Superfund Record of Decision Dover Air Force Base Wp 14 and LF 15 Dover DE


                                    EPA/ROD/R03-97/176
                                    1997
EPA Superfund
     Record of Decision:
     DOVER AIR FORCE BASE
     EPA ID: DE8570024010
     OU08
     DOVER, DE
     09/30/1997

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                            INSTALLATION RESTORATION PROGRAM

                                 RECORD OF DECISION
                     FOR NATURAL ATTENUATION OF GROUNDWATER AND
                             NO FURTHER ACTION FOR SOIL AT
                        LIQUID WASTE DISPOSAL AREA 14  (WP14) AND
               LANDFILL 15  (LF15), 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 QF FIGURES	iii

LIST OF TABLES 	iii

ACRONYMS	iv

1.  DECLARATION OF THE 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	3

2 .  DECISION SUMMARY	4
   2.1 INTRODUCTION	4
   2.2 PUBLIC PARTICIPATION	5
   2 . 3 SITE BACKGROUND	5
       2.3.1 Previous Investigations at WP14	8
       2.3.2 Previous Investigations at LF15	9
       2.3.3 Previous Investigations at Both WP14/LF15	10
   2 . 4 SUMMARY OF SITE RISKS	10
   2 . 5 REMEDIAL ACTION OBJECTIVE	19
   2 . 6 SUMMARY OF ALTERNATIVES	20
       2.6.1 Alternative 1-No Action	21
       2.6.2 Alternative 2-In Situ Remediation of Soil and Groundwater Using Natural
             Attenuation	22
       2.6.3 Alternative 3-In Situ Remediation Using Density-Driven Convection	23
       2.6.4 Alternative 4-In Situ Remediation Using Permeable Reactive Barrier Walls	27
       2.6.5 Alternative 5-Ex Situ Remediation Groundwater Using Air Stripping	28
   2 . 7 COMPARISON OF REMEDIAL ALTERNATIVES	30
       2.7.1 Overall Protection of Human Health and the Environment	30
       2.7.2 Compliance with ARARs	38
       2.7.3 Long-Term Effectiveness and Permanence	38
       2.7.4 Reduction of Toxicity,  Mobility,  and Volume	38
       2.7.5 Short-Term Effectiveness	42
       2.7.6 Implementability	43
       2.7.7 Cost	43
       2.7.8 Regulatory Acceptance	43
       2.7.9 Community Acceptance 	43
   2 . 8 SELECTED REMEDIAL ALTERNATIVE	45
       2.8.1 Performance Standard for the Selected Remedy	46
   2 . 9 STATUTORY DETERMINATION	46

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	6
Figure 2 Management Units and Areas of Investigation, Dover Air Force Base	7
Figure 3 Previous Sampling Locations at Liguid Waste Disposal Area 14 (WP14)	11
Figure 4 Previous Sampling Locations at Landfill 15  (LF 15)	12
Figure 5 EMU Monitoring Points, Dover Air Force Base	25


                                         LIST OF TABLES

Table 1.  Summary of Major Contaminants Detected During the RI in WP14 Soil	14
Table 2a. Hypothetical Current Commercial/Industrial Scenario for Soil at WP14	15
Table 2b. Hypothetical Future Commercial/Industrial Scenario for Soil at WP14	15
Table 3.  Summary of Major Contaminants Detected During the RI in LF15 Soil	16
Table 4a. Hypothetical Current Commercial/Industrial Scenario for Soil at LF15	17
Table 4b. Hypothetical Future Commercial/Industrial Scenario for Soil at LF15	17
Table 5.  Summary of Major Contaminants Detected During the RI in WP14/LF15 (Area 1)
          Groundwater	18
Table 6.  Hypothetical Future Commercial/Industrial Scenario for Groundwater at Area 1	19
Table 7 .  Comparative Analysis of ALTERNATIVES for WP14/LF15	31
Table 8 .  Summary of Comparative Analysis of ALTERNATIVES for WP14/LF15	37
Table 9.  Summary of Potential ARARs	39
Table 10. Action Alternative Cost Summary for WP14/LF15	44
                                                ACRONYMS
1,2-DCA   1,2-Dichloroethane
1,2-DCE   1,2-Dichloroethene
4,4'-DDE  1,l-dichloro-2,2-bis(p-chlorophenyl)ethylene
ARARs     Applicable or relevant and appropriate reguirements
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
FS        Feasibility Study
ft.       Feet or foot
ft 2      Sguare feet
FT03      Fire Training Area 3
GAG       Granular activated carbon
gpm       Gallons per minute
HI        Hazard Index
IRP       Installation Restoration Program
Ib        Pound
Ibs/day   Pounds per day
LECR      Lifetime excess cancer risk
LF13      Landfill 13
LF15      Landfill 15
MCL       Maximum Contaminant Level
Ig/kg     Micrograms per kilogram
Ig/L      Micrograms per Liter
mg/kg     Milligrams per kilogram

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NCP       National Oil and Hazardous Substances Pollution Contingency Plan
O&M       Operations and maintenance
PAH       Polycyclic aromatic hydrocarbon
PCB       Polychlorinated biphenyl
PCE       Tetrachloroethene
PP        Proposed Plan
psig      Pounds per square inch-gauge

RAO       Remedial action objective
RBC       Risk-based concentration
RI        Remedial Investigation
ROD       Record of Decision
SARA      Superfund Amendments and Reauthorization Act of 1986 and 1990
SDWA      Safe Drinking Water Act
SVE       Soil vapor extraction
SVOC      Semivolatile organic compound
TCE       Trichloroethene
TPH       Total petroleum hydrocarbon
USAGE     U.S. Army Corp of Engineers
USAF      U.S. Air Force
USEPA     U.S. environmental Protection Agency
USGS      U.S. Geological Survey
VOC       Volatile organic compound
WP14      Liquid Waste Disposal Area 14

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1. DECLARATION OF THE SELECTED REMEDY

1.1 SITE NAME AND LOCATION

Liquid Waste Disposal Area 14 (WP14) and Landfill 15 (LF15), Area 1, 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 soil and
groundwater at WP14/LF15 which was chosen in accordance with the requirements 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

Dover AFB identified soil and groundwater contamination related to the activities that
occurred in and around the WP14/LF15 site. WP14 and LF15 are inclose proximity to one
another and compose what is referred to as Area 1. WP14 is the location of a former liquid
waste disposal trench located in the northeast portion of the Base. This trench was used in the
1950s for the disposal of waste solvents, hydraulic fluids, waste oils, and other liquid wastes
generated in shop operations. No record exists whether or not this trench was lined. After
disposal activities ended at this site, probably in the early 1960s, the trench was filled with
3 to 4 feet (ft.) of local soil and seeded with grass. Free product recovery was actively
conducted at the site from 1994 to early 1996. WP14 has remained vacant since it was closed.

