Groundwater monitoring will be performed to track the long-term progress and effectiveness
of the groundwater remediation systems. It is proposed that one additional well will be
installed at FT03. The new well and one existing well will be used in the groundwater monitoring
program. Samples will be collected and analyzed from the wells semiannually. The
groundwater samples are assumed to be tested for all COCs. The actual freguency, duration, and
analytical parameters may change, depending on the long-term results of sampling. For
estimating purposes, monitoring for 5 years is assumed.

This alternative is considered capable of complying with the chemical-specific (e.g., MCLs)
and action-specific (e.g., active land treatment and long-term monitoring) ARARs (see Table 5).
In addition to monitoring, institutional controls such as land-use and groundwater-use
restrictions that prohibit the use of the contaminated aguifer will remain in place. This action
will prevent human exposure to the groundwater, thereby averting a public health risk.

Alternative 4

Cost Category Cost ($)
Capital 1,200,000
Annual Operations and 17,000
Maintenance
Present Worth 1,300,000

2.6.5 Alternative, 5-Ex Situ Remediation Groundwater Using Air Stripping

This alternative includes groundwater extraction, pretreatment of groundwater for metals
removal, air stripping treatment to remove chlorinated solvents and fuel compounds, and surface
water discharge of treated groundwater from FT03.

Groundwater extraction will be accomplished by using two new extraction wells installed at
the site. The extraction well locations were selected to control and capture the areas of
contaminated groundwater at the site. The extraction rates and capture area from the wells were
-------
estimated using the two-dimensional groundwater model TWODAM.

Two extraction wells operating at 7.5 gallons per minute (gpm) each will be reguired at
FT03. The two wells will create a capture zone that will limit further migration of contaminants
and prevent discharge to the adjacent drainage ditch.

The base-wide RI report indicates that the water table is located at a depth of
approximately 10 to 12 ft. bgs in the FT03 area. The RI/FS reports also indicate that the most
significant contamination is found in the upper third of the Columbia Aguifer. Therefore,
extraction wells at FT03 will be installed across the upper portion of the Columbia Aguifer and
will be screened using slotted stainless steel casing from 10 ft. bgs (screen length of
approximately 20 ft.) to 30 ft. bgs. The wells will be 6 in. in diameter. The filter pack for
the wells will extend a minimum of 1 ft. above the well screen. Above the filter pack, a minimum
2-ft. bentonite seal will be installed, and the wells will be grouted to the surface using a
bentonite grout.

Contaminated groundwater will be extracted using 4-in. stainless steel electric submersible
pumps. Following extraction, the groundwater will be pumped through 2-in. Schedule 80 plastic
piping to the treatment system. The piping will be buried below the frost line at a minimum
depth of three (3) ft.. An estimated 425 ft. of pipe will be reguired at FT03 to convey
extracted water from the recovery wells to the treatment system and from the treatment system to
the closest surface water discharge point.

The groundwater treatment system includes an initial pretreatment stage to reduce the metals
content. This stage is added to prevent iron and manganese fouling in the subseguent air
stripping unit as well as to ensure compliance with the National Pollutant Discharge Elimination
System discharge standards. Groundwater will be pumped on a continual to an egualization tank,
where it will be dosed with potassium permanganate to oxidize iron and manganese to their
insoluble forms followed by pH adjustment with sodium hydroxide. Next, a cationic polymer
will be introduced into a rapid mix tank, where it will be mixed instantly into solution. Rapid
mixing will be followed by slow mixing or flocculation. The clarification tank follows
flocculation and provides for guiescent settling of the metal-polymer floes. The floes will
settle and produce an agueous sludge. Clarified groundwater will be sent to subseguent treatment
systems void of high concentrations of iron and manganese, which can interfere with operation
of the system. A bench-scale treatability study (EA Engineering, 1994) was conducted for
groundwater at WP21 to determine the type and amount of chemicals reguired for the metals
pretreatment process. The results of this study were used to estimate the chemical dosage
reguired for metals pretreatment.

A sludge characterization test such as the Toxicity Characteristic Leachate Procedure test
will have to be conducted to determine the leachability of the metals and thus the method and
cost of disposal (see Table 5). For costing purposes, the sludge will be assumed to be
nonhazardous. The sludge will be dewatered to reduce the volume reguiring disposal.

After pretreatment for metals, groundwater will be pumped to the top of a low-profile, four-
tray air stripper. The water will be uniformly distributed across each tray and brought into
contact with air forced up from the bottom of the unit by a blower. The counter-current airflow
through the stripper unit transfers VOCs dissolved in the groundwater to the air stream. The air
stream containing the VOCs then exits through the top of the air stripper unit, while the
treated groundwater flows out through the bottom of the air stripper unit. The air stripper unit
selected has a liguid throughout capacity of up to 20 gpm.

