PB95-963917
EPA/ROD/R03-95/207
March 1996
EPA Superfund
Record of Decision:
Dover Air Force Base,
Target Area 1 of Area 6, DE
9/26/1995
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RECORD OF DECISION
DECLARATION OF THE SELECTED INTERIM REMEDY
Site Name and Location
Target Area 1 of Area 6, West Management Unit, Dover Air Force Base, Kent
County, Delaware.
Statement of Basis and Purpose
This Record of Decision (ROD) presents the selected interim remedial action
for Target Area 1, which was chosen in accordance with the requirements of the
Comprehensive Environmental Response, Compensation, and Liability Act of 1980
(CERCLA), as amended by the Superfund Amendments and Reauthorization Act of
1986 (SARA) and, to the extent practicable, the National Oil and Hazardous
Substances Pollution Contingency Plan (NCP), 40 CFR Part 300. This decision
prepared by the U.S. Air Force, the lead agency, as the 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 HI and the Delaware Department
of .Natural Resources and Environmental Control (DNREC).
The State of Delaware and the U.S. Environmental Protection Agency concur
with the selected interim remedy. The information supporting this interim remedial
action decision is contained in the information repository for the Administrative
Record located at the Dover Public Library, Dover, Delaware.
Assessment of the Site
Four regions were identified in Area 6 where shallow groundwater contained
combined concentrations of the chlorinated solvents trichloroethene, perchloroethene,
and 1,2-dicnloroethene in excess of 1,000 /xg/L. These regions were inferred to be in
the vicinity of the source areas for the chlorinated solvent plumes present in Area 6,
and were incorporated into areas for remediation termed Target Areas. This ROD
addresses the interim remedy for Target Area 1. The maximum concentration of total
chlorinated volatile organic compounds in Target Area 1 groundwater was 16,042
HgfL. While a Risk Assessment was not performed specifically for Target Area 1, the
risk associated with exposure to Area 6 groundwater^ under a hypothetical future
commercial/industrial land use scenario was 9 x 10*4.
Actual or threatened releases of hazardous substances from this Site, if not
addressed by implementing the interim response action selected in this ROD, may
present a current or potential threat to public health, welfare, or the environment.
Target Area 1
1
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Description of the Selected Interim Remedy
The selected interim remedy consists of in situ bioremediation of groundwater
utilizing intrinsic bioremediation. Intrinsic bioremediation is one of the
bioremediation technologies being applied to the Target Areas to promote the
development of alternate and innovative treatment technologies as encouraged under
CERCLA. Performance of the interim remedy and compliance with applicable or
relevant and appropriate requirements will be evaluated in the Final Basewide ROD.
Statutory Determinations
The selected interim remedial action satisfies the remedial selection process
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 under
CERCLA. The selected interim action provides protection of human health and the
environment, complies with federal and state requirements that are legally applicable
or relevant and appropriate to the action, and is cost effective. This interim remedy
utilizes permanent solutions and alternative treatment technology to the maximum
extent practicable, and satisfies the statutory preference for remedies that employ
treatment that reduces toxicity, mobility, or volume as a principal element. The Air
Force understands that although this interim remedy may not achieve MCLs for
certain contaminants, this interim action is only part of a total remedial action for the
Base that will be protective of the public health and welfare and of the environment
when completed (CERCLA 121d, 42 U.S.C. 9621.d).
CHARLES T. ROBERTSON, JR. Date 'THOMAS C. V6ura&GIQ Date
Lieutenant General, USAF Hazardous Waste-Management
Air Mobility Command Division Director
Chairperson, Environmental Environmental Protection Agency
Protection Committee Region IE
Target Area 1
2
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RECORD OF DECISION
FOR THE INTERIM REMEDY OF
TARGET AREA 1 OF AREA 6
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 1 OF AREA 6
WEST MANAGEMENT UNIT
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 interim
response. The FFS was undertaken as part of the U.S. Air Force's Installation
Restoration Program (IRP). The basis for the FFS was the Area 6 Remedial
Investigation (RI) report dated July 1994, which characterized contamination and
evaluated potential risks to public health and the environment. The interim FFS was
performed as the first phase of Feasibility Studies to be conducted on sites in the West
Management Unit, the management unit to which Area 6 belongs. The scope of the
FFS was limited to the evaluation of alternatives for remediation of primary
chlorinated solvent and pesticide source areas originating in the northern, upgradient
portion of the Area 6 region of investigation. The final remediation of source areas,
if necessary, and non-source area contamination in Area 6 posing human health or
environmental risks will be addressed in the final Base-wide Feasibility Study.
This Record of Decision (ROD) addresses Target Area 1, which is one of the
chlorinated solvent source areas evaluated in the FFS. This ROD summarizes the
FFS, describes the remedial alternatives that were evaluated, identifies the remedial
alternative selected by DAFB, and explains the reasons for this selection. The U.S.
Environmental Protection Agency (EPA) and the State of 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 is
provided at the end of the summary.
