EPA Supertiind
Record of Decision:
Indian Bend
Washington Area OU 3
Scottsdale, AZ
9/30/1998
PB98-964511
EPA541-R98-180
March 1999
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SFUMD RECORDS CTR
42379
RECORD OF DECISION
VOCs in Groundwater
OPERABLE UNIT
Indian Bend Wash Superfund Site, South Area
Tempo, Arizona
U.S. Environmental Protection Agency
Region IX
75 Hawthorne Street
San Francisco, California 94105
Declaration
Decision Summary
September 1998
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Contents
Page
Acronyms and Abbreviations- vii
I. Declaration 1-1
1. Site Name and Location 1-1
2. Statement of Basis and Purpose 1-1
3. Assessment of the Site 1-1
4. Description of the Selected Remedy 1-2
The Selected Remedy 1-2
Contingency Remedy 1-3
5. Statutory Determinations 1-4
II. Decision Summary ,. II-l
1.0 Site Summary II-l
1.1 Site Name, Location, and Description II-l
1.2 Area and Topography II-l
1.3 Land Use and Demographics H-2
1.4 General Surface^Water and Groundwater Resources 0-5
Surface Water H-5
Groundwater Resources n-6
2.0 Geology and Hydrogeology II-7
2.1 Stratigraphy H-7
2.2 Geology/Stratigraphy n-7
Upper Alluvial Unit D-7
Middle Alluvial Unit D-8
Lower Alluvial Unit II-8
Red Unit H-9
2.3 Groundwater Movement II-9
Groundwater Movement—Upper Alluvial Unit II-9
3.0 Site History and Enforcement Activities n-15
3.1 Site History H-15
Site Discovery and RODs Issued D-15
3.2 IBW-South Remedial Investigation for Groundwater 11-16
3.3 Enforcement Actions 11-16
Groundwater 11-16
Soil H-19
4.0 Highlights of Community Participation 11-20
5.0 Scope and Role of Operable Units D-23
6.0 Summary of Site Characteristics n-24
6.1 Extent of Contamination n-24
Upper Alluvial Unit n-24
Middle Alluvial Unit D-26
Lower Alluvial Unit n-28
6.2 Migration Pathways 11-28
Contaminant Movement from Source Areas H-29
RDD-SFO/982450013.DOC (CAH348.DOC)
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Contents, Continued
Page
Contaminant Movement in the Vadose Zone n-29
Contaminant Movement in the Upper Alluvial Unit n-30
Contaminant Movement in the Middle Alluvial Unit 11-30
Contaminant Transformation and Biodegradation 11-31
Natural Attenuation Processes 11-31
7.0 Site Risks 11-32
7.1 Summary of Site Risks n-32
Ecological Risk Assessment n-32
Summary of Human Health Risk Assessment II-32
8.0 Description of Remedial Alternatives n-39
Remedial Action Objectives 11-39
Cost Estimating Procedures 11-39
Features Common to All Remedial Alternatives 11-41
Groundwater Treatment Component n-42
8.1 Description of No-Action Alternative II-44
8.2 Alternative 2-Monitored Natural Attenuation 11-44
8.3 Alternative 3-Limited Action: Wellhead Treatment at COT No.7/COT
Potable Water 11-46
8.4 Alternative 4-Partial Containment Extraction Wells/Treatment Plant Air
Stripping/Discharge to Town Lake via City of Tempe Storm Drain/
Monitored Natural Attenuation n-47
As Described in Proposed Plan 11-47
Selected Remedy-Partial Containment: Extraction Wells/Treatment
Plant Air Stripping/Discharge to Town Lake, SRP Tempe Canal
No. 6, or Aquifer Reinjection/Monitored Natural Attenuation n-48
Contingency Remedy-Additional Groundwater Extraction and
Treatment n-48
8.5 Alternative 5—Regional Containment: Extraction Wells/Treatment
Plant Air Stripping/Discharge to SRP Tempe Canal No. 6 H-49
8.6 Alternative 6-Regional Containment: Extraction Wells/Treatment
Plant Air Stripping/Aquifer Reinjection 11-49
9.0 Comparative Analysis of Alternatives n-50
9.1 Threshold Criteria 11-51
Overall Protection of Human Health and the Environment 11-51
Compliance with ARARs 11-52
9.2 Primary Balancing Criteria 11-52
Long-Term Effectiveness and Permanence n-52
Reduction of Toxicity, Mobility, or Volume through Treatment n-56
Short-Term Effectiveness n-58
Implementability 11-59
Cost 11-60
9.3 Modifying Criteria 11-61
10.0 Explanation of Significant Differences 11-62
RDD-SttV982450013.DOC (CAH348.DOC)
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Contents, Continued
Page
10.1 Difference in Selected Remedy H-62
Contingency Remedy U-63
102 Differences in Cost II-64
10.3 Potential Differences in End Use of Treated Water 11-64
11.0 Selected Remedy 0-67
Contingency Remedy 11-68
11.1 Groundwater Restoration Component n-69
Groundwater Extraction n-69
Monitored Natural Attenuation n-69
Contingency Remedy - Additional Extraction and Treatment n-71
11.2 Groundwater Treatment and Discharge Component 0-71
Performance Standards n-72
11.3 Additional Components n-72
Well Sealing or Abandonment H-72
Institutional Controls U-72
Groundwater Monitoring H-73
11.4 5-Year Review H-73
11.5 Conceptual Design U-73
11.6 Cost of the Selected Remedy and Contingency Remedy H-78
Selected Remedy 11-78
Contingency Remedy H-78
12.0 ARARs for Indian Bend Wash-South U-79
12.1 Chemical-Specific ARARs H-80
Chemical-Specific ARARs for Groundwater Remedial Goals 11-80
ARARs Regulating Groundwater Discharge Concentrations D-83
12.2 Location-Specific ARARs O-84
12.3 Action-Specific ARARs U-85
Hazardous Waste Management ARARs Under RCRA H-85
Reinjection ARARs H-92
Groundwater Remediation Action-Specific ARARs H-92
Air Emissions Requirements H-93
13.0 Statutory Determinations H-95
13.1 Protection of Human Health and the Environment H-95
13.2 Compliance With Applicable or Relevant and Appropriate
Requirements D-95
13.3 Cost-Effectiveness H-96
13.4 Utilization of Permanent Solutions and Alternative Treatment
Technologies to the Maximum Extent Practicable H-96
13.5 Preference for Treatment as a Principal Element H-97
13.6 Five Year Review Requirements 11-97
13.7 Implementability n-97
13.8 Cost H-97
13.9 State Acceptance H-97
RDO-SFQ/982450013.DOC (CAH348.DOC)
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Contents, Continued
Page
13.10 Community Acceptance II-98
Appendix A—Cost Evaluation
Tables
1 Orders Issued for Focused RI Work at IBW-South 11-19
2 IBW-South Community Participation Highlights 11-21
3 Parameters for Estimating Chemical Intake From Ingestion of Contaminants
in Groundwater 11-34
4 Inhalation Parameters 11-34
5 Parameters for Estimating Chemical Absorption from Dermal Contact with
Groundwater n-35
6 Toxicity Information for COCs at IBW-South 11-36
7 Sitewide Risks for VOCs Detected Between January 1994 and February
1996 at IBW-South..: 11-37
8 Components of Selected Remedy, Contingency Remedy, and Alternatives
Evaluated in Feasibility Study 11-43
9 Results of Solute Transport Analysis for TCE and PCE II-45
10 Comparison of Alternatives with EPA's Nine Evaluation Criteria 11-53
11 Cost 11-61
12 Chemical-Specific ARARs for the IBW-South Site 11-81
13 Location-Specific and Action-Specific ARARs for the IBW-South Site 11-86
Figures
1 Site Location Map II-3
2 Conceptual Geologic Cross Section D-7
3 Contours of Equal Groundwater Elevation in UAU Wells, October 1994 II-l 1
4 Groundwater Elevations in MAU C and LAU Wells, October 1994 FI-13
5 Facility Locations 11-17
6 Estimated Extent of Contamination in UAU 11-25
7 Estimated Extent of Contamination in MAU 11-27
8 Conceptual Diagram of Migration Pathways 11-28
9 Comparative Cost of Alternatives 11-55
10 Compliance Boundary for UAU and MAU fl-65
11 Conceptual Design for Extraction and Treatment of Selected Remedy U-75
ROD-SFO/982450013.DOC (CAH348.DOC)
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Acronyms and Abbreviations
ug/L
A&Ww
ADEQ
ADOT
ADWR
APSOctotillo
Power Plant
ARAR
ASU
AT
bgs
BW
C.
Q.
CERCLA
CFR
COC
COPC
COT
DC
DCE
DNAPL
DO
EC
ED
EF
micrograms per liter
aquatic and wildlife (warm water fishery) (water quality criteria for the
State of Arizona)
Arizona Department of Environmental Quality
Arizona Department of Transportation
Arizona Department of Water Resources
Arizona Public Service Ocotillo Power Plant
applicable or relevant and appropriate requirement
Arizona State University
averaging time
below ground surface
body weight
chemical concentration in air
chemical concentration in water
Comprehensive Environmental Response, Compensation, and Liability
Act of 1980, as amended
Code of Federal Regulations
chemical of concern
chemical of potential concern
City of Tempe
dual-cast
dichloroethene
dense nonaqueous-phasee liquid
dissolved oxygen
electrical conductivity
exposure duration
exposure frequency
RDO-SFQi982450013.DOC (CAH348.DOC)
VII
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ACRONYMS AND ABBREVIATIONS
EPA U.S. Environmental Protection Agency
ESD Explanation of Significant Differences
FS Feasibility Study
ft/day feet per day
ft/ft foot per foot
ft2/day square feet per day
GRA General Response Action
HBGL Human Health-Based Guidance Levels
HOPE high-density polyethelyne
HEAST Health Effects Assessment Summary Tables
HI hazard index
HQ hazard quotient
IBW-North Indian Bend Wash Superfund Site-North Area
IBW-South Indian Bend Wash Superfund Site-South Area
ILCR increased lifetime cancer risk
Inw daily water ingesrion rate
Ir, daily inhalation rate
IRI Interim Remedial Investigation
IRIS Integrated Risk Information Service
kg kilogram
Kp dermal permeability coefficient
LAU Lower Alluvial Unit
LGAC liquid-phase granular activated carbon
m'/day cubic meters per day
MAU Middle Alluvial Unit
MCL Maximum Contaminant Level
MCLG Maximum Contaminant Level Goals
mg/kg-day milligrams per kilogram per day
mg/L milligrams per liter
mgd million gallons per day
RDD-SFCV982450013.DOC (CAH348.DOC)
VH
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ACRONYMS AND ABBREVIATIONS
MNA
MTBE
MW
NCP
NPL
O&M
OSWER
OU
PCE
ppb
PRG
PRP
QA
RAO
RCRA
RD
RD/RA
R/D
RI
RI/FS
RME
ROD
SA
SARA
SDWA
SRP
SVE
TBC
TCA
TCE
monitored natural attenuation
methyl tertiary butyl ether
Monitoring Well
National Oil and Hazardous Substances Pollution Contingency Plan
National Priorities List
operation and maintenance
EPA's Office of Solid Waste and Emergency Response
Operable Unit
perchloroethene (tetrachloroethene)
parts per billion
Preliminary Remediation Goal
potentially responsible party
quality assurance
Remedial Action Objective
Resource Conservation and Recovery Act, 42 USC Sec. 6901, et seq., as
amended
Remedial Design
Remedial Design/Remedial Action
reference dose
Remedial Investigation
Remedial Investigation/ Feasibility Study
reasonable maximum exposure
Record of Decision
exposed skin surface area
Superhind Amendments and Reauthorization Act of 1986
Safe Drinking Water Act
Salt River Project
soil vapor extraction
to be considered
trichloroethane
trichloroethene
RDD-SFCV982450013.DOC (CAH348.DOC)
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Acflonnns AND ABBREVIATIONS
TOG total organic carbon
UAU Upper Alluvial Unit
UIC underground injection control
USDW underground sources of drinking water
VGAC vapor-phase granular activated carbon
VOC volatile organic compound
RDD-SFOfl82450013.DOC (CAH348.DOC)
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I. DECLARATION
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I. Declaration
1. Site Name and Location
This Record of Decision (ROD) is for the Indian Bend Wash Superfurtd Site, South Area
(IBW-South), located in the City of Tempe and Maricopa County, Arizona.
2. Statement of Basis and Purpose
This ROD presents the selected remedial action for volatile organic compounds (VOCs) in
groundwater at IBW-South in accordance with the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980 (CERCLA) as amended by the Super-
fund Amendments and Reauthorization Act of 1986 (SARA) and, to the extent practicable,
the National Oil and Hazardous Substances Pollution Contingency Plan, (NCP). The deci-
sion in this ROD is based on the Administrative Record for this site.
The U.S. Environmental Protection Agency (EPA) has already addressed VOC contamina-
tion in the vadose zone for the soil operable unit (OU) at IBW-South in a ROD issued
September 1993. This ROD and the September 1993 ROD constitute the overall final remedy
for VOCs in groundwater at the IBW-South Site.
The State of Arizona, acting by and through its Department of Environmental Quality
(ADEQ), concurs with the remedy selected in this document.
3. Assessment of the Site
Releases of VOCs, e.g., common industrial solvents such as trichloroethene (TCE),
perchloroethene (PCE), and 1,1,1-trichloroethane (1,1,1-TCA), from several individual
facilities have contaminated the groundwater at IBW-South. Actual or threatened releases
of hazardous substances at or from this site, if not addressed by implementing the response
actions selected in this ROD, may present an imminent and substantial endangerment to
public health, welfare, or the environment.
