United States Office of
Environmental Protection Emergency and
Agency Remedial Response
EPA/ROD/R04-91/085
June 1991
EPA Superf und
Record of Decision:
USAF Robins Air Force Base,
GA
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S0272.101
LREPORT DOCUMENTATION 1'. REPORT NO.
PAGE EPA/ROD/R04-91/085
~ TIle and W,1IIe
SUPERFUND RECORD OF DECISION
USAF Robins Air Force Base, GA
First Remedial Action
7. Aulhor(.)
I ~
3. RecIpient'. Acce88lon No.
5. Aepor1 Date
06/25/91
6.
a. PtrIrlonnlng Org.nlDlion Aept. No.
8. PtrIrlonning OrgalnlDlion Name and Add,...
10. Proj8c:1/T88klWork Unit No.
11. ContnIct(C) or Grant(G) No.
IC)
1 ~ SponaorIng Organlz8tlon Name and AcIdr888
U.S. Environmental Protection
401 M Street, S.W.
Washington, D.C. 20460
(G)
13. Type of Repor1 & Period Covered
Agency
800/000
14.
15. Supplementery Notea
16. Abetr.ct (Umlt: 200 wonl.)
The 46.5-acre USAF Robins Air Force Base site is a logistics management and repair
center for aircraft, missiles, and support systems in Warner Robins, Houston County,
Georgia. The Zone 1 area, which includes a 45-acre inactive landfill and a 1.5-acre
sludge lagoon is part of the 8,8S5-acre Robins Air Force Base. Land use in the area
is mixed residential and industrial. A wetlands area borders the site to the east; in
addition, part of the site lies within the 100-year floodplain of the Ocmulgee River.
From 1965 to 1978, an onsite landfill (Landfill No.4) was used for disposal of
general refuse, and industrial and hazardous wastes. From 1962 to 1978, the sludge
lagoon was used for disposal of wastewater treatment plant sludge and other liquid
wastes. Types of wastes generated at the facility included electroplating wastes,
organic solvents from cleaning operations, and pesticides, all of which were disposed
of in the lagoon and landfill areas. Robins Air Force Base conducted a study in 1982
to identify and assess onsite hazardous waste disposal practices. Disposal areas were
grouped into eight zones based on location and type of activity. Zone 1 has been
divided into three operable units (OUs). This Record of Decision (ROD), which focuses
on OU1, addresses the remediation of Landfill No.4 and the sludge lagoon. Subsequent
(See Attached Page)
17. Doc:urrent Analy8l. L DeacrlplO"
Record of Decision - USAF Robins Air Force Base, GA
First Remedial Action
Contaminated Media: soil, sludge, gw
Key Contaminants: VOCs (PCE, TCE), other organics (pesticides), metals (arsenic,
chromium, lead)
b. 1denliller8l000000Ended Terma
Co COSA TI FIekSIGroup
18. AvaU.billy Stetement
18. SecwIty a... (Thl. Report)
None
:lO. SecwIty au. (Thl. Page)
Nnnp
21. No. 01 Pagea
58
22. Price
(See ANSl-Z3i1.18)
See In8trUC/J0f18 on RetlflIN
-"1
(Formerty NTlS-35)
Deparlment of Commerce
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EPA/ROD/R04-91/085
"'SAF Robins Air Force Base, GA
.rst Remedial Action
Abstract (Continued)
RODs will address remediation of the neighboring wetlands and surface waters (OU2) and
the ground water adjacent to Landfill No.4 and the sludge lagoon (OU3). The primary
contaminants of concern affecting the soil and ground water are VOCs including PCE and
TCE; and metals including arsenic, chromium, and lead.
The selected remedial action for this site includes treating 15,000 cubic yards of soil
in the sludge lagoon using in-situ soil vapor extraction; removing volatile contaminants
from the air using condensation, distillation, and carbon adsorption; controlling and
treating landfill leachate; renovating the landfill cover; treating the sludge lagoon to
remove VOCs, treating metals onsite in the sludge lagoon using solidification; onsite
pumping and treatment of ground water; diverting surface water near the sludge lagoon;
conducting long-term soil testing; and monitoring ground and surface water. The
estimated present worth cost for this remedial action ranges from $9,430,000 to
$24,000,000 with an annual O&M cost ranging from $321,400 to $334,400, depending on the
components of the landfill cap.
PERFORMANCE STANDARDS OR GOALS: Contaminant-specific remediation goals have not been
established for soil at the sludge lagoon because they are dependent on establishment of
ground water goals, which will be developed in a subsequent ROD. .
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U.S. AIR FORCE INSTALLATION
RESTORATION PROGRAM
SUPERFUND
RECORD OF DECISION
ROBINS AFB ZONE 1, GEORGIA
OPERABLE UNIT 1
SOURCE CONTROL
JUNE, 1991
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CONTENTS
SECTION
DEClARA TIO~ FOR THE RECORD OF DECISION
DECISION SUMMARY
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
Site Name and Location
Site Historv and Enforcement Activities
Highlights of Community Participation
Scope and Role of Operable Unit
Site Characteristics
Summary of Site Risks
Description of AJternatives
Summary of Comparative Analysis of AJternatives
Selected Remedy
Statutory Determinations
RESPONSlVENE 5S SUMMAR Y
1.0
2.0
3.0
Overview
Background on Community Involvement
Summary of Public Comment and Agency Response
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DECLARATION FOR THE
INTERIM ACTION RECORD
OF DECISION
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DECLARATION FOR THE INTERIM ACTION
RECORD OF DECISION
SITE :\AME AND ADDRESS
Zone 1 Robins Air Force Base
Operable Unit 1, Source Control
Warner Robins, Houston County, Georgia
STATEMENT OF PURPOSE
This Decision Document presents the selected remedial action for Operable Cnit 1 of
the Zone 1 Robins Air Force Base (AFB) Site, developed in accordance with the
Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA) as amended by the Superfund Amendments and Reauthorization Act
(SARA), and to the extent practicable, the National Contingency Plan (NCP). This
decision is based on the Administrative Record which is on file in the Directorate of
Environmental Management office, Building 43, Robins AFB, Georgia, 31098.
This interim remedial action is taken to protect human health and the environment
from the threat, while final remedial solutions are being developed.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from Zone 1, if not addressed
by implementing the response action selected in this Record of Decision (ROD), may
present a current or potential threat to public health, welfare, or the environment.
DESCRIPTION OF THE SELECTED REMEDY
The Zone 1 Robins AFB site is divided into three operable units. Operable Cnit 1
addresses Landfill No.4 and the Sludge Lagoon and comprises source control.
Operable Unit 2 addresses neighboring wetlands and surface waters and Operable
Unit 3 addresses the groundwater beneath and adjacent to Landfill No.4 and the
Sludge Lagoon. The scope of the this ROD is limited to Operable Unit 1.
The selected remedy for Operable Unit 1, source control, includes the following:
.
Surface water run-on diversion
.
Landfil1 No.4 cover renovation including clearing, filling, regrading,
addition of soil and clay cover material, and seeding
Leachate control for Landfill No.4 and treatment at Robins AFB
.
.
Sludge Lagoon groundwater collection and treatment at Robins AFB
Treatment of the Sludge Lagoon to remove Volatile Organic .
Compounds (VOCs), followed by solidification for the immobilization at
metals
.
-------
.
Environmental monitoring to determine effectiveness of the remedial
action
Further field investigations and treatability testing will be performed to refine design
parameters for the cover renovation, leachate control system, the leachate and
groundwater treatment systems, and the Sludge Lagoon treatment system.
STATUTORY DETERMINATIONS
The selected interim remedial actions are protective of human health and the
environment, comply with Federal and State requirements that are legally applicable
or relevant and appropriate to the remedial action, and are cost-effective. These
interim remedial actions utilize permanent solutions and alternative treatment
technologies to the maximum extent practicable for this site. The Sludge Lagoon soils
and recovered groundwater and landfill leachate will be treated. However, the size of
the landfill precludes excavation and treatment of all waste materials. Because this
interim remedial action does not constitute the Final Remedy for the Site, the
statutory preference for remedies as a principle element will be addressed by the
Final response action.
Because hazardous substances will remain onsite in amounts above health based
levels, a review will be -conducted within 5 years after commencement of remedial
action to ensure that the remedy continues to provide adequate protection of human
health and the environment. The review wi]] be conducted to ensure that the
remedy continues to provide adequate protection of human health and the
environment. .
.
~~
/??/
2
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DECISION SUMMARY
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1.0 SITE NAME, LOCATION AND DESCRIPTION
Robins AFB is an active facility occupying 8,855 acres about 18 miles south of Macon,
Georgia (Figure 1). Robins AFB is bounded on the immediate west by the City of
Warner Robins, on the north by a housing subdivision in Houston County, on the
south by unincorporated Bonaire, and on the east by the Ocmulgee River and its
flood plain.
The Zone 1, Robins AFB, National Priority List (NPL) site is located approximately
4,500 feet east of Georgia Highway 247 in the central portion of the base (Figure 2).
Zone 1 consists of Landfill No.4, which covers 45 acres, and an adjacent 1.5-acre
sludge lagoon (Figure 2).
Zone 1 is located adjacent to a bluff that forms the western boundary of the
Ocmulgee River flood plain. The flood plain extends about 1 to 2 miles eastward to
the river. Landfill No.4 was originally constructed by disposing of fill material into
the flood plain and wetland area from the bluff and advancing to the east. The
Sludge Lagoon was constructed on the northern boundary of Landfill No.4 by
excavating and building earthen dikes. Surface water at Robins AFB generally drains
from west to east into the Ocmulgee River flood plain.
1-1
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ROBINS AFB ZONE 1 ROO {.':1 ~ WI"
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. ROBINS AFB1ON£ ~~ ~~J:Il!'
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2.0 SITE HISTORY AND ENFORCEMENT ACTI~lTIES
Robins AFB currently serves as a worldwide logistics management center for aircraft.
mIssiles. and support systems and is a major repair center for aircraft and airborne
electromc systems.
Robins AfB has generated various types of solid wastes over the years, including
refuse and hazardous wastes. The hazardous wastes include electroplating wastes
containing heavy metals and cyanide, organic solvents from cleaning operations and
fire training exercises, and off-specification chemicals such as pesticides.
In 1982. Robins AFB conducted a basewide survey to identify and assess past
hazardous waste disposal practices. Disposal areas were grouped into eight zones
based primarily on location and type of disposal activity. Zone 1 (Landfill No.4 and
the Sludge Lagoon) was considered to have the highest potential for migration of
hazardous substances and as a result was placed on the: CERCLA NPL by the
U.S. Environmental Protection Agency (EP A) in 1987. Landfill No.4 reportedly
operated from 1965 until 1978 for disposal of general refuse and industrial wastes.
The Sludge Lagoon was used for disposal of industrial wastewater treatment plant
sludges and other liquid wastes from 1962 to 1978. The Landfill and the Sludge
Lagoon were both closed and covered with clean fill in 1978.
In June of 1989 Robins AFB entered into a Federal Facilities Agreement with the
Georgia Department of Environmental Protection (GEPD) and the EP A to estab!ish
a procedural framework and schedule for developing, implementing. and monitoring
appropriate response actions at the site in accordance with CERCLA the ~CP.
Superfund guidance and policy, Georgia Hazardous Waste Management Act
(GHWMA).
The following reports describe the results of investigations at Zone 1 to date:
Law Engineering Testing Company. Final Repon-
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HAZWRAP. U.S. Air Force Installation Restoration Program Phase IV A Remedial
Investigation Zone 1, Additional Site Investigations at Zones 1 and 5, Task S2 Report.
Robins AFB, Georgia. November 1988.
HAZWRAP. U.S. Air Force Installation Restoration Program Phase IV A. Remedial
Im:estigation Zone 1. Robins AFB, Georgia. May 1990.
HAZWRAP. U.S. Air Force Installation Restoration Program Phase IV A. Feasibility
Study, Landfill No.4 and Sludge Lagoon Source COlllrol, Operable Unil 1, Zone 1.
