PB98-963135
EPA 541-R98-146
March 1999
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
North Penn - Area 1
Souderton, PA
10/29/1997
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EXPLANATION OF SIGNIFICANT DIFFERENCES
NORTH PENN AREA 1 SUPBRFUND SITE
I. INTRODUCTION
Site Name: North Penn Area 1 Superfund Site
Site Location: Souderton, Montgomery 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
A Record of Decision ("ROD") for the North Penn Area 1 was
signed on September 30, 1994. This ROD addresses primarily
contamination of soil, but also includes an interim action to
address ground water contamination. This Explanation of
Significant Differences ("BSD") is issued in accordance with
Section 117 of the Comprehensive Environmental Response,
Compensation and Liability Act, as amended,("CERCLA"), 42 U.S.C.
§ 9617(c), and 40 C.F.R. § 300.435(c)(2)(I). This BSD has been
prepared to provide the public with an explanation of the nature
of the change made to the selected interim 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. The selected remedy for contaminated soil
remains unchanged.
II. SUMMARY OF THE SITE HISTORY AND SELECTED REMEDY
The North Penn Area 1 Site is located in Souderton,
Montgomery County, Pennsylvania, and is one of 12 Sites
identified in the North Penn area on the basis of contamination
of ground water by volatile organic compounds ("VOCs") in
production wells. The contamination at the Area 1 Site was first
noted in 1979 in North Penn Water Authority (NPWA) well S-9. The
well was immediately taken out of service because
tetrachloroethylene levels in the range of 10-13 ppb were found
in the ground water. (Tetrachloroethylene is also known as
perchloroethene, which is abbreviated as PCE. The term PCE will
be used in this document when referring to this compound.) On
the basis of this contamination, the site was proposed for the
National Priorities List ("NPL") in January 1987, and was placed
on the NPL in March 1989.
After the contamination was identified, Potentially
Responsible Party (PRP) searches by EPA identified five
facilities in the area that may have contributed to the ground
water contamination. These facilities and the ground water
contamination were evaluated in the Remedial Investigation/
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Feasibility Study ("RI/FS") . The results of the sampling work
done during the RI/FS revealed contamination at three of the five
properties. On September 30, 1994, EPA issued a ROD which
included the remedial action for contaminated soil and an interim
action for contaminated ground water. The selected remedy for
the contaminated soil was excavation and offsite disposal of
contaminated soil at the three properties of concern (Granite
Knitting Mills ("GKM") , Gentle Cleaners, and Parkside
Apartments}. For the contaminated ground water, the interim
action selected was pumping and treating of the upper interval of
the GKM well and the entire well S-9. However, the ROD indicates
that one option that may be pursued is the direct discharge of
the extracted water to the sewage treatment plant since the
ground water had low levels of contamination.
As part of the remedial design, soil sampling was conducted
in November 1995 at the three properties of concern to determine
the volume of soil that would need to be removed. Levels of
contamination in soils at the Parkside Apartments property were
below the remediation goals established in the ROD. Therefore,
excavation of soils is not planned at this property, only at the
Granite Knitting Mills and the Gentle Cleaners property. It is
important to note that the Parkside Apartments is the most
downgradient of the three properties of concern and down gradient
from well S-9. Also, as part of the remedial design activities,
three new wells were installed and sampled (See attached map).
Well S-9 was also sampled at that time. One of the new wells was
located adjacent to the GKM property, the.second well was located
between the GKM property and well S-9, and the third well was
located downgradient from well S-9. Results from the four wells
which were sampled showed that the highest" level of contamination
was found in the well adjacent to the GKM property (NPA1-S1) with
32 ppb of PCE, 10 ppb of 1,2 Dichloroethene, and 5 ppb of 1,1,1-
Trichloroethane. The well between the GKM property and S-9, well
NPA1-S2, and well S-9 each had 6 ppb of PCE, and the well
downgradient of S-9 (NPA1-D3) had no detectable levels of
contamination.
