Superfund Record of Decision Naval Air Development Center (8 Areas) OU 4 Warminster Township PA


                                   EPA/ROD/R03-97/178
                                   1997
EPA Superfund
     Record of Decision:
     NAVAL AIR DEVELOPMENT CENTER (8 WASTE
     AREAS)
     EPA ID: PA6170024545
     OU05
     WARMINSTER TOWNSHIP, PA
     09/30/1997

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EPA/541/R-97/178

                                 RECORD OF DECISION
                            NAVAL AIR DEVELOPMENT CENTER

                                    DECLARATION

SITE NAME AND LOCATION

Naval Air Development Center
Warminster Township
Bucks County, Pennsylvania

STATEMENT OF BASIS AND PURPOSE

This Record of Decision  (ROD) presents a selected interim remedial action for Operable Unit
Four (OU-4) at the former Naval Air Development Center in Warminster Township, Bucks
County, Pennsylvania  (the "Site"), chosen in accordance with the Comprehensive Environmental
Response, Compensation, and Liability Act (CERCLA) of 1980, as amended, 42 U.S.C. ° 9601
et seq. and, to the extent practicable, the National Oil and Hazardous Substances Pollution
Contingency Plan  (NCP), 40 C.F.R. Part 300.  This decision is based on the Administrative
Record for this Site. In January 1993, the facility was renamed Naval Air Warfare Center
(NAWC)  Aircraft Division Warminster. NAWC ceased operations on September 30, 1996 and
is now targeted for transfer to the private sector.

The Commonwealth of Pennsylvania has neither concurred nor non-concurred with the selected
remedy as of the date of this Record of Decision. The concurrence/non-concurrence letter from
the Commonwealth will be added to the Site Administrative Record upon receipt.

ASSESSMENT OF THE SITE

Actual or threatened releases of hazardous substances from this Site, if not addressed by
implementing the interim response action selected in this ROD, may present an imminent and
substantial endangerment to public health, or welfare, or the environment.

DESCRIPTION OF THE SELECTED REMEDY

The selected interim remedy for OU-4 is the fourth remedial action addressing the Site. OU-4
consists of contaminated groundwater underlying Area D at the Site.  (Previous response actions
have been selected and/or implemented to address Operable Unit One, which consists of
contaminated groundwater attributable to Areas A and B, Operable Unit Two, which consists of
contaminated drinking water supplies, and Operable Unit Three, which consists of contaminated
groundwater attributable to Area C.) The objective of the selected interim remedy for OU-4 is to
minimize the migration of the contaminated groundwater, initiate aguifer restoration, and obtain
information about the response of the aguifer to remediation measures. In addition, a secondary
objective is to limit or eliminate unacceptable exposure to the contaminated groundwater while
the remedy is being implemented. A final remedial action for OU-4 will be selected in a final
Record of Decision for OU-4 to be issued after the full nature and extent of contaminated
groundwater underlying Area D is identified and will consider the information generated during
the implementation of the interim remedial action. Future actions at the Site will address waste,
soils,  sediment, and/or other media as necessary.

The selected interim remedy for OU-4 is groundwater extraction, treatment of extracted
groundwater at an existing on-base groundwater treatment system, discharge to surface water at
the outfall of the subject treatment system, and institutional controls, to continue until the final
remedy is implemented. The components of this interim remedy include:

(1)   Determination of the contribution of on-base, open water supply wells on the vertical
      distribution of contamination in groundwater

(2)   Reconstruction or abandonment of the subject wells, as necessary, to limit further
      contaminant migration

(3)   Installation, operation and maintenance of groundwater extraction wells

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(4)    Pumping of contaminated groundwater and conveyance through piping to an existing on-
      base groundwater treatment system

(5)    Installation (if necessary)  and monitoring of observation wells to ensure effectiveness of
      the groundwater extraction wells

(6)    Periodic evaluation of hydrogeologic data and the effectiveness of the groundwater
      extraction system

(7)    Modification of the groundwater extraction well system as necessary based on periodic evaluations

(8)    Operation and maintenance of existing onsite groundwater treatment system and
      expansion of this system if necessary to treat extracted groundwater from Area D

(9)    Monitoring of treated water to ensure the effectiveness of the treatment system

(10)  Discharge of treated water to an unnamed tributary of Little Neshaminy Creek

(11)  Installation, operation and maintenance of vapor phase carbon adsorption units as
      necessary to control air emissions from treatment system

(12)  Offsite treatment and/or disposal of solid residuals generated during water treatment

(13)  Monitoring of groundwater in off-base monitoring wells

(14)  Institutional controls to prevent the use of groundwater which presents an unacceptable
      health risk

(15)  A review of the remedy on a five-year basis


STATUTORY DETERMINATIONS

Pursuant to duly delegated authority, we hereby determine, pursuant to Section 106 of CERCLA,
42 U.S.C. ° 9606, that this interim action is protective of human health and the environment,
complies with Federal and State applicable or relevant and appropriate reguirements directly
associated with this action, and is cost-effective. Although this action is not intended to fully
address the statutory mandate for permanence and treatment to the maximum extent practicable,
this interim action utilizes treatment and thus is in furtherance of that statutory mandate.
Because this action does not constitute the final remedy for Operable Unit Four, the statutory
preference for remedies that employ treatment that reduces toxicity, mobility, or volume as a
principal element, although partially addressed by this remedy, will be addressed by the final
response action. Subseguent actions are planned to address fully the threats posed by the
conditions at the Site.

Because the interim remedy addressing groundwater is likely to result in hazardous substances
remaining onsite above health-based levels, a review will be conducted within five years of the
remedial action to ensure that the remedy continues to provide adeguate protection of human
health and the environment. Because this is an interim action ROD, review of this Site and of
this remedy will be continuing as the U.S. Navy and EPA continue to develop final remedial
alternatives for Operable Unit Four.

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RECORD OF DECISION

TABLE OF CONTENTS

SECTION PAGE

I. SITE NAME, LOCATION, DESCRIPTION 1

II. SITE HISTORY 6

III. HIGHLIGHTS OF COMMUNITY PARTICIPATION 12

IV. SCOPE AND ROLE OF THIS RESPONSE ACTION 14

V. SUMMARY OF SITE CHARACTERISTICS/EXTENT OF CONTAMINATION 15

VI. SUMMARY OF SITE RISKS 23

VII. DESCRIPTION OF ALTERNATIVES 26

VIII. COMPARATIVE ANALYSIS OF ALTERNATIVES 27

IX. SELECTED REMEDY 29

X. STATUTORY DETERMINATIONS 32

XI. DOCUMENTATION OF SIGNIFICANT CHANGES 35

XII. RESPONSIVENESS SUMMARY 35

FIGURES

NUMBER PAGE

1 NAWC Warminster Site Location Map 3
2 NAWC Warminster Waste Disposal Locations Map 4
3 General Layout and Historic Features Map 5
4 Waste Disposal Locations Map 9
5 Municipal, Residential and Commercial Well Location Map 18
6 Monitoring Well Locations for Area D 20

TABLES

NUMBER PAGE

1 Summary of Waste Management and Site Operations 7
2 Occurrence/Distribution of Monitoring Well Organics, Inorganics, Pesticides/PCBs .. 21
3 Summary of Risks - Adult Receptors 25
4 Summary of Risks - Child Receptors 25

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RECORD OF DECISION

NAVAL AIR DEVELOPMENT CENTER

DECISION SUMMARY

I. SITE NAME, LOCATION, AND DESCRIPTION

The Naval Air Development Center is a 840-acre Naval facility located in Warminster
Township, Northampton Township and Ivyland Borough, Bucks County, Pennsylvania ("the
Site") (see Figure 1 for Site Location Map). In January 1993, the Naval facility was renamed
Naval Air Warfare Center (NAWC) Aircraft Division Warminster. The Site lies in a populated
suburban area surrounded by private homes, various commercial and industrial activities, and a
golf course. On-site areas include various buildings and other complexes connected by paved
roads, the runway and ramp area, mowed fields, and a wooded area.

The longest runway is generally located along the topographically highest area at the Site. Many
of the primary NAWC buildings are located west of the airstrip, along Jacksonville Road, a
public road which traverses the Site north to south. A housing development for military enlisted
personnel is within the southeastern portion of the Site. A wastewater treatment plant (WWTP)
owned and operated by NAWC is located in the northwestern corner of the Site.

Commissioned in 1944, NAWC's main function until 1949 was aircraft manufacturing. From
1949 to 1996, NAWC was a research, development, testing, and evaluation facility for Naval
aircraft systems. NAWC also conducted studies in anti-submarine warfare systems and software
development. Pursuant to the Defense Base Realignment and Closure Act of 1990 (Public Law
101-510), NAWC ceased operations on September 30, 1996, and is targeted for transfer to the
private sector. All activities have been relocated to Patuxent River, Maryland, with the
exception of an enlisted men's housing area in the southwestern corner of NAWC, which will be
retained by the Navy (see Figure 4).