LF15 is the location of a former trenched landfill located next to WP14. The site was
initially reported to cover an area of less than 0.5 acre; however, personnel familiar with the
site described it as much larger. During the 1960s, LF15 was reportedly used for the disposal
of general refuse and small quantities of industrial shop wastes. The disposal area was filled
to a depth of approximately 8 ft.. When disposal activities ceased at an unknown date, the site
was covered with several feet of local soil and seeded. LF15 is currently a grass-covered
field.

Environmental investigations identified significant volatile organic compounds (VOCs) in
groundwater at both sites including fuel-related floating product in a well near WP14 and metals
above action levels in LF15 groundwater. VOCs were also noted in surface water samples
collected for the LF15 study. Both fuel-related and chlorinated compounds were detected in
groundwater, but the fuel-related compounds were determined to not be migrating away from the
their source area. Chlorinated compounds, primarily 1,2-Dichloroethene (1,2-DCE),
Tetrachloroethene (PCE), and Trichloroethene (TCE), originate from both sites and are present in
all downgradient monitoring wells. The concentrations of these contaminants are not
sufficiently elevated to indicate the presence of free phase product.

The findings from the soil sampling conducted during the remedial investigation (RI) (Draft
Final RI Basewide Remedial Investigation, August 1995) showed the presence of chlorinated
solvents, fuel-related VOCs, and semivolatile organic compounds (SVOCs) contaminants in soil,
but their levels were generally below action levels and do not indicate a significant soil
problem at this site. Except for arsenic, metal concentrations were below or slightly over
background concentrations. Arsenic concentrations were detected above site background but below
risk based screening levels (RBSQ in several soil samples collected in portions of the site
called the tetraethyl lead disposal area and the primary disposal trench. The source of the
arsenic appears to be related to disposal activities at LF15. Remaining soil contaminants do
not appear to be a human health risk; therefore, no further action of the soil at WP14/LF15 is

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the selected remedy The sediments at WP14/LF15 may pose an ecological risk due to concentrations
of metals detected. These sediments, and other related site conditions, are planned to be
addressed in the final base-wide ROD.

A Baseline Risk Assessment (BRA) was conducted for WP14/LF15. The risks to exposure
of WP14 and LF15 soils produce a lifetime excess cancer risk (LECR) less than 1E-06 and
Hazard Index (HI) of less than 1 for both current and future commercial/industrial scenarios.
The LECR and HI associated with the hypothetical future commercial/industrial use of
groundwater are 9E-04 and 1, respectively. The HI is the criterion used to evaluate the
noncarcinogenic effects. Because the LECR value is above the 1E-04 to 1E-06 range, it is
appropriate to consider risk-reducing action for groundwater at this site. No action is
acceptable for soil due to low risk. The carcinogenic risk at WP14/LF15 is primarily
attributable to vinyl chloride in groundwater and arsenic in both soil and groundwater.

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 and performance of groundwater monitoring. Final evaluation of the performance of
this interim remedy, Remediation of contaminated groundwater at 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.

2.1 INTRODUCTION

DAFB recently completed a draft Feasibility Study (FS) and a technical assessment of natural
attenuation processes at DAFB that addressed contaminated soil and groundwater in the immediate
vicinity of WP14/LF15. The two sites comprise what is called Area 1 and are located along the
eastern boundary of DAFB. The sites are combined because of their close proximity and similar
contaminants.

The Draft Feasibility Study, East Management Unit, Dover Air Force Base (Dames & Moore May
1997) was undertaken as part of the U.S. Air Force's Installation Restoration Program (IRP).
The basis for the FS was the Draft Final Basewide Remedial Investigation, 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 document
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

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prepared by the U.S. Geological Survey (USGS), Baltimore, Maryland, in February and March 1997,
respectively.

Early environmental investigations identified significant VOCs in groundwater at both sites
including fuel-related, chlorinated compounds, and metals in LF15 groundwater. Floating product
was found in a well near WP14. VOCs were also noted in surface water samples collected for the
LF15 study. The fuel-related compounds (i.e., benzene, toluene, ethylbenzene, xylene (BTEX)] do
not appear to be migrating away from the source areas because of the absence of the compounds in
the downgradient wells. Chlorinated compounds, primarily 1,2-DCE, PCE, and TCE, originate from
both sites and are present in all downgradient monitoring wells. Most of the chlorinated
contaminants exceeded their respective Maximum Contaminant Levels (MCLs); however, the
concentrations of these contaminants are not sufficiently elevated to indicate the presence of
free phase product.

The investigations detected mainly fuel-related VOCs in soils. While still below the
risk-based screening concentration (RBSC), the only significant concentrations of VOCs detected
were ethylbenzene and xylenes, which were associated with one of the test pits at LF15. Other
VOCs were also detected at lower concentrations. SVOCs and pesticides were detected below
action, levels at a few locations. The SVOCs were predominantly fuel-related Polycyclic
aromatic hydrocarbons (PAHs) associated with disposed material and jet engine exhaust. The
pesticides detected maybe site related; however, the long-term use of pesticides by the
surrounding farms and the base is a more likely source. A few metals, especially arsenic,
exceeded background concentrations, but were not pervasive across the site. Arsenic
concentrations were above background levels but below their RBSC in several soil samples
collected in a portion of the site called the tetraethyl lead disposal area. The source of the
arsenic appears to be related to disposal activities at LF15.

Site related VOCs were detected in the surface water samples from Pipe Elm Branch. These
contaminants volatilized guickly and were not detected in off-base samples. Several metals were
slightly elevated in sediment samples.

This ROD addresses the potentially hazardous substances present in WP14/LF15 soil and
groundwater. This ROD summarizes the FS, describes the remedial ALTERNATIVES that were
evaluated, identifies the remedial alterative selected by DAFB, and explains the reasons for
this selection. The State of Delaware concurs with the remedy selected in this ROD.

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 WP14/LF15 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). 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.