Based on the average VOC concentration of groundwater samples collected at each site, an
appropriate extraction rate, and assuming complete removal during treatment, 0.28 pounds per
day (Ibs/day) of VOCs will be stripped from the groundwater at FT03. The air stream exiting the
air stripper will not reguire treatment before release to the atmosphere because the total VOC
discharge is less than 2.5 Ibs/day. Air samples will be collected monthly to ensure continued
compliance with air emission standards, (see Table 5)

Preliminary modeling of the air stripper performance using recent groundwater data from the
site and the expected flow rate indicate that the treated groundwater will meet the surface
water discharge standards without further polishing or treatment (see Table 5). The model also
shows that air emissions will be significantly below the emission standard of 2.5 Ibs/day (see
-------
Table 5).

Effluent samples will be collected from the groundwater treatment system at a rate required,
to satisfy regulatory requirements (which is assumed to be weekly for the first month and
semiannually thereafter) (see Table 5). All groundwater and effluent samples are assumed to be
tested for VOCs and manganese. Sampling is assumed to continue for 5 years.

The groundwater pump-and-treat system will address contamination in the source area. The
distal ends of the plume will be treated by natural attenuation. Groundwater monitoring will be
performed to track the long-term progress and effectiveness of the groundwater remediation
system. To perform the groundwater monitoring accurately, one additional well will be installed.
As was shown in Figure 4, the well (POC1) will be located at the base boundary. Samples will
be collected and analyzed from two wells semiannually.

Alternative 5

Cost Category Cost($)

Capital 190,000

Annual Operations and 27,000
Maintenance

Present Worth 260,000

This alternative is considered capable of complying with the chemical-specific (e.g., MCLs)
and action-specific (e.g., active land treatment, waste handling, and long-term monitoring)
ARARs (see Table 5). In addition to monitoring, institutional controls such as land-use and
groundwater-use restrictions that prohibit the use of the contaminated aquifer will remain in
place. This action will prevent human exposure to the groundwater, thereby averting a public
health risk.

2.7 SUMMARY OF COMPARATIVE ANALYSIS OF ALTERNATIVES

This section provides a comparative analysis of the five remedial alternatives that were
evaluated in detail in the FS and described in Section 2.6 of this ROD. The focus of the
comparative analysis is on the relative advantages and disadvantages offered by each of the
alternatives in relation to the seven evaluation criteria (excluding regulatory and community
acceptance) that were analyzed. A detailed summary of this analysis is provided in Table 3, and
an illustrative comparative summary is presented in Table 4.

2.7.1 Overall Protection of Human Health and the Environment

The overall protectiveness criterion is a composite of other evaluation criteria, especially
short-term effectiveness, long-term effectiveness, and compliance with ARARs. All five of the
alternatives are considered to be protective of human health because of institutional controls
that prohibit the unauthorized extraction or use of contaminated groundwater on-base, thereby
preventing human exposure. The institutional controls, however, do not apply to off-base
properties.

Alternative 1 (No Action) is not considered effective at protecting human health and the
environment past the base boundary because no provisions are made to monitor the groundwater
migration off-base or to evaluate compliance with the RAO.

Alternatives 2 (Natural Attenuation), 3 (Density-Driven Convection), 4 (Permeable Reactive
Barrier Wall/Pump and Treat), and 5 (Pump and Treat) will all meet the RAOs and are
considered highly protective of human health and the environment.

2.7.2 Compliance with ARARs

The RAOs that have been established for the EMU sites are based on achievement of MCLs
across the area of attainment. Alternative 1 (No Action) provides no mechanism to evaluate
compliance with the MCLs and therefore does not comply with chemical-specific ARARs. The
-------
treatment actions and groundwater monitoring provisions of Alternatives 2 through 5 will result
in demonstrated compliance with the MCLs. A summary of the ARARs used in the evaluation
of the alternatives is provided in Table 5. Table 5 specifies which ARARs are applicable to each
alternative.

A number of other ARARs including the Clean Air Act, Clean Water Act, and Resource
Conservation and Recovery Act must be considered for Alternatives 3, 4, and 5. Primary among
them are compliance with VOC emission limitations to the atmosphere, land treatment
regulations, and effluent discharge limitations to surface water. Alternatives 2 through 5 are
in
compliance with the ARARs relevant to their respective technologies.

2.7.3 Long-Term Effectiveness and Permanence

The long-term effectiveness and permanence criterion considers primarily the magnitude of
residual risk that would remain after the implementation of an alternative, and the adeguacy and
reliability of the controls instituted. All of the alternatives provide for the long-term
protection of human health through the existing land-use restrictions. However, reliance upon
land-use restrictions is considered neither a permanent remedy nor applied to off-base property.

Under Alternative 1 (No Action), the contamination in groundwater will not be monitored.
Therefore, as groundwater migrates from the EMU off-base, the adeguacy and reliability of this
alternative cannot be established. Hence, the long-term protectiveness of this alternative
cannot be demonstrated.

All of the action alternatives employ remedial measures to control the source areas and rely
upon natural attenuation to address the distal ends of the plumes. The magnitude of residual
contamination residing in the source area is dependent on the time allowed for the remediation
to continue. For Alternative 2 (Natural Attenuation), physical, chemical, and biochemical
attenuation processes will continue to reduce contaminant concentrations indefinitely into the
future. Alternatives 3 (Density-Driven Convection), 4 (Permeable Reactive Barrier Walls/Pump
and Treat), and 5 (Pump and Treat) will all be operated and/or maintained for finite periods of
time until high levels of confidence are reached that natural attenuation can address remaining
contamination.

