PB96-963117
EPA/ESD/R09-96/156
March 1997
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Litchfield Airport Area,
aka: Phoenix-Goodyear Airport,
Goodyear/Avondale, AZ
12/22/1995
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PHOENIX-GOODYEAR AIRPORT AREA SUPERFUND SITE
EXPLANATION OF SIGNIFICANT DIFFERENCES #3
for the FINAL REMEDY RECORD OF DECISION
s.
December 1995
I. INTRODUCTION
On September 26, 1989, the United States Environmental Protection Agency (EPA)
signed a Record of Decision (ROD) for the final remedy at the Phoenix-Goodyear Airport
(PGA) site in Goodyear, Arizona. The State of Arizona concurred with the remedy selected in
the 1989 ROD. In January 1991, EPA issued an Explanation of Significant Difference (ESD
#1) which modified and clarified the 1989 ROD on five points. In May 1993, EPA modified the
ROD a second time to explain the differences between the final remedy originally selected in
the 1989 ROD and the final remedy which will be implemented at the site (ESD #2). EPA is
now modifying the ROD a third time to explain further differences between the final remedy
selected in 1989 and the remedy currently being implemented at the site. These changes are
not fundamental alterations of the remedy described in the 1989 ROD.
Under Section 117 of the Comprehensive Environmental Response, Compensation,
and Liability Act of 1980 (CERCLA), as amended by the Superfund Amendment and
Reauthorization Act of 1986, and pursuant to 40 C.F.R. Section 300.435(c)(2)(i) (55 Fed.Reg.
8666, 8852 (March 8, 1990)), EPA is required to publish an ESD when significant (but not
fundamental) changes are being considered to a final remedial action plan as described in a
ROD. If the changes fundamentally alter the nature of the selected remedy, an amendment to
the ROD would be required [40 C.F.R. Section 300.435(c)(2)(ii)]. In this instance, EPA has
made a few important changes that modify the ROD requirements, but do not alter the
hazardous waste management approach that EPA selected in the ROD. The changes will
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enhance the effectiveness of the remedy, and promote more effective cleanup of the site.
The purpose for each of these changes is described in detail in Section III of this document.
This document provides a brief background of the site, a summary of the remedy
selected in the 1989 ROD and how that remedy was modified by the 1991 and 1993 ESDs, a
description of how this ESD affects the remedy originally selected by EPA in the 1989 ROD,
and an explanation of why EPA is making these changes to the ROD. EPA is issuing this
third ESD to the 1989 ROD in order to take into account information received by EPA after
EPA's issuance of the 1991 and 1993 ESDs.
The southern portion of the site consists of the Loral Defense Systems-Arizona (Loral)
property and the Phoenix-Goodyear Airport property and any groundwater contamination
emanating from these areas. The northern portion of the site consists of the Unidynamics
property and any groundwater contamination emanating from these areas. This ESD
proposes to modify the remedy selected for the site as follows:
(1) modify the groundwater remedy for Subunit A groundwater to allow air sparging of
Subunit A groundwater in areas where a soil vapor extraction system can collect and treat the
volatile organic compound (VOC) vapors emitted by the air sparging system in a manner
consistent with the ROD; and
(2) modify the groundwater remedy for Subunit A groundwater to include use of a
metal adsorption wellhead treatment system, where appropriate, for wells connected to the
existing groundwater treatment plant. This system would be used at any Subunit A
groundwater remedy extraction well with chromium contamination that, without such a system,
would result in the effluent at the Subunit A groundwater treatment plant exceeding site clean-
up standards for metal contaminants.
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This ESD modifies the remedy selected in the ROD for both the northern and the
southern portion of the PGA site, but will initially be implemented only at the southern portion
of the site. EPA will evaluate the effectiveness of air sparging at PGA-south before deciding
s.
whether to implement air sparging at PGA-north. Currently chromium is a contaminant of
concern at PGA-south but not at PGA-north; accordingly, metal adsorption wellhead treatment
is not anticipated at PGA-north at this time.
This ESD and supporting documentation will become part of the PGA Administrative
Record. Copies of the Administrative Record for the PGA site (including this ESD) have been
placed at the following locations:
Avondale Public Library
328 West Western Avenue
Avondale, Arizona 85323
(602) 932-9415
EPA Region 9 Superfund Records Center
95 Hawthorne Street - 4th floor
San Francisco, California 94105
(415) 536-2000
EPA provided a fifteen (15) working day comment period for the State of Arizona in
accordance with 40 C.F.R. Section 300.515(h)(3). State of Arizona comments on this ESD
are summarized in Section IV of this document and are also included in the PGA
Administrative Record file. Pursuant to 40 C.F.R. Section 300.435(c)(2)(i), EPA will publish a
notice summarizing this ESD in a major newspaper of general circulation. A formal public
comment period is not required for an ESD.
