EPA/ROD/R03-95/208
1995
EPA Superfund
Record of Decision:
DOVER AIR FORCE BASE
EPA ID: DE8570024010
OU10
DOVER, DE
09/26/1995
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Text:
RECORD OF DECISION
DECLARATION OF THE SELECTED INTERIM REMEDY
Site Name and Location
Target Area 2 of Area 6, West Management Unit, Dover Air Force Base, Ke
County, Delaware.
Statement of Basis and Purpose
This Record of Decision (ROD) presents the selected interim remedial ac
for Target Area 2, which was chosen in accordance with the requirements of th
Comprehensive Environmental Response, Compensation, and Liability Act of 1980
(CERCLA), as amended by the Superfund Amendments and Reauthorization Act of
1986 (SARA), 42 U.S.C Section 9601 et seq., and, to the extent practicable, t
National Oil and Hazardous Substances Pollution Contingency Plan (NCP), 40 CF
Part 300. This decision prepared by the U.S. Air Force, the lead agency, as
owner/operator of the Base is based on the Administrative Record for the Site
Support was provided by the U.S. Environmental Protection Agency (EPA) Region
III and the Delaware Department of Natural Resources and Environmental Contro
(DNREC).
The State of Delaware and the U.S. Environmental Protection Agency concu
with the selected interim remedy. The information supporting this interim re
action decision is contained in the information repository for the Administra
Record located at the Dover Public Library, Dover, Delaware.
Assessment of the Site
Four regions were identified in Area 6 where shallow groundwater contain
combined concentrations of the chlorinated solvents trichloroethene, perchlor
and 1,2-dichloroethene in excess of 1,000 sg/L. These regions were inferred
the vicinity of the source areas for the chlorinated solvent plumes present i
and were incorporated into areas for remediation termed Target Areas. This R
addresses the interim remedy for Target Area 2. The maximum concentration of
chlorinated volatile organic compounds in Target Area 2 groundwater was 17,93
ffig/L. While a Risks Assessment was not performed specifically for Target Are
risk associated with exposure to Area 6 groundwater under a hypothetical futu
commercial/industrial land use scenario was 9 x 10-4.
Actual or threatened releases of hazardous substances from this Site, if
addressed by implementing the interim response action selected in this ROD, m
present a current or potential threat to public health, welfare, or the envir
Target Area 2
1
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Description of the Selected Interim Remedy
The selected interim remedy consists of in situ bioremediation of groundwa
utilizing accelerated anaerobic biodegration. Accelerated anaerobic biodegra
one of the bioremediation technologies being applied to the Target Areas to p
the development of alternate and innovative treatment technologies as encoura
under CERCLA. Performance of the interim remedy and compliance with applicab
or relevant and appropriate requirements will be evaluated in the Final Basew
ROD.
Statutory Determinations
The selected interim remedial action satisfies the remedial selection pr
requirements of CERCLA and the NCP. The selected interim remedy provides the
best balance of trade-offs among the nine criteria required to be evaluated u
CERCLA. The selected interim action provides protection of human health and
environment, complies with federal and state requirements that are legally ap
or revelent and appropriate to the action, and is cost effective. This inter
utilizes permanent solutions and alternative treatment technology to the maxi
extent practicable, and satisfies the statutory preference for remedies that
treatment that reduces toxicity, mobility, or volume as a principal element.
Force understands that although this interim remedy may not achieve MCLs for
certain contaminants, this interim action is only part of a total remedial ac
Base that will be protective of the public health and welfare and of the envi
when completed (CERCLA 121d, 42 U.S.C 9621.d).
19 SEP 1995 SEP 26 1995
CHARLES T. ROBERTSON, JR. Date THOMAS C. VOLTAGGIO
Lieutenant General USAF Hazardous Waste Management
Air Mobility Command Division Direct
Chairperson, Environmental Environmental Protection Agency
Protection Committee Region III
Target Area 2
2
RECORD OF DECISION
FOR THE INTERIM REMEDY OF
TARGET AREA 2 OF AREA 6
WEST MANAGEMENT UNIT
DOVER AIR FORCE BASE, DOVER, DELAWARE
August 3, 1995
DECISION SUMMARY FOR THE RECORD OF DECISION
TARGET AREA 2 OF AREA 6
WEST MANAGEMENT UNIT
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DOVER AIR FORCE BASE
INTRODUCTION
Dover Air Force Base (DAFB) recently completed a Focused Feasibility Study
(FFS) conducted to address chlorinated solvent and pesticide source area
contamination in Area 6 of Dover Air Force Base (DAFB), Delaware as an interi
response. The FFS was undertaken as part of the U.S. Air Force's Installatio
Restoration Program (IRP). The basis for the FFS was the Area 6 Remedial
Investigation (RI) report dated July 1994, which characterized contamination
evaluated potential risks to public health and the environment. The interim
performed as the first phase of Feasibility Studies to be conducted on sites
Management Unit, the management unit to which Area 6 belongs. The scope of t
FFS was limited to the evaluation of alternatives for remediation of primary
chlorinated solvent and pesticide source areas originating in the northern, u
portion of the Area 6 region of investigation. The final remediation of sour
if necessary, and non-source area contamination in Area 6 posing human health
environmental risks will be addressed in the final Base-wide Feasibility Stud
This Record of Decision (ROD) addresses Target Area 2, which is one of t
chlorinated solvent source areas evaluated in the FFS. This ROD summarizes t
FSS, describes the remedial alternatives that were evaluated, identifies the
alternative selected by DAFB, and explains the reasons for this selection. T
Environmental Protection Agency (EPA) and the State Delaware concur with the
interim remedy selected in this ROD.