During its operation, NAWC had approximately 3,000 employees, and 1,000 people continue to
reside at the enlisted men's housing area year round. The residents living within the enlisted
men's housing area are the nearest population center. The closest off-base home is about 200
feet away from the NAWC property line. Residential development is located along the length of
the southern property line of NAWC, and to a lesser extent, along the northern property line.
Industrial development is located along the west and northwest perimeter of NAWC property.
Groundwater is used extensively as a source of water by both residents and industry in the
immediate vicinity of the Site. The Site is located on a ridge, generally oriented east-west, with
elevations ranging from 297 feet at the northwestern property boundary to 377 feet at the eastern
boundary. Onsite slopes are gentle and average three to five percent.

The northern portion of the Site (about 65 percent) drains into small, unnamed tributaries of
Little Neshaminy Creek. The remaining portion (about 35 percent) drains into unnamed
tributaries of Southampton Creek. These streams are used for recreation and industrial purposes.

An unnamed tributary of Little Neshaminy Creek which flows immediately adjacent to the
NAWC property line may be used for recreational purposes by children approximately 3000 feet
downgradient of the Site. There are no known endangered species or critical habitats within the
immediate vicinity of the Site.

Area D generally includes NAWC property located immediately northwest of the primary
building complex at NAWC, Buildings 1 and 2, and extends to the NAWC property boundary
northwest of this complex. Figure 2 provides the general location of Area D. Buildings 1 and 2
were built by the Brewster Aeronautical Corporation in 1942 and were subseguently transferred
to the Navy in 1944. From 1942 through 1944, these buildings were used to manufacture aircraft
and to support these manufacturing operations. Aircraft manufacturing operations continued
until 1949, when NAWC re-organized into an aircraft research and development center. Since
that time, Buildings 1 and 2 have housed miscellaneous laboratories and shops as part of this
function. More detailed information regarding the history of Buildings 1 and 2 appears in an
"Area D Remedial Investigation/Feasibility Study Workplan for NAWC" (Brown and Root
(1996)) and "Environmental Baseline Survey for NAWC" (EA Engineering, 1995). Also located
within Area D are a variety of other structures, including miscellaneous buildings, underground
storage tanks and hazardous waste storage areas. Again, Brown and Root (1996) and EA
Engineering (1995) provide detailed background information regarding this area. Figure 3

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provides a more detailed map of Area D.

II. SITE HISTORY

This section describes the history of waste disposal, and CERCLA investigations and response
actions at the Site.

A. HISTORY OF WASTE DISPOSAL

Historically, wastes containing hazardous substances were generated by NAWC during aircraft
manufacturing, maintenance and repair, pest control, fire-fighting training, machine and plating
shop operations, spray painting, and various materials research and testing activities in
laboratories. The wastes generated have included paints, solvents, sludges from industrial
wastewater treatment, and waste oils. From 1940 to 1980, these wastes were disposed in pits,
trenches, and landfills located on current NAWC property. In addition, wastes generated by
NAWC were burned in a fire training area until 1988.

To date, eight (8) areas on current NAWC property have been reported as areas used for the
disposal of wastes containing hazardous substances. A brief summary of these areas is provided
on Table 1-1. Figure 4 provides the locations of these waste disposal areas, which cover
approximately ten acres. None of these areas are currently used for waste disposal.

While no waste disposal has been reported within Area D, available groundwater data to be
discussed later in this Record of Decision indicates that hazardous substances have been released
to groundwater underlying Area D and that these hazardous substances may have been released
either within Area D or immediately adjacent areas. In addition to hazardous waste generation
and storage areas and areas of hazardous substance/material use within Area D, other potential
sources of this groundwater contamination include hazardous substance releases from sewer
lines under and adjacent to Buildings 1 and 2 and other operations within Area D. The
investigation of the potential source(s) of contaminant releases to groundwater underlying Area
D is discussed further in the next section.

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                                                   TABLE 1
                               SUMMARY OF WASTE MANAGEMENT AND SITE OPERATIONS
                                        NAWC WARMINSTER, PENNSYLVANIA

 SITE  DATES OF                    TYPES OF WASTES
  NO.  OPERATI
         ON
  1    1940 to   Paints, oils, asphalt, roofing material, unspecified
       1955      chemicals, firing range wastes
 METHOD OF
 OPERATION

Burn pit within
an eroded ravine
                     POTENTIAL HAZARDS
Various solvents, driers,
pigments, PAHs, creosote,
phenols, asbestos, binders,
lead
       1965 to   Industrial wastewater sludges
       1970
2 disposal
trenches
Biological wastes, heavy
metals
       1955 to   Solvents, paints, roofing materials, and unspecified         Burn pit
       1965      chemicals

       1966 to   Non-industrial solid wastes, paints, waste oils, waste       7  disposal
       1970      metals, construction debris, solvents, and sewage            trenches
                 treatment sludge
                     Various solvents, driers,
                     pigments, asbestos, binders

                     Various solvents, driers,
                     pigments, lead, PAHs,
                     biological wastes, heavy
                     metals
  5    1955 to   Paints, solvents, scrap metal, and 30 drums of asphalt
       1970
  6    1960 to   Paints, solvents, demolition wastes, waste oils, other
       1980      flammable wastes, and grease trap wastes
6 to 8 disposal
trenches
Unknown
number of
disposal pits or
trenches
Various solvents, driers,
pigments, creosote, phenols,
PAHs

Various solvents, driers,
pigments, lead, PAHs
  7    1950 to   Industrial wastewater sludge
       1955

  8    1961 to   Aviation fuel, lubricants, coolants
       1988
2 disposal
trenches

Firefighting
training area
Biological wastes, heavy
metals

PAHs, PCBs
ADAPTED FROM SMC MARTIN 1991  (TABLES 1-1 AND 4.3-4)

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B. CERCLA INVESTIGATIONS AND RESPONSES

The EPA completed CERCLA Preliminary Assessment (PA) and PA/Site Inspection (SI)
Reports in 1979 and 1985 respectively. In 1986, the Site was proposed for inclusion on the
National Priorities List (NPL). On October 4, 1989, the Site was placed on the final NPL. On
September 20, 1990, the Navy and EPA signed an Interagency Agreement (IAG) which
established a procedural framework for developing and implementing investigative and response
actions at the Site in accordance with CERCLA and the NCP.

In response to the inclusion of the Site on the NPL and in accordance with the IAG, the Navy has
investigated hazardous substance releases at the Site in multiple phases: a Phase I RI, Phase II
RI a Focused RI, and a Phase III RI, which is, currently in progress.

The Phase I Remedial Investigation (RI) was initiated in late 1988 and was completed on
September 11, 1990 with the release of the Phase I RI Report. Phase I initiated the investigation
of sites 1 through 8 by screening these sites for volatile organic compounds (VOCs) via soil gas
analysis and detecting any buried materials through electromagnetic surveys. The sites were also
investigated through soil borings and the installation and sampling of shallow monitoring wells
installed to monitor overburden and shallow bedrock aguifers. In addition, test pits were
excavated, nearby wells were inventoried, and a bedrock fracture-trace analysis was conducted.

The Phase II RI was initiated in late 1991. Phase II work included the installation of additional
overburden and shallow bedrock monitoring wells, sampling and analyzing groundwater, and an
evaluation of aguifer characteristics through water-level monitoring, slug and step-drawdown
tests and a pumping test. Four off-site wells were sampled during the Phase II RI.

Both the Phase I and Phase II RI investigated the nature and extent of shallow groundwater
contamination within the vicinity of sites 1, 2, and 3 (collectively referred to as Area A), sites 5,
6, and 7 (Area B) and sites 4 and 8 (collectively referred to as Area C).

Based on the results of these investigations, the Navy completed Remedial Investigation and
Feasibility Study Reports addressing contaminated groundwater in overburden and shallow
bedrock attributable to Areas A and B (identified as Operable Unit One or OU-1) in April of
1993. Then Navy subseguently issued a Proposed Plan addressing OU-1 on April 26, 1993 and
jointly signed a Record of Decision (ROD) with EPA for OU-1 on September 29, 1993. The
ROD for OU-1 selected an interim remedy which included the pumping and treatment of
groundwater to limit the migration of contaminated groundwater attributable to Areas A and B.

Beginning the week of April 28, 1993, the Navy initiated the sampling of off-base wells to assess
the impact of contaminated groundwater attributable to NAWC on off-base groundwater users.
Through September 30, 1994, the Navy had sampled more than 500 wells over several rounds of
guarterly sampling. Seven (7) residential wells sampled exceeded EPA Removal Action Levels,
while an additional thirty-nine (39) residential wells exceeded Maximum Contaminant Levels
(MCLs) (developed pursuant to the Safe Drinking Water Act). At least part of this
contamination is potentially attributable to the Site. In response, the Navy has conducted a
CERCLA removal action, installing a water treatment system in each residence where either
EPA Removal Action Levels or MCLs have been exceeded.

The EPA and the Navy determined this off-base groundwater contamination may present an
imminent threat to human health. In response, the EPA and the Navy have conducted additional
CERCLA removal action work which provided residences exceeding EPA Removal Action
Levels, as well as residences in the immediate path of the groundwater contamination, with
connections to public water supply systems. Residences addressed by these actions include all
residences on Kirk Road. The work completed under this Removal Action is considered to be
Operable Unit Two (OU-2).