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II. BACKGROUND
The following provides a brief background of the PGA site, short summaries of the
remedy selected in the original 1989 ROD and changes to the 1989 ROD established by the
1991 and 1993 ESDs. Additional background information can be found in the 1989 ROD, the
1991 BSD, the 1993 BSD, and in the PGA Administrative Record.
A. Site Background and Description
The PGA site is located primarily in Goodyear, Arizona, approximately seventeen (17)
miles west of Phoenix in the western part of the Salt River Valley. A groundwater flow divide
splits the site along Yuma Road into northern and southern portions. The northern portion of
the site consists of the Unidynamics property, located at 102 S. Litchfield Road and all areas
with groundwater contamination in excess of site clean-up standards related to and emanating
from the Unidynamics property. The southern portion of the site consists of the Loral Defense
Systems property located at 1300 S. Litchfield Road, the PGA property, and all areas with
groundwater contamination in excess of site clean-up standards related to and emanating
from the Loral and/or PGA properties. Attachment #1 provides a map indicating the
approximate site boundaries of the Phoenix-Goodyear Airport Superfund site. The current
land uses on and near the site are agricultural, industrial, and residential.
In 1981, the Arizona Department of Health Services (ADHS) discovered that
groundwater in certain areas of the site was contaminated with solvents and chromium. EPA
and ADHS conducted additional sampling of wells in 1982 and 1983 which revealed eighteen
(18) wells contaminated with trichloroethylene (TCE). As a result, EPA added the PGA site
(originally listed as the "Litchfield Airport Area Superfund Site") to the National Priorities List
(NPL) on September 8, 1983 (see Federal Register. Vol. 48, No. 175, p. 40671). Other
hazardous substances found at the PGA site include acetone, methyl ethyl ketone (MEK),
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1,1,1-trichloroethane (TCA), 1,1-dichloroethylene (DCE), other volatile organic compounds
(VOCs), and chromium.
Most of the groundwater and soil contamination in the southern portion of the site is
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located within the Loral and airport properties inside an area of the site designated as Section
16. Contaminated "shallow groundwater" (hereafter referred to as Subunit A groundwater)
within Section 16 was addressed in the first phase of the remedy for the PGA Superfund site
and is referred to as the Section 16 Operable Unit. A Record of Decision for the Section 16
Operable Unit was signed on September 29, 1987. The designated remedy of a pump and
treat system for Subunit A groundwater has been operating since December 1989. A primary
objective of the Section 16 Operable Unit is to protect human health and the environment by
preventing the migration of contaminated groundwater and resulting aquifer degradation.
Groundwater currently used for drinking water in the area of the site meets federal and
state drinking water standards. However, because municipal water supplies in the area of the
site are dependent on groundwater, future population growth in the area could require use of
groundwater in contaminated areas and may result in potential exposure to hazardous
substances.
The clean-up work in the northern portion of the site is being carried out by
Unidynamics, whereas the Goodyear Tire & Rubber Company is the lead party implementing
the work in the southern portion of the site. EPA, with the assistance of the Arizona
Department of Environmental Quality (ADEQ), authorizes and oversees all clean-up activities
at this Superfund site.
B. Remedy Selected in the 1989 ROD
The ROD for the final remedy at the PGA Site was signed by the EPA Regional
Administrator on September 26, 1989. In addition to selecting the remedial actions described
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below, the final remedy also incorporates the Section 16 Operable Unit. The groundwater
clean-up levels for the PGA site are identified in Table 2-5 of the ROD1. The groundwater
cleanup levels for the Section 16 Operable Unit are identified in Table 2-5 and in Table 1 of
the 1987 ROD.
ROD Remedy for Southern Portion of PGA Site
For the southern half of the site, the remedy consists of extraction and treatment of
contaminated Subunit A groundwater and "deep groundwater" (hereafter referred to as
Subunit B/C groundwater) and soil vapor extraction for contaminated soils. The Subunit A
groundwater and the Subunit B/C groundwater remedial actions require a pump and treat
system using air stripping to remove VOCs from the groundwater. The ROD states that
groundwater remedial action shall consist of three (3) new Subunit B/C groundwater wells for
extraction and treatment of Subunit B/C groundwater at a central treatment plant. The ROD
states that the central treatment plant may be operated without emissions controls as long as
compliance with Federal, State, and local air pollution regulations can be maintained. In
addition, the ROD requires that treated water from the central treatment plant will be made
available to the City of Goodyear for municipal use. The estimated total present worth cost of
the extraction and treatment facilities for the groundwater remedy for the southern portion of
the site is $14,500,000.
