EPA/ROD/R03-95/209
1995
EPA Superfund
Record of Decision:
DOVER AIR FORCE BASE
EPA ID: DE8570024010
OU05
DOVER, DE
08/03/1995
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Text:
RECORD OF DECISION
DECLARATION OF THE SELECTED INTERIM REMEDY
Site Name and Location
Target Area 3 of Area 6, West Management Unit, Dover Air Force
County, Delaware.
Statement of Basis Purpose
This Record of Decision (ROD) presents the selected interim rem
for Target Area 3, which was chosen in accordance with the requiremen
Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA), as amended by the Superfund Amendments and Reauthorizadon A
1986 (SARA) and, to the extent practicable, the National Oil and Haza
Substances Pollution Contingency Plan (NCP), 40 CFR Part 300. This d
prepared by the U.S. Air Force, the lead agency, as the owner/operato
is based on the Administrative Record for the Site. Support was prov
Environmental Protection Agency (EPA) Region III and the Delaware Dep
of Natural Resources and Environmental Control (DNREC).
The State of Delaware and the U.S. Environmental Protection Age
with the selected interim remedy. The information supporting this in
action decision is contained in the information repository for the Ad
Record located at the Dover Public Library, Dover, Delaware.
Assessment of the Site
Four regions were identified in Area 6 where shallow groundwate
combined concentrations of the chlorinated solvents trithloroethene,
and 1,2-dichloroethene in access of 1,000 aeg/L. These regions were i
the vicinity of the source areas for the chlorinated solvent plumes p
and were incorporated into areas for remediation termed Target Areas.
addresses the interim remedy for Target Area 3. The maximum concentr
chlorinated volatile organic compounds in Target Area 3 groundwater w
aeg/L. While a Risk Assessment was not performed specifically for Tar
risk associated with exposure to Area 6 groundwater under a hypotheti
commercial/industrial use scenario was 9 x 10-4.
A soil gas survey was conducted in the vicinity of Building 719
the vadose zone source of chlorinated solvent contamination. Several
solvent constituents were detected in soil gas samples. The maximum
concentrations of the particularly notable chlorinated solvents ident
trichloroethane (13,900 aeg/L), 1, 1-dichloroethane (385 aeg/L), and cis
Target Area 3
(>3,770 aeg/L). These soil gas detections are a clear indication of v
contamination near Building 719.
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Actual or threatened releases of hazardous substances from this
addressed by implementing the interim response action selected in thi
present a current or potential threat to public health, welfare, or t
Description of the Selected Interim Remedy
The selected interim remedy consists of in situ bioremediation
and soil utilizing co-metabolic bioventing and intrinsic bioremediati
bioventing and intrinsic bioremediation are two of the bioremediation
being applied to the Target Areas to promote the development of alter
innovative treatment technologies as encouraged under CERCLA. Perfor
the interim remedy and compliance with applicable or relevant and app
requirements will be evaluated in the Final Basewide ROD.
Statutory Determinations
The selected interim remedial action satisfies the remedial sel
requirements of CERCLA and the NCP. The selected interim remedy prov
best balance of trade-offs among the nine criteria required to be eva
CERCLA. The selected interim action provides protection of human hea
environment, complies with federal and state requirements that are le
or relevant and appropriate to the action, and is cost effective. Th
utilizes permanent solutions and alternative treatment technology to
extent practicable, and satisfies the statutory preference for remedi
treatment that reduces toxicity, mobility, or volume as a principal e
Force understands that although this interim remedy may not achieve M
certain contaminants, this interim action is only part of a total rem
Base that will be protective of the public health and welfare and of
when completed (CERCLA 121d, 42 U.S.C. 9621.d).
CHARLES T. ROBERTSON, JR. Date THOMAS C. VOLTAGGIO
Lieutenant General, USAF Hazardous Waste Management
Air Mobility Command Division Director
Chairperson, Environmental Environmental Protection Agen
Protection Committee Region III
Target Area 3
RECORD OF DECISION
FOR THE INTERIM REMEDY OF
TARGET AREA 3 OF AREA C
WEST MANAGEMENT UNIT
DOVER AIR FORCE BASE, DOVER, DELAWARE
August 3, 1995
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DECISION SUMMARY FOR THE RECORD OF DECISION
TARGET AREA 3 OF AREA 6
WEST MANAGEMENT UNIT
DOVER AIR FORCE BASE
INTRODUCTION
Dover Air Force Base (DAFB) recently completed a Focused Feasibi
(FFS) conducted to address chlorinated solvent and pesticide source a
contamination in Area 6 of Dover Air Force Base (DAFB), Delaware as a
response. The FFS was undertaken as part of the U.S. Air Force's Ins
Restoration Program (IRP). The basis for the FFS was the Area 6 Reme
Investigation (RI) report dated July 1994, which characterized contam
evaluated potential risks to public health and the environment. The
performed as the first phase of Feasibility Studies to be conducted o
Management Unit, the management unit to which Area 6 belongs. The sc
FFS was limited to the evaluation of alternatives for remediation of
chlorinated solvent and pesticide source areas originating in the nor
portion of the Area 6 region of investigation. The final remediation
if necessary, and non-source area contamination in Area 6 posing huma
environmental risks will be addressed in the final Base-wide Feasibil
This Record of Decision (ROD) addresses Target Area 3, which is
chlorinated solvent source areas evaluated in the FFS. This ROD summ
FFS, describes the remedial alternatives that were evaluated, identif
alternative selected by DAFB, and explains the reasons for this selec
Environmental Protection Agency (EPA) and the State of Delaware concu
interim remedy selected in this ROD.