A Focused RI was initiated in October 1993 to further investigate the nature and extent of
contaminated groundwater attributable to Areas A, B, and C. In addition, the Focused RI
initiated the CERCLA investigation of groundwater in the vicinity of Buildings 1 and 2.

Investigative work addressing Area C under the Focused RI was completed in 1994 and the
results of this work summarized in an RI Report for OU-3 dated August 1994, where OU-3 was
defined as contaminated groundwater attributable to Area C. In August 1994, the Navy also
released a Focused Feasibility Study (FFS) Report for OU-3. The Navy subseguently issued a
Proposed Plan addressing OU-3 on August 19, 1994, and jointly signed a ROD with EPA for

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OU-3 on March 10, 1995. The ROD for OU-3 selected a remedy which included pumping and
treatment of groundwater to restore contaminated groundwater attributable to Area C to a level
protective of human health and the environment.

While work under the Focused RI continued, the Phase III RI was initiated in early 1995 to
further investigate potential sources of contamination in Areas A, B and C, and to evaluate
potential impacts of contaminant sources on surface water and sediment. These investigations
have included soil gas and geophysical surveys, and sampling of wastes, soils, surface water and
sediment.

Based on a preliminary evaluation of the results of Phase III RI work, in June 1996, the Navy
initiated a removal action it Site 4. The response action at Site 4, a series of seven trenches used
for the disposal of miscellaneous waste, was excavation and removal of the subject waste. Work
was completed in December 1996. The former location of the subject trenches has now been
capped with soil and seeded.

In response to groundwater contamination in Area D, in July, 1996, the Navy initiated a remedial
investigation of the potential sources of this contamination. These investigations have included
soil gas surveys and soil sampling both within Area D and Buildings 1 and 2, and have addressed
sanitary and industrial sewer lines as well as numerous structures.

Based on the findings of the Focused RI work addressing groundwater, in October 1996, the
Navy issued Remedial Investigation and Focused Feasibility Study (FFS) reports for Area D
groundwater - OU-4. The FFS for OU-4 developed several interim remedial alternatives which
would minimize contaminant migration and initiate groundwater restoration while the
investigation of the Area D groundwater continues.

Again in response to findings of the Phase III RI work, in May 1997, the Navy initiated a
removal action at Site 6, a series of trenches and pits used for waste disposal purposes. This
response action, which includes waste excavation and removal, is in progress at this time.

III. HIGHLIGHTS OF COMMUNITY PARTICIPATION

Since 1988, the plans and results of ongoing CERCLA investigations and actions have been
presented to a Technical Review Committee (TRC) and/or Restoration Advisory Board
established for NAWC. The TRC and/or RAB has included representatives of Bucks County
Health Department, Warminster Township, Warminster Township Municipal Authority, Upper
Southampton Township, Upper Southampton Water and Sewer Authority, Northampton
Township, Northampton Municipal Authority and Ivyland Borough.

In accordance with Sections 113 and 117 of CERCLA, 42 U.S C. Sections 9613 and 9617, the
Navy, in conjunction with EPA, issued a Proposed Plan on June 5, 1997, presenting the
preferred interim remedy for OU-4. The Proposed Plan and RI and FFS reports for OU-4
became available for review at the time and are among documents which comprise the
CERCLA Administrative Record for NAWC. The Administrative Record is available for review
by the public at the following information repositories:

NAWC Public Affairs Office
Jacksonville Road
Warminster, Pennsylvania 18974

• Bucks County Library
150 South Pine Street
Doylestown, Pennsylvania 18901

An announcement of the public meeting, the comment period, and the availability of the
Administrative Record for the interim remedy for OU-4 was published in the Intelligencer,
Public-Spirit and Courier Times on June 4 and June 11, 1997. Additionally, the Proposed Plan
and the Notice of Availability were mailed to local municipal and government agencies and local
residents in the vicinity of the Site.

The public comment period for the Proposed Plan was from June 5 to July 3, 1997. A public
meeting was held at the Warminster Township Building, Henry and Gibson Avenues,
Warminster, Pennsylvania on June 16, 1997 to present the RI, FFS and Proposed Plan, answer
guestions, and accept both oral and written comments.

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A transcript of the meeting was maintained in accordance with Section 117(a)(2) of CERCLA,
42 U.S.C. °9617(a)(2). As a result, responses to many oral comments during the public meeting
are in the transcript of the meeting, which is now part of the Administrative Record. Responses
to written comments received during the public comment period are included in the
Responsiveness Summary section of this ROD.

This Record of Decision presents the selected interim remedial action for OU-4 at the Site
chosen in accordance with CERCLA and, to the extent practicable, the National Contingency
Plan (NCP).

All documents considered or relied upon in reaching the remedy selection decision contained in
this ROD are included in the Administrative Record for the Site and can be reviewed at the
information repositories.

IV. SCOPE AND ROLE OF THIS REMEDIAL ACTION

Section 300.430 (a)(1)(ii)(A) of the NCP, 40 C.F.R. Section 430(a)(1)(ii)(A) provides that
CERCLA NPL Sites "should generally be remediated in operable units when early actions are
necessary or appropriate to achieve significant risk reduction guickly, when phased analysis or
response is necessary or appropriate given the size or complexity of the Site, or to expedite the
completion of a total cleanup." In the case of NAWC, the Navy has organized work to date into
four operable units. These operable units (OUs) are as follows:

-OU-1: Contaminated groundwater attributable to Areas A and B
-OU-2: Contaminated off-base private wells
-OU-3: Contaminated groundwater attributable to Area C
-OU-4: Contaminated groundwater underlying Area D

The Navy and EPA selected an interim remedy for OU-1 in a ROD signed on September 29,
1993, while a removal action for OU-2 was selected by EPA in a Removal Action Memorandum
signed on July 14, 1993. The Navy and EPA selected a final remedy for OU-3 in a ROD signed
on March 10, 1995. The construction of the remedy for OU-1 was initiated by the Navy in
January 1995 and continues at this time. The EPA initiated construction of the removal action
for OU-2 in June 1994 and completed construction of this removal action in December 1994.
The operation of the remedy of OU-3 was initiated by the Navy in July 1996 and continues at
this time.

This ROD selects an interim remedial action for OU-4 - contaminated groundwater underlying
Area D at the Site, where Area D is the area of contaminated groundwater attributable to releases
adjacent to and/or under Buildings 1 and 2. This groundwater presents unacceptable risks to
human health. Sufficient information is available to select an interim remedy at this time.

The objective of the interim remedy in this case is to minimize the migration of the contaminated
groundwater, initiate aguifer restoration, and obtain information about the response of the aguifer
to remediation measures while additional RI work is performed to determine the full nature and
extent of contamination. In addition, to the extent possible at this time, a secondary objective is
to limit or eliminate unacceptable exposure to the contaminated groundwater while the remedy is
being implemented.

The final remedy for OU-4 will be selected after the full nature and extent of the problem are
identified and will consider the information generated during implementation of the interim
remedy. In the Preamble to the publication of the revised NCP, it is noted that operable units
"may include interim actions (e.g., pumping and treating of groundwater to retard plume
migration) that must be followed by subseguent actions which fully address the scope of the
problem (e.g., final groundwater operable unit that defines the remediation level and restoration
timeframe)." (55 Fed.Reg. at 8705 (March 8,1990)). Therefore, a final ROD for OU-4 will be
issued after the implementation of the interim action. The interim action will be consistent with
planned future actions to the extent possible.

Other media associated with the Site, including wastes, soils, sediment and surface water are
being further investigated under the RI/FS process. Additional remedial actions will be proposed
and selected as soon as adeguate information exists to support the selection of a remedy for a
particular medium or group of media. Any such medium (or group of media) will be designated

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as an Operable Unit by the Navy and EPA.

V. SUMMARY OF SITE CHARACTERISTICS AND EXTENT OF CONTAMINATION

Summarized below are the relevant findings of the RI work to date with regard to contaminated
groundwater underlying Area D at the Site.

A. SITE CHARACTERISTICS

1. Geology

The Site is located in the Piedmont Physiographic Province, Triassic Lowlands Section, of
southeastern Pennsylvania. The land forms have been modified by erosion to form moderate
slopes and gently rounded hills with a dendritic drainage pattern.

Surface soils in the vicinity of the Site are generally fine-textured, predominantly silty loams,
with moderate to low permeabilities. The soils are commonly underlain by saprolite (extensively
weathered bedrock) at an approximate depth of four to 10 feet. Available information indicates
saprolite on NAWC property varies from eight (8) and twenty-five (25) feet in thickness.

The bedrock underlying the saprolite belongs to the late Triassic age middle arkose member of
the Stockton Formation. These rocks consist of fine- to medium-grained arkosic sandstone
interbedded with red shale, siltstone and conglomerate. Units of varying lithology are irregularly
interbedded with coarse-grained units commonly overlying fine-grained units. Individual beds
commonly pinch out or form gradational contacts with overlying or underlying beds over lateral
distances greater than several hundred feet.