Robins AFB, Georgia. February 1991.
1-2
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3.0 HIGHLIGHTS OF COMMUNITY PARTICIPATION
The Remedial Investigation (RI) for the Robins AFB Zone 1 Operable Cnit 1-
Source Control Remedy was released to the public in May 1990 and the FS in April
1991. The Proposed Plan was released on April 25, 1991 for public comment. These
documents were made available to the public in the Administrative Record located at
the Directorate of Environmental Management. Building 43. Robins AFB and at the
Environmental Information Repository at the Nola Brantley Memorial Library in
Warner Robins. The nOtice of availability of these documents was published in the
Warner Robins Daily Sun and the Macon Telegraph on April 21, 1991. A public
comment period was held from April 25 to June 10, 1991. In addition. a public
meeting was held on May 8, 1991. At this meeting. representatives of Robins AFB.
EP A and the GEPD answered questions about the site and the remedial alternatives
under consideration. A response to the comments received during this period is
included in the Responsiveness Summary, which is part of this Record of Decision.
The proposed plan identified the preferred remedy for Landfill 4 as a variation of
Alternative 2, from the Feasibility Study (FS) (see Section 7); landfill cover
renovation with clay addition. leachate control and treatment and Sludge Lagoon
groundwater collection and treatment. It also identified Alternative 2. Soil Vapor
Extraction for Removal of VOCs Followed by Solidification for Immobilization of
Metals, as the preferred alternative for the Sludge Lagoon. Robins AFB. C.S. EP A
and GEPD reviewed all written and verbal comments submitted during the public
comment period. Upon review of these comments. it was determined that no
significant changes to the Proposed Plan preferred remedy were necessary.
,
3-1
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4.0 SCOPE AND ROLE OF OPERABLE UNIT 1
The overall strategy of Zone 1 is divided into three operable units. The interim
remedial actions selected in this ROD are applicable to operable Unit 1. Further
investigations are undelWay for operable Units 2 and J.
Operable Unit 1 is directed at the known source of contamination, Landfill No.4 and
the Sludge Lagoon, and interim remedial actions for reducing migration of the
groundwater contamination near the Sludge Lagoon. The final remedy for the
groundwater will be proposed following Operable Unit 3 work. Operable Unit 2 is
directed at determining the degree of impact that may have occurred in the wetlands
area and surface waters from the known source of contamination in Operable Unit 1
and remediation of the impacts identified. Operable Unit 3 is directed at determining
the degree of impact that may have occurred in the groundwater beneath and
adjacent to Landfill No.4 and the Sludge Lagoon and remediation of impacts
identified.
The known sources of contamination in Zone 1 are Landfill No.4 and.the Sludge
Lagoon. The Sludge Lagoon is estimated to contain 50 percent of the total Zone 1
contamination and appears to be contributing to groundwater contamination.
The overall strategies of the selected remedy for Landfill No.4 and groundwater
below and immediately adjacent to the Sludge Lagoon are:
.
Control hazardous substances releases
.
Minimize the pmential direct exposure to hazardous substances
Control the releases of hazardous substances to the groundwater near
the Sludge Lagoon .
.
These strategies would be achieved primarily by the reduction in mobility of
hazardous substances through containment with treatment of Landfill No.4 leachate
and groundwater near the Sludge Lagoon. The groundwater contamination would not
be fully remedied but will be addressed in Operable Unit 3.
The overall strategies addressed by the selected remedy for the Sludge Lagoon are:
.
Control hazardous substances releases
Minimize the potential of direct exposure to hazardous substances
These objectives are achieved by the reduction in mobility of hazardous substances by
containment with treatment. Groundwater contamination beyond the sludge lagoon
area will be addressed in a subsequent operable Unit 3 remedial action.
.
These interim remedial actions will be consistent with any planned future actions, to
the extent possible. .
4-1
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5.0 SUMMARY OF SITE CHARACTERISTICS
5.1 GEOLOGY
Robins AFB is underlain bv Cretaceous and Quaternarv sediments about 350 feet
thick. The Cretaceous deposits are divided into the following four geologic
formations: the Providence, the Ripley. the Cusseta. and the BlufftOWTI (Figure 3).
The Providence and Ripley formations tend to act as one hydrologic unit and are
referred to in this report as the Providence formation. The Providence Formation
consists of beds of sand, gravelly sand. silty sand, and clay. The formation is saturated
and yields large quantities of water. Beneath Zone 1 and the eastern portion of the
base, the Providence formation is overlain by Quaternary alluvial deposits (peat. clay.
and gravel). which comprise the flood plam of the Ocmu]gee River.
The Cusseta Formation, composed of about 15 to 50 feet of dense plastic clay and
sand. is saturated but yields ]ittle water to wells and is believed to act as a confining
or semiconfining bed. - The B]ufftOWTI Formation consists of saturated sand and gra~el
beds and is underlain by metamorphic basement rocks. It yields significant qua;tities
of water to wells and is the primary Robins AFB and ]ocal water supply aquifer. The
metamorphic rocks beneath the Bluff town generally will not yield water and are not
considered further in this report.
5.2 HYDROGEOLOGY
The groundwater flow system above the Cusseta Formation at Zone 1 is separated
into the saturated surficial fi]L the Quaternary aquifer, and the upper and lower
Providence aquifers.
The regional groundwater flow direction within the Cretaceous deposits is from west
to east, generally toward the Ocmulgee River. Water in the Quaternary aquifer also
generally flows tOward the river. Where tbe Ocmu]gee River has eroded part of the
Cretaceous sediments, there is a significant upward gradient from the deeper units
toward the Quaternary unit and surface waters. The Ocmu]gee River flood plain is a
broad discharge area for groundwater.
The groundwater flow pattern beneath Zone 1 has been altered. Runoff from a large
area of the base flows onto Landfill No.4. This water infiltrates and saturates the
]andfill waste mass. As a result a mounded water table has been established within
the landfill, creating a local flow system in the surficial fill where landfill leachate and
lagoon groundwater flow radially to the north, northeast, and east, ultimately
discharging into the adjacent wetlands (Figure 4).
5.3 GEOTECHNICAL CHARACTERISTICS
The peat and clay bed directly underlying the eastern tWo thirds of ]andfill wastes
consists of a clay bed overlain by peat constituting a total thickness of 5 to 14 feet.
Split-spoon samples of the clay showed it to be generally a plastic material penetrated
with roots and channels.
LaboratOry permeability measurements of the clay bed were approximately lO'R em, s.
whereas earlier field per!TIeability studies indicated that values averaged
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Figure 4
SCHEMATIC DIAGRAM OF CONCEPTUAL
GROUNDWA TER FLOW SYSTEM
ROBINS AFB ZONE' ROD
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approximately 10-4 cmls (LETCO 1980). Differences betWeen laboratory and field
test results are attributed to larger scale discontinuities in the stratum (e.g., seams.
joints, root holes) not measured by laboratory methods. Thus, higher permeabilities
indicated from field tests a're believed to be more representative of the actual
permeability in the peat and clay bed.
Within the eastern tWo-thirds of the landfill and the Sludge Lagoon the peat and clay
beds appear to retard flow of leachate into the underlying aquifers. Where the peat
and clay beds are absent from beneath the landfill, under the western third. the
wastes are lying directly upon the sands of the Providence Formation, and there is no
impedance to leachate flow out of the wastes.
Sands underlying the western end of the landfill and below the peat and clay bed
constitutes the most significant groundwater aquifer at the site, extending to depths of
several hundred feet. Field investigations using slug tests and observation of shallow
well pumping indicated a hydraulic conductivity in the Providence of 10-2 to 10-3 cm/s.
Laboratory permeability values varied betWeen 6 x 10-4 and 9 x 10-3 cmls for
disturbed samples compacted to relative densities of 60 and 90 percent.
The existing soil cap over the landfill varies in thickness from almost non-existent to
as much as 4-feet thick. The material is nonplastic, silty or clayey sand having less
than 25 percent silt or clay. The average field permeability of this layer was
measured as 3 x 10-4 cmls with a laboratory permeability of 2 x 10-5 to 5 x 10-6 cm/s.
5.4 NATURE AND EXTENT OF CONTAMINANTS
The nature, extent. and concentration of hazardous substance contamination in the
landfill and sludge lagoon area were studied in detail during a field sampling
investigation (Robins AFB 1987) and the Remedial Investigation Zone 1 (Robins
AFB 1989). The following summarizes the major observations from the previous
investigations. .
5.4.1 Contaminants of Concern
Hazardous substances detected in soil, sludge, and groundwater samples from the site
are listed in Table 1. To provide a focus for remedial action goals, contaminants of
concern were identified in the Baseline Risk Assessment of the RI report. The
following factors were considered in the selection of contaminants of concern:
.
Concentration and frequency of occurrence
Distribution in the groundwater and other media at the site
Regulatory criteria and toxicity - - '
Identified contribution to risks in media other than groundwater
.
.
.
The contaminants of concern identified for Zone 1 are:
.
Trichloroethene
1,2-Dichloroethene
Vinyl chloride
T etrachloroethene
Carbon tetrachloride
.
.
.
.
5-2
-------
Table 1.
Compounds Detected in Zone 1
Volatile Organic
Compounds
Semivolatile Organic
Compounds
Inorganic
Constituents
Pesticides
PCBs
Viny 1 Chloride
Methylene Chloride
Acetone
l,l-dichloroethene
l,2-dichloroethene
Chloroform
l,l-dichloroethane
l,2-dichloroethane
l,l,l-trichloroethane
Carbon Tetrachloride
Trichloroethylene
Benzene
Tetrachloroethene
Chlorobenzene
Total Xylenes
2-butanone
4-methyl-2-pentanone
Trichlorofluoromethane
l,l,2,2-tetrachloroethane
2-hexanone
Bromodichloromethane
Dibromochloromethane
Chloromethane
Carbon Disulfide
Cis-l,3-dichloropropene
l,2-dichloropropane
Toluene
Ethyl Benzene
Phenol
2-methylphenol
4-methylphenol
l,3-dichlorobenzene
l,2-dichlorobenzene
l,4-dichlorobenzene
Pentachlorophenol
Di-N-octyl-phthalate
8is(2-ethylhexyl)phthalate
Benzoic Acid
8is(2-chloroisopropyl)ether
Naphthalene
2-methylnaphthalene
N-nitroBodiphenylamine
Dibutyl Phthalate
Pyrene
Butylbenzyl Phthalate
Dibenzofuran
Chrysene
Benzo(g,h.i)perylene
Indeno(1.2,3-c,d)pyrene
Benzo(k)phenanthrene
4-chloro-3-methylphenol
Benzo(a)pyrene
Benzo(b)fluoranthene
Fluoranthene
Anthracene
Phenanthrene
Aluminum
Antimony
Arsenic
Barium
Beryllium
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Magnesium
Manganese
Mercury
Nickel
Potassium
Selenium
Silver
Sodium
Thallium
Vanadium
Zinc
Cyanide
Amenable
Sulfides
Cyanide
Dieldrin
Aldrin
4.4-DDE
4,4-DDO
4,4-DDT
Alpha Chlordane
Gamma Chlordane
Technical Chlordane
Heptachlor
4,4-methoxychlor
; CB-12S4
PCB-1260
GLT98S/043.51
-------
.
Lead
Arsenic
Cadmium
Chromium
.
.
.
A summary of the number of samples with detections and the concentrations found
are presented in Tables 2 and 3 for each of the contaminants of concern. The
compounds most widely distributed and at the highest levels in both soil and
groundwater included VOCs and metals. Of the contaminants of concern identified
in the RI, lead and trichloroethene (TCE) were the most widely distributed and
typically at higher concentrations than other. constituents. They are considered to be
representative of the distribution of organic and inorganic constituents at the site.
5.4.2 Zone l--Contaminant Sources
The highest concentrations of metals and VOCs occur in the Sludge Lagoon.
