Superfund Record of Decision Tobyhanna Army Depot OU 1 Tobyhanna PA


                                    EPA/ROD/R03-97/096
                                    1997
EPA Superfund
     Record of Decision:
     TOBYHANNA ARMY DEPOT
     EPA ID: PA5213820892
     OU01
     TOBYHANNA, PA
     09/30/1997

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                                              FINAL

                                                  TOBYHANNA ARMY DEPOT
                                                     OPERABLE UNIT 1
                                                     (Areas A and B)
                                                     RECORD OF DECISION

                                                       Prepared by:
                                                     Environmental Science & Engineering, Inc.
                                                     Gainesville, Florida


                                                         September 1997

                           Distribution limited to U.S. Government Agencies only for protection of privileged
information evaluating another command.  February 1996; Reguests for this document must be referred to:
Commander,  U.S. Army Environmental Center,  Aberdeen Proving Ground, MD 21010-5401; or Commander, Tobyhanna
PA.

                                                 Prepared for:

                                        U.S. Army Environmental Center
                                        Installation Restoration Division
                                     Aberdeen Proving Ground, MD 21010-5401

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Final

Tobyhanna Army Depot
Operable Unit 1
(Areas A and B)
Record of Decision

Prepared for:
U.S. Army Environmental Center

Prepared by:
Environmental Science & Engineering, Inc.
Gainesville, Florida
September 1997


ESE Project No. 3922039G

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                    Tobyhanna Army Depot Record of Decision

                              Declaration

Site Name and Location

Tobyhanna Army Depot
Tobyhanna, Pennsylvania
Operable Unit 1  (Areas A and B)


Statement of Basis and Purpose

This decision document presents the selected remedial action for Operable Unit 1  (OU1) at
Tobyhanna Army Depot  (TYAD),  in Tobyhanna, Pennsylvania, which was chosen in accordance
with the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA),
as amended by the Superfund Amendment and Reauthorization Act of 1986  (SARA) and, to the
extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan  (NCP).
This decision document explains the factual and legal basis for selecting the remedy for OU1 and
is based on the administrative record file for this site.

The Commonwealth of Pennsylvania concurs with the selected remedy.

Assessment of the Site

Actual or threatened releases of hazardous substances from OU1 can be addressed by
implementing the response action selected in this Record of Decision  (ROD),  thereby mitigating
any possible imminent and substantial endangerment to public health, welfare, or the
environment.

Description of the Selected Remedy

The remedial action jointly selected by the Army and U.S. Environmental Protection Agency
(EPA)  is the final remedy for OU1.  A previously conducted removal action removed a
groundwater contamination source in OU1, and represented a source control measure that
addressed principal threats posed by contaminated soil and significantly reduced the potential for
contaminants to further degrade groundwater.  The response action for groundwater, Natural
Attenuation/Long-Term Monitoring/Institutional Controls, will minimize the threat of migration of
contaminants in groundwater.   Implementing the selected remedy will reduce risks to human health
and the environment.

The major components of the selected remedy include periodic groundwater monitoring for the
purpose of ensuring that the strength and size of the groundwater plume continues to decrease
over time through the process of natural attenuation and institutional controls,  to ensure
contaminated groundwater above maximum contaminant levels  (MCLs) is not used for potable
purposes.  A removal action,  which removed a source of groundwater contamination within OU1,
was completed in 1995.  All soils in excess of soil cleanup levels developed for this site were
excavated and transported offsite to a disposal facility.  No further action, therefore, is reguired
for soils.

This ROD for OU1 is the third ROD issued for TYAD.  Two other RODs have been finalized at TYAD:

   •      OU2 addresses the former polychlorinated biphenyl (PCB)  transformer substation site
          (AOC#63), and
          OU3 addresses buildings IOC and S90 (AOC #37 and AOC #38,  respectively).

Three other operable units have been identified at TYAD:

   •      OU4 addresses AOC's associated with a metal finishing pre-treatment plant (AOC #9
          through AOC #18,  AOC #53,  and AOC #54),
   •      OU5 addresses AOC's associated with the  sewage treatment plant (AOC #19 through
          AOC #36,  and AOC #56),  and
   •      OU6 addresses AOC #42 and AOC #43 (waste motor oil/drum storage areas).

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Statutory Determinations

The selected remedy is protective of human health and the environment, complies with Federal
and State requirements that are legally applicable or relevant and appropriate to the remedial
action, and is cost effective.  This remedy uses permanent solutions and alternative treatment or
resource recovery technologies, to the maximum extent practicable, and satisfies the statutory
preference for remedies that employ treatment that reduces toxicity, mobility, or volume as a
principal element.

Because this remedy may result in hazardous substances remaining onsite above health-based
levels, a review will be conducted within 5 years after the commencement of remedial action,
to ensure that the remedy continues to provide adequate protection of human health and the
environment.

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                      Tobyhanna Army Depot Record of Decision

                               Table of Contents

Section                                                         Page

Declaration 	  i

1.0  Site Name,  Location,  and Description 	  1-1
     1.1 Site Topography 	  1-1
     1. 2 Adj acent Land Use 	  1-1
     1.3 Surface Water Hydrology 	  1-1
     1.4 Site Soils 	  1-1
     1. 5 Geohydrologic Setting	  1-7
         1.5.1 Shallow Unconsolidated Deposits 	  1-7
         1.5.2 Consolidated Bedrock 	  1-7
     1. 6 Groundwater	  1-10
         1.6.1 Shallow Unconsolidated Deposits	  1-10
         1.6.2 Consolidated Bedrock Aguifer 	  1-10
     1.7 Wetlands 	  1-10

2 . 0  Site History and Enforcement Activities 	   2-1
     2 .1 Site History 	   2-1
     2 . 2 Enforcement Activities 	   2-2

3.0  Highlights of Community Participation 	   3-1

4.0  Scope and Role of OU1 	   4-1

5 . 0  Summary of Site Characteristics 	   5-1
     5.1 Overview and Extent of Site Contamination 	   5-1
         5.1.1 Soil 	   5-2
         5.1.2 Groundwater 	   5-3
         5.1.3 Surface Water and Sediment 	   5-7
     5 .2 Routes of Exposure 	   5-7
         5.2.1 Direct Contact Route 	  5-10
         5.2.2 Ingestion Route 	  5-10
         5.2.3 Inhalation Route 	  5-11
         5.3 Contamination Migration 	  5-11

    6.0  Summary of Site Risks 	  6-1
         6.1 Introduction 	  6-1
         6.2 Human Health Risks 	  6-3
             6.2.1 Media of Concern 	  6-4
             6.2.2 COPCs 	  6-4
             6.2.3 Exposure Assessment 	  6-8
             6.2.4 Toxicity Assessment 	  6-14
             6.2.5 Risk Characterization 	  6-16
         6.3  Ecological Risks 	  6-26
         6.4  Residual Risk Evaluation 	  6-26

    7.0  Description of Alternatives 	  7-1
         7.1 Alternative Description 	  7-4
             7.1.1 Alternative 1:  Groundwater: No Action;  Soil:  No Further Action 	  7-4
             7.1.2 Alternative 2:  Groundwater: Natural Attenuation/Long-Term
                   Monitoring/Institutional Controls; Soil:   No Further Action 	  7-4
             7.1.3 Alternative 3:  Groundwater: Limited Groundwater Treatment/
                   Institutional Controls/Monitoring; Soil:  No Further Action 	  7-5

    8.0  Summary of Comparative Analysis of Alternatives 	  8-1
         8.1 Overall Protection of Human Health and the Environment 	  8-2
         8.2 Compliance with ARARs 	  8-2
         8.3 Long-Term Effectiveness and Permanence 	  8-4

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         8.4 Reduction of TMV through Treatment 	 8-4
         8.5 Short-Term Effectiveness 	 8-4
         8.6 Implementability 	 8-5
         8.7 Cost 	 8-5
         8 . 8 State Acceptance 	 8-5
         8 . 9 Community Acceptance 	 8-6

    9.0  Selected Remedy 	 9-1
         9.1 Description of Selected Remedy 	 9-1
         9.2 Estimated Costs 	 9-2

         9.3 Performance Standards 	   9-2

 10.0   Statutory Determinations 	 10-1
        10.1 Overall Protection of Human Health and the Environment 	 10-1
        10 . 2 Compliance with ARARs 	10-2
             10.2.1 Contaminant-Specific ARARs 	 10-3
             10.2.2 Action-Specific ARARs 	 10-3
             10.2.3 Location-Specific ARARs 	 10-3
        10.3 Cost Effectiveness 	 10-3
        10.4 Utilization of Permanent Solutions and Alternative Treatment
             Technologies or Resource Recovery Technologies to the Maximum Extent
             Practicable 	 10-3
        10.5 Preference for Treatment as a Principal Element 	 10-4

11. 0 References 	 11-1

Attachment A	  A-l

                         List of Tables


Table 2-1   Maximum Contaminant Concentrations in Soil-Areas A and B,  1994,
            and Area B Maximum Concentrations Following the 1995
            Removal Action 	 2-6
Table 5-1   Maximum Contaminant Concentrations in Groundwater 	 5-4
Table 5-2   Summary of Exposure Pathways for TYAD 	 5-9
Table 6-1   Final COPCs for Groundwater 	 6-5
Table 6-2   Current and Future Onpost and Offpost Groundwater
            Concentrations, UCL 95,  	  6-9
Table 6-3   Chronic Dose-Response Toxicity Constants for the Human COPCs
            at TYAD 	 6-15
Table 6-4   Summary of Area-Specific Carcinogenic Risks 	 6-18
Table 6-5   Summary of Area-Specific Noncarcinogenic Hazard Indices 	 6-19

                  List of Figures

Figure 1-1  Location and Current Boundaries of Tobyhanna Army Depot 	 1-2
Figure 1-2  Location of Areas A and B on Tobyhanna Army Depot 	 1-3
Figure 1-3  Topographic Relief - Tobyhanna Army Depot 	 1-4
Figure 1-4  Surface Drainage Features of Tobyhanna Army Depot 	 1-5
Figure 1-5  Soil Survey May,  Tobyhanna Army Depot 	 1-6
Figure 1-6  Geologic Map of Shallow,  Unconsolidated Materials of
            Tobyhanna Army Depot 	 1-8
Figure 1-7  Geologic Map of Consolidated Bedrock of Tobyhanna Army Depot 	 1-9
Figure 1-8  Groundwater Elevation Contours,  Glacial Till Aguifer,
            Areas A and B,  March 1996 	1-11
Figure 1-9  Groundwater Elevation Contours,  Bedrock Aguifer, Areas A and B,
            March 1996 	1-12
Figure 1-10 Wetlands Map, Tobyhanna Army Depot 	1-14
Figure 5-1  TCE Concentration Contours,  1988,  Bedrock Aguifer 	 5-5
Figure 5-2  TCE Concentration Contours,  Bedrock Aguifer, 1996 	 5-6
Figure 6-1  Groundwater Sampling Locations - Offpost Wells Included Within

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            Offpost Exposure Groups 	6-2
Figure 6-2  Onpost Monitor Well Locations, Tobyhanna Army Depot 	6-7
Figure 6-3  TCE Contaminant Contours - Bedrock Aguifer (October 1990),
            Tobyhanna Army Depot 	 6-12
Figure 6-4  PCE Contaminant Contours - Bedrock Aguifer (October 1990),
            Tobyhanna Army Depot 	 6-13

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                         List of Acronyms and Abbreviations

ARAR      applicable and relevant or appropriate requirement
BRA       Baseline Risk Assessment
C-E       communications-electronics
CERCLA    Comprehensive Environmental Response, Compensation, and Liability Act
CFR       Code of Federal Regulations
COPC      chemical of potential concern
CSF       cancer slope factor
1,2-DCE   1,2-dichloroethene
DDD       1,l-dichloro-2,2-bis-(p-chlorophenyl)ethane
DDE       1,l-dichloro-2,2-bis-(p-chlorophenyl)ethene
DDT       1,l-trichloro-2,2-bis-(p-chlorophenyl)ethane
DoD       U.S. Department of Defense
EA        Endangerment Assessment
EPA       U.S. Environmental Protection Agency
EPIC      Environmental Photographic Interpretation Center
ESE       Environmental Science & Engineering, Inc.
FR        Federal Register
FS        Feasibility Study
ft        foot
gpm       gallons per minute
HI        hazard index
HRS       Hazard Ranking System
H5        Henry's law
IIA       Initial Installation Assessment
IRP       Installation Restoration Program
m         meter
MCL       maximum contaminant level
mg/kg     milligrams per kilogram
mg/kg-day milligrams per kilogram per day
mg/L      milligrams per liter
mi -2     sguare mile
NA        not appropriate
NCP       National Oil and Hazardous Substances Pollution Contingency Plan
ND        not detected
nd        not determined
NE        not evaluated
NM        not modeled
NPDES     National Pollution Discharge Elimination System
NPL       National Priorities List
O&M       operation and maintenance
OSWER     Office of Solid Waste and Emergency Response
OU        operable unit
OU1       Operable Unit 1
PAH       polynuclear aromatic hydrocarbon
PADEP     Pennsylvania Department of Environmental Protection
PCB       polychlorinated biphenyl
PCE       tetrachloroethene
ppb       parts per billion
RA        Risk Assessment
RAB       Restoration Advisory Board
RAGS      Risk Assessment Guidance for Superfund
RfD       reference dose
RI        Remedial Investigation
RI/FS     Remedial Investigation/Feasibility Study
RME       reasonable maximum exposure
ROD       Record of Decision
SARA      Superfund Amendment and Reauthorization Act of 1986
SCS       Soil Conservation Service
SDWA      Safe Drinking Water Act
TBC       to be considered
TCE       trichloroethene

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TCLP Toxicity Characteristic Leaching Procedure
TMV toxicity, mobility, and volume
TYAD Tobyhanna Army Depot
UCL 95 95 percent upper confidence limit
Ig/L micrograms per liter
USAGE U.S. Army Corps of Engineers
USAEC U.S. Army Environmental Center
VOC volatile organic compound
WoE weight-of-evidence
WWI World War I
WWII World War 11
yd 3 cubic yard

1.0 Site Name, Location, and Description

The Tobyhanna Army Depot (TYAD) is located in the Pocono Mountains of northeastern
Pennsylvania, approximately 20 miles southeast of Scranton, Pennsylvania, in Coolbaugh
Township, Monroe County. Fig. 1-1 shows the location and current boundaries of TYAD. The
installation encompasses approximately 2.2 sguare miles (mi). Operable Unit I (OU1) consists of
Areas A and B. Fig. 1-2 shows the location of Areas A and B on TYAD.

1.1 Site Topography

TYAD lies in the southern New York section (locally termed the Pocono section) of the
Appalachian Plateau Physiographic Province. The section is characterized by mature glaciated
plateaus of moderate relief with broad intervening lowlands. Within TYAD, the relief varies over
a range of approximately 220 feet (ft); the lowest elevation (1,930 ft) occurs south of Barney's
Lake; the highest elevation (2,150 ft) occurs on Powder Smoke Ridge. Fig. 1-3 shows a
topographic relief map of TYAD.

1.2 Adjacent Land Use

TYAD is bordered to the north, east, and west by the Tobyhanna State Park Reserve (Fig. 1-1).
The area south of TYAD is owned by various residential property owners within the Village of
Tobyhanna.

1.3 Surface Water Hydrology

Fig. 14 shows the surface drainage features at TYAD. No through-flowing drainageways exist on
TYAD. Surface drainage, originating within TYAD, flows principally into Cross Keys Run,
Barney's Lake, and Hummler Run. Oakes Swamp receives drainage from the western and
northern portions of TYAD and discharges to the north-northwest.

1.4 Site Soils

The Monroe County Soil Survey (Lipscomb, 1981) identifies six soil series within the study area.
Fig. 1-5 depicts the soil series at TYAD. The site consists mostly of cut and fill land. The
Empeyville soils are present on the higher areas and particularly on the topographic rise that
divides the eastern and western wetland systems. Volusia soils are present toward the bottom of
gentle slopes and Chippewa, Norwich, and Mucky Peat soils are associated with topographically
low areas. Three of the six soil types within the study area (Chippewa, Norwich, and Mucky
Peat) are hydric. Two other units (Volusia and Empeyville) may have inclusions of hydric soils.
Descriptions of these soil types are presented in App. E of the Remedial Investigation/Feasibility
Study at Tobyhanna Army Depot, Draft Final Remedial Investigation Addendum (RI Addendum)
[Environmental Science & Engineering, Inc. (ESE), 1992c].

1.5 Geohydrologic Setting

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1.5.1 Shallow Unconsolidated Deposits

The shallow, unconsolidated geologic deposits present at TYAD consist primarily of materials
derived from glaciation. Fig. 1-6 shows the shallow unconsolidated deposits at TYAD. Glacial
advance and retreat cycles caused extensive bedrock surface scouring; conseguently, the depth to
bedrock at TYAD is highly variable. Due to the extremely large quantities of surface water runoff
associated with the end of the most recent glacial period, numerous cobbles and boulders were
deposited in the region now occupied by TYAD. These cobbles and boulders are interspersed with
varying amounts of sand and clay and comprise the unconsolidated material beneath TYAD,
which is knowp as glacial till. Although the till depth varies considerably throughout TYAD, the
average deposit thickness around Areas A and B is about 20 to 30 ft. Bedrock underlying TYAD
consists of fractured sandstone.