All four action alternatives are considered reliable. The efficacy of Alternative 2 was proven
in a 2-year natural attenuation study by USGS at the EMU sites. The technologies associated
with Alternatives 3, 4, and 5 have been applied successfully at other installations.

2.7.4 Reduction of Toxicity, Mobility, and Volume

Reduction in toxicity, mobility, or volume will not be documented with the implementation
of Alternative 1 (No Action). While dilution and dispersion of all contaminants occurs
naturally, only the organic contaminants will degrade, and it cannot be demonstrated that the
RAOs will be met at the base boundary for all contaminants over time. The four action
alternatives include components that are capable of reducing significantly the toxicity and/or
mobility of contaminants in groundwater through irreversible treatment processes.
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TABLE 3

Comparative Analysis of Alternatives for FT03

Alternative 1 Alternative 2 Alternative 3 Alternative 4 Alternative

Description No action.
6 Human Health Protection Offers a high level of overall Offers a high level of overall Offers a high level of overall Offers a high level of overall Offers a high level of overall
protection of human health protection of human health protection of human health
through the existing land-use through the existing land-use through the existing land-use
restrictions on-base, but restrictions on-base. restrictions. Active treatment restrictions. Active treatment restrictions. Active treatment
cannot be guaranteed Biodegradation ofsource of source area constituents of source area constituents of source area constituents
effictive past the base area constituents allow allow achievement of RAOs allow achievement of RAOs allow achievement of RAOs
boundary. achievement of RAOs off- off-base as demonstrated off-base as demonstrated off-base as demonstrated
base as demonstrated through through groundwater through groundwater through groundwater
groundwater monitoring. monitoring. monitoring. monitoring.

6 Environmental Protection Does not provide a
mechanism to monitor
groundwater constituent
concentrations. Therefore,
potential impacts to surface
water from discharging
groundwater cannot be
assessed.
Groundwater released to
surface water through pump
and treat operations will meet
surface water guality criteria
Compliance with ARARs
ARARs Success at meeting RAOs Natural attenuation is Density-driven convection This technology is capable of Pump and treat system
considered capable of treatment is considered maintaining RAO considered capable of
maintaining RAO capable of maintaining RAO compliance. maintaining RAO
compliance. compliance compliance.
Air stripper system
comply with DRGCAP
reguirements
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Criteria

Action-Specific ARARs
Alternative 1
Alternative 2
Alternative 3

Complies with DRGHW for
active land treatment. Long-
term groundwater monitoring
provided
Alternative 4

Complies with DRGHW for
active land treatment. Long-
term groundwater monitoring
provided.
Alternative
Long-term Effectiveness and Permanence
Because DAFB is expected
to remain active lot the
foreseeable future, the land-
use restrictions provided
under this alternative are
considered to provide long-
term protection of human
health on-base.
Because DAFB is expected
to remain active for the
foreseeable future, the land-
use restrictions provided
under this alternative are
considered to provide long-
term protection of human
heath on-base.
Because DAFB is expected
to remain active for the
foreseeable future, the land-
use restrictions provided
under this alternative are
considered to provide long-
term protection of human
health on-base.
Because DAFB is expected
to remain active for the
foreseeable future, the land-
use restrictions provided
under this alternative are
considered to provide long-
term protection of human
health on-base.
Because DAFB is expected
to remain active for the
foreseeable future, the land-
use restrictions provided
under this alternative are
considered to provide long-
term protection of human
health on-base.
However, this alternative
provides no mechanisms to
determine whether the RAOs
are achieved over time (i.e.,
preventing risks due to of f-
base migration of
contaminants above RAO
levels).
Risk for potential off-base
users will be eliminated as
contaminant levels are
lowered.
Land-use restrictions
enforced by DAFB are
considered extremely reliable
in preventing on-base
exposure

Off-base, the reliability of
this alternative is
guestionable because there is
no mechanism to determine
whether the RAOs are being
met
Land-use restrictions
enforced by DAFB are
considered extremely reliable
in preventing on-base
exposure.

The 2-year study conducted
by the USGS indicates that
natural attenuation can be
relied upon to achieve the
RAOs beyond the base
boundary
Land-use restrictions
enforced by DAFB are
considered extremely reliable
in preventing on-base
exposure.

