Superfund Record of Decision Dover Air Force Base Landfill D-10 Golfcourse Site LF-18 Area 9 South Management Unit Dover DE


                                    EPA/ROD/R03-96/236
                                    1996
EPA Superfund
     Record of Decision:
     DOVER AIR FORCE BASE
     EPA ID: DE8570024010
     OU07
     DOVER, DE
     09/24/1996

-------
RECORD OF DECISION
DECLARATION OF THE SELECTED REMEDY

Site Name and Location

Landfill D-10 Golfcourse (Site LF18), Area 9, South Management Unit, Dover
Air Force Base, Kent Country, Delaware.

Statement of Basis and Purpose

This record of decision (ROD) presents the selected remedial action for Site LF18,
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.
The U.S. Air Force, the lead agency, as he owner/operator of the base, prepared this decision
based on the Administrative Record for the site. The U.S. Environmental Protection Agency
(EPA) Region III and the Delaware Department of Natural Resources and Environmental
Control (DNREC) provided support.

The state of Delaware and the U.S. Environmental Protection Agency concur with the
selected remedy. The Information Repository for the Administrative Record contains the
information supporting this remedial action decision and is at the Dover Public Library, Dover,
Delaware.

Assessment of the Site

Dover AFB identified free waste oil and residual soil contamination in an area
immediately downgradient of the former LF18 landfill. They developed a ROD in 1992, along
with WP14, to address the free phase waste. Based on additional data developed, this ROD
supersedes the 1992 ROD for LF18. Dover AFB will address WP14 in a future decision
document. Hazardous substances detected in the oil include fuel constituents, chlorinated
solvents, and pesticides. The base identified the oil-impacted soil as a source are for
hazardous constituents being leached to groundwater. This area of oil-impacted soil,
downgradient of the landfill, is the area addressed in this ROD.

There is a risk assessment for Site LF18, but not specifically for the portion of LF18
addressed in this ROD. However, the total lifetime excess cancer risks (LECRs) associated with
exposure to LF18 groundwater as a whole under hypothetical commercial/industrial and
residential use scenarios are 7 x 10-6 and 4 x 10-5, respectively. The total LECRs associated
with exposure to soil under future hypothetical commercial/industrial and residential use
scenarios are 1 x 10-5 and 2 x 10-4, respectively. Since these values are within or above the 1
x 10-4 to 1 x 10-6 range, it is appropriate to consider risk reducing action at the site.

Actual or threatened releases of hazardous substances from this site, of not addressed by
implementing the response action selected in this ROD, may present a current or potential threat
to public health, welfare, or the environment.

Description of Selected Remedy

The selected remedy consists of the excavation of soil contaminated with waste fuel
constituents, chlorinated solvents, and pesticides; and the off site treatment of the excavated
soil by recycling as an asphalt aggregate. Final evaluation of the performance of this interim
remedy, remediation of contaminated groundwater beneath the site, and compliance with applicable
or relevant and appropriate requirements will occur in the final basewide ROD.

Statutory Determinations

The selected remedial action satisfies the remedial selection process requirements of
CERCLA and the NCP. As required under CERCLA, the selected remedy provides the best
balance of trade-offs among the nine evaluation criteria. The selected action provides
protection of human health and the environment, complies with federal and state requirements
that are legally applicable or relevant and appropriate to the action, and is cost effective.

-------
This remedy utilizes permanent solutions and alternative treatment technology to the maximum
extent
practicable, and satisfies the statutory preference for remedies that employ treatment which
reduce toxicity, mobility, or volume as a principal element.


JOHN B. SAMS, JR.    Date
Lieutenant General, USAF
Air Mobility Command
Chairperson, Environmental Protection Agency
 Protection Committee
THOMAS C. VOLTAGGIO        Date
Hazardous Waste Management
Division Director

Region III

-------
RECORD OF DECISION
SITE LF18
SOUTH MANAGEMENT UNIT
DOVER AIR FORCE BASE, DOVER, DELAWARE

August 1996
DECISION SUMMARY FOR THE RECORD OF DECISION
SITE LF18, SOUTH MANAGEMENT UNIT
DOVER AIR FORCE BASE
INTRODUCTION

Dover Air Force Base (DAFB) recently completed an Engineering Evaluation and Cost Analysis
(EECA) that addressed an area of contaminated soil in the immediate vicinity of the Landfill
D-10 Golfcourse (LF18) that is located along its southern boundary at DAFB, Delaware. LF18 is a
former landfill in the South Management Unit, and is located at the Base golf course.