1.5.2 Consolidated Bedrock

Fig. 1-7 shows a geologic map of consolidated bedrock on TYAD. The bedrock underlying
TYAD is dominated by the sandstones of the Catskill Formation of Upper Devonian age. Two
members of this formation, the Duncannon Member and the Poplar Gap Member, are represented
at TYAD; only the latter is found in Areas A and B. The Poplar Gap Member consists of fine to
medium-grained gray sandstones. The rock is well indurated and quartzitic, with abundant trough
crossbedding. The sandstones grade upward into grayish-red siltstones and shales, which comprise
up to 25 percent of the unit. The total thickness of the unit is approximately 320 meters (m).

1.6 Groundwater

1.6.1 Shallow Unconsolidated Deposits

Groundwater is present in both the glacial till and fractured bedrock aquifers. Water in the glacial
till is not used as a potable water source. Groundwater in the glacial till aquifer generally flows
from Areas A and B toward the west. Fig. 1-8 presents groundwater contours based on data
collected during March 1996. Since the glacial till and fractured bedrock aquifers are
hydraulically linked, volatile organic compounds (VOCs) in glacial till groundwater can move
downward into the bedrock. The presence of fractures is expected to influence strongly the
groundwater flow and VOC migration through the bedrock aquifer.

1.6.2 Consolidated Bedrock Aquifer

The Poplar Gap Member of the Catskill Formation, which underlies all of the study area, is the
major source of domestic water supply. This aquifer has the potential for large yields from wells
located on fracture traces and is suitable for industrial purposes. The water quality is considered
good, with an average yield of about 2.3 gallons per minute (gpm). Historic chemical analyses of
water from wells in the Catskill Formation indicate that dissolved solids concentrations average
about 100 milligrams per liter (mg/L). Considerable variation in well depth within the Catskill
Formation is typical and is related to thickness of surficial cover, with an average depth to
bedrock of 50 ft. Depth to the groundwater surface also averages 50 ft. Water in the fractured
bedrock represents a water supply source for nearby residents. Groundwater in the fractured
bedrock aquifer flows from Areas A and B in a south-southeast direction toward the Village of
Tobyhanna. Fig. 1-9 presents groundwater contours of the bedrock aquifer based on groundwater
elevation data collected in March 1996.

1.7 Wetlands

Most wetland areas are considered environmentally sensitive because of their functional values,
which provide habitat for wildlife, serve as potential groundwater recharge areas, and improve
water quality. Barney's Lake and Hummler Run comprise wetlands that could potentially be
affected adversely by contaminant runoff from Areas A and/or B at TYAD. Materials could flow
directly from Area B into Hummler Run, or materials reaching the Barney's Lake system could
ultimately flow into Hummiler Run and impact nearby wetlands and organisms. Field surveys were
conducted to verify the nature and extent of existing wetlands identified by aerial photography and

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National Wetland Inventory maps, as well as additional wetlands. Wetlands in the area are
identified on the National Wetlands Inventory Map, FICWD, 1989. The area of wetlands
delineation on TYAD is shown on Fig. 1-10. No remedial activities are expected to occur in
wetlands. Additional wetlands information is presented in Sec. 6.0 and App. E of the RI
Addendum (ESE, 1992c).

2.0 Site History and Enforcement Activities

2.1 Site History

TYAD was initially established as Camp Summerall when the government purchased 33 mi 2 of
land in northeastern Pennsylvania in 1909. In 1913, the area was used by the Army and National
Guard for machine gun and field artillery training, and later was renamed Tobyhanna Military
Reservation. The reservation became an ambulance and tank regiment training center and an
ordnance storage depot during World War I (WWI).

The installation was deactivated after WWI and remained inactive until 1932. From 1932 to 1938,
the area was used as a camp by the Civilian Conservation Corps. From 1938 to 1941, the area
was used by cadets from West Point for field artillery training.

In 1942, the installation was reactivated as an Army/Air Force Service Unit Training Center. The
area was also converted to a storage and supply area for gliders and other eguipment of the Air
Service Command in 1944. The installation was deactivated after World War II (WWII).

The Commonwealth of Pennsylvania purchased the Tobyhanna site from the War Assets
Administration in 1949. The Department of Forests and Waters and the Pennsylvania State Game
Commission maintained the property from 1949 to 1951. During January 1951, 2.2 mi # was
obtained by the Signal Corps for depot construction. Depot construction was performed by a
civilian contractor; this contractor used the southeastern comer of TYAD as a base of operations
and an equipment staging area. The balance of the tract remained as state-owned land with the
federal government exercising recovery rights. In the following years, up to and including the
present, much of this tract has been designated as state game lands and parks.

Tobyhanna Signal Depot was established as a Class II installation during February 1953, with an
assigned supply mission. In August 1962, the depot was redesignated as TOAD (In 1994, the call
letters for Tobyhanna Army Depot were changed from "TOAD" to "TYAD") and transferred to
the U.S. Army Materiel Command. Since 1962, TYAD has assumed a variety of missions
ranging from the U.S. Department of Defense (DoD) household goods movement and storage, to
maintaining the Army's central file of motion pictures and distribution of audio-visual materials,

Currently, TYAD is a communications-electronics (C-E) maintenance and supply depot assigned
to the U.S. Army Industrial Operations Command. The primary mission is logistics support for
C-E eguipment throughout the Army. TYAD is the largest C-E overhaul facility in the Army and
is responsible for overhauling, rebuilding, repairing, converting, inspecting, testing, and
assembling items including Tactical Fire Direction Systems and Satellite Communication Systems.
Since its activation, TYAD has been a Govermnent-Owned/Govermnent-Operated installation. No
industrial leases have existed at TYAD.

The locations of known contamination at OU1 may be separated into two distinct areas. The first
of these two areas is centered around a site that was used in the past as a burning ground;
designated in the Remedial Investigation/Feasibility Study at Tobyhanna Army Depot, Final
Remedial Investigation Report A011 (RI) (ESE, 1988a) as Area A (Fig. 1-2). This area consists of
trenches and pits that were excavated and used during the late 1950s and early 1960s for burning
waste generated by TYAD. No records are available concerning the specific identity or quantities
of materials deposited at this site; however, in addition to construction debris and similar types of
waste material, flammable liquids may have been disposed in the pits to act as a fuel source for
ignition of debris.

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A second area of potential contamination was identified after the investigation at Area A had
begun. At the suggestion of a long-term resident, an area near the southeastern corner of TYAD
was examined for possible contamination. On inspection, three potential areas of contamination
were identified: a large clearing near the middle of the site, a trench containing fragments of
rusted drums near the western edge of the site, and a pile of debris with additional drum
fragments on the ground surface near the southwestern edge of the site. This area was
subseguently termed Area B (Fig. 1-2).

2.2 Enforcement Activities

The initial stage of the TYAD Installation Restoration Program (IRP), the Discovery Phase,
consisted of an Initial Installation Assessment (IIA) (records search), which was conducted in
1979 and published in January 1980. Based on the results of this assessment and active efforts by
TYAD personnel to address several of the problem areas, the U.S. Army Environmental Center
(USAEC) concluded that additional investigative efforts were not warranted. Subseguently,
USAEC determined that some of the original record searches conducted nationwide during the
late 1970s and early 1980s should be reevaluated due to changes in the environmental laws. As a
result of environmental problems discovered subseguent to the original onsite visit and changes in
the mission of the installation, TYAD was included in this relook program. During October 1986,
a reevaluation of TYAD was conducted; the final report became available in February 1988 (ESE,
1988b). USAEC reguested aerial imagery analysis support from the U.S. Environmental
Protection Agency's (EPA's) Environmental Photographic Interpretation Center (EPIC), along
with the relook program. EPIC provided a summary of any possible Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA)-related problem areas at
TYAD identifiable through evaluation of historical aerial imagery. Based on information gathered
during this reevaluation phase, conditions that merited initiation of the next phase of the IRP (i.
RI/FS) were observed.

VOCs were first discovered at TYAD in 1981 in one of the onsite drinking water supply wells
(well ON-3, see location on Fig. 1-2). An activated carbon groundwater treatment system was
subseguently installed to remove VOCs prior to use. Later that same year, sampling conducted by
Pennsylvania Department of Environmental Protection (PADEP) revealed the presence of
trichloroethene (TCE) and tetrachloroethene (PCE) (collectively referred to as VOCs) in nearby
residential wells. Although residents were subseguently notified of elevated VOC levels, TCE
concentrations did not exceed PADEP's 1981 drinking water standard of 45 parts per billion (ppb).

In August 1986, the Monroe County Planning Commission collected groundwater samples from
residential wells near TYAD, which also showed elevated levels of VOCs were in several wells.
Follow-up sampling by PADEP confirmed these findings, as well as the fact that certain wells
contained TCE levels exceeding the new federal drinking water maximum containinant level
(MCL) of 5 ppb. Based on these new findings, the Army began supplying bottled water in March
1987 to affected residences.

In September 1987, the Army initiated a RI/FS at TYAD to determine the source of the VOCs in
groundwater and to characterize its nature and extent. Results from the RI/FS confirmed that
Area B was the source of VOCs in groundwater underlying TYAD and a portion of the Village of
Tobyhanna. Although Area A was also identified as a source of VOCs, groundwater from this
area has not migrated beyond the installation boundary.

In 1989, the Army replaced the previously mentioned activated carbon groundwater treatment
system with a permanent air stripper device to remove VOCs from drinking water supply well
ON-3.

EPA completed a Hazard Ranking System (HRS) evaluation of TYAD in July 1989. TYAD was
proposed for inclusion on the National Priorities List (NPL) on July 14, 1989, and subseguently
added to the final NPL on August 30, 1990. As a result of TYAD's NPL listing, the Army and
EPA negotiated a comprehensive Federal Facility Agreement, which was signed by EPA on
November 19, 1990, and became effective on January 31, 1991.

In June and July 1990, a treatment study was performed to assess the effectiveness of removing
TCE from soils with the passive volatilization technology. This pilot study involved excavating
32 cubic yards (yd 3) of TCE-contaminated soil from Area B. The pilot study concluded that
passive volatilization would be an effective technology for removing TCE from soil.

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In September 1990, the Army conducted the second phase of field investigations to more clearly
determine the extent of groundwater containing VOCs in Areas A and B, supplement existing
hydrogeology information in the southeast portion of TYAD, confirm results from previous
surface water and sediment sampling, and examine potential impacts to environmental receptors
and critical habitats.  Results are included in the RI Addendum report.

In June 1991, the Army installed a waterline from TYAD to 23 affected residences/businesses to
provide a more continuous potable water source.  One additional resident was connected to this
supply in June 1995.  In 1991, TYAD implemented a waterline agreement with the affected
residents which provides that they will stop using their wells, and in return TYAD will
continually supply water to the 24 residences/businesses until groundwater at the affected private
wells is safe for potable purposes.  Although these residences/businesses no longer use their wells,
the waterline agreement stipulates that the wells shall continue to be made available to the Army
for monitoring purposes.  Additionally, other residents/businesses will be connected to the TYAD
water supply if VOC contaminant concentrations in their wells exceed MCLs, and this exceedance
is a result of groundwater contaminated at TYAD.  Since 1988, offsite residential wells have been
sampled semi-annually.

During the RI/FS, coal ash was discovered in soil samples collected at Area A.  Coal ash is
residue generated from the burning of anthracite coal.  To determine the extent of coal ash in
Area A and assess potential impacts to human health and the environment, the Army conducted
supplemental sampling in April 1992.  Although discrete areas of coal ash were not observed,
several samples contained a mixture of soil and coal ash.  Results from supplemental sampling
have also been included in the RI Addendum report.  A final RI report was accepted by EPA in
1988.  EPA approved the RI Addendum; Remedial Investigation/Feasibility Study at Tobyhanna
Army Depot, Endangerment Assessment (EA) ; and Remedial Investigation/Feasibility Study at
Tobyhanna Army Depot, Draft Final Feasibility Study Report for the Areas A and B Operable
Unit (FS) in 1993.

In September 1993, the Army issued the proposed Remedial Action Plan for Operable Unit 1 at
Tobyhanna Army Depot  (Remedial Action Plan).   This document presented five alternatives for
remediating contaminated soil and groundwater at TYAD.  A public meeting was held on
November 4, 1993, to discuss the alternatives presented in the Proposed Plan and explain the
reasons for the recommendation of the preferred alternative.  There was no significant comment to
the recommended alternative from the public during the public comment period.

The preferred alternative presented at the November 1993 public meeting was Alternative 4P,
which involved soil and groundwater treatment.  (The "P" denotes that this alternative was
previously considered.  However, since the collection of predesign field data, this alternative is no
longer considered applicable.)  Soil treatment was to involve excavating soil in excess of soil
cleanup levels at Areas A and B and reducing VOC concentrations using a technology called
passive volatilization.  This approach would have involved placing soil within a lined treatment
cell, which is referred to as a bubble, and forcibly drawing air through the soils to remove VOCs.

Soil cleanup levels were developed by the Summer's Model, a fate and transport model used to
determine levels to which the VOCs in soils should be reduced in order to ensure that leaching of
any contaminants from soil to groundwater would not cause the groundwater to exceed the federal
MCLs.  The cleanup levels developed for soils by the Summer's Model are as follows:

                                                            Area A    Area B

D Trichloroethene (TCE) - milligrams per kilogram (mg/kg)   0.067     1.67
D Tetrachloroethene  (PCE) - mg/kg                           0.180     4.66

The Pennsylvania Land Recycling Act of 1995,  Act 2,  also establishes cleanup levels for soil.
The Act 2 standard for both TCE and PCE in soil is 2 mg/kg.  Since the modeled soil cleanup
level for Area B is greater than 2 mg/kg (4.66 mg/kg), the Act 2 standard of 2 mg/kg was used
as the established cleanup level for PCE in soils at Area B.  Hereinafter, the Summer's model and
Act 2 cleanup levels which were used as the basis for remediation of soils at OU1 will be referred
to collectively as "soil cleanup levels".

Groundwater treatment was to involve an extraction and treatment system consisting of four
onpost extraction wells and one offpost extraction well.  Groundwater would be processed through

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an onpost treatment system, which would consist of an air stripper to remove VOCs from the
groundwater. If necessary, VOC emissions from the air stripping tower would be treated, using
vapor phase carbon, prior to discharging air to the atmosphere. After treatment, groundwater
would be discharged to one of several locations; the specific location was to be defined in a later
phase of work.

After the public comment period, the Army collected site data to evaluate the feasibility of
implementing the preferred alternative at TYAD (i.e., first two data columns of Table 2-1). For
soils, the results of the 1994 data collection effort showed that the actual extent of soil contamina-
tion was less than that originally estimated. In fact, the levels of constituents detected in soils in
Area A were less than soil cleanup levels, and therefore, no treatment was reguired at this site.
Due to the limited soil contamination found onsite in Area B, the Army conducted a Removal
Action in July 1995 and removed approximately 2,100 yd 3 of VOC-contaminated soils. The
removal action, which entailed excavation and offsite disposal of contaminated soil, was
conducted instead of using the passive volatilization technology because it was more cost
effective. Sampling of remaining site soils, conducted after the removal action was complete,
showed concentrations of VOCs (last column of Table 2-1) in soils were less than soil cleanup
levels.

Because a removal action was completed in Area B, and remaining soil concentrations in Areas A
and B are less than soil cleanup levels, no further action is warranted for VOCs in soil.

Table 2-1. Maximum Contaminant Concentrations in Soil-Areas A and B in 1994, and Area B Maximum
Concentrations following the 1995 Removal Action

Concentration (mg/kg)

Area B (prior to Area B (following
Contaminant Area A 1 removal action 2) removal action)

PCE* 0.110 14.0 0.88

TCE* 0.043 7.80 0.56

Note: mg/kg = milligrams per kilogram.
PCE = tetrachloroethene.
TCE = trichloroethene.

1 Maximum concentrations reported during original RI effort (1987): TCE = 0.449 mg/kg, PCE = ND.

2 Maximum concentrations reported during original RI effort (1987): TCE =5.05 mg/kg.
PCE =5.48 mg/kg.

*Pennsylvania's Land Recycling Act of 1995, Act 2, cleanup level is 2 mg/kg for both contaminants.
Site-specific cleanup levels are 0.067 mg/kg for TCE and 0.180 mg\kg for PCE at Area A, and
1.67 mg/kg for TCE and 4.66 mg/kg for PCE at Area B, and are based on the Summer's Model.

In December 1996, TYAD sampled additional onpost areas where coal ash material was deposited
for comparison to Area A samples collected in 1992. EPA performed a statistical comparison of
1992 and 1996 data and determined that, with the exception of one sample in Area A taken at a
depth of 4 ft, only aluminum and manganese were above background range for similar types of
soil. However, the concentrations of aluminum and manganese were below EPA's risk-based
concentration levels for industrial soil. Therefore, as long as future use remains industrial at
TYAD, no further action is necessary for soils.

For groundwater, site data showed extraction of contaminated groundwater was impractical due to
the inability of extraction wells to efficiently recover contaminated groundwater. EPA and
PADEP agreed with the Army's conclusions and recommended that the Army revise the original
Proposed Plan to delete four of the original alternatives and address two new alternatives: (1)
natural attenuation (the current preferred alternative), and (2) limited groundwater treatment. The
two new alternatives, in addition to a revised no-action alternative, were presented to the public at

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a meeting held on March 26, 1997.