Maximum concentrations of VOCs and metals in the Sludge Lagoon were detected in
samples collected from a depth of 8 to 10 feet. High concentrations of contaminants
were also detected in leachate samples from the Sludge Lagoon. Contaminant
concentrations decreased in soils nearer the surface of the Sludge Lagoon.
Concentrations of contaminants detected in soils and leachate in the landfill were
generally one to two orders of magnitude lower than concentrations in the Sludge
Lagoon. The surface soil samples collected during the RI indicate that the landfill
cover is generally uncontaminated, although localized "hot spots" may exist.
5.4.3 Groundwater Contamination
Concentrations of hazardous substances in groundwater migrating from the landfill
and especially the Sludge Lagoon are highest in the Quaternary alluvium.
Contaminants in the Quaternary al]uvium also demonstrate the greatest lateral
migration. As the contaminants migrate away from the source areas, the
concentrations generally decrease. The general groundwater migration pathway
appears to be to the north and northeast toward the drainage channel and to the
wetlands east and northeast of the source areas. Hannah Road is approximately the
downgradient limit for waste migration in the groundwater from Zone 1.
The distribution of lead in the Quaternary aquifer is shown in Figure 5. Lateral
migration of lead in the Quaternary aquifer near the Sludge Lagoon is evident. Lead
may have migrated 400 feet beyond the eastern edge of the landfin. The potential
lead plume is bounded to the east by several monitoring wens where lead was not
detected. Samples from several wells along Second Street (Figure 5) revealed lead
concentrations that could be from sources other than Zone 1. Similarly, samples from
wells along Hannah Road had lead concentrations that indicate that either naturally
occurring lead is present or local sources of lead contamination are present in the
vicinity of the road within the wetland. The vertical distribution of lead across Zone 1
is shown in Figure 6. This vertical interpretation is based on RI data and
assumptions using the conceptual groundwater flow model.
. .
The distribution of TCE in the Quaternary aquifer is shown in Figure 7. Lateral
migration of TCE in the Quaternary aquifer is similar to the migration of lead except
5-3
-------
Table 2 Contaminants 0' Concern
Found in Soils
Robins Air Force Base
Page 1 01 1
SurlKe Soil. Sludge Lagoon 80.'..'ng8 Landfill BOllng8 Sedlment8
-----------
Frequency Geometric Frequency Geometllc Frequency Geomelnc Frequency GtHJOlutr IC
01 Maximum Mean 0' Max,mum Mean 01 Maximum Mean 01 Maximum MtHtft
Conlaminanl 0' Concern Detection Concenlration Concenlrallon Delecllon Concentral'on Concentrahon Detection Concenl,ahon Concentrahon Detechon Concenlr al,on ConCtlnt.sllOfl
---~- ~-_._-------_._--- - --
carbon letrachloride (uglkgl
1.2-DlchlofOelhene (ug/kg} eI23 100.000 225
T elr achloroelhene (uglkg} 5/23 5".000 12" 1/27 330
Tnchloroethylene (uglkgl 3123 2.500.000 135 3127 32 763
Vrnyl chloride (uglkg} 1/23 110
AI Genrc (mglkg) 6113 1 110 0 5.JO 22123 450 "84 14/14 120 52" ''''27 272 157
CadmIum (mglkg} 1/13 187 20123 599 733 13114 150 371 6127 2100 1 77
Chromium - Total (mglkgl 12/13 153 543 23123 8.41& 738 14/14 520 IIU 24/27 230 147
Lead (mglkg) 13113 122 43«1 22/23 "72 107 14/14 155 Je 1 27/27 228 281
--~--- -~~-- --
-- = Not Detected
-------
Table 3 Contaminants 01 Concern
Found in Water
Robins Air Force Base
Page 1 01 1
-
Sludge lagoon Leachale Landlill Leachate Groundwater Surlace Waler
--
Frequency Geome.ric Frequency Geometric Frequency Geomelric Frequency Geometric
01 Maximum Mean 01 Maximum Mean 01 Maximum Mean 01 Maximum Mean
Contamlnan' 01 Concern De.ection Concentration Concentration Detection Concenll ation Concentration Deteclion Concenlralion Concentration Delection Concentralion Concenlration
Carbon .etrachloride (ugll) - - 251121 110 5.18 --
1.2-Dichloroethene (ugn) 818 38,000 28.3 3115 3. 3.a7 27/12' '9.000 5.85 3112 '.0
Telrachloroelhene (ugll) 41a 1.100 21.3 -- 201121 290 5.40 --
Trichloroethylene (ugll) 818 130,000 30a 4/15 8.10 2.70 48/12' 21.000 10.8 9112 7.00
Vinyl chloride (ugll) 6IQ 12,000 37.a 31.5 12.0 3.60 8/12' 11,700 7.67 --
Arsenic (ugll) 818 2t.000 852 14/14 13.000 837 tltl1t2 loa 2.12 3/11 12.0 245
Cadmium (ugll) 818 34.800 4.634 14114 a.300 279 1t1112 800 2.57 5111 128 722
Chromium - Tdal (ugn) 8/8 13,163,000 13.851 14/14 88,000 ',085 4'/112 2.720 8.35 8/11 1.390 .99
Lead (ugll) 518 80.000 5,880 14/14 10.400 2.478 731112 5.240 5.83 7/1' 1.400 252
-- = Not Detected
-------
o
--'
>
~
M
.;,
'to
"
o
.:
t
"ryS
Og
00 ~
7=J ";v ~
C) 0 ~
ZC~
» » f1
. r-I
-""
~
,u' . ..
~ :~ r..t
..i)
..
l
:J .;
.' ...
~.
~,'
. ;' i:<>
@~ ~i
, ,:rl,i;j '.... ~
I,r\ 'i". ~." '.I.,,,:: . ".
jV~J~!;\" ,~ .'
tilh.." '.~.' .
li+-';.J""",,"~
. , IU t:~.; :.!n
. \ ..
::..l:1
,..i4.'"
~lONE5~
'~''''''''''''J
'~ 01.1
i)I
~j
~c:;
.a~'
:ft~'
I
\1
31,31.1 0
. '
I
.I
.~
"(L __JBIoIOl' -
Appn>"rNll. BMOt.
LJm~. 01
Sludge
Ugcahon.
010.4
010.4
LEGEND
04.2
~
E7ZJ
~
07.5
5.10
MDL > 100 ugl1
MDL .'00 ugiI
MDl.\O~1
01.'
MONITORING WELL OR
WElL POINT WITH TOTAl
l [AD CONCENT RAT ION
IN ugI1
BYOl MEANS -SHOW METHOD
DE! ECTION LIMIT'
~
270
o JOO 800 goo 1 2'00
..... ---=.......
SCALE" fEET
Flguro 5
LEAD CONCENTRATIONS IN
THE QUATERNARY AOUIFER
ROBJ~ AI 8 ZONl , Rc. V
-
-
{,'T;T 1:"r,
.....
-------
landfill No.4
ATl218!>60800lMrbubonl- 8.II.9IVlO
..~[[['.'8JCI ,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,., R
,~.,.~.,.,.~.,.,.,.,.~.,.,.,.,.,.,.,.~.,.,.,.,.,.,.,.,.,.,.,.,.,.,.~.~.,.,.,.,.,.,.,.,.,.,.,.~.,.~.,.~.,.,.,.,.,. a~ ,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.- J;
.. .. .~... ... .. .. ... ... .. ... ... -_.~ -- -- -- 8- -- --... --... --... A_.. ... ... ... .. _.... .. .. ... ... ... .. _... .. .. .. .. .. .. _... .. .. .. .~.. _... .. --.. .. .. .. .. .. .. .. .. .. .. .. .. _... _... .
=
B
WEST
Not to Scale
LEGEND
"..---..
LEAD CONCENTRATIONS
> 1,000 ugll
Groundwater Flow
.....
--
,
Ililijilijill
~
I. -:. .1
Boundary of Plume of
Contaminated Groundwater
20-100 ug/l
10-20 ugll
<10 ug/l
~
/
'"
Mixing Zone Between
Plume and Natural Waters
,
. . . . . . . . . . . . . . . . .
Sand & Gravel
-------
(
(." (
>,
(~ ('I
, I
- .>
...t. .
"'-
"
-,
c::.
"
ATUJI,
~ C .~ i.;
, \,1
,,'1:' ; ",1tti
:.; Lm
I' ( ,
: ' ~.
'~
,J
JdLi,
".) ICl LonC8f1I.'U11
'r
......"'. ..1 ;... ...J '
I, ,
!
,,' 1 ,
~
J.
~ U'il1IJlO
t "
,,-,
J....."""
Nolo:
1h. ."'.nl of oonlamlilalion indIcated on the l.gur. W0i6
generaliled trom and Inlerpolated between lamJ)"
kxAahonl In'ormatlon on AC1uaJ condlllOn. ..'61& only allhe
IJMK:"te: "'cahons. Confamlnahon at other IoCahorl6 may
otter horn condf1lOn5 occuflng allhe iamplHlQ 'ocallo('6
AI60, the pa606AQ8 at lime ~y r..ut\ In a. change In Inti
oond'hOn5 .Illhew local Ions
~
~l~ES~~
. ,(".~U~) .
/','j
;;.....1
- ..',I
Appto.,m,,'o '
. ltmlts 01 ' ..
'Sludge ,_1-1-~ 1~1,..--,.--.-1--,,'--,-1----,-.,-1-:--..,
" ' L.>goon '\ ,~"""",'"", ""',',
,>/'~'f~J.,H.......... ,///
t ' : : : ::: : ~I
, LANDFILL NO, 4 f',',"',' , , , , '/
\', ,;;:>,-::::::::,
, t, -,',',','!
, "pp",.,mat8 I, ' , ' , ' , ' , "
, L,ml', 01 , ' , , '/
' U,ndI,' No 4) J. :: :: :: ::
I i.. ..,
, ...-.J,' , ' '/
...._-, ''':"---:',".".'.'
, , ~ ' - , , ;...>-'"
'- -~,--'--"'1
c=J
c:=J
r==J
[';:';">1
-
LEGEND
"
'"
.:s~
BMOL 10 uW1
10,100 ugI1
100 1,000 "Itl
1,000,10,000 ug~
10,~ 1 00,000 uiY1
LandlW Bour&1ary. Groundwcll8(
Oaf. UNI'w'allable Below I and'.U
~
o ]00 800
............ ,.
SCALE IN fln
QOO '.;'(.0
~
Figuro 1
ZONE 1 TCE CONCENTRATIONS IN THE -
OUATERNARY AOUIFER l~'
R'-'8IN~A.J8ltWlI R("{) "':l',.IL.
--
-------
that the plume appears to extend farther to the east, to the creek at Hannah Road.
TCE was detected in three wells north and northwest of the Sludge Lagoon and
Landfill No.4. TCE in groundwater at these wells could be from Zone 5, the
industrial ~rea. TCE contamination, and from Zone 1. Portions of the TCE plume
boundary In Figure 7 are shown as questionable to represent the uncertainty of the
TCE sources. The vertical distribution of TCE across Zone 1 is shown schematically
in Figure 8. This vertical interpretation considers the RI data, possible input from -
other upgradient sources, and assumptions using the conceptual groundwater flow
mode \.
The concentration of contaminants generally decreases about one order of magnitude
downward from the waste sources; i.e., the concentration of contaminants in the
Quaternary gravel is about one order of magnitude less than in the adjacent waste
mass. This trend also applies to deeper monitoring zones; i.e., the contaminant levels
in monitoring wells in the upper Providence Formation are generally one order of
magnitude less than the concentration of similar contaminants in adjacent overlying
Quaternary gravel monitoring wells, and concentrations in the lower Providence
Formations are roughly an order of magnitude lower than those in the upper
Providence Formation.