The EECA was undertaken as part of the U.S. Air Force's (USAF) Installation Restoration
Program (IRP). The basis for the EECA was the draft South Management Unit Remedial
Investigation (RI) report dated July 1995, which characterized contamination and evaluated
potential risks to public health and the environment. This was supplemented by a subseguent
soil investigation conducted by the U.S. Army Corps of Engineers (USAGE), Kansas City District
in August 1995, and
by EECA fields activities in October and November 1995.

Findings from the RI indicated that free phase was present in monitoring well situated in
the southern portion LF18 downgradient of the former landfill. The free phase was analyzed and
found to contain volatile fuel constituents, chlorinated solvents, semivolatile organic
compounds, pesticides, and possibly polychlorinated biphenyls (PCBs). Distinct groundwater
plumes of the volatile fuel constituents-benzene, toluene, ethylbenzene, and xylene
(BTEX)--originate from this source area. Other detected groundwater constituents that appear to
be contributed by this source are methylene chloride and several pesticides including 4,4'-DDE,
alpha-BHC, beta-BHC, gamma-BHC, and delta-BHC. The USAGE, Kansas City District and the EECA
investigations focused on delineating the extent of the source area; remediation of the source
area was the subject of the EECA. Remediation of other source areas in the vicinity of LF18 and
groundwater contamination will be addressed in the South Management Unit Feasibility Study.

This Record of Decision (ROD) addresses the petroleum-based source of potentially
hazardous constituents present in LF18 soil that was evaluated in the EECA. This ROD summarizes
the EECA, 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 remedy selected
in this ROD.

As an aid to the reader, a glossary of the technical terms used in this Proposed Plan is
provided at the end of the summary.

PUBLIC PARTICIPATION

The Proposed Plan for this site was issued on June 20, 1996. The public comment period on
the Plan was open through July 22, 1996. Documents comprising the information repository for
the Administrative Record for the site are available at the Dover Public Library. No public
comments were received.

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, eguipment, and
relief supplies.

DAFB is the U.S. East Coast home terminal for the C-5 Galaxy aircraft. The Base also
serves as the joint services port mortuary, designed to accept casualties in the event of war.
The C-5 Galaxy, a cargo transport plane, is the largest aircraft in the USAF, and DAFB is one of
a few military bases at which hangers and runways are designed to accommodate these planes.

The portion of DAFB addressed in this ROD—IRP site LF18—is located within Area 9 of the
South Management Unit. The South Management Unit is one of four Management Units into which the
Base has been divided (Figure 3). Area 9--one of three associated areas identified in the South
Management Unit—extends from approximately US Route 113 to the Golf Course Tributary and the
Base boundary (Figure 4). LF18 is the site of a former landfill that underlies the DAFB golf
course and is next to the Base boundary along the southern edge of Area 9.

DAFB is relatively flat, with elevations ranging from approximately 10 to 30 feet above
mean sea level (msl) . The ground surface at the golf course is covered almost entirely by
carefully maintained grass turf. Surface water runoff at the Golf Course is directed to a small
creek on the south side of the site which discharges to the golf course tributary and
subseguently to the St. Jones River.

The Columbia Formation is the shallowest water-bearing unit and holds the water table
aguifer. Deeper aguifers are protected by the extensive upper clay of the Calvert Formation.
The upper portion of the Columbia Formation is finer grained and contains more silt and clay
lenses that the deeper portions. The deeper portion of the Columbia Formation typically
consists of fine to coarse grained sand with occasional lenses of fine to medium sand
discontinuous gravel lenses interpreted as channel lag deposits. The thickness of the Columbia
Formation at LF18 is
approximately 50 to 60 feet. The water table is generally encountered at a depth of 8 to 10
feet below ground surface (gbs) at LF18 and shallows to within a few feet of the surface near
the golf course tributary. The groundwater elevations of both the shallow and deep portions of
the Columbia Aguifer range from approximately 5 feet msl at LF18 to less than 3 feet msl near
the Golf Course tributary.