As an aid to the reader, a glossary of the technical terms used
provided at the end of the summary.
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Target Area 3
PUBLIC PARTICIPATION
The Proposed Plan for this site was issued on June 16, 1995. Th
comment period on the Plan was open through July 31, 1995. Documents
the Administrative Record for the site were available at the Dover Pu
The only comments received during the public comment period were from
Remediation Technologies Development Forum expressing support for the
interim remedy.
SITE BACKGROUND
DAFB is located in Kent County, Delaware, 3.5 miles southeast of
Dover (Figure 1) and is bounded to the southwest by the St. Jones Riv
comprises approximately 4,000 acres of land, including annexes, easem
propery (Figure 2). The surrounding area is primarily cropland and w
DAFB began operation in December 1941. Since then, various mill
have operated out of DAFB. The present host organization is the 436t
Its mission is to provide global airlift capability, including transp
equipment, and relief supplies.
DAFB is the U.S. East Coast home terminal for the C-5 Galaxy air
Base also serves as the joint services port mortuary, designed to ace
the event of war. The C-5 Galaxy, a cargo transport plane, is the la
the USAF, and DAFB is one of a few military bases at which hangars an
designed to accommodate these planes.
The portion of DAFB addressed in this ROD is located within Area
West Management Unit. The West Management Unit is one of four Manage
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Units into which the Base has been divided (Figure 3). Area 6 is the
associated areas identified in the West Management Unit. The Area 6
investigation extends approximately 8,400 feet from its northern most
hardstand and Building 723 to its southern most point near the St. Jo
(Figure 4). The area north of U.S. Highway 113 contains the industri
Target Area 3
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portion. The water table is generally encountered at a depth of 10 t
ground surface (bgs) in the northern portion of Area 6 and shallows t
feet of the surface in the Base housing area near the St. Jones River
groundwater elevation or potentiometric surface of both the shallow a
of the Columbia Aquifer range from approximately 13.5 feet MSL in the
portion to less than 3 feet MSL near the St. Jones River. The thickn
Columbia Formation in Area 6 ranges from 28 to 64 feet.
Unconformably underlying the Columbia Formation is the upper uni
Calvert Formation, which generally consists of gray to dark gray firm
clay, with thin laminations of silt and fine sand. This upper silt a
in thickness from 15 to 21 feet in the northern portion of Area 6. T
conductivity of this unit range from 6.83 x 10-3 to 1.53 x 19-3 ft/da
x 10-7 cm/sec), which are three to five orders of magnitude lower tha
Columbia Formation. These significantly lower hydraulic conductiviti
to the vertical migration of constituents identified in the Columbia
Underlying this confining unit is the upper sand unit of the Calvert
Target Area 3
Frederica Aquifer. This aquifer averages 22 feet in thickness in the
No constituents of concern were identified in the three Frederica mon
installed in Area 6. Additionally, no production wells are installed
Aquifer in the vicinity of DAFB.
Area 6 is defined by the association of chlorinated solvents in
forming a plume in the Columbia Aquifer. Several separate potential
identified in the Area 6 RI that may have contributed to the chlorina
contamination. These potential sources include some of the twelve IR
the Area 6 groundwater flow regime shown in Figure 4. Additionally,
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and hangars where solvents are used may also be sources. The shop ac
solvent use is common include painting or paint stripping, aircraft a
maintenance, and plating or welding. The northern most point of chlo
contamination is the aircraft maintenance area located north of Atlan
chlorinated solvent plumes extend approximately 4,600 feet south into
The Area 6 RI identified four regions where shallow groundwater
ten feet of the Columbia Aquifer) contained combined concentrations o
chlorinated solvents trichloroethene (TCE), perchloroethene (PCE), an
dichloroethene (DCE) in excess of 1,000 aeg/L. These regions were inf
the vicinity of the source areas for the chlorinated solvent plumes t
Area 6. The groundwater data suggested that primary source areas res
vicinity of the following reference points, which were incorporated i
remediation termed Target Areas:
Paint Washout Area (Site SS59) located along the eastern po
open storage yard. (Target Area 1)
Civil Engineering (CE) Shops Area including Building 607 (C
Shop), Buildings 608 and 609 (Material Control/Supply Offic
615 (Interior and Exterior Electrical Shop, Power Productio
and Sheet Metal Shop), and Building 650 (Sign Shop). (Targ
Building 719 housing the Jet Engine Repair Shop. (Target A
Target Area 3
Buildings 715 and 716 housing the ISO-Dock and an engine st
respectively. (Target Area 4)
The four Target Areas that have been identified are shown in Fig
Target Area incorporates one of the primary suspected source areas an
significantly impacted portions of the shallow and deep groundwater p
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with the respective source area. Plume maps of total chlorinated VOC
and deep groundwater are shown in Figures 6 and 7, respectively. The
are the regions of chlorinated solvent groundwater contamination that
in the FFS.