The beds of the Stockton Formation strike to the northeast and dip from seven to 16 degrees to
the northwest with an average dip of 12 degrees. The thickness of the middle arkose member of
the Stockton Formation is estimated to be approximately 500 feet near the southeastern property
boundary of NAWC, increasing to between 1,500 and 2,000 feet near the northwestern
boundary. The Stockton Formation is extensively faulted and is cut by a well-developed joint or
fracture system.

2. Hydrogeology

The Stockton Formation forms a multi-aguifer system of relatively discrete water-bearing zones
separated by thicker, less permeable zones. Transmissivity and groundwater movement within
water-bearing zones are greater parallel to bedding than across bedding. Vertical or nearly
vertical fractures cutting across bedding and the weathering of various beds are expected to
permit varying degrees of leakage between the main water-bearing zones, particularly near the
surface. Groundwater in the Stockton Formation occurs locally under both confined and
unconfined conditions.

Within water-bearing zones in the fine- and medium-grained sandstone of the Stockton
Formation, groundwater is transmitted through primary intergranular porosity, as well as along
fractures, joints, and bedding planes (secondary porosity). The shale and siltstone beds are
commonly too fine-grained to transmit large amounts of groundwater through primary porosity,
and fractures and joints are typically not well developed in these fine-grained beds.
Conseguently, the shale and siltstone beds often act as confining layers to groundwater. Fracture
permeability is generally better developed in the sandstone layers compared to the shale and
siltstone layers of the formation. This, along with greater primary permeability, allows the
sandstone layers to function as the most productive water-bearing units of the Stockton Formation.

Groundwater in Area D occurs primarily within the bedrock (Stockton Formation) underlying
the Site. Groundwater occurrence and movement through the Stockton Formation is primarily
through secondary porosity (fractures) that exists within the rock mass. These fractures include
both bedding plane partings and fractures that extend through individual rock units. In addition
to the secondary porosity, there is likely some minor primary porosity, especially in the
sandstone units, that contributes to groundwater occurrence and movement. In general, the
coarser-grained (sandstone) units were observed to yield water more so than the finer-grained
(siltstone and shale) units, although significant water-yielding fractures were encountered in all
rock types.

Minor guantities of groundwater are also encountered within the lower portions of the thin

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veneer of soils and weathered rock overlying competent bedrock. The observed saturated
thickness of the soils and weathered rock (i.e., overburden) within Area D ranged from
approximately 3 to 12 feet. Due to the overall clayey nature and resulting low permeability of
the overburden, groundwater movement through the overburden is likely to be restricted in
comparison to the migration through the underlying fractures in bedrock.

3. Hydrology

The Site is located in an upland area lying between two local drainage basins. The northern
portion of the Site (including Area D) drains toward the north through several swales and storm
sewers into a small unnamed tributary of Little Neshaminy Creek. The local drainage basin lies
within the regional drainage basin of the Delaware River. Various studies conducted on the Site
have revealed that no areas within the Site are included in the 100-year or 500-year floodplains.

Much of the natural drainage pattern has been altered by development and drainage within
developed areas of the NAWC property is controlled primarily through constructed drainage
systems. A significant portion of precipitation runoff from Area D is directed by surface grading
and paving to culverts and storm sewers. The tributary of Little Neshaminy originates at the
outfall points of a culvert on NAWC boundary.

4. Meteorology

The climate of the area is humid continental and is modified by the Atlantic Ocean.
Temperatures average 76 !F (24.4IC) in July and 32!F (OlC) in January. The average daily
temperature for the NAWC location is 53.3!F (11.8IC). Precipitation averages 42.5 inches per
year (106.25 cm per year), and snowfall averages 22 inches per year (55 cm per year). The
distribution of precipitation is fairly even throughout the year. The relative humidity for the Site
averages 70 percent. The mean wind speed for this area is 9.6 mph, with prevailing direction of
west-southwest.

5. Ecology

Open land, woodland, and wetland habitats are all found within or near NAWC. These include
mowed fields and lawns, nonfcrested overgrown land, wooded areas, forested wetlands,
scrub/shrub wetlands, and streams with associated riparian areas. While the majority of Area D
is paved, runoff from the area is directed to a tributary of Little Neshaminy Creek which runs
through wetlands and wooded areas.

There are no permanent threatened or endangered species on or near NAWC; however, some
transient species do traverse the area. No areas have been designated as wetlands on NAWC
property according to Army Corps of Engineers criteria.

6. Soils

NAWC is underlain by soils of the Lansdale-Lawrenceville Association. This unit consists of
nearly level to sloping, moderately well-drained soils and well-drained soils on uplands. The
soils are deep and have a medium-textured surface layer and a medium-textured or moderately
coarse-textured subsoil. They formed in material weathered from shale and sandstone and in
silty, windblown deposits. They consist primarily of silt loam, shaly silt loam, silty clay loam,
and some sandy loam. Some of the soils in this association have a seasonal high water table and
restricted permeability.

Large portions of NAWC, including Area D, are urban land areas where the original soils have
been graded, disturbed, filled over, paved over, or otherwise altered prior to construction of the
base facilities. Various types of fill material, including the contents of the known waste areas at
the Site, are included in the urban land areas. Much of Area D is covered by paved surfaces,
buildings, or other engineered structures.

7. Groundwater Use

Groundwater has been the only source of water for NAWC and is the primary source of water for
residences and commercial operations in the immediate vicinity of NAWC and Area D.
Groundwater has been withdrawn from within Area D by NAWC and been used for drinking
water, firefighting and miscellaneous purposes. Off-base, privately-owned wells have been used
for domestic and commercial purposes and have been located as close as 1000 feet from Area D.

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A public water supply well is presently located approximately 3000 feet from Area D. Figure 5
provides the location of municipal, residential and commercial wells known to be located within
3000 feet of Area D as well as the location of on-base supply wells located within and adjacent
to Area D.

B. NATURE AND EXTENT OF CONTAMINATION

The findings of the RI to date with respect to groundwater are provided in detail within the
Interim Remedial Investigation (RI) Report for OU-4. A summary of the major findings for
groundwater underlying Area D is presented below.

1. On-Base Supply Wells

Four on-base water supply wells are located either within or in the immediate vicinity of Area D.
Figures 5 and 6 indicate the locations of these wells. Wells SW-1 and SW-2 are 247 and 248
feet deep respectively, while Wells SW-3 and SW-4 are 570 and 591 feet deep, respectively.

Groundwater contamination underlying Area D was initially detected as part of testing of
NAWC supply water guality in October 1979. Testing from that date through August 1981
found levels of trichloroethylene (TCE) and, to a lesser extent, tetrachloroethylene (PCE) and
1,1,1-trichloroethane (1,1,1-TCA) in wells SW-1 and SW-2. TCE levels in well SW-2 were
detected at up to 293 micrograms per liter (ug/1), while maximum levels of PCE and 1,1,1-TCA
in this well were detected at up to 33 ug/1 and 67 ug/1, respectively. Based on the results of this
testing, wells SW-1 and SW-2 were permanently removed from service as a source of drinking water.

2. On-Base Monitoring Wells

Since the detection of contaminants in the subject on-base wells, numerous monitoring wells
have been installed and tested on NAWC property. The location of all of these wells is provided
in Figure 6.

In 1983, prior to the start of CERCLA RI work, monitoring wells MP-1, MP-2 and MP-3 were
installed to monitor groundwater from 18 to 132 feet in depth. Initial testing of these wells
found concentrations of trichloroethene (TCE) of up to 520 ug/1, as well as low concentrations of
tetrachloroethylene (PCE) and 1,1,1-trichloroethane (1,1,1-TCA).

The remainder of monitoring wells indicated on Figure 6 were installed and tested as part of RI
work. These wells monitor groundwater at depths from 24 to 300 feet.

During testing conducted as part of the RI in 1994 and 1995, the direction of groundwater flow
within the area of these wells was variable with depth, with flow in shallow bedrock (less than
100 feet in depth) generally in a northwest direction and flow in deeper bedrock trending more
toward the west.

Table 2 summarizes the analytical results for samples collected from the aforementioned supply
and monitoring wells in June 1994. Trichloroethylene (TCE) was the organic contaminant
detected at the most significant concentration and freguency. The highest level of TCE (170
ug/1) detected during this sampling event was in Well SW-2, which is located approximately 50
feet from the NAWC property boundary. During a subseguent sampling event in April 1996, the
highest level of TCE (320 ug/1) was detected in HN-32S. (The full results of this sampling event
will be issued at a future date.)

Samples were also collected in June 1994 to identify both total (unfiltered) and dissolved
(filtered) concentrations of inorganics (metals). Generally, this round of testing did not confirm
that inorganics concentrations were significantly above background. However, certain results
were inconclusive (e.g., HN-201) and additional testing will be necessary to identify the extent of
releases of inorganics, if any, to groundwater.

