Superfund Record of Decision Dover Air Force Base (lF 13) Dover DE


                                    EPA/ROD/R03-97/175
                                    1997
EPA Superfund
     Record of Decision:
     DOVER AIR FORCE BASE
     EPA ID: DE8570024010
     OU06
     DOVER, DE
     09/30/1997

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                                                    EPA/541/R-97/175


                          INSTALLATION RESTORATION PROGRAM

                                  RECORD OF DECISION
                       FOR NATURAL ATTENUATION OF GROUNDWATER
                 AND NO FURTHER ACTION FOR SOIL AT LANDFILL 13  (LF13)
                          WITHIN THE EAST MANAGEMENT UNIT AT
                            DOVER AIR FORCE BASE, DELAWARE

                                      AUGUST 1997

                                      Submitted to
                              436th Airlift Wing, CES/CEV
                        Dover Air Force Base, Delaware 19902-6600

                                      Submitted by
                       HAZARDOUS WASTE REMEDIAL ACTIONS PROGRAM
                       Environmental Restoration and Waste Management Programs
                                  Oak Ridge, Tennessee 37831-7606
                                       managed by
                          LOCKHEED MARTIN ENERGY SYSTEMS, INC.
                                         for the
                                 U.S. Department of Energy
                               Under Contract DE-AC05-840R21400

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CONTENTS

LIST OF FIGURES ii

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 2

2 . DECISION SUMMARY 4
2.1 INTRODUCTION 4
2.2 PUBLIC PARTICIPATION 5
2 . 3 SITE BACKGROUND 5

2 . 4 SUMMARY OF SITE RISKS 10
2 . 5 REMEDIAL ACTION OBJECTIVE 15
2 . 6 SUMMARY OF ALTERNATIVES 16
2.6.1 Alternative -C No Action 18
2.6.2 Alternative 2-In Situ Remediation of Soil and Groundwater Using Natural
Attenuation 18
2.6.3 Alternative 3-In Situ Remediation Using Density-Driven Convection 20
2.6.4 Alternative 4-Ex Situ Treatment of LF13 Groundwater Using Air Stripping 23
2.6.5 Alternative 5-Ex Situ Remediation Groundwater Using Air Stripping 24
2 . 7 COMPARISON OF REMEDIAL ALTERNATIVES 26
2.7.1 Overall Protection of Human Health and the Environment 26
2.7.2 Compliance with ARARs 27
2.7.3 Long-Term Effectiveness and Permanence 27
2.7.4 Reduction of Toxicity, Mobility, and Volume 38
2.7.5 Short-Term Effectiveness 38
2.7.6 Implementability 39
2.7.7 Cost 39
2.7.8 Regulatory Acceptance 39
2.7.9 Community Acceptance 41
2 . 8 SELECTED REMEDY 41
2.8.1 Performance Standard 42
2 . 9 STATUTORY DETERMINATION 42

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 Landfill 13 (LF13)	13
Figure 4 EMU Monitoring Points,  Dover Air Force Base	21

                                       LIST OF TABLES

Table 1.  Summary of Major Contaminants Detected During the RI in LF13 Soil	11
Table 2.  Summary of Major Contaminants Detected During the RI in LF13 Groundwater	12
Table 3a. Hypothetical Current CommercialAndustrial Scenario for Soil at LF13	14
Table 3b. Hypothetical Future Commercial/Industrial Scenario for Soil at LF13	14
Table 4.  Hypothetical Future Commercial/Industrial Scenario for Groundwater at Area	15
Table 5   Comparative Analysis of Alternatives for LF13	28
Table 6   Summary of Comparative Analysis of Alternatives for LF13	34
Table 7   Summary of Potential ARARs	35
Table 8   Action Alternative Cost Summary for LF13	40

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                                         ACRONYMS
4,4'-DDD 1,1 -dichloro-2.2-bis(p-chlorophenyl)ethane
ARARs     Applicable or relevant and appropriate requirements
AS        Air sparging
AWQC      Ambient Water Quality Criteria
bgs       Below ground surface
BRA       Baseline Risk Assessment
BTEX      Benzene, toluene,  ethylbenzene,  and xylene
CERCLA   Comprehensive Environmental Response, Compensation, and Liability Act of 1980
cfm       Cubic feet per minute
COG       Contaminant of concern
DAFB      Dover Air Force Base
DCA       1,2-Dichloroethane
DCE       1,2-Dichloroethene
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     Square feet
FT03      Fire Training Area 3
GAG       Granular activated carbon
gal       Gallon
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
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
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

Landfill 13 (LF13), 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 LF13 which was chosen in accordance with the reguirements of the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980 (CERCLA), as amended and, to the extent
practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40 Code
of Federal Regulations Part 300. The U.S. Air Force (USAF), the lead agency, as the
owner/operator of the Base, prepared this decision based on the Administrative Record for the
site. The U.S. Environmental Protection Agency (USEPA) Region III and the State of Delaware
Department of Natural Resources and Environmental Control (DNREC) provided support.

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

1.3 ASSESSMENT OF THE SITE

Dover AFB identified soil and groundwater contamination related to the activities that
occurred in and around the LF13 site. LF13 is the location of an inactive surface landfill
located in the eastern portion of the Base. It is located north of the ammunition storage
facility and approximately 1000 feet (ft.) to the southeast of Site LF15. The approximately
eight (8) acre site is covered with small trees and underbrush and has a gravel road down the
center. The landfill slopes upward to the east; with the western edge of the site ending
abruptly at a 20-ft. ledge of concrete and debris. Abundant rubble and concrete debris litter
the toe of the landfill. The area surrounding LF13 was delineated as a wetland, and portions are
densely forested.

LF13 was used in the 1960s for the disposal of small guantities of general refuse and large
guantities of construction rubble. From the late 1960s to the early 1990s, the site primarily
received construction rubble. Buried metal was indicated by ground-penetrating radar anomalies.
The dumping of rubble over the edge of the site, with subseguent covering and grading of the
slope, created a 15- to 20-ft. mound on the former lowlands as the landfill was advanced toward
the Base boundary. At present, this site is inactive and is partially covered with lumber and
construction rubble such as concrete, metal scraps, and cans.

The findings from the soil sampling conducted during the remedial investigation (RI) (Draft
Final Basewide Remedial Investigation, August 1995) showed the presence of contaminants in
soil and sediments, but their levels are below action levels and do not indicate a soil problem
at this site. Analyses of the soil detected volatile organic compounds (VOCs), semivolatile
organic compounds (SVOCs), pesticides, polychlorinated biphenyls (PCBs), metals, and total
petroleum hydrocarbons (TPH). The highest TPH detection was 1,750 mg/kg. Several metals were
detected above their background concentrations, mostly in association with areas identified by a
geophysical survey as having buried metals. Remaining soil contaminants do not appear to be a
human health or ecological risk; therefore, No Further Action of soils and sediments at LF13 is
the selected remedy.