TARGET AREA/SOURCE AREA CHARACTERISTICS
The following section describes the physical and chemical charac
Target Area 3, which is addressed in this Proposed Plan.
Target Area 3 is located north of Target Area 1, originating nea
and extending south about 800 feet where it joins Target Area 1. Bui
Jet Engine Repair Shop - once contained large dip tanks of TCE. The
of TCE from the dip tanks is a suspected source of the contamination.
suspected source is two former underground storage tanks (USTs) that
in 1992 from the northeast side of Building 719. The USTs were conne
building's drain system and collected waste oils and spent solvents u
Target Area 3 is elliptically shaped and is approximately 3.7 acres i
scale maps of the chlorinated solvent plumes residing in the shallow
of the aquifer within Target Area 3 are shown in Figures 8 and 9, res
maximum concentration of total chlorinated VOCs in Target Area 3 grou
found in the shallow Columbia at a concentration of 21,310 sg/L in th
source location near Building 719. Migration of the plume appears to
occurred through the deeper portion of the aquifer.
A soil gas survey was conducted in March 1995 in the vicinity of
to better define the vadose zone source of chlorinated solvent contam
Target Area 3
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chlorinated solvent constituents were detected in soil gas samples.
detected concentrations of the particularly notable chlorinated solve
include 1,1,1-trichloroethane (13,900 aeg/L), 1, 1-dichloroethane (385
cis-1,2-dichloroethene (>3,770 aeg/L). These soil gas detections are
of vadose zone contamination near Building 719.
SUMMARY OF SITE RISKS
The full Risk Assessment (RA) for Area 6 can be found in the fin
report dated July 1994. The purpose of the RA is to determine whethe
site-related contaminants could adversely affect human health and the
The focus of the baseline RA is on the possible human health and envi
effects that could occur under current or potential future use condit
that the contamination is not remediated. The risk is expressed as 1
cancer risk (LECR) for carcinogens, and hazard quotient (HQ) for none
For example, an LECR of 1 x 10-6 represents one additional case of ca
million exposed population, wheresas a hazard quotient above one pres
of noncarcinogenic health effects in exposed populations.
The baseline RA focused on potential pathways by which maintenan
construction workers could be exposed to contaminated materials in Ar
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workers' exposure to groundwater and soil have been evaluated under a
maintenance scenario; a future construction scenario; and a hypotheti
groundwater use from the Columbia Aquifer under a commercial/industri
Although a specific Target Area 3 RA has not been performed, the risk
the Area 6 Remedial Investigation from the hypothetical future exposu
groundwater within Area 6 had an LECR of 9 x 10-4, which exceeds the
x 10-6 risk range used to evaluate the need for remediation. In addi
Area 6 risk the Target Area 3 constituents of concern have been compa
risk-based screening concentrations (RBSCs) approved by EPA for the c
industrial scenario at DAFB to identify the chlorinated solvents that
based concern.
Target Area 3
The possibility exists for exposure of workers to hazardous subs
during excavation activities. Source areas identified during excavat
worker protection as per health and safety protocols. All workers pe
excavation work at DAFB will be health and safety trained for work at
Based on the direction of groundwater flow, the Area 6 plume ext
southerly direction towards the St. Jones River. There are no surfac
points within Area 6 between the Target Area and the river. Presentl
plume is confined within the Base property, and has not reached the S
The future use of groundwater from the Columbia Aquifer by Base
is quite unlikely and hypothetical. This hypothetical future groundw
that groundwater from the Columbia Aquifer will be used for drinking
purposes by Base personnel under a commercial/industrial scenario. T
compared with the maximum detected concentrations of chlorinated solv
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Area 3 (Table 1). Concentrations of three of the five detected chlor
1,2-dichloroethene, perchloroethene, and trichloroethene-in Target Ar
their corresponding RBSCs in groundwater. The concentrations of the
detected compounds, 1,1-dichloroethane and 1,1,1-trithloroethane, wer
corresponding RBSCs.