With respect to VOC soil contamination at the southern portion of the PGA site, the
ROD selected a soil vapor extraction (SVE) system with emission controls. The SVE system
is being implemented in certain required areas within an area identified as Target Area 2 in
1 The groundwater cleanup levels in Table 2-5 of the ROD consist of: a) Federal and State of Arizona
legally Applicable or Relevant and Appropriate Requirements (ARARs); and, b) other criteria used to ensure
the protectiveness of the remedy (known as To Be Considered (TBCs)).
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Figure 5-2 of the ROD. The total present worth cost of the soil remedy for the southern
portion of the site is estimated to be $3,900,000 for a phased implementation.
ROD Remedy for Northern Portion of the PGA Site
The remedial action selected for the northern portion of the site is similar to that
chosen for the south and includes a Subunit A groundwater remedy, a Subunit C groundwater
remedy, and a soil remedy. The Subunit A groundwater remedy consists of a pump and treat
system using air stripping, followed by liquid phase granular activated carbon. Vapor-phase
GAC air emission controls are required for the Subunit A groundwater remedy. The ROD
requires that the treated water from Subunit A groundwater remedy be reinjected, and the
treated water from the Subunit C groundwater remedy be incorporated into the community
water supply. The estimated present worth cost of the groundwater remedy for the northern
portion of the site is $14,000,000.
The soil remedy consists of a SVE system with vapor-phase GAC air emission controls
to be implemented in the target area. The ROD identifies the target area as that area where
VOCs were detected in soil samples and the area where soil gas samples exhibited VOCs
greater than 1 microgram per liter. The ROD provides that this area may be expanded or
reduced, as necessary, to include removal of 99 percent of the contaminants. In addition, the
ROD states that excavation and treatment may be required to remove residual contamination
where soil vapor extraction is not effective. The estimated present worth cost of the SVE
system is $3,100,000.
C. The 1991 ESD changes to the 1989 ROD
The ESD issued by EPA in January 1991 clarified and modified portions of EPA's
September 1989 ROD. To the extent that the 1991 ESD differed from the ROD, the 1991
ESD supersedes the ROD. The 1991 ESD modified the ROD as. follows:
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(1) The 1991 ESD revised the clean-up level for methyl ethyl ketone (MEK) in
groundwater from 170 parts per billion (ppb) to 350 ppb;
(2) The 1991 ESD set a clean-up level for acetone in groundwater at 70Q ppb;
(3) The 1991 ESD clarified the target area for the soil remedy in the northern portion
of the site and the criteria for establishing the clean-up levels. On page four of the 1989
ROD, the soil remedy target area is described as "that area where VOCs were detected in soil
samples and the area where soil gas samples quantified VOCs greater than 1 microgram per
liter. The area may be expanded or reduced to include removal of 99 percent of the
contaminant." In the 1991 ESD, EPA defined these statements to identify the soil remedy
target area for the northern portion of the PGA site to consist of target areas B and C defined
by all four circles in Figure 5-7 of the 1989 ROD;
(4) The 1991 ESD clarified the role of soil excavation as a remedy option, should the
selected soil remedy (soil vapor extraction) at the northern portion of the site prove ineffective.
The 1989 ROD states on page four that "excavation and treatment may be required to remove
residual contamination where soil vapor extraction is not effective." In the 1991 ESD, EPA
interpreted this to mean that excavation and treatment of soil is one, but not the only, remedial
alternative EPA will consider for the soil in the northern portion of the site if soil vapor
extraction is ineffective; and
(5) The 1991 ESD revised the selected remedy for an off-site agricultural well referred
to as the "Phillips Well" from wellhead treatment to routine water quality monitoring. The 1991
ESD did not alter EPA authority to reimpose the requirement for wellhead treatment at the
Phillips Well should future monitoring indicate that the concentration of any VOC has
exceeded the clean-up level identified in Table 2-5 of the 1989 ROD. EPA's decision to
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reimpose wellhead treatment will be based on the Agency's review of water quality sampling
results for the Phillips well.
D. The 1993 ESD Changes to the 1989 ROD
The ESD issued by EPA in April 1993 further modified portions of EPA's September
1989 ROD. To the extent that the April 1993 ESD differed from the ROD, the 1993 ESD
supersedes the ROD.
