PB97-963107
EPA/541/R-97/013
November 1997
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Croydon TCE,
Croydon, PA
12/31/1996
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EXPLANATION OF SIGNIFICANT DIFFERENCES
CROYDON TCE SUPERFUND SITE
OPERABLE UNIT 2
I. INTRODUCTION
Site Name: Croydon TCE Superfund Site
Site Location: Bristol Township, Bucks County, Pennsylvania
Lead Agency: U.S. Environmental Protection Agency,
Region III ("EPA" or "the Agency")
Support Agency: Pennsylvania Department of Environmental
Protection ("PADEP")
Statement of Purpose
The EPA has initiated remedial action activities at the
Croydon TCE Site ("the Site") under the authority of the
Comprehensive Environmental Response, Compensation and Liability
Act of 1980, as amended ("CERCLA"), 42 U.S.C. § 9601 et seq.,
commonly referred to as Superfund. The remedial action is being
performed in accordance with the Record of Decision ("ROD") for
operable unit 2 of the Site which was signed on June 29, 1990.
This ROD addresses the containment, treatment, and discharge of a
contaminated ground water plume. This Explanation of Significant
Differences ("BSD") is issued in accordance with Section 117 of
CERCLA, 42 U.S.C. § 9617, and the National Contingency Plan
("NCP") at 40 C.F.R. § 3'00.435(c) (2) (I) . The NCP requires the
publication of an BSD when the differences in a remedial action
significantly change, but do not fundamentally alter the remedy
selected in the ROD with respect to scope, performance, or cost.
In this case, the discovery of a separate and distinct smaller
contaminant plume resulted in significant changes to the remedy
but did not fundamentally alter the remedy with respect to scope,
performance, or cost. This BSD has been prepared to provide an
explanation of the nature of the change made to the selected
remedial action for contaminated ground water, and to demonstrate
that the revised remedy complies with the statutory requirements
of CERCLA § 121, 42 U.S.C. § 9621.
II. SUMMARY OF THE SITE HISTORY AND SELECTED REMEDY
The Croydon TCE Site is located in the southernmost portion
of Bristol Township, Bucks County, Pennsylvania, approximately 15
miles north of Philadelphia. Elevated levels of volatile
organics, primarily trichloroethene ("TCE") , are present in
ground water and surface water; however all of the sources have
not been determined. The site, approximately 3.5 square miles in
total area, is bordered by Interstate 95 to the north, the
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Delaware River to the south, Route 413 to the east, and Neshaminy
Creek to the west. The site is quite large because the source
and extent of ground water contamination was unknown, and
widespread ground water contamination was observed throughout
this portion of Bucks County. The Phase I Remedial Investigation
("RI"), conducted in 1988, assessed the entire site.
Within the site boundaries is a smaller area on which the
Phase I and II RIs were primarily focused. This area is referred
to as the "focused area of investigation" and encompasses the
area east of the Mary Devine Elementary School, west of Route
413, and north of River Road to just north of U.S. Route 13. The
focused area of investigation was studied extensively for the
following reasons:
• Ground water in this area was known to be contaminated with
volatile organic compounds, primarily elevated levels of
TCE.
• Previous studies in the local area provided data which
indicated that the source of the TCE-contaminated ground
water might be located within this area.
• Analysis of historical aerial photographs identified 11
potential source areas within the focused area of
investigation.
The focused area of investigation includes a portion of the
Croydon residential community and an area where several small to
large-scale manufacturing and commercial establishments are
located. Most of the commercial establishments are located along
State Road and U.S. Route 13; the large manufacturing facilities
are located between these two roads in the southeast portion of
the focused area of investigation.
The area outside of the focused area of investigation is
mainly residential communities, constructed from the 1940s to
1960s. These communities include Croydon, Croydon Heights,
Croydon Acres, Maple Shade, West Bristol, Belardly, and Rockdale.
The site is located in the Delaware River Basin. On a
regional and local basis, the Delaware River is the local
discharge point for both ground water and surface water.