Environmental investigations identified VOCs in groundwater. Both fuel-related and
chlorinated compounds were detected in groundwater. Although floating product was observed
once in one well, its presence was never confirmed by subseguent observations at that well.
Chlorinated compounds detected in groundwater included 1,2-dichloroethane (1,2-DCA),
tetrachloroethene (PCE), vinyl chloride, and methylene chloride. The concentrations of these
contaminants are not sufficiently elevated to indicate the presence of free-phase product. Data
collected during the investigations suggest that LF13 is a source for organic and inorganic
contaminants in soil and groundwater.

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A Baseline Risk Assessment (BRA) (Draft Final RI Report, August 1995) was conducted for
LF13. The risks to exposure of LF13 soils produce a lifetime excess cancer risk (LECR) less
than 1E-04 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
further action is selected for soil and sediment. The carcinogenic risk at LF13 is primarily
attributable to vinyl chloride and arsenic in groundwater and beryllium in soil. The
noncarcinogenic: risk in groundwater is primarily attributable to antimony.

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 soil and groundwater using natural
attenuation, institutional controls consisting of continuation of the restrictions on using
on-Base groundwater from the Columbia Aguifer, and performance of groundwater monitoring. Final
evaluation of the performance of this interim remedy, remediation of contaminated soil and
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 the 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 300.43 (f)(4)(ii). This 5 year review will be
performed as a part of a Basewide monitoring program.

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                                      2. DECISION SUMMARY

2.1 INTRODUCTION

    DAFB recently completed a Feasibility Study  (FS) and a technical assessment of natural
attenuation processes at DAFB that addressed contaminated soil and groundwater in the immediate
vicinity of LF13. LF13 is located along its eastern boundary at DAFB, Delaware.

    The Draft Feasibility Study, East Management Unit, Dover Air Force Base  (Dames & Moore May
1997)  was undertaken as part of the USAF's Installation Restoration Program  (IRP). The basis for
the FS was the Draft Final Basewide Remedial Investigation, 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
prepared by the U.S. Geological Survey  (USGS),  Baltimore, Maryland, in February and March 1997,
respectively.

    Early environmental investigations suggested that LF13 was a source of organic and inorganic
contaminants in soil and groundwater. VOCs found in groundwater included fuel-related and
chlorinated compounds. The fuel-related compounds [i.e., benzene, toluene, ethylbenzene, xylene
(BTEX)]1 were not migrating away from the their source area because of the absence of the
compounds in the downgradient wells. Although floating product was observed once in one well its
presence was never confirmed by subseguent observations at that well. Chlorinated compounds
detected in groundwater included 1,2-DCA, PCE,  chloroform, and methylene chloride. The
concentrations of these contaminants were not sufficiently elevated to indicate the presence of
free-phase product.

    During the RI, analyses of the soil detected VOCs, SVOCs, pesticides, PCBs, metals and TPH.
Nine metals were detected above their respective background concentrations in soil, and one TPH
value was measured at 1,750 mg,/kg. No other contaminants were detected above regulatory limits
in soil. Nine VOCs were detected in groundwater during the RI, primarily in two well pairs:
MW61S/MW61D and DM110S/DM110D. Groundwater samples from these wells had the highest VOC
concentrations at the site. 1,2-Dichloroethene (1,2-DCE), vinyl chloride, and benzene each
exceeded their MCLs in at least one sample. All other VOCs [except bis(2-ethylhexyl)phthalate, a
common laboratory artifact],  SVOCs, pesticides, and PCBs were detected at concentrations below
their MCLs. Several metals (including arsenic,  antimony, calcium, cobalt magnesium, nickel,
potassium, and sodium) exceeded their DAFB background concentrations.

    This ROD addresses the source of potentially hazardous substances present in LF13 soil and
groundwater. Also, this ROD summarizes the FS,  describes the remedial alternatives that were
evaluated, identifies the remedial alternative selected by DAFB, and explains the reasons for
this selection. The USEPA and the State of Delaware concur 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 LF13 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

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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.

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 LF13 is located within the EMU, one of
four management units into which the Base has been divided (Figure 2). LF13 is the site of an
inactive surface landfill located in the eastern portion of the Base. It is located north of the
ammunition storage facility and approximately 1000 ft. to the southeast of Site LF15. The
approximately 8-acre site is covered with small trees and underbrush and has a gravel road down
the center. The landfill slopes upward to the east; with the western edge of the site ending
abruptly at a 20-ft. ledge of concrete and debris. Abundant rubble and concrete debris litter
the toe of the landfill. The area surrounding LF13 was delineated as a wetland, and portions are
densely forested.

LF13 was used in the 1960s for the disposal of small guantities of general refuse and
large guantities of construction rubble. From the late 1960s to the early 1990s, the site
primarily received construction rubble. Buried metal was indicated by ground-penetrating radar
anomalies. The dumping of rubble over the edge of the site, with subseguent covering and grading
of the slope, created a 15- to 20-ft. mound on the former lowlands as the landfill was advanced
toward the Base boundary. At present, this site is inactive and is partially covered with lumber
and construction rubble such as concrete, metal scraps, and cans.

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gravel lenses interpreted as channel lag deposits. The thickness of the Columbia Formation at
LF13 is approximately 50 feet. The shallow water table is generally encountered at a depth of 12
to 16 ft. bgs at LF13.

Other structures near LF13 include an inactive JP-4 fuel pipeline approximately 1000 feet
downgradient (north) of the area.

LF13 has undergone several previous investigations, two conducted by Science Application
International Corporation (1986 and 1989) and one, the RI, conducted by Dames & Moore (1995) .
During the early investigations both fuel-related (i.e., BTEX) and chlorinated compounds were
detected in groundwater. Chlorinated compounds detected in groundwater included 1,2-DCA, PCE,
chloroform, and methylene chloride. Although floating product was observed once in one well, its
presence was never confirmed by subseguent observations at that well. The concentrations of
these contaminants were not sufficiently elevated to indicate the presence of free-phase
product. A geophysical survey across the site indicated several area of buried metals as deep as
25 ft. bgs. The early investigation indicated that there were two potential source areas of
contamination.

The RI further helped define the areas of potential contamination. The first area is along
the access road to LF13 near the southwestern edge of the landfill. Groundwater samples from
DM110S and DM110D had the highest VOC concentrations at the site. 1,2-DCE and vinyl chloride
exceeded the Maximum Contaminant Levels (MCLs). The limited number of contaminants implies the
source may have been a discrete spill or dumping of chlorinated solvents rather than extensive
disposal of liguid wastes. The extent of contaminants in groundwater appears limited because
contaminants were not detected in downgradient wells.