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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 WP14/LF15 Cis located within the EMU, one
of four management units into which the base has been divided (Figure 2). WP14/LF15 are in
close proximity to each other and are collectively known as Area 1

WP14 is the site of a liguid waste disposal area. Waste activities occurred at three
potential areas; a tetraethyl lead disposal area, the primary trench, and a liguid-stained area.
WP14 is located in the northeast portion of DAFB, east of the N/S runway, near the access road
leading to the Receiver Station and Reno Road. It is situated approximately 500 ft. to the east
of the hammerhead taxiway which is a hazardous cargo loading zone. The trench at WP14 was
initially delineated in 1983 by a heavy eguipment operator who was involved in its construction.

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2.3.1 Previous Investigations at WP14

The 1986 investigation of WP14 identified VOCs, oil and grease, lead, total organic halogens,
and total organic carbon as site contaminants. The data indicated that WP14 may be the source
of high (above action reguirements) levels of VOCs in groundwater; however, there was
insufficient information to discern WP14-related contamination versus nearby sites or background
conditions.

The second investigation included an extensive soil gas sampling effort, a magnetometer survey,
and soil and groundwater sampling. The soil gas results indicated the presence of high
concentrations of volatile compounds in the center of WP14. The elevated levels of methane at
the center of the site were interpreted as the decomposition of subsurface organic material in
the vicinity of the trench. The magnetometer survey defined the trench as approximately 20 ft.
wide by 45 ft. long and oriented northeast by southwest. The previous site description was
larger, suggesting that the magnetometer survey identified only where metal objects reside in
the trench.

Soil data revealed VOCs, SVOCs, and nine metals at concentrations of concern, but below
action levels or background concentrations. In groundwater, PCE was present directly
downgradient of WP14. The presence of floating product in MW13, which is closest to the
suspected trench, suggests that subsurface soil around the trench may be a source of
contaminants in groundwater. In general, groundwater data indicated that VOCs were present in
the upper portion of the Columbia Aguifer around WP14 and extending downgradient toward the
drainage ditch. Organic compounds were not present at high concentrations in any of the deep
groundwater samples in this area.

The data from the sediment and surface water sampling indicated that chlorinated solvents
(e.g., TCE), and potentially, other VOCs and metals, may have migrated in groundwater from WP14
to Pipe Elm Branch, but concentrations are below action levels or background concentrations.
Also, the data would suggest an attenuation of the compounds in groundwater through natural
processes before reaching the discharge point at the drainage ditch.

2.3.2 Previous Investigations at LF15

The 1984 investigation of LF15 identified VOCs and metals in groundwater. The data was
insufficient to evaluate whether LF15 or nearby Site WP14 was the source of organic
contaminants. LF15 was identified as a possible source for chromium and nickel concentrations
above action levels in groundwater.

The next investigation included an extensive soil gas sampling effort, geophysical surveys
using electromagnetic conductivity, magnetic, and ground penetrating radar, and soil and
groundwater sampling. The soil gas results indicated the presence of chlorinated compounds in
the western portion (filled area) of LF15. The geophysical surveys identified several
anomalies, the first was interpreted as a 0.5 to 0.75-acre fill area containing metal and debris
in the western portion of the site. A second anomaly, east of the fill area, was interpreted as
a potential buried trench.

During the 1989 investigation, LF15 was identified as a probable source for VOC contamination
of groundwater. Metals and inorganics did not appear to be significantly above action levels or
background concentrations at this site in groundwater. Toluene, chlorinated solvents, and
metals were detected in surface water samples, and total petroleum hydrocarbons (TPH) and metals
were present in sediment. The report concluded that the LF15 and WP14 were the sources of these
contaminants, and that they may migrate in groundwater and discharge to the stream channel.

The third investigation focused primarily on WP14, but additional soil gas and groundwater
samples were collected. Solvent-related VOCs were detected downgradient of the western portion
of the site, metals were detected at shallow and deep wells throughout the site. The report
concluded that VOCs from LF15 were present in the top of the Columbia Aguifer. Several metals
(e.g., chromium and mercury) were reportedly above background concentrations, but attributed to
another nearby site [Landfill 13 (LF13)]. Sediment and surface wafer samples collected from
Pipe Elm Branch detected no site-related organic contaminants. Metals appeared to be a possible
concern in surface water, but not no sediment. The report concluded that there was no
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significant migration of WP14/LF15 contaminants to or through Pipe Elm Branch.

2.3.3 Previous Investigations at Both WP14/LF15

The RI, conducted from February 1993 to May 1994, showed that WP14 and LF15 appear to be the
sources of organics in the groundwater. Although the investigations detected chlorinated
solvents and fuel-related VOCs and SVOCs in the soil, their concentrations are below RBSCs and
do not indicate a soil problem at this site. Organic contaminants detected in samples include
SVOCs at 77 Ig/kg or less, pesticides at 11 Ig/kg or less, and TPH at 31 Ig/kg or less. Several
pesticides were detected below action levels in surface soil samples, with concentrations
decreasing with depth. These contaminants do not appear to be related to WP14/LF15, but rather
to the widespread use of these pesticides across the base. Except for arsenic, metal
concentrations were below or only slightly over background concentrations. Arsenic
concentrations were above background concentrations in several soil samples collected in a
portion of the site called the tetraethyl lead disposal area and the primary disposal trench.
The source of the arsenic may be related to the disposal activities at the site.

The fuel-related compounds (i.e., BTEX) are not migrating away from their source area as
evidenced by the absence of the compounds in the downgradient wells. Chlorinated compounds,
primarily 1,2-DCE, PCE, and TCE, originate from both sites and are present in all downgradient
monitoring wells. Most of the chlorinated compounds exceeded their respective MCLs; however, the
concentrations of these contaminants are not sufficiently elevated to indicate the presence of
free-phase product.

Pesticides and Polychlorinated biphenyls (PCBs) were detected in soil and groundwater at the
site; however, their concentrations were generally at concentrations below their action levels
for commercial/ industrial soil ingestion and MCLs for water. Aroclor 1260 was detected in
several soil samples at low concentrations, but not above its action level. Dieldrin (a
pesticide) was detected in two surface soil samples above its action level for commercial/
industrial soil ingestion; however, it and other pesticides in soil and groundwater are
generally attributed to manufacturer-specified long-term application of these compounds across
the base and surrounding farmlands.

Approximately 36 soil borings and 38 monitoring wells have been installed during the
investigation of WP14 and 6 soil borings and 15 monitoring wells for LF15. Figures 3 and 4
illustrate the WP14 and LF15 site areas and sampling locations, respectively. The estimated
sizes of the WP14 and LF15 source areas are 8,800 sguare feet (ft 2) and 13,000 ft. 2
respectively.