Target Area 1
ROD-1
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PUBLIC PARTICIPATION
The Proposed Plan for this site was issued on June 16, 1995. The public
comment period on the Plan was open through July 31,1995. Documents comprising
the Administrative Record for the site were available at the Dover Public Library.
The only comments received during the public comment period were from the
Remediation Technologies Development. Forum expressing support for the proposed
interim remedy.
SITE BACKGROUND
DAFB is located in Kent County, Delaware, 3.5 miles southeast of the city of
Dover (Figure 1) and is bounded to the southwest by the St. Jones River. DAFB
comprises approximately 4,000 acres of land, including annexes, easements, and leased
property (Figure 2). 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 present host organization is the 436th Airlift Wing.
Its mission is to provide global airlift capability, including transport of cargo, troops,
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 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 a few military bases at which hangars and runways are
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
*' ' a3^
Units into which the Base has been divided (Figure 3JI Area 6 is the largest of five
associated areas identified in the West Management Unit. The Area 6 region of
investigation extends approximately 8,400 feet from its northern most point near the
hardstand and Building 723 to its southern most point near the St. Jones River
(Figure 4). The area north of U.S. Highway 113 contains the industrialized portion
Target Area 1
ROD-2
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PORT
MAHON
POL ANNEX
DOVER
AIR FORCE
BASE
Delaware
VER
FAMILY
^.HOUSING
.ANNEX
113
MAPS PREPARED Bft
LOCATION OF
DOVER AIR FORCE BASE
DAMES & MOORE
Target Area 1
ROD-3
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BERGOLD FARM
PORT MAHON
FACILITY LOCATED
IN FLOOD-PRONE AREA
* Man Northtoil ol DAfB
DOVER TAMILY HOUSING ANNEX
Mol«: Aop»»lmtiV 1 Hh SmiHwnl ol WFB
— — USAF PROPERTY LINE
IMPS PREPARED
DAMES & MOORE
FIGURE 2
BASE BOUNDARIES
DOVER AIR FORCE
BASE
Modified from
ENgineering Science. 1983
Original Base Mop Produced by HAZWRAP.
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Region
Investigation
FIGURE 4
AREA 6
REGION OF
INVESTIGATION
I
!
*
5
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of the Area 6 region of investigation. The location addressed in this ROD falls within
this industrialized portion of Area 6.
DAFB is relatively flat, with elevations ranging from approximately 10 to 30
feet above mean sea level (MSL). The ground surface is covered almost entirely by
buildings, concrete, and asphalt. Surface water runoff throughout the industrialized
portion of Area 6 is controlled by an extensive storm drainage system. The storm
drains direct most runoff to either Pipe Elm Branch or the golf course tributary to the
St Jones River.
The Columbia Formation is the shallowest water-bearing unit and holds the
water table aquifer. The Columbia Formation typically consists of fine to coarse
grained sand with varying amounts of silt, clay, and gravel. Discontinuous lenses of
gravel, silt and clay are also common. Generally, the upper portion of the Columbia
Formation is finer grained and contains more silt and clay lenses than the deeper
portion. The water table is generally encountered at a depth of 10 to 12 feet below
ground surface (bgs) in the northern portion of Area 6 and shallows to within a few
feet of the surface in the Base housing area near the St. Jones River. The
groundwater elevation or potentiometric surface of both the shallow and deep zones
of the Columbia Aquifer range from approximately 13.5 feet MSL in the northern
portion to less than 3 feet MSL near the St. Jones River. The thickness of the
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 silt and
clay, with thin laminations of silt and fine sand. This upper silt and clay unit ranges.
in thickness from 15 to 21 feet in the northern portion of Area 6. The hydraulic
conductivity of this unit range from 6.83 x 10'3 to 1.53 x-19"3 ft/day (2.411^16'6 to 539
x 10"7 cm/sec), which are three to five orders of magnitude lower than the overlying
Columbia Formation. These significantly lower hydraulic conductivities form a barrier
to the vertical migration of constituents identified in the Columbia Aquifer.
Underlying this confining unit is the upper sand unit of the Calvert Formation or the
Target Area 1
ROD-7
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Frederica Aquifer. This aquifer averages 22 feet in thickness in the vicinity of DAFB.
No constituents of concern were identified in the three Frederica monitoring wells
installed in Area 6. Additionally, no production wells are installed the Frederica
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 were
identified in the Area 6 RI that may have contributed to the chlorinated solvent
contamination. These potential sources include some of the twelve IRP sites within
the Area 6 groundwater flow regime shown in Figure 4. Additionally, various shops
and hangars where solvents are used may also be sources. The shop activities where
solvent use is common include painting or paint stripping, aircraft and vehicle
maintenance, and plating or welding. The northern most point of chlorinated solvent
contamination is the aircraft maintenance area located north of Atlantic Street. The
chlorinated solvent plumes extend approximately 4,600 feet south into Base Housing.