The DDC technology is
considered reliable.
However, because operation
of the DDC system will
change the redox condition
of the aguifer in the source
areas, high efficiency
removal of the
polychorinated constituents
will be reguired
Land-use restrictions Land-use restrictions
enforced by DAFB are enforced by DAFB are
considered extremely reliable considered extremely reliable
in preventing on-base in preventing on-base
exposure. exposure.
Treatability studies are
reguired to design the
reactive barrier walls.
Reductions achieved via
abiotic reactions catalyzed by preventing the further
the reactive metal will migration of contaminants.
supplement the active
biodegradation processes.
The extraction system will
establish hydraulic control
over the source areas in a
relatively short time
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TABLE 3 (cont'd)
Alternative 1
Alternative 2
Alternative 3
Alternative 4
Alternative
Dominant process is Source area treatment using
biodegradation. Other density-driven convection
attenuation processes include combined with soil vapor
volatilization, adsorption, extraction (SVE).
and dilution.
Source are groundwater
addressed by extraction
followed by metals
pretreatment and air
stripping
Distal ends of plumes treated Sludge generated during
by natural attenuation metals pretreatment will be
processes. sent off-site for disposal.
Not applicable.
natural attenuation p.
No reductions in mobility or
volume.
Reduction in groundwater DDC process reduces
toxicity achieved through groundwater toxicity in the
natural attenuation processes.source area. Contaminant
mobility is increased during
treatment, but mobilized
contaminant should be
captured by SVE.

Natural attenuation reduces
the toxicity of the distal ends
of the plumes.
In situ reductive
dehalogenation reduces
groundwater toxicity in
source areas. The technology
does not impact the volume
of contamination.
Groundwater extraction will
provide hydraulic control of
the source areas thereby
reducing the mobility of
contaminants away from the
EMU.
Natural attenuation reduces Removal of volatile organic
the toxicity of the distal endsconstituents present in
of the plumes. groundwater by air stripping
will reduce the toxicity of
groundwater. The volume of
contaminated media is not
affected.
Natural attenuation will
provide permanent removal
of constituents through
irreversible processes
DDC treatment results in
permanent removal of
constituents through
irreversible processes.
Reductive dehalogenation
treatment results in the
permanent removal of
constituents through
irreversible processes
Air stripping treatment
results in the permanent
removal of constituents
through irreversible
processes
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TABLE 3 (cont'd)
6 Type and Quality
residue
Alternative 3
Alternative 5

Metals pretreatment
generates small volumes of
sludge which will reguire
disposal
Short-term Effectiveness
No short term impact on the No short-term impact on the
community surrounding the community surrounding the
site. site.
Not applicable.
Standard health and safety
procedures and personal
protective eguipment will
prevent exposure during well
installations and sampling
No significant risk to the
community surrounding the
site during construction or
operation.

Worker's exposure will be
minimized by applying dust
control technigues and
providing personal protection
eguipment during
construction.
No significant risk to the
community surrounding the
site during construction or
operation.
No significant risk to the
community surrounding the
site during construction of
operation.
6 Environmental Impact
Minimal disturbance will
result from installing new
monitoring wells.
Environmental impacts
related to construction are
minimal.
Moderate land disturbance
due to installment of new
DDC, SVE, and monitoring
wells. Environmental
impacts related so
construction are minimal.
Moderate land disturbance Moderate land disturbance
due to installation of barrier due to installation of
walls and grout curtains. extraction and monitoring
Environmental impacts wells. Environmental
related to construction are impacts related to
minimal. construction are minimal
Discharge of treated
groundwater to Pipe Elm
Branch is not expected to
adversely impact the
environment
6 Time Reguired
It is predicted that RAOs
continue to be met while
contaminants naturally
degrade. Data will be
evaluated after 5 years of
monitoring to determine
whether contaminant
concentrations are significant
enough to warrant continued
monitoring
ill It is predicted RAO
compliance will be
maintained during the course
of remediation. Two years of
source area treatment is
estimated.
It is predicted RAO
compliance will be
maintained during the course
of remediation. Five years of
treatment at FT03 is
estimated.
It is predicicd RAO
compliance will be
maintained during the course
or remediation. Two years of
source area treatment is
estimated.
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Criteria

Implementability
Alternative 1
Not applicable.
6 Ease of Undertaking
Additional Action
6 Ability to Monitor
Alternative 2
This alternative requires the
installation of new
monitoring wells. No
difficulties are anticipated.
USGS confirms ongoing
natural attenuation in the
EMU. Continued attenuation
of constituents is anticipated
in the future.
Alternative 3
No difficulties are anticipated
in installation of the
DDC/SVE wells or
equipment. Operation of the
DDC system is straight
forward.
DDC and SVE are reliable
technologies for removal and
destruction of VOCs
homogenous permeable soils.
However, presence of clay
layers in the EMU reduces
the reliability of these
technologies.
If contaminant rebound
occurs that may result in
RAO failure, additional
remediation can be
performed by restarting the in
situ treatment. The
DDC/SVE well networks
could be expanded of
scrapped and replaced with
new technologies if
necessary.
Alternative 4
Alternative
No difficulties are anticipated No difficulties are anticipated
in construction of the barrier in construction of
walls or grout curtains. groundwater extraction wells
and operation of the
technology.
Technology is innovative and
has been minimally field
tested. However, technology
is extremely simple. Very
little to go wrong.
Reactive barrier wall
placement is permanent.
However, additional actions
could easily be performed if
necessary.
If containinant rebound
occurs that may result in
RAO failure, additional
remediation can be
performed by restarting the
treatment system. The
extraction network and/or
treatment system could be
expanded or augmented if
necessary, or replaced with
new technologies
Coordination with
appropriate personnel at
DAFB is necessary.
Groundwater wells will
require state permits.
Coordination with
appropriate personnel at
DAFB is necessary.
Groundwater wells will
require state permits
Coordination with
appropriate personnel at
DAFB is necessary
Groundwater wells will
require state permits
Effluent limits set by
DNREC's NPDES branch
have to be met prior to
discharge to surface water
Groundwater wells will
require State permits.
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TABLE 3 (cont'd)
Criteria Alternative 1