LF18 consists of a former landfill and the area immediately downgradient (south) of the
landfill. The landfill was used in the mid-1950s for the disposal of general refuse, drums of
waste solvents, and other shop wastes. The disposal area (40 by 600 feet) consisted of four
trenches that were reportedly filled with refuse to depths of 10 to 15 feet bgs. Information on
the exact locations of these trenches is not available. Based on interviews with personnel
familiar with site operations, the trenches were dug below the level of groundwater and
backfilled with waste material. When disposal activities ceased in 1959, the landfill was
covered with several feet of local soil and seeded with grass. The site was subseguently
converted to a portion of the DAFB golf course in 1960.

The area immediately downgradient of the landfill was also used for the disposal of waste
materials. The type of waste disposed of in this location was a substance having the appearance
of waste oil. Previous investigations in this area have identified the presence of soil
contamination and noted the presence of a free oil phase. This contaminated source area located
immediately downgradient of the landfill is the subject of this ROD (Figure 5).

The area downgradient of the landfill was studied during the Basewide RI because of the
known presence of free phase in MW07j. A sample of the free oil phase was collected and
analyzed for Target Compound List volatile organic, semivolatile organic, and pesticide/PCB
compounds, and Target Analyte List metals. The results of this analysis are presented in Table

-------
1.  Detected constituents included BTEX, chlorinated solvents, and several pesticides.
Groundwater samples were collected from wells and groundwater probe locations in and
downgradient of the area of the free oil phase.  The total concentrations of BTEX are plotted
and contoured in Figure 6.  This figure illustrates that elevated BTEX in groundwater approaches
the Base boundary.

       In August 1995 the USAGE, Kansas City District,  conducted and investigation at the
southern end of LF18 to help delineate the extent of free phase near MW07J.  This investigation
involved the use of the Site Characterization and Analysis Penetrometer System  (SCAPS) coupled
with a laser-induced fluorescence (LIF) device.  Figure 7 presents the SCAPS-LIF data, and
indicates the thickness of contaminated soils that registered a fluorescence intensity of
greater than 10,000
counts.  The presence of high fluorescence counts at and above the approximate depth of the
water table most likely indicates residual hydrocarbon saturation in the interval of groundwater
fluctuation.

-------
                          TABLE 1

       Constituents in Free Phase Sample from MW07J
                                         L(a)   V(b)
VOCs  (• g/kg)
Benzene                            1,400,000             J
Ethylbenzene                       1,800,000             J
Methylene Chloride                    50,000     BJ      J
Toluene                            3,100,000             J
Xylene  (total)                     6,200,000      E      J
SVOCs  (• g/kg)
2-Methylnaphthalene                  150,000
Acenaphthene                          16,000      J
Acenaphthylene                        20,000      J
Di-n-butyl phthalate                  19,000      J
Dibenzofuran                          24,000      J
Fluoranthene                          16,000      J
Fluorene                       49,000     J
Naphthalene                   530,000
Phenanthrene                          70,000      J
Pyrene                                18,000      J
Pesticides/PCBs  (• g/kg)
4,4'-DDD                        6,700    PCD     J
4,4'-DDE                           40    JP      J
Alpha-BHC                          62     P      J
Beta-BHC                        1,400     D
Chlordane-alpha                          97      P      J
Delta-BHC                      13,000    CD
Dieldrin                           45    JP      J
Endrin aldehyde                          97     JP      J
Endrin ketone                             7.1   JP      J
Gamma-BHC                          28     J
PCB 1260                       15,000    YD

-------
                     TABLE 1  (cont'd)

                                         L(a)   V(b)
Metals  (• g/L)
Aluminum                         31.6     B
Arsenic                                  1.7      B
Barium                                 36.8      B
Calcium                                64.8      B
Copper                                   2.6      B
Iron                             26.4
Lead                             65.9
Magnesium                        24.8     B
Sodium                                 112               B
Vanadium                          1.1     B
Zinc                              2.7     B

(a)  Laboratory Flags:
ORGANICS
       B-  Analyte found in associated blank as well as in the sample.
       C-  Identification confirmed by gas chromatography/mass spectrometry
           (GC/MS).
       D-  Compound identified in the analysis at a secondary dilution factor.
       J-  Value is estimated.
       P-  Greater than 25% difference in analyte concentration between
           primary and confirmation analysis.  Lower concentration assorted.
       Y-  Analyte was not identified during confirmatory GC/MS analysis.
INORGANICS
       B-  Reported value is greater than the instrument detection limit but
           less than the contract-reguired detection limit.