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. The focus of the BRA is on
the possible human health 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 1 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 1 may not
necessarily reguire an action under CERCLA in order to be protective of human health. It Is
considered very unlikely that the Columbia Aguifer would be used by the base. To ensure the
Columbia Aguifer would not be used, institutional controls for restrictions of the groundwater
use at WP14, LF15 would be implemented as part of the selected alterative. The restriction
would be applicable to all scenarios of groundwater use including residential, recreational, and
commercial/industrial.

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The RI/FS focused on the collection of data to determine extent of contamination in the
vicinity of WP14/LF15. The BRA identified several contaminants of concern (COCs) in soils at
WP14:
SVOCs: 2-Methylnaphthalene
Benzo[g,h,i]perylene
Dibenzofuran
Phenanthrene
Metals:
Arsenic
Beryllium
Calcium
Cobalt
Pesticides: Delta-benzene hexachloride
Dieldrin
Endosulfan II
Endosulfan sulfate
Endrin ketone
A summary of the major contaminants and their concentrations detected in soil samples from
WP14 during the RI is given in Table 1. The BRA, performed as part of the Basewide RI,
considered hypothetical current and future soil use under the commercial/industrial scenario.
Details concerning the selection of COCs and the human health risks may be reviewed in the Draft
Final RI. Volumes III and IV, August 1995.

The total LECRs for the hypothetical current and future commercial/industrial exposure to
soil is 2E-07 and 4E-06, respectively. Arsenic is the primary contributor to the LECR. The
resulting risk exposures are given in Table 2.

Soil COCs identified at LF15 are:
SVOC s: 2-Methylnaphthalene
Dibenzofuran
Phenanthrene
Metals:
Arsenic
Calcium
Cobalt
Magnesium
Pesticides: Delta-benzene hexachloride
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Table 1. Summary of Major Contaminant Detected During the RI in WP14 Soil

Analyte
Volatile organic compounds

Chloroform
Toluene
Xylene (Total)

Semivolatile organic
compounds

2-Methylnaphthalene
Bis(2-ethylhexyl)phthalate
Naphthalene
Pentachlorophenol
Phenanthrene

Pesticides/PCBs

4,4'-DDE
Metals
Aluminum
Arsenic
Beryllium
Calcium
Cobalt
Copper
Lead
Mercury
Highest
concentration
(Ig/kg)
2.0
3
2
2100
210
1900
100
920
4700
(mg/kg)
37,900
71.7
1.8
2490
8.9
12.1
85.6
0.25
Number
of hits
11

38
29
5
38
29
26
37
11
Number of
samples
38
38
38
17
17
17
17
17
17

38
38
38
38
39
33
38
38
Background
cone.
(Ig/kg)
940,000*
4.1E+08*
IE+09*
410,000*
8.2E+07*
48,000*
17,000*
(mg/kg)
23,855
19.8
1.7
1080
6
7.8
33.1
0.16
USEPA Risk-Based Concentrations for Commercial/Industrial soil ingestion scenario.
-------
Table 2a. Hypothetical Current Commercial/Industrial Scenario for Soil at WP14

Pathway Hazard Index LECR

Ingestion IE-OS 2E-07

Inhalation NA 1E-10

Total IE-OS 2E-07

NA = Not Applicable.

Table 2b. Hypothetical Future Commercial/Industrial Scenario for Soil at WP14

Pathway Hazard Index LECR

Ingestion 2E-01 4E-06

Inhalation NA 1E-08

Total 2E-01 4E-06

NA = Not Applicable.

A summary of the major contaminants and their concentrations detected in soil samples from
LF15 during the RI is given in Table 3. The BRA, performed as part of the Basewide RI,
considered hypothetical current and future soil use under the commercial/industrial scenario.
Details concerning the selection of COCs and the human health risks may be reviewed in the Draft
Final RI, Volumes III and IV, August 1995.

The total LECRs for the hypothetical current and future commercial/industrial exposure to
soil is 1E-07 and 2E-06 respectively. Arsenic is the primary contributor to the LECR. The
resulting risk exposures are given in Table 4.

Area 1 groundwater contained several COCs:

Vocs: 1,1,2,2-tetrachloroethane Pesticides: Delta-benzene hexachloride
1,2-DCA Endosulfan II
1,1-DCE Endosulfan sulfate
1,2-DCE Endrin aldehyde
2-Hexanone Endrin ketone
Benzene Heptachlor
Ethylbenzene Heptachlor epoxide
PCE
TCE
Vinyl chloride
-------
Table 3. Summary of Major Contaminants Detected During the RI in LF15 Soil
Analyte
Volatile organic compounds
Ethylbenzene
Xylene (Total)
Semivolatile organic compounds
2-Methylnaphthalene
Bis (2-ethylhexyl)phthalate
Naphthalene
Metals
Aluminum
Arsenic
Cadmium
Calcium
Cobalt
Copper
Lead
Magnesium
Mercury
Nickel
Highest
concentration
(Ig/kg)
2000
9600

590
87
1300
(mg/kg)
40,300
39.2
1.3
20,200
16
10.2
139
12,000
0.23
22.7
Number
of hits
Number of
samples
2
2
1
3
1
16
11
1
16
10
10
16
16
9
8
16
16
10
10
10
16
16
16
16
16
16
16
16
16
16
Background
cone.
(Ig/kg)
2E+08*
1E-09*
410,000*
8.2E+07*
(mg/kg)
23,855
19.8
0.84
1080
6
7.8
33.1
10,166
0.16
15
USEPA Risk-Based Concentrations for Commercial/Industrial soil ingestion scenario.
-------
Table 4a. Hypothetical Current Commercial/Industrial Scenario for Soil at LF15

Pathway Hazard Index LECR

Ingestion 5E-04 1E-07

Inhalation NA 8E-11

Total 5E-04 1E-07

NA = Not Applicable.

Table 4b. Hypothetical Future Commercial/Industrial Scenario for Soil at LF15

Pathway Hazard Index LECR

Ingestion 1E-01 2E-06

Inhalation NA 7E-09

Total 1E-01 2E-06

NA = Not Applicable.