The second area of associated contaminants occurred at MW61. Benzene was detected at 5 Ig/L
egual to its MCL. All other VOCs were present below their MCLs at this location. The extent of
the VOC contaminants in groundwater in the vicinity of MW61 appears to be limited because the
detected concentrations were below their MCLs and they were not detected in downgradient wells.
No SVOCs were detected in LF13 groundwater. As in the VOC data, SVOCs data suggest a localized
occurrence of fuel-related compounds. Pesticides were detected; all at exceedingly low estimated
concentrations of 0.0098 Ig/L or less. Of all the metals, only antimony exceeded its MCL in a
filtered sample. In addition to antimony, several other metals exceeded their DAFB background
levels. These metals were arsenic, calcium, cobalt, magnesium, nickel, potassium, and sodium.
The metals were primarily elevated in shallow wells screened in the perched groundwater. The
types of contaminants detected between the two areas and their difference in concentrations
indicate that separate areas of associated VOCs may exist in groundwater at LF13. The area
around DM110 is dominated by chlorinated hydrocarbons and the area around MW61 by fuel-related
hydrocarbons.

Only pesticides and metals were detected in unfiltered surface water samples collected from
LF13. All pesticides were detected in exceedingly low estimated concentrations, often less than
one part per trillion. Iron exceeded the chronic Ambient Water Quality Criteria (AWQC) in
filtered and unfiltered samples, and copper slightly exceeded its chronic freshwater AWQC.
Pesticides and metals were detected in sediment. The pesticides were limited to low, estimated
concentrations. Only cobalt and copper slightly exceeded background levels. No other metals
appeared to be elevated. The investigations concluded that associated surface water and sediment
do not appear to have been impacted by the site activities and the substances in them do not
appear to be a significant concern.

Analyses of the soil detected VOC concentrations below action levels, all metals except
arsenic are below background or cleanup concentrations, and a TPH detection as high as 1,750
mg/kg. All VOCs except chlorobenzene and total xylenes were detected at concentrations of 15
Ig/kg or less. The maximum concentration of chlorobenzene was 130 Ig/kg in one boring and 47
Ig/kg for total xylenes in a test pit sample. While most SVOCs were detected at concentrations
of 1,100 Ig/kg or less, higher concentrations of several fuel-related polycyclic aromatic
hydrocarbons (PAHs) were detected in test pit samples. These PAHs are believed to be related to
the numerous JP-4 fuel filters, auto filters, and motor parts encountered in the test pits. TPH
detections also corresponded to the SVOC concentrations. The elevated TPH concentration was
detected along the southern edge of the landfill.

Most pesticide/PCB detections in soil were at concentrations of 12 Ig/kg or less. However,
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some significant concentrations of pesticides up to 470 Ig/kg and PCBs up to 2,600 Ig/kg were
detected in soil samples from the western portion of the landfill. No pesticide or PCB,
contaminants exceeded their regulatory limits for the commercial/industrial soil ingestion
scenario. Also the concentrations decreased with depth. Only arsenic exceeded its background or
cleanup concentrations for DAFB soils. The investigation concluded that this metal may be
related to wastes in LF13 disposal pits. Data collected during the investigations suggest that
LF13 is a source for organic and inorganic contaminants in soil and groundwater. Summaries of
the major contaminants detected in soil and groundwater during the RI are given on Tables 1 and
2, respectively.

Pesticides and PCBs were detected in soil and groundwater at the site; however, their
concentrations were below their regulatory levels for commercial/industrial soil ingestion and
MCLs for water. The concentrations of PCBs and pesticides in the soil from the western portion
of LF13 indicated they may be site related. The occurrence of most pesticides in groundwater
across the site is generally attributed to the proper long-term application of these compounds
across the Base and surrounding farmlands and is not related to improper use, spills, or
releases.

Approximately 6 soil borings and 14 monitoring wells have been installed during the
investigation of LF13. Figure 3 illustrates the LF13 site area and sampling locations. The
estimated size of the LF13 source area is 183,000 sguare feet (ft.2).

2.4 SUMMARY OF SITE RISKS

The purpose of the BRA (Draft Final RI Report, August 1995) is to determine whether exposure
to site-related contaminants could adversely affect human health and the environment. The focus
of the BRA is on the possible human health and environmental effects that could occur under
current or potential future use conditions if the contamination is not remediated. The risk is
expressed as LECR for carcinogens and as HI for noncarcinogens. For example, an LECR of 1E-06
represents one additional case of cancer in one million exposed population, whereas an HI above
one presents a likelihood of noncarcinogenic health effects in exposed populations. The USEPA
has established the target risk range of 1E-04 to 1E-06 for LECR. Risks greater than 1E-04
generally warrant an action under CERCLA. An HI greater than 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 LF13 would be implemented as part of the selected alternative. The
restriction would
be applicable to all scenarios of groundwater use, including residential, recreational, and
commercial/industrial.

The RI/FS focused, on the collection of data to determine extent of contamination in the
vicinity of LF13. The BRA identified several contaminants of concern (COCs) in soils:

SVOCS: 2-Methylnaphthalene
4-Chloro-3-methylphenol
Benzo[g,h,i]perylene
Dibenzofuran
Phenanthrene

Pesticides/PCBs: Delta-benzene hexachloride
Endosulfan sulfate
Endosulfan aldehyde
Endrin ketone
PCB 1242, 1248, and 1260
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Table 1. Summary of Major Contaminants Detected During the RI in LF13 Soil
Analyte
Volatile organic compounds

Chlorobenzene
Xylene (total)

Semivolatile organic
compounds

2-Methylnaphthalene
Bis(2-ethylhexyl)phthalate
Naphthalene

Pesticides/PCBs

4,4'-ODD
PCB 1242
PCB 1248

Metals (mg/kg)

Aluminum
Arsenic
Cadmium
Calcium
Cobalt
Copper
Lead
Mercury
Silver
Total petroleum
hydrocarbons (mg/kg)
Highest
Concentration
;lg/kg)
130
47
10,000
8700
3500
470
2600
260
25,200
39
52.8
1240
11.4
16.5
152
0.48
1.4
1750
Number
of hits

4
4
3
3
5
6
1
1
17
12
1
17
13
14
17
8
1
151
Number of
samples

17
17
17
17
17
17
17
17
17
17
17
17
17
17
17
17
17
15
Background
Cone.
(Ig/kg)
4.1 E+07*
1E+09*
410,000*
8.2E+07*
24,000*
740*
740*
23,855
19.8
0.84
1080
6
7.8
33.1
0.16
0.97
USEPA, Region III, Risk-Based Concentrations for Commercial/Industrial Soil Ingestion
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Table 2. Summary of Major Contaminants Detected During the RI in LF13 Groundwater
Analyte
Volatile organic compounds

Benzene
Chlorobenzene
1,2-Dichloroethene
Vinyl chloride

Semivolatile organic
compounds
Highest Number Number of
Concentration of hits samples
(Ig/L)
Maximum
Contaminant
Levels
(Ig/L)
5
41.0
1400
520
1
3
2
2
14
14
14
14
5
100
70
2
Bis (2-ethylhexyl)phthalate