(b)    Validation Flags:
       J-  Analyte was positively identified; the associated numerical value is
           the approximate concentration.

-------
The SCAPS study suggests that petroleum-contaminated soil is present in an area directly
downgradient of the landfill, and that potential exists for free phase to be present over a
greater area than just the localized vicinity of MW07J. Hence, an EECA investigation was
designed to evaluate the presence of contamination in subsurface soil including petroleum; to
determine the presence or absence of free phase at the southern end of LF18; and to determine if
the area of potential free phase coincides with the former waste trenches. The solubility of
the hazardous constituents present are much higher in petroleum than they are in water, and
hence
petroleum can be used as an indicator of the potential presence of these constituents.

Soil samples collected within the delineated SCAPS area during the EECA study contained
elevated total petroleum hydrocarbons (TPH)-diesel range organics (DRO). Hand auger samples
indicated that the edge of the LF18 trenches are northeast of the petroleum-contaminated soil
and do not coincide with this area of interest.

Six monitoring wells were installed as part of the EECA investigation in areas where the
SCAPS data suggested the existence of residual saturation. Although the newly installed wells
at LF18 indicate that the areal extent of free phase is more limited than that interpreted from
the SCAPS data, the data sets support each other with respect to delineation of contaminated
soil. Based on the absence of free phase in the EECA wells, which is more definitive that the
screening-level SCAPS data, the high SCAPS-LIF levels (>10,000 counts) most likely represent
residual soil contamination. Residual soil contamination results from free phase coming into
contact with and adsorbing onto soil particles. Residual contamination is not referred to as
free phase because it does not flow under gravitational influences.

Figure 8 illustrates the minimum and maximum areas of contaminated soil based on the SCAPS
and EECA data. The in-place volume of contaminated soil is estimated to be 1,170 cubic yards at
a minimum. This estimate assumes that the average thickness of contaminated soil within a
6,300-sguare-foot area is 5 feet. The depth at which contaminated soil is first encountered
varies from 5 to 8 feet, and the contamination extends to the depth of the seasonal low water
table elevation. The estimated maximum volume is approximately 2,340 cubic yards.

SUMMARY OF SITE RISKS

The purpose of the Risk Assessment (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 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 index (HI) 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 index above one presents a likelihood of
noncarcinogenic health effects in exposed populations.

The EECA investigation focused on the collection of data to determine the extent of free
phase present in the vicinity of MW07J and to delineate the extent of contaminant-impacted soil.
The type of chemical data collected during the EECA investigation, TPH (DRO), is not useful from
a risk assessment standpoint because a TPH (DRO) result represents the concentration of an
amalgam of compounds for which the toxicity is unknown. Nevertheless, some qualitative
observations regarding the portion of LF18 assessed during the EECA investigation can be made.
The contaminated soil contributes volatile organic and pesticide constituents to groundwater,
including BTEX constituents. The BTEX concentrations in shallow groundwater are illustrated in
Figure 6. The detected concentrations of all four BTEX constituents in groundwater exceeded
their respective MCLs in at least one of the samples collected during the RI in the vicinity of
the soil source area. The soil source area is located in close proximity to the Base boundary
and a groundwater discharge point to the golf course tributary. Hence, the potential exists for
the future off-Base migration of constituents with groundwater.

The baseline RA, performed as as part of the Basewide RI, considered hypothetical future
groundwater use from the Columbia Aguifer under commercial/industrial and residential scenarios.
Similar scenarios were used for current and future soil exposure.

-------
The total lifetime excess cancer risks (LECRs) for the hypothetical commercial/industrial
and residential exposures to groundwater are 7E-06 and 4E-05, respectively. The cancer risk from
future industrial exposure to groundwater is primarily attributable to the pesticide beta-BHC
and trichloroethene. The groundwater at DAFB is not currently used and the risk numbers
represent a hypothetical future groundwater use scenario. The total LECRs for current and
future industrial exposure to soil are 8E-07 and IE-OS, respectively. The risk from future
industrial exposure to
soil is primarily attributable to benzo(a)pyrene. The total LECR for a future residential
exposure to soil is 2E-04. Benzo(a)pyrene, benzo(b)fluoranthene, and benzo(a)anthracene are the
primary contributors to soil cancer risk.