SVOCS: 2-Methylnaphthalene Metals: Arsenic
Bis(2-ethylhexyl)phthalate Beryllium
Phenanthrene Cobalt
-------
A summary of the major contaminants and their concentrations detected in Area 1 groundwater
samples is given in Table 5. The detected concentrations of 13 contaminants in groundwater
exceeded their respective MCLs in at least one of the samples collected during the RI in the
vicinity of the source area. The source area for groundwater contamination is in close
proximity to the base boundary and the groundwater discharge point is to a drainage ditch
connected to Pipe Elm Branch of Little River, hence the potential exists for the future off-base
migration of contaminants with groundwater.

The BRA, performed as part of the Basewide RI, considered hypothetical future groundwater use
from the Columbia Aguifer under the commercial/industrial scenario. Details concerning the
selection of the COCs and the human health risks may be reviewed in the Draft Final RI. Volumes
III and IV, August 1995.

The total LECRs for the hypothetical future commercial/industrial exposure to groundwater is
1E-04. Vinyl chloride and arsenic are the primary contributors to the LECR. The resulting risk
exposures are presented in Table 6.
-------
Table 5. Summary of Major Contaminants Detected During the RI
in WP14/LF15 (Area 1) Groundwater
Analyte
Highest
concentration
(Ig/L)
Volatile organic compounds

1,2-Dichloroethane
1,2-Dichloroethene
Benzene
Methylene Chloride
Tetrachloroethene
Trichloroethene
Vinyl Chloride

Semivolatile organic compounds

Bis(2-ethylhexyl)phthalate
Metals
Antimony
Arsenic
Beryllium
Chromium
Lead
Magnesium
Manganese
Nickel
Number
of hits
Number of
samples
74
130
22.0
33.0
890
260
59.0
4
14
3
2
10
13
1
39
39
39
39
39
39
39
Maximum
contaminant
levels
(Ig/L)
5
70
5
5
5
5
2
350
(mg/kg)
80.9
36.3
15.5
249
101
31,000
4280
187
1

1
13
20
21
18
24
22
14
15

24
24
24
24
24
24
24
24
6
(mg/kg)
6
50
4
100
15

100
-------
Table 6. Hypothetical Future Commercial/Industrial Scenario for Groundwater at Area 1

Pathway Hazard Index LECR

Ingestion 3E-01 9E-05

Inhalation 5E-02 2E-05

Total 4E-01 1E-04

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. hese 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 WP14/LF15 is the reduction of contaminant concentrations in soil to the USEPA Region III
Risk-Based Concentrations (RBCs) for the commercial/industrial ingestion scenario. The RAO for
groundwater is the Safe Drinking Water Act (SDWA) MCLs or Delaware's DNREC regulatory levels.
The selected acceptable contaminant levels in groundwater are MCLs. For COCs that do not have a
RBC or an MCL, the base-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 soil and groundwater is to reduce the concentrations of the COCs below
their remedial action levels.

Groundwater-use is controlled by the existing DAFB water-supply program. Within the
boundaries of the base, DAFB does not use the Columbia Aguifer for two primary reasons: 1) the
aguifer cannot meet the base's residential and industrial demands and (2) the water guality of
the Columbia Aguifer 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 and it very likely will remain a USAF base in the distant future. These institutional
controls help minimize exposure to site contaminants.

The potential exposure routes for WP14/LF15 contaminants are ingestion/inhalation of soil
particles that have sorbed contaminants and contact and ingestion of contaminants in
groundwater/surface water. 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 RAO
within the area of attainment.

The selected acceptable contaminant levels are base-specific background concentrations for
soil and MCLs for groundwater, which are available for most of the COCs at WP14/LF15. The
primary contributor to the total LECR in soil is arsenic, which the DAFB-specific background
concentration is 1.70 mg/kg. In groundwater vinyl chloride and arsenic are the primary
contributors to the total LECR. The MCLs for vinyl chloride and arsenic are 2 Ig/L and 50 Ig/L
respectively.

2.6 SUMMARY OF ALTERNATIVES

General response actions are the steps that could be taken to achieve the RAOs for the soil
and groundwater at WP14/LF15. 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
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• In situ Groundwater Treatment
- Natural attenuation
- Density-driven convection
- Permeable reactive barrier wall

• Groundwater Collection
- Vertical groundwater extraction wells

• Ex situ Groundwater Treatment
- Metals pretreatment
- Air stripping

• Groundwater Disposal
- Surface water discharge

These technologies are combined to form five distinct alternatives that have varying
degrees of success at achieving the RAOs for WP14/LF15. The five alternatives and features of
each technology are summarized as follows.

• Alternative l--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 Soil and Groundwater Using Natural
Attenuation. This alterative relies on passive treatment of contaminated soil and
groundwater through natural physical, chemical, and biochemical processes. These
processes, particularly biodegradation processes, result in the reduction of soil
and groundwater contaminant concentrations at reasonably predicted rates.
Institutional controls consisting of continuation of the restrictions on using
on-base groundwater 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. Soil contamination is addressed
by use of soil vapor extraction technology. The distal end of the plume is
addressed by natural attenuation. Institutional controls consisting of continuation
of the restrictions on using on-base groundwater 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 and soil are addressed by
natural attenuation. Institutional controls consisting of continuation of the
restrictions on using on-base groundwater 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 strewn: ipe Elm Branch. The
distal end of the plume and soil are addressed by natural attenuation. Institutional
controls consisting of continuation of the restrictions on using on-base groundwater
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 require active remediation. The NCP and
CERCLA guidance require 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 soil and 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.
-------
Alternative 1

Cost Category Cost ($)

Capital 0
Annual Operations and 0
Maintenance
Present Worth 0

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 base-specific background
concentrations for soil and SDWA MCLs for groundwater (See Table 9). The success of meeting the
RAOs must be determined. No cost is associated with this alternative.

2.6.2 Alternative 2-In Situ Remediation of Soil and Groundwater Using Natural Attenuation

Alternative 2, in situ remediation of soil and groundwater using natural attenuation, relies
on passive treatment of contaminated soil and 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 soil and 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., TCE, PCE, 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 LF13 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 the ROD 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 Fire Training Area 3 (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 PCE
and 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 WP14/LF15
are described in the following paragraphs.