3.0 Highlights of Community Participation

The RI Addendum, EA, and FS and the first proposed Remedial Action Plan  (Areas A and B)
(ESE, 1993a) at TYAD were released to the public in September 1993.  These documents were
made available to the public through information repositories maintained at the Coolbaugh
Township Municipal Building in Tobyhanna, Pennsylvania, and the Public Affairs Office at
TYAD.  The notice of availability of the RI, RI Addendum, EA, FS, and proposed Remedial
Action Plan was published in The Pocono Record on September 30, 1993.  A formal public
comment period was held from September 30 through November 13, 1993.  A public availability/
public meeting was also held on November 4, 1993, at the Coolbaugh Township Volunteer Fire
Company Hall.  The Proposed Remedial Action Plan (Revised) for Operable Unit 1 at Tobyhanna
Army Depot  (Revised Remedial Action Plan) was released to the public in March 1997.  A new
availability/public meeting announcement for the RI; RI Addendum; EA; FS; proposed Remedial
Action Plan, as well as new documents which include the Preliminary Remedial Design
(Weston, 1996) and the Contaminated Soil Removal from Area B report  (OHM, 1996) was
published in The Pocono Record on March 19, 1997.  A second public meeting for the new
Revised Remedial Action Plan was held on March 26,  1997, at the Coolbaugh Township
Municipal Bldg.

At each of the two Proposed Remedial Action Plan meetings, representatives from the Army,
EPA, and PADEP were available to summarize the remedial alternatives presented in the
proposed Remedial Action Plan (ESE, 1993a)  and Revised Remedial Action Plan  (ESE, 1997),
discuss the rationale for selecting the preferred alternative, and discuss site-related issues raised
by the public and the remedial alternatives under consideration.  In addition, during the second
public meeting, representatives from the Army, EPA, and PADEP discussed the rationale for
revising the 1993 proposed Remedial Action Plan.

A response to the comments received for the proposed Remedial Action Plan (1997) during the
public comment period is included in the Responsiveness Summary  (Attachment A) of this Record
of Decision  (ROD).  No written comments were received during the 30-day public comment
period.  In addition, no verbal comments were presented during the March 26, 1997 public
meeting regarding OU1.   This decision document presents the selected remedial action for the
OUI at TYAD, chosen in accordance with CERCLA, as amended by the Superfund Amendments
and Reauthorization Act of 1986  (SARA) and the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP).  The decision for this operable unit  (OU)  is based on the
administrative record.

In addition to the community being involved in the planning phase of activities at TYAD, a
Restoration Advisory Board (RAB) was established in June 1994 and meets quarterly at the
Coolbaugh Township Municipal Bldg.  The RAB was kept informed of information developed for
OUI and had the opportunity to comment on any issues at the quarterly RAB meetings.


                                  4.0 Scope and Role of OUI

Discrete portions of an NPL site are often managed more effectively as OUs.   This ROD for OUI
[Area A (AOC#4) and Area B (AOC#7)] addresses VOC-contaminated groundwater underlying
the southeastern portion of TYAD and the Village of Tobyhanna, Pennsylvania  (Fig. 1-2).  Two
other RODs have been finalized at TYAD:

   •      OU2 addresses the former polychlorinated  biphenyl (PCB)  transformer substation site
         (AOC # 63), and
          OU3 addresses Bldgs.  IOC and S90  (AOC # 37 and AOC # 38,  respectively).

Contaminated soils within OUI were previously addressed by a removal action completed in
1995.  The general objectives of response actions at OUI are to: (1) minimize the potential for
future migration of VOCs in groundwater, and  (2) restore groundwater in the glacial till and
bedrock aquifers to beneficial use and to levels protective of human health and the environment,
as soon as practicable, through natural attenuation.  An interim objective of the response actions is
to continue to prevent exposure of groundwater until it has been restored to federal MCLs.  With

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the completion of the removal action at OU1, contaminated soil was removed and resulted in a
permanent reduction in the toxicity and volume of contaminated soil, and minimized future
releases of VOCs to groundwater.

The selected alternative for OU1, Natural Attenuation/Long-Term Monitoring/Institutional
Controls for groundwater and no further action for soils, involves collecting groundwater samples
twice per year. These data will be evaluated to determine if the size and strength of the
groundwater plume is decreasing over time. If future data collection shows that the plume size
and strength is not decreasing over time, the implementation of a different alternative, Limited
Groundwater Treatment/Institutional Controls/Monitoring, may be necessary to remove
groundwater in areas of highest contaminant concentrations. As presented in Sec. 2.0, a removal
action was conducted in Area B in 1995. The removal action removed all soils that exceeded soil
cleanup levels (see Page 2-5). Sampling in Area A showed that no remediation was reguired in
this area. EPA and PADEP agreed that no further action is reguired to address VOC
contaminated soils in OU1.

5.0 Summary of Site Characteristics

5.1 Overview and Extent of Site Contamination

The primary environmental concerns at TYAD OU1 are represented by VOC-contaminated
groundwater. Contaminated soil was also a concern at TYAD OU1; however, the removal action
completed in 1995 remediated contaminated soils to soil cleanup levels (see page 2-5).

Analytical results indicate that the groundwater in the southeastern portion of TYAD, and in a
semicircular area southeast (offpost) of TYAD, has become contaminated with VOCs that originate
from a source area located in the southeastern corner of TYAD. The offPost area, encompassing a
portion of the Village of Tobyhanna, has been affected. A well (also referred to as R2-28) located
in Tobyhanna, operated by the Tobyhanna Water Company, has also been found to contain detectable
guantities of VOCs. To date, a total of 26 different offsite residential wells were reported
with detectable levels of VOCs, of which 24 receive a potable water supply from TYAD. Fifteen
of the 26 residential wells have reported VOC detections in excess of MCLs.

The locations of known contamination may be separated into two distinct areas. The first of these
two areas is centered around a site that was used in the past as a burning ground; this is designated
in the RI (ESE, 1988a) as Area A (Fig. 1-2). This area consists of trenches and pits that were
excavated and used during the late 1950s and early 1960s for the burning of waste generated by
TYAD. No records are available concerning the specific identity or guantities of materials
deposited at this site; however, it is believed that, in addition to construction debris and similar
types of waste material, flammable liguids may have been disposed in the pits to act as a fuel
source for ignition of the debris.

A second area of potential contamination was identified after the investigation at Area A had begun.
At the suggestion of a long-term resident, an area near the southeastern corner of TYAD was
examined for possible contamination, On inspection, three potential areas of contamination were
identified: a large clearing near the middle of the site, a trench containing fragments of rusted
drums near the western edge of the site, and a pile of debris with additional drum fragments on the
ground surface near the southwestern edge of the site. This area was subseguently termed Area B
(Fig. 1-2).

The results of field sampling investigations (e.g., soil, surface water, sediment, and groundwater)
are briefly summarized in Sees. 5.1.1 through 5.1.3. Additional information regarding sampling
locations and methodology is presented in the RI (ESE, 1988a) and RI Addendum (ESE, 1992c).

5.1.1 Soil

Soil sampling conducted during the RI showed the presence of VOCs at Areas A and B (see
Table 2-1). The column denoting "Area A" in Table 2-1 shows TCE and PCE concentrations as
they were reported during the RI (1988a), and are the highest historical concentrations reported at
Area A. These detected levels are below soil cleanup levels. The locations from where the RI
samples were collected were sampled again during the predesign investigations conducted in 1994.

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The results of the predesign investigation showed that the maximum reported concentration of any
VOC was less than one-tenth of the maximum level reported in the RI. Based on these data, and
since contaminant levels were less than soil cleanup levels at Area A, it was determined that soil
remediation in Area A was not necessary. Therefore, response action for Area A is deemed
unnecessary to protect human health and the environment.

The column denoting "Area B (prior to removal action)" in Table 2-1 shows TCE and PCE
concentrations as they were reported during the predesign investigation (1994). These
concentrations were the maximum historical concentrations reported at Area B. All soils
exceeding soil cleanup levels were removed during the removal action conducted in 1995. The
last column in Table 2-1, "Area B (following the removal action)" shows the highest
concentrations of TCE and PCE that remain at Area B following the removal action. These levels
are below soil cleanup levels. Therefore, further response action for Area B is deemed
unnecessary to protect human health and the environment.

Sample results from the RI showed detectable levels of the pesticides 1,l-dichloro-2,2-bis-(p-
chlorophenyl)ethane (DDD); 1,l-dichloro-2,2-bis-(p-chlorophenyl)ethene (DDE); and 1,1-
trichloro-2,2-bis-(p-chlorophenyl)ethane (DDT) in soil samples from Area A. These levels are
below EPA's risk-based concentrations for soil. Also, in December 1995, TYAD conducted a
basewide ecological risk assessment. Low levels of DDT, DDD, and DDE were found in several
upland soil samples both on and offpost. A likely explanation for the presence of DDT and its
related compounds is that the pesticide was widely used at TYAD and surrounding private and
state lands in the past for insect control. There is no evidence that these compounds were
disposed at Area A.

Elevated levels of metals were reported in Area A during the RI, and coal ash was reported in
samples collected from this area. TYAD concluded that the observed soil concentrations appear to
be indicative of soils mixed with coal ash, a common occurrence in northeastern Pennsylvania.

Coal ash is sometimes used for construction and maintenance material in northeast Pennsylvania
and is commonly used throughout northeast Pennsylvania as an anti-skid material. Coal ash was
also applied to the TYAD running track as a finishing layer and was used to a great degree in the
construction of the railroad spur running through the depot.

In December 1996, TYAD sampled additional onpost areas where coal ash material was deposited
for comparison to Area A samples. The purpose of this analysis was to collect actual site data
(coal ash) to confirm if elevated metals reported in the burn pits of Area A (as reported in 1992)
are associated with coal ash. EPA performed a statistical comparison of 1992 and 1996 data and
determined that, with the exception of one sample in Area A taken at a depth of 4 ft (i.e., within
the burn pit), only aluminum and manganese were above background range for similar types of
soil. However, the concentrations of aluminum and manganese were below EPA's risk-based
concentration levels for industrial soil; therefore, as long as future use remains industrial, no
further action is necessary with respect to inorganics in soils at Area A. The use (and related
exposure) is an important determinant of risk from overall soil exposure to aluminum and
manganese, and localized exposure (if any) to burn pit subsoil. The Army anticipates that TYAD
will continue to function as an active military installation zoned for industrial use. In the event
that TYAD is closed at some point in the future, and the land transferred/sold to private or other
public interests, DoD policy would reguire a re-evaluation of the risks based on intended reuse.

PADEP has determined that soils at Areas A and B and underlying groundwater do not contain
listed hazardous wastes, as defined under 25 Pa. Code 261.30, et. seg. Since a review of
published literature indicated that elevated metal levels are commonly present in coal-ash residue,
Toxicity Characteristic Leaching Procedure (TCLP) testing was performed on soil and ash soil
samples collected during supplemental sampling conducted in April 1992. Neither VOCs nor
metals were present in concentrations exceeding TCLP standards.

5.1.2 Groundwater

VOCs have been identified in groundwater underlying the southeast portion of TYAD and the
Village of Tobyhanna. VOCs in excess of federal MCLs have been observed in onpost monitor
wells and offpost residential wells.

Low levels of VOCs (less than the federal MCLs) have been consistently detected in a well

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operated by the Tobyhanna Water Company (identified as R2-28 in the lower central portion of
Fig. 1-2), which supplies groundwater from the fractured bedrock to a number of homes in the
area.  Residents connected to the Tobyhanna Water Company,  as well as those on private wells,
will be supplied potable water if,  in the future, monitoring confirms VOCs are present in excess
of federal MCLs.  All present and future private wells which have been confirmed to have VOCs
in excess of federal MCLs will only be used for sampling, until such time that monitoring ensures
that the private well is again safe for use as a domestic water supply.

Table 5-1 summarizes maximum levels of VOCs detected to date in onpost monitor wells, onpost
drinking water supply wells,  and offpost residential wells and a comparison to the respective
MCLs for the period between January 1988 and March 1996.  In general, all wells were sampled
2 times per year during this period.

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 Table 5-1.  Maximum Contaminant Concentrations in Groundwater

                                                    Concentration  (ug/L)
    Contaminant

  PCE


  TCE


  Trans-l,2-DCE


  Vinyl Chloride
                   Fractured
Glacial Till 1     Bedrock 1
                   Water
                  Supply 2     Residential 3   MCL
 190 (06/88
 and 08/93)

   1,000
  (01/88)

   3,000
  (01/88)

500(03/89)
 100 (08/88)     1.4(08/88)


 700 (01/88)    14.0 (01/92)


5,000 (03/89)    9.7(08/92)
1,000 (03/89)
ND
              12.0
            (08/88)

            41  (08/88)
                5.24       100
               (08/92)

                ND          2
 Note:    MCL = maximum contaminant level.
           ND = not detected.
          PCE = tetrachloroethene.
          TCE = trichloroethene.
Trans-1,2-DCE = trans-1,2-dichloroethene.
         Ig/L = micrograms per liter.
Values in parentheses represent month and year of maximum concentration.

1 Monitor well  (MW-) series wells
2 Onsite  (ON-) series wells
3 Residential  (R-) series wells

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Figs. 5-1 and 5-2 show the area of groundwater contaminated with TCE (the predominant
contaminant in groundwater) at levels greater than the MCL, as it was reported in January 1988
and March 1996, respectively. The area of groundwater contaminated by TCE with levels in
excess of the MCL has decreased by more than 77 percent over the referenced period. When the
RI/FS began a total of six onpost bedrock monitor wells exceeded MCLs; while in 1996, a total
of three wells exceeded MCLs. In 1988, 12 residential wells exceeded VOC MCLs, while only
two wells were above MCLs for TCE and/or PCE in March 1996. The reasons for the decreasing
plume size are believed to be direct removal of source contamination in the Area B, adsorption of
TCE and PCE on aquifer media, degradation of VOCs, dispersion, dilution, and other natural
processes. As of March 1996, concentrations exceeding MCLs were present in two residential
wells and four onsite monitor wells.

Certain metals such as lead and mercury were detected in onpost and offpost wells at levels
exceeding applicable drinking water standards. Mercury has not been detected in an onsite
monitor well, above drinking water standards, since 1989. Since 1989, mercury has been reported
at levels above drinking water standards three times; all of these values correspond to only offsite
residential wells. Lead was sporadically detected in onsite monitor wells and some offsite
residential wells. However, several offsite residential wells consistently report levels of lead in
excess of the drinking water standard. After evaluating several rounds of groundwater monitoring
data, the RI Addendum reported that existing data suggest that the elevated metals levels are
related to area wide variations in the metals content of the glacial till and bedrock, in combination
with the natural acidity of the groundwater. An additional contributing factor may be the
deteriorating condition of offpost residential well casings (metal) in response to continued
exposure to low pH groundwater. Based on this information, the Army concluded that it was not
possible to attribute the presence of metals to past disposal of coal ash or other waste at Areas A
and B.

5.1.3 Surface Water and Sediment

VOCs were not detected in any surface water samples collected during the RI and RI Addendum.
Although a low level of PCE was observed in one sediment sample, this particular location
receives stormwater runoff from many sources on TYAD and may not be attributable to Areas A
and B. Based on the data obtained to date, VOCs at Areas A and B do not appear to be adversely
impacting the surface water or sediment quality. Therefore, the Army does not plan to address
surface water or sediment as part of this OU.

5.2 Routes of Exposure

As previously stated, due to the limited amount of contaminated soils identified, during the
pre-design and remedial design investigations, the Army conducted a removal action in July 1995
and removed approximately 2,100 yd 3 of VOC-contaminated soils from Area B. Following the
completion of the removal action, site sampling showed concentrations of VOCs in soils were less
than soil cleanup levels (see page 2-5). With this information, the EPA and Army agreed that no
further action was necessary for soils in Area B. Although soils were considered in the Risk
Assessment (RA), this discussion of exposure pathways only addresses groundwater, since all
soils with concentrations of VOCs greater than soil cleanup levels were removed during the 1995
removal action.

Based on EPA guidance, one or more exposure routes (i.e., ingestion, inhalation, and/or dermal
contact) are associated with contaminated groundwater. Therefore, several routes of exposure
exist, depending on the receptor and the land use scenario being considered. Each potential
exposure pathway was evaluated in the exposure assessment and is briefly described in Sees.
5.2.1 through 5.2.3. Table 5-2 provides a list of the potential exposure pathways, including those
that were selected and those that were not selected for quantification.

For the purposes of the RA for groundwater, the Army assumed unrestricted use of offsite
contaminated groundwater. This scenario is conservative in that residences/businesses private
wells which do have levels of VOCs in excess of MCLs have been provided an alternative water
source. However, assuming offsite receptors that are currently connected to the waterline are
exposed to groundwater, through these uses of groundwater, persons may be exposed to

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contaminants originating from the two identified source areas.
included in the exposure analysis for TYAD.
Therefore, these pathways are
For the exposure pathways discussed in the following sections, current use and future use
exposure scenarios were developed to evaluate the risks to human health from exposure to
groundwater. Current use at the offpost area considers only residential users (adults and children)
Future use at onpost and offpost areas is represented by residential users. A current use onsite
scenario is not presented herein because contaminated soils have been removed from the site and
there is no current use of contaminated groundwater.

The RAs for Offpost Area 1, Offpost Area 2, and Offpost Area 3 consist of the effects to
receptors through domestic uses of groundwater (inhalation, ingestion, and dermal contact),
exposure associated with watering vegetables (inhalation), and consuming vegetables (ingestion).