REMEDIAL ACTION OBJECTIVE

The remedial action objective (RAO) is the reduction of contaminant concentrations in
soils to the Delaware's Department of Natural Resources and Environmental Control (DNREC)
regulatory levels of 1,000 mg/kg TPH and 10 mg/kg total BTEX. DNREC's regulatory levels are
considered applicable or relevant and appropriate requirements (ARARs) for this site. These
levels are not strictly "applicable" because they originate from DNREC's Underground Storage
Tank (UST) guidance and there is no UST at LF18. However, they are still "relevant and
appropriate" as the site is a petroleum source. Remediation of the contaminated soils to these
levels will correspondingly significantly reduce residual concentrations of chlorinated solvents
and pesticides/PCBs associated with the petroleum.

Concentrations of TPH (DRO) detected in this area ranged up to 9,600 mg/kg. Reduction of
TPH and BTEX concentrations to the 1,100 mg/kg and 10 mg/kg levels, respectively, will
substantially reduce the leaching of constituents to groundwater. Elimination of this source
area is important because BTEX and other constituents are being transported by groundwater in
the general direction of the Base boundary and toward groundwater discharge points to surface
water. Remediation of the source area will significantly reduce further leaching to
groundwater.

The remedial action is scheduled to be implemented during the winter months of 1996-1997.
LF18 is located within a frequently used recreation area that will be affected by remedial
construction activities. Performance of the remedial action during the winter months when the
golf course is less frequently used will minimize disruptions to Base personnel.

The remediation should be completed within a period of 5 years or less. Until remediation
is completed, hazardous constituents will be available in the soil to leach into groundwater.
Five years is considered a reasonable upper boundary to allow remedial activities to be
completed. Completion of remedial activities in less than this 5-year maximum is considered
desirable.

SUMMARY OF ALTERNATIVES

Two of the most common engineering technologies applicable to remediating contaminated
soil were evaluated in the EECA--excavation and removal, and bioventing. These two
technologies, along with no action, formed the basis for the alternatives developed in the EECA
as identified below:

Alternative l--No Action.
Alternative 2--Excavation of TPH-Contaminated Soil and Offsite Treatment.
Alternative 3--Bioventing.

These three remedial alternatives are described below. In addition, the capital,
annual operation and maintenance (O&M), and present worth costs of each
alternative are provided.

Alternative 1

LF18
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 alternative. Under this alternative, no efforts are
undertaken to reduce the soil concentrations of TPH or BTEX at LF18.

Alternative 2

LF18
Capital Cost $203,000*
Annual O&M Cost $000
Present Worth $203,000*

*Assumes minimum area of excavation and non-hazardous
soil disposal.

Alternative 2 consists of the physical removal of the TPH and BTEX-contaminated soils
delineated during the EECA investigation through excavation, offsite treatment, and reuse. The
area to be excavated encompasses an estimated minimum of 6,300 sguare feet; but may encompass an
estimated maximum of 12,600 sguare feet. The excavation depth will extend to the seasonal low
depth of the water table, which is approximately 19 feet bgs. The EECA and SCAPS investigation
data indicates that contaminated soils are first encountered at an approximate depth of 5 feet
bgs. The overlying layer of uncontaminated soil eguals approximately 1,170 in-place cubic
yards, and the zone of contaminated soil approximately eguals another 1,170 in-place cubic
yards.

The excavation will be performed in a manner that allows uncontaminated soils to be
segregated from contaminated soils. Uncontaminated soils will be stockpiled on the site and
saved for use as backfill. Contaminated soils will be excavated and placed either in dump
trucks or rolloff boxes that can be loaded onto flatbed trucks. Existing data indicates that
the soils to be excavated are nonhazardous. This is based on the Toxicity Characteristic
Leaching Procedure (TCLP) analysis that was conducted on a soil sample during the EECA field
investigation. However, samples from the excavated contaminated soil will be analyzed using the
TCLP to determine whether any unanticipated hazardous characteristics are exhibited.
Confirmatory soil samples will be collected from the bottom and walls of the excavation to
confirm the complete compliance with the RAO. These samples will be analyzed for TPH-gasoline
range organics (GRO), TPH (DRO), and BTEX.