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                                        TABLE 2
               FREQUENCY/RANGE SUMMARY, POSITIVELY DETECTED ANALYTES
                                     JUNE 1994
                           NAWC WARMINSTER, PENNSYLVANIA
        Chemical

     1,1,1-TCA
     1,1-DCA
     1,1-DCE
     Chloromethane
     Acetone
     Benzene
     Carbon disulfide
     Carbon tetrachloride
     Chloroform
     1,2-Dichloroethene  (total)
     Ethylbenzene
     Tetrachloroethene
     Toluene
     Trichloroethene
     Xylenes  (total)
     Diethyl phthalate
     Dimethyl phthalate
     Fluoranthene
     Aluminum
     Antimony
     Arsenic
     Barium
     Beryllium
     Cadmium
     Calcium
     Chromium
     Copper
     Iron
     Lead
     Magnesium
     Manganese
     Mercury
     Nickel
     Potassium
     Sodium
     Vanadium
     Zinc
Metals sample results are for total metals unless otherwise noted.
F - Filtered Sample
AVG - Average Concentration between sample and duplicate.
Freguency of
Detection
1/23
2/23
1/23
2/23
2/23
1/23
1/23
1/23
3/23
1/23
1/23
4/23
5/23
18/23
1/23
6/16
3/16
1/16
16/44
4/44
9/44
37/44
4/44
1/44
44/44
7/44
14/44
16/44
8/44
42/44
39/44
10/44
4/44
42/44
44/44
2/44
20/44
Range (Ig/L)

4
3-4
4
4.5-8
12-14
3
1
1.5
1-6
4
2
2-3.5
2-12
2-170
8
1-11
1-4
2
29-106,000
28-65
4-25
68-4290
2-14
5
18,100-104,000
7-50
5-20
367-91,000
2-159
5.390-40,200
19-3,380
0.2-0.9
14-41
687-46, 600
8,870-221,000
8-17
5-461
Location of
Maximum (Ig/L)
HN-33S
SW-1
HN-33S
MP-l-AVG
HN-211
HN-331
HN-201
HN-31S
HN-42S
HN-33S
HN-331
HN-31S
HN-331
SW-2
HN-331
MP-1
MP-1
HN-201
HN-201
HN-32S-F
HN-201
HN-201
HN-201
MP-2
HN-031S-F-AVG
HN-31S-AVG
HN-201
MP-2
HN-201
HN-201
MP-2
MP-2-F
HN-201
HN-17D
HN-201
MP-2
HN-201

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3. Off-Base Monitoring and Private Wells

As noted earlier, RI work for Area D groundwater continues at this time. This work includes the
installation and testing of monitoring wells at off-base locations. Work conducted to date
indicates that a level of 88 ug/1 of TCE has been detected in a monitoring well installed at an off-
base location west of Buildings 1 and 2. (The full results of this ongoing work will be issued at a
future date.)

As indicated in Figure 5, a municipal water supply well is located approximately 3000 feet
northwest of Area D. Historic sampling of this water prior to treatment and distribution has
indicated the presence of TCE and other volatile organic compounds. Based on available
information, the extent of contaminant migration toward this supply well and/or other off-base
private wells identified in Figure 5 is unknown.

4. Vertical Extent of Contamination

Historical data from deep on-base wells indicate contamination at varying depths within the
aguifer. These data-include MP-2, with a depth of 101 feet, which has had a reported
concentration of 125 ug/1 TCE; MP-3, with a depth of 132 feet, has had a reported
concentration of 520 ug/1 TCE; SW-1, 247 feet, had 104 ug/1 TCE; and SW-2, 246 feet deep,
had 188 ug/1 TCE. Additional deep monitoring wells were installed in Area D during the
Interim RI and although only trace levels of chlorinated organics were found, it appears that
further studies are necessary to fully characterize deep groundwater downgradient of shallow
groundwater contaminant sources.

In addition, in 1985, PCE was reportedly detected at 13 ug/1 at 450 feet in supply well SW-3.
Further RI work is necessary to determine whether contamination is present at this time at this
location and depth and/or whether it is part of Area D groundwater.

VI. SUMMARY OF SITE RISKS

This section summarizes available assessments of risk posed by contaminated groundwater
attributable to the Site in overburden and shallow bedrock aguifers to human health and the
environment. These assessments are based on RI information generated to date.

A final assessment of risk presented by OU-4 will be included in the final Record of Decision
for OU-4 to be issued after the full nature and extent of the groundwater contamination are identified.

A. HUMAN HEALTH

As part of the RI work to date, a risk assessment was conducted with available data to
estimate the potential risks to human health posed by the contaminated groundwater
underlying Area D. Since there is no current, known exposure to this groundwater, only
potential exposure was evaluated.

The following exposure pathways were determined to present a potential risk to human health:

• Ingestion of the groundwater as a drinking water source.
• Dermal exposure to the groundwater (e.g., through handwashing, showering, and bathing).
• Inhalation of contaminants in groundwater (i.e., volatile compounds emitted during showering).

Potential human health risks were categorized as carcinogenic or noncarcinogenic. A
hypothetical carcinogenic risk increase from exposure should ideally fall within a range of
1 X 10-6 (an increase of one case of cancer for one million people exposed) to 1 X 10 -4 (one
additional case per 10,000 people exposed). Noncarcinogenic risks were estimated utilizing
Hazard Indices (HI), where an HI exceeding one is considered an unacceptable health risk.
Federal Maximum Contaminant Levels (MCLs) for public drinking water supplies were also
utilized to assess potential risks posed by exposure to groundwater.

Carcinogenic and noncarcinogenic risks posed by hypothetical exposure to contaminated
groundwater in overburden and shallow bedrock were estimated for adult residents, child
residents and adult employees. To assess these carcinogenic and noncarcinogenic risks,
potential contaminants of concern were selected based on their occurrence and distribution,
mobility, persistence and toxicity.

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An important component of the risk assessment process is the relationship between the intake
of a contaminant and the potential for adverse health effects resulting from that exposure.
Dose-response relationships provide a means by which potential human health impacts may be
quantified. The dose-response relationships for carcinogenic and noncarcinogenic effects are
reference doses (RfDs) and cancer slope factors (CSFs), respectively. The RfD is developed
by EPA for chronic and/or subchronic human exposure to hazardous chemicals and is usually
expressed as a dose per unit body weight per unit time (mg/kg/day). CSFs are applicable for
estimating the lifetime probability of developing cancer as a result of exposure to known or
potential carcinogens, are generally reported in units of I/(mg/kg/day), and are derived
through an assumed low-dosage linear relationship of extrapolation from high to low dose-
responses determined form animal studies. RfDs and CSFs used to calculate estimated risks
in this case are identified in the RI.

The Interim RI Report for OU-4 contains a detailed risk assessment for contaminated
groundwater underlying Area D. The assumptions utilized in conducting this assessment are
identified therein. These assumptions include exposure input parameters which estimate the
exposure of an individual to a contaminant over time. Exposure to representative contaminant
concentrations derived from data summarized in Table 2 was assumed.

In conducting this risk assessment, it is acknowledged that there are uncertainties associated
with the evaluation of chemical toxicity and potential exposures. For example, uncertainties
arise in the derivation of RfDs and CSFs and estimation of exposure point concentrations.

Cumulative, total estimated risks to human health due to potential exposure to
noncarcinogenic and carcinogenic groundwater contaminants for adult and child receptors
attributable to Area D at the Site in overburden and shallow bedrock are summarized in
Tables 3 and 4, respectively.

The total HI and carcinogenic risk for hypothetical exposure to this groundwater exceeds
values of one and 1 X 10 -4, respectively. Primary contributors to the unacceptable
noncarcinogenic risk are manganese, iron, aluminum, and trichloroethene (TCE). Primary
contributors to unacceptable carcinogenic risk are 1,1-dichloroethene, TCE, arsenic and beryllium.

Based on the sampling performed in 1994, trichloroethene, aluminum, barium, beryllium,
cadmium, iron, lead, and manganese have been detected at concentrations that exceed MCLs
in one or more wells within Area D.

B. ENVIRONMENT

While available RI data are inadequate to fully assess risk to the environment (e.g., risk to
aquatic life in surface water) posed by contaminated groundwater underlying Area D, this data
suggests that any such impacts are likely to be insignificant.

C. CONCLUSIONS

Contaminated groundwater underlying Area D at the Site has been determined to present an
unacceptable risk to human health and/or the environment. As indicated in Section V., off
base water supplies may be at risk.

Actual or threatened releases of hazardous substances from the Site, if not addressed by
implementing the interim remedial action selected in this ROD, may present an imminent and
substantial endangerment to public health or welfare, or the environment.