In the vicinity of the Sludge Lagoon, the concentration of contaminants in the source
is elevated such that contamination migrating downward within the tested depths is
not diluted or attenuated to concentrations below detection limits. To represent
surficial contamination, the concentration and distribution of lead in the saturated
surficial fill is shown in Figure 9. As a result of downward migration from the
surficial zone. contamination has been detected deeper in groundwater near the
Sludge Lagoon than anywhere else in Zone 1. Based on very limited data. it appears
that hazardous substances may have migrated as far down as the lower Providence
aquifer on the north side of the lagoon. However, it is unknown whether these
substances might have migrated from other sources due to limited background
information.
No monitoring well has been placed in Landfill No.4 or the Sludge Lagoon through
the peat and clay layer, so the vertical extent of contaminant migration directly
beneath the sources has not been measured. The Cusseta Formation is believed to
be a confining bed and most likely inhibits downward migration of contaminants
beneath the site.
Robins AFB water supply Well No.3 is located about 1,500 feet northwest of Zone L
The well has been removed from service. Water in the well contains low levels (less
than drinking water standards) of contaminants. The cQntaminants include some of
the same contaminants as those that occur in the groundwater in Zone 1.
Contaminant sources upgradient of WeJl No.3, and closer to it than Zone 1, are
more likely sources of the contamination than Zone 1, but this has not been
completely evaluated. The Robins AFB industrial area TCE contamination and its
potential sources are being investigated as part of the Resource Conservation and
Recovery Act (RCRA) facility investigations.
5-4
-------
WEST
Landfill No.4
ATL278~ 08 00 Oslri:>uhon TCE 6-1181VlO
EAST
. .... . ...
~\..~::::::::<:::::>;.~~..:- -X ./
........./ ~ ~
',?' . ?'
. . ,,?
.~.~.~.,.~.,.~.,.,.,.,.~.,-,.,.,.,.,.~.,.,.\.,:,.,.,.,.'.'.'.'.'.'.'.'.'.'.'.'.'.,.,.,.,.,.,.,.,.,.,.,..-,-'.'.'.~.'.~.....................................
~,~,~,~,~,~,~,~,~,~,~,{,~,~,~,~,~,~,~,~,~,~,~,~,~,~,~,~.:~,~,~,~,~.:~,~,\,~,~,~,~.:~,~,~,~.:\"" ~,~,~,~,~-:~,~,~,~-:~-:~,~ Cia 'I :~-:~,~-:~-:~,~,~,~-:~-:~-:~,~-:~,~-:~-:~-:~,{ ca
. . . . . . . . . . . . . . . . . . . . . . . . . . . " """""""""" .,... Sand' . . . . . . . . . . . . . . .. !
.~.~.,.,.~[[[- . . -~.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,.,. j
~,!:..!:.!,!:.!,!,!,!,'!,!:.!:.!,!:.!,!,!:.!:.!:.!,!,!:.!,!:.!,!,!,!:''!":.!:.-::.!:.-::.-::.-::.!:::,!:.!:.! :,!, -::.! :,"::.'::.-::.'::.-::..'::.!,-::.-::..-::.-::.-::.-:.:~ .Clay :-::,-::,!:,!:;!:,-::,-::.-::.-:,-::,-::,-::,-:,-::,-::,-::,-::,-: 0
LEGEND
~
TCE CONCENTRATIONS
Groundwater Flow
1,000-20,000 ug/l
"-
....-
,
Boundary of Plume of
Contaminated Groundwater
1«>1
c::J
c=J
c=J
100-1,000 ug/l
10-100ug/l
./
",
'"
Mixing Zone Between
Plume and Natural Waters
MOL -1 Oug/l
BMOL
,
NOTE: Groundwater contamination below landfill based on data north of landfill
. . . . .
Sand & Gravel
Nof to Scale
" sludge lagoon
I
Figure 8
DISTRIBUTION OF TCE
UNDERNEA TH ZONE 1
-------
"'0
o
00
~ -;-\3
G1 .-'
.t:,.
»
.-
I;' .
;;.}~,--.d
I
L .;
, \j'
"..,
~~I.;~
Afl4!16~0800 l..dConc_."."",.
.
r,;.,
;~. \.
.,
.J;t r ::' " I..;
l.~'::. :f.i"
:'C.:1;:;
ji:~1 '
~ .
"
~~.....
"
~ 2).81VlO
w
"I
Ii
Note:
The elllenl 01 conlaminalion micaled on the ligure --
generalized Irom and inlerpolated beI_n aample locatio.....
Intormalion on aclual cond-ions e."'I. only al the .pedic
location.. Conlamination at oIher local ions may ddler trom
conditio... occuring at lhe sampling location.. Also, the
paoaage 01 lime may re.uK in 8 change in the conditio.... 81
lheoe Iocationa.
..~~ ~.1
'.
".
:'
~,'" -
LEGEND
C=:J
r.=J
1:-:-:-:-;.:-1
1,',;,',;,;,;1
..
o JOG
II..,...'
. .
.,
BNOL.tO ugII
to-IOO ugll
too-I,OOO ugt
1,000-10,000 ugII
10,000-100.000 ~I
LANDFIll BOUNDARY
~
100
,
SCAlE IN FEET
IlOO
,
Figuro 9
LEAD CONCENTRATIONS IN SOURCE
BORINGS AND SURFICIAL GROUNDWATER
ROBINS A/8 lONE. f '400
"
.-
.
-
-
l":::~.:l;!.~'
-
-------
Available data on the Robins AFB water supply wells indicate that they are
completed in the Bluff town Formation. but some wells have multiple completion
zones that may include more than the Blufftown Formation. Because of this
uncertainty, it 'is possible that supply Well ~o. 3 (and other Robins AFB wells) is
completed in more than one aquIfer.
5-5
-------
6.0 SUMMARY OF SITE RISKS
The risk assessme,nt (Robins AFB, 1990) evaluates potential risks to human health
and the environment from actual or threatened releases from Zone 1 at Robins AFB,
Georgia.
In summary, actual or threatened releases of hazardous substances from this site, if
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.
6.1 EXPOSURE ASSESSMENT
Risks are estimated for two potential pathways: ingestion and inhalation of
contaminated media or waste. A number of conservative assumptions and procedures
were used in the risk calculations. The three most important ones were the use of
maximum detected concentrations, the assumption that the chemical was present in
its most toxic form (e.g., hexavalent chromium), and the use of frequency of
exposures greater than anticipated.
Access to Robins AFB is restricted. Only active duty military personnel and their
families reside on the base, and these personnel would generally be stationed at the
base for less than 5 years. Access to Zone 1 is further restricted by a locked gate and
fence at the landfill entrance. Adjacent to the wetland areas located to the north,
south, and east of Zone 1 the site boundary is not fenced because natural conditions
discourage trespassing.
Because access to the site is 'restricted and groundwater from the site is not used for
domestic or agricultural purposes, human health exposure pathways are limited.
B'ase housing is located south of Zone 1 and the adjacent wetland. Because the
organic portions of landfilled materials typically decompose, methane and other
VOCs may be released in gaseous form from Zone 1 and migrate offsite. Therefore,
a principal potential pathway for human exposure is inhalation of these gases
migrating from the site to the offsite base housing.
Trespassing has not been observed on the landfill due to natural and imposed access
restrictions; however, personnel have been observed fishing in ponds east of the site
at the runway approach along Lights Service Road and Hannah Road. No one has
been observed in the wetland or shallow standing water in this area. Although
trespassing is not expected to be prevalent, potential exposures to contaminated
surface soil, sediments, and surface water were evaluated to conservatively estimate
human risk.
6.2 RISK ASSESSMENT METHODSrrOXICITY ASSESSMENT
Cancer potency factors (CPFs) for chemicals detected in Zone 1 are presented in
Table 4. CPFs have been developed by EP A's Carcinogenic Assessment Group for
estimating excess lifetime cancer risks associated with exposure to potential\y
carcinogenic ,chemicals. CPFs, which are expressed in units of (mg/kg-day)" , are
multiplied by the estimated intake of the potential carcinogen, in mg/kg-day, to
6-1
-------
TaDle1
CarCinogenic Classification and POlency Faclors lor
Chemicals Detected al Zone 1
,Revised 3-4 91 Ingestion Route Inhalation Route
CarCinogenic Car C I n og a n I C
U S EPA(b) Potency iUS EPA,Dj Potency
Carcinogen Factor Carcinogen Factor
I Chemical Class (kg-
-------
provide an upper-bound estimate of the excess lifetime cancer risk associated with
exposure at that intake level. The term "upper bound" reflects the conservative
estimate of the risks calculated from the CPF. Use of this approach makes
underestimation of the actual cancer risk highly unlikely. Cancer potency factors are
derived from the results of human epidemiological studies or chronic animal bioassays
to which animal-to-human extrapolation and uncertainty factors have been applied.
Excess lifetime cancer risks are determined by multiplying the intake level with the
cancer potency factor. These risks are probabilities that are generally expressed in.
scientific notation (e.g., 1 x 10.0 or lE-6). An excess lifetime cancer risk of 1 x 1O.()
indicates that, as plausible upper bound, an individual has a one in one million chance
of developing cancer as a result of site-related exposure to a carcinogen over a
70-year lifetime under the specific exposure conditions at a site.
Reference doses (RIDs) have been developed by EPA for indicating the potential for
adverse health effects from exposure to chemicals exhibiting noncarcinogenic effects.
RIDs, which are expressed in units of mg/kg-day, are estimates of lifetime daily
exposure levels for humans, including sensitive individuals. Estimated intakes of
chemicals from environmental media (e.g., the amount of a chemical ingested from
contaminated drinking water) can be compared to the RID. RIDs are derived from
human epidemiological studies or animal studies to which uncertainty factors have
been applied (e.g., to account for the use of animal data to predict effects on
humans). These uncertainty factors help ensure that the RIDs will not underestimate
the potential for adverse noncarcinogenic effects to occur.
Potential concern for noncarcinogenic effects of a single contaminant in a single
medium is expressed as the hazard quotient (HQ) (or the ratio of the estimated
intake derived from the contaminant concentration in a given medium to the
contaminant's reference dose). The Hazard Index (HI) is the sum of the HQs for all
contaminants within a medium or across all media to which a given population may
reasonably be exposed. The HI provides a useful reference point for gauging the
potential significance of multiple contaminant exposures within a single medium or
several media. .
6.3 RISK CHARACTERIZATION
Potential residential and trespasser exposure scenarios were evaluated, and the risk
summaries for inhalation are shown in Table 5. The results for inhalation suggest an
excess lifetime cancer risk of 3 x 10.0 (3 in 1 million) for residential exposures. This
value is calculated for exposure to resuspended (airborne) material and is based on
modeling and use of maximum concentrations measured ip a single sample. Because
the site has a vegetative cover and little or no traffic, the -generation of dust is limited.
The risk from inhalation of resuspended material based on the average concentrations
in surface soils is 1 x 10". Residential risk due to inhalation of VOCs is calculated at
2 x 10.0. However, the risk from inhalation of VOCs is not site-related because
upwind concentrations were similar to downwind. In the evaluations conducted as
part of this risk assessment, each hazard index calculated for inhalation exposures was
less than 1.
Trespassing onsite, in the wetland, or in standing water was evaluated for incidental
ingestion and dermal absorption of surface soil, sediments, or surface water. The risk
6-2
-------
Table 5 l~
Summary of Ambient Air Inhalation
Risks by "'edia and Exposure Setting
Robins AFB
~faximum Maximum
Excess Lifetime Hazard
Source Assumed Receptor Cancer Risk Index Major Contaminants
Volatized Contaminants Inhalation by child 1 )( 10-0 OA1 Chloroform. benzcne
in Ambient Air trespasser
Volatized Contaminants Inhalation by child ~ x 10,8 0.005 Chloroform. VIn\ I
from Landfill Gas trespasser chlorIde. benzene
Resuspended Material Inhalation by child 2 x 10-6 0.047 Chromium. cadmIum.
in Ambient Air trespasser arsenic
Volatized Contaminants Inhalation by offsite adult 2 x 10-0 0.066 Chloroform. benzene
residents
Volatized Contaminants Inhalation by offsite adult 7 )( 10.8 0.001 Chloroform. vinyl
from Landfill Gas residents chloride. benzene
Resuspended \1atenal Inhalation by offsitt - ult 3 )( 10-0 0.008 Chromium. cadmIUm.
residen ts arsenic
-------
summaries are shown in Table 6. The excess lifetime cancer risk exceeded 1 x 10-6
only for sediment ingestion (9 x 10-6), and sediment dermal absorption (3 x 10-5).