The current use scenario included the use of groundwater as a source of drinking water. The
Army has installed a waterline to provide a continuous source of potable water to nearby
residents. Conseguently, many individuals within Offpost Area 1 or Offpost Area 2 are not
currently using groundwater.

Table 5-2. Summary of Exposure Pathways for TYAD
Potentially Exposed
Population
Exposure Route, Medium
and Exposure Point
Selected for
Evaluation?
Reason for Selection
Areas A and B
Current Land Us

Adult, Child
Ingestion of
contaminated fish
from Barney's Lake
No
Hypothetical Future Land Use
Resident
Adult, Child
Ingestion of ground-
water, inhalation of
volatiles
Yes
The volatile
COCs are not
bioaccumulated
Area could be
developed in the future
as a residential area
Area B-Offpost Sites
Current and Hypothetical Future Land Use
Resident
Adult, Child
Direct dermal contact,
ingestion of ground-
water, ingestion of
contaminated vegetables,
and inhalation from
watering vegetables
Yes
Area is currently a
residential area
Source: ESE, 1992a.

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Future use at Areas A and B includes receptors who use groundwater for domestic purpose
(inhalation, ingestion, and dermal contact). Exposure pathways for groundwater in Offpost Areas
1 and 2 include receptors who may use groundwater for domestic purposes (inhalation, ingestion,
and dermal contact) and who might also become exposed while watering vegetables (inhalation)
and consuming vegetables (ingestion). Offpost Area 3 includes receptors who may use
groundwater for domestic purposes (inhalation, dermal contact, and ingestion).

The future residential use scenario is hypothetical and assumes that the source areas in Areas A
and B can be used for unrestricted land use. An unrestricted land use would permit groundwater
wells and residential areas to be constructed anywhere in Areas A and B. The future residential
use scenario, which was evaluated for comparative purposes, is the most conservative choice for
land use and will generate the greatest potential exposure. However, it is unlikely that TYAD's
missions will be eliminated and the depot land be used for residential purposes. Since TYAD
currently fulfills a critical mission that will be necessary as part of future Army operations, and it
is Army practice to clean up to the current land use scenario, no soil cleanup levels were based
on the onsite future residential use scenario (groundwater risks are based on potential residential
use, as appropriate for this medium, particularly offsite). If, in the future, TYAD would be
subject to base closure, site-related risk would be re-evaluated in accordance with DoD base
closure policy (10 U.S.C. 2687 and NOTE).

5.2.1 Direct Contact Route

The greatest dermal exposure potential associated with exposure to groundwater was expected to
occur to individuals taking baths, with showering representing a smaller potential exposure and
the other activities mentioned (e.g., running through sprinklers and playing in small child pools)
representing even lower potential exposures.

5.2.2 Ingestion Route

Residents with wells where VOC constituents exceeded the MCLs were initially supplied bottled
water for all drinking and cooking purposes. These homes have now been connected to a
waterline from TYAD that provides potable water. While the wells at these homes were to have
been rendered unusable, it was considered possible that some of the contaminated wells may still
be accessible. Alternatively, in the absence of any remedial action or controls, future wells could
be installed or contaminants could migrate. In accordance with EPA (1989) guidance, ingestion of
contaminated water is included as a possible exposure pathway. This pathway included residents
who may incidentally ingest small guantities of contaminated water during bathing or showering
or from cooking with contaminated water, and those who may use the contaminated water as a
potable water source. In addition, children may ingest small guantities of water during outdoor
summer water play activities such as running through water sprinklers or playing in small child
pools filled with well water.

Indirect ingestion of contaminants from groundwater was also evaluated in the exposure analysis.
During the summer growing season, residents may use water from contaminated wells to spray-
or flood-irrigate home vegetable gardens. Contaminants in plants would be present in edible
portions. Residents consuming homegrown vegetables watered with contaminated water may
ingest contaminants that have bioaccumulated from the groundwater.

Through these uses of groundwater, persons may be exposed to contaminants originating from the
two identified source areas. Therefore, these pathways were included in the exposure analysis at TYAD.

5.2.3 Inhalation Route

Volatilization from groundwater use was evaluated in the exposure analysis. Residents using
contaminated well water for showers, baths, and other nonconsumptive household uses may be
exposed to vapors released during these activities, inhalation of vapors during showering was
guantified in the exposure analysis for TYAD. Residents using contaminated well water for
showers, baths, and other nonconsumptive household uses may be exposed to vapors released
during these activities (e.g., running through sprinklers or playing in small child pools);
therefore, this exposure route was guantified in the exposure analysis for TYAD. Residents may
receive repeated exposures through these activities and may accumulate a significant intake of the
contaminants over time. Therefore, this pathway was included in the exposure analysis for TYAD.

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5.3 Contamination Migration

Prior to the removal action conducted in 1995, contaminants detected in the two source areas
(Areas A and B) could migrate toward potential receptor areas and into other environmental media
adjacent to the source areas. Contaminants in the soil could either have leached through rainfall
infiltration to the groundwater or been transported via surface runoff to surface water bodies. As a
result of their high vapor pressures and Henry's law (H5) constants, any volatile contaminants at
the soil surface and in surface water were likely to volatilize into the atmosphere where
contaminant oxidation can occur. It is also possible for the VOCs that have reached groundwater
to volatilize from the water table and diffuse through soil pore spaces to reach the surface where
the compounds eventually are released to the atmosphere. However, because VOC contaminated
soils have been removed, the chemical migration pathway discussion focuses on groundwater pathways.
Based on groundwater flow patterns in conjunction with surface water and sediment analytical
data, no contaminants from either Area A or B are expected to reach any of the surface waters
adjacent to Areas A and B. These sources are not thought to represent a significant pathway in
terms of exposure to contaminants originating from either Area A or B.

6.0 Summary of Site Risks

6.1 Introduction

The Baseline Risk Assessment for air, groundwater, surface water, sediment, and soil
contamination at TYAD was performed as part of the EA (ESE, 1992a) to determine if the
chemical concentrations observed in the soil and groundwater samples from the site pose a
significant risk to human health and the environment. Although certain chemicals of potential
concern (COPCs) were detected in sediments and surface waters, they did not pose unacceptable
risks to human health and the environment and were not considered during the RA. Conseguently,
with respect to OU1, the EA only evaluated potential risks in terms of air, soil, and groundwater.

As previously stated, due to the limited amount of contaminated soils identified during predesign
and remedial design investigations, the Army conducted a removal action in July 1995 and
removed approximately 2,100 yd 3 of VOC-contaminated soils from Area B. Following the
completion of the removal action, site sampling showed concentrations of VOCs in soils were less
than soil cleanup levels (see page 2-5). With this information, PADEP agreed with EPA and the
Army that no further action was necessary for soils in Area B; therefore, this RA section only
addresses groundwater.

The RA was developed for both onpost and offpost populations. With respect to the onpost
population, exposure to Areas A and B were considered separately. Offpost exposure from
Area B was evaluated by dividing the community into three distinct areas (Offpost Areas 1, 2,
and 3), based on the movement of VOCs determined from groundwater monitoring data. OffPost
Area 1 is defined by the land overlying groundwater where VOCs have been found. The Army
has already provided a drinking water supply to the majority of individuals within Offpost Area 1.
Offpost Area 2 consists of areas downgradient of the groundwater plume. Some of these
individuals are also currently receiving a water supply from TYAD. Although groundwater from
Tobyhanna Water Company supply well [designated as R2-28 in the RI (ESE, 1988a) and RI
Addendum (ESE, 1992c)] is included within Offpost Area 2, it was evaluated as a separate area
from the wells in Offpost Area 2 because it is a water supply well (OffPost Area 3). All three
offpost areas are shown on Fig. 6-1.

6.2 Human Health Risks

The methods used in assessing the risks associated with reasonable maximum exposure (RME) to
the site contaminants are those presented in EPA's Risk Assessment Guidance for Superfund
(RAGS), Human Health Evaluation Manual (1989a); RAGS Supplemental Guidance, Standard
Default Exposure Factors (1991); and other EPA guidance. According to RAGS, actions at
Superfund sites should be based on an estimate of the RME expected to occur under both current
and future land-use conditions. The RME is defined in RAGS as "the highest exposure that is
reasonably expected to occur at a site." The intent of the RME is to estimate a conservative
exposure case (i.e., well above the average case) (EPA, 1989a).

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Based on RAGS, RME human health risks were determined for each exposure pathway at each
study area and offsite receptor location (See. 6.2.5) based on RME concentrations and exposure
factors [Sec. 5.0 and Apps. E and F-l of the EA (ESE, 1992a)]. The exposure factor values are a
combination of 50th percentile (for factors such as body weight) and 90th percentile (for factors
such as exposure duration) values. The combination of values is selected to obtain an overall
RME estimate. Because of the uncertainty associated with any estimate of exposure concentration,
the upper confidence limit [i.e., the 95 percent upper confidence limit (UCL 95)] on the mean is
the preferred exposure concentration to use in determining potential health risks. However,
according to RAGS, if there is great variability in measured or modeled concentration values, the
UCL. 95 may be high, and could exceed the maximum detected value. In this case, the maximum
detected or modeled concentration was used as the exposure concentration. A majority of the
exposure factors were provided in RAGs while several were site-specific factors obtained from
site information (e.g., climatic conditions conducive to dermal exposure).

The health risks were evaluated separately for carcinogenic and noncarcinogenic effects, with
potential carcinogens evaluated for their carcinogenic and noncarcinogenic effects, where a
specific carcinogen has published noncarcinogen criteria.

Risk estimates relevant to aguifer uses are presented for hypothetical future onpost exposure
pathways and both current and future offpost water uses. Worker exposure to contaminated
groundwater exceeding MCLs was not evaluated under the current use exposure scenario since
these individuals are not currently using contaminated groundwater. Therefore, in the case of
OUI, it was not necessary to evaluate risk under the current land use scenario because workers
are not being exposed to either groundwater exceeding MCLs or unacceptable risks. Although the
waterline extension provides water to residences/businesses that have wells that exceed TCE and
PCE MCLs, the RA assumed those affected residences/businesses were still using well water.

Offpost exposure scenarios also include the ingestion of potentially contaminated vegetables, and
the inhalation of volatile COPCs from irrigation water.

6.2.1 Media of Concern

The RA process outlined in the EA (ESE, 1992a) involves a consideration of COPCs for each
medium and routes of current and future exposure for human and nonhuman populations.
Although certain COPCs were detected in sediments and surface water, they did not pose
unacceptable risks to human health and were not considered further during the human RA.
Conseguently, with respect to OUI, the potential risks in terms of air, groundwater, and related
media were only evaluated for potential impacts to human health in the EA (ESE, 1992a).

6.2.2 COPCs

During the initial steps of the RA, COPCs for human receptors were developed based on the
information contained in the RI (ESE, 1988a) and RI Addendum (ESE, 1992c). COPCs were
developed and evaluated separately for all environmental media.

The final list of COPCs for the TYAD human endangerment assessment (Table 6-1) was
determined by evaluating the results of the ChemScreen analysis and other site-specific evaluation
criteria. ChemScreen is a process that compares site maximum chemical concentrations to
published toxicity data and provides a general basis for comparison between chemicals. Other site-
specific evaluation criteria include background concentration, freguency of detection, and extent
of contamination. The following sections (Sees. 6.2.2.1 through 6.2.2.6) provide a description of
the COPCs selected for groundwater, surface water, and/or sediment in Areas A and B.

6.2.2.1 Area A

Area A groundwater data indicate the presence of VOCs and inorganics. No potential human
COPCs were identified based on the chemical-toxicity screening procedure. Based on the
freguency of detection, only seven inorganics (arsenic, chromium, copper, mercury, lead,
manganese, and zinc) and three VOCs [TCE, 1,2-dichloroethene (1,2-DCE), and vinyl chloride]
of the 31 identified compounds may be considered potential human COPCs. Of the seven
inorganics, lead and mercury were evaluated guantitatively in the RA to represent the inorganic
class of compounds. However, as discussed in Sec. 5.1.2, lead and mercury are not considered
attributable to Area A. A fourth VOC, PCE, was added as a final human COPC based on

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available information concerning the past practices at this OU.


Table 6-1. Final COPCs for Groundwater

Site                                   COPC

Area A                                 1,2-DCE
                                       PCE
                                       TCE
                                       Vinyl chloride
                                       Lead
                                       Mercury

Area B                                 1,2-DCE
                                       PCE
                                       TCE
                                       Lead
Area B-Offpost Area 1                  1,2-DCE
                                       PCE

Area B-Offpost Areas 2 and 3           TCE
                                       PCE
Note: COPC = chemical of potential concern.
   1,2-DCE = 1,2-dichloroethene.
       PCE = tetrachloroethene.
       TCE = trichloroethene.

Source: ESE.

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6.2.2.2 Area B

Area B groundwater data indicate the presence of VOCs and inorganics. Based on the freguency
of detection, five inorganics (copper, lead, manganese, mercury, and zinc) and three VOCs (TCE,
PCE, and 1,2-DCE) were considered as potential human COPCs. Of the five inorganics, lead and
mercury were evaluated guantitatively in the RA to represent the inorganic class of compounds.

6.2.2.3 Offpost Area 1 From Area B

The screening process for Offpost Area 1 (Fig. 6-1) resulted in the selection of three VOCs
(TCE, PCE, and 1,2-13CE) as the human COPCs for the groundwater media.

6.2.2.4 Offpost Area 2 From Area B

The screening process for Offpost Area 2 (Fig. 6-1) resulted in the selection of two VOCs (TCE
and PCE) as the human COPCs for the groundwater media.

6.2.2.5 Offpost Area 3 From Area B

The analytical data for Offpost Area 3 indicate the presence of TCE and inorganics in well R2-28.
Although this well is within Offpost Area 2, it was evaluated as a separate area from the monitor
wells in Offpost Area 2 because it is a water supply well for the Tobyhanna Water Company.
Based on these analytical results, TCE and PCE were selected as COPCs for groundwater at this
location.

6.2.2.6 COPC Concentrations

Groundwater sampling locations at Offpost Areas 1, 2, and 3 are presented on Fig. 6-1. Onpost
monitor well locations are presented on Fig. 6-2.

A fate and transport model was implemented as part of the exposure assessment to evaluate the
maximum areal movement of the contaminant plume at the site and assess the migration potential
of VOCs in three downgradient wells, Rl-110-2, R-102, and R2-28. Rl-110-2 was selected
because it is near the installation boundary. Rl-102 was selected because, based on RI
Addendum data, this well contained a high concentration of total VOCs. The third well modeled
was R2-28 (Tobyhanna Water Company supply well) because it is representative of Offpost
Area 2 as well as a source for potable water supply for a number of residences in the area.

The model was adapted to account for the time-decay of contaminants leaching into groundwater
and migrating offpost to potential receptor well locations. Contamination present at Areas A and
B [prior to the 1995 removal action and based on data reported in the RI (ESE 1988a)], represent
the source concentrations for input into the model. The model treated the contaminant sources in
Areas A and B as one large source to model to the downgradient locations previously described.
Because the model assumed the continued leaching of contaminants from the soils (which have
since been determined to not reguire further action due to new data collected in 1994 and the
completion of the removal action in 1995), future concentrations (Table 6-2) predicted by the
groundwater model are likely over estimated; therefore, related risks calculated using these
modeled concentrations should be considered conservative.

6.2.3 Exposure Assessment

The exposure assessment performed for TYAD focuses on Areas A and B, the two primary
source areas, described in the RI (ESE, 1988a) and RI Addendum (ESE, 1992c).
Environmental monitoring has confirmed that these areas are the principal sources of volatile
chlorinated hydrocarbons detected in soil and groundwater.

Groundwater from Areas A and B has been found to be contaminated with VOCs. Groundwater
contamination at Area A is contained onpost; however, groundwater contamination at Area B has
been identified both onpost and offpost. Currently, onpost personnel receive supplied water for
potable purposes. Offpost individuals who were receiving bottled water are now connected to a
waterline from TYAD that provides water for domestic use. The wells in the homes to the

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waterline were to have been rendered unusable for domestic purposes  (however, these wells are
still accessible to the Army for monitoring purposes); therefore, all exposure to contaminated
groundwater for those individuals should have been eliminated.  However, because some of the
contaminated wells may still be accessible, and because baseline  (no action) evaluation was
necessary, residential consumption of groundwater was included in the RA (i.e., the waterline was
not factored into the RA).

Many of the exposure pathways and potential receptors are similar for the two identified source
areas (Areas A and B).  These similarities allow consolidated discussions of common exposure
pathways and the application of common exposure assumptions and factors in the risk estimation
process.  For those exposure pathways that are not shared or are more site specific, independent
discussions and exposure analyses are presented in this ROD.