The Area 6 RI identified four regions where shallow groundwater (i.e., the top
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 ng/L. These regions were inferred to be in
the vicinity of the source areas for the chlorinated solvent plumes that are present in
Area 6. The groundwater data suggested that primary source areas reside in the
vicinity of the following reference points, which were incorporated into areas for
remediation termed Target Areas:
. • Paint Washout Area (Site SS59) located along the eastern portion of the
open storage yard. (Target Area 1)
' j? •- .<*
• Civil Engineering (CE) Shops Area including Building 607 (Carpentry
Shop), Buildings 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)
• Building 719 housing the Jet Engine Repair Shop. (Target Area 3)
Target Area 1
ROD-8
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• 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. Each
Target Area incorporates one of the primary suspected source areas and the
significantly impacted portions of the shallow and deep groundwater plumes associated
with the respective source area. Plume maps of total chlorinated VOCs in shallow
and deep groundwater are shown in Figures 6 and 7, respectively. The Target Areas
are the regions of chlorinated solvent groundwater contamination that were evaluated
in the FFS.
TARGET AREA/SOURCE AREA CHARACTERISTICS
The following section describes the physical and chemical characteristics of
Target Area 1, which is addressed in this Record of Decision.
Target Area 1 originates at the Paint Washout Area (Site SS59) and extends
south approximately 800 feet between 8th and 9th Streets. Target Area 1 is elliptically
shaped and is approximately 5.2 acres in size. Target Area 1 adjoins Target Area 3
on its northern boundary. Expanded scale maps of the chlorinated solvent plumes
residing in the shallow and deep portions of the aquifer within Target Area 1 are
shown in Figures 8 and 9, respectively. The maximum concentration of total
chlorinated VOCs in Target Area 1 groundwater was found in the shallow Columbia
at a concentration of 16,042 pg/L in the presumed source location. Comparing the
concentrations of chlorinated VOCs in the shallow and deep portions of the Columbia
Aquifer, it is apparent that the constituents migrated downward through the Columbia
Aquifer where most of the plume expansion occurred.
SUMMARY OF SITE RISKS '' " •* .
The full Risk Assessment (RA) for Area 6 can be found in the final Area 6 RI
report dated July 1994. The purpose of the RA is to determine whether exposure to
site-related contaminants could adversely affect human health and the environment.
The focus of the baseline RA is on the possible human health and environmental
Target Area 1
ROD-9
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FIGURE 5
LOCATION OF
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UCCND:
IOA Monitoring W.ll/
™ Plciomcltr
CP-101
® Groundwotor Prob*
BDL Btlow 0«Ucllon UmM
.„„ TO<<>| Chlorlnol.d
'IOOX Vololll»t Contourt.
•cue i MEM - TOO ror
MAPS PREPARED BY:
DAMES & MOORE
FIGURE 6
TOTAL CHLORINATED
VOLATILES
SHALLOW COLUMBIA
Boat mop produced by WZORAP.
I
I
n
2
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HCURE 7
TOTAL CHLORINATED
VOLATILE*
DEEP COLUMBIA
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Legend:
IMPS PREPARED BT:
DAMES & MOORE
M nap produced by HA2WMP.
Target Area
Total Chlorinated
Solvent Concentration
(ug/L)
(Dashed where approximate)
FIGURE 8
TARGET AREA 1
SHALLOW COLUMBIA
TOTAL CHLORINATED
SOLVENTS
Target Area 1
ROD-13
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•CM£ 1 «CM • SCO MET
MAPS PREPARED BY:
DAMES & MOORE
Ordinal BOM mop product^ B/
Target Area
Total Chlorinated
Solvent Concentration
(ug/L)
(Dashed where approximate)
FIGURE 9
TARGET AREA 1
DEEP COLUMBIA
TOTAL CHLORINATED
SOLVENTS
Target Area 1
ROD-14
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effects that could occur under current or potential future use conditions in the event
that the contamination is not remediated. The risk is expressed as lifetime excess
cancer risk (LECR) for carcinogens, and hazard quotient (HQ) for noncarcinogens. For
example, an LECR of 1 x 10"6 represents one additional case of cancer in one million
exposed population, whereas a hazard quotient above one presents a likelihood 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. The workers'
exposure to groundwater and soil have been evaluated under a regular maintenance
scenario; a future construction scenario; and a hypothetical future groundwater use from
the Columbia Aquifer under a commercial/industrial scenario. Although a specific Target
Area 1 RA has not been performed, the risk calculated in the Area 6 Remedial
Investigation from the hypothetical future exposure to groundwater within Area 6 had an
LECR of 9 x 10"*, which exceeds the 1 x KT4 to 1 x 10"6 risk range used to evaluate the
need for remediation. In addition to the overall Area 6 risk, the Target Area 1
constituents of concern have been compared to the risk-based screening concentrations
(RBSCs) developed for the commercial/industrial scenario at DAFB to identify the
chlorinated solvents that present a risk-based concern.