For WP14/LF15, concentrations of 1,2-dichloroethane (1,2-DCA) (74 Ig/L) and PCE (890 Ig/L) in
groundwater may be sufficiently high that natural attenuation could be ineffective to meet the
remedial objective of 5 Ig/L each. This assumes the worst case of a flow path of 1500 ft. to a
surface water body, a high flow velocity of 376 ft./year, and the highest contaminant
concentrations detected in the RI. The estimated remediation time through the natural
attenuation process of bio-remediation for WP15/LF15 groundwater ranges from 4 to 8 years for
PCE and 200 to 500 years for 1,2-DCA. The 200 to 500 years bio-remediation restoration time
frame for 1,2-DCA is unacceptable to EPA and DNREC. However, because of the relatively low
levels of 1,2-DCA present at this site, it is expected that even under the worst case scenario,
the 1,2-DCA will naturally attenuate to MCLs due to dilution within a relatively short period of
time. It is assumed that soil remediation times would be comparable because similar degradation
-------
processes are also occurring.

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 5 and consists of five groundwater
wells. During the Remedial Design, the base will develop, with DNREIL 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.

Alternative 2

Cost Category Cost ($)

Capital 4,200
Annual Operations and 8,400
Maintenance
Present Worth 40,000
This alternative is considered capable of complying with the chemical-specific (e.g.,
base-specific background concentrations and MCLs) and action-specific (e.g.,long-term
monitoring) ARARs (See Table 9). In addition to monitoring, institutional controls such as
land-use and groundwater-use restrictions that prohibit use of the contaminated soil and aguifer
will remain in place.

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 snip 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 Atee@ with a capped 3-foot 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 Area 1. 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/liguid separator is used to remove liguids before entering the vacuum blower. An offgas
carbon adsorption treatment system is included to remove extracted VOCs before atmosphere
discharge of the gas stream.

Based on the formation permeability and thickness, the vendor that offers this technology
(Wasatch Environmental) estimated that the effective radius of influence for single 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 reguired to remediate the source areas. The radius of influence for an
SVE well is estimated to be 45 ft. based on the air sparging (AS)/SVE treatability study
conducted at WP21 in the West Management Unit [Extended Aguifer Air Sparging/Soil Vapor
Extraction Treatability Study for Site SS59 (WP21), Dover Air Force Base, EA Engineering,
Science and Technology, 1994]. SVE wells were spaced approximately 80 ft. apart allowing for
some overlap and providing full coverage. Based on the spacing reguirements, WP14/LF15 is
estimated to need 5 DDC wells and 14 SVE wells.

Using the results of the air sparging/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 WP14/LF15 SVE wells, an estimated 1 vapor extraction station will be used.
The extraction station will receive and treat vapors from 14 SVE 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 gas stream. Water
generated in each knock-out pot will be piped to a 55-gallon liguid phase carbon adsorption
unit. Liguid phase granular activated carbon (GAG) treatment units will be used to reduce the
level of the organics to levels that comply with discharge reguirements (See Table 9). Following
treatment, the treated water will be discharged into surface drainage that flows into Pipe
Elm Branch.

Vapor from the knock-out pot will be treated in vapor-phase carbon adsorption units where
organic contaminants will be removed. The air flow at each station will be split into two
parallel streams, each of which will be treated using a 150-pound (Ib) canister of GAG. For the
one vapor extraction station, two carbon canisters will be reguired. 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. During subseguent years of
operation, the carbon consumption rate will be progressively less as the contaminant extraction
rates decline.

The SVE system will reguire periodic monitoring. For costing purposes, 12 air samples are
assumed to be collected and analyzed the first month during 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 progress 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 9).

A field pilot test of the DDC system will be necessary before final design of the remediation
action. The study will be used for system design and modeling 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 operating
conditions. The system addresses the source area at the site. The distal ends of the plume
will be allowed to attenuate naturally.

Groundwater monitoring will be performed to track the long-term progress and effectiveness of
-------
groundwater remediation and to monitor contaminant migration. One new monitoring well (POC2)
will be installed at WP14/LF15. The new well, in addition to the 4 existing wells, will be used
to monitor plume migration. Samples will be collected and analyzed from the 5 wells
semiannually. All groundwater samples will be tested for all COCs. The actual freguency,
duration, and analytical parameters may change, depending on the long-term results of sampling.
For costing purposes, monitoring is assumed to occur for 5 years.

Alternative 3

Cost Category Cost ($)

Capital 150,000
Annual Operations and 20,000
Maintenance
Present Worth 210,000
This alterative is considered capable of complying with the chemical-specific (e.g.,
emissions, base-specific background concentrations, and MCLs) and action-specific (e.g., active
land treatment and long-term monitoring) ARARs (See Table 9). In addition to monitoring,
institutional controls such as land-use and groundwater-use restrictions that prohibit use of
the contaminated soil and aguifer will remain in place. This action will prevent human exposure
to the contaminated soil and 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 WP14/LF15, this alternative includes the construction of two 375-ft. long impermeable
barriers and the installation of 500 cubic yards of reactive iron filings in a 75-ft. trench 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 Basewide 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. Each of the impermeable barriers constructed at
WP14/LF15 will bekeyed into the top of the Calvert Formation (approximately 40 to 60 ft. bgs)
for their entire length. The impermeable barriers will be installed using either displacement
drilling or displacement trenching, whereby a cement slurry is used to hold open the trench/hole
while excavation advances. The slurry is then displaced by pumping in the final cement/grout
mixture.

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 1 additional well (POC2) will be
installed at WP14/LF15. The new well, and 4 existing wells, 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-tern 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 9).
In addition to monitoring, institutional controls such as land-use and groundwater-use
restrictions that prohibit use of the contaminated soil and 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 18,000
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 contaminants, and
surface water discharge of treated groundwater from WP14/LF15.

Groundwater extraction will be accomplished by using one new extraction well installed at the
site. The extraction well location was selected to control and capture the areas of contaminated
groundwater at the site. The extraction rate and capture area from the well was estimated using
the two-dimensional groundwater model TWODAN.

An extraction well operating at 10 gallons per minute (gpm) will be reguired at WP14/LF15.
The well will create a capture zone that will limit further migration of contaminants and
prevent discharge to the Pipe Elm Branch.

The Basewide RI report indicates that the water table is located at a depth of approximately
10 to 12 ft. bgs, in the WP14/LF15 area. The RI/FS reports also indicate that the most
significant contamination is found in the upper third of the Columbia Aguifer. Therefore, the
extraction well at WP14/LF15 will be installed across the upper portion of the Columbia Aguifer
and will he screened using slotted stainless steel casing from 10 ft. bgs (screen length of
approximately 20 ft.)- 30 ft. bgs. The well will be 6 in. in diameter. The filter pack 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 well will be grouted to the surface using a bentonite
grout.