As an aid to the reader, a glossary of the technical terms used in this ROD
provided at the end of the summary.
Target Area 2
ROD-1
PUBLIC PARTICIPATION
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The Proposed Plan for this site was issued on June 16, 1995. The public
comment period on the Plan was open through July 13, 1995. Documents compris
the Administrative Record for the site were available at the Dover Public Lib
The only comments received during the public period were from the
Remediation Technologies Development Forum expressing support for the propose
interim remedy.
SITE BACKGROUND
DAFB is located in Kent County, Delaware, 3.5 miles southeast of the city o
Dover (Figure 1) and is bound to the southwest by the St. Jones River. DAFB
comprises approximately 4,000 acres of land, including annexes, easements, an
property (Figure 2). The surrounding area is primarily cropland and wetlands
DAFB began operation in December 1941. Since then, various military servic
have operated out of DAFB. The present host organization is the 436th Airlif
Its mission is to provide global airlift capability, including transport of c
equipment, 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 casu
the event of war. The C-5 Galaxy, a cargo transport plane, is the largest ai
the USAF, and DAFB is one of a few military bases at which hangars and runway
designed to accommodate these planes.
The portion of DAFB addressed in this ROD is located within Area 6 of the
West Management Unit. The West Management Unit is one of four Management
Units into which the Base has been divided (Figure 3). Area 6 is the largest
associated areas identifies in the West Management Unit. The Area 6 region o
investigation extends approximately 8,400 feet from its northern most point n
hardstand and Building 723 to its southern most point near the St. Jones Rive
(Figure 4). The area north of U.S. Highway 113 contains the industrialized p
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Target Area 2
ROD-2
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Columbia Formation in Area 6 ranges from 28 to 64 feet.
Unconformably underlying the Columbia Formation is the upper unit of the
Calvert Formation, which generally consists of gray to dark gray firm, dense
clay, with thin laminations of silt and fine sand. This upper silt and clay
in thickness from 15 to 21 feet in the northern portion of Area 6. The hydra
conductivity of this unit range from 6.83 x 10-3 to 1.53 x 19-3 ft/day (2.41
x 10-7 cm/sec), which are three to five orders of magnitude lower than the ov
Columbia Formation. These significantly lower hydraulic conductivities form
to the vertical migration of constituents identified in the Columbia Aquifer.
Underlying this confining unit is the upper sand unit of the Calvert Formatio
Target Area 2
ROD-7
Frederica Aquifer. This aquifer averages 22 feet in thickness in the vicinit
No constituents of concern were identified in the three Frederica monitoring
installed in Area 6. Additionally, no production wells are installed the Fre
Aquifer in the vicinity of DAFB.
Area 6 is defined by the association of chlorinated solvents in groundwater
forming a plume in the Columbia Aquifer. Several separate potential sources
identified in the Area 6 RI that may have contributed to the chlorinated solv
contamination. These potential sources include some of the twelve IRP sites
the Area 6 groundwater flow regime shown in Figure 4. Additionally, various
and hangars where solvents are used may also be sources. The shop activities
solvent use is common include painting or paint stripping, aircraft and vehic
maintenance, and plating or welding. The northern most point of chlorinated
contamination is the aircraft maintenance area located north of Atlantic Stre
chlorinated solvent plumes extend approximately 4,600 feet south into Base Ho
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The Area 6 RI identifed four regions where shallow groundwater (i.e., the t
ten feet of the Columbia Aquifer) contained combined concentrations of the
chlorinated solvents trichloroethene (TCE), perchloroethene (PCE), and 1,2-
dichloroethene (DCE) in excess of 1,000 aeg/L. These regions were inferred to
the vicinity of the source areas for the chlorinated solvent plumes that are
Area 6. The groundwater data suggested that primary source areas reside in t
vicinity of the following reference points, which were incorporated into area
remediation termed Target Areas:
Paint Washout Area m(Site SS59) located along the eastern portion of t
open storage yard. (Target Area 1)
Civil Engineering (CE) Shops Area including Building 607 (Carpentry
Shop), Building 608 and 609 (Material Control/Supply Offices),
Building 615 (Interior and Exterior Electrical Shop, Power Production,
Paint Shop, and Sheet Metal Shop), and Building 650 (Sign Shop).