The possibility exists for exposure of workers to hazardous substances in soil
during excavation activities. Source areas identified during excavation will require worker
protection as per health and safety protocols. All the workers performing excavation work
at DAFB will be health and safety trained for work at CERCLA 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 discharge
points within Area 6 between the Target Area and the-river. Presently, the 4rea 6 plume
is confined within the Base property and has not reached the St. Jones River.
The future use of groundwater from the Columbia Aquifer by Base personnel is
quite unlikely and hypothetical. This hypothetical future groundwater use assumes that
groundwater from the Columbia Aquifer will be used for drinking and showering purposes
by Base personnel under a commercial/industrial scenario. The RBSCs were compared
Target Area 1
ROD-15
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with the maximum detected concentrations of chlorinated solvents in Target Area 1
(Table 1). Concentrations of seven of the eight detected chlorinated solvents--1,2-
dichloroethane, 1,1-dichloroethene, 1,2-dichloroethene, perchloroethene, 1,1,1-
trichloroethane, trichloroethene, and vinyl chloride-in Target Area 1 exceeded their
corresponding RBSCs in groundwater. The concentration of the other detected compound,
1,1-dichloroethane, was below its RBSC.
Actual or threatened releases of hazardous substances from this Site, if not
addressed by the selected alternative or one of the other active measures considered, may
present a current or potential threat to public health, welfare, or the environment.
REMEDIAL ACTION OBJECTIVE
Within the groundwater in Target Area 1, the interim Remedial Action Objective
(RAO) is to reduce the concentration of each ethyl-based chlorinated volatile organic
compound (VOC) by 90 percent. The ethyl-based chlorinated VOCs include PCE, TCE,
1,1-DCE, 1,2-DCE, vinyl chloride, 1,1,1-trichloroethane, 1,1-dichloroethane, and 1,2-
dichloroethane. These VOCs are considered to be the most toxic and therefore the 90
percent reduction interim RAO is applied to each of these compounds individually rather
than to the aggregate concentration of all the chlorinated VOCs. For reasons of
consistency, the 90-percent reduction, model was based upon the RCRA Post-Closure
Permit (Reference No. DE8570024010, Permit No. HW05A05) for Site WP21 of DAFB,
which is a unit that adjoins Target Area 3 to the west.
The maximum concentrations of the detected chlorinated solvent compounds in
Target Area 1 are summarized in Table 2, along with the compound and Target Area
specific interim RAO. Table 2 also includes interim RAO concentrations for some select
compounds that have not yet been detected in the Target Area. These select compounds
"•' - «x
are chemical degradation products of some of the currently detected chlorinated solvent
constituents. Thus, reducing the concentration of detected compounds at the expense of
producing other chlorinated VOC degradation products will not itself be sufficient to
satisfy the interim RAO. Note that if a ten-fold reduction from the maximum
Target Area 1
ROD-16
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TABLE 1
Maximum Concentration Detected of Ethyl-Based Chlorinated Volatiles
in Target Area 1, and Corresponding Risk-Based Screening Concentrations
" Compound
1,1-Dichloroethane
1^2-Dichloroethane
1,1-Dichloroethene
1,2-Dichloroethene
Perchloroethene
1,1,1-Trichloroethane
Trichloroethenc
Vinyl chloride
Target Area 1
>fl»Timi?rn
Detected
540
70
1^00
7,300
710
5,700
1,600
180
RBSC
UOO
029
0.12
84
4
2,200
4
0.058
Concentrations reported in units of
RBSC - Risk-Based Screening Concentration for Commercial/Industrial scenario at Dover Air Force
Base. The RBSCs are based on a lifetime cancer risk of 1 x 10* or a hazard quotient of one,
whichever is lower.
Target Area 1
ROD-17
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TABLE 2
Maximum Concentration Detected of Ethyl-Based Chlorinated Volatiles
in Target Area 1, and Corresponding Compound and Target Area
Specific Interim Remedial Action Objectives
Compound
1,1-Dichloroethane
1^-Dichloroethane
1,1-Dichloroethene
1^-Dichloroethene
Perchloroethene
1,1,1-Trichloroethane
Trichloroethene
Vinyl chloride
Target Ami
Maximum
Detected
540
70
UOO
7300
710
5,700
1,600
180
Interim
RAO
54
7
150
730
71
570
160
18
Concentrations reported in units o
RAO - Remedial Action Objective
Target Area 1
ROD-18
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concentration detected of a compound is below that compound's MCL, the MCL is used
as the interim RAO.
The issues of final cleanup levels and attainment of ARARs will be addressed in
the Final Basewide Record of Decision. The remedial action selected for this ROD is only
part of the remedial action which will be selected in a Final Basewide ROD.
SUMMARY OF ALTERNATIVES
Engineering technologies applicable to remediating the contaminated media were
screened according to their effectiveness and implementability. Those technologies that
were determined to be most applicable were then developed into remedial alternatives.