The April 1993 ESD modified the selected remedy in the ROD for the northern portion
of the site as follows:
(1) changed the emission control technology for the Soil Vapor Extraction System from
vapor-phase granular activated carbon (GAC) to treatment by thermal oxidation with wet
scrubbing;
(2) changed the designated end use for water treated by the Subunit C groundwater
remedy from incorporation into the community potable water supply to reinjection back into the
Subunit C section of the aquifer2; and
(3) suspended the remedial design and construction of the liquid-phase GAC treatment
requirement (or other similar effective technology) from the Subunit A groundwater remedy
until treatment plant influent data quality indicates the presence of a lower volatile compound
(e.g. ketones) at a concentration of 50% or more of its site groundwater cleanup standard.
The April 1993 ESD modified the remedy selected for the southern portion of the site
as follows:
2 An explanation of when municipal end-use may still be considered is explained in Section III.E of the
1993 ESD.
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(1) changed the requirement for a centralized air stripping system for the Subunit B/C
groundwater remedy to a decentralized system (e.g., two or more independent liquid-phase
GAG treatment systems);
(2) changed the designated end use for water treated by the Subunit B/C groundwater
remedy from municipal use to reinjection back into the Subunit B/C section of the aquifer3;
The April 1993 ESD modified the selected remedy in the ROD for both portions of the
site as follows:
(1) added the requirement that should any private or municipal drinking water well in
the vicinity of the PGA site, including but not limited to City of Goodyear wells number 1, 2, 3,
7, 10, 11 and the Parkshadows drinking water well, have an occurrence of a contaminant
listed in Table 2-5 of the ROD in a concentration in excess of its groundwater clean-up
standard and such contamination is related to contamination in the Unidynamics or airport
areas, such drinking water well(s) shall be treated as soon as possible by wellhead liquid-
phase GAG treatment or other similar technology as approved by EPA.
(2) established four additional groundwater clean-up standards for Table 2-5 of the
ROD as follows:
Benzene - 5 parts per billion (ppb)
Ethylbenzene - 700 ppb
1,1,2,2 Tetrachloroethane - 0.18 ppb
Tetrachloroethene - 5 ppb
3 same as footnote 2.
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III. MODIFICATIONS TO THE ROD REMEDY
A. Air Sparging
This ESD modifies the groundwater remedy for Subunit A groundwater to allow air
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sparging of Subunit A groundwater. Air Sparging technology acts to transfer liquid-phase
VOC groundwater contamination to vapor-phase VOC in unsaturated soils lying above the
groundwater which can then be easily removed by a SVE system. Successfully implemented,
air sparging can accelerate the removal of VOCs from the groundwater and reduce the time
needed for restoration of the aquifer. Air sparging will only be allowed to operate in Subunit A
groundwater in areas where an overlying soil vapor extraction system can collect and treat the
VOC vapors emitted by the air sparging system. The overlying SVE system must treat all
collected VOC vapors in a manner allowed by and consistent with the ROD.
An air sparging system works in the following manner: (a) air sparging wells introduce
contaminant-free air bubbles into groundwater contaminated with VOCs; (b) the sparged air
bubbles force the transfer of VOCs dissolved in groundwater (or VOCs sorbed on soil particles
in the groundwater zone) into the sparged air bubbles themselves due to the preference of
VOCs for the vapor phase; (c) the sparged air bubbles naturally rise to the top of the
groundwater, collecting VOCs along the way, until the bubbles leave the groundwater and
enter into pore spaces in the unsaturated soils lying above the groundwater; and (d) the
vapor-phase VOC contamination in the pore spaces of the unsaturated soils is then vacuumed
and removed from the soils by SVE wells for subsequent treatment. Successful application of
air sparging technology would lead to an acceleration of VOC mass removal and ultimate
cleanup of Subunit A groundwater.
Given the fact that cost per pound of VOCs removed from the groundwater via pump
and treat technology is considerably higher than the cost of air sparging plus SVE, EPA has
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concluded that air sparging is a cost-effective technology when applied appropriately. In
December 1994, with EPA approval, Goodyear Tire & Rubber Company conducted a pilot test
of air sparging technology at PGA-south (Reference 1). The pilot test results indicated that air
sparging could effectively accelerate the Subunit A groundwater cleanup. By a project
summary document dated September 1992 (EPA/600/SR-92/173), EPA studies of this
technology indicate that air sparging may make it possible to substantially decrease the time
required to achieve site closure (Reference 2). The estimated cost of this component of the
ESD at PGA-south is $131,800. The estimated cost of this component has not yet been
evaluated for PGA-north. It is anticipated that by accelerating the groundwater cleanup, the
overall cost of groundwater cleanup will be significantly reduced.