Actual or threatened releases of hazardous substances from this
addressed by the selected alternative or one of the other active meas
may present a current or potential threat to public health, welfare,
REMEDIAL ACTION OBJECTIVE
Within the soils of Target Area 3, the interim Remedial Action O
(RAO) is to reduce the concentration of each ethyl-based chlorinated
compound (VOC) by 90 percent. The ethyl-based chlorinated VOCs inclu
TCE, 1,1-DCE, 1,2-DCE, vinyl chloride, 1,1,1-trichloroethane, 1,1-dic
1,2-dichloroethane. These VOCs are considered to be the most toxic a
the 90 percent reduction interim RAO is applied to each of these comp
Target Area 3
TABLE 2
Maximum Concentration Detected of Ethyl-Based Chlorinated Volatiles
in Target Area 3, and Corresponding Compound and Target Area
Specific Interim Remedial Action Objectives
Compound
Target Area 3
Maximum Interim
Detected RAO
1,1-Dichloroethane
1,2-Dichloroethane
1,1-Dichloroethene
1,2-Dichloroethene
Perchloroethene
1,1,1-Trichloroethane
3 -(d)
ND 5(e)
ND 7(a)
2,300 230
1,000 100
9 200(b)
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Trichloroethene 19,000 1,900
Vinyl chloride ND 2(c)
Concentrations reported in units of aeg/L.
ND - Not Detected
RAO - Remedial Action Objective
(a) - Maximum Contaminant Level for 1,1-Dichloroethene
(b) - Maximum Contaminant Level for 1,1,1-Trichloroethane
(c) - Maximum Contaminant Level for Vinyl chloride
(d) - Maximum Contaminant Level has not been established for 1,1-Dichloroet
(e) - Maximum Contaminant Level for 1,2-Dichloroethane.
Target Area 3
individually rather than to the aggregate concentration of all the ch
For reasons of consistency, the 90-percent reduction model was based
Post-Closure Permit (Reference No. DE8570024010, Pemit No. HW05A05) f
WP21 of DAFB, which is a unit that adjoins Target Area 3 to the west.
The maximum concentrations of the detected chlorinated solvent c
in Target Area 3 are summarized in Table 2, along with the compound a
Area specific interim RAO. Table 2 also includes interim RAO concent
some select compounds that have not yet been detected in the Target A
select compounds are chemical degradation products of some of the cur
chlorinated solvent constituents. Thus, reducing the concentration o
compounds at the expense of producing other chlorinated VOC degradati
will not itself be sufficient to satisfy the interim RAO. Note that
reduction from the maximum concentration detected of a compound is be
compound's MCL, the MCL is used as the interim RAO.
The issues of final cleanup levels and attainment of ARARs will b
in the Final Basewide Record of Decision. The remedial action select
is only part of the remedial action which will be selected in a Final
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SUMMARY OF ALTERNATIVES
Engineering technologies applicable to remediating the contamina
were screened according to their effectiveness and implementability.
technologies that were determined to be the most applicable were then
remedial alternatives. The following remedial alternatives are numbe
correspond to the alternatives described in the FFS report.
Alternative 1-No Action.
Alternative 2-Collection, Ex Situ Treatment, and Surface W
of Groundwater, and Performance of Soil Vapor Extraction i
Solvent Source Areas if Necessary.
Alternative 3-In Situ Groundwater Treatment Using Air Spar
Density-Driven Convection Technologies Combined With Soil
Target Area 3
TABLE 1
Maximum Concentration Detected of Ethyl-Based Chlorinated Volatiles
in Target Area 3, and Corresponding Risk-Based Screening Concentrations
Target Area 3
Maximum
Compound Detected RBSC
1,1-Dichloroethane 3 1,300
1,2-Dichloroethene 2,300 84
Perchloroethene 1,000
1,1,1-Trichloroethane 9 2,200
Trichloroehtene 19,000
Concentrations reported in units of sg/L.
RBSC - Risk-Based Screening Concentration for Commerical/Industrial scenari
Base. The RBSCs are based on a lifetime cancer risk of 1 x 10-6 or
whichever is lower.
Target Area 3
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Alternative 4-In Situ Bioremediation of Groundwater and So
Intrinsic Bioremediation and Co-Metabolic Bioventing Techn
The four remedial alternatives that were evaluated in detail are
below. In addition, the capital, annual operation and maintenance (O
present worth costs of each alternative are provided.
Alternative 1
Target Area 3
Capital Cost $000
Annual O&M Cost $000
Present Worth $000
The no action alternative is evaluated in order to establish a b
comparison against other alternatives. Under this alternative, no ef
undertaken to reduce the groundwater concentrations of chlorinated solve
Target Area.
Alternative 2
Target Area 3
Capital Cost $330,000
Annual O&M Cost $64,000(a)
Present Worth $660,000(b)
(a)Frst year O&M cost. Refer to text.
(a)Based on 10 years of operation.