   Table 6-2. Current and Future Onpost and Offpost Groundwater Concentrations, UCL 95

                                                           Area  (Ig/L)
   Compound           A                   B           Offpost 1         Offpost 2       Offpost 3
                                                                                      (R2-28)
   Current (UCL 95)

   PCE
   TCE
   1,2-DCE
   Vinyl Chloride
   Lead
   Mercury
1.05
3.59 x 10 +2
4.85 x 10 +3
1.04 x 10 +3
6.42 x 10 +1
1.30
1.12 x 10 +2
4.59 x 10 +1
1.94 x 10 +2
—
5.20 x 10 +1
4.38
4.83
1.14 x
3.98 x
—
NA
NA

10 +1
10 -1



                                                              1.30
                                                               NA
                                                               NA
   Future (Modeled Concentrations) ++
   PCE
   TCE
 7 year
70 year

 7 year
70 year
   1,2-DCE  7 year
           70 year
NM
NM

NM
NM

NM
NM
NM
NM

NM
NM

NM
NM
4.41
3.76

9.37
7.99
                                            4.0 x 10 -3
4.17 x 10 -1
3.44 x 10 -1

    3.45
    2.67
   Note: 1,2-DCE = 1,2-dichloroethene.
           NA = not appropriate to include as constituent may be due to plumbing in residential wells.
           NM = not modeled.
          PCE = tetrachloroethene.
          TCE = trichloroethene.
       UCL 95 = 95 percent upper confidence level.
         Ig/L = micrograms per liter.
           -- = below detection limits.
            + = not modeled; however,  data for Offpost 3 (which is a subset of Offpost 2)  is
          representative of this area.
          ++ = lead and mercury were not modeled because levels reported in groundwater are not
               considered attributable to Areas A and B  (Sec. 5.1.2) .   Vinyl chloride was not modeled
               because it has only be reported in MW01 and MW02, both of which are located in Area A.
   Source: ESE.

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6.2.3.1 Exposure Pathways

Based on EPA (1989) guidance, a number of potential exposure pathways were considered for
inclusion in the exposure assessment and are described in the following sections. A list of the
potential exposure pathways, including those that were selected and those that were not selected
for guantification were presented in Sec. 5.2 (Table 5-2) of this ROD.

As stated in Sec. 6.2.3, current use and hypothetical future use exposure scenarios were
developed to evaluate the risks to human health from exposure to groundwater. The future
residential use scenario is hypothetical and assumes that the source areas in Areas A and B can be
used for unrestricted land use. An unrestricted land use would permit groundwater wells and
residential areas to be constructed anywhere in Areas A and B. The hypothetical future residential
use scenario, which was evaluated for comparative purposes, is the most conservative choice for
land use and will generate the greatest potential exposure. However, it is unlikely that TYAD's
mission will be eliminated and the land used for residential purposes. Since TYAD currently
fulfills a critical mission that will be necessary as part of future Army operations and it is Army
practice to clean up to the current land use scenario, no soil cleanup levels were based on the
future residential use scenario (groundwater risks are based on potential residential use, as
appropriate for this medium, particularly offsite). If, in the future, TYAD would be subject to
base closure, site-related risk would be re-evaluated in accordance with DoD base closure policy
(10 U.S.C. 2687 and NOTE).

6.2.3.2 Potentially Exposed Populations

The potentially exposed populations that may be affected by the VOC groundwater contamination
were estimated by running a contaminant transport model of VOCs in the groundwater media
(Sec. 6.2.3.3) .

6.2.3.3 Exposure Point Concentrations

Exposure point concentration levels represent the contaminant concentrations in an environment
medium (i.e., groundwater) that may impact potential human or nonhuman receptors through
direct contact of the receptor with the contaminated environmental medium. The exposure
concentrations are defined by EPA as the RME. The RME represents the highest exposure that is
reasonably expected to occur at the site.

Two exposure scenarios to groundwater are evaluated: current and hypothetical future. For the
current scenario, RME concentrations [App. E, of the EA (ESE, 1992a)] derived from the
analytical data were used as the exposure concentrations, while the hypothetical future scenario
used groundwater modeled values. A fate and transport model was implemented as part of the
exposure assessment to evaluate the maximum areal movement of the contaminant plume at the
site and assess the migration potential of VOCs in three downgradient wells, Rl-110-2, R-102,
and R2-28. Rl-110-2 was selected because it is near the installation boundary. Rl-102 was
selected because, based on RI Addendum data, this well contained a high concentration of total
VOCs. The third well modeled was R2-28 (Tobyhanna Water Company supply well) because it is
representative of Offpost Area 2 as well as a source for potable water supply for a number of
residences in the area.

Current Use

Groundwater--The extent of TCE contamination presented in Fig. 6-3 is based on data obtained
during the 1990 groundwater sampling event, and served as the basis for TCE characterization in
the EA. TCE is the most widespread of the contaminants and occurs in wells offpost. The highest
concentrations of TCE are well distributed vertically, and concentrations are greater in the aguifer
in some areas (Fig. 6-3).

The extent of PCE contamination presented in Fig. 6-4 is based on the data obtained during the
1990 groundwater sampling event, and served as the basis for PCE characterization in the EA.
PCE was not detected in the bedrock in Area A. PCE was present in a very localized area in the
shallow zone wells of Area B and widely dispersed in the deep zone downgradient of Area B,
extending several hundred feet offpost.

Risk calculations were based on groundwater data collected through 1990. Risks have not been

-------
quantified since finalization of the EA in 1992; however, because contaminant concentrations have
decreased over time, overall site risks are expected to be lower than those presented in the EA.

Hypothetical Future Use

Areas A and B--Risks associated with the future residential use scenario are hypothetical and are
based on the assumption that unrestricted land use would occur at Areas A and B. The Army
anticipates that TYAD will continue to function as an active military installation, in which case,
the hypothetical future exposure scenario would not occur. Since contaminated groundwater would
be addressed as part of OUI, it is highly unlikely that such exposure would occur in the future.

6.2.3.4 Exposure Assessment Assumptions

Area-specific carcinogenic risks and noncarcinogenic hazard indexes (His) were calculated in the
EA (ESE, 1992a). Assumptions used when calculating carcinogenic and noncarcinogenic risks are
presented in App. F of the EA. Based on the conservative assumptions presented in App. F of
this report, excess cancer risks and His were calculated for each of the exposure scenarios.

6.2.4 Toxicity Assessment

The objective of the toxicity assessment is to characterize the nature of the potential health effects
to human receptors associated with the COPCs identified at TYAD. The characterization includes
a qualitative evaluation of the available pharmacokinetic and health effects data to provide a
toxicological profile for each COPC, and a quantitative evaluation of the available dose-response
information to provide values for estimating acceptable intake levels and quantifying risks.

Cancer slope factors (CSFs) have been developed by EPA's Carcinogenic Assessment Group for
estimating lifetime cancer risks associated with exposure to potentially carcinogenic chemicals.
CSFs, which are expressed in units of milligrams per kilogram per day (mg/kg-day) -1, are
multiplied by the estimated intake of a potential carcinogen, in mg/kg-day, to 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 CSF. Use
of this approach makes underestimation of the actual cancer risk highly unlikely. CSFs 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.

Reference doses (RfDs) have been developed by EPA for indicating the potential for adverse
health effects from exposure to chemicals exhibiting noncarcinogenic effects. RfDs, 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
RfD. RfDs 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 RfDs will not underestimate the potential
for adverse noncarcinogenic effects to occur.

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Table 6-3. Chronic Dose-Response Toxicity Constants for the Human COPCs at TYAD
Chemical
                       Oral RfD  (UF) '
                          Inhal RfD (UF) •
                                                                     Oral CSF*    Oral WoE*   Inhal CSF*
                                                                                                             Inhal WoE*
Inorganic Chemicals
 Lead
 Mercury
    — 11
3.0E-04 (1,000)
Volatile Organic Chemicals
 1,2-DCE              9.0E-03  (1,000)
 PCE                  l.OE-02  (1,000)
 TCE
 Vinyl chloride
8.6E-05 (30)
                                                  nd 12
                                              5.1E-02 vl
                                              1.1E-02 vl
                                              1.9E+00
                                                                B2
                                                                           nd 12
                                 B2 vl   1.8E-03 vl
                                 B2 vl   5.9E-03 vl
                                  A      3.0E-01
                                                                                            B2
B2 vl
B2 vl
 A
Note:    COPC = chemical of potential concern.
          CSF = cander slope factor  [(mg/kg/day) -1].
      1,2-DCE = 1,2-dichloroethene.
        inhal = inhalation.
    mg/kg/day = milligrams per kilogram per day.
           nd = not determined.
                                                PCE = tetrachloroethane.
                                                RfD = reference dose  (mg/kg/day].
                                                 UF = uncertainty factor.
                                                TCE = trichloroethene.
                                                WoE = weight-of-evidence for ranking as a human carcinogen.
11 EPA prefers to use a biokinetic uptake model to evaluate lead exposure rather than the reference dose method.
12 Although EPA has classified lead as a Group B2 suspect human carcinogen via ingestion and inhalation, no CSF has been developed for either of these exposure
   pathways.
VI CSFs and WoEs for this VOC have been withdrawn from IRIS pending further review.

 * All RfDs,  CSFs, and WoEs are available in IRIS, 1992; EPA/HEAST, 1992 Annual Update, or EPA/HEAST, Supplement A to the 1992 Annual Update, unless
   otherwise noted.
 Source: ESE.

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Table 6-3 provides a summary of the available noncarcinogenic and carcinogenic chronic
dose-response information for both the oral and inhalation exposure routes for each COPC. Due
to the absence of established dermal dose-response values, dermal exposure was estimated using
the oral dose-response values. When insufficient data are available to determine dose-response
values for human risk characterization, health-based values are developed using the available
regulatory references and resources for human health dose-response values.

6.2.5 Risk Characterization

The objective of the risk characterization is to integrate information developed in the toxicity
assessment and the exposure assessment into a complete evaluation of the potential and actual
health risks associated with contaminants at TYAD. The RA evaluates the nature and degree of
risk to potential receptor populations. Wherever possible, risks are derived for individual source
areas and for the total contaminant contribution from the identified sources to aid in developing
priorities for remedial action planning.

The carcinogenic risks and His were calculated for both onpost areas and the three offpost
receptor locations. Because the activities performed at each of the five study areas differ and the
areas are not in close proximity to each other, the risks were presented separately for each area.
Characterizing each study area separately allows for prioritization of remedial activities that may
be reguired.

The EA (ESE, 1992a) indicated that contaminated groundwater at this site is well within the target
risk range of 1 x 10 -6 to 1 x 10 -4 for carcinogens [which complies with Office of Solid Waste and
Emergency Response (OSWER) Directive 9355, 0-30] for the current use scenario. A future use
scenario was evaluated in the EA; however, the future residential use scenario is hypothetical and
assumes that the source areas in Areas A and B can be used for unrestricted land use. An
unrestricted land use would permit groundwater wells and residential areas to be constructed
anywhere in Areas A and B. The future residential use scenario, which was evaluated for
comparative purposes, is the most conservative choice for land use and will generate the greatest
potential exposure, and hence risk. However, it is unlikely that TYAD's mission will be
eliminated and the depot land be used for residential purposes. Since TYAD currently fulfills a
critical mission that will be necessary as part of future Army operations and it is Army practice to
clean up to the current land use scenario, no soil cleanup levels were based on the future
residential use scenario (groundwater risks are based on potential residential use, as appropriate
for this medium, particularly offsite). If, in the future, TYAD would be subject to base closure,
site-related risk would be re-evaluated in accordance with DoD base closure policy (10 U.S.C.
2687 and NOTE).

Although EPA generally uses the upper boundary of the carcinogenic risk range (i.e., 1 x 10 -4) to
make risk management decisions, the necessity of taking remedial actions would also involve
consideration of factors such as exceedances, of the noncarcinogenic hazard guotient, compliance
with chemical-specific applicable and relevant or appropriate reguirements (ARARs) and potential
adverse impacts to the environment, along with an evaluation of unigue site-specific conditions.
The acceptability of a particular level of risk is the provence of risk management, where the
guantitative estimates of risk are just one of many factors considered in the decision-making
process. A cancer risk of 10 -4 is not a de facto decision point, nor is it a "target" risk level.
However, it is generally accepted that risks above the range of 10 -4 to 10 -6 reguire attention. The
10 -6 level of risk is often referred to as the de minimis level of risk, although that level has not
been endorsed as a universally acceptable risk level. If risks are below 1 x 10 -2, then a linear
eguation is used (e.g., Risk = CSF x intake); however, if the risk exceeds 1 X 10 -2, then an
exponential eguation is used instead [i.e., 1-exp (-intake x CSF)].

An HI is used to determine whether the most sensitive individuals in a population could be
adversely affected by noncarcinogenic chemicals. An HI exceeding 1.0 is a possible concern for
potential noncarcinogenic or toxic effects. The EA (ESE, 1992a) indicated that contaminated
groundwater at this site does exceed HI levels of 1. The acceptability of a particular level of HI is
the provence of risk management, where guantitative estimates of HI are just one of many factors
considered in the decision-making process. An HI of 1 is not a defacto decision point, or is it a
"target" level. However, it is generally accepted that His greater than 1 reguire attention.

Table 6-4 presents a summary of the current and hypothetical future area-specific carcinogenic
risks for the exposure scenarios that were evaluated at the TYAD site. Table 6-5 presents a

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summary of the current and hypothetical future area-specific noncarcinogenic His for the exposure
scenarios that were evaluated.  Presenting the risks and His in this manner allows for the
identification of those exposure pathways and COPCs that contribute the most risk or HI.  The
industrial HI and risk values for all COPCs and all exposure scenarios are presented in App.  F-3
of the EA (ESE, 1992a).

The following sections summarize the carcinogenic risks and noncarcinogenic His associated with
the COPCs in each of the five areas: Area A; Area B; and Offpost Area 1, Offpost Area 2, and
Offpost Area 3 from Area B.

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 Table 64.  Summary of Area-Specific Carcinogenic Risks
 Exposure
 Scenario
  Media
        Risk
Current        Future
 Area A
 Hypothetical Lifetime
  Residential
Groundwater

          TOTAL
                        NE
               2.5E-02 -+

               2.5E-02
 Area B
 Hypothetical Lifetime
  Residential
Groundwater
                        NE
                                     7.2E-05
                                         TOTAL
                                                                    7.2E-05
 Area B-OffPost 1

 Lifetime Residential
                               Groundwater             4.3E-06      3.8E-06
                               Irrigation—Air         1.5E-10      1.1E-10
                               Vegetables—Ingestion   3.9E-07      2.9E-07
                                           TOTAL       4.7E-06      4.1E-06
 Area B-Offpost 2

 Lifetime Residential
                               Groundwater             1.6E-07
                               Irrigation—Air         1.5E-11
                               Vegetables—Ingestion   1.2E-08
                                           TOTAL       1.7E-07
                                       * *
                                       **
                                       **
 Area B-Offpost 3

 Lifetime Residential
                               Groundwater
                                         TOTAL
                                       7.0E-07***
                                       7.0E-07
 Note:  NE = not evaluated for this scenario.

  + 84  percent of groundwater risk is due to the presence of vinyl chloride.
 **Not  modeled; however,  data for Offpost 3 (which is a subset of Offpost 2)  is representative of this
   area.
 ++Area B—Offpost 3 is represented by one well, R2-28 (Tobyhanna Water Company supply well),
   which was evaluated as part of Area B--Offpost 2 because this supply well  is located within that
   area.
***Future concentrations  were modeled separately for the R2-28 to determine the potential future risks
   associated with this supply well.

Source: ESE.

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 Table 6-5. Summary of Area-Specific Noncarcinogenic Hazard Indices

                                       Current HI       Future HI

                         Media          Adult  Child    Adult    Child
Exposure
Scenario
 Area A
 Hypothetical Lifetime   Groundwater
  Residential
                         TOTAL
 Area B
 Hypothetical Lifetime   Groundwater
  Residential
                         TOTAL
 Area B-Offpost 1

 Lifetime
  Residential
 Area B-Offpost 2

 Lifetime
  Residential
 Area B-Off-post 3

 Lifetime
  Residential
                        Groundwater

                        TOTAL
                                            NE
                                                      NE
                                            NE
                                                      NE
                                                                14.7+
                                                                 14.7
                                                                1.3*
                                                                 1.3
                                                                         35.0 +
                                                                          35.0
                                                                         3.0*
                                                                          3.0
                        Groundwater         0.015     0.035     0.013    0.030
                        Irrigation—Air     NA        NA        NA       NA
                        Vegetables—        0.0015    0.0034    0.0013   0.003C
                        Ingestion

                        TOTAL               0.02      0.04      0.02      0.03
                        Groundwater         NA        NA
                        Irrigation—Air     NA        NA
                        Vegetables--        NA        NA
                        Ingestion

                        TOTAL               NA        NA
0.001  0.003+++

0.001  0.003
  Note:    HI = hazard index.
           NA = dose-response information has not been established for the compounds evaluated for this
                pathway.
           NE = not evaluated for this scenario.

  + Majority of HI (99 percent,  97 percent for child)  due to 1,2-DCE.
 **Exceedance of HI of 1 due to 1,2-DCE (46 percent),  mercury (30 percent), and PCE (24 percent).
 ++Not modeled; however, data for Offpost 3  (which is a subset of Offpost 2)  is representative of this
   area.
***Area B—Offpost 3 is represented by one well, R2-28 (Tobyhanna Water Company supply well),
   which was evaluated as part of Area B--Offpost 2 because this supply well is located within that
    area.
+++Future concentrations were modeled separately for the R2-28 to determine the potential future HI
   associated with this supply well.
  Source: ESE.

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The hypothetical future residential land use scenario was evaluated in the EA (ESE, 1992a). This
scenario was evaluated because it is the most conservative and will generate the greatest potential
exposure to risk. However, the probability that TYAD's mission would be eliminated and the land
then used for residential purposes is remote. TYAD fulfills a critical mission for the Army and
there are no plans to eliminate any property near Areas A and B; however, if plans were to
change, the Army would evaluate the site conditions and risks.

6.2.5.1 Area A

One exposure scenario was evaluated for Area A: hypothetical lifetime residential exposure. The
risk characterization of this scenario is described below.