B. Metal Adsorption
In addition, this ESD modifies the groundwater remedy for Subunit A groundwater to
include the use of a metal adsorption treatment system at certain Subunit A groundwater
remedy extraction wells. This system is required at any Subunit A groundwater remedy
extraction well with chromium contamination that, without such a system, would result in the
effluent at the Subunit A groundwater treatment plant exceeding site clean-up standards for
metal contaminants. Adsorption systems like those employing Granular Activated Carbon
(GAC) are a common treatment technology for groundwater cleanup with VOCs. As explained
above, pursuant to ESD #2, GAC was made part of the ROD remedy for Subunit B/C
groundwater at PGA-south. By document dated June 1992, EPA issued a June 1992 fact
sheet providing basic information regarding GAC (Reference 3). GAC and other support
media can be manufactured to be "ion-specific," which means that certain metal contaminants
will be especially attracted to and adsorbed onto the media. This ESD allows the use of metal
adsorption systems at the wellheads of certain Subunit A remedy extraction wells that meet
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the above-described conditions. With EPA approval, Goodyear Tire & Rubber Company
conducted a treatability study in November 1994 of groundwater extracted by Subunit A
remedy well E-17 by two metal adsorption technologies: one using chromium-specific treated
GAG and one using chromium-specific treated media known as N-Tech Advanced Affinity
Chromatography (References 4 and 5). These treatability studies concluded that either
chromium-specific treated media would effectively remove chromium from chromium
contaminated Subunit A groundwater at PGA-south (Reference 6). The estimated cost of this
component of the ESD for implementation at PGA-south is $142,000.
IV. SUPPORT AGENCY COMMENTS
The Arizona Department of Environmental Quality (ADEQ) and the Arizona Department
of Water Resources (ADWR) reviewed and concurred with this ESD. Both ADWR and ADEQ
considered the ESD to be an adequate document and submitted no comments.
V. STATUTORY DETERMINATIONS
Considering the new information that has been developed and the changes made to
the selected remedy upon implementation of this ESD, EPA believes that the remedy for the
PGA site will remain protective of human health and the environment, will continue to comply
with federal and state requirements that are applicable or relevant and appropriate to this
remedial action, and will continue to be cost-effective. In addition, the revised remedy uses
permanent solutions and alternative treatment technologies to the maximum extent practicable
for this site. Some of the changes and clarifications contained in this ESD are significant, but
none of the proposed changes fundamentally change the remedy. EPA also believes these
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modifications to the remedy will be cost effective, accelerating the clean-up and restoration of
the groundwater at PGA.
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VI. PUBLIC PARTICIPATION ACTIVITIES
EPA has presented these changes to the remedy in the form of an ESD because the
changes are of a significant but not fundamental nature. EPA provided the State of Arizona
with a fifteen (15) day comment period on this ESD. In accordance with Section 117(c) of
CERCLA, 42 U.S.C. Section 9617, EPA will publish a notice in the Arizona Republic and the
West Valley View newspapers which describes this ESD and its availability for review. In
accordance with 40 C.F.R. Section 300.435(c)(2)(ii), this ESD and all documents that support
the changes and clarifications herein will be contained in the Administrative Record for the
PGA site prior to the commencement of the remedial actions affected by the final ESD.
-) .
—Z^ ' /
<^"~f^( Keith Takata Date
^\/ Deputy Director, Superfund
A
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-ATTACHMENT 1
Approximate Boundaries of
Phoenix Goodyear Airport Area Superfund Site
Camelback Road
Indian School
Thomas Road
McDowell
Van Buren
UNIDVNAMICS
PHOENIX,
Phoenix Y/
Goodyear
Airport
Lower Buck
eye Road
Broadway
Gila River
_ _.„. Approximate
"""""" Site Boundaries
\pga\BM\widMrM4we r»v.M17B3 ItUAtml
A-1
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ATTACHMENT 2
Index of References
1. Phoenix-Goodyear Airport (South) Subunit A Groundwater Remedy Acceleration - Air
Sparging, Scott Zachary, Metcalf & Eddy, May 1, 1995
2. Project Summary: A Technology Assessment of Soil Vapor Extraction and Air
Sparging, US EPA RREL, EPA/600/SR-92/173, September 1992
3. EPA Facts About Activated Carbon Treatment, US EPA, June 1992
4. "New Activated Carbon Technology Recovers Heavy Metals", Tom Lewis III, Industrial
Wastewater, July/August 1994
5. Advanced Affinity Chromatography, NTEC Solutions, Inc.
6. Chromium Removal Options for Well E-17 - Phoenix-Goodyear Airport, Goodyear,
Arizona, Sharp & Associates via fax, May 2, 1995
A-2
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