Alternative 2 consists of groundwater extraction, groundwater pr
metals, groundwater treatment using air stripping for removal of chlo
and carbon adsorption for removal of residual contaminants, and surfa
discharge of treated groundwater; performance of soil vapor extractio
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Target Area 3
shallow chlorinated solvent source areas if determined to be necessary d
design; and treatment of the offgases from the air stripper and, if i
SVE system.
A total of two extraction wells are estimated to be installed in
for cost estimating purposes only, to extract contaminated groundwate
pumping rate of approximately 20 gallons per minute. If this alterna
selected for this interim response, then the exact number of wells an
will be determined during the remedial design. Extracted groundwater
pretreated for metals to reduce the concentrations of iron and mangan
pretreatment reduces the possibility of iron and manganese fouling su
treatment systems as well as ensuring compliance with surface water d
standards for metals.
Pretreated groundwater will then be pumped to the top of a low p
tray air stripper that will transfer over 95 percent of the VOCs diss
groundwater to the air stream. The air stream containing the VOCs wi
air stripper unit where it will be treated using carbon adsorption pr
the atmosphere. Routine air sampling at a frequency determined durin
design will be performed to ensure compliance with air emission stand
Treated groundwater the air stripper will be pumped to a liquid
carbon adsorption unit to reduce the concentration of residual contam
that comply with the surface water discharge standards prior to relea
course tributary of the St. Jones River. Semi-annual water samples,
estimating purposes only, will be collected to ensure compliance with
standards. Annual sampling frequency will be determined during the r
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Vadose zone chlorinated solvent contamination is present in the Tar
the location where significant shallow groundwatcr contamination has
To address this source, performance of SVE in a limited sized area ha
with this alternative. A total of two SVE wells are estimated to be
remediate the source areas presumed to be present. Soil sources woul
Target Area 3
to be remediated in less than 2 years with SVE treatment; 2 years of
assumed for costing purposes. If SVE is implemented, vapor collected
system would be treated for organic constituents by vapor phase carbo
being released to the atmosphere. The necessity of performing SVE wi
determined during the remedial design.
Groundwater monitoring will be performed to monitor the progress
groundwater remediation. In addition, existing land use restrictions
the military operation of DAFB will be enforced through out the cours
to prevent unauthorized extraction and use of the contaminated ground
Columbia Aquifer.
The time required to achieve the interim RAO is estimated to be
of 5 to 10 years, provided no free phase solvents are present in the
phase solvents are present, the time required to achieve the interim
extended to 30 years or more. The present worth cost of this alterna
is calculated based on an assumed 10 year operation.
Alternative 3
Target Area 3
Capital Cost $330,000
Annual O&M Cost $40,000(a)
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Present Worth $540,0000(b)
(a)First year O&M cost. Refer to text.
(b)Based on 6 years of operation.
Alternative 3 consists of the in situ treatment of groundwater u
combination of air sparging (AS) and density driven convection (DDC)
combined with SVE over the entire areas where in situ groundwater tre
performed; and carbon adsorption treatment of the offgases from the S
Target Area 3
For in situ treatment at Target Area 3, 30 SVE wells, 14 AS well
wells are estimated to be required for cost estimating purposes only.
is ultimately selected for this interim response, then the exact numb
their placement will be determined during the remedial design. AS wi
areas where soil is highly permeable and free of clay. DDC will be u
where significant clay layers are present. The SVE system operates i
the AS/DDC system to capture volatile contaminants stripped from the
zone. Vapor phase carbon adsorption treatment units will be used to
extracted VOCs from the air stream prior to release to atmosphere. E
will be separated by knockout pots and sent to liquid phase carbon ad
to reduce contaminant concentration to levels acceptable for discharg
Groundwater monitoring will be performed to monitor the groundwa
remediation progress and plume migration. In addition, existing land
associated with the military operation of DAFB will be enforced throu
course of remediation to prevent unauthorized extraction and use of t
groundwater from the Columbia Aquifer.
The time required to achieve the interim RAO is estimated to be
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and 13 years, with 6 years being the estimate used for costing purpos
worth cost is estimated to be $1,000,000. The remediation time estim
on removal rate data from the AS/SVE pilot study performed at Site WP
Alternative 4
Target Area 3
Capital Cost $80,000
Annual O&M Cost $50,000(a)
Present Worth $170,000(b)
(a)First year O&M cost. Refer to text.
(b)Net cost to government.
Target Area 3
Alternative 4 consists of in situ bioremediation of groundwater
co-metabolic bioventing and intrinsic bioremediation in Target Area 3
bioventing and intrinsic bioremediation are two of the bioremediation
being applied to the Target Areas to promote the development of alter
innovative treatment technologies as encouraged under CERCLA.