Pesticides/PCBs
39
14
Chlordane - Gamma,
Lindane
Methoxychlor
0.0018
0.0047
0.0072
14
14
14
2
0.2
40
Metals (Dissolved)
Antimony
Arsenic
Barium
Copper
Nickel
59.9
9.4
430
4.6
46.8
1
2
14
2
2
14
14
14
14
14
6
50
2000
1300
100

Metals:
Arsenic
Beryllium
Cadmium
Calcium
Cobalt
Manganese
Silicon
Thallium
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 3E-06, respectively. Beryllium is the primary contributor to the LECR for
soil. The resulting risk exposures are presented in Table 3.
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Table 3a. Hypothetical Current Commercial/Industrial Scenario for Soil at LF13

Pathway Hazard Index LECR
Ingestion
Inhalation
Total
IE-OS
2E-05
IE-OS
2E-07
7E-11
2E-07
Table 3b. Hypothetical Future Commercial/Industrial Scenario for Soil at LF13

Pathway Hazard Index LECR
Ingestion
Inhalation
Total
3E-01
2E-02
3E-01
3E-06
6E-09
3E-06
The BRA identified several groundwater COCs at LF13:
VOCs: 1,2-DCA
1,2-DCE
1,4-Dichlorobenzene
Benzene
Chlorobenzene
Vinyl chloride
SVOCs: 4-Chloro-3-methylphenol
Bis(2-chloroethoxy)methane
Bis(2-ethylhexyl)phthalate
Metals:
Pesticides:
Antimony
Arsenic
Calcium
Cobalt
Magnesium
Potassium
Sodium

Endosulfan sulfate
Endrin ketone
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The detected concentrations of three contaminants (e.g., 1.2-DCE, benzene, and vinyl
chloride) 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. Groundwater discharges to Pipe Elm Branch through a
deep flow system, 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 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
9E-04. Vinyl chloride and arsenic are the primary contributors to the LECR and antimony is the
primary contributor to the HI for groundwater. The resulting risk exposures are presented in
Table 4.
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Table 4. Hypothetical Future Commercial/Industrial Scenario for Groundwater at Area 1

Pathway Hazard Index LECR

Ingestion 1E+00 7E-04
Inhalation 6E-02 2E-04
1E+00 9E-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. These objectives are typically achieved by
preventing exposure and reducing contaminant levels (Guidance for Conducting Remedial
Investigations and Feasibility Studies Under CERCLA, Interim Final, USEPA, October 1988). The
RAO for LF13 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 DAFB-specific background level will be used. The selected acceptable
contaminant levels for soil are Base-specific background concentrations and are available for
most of the COCs at LF13. The primary contributor to the total LECR in soil is beryllium, 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, and antimony is the primary contributor
for the HI. The MCLs for vinyl chloride, arsenic, and antimony are 2 Ig/L, 50 Ig/L, and 6 Ig/L
respectively. Antimony was detected in only 1 of 14 samples. This single detection is only about
6% above background.

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 COCs below their RAOs.

DAFB does not use the Columbia Aguifer for two primary reasons: (1) the aguifer cannot
meet the residential and industrial demand and (2) the water guality is less desirable than that
of the deeper aguifer. Land-use restrictions, which are more fully described in DAFB's Real
Estate Property Management System, 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 LF13 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.

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 LF13. Based on results of the initial screening of the response action
technologies presented in the FS and the selection of representative process options, the
following six technologies are considered to be applicable:

• No Action

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

• In situ Groundwater Treatment
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- 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 LF13. The five alternatives and features of each technology
are summarized as follows.

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

• Alternative 2-In Situ Remediation of Soil and Groundwater Using Natural Attenuation.
This alternative 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 the Columbia Aguifer and performance of
groundwater monitoring are also included.

• Alternative 3-In Situ Remediation of Groundwater Using Density-Driven Convection.
Density-driven convection is an in situ groundwater treatment technology that specifically
addresses source-area contamination. 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 the
Columbia Aguifer and performance of groundwater monitoring are also included.

• Alternative 4-In Situ Remediation of Groundwater Using Permeable Reactive Barrier
Walls and Ex Situ Remediation of Groundwater Using Air Stripping at LF13. The
alternatives were developed with the assumption that remedial actions would be implemented
concurrently at three EMU sites which included LF13, Fire Training Area 3 (FT03), and
WP14/LF15. This alternative reflects that concurrent action. The technology described in
Alternative 4 for LF13 is the same as that presented in Alternative 5, ex situ remediation
of groundwater using air stripping. For Alternative 4, groundwater in the source area is
treated in situ using a permeable wall of reactive iron filings at FT03 and WP14/LF15. In
the ex situ treatment system for LF13, groundwater is removed from the source areas using
extraction wells. The extracted water undergoes metals pretreatment and is then processed
through an air stripper. The treated water is subseguently discharged to an on-Base
stream:
Pipe Elm Branch. The distal end of the plumes and soil are addressed by natural
attenuation. Institutional controls consisting of continuation of the restrictions on
using
the Columbia Aguifer and performance of groundwater monitoring are also included.

• Alternative 5-Ex Situ Remediation of Groundwater Using Air Stripping. Groundwater is
removed from the source areas using extraction wells. The extracted water undergoes metals
pretreatment and is then processed through an air stripper. The treated water is
subseguently discharged to an on-Base stream: Pipe Elm Branch. The distal end of the plume
and soil are addressed by natural attenuation. Institutional controls consisting of
continuation of the restrictions on using the Columbia Aguifer and performance of
groundwater monitoring are also included.
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These remedial alternatives are described in the following subsections. In addition, the
capital, annual operation and maintenance (O&M), and present worth costs of each alternative are
provided.

2.6.1 Alternative 1-No Action

Alternative 1, the No Action alternative, is considered in the range of alternatives to
serve as a baseline or to address sites that do not reguire active remediation. The NCP and
CERCLA guidance reguire that the No Action alternative be evaluated. This alternative assumes
that no remedial action will occur and that the site would be left in its present condition. No
efforts are undertaken to reduce groundwater contaminants. Any changes to the site would be a
direct result of natural processes, and no monitoring would be conducted to document changes in
contaminant levels. Existing land-use restriction in place at DAFB will continue to be enforced
to prohibit the unauthorized extraction and use of groundwater from the Columbia Aguifer. This
action will prevent human exposure to the groundwater, thereby averting a public health risk at
DAFB. This alternative does not comply with the chemical-specific ARARs of the Base-specific
background concentrations for soil and SDWA MCLs for groundwater (See Table 7). The success of
meeting the RAOs must be determined. No cost is associated with this alternative.

