PB98-963114
EPA 541-R98-048
October 1998
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
North Penn
Area 1
Souderton, PA
9/24/1998
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EXPLANATION OF SIGNIFICANT DIFFERENCES
NORTH PENN AREA 1 SUPERFUND SITE
I. INTRODUCTION
Site Name: North Penn Area 1 Superftmd 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. That ROD addressed primarily contamination of soil, but also included an interim
remedial action to address ground water contamination. This Explanation of Significant
Differences ("ESD") 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 ESD has been prepared to provide the public
with an explanation of the nature of the change made with regard to the interim remedial action
for the 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. (TetrachJoroethylene 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
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Remedial Investigation/ Feasibility Study ("RI/FS"). The results of the sampling work done
during the RI/FS revealed soil contamination at three of the five properties. These three
properties are: Gentle Cleaners, Granite Knitting Mills (GKM) and Parkside Apartments. On
September 30, 1994, EPA issued a ROD which included the remedial action for contaminated
soil and an interim remedial action for contaminated ground water. An interim action for ground
water was selected because enough information about groundwater contamination was not
available at that time. The selected remedy was excavation of contaminated soils at each of the
three properties with PCE contamination and installation of an extraction system to extract water
from the upper interval (0-28 ft) of a well at the GKM property and the entire (0-270 ft) NPWA
well S-9 (See Figure 1 for property and well locations). The extracted water was to be combined
and treated in one treatment system. An option to treatment is the direct discharge of the
extracted water to a publicly owned sewage treatment plant.
A remedial design was approved by EPA on September 12, 1996. As part of the remedial
design, soil sampling was conducted 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 was not required at this property, only at the Granite Knitting Mills and the
Gentle Cleaners property. Also, as part of the remedial design activities, three new wells were
installed and sampled. Well S-9 was also sampled at that time. Since sampling results revealed
low levels of contamination, it was determined that extracted water would be discharged to a
publicly owned sewage treatment plant instead of treating it. :
On October 29, 1997 EPA issued an Explanation of Significant Differences (ESD) for the
site. The purpose of the ESD was to document EPA's decision not to pump well S-9. In
addition, although not a significant change, the ESD documented EPA's decision that excavation
at the Parkside Apartments was not necessary because soil contamination levels were below the
cleanup goals. The decision not to pump well S-9 was based on the low PCE levels detected in
this well during the RI/FS and the remedial design sampling activities, as well as, a change in the
Commonwealth of Pennsylvania's remediation standards. At the time the ROD was prepared,
the Commonwealth of Pennsylvania's remediation standards required that 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. 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 determined that
Maximum Contaminant levels (MCLs) will be used instead of the background levels. The MCLs
are the maximum permissible concentrations of a chemical in drinking water as established in the
Safe Drinking Water Act. Since contamination levels at well S-9 are expected to be below the
MCL, EPA determined that pumping of well S-9 was not necessary.
Construction of the remedial action, as outlined in the ROD, with the changes included in
the October 29, 1997 ESD, was completed on July 13, 1998. A total of 482 tons were excavated
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from the GKM and the Gentle Cleaners properties. Also, an extraction system was installed at
the GKM well which consisted of an extraction pump and conveyance piping, with direct
discharge to the sanitary sewer.
Ill DESCRIPTION OF SIGNIFICANT DIFFERENCES AND THE BASIS FOR THOSE
DIFFERENCES
EPA has determined that the interim remedy selected for OU2- groundwater should be
the final remedy for contaminated groundwater. 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 ESD is required. A ROD Amendment is not
required because 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.
When the ROD was prepared, the remedy for contaminated ground water was an interim
action because there was not enough information about the ground water contamination to make
a determination for a final remedial action. Also, since there was a documented PCE spill at the
Gentle Cleaners property in the early 1970s, there was a possibility that Dense Non-Aqueous
Phase Liquids (DNAPLs) were introduced to the subsurface. During the remedial design, three
new wells were installed: well NPA1-S1, NPA1-S2, and NPA1-D3 (See Figure 1). Sampling of
these wells during the remedial design revealed the highest concentration of contamination at the
NPA1-S1 well (32 ppb of PCE, 10 ppb of 1,2 - DichJoroethene, and 5 ppb of 1,1,1 -
Trichloroethane). Well NPA1-S2 showed only PCE at a concentration of 6 ppb. NPA1-D3 had
no detectable levels of contamination. These data shows that the levels of contamination in the
wells were low and that there was not evidence of the presence of DNAPLs. Based on these
results, the extraction system constructed should be sufficient to remediate the contaminated
ground water. In addition, as indicated above, MCLs instead of background levels will be used
as cleanup goals. MCLs are higher than background levels and therefore easier to achieve. Also,
the source of ground water contamination (contaminated soil) was removed and the levels of
contamination are not expected to increase.
EPA will monitor the levels of contamination by conducting periodic sampling using the
monitoring program established in the ROD. This monitoring program requires sampling and
analysis of the downgradient monitoring wells installed during the remedial design, and the
GKM and S-9 wells. Since hazardous substance will remain at the Site above health-based levels
(MCLs are health-based levels), pursuant to CERCLA section 121(c) and as provided in OSWER
Directive 9355.7-02, Structure and Components of Five-Year Reviews, May 23, 1991, and
OSWER Directive 9355.702A, Supplemental Five-Year Review Guidance, July 26,1994, EPA
must conduct policy five-year reviews until ground water cleanup levels (MCLs) have been
attained. The data collected during the monitoring program will be used to evaluate the
performance of the extraction system.
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IV PUBLIC PARTICIPATION
The ESD 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
1650 Arch Street
Philadelphia, PA 19103-2029
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 ESD in accordance with 40
C.F.R. § 300.435(c)(2) and PADEP has verbally concurred with the ESD. PADEP has informed
EPA that it will send a concurrence letter to EPA soon.
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, Director
Hazardous Waste Management Division
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N36575
E2643750
N36550
N36525
N36500
N36475
N36450
N36425
E2644750 N36400
Source: Dynamac Corporation Environmental Services
98P-2386 8/27/98
FIGURE 1 SITE LOCATION MAP
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