The distribution of chlorinated solvent constituents in groundwa
downgradient of the Target Areas indicates that intrinsic bioremediat
active. The degradation rates and reaction mechanisms associated wit
bioremediation processes occurring in Target Area 3 will be studied o
period by the Remediation Technologies Development Forum (RTDF), whic
consortium of partners from industry, govermnent, and academia workin
more effective and less costly remedial treatment technologies. Intr
bioremediation is a passive remediation technology; that is it does n
installation of any extraction or physical/chemical treatment systems
remediation of the aquifer. Instead, this technology relies on the i
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microorganisms to biologically degrade organic contaminants. Althoug
technology is passive, it should not be confused with the no action a
Establishing the efficacy of intrinsic bioremediation requires that a
characterization be made, which includes sampling, testing, modeling,
microbial activity and biotransformation rates. The RTDF study will
whether intrinsic bioremediation holds promise as a long-term remedy
contaminants present. Monitoring of the Target Area 3 groundwater pi
conducted from an estimated six monitoring wells for cost estimating
the study and rate measurement of the intrinsic bioremediation proces
monitoring period will extend until the final FS and ROD is completed
estimated to be within a period of 5 years for costing purposes.
The vadose zone chlorinated solvent contamination present in Tar
near Building 719 will be remediated in situ using co-metabolic biove
combined mixture of air and an organic substrate such as propane will
the vadose zone to promote the biodegradation of the solvents present
Target Area 3
microorganisms. An SVE system will also be installed to allow materi
be conducted and to prevent vapors from entering the building.
The bioremediation process utilized is not expected to generate
products that can migrate beyond the Base boundary. Groundwater moni
be performed to monitor the groundwater remediation progress and down
water quality to ensure that offbase plume migration does not occur.
existing land use restrictions associated with the military operation
enforced throughout the course of remediation to prevent unauthorized
use of the contaminated groundwater from the Columbia Aquifer.
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The time required to achieve the interim RAO will vary with the
bioremediation technology. Intrinsic bioremediation rates for Target
evaluated during the RTDF study. The co-metabolic bioventing initiat
Area 3 is estimated to be completed within 2 years. The present wort
alternative is estimated to be $170,000.
EVALUATION OF ALTERNATIVES
The selected alternative for remediating the contamination in th
is Alternative 4 (bioremediation). Based on current information, thi
provides the best balance of trade-offs among the alternatives with r
criteria that are required to be evaluated under CERCLA. This sectio
performance of the selected alternative against the nine criteria and
compares to the other alternatives under consideration.
Overall Protection of Human Health and the Environment
The overall protectiveness criterion is a composite of other eva
especially short-term effectiveness, long-term effectiveness, and com
ARARs. Alternatives 1, 2, 3, and 4 are all considered to be protect!
health during their period of implementation because of the existence
restrictions that prohibit the unauthorized extraction or use of cont
groundwater in the Target Areas, thereby preventing human exposure.
Target Area 3
Alternative 1 (no action) is not considered effective because no
made to monitor the Target Area plume to evaluate compliance with the
RAO. Alternatives 2 (pump and treat), 3 (air sparging), and 4 (biore
all meet the interim RAOs and are considered effective.
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Compliance With ARARs
The interim RAOs that have been set for chlorinated solvent cons
groundwater will allow for the resultant concentration of several of
to exceed their federal Maximum Contaminant Levels (MCLs). MCLs, as
for in CERCLA 121(d)(2)(A)(ii), are relevant and appropriate requir
final actions expected to be taken as a result of the Base-wide inves
Offsite contaminant migration, even for interim actions, require
of other ARARs be considered. The principal ARARs that pertain to th
movement of contaminants are the Delaware regulations implementing th
Clean Air Act and Clean Water Act. These regulations are the Delawar
Governing the Control of Air Pollution (DRGCAP 1 through 3, 21 and 24
Delaware Water Pollution Control Regulations (DWPCR 1 through 6) , the
Industrial Waste Effluent Limitations (SWPCR 8), and the Delaware Sur
Quality Standards (DSWQS 1 through 9, 11 and 12). The above referenc
regulations regarding emissions of volatile organic compounds to the
be complied with in Alternatives 2, 3, and 4 to ensure that acceptabl
emissions are met. Alternative 2 will require discharge to surface w
referenced regulations regarding surface water discharge define limit
chemical concentrations for wastewater, and attainment of these limit
requirement for this alternative. Alternatives 2, 3, and 4 meet all
regulations that pertain to the offsite movement of contaminants.
Long-Term Effectiveness and Permanence
The long-term effectiveness and permanence criterion primarily c
magnitude of residual risk that would remain after the implementation
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Target Area 3
alternative, and the adequacy and reliability of the controls institu
alternatives provide for the long-term protection of human health thr
and use restrictions. However, reliance upon land use restrictions i
a permanent remedy.
Under Alternative 1 (no action), the chlorinated solvent contami
groundwater will not be monitored. Therefore, the adquacy and reliab
alternative cannot be established.