Because the excavation must extend down to the seasonal low depth of the water table, it
is likely that the last 1 to 2 feet of excavation depth will be below the water table. This is
because of the anticipated difficulty of predicting and scheduling the precise time to perform
the remediation so that it coincides with the seasonal water table low. For estimating
purposes, 2,000 gallons of groundwater are assumed to be dewatered from the minimum-sized
excavation and 4,000 gallons from the maximum possible excavation. Removed groundwater will be
tested for RCRA
characteristics and transported to an appropriate offsite treatment, storage, and disposal (TSD)
facility for treatment in conformance with all state and Federal regulations.

The method of treatment and disposal for the contaminated soil is dependent upon the
chemical characteristics of the contaminants. However as indicated above, the TCLP analysis
conducted on a soil sample during the EECA investigation confirmed that the soil appears to be
nonhazardous. If this nonhazardous status of the soil is confirmed during remediation as
expected, the soil will be recycled as an aggregate/petroleum feed in a local asphalt processing
plant. In the asphalt recycling process, volatile organics are desorbed and combusted while
nonvolatile constituents are fixed into the asphalt mix. This is the anticipated method of
treatment for the LF18 soils.

A minimal potential exists that hazardous constituents may be encountered in the excavated
soils due to the heterogeneous nature of landfill disposal. This is considered a low
probability because the removal site is not directly in the fill and testing has not detected
them previously. However, in the unlikely event the excavated soil is found to exhibit
hazardous characteristics, the soil will be sent to a RCRA-permitted TSD facility where it will
likely be landfilled. If hazardous waste is sent out of Delaware for disposal, appropriate
acknowledgement and approval will be obtained from the receiving state prior to the transfer.

-------
The uncontaminated soil that is excavated and stockpiled to allow access to the
contaminated soil will be replaced in the excavation and compacted. Fill material will be
brought from an offsite borrow source to complete closure of the excavation. The area will then
be regraded and landscaped to restore the golf course.

Implementation of this alternative will be between the months of November and February
when the golf course is infreguently used. Re-sodding would occur in the following spring. The
actual excavation work can be performed in a matter of weeks. The present worth costs estimated
for Alternative 2 range between $203,000 and $363,000 depending on the volume of soil removed,
assuming nonhazardous soil recycling. In the unanticipated event that the soil is found to
exhibit hazardous characteristics, the present worth costs range between $437,000 and $831,000
depending on volume for disposal at a RCRA-permitted landfill.

Alternative 3
LF18
Capital Cost $128,000
Annual O&M Cost $79,000(a)
Present Worth $207,000(b)

(a)First year O&M cost. Refer to text.
(b)Assumes 5 years of operation.
Alternative 3 consists of the in situ treatment of soil using a bioventing technology.
Bioventing is a process which delivers oxygen to contaminated vadose zone soils in order to
stimulate the aerobic in situ biodegradation of contaminants. Bioventing eguipment uses a
relatively low air flow rate that is intended to minimize volatilization and transport of
constituents, while providing sufficient guantities of oxygen to the aerobic bacteria present in
the soil to stimulate contaminant biodegradation. The natural biodegradation of petroleum
contaminants is freguently limited by the available of oxygen in the contaminated zone.
Bioventing provides a mechanism for replenishing this rate-limiting chemical.

Bioventing has produced encouraging results when the degradation of light, aromatic
hydrocarbon compounds such as BTEX is examined. Results are much less positive when examining
the degradation of heavier, more complex compounds. Because much of the petroleum contamination
found at the southern portion of LF18 is comprised of DRO compounds containing from 10 to 28
carbon atoms per molecule, there is some concern as to the effectiveness of bioventing when used
for this application.

Based on the air permeability test conducted as part of the EECA investigation, the radius
of influence of the bioventing wells will be approximately 30 feet, with estimates of air
permeability ranging from 84 to 149 darcys. The horizontal wells will be placed with a spacing
of approximately 50 feet. Based on this parameter, the system of wells will consist of one
injection well surrounded by six extraction wells.

The time reguired to achieve the RAO will be dependent on the biodegradation rate achieved
during bioventing operations, and is estimated to be between 1 and 50 years. The large range in
the estimated time reflects uncertainty in the biodegradation rates. The present worth cost for
this alternative, based on 5 years of operation, is $207,000.