(Target Area 2)
Target Area 2
ROD-8
Building 719 housing the Jet Engine Repair Shop. (Target Area 3)
Buildings 715 and 716 housing the ISO-Dock and an engine storage
facility, respectively. (Target Area 4)
The four Target Areas that have been identified are shown in Figure 5. Eac
Target Area incorporates one of the primary suspected source areas and the
significantly impacted portions of the shallow and deep groundwater plumes as
with the respective source area. Plume maps of total chlorinated VOCs in sha
and deep groundwater are shown in Figures 6 and 7, respectively. The Target
are the regions of chlorinated solvent groundwater contamination that were ev
in the FFS.
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TARGET AREA/SOURCE AREA CHARACTERISTICS
The following section described the physical and chemical characteristics o
Target Area 2, which is addressed in this Record of Decision.
Target Area 2 is located to the east of Target Area 1, originating in the v
of the CE Shops and extending south about 1,500 feet. Historically, a vehicl
maintenance facility also reportedly resided in the vicinity of the CE shops,
another potential source of the contamination. Target Area 2 is elliptically
and is approximately 13.1 acres in size. Expanded scale maps of the chlorina
solvent plumes residing in the shallow and deep portions of the aquifer withi
Area 2 are shown in Figures 8 and 9, respectively. The maximum concentration
total chlorinated VOCs in Target Area 2 groundwater was found in the deep
Columbia at a concentration of 17,930 sg/L. This detection was made approxim
600 feet downgradient of the CE Shops, and indicates a rapid downward migrati
chlorinated constituents in the aquifer in this location.
SUMMARY OF SITE RISKS.
The full Risk Assessment (RA) for Area 6 can be found in the final Area 6 R
report dated July 1994. The purpose of the RA is to determine whether exposu
site-related contaminants could adversely affect human health and the environ
Target Area 2
ROD-9
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The focus of the baseline RA is on the possible human health and environmenta
effects that could occur under current or potential future use conditions in
that the contamination is not remediated. The risk is expressed as lifetime
cancer risk (LECR) for carcinogens, and hazard quotient (HQ) for noncarcinoge
For example, and LECR of 1 x 10-6 represents one additional case of cancer in
million exposed population, whereas a hazard quotient above one presents a li
of noncarcinogenic health effects in exposed populations.
The baseline RA focused on potential pathways by which maintenance and
construction workers could be exposed to contaminated materials in Area 6. T
workers' exposure to groundwater and soil have been evaluated under a regular
maintenance scenario; a future contruction scenario; and a hypothetical futur
groundwater use from the Columbia Aquifer under a commercial/industrial scena
Although a specific Target Area 2 RA has not been performed, the risk calcula
Area 6 Remedial Investigation from the hypothetical future exposure to ground
within Area 6 had an LECR of 9 x 10-4, which exceeds the 1 x 10-4 to 1 x 10-6
used to evaluate the need for remediation. In addition to the overall Area 6
Target Area 2 constituents of concern have been compared to the risk-based sc
concentrations (RBSCs) developed for the commercial/industrial scenario at DA
identify the chlorinated solvents that present a risk-based concern.
The possibility exists for exposure of workers to hazardous substances in s
during excavation activities. Source areas identified during excavation will
protection as per health and safety protocols. All workers performing excava
at DAFB will be health and safety trained for work at CERLA sites.
Based on the direction of groundwater flow, the Area 6 plume extends in a
southerly direction towards the St. Jones River. There are no surface water
points within Area 6 between the Target Area and the river. Presently, the A
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is confined within the Base property and has not reached the St. Jones River.
The future use of groundwater from the Columbia Aquifer by the Base personn
quite unlikely and hypothetical. This hypothetical future groundwater use as
Taget Area 2
ROD-15
groundwater from the Columbia Aquifer will be used for drinking and showering
by Base personnel under a commercial/industrial scenario. The RBSCs were com
with the maximum detected concentrations of chlorinated solvents in Target Ar
(Table 1). Concentrations of five of the six detected chlorinated solvents--
dichloroethane, 1,1-dichloroethene, 1,2-dichloroethene, perchloroethene, and
trichloroethene--in Target Area 2 exceed their corresponding RBSCs in groundw
The concentrations of the other detected compound, 1,1-dichloroethane, was be
RBSC.