Alternative 1

Cost Category Cost ($)

Capital 0
Annual Operations and 0
Maintenance

Present Worth 0

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., 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
traveltimes 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 FT03) and high flow velocities (i.e., 376
ft./year), natural attenuation processes are insufficient to decrease concentrations by one
order of magnitude. In a couple of cases, the intermediate flow path of 1500 ft. and a high flow
velocity was not satisfactory to decrease concentrations of TCE by one order of magnitude. It
should be noted that the initial concentration of a specific contaminant will dictate cause for
concern that groundwater will discharge to a surface water body and pose a risk to human health
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or the environment. Potential concerns for LF13 are described in the following paragraphs.

For LF13, all scenarios showed there is sufficient time for natural attenuation to
effectively reduce the contaminant concentrations to below their RAOs. This assumes the worst
case of a flow path of 3000 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 natural attenuation processes for LF13 groundwater ranges from less than 1 year to 2.5
years. 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 4 and consists of five groundwater
wells. To the extent possible, existing wells were selected for monitoring. At LF13, four wells
(i.e., MW62S, MW64S, DMW101S, and DM110S) and a new well (NEW 1) will be monitored to confirm
the predicted decrease in concentrations and to observe that contaminant levels are below MCLs
around the perimeter of the site. Groundwater from this source will eventually be entrained in
the overall flow path toward Area 1 And finally to the Base boundary. Well MW227M and the
monitoring wells GSCP3M and POC2 used for Area 1 will also serve as final downgradient
monitoring points for LF13, which is hydraulically upgradient to Area 1.

Groundwater samples will be collected using dedicated pumps installed in each of the
monitoring wells. During the Remedial Design, the base will develop, with DNREC and EPA review
and approval, an "Operation and Maintenance" plan which will detail the monitoring wells,
sampling parameters, freguency, and performance standards necessary to support the natural
attenuation decision both prior to and after the issuance of the final base-wide ROD.

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 7). In addition to monitoring, institutional controls such as
land-use and groundwater-use restrictions that prohibit the use of the contaminated soil mid
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 creates a turbulent, frothing action inside of the wellbore.
The rising air bubbles strip contaminants from the water and increase the dissolved oxygen
content of the water. The rising bubbles create a frictional drag, which produces a positive
hydraulic head (i.e., greater than static aguifer head) at the bottom of the well. Thus, the
frictional drag acts as a groundwater pump sucking contaminated water from the surrounding
aguifer through the bottom well screen and pushing the water through the wellbore and out of the
top well screen. Aerated water discharged through the top well screen then infiltrates back down
to the water table, while the discharged air bubbles travel through the vadose zone and are
captured by
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soil vapor extraction (SVE) wells. The designed air injection pressures range from 12 to 16
pounds per square inch - gauge (psig) with an injection flow rate of 20 cubic feet per minute
(cfm) for DDC wells.

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

The DDC wells will be operated by injecting air into the wells with a blower or compressor.
Based on the estimated number of DDC wells, two air compressor units will be used at LF13. The
compressor stations can each service 4 to 15 DDC wells. For costing purposes, each air
compressor is assumed to have a 5-horse power motor producing 36 cfm at 16 psig. Each air
compressor unit will have a control panel and will be located within a weatherproofed shed. The
control panels will have pressure controls, flow rate indicators, and control valves for each
sparging line.

The DDC systems will operate in tandem with the SVE systems 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. Offgas carbon
adsorption treatment systems are 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 required 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 Aquifer 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 requirements, LF13 is estimated
to need 20 DDC wells and 27 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 LF13 SVE wells, an estimated 2 vapor extraction stations will be used. The
extraction stations will receive and treat vapors from 27 SVE wells. Each 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 (gal) liquid phase carbon
adsorption unit. Liquid phase granular activated carbon (GAG) treatment units will be used to
reduce the level of the organics to levels that comply with discharge requirements (See Table
7). 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 each
vapor extraction station, two carbon canisters will be required. Initially (i.e., the first year
of operation), the carbon canisters will have to be replaced about every 6 months. Each
-------
extraction station will be located within a weatherproofed shed. During subsequent years of
operation, the carbon consumption rate will be progressively less as the contaminant extraction
rates decline.

The SVE systems will require periodic monitoring. For costing purposes, 24 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,
two air samples/month will be, collected to track the progress and efficiency of remediation. In
addition, the emissions from the SVE stations will be monitored semiannually to ensure that it
is in compliance with standards (See Table 7).

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 (NEW1)
will
be installed at LF13. 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 frequency, 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 380,000
Annual Operations and 27,000
Maintenance
Present Worth 440,000

This alternative 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 7). 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 huma exposure
to the contaminated soil and groundwater, thereby averting a public health risk.

2.6.4 Alternative 4-Ex Situ Treatment of LF13 Groundwater Using Air Stripping

Alternative 4 is the ex situ treatment system of LF13 groundwater using air stripping. The
LF13 treatment system will consist of one extraction well and will be operational over the
course of approximately 2 years. Because contamination exists primarily in the perched water,
the well will be installed and screened across that interval (i.e, 10 to 12 ft. bgs). The
pumping rate is estimated to be 10 gallons per minute (gpm). Collected groundwater will be
passed through two 500-lb liquid-phase carbon canisters and then will be discharged to Pipe Elm
Branch.

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 (NEW1) will be
installed at LF13. 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 frequency, duration, and analytical
parameters may change, depending on the long term results of sampling. For estimating purposes,
monitoring for 5 years is assumed. Groundwater from this source will eventually be entrained in
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the overall flow path toward Area 1 and finally to the Base boundary. Well MW227M and monitoring
wells GSCP3M and POC2 used for Area 1 will also serve as final downgradient monitoring points
for LF13, which is hydraulically upgradient to Area 1.

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 7). 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 170,000

Annual Operations and 28,000
Maintenance

Present Worth 240,000

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-related compounds, and
surface water discharge of treated groundwater from LF13.

Groundwater extraction will be accomplished by using 1 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. The extraction well will operate
at 10 gpm and 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 perched water table is located at a depth of
approximately 10 to 12 ft. bgs in the LF13 area. The RI/FS reports also indicate that the most
significant contamination is found in the perched water and not in the Columbia Aguifer.
Therefore, the extraction well at LF13 will be installed across the shallow perched water and
will be screened using slotted stainless steel casing from 10 ft. bgs (screen length of
approximately 5 ft.) to 15 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 100 ft. of pipe will be reguired at LF13 to convey
extracted water from the recovery well to the treatment system and from the treatment system to
the closest surface water discharge point.

The groundwater treatment system includes an initial pretreatment stage to reduce the
metals content. This stage is added to prevent iron and manganese fouling in the subseguent air
stripping unit as well as to ensure compliance with the National Pollutant Discharge Elimination
System discharge standards (See Table 7). 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
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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 required for the metals
pretreatment process. The results of this study were used to estimate the chemical dosage
required for metals pretreatment.