IBW-South contains multiple, distinct facilities that are releasing or that have released VOCs
into groundwater. VOCs were originally detected in groundwater production wells in the
Tempe area in 1982. Since then, EPA has detected VOCs in groundwater production and
monitoring wells and in soil at individual properties within the study area. This contamina-
tion has moved downward through the soil above the water table and reached ground-
water. City of Tempe public water supply wells exist within and surrounding the
IBW-South site; however, City of Tempe (City) residents currently receive water from
surface-water supplies, not from City of Tempe wells with contaminated groundwater in
the IBW-South area. Nonetheless, contamination in the groundwater represents loss of a
groundwater resource that is considered a future source of drinking water by the State of
Arizona and the City of Tempe. The City has expressed the desire that the groundwater be
restored.
ROO-SFO962450001 .DOC (CAH346.DOC) (97) 1-1
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OECUflATKM
4. Description of the Selected Remedy
This ROD presents EPA's remedy and contingency remedy for groundwater. A remedy for
the Operable Unit for VOCs in Soils was established in a 1993 ROD. This ROD addresses the
Groundwater Operable Unit. Together the 1993 ROD and this ROD form the remedy for
VOC contamination at IBW-South.
The Selected Remedy
This remedy addresses VOC contamination in groundwater at IBW-South through the
following actions:
• Extraction of the western Upper Alluvial Unit (UAU) area of VOC-contaminated
groundwater to attain aquifer cleanup standards and hydraulic containment of the
contaminated areas to inhibit both lateral and vertical migration.
• Treatment of extracted water to performance standards using liquid granular activated
carbon (LGAC), air stripping with vapor granular activated carbon (VGAC)/ or
ultraviolet light oxidation (UV/Ox)
• Discharge of treated groundwater to the City of Tempe storm drain system leading to
Town Lake, the Salt River Project's (SRP) Tempe Canal No. 6, or reinjection.1
• Monitored natural attenuation (MNA) of the central and eastern UAU areas of VOC-
contaminated groundwater and the Middle Alluvial Unit (MAU) areas of VOC-
contaminated groundwater to attain aquifer cleanup standards within those areas/ and
to prevent migration of groundwater contaminated above the aquifer cleanup standards
to and beyond the compliance boundaries established in this ROD.
• The establishment of compliance boundaries for those areas where the MNA remedy is
selected. The compliance boundaries represent borders beyond which VOC-
contaminated groundwater above aquifer cleanup standards will not be allowed to
migrate. The compliance boundary for the central and eastern UAU areas of contami-
nation is located approximately 2,000 feet south of Broadway Road, bounded by Price
Road to the east and Dorsey Lane to the west. Sentinel wells will be located in the UAU
upgradient of the UAU compliance boundary in an area bounded by Broadway Road to
the north, approximately 1,000 feet south of Broadway Road to the south, approximately
1,000 feet east of Price Road to the east, and Dorsey Lane to the west. The location of the
compliance boundaries and areas for sentinel wells are shown in Figure 10 in Section
10.0. The sentinel wells will be monitored at least quarterly for the hazardous
substances for which aquifer cleanup standards are established (see Section 12.0), and
for other substances as appropriate.
The compliance boundary for the MAU areas of contamination is located approximately
2,000 feet east of the current extent of VOC contamination and is bounded by Rio Salado
Parkway to the north and Apache Boulevard to the south. Sentinel wells will be located
approximately 1,000 feet upgradient of the MAU compliance boundary, as shown in
1 Public comments were received during
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I. OECURATON
Figure 10 in Section 110.0. The sentinel wells will be monitored at least quarterly for the
substances for which cleanup standards are established and for other substances as
appropriate.
• Continued monitoring of groundwater to verify the effectiveness of the extraction and
treatment and MNA remedies and to ensure that aquifer cleanup goals are met
throughout the areas of VOC contamination.
• Institutional controls to protect the public from exposure to contaminated groundwater
exceeding aquifer cleanup levels until cleanup levels are met. Institutional controls will
include various Arizona well siting, permitting, and construction restrictions, and
notices distributed by the Arizona Department of Water Resources, Arizona
Department of Health Services, or EPA concerning risks from exposure to contaminated
groundwater. Additional institutional controls to prevent interference with EPA's
remedial efforts also may be established.
• Sealing or abandonment of Well SRP23E, 2.9N to eliminate this potential path of VOC
contaminant migration from the UAU to the MAU. This well is located in an area of
shallow contamination and represents a potential conduit for downward contaminant
migration. Other monitoring wells that will not be included in the long-term monitoring
network will be abandoned as appropriate.
Contingency Remedy
A contingency remedy of extraction and treatment of appropriate target volumes of
contaminated groundwater in MNA areas may be triggered to satisfy the following two
criteria: (1) attaining aquifer cleanup standards within a reasonable time frame of
approximately 30 years, and (2) preventing migration of groundwater contaminated above
the aquifer cleanup standards to and beyond the compliance boundaries. The appropriate
"target volume" of contaminated groundwater to be extracted and treated will be
determined to ensure that these two criteria are met.
For the UAU or MAU, the contingency remedy will be triggered if either one of the
following situations occurs:
(a) If verification sampling at the sentinel wells confirms that data collected during
quarterly sampling exceed the aquifer cleanup standards, and if the average
contaminant concentration collected from the next two consecutive quarterly sampling
rounds from this well exceeds the aquifer cleanup standards, then the contingency
remedy will be activated. The contingency remedy may be implemented sooner, if
needed.
(b) EPA-approved flow and transport modeling will be conducted using data collected
during each EPA 5-year review period. If the modeling evaluation indicates that the
MNA remedy will not attain aquifer cleanup standards within a reasonable time frame
of approximately 30 years from the start of remedial action, then the contingency
remedy will be activated.
RDD-SFO/982450001 .DOC (CAH346.DOC) (97) 1-3
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I. DECLARATION
5. Statutory Determinations
The selected remedy and the contingency remedy for the Groundwater Operable Unit at
IBW-South:
• Are protective of human health and the environment;
• Comply with federal and state requirements that are legally applicable or relevant and
appropriate to the remedial action;
• Are cost-effective;
• Use permanent solutions and alternative treatment or resource recovery technologies to
the maximum extent practicable; and
• Satisfy the statutory preference for remedies that employ treatment that reduces the
toxicity, mobility, or volume of contaminants as a principal element.
This remedial action is expected to take more than 5 years to achieve aquifer cleanup levels
to allow for unlimited use and unrestricted exposure. Accordingly, by policy, EPA will
perform a review not less than 5 years after completion of the construction for all remedial
actions at the site, and may continue such reviews until EPA determines that hazardous
substances have been reduced to levels protective of human health and the environment.
1-
Keith A. Takata Date
Director of Superfund Division
U.S. Environmental Protection Agency, Region DC
RDD-SFQ/M2450001.00C(CAH346.DOC)(97)
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II. DECISION SUMMARY
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II. Decision Summary
This Decision Summary summarizes the information and approaches used that led to EPA's
decision on this remedy. It also establishes the remedy that EPA has selected. This ROD
addresses remedial actions to be applied to the VOCs-in-Groundwater Operable Unit at
IBW South. A ROD for VOCs in the Vadose Zone at IBW-South was issued in September
1993. Other RODs address various operable units (OUs) at the Indian Bend Wash
Superfund Site-North (IBW-North) Site (See Section 3.1, Site History).
1.0 Site Summary
1.1 Site Name, Location, and Description
The Indian Bend Wash Superfund Site includes both North and South Study Areas. This
ROD pertains only to the South Study Area. The two study areas, IBW-North and
IBW-South, are divided approximately at the Salt River. The overall Indian Bend Wash
Superfund Site comprises approximately 13 square miles and is bordered by Chaparral
Road in Scottsdale on the north, Apache Boulevard on the south, Rural Road (in Tempe)
and Scottsdale Road on the west, and Price Road (in Tempe) and Pima Road (in Scottsdale)
on the east.
The IBW-South Study Area comprises approximately 3 square miles in the City of Tempe
(COT), Arizona. Some portions of the site lie outside of Tempe in jurisdictional "islands" of
Maricopa County. As shown on Figure 1, IBW-South is bounded by Apache Boulevard on
the south. Rural/Scottsdale Road on the west, Price Road on the east, and is proximate to
Curry Road on the north. IBW-South also includes the Salt River itself, which is ephemeral
and flows during storm events and releases from Roosevelt Dam.
The site includes developed land for residential, commercial, and industrial uses. The area
between Apache Boulevard and University Drive is primarily residential. North of Univer-
sity Drive, the site is largely retail and commercial, including light-industrial and auto
repair/scrap facilities in the area south of the Salt River. The industry in the area includes
circuit and electronics manufacturing, metal plating, plastics manufacturing, and dry
cleaning.
1.2 Area and Topography
IBW-South encompasses flections 13 and 14 and the northern halves of Sections 23 and 24,
Township 1 North, Range 4 East. The total area of the IBW-South study area is approxi-
mately 3 square miles. The Indian Bend Wash is a desert wash that has been converted to a
series of urban ponds linked by channels, and the wash meets the Salt River at the northern
boundary of the IBW-South study area. The surface topography of the IBW-South area is
generally flat. The IBW-South area is broken by buttes of rock and surrounded by
mountains at the edges of the valley.
RDD-SFCV9e2450002.DOC (CAH347.DOC) IM
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». DECISION SUMMARY
The surface ranges from 1,150 to 1,200 feet above mean sea level. Slopes do not generally
exceed 2 percent. Slopes of over 100 percent exist only at the banks of the Salt River.
IBW-South is located along the southwestern margin of the Paradise Valley trough.
1.3 Land Use and Demographics
The October 1994 zoning map for the City of Tempe indicates that the southern half of
Section 13 is 91 percent industrial. Approximately 8 percent of the section is zoned for agri-
culture, with 1 percent for commercial developments. The agricultural zoning consists of
open lots held for future development; currently no agricultural activities are taking place at
the site. The northern half of Section 13 has undergone a number of physical changes over
the past 20 years as a result of the ongoing mining of gravel along the southern edge of the
Salt River.
A variety of businesses are engaged in various industrial processes within the southern half
of Section 13, including manufacturing, reconditioning, metal plating, dry cleaning, and
other activities. The majority of the facilities under investigation are within this area. VOCs
and inorganic compounds were used by the businesses or were a result of their operations.
Some of these compounds have been discharged into soils and groundwater in IBW-South.
Contamination of groundwater resources has resulted from contaminant discharge, and the
existing situation may pose a future threat to human health.
Seven known active or inactive landfills exist in the northern half of Section 13 along the
Salt River. Many non-landfill-related businesses have operated or currently are operating
on top of landfill material in this area. Therefore, it is possible that both the landfill material
and the current businesses may have contributed to contamination at this portion of the
site.
Current land use in Section 14 includes industrial, commercial, and recreational activities.
The southern half of Section 14 is more than 70 percent industrialized because of the
Arizona Public Service (APS) Ocotillo Power Plant. The remaining 30 percent consists of a
commercial center, a golf course, and the Arizona State University (ASU) sports practice
fields. The northern half of Section 14 is similar to the northern half of Section 13. Many
changes have taken place because of gravel mining activities. Two known landfills flank
Indian Bend Wash on the north bank of the Salt River; another landfill may exist on the
south bank. A portion of the Karsten Golf Course is located in the northern half of
Section 14.
The northern halves of Sections 23 and 24 are more than 80 percent residential in the form
of apartments, condominiums, and single-family dwellings, occupied primarily by college
students. The remaining 10 to 20 percent of land in these sections is light industrial and
commercial developments such as restaurants, shops, and service stations.
Some demographics of IBW-South are listed below. The Statistical Report 1993 (City of
Tempe, 1993) has a more complete compilation of census data specific to the City of Tempe.
The principal area of investigation within IBW-South lies in Sections 13 and 14. According
to 1990 census information, Section 14 is strictly industrial and has a zero population.
Section 13 has a population of 112, with most of the residents in this section living in mobile
homes or trailers. The median age of the population in Section 13 is difficult to quantify
H-2 RDD-SFO9e2450002.DOC (CAH347.DOC)
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W?mm^'^*3^^ ••-*-iii/
:';y-f^
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«. DECISION SUMMARY
because census figures combine populations by census tract numbers. In this case,
Sections 11,13, and 14 are considered one tract. The majority of the population resides in
Section 11. Sixty-six percent of the population in this tract are between the ages of 18 and 59.
Nearly 24 percent are under 17 years of age, and the remaining 10 percent are over 60 years
of age.
Although only the northern halves of Sections 23 and 24 reside within IBW-South, available
census data apply to the entire section. Section 23, with a population of 12,500, is adjacent to
ASU and contains a large percentage of the off-campus housing available to resident stu-
dents. Within Section 23,86 percent of the population are between 18 and 59 years of age.
The Tempe 2000 General Plan Summary calls for more than 50 acres of land in the northeast
comer of Section 23 to be rezoned as mixed use, with a park located within the center of the
area. Currently, the area is zoned 90 percent industrial and 10 percent commercial.
According to the City of Tempe Long-Range Planning Department, a portion of the mixed
use area will be residential because all currently zoned residential areas have been
developed.
Portions of the IBW-South are located within the 100-year floodplain of the Salt River.