Actual or threatened releases of hazardous substances from this Site, if no
addressed by the selected alternative or one of the other active measures con
present a current or potential threat to public health, welfare, or the envir
REMEDIAL ACTION OBJECTIVE
Within the groundwater in Target Area 2, the interim Remedial Action Object
(RAO) is to reduce the concentration of each ethyl-based chlorinared volatile
compound (VOC) by 90 percent. The ethyl-based chlorinated VOCs include PCE,
1,1-DCE, 1,2-DCE, vinyl chloride, 1,1,1-trichloroethane, 1,1-dichloroethane,
dichloroethane. The listed VOCs include primary contaminants and their commo
breakdown products. Because these constituents are considered to be the most
90 percent reduction interim RAO is applied to each of these compounds indivi
rather than to the aggregate concentration of all the chlorinated VOCs. For
consistency, the 90-percent reduction model was based upon the RCRA Post-Clos
Permit (Reference No. DE8570024010, Permit No. HW05A05) for Site WP21 of DAFB
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which is a unit that adjoins Target Area 3 to the west.
The maximum concentrations of the detected chlorinated solvent compounds in
Target Area 2 are summarized in Table 2, along with the compound and Target A
specific interim RAO. Table 2 also included interim RAO concentrations for s
compounds that have not yet been detected in the Target Area. These select c
are chemical degradation products of some of the currently detected chlorinat
constituents. Thus, reducing the concentration of detected compounds at the
Target Area 2
ROD-16
Table 1
Maximum Concentration Detected of Ethyl-Based Chlorinated Volatiles
in Target Area 2, and Corresponding Risk-Based Screening Concentration
Target Area 2
Maximum
Compound Detected RBSC
1,1-Dichloroethane 5 1,300
1,2-Dichloroethane 150 0.29
1,1-Dichloroethene 5 0.12
1,2-Dichloroethene 2,600 84
Perchloroethene 710 4
Trichloroethene 15,000 4
Concentrations reported in units of sg/L.
RBSC - Risk-Based Screening Concentration for Commercial/Industrial scenario
Base. The RBSCs are based on a lifetime cancer risk of 1 x 10-6 or a haz
whichever is lower.
Target Area 2
ROD-17
Table 2
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Maximum Concentration Detected of Ethyl-Based Chlorinated Volatiles
in Target Area 2, and Corresponding Compound and Target Area
Specific Interim Remdial Action Objectives.
Target Area 2
Maximum Interim
Compound Detected RAO
1,1-Dichloroethane 5 (d)
1,2-Dichloroethane 150 15
1,1-Dichloroethene 5 7(a)
1,2-Dichloroethene 2,600 260
Perchloroethene 710 71
1,1,1-Trichloroethane ND 200(b)
Trichloroethene 15,000 1,500
Vinyl chloride ND 2(c)
Concentrations reported in units of sg/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 Level has not been established for 1,1-Dichloroethane.
Target Area
ROD-18
producing other chlorinated VOC degradation products will not itself be suffi
satsify the interim RAO. Note that if a ten-fold reduction from the maximum
concentration detected of a compound is below that compound's MCL, the MCL is
as the interim RAO.
The issues of final cleanup levels and attainment of ARARs will be addresse
the Final Basewide Record of Decision. The remedial action selected for this
part of the remedial action which will be selected in a Final Basewide ROD.
SUMMARY OF ALTERNATIVES
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Engineering technologies applicable to remediating the contaminated media w
screened according to their effectiveness and implementability. Those techno
were determined to be the most applicable were then developed into remedial a
The following remedial alternatives are numbered to correspond to the alterna
described in the FFS report.
Alternative l--No Action.
Alternative 2--Collection, Ex Situ Treatment, and Surface Water Disc
of Groundwater; and Performance of Soil Vapor Extraction in Chlorina
Solvent Source Areas if Necessary.
Alternative 3--In Situ Groundwater Treatment Using Air Sparging and
Density-Driven Convection Technologies Combined With Soil Vapor
Extraction.
Alternative 4--In Situ Bioremediation of Groundwater Utilizing Accel
Anaerobic Biodegradation.
The four remedial alternatives that were evaluated in detail are described
In addition, the capital, annual operation and maintenance (O&M), and present
of each alternative are provided.
Target Area 2
ROD-19
Alternative 1
Target Area 2
Capital Cost $000
Annual O&M Cost $000
Present Worth $000
The no action alternative is evaluated in order to establish a baseline for
comparison against other alternatives. Under this alternative, no efforts ar
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to reduce the groundwater concentrations of chlorinated solvents in the Targe
Alternative 2
Target Area 2
Capital Cost $500,000
Annual O&M Cost $94,000(a)
Present Worth $980,000(b)
(a)First year O&M cost. Refer to text.
(b)Assumes 10 years of operation.
Alternative 2 consists of groundwater extraction, groundwater pretreatment
metals, groundwater treatments using air stripping for removal of chlorinated
carbon adsorption for removal of residual contaminants, and surface water dis
treated groundwater; performance of soil vapor extraction (SVE) in the shallo
solvent source areas if determined to be necessary during remedial design; an
of the offgases from the air stripper and, if implemented, the SVE system.