The following remedial alternatives are numbered to correspond to the alternatives
described in the FFS report.
• Alternative 1-No Action.
• Alternative 2-Collection, Ex Situ Treatment, and Surface Water Discharge of
Groundwater; and Performance of Soil Vapor Extraction in Chlorinated
Solvent Source Areas if Necessary.
• Alternative 3--//I Situ Groundwater Treatment Using Air Sparging and Density-
Driven Convection Technologies Combined With Soil Vapor Extraction.
• Alternative 4—In Situ Bioremediation of Groundwater Utilizing Intrinsic
Bioremediation.
The four remedial alternatives that were evaluated in detail are described below.
In addition, the capital, annual operation and maintenance (O&M), and present worth costs
of each alternative are provided.
Alternative 1
.
Capital Cost
Annual O&M Cost
Present Worth
Target Area
i
$000
$000
$000
Target Area 1
ROD-19
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The no action alternative is evaluated in order to establish a baseline for
comparison against other alternatives. Under this alternative, no efforts are undertaken
to reduce the groundwater concentrations of chlorinated solvents in Target Area 1.
Alternative 2
•
Capital Cost
Annual O&M Cost
Present Worth
Target Area 1
$170,000
$32,000
$330,000^
(a)First year O&M cost. Refer to text
^Assumes 10 years of operation.
Alternative 2 consists of groundwater extraction, groundwater pretreatment for
metals, groundwater treatment using air stripping for removal of chlorinated solvents and
carbon adsorption for removal of residual contaminants, and surface water discharge of
treated groundwater; performance of soil vapor extraction (SVE) in the shallow chlorinated
solvent source areas if determined to be necessary during remedial design; and treatment
of the offgases from the air stripper and, if implemented, the SVE system.
A total of one extraction well is estimated to be installed in Target Area 1, for cost
estimating purposes only, to extract contaminated groundwater at a pumping rate of
approximately 10 gallons per minute. If this alternative is ultimately selected for this
interim response, then the exact number of wells and their placement will be determined
during the remedial design. Extracted groundwater will be pretreated for metals to reduce
the concentrations of iron and manganese. Metals pretreatment reduces the possibility of
iron and manganese fouling subsequent treatment systems as well as ensuring compliance
with surface water discharge standards for metals.
Pretreated groundwater will then be pumped to the top of a low profile, three-tray
air stripper that will transfer over 95 percent of the VOCs dissolved in the groundwater
to the air stream. The air stream containing the VOCs will then exit the air stripper unit
where it will be treated using carbon adsorption prior to release to the atmosphere.
Target Area 1
ROD-20
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Routine air sampling at a frequency determined during remedial design will be performed
to ensure compliance with air emission standards.
Treated groundwater exiting the air stripper will be pumped to a liquid phase
carbon adsorption unit to reduce the concentration of residual contaminants to levels that
comply with the surface water discharge standards prior to release to the golf course
tributary of the St. Jones River. Semi-annual water samples, assumed for cost estimating
purposes only, will be collected to ensure compliance with discharge standards. Actual
sampling frequency will be determined during the remedial design.
Vadose zone chlorinated solvent contamination is present in Target Area 1 in the
location where significant shallow groundwater contamination has been identified. To
address this potential source, performance of SVE in a limited sized area has been
included with this area. A total of two SVE wells are estimated to be sufficient to
remediate the source areas presumed to be present. Soil sources would be expected to be
remediated in less than 2 years with SVE treatment; 2 years of operation is assumed for
costing purposes. If SVE is implemented, vapor collected by the SVE system would be
treated for organic constituents by vapor phase carbon units prior to being released to the
atmosphere. The necessity of performing SVE will be determined during the remedial
design.
Groundwater monitoring will be performed to monitor the progress of groundwater
remediation. In addition, existing land use restrictions associated with the military
operation of DAFB will be enforced throughout the course of remediation to prevent
unauthorized extraction and use of the contaminated groundwater from the Columbia
Aquifer.
The time required to achieve the interim RAO is estimated to be in the range of 5
"i •„ . •**
to 10 years, provided no free phase solvents are present in the aquifer. If free phase
solvents are present, the time required to achieve the interim RAO may be extended to
30 years or more. The present worth cost of this alternative ($330,000) is calculated
based on an assumed 10 year operation.
Target Area 1
ROD-21
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Alternative 3
Capita] Cost
Annual O&M Cost
Present Worth*
Target Area 1
$440,000
$50,000(a>
STSO.OOO^
First year O&M cost. Refer to text.
^Assumes 6 years of operation.
Alternative 3 consists of the in situ treatment of groundwater using a combination
of air sparging (AS) and density-driven convection (DDC) technologies, combined with
SVE over the entire areas where in situ groundwater treatment is performed; and carbon
adsorption treatment of the offgases from the SVE system.