Availability of Services Not applicable.
6 Availability or Equipment Not applicable

6 Availability of Technology Not applicable.

Cost (IRP Site FT03)
Alternative

Readily available
Alternative 3

The density-driven
convection component will
require a specialty contractor,
however, the remaining
portions of this alternative
are readily available

Readily available

Readily available.
Alternative 4
Alternative 5

Readily available
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Table 5. Summary of ARARs
Environmental Laws and Regulations
Standards applicable to surface impoundments, waste piles, land
treatment facilities (other than closure and post-closure requirements)
(DRGHW Part 264, Subpart K, L, and M)
7. Incinerator Standards (DRGHW Pan 264, Subpart 0)

8. Landfill Standards (DRGHW Part 264, Subpart N)
In Situ treatment technologies such as air sparging and soil vapor
extraction may be considered land treatment. Excavated soil may be
temporarily stored in piles awaiting shipment for off-site disposal
On-site incineration is not considered a remedial alternative

A hazardous waste landfill will not be constructed on-base

LIST rules are not applicable to remedial alternatives for this site
No

No
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Environmental Laws and Regulations
IV. Safe Drinking Water Act (SDWA), 42 USC 300f

A. Underground Injection Control (40 CFR Parts 144-147)

B. Maximum Contaminant Levels (MCLs)(40 CFR Parts 141 and 143)

V. Marine Protection, Research, and Sanctuaries Act

A. Incineration at sea requirements (40 CFR Part 761)

VI. Toxic Substances Control Act (TSCA)

A. Polychorinated biphenyls (PCB) requirements (40 CFR Part 761) PCBs are not present at the site.
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Environmental Laws and Regulations

VII. U.S. Army Corps of Engineers Program

A. Dredge and fill (33 CFR Part 323)
VIII. Clean Air Act (CAA) (42 USC Sections 7401-7671g)

A. National Ambient Air Quality Standards (NAAQS) (40 CFR Pan 50)

IX.
Threatened or endangered species are not found at the site. If they are
found, remedial action shall be implemented so as to conserve threatened
or endangered species or resources.

XIII. Wild and Scenic Rivers Act (16 USC 1274; 50 CFR 27) No wild and scenic rivers are found in the vicinity of the site.
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Alternative 2 (Natural Attenuation) relies upon a variety of physical, chemical, and
biochemical processes to achieve reductions in contaminant concentrations and lowered
groundwater toxicity. Anaerobic biodegradation is the dominant process.

Alternative 3 (Density-Driven Convection) uses an in situ technology to strip volatile
compounds from the source area and oxygenate the groundwater. Oxygenating the groundwater
will stimulate aerobic biodegradation processes, which will augment one another to reduce
groundwater toxicity.

Alternative 4 (Permeable Reactive Barrier Wall/Pump and Treat) uses two separate
technologies. Contact with the reactive barrier wall causes contaminated groundwater to undergo
an abiotic reductive dehalogenation reaction, thus reducing the toxicity of the groundwater.
The pump-and-treat component creates a hydraulic barrier to contaminant migration, thus
limiting mobility. Treatment of the extracted groundwater using air stripping reduces its
toxicity.

Alternative 5 (Pump and Treat) offers the benefits of extraction and treatment discussed for
Alternative 4 but includes all of the EMU sites.

All of the action alternatives satisfy the CERCLA statutory preference for treatment.

2.7.5 Short-Term Effectiveness

Alternative 1 (No Action) provides no remedial actions. Therefore no short-term effects on
community or worker health or the environment will result from construction activities.
However, because Alternative 1 does not provide monitoring to ensure compliance with the
RAOs established for this project, it is considered to be ineffective.

Alternatives 2 (Natural Attenuation), 3 (Density-Driven Convection), 4 (Permeable Reactive
Barrier Wall/Pump and Treat), and 5 (Pump and Treat) will be effective in reducing groundwater
contaminant concentrations in the EMU. None of the alternatives is expected to have significant
impacts on worker or public health or the environment.

Alternative 2 is currently meeting the RAOs and is projected to continue meeting them in the
future. Alternative 3 will change the redox character of the source areas from anaerobic
(reducing) to aerobic (oxidative). An aerobic environment is less conducive to the
biodegradation of polychlorinated alkenes than an anaerobic environment, thus the DDC system
operation will have to continue until the polychlorinated compounds are removed to low levels.
DDC system operation is estimated to continue for 2 years. Alternative 4 includes the permanent
installation of reactive barrier walls, which will greatly enhance the rate of abiotic reductive
dehalogenation reactions. These abiotic reactions augment the naturally occurring
biodegradation reactions. Maintenance of the barrier wall is estimated to continue for 5 years.
The pump-and-treat components of Alternatives 4 and 5 are estimated to continue for 2 years.