A total of three extraction wells are estimated to be installed in Target A
cost estimating purposes only, to extract contaminated groundwater at a combi
pumping rate of approximately 35 gallons per minute. If this alternative is
selected for this interim response, then the exact number of wells and their
Target Area 2
ROD-20
be determined during the remedial design. Extracted groundwater will be pret
metals to reduce the concentrations of iron and manganese. Metals pretreatme
the possibility of iron and manganese fouling subsequent treatment systems as
ensure compliance with surface water discharge standards for metals.
Pretreated groundwater will then be pumped to the top of a low profile, thr
air stripper that will transfer over 95 percent of the VOCs dissolved in the
to the air stream. The air stream containing the VOCs will then exit the air
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where it will be treated using carbon adsorption prior to release to the atmo
Routine air sampling at a frequency determined during remedial design will be
to ensure compliance with air emission standards.
Treated groundwater exiting the air stripper will be pumped to a liquid pha
carbon adsorption unit to reduce the concentration to residual contaminants t
comply with the surface water discharge standards prior to release to the gol
tributary of the St. Jones River. Semi-annual water samples, assumed for cos
purpose only, will be collected to ensure compliance with discharge standards
sampling frequency will be determined during the remedial design.
Vadose zone chlorinated solvent contamination is present in the Target Area
location where significant shallow groundwater contamination has been identif
address this potential source, performance of SVE in a limited size area has
included with this alternative. A total of two SVE wells are estimated to be
remediate the source area presumed to be present. Soil sources would be expe
remediated in less thawn 2 years with SVE treatment; 2 years of operation is
costing purposes. If SVE is implemented, vapor collected by the SVE system w
treated for organic constituents by vapor phase carbon units prior to being r
atmosphere. The necessity of performing SVE will be determined during the re
design.
Groundwater monitoring will be performed to monitor the progress of groundw
remediation. In addition, existing land use restrictions associated with the
operation of DAFB will be enforced throughout the course of remediation to pr
Target Area 2
ROD-21
unauthorized extraction and use of the contaminated groundwater from the Colu
Aquifer.
The time required to achieve the interim RAO is estimated to be in the rang
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5 to 10 years, provided no free phase solvents are present in the aquifer. I
solvents are present, the time required to achieve the interim RAO may be ext
30 years or more. The present worth cost of this alternative ($980,000) is c
based on an assumed 10 year operation.
Alternative 3
Target Area 2
Capital Cost $1,150,000
Annual O&M Cost $140,000(a)
Present Worth $1,900,000(b)
(a)First year O&M cost. Refer to text.
(b)Assumes 6 years of operation.
Alternative 3 consists of the in situ treatment of groundwater using a comb
of air sparging (AS) and density-driven convection (DDC) technologies, combin
SVE over the entire areas where in situ groundwater treatment is performed; a
adsorption treatment of the offgases from the SVE system.
For in situ treatment at Target Area 2, 97 SVE wells, 31 AS wells, and 46 D
wells are estimated to be required for cost estimating purposes only. If thi
ultimately selected for this interim response, then the exact number of wells
placement will be determined during the remedial design. AS will be used in
soil is highly permeable and free of clay. DDC will be used in areas where s
clay layers are present. The SVE system operates in tandem with the AS/DDC s
to capture volatile contaminants stripped from the saturated zone. Vapor pha
adsorption treatment units will be used to remove extracted VOCs from the air
prior to release to atmosphere. Entrained water will be separated by knockou
Target Area 2
ROD-22
sent to liquid phase carbon adsorption units to reduce contaminant concentrat
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acceptable for discharge.
Groundwater monitoring will be performed to monitor the groundwater remedia
progress and plume migration. In addition, existing land use restrictions as
the military operation of DAFB will be enforced throughout the course of reme
prevent unauthorized extraction and use of the contaminated groundwater from
Columbia Aquifer.
The time required to achieve the interim RAO is estimated to be between 4 a
13 years, with 6 years being the estimate used for costing purposes. The pre
cost is estimated to be $1,900,000. The remediation time estimates are based
rate data from the AS/SVE pilot study performed at Site WP-21.
Alternative 4
Target Area 2
Capital Cost $230,000
Annual O&M Cost $40,000(a)
Present Worth $350,000
(a)First Year O&M cost.
Alternative 4 consists of in situ bioremediation of groundwater utilizing a
anaerobic biodegradation in Target Area 2. Accelerated anaerobic biodegradat
of the bioremediation technologies being applied to the Target Areas to promo
development of alternate and innovative treatment technologies as encouraged
CERLA.
The chlorinated solvent groundwater plume in Target Area 2 will be remediat
using accelerated anaerobic biodegradation technology. The native microorgan
population that is intrinsically biodegrading the chlorinated solvent constit
stimulated through the addition of an easily co-metabolized food source and e
nutrients such as yeast extract. The food and nutrients will be delivered by
with extracted groundwater and then injecting the enriched groundwater back i
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Target Area 2
ROD-23
aquifer. Groundwater injection will be performed in compliance with Delaware
Regulations Governing Construction of Water Wells (DRGCWW), Section 3.15.