1.4 General Surface-Water and Groundwater Resources
Surface Water
The Salt River is the primary surface-water body present within IBW-South. Also, two
minor surface-water bodies exist within or near the boundaries of IBW-South. The Hayden
Canal is a concrete-lined canal /underground pipeline used to distribute irrigation water by
the SRP. The City of Mesa operates wastewater recharge ponds offsite from IBW-South to
the northeast.
The Salt River flows only about 10 percent of the time, but its flow is unpredictable in any
given year. Currently, the Salt River bed is mostly dry within IBW-South. Prior to the 1940s,
the Salt River was a perennial stream providing water to the Phoenix area for irrigation and
recreation. Following development of the SRP, the river became a dry riverbed for most of
the year, flowing only in response to major rainfall. Over the years, sand and gravel extrac-
tion from the riverbed and floodplains and the creation of several landfills have dramati-
cally altered the environment and habitat of the Salt River. In response to these develop-
ments, the Rio Salado Project was conceived to restore the Salt River through the creation of
a series of lakes and streams over a length of 38 miles from Granite Reef Dam to the Gila
River. The City of Tempe eventually assumed a leadership role in promoting the Rio Salado
Project, focusing on the portion of the Salt River within the City boundaries. This portion of
the Salt River restoration is referred to as the Rio Salado Town Lake Project, henceforth
referred to as simply Town Lake.
Town Lake was conceived as a project to transform a portion of the dry Salt River bed into
an urban lake to provide recreational opportunities and economic benefits. The proposed
location of Town Lake near the IBW-South Study Area is shown on the Site Location Map
(Figure 1). The 2-mile-long, 200-acre lake will be created by placing air-inflatable dams in
the river channel to impound supplied water. The depth of the lake will vary from 6 feet at
the upstream end to 19 feet at the downstream end. During seasonal flooding, the dams will
RDD-SFO/98245000e.DOC (CAH347.DOC) 11-5
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II. DECISION SUMMARY
be lowered to allow flood waters to pass downstream. When flooding stops, the dams will
be raised to impound water for the lake once again.
The downstream dam will consist of a 16-foot-high rubber dam to control the water level in
the lake. A smaller, 6-foot-high rubber dam at the upstream end will capture local river dis-
charges and create a wetlands-type riparian enhancement zone while reducing the flow of
surface-water pollutants into the lake.
Infiltration from the lake into the surrounding soils will be controlled by a combination of
cutoff walls and groundwater extraction/recovery wells. Approximately 10 wells will be
used along the upstream (eastern) portion of the lake (in the northwest portion of the
IBW-South Study Area) to collect an estimated 20 to 30 million gallons per day (mgd) of
infiltrated water and pump the water back into the lake.
A stormwater management system will be constructed to improve the water quality in the
lake by reducing the inflow of potential pollutants and contaminants. Stormwater diver-
sions will capture and bypass the "first flush" from several major stormwater discharges to a
point either upstream or downstream of the lake. In addition, detention areas will be pro-
vided to reduce the potential for spills from the Red Mountain Freeway from entering the
lake.
Construction of Town Lake began in late 1997 and is scheduled to be completed in 1999.
Groundwater Resources
Groundwater at IBW-South was used as a drinking water source until contamination was
discovered in two wells owned by the City of Tempe. These wells have not served water
since 1989; however, one well, COT No. 7, was used once as a backup emergency potable
supply.
Currently, the aquifer is used for industrial and agricultural purposes. The largest industrial
use is for cooling water by the APS Ocotillo Power Plant.
«•« HDD-SFO/982450002.0OC (CAH347.DOC)
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II. DECISION SUMMARY
2.0 Geology and Hydrogeology
This section describes the geology and hydrogeology for the Groundwater Operable Unit at
IBW-South.
2.1 Stratigraphy
The materials at the IBW-South site are primarily a thick basin-fill sequence of alluvial
sediments derived from surrounding mountains. Igneous rocks may intrude in places, and
a crystalline bedrock exists in juxtaposition to the alluvial units as a result of block faulting.
2.2 Geology/Stratigraphy
The complex geological formations underlying IBW-South are generally divided into three
layers, designated as alluvial units. Portions of the alluvial units that can store and transmit
significant quantities of groundwater are called aquifers. In general, three main alluvial
units underlie the IBW-South site: upper, middle, and lower (UAU, MAU, and LAU,
respectively). A conceptual geologic cross section is shown on Figure 2. In some locations,
the LAU is underlain by the Red Unit, which consists of cemented sands, gravel, and clays.
TwnptButtn
~ i Estrudon)
Oroundwtttr
(11(M70lM4IMck)
MimMtMKMMf)
RGURE 2
CONCEPTUAL GEOLOGIC
CROSS SECTION
INDIAN BEND WASH-SOUTH
GROUNDWATER CXI ROD
Upper Alluvial Unit
The UAU is distributed across the entire IBW-South study area, and generally has a uni-
form thickness. The UAU typically is found near or at the ground surface and extends to
approximately 110 to 170 feet below ground surface (bgs). The UAU is normally divided
into an upper layer of clay and sandy silt and a lower layer dominated by sand, gravel,
cobbles, and boulders. The upper layer is typically not present near the Salt River channel,
and thickens to more than 20 feet south of the channel.
RDD-SfO982450002.DOC (CAH347.00C)
11-7
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II. DECISION SUMMARY
Transmissivity data for the UAU have been gathered through 36 aquifer tests performed on
UAU wells at the site to date. The estimated transmissivity values varied widely from a low
of 1,900 square feet per day (ftVday) to a high of 73,000 fr/day. The range of transmissiv-
ities corresponds to hydraulic conductivity values between approximately 30 feet per day
(ft/day) and 1,000 ft/day. The results of these tests suggest that no clear spatial trend in
transmissivity values can be identified; however, the values obtained appear to be
log-normally distributed. This suggests that calculating the geometric mean of the trans-
missivity values is an appropriate method by which to obtain an average value for the data
set. The geometric mean of the UAU transmissivity values is approximately 17,000 fr/day.
Middle Alluvial Unit
The MAU consists primarily of clay and sandy silt with significant interbedded layers of
sand-gravel mixtures. These coarser-grained interbedded layers generally represent the
zones with higher hydraulic conductivity in the MAU. Weak to strong calcium carbonate
cementation is also present in the MAU.
The interbedded stratigraphy encountered within the MAU is subdivided into three
subunits described below:
• MAU Subunit A-Ranges in thickness from 5 to 20 feet and is typically found between
170 to 200 feet bgs. Sand, cemented sand, and silty sand dominate the composition of
Subunit A. This subunit tends to be laterally discontinuous and is frequently not
encountered in the study area.
• MAU Subunit B-Ranges in thickness from 20 to 70 feet and is typically found between
250 and 300 feet bgs. Sand, gravel, and silty sand dominate the composition of MAU
Subunit B. MAU Subunit B appears to have the widest extent of all the MAU subunits
within the IBW-South study area.
• MAU Subunit C-Ranges in thickness from 70 to 150 feet and is typically found between
380 and 550 feet bgs. Sand, gravel, and silty sand dominate the composition of MAU
Subunit C.
Aquifer tests have been performed on five monitoring wells screened in MAU Subunit B,
and seven wells screened in MAU Subunit C. Transmissiviries estimated from the MAU
Subunit B tests range from 1,000 to 12300 ftVday. This corresponds to a range of hydraulic
conductivities of between 5 ft/day and 250 ft/day. Results from the MAU Subunit C
aquifer tests suggest a range of transmissivities between 2,500 and 11,000 ftVday. These
values correspond to a range of hydraulic conductivities from 45 ft/day to 500 ft/day.
Lower Alluvial Unit
The LAU underlies the MAU and, for most of the study area, exceeds the depths explored
during the remedial investigation (RI). The LAU was first encountered at 500 feet bgs in
Well SIBW-12L, and the base of the LAU was typically not encountered. Observations of the
LAU indicate that the composition of the LAU is a conglomerate, dominated by weakly
cemented gravel, sand, silt, and rock fragments. The aquifer test performed in Well
SIBW-12L suggests that the transmissivity of the LAU is significantly lower than the other
units with a value between 100 and 200 ft'/day. These data suggest a hydraulic conduc-
tivity for the LAU of about 5 ft/day.
11-6 ROD-SFO/982450002.DOC (CAH347.DOC)
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I. DECISION SUMMARY
Red Unit
The Red Unit is the deepest of the alluvial units, and comprises a wide range of Tertiary
sediments with a reddish-brown color and distinctive cementation.
Groundwater is expected to flow through the Red Unit as a continuous porous medium
with enhanced flow potential where it has been fractured and faulted. However, the Red
Unit was not investigated during the IBW-South RI and is not expected to have a significant
role in the movement and distribution of contamination within the study area.
2.3 Groundwater Movement
The following sections provide summary descriptions of the movement of groundwater in
the UAU, MAU, and LAU. Groundwater elevations for the UAU measured in October 1994
are shown on Figure 3; groundwater elevations for the MAU and LAU measured in October
1994 are shown on Figure 4. These figures and the text below were presented in the RI.
Data collected since the RI support the conclusions presented below.
Groundwater Movement—Upper Alluvial Unit
The following list summarizes conclusions regarding groundwater movement in the UAU
within the study area:
• Groundwater flow directions in the UAU are south to southwest during non-riverflow
conditions in the Salt River. These flow directions shift to south to southeast during
riverflow conditions in the Salt River when recharge influences groundwater flow
directions.
• Groundwater flow through the UAU originates mainly from Salt River recharge (during
flow events) and lateral inflow moves vertically downward, eventually entering the
MAU.
• The horizontal gradient in the UAU ranges from 0.0015 to 0.004 foot per foot (ft/ft)
during non-riverflow conditions in the Salt River. Salt River recharge during riverflow
conditions increases the horizontal gradient to 0.006 to 0.012 ft/ft.
• The vertical gradient from the UAU to the MAU is downward throughout the study
area and ranges from 0.15 ft/ft to 0.20 ft/ft without influence from Salt River flows. This
downward gradient can increase to as high as 0.27 ft/ft during and directly following
riverflow events.
• The Salt River does not function as a groundwater divide during non-riverflow
conditions when the river is dry, but becomes a groundwater divide during riverflow
events.
• No evidence exists to suggest that groundwater contamination originating from
IBW-North has been transmitted to IBW-South, regardless of riverflow conditions.
RDCXSFO/982450002.DOC (CAH347.DOC) lt-9
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H. DEOaON SUMMARY
The following list summarizes conclusions regarding groundwater movement in the MAU
and LAU. MAU Subunit A is not included in this discussion because in this area it is very
thin and discontinuous. Consequently, no EPA wells are screened in this subunit:
• The groundwater flow direction in MAU Subunit B is generally west to east, but
insufficient data exist to fully characterize the flow direction. The groundwater flow
direction in MAU Subunit C varies from due north to east, with northeast appearing to
be the predominant flow direction.
• According to limited data, the horizontal gradient in MAU Subunit B appears to be
approximately 0.001 ft/ft. The horizontal gradient in MAU Subunit C ranges from 0.002
to 0.004 ft/ft.
• The vertical gradient from MAU Subunit B to MAU Subunit C is downward across the
study area and ranges from 0.02 to 0.13 ft/ft. Salt River flows do not appear to directly
influence vertical gradients from MAU Subunit B to MAU Subunit C.
• Limited data exist to estimate groundwater flow directions in the LAU. The general
flow direction is to the east or northeast, similar to the MAU.
RDD-SFO9824500Q2.DOC (CAH347.DOC)
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II. DECISION SUMMARY
3.0 Site History and Enforcement Activities
3.1 Site History
Site Discovery and RODs Issued
In 1981, the City of Phoenix sampled water from several wells in Scottsdale and detected
VOC contamination. These wells were subsequently taken out of service to protect public
health. In 1982, EPA sampled 20 wells belonging to the SRP and the cities of Phoenix,
Scottsdale, and Tempe. Chemical analyses determined that 11 of the 20 wells were contam-
inated with VOCs, and these wells were also shut down. Subsequently, groundwater
contamination was detected in wells located in the northern part of Tempe, and these wells
were shut down as well. Information from the City of Tempe indicated that COT No. 7 has
been used extremely rarely as backup emergency potable water supply wells (once since
1990).
Following the discovery of groundwater contamination in the area, EPA established the
Indian Bend Wash Superfund Site on the National Priorities List (NPL) in September 1983.
Since that time, EPA has conducted several investigations to determine the nature and
extent of soil and groundwater contamination at the site. These investigations concluded
that the VOCs of primary concern included TCE; 1,1,1-TCA; 1,1- and 1,2-dichloroethene
(1,1- and 1,2-DCE); and PCE. The contamination in IBW-North was found to have
originated from a limited number of larger industrial facilities. Conversely, within the
IBW-South Study Area, the groundwater contamination appears to have had several
sources, from mid-size industrial facilities to small privately owned businesses.
At the beginning of the Superfund remedial investigations in 1984, higher levels of contam-
ination were detected at IBW-North (Scottsdale) than were detected at IBW-South (Tempe).
Therefore, EPA allocated more resources to address the greater potential health risk posed
at IBW-North, given the limited information available at that time. At the end of 1987, EPA
informally split the overall IBW Study Area into the IBW-North and IBW-South areas for
more efficient management. This ROD does not address remedial action for IBW-North.
IBW-South has been divided into two OUs, soil and groundwater, in accordance with NCP
§ 300.430(a)(l)(ii)(A). For IBW-South, EPA issued a ROD for the operable unit pertaining to
VOCs in soils in 1993. That ROD established criteria for determining whether soils at a
particular location might contribute to future groundwater contamination or public health
risk, and selected soil vapor extraction (SVE) as the remedy when those criteria are met.