For in situ treatment at Target Area 1,31 SVE wells and 28 AS/DDC wells are
estimated to be required for cost estimating purposes only. If this alternative is ultimately
selected for this interim response, then the exact number of wells and their placement will
be determined during the remedial design. AS will be used in areas where soil is highly
permeable and free of clay. DDC will be used in areas where significant clay layers are
present. The SVE system operates in tandem with the AS/DDC system to capture volatile
contaminants stripped from the saturated zone. Vapor phase carbon adsorption treatment
units will be used to remove extracted VOCs from the air stream prior to release to
atmosphere. Entrained water will be separated by knockout pots and sent to liquid phase
carbon adsorption units to reduce contaminant concentration to levels acceptable for
discharge.
Groundwater monitoring will be performed to monitor the groundwatd5 remediation
progress and plume migration. In addition, existing land use restrictions associated with
die military operation of DAFB will be enforced throughout the course of remediation to
prevent unauthorized extraction and use of the contaminated groundwater from the
Columbia Aquifer.
Target Area 1
ROD-22
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The time required to achieve the interim RAO is estimated to be between 4 and
13 years, with 6 years being the estimate used for costing purposes. The present worth
cost is estimated to be $730,000. The remediation time estimates are based on removal
rate data from the AS/SVE pilot study performed at Site WP-21.
Alternative 4
Capital Cost
Annual O&M Cost
Present Worth
Target Area 1
$000
$30,000(a>
$50,000
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evaluating microbial activity and biotransformation rates. The RTDF study will determine
whether intrinsic bioremediation holds promise as a long-term remedy for the contaminants
present. Monitoring of the Target Area 1 groundwater plume will be conducted from an
estimated six monitoring wells for cost estimating purposes to allow the study and rate
measurement of the intrinsic bioremediation processes. The monitoring period will extend
until the final FS and ROD is completed, which is estimated to be within a period of
5 years for costing purposes.
The bioremediation process utilized is not expected to generate degradation
products that can migrate beyond the Base boundary. Groundwater monitoring will be
performed to monitor the groundwater remediation progress and downgradient water
quality to ensure that offbase plume migration does not occur. In addition, existing land
use restrictions associated with the military operation of DAFB will be enforced
throughout the course of remediation to prevent unauthorized extraction and use of the
contaminated groundwater from the Columbia Aquifer.
The time required to achieve the interim RAO will be evaluated during the RTDF
study. It is anticipated that this interim remedy will remain active until the final remedy
is selected, which for costing purposes is estimated to be 5 years.
EVALUATION OF ALTERNATIVES
The selected alternative for remediating the contamination in the Target Area is
Alternative 4 (bioremediation). Based on current information, this alternative provides the
best balance of trade-offs among the alternatives with respect to the nine criteria that are
required to be evaluated under CERCLA. This section profiles the performance of the
selected alternative against the nine criteria and explains how it compares to the other
alternatives under consideration.
'} ». •<*&
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.
Alternatives 1,2,3, and 4 are all considered to be protective of human health during their
Target Area 1
ROD-24
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period of implementation because of the existence of land use restrictions that prohibit the
unauthorized extraction or use of contaminated groundwater in the Target Areas, thereby
preventing human exposure.
Alternative 1 (no action) is not considered effective because no provisions are made
to monitor the Target Area plume to evaluate compliance with the interim RAO.
Alternatives 2 (pump and treat), 3 (air sparging), and 4 (bioremediation) will all meet the
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 constituents to
exceed their federal Maximum Contaminant Levels (MCLs). MCLs, as provided for in
CERCLA § 121 (d)(2)(A)(ii), are relevant and appropriate requirements for any final
actions expected to be taken as a result of the Base-wide investigation.
Offsite contaminant migration, even for interim actions, requires that a number of
other ARARs be considered. The principal ARARs that pertain to the offsite movement
of contaminants are the Delaware regulations implementing the Federal Clean Air Act and
Clean Water Act. These regulations are the Delaware Regulations Governing the Control
of Air Pollution (DRGCAP 1 through 3, 21 and 24), the Delaware Water Pollution
Control Regulations (DWPCR1 through 6), the Delaware Industrial Waste Effluent
Limitations (DWPCR 8), and .the Delaware Surface Water Quality Standard (DSWQS 1
through 9, 11 and 12). The above referenced regulations regarding emissions of volatile
organic compounds to the atmosphere will be complied with in Alternatives 2 and 3 to
ensure that acceptable levels of emissions are met. Alternative 2 will require discharge
to surface water. The above referenced regulations regarding surface water discharge
define limits of acceptable chemical concentrations for wastewater, and attainment of these
limits will be a requirement for this alternative. For Alternative 4, there will be no offsite
migration or releases of contaminants. Alternatives 2 and 3 both meet all previously
identified regulations that pertain to the offsite movement of contaminants.
Target Area 1
ROD-25
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Long-Term Effectiveness and Permanence
The long-term effectiveness and permanence criterion primarily considers the
magnitude of residual risk that would remain after the implementation of an alternative,
and the adequacy and reliability of the controls instituted. All of the alternatives provide
for the long-term protection of human health through the existing land use restrictions.