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                                   TABLE 3
                     SUMMARY OF RISKS - ADULT RECEPTORS
                        AREA D GROUNDWATER EXPOSURES
                       NAWC WARMINSTER, PENNSYLVANIA
 RECEPTOR
   RISK

Ingestion
Dermal Contact
Inhalation
Total Risk
                     RME RECEPTOR
ard Index

12.7
0.44
0.037
13.2
Incremental
Cancer Risk
6.1 x 10 -5
8.1 x 10 -6
5.9 x 10 -6
7.5 x 10 -5
Hazard Index

6
0.29
0.025
6.3
CT RECEPTOR
            Incremental
            Cancer Risk
            1.07 x 10 -5
            2.0 x 10 -6
            1.5 x 10 -6
            1.4 X 10 -5
RME - Reasonable maximum exposure
CT - Central tendency
(Tables 3 and 4 risks exclude HN-201 inorganics)

                                   TABLE 4
                     SUMMARY OF RISKS - CHILD RECEPTORS
                        AREA D GROUNDWATER EXPOSURES
                       NAWC WARMINSTER, PENNSYLVANIA
 RECEPTOR
   RISK

Ingestion
Dermal Contact
Inhalation
Total Risk
                     RME RECEPTOR
                                                        CT RECEPTOR
ard Index

29.7
0.74
0.098
30.5
Incremental
Cancer Risk
3.6 x 10 -5
3.5 x 10 -6
3.9 x 10 -6
4.3 x 10 -5
Hazard Index

13.9
0.49
0.065
14.4
Incremental
Cancer Risk
1.7 x 10 -5
2.3 x 10 -6
2.6 x 10 -6
2.2 x 10 -5
RME - Reasonable maximum exposure
CT - Central tendency
(Tables 3 and 4 risks exclude HN-201 inorganics)

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VII. DESCRIPTION OF ALTERNATIVES

An FFS was conducted by the Navy to identify and evaluate remedial alternatives for
contaminated groundwater underlying Area D. Applicable engineering technologies for
achieving the interim remedy objective of minimizing contaminant migration were initially
screened in the FFS based on effectiveness, implementability, and cost. The alternatives
meeting these criteria were then evaluated and compared to nine criteria reguired by
CERCLA. Three interim remedy alternatives were developed for OU-4. Costs and
implementation times were estimated for each alternative described in this section.

Costs and implementation times were estimated for each alternative described in this section.
Costs shown represent a range from the estimated cost to 20% above the estimate within
which the project is expected to be completed, including present unknowns

Alternative 1: No Action with Groundwater Monitoring

The NCP reguires that a "no action' alternative be considered to provide a base-line for
comparison with action alternatives.

Under this alternative, no remedial action would be undertaken at this time to address
contaminated groundwater underlying Area D. Instead, additional studies necessary to fully
identify the nature and extent of groundwater contamination would be continued as part of RI
work at NAWC. In addition to these studies, monitoring of the groundwater would be
initiated and conducted for an estimated thirty years.

Because this alternative would result in contaminated groundwater remaining at the facility,
five year reviews would be reguired to monitor the effectiveness of this alternative. The
present worth of this alternative is estimated to be $ 0 over a 30-year period with a capital
cost of $0 and an operation and maintenance cost of $ 150,000 annually.

Alternative 2: Groundwater Extraction, Treatment at the Existing Treatment System,
and Discharge to Area A System Outfall

Under this alternative, contaminated groundwater underlying Area D would be extracted using
a series of extraction wells. The extraction well network would be located as necessary to
maximize the effectiveness of the system. The extracted groundwater would be pumped to an
existing, on-site groundwater treatment system which has been constructed specifically to treat
groundwater. The existing plant would be modified and/or expanded as needed to treat
groundwater being pumped from Area D. Water treatment would include air stripping to
remove VOCs and carbon adsorption to remove semivolatile organics (or other means, if
necessary). Emissions from the air stripper would be treated by vapor phase carbon
adsorption as reguired by PA Code Chapter 127 and the National Ambient Air Quality
Standards for Hazardous Air Pollutants (NAAQS) and National Emissions Standards for
Hazardous Air Pollutants (NESHAPS) under the Federal Clean Air Act. Metals in the water
would be treated by precipitation and filtration (or other means, if necessary). Organic and
inorganic treatment residuals would be disposed offsite as reguired by treatment, storage and
disposal regulations under the Federal Resource Conservation and Recovery Act (RCRA),
including Land Disposal Restrictions (LDRs) under 40 C.F.R. Parts 262 and 268,
Pennsylvania Hazardous Waste Management (25 PA Code, Article VII) and Residual Waste
Regulation (25 PA Code, Article IX). Upon meeting effluent limits consistent with National
Pollution Discharge Elimination System (NPDES) reguirements under the Federal Clean
Water Act and Pennsylvania Clean Streams Law, the treated water would be discharged to an
unnamed tributary of Little Neshaminy Creek via an established outfall for the existing treatment system.

Concurrent with the design, construction, and operation of the initial extraction well network
and treatment system, investigations would be conducted both on and off NAWC property as
necessary to fully identify the extent of groundwater contamination underlying Area D. If
additional contamination is identified, the extraction well network and treatment system would
be modified as necessary during the interim action for OU4 to minimize migration of
contaminants and to maximize the effectiveness of the extraction well network.

This alternative would also incorporate the sampling of existing on-site and off-site wells.
Monitoring of groundwater in overburden and shallow bedrock aguifers would be conducted
for an estimated 30 years.

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To estimate the cost of this alternative, the following assumptions were made: a total of 25
extraction wells would be installed; a total flow of 56 gallons per minute (gpm) would be
pumped to the existing treatment plant; and on-site and off-site wells would be constructed
and monitored on a guarterly basis for an estimated 30 years. (Additional costs would be
incurred if additional groundwater was extracted and treated.) Based on these assumptions,
the present worth of this alternative was estimated at $1,528,000 to $1,840,000, with a capital
cost of $675,000 to $810,000 and an operation and maintenance cost ranging from $50,000 to
$60,000 annually. This alternative could be constructed in 12 months or less.

Alternative 3: Groundwater Extraction, Treatment at the Existing Treatment System,
Discharge to Area A System Outfall, and Institutional Controls

Alternative 3 would include all of the elements of Alternative 2.

Alternative 3 would also include institutional control measures to prevent exposure to
contaminated groundwater underlying Area D. The institutional control measures would
consist of groundwater use restrictions for property determined to be affected by the
contamination of concern. These restrictions would prevent the use of untreated,
contaminated water underlying Area D where such water presents an unacceptable health risk.
The restrictions would be applied to property which is presently owned by NAWC, as well as
off-base property, to the extent possible at this time.

The present worth of Alternative 3 has been estimated to range from $2,100,000 to
$2,500,000 with a capital cost ranging from $675,000 to $810,000, and an operation and
maintenance cost ranging from $82,000 to $100,000 annually. This alternative could be
constructed in 12 months or less.

VIII. COMPARATIVE ANALYSIS OF ALTERNATIVES

To help select a remedial action, CERCLA reguires that remedial alternatives be evaluated
under the nine criteria discussed below.

A. OVERALL PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT

Alternatives 2 and 3 would both limit the migration of contaminated groundwater attributable
to Area D and provide valuable aguifer characterization. Alternative 3 would be further
protective of human health and the environment by implementing institutional controls
designed to minimize exposure to contaminated groundwater attributable to Area D. Under
Alternative 1, the selection of a remedy addressing the contaminated groundwater would not
be initiated until the completion of the studies necessary to fully identify the nature and
extent of contaminated groundwater attributable to Area D.

B. COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS (ARARs)

Under Alternatives 2 and 3, all applicable or relevant and appropriate reguirements (ARARs),
including those for discharge of treated water and air emissions, would be met. (Specific
ARARs for the interim remedy in this case are identified in Section X.B. of this ROD.)

Since no remedial action would be taken under Alternative 1, there would be no action-
specific ARARs. Chemical-specific and location-specific ARARs would not be met.

C. LONG-TERM EFFECTIVENESS AND PERMANENCE

By initiating an interim action at this time, Alternatives 2 and 3 may reduce the time
necessary to restore affected groundwater relative to Alternative 1. Alternative 3 would have
the added long-term benefit of institutional measures to prevent exposure to the contaminated
groundwater. Alternatives 1, 2 and 3 all include long-term groundwater monitoring.
Operation and maintenance of the treatment plant and monitoring of treated discharges would
be reguired under Alternatives 2 and 3.

D. REDUCTION OF TOXICITY MOBILITY, OR VOLUME BY TREATMENT

Alternatives 2 and 3 would reduce the toxicity, mobility, and volume of groundwater
contaminants by treatment. The treatment systems for these alternatives would generate
residuals that would reguire further treatment or disposal.

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Alternative 1 would not use treatment to reduce the toxicity, mobility, or volume of
groundwater contaminants.

E.  SHORT-TERM EFFECTIVENESS

There would be no additional risks to the public or the environment under Alternatives
2 and 3. In the case of these alternatives, workers would be required to wear protective
equipment durinq activities where they may be exposed to hazardous materials.

Under Alternative 1, qroundwater contaminants would continue to miqrate and present a
potential unacceptable risk to human health.

F.  IMPLEMENTABILITY

For Alternatives 2 and 3, the remedial technoloqies and process options for qroundwater
extraction and treatment are all demonstrated and commercially available.

Under Alternative 3, planninq and coordination with the Commonwealth of Pennsylvania,
local municipalities and/or municipal authorities would be required to insure the successful
implementation of the institutional measures for preventinq exposure to contaminated qroundwater.

No remedial action is included under Alternative 1.

G.  COST

The present worth of Alternative 1 is $0. The present worth of Alternative 2 ranqes from
$1,528,000 to $1,840,000. The present worth of Alternative 3 ranqes from $2,100,000 to $2,500,000.

H.  STATE ACCEPTANCE

The Commonwealth of Pennsylvania neither concurs nor non-concurs with the remedy
selected below at this time. A concurrence/non-concurrence letter from the Commonwealth
will be added to the Site Administrative Record upon receipt.