Focused RIs have been and are being performed to determine which subsites would meet,
or "plug-in" to, those criteria for potential future contribution to groundwater contamin-
ation. If a subsite or property "plugs in/' EPA will issue a "Plug-In Determination" for that
subsite or facility calling for the SVE remedy.
To date, one Plug-in Determination has been made for the former DCE Circuits subsite, and
an SVE system has been constructed and is currently in operation. Focused RI work is
continuing at other subsites within IBW-South, and EPA expects to complete the Plug-In
Determinations for those subsites once the Focused RI work is complete.
RDD-SFCM982450002.DOC (CAH347.DOC) 11-15
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U. DECISION SUMMARY
3.2 IBW-South Remedial Investigation for Groundwater
In 1988, EPA began more intensive investigation of contamination in IBW-South after
addressing the higher potential risk contamination in IBW-North. The data available at the
time indicated that the concentrations of VOCs in groundwater were much lower in
IBW-South than in IBW-North, but were still above drinking water standards. All known
contaminated groundwater production wells in IBW-South had been shut down to prevent
exposures to groundwater contaminated above drinking water standards.
EPA's RI for IBW-South achieved two objectives:
• Performed soil and source investigations; and
• Performed a regional groundwater investigation.
During the source investigations, soil and soil gas sampling were conducted at the facilities
representing potential sources of groundwater contamination. A source investigation was
conducted at each facility. The facilities investigated during the RI are shown on Figure 5.
Preliminary evaluation of data collected during soil gas investigations has resulted in the
delineation of eight "subsites" at IBW-South. EPA and ADEQ may refine and further delin-
eate subsite areas that might need further investigation. The source investigation, combined
with the regional groundwater investigation, showed that the groundwater contamination
at IBW-North did not originate at IBW-South, and vice versa.
The regional groundwater investigation examined the overall presence of contaminants in
groundwater and the movement of groundwater across the entire site. Contamination in the
soil or soil gas at a facility can migrate downward and enter groundwater. Once in
groundwater, it can flow away from the facility and become more widespread or a potential
regional problem. The regional groundwater investigation therefore recognized individual
sources, but adopted a regional perspective on contaminant movement.
Soil, soil gas, and groundwater data and interpretations were collectively incorporated into
the Final RI Report (EPA, 1997).
3.3 Enforcement Actions
Groundwater
In December 1997 and January 1998, EPA issued general notice letters specifically for the
groundwater contamination at IBW-South. These general notice letters were sent to
approximately 14 parties associated with 6 facilities or subsites believed to be sources of
groundwater contamination at IBW-South. The majority of these parties had already
received general notice letters from EPA between 1988 and 1993. EPA will continue to
identify potentially responsible parties (PRPs) should additional information come to light.
11-16 RDO-SFOW2450002.DOC (CAKM7.DOC)
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II. 06CISON SUMMUflY
Soil
EPA issued four Unilateral Administrative Orders (UAOs) under CERCLA §106 and one
Administrative Order on Consent (AOC) under CERCLA §122 to PRPs to obtain Focused
RIs for soil contamination and to install groundwater monitoring wells that would be
included in the overall IBW-South regional groundwater investigation. The orders issued
are shown in Table 1.
TABLE 1
Orders Issued for Focused Rl Work at IBW-South
Facility Order Type Respondents
OCE Circuits (former operator) UAO VAFCO (Rudy vafadari, et al.); Arden Properties
IMC Magnetics UAO IMC Magnetics, Arizona Division, Inc.
Prestige Cleaners, Inc. UAO Prestige Cleaners, Inc.
Eldon Drapery UAO Leibovte Enterprises Limited Partnership; YAS, Inc.
Unitog Rental Services AOC Unitog Rental Services. Inc.
UAO = Unilateral Administrative Order
AOC = Administrative Order on Consent
EPA is continuing its investigation of potential source areas, and at this time, EPA estimates
that approximately eight subsites may be contributing or have contributed VOCs to the
environment within the IBW-South study area. These subsites may consist of one or more
facilities or properties. These eight subsites are identified in the final RI report for IBW-
South (EPA, 1997). The results of the final investigations of these subsites will be presented
in Focused RI reports as explained in the ROD issued in September 1993 regarding the
VOCs in the Vadose Zone.
EPA has issued information request letters pursuant to CERCLA §104(e) to more than
100 parties within IBW-South. These letters request information about solvent usage and
other practices of operation; waste handling and disposal; spills; the presence of tanks, dry
wells, drains, leach lines and degreasers; and related matters. EPA used this information to
assist in identifying potential sources of VOC contamination.
In 1988 and 1990, EPA issued general notice letters to approximately 30 parties. In June
1993, EPA issued a second general notice letter to about 65 parties informing them of
potential liability. Some of the 65 parties who received this notice had also received the
original general notice in 1988 or 1990. In addition, EPA has sent approximately 12 letters to
parties informing them that unless further data or information becomes available, EPA does
not plan to conduct further investigation at their facility and/or property. These 12 parties
had previously received general notice letters from EPA.
As EPA identifies which subsites are sources and which facilities will warrant remedial
action activities, EPA will continue to gather information to identify those PRPs related to
these subsites. As a result of identifying PRPs related to these subsites, EPA may issue
additional general notice letters to parties currently associated with these subsites if they
have not already received notice from EPA.
RDD-SFO/982450002.DOC (CAH347.DOC) 11-19
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II. D6CISION SUMMARY
4.0 Highlights of Community Participation
Because the IBW-South and IBW-North study areas are part of one overall IBW site, EPA
has joined community relations planning and execution for both areas. The Community
Relations Program therefore addresses the IBW community as a whole, although a given
fact sheet or meeting usually pertains specifically to only one study area.
EPA currently maintains IBW-South information repositories at EPA Region DC Office in
San Francisco, and at the Scottsdale, Tempe, and Phoenix Public Libraries. EPA Region IX
Office and the Tempe and Scottsdale Public Libraries maintain copies of the Administrative
Record file on microfilm; the Phoenix Public Library maintains a collection of selected key
documents, including the Interim and Final Remedial Investigation reports, the Feasibility
Study (FS), the Proposed Plan, and this ROD. In addition, ADEQ maintains an information
repository, with various key documents, in its Phoenix office. EPA also maintains a
computerized mailing list database for all of Indian Bend Wash. This list currently contains
more than 1,700 addresses. In addition to continually updating the mailing list, EPA sent a
fact sheet in December 1990 to approximately 35,000 addresses in the area of the Indian
Bend Wash Superfund site in an effort to expand the list. This fact sheet (and all EPA fact
sheets for IBW-South) provided a return coupon and telephone numbers that one could use
to be placed on the mailing list.
EPA also operates a toll-free information message line (800/231-3075) to enable interested
community members to call EPA with questions or concerns about Indian Bend Wash
Superfund site activities. The message line is publicized through newspaper notices and the
mailing list. EPA has been responding to numerous inquiries about the effects of potential
Superfund liability upon residential and small business property located within or near the
study area boundaries. Some of these concerns are addressed in the Responsiveness
Summary of this ROD.
Table 2 presents a chronological list of other community relations activities that EPA has
conducted for IBW-South to ensure community involvement and to comply with the public
participation requirements of CERCLA §113(k)(2)(B) and CERCLA §117. Activities that
were specific to IBW-North only are excluded from this list.
This ROD presents the selected remedy for the groundwater OU for IBW-South, chosen in
accordance with CERCLA, amended by SARA, and, to the extent practicable, the NCP. The
decision for IBW-South is based on the Administrative Record, which is available to the
public.
H-20 RDO-SFO/9B24S0002.DOC (CAH347.DOC)
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.DECISION SUMMARY
TABLE 2
IBW-South Community Participation Highlights
September 1984
1984through1988
December 1990
Throughout 1991
May 1991
January 1992
September 1992
December 1992
April 1993
May 1993
June 1993
June 1993
June 7,1993
June 9,1993
Released a community relations plan based upon interviews with Phoenix, Scottsdale,
and Tempe residents and state and local officials.
During this period, community relations activities addressed all interested persons in
the IBW community, but information transfer centered on IBW-North.
Distributed a fact sheet to all persons on the mailing list providing information on
IBW-South and groundwater monitoring and soils investigations.
Distributed a flyer to residents near EPA's well drilling activities throughout the study
area, which explained the reason for, and nature and context of, the well drilling.
Distributed a flyer and held a public meeting to update the community on the findings of
the remedial investigation, the type of contamination, movements of groundwater, the
potential sources, and EPA's remedial and enforcement strategies: addressed
community questions and concerns.
Updated the 1984 community relations plan to reflect new site communication strate-
gies and information from residents, officials, and other members of the community.
Distributed a fact sheet providing information about investigation activities and Admin-
istrative Orders that had been issued, and also announcing a public comment period
on a Contingency Plan for Removal of Landfill Materials, which the Arizona Department
of Transportation (ADOT) was proposing as part of its work under its agreement with
EPA. Held a 30-day public comment period on this issue.
Issued a flyer to residents in a surrounding neighborhood of the former DCE Circuits
facility where EPA was beginning fieldwork as part of a Focused Remedial Investiga-
tion. Ryer explained the reason for, and nature and context of, the activities and gave
contact names.
Distributed a fact sheet updating the community on activities at IBW-South, including
Administrative Orders, groundwater, and an initial description of the Plug-in Approach
to be used in the upcoming VOCs-in-Vadose-Zone remedy.
Issued a flyer to residents affected by EPA's well drilling activities informing them of the
reason for, and nature and context of. the activities.
Mailed IBW-South Administrative Record file on microfilm for the Soils ROD and
including groundwater information to Scottsdale and Tempe Public Libraries. Hard
copies of the IBW-South IRI Report were sent to these libraries and trie Phoenix Public
Library.
Held informal meetings with citizens and PRP groups to present EPA's proposal for
VOCs-irvVadose-Zone remedy and to answer questions and concerns.
Distributed the Proposed Plan Fact sheet for the VOCs-in-Vadose-Zone remedy to all
persons on the mailing list, to local officials, the state, and to libraries, announcing
EPA's proposal for the soils remedy, the comment period, the scheduled public
meeting and open house session, and the availability of the Administrative Record file.
Issued press releases to the Scottsdale, Tempe, and Phoenix media about the pro-
posed VOCs-in-Vadose-Zone remedy, the scheduled public comment period and open
house session, and the availability of the Administrative Record file.
RDO-SFCV9824S0002.DOC (CAH347.DOC)
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». DECISION SUMMARY
TABLE 2
IBW-South Community Participation Highlights
July 1993
July 1993
July?, 1993
August 1996
September 1997
September 1997
September 24,
1997
October 1997
February 1998
May 1998
June 1998
August 1998
Held an open house session at Gililland Jr. High School in Tempo to present EPA's
proposed remedy for VOCs in the Vadose Zone.
Extended Public Comment period to August 14,1993, on VOCs-in-Vadose-Zone
remedy.
Held a formal public meeting at Gililland Middle School in Tempe, from 7-10 PM. to
present EPA's proposed remedy for VOCs in the Vadose Zone, answer questions, and
to receive written and oral public comments; all proceedings were recorded and the
transcript made part of the Administrative Record file.
Issued fact sheet on SVE at the DCE Circuits Site.
Issued Proposed Plan for deanup of contaminated groundwater at the IBW-South Site.
Mailed the Administrative Record file for the Groundwater OU remedy to the Scottsdale
and Tempe Public Libraries.
Held a formal public meeting on Proposed Plan for groundwater remediation held at
Gilliland Middle School, Tempe, AZ. The Public Comment Period was set for
September 15 to October 14,1997.
Extended Public Comment Period to November 28, 1997. on the Proposed Plan for
groundwater cleanup.
Held meeting with PRPs and ADEQ to further discuss PRP comments and concerns
regarding the Proposed Plan.
Met with PRPs to describe additional groundwater data collected and modeling per-
formed since the Groundwater FS cutoff date for data inclusion.
Met with City of Tempe for a tour of the Rio Salado Town Lake Project and presented
and discussed the additional data and modeling performed since the Groundwater FS
cutoff date for data inclusion.
Met with stakeholders to describe the ROD contingency plans for the MNA portions of
the remedy. _^___
1-22
RDO-SFO982450002.DOC (CAH347.DOC)
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II. DECISION SUMMARY
5.0 Scope and Role of Operable Units
This ROD addresses VOC groundwater contamination at IBW-South, and is known as the
VOCs in Groundwater Operable Unit ROD. EPA has already addressed VOC contamin-
ation in the vadose zone for the soil operable unit at IBW-South in a ROD issued in
September 1993. As described in Section 3.1, the Soil OU ROD provides a presumptive
remedy of SVE for soil remediation at IBW-South and a set of decision criteria to determine
whether a particular subsite meets or "plugs in" to the ROD. One Plug-In Determination
has been made to date, and other subsites are in various stages of characterization. The
overall final remedy for the IBW-South Area encompasses both RODs for VOCs in soil and
groundwater OUs.
EPA's vadose zone OU remedy addresses VOC contaminants in the vadose zone which
could migrate to groundwater. That ROD does not address non-VOC contaminants that
may be in soils, such as metals. That vadose zone OU remedy, in combination with the
active treatment portions of this groundwater remedy, addresses the principal threats
posed by VOCs at IBW-South through treatment. Where necessary, EPA will use removal
actions, or select other remedies for such contaminants, or modify this or the Vadose Zone
OU remedy to address them with an amendment or an explanation of significant
differences (ESD).