There were two primary contributors to this calculated cancer risk: polynuclear
aromatic hydrocarbons (P AHs) and arsenic. The high molecular weight P AH
compounds seen in the sediments do not appear to have resulted from Zone 1
because these compounds were not seen in the Zone 1 groundwater or surface soil
analyses. However. Zone 1 appears to be the source of arsenic contamination
because highest arsenic concentrations were seen in the sediments and groundwater
near the landfill.
The hazard indexes exceeded 1 for maximum sediment and surface-water values.
These samples were collected near the Lights Service Road, where trespassing may
occur. The hazard indexes for the average concentrations were less than 1.
Risk calculations for consumption of fish are shown in the RA (Robins AFB. 1990).
Arsenic was the only parameter which had a surface-water concentration that
exceeded the Federal Ambient Water Quality Criteria.(FAWQC) for protection of
human health from the consumption of fish. Arsenic and dieldrin exceeded EPA fish
tissue concentrations for 10-6 risk levels assuming 6.5 gm/day consumption. Assuming
fish from this location were eaten 12 times/year for 10 years, the excess lifetime
cancer risk is estimated at 4 x 10-6.
Risks from potable use of the shallow groundwater were not estimated. However,
drinking water standards for several parameters have been exceeded in groundwater
samples collected in the surficial and quaternary alluvial aquifer in the vicinity of
Zone 1. This shallow groundwater is not currently used for water supply, and
discharges into the wetland. The groundwater, particularly in the vicinity of the
sludge lagoon, exceeds the water quality criteria for protection of aquatic life,
suggesting the discharge of these waters to the adjacent surface waters may contribute
to exceedances of acceptable levels at that location.
The assumptions used in the risk assessment regarding exposure of a child trespasser
are considered conservative. Such exposures would not be likely to increase if access
to the landfill were not restricted, since the assumption of 2 days per week at the.
landfill during the summer months for 10 years may be considered a reasonable
recreational exposure scenario.
Potential exposure pathways for a child at the landfill may include inhalation, dermal
absorption via soiJ, and incidental ingestion. In the wetland, the exposure pathways
include dermal absorption and incidental ingestion of surface water or sediment. The
risks from these two areas are not additive, since the assumption that a child would
spend 4 days per week during the summer months in these two areas of the base is
extremely conservative.
The summation of risks is a total of the risks for various media from both Zone 1 and
ambient sources.
6.3
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Table 6
Summary of Surface S !. Sediment. Fish. and Water Ingestion
and Dermal Absorption Risks b) 'tedia and Exposure Sening
Zone I-Robins AFB
\1aximum
Calculated Maximum
Excess Lifetime Hazard
Source Assumed Receptor Cancer Risk Index \1ajor Contaminants
Surface Soil Ingestion by child 2 x 10,7 0.5 Benzo[b jfluoranlhene
trespasser chlordane
Dermal absorption by 2.5 x 10,7 0.122 Benzo[b]fluoranrhene
child trespasser cadmium. chromIum
Sediments Ingestion by child 9 x 10-0 1.1 Arsenic. P AH. lead
trespasser
Dermal absorption by 3 x 10,5 0.477 P AH. dieldnn
child trespasser
Surface Water Ingestion by child 4 x 10,7 2.8 Arsenic. lead.
trespasser cadmium. chromIUm
Dermal absorption by 1 x 10-8 0.038 Arsenic. chromIUm
child trespasser
Fish Ingestion by Adult 4 x 10-0 -- Arsenic. dieldrIn
PAH: Polynuclear Aromatic Hydrocarbons "
-------
Exposure
Pathway
Landfill
Soil-incidental ingestion
Soil-dermal absorption
Air-resuspended material
Air-ambient air
Sum of risks
Wetland
Surface water
- incidental ingestion
- dermal absorption
Sediment
- incidental ingestion
- dermal absorption
Sum of risks.
Average
Excess Lifetime
Cancer Risk
Average
Hazard Index
3 x 10-8
2.5 x'1O-7
7 x 10-8
1 x 10-0
1.35 x 10-0
0.04
0.122
0.012
0.41
0.584
9 x 10-8
1 x 10-8
3 x 10-0
1.2 x 10-5
1.51 x 10-5
0.16
0.0037
0.16
0.477
0.80
6.4 ECOLOGICAL EV ALVA nON
Zone 1 and the surrounding area consist of field and planted pine habitats on the
landfill and to the east, grading into a permanently inundated wetland forest at
Hannah Road and into flood plain bottomland hardwood farther to the east in the
Horse Creek area.
The ditch and standing water near the Lights Service Road and Hannah.Road
provide a more open water habitat than the hardwood wetland. However, the Lights
Service Road area has been, and is likely to continue to be, affected by various
human activities. The open water habitat results from the impoundment of water by
the roads, and most of the water in this area is from the wastewater treatment plant.
Trees have been cleared to provide better visibility for aircraft, and the water level is
periodically lowered to discourage the establishment of wading bird populations.
Metal concentrations found in the area may have resulted from a number of sources
and from current and past waste management practices. Concentrations of cadmium,
chromium, copper, cyanide, iron, lead, mercury, silver, and zinc in' water samples from
this are~ exceeded FA WQC for protection of aquatic life. These elevated
concentrations may be due to the presence of particulates in samples preserved prior
to filtration. Currently, the Zone 1 monitoring wells are 1?eing resampled and metals
concentrations re-analyzed on filtered and unfiltered samples.
Field observations suggest that the various ecological stresses in the area of the Lights
Service Road appear to be a result of either flooding or human activities unrelated to
waste management, such as tree cutting. Vegetative stresses that can be attributed to
contaminant'release from Zone 1 were not observed in the hardwood forest onsite or
in the adjacent wetland.
6-4
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'-
6.5 CO~CLLSIO~S
Based on the results of this risk assessment. Zone 1 does not appear to present an
unacceptable current public hea]th risk via the inha]ation exposure route. There is a
porential for environmental risk, and possibly human health impacts, from exposure to
metals in surface water, sediment, or fish tissues in which the metals may have
bioaccumulated. -
Landfill ~o. 4 and the Sludge Lagoon are contributing to the degradation of the site
groundwater. The alluvial aquifer is an unconfined aquifer system that discharges to
the wetlands bordering the Ocmulgee River. Site groundwater data indicate that
standards and criteria for the protection of human health and aquatic life are being
exceeded in the site groundwater. A further assessment of risks to human health and
the environment resulting from Zone 1 groundwater contamination will be addressed
in Operable Units 2 and 3.
In summarY, actual or threatened releases of hazardous substances from this site. if
not addressed by implementing the response action selected in this ROD, may
present a current or potential threat to pubJic health, welfare, or the environment.
6-5
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7.0 DESCRIPTION OF ALTERNATIVES
The alternatives developed in the FS and presented below represent conceptual
approaches to site. remediation. Specific details of alternatives were developed to
allow order-of-magnitude cost estimations. The selected remedy incorporates'the
concepts of the FS alternatives selected. Details are defined during the design
process where further field investigations and/or bench and pilot scale testing may be
performed.
7.1 LANDFILL NO.4
7.1.1 Alternative I-No Action
Consideration of a no-action alternative is required by the NCP. Under Alternative l.
no response actions would be implemented.
7.1.2 Alternative lA-Limited Action
The limited action alternative consists of institutional controls for future site access,
groundwater use restrictions, and long-term groundwater monitoring. Waste will
remain in place and contamination will not be addressed. Costs are associated with
fence construction and the placement of warning signs around the perimeter and the
installation of monitoring wells.
7.1.3 Alternative 2--Cover Renovation and Lagoon
Groundwater Source Control
Under Alternative 2, landfill infiltration would be reduced and groundwater from the
Quaternary and upper Providence aquifers below and immediately downgradient of
the Sludge Lagoon would be extracted. Surface water run-on would be intercepted
and diverted around Landfill No.4. The landfill cover would be renovated bv
clearing the landfill surface, regrading the site to maintain a minimum 2-foot cover
over the waste materials, and sloping the surface to promote runoff and limit the
effects of differential settlement. The site would be seeded to promote
evapotranspiration of precipitation and to prevent surface erosion.
Two groundwater extraction wells near the perimeter of the Sludge Lagoon screened
in the Quaternary and upper Providence aquifers would intercept the more highly
contaminated groundwater being released in Zone 1. Based on pump test results, a
combined pumping rate of 110 gpm is expected to capture the lagoon groundwater
plume. Groundwater extracted from the lagoon area wo~ld be treated at the base to
National Pollution Discharge Elimination System (NPDES) limits.
7.1.4 Alternative 3-Multilayer Cap and Leachate
and Lagoon Groundwater Source Control
Under Alternative 3, landfill infiltration would be greatly reduced, landfill leachate
would be collected, and groundwater from the Quaternary and upper Providence
aquifers below and immediately downgradient of the Sludge Lagoon would be
extracted in the same manner as in Alternative 2. The existing landfill cover would
be replaced with a new cap incorporating a flexible membrane liner (FML) as the
7-1
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impervious barrier. The cap is expected to meet objectives for the landfill bv greatly
reducing run-on and infjltration and the resulting contaminant migration. L3'ncifiJ! ga~
would be collected and released to the atmosphere after treatment to meet
Applicable or Relevant and Appropriate Requirements (ARARs).
Cnder Alternative 3, leachate would be extracted from the landfill area. The
conceptual leachate collection system would consist of a series of trenches and
perforated collection pipes manifolded into a central collection line and pump station.
Leachate wouJd be treated at the base to :\PDES limits. The leachate co]]ection
system would meet Operable Unit 1 goals by essentially eliminating leaching of
hazardous substances to the QuaternaI)' and Providence aquifers.
7.2 SLt:DGE L\GOON
7.2.1 Alternath'e l-!'io Action
Consideration of a no-action alternative is required by the NCP. Alternative 1 for
Robins AFB does not include any response actions.
7.2.2 Alternative lA-limited Action
The Limited Action alternative provides for institutional controls for restriction to the
area and future land use. ~o remedial actions to upgrade the Sludge Lagoon cover
or to provide treatment would be taken.
7.2.3 Alterative 2-ln Situ Soil Vapor Extraction
and In Situ Solidification
Alternative 2 would address the hazardous substances in the Sludge Lagoon by means
of in situ treatment methods. It is intended to provide treatment of hazardous
substances without excavation. This general approach addresses the CERCLA
preference for treatment while avoiding excavation and consequent risks from release
of VOCs. The RCRA land disposal restriction requirements. which are considered to
be ARARs, would not affect implememability of Alternative 2.
Costs were developed in the FS for the following treatment system. Cnder
Alternative 2. stearn would be injected intO the ground, and then the stearn containing
the VOCs would be removed by a "vacuum" system in the soil. Volatile
contaminants would be removed from the air bv condensation, distillation, and
adsorption on activated carbon. After most of -the organic compounds have been
removed, the soil containing the non-volatile compounds..such as metals, would be
solidified in place. Long-term testing would be performed to verify the effectiveness
of treatment. An estimated 15,000 cubic yards of soil would be treated. It is
estimated that 75 to 90 percent of the v6Cs would be removed during the in situ soli
vapor extraction (lSVE) process, greatly reducing the risk of releases.
The practical implementability of Alternative 2 is intluenced by the high groundwater
table at the lagoon and the physical properties of the peat. Bench scale and pilot
testing would be required during predesign to confirm system performance,
practicality and develop performance criteria.