EVALUATION OF ALTERNATIVES

The selected alternative for remediating the soil contamination at LF18 is Alternative
2-excavation and offsite treatment by recycling. Based on current information, this alternative
provides the best balance of trade-offs among the alternatives with respect to the nine criteria
that are reguired 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 and the Environment

Overall protection is a composite of other evaluation criteria, especially short-term
effectiveness, long-term effectiveness, and compliance with ARARs. Because Alternative 1 (no

-------
action) provides no method of soil remediation, it is not protective of human health and the
environment. Alternative 3 (bioventing) provides an uncertain degree of overall protection of
human health and environment, since it is unclear as to how effective this remedial action will
be on the constituents present at LF18. Leaching of constituents will continue to occur while
bioremediation is ongoing, which is a concern if the time required by Alternative 3 to achieve
the RAO is extensive. Alternative 2 (excavation) will completely remove the contaminated soil
from the site within weeks of beginning the action and thus, will be protective of human health
and the environment.

Compliance With ARARs

Alternative 1 (no action) provides no means of reducing petroleum constituents in soil.
As a result these constituents will continue to be available to leach into groundwater. Soil
concentrations of TPH and BTEX exceed DNREC's UST program action levels and BTEX concentrations
in groundwater exceed MCLs.

The soil excavation of Alternative 2 will be conducted in accordance with the Delaware
Erosion and Sedimentation Act (7 Delaware Code Annotated Chapter 40). Uncontaminated soil will
be stockpiled while contaminated soil will be placed directly into trucks or roll off boxes.
Offsite transport and recycling of the contaminated soil will be in compliance with the Delaware
Regulations Governing Solid Waste. This remedial action will reduce TPH and BTEX concentrations
in soil to below the respective 1,000 mg/kg and 10 mg/kg standards typically applied by DNREC to
petroleum-contaminated soil. The asphalt recycling facility will operate in compliance with its
State's environmental permitting requirements. Restoration of the site will be conducted in
compliance with "Office of the Federal Environmental Executive; Guidance for Presidential
Memorandum on Environmentally and Economically Beneficial Landscape Practices on Federal
Landscaped Grounds," Federal Register Volume 60, Number 154.

The bioventing system of Alternative 3 is anticipated to operate within the Delaware
Regulations Governing the Control of Air Pollution and requirements for land treatment under
Delaware Regulations Governing Hazardous Waste (DRGHW) Part 264, Subpart M. It is uncertain,
however, that bioventing is capable of reducing TPH (DRO) concentrations to below the 1,000 ppm
standard.

Long-Term Effectiveness and Permanence

The long-term effectiveness and permanence criterion primarily considers the magnitude of
residual risk that remains after the implementation of an alternative, and the adequacy and
reliability of the instituted controls. Under Alternative 1 (no action), TPH contamination in
the soil is left in place and hence, offers no long-term effectiveness or permanence.
Alternative 2 (excavation) results in the complete removal of contaminated soils from the site.
Excavation, removal, and offsite recycling is an extremely effective and permanent solution to
the contamination. The long-term effectiveness of Alternative 3 (bioventing) on TPH
(DRO)-contaminated soil is uncertain. In addition, because the entire contaminated zone is not
always exposed due to seasonal fluctuations in the height of the water table, recontamination of
soils through smearing may occur.

Reduction of Toxicity, Mobility, and Volume

Alternative 1 (no action) will not result in any reductions of contaminant toxicity,
mobility, or volume. Alternative 2 (excavation) includes the offsite treatment of contaminated
soil by recycling at an asphalt plant. In this process, the volatile constituents will be
desorbed and combusted while the nonvolatile constituents will be immobilized as an aggregate
mix in the asphalt. Alternative 3 (bioventing) will result in reductions in contaminated soil
toxicity as the concentration of contaminants are reduced over time.

Short-Term Effectiveness

Alternative 1 has no short-term effectiveness considerations associated with it. Neither
Alternative 2 nor Alternative 3 are expected to have adverse impacts on construction workers or
the surrounding community. Alternative 2 will rapidly achieve the RAO, though the time required
for Alternative 3 to achieve the RAO is uncertain.

-------
Implementability

Three main factors are considered under implementability--technically feasibility,
administrative feasibility, and availability of services and materials. Both of the action
alternatives are administratively feasible, and required services and materials are readily
available. Alternatives 2 and 3 are technically feasible. No technical feasibility
considerations are associated with Alternative 1.