Alternatives 2 (pump and treat), 3 (air sparging), and 4 (biorem
all result in significant reductions of chlorinated solvent concentra
Area. If any one of these treatment alternatives is selected, that s
operated until the interim RAO is achieved. Hence, no more than 10 p
maximum observed concentration of each ethyl-based chlorinated solven
in the Target Area. The magnitude of residual contamination remainin
Area is a function of the time the treatment alternative is operated
continue. Continued operation of the treatment system beyond the poi
interim RAO is reached may allow further reductions in contaminant le
achieved. Performance of the interim remedy and compliance with ARAR
evaluated in the final Base-wide FS and ROD.
Reduction of Toxicity, Mobility, and Volume
No reduction of toxicity, mobility, or volume will be achieved b
implementation of Alternative 1. The three action alternatives inclu
which are capable of significantly reducing the toxicity of groundwat
Area.
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The groundwater extraction system proposed under Alternative 2 w
hydraulic control over the plume, thereby limiting the mobility of co
from the Target Area. The air sparging in situ treatment technology
Alternative 3 operates by increasing the mobility of contaminants. T
mobility may result in some spreading of contamination beyond the eff
these alternatives during the course of contaminant removal; however,
Target Area 3
volume of the contaminants will be reduced. The groundwater bioremediat
technology proposed under Alternative 4 will have no impact on contam
The toxicity profile of the groundwater may shift somewhat during the
process, as vinyl chloride is generated during the degradation of the
ethyl-based compounds. However, because little vinyl chloride has be
the groundwater thus far, the evidence suggests that vinyl chloride i
to carbon dioxide, water, and chloride ion under the aerobic conditio
downgradient of the Target Areas.
Short-Term Effectiveness
Alternative 1 (no action) includes no remedial actions. Therefo
be no short-term impacts on community or worker health or the environ
construction activities. However, because Alternative 1 will not mon
with the interim RAOs established for this project, it is considered
Alternatives 2 (pump and treat) , 3 (air sparging) and 4 (bioreme
all be effective in reducing groundwater contaminant concentrations i
Area. None of these alternatives are expected to have significant im
or public health or the environment. Alternative 2 is estimated to b
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meeting the interim RAO within a 5 to 10 year time frame. However, a
believed present, isolated pockets of DNAPLs in the aquifer could cau
frame to increase to 30 years or more.
The presence of DNAPLs will also affect the length of time requi
the interim RAO under Alternative 3, though to a lesser extent than w
presence on Alternative 2. There are two reasons for this. First, t
more air sparging/density-driven convection wells under Alternative 3
would be extraction wells under Alternative 2. Thus, the chance of 1
remediation well near a pocket of free product is much greater under
Secondly, the in situ remediation is a more aggressive remediation pr
and treat. High mass transfer rates from water to air would be achie
physical in situ treatment technologies lowering the concentration of
Target Area 3
the plume. Lowered groundwater concentrations would increase the dri
solubilization of free product in order to maintain equilibrinm. The
meet the interim RAO under Alternative 3 is estimated to be between 4
Alternative 4 is estimated to be capable of achieving the interi
Target Area 3, though 50 years or more may be required relying upon i
bioremediation. As with the other action alternatives, these time fr
extended if DNAPLs are present. A DNAPL would present a continuing s
contaminants to the aquifer as the DNAPL constituents were solubilize
groundwater. This transfer of constituents from free phase to dissol
occur through the physical processes of desorption and liquid-liquid
These equilibrium-driven processes typically occur slowly because of
surface area of DNAPL in contact with the groundwater in comparison t
volume. The solubilization rate of DNAPLs would likely be slower tha
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degradation of the dissolved constituents. Thus, the solubilization
likely be the rate-limiting step. The co-metabolic bioventing treatm
3 will be accomplished within approximately 2 years.
Implementability
Three main factors are considered under this criterion: technic
administrative feasibility, and availability of services and material
alternatives are administratively feasible and the required services
readily available. Hence, the comparison will focus on the technical
alternatives.
Alternative 1 (no action) has no technical feasibility considera
Alternatives 2 (pump and treat), 3 (air sparging), and 4 (bioremediat
technical feasibility concerns associated with them. These concerns
highly developed character of the Target Area and the numerous space
that are present. However, of the three action alternatives, Alterna
least difficult to implement. Alternative 4 requires the installatio
four air injection/SVE wells plus equipment to support the bioventing
Target Area 3
Alternative 4 system is easier to install than the Alternative 2 syst
six groundwater extraction and air injection/SVE wells and a more ext
network. Both Alternatives 2 and 4 are considered much less complica
than Alternative 3, which consists of 51 air sparge, DDC, and SVE wel
expansive piping and numerous treatment stations. Overall Alternativ
to be the most easily implemented action alternative.
COST
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No direct costs are associated with the implementation of Altern
action). The capital cost of Alternative 4 (bioremediation) is $80,0
cost of Alternatives 2 (pump and treat) and 3 (air sparging) are both
$330,000.