7-2
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7.2.4 Alternative 3-Excavation, Low-Temperature Volatilization, Solidification, and
Onsite RCRA Landfill
Under Alternative. 3, hazardous substances in the Sludge Lagoon would be excavated.
treated by low-temperature volatilization (L TV), solidified. and placed in a RCRA
landfill on Robins AFB property.
In the L TV process an estimated 15,000 cubic yards of contaminated soil would be
agitated and heated to 500° to 800°F, which would volatilize many of the organic
contaminants from the soil. L TV has been shown in both bench- and pilOt-scale tests
to remove more than 99 percent of chlorinated VOCs from soil. Offgases would be
passed through an afterburner to oxidize the volatilized organic compounds to carbon
dioxide and water. The offgases would also pass through pollution control devices for
particulate and acid gas removal as needed to meet ARARs before discharge to the'
atmosphere.
The residual material discharged from the volatilization unit would be solidified to
immobilize metals and unvolatized organic compounds. It is likely that solidification
to meet the RCRA land disposal restrictions would be necessary. Solidification is an
assumed requirement only for the purpose of estimating the cost for this alternative.
A RCRA cell with a design capacity of 25,000 cubic yards would be constructed to
contain the treatment residue. The RCRA cell would be designed to satisfy the
EP A's minimum technology guidance requirements for hazardous waste management
facilities. The conceptual design of the RCRA cell would probably consist of a
double liner system with primary and secondary leachate detection, collection. and
removal systems and a double layer cap system with a drainage layer and topsoil-fill
cover layer.
Alternative 3 is intended to minimize treatment costs while meeting RCRA Land
Disposal Restrictions (LDRs) applicable to FOOl and F006 wastes before placement
in a RCRA landfill at Robins AFB. This general approach addresses the CERCLA
preference for use of treatment to reduce the tOxicity, mobility, or volume of
hazardous substances. .
7.2.5 Alternative 4--Excavation, Incineration, Solidification,
and Replacement Onsite
Under Alternative 4, hazardous substances in the Sludge Lagoon would be managed
by excavation followed by treatment sufficient to replace the materials onsite.
Incineration of the estimated 15,000 cubic yards of soil would be performed using a .
portable unit operated near the Sludge Lagoon. Incinera-tion is expected to remove
more than 99.9 percent of all organic hazardous substances in the soil. The residual
soils would be solidified to immobilize metals, delisted as a hazardous waste, and
replaced at Zone 1.
7-3
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Alternative ~ is intended to provide a treatment approach that would generate a
residue suitable for replacement onsite. This general approach addresses the
CERCLA preference for use of treatment to reduce the toxicity. mobility. or volume
of hazardous substances while complying with the ARARs of the RCRA land disposal
restrictions on handling both FOOl solvent wastes and F006 electroplating wastes.
7-4
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8.0 SUMMARY OF COMPARATIVE ANALYSIS OF ALTER1~ATIVES
8.1 LANDFILL NO.4
8.1.1 Overall Protection of Human Health and the Environment
Based on the RA, it is believed that site contamination is not posing risks to human
health due to the lack of exposure. However. it is possible that contaminants are
migrating to wetlands at levels that pose risks to environmental receptors near the
Sludge Lagoon. Under Alternative 1, these conditions would remain unchanged. It is
reasonable to expect that some ecological/environmental benefits are achieved by
controlling the source of contamination from Zone 1 in Operable Unit 1.
Alternatives 2 and 3 will achieve source control and attain the remedial action
objectives for protection of public health and the environment. Protection of the
environment and the ecology in the surrounding wetlands from releases is provided by
Alternatives 2 and 3 through Landfill No.4 and Sludge Lagoon source control and
Sludge Lagoon groundwater collection and treatment.
Alternative 3 will provide additional prOtection to public health and the environment
through two remedial technologies-the multilayer cap and leachate collection.
Reliance on monitoring, although still important, is not as great under Alternative 2.
8.1.2 Compliance with ARARs
Alternatives 1 or 1A will not comply with action-specific ARARs because the Sludge
Lagoon and the landfill will have a cover less permeable than the clay-peat below
them. Alternatives 1 or lA will not comply with the chemical-specific ARARs
because hazardous substances will continue to be released from the Sludge Lagoon
and the landfill.
Renovation of the Landfill No.4 cover is proposed for Alternative 2. This action
may not produce a cover that is less permeable than the layer below the landfill.
Alternative 2 includes a Sludge Lagoon groundwater collection system that would
control releases of hazardous substances. The collected water would be treated at
Robins AFB. Robins AFB would comply with the conditions of the applicable
permits during the treatment of the contaminated groundwater. Monitoring would be
required to protect the nearby wetlands.
The soil-FML cap proposed for Alternative 3 will comply with the RCRA cover
ARAR requirement for covers to be less permeable than'the bottom liner system or
natural subsoils. Alternative 3 includes a Sludge Lagoon groundwater recovery
system. The collected water will be treated at Robins AFB. Alternative 3 also
includes collection of contaminated leachate in the landfill and treatment at Robins
AFB. Robins AFB will comply with the conditions of applicable permits during the
treatment of the contaminated groundwater.
8-1
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8.1.3 wng-term Effectiveness aDd Permanence
Alternative 2 would reduce infiltration through the landfill by an estimated
10 percent. ~-
Alternative 3 consists of a leachate collection system for Landfill ~o. 4 and a soil
Flexible Membrane Liner (FML) cap that wouid reduce infiltration by an estimated
80 percent. This configuration of technologies will provide an increase in the overall
reliability of the landfill remediation.
8.104 Reduction of Toxicity, ~obility, or Volume Through Treatment
Alternatives 1 or lA would reduce the amount of contaminants through natural
attenuation. but the magnitude of the reduction is unknown.
Leachate and groundwater would be treated in Alternatives 2 and 3. The treatment
would remove 80 to 99 percent of the organic concentrations and betWeen 80 to
90 percent of the metals concentrations.
8.1.5 Short-Term Effectiveness
Short-term construction effects related to dust and noise generation are expected for
all alternatives except Alternatives 1 or lA. Release of VOCs during the excavatIon
of the leachate collection system is a concern for Alternative 3. Workers would be at
risk from inhalation or dermal absorption of hazardous substances during excavation.
Alternative 2 will reduce the contaminants leaching to the groundwater. It is
estimated that the Sludge Lagoon groundwater collection system would operate for
5 years to remove the majority of the contaminants in the area of the Sludge Lagoon
groundwater collection.
The time periods estimated for implementing the alternatives as described in the
summary of alternatives are 6 months for Alternative 2 and 18 months for
Alternative 3.
8.1.6 Implementability
Each alternative is believed to be technically feasible to construct and operate. Cap
renovation and groundwater collection technologies are technically and
administratively feasible. Commercial services and materials are readily available.
The soil-FML cap and the leachate collection systems of Alternative 3 may pose some
problems. The soil-FML cap requires special contractors and careful quality control
during installation. Because of the potential for damaging the FML during
uncovering for post-installation inspection, maintenance will be limited only to areas
of substantial subsidence.
Construction of the leachate collection system in the landfill may pose some problems
because of the heterogeneous nature of the solid waste. However, excavators that la:
pipe and backfill without the need of an open trench are available from specialty
contractors.
8-2
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8.1.7 Cost
The cost for Alternative 2 is estimated to be significantlv less than Alternative 3 for
Landfill No.4. (Table 7). . . .
I Table 7 !
Landfill No. .. Alternatives
I I
1 lA 2 3
Cover Renovation, Multilayer Cap.
Sludge Lagoon Leachate and Sludge
Limited Groundwater Lagoon Groundwater
No Action Action Source Control Collection
Estimated Oipital SO S385.000 S2.38O.000 SlO.800.000
Cos ts
Estimated Annual 0 36.000 220.000 230.000
O&M Costs
Estimated Present- 0 756.000 3.630.000 11.200.000
Worth Costs
8.1.8 Agency Acceptance
The U.S. EPA and GEPD have rejected Alternatives 1 and lA since they are' not
sufficiently protective of public health and the environment. Alternative 2 has also
been rejected since it does not comply with the RCRA ARAR requirement for a
landfill cover of lower permeability than the underlying layer.
8.1.9 Community Acceptance
Two comments regarding the Landfill No.4 selected remedy were received. One was
in favor of the selected remedy and the other questioned the cost effectiveness of
placing a low permeability cover over the landfill since the leachate collection system
would capture infiltrating water anyway. Robins AFB believes reduction of
infiltration is an important aspect of the selected remedy since the waste will remain
onsite and contaminant leaching could continue far into the future.
Judging by the comments received, it is believed that the community is supportive of
the Landfill No.4 selected remedy.
8.2 SLUDGE LAGOON
8.2.1 Overall Protection of Human Health and the Environment
The overall protection of public health and the environment for the Sludge Lagoon is
related to the reduction of mass and migration of hazardous substances and reduced
potential for direct contact with hazardous substances.
8-3
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1-- -
Based on the ecological assessment. the risk to the environment wi}] be reduced or
eliminated by imp!e~mentation of a final remedy. whIch includes a ROD for all
operable units. It is reasonable to e:l::pect that some ecologicalenvironmental henetits
are achieved by controlling the source of contamInation from Zone 1 in Operahk
Lmt 1.
Alternative 1 provides no protection. Alternative 2 provides for an estimated 75 to
90 percent removal of VOCs and greatly reduces the risk of releases through
solidification of residual contaminants. Alternative 4 offers the advantage of more
complete organic contaminant destruction-an estimated 99.99 percent-of tOtal
organic contaminants versus 90 to 99 percent of volatile organic under Alternative 3.
Alternative 3. however, destroys mobile organics contaminants as well as disposes of
the treated residuals in an RCRA Jandfill.
8.2.2 Compliance with AR.\Rs
Alternatives 1 or lA do not comply with action-specific or chemical-specific ARARs
associated with the Sludge Lagoon. Alternative 2 complies with ARARs includes a
cap over the Sludge Lagoon to minimize leaching and meet closure requirements.
Once Alternative 2 is completed it should be easier to achieve the chemical-specific
ARARs in the groundwater. Alternative 4 complies with the ARARs.
Alternative 3 wiJJ be conducted in accordance with requirements for RCRA land
disposal. since the Sludge Lagoon will be excavated. The L TV is estimated to be able
to achieve the land disposal restriction requirements.
Because the treated waste will be placed in a RCRA permitted landfill. management
of ash and other residual materials wjJJ meet RCRA ARARs.
8.2.3 Long-Term Effectiveness and Permanence
The four alternatives represent a range of technologies for remediation of the Sludge
Lagoon wastes. from naturaJ attenuation, in Alternatives 1 and lA to incineration
with ash solidification in Alternative 4.
Alternative 2 includes ISVE and in situ solidification of remaining contaminants.
In situ techniques cannot guarantee complete mixing of the sludge-contaminated soil
mass. Long-term monitoring will be required to evaluate the effectiveness of the
remedy.
The residual risks from Alternative 3 are expected to be 19wer than Alternative 2
residual risks because the hazardous substances are excavated, treated, and disposed
of in an onsite RCRA landfill. The potential for release of contaminants from a
RCRA landfill is considered small, because organic contaminants will have first been
reduced by about 90 percent and inorganic contaminants immobilized.
The residual risks from Alternative 4 are expected to be somewhat lower than for
Alternative 3 because of the greater destruction efficiency of incineration-about
99.99 percent. The inorganic contaminants will be immobilized through solidification.
8-4
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8.2.4 Reduction of Toxicity, Mobility, or Volume Through Treatment
Alternatives 1 or 1A offer no reductions through treatment.
The use of various organic treatment technologies—Alternative 2, ISVE;
Alternative 3, LTV; Alternative 4, incineration—would have increasing effectiveness
on the reduction of toxicity, mobility, or volume. It is estimated that Alternative 2
would remove 75 to 80 percent of VOCs; Alternative 3 will remove 80 to 99 percent
VOCs and a broader range of semivolatile contaminants and Alternative 4 will
destroy more than 99.99 percent of the organic hazardous substances.