Cost

No direct costs are associated with the implementation of Alternative 1. Of the action
alternatives, the estimated capital cost of Alternative 2 (assuming non-hazardous disposal)
ranges between $203,000 and $363,000 depending on the volume of soil removed. The capital costs
for installation and startup of bioventing (Alternative 3) is estimated to be $128,000. Annual
O&M costs for Alternative 3 are estimated to be approximately $20,200. Because the time
required to achieve the remedial action objective is unknown, present worth costs are provided
for three
different operating periods. Using a discount rate of 9 percent, the present worth costs of
Alternative 3 for scenarios of 1, 5, and 50 years of operation are $148,000, $207,000, and
$369,000 respectively.

State Acceptance

The State of Delaware concurs with the selected remedy for Site LF18.

Community Acceptance

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

CONCLUSION

Based on the evaluation of the alternatives using the nine criteria, Alternative 2 -
Excavation and Offsite Treatment of TPH-Contaminated Soil is selected. Alternative 2 is
protective of human health and the environment, complies with all ARARs, represents a permanent
remedy that reduces soil toxicity and contaminant mobility, and is cost effective. The selected
alternative utilizes permanent solutions and alternative treatment technologies to the maximum
extent practicable.

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.

-------
                         ABBREVIATIONS AND GLOSSARY
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 regulations that must be considered in the evaluation
       remedial alternatives.

bgs - Below ground surface

BTEX - Benzene, toluene, ethylbenzene, and xylene

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

Bioventing - A treatment process that delivers oxygen to contaminated vadose zone
       soils to stimulate the aerobic in situ biodegradation of contaminants.

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.

DAFB - Dover Air Force Base

DNREC - Department of Natural Resources and Environmental Control

DRO - Diesel Range Organics.  This term is used to describe a TPH analysis that
       measures a total hydrocarbon concentration for organics  in the No.  2 Fuel
       range which have hydrocarbon chains from CIO to C28.

EECA - Engineering Evaluation/Cost Analysis

EPA - U.S. Environmental Protection Agency

GRO - Gasoline Range Organics.  This term is used to describe a TPH analysis that
       measures a total hydrocarbon concentration for organics  in the more volatile
       range that DRO (pentane to naphthalene).

Groundwater - Surface water residing in a zone of saturation.

HI - Hazard Index.  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.

LIF - Laser-induced fluorescence.  This is the process whereby ultraviolet light is
       emitted into the surrounding subsurface formation and the resulting
       fluorescence of organic material,  such as hydrocarbons,  is measured.

Light Non-Aqueous Phase Liquid (LNAPL) - An organic liquid with a low water
       solubility and density lower than that of water.   LNAPLs retain their physical
       and chemical properties when in contact with water and tend to float on an
       aquifer when released to groundwater.

-------
Maximum Contaminant Levels  (MCLs) - Federal drinking water standards.

mg/kg - Milligrams per kilogram

msl - Mean seal level

O&M Cost - Annual cost incurred for operation and maintenance of a facility.

PCB - Polychlorinated biphenyl

Plume - A recognizable distribution of constituents in groundwater.

RA - Risk assessment

RCRA - Resource Conservation and Recovery Act

RI - Remedial Investigation

SCAPS - Site Characterization and Analysis Penetrometer System

RAO - Remedial Action Objective.  Cleanup goal established for the remediation.

TCLP - Toxicity Characteristics Leaching Procedure.  An analytical procedure which
       measures the level of organic leachate from a soil sample.   This method is
       commonly used to determine whether soil to be disposed of is hazardous.

TPH - Total Petroleum Hydrocarbons.  This analytical parameter is a measure of total
       hydrocarbons,  often within a particular petroleum weight range (see DRO and
       GRO) .

TSD - Treatment, storage, and disposal

USAGE - U.S.  Army Corps of Engineers

UST - Underground storage tank

Vadose Zone - Soil zone above the water table.

• g/L  - Micrograms per  liter

-------
Responsiveness Summary

No comments were received during the 30-day public comment period beginning June 23,  1996 and
ending July 23,  1996.  In addition,  as offered in the press release printed in the June 23,  1996
edition of the Delaware State News,  no verbal or written reguest was received by Dover Air Force
Base or EPA reguesting that a public meeting be held.

-------