Portions of the study area which are near to Neshaminy Creek and
the Delaware River are within the boundary of the 100-year
FLOODPLAIN. However, the focused area of investigation is not
within this boundary.
Hog Run Creek and its tributaries are located within the
site boundaries. The tributaries emanate in the area between
State Road and River Road and form Hog Run Creek just north of
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River Road. Hog Run Creek then flows southward and discharges
into the Delaware River.
An industrial landfill owned by Rohm & Haas is located south
of River Road. This landfill which was operated from 1952 to
1975, is being studied by Rohm & Haas under a Resource
Conservation and Recovery Act (RCRA) corrective action order.
Based on the findings contained within the Phase I RI, the
landfill has been ruled out as the source of the TCE
contamination in the Croydon community.
The ROD for operable unit 2 is part of the available
administrative record and describes in detail conditions and
contamination requiring remedial action. The site was identified
by EPA after several investigations of the Rohm & Haas Site in
Bristol Township. Since 1983, Rohm & Haas conducted studies and
prepared various reports concerning its Bristol Township
property, including the landfill. One report entitled, TCE in
Ground Water in the Vicinity of River Road, Bristol Township. PA
dated March 1986, concluded that the primary TCE plume of concern
in the ROD was emanating north of and not from the Rohm & Haas
property. EPA reviewed the report and eventually concurred with
this conclusion (ROD, pg. 6).
EPA was uncertain whether many of the businesses in the area
used products containing TCE, because of this EPA determined that
a separate Remedial Investigation/Feasibility Study ("RI/FS") was
necessary. Although numerous studies were conducted, including
both a Phase I RI and a Phase II RI, in order to locate the
source(s) of TCE ground water contamination, no source could be
positively confirmed. -In addition, EPA conducted a thorough
investigation to identify and locate possible Potential
Responsible Parties ("PRPs"), as well as gather any information
regarding the contamination at the Site.
Based on the Phase I RI, and as outlined in the ROD for
operable unit 1 dated December 1988, EPA provided public water to
residents affected. The objective of the selected remedy for the
operable unit 2 ROD was to contain further migration of the
primary TCE plume of concern while attempting to reduce ground
water contaminant levels.
The selected remedy for operable unit 2 included the
following major components:
• Construction and long-term operation of pumping/extraction
wells located in positions to adequately contain the
migration of the contaminant plume.
• Treatment of extracted ground water via air stripping,
followed by carbon adsorption as an ancillary treatment
step.
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Onsite discharge of the treated ground water to the East
Branch of Hog Run Creek.
Ground water sampling conducted outside of the TCE plume
area to monitor the possible advancement of ground water
contaminants. Wells sampled and analyzed for TCE,
tetrachloroethane, vinyl chloride, 1,1,1-trichloroethane,
1,1-dichloroethane, and 1,l-dichloroethene.
Ill DESCRIPTION OF SIGNIFICANT DIFFERENCES AND THE BASIS FOR
THOSE DIFFERENCES
EPA has determined that a change in the remedy, resulting in
a significant difference from the original remedy selected in the
ROD for operable unit 2, is warranted. The information gathered
during the remedial design process supports the need for a change
in the selected remedy.
This significant difference exists in the areal extent and
source area(s) of the "TCE plume" as identified in the ROD.
Extensive ground water sampling, during the remedial design,
revealed the presence of ammonium sulfate as well as other
contaminants in the portion of the "TCE plume" near the Rohm &
Haas facility (see attached figure). In March 1993, a thorough
review of this remedial design data and all other existing ground
water data was conducted by an EPA Hydrogeologist. This review
included the Phase I Rl Report dated August 1988, the Phase II RI
Report dated January 1990, remedial design ground water data, and
a collection of various ground water data gathered by Rohm & Haas
over several years. The resulting conclusion of this review was
that the "TCE plume" is actually two distinct and separate
contaminant plumes. The pre-ROD hydrogeologic investigations
alone did not uncover this fact. These two plumes, as shown on
the attached figure, are the main TCE plume or Plume A (located
west of Hog Run Creek) and a smaller secondary plume or Plume B
(located east of Hog Run Creek). As the figure demonstrates,
these two plumes flow in opposite directions and based on
information gathered to date, EPA has concluded that they result
from different sources.