Alternatives 2, 3, and 4 include solidification intended to render treated contaminants
immobile.
8.2.5 Short-Term Effectiveness
Impacts to the Robins AFB community during the remedial action are related to:
1) the potential release of VOCs; 2) onsite dust, noise, and erosion effects generated
by construction activities, and 3) truck traffic associated with hauling materials and
equipment.
Workers have a greater potential for exposure to hazardous substances for
Alternatives 3 and 4 compared to Alternative 2 because the Sludge Lagoon waste is
excavated and handled.
The time periods estimated to implement the alternative are 31 months for
Alternative 2, 48 months for Alternative 3, and 48 months for Alternative 4.
8.2.6 Implementability
Alternatives 2, 3, and 4 involve technologies that have multiple vendors. These
technologies require specialized procedures and equipment, but are commercially
available.
8.2.7 Cost
The costs for Alternative 2 is estimated to be significantly less than the costs of
Alternative 3 or Alternative 4 for the Sludge Lagoon. (Table 8).
8-5
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I Table 8 I
Sludge Lagoon Altemathes
-'
I 3 Exca\ation,
IA Exca\'ation and Incineration,
2 L TV Followed by Solidification
ISVE and Solidification and and
~o Limited In Situ Onsite RCR.\ Replacement
Action Action Solidification Landfill Disposal Onsite
EstImated Capital SO SO S6,2oo.000 S 1-',2oo.CXXJ S 1 - .5()O.(~ ~ I
Costs
Estimated Annual a 0 1"+00 5.200 5.2i))
0&\1 Costs
Estimated Present- a a 6.300,000 1,+,300.000 1'7 .500.00U
Worth Costs
8.2.8 Agency Acceptance
The C.S, EPA and GEPD have rejected Alternatives 1 and lA since they are not
protective of public health and the environment and do not meet site AR-\Rs.
8.2.9 Community Acceptance
Several comments on the Sludge Lagoon selected remedy were received. Concern
was expressed over the potential for leaching of contaminants from the solidified
waste and for potential air emissions from the treatment process. The degree of
contaminant leaching from the treatment soils will be determined dunng desIgn
treatability testing, The selected remedy would be implemented only if the testing
showed remedial goals are achievable. Air emission controls will be used in the
selected remedy to control volatile organic contaminant emissions to concentrations
below those posing risks to human health,
Given the treatability test and monitoring that will be performed. it is believed that
the community is supportive of the selected remedy for the Sludge Lagoon.
8-6
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~
9.0 SELECTED REMEDY
Based upon consideration of the requirements of CERCLA. the detailed analysis of
the alternatives, and public comments. Robins AFB in consultation with U.S. EP A
and G EPD have determined that the most appropriate remedy for Landfill ~o. 4 is
~ternative 2 plus the addition of clay to the cover and a leachate control system. and
tor the Sludge Lagoon the most appropriate remedy is Alternative 2.
The complete remedy for Operable Unit 1, Source Control includes:
.
.
.
.
.
.
Surface water run-on diversion
Landfill No.4 cover renovation including clearing, filling, regrading,
addition of soil and clay cover material, and seeding
Leachate control for Landfill No.4 and treatment at Robins AFB
Sludge Lagoon groundwater collection and treatment at Robins AFB
Treatment of the Sludge Lagoon to remove VOCs, followed by
solidification for the immobilization of metals.
Environmental monitoring to determine effectiveness of the remedial
action
Prior to final design several bench and pilot scale tests will be needed. Pilot scak
leachate collection tests are planned and bench and pilot scale tre.atability testing of
the landfill leachate, Sludge Lagoon soils. and groundwater will be performed. The
results of these tests will enable adjustments to the final design, recalculation of
implementation costs, and determination of performance criteria to meet the
conceptual approach and outlined objectives.
The estimated cost of the selected remedy is presented in Table 9.
9.1 REMEDIATION GOALS
The specific objectives of the selected remedy are to:
1.
Significantly reduce surface water run-on to Landfill No.4 and reduce
the potential for infiltration and leaching of ~ontaminants from the
landfill to the groundwater.
Reduce infiltration through increasing run-off of precipitation from the
landfill cover and achieving a landfill cover permeability less than the
underlying soils.
2.
3.
Reduce the groundwater mound in the landfill to reduce groundwater
contact with contaminants in the fill.
9-1
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I Table 9 I
Selected Remedy Cost Estimate"
I
Landfill ~o. 4 Leachate
Sludge Co\'er Renovation Collection Lagoon
Lagoon ~ith Addition GW Collection
Treatment of Cla~,b and Treatment
Estimated Capital Cost 56.200.000 54.000.000-13.000.000 S2.500.0(l()
Estimated Annual 0&\1 Cost 1. 400 43.000-30.000 290.0()()
Estimated Present Worth Cost 56.300.000 4.400.000-13.300.000 4AOO.()()1)
a Order-of-magnitude cost estimates based on FS assumptions for remedial componenh
t- Cost range based on varying assumptions on:
. Clay rhickness (1' vs. 2')
. Clay source (local clayey sand vs. bentonite plus local clay)
. Cover slope (10(; vs. 30(;)
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4.
Treat Sludge Lagoon contaminants that could cause exceedance of
groundwater and surface water goals based on information obtained
from. Toxicity Characteristics Leaching Procedure (TCLP) extraction
tests.
5.
Collect and treat contaminated groundwater in the Quaternarv and
Providence aquifers from below-and immediately downgradie~t of the
lagoon that has a potential to adversely impact wetlands and surface
water receptors.
Formally establish institutional controls to eliminate potential exposures
to hazardous substances through property restrictions.
Contaminant specific remedial goals have not yet been established for the treatment
of soils at the Sludge Lagoon since they are dependent on establishment of
groundwater goals (to be developed in Operable Unit 3) protective of groundwater
and surface water receptors. The Zone 1 groundwater operable unit RIIFS currently
underway will develop goals for groundwater based on potential receptOr locations
and fate and transport analysis. It is anticipated that the Sludge Lagoon remedial
goals will be based on meeting the groundwater goals in a TCL? extract.
6.
9-2
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L
I
10.0 STATUTORY DETER.\IINATIONS
Cnder its legal authorities. the EPA's primary responsibility at Superfund SiteS IS tll
under13.ke remedIal actions that achieve adequate protectIon of human health cwJ the
en\ironment. In addition. Section] 21 of CERCLA establishes several other St:.ltut"r\
reqUIrements and preferences. These specify that when complete. the selected'
remedial action for thIs site must comply with applicable or relevant 3.nd approprICJte
environmental standards established under Federal and State environmental laws
unless a statutory walVer is justified. The selected remedy also must be cost-effect!\ e
and utilize permanent solutions and alternative treatment technologies or reSllurce
recovery technologies to the maximum extent practicable. FinalJy. the statute IncluJe~
a preference for remedies that employ treatments that permanently and significantly
reduce the volume. toxicity. or mobility of hazardous wastes as their principal
element. The followmg sections discuss how the selected remedy meets these
statutory requirements.
10.1 PROTECTIO' OF HL\t\' HEALTH A'D THE E~"lRO'\IE'T
The selected remedy protects human health and the environment through cappIn:: l\t
Landfill :\0. ~. collection of landfill leachate. treatment of VOC contaminated Slill In
the Sludge Lagoon. solidification of the Sludge Lagoon soil and collection and
treatment of groundwater adjacent to the Sl~dge Lagoon.
The landfill cover and treatment of the Sludge Lagoon are expected to reduce the
site related risks from inhalation of dust and VOCs and ingestion of sOIl to below the
range of acceptable exposure levels (1O~ to 10-<». In addit10n. contributions ot
contaminants to the groundwater will be significantlv reduced bv the selected remeJ\,
Remediation of groundwater will be addressed in Operable Cnlt 3. Short-term mk~
occurring during construction will be controlled through a stringent health and ~Jtc::
program. '0 adverse cross media impacts are expected.
10.2 CO\IPLL\'CE \\lTH APPLICABLE OR RELEVA'T
A'D APPROPRL\ TE REQLIRE\IE'TS
The selected remedy will comply with all ARARs. The following were identified as
ARARs for Operable Unit 1:
RCRA requirements for landfill closure in 40 CFR 26~.111 Subpart G.
which specifies a cap with a permeability less than or equal to the
permeability of any bottom liner or natural subsoils present at the site.
.
.
RCRA disposal requirements. 40 CPR 26~, '
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.
Georgia Air Quality Act requirements for treatment of air emissions
from removal of VOCs from the sludge lagoon soil.
.
Requirements to avoid adverse effects from construction in a 100-vear
flood plain under Executive Order 11988. .+0 CFR 6 and .
40 CFR 264.18(b) .
.
Requirements to minimize destruction. loss or degradation of wetlands
under Executive Order 11990 and 40 CFR 6.
.
Endangered Species Act. The existance of endangered or threatened
species will be investigated in Operable Unit 2.
10.3 COST.EFFECTIVENESS
The selected remedy for Landfill No.4 has been determined to provide overall
effectiveness proportional to its costs. The selected remedy is protective of public
health and the environment and is less expensive than Alternative 3. The selected
remedy for the Sludge Lagoon has also been determined to be protective of public
health and the environment and is substantially less expensive than low temperature
thermal volatilization or incineration.
10.4 UTILIZATION OF PERMANENT SOLUTIO~S AND ALTERNATIVE
TREAT\IENT TECHNOLOGIES (OR RES01.:RCE RECOVERY TECHNOLOGIES)
TO THE MAXIMUM EXTENT PRACTICABLE
It has been determined that the selected remedy for operable Unit 1 represents (he
maximum extent to which permanent solutions and treatment technologies can be
utilized in a cost-effective manner for Landfill No.4 and Sludge Lagoon source
control operable unit. Treatment of the LandfiJI No.4 contents was found to be
impractical because of the large size of the landfiJI (45 acres).
Of the alternatives that are protective of human health and the environment and
comply with ARARs. Robins AFB has determined that the selected remedy provides
the best balance of tradeoffs in terms of long-term effectiveness and permanence.
reduction in toxicity, mobility or volume achieved through treatment, short-term
effectiveness. implementability, cost, while also considering the statutory preference
for treatment as a principle element and considering state and community acceptance.
While the LandfiJI No.4 Alternative 3 offers the greatest long-term effectiveness and
permanence because it includes both a low permeability ~ap and a leachate collection
system. it was concluded that the extra costs of this redundancy were not justified in
view of the overall risks from the site. The selected remedy for Landfill No.4
reduces the potential for infiltration and collects infiltration via the leachate collection
system. The selected remedy for LandfiJI No.4 offers the same or better reduction in
toxicity, mobility, or volume through treatment than that provided by the three FS
alternatives through collection and treatment of the l~ndfill leachate and
contaminated lagoon groundwater. While short-term construction risks to workers are
expected during installation of the leachate collection system, it is believed that this
risk is outweighed by the need to install the leachate system for the protection of
public health and the environment.
10-2
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The selected remedy for the Sludge Lagoon does not offer as high a degree ut long-
term effectiveness and permanence as the L TV or incineration alternatIve. However.
it is expected to signIficantly reduce the risks associated with the Sludge Lagoon
through removal of the VOCs and solidification of the metals. Treatabilitv testlnc W1!]
be co~ducted to verify the abiJity of vapor extraction and solidification to reduce the
amount of contaminant leaching to concentrations below those causing unacceptable
risks. The greater COSts associated with L TV and incineration are not considered !()
be JustIfiable In view of the expected effectiveness of the selected remedy. The
selected remedy uses treatment to reduce the VOC content in the Sludge Lagoon b\
an estimated 7) to 80 percent. WhiJe L TV and incineration wiJl remove greater'
amounts. solidification of the residuals is expected to reduce mobiliry to be!cw.
concentrations posing risks. Short-term construction related effecrs on the communlt~
and workers would be the least under the selected remedv if in situ treatment IS
viabJe. otherwise effects are generally similar between alternatives.