I.  COMMUNITY ACCEPTANCE

A public meetinq on the Proposed Plan was held on June 16, 1997 in Warminster,
Pennsylvania. Comments received orally at the public meetinq and in writinq durinq the
public comment period are referenced in the Responsiveness Summary  (Section XII of this ROD).

IX. SELECTED REMEDY

The Navy and the EPA have selected Alternative 3: Groundwater Extraction, Treatment at the
Existinq Treatment System, Discharqe to Surface Water at Area A System Outfall and
Institutional Controls as the interim remedy for remediation of contaminated qroundwater
underlyinq Area D at NAWC. This alternative includes the desiqn and implementation of an
interim remedial action to protect human health and the environment. More specifically, this
alternative meets the objectives of minimizinq the miqration of contaminated qroundwater,
initiatinq aquifer restoration, and obtaininq information about the response of the aquifer to
remediation measures while additional RI work is performed to determine the full nature and
extent of contamination. In addition, this alternative meets the secondary objective of limitinq
or eliminatinq unacceptable exposure to the contaminated qroundwater while the remedy is
beinq implemented. The final remedy for OU-4 will be selected after the full nature and
extent of the contamination are identified and will utilize information qenerated durinq the
implementation of the interim remedy. The final remedial action may incorporate elements of
the interim remedial action.

The selected interim remedy is believed to provide the best balance of trade-offs amonq the
alternatives with respect to the response criteria. Based on available information, the Navy
and EPA believe the selected interim remedy would be cost effective and would comply with
applicable or relevant and appropriate requirements. Althouqh this interim action is not
intended to fully address the statutory mandate for permanence and treatment to the maximum
extent practicable, this interim action utilizes treatment to reduce volume and toxicity and thus
is in furtherance of that statutory mandate.

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The selected interim remedy for OU-4 includes the following major components:

(1)  Determination of the contribution of on-base, open water supply wells on the vertical
     distribution of contamination in groundwater

(2)  Reconstruction or abandonment of the subject wells, as necessary, to limit further
     contaminant migration

(3)  Installation, operation and maintenance of groundwater extraction wells

(4)  Pumping of contaminated groundwater and conveyance through piping to an existing on-
     base groundwater treatment system

(5)  Installation (if necessary) and monitoring of observation wells to ensure effectiveness of
     the groundwater extraction wells

(6)  Periodic evaluation of hydrogeologic data and the effectiveness of the groundwater extraction system

(7)  Modification of the groundwater extraction well system as necessary based on periodic evaluations

(8)  Operation and maintenance of existing onsite groundwater treatment system and
     expansion of this system if necessary to treat extracted groundwater from Area D

(9)  Monitoring of treated water to ensure the effectiveness of the treatment system

(10) Discharge of treated water to an unnamed tributary of Little Neshaminy Creek

(11) Installation, operation and maintenance of vapor phase carbon adsorption units as necessary to
     control air emissions from treatment system to satisfy applicable or relevant and appropriate
     reguirements

(12) Offsite treatment and/or disposal of solid residuals generated
     during water treatment

(13) Monitoring of groundwater in off-base monitoring wells

(14) Institutional controls to prevent the use of groundwater which presents an unacceptable health risk

(15) A review of the remedy on a five-year basis

The FFS estimated the present worth of this remedy at $2,100,000 to $2,500,000, with a
capital cost of $675,000 to $800,000 and an annual O&M cost of $82,000 to $100,000.

B.  PERFORMANCE STANDARDS

Performance standards for the subject interim remedy components are identified below. This
section identifies or discusses ARARs in certain cases. However, all ARARs are not
necessarily identified or discussed in this section. For a comprehensive identification of
ARARs, see Section X.B. of this ROD.

Components 1 through 4

Migration of the contaminated groundwater will be minimized by pumping groundwater to
achieve and maintain an inward and upward hydraulic gradient about the extraction wells.

Components 5 through 7

Hydraulic gradients shall be confirmed and the response of the aguifer and the contaminant
plume to the extraction well operation characterized. A Performance Monitoring Plan shall be
developed, approved by EPA by the EPA in consultation with PADEP, and implemented to
achieve these goals. The information generated by work performed under the Performance
Monitoring Plan will be evaluated in conjunction with additional hydrogeologic and contaminant
distribution data generated during ongoing RI work. Based on these evaluations, the extraction
well system will be modified as necessary during the interim action to optimize aguifer
restoration and minimize groundwater contaminant migration.

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Components 8 through 10

All extracted groundwater will be treated and will meet effluent limits developed in accordance
with National Pollution Discharge Elimination System (NPDES) reguirements under the Federal
Clean Water Act, NPDES reguirements under the Pennsylvania Clean Streams Law (25 PA
Code, Chapter 92) and Pennsylvania Wastewater Treatment Reguirements (25 PA Code, Chapter 95).

Component 11

All volatile organic compound emissions from the air stripper will be treated by vapor-phase
carbon adsorption to meet the standards established by 25 PA Code, Chapter 127, Subchapter A,
as well as the National Emissions Standards for Hazardous Air Pollutants (NESHAPs) and the
National Ambient Air Quality Standards for Criteria Pollutants (NAAQS) under the Federal
Clean Air Act. EPA Directive 9355.0-28, which covers emissions from air strippers at CERCLA
sites, is a standard to be considered.

Component 12

Spent carbon from the carbon adsorption unit, spent carbon from the vapor-phase carbon
adsorption unit and sludge generated during the treatment of metals will be handled in
accordance with treatment, storage and disposal reguirements under RCRA, including RCRA
Land Disposal Restrictions in 40 C.F.R. Parts 262 and 268, Pennsylvania Hazardous Waste
Management Regulations (25 PA Code, Article VII) and Residual Waste Regulations (25 PA Code, Article IX)

Component 13

To ensure that off-base groundwater does not present a threat to human health and the
environment, a Groundwater Monitoring Plan will be developed and implemented. The Plan
will be approved by EPA in consultation with PADEP and be revised on a periodic basis as
necessary. The Plan will include monitoring of wells installed by the Navy and off-base wells
used as a source of water supply. Additional monitoring wells shall be installed on off-base
property as necessary. Monitoring will be conducted through the selection and implementation
of the final remedy for OU-4 and for a projected thirty years.

Component 14

Existing supply wells within Area D shall not be used and no additional supply wells shall be
installed within Area D. Institutional controls shall be implemented to prevent supply well use
and installation. These institutional controls can be divided into two categories - those that
address portions of Area D on current Navy property and those on current private property.

The institutional controls addressing Navy property will consist of restrictions on the use of
water from existing wells and restrictions on the future installation of wells and/or the use of
water from wells installed in the future. These restrictions will be included in leases for affected
property and deeds entered into for the transfer of such property. The need for such restrictions
shall initially be identified in Findings of Suitability to Lease and Findings of Suitability to
Transfer, respectively, issued by the Navy.

Under this interim remedy, the institutional controls for affected private property will consist of
the continued enforcement by the Township of Warminster of its Ordinance No. 32, which
regulates well drilling in Warminster Township in order to promote the health of township residents.

Institutional controls must remain in place so long as a threat to human health and the
environment is posed by the contaminated groundwater.

Component 15

The performance of the remediation with regard to the performance standards and the goals of
protecting human health and the environment shall be reviewed every five years. A Five-Year
Review Work Plan will be developed and approved by EPA in consultation with PADEP.

X. STATUTORY DETERMINATIONS

A. PROTECTION OF HUMAN HEALTH AND THE ENVIRONMENT

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This interim action is protective of human health or the environment by minimizing the
migration of and initiating restoration of groundwater contamination underlying Area D. This
interim action is also protective by limiting or eliminating unacceptable exposure to the
contaminated groundwater to the extent possible. The selected interim remedy will not pose
unacceptable short-term risks to human health and the environment during implementation.

B. COMPLIANCE WITH ARARS

The selected interim remedy will comply with all applicable or relevant and appropriate
reguirements specific to this interim action. These ARARs include those identified in Section
IX and those listed below:

1. Location-Specific ARARs

The substantive reguirements of the Delaware River Basin Commission (18 C.F.R. Part 430) are
applicable. These regulations establish reguirements for the extraction and discharge of
groundwater within the Delaware River Basin.

2. Action-Specific ARARs

Federal Clean Air Act reguirements, 42 U.S.C. °°7401 et. seq., are applicable and must be met
for the discharge of contaminants to the air. Pennsylvania's Air Pollution Control Act is also
applicable, as are Pennsylvania's Air Pollution Control Regulations (25 PA Code, Chapters 121-142).

The reguirements of Subpart AA (Air Emission Standards for Process Vents) of the Federal
Resource Conservation and Recovery Act ("RCRA") regulations set forth at 40 C.F.R. Part 264
are relevant and appropriate and, (depending upon the levels of organics in the extracted
groundwater and treatment residuals) may be applicable to the air stripping operations conducted
as part of the selected interim remedy. These regulations require that total organic emissions
from the air stripping process vents must be less than 1.4 kg/hr (3 Ib/hr) and 2800 kg/yr (3.1 tons/yr)

25 PA Code, Section 123.31 is applicable to the selected remedial alternative and prohibits
malodors detectable beyond the NAWC property line.