However, reliance upon land use restrictions is not considered a permanent remedy.
Under Alternative 1 (no action), the chlorinated solvent contamination in
groundwater will not be monitored. Therefore, the adequacy and reliability of this
alternative cannot be established.
Alternatives 2 (pump and treat), 3 (air sparging), and 4 (bioremediation) will all
result in significant reductions of chlorinated solvent concentrations in the Target Area.
If any one of these treatment alternatives is selected, that system will be operated until the
interim RAO is achieved. Hence, no more than 10 percent of the maximum observed
concentration of each ethyl-based chlorinated solvent will remain in the Target Area. The
magnitude of residual contamination remaining in the Target Area is a function of the time
the treatment alternative is operated or allowed to continue. Continued operation of the
treatment system beyond the point at which the interim RAO is reached may allow further
reductions in contaminant levels to be achieved. Performance of the interim remedy and
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 implementation
of Alternative 1. The three action alternatives include components which are capable of
significantly reducing the toxicity of groundwater in the Target Area. ^
The groundwater extraction system proposed under Alternative 2 will establish
hydraulic control over the plume, thereby limiting the mobility of contaminants away from
the Target Area. The air sparging in situ treatment technology included in Alternative 3
operates by increasing the mobility of contaminants. This increased mobility may result
Target Area 1
ROD-26
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in some spreading of contamination beyond the effective zones of these alternatives during
the course of contaminant removal, however, the overall volume of the contaminants will
be reduced. The bioremediation technology proposed under Alternative 4 will have no
impact on contaminant mobility. The toxicity profile of the groundwater may shift
somewhat during the biodegradation process, as vinyl chloride is generated during the
degradation of the more chlorinated ethyl-based compounds. However, because little vinyl
chloride has been detected in the groundwater thus far, the evidence suggests that vinyl
chloride is rapidly degraded to carbon dioxide, water, and chloride ion under the aerobic
conditions found downgradient of the Target Areas.
Short-Term Effectiveness
Alternative 1 (no action) includes no remedial actions. Therefore, there will be no
short-term impacts on community or worker health or the environment from construction
activities. However, because Alternative 1 will not monitor compliance with the interim
RAOs established for this project, it is considered to be ineffective.
Alternatives 2 (pump and treat), 3 (air sparging), and 4 (bioremediation) will all
be effective in reducing groundwater contaminant concentrations in the Target Area.
None of these alternatives are expected to have significant impacts on worker or public
health or the environment. Alternative 2 is estimated to be capable of meeting the interim
RAO within a 5 to 10 year time frame. However, although not believed present, isolated
pockets of DNAPLs in the aquifer could cause this time frame to increase to 30 years or
more.
The presence of DNAPLs will also affect the length of time required to achieve the
interim RAO under Alternative 3, though to a lesser extent than will their presence on
Alternative 2. There are two reasons for this. First, there would be many more air
sparging/density-driven convection wells under Alternatives than there would be
extraction wells under Alternative 2. Thus, the chance of locating a remediation well near
a pocket of free product is much greater under Alternative 3. Secondly, the in situ
remediation is a more aggressive remediation process than pump and treat. High mass
transfer rates from water to air would be achieved with the physical in situ treatment
Target Area 1
ROD-27
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technologies lowering the concentration of solvents within the plume. Lowered
groundwater concentrations would increase the driving force for solubilization of free
product in order to maintain equilibrium. The time required to meet the interim RAO
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 Target
Area 1, though SO years or more may be required. As with the other action alternatives,
these time frames may be extended if DNAPLs are present. A DNAPL would present a
continuing source of contaminants to the aquifer as the DNAPL constituents were
solubilized in the groundwater. This transfer of constituents from free phase to dissolved
phase would occur through the physical processes of desorption and liquid-liquid
partitioning. These equilibrium-driven processes typically occur slowly because of the
relatively low surface area of DNAPL in contact with the groundwater in comparison to
DNAPL volume. The solubilization rate of DNAPLs would likely be slower than the rate
of-degradation of the dissolved constituents. Thus, the solubilization of DNAPLs would
likely be the rate-limiting step.
Implementability
Three main factors are considered under this criterion: technical feasibility,
administrative feasibility, and availability of services and materials. All four alternatives
are administratively feasible and the required services and materials are readily available.
Hence, the comparison will focus on the technical feasibility of the alternatives.
Alternative 1 (no action) and Alternative 4 (bioremediation) have no technical
feasibility considerations. Alternatives 2 (pump and treat) and 3 (air sparging) have
technical feasibility concerns associated with them. These concerns are related to the
highly developed character of the Target Area and the numerous space constraints that are
"^ ".jw . ifl3fe
present. The Alternative 2 system includes only 5 groundwater extraction and SVE wells
and a limited piping network. Alternative 3 consists of 59 air sparge, DDC, SVE wells,
plus expansive piping and numerous treatment stations. Overall, Alternative 4 is judged
to be the most easily implemented action alternative.