Approximately nine extraction and nine injection wells are estimated to be re
Target Area 2 for cost estimating purposes only. If this alternative is ulti
for this interim response, then the exact number of wells and their placement
determined during the remedial design. A pilot-scale version of this system
installed and studied by the Remediation Technologies Development Forum (RTDF
which is a consortium of partners from industry, government, and academia wor
develop more effective and less costly remedial treatment technologies. Prel
performance data indicate the technology should work well at this location.
design data are expected to be available by December 1995.
The bioremediation process utilized is not expected to generate degradation
products that can migrate beyond the Base boundary. Groundwater monitoring w
performed to monitor the groundwater remediation progress and downgradient wa
quality to ensure the offbase plume migration does not occur. In addition, e
use restrictions associated with the military operation of DAFB will be enfor
throughout the course of remediation to prevent unauthorized extraction and u
contaminated groundwater from the Columbia Aquifer.
The time required to achieve the interim RAO in Target Area 2 using the
accelerated anaerobic bioremediation technology will be evaluated during the
but at this time the goal is estimated to be achieved within 2 years for cost
EVALUATION OF ALTERNATIVES
The selected alternative for remediating the contamination in the Target Ar
Alternative 4 (bioremediation). Based on current information, this alternati
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best balance of trade-offs among the alternatives with respect to the nine cr
required to be evaluated under CERCLA. This section profiles the performance
selected alternative against the nine criteria and explains how it compares t
alternatives under consideration.
Target Area 2
ROD-24
Overall Protection of Human Health and the Environment
The overall protectiveness criterion is a composite of other evaluation cri
especially short-term effectiveness, long-term effectiveness, and compliance
Alternativess 1, 2, 3 and 4 are all considered to be protective of human heal
period of implementation because of the existence of land use restrictions th
unauthorized extraction or use of contaminated groundwater in the Target Area
preventing human exposure.
Alternative 1 (no action) is not considered effective because no provisions
to monitor the Target Area plum to evaluate compliance with the interim RAO.
Alternatives 2 (pump and treat), 3 (air sparging), and 4 (bioremediation) wil
interim RAOs and are considered effective.
Compliance With ARARs
The interim RAOs that have been set for chlorinated solvent constituents in
groundwater will allow for the resultant concentration of several of these co
exceed their federal Maximum Contaminant Levels (MCLs). MCLs, as provided fo
CERCLA 121 (d)(2)(A)(ii), are relevant and appropriate requirements for any
actions expected to be taken as a result of the Base-wide investigation.
Offsite contaminant migration, even for interim actions, requires that a nu
other ARARs be considered. The principal ARARs that pertain to the offsite m
of contaminants are the Delaware regulations implementing the Federal Clean A
Clean Water Act. These regulations are the Delaware Regulations Governing th
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of Air Pollution (DRGCAP 1 through 3, 21, and 24), the Delaware Water Polluti
Control Regulations (DWPCR 1 through 6), the Delaware Industrial Waste Efflue
Limitations (DWPCR 8), and the Delaware surface Water Quality Standard (DSWQS
through 9,11 and 12). The above referenced regulations regarding emissions o
organic compounds to the atmosphere will be complied with in Alternatives 2 a
ensure that acceptable levels of emissions are met. Alternative 2 will requi
to surface water. The above referenced regulations regarding surface water d
define limits of acceptable chemical concentrations for wastewater, and attai
Target Area 2
ROD-25
limits will be a requirement for this alternative. For Alternative 4, there
migration or releases of contaminants. The underground injection of recircu
groundwater, which is an essential component of Alternative 4, will be perfor
compliance with Delaware Regulations Governing the Construction of Water Well
(DRGCWW, Section 3.15). Alternatives 2 and 3 both meet all previously identi
regulations that pertain to the offsite movements of contaminants.
Long-Term Effectiveness and Permanence
The long-term effectiveness and permanence criterion primarily considers th
magnitude of residual risk that would remain after the implementation of an a
and the adequacy and reliability of the control instituted. All the alternat
for the long-term protection of human health through the existing land use re
However, reliance upon land use restrictions is not considered a permanent re
Under Alternative 1 (no action), the chlorinated solvent contamination in
groundwater will not be monitored. Therefore, the adequacy and reliability o
alternative cannot be established.