Hypothetical Future Exposure Evaluation
Carcinogenic Risks—The risk analysis results indicate that the hypothetical future (lifetime)
residential exposure scenario may result in an overall lifetime risk that exceeds EPA's target risk
range of 1.0 x 10 -4 to 1.0 x 10 -6. Based on the exposure assumptions evaluated, the risk
exceedance is due to potential future potable use of the groundwater at Area A. A majority of the
total risk of 2.5 x 10 -2 is due to the presence of vinyl chloride, which contributes 99.8 percent of
the total risk (84 percent from oral exposure to groundwater and 15 percent from inhalation of
vapors volatilized from groundwater). The remaining risk is primarily due to the presence of TCE
(App. F-3 of the EA (ESE, 1992a). The contribution by TCE results in a risk of 6.8 x 10 -5,
which is less than the acceptable cumulative risk level of 1.0 x 10 -4.

Noncarcinogenic HIs--As with the risk analysis, the HI analysis indicates that the hypothetical
future residential exposure scenario results in total His greater than 1 for both adult and child
exposures due to groundwater use as a potable water source. Exposure of adults and children
result in calculated His of 14.7 and 35.0, respectively. These His indicate that potential adverse
effects cannot be ruled out. The HI exceedance is due to the presence of 1,2-DCE.

As described in the EA (ESE, 1992a) and in the RI Addendum (ESE, 1992c), there are no
patterns or trends of lead in groundwater. The analytical results of onpost and offpost monitoring
indicate that lead is not attributable to the site. However, to provide a perspective on the
contribution of nonsite-related compounds to the overall site risks, lead was included in the risk
evaluation. The lead concentrations in groundwater samples collected from some wells at this area
exceed the EPA Action Level of 15 micrograms per liter (ug/L) [56 Federal Register
(FR) 26478], indicating that potential adverse effects cannot be ruled out should the groundwater
be used for potable purposes. The exceedances are also higher in upgradient wells, indicating that
lead is not attributable to activities at Area A, and may be of concern at offpost locations as well.

6.2.5.2 Area B

One exposure scenario was evaluated for Area B: hypothetical future lifetime residential exposure.
The risk characterization of this scenario is described in the following section.

Hypothetical Future Exposure Evaluation
Carcinogenic Risks—The risk analysis results indicate that the hypothetical future lifetime
residential exposure scenario resulted in a total risk of 7.2 x 10-5, which does not result in risks
that exceed EPA's 1.0 x 10-4 acceptable cumulative risk level. This lifetime risk indicates that
unacceptable risks are not posed to future residential exposures, based on the exposure
assumptions evaluated.

Noncarcinogenic HIs-The HI analysis indicates that the hypothetical future residential exposure
results in total His of 1.3 and 3.0 for adult and child exposures, respectively. The HI exceedance
indicates that potential adverse effects cannot be ruled out based on the exposure assumptions
evaluated. The exceedance is due to the presence of 1,2-DCE, PCE, and mercury in groundwater.

As described for Area A, the lead concentrations in offpost and onpost areas do not indicate any
pattern or trends. Furthermore, as discussed in Sec. 5.1.2, mercury concentrations have not
exceeded drinking water standards in onsite wells since 1989. As such, lead and mercury do not
appear attributable to the activities of Area B. However, to provide a perspective on the
contribution of nonsite-related compounds to the overall site risk, lead was included in the risk
analysis. The lead concentrations in groundwater samples collected from some wells at this area
exceed the EPA Action Level of 15 Ig/L (56 FR 26478), indicating that potential adverse effects,

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associated with exposure to lead in groundwater, cannot be ruled out in the event that the
groundwater at Area B is used for potable purposes.

6.2.5.3 Offpost Area 1 From Area B

Two exposure scenarios were evaluated for Offpost Area 1:  (1) current, and  (2) future residential
exposure.  The risk characterization of these scenarios is described in the following sections.
Current Exposure Evaluation
Carcinogenic Risks—Based on the exposure assumptions evaluated, current exposure to Offpost
Area 1 by domestic groundwater uses, ingestion of homegrown vegetables, and vapors from using
groundwater for irrigation, results in a total carcinogenic risk of 4.7 x 10 -6, which does not result
in a risk that exceeds EPA's target risk range of 1.0 x 10 -4 to 1.0 x 10 -6.

Noncarcinogenic HIs--The results of the HI analysis indicate that current residential exposure
results in total His of < 1, indicating that this scenario should not result in chronic adverse health
effects, based on the exposure assumptions evaluated.

Hypothetical Future Exposure Evaluation
Carcinogenic Risks—Hypothetical future residential exposure Offpost Area 1 by domestic
groundwater uses, ingestion of homegrown vegetables, and vapors from using groundwater for
irrigation, results in a total carcinogenic risk of 4.1 x 10-6, which does not result in a risk that
exceeds EPA's target risk range of 1.0 x 10 -4 to 1.0 x 10 -6.

Noncarcinogenic HIs--The HI analysis results indicate that hypothetical future residential
exposure results in total His of < 1, indicating that future residential exposure should not result in
chronic adverse health effects based on the exposure assumptions evaluated.

As described for Areas A and B, lead does not appear attributable to the site; however, it was
included in the risk evaluation to provide a perspective on the relative risk contribution of nonsite-
related compounds to the overall site risk.  The lead concentrations in groundwater samples
collected from some wells at this area exceed the EPA Action Level of 15 ug/L (56 FR 26478),
indicating that potential adverse effects, associated with exposure to lead in groundwater, cannot
be ruled out in the event that the groundwater at Offpost Area 1 is used for potable purposes.

6.2.5.4 Offpost Area 2 From Area B

Two exposure scenarios were evaluated for Offpost Area 2:  (1) current, and  (2) future residential
exposure.  The risk characterization of these scenarios is described in the following sections.

Current Exposure Evaluation
Carcinogenic Risks—Current exposure to Offpost Area 2 by domestic uses of groundwater,
ingestion of homegrown vegetables, and inhalation of vapors from using groundwater for
irrigation, resulted in a total carcinogenic risk of 1.7 x 10 -7, which does not result in a risk that
exceeds EPA's target risk range of 1.0 x 10 -4 to 1.0 x 10 -6.

Noncarcinogenic HIs-The results of the HI analysis indicate that current residential exposure
results in total His of < 1, indicating that this exposure scenario should not result in chronic
adverse health effects based on the exposure assumptions evaluated.

Hypothetical Future Exposure Evaluation
Modeling was not specifically completed for Offpost Area 2.  However, because Offpost Area 3
is a subarea of Offpost Area 2, results for Offpost Area 3 would be representative of Offpost
Area 2.  Refer to Sec. 6.2.5.5 (next section) for further information.

As described for Areas A and B, lead does not appear attributable to the site; however, it was
included in the risk evaluation to provide a perspective on the relative risk contribution of nonsite-
related compounds to the overall site risk.  The lead concentrations in groundwater samples
collected from some wells at this area exceed the EPA Action Level of 15 Ig/L (56 FR 26478),
indicating that potential adverse effects, associated with exposure to lead in groundwater, cannot
be ruled out in the event the groundwater monitored at Offpost Area 2 is used for potable
purposes.

6.2.5.5 Offpost Area 3 From Area B  (Future Exposure Evaluation)

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This area is located within the area designated as Offpost Area 2, and is represented by a single
well (R2-28), which is the Tobyhanna Water Company supply well. This well was evaluated as
part of the Offpost Area 2 current lifetime residential scenario, but was evaluated separately in the
hypothetical future residential scenario to determine the potential future impacts associated with a
supply well that serves residences.

Carcinogenic Risks
Based on the exposure assumptions evaluated, one hypothetical future exposure scenario was
evaluated for Offpost Area 3, residential exposure. The risk analysis for total exposure to
groundwater (domestic uses), ingestion of homegrown vegetables, and inhalation of vapors from
using groundwater for irrigation, resulted in a total risk of 7.0 x 10 -7, which does not result in a
risk level that exceeds EPA's target risk range of 1.0 x 10 -4 to 1.0 x 10 -6.

Noncarcinogenic His
The results of the HI analysis indicate that hypothetical future residential exposure results in total
His of < 1, indicating that exposures to the media evaluated should not result in chronic adverse
health effects based on the exposure assumptions evaluated.

As described for Areas A and B, lead does not appear attributable to the site; however, it was
included in the risk evaluation to provide a perspective on the relative risk contribution of nonsite-
related compounds to the overall site risk. The maximum lead concentration detected in R2-28
(the Tobyhanna Water Company supply well) was 18.97 ug/L, and the mean concentration
detected was 8.91 Ig/L. The maximum concentration exceeds EPA's Action Level of 15 Ig/L
(56 FR 26478), indicating that potential adverse effects cannot be ruled out if the water supply
concentration remains at the maximum concentration.

6.2.5.6 Conclusions

A summary of the risk characterization for the site indicates that the highest current lifetime
residential exposure in the offpost area results in a cumulative cancer risk that is within the EPA's
target risk range of 1.0 x 10-4 to 1.0 x 10 -6.

Although the calculated risks and His do not indicate that the current land use scenario will have
an adverse impact on human health, constituents in groundwater exceed MCLs at both onpost and
offpost locations. The Army has developed response action objectives that will prevent further
groundwater degradation and decrease the concentrations of VOCs in groundwater to levels safe
for human use.

For the hypothetical future onpost residential scenarios, the cumulative cancer risks associated
with exposures to Area A exceed the upperbound of the EPA acceptable risk range. However, the
hypothetical future onpost residential cumulative risk associated with exposures to Area B are
within the EPA limits. For the noncarcinogenic health evaluation, none of the current exposures
should result in chronic adverse effects. In addition, hypothetical future offpost exposures are not
expected to result in adverse chronic effects. However, potential hypothetical future onpost
residential exposures to Areas A and B may result in an HI greater than 1 indicating that potential
adverse effects cannot be ruled out based on the assumption evaluated.

SARA reguires that remedial actions attain a degree of contaminant remediation that assures the
protection of public health and the environment.

Actual or threatened releases of hazardous substances from OU1, if not addressed by
implementing the response action selected in this ROD, may present an imminent and substantial
endangerment to public health, welfare, or the environment. Actual releases have been addressed
via the waterline extension that connects impacted users to the depot water supply system.

6.3 Ecological Risks

A basewide ecological RA for TYAD was conducted in 1994. Results of that risk assessment are
contained in the 30 January 1997 Draft Ecological Risk Assessment Report which has been
reviewed by the regulators and is currently under revision. The report concludes that, while a
high concentration of DDT has been found in one mammal tissue collected at Area A, there is no
record of disposal of DDT in this location. DDT was also found in several upland soil samples
both on- and offpost. A more likely explanation of the presence of DDT is that the pesticide was

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   widely used at TYAD and surrounding private and state lands in the past for insect control.
   Therefore, it was concluded that no significant impacts to ecological receptors have been
   identified as being associated with contaminants disposed at either Area A or Area B.

   6.4 Residual Risk Evaluation

   The groundwater ARARs were determined to be 5.0 Ig/L for TCE and PCE, 2.0 Ig/L for vinyl
   chloride, and 70 Ig/L for 1,2-DCE.  These values represent MCLs, pursuant to the Safe Drinking
   Water Act, as defined in 40 CFR Part 141.61. EPA,  PADEP, and TYAD have agreed that MCLs
   are protective of human health and the environment.  Residual risks associated with a lifetime
   exposure to these constituents at MCLs are presented as follows:


                    MCL             HI                HI
      Chemical      (ug/L)          Adult             Child        Cancer Risk

   PCE                5             0.05             0.2             2E-05
   TCE                5             0.05             0.2             3E-06
   DCE*              70             0.2              0.5         Not Applicable
   Vinyl Chloride     2         Not Applicable   Not Applicable      7E-05
   Total       Not Applicable       0.3              0.9             9E-05


Note:   These risks were derived based on standard default assumptions for ingestion, the 1992
        non-steady state eguations for dermal exposure, and the 1987 Foster and Chrostowski
        Model for showing exposure.

      * The MCL shown for 1,2-DCE is for cis-l,2-DCE which is more conservative than that
        of trans-l,2-DCE.

  This table shows that the total HI is less than 1 and the total cancer risk is within the risk range of
  1 x 10 -6 to 1 x 10-4.  It is assumed for this table that once MCLs are achieved at the site, the
  concentrations of VOCs in groundwater would not change overtime.

                            7.0 Description of Alternatives


   In accordance with Sec.  300.430 of the NCP, 40 Code of Federal Regulations (CFR), a list of a
   number of remedial response actions and representative technologies were identified and screened
   to determine whether they would meet the remedial action objectives  (discussed in Sec. 4.0) at
   OU1 Those that would meet the remedial action objectives are discussed below as Remedial
   Alternatives.  Sec. 121(d)  of CERCLA reguires that remedial actions at CERCLA sites at least
   attain legally applicable or relevant and appropriate federal and state standards, reguirements,
   criteria and limitations, which are collectively referred to as "ARARs," unless such ARARs are
   waived under CERCLA Sec.  121 (d)   (4).  Applicable reguirements are those substantive
   environmental protection standards, reguirements,  criteria or limitations promulgated under
   federal or state law that specifically address hazardous substances found at the site, the remedial
   action to be implemented at the site, the location of the site, or other circumstances present at the
   site.  Relevant and appropriate reguirements are those substantive environmental protection
   standards, reguirements,  criteria or limitations promulgated under federal or state law which,
   while not applicable to the hazardous substances found at the site, the remedial action itself, the
   site location, or other circumstances at the site, nevertheless address problems or situations
   sufficiently similar to those encountered at the site that their use is well-suited to the site.
   ARARs may relate to the substances addressed by the remedial action  (chemical-specific), to the
   location of the site  (location-specific)  or to the manner in which the remedial action is implemented
   (action-specific).

   The five alternatives presented in the FS, and originally presented to the public in November 1993
   are as follows:  (The "P" in the alternative titles below denotes that this alternative was previously
   considered.  However, since the collection of pre-design field data, this alternative is no longer
   considered applicable.)

      •      Alternative 1P--NO action;

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• Alternative 2P--Installation of multimedia caps, extraction wells, air stripping, ion-exchange
(may have been necessary if water was discharged to Hummler Run), and discharge to the TYAD
potable water system and Hummler Run;

• Alternative 3P--In situ volatilization of soils, in situ biodegradation of groundwater,
extraction wells, air stripping, ion-exchange (may have been necessary if water was discharged
to Hummler Run), and discharge to the TYAD potable water system and Hummler Run;

• Alternative 4P--Passive soil volatilization, extraction wells, air stripping, ion-exchange (may
have been necessary if water was discharged to Hummler Run), and discharge to TYAD
potable water system and Hummler Run;

• Alternative 5P--Thermal desorption of soils, extraction wells, air stripping, ion-exchange (may
have been necessary if water was discharged to Hummler Run), and discharge to TYAD
potable water system and Hummler Run.

The preferred alternative presented at the November 1993 public meeting was Alternative 4P,
which involved soil and groundwater treatment. Soil treatment would have consisted of excavating
soil in excess of soil cleanup levels at Areas A and B and reducing VOC concentrations using a
technology called passive volatilization. This approach would have involved placing soil within a
lined treatment cell, which is referred to as a bubble, and forcibly drawing air through the soils to
remove VOCs.

Groundwater treatment was to have involved an extraction and treatment system consisting of four
onpost extraction wells and one offpost extraction well. Groundwater would have been processed
through an onpost treatment system, consisting of an air stripper to remove VOCs from the
groundwater. If necessary, VOC emissions from the air stripping tower would have been treated,
using vapor phase carbon, prior to discharging air to the atmosphere. After treatment,
groundwater would have been discharged to one of several locations; the specific location was to
have been defined in a later phase of work.

Groundwater at TYAD was contaminated by VOCs that were leached from soils that had been
exposed to spills and leaks. Therefore, EPA and PADEP reguired the Army to evaluate the site to
predict levels that would not allow groundwater to be contaminated at levels above those safe for
human health and the environment. Soil cleanup levels are discussed on page 2-5.

These soil cleanup levels represent the maximum allowable concentrations of TCE and PCE in
soil that will not result in groundwater being contaminated at levels above MCLs.

The results of the predesign and remedial design investigation conducted in 1994 indicated that the
conditions on which the proposed Remedial Action Plan (ESE, 1993a) were based had changed
since the RI/FS report. The remedial design soil sampling results indicated a much smaller
volume of contaminated soil existed, as compared to the original volume estimate. The soils data
also indicated that VOCs were not present in Area A at levels that exceeded cleanup criteria. Only
a limited amount of soil from Area B was found to contain VOCs at concentrations that exceeded
soil cleanup levels. Furthermore, the four onsite extraction wells installed for groundwater
recovery had little or no VOCs when tested.

Due to the limited amount of contaminated soils identified during predesign and remedial design
investigations, the Army conducted a removal action in July 1995 and removed approximately
2,100 yd 3 of VOC-contaminated soils from Area B. Following the completion of the removal
action, site sampling showed concentrations of VOCs in soils were less than soil cleanup levels.
With this information, the EPA and Army agreed that no further action was necessary for soils in
Area B. As discussed in the previous paragraph, contaminant concentrations in Area A were
present at concentrations less than soil cleanup levels.

Field testing showed that optimally placed newly installed groundwater extraction wells would be
inefficient in recovering contaminated groundwater. This led the Army to conclude the installation
of extraction wells would not recover contaminated groundwater efficiently. The Army also
performed tests to determine if groundwater could be efficiently recovered from existing monitor
wells. These tests concluded that appropriate flow rates of groundwater could not be sustained

-------
from monitor wells.