Target Area 1
ROD-28
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Cost
No direct costs are associated with the implementation of Alternative 1 (no action)
nor with Alternative 4 (bioremediadon). The capital cost of Alternative 2 (pump and
treat) is $170,000 and the capital cost of Alternative 3 (air sparging) is $440,000.
The O&M cost of Alternative 2 will initially be $32,000 per year, but will drop to
$20,000 per year after 2 years of operation when SVE operations are discontinued. The
O&M cost of Alternative 3 will be almost $50,000 the first year, but will drop several
thousand dollars per year thereafter as the carbon consumption rate associated with the
SVE system's offgas treatment units decreases. The O&M costs of Alternative 4 will be
approximately $30,000 per year for monitoring intrinsic bioremediation in Target Area 1.
However, the first 2 years of monitoring will be performed by the RTDF as part of their
intrinsic bioremediation pilot study at no cost to the government.
The present worth cost of the alternatives will depend upon the time they are
operated. The present worth costs of Alternative 2 under operating scenarios of 5, 10,
and 30 years are $270,000, $330,000, and $440,000, respectively. The present worth
costs of Alternative 3 under operating scenarios of 4, 6, and 13 years, respectively are
$690,000, $730,000, and $940,000. The present worth net cost to the government of
Alternative 4 assuming 3 years of monitoring in Target Area 1 following 2 years of
assumed monitoring by the RTDF is $50,000. Thus, Alternative 4 has the lowest present
worth cost
State Acceptance
The State of Delaware concurs with the selected interim remedy for Target Area 1.
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 the
proposed remedy was noted.
Target Area 1
ROD-29
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CONCLUSION
Based on the evaluation of the alternatives using the nine criteria, Alternative 4
(bioremediation) is preferred. Alternative 4 is protective of human health and the
environment, complies with all ARARs, represents a permanent remedy that reduces
groundwater toxicity, provides the greatest ease of implementation, and is the most cost
effective action alternative.
The selected alternative utilizes permanent solutions and alternative treatment
technologies to the maximum extent practicable. This interim action will not negatively
impact the ability to implement a final action, if it is required. The final remedy will be
selected in the final Base-wide ROD.
Actual or threatened releases of hazardous substances from this Site, if not
addressed by the selected alternative, may present a current or potential threat to public
health, welfare, or the environment.
Target Area 1
ROD-30
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GLOSSARY AND ACRONYMS
Air Sparging - Underground injection of air into saturated soil and groundwater, resulting
in the in situ air stripping of volatile constituents.
Air Stripping - Transfer of volatile constituents from water to air by induced contact
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 forth by
federal and state statute and regulations that must be considered in the evaluation
of remedial alternatives.
Biodegradation - The breakdown of organic constituents by microorganisms into less
complex compounds.
Capital Cost - Cost incurred for the construction and startup of a facility.
CERCLA • Comprehensive Environmental Response, Compensation, and Liability Act.
Federal law creating the Superfund program.
Dense Non-Aqueous Phase Liquid (DNAPL) - An organic liquid with a low water
solubility and a density greater than that of water. DNAPLs-retain their physical
and chemical properties when in contact with water and tend to sink in an aquifer
when released to groundwater.
Density-Driven Convection - Modified in-ground air sparging system which induces a
flow pattern in the vicinity of the sparging well.
EPA - U.S. Environmental Protection Agency.
Ex Situ - Performed above ground. ,t „
FS - Feasibility Study. Study undertaken to evaluate remedial alternatives.
FFS - Focused Feasibility Study.
Groundwater - Subsurface water residing in a zone of saturation.
Target Area 1
ROD-31
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GLOSSARY AND ACRONYMS (cont'd)
HO - Hazaid Quotient. An indicator of the noncarcinogenic health risk associated with
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 percolation of
surface water to groundwater.
LECR - Lifetime Excess Cancer Risk. The probability of the carcinogenic health risk
associated with exposure to the chemicals of concern.
O&M Cost - Annual cost incurred for operation and maintenance of a facility.
Maximum Contaminant T^vpfe flyfC!^) - Federal drinking water standards.
Plume - A recognizable distribution of constituents in groundwater.
Potentiometric Surface - An imaginary surface that represents the static head of
groundwater and is defined by the level to which water will rise.
RBSC - Risk Based Screening Concentration. A chemical-specific concentration used to
preliminarily assess whether exposure to a chemical poses a potential health risk.
RAO - Remedial Action Objective. Cleanup goal established for the remediation.
RCRA - Resource Conservation and Recovery Act.
ROD - Record of Decision. A legal document issued by the lead governmental 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 to volatilize and
withdraw VOCs from subsurface soil residing above the groundwater table.
Vadose Zoos - Soil zone above the water table.
VOCs - Volatile organic compounds.
Target Area 1
ROD-32
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