2.7.6 Implementability

Three main factors are considered under this criterion: technical feasibility, administrative
feasibility, and availability of services and materials. All five alternatives are
administratively feasible, and the reguired services and materials are readily available. Hence,
the comparison will focus on the technical feasibility of implementing the alternatives.

No technical feasibility considerations are associated with Alternative 1 (No Action). Of the
action alternatives, Alternative 2 (Natural Attenuation) has by far the fewest implementability
considerations. Because the USGS natural attenuation study in the EMU has already been
completed, long-term, groundwater monitoring is the only component remaining and is easily
implemented.

Alternatives 3 (Density-Driven Convection) and 4 (Permeable Reactive Barrier Wall/Pump
and Treat) are relatively the most complex systems to design, construct, and operate. Both of
these alternatives reguire treatability studies before their design and include the most
extensive construction. Alternative 3 includes installing and balancing a total of 31 DDC wells
and 50 SVE wells for three sites, whereas Alternative 4 includes installing a total of 750
linear feet of grout curtains and 375 linear feet of reactive barrier wall, all to depths of 40
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ft.

Alternative 5 (Pump and Treat) involves systems that are much easier to design, install, and
operate relative to the systems included under Alternatives 3 and 4, but it is still more
complex than Alternative 2.

All of the technologies considered in the action alternatives are considered reliable and are
easily monitored. None of the technologies precludes the implementation of additional remedial
measures at a later time if they are deemed necessary.

2.7.7 Cost

No direct costs are associated with the implementation of Alternative 1 (No Action). The
estimated costs of the four action alternatives, including capital costs, annual O&M costs, and
present net worth, are summarized in Table 6. Alternative 2 (Natural Attenuation) offers a
substantial cost advantage over the other action alternatives with a present worth cost of
$35,000. Alternatives 3 (Density-Driven Convection) and 5 (Pump and Treat) offer higher present
worth costs of $210,000 and $290,000, respectively. The present worth cost of Alternative 4
(Permeable Reactive Barrier Wall/Pump and Treat) is substantially more costly at $1,300,000.

2.7.8 Regulatory Acceptance

The USEPA and the state of Delaware have reviewed the alternatives and are in agreement
with the selected remedy for FT03.

2.7.9 Community Acceptance

No comments were received during the public comment period, and no community
opposition to the preferred remedy was noted.

2.8 SELECTED REMEDY

The selected remedy for cleanup of groundwater at Site FT03 is Alternative 2, which
includes the following major components:

• natural attenuation,

• continued enforcement of existing land-use restrictions,
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TABLE 6
Action Alternative Cost Summary
for FT03
Alternative

2. Natural Attentuation

3. Density Driven Convection

4. Permeable Reactive Barrier Wall

5. Groundwater Extraction with Air
Stripping
Capital Cost
$4,200
$160,000
$1,200,000
$190,000
Annual O&M*
$7,
$19,
$17,
$27,
300
000
000
000
Net Worth
$35,
$210
000
,000
$1,300,000
$260
,000
First year O&M costs.
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• restrictions of groundwater use, and

• groundwater monitoring.

The reasoning to support the selected remedy for cleanup of groundwater at FT03 is
summarized as follows:

• Natural attenuation is capable of meeting the RAOs. The USGS conducted an extensive
natural attenuation study of the site and concluded that none of the COCs were currently
migrating past the base boundary above MCL concentrations in either groundwater or surface
water. In addition, the COCs are not predicted to migrate off-base in the future.

• Alternative 2 is considered protective of human health and the environment. It complies
with all ARARs that address off-site migration or movement of contamination and reduces
the toxicity of contaminants in the groundwater.

• The technology offers good long-term and short-term effectiveness.

• Alternative 2 offers a great implementability advantage over all other alternatives. The
only component of Alternative 2 still reguiring implementation is the long-term
groundwater monitoring. Simple monitoring well construction and operation considerations
are reguired in addition to the groundwater monitoring reguirements. The monitoring
program will verify the status of the groundwater contamination and therefore protect
future receptors before exposure. The monitoring program is currently being developed in
consultation with the USEPA and DNREC. As Alternative 2 is implemented, the monitoring
program will provide the data necessary to verify that natural attenuation of groundwater
contaminants is working.

• Alternative 2 offers substantially lower capital, O&M, and present worth costs than any of
the other action alternatives. This cost advantage is particularly important given that
all of the alternatives offer similar performance. There are no treatment by-products
(e.g., spent carbon and sludges) produced and no hazardous chemicals (e.g., oxidizing
agents) need to be stored on-site with Alternative 2.

• Institutional controls are already in place to limit access to or use of the site
resources, including soil and groundwater.

DAFB, USEPA, and DNREC have agreed that the installation of additional monitoring
points (i.e., monitoring wells, well points, etc.) is necessary to help demonstrate that the
remedial action will accomplish its intended goal and that if the additional data collected
during the remedial action suggests otherwise, that the remedial action will be readdressed in
the basewide ROD.