EPA and PADEP agreed with the Army's conclusions and recommended that the Army revise the
original proposed Remedial Action Plan to delete four of the original alternatives and address two
new alternatives:

   •      Groundwater:  Natural Attenuation/Long-Term Monitoring/Institutional Controls (the
          preferred alternative); Soils:  No Further Action,  and

   •      Groundwater:  Limited Groundwater Treatment/Institutional Controls/Monitoring;  Soils:  No
          Further Action

These two alternatives, in addition to the revised no-action alternative were presented for public
evaluation and comment in the Revised Remedial Action Plan  (ESE, 1997).


As previously stated, because contaminated soils were removed from Area B in July 1995 and all
soils in Area A and B have PCE and TCE concentrations less than the soil cleanup level,  EPA
has stated (correspondence dated February 13, 1996) that no further soil cleanup is reguired in
OU1.  Therefore, the following alternatives only address VOC-contaminated groundwater.

Implementation time-frames and treatment rates  (presented for the following alternatives) are
estimates based on the Administrative Record for OU1.   [Summary of Technical Data Regarding
Predesign Engineering Services for Areas A and B (Weston, 1995) and Remedial Design for Areas
A and B Soil and Groundwater Treatment Systems  (Weston, 1995)] .  This information will be
further refined with respect to the selected remedial alternative during the remedial design phase
of work.

7.1 Alternative Description

7.1.1 Alternative 1: Groundwater: No Action; Soil:  No Further Action


CERCLA/SARA and the NCP reguire that the no-action alternative be evaluated at every NPL
site to establish a baseline for comparison with other remedial alternatives.  Under this alternative,
current and/or future VOC-containing groundwater associated with Areas A and B would not be
addressed; there would be no groundwater monitoring or institutional controls implemented with
this alternative.

This alternative also incorporates a no further action component for soils. As previously stated,
soils in Area A did not have VOC contaminants at levels in excess of soil cleanup levels
(see page 2-5).   All soils with contaminants in excess of soil cleanup levels in Area B were
removed in an action conducted in July 1995.


    Capital costs:                            $0
    Present-worth operation and
    maintenance  (O&M) costs:                  $0
    Present worth:                            $0
    Time to complete:                     0 year


7.1.2  Alternative 2: Groundwater: Natural Attenuation/Long-Term
       Monitoring/Institutional Controls; Soil: No Further Action

Alternative 2 involves natural attenuation, which is defined as a natural process that results in a
reduction of contaminant concentrations in the environment through biological processes, physical
phenomena, and chemical reactions.  In addition, semiannual monitoring would be conducted to
continually assess the effectiveness of natural processes in reducing the extent of groundwater
contamination over time.

Details of the monitoring plan, such as constituents to be evaluated, freguency, duration, and
wells to be monitored,  will be outlined in the remedial action work plan. Data collected since

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1988 show that the areal extent of groundwater contamination is decreasing over time and that
contaminant levels are declining. This would be an indication that the contaminants in the
groundwater are being controlled through natural attenuation.

Institutional Controls prevent human consumption of contaminated groundwater until monitoring
determines that controls are no longer necessary. Institutional controls have already been
implemented and include the waterline agreement with the residents and an agreement between
TYAD and the Coolbaugh Township Zoning Office to ensure that future residents will not be
exposed to groundwater contaminated at levels above MCLs. These existing institutional controls
will become part of the selected remedy. Additionally, an institutional control prohibiting the
construction of any onpost drinking water well in the plume of groundwater contamination will be
implemented. This institutional control will be incorporated into the TYAD Master Plan and will
also become part of the selected remedy.

As this alternative involves natural attenuation and monitoring, information will be provided about
changes in the VOC plume and concentrations over time. These data would project potential
future plume movements over time. Until VOC levels in groundwater are restored to
concentrations below MCLs, users of groundwater near TYAD would be protected against using
water in excess of MCLs through continued the use of interim measures (i.e., the waterline or
other source of safe water).

This alternative also incorporates a no further action component for soils. As previously stated,
soils in Area A did not have contaminants at levels in excess of soil cleanup levels (see page 2-5).
All soils with contaminants in excess of soil cleanup levels in Area B were removed in an action
conducted in July 1995. The residual contamination in soils in Areas A and B are not considered
to be a threat to human health and the environment.

In the event that future data shows this alternative to be ineffective, Alternative 3, or another new
alternative, may be implemented. This alternative will be re-evaluated in 5 years. Costs are based
on groundwater monitoring for a 15-year period.

Capital costs: $0
Present-worth O&M costs: $1,038,000
Present worth: $1,038,000
Time to complete: 15 years

7.1.3 Alternative 3: Groundwater: Limited Groundwater Treatment/Institutional
Controls/Monitoring; Soil: No Further Action

With this alternative, several monitor wells with the highest VOCs concentrations would be
eguipped with pumps that would be used to extract groundwater. Based on field testing, the
maximum withdrawal rate of groundwater is expected to be low, on the order of less than 2 gpm.

The limited amount of groundwater that can be recovered will be processed through diffused
aeration, an air stripper, or carbon adsorption unit, which would be located next to each monitor
well. The first two processes involve the transfer of VOCs in the groundwater to the air which is
then passed out of the system. When treatment of air is reguired, this air is then passed through a
carbon filter which removes the VOCs in the air before it is released to the atmosphere. Carbon
adsorption involves the transfer of VOCs from water directly to carbon. Carbon that has been
exhausted would be replaced with new carbon. The exhausted carbon would be managed at an
appropriately permitted offsite waste management facility. The treated groundwater would be
discharged to the TYAD wastewater treatment plant through underground piping.

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This alternative also incorporates groundwater sample collection. Details of the monitoring plan,
such as constituents to be evaluated, freguency, duration, and wells to be monitored, will be
outlined in the remedial action work plan. Data from this collection effort would be evaluated to
assess the effectiveness of this alternative with respect to decreasing plume size and strength over
time.

As this alternative involves monitoring, information will be provided about changes in the VOC
plume and concentrations over time. These data would project potential future plume movements
over time. Until VOC levels in groundwater are restored to concentrations below MCLs, users of
groundwater near TYAD would be protected against using water in excess of MCLs.

This alternative will be re-evaluated in 5 years. Costs are based on groundwater treatment and
monitoring for a 15-year period.

Capital costs: $65,000
Present-worth O&M costs: $1,660,752
Present worth: $1,726,000
Time to complete: 15 years

8.0 Summary of Comparative Analysis of Alternatives

The remedial action alternatives for OU1 described in the preceding section were evaluated under
the nine evaluation criteria set forth in the NCP at 40 CFR ° 300.430(e) (9). These nine criteria
are organized according to the following categories listed in 40 CFR ° 300.430(f)(1):

Threshold Criteria
• Protection of human health and the environment, and
• Compliance with ARARs.

Primary Balancing Criteria
• Long-term effectiveness,
• Reduction in toxicity, mobility, and volume (TMV),
• Short-term effectiveness,
• Implementability, and
Cost.

Modifying Criteria
• State acceptance, and
• Community acceptance.

In accordance with the provisions set forth in CERCLA/SARA and the NCP, the Army evaluated
the groundwater components for each of the alternatives against nine established criteria.

Overall protection of human health and the environment and attainment of ARARs are threshold
criteria and the primary objectives of a remedial action. In addition, the selected remedial
alternative must reflect the best balance among criteria such as reduction of TMV of hazardous
substances; short- and long-term effectiveness; implementability; and cost. Finally, the remedial
action must also consider support agency and community acceptance.

This section details the comparative analysis of all three alternatives against the nine evaluation
criteria.

8.1 Overall Protection of Human Health and the Environment

Risks associated with the future residential use scenario are hypothetical and are based on the
assumption that unrestricted land use would occur at Areas A and B. The Army anticipates that
TYAD will continue to function as an active military installation, in which case, the hypothetical

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scenario would not occur.  In the event that TYAD is closed at some point in the future, and the
land transferred/sold to private or other public interests, DoD policy would require a re-evaluation
of the carcinogenic risks and noncarcinogenic His presented in Tables 6-4 and 6-5, respectively.
The scenario relevant to TYAD is the industrial use scenario.  Calculations for this scenario show
that exposure to site media results in risks that are within an acceptable range to EPA.
Additionally, no unacceptable chronic adverse health effects to exposed populations are anticipated.

Alternative 2, Natural Attenuation, and Alternative 3, Limited Groundwater Treatment, were
rated highest with respect to this criterion, because data would be collected to evaluate whether
human health and the environment are continually protected.  Alternative 1, No Action, does not
provide adequate protection for human health because residences/businesses with private wells
would not be provided with safe water to drink, and thus may be exposed to groundwater with
VOCs in excess of MCLs.   Additionally, without monitoring, the community would not know the
nature and extent of contaminated groundwater downgradient from TYAD; thus, there would be
no control over where new wells are installed by the Township of Tobyhanna or private residences in
the area.


8.2 Compliance with ARARs

The Safe Drinking Water Act (SDWA) requires that domestic water supplies comply with MCLs.
Currently, VOCs are exceeding MCLs in groundwater.  However, because the Army has supplied
water to all residences/businesses where MCLs are exceeded by installing a waterline, no one is
exposed to groundwater that does not comply with the SDWA requirements. Because
Alternatives 2 (Natural Attenuation) and 3  (Limited Groundwater Treatment) require continued
groundwater data collection,  the Army would be able to evaluate the continued protection of
human health and the environment over time.  The plan for data collection involves analyzing
information that would detect a potential threat to human health and the environment before it
could actually impact offsite residences or businesses.  If data collected show an unanticipated
change in site conditions, the Army would institute a measure that would ensure continued
compliance with ARARs (for example, implementation of Alternative 3, or another alternative)
and would be able to change the selected remedy to ensure that everyone whose groundwater
exceeds MCLs, could be provided safe water to drink.  Prior to changing the selected remedy, the
Army would present the changed alternative to the public to allow their participation in the
revision of the selected alternative.  The monitoring and alternate water supply will provide
interim protection to the communities in the short term, until MCL compliance for Alternatives 2
or 3 can be achieved.  In the case of Alternative 2, MCL compliance will be achieved through
natural attenuation.

Alternative 3 (Limited Groundwater Treatment) involves pumping and treatment of groundwater.
Extracted groundwater would be treated to levels that would comply with ARARs that address
water discharges.  In the case of Alternative 3, the treated groundwater would be discharged to the
TYAD wastewater treatment system, which must comply with National Pollution Discharge
Elimination System  (NPDES),  as specified by the Clean Water Act.  The discharge of treated
groundwater to the TYAD wastewater treatment plant would not prevent the system from
complying with its discharge requirements.  Any air emissions from the groundwater treatment
system would comply with all federal, state, and local requirements.  Air pollution control devices
would be installed on the groundwater treatment units as necessary to meet these requirements.

The PADEP has identified Pennsylvania's Land Recycling and Environmental Remediation
Standards Act (Act 2 of 1995)  as an ARAR. EPA had determined that, with regard to the
remediation of groundwater,  Act 2 does not under the facts and circumstances impose any
requirements that are more stringent than the Federal MCLs.

During the course of preparation of this ROD, PADEP has submitted correspondence to EPA and
the Army dated January 11, 1993; November 16, 1995; September 27, 1995; and
December 14, 1995. ARARs cited by PADEP include:

    25 Pa. Code 287.1 et seq (residual waste), and
    25 Pa. Code 264.100 et seq  (groundwater monitoring).

Because Alternative 1, No Action, does not provide for continued data collection, there is no
assurance that future residential wells would comply with SDWA ARARs.

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For an alternative to be considered for site rehabilitation, it must meet the threshold criteria of
being both ARAR compliant and protective of human health and the environment. Because
Alternative 1 is not ARAR compliant, this alternative does not meet the threshold criteria and
therefore is not eligible for selection as the preferred alternative. For this reason, Alternative 1
is not further discussed in the evaluation of alternatives.

Alternatives 2 (Natural Attenuation) and 3 (Limited Groundwater Treatment) are both ARAR
compliant, as both alternatives will result in decreasing concentrations of contaminants in
groundwater to levels below MCLs and protection of current and potential future users of
groundwater with institutional controls and the waterline agreement.

8.3 Long-Term Effectiveness and Permanence

Implementation of either Alternatives 2 (Natural Attenuation) or 3 (Limited Groundwater
Treatment) are both expected to result in the decrease of VOC levels in groundwater below
MCLs. Both these alternatives are expected to provide a high degree of long-term effectiveness
and permanence because once groundwater is restored to levels safe for drinking (i.e., less than
MCLs), the restoration would be permanent, as the source of contaminated groundwater (soils in
Area B) have been removed from TYAD.

8.4 Reduction of TMV through Treatment

Alternative 2 (Natural Attenuation) does not reduce TMV through treatment. However, through
natural environmental processes, reduction in contaminant concentrations over time is expected
with Alternative 2. Alternative 3 (Limited Groundwater Treatment) would reduce TMV through
the collection and treatment of contaminated groundwater. However, the amount of groundwater
that could be recovered with this alternative is considered insignificant, and the reduction in TMV
is expected to be minimal.

8.5 Short-Term Effectiveness

No construction is reguired with Alternative 2 (Natural Attenuation). Thus no short-term impacts
to workers or community are associated with implementation of this alternative. Construction
associated with Alternative 3 (Limited Groundwater Treatment) consists of retrofitting selected
monitor wells with a submersible pump, modular treatment units (e.g., carbon adsorption,
diffused aeration, or air stripper) and construction of a sub-surface discharge line. The
construction associated with Alternative 3 (Limited Groundwater Treatment) is minimal and no
negative short-term impacts to workers or community are anticipated. Because Alternative 3
(Limited Groundwater Treatment) reguires construction, and Alternative 2 (Natural Attenuation)
does not, the short term impact to workers and community associated with the former would be
greater, albeit minimal.

Alternatives 2 (Natural Attenuation) and 3 (Limited Groundwater Treatment) were considered to
be egually practical with respect to short-term effectiveness because no one is exposed to
groundwater that does not comply with the MCLs, and site data will continue to be collected to
assess the continued protection of human health and the environment until groundwater is restored
to levels safe for human consumption.

The estimated time for completion for both alternatives is 15 years. No adverse impacts are
anticipated during the period reguired for completion. Until groundwater is restored to levels safe
for human health and the environment, an interim measure, which provides water to private
residences/businesses where VOC concentrations are greater than MCLs, will provide protection
to human health. Additionally, institutional controls such as monitoring and the agreement that
TYAD has with the Coolbaugh Township Zoning Officer (an agreement that reguests TYAD "...
be notified of any new construction that will reguire potable water..,") will ensure that potential
migration of the VOC plume can not adversely effect other residences/businesses.

8.6 Implementability

Alternative 2 (Natural Attenuation) was considered more implementable than Alternative 3
(Limited Groundwater Treatment) because pump tests performed in March 1996 showed only low
groundwater flow rates could be sustained from pumping wells. Low flows from extraction wells

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would make the system impractical; therefore, Alternative 3 is considered to be inferior to
Alternative 2 with respect to implementability because the effectiveness of the alternative is
questionable and does require more effort and coordination to implement. Both alternatives are
administratively feasible.

8.7 Cost

Alternative 2  (Natural Attenuation) is a less expensive alternative, with a net present-worth cost of
$1,038,000.  Alternative 3 (Limited Groundwater Treatment) has a net present-worth cost of
$1,726,000 for implementation.

8.8 State Acceptance

PADEP documented their concurrence with the selected remedy in a letter to TYAD dated
April 4, 1997.

8.9 Community Acceptance

The Revised Remedial Action Plan was released to the public in March 1997.  An
availability/public meeting announcement was published in The Pocono Record on March 19,
1997.  A public meeting was held on March 26, 1997, at the Coolbaugh Township Municipal
Building to discuss the extent of contamination, previous work, alternatives evaluated for OU1,
and present the preferred alternative.  No verbal comments were presented during the March 26,
1997 public meeting regarding OU1.  In addition, no written comments were received during the
30-day public comment period.  Based on this, the Army concluded that the community does not
oppose the selected remedy for OU1.


                                    9.0 Selected Remedy


9.1 Description of Selected Remedy

Following review and consideration of the information in the Administrative Record file, the
requirements of CERCLA and the NCP, and public comments received on the Revised Remedial
Action Plan, the Army and EPA, in consultation with PADEP, have selected
Alternative 2: Natural Attenuation/Long-Term Monitoring/Institutional Controls for groundwater
and No Further Action for soils.  Alternative 2 meets the threshold criteria of overall protection of
human health and the environment and compliance with ARARs, and provides the best balance of
long-term effectiveness, reductions in TMV of contaminants through treatment, short-term
effectiveness, implementability and cost.

The selected remedy would protect human health and the environment, comply with ARARs or to
be considered  (TBC) guidance, and reduce VOCs in a cost-effective manner.  Therefore, based on
current information, the Army believes that the selected remedy would provide the best balance of
trade-offs among the remedial alternatives with respect to the nine evaluation criteria.

In the event that TYAD is closed at some point in the future, and the land transferred/sold to
private or other public interests, DoD policy would require a re-evaluation of potential site risks
at the property prior to transfer of property, to ensure future land owners are protected.