A sludge characterization test such as the Toxicity Characteristic Leachate Procedure
test will have to be conducted to determine the leachability of the metals and thus the method
and cost of disposal (See Table 7). For costing purposes, the sludge will be assumed to be
nonhazardous. The sludge will be dewatered to reduce the volume requiring 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 liquid 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, 0.033 pounds per
day (Ibs/day) of VOCs will be stripped from the groundwater at LF13. The air stream exiting the
air stripper will not require treatment before release to the atmosphere since 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 7).

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 (See Table 7) without further polishing or treatment. The model also
shows that air emissions will be significantly below the emission standard of 2.5 Ibs/day (See
Table 7).

Effluent samples will be collected from the groundwater treatment system at a rate
required to satisfy regulatory requirements (See Table 7)(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, one additional well (NEW 1) will be
installed. As was shown in Figure 4, the well will be located at the south of the site. Samples
will be collected and analyzed from five wells semiannually. Groundwater from this source will
eventually be entrained in the overall flow path toward Area 1 and finally to the Base boundary.
Well MW227M and monitoring wells GSCP3M and POC2 used for Area will also serve as final
downgradient monitoring points for LF13, which is hydraulically upgradient to Area 1.

Alternative 5

Cost Category Cost ($)

Capital 170,000

Annual Operations and 28,000
Maintenance

Present Worth 240,000

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 7). 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.
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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 are 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 5, and
an illustrative comparative summary is presented in Table 6.

2.7.1 Overall Protection of Human Health and the Environment

The overall protectiveness criterion is a composite of other evaluation criteria,
especially short-term effectiveness, long-term effectiveness, and compliance with ARARs. All
five of the alternatives are considered to be protective of human health because of
institutional controls, 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, Tump and Treat), and 5 (Pump and Treat) will all meet the RAOs and are
considered highly protective of human health and the environment.

2.7.2 Compliance with ARARs

The RAOs that have been established for the EMU sites are based on achievement of 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 2
through 5 will result in demonstrated compliance with the MCLs. A summary of the ARARs used in
the evaluation of the alternatives is provided in Table 7. Table 7 specifies which ARARs are
applicable to each alternative.

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

2.7.3 Long-Term Effectiveness and Permanence

The long-term effectiveness and permanence criterion considers primarily the magnitude
of residual risk that would remain after the implementation of an alternative, and the adeguacy
and reliability of the controls instituted. All of the alternatives provide for the long-term
protection of human health through the existing institutional controls such as land-use and
groundwater-use restrictions. However, reliance upon institutional controls 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-tern 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.
-------
Criteria
TABLE 5

Comparative Analysis of Alternatives for LF13

Alternative 1 Alternative 2
Alternative 4
Alternative
Description
LF13
In situ remediation of LF13
D Human Health Protection
overall

health

land-use
In situ remediation of LF13

groundwater using natural
attenuation.
Offers a high level of overall Offers a high level of overall Offers a high level of overall

protection of human health protection of human health protection of human health

through the existing land-use through the existing land-use through the existing land-use

restrictions. Active treatment
of source area constituents
D Environmental Protection Does not provide a
constituents
mechanism to monitor
water
groundwater constituent
concentrations. Therefore,
potential impacts of surface
water from discharging
groundwater cannot be
assessed
Compliance with ARARs

D Chemical-Specific ARARs Success at meeting RAOs
is
will be determined

will
Groundwater constituents

discharging to surface water

meet MCLs off-Base.
Natural attenuation is
Groundwater constituents

discharging to surface water

meet MCLs off-Base
Groundwater released to
surface water through pump
and treat operations will meet
surface water quality criteria.
Ex situ treatment of LF13

groundwater using air
stripping.
Offers a high level of overall

protection of human health

through the existing land-use
Groundwater constituents

discharging to surface water

meet MCLs off-Base
Groundwater released to
surface water through pump
and treat operations will
meet surface water quality
criteria.
treatment is considered
capable of maintaining RAO
compliance.
Air stripper system will

comply with DRGCAP
requirements
Ex situ treatment of

groundwater using air
stripping.
Offers a high level of

protection of human

through the existing

restrictions. Active
treatment of source
Groundwater

discharging to surface

meet MCLs off-Base.
Air stripper system
-------
TABLE 5 (cont'd)
D Action-Specific ARARs
groundwater
Alternative 1

Does not provide for long-

term groundwater
monitoring.
Alternative 2

Long term groundwater

monitoring is provided.
Alternative 3

Complies with DRGHW for
Alternative 4

Complies with DRGHW for
Long-term Effectiveness and Permanence

Because DAFB is expected

to remain active for the
D Magnitude of risk
expected
for the

the land-

provided

alternative are

provide long-

human
D Reliability of Controls
restrictions
foreseeable future, the land- foreseeable future, the land- foreseeable future, the land-
use restrictions provided

under this alternative are

considered to provide long-

term protection of human

health on-Base.

However, this alternative

provides no mechanisms to

determine whether the RAOs

are achieved over time (i.e.
preventing risks due to off-
Base migration of
contaminants above RAO
levels).

Land-use restrictions

enforced byn DAFB are

considered extremely reliable considered extremely reliable considered extremely reliable

in preventing on-Base in preventing on-Base in preventing on-Base

exposure. exposure . exposure.
use restrictions provided

under this alternative are

considered to provide long-

term protection of human

health on-Base.

Risk for potential off-Base

users will be reduced as

contaminant levels are

lowered.
active land treatment. Long- active land treatment. Long-
term groundwater monitoring term groundwater monitoring
provided. 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.

Risk for potential off-Base

users will be reduced as

contaminant levels are

lowered.
Land-use restrictions

enforced by DAFB are

considered extremely reliable

in preventing on-Base

exposure.
use restrictions provided

under this alternative are

considered to provide long-

term protection of human

health on-Base.

Risk for potential off-Base

users will be reduced as

contaminant levels are

lowered.
Alternative 5

Long-term

monitoring provided
Because DAFB is

to remain active

foreseeable future,

use restrictions

under this

considered to

term protection of

health on-Base.

Risk for potential

users will be

contaminant levels

lowered
Land-use

enforced by DAFB

considered

in preventing

exposure.
time
preventing the further
Off-Base, the reliability of The 2-year study conducted The DDC technology is

this alternative is by the USGS indicates that considered reliable.

questionable because there is natural attenuation can be However, because operation
The extraction system will

establish hydraulic control

over the source areas in a
The extraction

establish hydraulic

over the source
no mechanisms to determine relied upon to achieve the of the DDC system will relatively short time relatively short
whether the RAOs are being whether the RAOs are being change the redox condition preventing the further

of the aqui fer in the source migration of contaminants.
-------
groundwater are proven and
highly reliable
The proposed

are proven and

reliable
-------
TABLE 5 (cont'd)

Criteria Alternative 1 Alternative 2 Alternative 3 Alternative 4

Reduction of Toxicity, Mobility, and Volume

D Treatment Process Used Not applicable Dominant process is Source are treatment using Source areas treated ex situ
groundwater
biodegradation. Other density-driven convection using metals pretreatment

and air stripping.

and dilution. stripping.