Plume A is migrating eastward toward Hog Run Creek. This
plume is primarily discharging to the creek. The exact source
area for Plume A is unknown and may include many small source
areas from either facility spills or uncontrolled dumping.
Although hydrogeological ground water information indicates that
the source(s) of Plume A appear to have been located to the west
of Hog Run Creek, no sources were positively confirmed.
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The smaller Plume B is migrating from the Rohm & Haas
Manufacturing Area westward toward Hog Run Creek. The shallow
portion of this plume will also discharge to Hog Run Creek. The
source area for Plume B is located on the Rohm & Haas
Manufacturing Area east of Hog Run Creek. The determination of
this source area is based on known ground water flow directions.
EPA has determined that this smaller Plume B contains a
different contaminant mix, primarily ammonium sulfate, and
emanates from a separate source (the Rohm & Haas Manufacturing
Area) than the contamination of the primary Plume A. Therefore,
EPA has concluded that these are two separate and distinct plumes
that flow in opposite directions. EPA has determined that Plume
B should not be addressed as part of the remedial action for the
Croydon TCE Superfund Site. However, Plume B has been considered
and will be addressed under the jurisdiction of EPA's RCRA
Authority for which a case file already exists.
Because the main TCE plume, or Plume A, is a distinct and
separate contaminant plume, the original remedy selected for
operable unit 2 is revised only insofar as it will no longer be
applicable to the area east of Hog Run Creek (i.e. Plume B). In
all other significant respects the original remedy selected in
the ROD will be implemented at the main TCE plume, or Plume A.
Additionally, Plume B will be addressed under RCRA, which is
consistent with EPA's practice to coordinate between RCRA and
CERCLA Site activities (memorandum of Steven A. Herman, September
24, 1996). Accordingly, the change to the remedy is significant,
but not fundamental as to scope, performance or cost.
PUBLIC PARTICIPATION
The BSD and the information upon which it is based will be
included in the Administrative Record file and the information
repository for this Site. The Administrative Record is available
for public review at the locations listed below:
U.S. EPA Region III
841 Chestnut Building
Philadelphia, PA 19107
Hours: Monday - Friday, 9:00 a.m. - 4:30 p.m.
Contact: Anna Butch
(215) 566-2077
Margaret R. Grundy Memorial Library
680 Radcliffe Street
Bristol, Pennsylvania 19007
Contact: Mary Jane Mannherz
(215) 788-7891
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VII SUPPORT AGENCY COMMENTS
EPA has notified PADEP of the changes proposed in this BSD
in accordance with 40 C.F.R. § 300.4435(c)(2). By letter dated
December 20, 1996, PADEP informed EPA that it concurs with this
BSD.
VIII. AFFIRMATION OF THE STATUTORY DETERMINATIONS
EPA has determined that the revised remedy complies with the
statutory requirements of CERCLA § 121, 42. U.S.C. § 9621.
Considering the new information that has been developed and the
changes that have been made to the selected remedy, EPA and PADEP
believe that in spite of the significant difference between the
two remedies, the current selected remedy remains protective of
human health and the environment, and complies with Section
121(d) of CERCLA, 42 U.S.C. § 9621 (d) and EPA's off-Site Policy,
and is cost-effective. In addition, the revised remedy utilizes
permanent solutions and alternative treatment technologies to the
maximum extent practicable for this Site.
Date Thomas C~ VoltVggij^, Director
Hazardous Wa-steRanagement Division
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Croydon TCE Site Area Map
Bucks County, Pennsylvania
Deep Ground Water Contaminant Plumes
Ground Water Flow Direction
ROHM & HAAS
FACILITY
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