Alternatives 2 (pump and treat) , 3 (air sparging) , and 4 (bioremediation) w
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result in significant reductions of chlorinated solvent concentrations in the
If any one of these treatment alternatives is selected, that system will be o
interim RAO is achieved. Hence, no more than 10 percent of the maximum obser
concentration of each ethyl-based chlorinated solvent will remain in the Targ
magnitude of residual contamination remaining in the Target Area is a functio
the treatment alternative is operated or allowed to continue. Continued oper
treatment system beyond the point at which the interim RAO is reached may all
reductions in contaminant levels to be achieved. Performance of the interim
compliance with ARARs will be 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 by the
implementation of Alternative 1. The three action alternatives include compo
are capable of significantly reducing the toxicity of groundwater in the Targ
Target Area 2
ROD-26
The groundwater extraction system proposed under Alternative 2 will establi
hydraulic control over the plume, thereby limiting the mobility of contaminan
the Target Area. The air sparging in situ treatment technology included in A
operates by increasing the mobility of contaminants. This increased mobility
in some spreading of contamination beyond the effective zones of these altern
the course of contaminant removal; however, the overall volume of the contami
be reduced. The bioremediation technology proposed under Alternative 4 will
impact on contaminant mobility. The toxicity profile of the groundwater may
somewhat during the biodegradation process, as vinyl chloride is generated du
degradation of the more chlorinated ethyl-based compounds. However, because
chloride has been detected in the groundwater thus far, the evidence suggests
chloride is rapidly degraded to carbon dioxide, water, and chloride ion under
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conditions found downgradient of the Target Areas.
Short-Term Effectiveness
Alternative 1 (no action) includes no remedial actions. Therefore, there w
short-term impacts on community or worker health or the environment from cons
activities. However, because Alternative 1 will not monitor compliance with
RAOs established for this project, it is considered to be ineffective.
Alternatives 2 (pump and treat) , 3 (air sparging) , and 4 (bioremediation) w
be effective in reducing groundwater contaminant concentrations in the Target
None of these alternatives are expected to have significant impacts on worker
health or the environment. Alternative 2 is estimated to be capable of meeti
RAO within a 5 to 10 year time frame. However, although not believed present
pockets of DNAPLs in the aquifer could cause this time frame to increase to 3
more.
The presence of DNAPLs will also affect the length of time required to achi
interim RAO under Alternative 3, though to a lesser extent than will their pr
Alternative 2. There are two reasons for this. First, there would be many m
sparging/density-driven convection wells under Alternative 3 than there would
Target Area 2
ROD-27
extraction wells under Alternative 2. Thus, the chance of locating a remedia
a pocket of free product is much greater under Alternative 3. Secondly, the
remediation is a more aggressive remediation process than pump and treat. Hi
transfer rates from water to air would be achieved with the physical in situ
technologies lowering the concentration of solvents within the plume. Lowere
groundwater concentrations would increase the driving force for solubilizatio
product in order to maintain equilibrium. The time required to meet the inte
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under Alternative 3 is estimated to be between 4 and 13 years.
Alternative 4 is estimated to be capable of achieving the interim RAO in Ta
Area 2 within approximately 2 years using accelerated anaerobic bioremediatio
the other action alternatives, these time frames may be extended if DNAPLs ar
A DNAPL would present a continuing source of contaminants to the aquifer as t
DNAPL constituents were solubilized in the groundwater. This transfer of con
from free phase to dissoved phase would occur through the physical processes
desorption and liquid-liquid partitioning. These equilibrium-driven processe
occur slowly because of the relatively low surface area of DNAPL in contact w
groundwater in comparison to DNAPL volume. The solubilization rate of DNAPLs
likely be slower than the rate of degradation of the dissolved constituents.
solubilization of DNAPLs would likely be the rate-limiting step.
Implementability
Three main factors are considered under this criterion: technical feasibil
administrative feasibility, and availability of services and materials. All
are administratively feasible and the required services and materials are rea
Hence, the comparison will focus on the technical feasibility of the alternat
Alternative 1 (no action) has no technical feasibility considerations. Alt
2 (pump and treat), 3 (air sparging) , and 4 (bioremediation) have technical f
concerns associated with them. These concerns are related to the highly deve
character of the Target Area and the the numerous space contraints that are p
However, of the three action alternatives, Alternative 4 will be least diffic
implement. Alternative 4 requires the installation of approximately 18 groun
Target Area 2
ROD-28
injection/extraction wells in Target Area 2 plus the ancillary piping and sup
equipment. The alternative 4 system is considered slightly easier to install
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Alternative 2 system, which includes only seven groundwater extraction, SVE,
inlet wells, but a more extensive piping network. Both Alternative 2 and 4 a
considered much less complicated to install than Alternative 3, which consist
sparge, DDC, and SVE wells, more expansive piping and numerous treatment stat
Overall, Alternative 4 is judged to be the most easily implemented action alt
Cost