Contaminated groundwater will be extracted using a 4-in. stainless steel electric submersible
pump. 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 3 ft.. An estimated 375 ft. of pipe will be reguired at WP14/LF15 to convey extracted
water from the recovery well to the treatment system and from the treatment system to die
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 basis 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 (USAGE, 1994) was conducted for
groundwater at Site 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 teachability of the metals and thus the method and
cost of disposal (See Table 9). 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 throughput capacity of up to 20 gpm.

Based on the average VOC concentration of groundwater samples collected at the site, an
appropriate extraction rate, and assuming complete removal during treatment, 0.104 Ibs/day
(pounds per day) of VOCs will be stripped from the groundwater at WP14/LF15. The air stream
exiting the air stripper will not require 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 9).

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 9). The model also
shows that air emissions will be significantly below the emission standard of 2.5 Ibs/day.

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). All groundwater and effluent samples are assumed to be tested for all
COCs. 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, 1 additional well (POC2) will be
installed. As was shown In Figure 4, the well will be located at the edge to Pipe Elm Branch.
Samples will be collected and analyzed from five wells semiannually.
Alternative 5

Cost Category Cost ($)

Capital 190,000

Annual Operations and 28,000
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 9). In addition to monitoring, institutional controls such as land-use and
groundwater-use restrictions that prohibit use of the contaminated soil and aquifer will remain
in place. This action will prevent human exposure to the groundwater, thereby averting a public
health risk.

2.7 COMPARISON OF REMEDIAL 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 7, and
an illustrative comparative summary is presented in Table 8.

2.7.1 Overall Protection of Human Health and the Environment
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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,
such as land-use restrictions, that prohibit the unauthorized extraction or use of contaminated
soil and groundwater on-base. 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.
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TABLE 7

Comparative Analysis of Alternatives for WP14/LF15

Alternative 1

No Action
In situ remediation of
WP14/LF/15 groundwater
using density-driven
convection.
Alternative 4

In situ remediation of
WP/14/LF/15 groundwater
using permeable reactive
barrier walls.
6 Environmental Protection
Compliance with ARARs

6 Chemical-Specific ARARs
Offers a high level of overall
protection of human health
through the existing land-use
restrictions on-Base, but
cannot be guaranteed
effective past the Base
boundary.
Does not provide a
mechanism to monitor
ground-water constituent
concentrations. Therefore,
potential impacts to surface
water from discharging
groundwater cannot be
assessed.
Success at meeting RAOs
will be determined.
Offers a high level of overall
protection of human health
through the existing land-use
restrictions on-Base.
Biodegradation of source
are constituents allow
achievement of RAOs off-
Base as demonstrated
through groundwater
monitoring.
Offers a high level of overall
protection of human health
through the existing land-use
restrictions. Active treatment
of source area constituents
allow achievement of RAOs
off-Base as demonstrated
through groundwater
monitoring.
Density-driven convection
treatment is considered
capable of maintaining RAO
compliance.
Offers a high level of overall
protection of human health
through the existing land-use
restrictions. Active treatment
of source area constituents
allow achievement of RAOs
off-Base as demonstrated
through groundwater
monitoring.
Offers a high level of overall
protection of human health
through the existing land-use
restrictions. Active
treatment of source area
constituents allow
achievement of RAOs of f-
Base as demonstrated
through groundwater
monitoring.
Groundwater released to
surface water through pump
and treat operations will
meet surface water guality
criteria.
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TABLE 7 (cont'd)
Alternative 1
Alternative 2
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.
Alternative 3

Complies with DRGHW for
active land treatment. Long-
term groundwater monitoring
provided.
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.
determine whether the RAOs
are achieved over time (i.e.,
preventing risks due to of f-
base migration of
contaminants above RAO
levels.)

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 mechanisms 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
polychlorinated consitituents
will be reguired.
Land use restrictions
enforced by DAFB are
considered extremely reliable
in preventing on-Base
exposure.

Treatability studies are
reguired to design the
reactive barrier walls.
Reductions achieved via
abiotic reactions catalyzed by
the reactive metal will
supplement the active
biodegradation processes.
Land use restrictions
enforced by DAFB are
considered extremely reliable
in preventing on-Base
exposure.

The extraction system will
establish hydraulic control
over the source areas in a
relatively short time
preventing the further
migration of contaminants
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TABLE 7 (cont'd)

Alternative 1

No residues generated
Alternative 4

No residues generated
Alternative 5

Metals pretreatment
generated small volumes of
sludge which will reguire
disposal.
Not applicable.
Standard Health & Safety
procedures and personal
protective eguipment will
prevent exposure during well
installations and sampling.
Worker's exposure will be
minimized by applying dust
control technigues and
providing personal protection
eguipment during
construction.
Worker's exposure will be
minimized by applying dust
control technigues and
providing personal protection
eguipment during
construction.
Worker's exposure will be
minimized by applying dust
control technigues and
providing personal
protection eguipment during
construction.
6 Environmental Impact
Minimal disturbance will
result from installing three
new monitoring wells.
Environmental impacts
related to construction are
minimal.
Moderate land disturbance
due to installment of a
number of wells throughout
the sites. Environmental
impacts related to
construction are minimal.
Moderate land disturbance
due to installation of barrier
walls and grout curtains.
Environmental impacts
related to construction are
minimal.
Moderate land disturbance
due to installation of barrier
walls and grout curtains
Environmental impacts
related to construction are
minimal.
Discharge of treated
groundwater to Pipe Elm
Branch not expected to
adversely impact the
environment.
6 Time Reguired
It is predicted that RAOs will
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.
maintained during the course
of remediation. Two years of
source area treatment is
estimated.
maintained during the course
of remediation. Five years of
treatment at WP14/LF15 is
estimated.
maintained during the course
or remediation. Two years
of source area treatment is
estimated.
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Criteria Alternative 1

Reduction of Toxicity, Mobility, and Volume

6 Treatment Process Used Not applicable.
Alternative 4
6 Amount Treated
Dominant process is
biodegradation. Other
attenuation processes include
volatilization adsorption,
and dilution.
Area covered by WP14/LF15
is approximately 4 acres.
Source area treatment using
density-driven convection
combined with soil vapor
extraction (SVE).
Area covered WP14/LF15
is approximately 4 acres.
Source area groundwater
addressed by extraction
followed by metals
pretreatment and air
stripping.
Area covered WP14/LF15
is approximately 4 acres.
None demonstrated.
Reduction in groundwater
toxicity achieved through
natural attenuation processes
No reductions in mobility or
volume.
source area. Contamin^^^.
mobility is increased during
but mobilized
In situ reductive
dehalgenation 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 or the mobility of
contaminants away from the
EMU.
will reduce the toxicity of
groundwater. The volume of
contaminated media is not
affected.
Irreversibility of Treatment
Natural attenuation will
provide 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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Criteria