The O&M cost of Alternative 2 will initially be $64,000 per year
to $40,000 per year after 2 years of operation when SVE operations ar
The O&M cost of Alternative 3 will be almost $40,000 the first year,
several thousand dollars per year thereafter as the carbon consumptio
with the SVE system's offgas treatment units decreases. The O&M cost
Alternative 4 will be approximately $50,000 per year for the first 2
decrease to $30,000 per year after completion of the co-metabolic bio
treatment. Additionally, the first several years of monitoring will
performed by the RTDF as part of their intrinsic bioremediation pilot
to the government.
The present worth cost of the alternatives will depend upon the
operated. The present worth costs of Alternative 2 under operating s
and 30 years are $540,000, $660,000, and $880,000 respectively. The
costs of Alternative 3 under operating scenarios of 4, 6, and 13 year
$490,000, $540,000, and $660,000. The present worth cost of Alternat
government assuming 2 years of operation of the co-metabolic bioventi
3 years of monitoring in Target Area 3 following 2 years of monitorin
is $170,000. Thus, Alternative 4 has the lowest present worth cost.
Target Area 3
State Acceptance
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The State of Delaware concurs with the selected interim remedy f
Area 3.
Community Acceptance
The only comments received during the public comment period were
RTDF expressing support for the proposed remedy. No community opposi
proposed remedy was noted.
CONCLUSION
Based on the evaluation of the alternatives using the nine crite
4 (bioremediation) is preferred. Alternative 4 is protective of huma
environment, complies with all ARARs, represents a permanent remedy t
groundwater toxicity, provides the greatest ease of implementation, a
cost effective action alternative.
The selected alternative utilizes permanent solutions and altern
technologies to the maximum extent practicable. This interim action
negatively impact the ability to implement a final action if it is re
remedy will be selected in the final Base-wide ROD.
Actual or threatened releases of hazardous substances from this
addressed by the selected alternative, may present a current or poten
public health, welfare, or the environment.
Target Area 3
GLOSSARY AND ACRONYMS
Air Sparging - Underground injection of air into saturated soil and g
resulting in the in situ air stripping of volatile constituents.
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Air Stripping - Transfer of volatile constituents from water to air b
between air and water streams.
Aquifer - A geologic formation capable of yielding water to wells and
ARARs - Applicable or Relevant and Appropriate Requirements. Criteri
by federal and state statute and regulations that must be considered
evaluation of remedial alternatives.
Biodegradation - The breakdown of organic constituents by microorgani
complex compounds.
Capital Cost - Cost incurred for the construction and startup of a fa
CERCLA - Comprehensive Environmental Response, Compensation, and Liabili
Act. Federal law creating the Superfund program.
Dense Non-Aqueous Phase Liquid (DNAPL) - An organic liquid with a low
solubility and a density greater than that of water. DNAPLs retain t
physical and chemical properties when in contact with water and
in an aquifer when released to groundwater.
Density-Driven Convection - Modified in-ground air sparging system wh
flow pattern in the vicinity of the sparging well.
EPA - U.S. Environmental Protection Agency.
Ex Situ - Performed above ground.
FS - Feasibility Study. Study undertaken to evaluate remedial altern
FFS - Focused Feasibility Study.
Groundwater - Subsurface water residing in a zone of saturation.
Target Area 3
GLOSSARY (cont'd)
HQ - Hazard Quotient. An indicator of the noncarcinogenic health ris
with exposure to a chemical.
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In Situ - In the original location (in the ground for this report).
IRP - The U.S. Air Force Installation Restoration Program
Leach - The solubilization and transport of constituents in soil thro
of surface water to groundwater.
LECR - Lifetime Excess Cancer Risk. The probability of the carcinoge
associated with exposure to the chemicals of concern.
O&M Cost - Annual cost incurred for operation and maintenance of a fa
Maximum Contaminant Levels (MCLs) - Federal drinking water standards.
Plume - A recognizable distribution of constituents in groundwater.
Potentiometric Surface - An imaginary surface that represents the sta
groundwater and is defined by the level to which water will rise.
RBSC - Risk Based Screening Concentration. A chemical-specific conce
to preliminarily assess whether exposure to a chemical poses a potent
risk.
RAO - Remedial Action Objective. Cleanup goal established for the re
RCRA - Resource Conservation and Recovery Act.
ROD - Record of Decision. A legal document issued by the lead govern
agency selecting the remedy to be implemented at a CERCLA site.
RTDF - Remediation Technologies Development Forum.
Soil Vapor Extraction (SVE) - An in situ physical treatment process t
withdraw VOCs from subsurface soil residing above the groundwater tab
Target Area 3
GLOSSARY (cont'd)
Vadose Zone - Soil zone above the water table.
VOCs - Volatile organic compounds.
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Target Area 3
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