Alternative 2, Natural Attenuation, involves collecting groundwater data twice per year.
Groundwater data would be evaluated to determine if the size and strength of the groundwater
plume is decreasing over time.  If future data collection shows that the plume size and strength is
not decreasing over time, implementing Alternative 3, Limited Groundwater Treatment, or
another alternative, may be necessary to remove groundwater in areas of highest contaminant
concentrations.

This alternative also incorporates an ongoing interim measure that involves supplying water to
residences/businesses which have wells with VOC concentrations in excess of MCLs.
Additionally, residences/businesses that show VOCs in excess of MCLs in the future will also be
supplied with potable water and included in the waterline agreement.  An institutional control that
requests the Coolbaugh Township Zoning Officer notify TYAD of new construction involving

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potable water is also incorporated as part of this alternative; this control will ensure that new
wells are not placed in areas of known or suspected contamination. An institutional control
prohibiting the construction of any onpost drinking water well in the plume of groundwater
contamination will also be implemented. This institutional control will be incorporated into the
TYAD Master Plan and will also become part of the selected remedy.

Data collected since the initiation of RI/FS studies at TYAD show that natural attenuation is
working in groundwater. The area of TCE contamination in excess of MCLs has decreased by
more than 77 percent over the period from January 1988 to March 1996. When the RI/FS began,
a total of six onpost bedrock monitor wells exceeded MCLs, while in March 1996, a total of three
wells exceeded MCLs. In 1988, 12 residential wells exceeded VOC MCLs, while only two wells
were above MCLs for TCE and PCE in March 1996. It is anticipated that the natural processes
that have caused the groundwater plume to decrease in size and strength will continue with time.

9.2 Estimated Costs

There are no capital costs associated with this alternative. VOC levels in groundwater will be
monitored using the existing network of onsite monitor wells, onsite water supply wells, and the
offsite residential wells.

The O&M components of this alternative involve groundwater sample collection, groundwater
sample analysis, water level measurement, and preparing semi-annual groundwater reports. O&M
costs are estimated as $100,000 per year. Assuming a 15-year O&M period, the total prestnt
value cost of this alternative is approximately $1,038,000 (assuming a discount rate of 5 percent).

9.3 Performance Standards

The Performance Standard for the selected remedy is the remediation of vinyl chloride, TCE, and
PCE to MCLs throughout the entire plume of groundwater contamination. The MCLs are set
forth at 40 CFR ° 141.61(a) and are as follows: vinyl chloride (2 Ig/1), TCE (5 Igl) and PCE
(5 Ig/1). Attainment of the Performance Standard will be achieved by the selected remedy in the
following manner:

1) Natural Attenuation

The selected remedy includes natural attenuation of groundwater which shall be monitored until
such time as EPA and the Army, in consultation with PADEP, determine that the Performance
Standard has been achieved throughout the entire plume of groundwater contamination.

Performance data will be evaluated to assess the effectiveness of the selected alternative. The
initial annual performance evaluation will be conducted within 1 year after the remedial design is
finalized. The initial and subseguent annual performance evaluation reports will be based on
previously collected data from onsite monitor and water supply wells, as well as offsite residential
wells, and will include water level analyses and statistical evaluation of the magnitude and areal
extent of VOC contamination. The Army will submit the initial and subseguent annual
performance evaluation reports to EPA and PADEP for review. The contents of the annual
performance evaluation and the schedule for submitting these reports will be determined during
the remedial design.

The Army and EPA, in consultation with PADEP, will review the annual performance evaluation
reports to determine whether the selected alternative is achieving general response action
objectives. In the event that future data shows this alternative to be ineffective, Alternative 3,
discussed in Sees. 7.0 and 8.0, or a new alternative, may be implemented.

2) Long-Term Monitoring

A long-term groundwater monitoring program shall be implemented to evaluate the effectiveness
of the natural attenuation alternative. Semi-annual monitoring of the groundwater shall continue
until such time as EPA and the Army, in consultation with PADEP, determine that the
Performance Standard has been achieved throughout the entire plume of groundwater contamination.

The number, location, and depth intervals of these wells, along with the list of sampling analytical
parameters, will be determined by the Army and EPA, in consultation with PADEP, during

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Remedial Design. To the extent deemed practicable by the Army and EPA, in consultation with
PADEP, residential wells will be used to augment the existing groundwater monitoring program.
The monitoring program shall be consistent with the objectives of the annual performance
evaluations. The Remedial Design will be approved by EPA, in consultation with PADEP.

3) Institutional Controls

Institutional controls have been implemented and will continue to be administered until such time
that EPA and the Army, in consultation with PADEP, determine that the Performance Standard
has been achieved throughout the entire plume of groundwater contamination.

The Army has implemented a waterline agreement with the affected residents which specifies that
individual residential wells will not be used for any purpose except for monitoring by the Army
until such time that the Army determines that the groundwater from the well does not pose an
unacceptable risk to human health. In return, the residents will receive potable water from the
TYAD water supply.

The Army has implemented an agreement with the Coolbaugh Township Zoning Office reguiring
that the Army be alerted when the Zoning Office learns of a resident who plans to construct a
well in the area of the contaminated plume. That resident will be connected to the TYAD water supply.

An institutional control which would prohibit the construction of any onpost well in the plume of
groundwater contamination will be implemented. This institutional control will be incorporated in
the TYAD Master Plan and will remain in effect until such time that the Performance Standard is
achieved.

4) Five Year Reviews

Five Year reviews shall be conducted after the remedy is implemented to assure that the remedy
continues to protect human health and the environment.

Based on information obtained during the RI/FS, and as documented in the Administrative
Record, the Army and EPA believe that it will be possible to achieve general response action
objectives for this OU. If the Army and EPA, in consultation with PADEP, determine, on the
basis of performance evaluation data, that the general response action objectives cannot be
achieved throughout the contaminant plume or area of attainment, additional measures to protect
human health and the environment may be undertaken. Such measures will be determined by the
Army and EPA, in consultation with PADEP, and may include, but are not limited to, any of the
following actions:

• Invoke a waiver of the federal MCL for those portions of the aguifer in which it is
technically impractical to achieve further reduction of VOCs.
• Continue to collect and analyze samples as part of the groundwater monitoring program.
• Re-evaluate remedial technologies for groundwater restoration.

The decision to take any or all of these measures may be made during implementation/operation
of the remedy, during the annual performance evaluations, or during the 5-year reviews of the
remedial action under CERCLA, Sec. 121(c). In the event that such a decision is made, the Army
and EPA, in consultation with PADEP, will either issue an Explanation of Significant Differences
in accordance with procedures set forth in NCP ° 300.435 (c) (2) (i) or propose an amendment to
the ROD in accordance with procedures set forth in NCP ° 300.435 (c) (2) (ii) .

10.0 Statutory Determinations

Under CERCLA, Sec. 121, EPA must select remedies that are protective of human health and the
environment, comply with ARARs (unless a statutory waiver is justified), are cost-effective, and
use permanent solutions and alternative treatment technologies or resource recovery technologies
to the maximum extent practicable. In addition, CERCLA includes a preference for remedies that
employ treatment that permanently and significantly reduce the volume, toxicity, or mobility of
hazardous wastes as their principal element. The following sections discuss each of the statutory
determinations.

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10.1 Overall Protection of Human Health and the Environment

The selected remedy (Alternative 2) would protect human health and the environment by
permanently reducing VOCs in groundwater to levels below MCLs via natural processes (i.e.,
natural attenuation).

Under a previously completed removal action, TYAD extended the Depot's existing water
distribution system to provide a potable water supply to 24 affected residences/businesses. As
specified in Agreement for Alternate Water Supply and Services (Waterline Agreement) between
the residents of the Village of Tobyhanna and the United States Government, which was executed
in November 1990, existing wells at affected residences/businesses were disconnected and may be
used only for continued testing as part of TYAD's ongoing groundwater monitoring program.
This agreement is transferable to new owners.

Because the Waterline Agreement reguires that residences/businesses wells be disconnected, those
residences/businesses connected to the waterline will be protected from exposure to contaminated
groundwater. Continued groundwater monitoring will ensure that new residences/businesses, that
potentially are affected by water with VOCs in excess of MCLs in the future, are identified for
the purposes of supplying an alternative water supply, and thus, prevented from exposure to
unsafe groundwater.

TYAD will continue to provide a source of potable water to affected residents and extend service
as necessary until such time that PADEP or EPA determines that levels of contaminants in these
wells or in the aguifer used to supply potable water meet applicable SDWA standards. At that
time, affected residents may choose to resume service from their private wells. Therefore,
long-term unacceptable risks at these residences/businesses have already been effectively
eliminated by this removal action.

An institutional control that reguests the Coolbaugh Township Zoning Officer notify TYAD of
new construction involving potable water is also incorporated as part of the selected remedy; this
control will ensure that new wells are not placed in areas of known or suspected contamination.
An institutional control prohibiting the construction of any onpost drinking water well in the
plume of groundwater contamination will also be implemented. This institutional control will be
incorporated into the TYAD Master Plan and will also become part of the selected remedy.

Once MCLs have been achieved for groundwater under the selected remedy, the carcinogenic risk
associated with current and future groundwater exposure will be within EPA's target risk range of
1.0 X 10 -4 to 1.0 X 10 -6 and there will be no significant potential for adverse noncarcinogenic
health effects as a result of exposure to groundwater (i.e., the HI shall be less than or egual to
one). Throughout the performance of groundwater remediation, contaminant levels in the bedrock
aguifer will be monitored to assess the effectiveness of natural attenuation.

There are no short-term risks associated with the implementation of this alternative. The Army
will continue to monitor groundwater, and assess potential future impacts to residents not
connected to the TYAD waterline. If monitoring data concludes that other resident's and/or
businesses' wells could be impacted by groundwater above MCLs, the Army will extend the
waterline service to these locations.

VOCs in groundwater are expected to be reduced to levels below the MCLs by natural
attenuation. This remedial action provides long-term effectiveness because it would reduce the
existing health risks to onpost and offpost users caused by VOCs in groundwater migrating
offsite.

Groundwater compliance levels were chosen as federal and state MCLs since the contamination
was detected in the offpost residential wells and the municipal supply well. Onpost soils are not a
concern as these soils have been remediated to levels acceptable to EPA and PADEP. Onsite
groundwater is not of direct concern as there are no current pathways for exposure. Therefore,
because there are no current exposure pathways for onsite contaminated groundwater (no one
onpost has access to untreated groundwater), interim measures instituted offsite (i.e., the
Waterline Agreement) are not necessary for onsite wells.

10.2 Compliance with ARARs

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The selected remedy, when complete, will have reduced VOC concentrations in groundwater to
cleanup standards, thereby satisfying the chemical-specific ARARs (federal and state MCLs).

10.2.1 Contaminant-Specific ARARs

The contaminant-specific ARARs for groundwater remediation are federal [40 CFR ° 141.61(a)]
and state [Pa ° 109.202(a)(2) and (3)] MCLs. The natural attenuation process is expected to
comply with these ARARS.

The "Statewide Human Health Standards" under the Land Recycling and Environmental
Remediation Standards Act is a TBC reguirement. The selected remedy is expected to comply
with this TBC reguirement.

10.2.2 Action-Specific ARARs

There are no action-specific ARARs associated with the implementation of Alternative 2.

10.2.3 Location-Specific ARARs

No location-specific ARARs have been identified for TYAD Areas A and B.

10.3 Cost Effectiveness

The selected remedy, as compared to the alternatives evaluated in Sec. 7.0, achieved an egual or
better level of performance at less cost. The net present-worth cost of Alternative 2 has been
estimated at approximately $1,038,000.

10.4 Utilization of Permanent Solutions and Alternative Treatment
Technologies or Resource Recovery Technologies to the Maximum
Extent Practicable

The use of resource recovery technologies is not appropriate for OU1 at TYAD. Alternative
treatment technologies cannot be practically used to reduce levels of VOCS in groundwater at
TYAD. Implementation of a large-scale groundwater treatment system was determined to be
impracticable. Field testing showed that optimally placed, newly installed groundwater extraction
wells were inefficient in recovering contaminated groundwater. This led the Army to conclude the
installation of extraction wells would not recover contaminated groundwater efficiently. The Army
also performed tests to determine if groundwater could be efficiently recovered from existing
monitor wells. These tests concluded that appropriate flow rates of groundwater could not be
sustained from monitor wells.

With respect to alternatives evaluated that are protective of human health and the environment and
meet ARARs, the selected remedy provides the best balance of tradeoffs in terms of long- and
short-term effectiveness and permanence, cost implementability, reduction in toxicity, mobility
and volume, support agency and community acceptance, and preference for treatment as a
principal element. Although no active treatment is employed with the selected remedy, natural
attenuation is considered treatment as natural biological processes, physical phenomena, and
chemical reactions will reduce contaminant levels over time.

10.5 Preference for Treatment as a Principal Element

The selected remedy satisfies the statutory preference for treatment as a principal element.
Although no active treatment is employed with the selected remedy, natural attenuation is
considered treatment as natural biological processes, physical phenomena, and chemical reactions
will reduce contaminant levels over time.

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                                  11.0 References

Environmental Science & Engineering, Inc. (ESE).  1997. Proposed Remedial Action Plan
        (Revised)  for Operable Unit 1 at Tobyhanna Army Depot, Tobyhanna, Pennsylvania.

Environmental Science & Engineering, Inc. (ESE).  1993a. Remedial Action Plan for Operable
        Unit 1 at Tobyhanna Army Depot, Tobyhanna, Pennsylvania.

Environmental Science & Engineering, Inc. (ESE).  1992a. Remedial Investigation/Feasibilily
        Study at Tobyhanna Army Depot. Endangerment Assessment.

Environmental Science & Engineering, Inc. (ESE).  1992b. Remedial Investigation/Feasibility
        Study at Tobyhanna Army Depot. Draft Final Feasibility Study Report for the Areas A
        and B Operable Unit.

Environmental Science & Engineering, Inc. (ESE).  1992c. Remedial InvestigationlFeasibility
        Study at Tobyhanna Army Depot. Draft Final Remedial Investigation Addendum.

Environmental Science & Engineering, Inc. (ESE).  1992d. Final Engineering Reportfor
        Tobyhanna Army Depot, Coolbaugh Township, Monroe County, Pennsylvania.

Environmental Science & Engineering, Inc. (ESE).  1988a. Remedial InvestigationlFeasibility
        Study at Tobyhanna Army Depot. Final Remedial Investigation Report A011.

  Environmental Science & Engineering, Inc.  (ESE). 1988b. Update the Original Installation
  Assessment at Tobyhanna Army Depot.

Federal Interagency Committee for Wetland Delineation  (FICWD). 1989. National Wetland
        Inventory Map.

Federal Manual for Identifying and Delineating Jurisdictional Wetlands. U.S. Army Corps of
        Engineers (USAGE), U.S. Environmental Protection Agency (EPA), U.S. Fish and
        Wildlife Service  (USFWS),  and U.S. Department of Agriculture, Soil Conservation
        Service (SCS), Washington, DC.

 Geary, T. 1988. Personal Communication to Geri Kountzman, ESE, Inc. on July 7, 1988.
       Gainesville,  Florida. Pennsylvania Department of Environmental Regulation.
       Wilkes-Barre,  Pennsylvania.

 Lipscomb, G.H. 1981. Soil Survey of Monroe County, Pennsylvania.  U.S. Department of
       Agriculture,  Soil Conservation Service  (SCS),  Washington, DC.

  OHM. 1996. Contaminated Soil Removal from Area B, Tobyhanna Army Depot.

 Summers,  Gherini, and Chen. 1980. Methodology to Evaluate the Potentialfor Groundwater
       Contamination from Geothermal Fluid Release. EPA-600/7-80-117.

 U.S. Environmental Protection Agency  (EPA). 1991. Supplemental Guidance: Standard Default
       Exposure Factors. Supplement to Risk Assessment Guidance for Superfund  (RAGS):
       Human Health Evaluation Manual.

 U.S. Environmental Protection Agency  (EPA). 1989a. Vol. I. Risk Assessment Guidance for
       Superfund  (RAGS): Human Health Evaluation Manual.

 U.S. Environmental Protection Agency  (EPA). 1989b. Vol II. Risk Assessment Guidance for
       Superfund  (RAGS): Environmental Evaluation Manual.

 R. F. Weston, Inc.  1995. Remedial Design for Areas A and B Soil and Groundwater Treatment
       Systems, Tobyhanna Army Depot: Draft 35% Concept Design Submittal.

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                                      Attachment A

                                 Responsiveness Summary

The purpose of the Responsiveness Summary is to provide the public with a summary of citizen
comments,  concerns,  and questions about OU1.

The Proposed Remedial Action Plan (Revised)for Operable Unit 1 at Tobyhanna Army Depot was
released to the public in March 1997.  An availability/public meeting announcement for the RI;
RI Addendum, EA; FS; proposed Remedial Action Plan,  as well as new documents which include
the Preliminary Remedial Design (Weston, 1996)  and the Contaminated Soil Removal from Area B
report (OHM, 1996) was published in The Pocono Record on March 19, 1997.

The public meeting for the Revised Remedial Action Plan was held on March 26, 1997,  at the
Coolbaugh Township Municipal Building. At this meeting, representatives from the Army, EPA,
and PADEP were available to summarize the remedial alternatives presented in the proposed
Revised Remedial Action Plan,  discuss rationale for selecting the preferred alternative, and
discuss any site-related issues raised by the public and the remedial alternatives under
consideration.  No written comments were received during the 30-day public comment period.  In
addition,  no verbal comments were presented during the March 26,  1997 public meeting
regarding OU 1.

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