Implementability
Alternative 1
Not applicable
Alternative 2
This alternative requires the
installation of monitoring
wells. No difficulties are
anticipated.
No difficulties are anticipated
in installation of the
DDC/SVE wells or
equipment. Operation of the
DDC system is straight
Alternative 4
Alternative 5
No difficulties are
anticipated in construction of
groundwater extraction wells
and operation of selected
technologies.
Not applicable
Ability to Monitor
USGS confirms ongoing
natural attenuation in the
EMU. Continued attenuation
of constituents is anticipated
in the future.
Coordination with
appropriate personnel at
DAFB is necessary
Groundwater wells will
require State permits.
DDC and SVE are reliable
technologies for removal and
destruction of VOCs in
homogenous permeable soils.
However, presence of clay
layers in the EMU reduces
the reliability of these
technologies.

If contaminant rebound occur
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 or
scrapped and replaced with
new technologies if
necessary.
Coordination with
appropriate personnel at
DAFB is necessary
Groundwater wells will
require State permits.
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.
Coordination with
appropriate personnel at
DAFB is necessary.
Groundwater wells will
require State permits.
If contaminant 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

Performance of the reactive
barrier walls and pump and
treat systems are easily
monitored.

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 7 (cont'd)
6 Availability of Equipment

6 Availability of Technology

Cost (IRP Site WP14/LF15)
Alternative 1

Not applicable.
Not applicable.

Not applicable.
Alternative 4
The density-driven
convection component will
require a specialty contractor,
however, the remaining
portions of this alternative
are readily available.
In place.
Readily available.
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2.7.2 Compliance with ARARs

The RAOs that have been established for the EMU sites are based on achievement of the base-
specific background concentrations and 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 ARARs. The treatment actions and groundwater monitoring provisions of Alternatives 21
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 9. Table 9 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. All of the action alternatives will comply
with all ARARs.

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 the USGS at the EMU sites. The technologies
associated with Alternative 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
-------
Table 9. Summary of ARARs
Environmental Laws and Regulations
No

Yes
4. Standards applicable to surface impoundments, waste piles, land
treatment facilities (other than closure and post-closure requirements)
(DRGIIW Part 264, Subpart K, L, and M)

5. Location Standards (DRGHW Pan 264.18)

6. Transportation Standards (DRGHW Pan 263)
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.
3. Landfill Standards (DRGHW Part 264, Subpart N),
A hazardous waste landfill will not be constructed on-base.

LIST rules are not applicable to remedial alternatives for this site
-------
Table 9. (cont.) Summary of ARARs
Environmental Laws and Regulations
3. Delaware Industrial Waste Effluent Limitations (DWPCR Sections 8)
Effluents generated by site remedial activities may reguire pretreatment
Any effluent discharge to POTWs must meet pretreatment standards
Effluents discharged to a POTW would be subject to general
pretreatment guidelines
Safe During Water Act (SDWA), 42 USC 300F

A. Underground Injection Control (40 CFR Parts 144-147)
Extracted groundwater may be reinjected under some remedial
alternatives.
B. Maximum Contaminant Levels (MCLs)(40 CFR Parts 141 and 143)

Marine Protection, Research, and Sanctuaries Act.

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

Toxic Substances Control Act (TSCA)

A. Polychlornated biphenyls (PCB) reguirements (40 CFR Part 761)
-------
Table 9. (cont.) Summary of ARARs
Environmental Laws and Regulations

VII. U.S. Army Corps of Engineers Program

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

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

Delaware Regulations Governing the Control of A Pollution (8 Code of Del.Reg.

U S. Department Transportation Regulations (49 CFR Parts 170 -179)
Preservation of Scientific, Historic, or Archaeological Data (National Historic
Preservation Act,16 U.S.C. 470, 40 CFR 6.301(b), 36 CFR 800; Archaeological and
Historic Preservation Act of 1974, 16 U.S.C. 469, 40 CFR 6.301 (c) ; Historic Site
Buildings, and Antiguities Act, 15 U.S.C. 461-467,40 CFR 6.301 (a), 36 CFR Part
65)
Groundwater treatment alternatives may involve emissions to air.

Groundwater treatment alternatives may involve emissions to air
No wild and scenic rivers are found in the vicinity of the site.
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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.

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
contaminants 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
dehalgenation 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 require 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 across three sites, whereas Alternative 4 includes installing 750 linear feet of grout
curtains and 375 linear feet of reactive barrier wall, all to depths of 40 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 10. Alternative 2 (Natural Attenuation) offers a
substantial cost advantage over the other action alternatives with a present worth cost of
$40,000. Alternatives 3 (Density Convection) and 5 (Pump and treat) offer higher present worth
costs of $210,000 and $260,000, 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 WP14/LF15.

2.7.9 Community Acceptance

No comments were received during the public comment period and no community opposition to the
preferred remedy was noted.
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TABLE 10
Action Alternative Cost Summary
for WP14/LF15 (Area 1)

Alternative Capital Cost Annual O&M* Net Worth

2. Natural Attenuation $4,200 $8,400 $40,000

3. Density Driven Convection $150,000 $20,000 $210,000

4. Permeable Reactive Barrier Wall $1,200,000 $18,000 $1,300,000

5. Groundwater Extraction with Air $190,000 $28,000 $260,000
Stripping

* First year O&M costs.
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2.8 SELECTED REMEDIAL ALTERNATIVE

The selected remedy for cleanup of soil and groundwater at WP14/LF15 is Alternative 2, which
includes the following major components:

• natural attenuation,

• continued enforcement of existing land use restrictions,

• restrictions of groundwater use, and

• groundwater monitoring.

The reasoning to support the selected remedy for cleanup of groundwater at LF13 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 soil and groundwater.

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

• Alternative 2 offers a great implementability advantage over all other alterative. The
only component of Alterative 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 Alterative 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.

2.81 PERFORMANCE STANDARD FOR THE SELECTED REMEDY

The COCs in groundwater at this site, which are listed in Section 14 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
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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 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 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
reguirements 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 soil and 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 groundwater at Site WP14/LF15. 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 1996 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 (GAQ - Carbon material that is has ironically 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 compound
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
organic 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.
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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