Distal ends of plumes treated Sludge generated during Sludge generated
during
by natural attenuation metals pretreatment will be metals
pretreatment will be
processes. sent offsite for disposal. sent offsite for
disposal.

Distal ends of plumes treated Distal ends of
plumes treated
by natural attenuation by natural
attenuation
processes. processes.

D Amount Treated Not applicable. Area covered by LF13 is Area covered by LF13 is Area covered by LF13 is Area covered by
LF13 is
approximately 8 acres. approximately 8
D Reduction in toxicity None demonstrated. Reduction in groundwater DDC process reduces Groundwater extraction and Groundwater
extraction and
mobility, and volume toxicity achieved through groundwater toxicity in the treatment reduces treatment reduces
through treatment natural attenuation processes, source area. Contaminant groundwater toxicity and groundwater
toxicity and
No reductions in mobility or mobility is increased during limits constituents mobility limits
constituents nobility
volume. treatment, but mobili zed inthe capture area.The in the capture
area. The
contaminant should be technology does not impact technology does
not impact
captured by SVE. the volume of contamination the volume of
contamination

Natural attenuation reduces Removal of volatile organic Removal of
the toxicity of the distal ends constituents present in

of the plumes. groundwater by air stripping groundwater by air

will reduce the toxicity of will reduce the

groundwater. The volume of groundwater. The

contaminated media is not contaminated media

affected. affected.

Natural attenuation reduces Natural
attenuation reduces
-------
distal ends of
the plumes

D Irreversibility of Treatment Not applicable
treatment
Natural attenuation will

provide premanent removal

of constituents through

irreversible processes.
the toxicity of the distal the toxicity of
of the plumes.
DDC treatment results in

permanent removal of

constituents through

irreversible processes.
Air stripping treatment

results in the permanent

removal of constituents

through irreversible

processes
Air stripping

results in the

removal of

through

processes
-------
TABLE 5 (cont'd)

Alternative 1 Alternative 2 Alternative 3 Alternative 4

D Type and Quality of No residues generated No residues generated Spend activated carbon will Small quantities of sludge Metals pretreatment
residue be generated from air will be generated by the ex generates small
volumes of
treatment. situ metals pretreatment sludge which will
process at LF13. disposal

Short-term Effectiveness

D Protection of Community No short term impact on the No short term impact on the No short term impact on the No short term impact on the No short term
impact on the
During Remedial Action community surrounding the community surrounding the community surrounding the community surrounding the community
surrounding the
site. site. site during construction or site during construction or site during
construction or
operation. operation. operation.

D Protection of Workers Not applicable. Standard Health & Safety Worker's exposure will be Worker's exposure will be Worker's exposure
will be
During Remedial Action procedures and personal minimi zed by applying dust minimized by applying dust minimized by
applying dust
protective equipment will control techniques and control techniques and control techniques
equipment during

construction. construction. construction

D Environmental Impact None Minimal disturbance will Moderate land disturbance Moderate land disturbance Moderate land
disturbance
result from installing three due to installment ofa result from installing new result from
installing new
new monitoring wells. number of wells throughout monitoring wells. monitoring wells
Environmental impacts the sites. Environmental Environmental impacts Environmental
impacts
related to construction are impacts related to related to construction are related to
construction are
minimal. construction are minimal. minimal. minimal.

Discharge of treated Discharge of
treated
groundwater to Pipe Elm groundwater to Pipe
Elm
Branch not expected to Branch not expected
to
adversely impact the adversely impact
the
environment. environment.

D Time Required Unkown This alternative It is predicted that RAOs will It is predicted RAO It is predicted RAO It is predicted RAO
continue to be met while compliance will be compliance will be compliance will be
contaminants naturally maintained during the course
the course
or remediation. Two years of
treatment of LF13 is of treatment of LF13 is
monitoring to determine estimated. estimated.
whether contaminant
concentrations are significant
-------
-------
Criteria

Implementability

D Ability to Construct and
are
Operate Technology
construction of
D Reliability of Technology
technology is
D Ease of Undertaking
rebound
Additional Action
result in

additional

restarting the

The

network and/or

could be

augmented if

replaced with
D Ability to Monitor
the pump
D Regulatory Agency
set by
Coordination/Approval
branch
Alternative 1
Not applicable
Not applicable
Not applicable.
TABLE 5 (cont'd)

Alternative 2

This alternative requires the

installation of only three

monitoring wells. No

difficulties are anticipated

USGS confirms ongoing

natural attenuation in the

EMU. Continued attenuation
Alternative 3
Alternative 4
Performance of natural

attenuation is easily

monitored.

Coordination with

appropriate personnel at

DAFB is necessary

Groundwater wells will
No difficulties are anticipated No difficulties are anticipated No difficulties
in installation of the

DDC/SVE wells or

equipment. Operation of the
DDC system is straight
forward.

DDC and SVE are reliable

technologies for removal and

destruction of VOCs 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 i f

necessary.

Performance of the DDC

system is easily monitored.

Coordination with

appropriate personnel at

DAFB is necessary.

Groundwater wells will
in construction of the

extraction and treatment

system.

Air stripping technology is

highly reliable for removal of

volatile organic constituents.
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 i f

necessary, or replaced with

new technologies.

Performance of the pump and

treat system is easily

monitored.

Effluent limits set by

DNREC's NPDES branch

have to be met prior to

discharge to surface water
anticipated in

the extraction

system

Air stripping

highly reliable

volatile organic
If contaminant

occurs that may

RAO failure,

remediation can

performed by

treatment system

extraction

treatment system

expanded or
new technologies

Performance of

and treat system

monitored.

Effluent limits

DNREC's NPDES

have to be met

discharge to
-------
surface water

wells wi11

permits
require State permits.
Groundwater wells will

require State permits.

Coordination with

appropriate personnel at

DAFB is necessary
Groundwater

require State
DAFB is
-------
Criteria Alternative 1

D Availability of Services Not applicable.
D Availability of Equipment Not applicable.

D Availability of Technology Not applicable.