To ensure that aquifer cleanup standards are met within a reasonable time frame of 30 years
and to limit migration of contaminated areas where MNA is the selected remedy, EPA has
established a contingency remedy for groundwater. The contingency remedy is extraction
and treatment of a "target volume" that is necessary to meet the performance standards.
The criteria that will trigger the contingency remedy and the target volume are discussed in
Section 11.0 and throughout this ROD.
RDD-SFO/98245000Z.DOC (CAH347.DOC) 11-23
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I. DECISION SUMMARY
6.0 Summary of Site Characteristics
This section summarizes the current extent of VOC contamination at IBW-South, and
describes the pathways for contaminant migration. Actual routes of exposure and exposure
pathways are discussed in Section 7.0.
Over 50 monitoring wells have been installed at IBW-South. Groundwater contamination
has been evaluated according to the Safe Drinking Water Act (SDWA) maximum contam-
inant levels (MCLs). The most consistently detected VOC contaminants in the groundwater
are TCE and PCE. The MCLs for both TCE and PCE are 5 micrograms per liter (ug/L). This
summary descripton focuses on the two main COCs, PCE and TCE; other VOC
contaminants are addressed in the RI.
The RI was conducted over a period of many years, and IRI reports were published in 1991
and 1993. The final RI, published in 1997, presented the following information on ground-
water contamination at IBW-South, herein updated to reflect the most current validated
groundwater sampling results (April 1998).
6.1 Extent of Contamination
Upper Alluvial Unit
Contamination in the UAU is estimated to form approximately three contaminated areas
referred to as the western, central, and eastern contaminated areas, as shown on Figure 6
and described below:
• Western area of contamination. The highest levels of VOC contamination at IBW-South
have been detected here. The contamination consists mainly of TCE and PCE occurring
throughout the contaminated area. This area is partially defined, from northeast to
southwest, by Wells SIBW-5U, SIBW-23U, SIBW-24U, SIBW^tOU, and SIBW-28U.
Groundwater contaminated with TCE exists in the vicinity of the DCE Circuits facility
and is moving southwest with the prevailing groundwater flow direction. TCE concen-
trations have been detected as high as 540 ug/L in Well SIBW-5U. The downgradient
edge of this contaminated area is undefined to the southwest of Well SIBW-28U. TCE
concentrations have decreased in SIBW-5U since 1991. The highest TCE concentration
observed between 1994 and 1996 was 90 ug/L in SIBW-5U in October 1994. The TCE
concentration in SIBW-5U has decreased to less than 5 ug/L in 1998. Analytical results
of samples collected from the farthest downgradient well, SIBW-28U, indicate TCE
concentrations have increased from 20 ug/L in October 1994 to 43 ug/L in April 1998.
• Central area of contamination. A second, central area of PCE- and TCE-contaminated
groundwater is found in the vicinity of the IMC Magnetics, Inc., facility. This area is
partially defined, from northeast to southwest, by Wells PHHW-2, SIBW-21U, SIBW-3U,
and SIBW-48U. TCE concentrations of up to approximately 53 ug/L have been detected
in this area. The highest TCE concentration observed between 1994 and 1996 was
26 ug/L in SIBW-3U in July 1994, and the concentrations have decreased to less than
5 ug/L in 1998. The downgradient extent of groundwater contaminated above MCLs in
11-24 RDD-SFO/982450002.DOC (CAH347.DOC)
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MONITORING WELL
SCREENED IN UAU
TCE (MS/L) PCE (pg/L)
X* ESTIMATED EXTENT OF
CONTAMINATION ABOVE MCL« IN UAU
DATA PRESENTED ARE MOST
RECENT VALUES AVAILABLE
FROM JANUARY AND APRIL 1998
SAMPLING.
FIGURE 6
ESTIMATED EXTENT OP
CONTAMINATION IN UAU
NOIAN BEND WASH-SOUTH
GROUNDWATER OU ROD
-------
H. DECISION SUMMARY
the central contaminated area appears to be near SIBW-48U. PCE is also detected in
Wells SIBW-3U and SIBW-48U. The eastern and western extent of the central
contaminated area is not well defined. Methyl tertiary butyl ether (MTBE) recently has
been detected at levels significantly above Arizona's Health Based Guidance Level
(HBGL) of 35 ug/L and EPA's health advisory range of 20 to 40 ug/L for taste and
odor. The higher levels of MTBE are located near the central contaminated area, where
ADEQ has issued a corrective action plan under its Leaking Underground Storage
Tank (UST) program. If it becomes apparent that ADEQ's UST efforts will not result in
the cleanup of MTBE in the aquifer, EPA will evaluate the necessity and appropriate-
ness of remedial action for MTBE.
• Eastern area of contamination. A third, relatively broad area of PCE-contaminated
groundwater is found in the eastern portion of the study area. This area is partially
defined, from northeast to southwest, by Wells SIBW-50U, SIBW-36U, SIBW-46U,
SIBW-6U, SIBW-31U, SIBW-10U, SIBW-26U, SIBW-27U, and SIBW-39U. PCE
concentrations of 59 ug/L were observed in SIBW-51U in February 1994, and may
indicate the well is located near a source of contamination. The downgradient extent of
this contamination is undefined. Since 1994, the PCE concentrations have decreased in
SIBW-51U to less than 5 ug/L, and have remained relatively constant in most of the
other UAU wells in this area. PCE concentrations have equaled or exceeded 10 ug/L in
SIBW-39, the farthest downgradient well in this contaminated area from April 1995 to
April 1998. As with the western and central contaminated areas, the eastern and
western extent of this contaminated area is not well defined.
Middle Alluvial Unit
Two areas of VOC contamination are found in the MALI, one in MAU Subunit B, the other
in MAU Subunit C. The MAU subunits primarily are found in, and thus also have been
sampled in, the eastern and central areas of IBW-South. PCE was not detected during the
April 1998 sampling event in groundwater samples collected from the MAU or LAU. The
current interpretation of the extent of the VOC contamination in the MAU, as shown on
Figure 7, and LAU is summarized below:
• Subunit B. Groundwater contaminated with TCE is found in MAU Subunit B in the
vicinity of SIBW-16MB in the south-central portion of the study area. Measured TCE
concentrations range from 9 to 4 ug/L. The horizontal extent of this contamination is
undefined.
• Subunit C. Groundwater contaminated with TCE occurs in MAU Subunit C in the
eastern portion of the study area. This low concentration area (up to 12 ug/L) is defined
by Wells SIBW-11MC, SIBW-13MC, SIBW-56MC, SIBW-57MC, and SIBW-58MC. The
eastern and southern limits of this area of contamination are undefined. The TCE
concentrations have not fluctuated significantly in this contaminated area since 1992.
MAU Subunit C is believed to pinch out directly west of the currently defined TCE area
of contamination (approximately 500 to 1,000 feet west of COT No. 7). This suggests that
the observed MAU Subunit C contamination may be related to the observed
contamination upgradient in MAU Subunit B.
11-26 RDD-SFCV982450002.DOC (CAH347.DOC)
-------
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LEGEND:
MONITORING WELL
SCREENED IN MAU
•
TCE (M9rt.) PCE (pg/L)
,-> ESTIMATED EXTENT OF
^/ CONTAMINATION ABOVE MCLs IN MAU
DATA PRESENTED ARE MOST
RECENT VALUES AVAILABLE
FROM JANUARY AND APRIL 1998
SAMPLING.
FIGURE 7
ESTIMATED EXTENT OF
CONTAMINATION IN MAU
INDIAN BEND WASH-SOUTH
-------
(I. DECiSiC*,'SUWWAHv
PCE has not been detected above MCLs in the MAU or LAU sinc« 1985.
Lower Alluvial Unit
Low concentrations of contamination have been detected in the LAU. A 1984 sample from
the Kachina well, in the north-central portion of the IBW-South study area, contained PCE
at 5 Hg/L. Since that sampling event, all samples collected from this well have been below
2 ug/L for PCE. Another well, SRP Well 23E,2.9N, had detected concentrations of ICE, but
it is screened across the UAU, MAU and LAU, and is therefore not useful in determining
the extent of contamination in the LAU. EPA installed one LAU well, SIBW-12L, in early
1991 in the south-central portion of the IBW-xSouth study area, as part of the RI.
Concentrations of PCE and TCE in samples collected from SIBVV-12L to date have not
exceeded 1 ug/L.
6.2 Migration Pathways
This section describes surface and subsurface migration pathways for the VOCs in ground-
water. Figure 8 is a conceptual diagram of the migration pathways for VOCs at IBVV-South.
FIGURE 8
CONCEPTUAL DIAGRAM
OF MIGRATION PATHWAYS
INDIAN BEND WASH-SOL'fH
'.VATER OU POD
Migration pathway.-; considered the following for VOCs in groundwater al IBW-Soutiv
• Contanviru'inl movement from source areas
• Chemical and biological processes that may degrade contaminants as they move
through thf IBVV-South hydrogfologic system
-------
II. OCCISION SUMMARY
• Mechanisms that affect contaminant movement through the vadose zone
• Mechanisms that affect movement through the saturated water-bearing zones
Contaminant Movement from Source Areas
A wide variety of manufacturing industries currently operates, or has operated in the past,
at IBW-South. Printed electronic circuit-board manufacturing, metal plating, commercial
laundry cleaning, engine repair and manufacturing, vehicle repair, jewelry manufacturing,
plastics manufacturing, and mortar and grout manufacturing represent some of the indus-
trial activities that have occurred in the past. Landfills currently operate or have operated in
the past at IBW-South. Some of these industries used hazardous substances in their
manufacturing process that could, if discharged into the ground in sufficient quantity, pose
a threat to human health and the environment. Hazardous substances most commonly used
by industries at IBW-South include degreasing and dry cleaning solvents, metal plating
solutions, acid and base solutions, and fuel oils. When the hazardous substances used by a
facility are released into the ground, the facility becomes a source of contamination.
Possible mechanisms for release of hazardous substances into the subsurface at IBW-South
are:
• Spills or leakage from drums or other hazardous substances containers
• Disposal of used or unneeded hazardous substances into dry wells, septic systems, or
directly onto the ground surface
• Infiltration from industrial wastewater surface impoundments
• Leakage from underground storage tanks
Contaminant Movement in the Vadose Zone
One mechanism that affects contaminant movement in the vadose zone at IBW-South is
infiltration from source areas. Contaminants discharged from source areas migrate vertic-
ally downward under gravitational forces and may also disperse horizontally as a result of
capillary action. Infiltration of precipitation at IBW-South serves to dissolve and/or displace
the contaminants and transport them downward toward the groundwater table.
The water table elevation at IBW-South exhibits significant temporal variation (elevation
changes of up to 40 feet were observed during 1993). When the water table drops, some of
the groundwater contamination may be left behind in the vadose zone, creating a "smear
zone" of residual contamination in the vadose zone. Similarly, when the water table rises,
some of the contamination adsorbed to sediments near the groundwater table may dissolve
into the groundwater.
When contaminants move through the vadose zone, they will partition between mobile
phases and relatively immobile phases when the contaminants are either sorbed by organic
material or soil minerals. The mobility of contaminants through the vadose zone depends
on both the contaminant and the vadose zone chemical and physical properties.
RDOSFO/982450002.DOC (CAH347.DOC) lt-29
-------
II. DECISION SUMMAY
Contaminant Movement in the Upper Alluvial Unit
Groundwater and VOC contaminant movement varies throughout the site and with depth.
The following is a brief discussion of the predominant paths of contaminant movement
within the shallowest water-bearing unit, the UAU. The UAU mainly comprises permeable,
coarse-grained sands and gravel. Contaminants enter the UAU by moving downward
through the vadose zone, dissolving, and moving with the groundwater flow. Contamin-
ants can also enter the UAU when the water table rises into contamination in the vadose
zone. The contaminants then become soluble and move with prevailing groundwater flow.
Important characteristics of groundwater movement in the UAU at IBW-South are the
strong downward vertical hydraulic gradients, changes in groundwater flow directions,
and high horizontal hydraulic gradients caused by flow events in the Salt River. The
changes in groundwater recharge patterns caused by intermittent flow in the Salt River
have significant implications for contaminant transport at IBW-South. The groundwater
flow direction in the UAU shifts from south-southwest to south-southeast, and these shifts
in flow direction may spread out areas of contamination. Also, the increased horizontal
gradient may cause contaminants to move large distances over short time periods.
Future groundwater conditions are expected to be similar to those observed in recent
history, e.g., the flow directions and rate of groundwater movement will vary within similar
ranges, and will be most affected by the frequency and durations of flow events in the Salt
River. The construction of Town Lake is not expected to significantly affect regional
groundwater flow patterns. Extraction wells surrounding the upstream (eastern) boundary
of the lake will be operated to recirculate water that recharges through the lake bottom.
These wells are expected to prevent significant amounts of recharge from impacting the
volume of water that flows through the contaminated portions of groundwater at the site.
The groundwater table fluctuates more than 50 feet at the site. These fluctuations in
groundwater levels can either leave residual areas of contamination when the water table
falls, or cause vadose zone contaminants to become dissolved in the groundwater when the
groundwater table rises.
Contaminant Movement in the Middle Alluvial Unit
The MAU is finer-grained than the UAU. Contaminants are introduced into the MAU by
downward-migrating groundwater from the UAU moving through relatively finer-grained
sediments to the coarser-grained water-producing zones within the MAU. Significant
amounts of contamination can also move to the MAU by groundwater flowing or cascading
down wells that are screened across both the UAU and MAU. The downward gradients
observed at IBW-South can cause contaminant-laden groundwater entering the well in the
UAU to move downward and exit the well in the MAU.