2.8.1 PERFORMANCE STANDARD FOR THE SELECTED REMEDY

The COCs in groundwater at this site, which are listed in Section 2.4 of this ROD, shall not
exceed their respective federal MCLs at or beyond the boundary of DAFB. COCs that do not
have an MCL shall not exceed DAFB-specific background levels at or beyond the boundary of
DAFB.

The concentrations of the COCs in groundwater at this site, also listed in Section 2.4 of this
ROD, shall be reduced to below federal MCLs (or, if no MCL exists, the DAFB-specific
background level) within the area of attainment within a reasonable time, not to exceed 30
years. The area of attainment is the area outside the boundary of any waste that remains in
place at the site and up to the boundary of the contaminant plume. Existing institutional
controls, which are more fully described in DAFB's Real Estate Property Management System, and
site use restrictions shall continue to remain in effect.

2.9 STATUTORY DETERMINATION

Based on consideration of the reguirements of CERCLA, the comparative analysis, and
comments, DAFB, USEPA, and the State of Delaware believe Alternative 2 provides the best
balance of the trade-offs among the alternatives with respect to the criteria used to evaluate
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remedies. The selected remedy is consistent with CERCLA and, to the extent practicable, the
NCP. The selected remedy is protective of human health and the environment, complies with
federal and state requirements that are legally applicable or relevant and appropriate to the
remedial action, is cost-effective, and uses permanent solutions and alternative treatment to
the maximum extent practicable.

The reliability of natural attenuation mechanisms such as bio-degradation,
adsorption/desorption, and dilution for the cleanup of petroleum and chlorinated-based media,
has been demonstrated at various sites around the country to be cost effective and, if properly
monitored, an environmentally sound solution to groundwater contamination. It results in
permanent reduction in concentrations of contaminants in the subsurface. Investigative data
show natural attenuation is already at work within the site area. Therefore, Alternative 2 is
the selected remedial action for Site FT03.

Because the hazard index and LECR calculated for the different soil scenarios in the BRA are
within an acceptable risk range, no further action, than that already taken, is determined to be
appropriate for site soils.
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GLOSSARY

air sparging - A process whereby air is pumped into the subsurface, groundwater, or soils to
enhance the volatilization or aerobic biodegradation of compounds.

air stripper - A device to remove (strip) volatile organics from contaminated water by bringing
the water into contact with air, causing volatile compounds to change from liguid phase to the
vapor phase.

aguifer - A geologic formation capable of yielding water to wells and springs.

Applicable or Relevant and Appropriate Reguirements (ARARs) - Criteria set forth by federal,
state, or local regulations that must be considered in the evaluation of remedial alternatives
and govern the environmental actions at a particular site.

Ambient Water Quality Criteria (AWQC) - Regulatory standards for surface water guality.

Baseline Risk Assessment (BRA) - A statistical evaluation of the current and future risks to
human health and the environment from the exposure to contaminants at a site if no remedial
actions are taken.

Benzene, toluene, ethylbenzene, and xylene (BTEX) - Chemical compounds that are common
constituents of fuels and petroleum products.

biodegradation - The breakdown of organic constituents by microorganisms into less complex
compounds.

bioremediation - The cleanup of a contaminated medium through natural biological processes.

bioventing - A treatment process that introduces air into the subsurface soils to stimulate the
growth of microorganisms that naturally attack certain compounds. This process speeds up the
rate at which some chemicals biodegrade.

Capital Cost - Cost incurred for the construction and startup of a facility.

Carcinogen - A chemical capable or suspected of producing cancer as a result of exposure.

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) - A federal
law passed in 1980 and revised in 1986 by the Superfund Amendments and Reauthorization Act
(SARA). CERCLA provides federal authority and money for the USEPA to respond directly to the
release or threatened release of hazardous substances into the environment at inactive sites.

Density-driven convection (DDC) - An in situ process for removal of VOCs from the groundwater
using air to strip contaminants from the water.

The State of Delaware Department of Natural Resources and Environmental Control (DNREC) -
State regulatory agency in charge of overseeing environmental programs at DAFB.

Delaware Regulations Governing the Control of Air Pollution (DRGCAP) - Regulatory protocols
and standards for control of particulates and emissions to the air within the state.

Delaware Regulations Governing Hazardous Waste (DRGHW) - Regulatory protocols and standards
for control of handling, transport, storage, and disposal of hazardous wastes within the state.

Electromagnetic (EM) - A geophysical survey instrument used to locate changes in specific
conductance in subsurface materials.

Feasibility Study - A study to develop and evaluate options for remedial actions.

Granular activated carbon (GAG) - Carbon material that is has ionically charged sites capable of
filtering organic and inorganic compounds from a waste stream.

Groundwater - Subsurface water residing in a zone of saturation.
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Ground penetrating radar (GPR) - A geophysical survey instrument used primarily to locate
changes in lithological character of the subsurface soil.