Ill DESCRIPTION OF SIGNIFICANT DIFFERENCES AND TBE BASIS FOR
THOSE DIFFERENCES
EPA has determined that a change in the interim remedy
selected in the ROD is warranted. The selected remedy for
contaminated soil basically remains unchanged. Although soil at
the Parkside Apartments will not be excavated, this is not a
significant change since the levels of contamination found during
the remedial design field sampling are below the cleanup goals
established in the ROD. For the ground water interim remedy,
ground water will be discharged to a POTW instead of treating it
with an air stripper. Sampling results from the remedial design
activities revealed low levels of contamination which can be
handled by the POTW. This is not a significant change since the
ROD established that this was an option that will be considered
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in the remedial design. However, EPA has determined that
extraction of ground water from well S-9 is not necessary, but is
still required at the GKM well. This change is a significant
change as defined in 40 C.F.R. §300.435(c)(2)(I), the National
Oil and Hazardous Substances Pollution Contingency Plan ("NCP"),
therefore, preparation of this BSD is required. A ROD Amendment
is not required because the changes reflect revision in the
underlying applicable or relevant and appropriate requirements
("ARARs") . The overall goal of the remedy is the same, that is;
to eliminate the potential exposure risk from the contaminated
soil, to eliminate the source of contamination migrating to
ground water, and to prevent the spread of contaminated ground
water.
The ROD issued for the Site on September 30, 1994 selected,
as an interim action for the ground water, pumping and treating
of the upper interval at the GKM well and the entire S-9 well.
The ROD established that the extraction/treatment system shall be
operated until the ground water is cleaned up to background
levels. This requirement was based on the Pennsylvania
requirement that contaminated ground water be cleaned up to
background levels, i.e., those levels of each contaminant that
would be found in the area in the absence of a source of
contamination (the Site). According to the ROD, the background
concentration for each contaminant of concern for the Site shall
be established by EPA during the Remedial Design.
Subsequent to the issuance of the ROD, the Commonwealth of
Pennsylvania signed into law the Land Recycling and Remediation
Standards Act (ACT 2 of 1995). The Commonwealth of Pennsylvania,
Department of Environmental Protection has identified Act 2 as an
ARAR. EPA has determined that Act 2 does not, under the
circumstances at the Site, impose any requirements that are more
stringent than the federal standards. Based on this change in
Pennsylvania's remediation standards, EPA has determined that for
this Site, Maximum Contaminant Levels ("MCL") will be used
instead of the background levels. The MCLs (which are health
based levels) are the maximum permissible concentrations of a
chemical in drinking water as established in the Safe Drinking
Water Act. The MCL for TCE is 5 ppb. Also, EPA has determined
that pumping of well S-9 is not necessary since the levels of
contamination (PCE) detected in that well are expected to be
below the MCL.
During the RI/FS sampling activities the highest detection
for PCE in well S-9 was 5 ppb. Sampling conducted again during
the remedial design sampling activities showed 6 ppb. Although
the level during the remedial design sampling activities was 1
ppb higher than the level detected during the RI/FS activities,
the result from a single sample may not be statistically
significantly different than previous results. In fact,
contaminated soil from the two properties upgradient, which is
the source of ground water contamination, will be excavated and
disposed offsite. Therefore, the levels of PCE are not expected
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to increase in the future. Furthermore, one of the new wells
installed during the remedial design sampling activities which is
located 500 ft downgradient from well S-9, revealed no
contamination. EPA will monitor the levels of contamination in
well S-9 by conducting periodic sampling using the monitoring
program established in the ROD which requires sampling and
analysis of the downgradient monitoring wells (NPA1-S1, NPA1-S2,
and NPA1-D3), the GKM and S-9 wells. The monitoring program in
the ROD was designed based on achievement of background
concentrations. Since operation of the extraction system now
will be based on MCLs, the monitoring program will be based on
MCLs instead of background concentrations. According to the ROD,
the data collected as part of the long term monitoring program,
will be used to evaluate the effectiveness of the extraction
system. The data will be evaluated to determine whether or not
the interim ground water extraction system is sufficient to
remediate the contamination in the entire plume area. This
determination will be made as part of the final action for this
operable unit.
There will be no impacts in the remedial design if well S-9
is not included in the extraction and discharge system since the
connection for the GKM well is independent from the connection
for well S-9. Also, there will be some savings associated with
the equipment, installation, and operation and maintenance of the
extraction system at well S-9.
IV 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. - 4:00 p.m.
Indian Valley Public Library
100 East Church Avenue
Telford, PA 18969
215-723-9109
V. SUPPORT AGENCY COMMENTS
EPA has notified the PADEP of the changes proposed in this
BSD in accordance with 40 C.F.R. 300.435(c)(2). By letter dated
March 25, 1997 from Carol R. Collier, PADEP Southeast Office
Regional Director, to Mr. W. Michael McCabe, EPA Regional
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Administrator, PADEP*informed EPA that it concurs with this BSD.
VI. 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 believes
that the 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 Abraham Ferdas, Acting Director
Hazardous Waste Management Division
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