The MAU groundwater flow directions and gradients differ from those in the UAU.
Current data suggest that the northeast MAU flow direction may be completely opposite to
UAU groundwater flow because of naturally and artificially induced regional flow patterns.
Vertical hydraulic gradients present in the MAU also tend to move the contaminants
downward within the MAU.
11-30 RDD-SFO/982450002.DOC (CAH347.DOC)
-------
«. DECISION SUMMARY
Contaminant Transformation and Biodegradation
VOC contaminants will be subject to transformation and degradation via chemical and
biological processes. Chlorinated solvents, which are the most commonly detected
contaminants in the IBW-South groundwater system, may degrade to produce a variety of
products such as alkanes, alcohols, acetates, aldehydes, carbon dioxide, and chloride ions.
The VOX! contaminants also degrade into other chlorinated solvent species. The measured
presence of 1,1-DCA and 1,2-DCE in some groundwater samples collected from IBW-South
provides evidence that biodegradation is occurring in limited areas. Biodegradation may be
taking place under localized anaerobic conditions. However, estimated rates of biodegrada-
tion are not fast enough to prevent contaminated groundwater from migrating.
Natural Attenuation Processes
It appears that dispersion, dilution, and related natural attenuation processes that reduce
VOC contaminants are occurring at IBW-South. Contaminant movement patterns and
decreasing levels of contaminants in groundwater at source areas indicate the effectiveness
of natural attenuation processes at IBW-South. Modeling based on these data trends further
supports these observations and is discussed in Section 8.0 of this ROD.
RDD-SFO982450002.DOC (CAH347.DOC) 11-31
-------
tt DECISION SUMMAY
7.0 Site Risks
This section presents a summary of the baseline human health risk assessment presented in
Appendix A and Chapter 4.0 of EPA's Final Groundwater Feasibility Study Report, dated
August 1997. The baseline risk assessment provides the basis for taking action and indicates the
exposure pathways that need to be addressed by the remedial action. It serves as the baseline
indicating what risks could exist if no action were taken at the site.
7.1 Summary of Site Risks
According to the results of the Baseline Risk Assessment presented as Appendix A in the
Groundwater FS (EPA, 1997), exposure to contaminated ground water might in the future pose
levels of risk considered unacceptable under the NCP. The potential exposure pathway
includes future use of untreated groundwater at IBW-South for drinking or showering. It must
be noted that no exposure pathways currently exist because the groundwater at IBW-South
does not serve as a source of water supply at this time. An exception is COT No. 7, which has
been used as an emergency backup water supply only once since 1990.
Although the contaminated groundwater at IBW-South is not currently used for drinking
water, it is classified as a drinking water source by the State of Arizona. Both the state and the
City of Tempe have expressed the desire that the groundwater be restored to this beneficial use,
which is consistent with the expectation in the NCP.
Ecological Risk Assessment
An ecological risk assessment evaluates risks posed to ecological receptors. An ecological risk
assessment need not be performed for the Groundwater OU at IBW-South because
groundwater does not discharge to surface water. No upwelling is known to occur in the
vicinity of the Salt River, and vertical gradients are downward. Because no current or future
pathways of exposure to VOC-contaminated groundwater exist for ecological receptors at IBW-
South, an ecological risk assessment was not performed.
Summary of Human Health Risk Assessment
This section briefly summarizes the results of the human health risk assessment. The baseline
risk assessment estimates what risks the site poses if no action is taken. It provides a basis for
taking action and identifies the contaminants and exposure pathways that need to be addressed
by the remedial action. This section of the ROD summarizes the results of the baseline risk
assessment for this site, which were presented in Appendix A of the Groundwater Feasibility
Study (EPA, 1997). This summary of the human health risk assessment includes the following
elements:
• Identification of the chemicals of concern (COCs)
• Exposure assessment
• Toxiciry assessment
• Risk characterization
11-32 RDD-SFO/982450006.DOC (CLfl263.DOC) (97)
-------
n DECISION SUMMARY
Identification of Chemicals of Concern
COCs (i.e., the chemicals that are the most toxic, mobile, persistent, or prevalent of those
detected at the site) are selected from among the entire set of chemicals associated with
groundwater at IBW-South. The purpose for identifying and selecting the COCs is to focus the
risk assessment on the most important chemicals (i.e., those chemicals presenting 99 percent of
the total risk) detected at the site.
Monitoring well samples from IBW-South were analyzed for 56 different VOC parameters.
Thirty-five of the VOC parameters were detected at least once in the groundwater samples
analyzed and 21 of the VOCs were never detected. PCE and TCE were detected most
frequently. VOCs other than PCE and TCE were detected; however, they were detected at
considerably lower frequencies.
PCE and TCE in groundwater are the COCs at IBW-South. These chlorinated solvents
constitute the largest portion of the risk in both the UAU and the MAU/LAU. TCE and PCE
were detected in approximately 40 percent of the samples collected between January 1994 and
February 1996, and also have been consistently detected in the same monitoring wells over
many sampling periods. Because TCE and PCE are frequently detected, the potential for
exposure to these contaminants is also higher.
Exposure Assessment
Exposure refers to the potential contact of an individual with a chemical. Human exposure to
chemicals is typically evaluated by estimating the amount of chemicals which could come into
contact with the lungs, gastrointestinal tract, or skin during a specified period of time. The
potential pathways of exposure; frequency and duration of potential exposures; rates of contact
with air and water; and the concentrations of chemicals in groundwater are evaluated in the
assessment of human intake of COCs.
Groundwater supply wells exist at the IBW-South Site. These wells are owned by the City of
Tempe, and contamination discovered in these wells in 1981 (see Site History) is a reason that
IBW is listed as a Superfund Site. These wells are not currently used for domestic supply,
although COT No. 7 was used as an emergency backup water supply once since the wells were
placed out of service in 1989.
The risk assessment therefore evaluated potential future exposures to untreated groundwater
for the following domestic uses:
• Direct ingestion as a drinking water source (i.e., drinking and cooking)
• Inhalation and dermal absorption of contaminants during bathing and showering and
VOCs released to the air during cooking or the use of household appliances such as wash-
ing machines.
Ingestion. The magnitude of exposure to contaminants through ingestion depends on the
amount of water ingested on a daily basis. This assessment assumed that adult residents
consume 2 liters of water per day, 350 days per year for approximately 30 years. The
2-liters-per-day value is close to the 90th percentile for drinking water ingestion (EPA, 1990b).
The 30-year exposure durah'on is considered to be a 90th percentile value for time spent at one
residence. The other parameters used in this intake equation also represent reasonable
maximum values.
RDD-SFO/982450006.DOC (CUC63.00C) (97) 11-33
-------
n DECISION SUMMARY
The parameters used for estimating chemical intake from ingestion of contaminants in
groundwater are shown in Table 3.
TABLES
Parameters for Estimating Chemical Intake From Ingestion of Contaminants in Groundwater
Parameter
Intake
Cw
BW
AT
EF
ED
Irw
Description
Chemical intake rate
Chemical concentration in water
Body weight
Averaging time
Exposure frequency
Exposure duration
Daily water ingestion rate
Units
mg/kg-day
mg/L
kg
years
days/years
years
L/day
Value
Calculated
modeled or measured value
70
70 (cancer effects)
30 (noncancer effects)
350
30
2
A lifetime average intake of a chemical is estimated for carcinogens. This acts to prorate the
total cumulative intake over a lifetime. An averaging time of a 70-year lifetime is used for car-
cinogens. Chemical intake rates for noncarcinogens are calculated using an averaging time that
is equal to the exposure duration.
Inhalation. Exposure to VOCs in air in a residential exposure scenario was estimated from an
inhalation rate of 15 cubic meters per day (mVday). This inhalation rate considers the potential
for exposure during household water uses, such as cooking, laundry, bathing, and showering.
Activity-specific inhalation rates were combined with time/activity level data for populations
that spend a majority of their time at home to derive daily inhalation values. The inhalation rate
of 15 mVday was found to represent a reasonable upper-bound value for daily, indoor
residential activities (EPA, 1991a).
The parameters used for estimating intake from inhalation of VOCs are shown in Table 4.
TABLE 4
Inhalation Parameters
Parameter
Intake
ca
BW
AT
EF
ED
"a
Description
Chemical intake rate
Chemical concentration in air
Body weight
Averaging time
Exposure frequency
Exposure duration
Daily inhalation rate
Units
mg/kg-day
mg/m3
kg
years
days/year
years
m3/day
Value
calculated
modeled value
70
70 (cancer effects)
30 (noncancer effects
350
30
15
11-34
ROO-SFCV982450006.DOC (CLfl263.DOC) (97)
-------
I DECISION SUMMARY
Dermal Absorption. Individuals can become exposed through dermal absorption of contami-
nants in water. The magnitude of potential exposure through this pathway is related to the
concentration in water and surface area of exposed skin, the ability of the contaminant to
penetrate through the skin, and frequency and duration of exposure.
The parameters used for estimating intake of VOCs from dermal contact with groundwater are
shown in Table 5.
TABLES
Parameters for Estimating Chemical Absorption from Dermal Contact with Groundwater
Parameter
Absorbed dose
Cw
SA
ET
EF
ED
BW
AT
Kp
Description
Chemical intake rate
Concentration in water
Exposed skin surface area
Exposure time
Exposure frequency
Exposure duration
Body weight
Averaging time
Dermal permeability
coefficient
Units
mg/kg-day
mg/L
cm*/event
hours/day
event/year
years
k9
years
cm/hour
Value
Calculated value
Modeled or measured value
23,000
0.25
350
30
70
70 (cancer effects)
30 (noncancer effects)
Chemical-specific
Toxicity Assessment
The toxicity assessment determines the relationship between the magnitude of exposure to a
chemical and the adverse health effects. This assessment provided, where possible, a numerical
estimate of the increased likelihood and/or severity of adverse effects associated with chemical
exposure. These toxicity values represent the potential magnitude of adverse health effects
associated with exposure to chemicals, and are developed by EPA. These values represent
allowable levels of exposure based upon the results of toxicity studies or epidemiological
studies. The toxicity values are then combined with the exposure estimates (as presented in the
previous sections) to develop the numerical estimates of carcinogenic risk and noncarcinogenic
health risks. These numerical estimates are then used in the risk characterization process to
estimate adverse effects from chemicals potentially originating in groundwater.
Toxicity values (cancer slope factors and reference doses) used in the risk assessment were
obtained from these sources:
• The Integrated Risk Information System (IRIS), EPA, 1996, a database available through
EPA National Center for Environmental Assessment in Cincinnati, Ohio. IRIS, prepared
and maintained by EPA, is an electronic database containing health risk and EPA regu-
latory information on specific chemicals.
RDO-SFCV982450006.DOC (CLR263.00C) (97) 11-35
-------
H DECISION SUMMWV
• The Health Effects Assessment Summary Tables (HEAST), provided by EPA's Office of
Solid Waste and Emergency Response (OSWER) (EPA, 1995). HEAST is a compilation of
toxicity values published in health effects documents issued by EPA. HEAST is for use in
Superfund and RCRA programs.
Toxicity information for the COCs at IBW-south is summarized in Table 6.
TABU 6
Toxicity Information for COCs at IBW-South
Chemical
of Concern
Slope
Factor
Ingestion
1/(mg/kg-d)
Reference
Dose,
Ingestion
(mg/kg-d)
Slope
factor
Inhalation
l/(mg/kg-d)
Reference
Dose
Inhalation
(mg/kg-d)
Weight of Evidence
Classification System for
Carclnogenlclty
Tetrachloroethene (PCE) 5.1E-O2
Trichloroetnene (TCE)
1.1E-02
1.0E-02 2.0E-03 1.0E-02 (Category B2) Probable human
carcinogen, based on sufficient
evidence in animals and inade-
quate or no evidence in
humans
6.0E-03 6.0E-03 6.0E-03 (Category B2) Probable human
carcinogen, based on sufficient
evidence in animals and inade-
quate or no evidence in
humans
Risk Characterization
Increased lifetime cancer risk (ILCR) estimates and noncancer hazard indexes (His) were
calculated for all compounds detected in samples collected between January 1994 and February
1996. The data collected between these dates provide the best evaluation of the spatial extent of
groundwater contamination. Total ILCR and noncancer His were calculated by summing the
risk from the ingestion, inhalation, and dermal contact pathways associated with each
compound in each sample collected between January 1994 and February 1996.
A summary of the most frequently detected compounds in the UAU and the MAU/LAU is
presented in Table 7. This table contains the minimum and maximum concentration detected;
the minimum, maximum, and mean total ILCR; and the minimum, maximum, and mean HI for
each compound detected.
PCE and TCE were detected most frequently in the UAU and the MAU/LAU wells. The
highest ILCR associated with PCE and TCE in the UAU was 5 x 10"5 and 4 x 105, respectively.
The highest ILCR associated with PCE and TCE in the MAU/LAU was 8 x 10'7 and 5 x 10",
respectively. 1,2-Dibromoethane (ILCR=3 x 103) and benzene (ILCR=2 x 10"*) have the highest
ILCRs. An HI greater than one is also associated with 1,2-dibromoethane (HI=5) and benzene
(HI=8).