Cost (IRP Site LF13)
TABLE 5 (cont'd)

Alternative 2
Alternative 3
The density-driven
convection component will
require a specialty contractor,
however, the remaining
portions of this alternative
are readily available.
Readily available. Readily available.
Alternative 4

Readily available.
Alternative

Readily available
-------
Retain for
Environmental Laws and Regulations
I .
Consideration as an ARAR
B. Delaware Hazardous Waste Management Regulations(DNREC Regulations
Governing Hazardous Waste (DRGHW)
1.
Closure and Postclosure (DRGHW Part 264, Subpart G)

Groundwater Monitoring and Protection (DRGHW Part 264, Subpart F)
Waste will not be contained in place

Groundwater monitoring shall be conducted in accordance with
4. Standards applicable to surface impoundments, waste piles, land
treatment facilities (other than closure and post-do sure requirements
(DRGHW Part 264, Subpart K, L, and M)

5. Location Standards (DRGHW Part 264.18)

6. Transportation Standards (DRGHW Part 263)

7. Incinerator Standards (DRGHW Part 264, Subpart O)

8. Landfill Standards (DRGHW Part 264, Subpart N)

9. Underground Storage Tank Regulations (Delaware Regulations

10. Land Diposal Restrictions (DRGHW Part 268)
The site is not located in a 100-year floowplain, as defined by RCRA
On-site incineration is not considered a remedial alternative

A hazardous waste landfill will not be constructed on-base

UST rules are not applicable to remedial alternatives for this site
-------
Environmental Laws and Regulations
B. Delaware Industrial Waste Effluent Limitations (DWPCR Section 8)
III. Clean Water Act, 33 USC 1251-1387, exp. 1311-17

A. Effluent guidlines (40 CFR 403)
IV. Safe Drinking Water Act (SDWA), 42 USC 300f

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

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

V. Marine Protection, Research, and Sanctuaries Act.

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

VI. Toxic Substances Control Act (TSCA)

A. Polychlorinated biphenyls (PCB) requirements (40 CFR Part 761)
Retain for
ARAR
Analysis?
Effluents generated by site remedial activities may require pretreatment Yes
Any effluent discharge to POTWs must meet pretreatment standards
Effluents discharged to a POTW would be subject to general Yes
pretreatment guidelines

Erosion of soils during remediation activities may affect the surrounding Yes
surface water.
No
-------
Environmental Laws and Regulations

VII. U. S. Army Corps of Engineers Program

A. Dredge and fill (33 CFR Part 323)

B. Construction in waterways (40 CFR Part 323)

VIII. Clean Air Act (CAA) (42 USC Sections 7401-7671q)

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

IX.
X. U.S. Department of Transportation Regulations 49 CFR Part 170-179)
XIII. Wild and Scenic Rivers Act (16 USC 1274; 50 CFR 27)

XIV. Preservation of Scientific, Historic, or Archaeological Data (National Historic
Preservation Act, 16 U.S.C. 470, 40 CFR 6.301(b), 46 CFR 800; Archaeological and
Historic Preservation Act of 1974, 16 U.S.C. 469, 40 CFR 6.301(c); Historic Sites,
Buildings, and Antiquities Act, 15 U.S.C. 461-467; 40 CFR 6.301(a), 36 CFR Part
65)
Retain for
ARAR
Remedial alternatives under consideration will not involved dredging or No
filling in of a navigable waterway.

No construction in navigable waters will be required for the remedial No
actions under consideration.
Waste may be transported off-site for treatment of disposal under the
considered remedial alternatives.

The site is not located within a 100-year floodplain
No wild and scenic rivers are found in the vicinity of the site.
No
Alternatives resulting in the disturbance of soil will require measures to
control erosion.
-------
All four action alternatives are considered reliable. The efficacy of Alternative 2 was
proven in a 2-year natural attenuation study performed by the USGS at the EMU sites. The
technologies associated with Alternative 3, 4, and 5 ahve been applied successfully at other
installations.

2.7.4 Reduction of Toxicity, Mobility, and Volume

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

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 are and oxygenate the groundwater. Oxygenating the groundwater will
stimulateaerobic biodegradation processes, which will augment other attenuation processes 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.

Alternative 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 conductive to the
biodegradation of polychlorinated alkenes than an anerobic environment, thus the DDC system
operation will have to continue until the polychlorinated compounds are removed to low levels.
DDC system operation is estimated to continue for 2 years. Alternative 4 includes the permanent
installation of reactive barrier walls, which will greatly enhance the rate of abiotic reductive
dehalogenation reaction. These abiotic reaction 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
implentability 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 Barier Wall/Pump and
Treat) are relatively the most complex systems to design, construct, and operate. Both of these
alternatives reguire treatability studies before their design and include the most extensive
construction. Alternative 3 includes installing and balancing a total of 31 DDC wells and 50 SVE
wells across three sites (includes FT03 and WP14/LF15). Alternative 4/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 implentation 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 8. 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 Driven Convection) and 4/5 (Pump and Treat) offer higher
present worth costs of $440,000 and $240,000, respectively.

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 LF13.
-------
TABLE 8
Action Alternative Cost Summary
for LF13
Alternative

2. Natural Attentuation

3. Density Driven Convection

4. Ex Situ Treatment

5. Groundwater Extraction with Air $170,000
Stripping
Capital Cost
$4,
$380
$170
$170
200
,000
,000
,000
Annual
$8,
$27,
$28,
$28,
O&M*
400
000
000
000
Net Worth
$40,000
$440,000
$240,000
$240,000
First year O&M costs.
-------
2.7.9 Community Acceptance

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

2.8 SELECTED REMEDY

The selected remedy for cleanup of soil and groundwater at LF13 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 alternatives. The
only component of Alternative 2 still reguiring implementation is the long-term
groundwater monitoring. Simple monitoring well construction and operation considerations
are reguired in addition to the groundwater monitoring reguirements. The monitoring
program will verify the status of the groundwater contamination and therefore protect
future receptors before exposure. The monitoring program is currently being developed in
consultation with the USEPA and DNREC. As Alternative 2 is implemented, the monitoring
program will provide the data necessary to verify that natural attenuation of groundwater
contaminants is working.

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

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

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

2.8.1 PERFORMANCE STANDARD FOR THE SELECTED REMEDY

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

2.9 STATUTORY DETERMINATION

Based on consideration of the requirements 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
requirements that are legally applicable or relevant and appropriate to the remedial action, is
cost-effective, and uses permanent solutions and alternative treatment to the maximum extent
practicable.

The reliability of natural attenuation mechanisms, such as bio-degradation, adsorption/
desorption, and dilution for the cleanup of petroleum- and chlorinated-based media has been
demonstrated at various sites around the country to be cost effective and, if properly
monitored, an environmentally sound solution to 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 Site LF13. 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.
-------
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
quality.

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, ethylbonzene, and xylone (BTZX) - Chemical compounds that
are common constituents of fuels and petroleum products.

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

bioremodiation - 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 what naturally attack certain
compounds. This process speeds up the rate at which some chemicals
biodegrade.

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

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

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

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

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

Delaware Regulations Governing the Control of Air Pollution (DRGCJLP) -
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.
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Electromagnetic (EM) - A geophysical survey instrument used to locate changes
in specific conductance in subsurface materials.

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

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

Groundwater - Subsurface water residing in a zone of saturation.

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 or this report).

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

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

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

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

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

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

Remedial investigation (RI) - An investigation that involves sampling the air,
soil, and water to determine the nature and extent of contamination at an
abandoned waste sit 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.
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.

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

Dover Air Force Base (DAFB) offered opportunities for public input and community
participation during the Remedial Investigation (Rl)/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 11 7(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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