25 PA Code, Section 127.12(a)(5) will apply to new point source air emissions that result from
implementation of the selected interim remedy. These Commonwealth of Pennsylvania
regulations reguire that emissions be reduced to the minimum obtainable levels through the use
of best available technology ("BAT") as defined in 25 PA Code, Section 121.1.

The substantive reguirements of 25 PA Code, Section 127.11 will apply to the selected interim
remedy. These Commonwealth of Pennsylvania regulations reguire a plan for approval for most
air stripping and soil venting/decontamination projects designed to remove volatile contaminants
from soil, water, and other materials.

Regulations concerning well drilling as set forth in 25 PA Code, Chapter 107 are applicable.
These regulations are established pursuant to the Water Well Drillers License Act, 32 P.S. °°
645.1 et seg. Only substantive reguirements of these regulations need be followed for onsite actions.

The groundwater collection and treatment operations may constitute treatment of hazardous
waste (i.e., if the contaminated groundwater exhibits characteristics of hazardous waste), and
may result in the generation of hazardous wastes derived from the treatment of the contaminated
groundwater (i.e., spent carbon filters from carbon adsorption treatment of water and from
vapor-phase carbon adsorption treatment of air emissions from air stripping operations). The
interim remedy will be implemented in a manner consistent with the reguirements of 25 PA
Code, Chapter 262, Subparts A (relating to hazardous waste determination and identification
numbers), B (relating to manifesting reguirements for off-site shipments of spent carbon or other
hazardous wastes), and C (relating to pretransport reguirements); 25 PA Code, Chapter 263
(relating to transporters of hazardous wastes); and with respect to the operations at the Site
generally, with the substantive reguirements of 25 PA Code, Chapter 264, Subparts B-D, I (in
the event that hazardous waste generated as part of the interim remedy is managed in containers)
and 25 PA Code, Chapter 264, Subpart J (in the event that hazardous waste is managed, treated
or stored in tanks). The interim remedy will be also be implemented in a manner consistent with
40 C.F.R. Part 264, Subpart AA (relating to air emissions from process vents), 40 C.F.R. Part
268, Subpart C, Section 268.30 and Subpart E (regarding prohibitions on land disposal and
prohibitions on storage of hazardous waste) and 40 C.F.R. Part 264, Subpart AA (relating to air

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emission standards for process vents).

25 PA Code, Chapter 264, Subchapter F, regarding groundwater monitoring is applicable to the
selected interim remedy.

Any surface water discharge of treated effluent will comply with the substantive reguirements of
the Section 402 of the Clean Water Act, 33 U.S.C. ° 1342, and the National Pollutant Discharge
Elimination System ("NPDES") discharge regulations set forth at 40 C.F.R. Parts 122-124, the
Pennsylvania NPDES regulations (25 PA Code, Section 92.31), and the Pennsylvania Water
Quality Standards (25 PA Code, Sections 93.1-93.9).

25 PA Code, Sections 261.24 and 273.421 are applicable regulations for the handling of residual
and other waste and for the determination of hazardous waste by the Toxic Characteristic
Leaching Procedure ("TCLP").

3. Standards To Be Considered

Pennsylvania's Ground Water Quality Protection Strategy, dated February 1992.

EPA Directive 9355.0-28, which covers emissions from air strippers at Superfund groundwater
remediation sites.

Pennsylvania Bureau of Air Quality Memorandum, "Air Quality Permitting Criteria for
Remediation Projects Involving Air Strippers and Soil Decontamination Units".

EPA's Ground Water Protection Strategy, dated July 1991.

EPA OSWER Directive 9834.11 which prohibits the disposal of Superfund Site waste at a
facility not in compliance with °3004 and °3005 of RCRA and all applicable State reguirements.

C. COST-EFFECTIVENESS

The selected remedy is cost-effective in providing overall protection in proportion to cost.

D. UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE
TREATMENT TECHNOLOGIES OR RESOURCE RECOVERY
TECHNOLOGIES TO THE MAXIMUM EXTENT PRACTICABLE

Although this action is not intended to fully address the statutory mandate for permanence and
treatment to the maximum extent practicable, this interim action utilizes treatment and thus is in
furtherance of that statutory mandate.

E. PREFERENCE FOR TREATMENT AS A PRINCIPAL ELEMENT

Because this action does not constitute the final remedy for Operable Unit Four, the statutory
preference for remedies that employ treatment that reduces toxicity, mobility, or volume as a
principal element, although partially addressed by this remedy, will be addressed by the final
response action.

XI. DOCUMENTATION OF SIGNIFICANT CHANGES

None. The preferred alternative presented in the Proposed Plan was Alternative 3: Groundwater
Extraction, Treatment at the Existing Treatment System, Discharge to Area A System Outfall,
and Institutional Controls is the selected remedy based on public comments. The selected
interim remedy for OU-4 is as described in the FFS and the Proposed Plan. Should additional RI
work determine a remedial action is necessary to address groundwater in overburden and
shallow bedrock attributable to another area at the Site, a Proposed Plan for that action shall be
released to the public for comment prior to selecting a remedy.

XII. RESPONSIVENESS SUMMARY

A. OVERVIEW

In a Proposed Plan released for public comment on June 5, 1997, the Navy, with the support of
EPA, identified Alternative 3 as the preferred interim remedial alternative for OU-4 at the Site.

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Alternative 3 in the Proposed Plan was as described in Section VIII. of this ROD.

The majority of written and oral comments received during the public comment period were in
support of Alternative 3 as described in the Proposed Plan and Section VIII. of this ROD. Based
on these and other comments received during the public comment period, the Navy and EPA
have selected Alternative 3 as the interim remedy for OU4.  Other comments and the associated
responses of the Navy and EPA are described below after a brief discussion of community
involvement to date.

B. COMMUNITY INVOLVEMENT TO DATE

In July 1989, NAWC Warminster prepared a draft Community Relations Plan for RI/FS
activities. Community relations activities to date have been conducted in accordance with this
plan. These activities have included regular Technical Review Committee meetings with local
officials, communications with the media and the establishment of information repositories.

The Navy and EPA established a public comment period from June 5, 1997 to July 3, 1997 for
interested parties to comment on the Proposed Plan, the RI  Report, the FFS Report and other
documents pertaining to OU4.  These and all other documents  considered or relied upon during
the interim remedy selection process for OU-4 are included in the Administrative Record, which
has been in two information repositories accessible to the  public since the beginning of the
public comment period for OU4. A public meeting was held at the Warminster Township
Building, Henry and Gibson Avenues, Warminster, Pennsylvania on June 16, 1997 to present the
RI/FFS Reports and Proposed Plan, answer guestions, and accept both oral and written
comments for the OU-4 interim remedy. Approximately 15 people attended this meeting.

This Responsiveness Summary,  reguired by CERCLA, provides a summary of citizens'
comments identified and received during the public comment  period and the responses of the
Navy and EPA to those comments. All comments received by the Navy and EPA during the
public comment period were considered by the Navy and EPA in selecting the interim remedy
for OU-4. Responses to these comments are included in the section below.

C.  SUMMARY OF COMMENTS RECEIVED DURING PUBLIC COMMENT PERIOD AND COMMENT RESPONSES

Comment #1:

Additional details should be provided on the institutional  controls which are part of the preferred
alternative.

Response #1:

A detailed descriptiin of the institutional controls which are a part of the selected remedy
appears on page 34 (see Component 14) of this ROD.

Comment #2:

The institutional controls should be considered temporary in nature and readily adapt to
changing circumstances.

Response #2:

See page 34  (Component 14) for a detailed description of institutional controls which are part of
the selected remedy.

Comment #3:

The projected time frame for implementation of the final remedy should be provided.

Response #3:

The final remedy for OU4 will be selected and implemented after the full nature and extent of
contamination attributable to Area D is identified and specific restoration standards for the
affected groundwater can be established. The time frame in this case is dependent on the
findings of ongoing and future Remedial Investigation work  addressing OU-4 and information
about the response of the aguifer to remediation measures.  As a result, the timeframe cannot be

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accurately projected at this time. However, because a final remedy for Area D groundwater on
NAWC property should be operating properly and successfully before this property is
transferred, every effort shall be made to select and implement the final remedy in this case as
soon as possible.

Comment #4:

What is depth of groundwater contamination in Area D?

Response #4:

See Section V.B.4 of this ROD for a detailed discussion regarding the depth of groundwater
contamination in Area D.

Comment #5:

The selected alternative should address containment of all contaminated groundwater in Area D:
shallow, intermediate and deep. The extraction wells should be designed to contain deep contamination.

Response #5:

The interim remedy will be designed to minimize migration of and initiate restoration of all
contaminated groundwater underlying Area D, including deep contamination. To facilitate this,
certain additional RI work and/or design work will need to be completed and the results
considered in the design of the initial extraction well network to be constructed and operated
under the selected interim remedy. In particular, this work will include additional investigations
on NAWC property to delineate the vertical distribution of contamination and to identify the
effects of open pumping wells and long open boreholes in Area D which may locally induce
contaminant movement in the aguifer.

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