11-36
RDD-SFO/982450006.DOC (CLfl263.DOC) (97)
-------
TABLE 7
Sitewide Risks tor VOCs Detected between January 1994 and February 1996 at IBW-Soutti
Concentration (mg/L)
Parameter
No. of
Detects
No. Of
Samples
Mln
Max
Mln
Risk
Max
Hazard Index
Mean
Mln
Max
Mean
Upper Alluvial Unit
1 ,2-Dibromoethane
Benzene
Trichloroethene (TCE)
Tetrachloroethene
(PCE)
Lower and Middle Alluvial
1 ,2-Dibromoethane
Bromodichloromethane
Trichloroethene
1,2-Dichloroethane
Tetrachloroethene
Chloromethane
Benzene
Methylene Chloride
8
12
139
194
Unit
5
2
116
4
96
1
1
9
205
355
354
355
92
243
258
243
253
241
238
247
0.0002
0.002
0.0001
0.00006
0.0006
0.0008
0.0002
0.0002
0.0001
0.0008
0.0002
0.0002
0.003
0.14
0.09
0.059
0.002
0.002
0.0174
0.0014
0.006
0.0008
0.0002
0.001
2.1E-04
3.3E-07
4.1E-08
4.6E-08
6.3E-04
2.8E-06
8.1E-06
1.0E-06
7.7E-08
3.5E-07
3.3E-07
3.3E-08
3.1E-03
2.3E-04
3.6E-05
4.6E-OS
2.1E-03
6.9E-06
5.3E-06
2.0E-06
7.7E-07
3.5E-07
3.3E-07
5.9E-08
1.3E-03
8.7E-05
5.7E-06
4.1E-06
1.3E-03
4.9E-06
2.2E-06
1.4E-06
3.8E-07
3.5E3-05
3.3E-07
5.9E-08
3.6E-01
1.2E-02
2.2E-03
8.0E-04
1.1E+00
5.2E-03
4.4E-03
7.2E-03
1.3E-03
2.9E-02
1.2E-02
1.2E-04
5.4E+00
8.4E-t-00
2.0E+00
6.5E-01
3.6E+00
1.3E-02
2.9E-01
1.4E-02
1.3E-02
2.9E-02
1.2E-02
4.1E-04
2.2E-00
3.2E+00
3.1E-01
7.9E-02
2.4Et£0
9.1E-03
1.2E-01
9.6E-03
6.5E-03
2.9E-02
1.2E-02
2.1E-04
ROD SFO/982460003 DOC-1 (CAH349.DOC)
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R DECISION SUMMARY
Under the NCP, remediation goals are based on ARARs or other reliable information (NCP,
40 CFR Section 300.430(e)(2)). For known or suspected carcinogens, acceptable exposure levels
are generally concentration levels that represent an excess upper bound lifetime cancer risk to
an individual of between 1 x 10"* and 1 x 10"* using information on the relationship between
dose and response. The 1 x 10* risk level is a point of departure for determining remediation
goals when ARARs are not available or are not sufficiently protective because of the presence of
multiple contaminants at a site or multiple exposure pathways. An HI (the ratio of chemical
intake to the reference dose) greater than one indicates that some potential exists for adverse
noncancer health effects associated with exposure to the contaminants of concern.
If residents were exposed to TCE and PCE in the groundwater through drinking water or
routine household uses, the potential for increased cancer risks and noncancer health effects
exists. Action is warranted under EPA's risk assessment for that reason and because contami-
nation exceeds MCLs, which are standards adopted for the protection of human health and
which are, under the NCP, standards relevant and appropriate for the restoration of drinking
water, and because it is expected that the aquifer will be restored to meet drinking water
standards.
11-38 RDD-SFO/982450006.DOC (CLH263.00C) (97)
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H DECISION SUMMAflY
8.0 Description of Remedial Alternatives
An FS was prepared in August 1997 to evaluate remedial alternatives for VOCs in groundwater
at IBW-South. The remedial alternatives were developed to meet the Remedial Action Objec-
tives (RAOs). RAOs are narrative statements that define the extent to which sites require
cleanup to meet the underlying objectives of protecting human health and the environment.
RAOs reflect COCs, exposure routes and receptors, and acceptable contaminant levels (or a
range of acceptable contaminant levels) for each medium. RAOs can be divided into general
RAOs that can be applied to all CERCLA sites, and specific RAOs that reflect site-specific
conditions at IBW-South.
Remedial Action Objectives
The general RAOs for remedial actions at IBW-South include the following:
• Maintain protection of human health and the environment by reducing the risk of potential
exposure to contaminants
• Expedite site cleanup and restoration
• Use permanent solutions Ito the maximum extent practicable
• Restore contaminated groundwater to the extent practicable to support existing and future
uses
• Achieve compliance with applicable or relevant and appropriate requirements (ARARs)
• Minimize untreated waste
The specific RAOs for the groundwater below IBW-South include the following:
• Protect human health by minimizing the potential for human exposure to groundwater
exceeding cleanup goals
• Cost-effectively reduce contamination in groundwater to concentrations that meet cleanup
goals to return ground waters to their beneficial uses to the extent practicable within a time
frame that is reasonable, given the particular circumstances of the site
• Protect groundwater resources by preventing or reducing migration of groundwater
contamination above ARARs.
Action is warranted because groundwater contamination exceeds MCLs, which are associated
with unacceptable risk to human health and the environment, and it is expected that the aquifer
will be restored to meet these drinking water standards. Thus, remedial actions should
minimize the potential for future human exposure to contaminated groundwater.
Given these RAOs, several alternatives were assembled from the applicable remedial tech-
nology process options and were screened for their effectiveness, implementability, and cost.
The alternatives passing this screening were then evaluated in further detail against the nine
criteria required by the NCP. This section provides a description of each alternative that was
RDD-SFOV982450006.DOC (CUC63.00C) (97) 11-39
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I DECISION SUMMARY
retained for the detailed screening analyses in the FS. These alternatives consider No Action, as
required by the NCP, to provide a point of comparison for other alternatives.
The six alternatives that were retained for detailed analysis in the FS are:
• Alternative 1: No Action
• Alternative 2: Monitored Natural Attenuation
• Alternative 3: Limited Action: Wellhead Treatment at COT No. II
COT Potable Water
• Alternative 4: Partial Containment: Extraction Wells/Treatment Plant Air
Stripping/Discharge to Town Lake via City of Tempe Storm
Drain/Monitored Natural Attenuation
• Alternative 5: Regional Containment: Extraction Wells/Treatment Plant Air
Stripping/Discharge to SRP Tempe Canal No. 6
• Alternative 6: Regional Containment: Extraction Wells/Treatment Plant Air
Stripping/Aquifer Reinjection
In the Proposed Plan, EPA selected Alternative 4 as the preferred remedy. After reviewing
public comments on the Proposed Plan, and after additional data were collected and evaluated,
that alternative was modified from that described in the Proposed Plan, although the general
components of the preferred remedy remained the same. Section 10.0 provides an explanation
of the significant differences between the preferred alternative in the proposed plan and the
selected remedy. The components of the selected remedy and the contingency remedy are
described in this section, along with the alternatives listed above that were evaluated in the FS
and the Proposed Plan. Additional information and analysis of the selected remedy and
contingency remedy are provided in Sections 9.0,10.0, and 11.0.
A description of the cost estimating procedures is provided below, followed by additional
information for each alternative.
Cost Estimating Procedures
The alternatives were evaluated in terms of capital costs, annual operation and maintenance
(O&M) costs, and present worth costs. Capital costs include the sum of the direct capital costs
(materials, equipment, labor, land purchases) and indirect capital costs (engineering, licenses,
or permits). Annual costs include the cost for labor, O&M, materials, energy, equipment
replacement, disposal, and sampling to operate the treatment facilities. Present worth costs
include capital costs and O&M costs calculated over an approximate 30-year period.
The accuracy of costs is subject to substantial variation because the specific design of each
alternative (e.g., design details, the bidding climate, changes during construction and opera-
tion, interest rates, labor and equipment rates, tax effects, and other similar items) will not be
known until the time of actual implementation of the remedy.
Remedial Design efforts may reveal that it is possible to reduce the original project cost esti-
mates. Design assumptions presented here may change. This is acceptable because details of the
remedial alternatives presented here are conceptual in nature and subject to refinement during
remedial design. Reductions in the estimated costs could be the result of value engineering
H-40 RDD-SFO/982450006.DOC (Ofl263.DOC) (97)
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• DECISION SUMMARY
conducted during Remedial Design (RD). Through the value engineering process, modifica-
tions could be made to the functional specifications of the remedy to optimize performance and
minimize costs. These changes would fall within the definition of "non-significant modifica-
tions," as defined by EPA's guidance for preparing Superfund decision documents. For exam-
ple, it may be determined that a reduction in costs could be affected by non-significant changes
to type, quantity, and/or cost of materials, equipment, facilities, services, and supplies used to
implement the remedy. It should be noted that this type of design variance may have a notice-
able impact on the estimated cost of the remedy, but will not affect the remedy's ability to com-
ply with the performance standards.
The present worth analysis is used to evaluate expenditures that would occur over an assumed
30-year operation period by discounting all future costs to a common base year. This allows the
cost of remedial action alternatives to be compared on the basis of a single figure representing
the amount of money that, if invested in the base year and disbursed as scheduled, would be
sufficient to cover the costs associated with the remedial alternative over its planned life.
Features Common to All Remedial Alternatives
The five remedial alternatives (other than the No-Action Alternative) evaluated in the FS, and
the selected remedy and contingency remedy have common features. The cost estimates for
each alternative include costs for each of these features. The common features are listed below:
• Institutional Controls—Institutional controls are put in place to protect the public from
exposure to contaminated groundwater exceeding aquifer cleanup levels until cleanup
goals are met. Institutional controls will include various Arizona well siting, permitting/
and construction restrictions, and notices distributed by the Arizona Department of Water
Resources, Arizona Department of Health Services, or EPA concerning risks from exposure
to contaminated groundwater. Additional institutional controls to prevent interference with
EPA's remedial efforts also may be established.
• Compliance Monitoring-To ensure that the performance standards are met for ground-
water, a long-term monitoring program was included in each alternative and the selected
remedy and contingency remedy. The monitoring program will be designed and imple-
mented during Remedial Design/Remedial Action (RD/RA) and will continue throughout
the implementation of the selected groundwater remedy. The monitoring program will
assess compliance with the remediation levels in the groundwater system, monitor effluent
chemical concentrations after VOC treatment, and evaluate the horizontal and vertical
migration of contamination. Details of the monitoring program will be determined by EPA
during the RD. The monitoring program will include, at a minimum, the following:
analytical parameters and methods; indicator parameters; monitoring locations; monitoring
frequency and duration; sampling methods; well installation, and maintenance and aban-
donment procedures; reporting methods and procedures for tracking and maintaining
sample records; and quality assurance (QA) methods.
• Well Sealing or Abandonment-Well SRP23E,2.9N will be sealed to eliminate this potential
path of VOC contamination from the UAU to the MAU. In addition, other monitoring wells
that are not required for compliance or natural attenuation monitoring will be properly
abandoned as appropriate.
RDD-SFO/962450006.DOC(CLR263.00C)(97) Ml
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IIOEOSJONSUMMRV
Another common feature to all alternatives is the Five-Year Review. The cost of this review was
not included in the alternatives. Five-year reviews will be conducted as a matter of policy,
because it will take more than 5 years to achieve aquifer cleanup levels to allow for unlimited
use and unrestricted exposure. EPA will conduct a 5-year review within 5 years of construction
completion to ensure protection of human health and the environment. This review will eval-
uate the effectiveness of the remedy and institutional controls. An additional purpose for the
review is to evaluate whether the performance standards specified in this ROD remain
protective of human health and the environment. EPA will continue the reviews until no haz-
ardous substances, pollutants, or contaminants remain at IBW-South above aquifer cleanup
standards.
Groundwater Treatment Component
A common feature to Alternatives 4,5, and 6 is the use of a representative treatment process
option for the ex-situ treatment component of the groundwater remedy. Air stripping with
vapor-phase granular activated carbon (VGAC) for offgas treatment was selected as the
representative treatment process option, as described in Section 6.2.3 and Appendix C of the
Groundwater FS (EPA, 1997.) A representative process option was selected to simplify the
subsequent development and evaluation of alternatives and the cost estimate. The treatment
component of the remedy will use presumptive technologies identified in OSWER Directive
9283.1-12. One or a combination of those technologies will be used for VOCs in extracted
groundwater. The specific treatment process will be finalized during the remedial design
phase, based on information to be gathered at that time..
The following treatment processes passed the screening of treatment options using the criteria
of effectiveness, implementability, and cost: liquid-phase granular activated carbon (LGAC),
air stripping with VGAC, and Ultraviolet Light Oxidation (UV/Ox). Each of these treatment
processes could be used for groundwater remediation at IBW-South. A brief description of each
treatment is provided below:
• LGAC—This process option uses direct contact of the contaminated water with activated-
carbon to promote adsorption of contaminants onto the carbon.
• Air Stripping/VGAC Offgas Treatment—This process option combination uses air-water
contacting towers to promote transfer of contaminants from the water into an airsrream.
The airsrream is then passed through an activated carbon bed where the contaminants
adsorb onto the carbon.
• UV/Ox—This process option uses a chemical reagent and UV light to oxidize the con-
taminants. The reagent used is an aqueous solution of hydrogen peroxide or ozone.
Each of these technologies, if selected, would be designed to attain chemical-specific discharge
requirements and to maximize long-term effectiveness and reliability while minimizing long-
term operating costs.
Table 8 describes the components, cost, and estimated restoration time frame for the alter-
natives evaluated in the FS. The selected remedy and contingency remedy are also described.