No direct costs are associated with the implementation of Alternative 1 (no
Of the action alternatives, the capital cost of Alternative 4 (bioremediation
which is significantly lower than the $500,000 capital cost of Alternative 2
treat) and the $1,150,000 capital cost of Alternative 3 (air sparging). The
capital costs of Alternative 4 represent the net expenditures required by the
to implement the alternative. Some of the required capital costs will assume
expended by the RTDF in setting up their treatability study in the Target Are
The O&M cost of Alternative 2 will initially be $94,000 per year, but will
to $60,000 per year after 2 years of operation when SVE operations are discon
The O&M cost of Alternative 3 will be almost $140,000 the first year, but wil
several thousand dollars per year thereafter as the carbon consumption rate a
the SVE system's offgass treatment units decreases. The O&M costs of Alterna
be approximately $40,000 per year for operating and monitoring the accelerate
biodegradation system in Target Area 2. After shut-down of the system, groun
monitoring will be performed at an annual cost of approximately $10,000 per y
The present worth cost of the alternatives will depend upon the time they a
operated. The present worth costs of Alternative 2 under operating scenario
and 30 years are $810,000, $980,000, and $1,300,000, respectively. The prese
costs of Alternative 3 under operating scenarios of 4, 6, and 13 years, respe
$1,710,000, $1,900,000, and $2,340,000. The present worth cost of Alternativ
assuming 2 years of operation in Target Area 2 followed by 3 years of groundw
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monitoring is $350,000. Thus, Alternative 4 will have the lowest present wor
Target Area 2
ROD-29
assuming 2 years of operation in Target Area 2 followed by 3 years of groundw
monitoring is $350,000. Thus, Alternative 4 will have the lowest present wor
State Acceptance
The State of Delaware concurs with the selected interim remedy for Target A
Community Acceptance
The only comments received during the public comment period were from the
RTDF expressing support for the proposed remedy. No community opposition to
proposed remedy was noted.
CONCLUSION
Based on the evaluation of the alternatives using the nine criteria, Altern
(bioremediation) is preferred. Alternative 4 is protective of human health a
environment, complies with all ARARs, presents a permanent remedy that reduce
groundwater toxicity, provides the greatest ease of implementation, and is th
effective action alternative.
The selected alternative utilizes permanent solutions and alternative treat
technologies to the maximum extent practicable. This interim action will not
impact the ability to implement a final action, if it is required. The final
selected in the final Base-wide ROD.
Actual or threatened releases of hazardous substances from this Site, if no
addressed by the selected alternative, may present a current or potential thr
health, welfare, or the environment.
Target Area 2
ROD-30
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GLOSSARY AND ACRONYMS
Air Sparging - Underground injection of air into saturated soil and groundwat
in the in situ air stripping of volatile constituents.
Air Stripping - Transfer of volatile constituents from water to air by induce
between air and water streams.
Aquifer - A geologic formation capable of yielding water to wells and springs
ARARs - Applicable or Relevant and Appropriate Requirements. Criteria set fo
federal and state statute and regulations that must be considered in the
of remedial alternatives.
Biodegradation - The breakdown of organic constituents by microorganisms into
complex compounds.
Capital Cost - Cost incurred for the construction and startup of a facility.
CERCLA - Comprehensive Environmental Response, Compensation, and Liability Ac
Federal law creating the Superfund program.
Dense Non-Aqueous Phase Liquid (DNAPL) - An organic liquid with a low water
solubility and density greater than that of water. DNAPLs retain their p
and chemical properties when in contact with water and tend to sink in an
when released to groundwater.
Density-Driven Convection - Modified in ground air sparging system which indu
flow pattern in the vicinity of the sparging well.
EPA - U.S. Environmental Protection Agency.
Ex Situ - Performed above ground.
RS - Feasibility Study. Study undertaken to evaluate remedial alternatives.
FFS - Focused Feasibility Study.
Groundwater - Subsurface water residing in a zone of saturation.
Target Area 2
ROD-31
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GLOSSARY (Cont'd)
HQ - Hazard Quotient. An indicator of the noncarcinogenic health risk associ
exposure to a chemical.
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 through the
surface water to groundwater.
LECR - Lifetime Excess Cancer Risk. The probability of the carcinogenic heal
associated with exposure to the chemicals of concern.
O&M Cost - Annual cost incurred for operation and maintenace of a facility.
Maximum Contaminant Levels (MCLs) - Federal drinking water standards.
Plume - A recognizable distribution of constituents in groundwater.
Potentiometric Surface - An imaginary surface that represents the static head
groundwater and is defined by the level to which water will rise.
RBSC - Risk Based Screening Concentration. A chemical-specific concentration
preliminarily assess whether exposure to a chemical poses a potential hea
RAO - Remedial Action Objective. Cleanup goal established for the remediatio
RCRA - Resource Conservation and Recovery Act.
ROD - Record of Decision. A legal document issued by the lead governmental a
selecting the remedy to be implemented at a CERCLA site.
RTDF - Remediation Technologies Development Forum.
Soil Vapor Extraction (SVE) - An in sity physical treatment process to volati
withdraw VOCs from subsurface soil residing above the groundwater table.
Vadose Zone - Soild zone above the water table.
VOCs - Volatile organic compounds.
Target Area 2
ROD-32
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