Hazard Index (HI) - An indicator of the health risk associated with exposure to a
noncarcinogenic chemical.

in situ - In the original location (in the ground for this report).

Installation Restoration Program (IRP) - The Department of Defense (DOD) program designed to
identify, report, and correct environmental deficiencies at DOD installations. At DAFB, this
program implements the reguirements for cleanup under CERCLA.

leachate - The solubilization and transport of constituents in soil through the percolation of
surface water to groundwater.

Lifetime Excess Cancer Risk (LECR) - Represents the risk of exposure to cancer-causing compounds
over a lifetime.

Maximum Contaminant Level (MCL) - Federal drinking water standards enacted by the Safe Drinking
Water Act.

Natural attenuation - A remediation approach that depends upon natural processes such as
dilution, dispersion, sorption, volatilization, chemical transformation, and biodegradation,
that act to contain contaminants, reduce contaminant concentrations, and restore soil and
groundwater quality.

National Oil and Hazardous Substances Pollution Contingency Plan (NCP) - The federal regulation
that provides a contingency plan for discharges or releases of hazardous substances, pollutants,
contaminants, or oil into the environment that may present an immediate danger to public health
or welfare.

Operation and Maintenance Costs (O&M) - Annual costs incurred for operation and maintenance of a
facility.

plume - A recognizable distribution of constituents in groundwater.

Selected Alternative - The clean-up strategy that offers the best chance of success in
protecting human health and the environment from contamination at a site. The selected
alternative is selected from several clean-up strategies because it satisfies USEPA criteria for
effectiveness, implementability, cost, and public and regulatory acceptance.

Remedial Action Objective (RAO) - Clean-up goal established for remediation.

Reactive iron filings - For the case proposed in Alternative 4, metal shavings are placed in the
path of a contaminant plume to act as a catalyst in the abiotic degradation of halogenated
oiganic compounds. The plume is allowed to pass through a permeable wall that contains the iron
filings. This actual physicochemical degradation process is also called dehalogenation.

Resource Conservation and Recovery Act (RCRA) - Federal law enacted to address environmental
issues created by current waste disposal, spills, and handling practices.

Remedial Investigation (RCRA) - An investigation that involves sampling the air, soil, and water
to determine the nature and extent of contamination at an abandoned waste site and the human
health and environmental risks that result from that contamination.

Record of Decision (ROD) - A legal document that explains the specific clean-up alternative to
be implemented at a Superfund site.

Superfund Amendments and Reauthorization Act (SARA) - A congressional act that modified
CERCLA. SARA was enacted in 1986 and again in 1990 to authorize additional funding for the
Superfund program.
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Soil vapor extraction (SVE) - A process by which air and volatilized compounds are extracted
from the subsurface soils through screened wells using a vacuum.

Toxicity Characteristics Leaching Procedure (TCLP) - An analytical procedure that measures the
level of organic leachate from a soil sample. This method is commonly used to determine whether
soil to be disposed of is hazardous.

Total Petroleum Hydrocarbons (TPH) - This analytical parameter is a measure of the hydrocarbons,
often within a particular petroleum weight range.

U.S. Environmental Protection Agency (USEPA) - The federal regulatory agency in charge of
overseeing environmental programs at DAFB.

vadose zone - Soil zone above the water table.
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RESPONSIVENESS SUMMARY

The following Responsiveness Summary is a compilation of the comments and responses on the
Proposed Plan for Natural Attenuation of Groundwater, Fire Training Area 3 (FT03), Dover Air
Force Base, Dover, Delaware (HAZWRAP, June 1997), Proposed Plan for Natural Attenuation of
Groundwater, Liguid Waste Disposal Area 14 (WP14) and Landfill 15 (LF15), Dover Air Force Base,
Dover, Delaware (HAZWRAP, June 1997), and Proposed Plan for Natural Attenuation of Groundwater,
Landfill 13 (LF13), Dover Air Force Base, Dover, Delaware (HAZWRAP, June 1997).

Dover Air Force Base (DAFB) offered opportunities for public input and community participation
during the Remedial Investigation (RI)/Feasibility Study (FS)and Proposed Plans (PP) for all
three site in the East Management Unit. The PPs was made available to the public in the
Administrative Record. Documents composing the Information Repository for the Administrative
Record for the site are available at the Dover Public Library, Dover, Delaware. The notice of
availability for the PPs was published in the local newspaper and the Base newspaper. A public
comment period was held from Monday, June 16, 1997 until Wednesday, July 15, 1997. The public
comment period was not extended as there were no reguests for an extension. No written comments
were received from the public and no public meeting was reguested. These community participation
activities fulfill the reguirements of Section 113(k)(2)(B)(i-v) and 117(a)(2) of the
Comprehensive Environmental Response, Compensation, and Liability Act of 1980.

Comments submitted by the U.S. Environmental Protection Agency (USEPA) and the State of
Delaware Department of Natural Resources and Environmental Control (DNREC), reguested editorial
changes and clarification of some issues; however, the editing and clarification did not result
in any significant change to the preferred alternative presented in the PPs.

TIME CALCULATIONS FOR NATURAL ATTENUATION

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