The selected remedy for Landfill No.4 and the Sludge Lagoon is consistent with
program objectives that indicate highly toxic or mobile wastes are a priomy for
treatment. Treatment of the less concentrated wastes of Landfill ~o. ~ was found t,~
be impracticable. In general. the differences in long-term effectiveness and reductlon~
in toxicity. mobility. or voJume between the protectIve alternatives were Judged !l1 be
relatively minor in view of the potential risks. The selected remedy is the least
expensive of the alternatives that are protective of human health and the emlronmem
and that meet ARARs. In addition. the selected remedy for the Sludge Lagoon may
be performed in situ. thus reducing potential short-term risks to workers and
resIdents.
10.5 PREFERE:\CE FOR TREA T'tE:\T AS A PRI:\CIPAL ELE'IE'T
Treatment of the Sludge Lagoon is a principal element of the selected remedy.
Because the Sludge Lagoon contains the most concentrated area of COntamlOants It
represents one of the principal threats of Zone 1. Therefore. the statutory preference
for remedies that employ treatment as a principal element is satisfied.
10.6 DOCl"'tE'TATIO' OF SIG:\IFICA'T CHA:\GES
'0 significant changes from the proposed plan were made.
10-3
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COMMUNI1Y RELATIONS
RESPONSIVENESS SUMMARY
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CO\tl\tU~ITY RELA TIO~S RESPO~SIVE~ESS SU't:\L\RY
1.0 O\'ER\lEW
R"bms AFB along with C.S. EPA and G EPO he Id a publIc meermg on \1ay S. 1 YY l.
at the Warner Robins City HalJ to discuss the results of the RLFS. present the
prl)posed plan and solicit comments and questIons from the public. The majorIty l,t
questluns and comments received during the public comment period were received
during the public meeting. In general the comments were supportive of the ProposeJ
Plan for Landfill ~o. -+ and the Sludge Lagoon.
2.0 BACKGROC\D O~ CO:\1\IL~ITI' I~\lOLVE:\IE~T
An active community relations program providing information and soliciting mput has
been conducted bv Robins AFB for Zone 1. Interviews of citizens on base and m
Warner Robins were conducted in the summer of 1990 to identify community
concerns. ~o significant concerns that required focused response were Ident'lfied.
Regular mformational project updates have been provided to the public through
tele\'ision programs. the Robins AFB newspaper. nle Rev-Up. the Wanzer Rohim
Dad\' SUIl. and the .\facon Telegraph. Rohim Report. a weekly IS-mmute releVlS10n
program produced by the Office of Public Affairs has provided routine progress
updates. This program is aired Sunday mornings on W\1AZ-TV in \1aclm. Georg!J,
It also is telecast on Cox Cable and Watson Communications Cable. whIch are
available to Robins AFB and Warner Robins. Weeklv informational articles ha\ e
appeared in nle Rev-Up newspaper. In addition. ~PL site and IRP fact sheets hJ\ e
been prepared and made available in the Environmental Information Repository.
located in the ~ola Brantley Ytemorial Library in Warner Robins.
3.0 SL~1\L\RY OF Pl'BLIC CO:\1\IE~T A~D AGE~CY RESPO:\'SE
Comments and questions raised during the public meeting held on \1ay 8. 1991. and
those received during the public comment period are summarized below.
1.
One resident asked when was disposal at the landfill stOpped. An ex-employee
stated that he believed dumping in the area continued at least until 198~.
Robins AFB Response: Landfill ~o. 4 and Sludge Lagoon were closed in 1978. After
that time sludges from the Industrial Wastewater Treatment Plant (I\\-TP) and
Sewage Treatment Plant (STP) have been dumped in a nearby area outside Zone I.
The state of Georgia has been notified and this area is listed in the base Installatlon
Restoration Program (IRP) and is being evaluated.
..,
One resident asked how the landfill investigation was performed and where are
the records of the investigations.
Robins AFB Response: Samples were taken of the soil and materials in the Sludge
Lagoon and LandfilJ ~o. 4 and analyzed for a comprehensive list of contaminants.
Results are available in the Remedial Investigation Report located in the
Environmental Information RepositOry.
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3.
Two residents questioned whether local drinking water wells would be
monitOred, .
Robins AFB Response: Oftbase. the City of Warner Robins performs routine
monitoring of its drinking water. Robins AFB tests its water supply routinely and
analyzes for a full range of contaminants. Wells west of Highway 247 cannot be
contaminated as a result of Robins AFB because groundwater tlow on the base is to
the east. directly away from Highway 247.
4.
One resident commented that no one from the local community or employee
representative of the base was on the panel at the public meeting. .
Robins ArB Response: While the comment is true for the panel presenting and
answering questions at the public meeting. the community relations process did
include interviews with community residents to solicit input on community concerns.
5.
The Houston CountY Board of Health commended Robins AFB on its
openness, responsiveness. and its desire to accelerate the cleanup program. A
resident also commended the base for serving as a leader in the environmental
world.
Robins ArB Response: Robins AFB has had an active community relations program
and will continue the program through remediation. The commendations are
appreciated.
6.
Citizens for Responsible Environmental Planning commented that the reason
for lack of public participation may be due to the fact that Robins AFB is the
largest employer in the area and that Robins AFB has downplayed the
significance of the health risk.
Robins ArB Response: Robins AFB believes community involvement in the remedy
selection process was good. The base has nOt misrepresented the risks to public
health. but rather has tried to accurately present the results of the remedial
investigations and the risk assessment for Landfill No.4 and the Sludge Lagoon.
7.
A letter from the Ocmulgee Sierra Club stated that citizen participation was
limited due to the inability of the base to incorporate public scrutiny and that
the base holds a power over people who work on the base.
Robins AFB Response: Robins AFB believes community relations in the remedy
selection process was good. A community relations plan was written in March 1990
and was used during the process. Several newspaper ariicles and news stations
presented information about the site, the remedial alternatives, and risks associated to
health and the environment. The public meeting also provided the community an
opportunity to express concerns of the preferred alternative for the remedial action of
the source control.
8.
Several residents and the HoustOn County Bo~rd of Health expressed concern
about the long-term monitoring of the site. In particular, questions were asked
about who will perform the monitOring, will it be continued as long as the
wastes remain, a~d will adequate records be maintained.
.,
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Robins AFB Response: Robins AFB will ContInue monitoring the site ground\'. ,Hc'r
and surface water as long as the wastes remain onsite. The frequency of monlt('f1n~
may diminIsh In the future If the data indicate that risks are not occurrin.:: dnd Me n\)!
likely to occur. G EPO and EPA will be kept Informed of monitoring res-ults dnd
records documenting the results will he maIntaIned at Robins ,-\FE. G EPO. anJ In the
EmJronmental ReposItory. In addItion. every 5 years a formal review of the
performance of the selected remedy is performed. and if necessary. modifications !\)
the remedv \\111 be made. Also the remedv is revJewed bv G EPD when the R,)htns
,-\FB RCRA permit is renewed. - .
9.
One resident requested a list of example sites where the selected remeJy \''',is
similar to the one for Zone 1.
Robins AFB Response: A !ist of sites with descriptions of the remedies will he sent t,.'
the resident. Some of the sites using similar solidification techniques are: Kerr-
\1cGee Refining Corp. in Dubach. Louisiana. an oil reprocessing plant in
Douglasville. Pennsylvania. the Portable Equipment Salvage Company In ClachamCls.
Oregon. Soil vapor extraction has been used at numerous sites including the Verllnd
site in Battle Creek. \1ichigan.
10.
A question was asked as to the potential for leaching of contamInants trllm ,he
solidified waste.
Robins AFB Response: TreatabiJity tests will be performed on the Sludge La~oon
wastes prior to Implementation of the remedy. The objective of the tests wIll be !()
determine if contaminant leaching occurs and if so, how much leaching occurs. The'
remedy will not be implemented if the testing shows that leaching at concentratIons
that could adversely affect groundwater or surface water can occur. One aspect ()t
the remedy. soiJ vapor extraction. is intended to reduce the potential for leachJn~ h:
remOYing the mobile contaminants prior to solidification.
11.
A resident commented that he felt the selected remedy for the landfill IS J
good alternative. but that he was concerned with whether the soil vapor
extraction system would work and concerned with the concept of Jeavmg the'
treated soil in place. His preference for the Sludge Lagoon is disposal in a
RCRA landfill.
Robins AFB Response: Treatability testing of the soil vapor extraction system is also
planned prior to implementation. As stated above, the remedy will not be
implemented if sufficient organics cannot be removed. Disposal of the treated wastes
in a RCRA landfill is not considered cost effective becat1se the potential for leachIng
of the solidified wastes at concentrations posing risks is not considered significant. In
addition. construction of a RCRA landfill on base mav not be desirable because of
the added burden of maintenance and long-term monItoring of the facility.
12.
A resident expressed concern over the potential for air pollution from the soIl
vapor extraction system.
Robins AFB Response: The soil vapor extraction system will include emission
controls to remove the volatilized organic contaminants to concentrations below those
posing risks to human health.
..,
.)
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13.
A question was asked as to what role C.S. EPA and GEPD played in the
remedy selection process and if the agencies were in agreement with the
selected remedy.
Robins A~ Response: Georgia EPD serves as the regulatory agency for Zone l.
U.S. EP A IS also a regulatory agency while Robins AFB is the lead agency. C.5. EP A
and GEPD were consulted throughout the RI/FS and remedy selection process and
modifications to the remedy were made as a result of their input. C .5. EP A and
GEPD are in agreement with the proposed plan.
14.
A resident expressed concern as to the cost effectiveness of placing a cover
over the landfill if the leachate collection system will capture infiltrating water
anyway.
Robins AFB Response: The cover renovation will include removing the trees on the
landfill and adding clay to the cover. These actions are expected to reduce infiltration
reaching the leachate collection system and thus reduce the cost of leachate .
treatment. Because the waste will remain onsite and contaminant leaching could
continue far intO the future, Robins AFB believes the reduction of infiltration is an
important objective of the selected remedy.
15.
Citizens for Responsible Environmental Planning expressed their preference
for Sludge Lagoon Alternative 3-Excavation, L TV, Solidification. and Onsite
RCRA Landfill. They commented that the proposed plan alternative is not
the best available technology, has a high level of uncertainty to its effecti\"eness
and that their is a lack of histOric operational data available. In addition. they
commented that an onsite RCRA landfill would be useful for remediation of
other Robins AFB sites.
Robins AFB Response: As stated in response to comment number 4, treatability
testing of the soil extraction system and solidification system is planned to determine
the effectiveness of the proposed remedy prior to implementation. If they are not
capable of reducing contaminant leaching to concentrations below those causing risks
to public heath or the environment, they would not be irriplemented. If this were to
occur, Robins AFB would re-evaluate Alternatives 3 and 4 and propose one of the
two in another proposed plan. The treatability testing is expected to address the
concern over uncenainties in effectiveness and lack of site-specific operational data.
Innovative or alternate treatment technologies cannot be ruled out because historic
operational performance data is not as great as other technologies.
Citizens for Responsible Environmental Planning expressed their preference
for Landfill No.4 Alternative 3--Multilayer Cap and Leachate and Lagoon
Groundwater Source Contro\. They commented that the proposed plan
alternative would allow a significant amount of contamination to leach into the
groundwater, that it may still not be in compliance with ARARs, that it does
not include needed groundwater collection and treatment, and that additional
studies of wildlife in the wetland be performed..
Robins AFB Response: The proposed plan includes a leachate control system to
intercept infiltrating contaminants and to control groundwater that is in contact with
the landfilled waste. It appears that the comments assumed that a leachate control
16.
4
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system was not included in the proposed plan. Reducing infiltration to very low
amounts, as in Alternative 3 is not believed to be cost-effective since the objective of
the leachate control system is to capture the leaching, contaminants. '
V.S. EPA
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