The area that will be hydraulically contained is listed in addition to the treatment technology
and discharge location. Table 8 provides the number of new monitoring and extraction wells
included in each alternative, and the total annual extraction rate. The capital cost, annual O&M
cost, and 30-year present worth costs are provided. The estimated total lengths of conveyance
IM2 RDD-SFO/982450006.DOC (OR263.DOC) (97)
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TABLES
Components of Selected Remedy, Contingency Remedy, and Alternatives Evaluated in Feasibility Study
Component Alternative 1«
Estimated Restoration Time >50
Frame (years)0
Conlainmentd None
Treatment6 Non*
Discharge End Use1 Nooe
Number of New Monitoring and 0
Extraction WellsO
Total Extraction Rate (ac-ft/yr) 0
Capital Cost (S) 0
Annual O*M cost ($) 0
30-year Present Worth Cost ($) 0
Conveyance Pipeline Length None
from Extraction Wells to
Treatment Plant (linear feet)
Distribution Pipeline Length Irom None
Treatment Plant to Discharge
Location (linear feet)
Alternative!
>50
None
None
None
Five monitoring welt
0
890.000
100.000
2.580.000
Nooe
None
Alternatives
>50
None
Wellhead air stripping at
COT No. 7 with oftgas
treatment by VGAC
City of Tempe Potable Water
Distribution System by pipeline
Negligible
1.240.000
440.000
8.000.000
None
None
Alternative 4
(Selected Remedy)
<30
Partial
Air stripping with olfgas
treatment by VGAC
To be d«imrtWi6dc
Three UAU extraction wells. 10
UAU monitoring wels
4.740
6.170,000
1.060.000
22,460.000
10.900
50
r*ftr»tJnr*» n rtt
vontinpteicy
H§flWrtjp
<30
Partial
Air stripping with olfgas
treatment by VGAC
(1 additional tower)
To be aetermned*
To be determined during
Remedial Design for the
contingency
2.420
2.410.000
10.000
2.570.000
11,300
0
Alternatives
<30
Complete
Air stripping with offgas
treatment by VGAC
SRP Temps Cera! No. 6 by
pipeline
Twelve extraction wells; fjve
monitoring wets
14.070
12.600.000
1.540.000
36.270.000
20.240
3.600
Alternative 6
<30
Complete
Air stripping with otfgas
treatment by VGAC
Aquifer rsnjecSon to
MAU
Twelve extraction wells,
eight monitoring weds
15,660
21.260.000
1.800.000
48.930.000
31.240
27.000
Alternative 1: No action.
Alternative 2: Monitored Natural Attenuation
Alternative 3: Limited Action: WeUhead Treatment at City of Tempo Wall No. 7 /City of Tempe Potable Water
Alternative 4: Partial Containment: Extraction Wels/Treatmant Plant Air Stripping/ Discharge to Town Lake via City of Tempe Storm Drain/Monitored Natural Attenuation
Alternative 5: Regional Containment: Extraction WeBs/Treatment Plant Air Stripping/ Discharge to SRP Tempe Canal No. 6
Alternative 6: Regional Containment: Extraction WeRs/Treatment Plant Air Stripping/Aquiter Reinfection
b
Only the components that need to be added to the selected remedy are listed. I.e.. only the additional cost is shown, not th* total cost of the selected and contingency remedies.
As described in Table 9.
4 Partial containment refers to a volume of groundwater contaminated above MCLs that is less than the total volume of contaminated groundwater at the site, and includes only contamination in the upper aquifer (UAU). Complete
containment refers to the entire volume of contamination above MCLs both in the UAU and MAU.
' Another treatment option may be implemented as described in the Proposed Plan, either LGAC or UV/Ox.
1 The final discharge end use will be determined during Remedial Design, and will be to one of the end uses evaluated in the FS and Proposed Plan, specificaty Town Lake, SRP Tempe Canal No. 6, and/or aquifer reinjection to the
MAU. For costing purposes. Town Lake was assumed to be the discharge location.
' The number of new monitoring and extraction wells is an estimate and may increase or decrease depending on site condtttona during Remedial Design.
ROD-SFO/S82650002 982650002 DOC (V1N3S3 DOC) (97)
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II DECISION SUMMOflY
and distribution pipeline that must be constructed are also included in the table. The estimated
restoration time frame is provided, which is the number of years estimated for groundwater
concentrations to reach MCLs throughout the entire contaminated areas. These numbers were
estimated using a groundwater flow and solute transport model documented in the Technical
Memorandum re Documentation of the Indian Bend Wash-South Groundwater Flow and Solute
Transport Models (EPA, 1998), which is part of the Administrative Record.
Included in the description of each alternative below is a discussion of whether the RAOs
would be met by the alternative. A component in the evaluation of overall protection of human
health and the environment is the prediction of how far the contaminated areas will migrate. A
groundwater flow model and a solute transport model were used to simulate migration of the
contaminant plumes. The results were presented in Appendix E of the Groundwater FS
(EPA, 1997c). The model simulations required an initial concentration for the contaminant
being modeled. In the FS, these initial concentrations were specified using water quality data
through July 1994.
An updated solute transport analysis was performed subsequent to the publication of the
Proposed Plan. The update incorporated more recent water quality data collected as of October
1997. The results of the updated solute transport analysis were presented in a technical memo-
randum (EPA, 1998), and were used to answer the following two questions for each alternative:
• Will MCLs (in situ groundwater cleanup ARARs) be met within a reasonable time?
• Does the MCL target volume expand before remediation goals are met?
The answers to these two questions for each alternative are summarized in Table 9 and will be
discussed in more detail below in each alternative description.
8.1 Description of No-Action Alternative
Evaluation of the No-Action Alternative is required under CERCLA because it is used as a
baseline to compare alternatives. Under this alternative, no remedial action would be under-
taken to treat, contain, or remove contaminated groundwater at IBW-South. No monitoring
would be conducted and no institutional controls established.
Some reduction in the volume, toxicity, or mobility of the contaminants would occur as a result
of unmonitored natural attenuation processes.
No treatment or containment components would be associated with this alternative. Under the
No-Action Alternative, some reduction in risk would occur but it would be unmonitored. The
RAOs would not be met for this alternative because contaminants would migrate offsite
without reaching MCLs within a reasonable time frame, and protection of human health and
the environment would not be achieved.
In addition, chemical-, location-, and action-specific ARARs would not be met.
8.2 Alternative 2-Monitored Natural Attenuation
Under Alternative 2, contamination in the groundwater would be reduced by natural attenua-
tion alone. Groundwater contaminants would be allowed to degrade, dilute, or disperse
through naturally occurring physical, chemical, and biological processes. Monitoring to verify
H-44 RDD-SFO/962450006.DOC (CXR263.DOC) (97)
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TABLE 9
Results of Solute Transport Analysis for TCE and PCE
f. Will MCLs (in situ groundwater cleanup ARARs) be met within a reasonable lime?
2. Does the MCL target volume expand before remediation goals are met?
Contaminant
Area
Alternatives 1.2.3
No Action, Natural Attenuation, and
Limited Action at COT Well No. 7
Alternative 4
Selected Remedy
Alternatives 5,6
Groundwater Extraction and
Treatment of Entire Contaminant
Area* in UAU and MAU
UAU Western
Contaminant Arm
(TCE)
1. No. MCLs will not be met within
approximately 30 years.
2. Trie westernmost contaminant area
would migrate at least 7,000 (eet
downgradient.
1. Yes. MCLs could be met within
less than approximately 30 years.
2. Contaminant area does not
expand.
1. Yes. MCLs are achieved In less than
approximately 30 years.
2. Contaminant area does not expand.
UAU Central
Contaminant Area
(TCE)
1. Yes. MCLs will be met in less than
approximately 30 years.
2. Contaminant area would expand less
than 500 feel.
1. Same results as Alternatives 1,
2. and 3.
2. Same results as Alternatives 1.
2. and 3.
1. Yes. MCLs are achieved in less than
approximately 30 years.
2. Contaminant area does not expand.
UAU Eastern
Contaminant Area
(PCE)
1. Yes. MCLs will be met within a
reasonable time.
2. Contaminant area migrates about 2.000
feet in the UAU.
I.Yes. MCLs could be met in less
than approximately 30 years
within the entire contaminant
area.
2. A portion of the contaminant
area migrates approximately
2,000 feet before it reaches
MCLs.
1. Yes. MCLs can be met In less than
approximately 30 years.
2. Contaminant area does not expand.
MAU-B (TCE)
1. Yes. TCE concentrations would reduce
from 11 ppb to below 5 ppb in less than
approximately 30 years.
2. MCL contaminant area In MAU-B would
expand downgradient less than 2,000 feet.
1. Same results as Alternatives 1,
2, and 3.
2. Same results as Alternatives 1,
2, and 3.
1. Yes. MCLs can be met in less than
approximately 30 years.
2. Contaminant area does not expand.
MAU-C (TCE)
1. Yes. TCE concentrations would reduce
from 7 ppb to below 5 ppb in less than
approximately 30 years.
2. MCL contaminant area in MAU-C would
expand downgradient less than 2.000 feet.
1. Same results as Alternatives 1,
2. and 3.
2. Same results as Alternatives 1.
2. and 3.
1. Yes. MCLs can be met In less than
approximately 30 years.
2. Contaminant area does not expand.
RDD-SFO/982650003 DOC (VIN354.DOC)
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U DECISION SUMMARY
that these processes are occurring is included in this alternative. The potential for the biological
component of the natural attenuation process to be occurring at IBW-South was evaluated in
the Groundwater FS. There is not evidence that widespread biodegradation is occurring. The
physical processes of dilution and dispersion are the most significant components of natural
attenuation at the site.
Groundwater monitoring would be conducted to assess and verify the effectiveness of the
natural attenuation processes. Institutional controls would be needed to protect the public from
exposure to contaminated groundwater while natural attenuation was taking place.
Approximately 50 existing wells would be in the monitoring network. The monitoring program
for natural attenuation in this alternative, and as a component in the remaining alternatives,
will follow EPA's interim final OSWER Directive 9200.4-17.
Data that may be required as part of a natural attenuation verification program include the
following: VOCs; dissolved oxygen (DO); nitrate; ferrous iron (Iron II); dissolved manganese;
sulfate; sulfide; methane, ethane, and ethene; alkalinity; oxidation/reduction potential (Redox);
pH; temperature; electrical conductivity (EC); chloride; and total organic carbon (TOC).
ARARs would eventually be met in most of the contaminated areas; however, the aquifer
cleanup goals would not be met within a reasonable time frame in the western contaminated
area. The contaminated area in the MALI would migrate approximately 2,000 feet before TCE
concentrations were reduced to the MCL of 5 ug/L. The eastern UAU area of contamination
would migrate approximately 2,000 feet before PCE concentrations were reduced to MCLs. The
western area of contamination would migrate greater than 7,000 feet before TCE concentrations
were reduced to MCLs.
8.3 Alternative 3-Limited Action: Wellhead Treatment
at COT NoJ/COT Potable Water
The objective of Alternative 3 is to provide a limited action that would allow the City of Tempe
to use COT No. 7 to provide water meeting drinking water standards for public water supplies
on an as-needed basis.
Under Alternative 3, the well would be used intermittently, and wellhead air stripping would
be conducted to remove VOCs from the existing COT No. 7. Following treatment, the treated
water would be conveyed by pipeline to the City of Tempe potable water distribution system.
Offgas generated from the air stripping process would be treated using VGAC. Routine
monitoring of the influent to and effluent from the treatment unit would be conducted to assess
operational conditions and to ensure that drinking water standards were achieved. No
additional monitoring of the contaminated areas, or of MNA, would be performed. The major
components of Alternative 3 are provided in Table 8.
Similar to Alternative 2, ARARs related to drinking water source protection would not be met
because the migrating areas of contamination would exceed MCLs in currently uncontaminated
areas,and the western area of contamination would not reach MCLs within a reasonable time
frame. The migration of the areas of contamination and the risk reduction would be the same as
in Alternative 2. The extent of contaminant migration was described in Table 9.
IM6 RDO-SFO/9824S0006.DOC (CIR263.DOC) (97)
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« DECISION SUMMARY
8.4 Alternative 4-Partial Containment: Extraction Wells/
Treatment Plant Air Stripping/Discharge to Town Lake via
City of Tempe Storm Drain/Monitored Natural Attenuation
As Described in Proposed Plan
This alternative included extraction of a partial target volume, which was defined as the area of
highest VOC-contaminated groundwater from the UAU aquifer in the central and eastern con-
taminated areas where concentrations are above 20 to 30 ug/L and the entire western UAU
contaminated area where VOCs are above MCLs. The partial target volume was developed to
establish a volume of water that is less than the regional target volume (defined as ground-
water in which VOC concentrations are above the MCLs) which, when pumped and treated
and combined with natural attenuation of the remaining portions of the regional target volume,
would meet cleanup levels within a reasonable time frame. The partial target volume was
established based on extracting the highest levels of contamination in the UAU and performing
groundwater modeling to determine if this volume is sufficient to ensure that groundwater
MCLs will be met within a reasonable time frame (less than 100 years, as described in the
Proposed Plan) without migrating a far distance before cleanup levels are met.
The extracted groundwater within the partial target volume is piped to a centralized treatment
system and the VOCs are removed from the groundwater by air stripping. VOC-contaminated
offgas from air stripping is treated by using VGAC vessels. The treated water would then be
delivered to the City of Tempe storm drain system, the SRP Tempe Canal No. 6, or reinjected to
the MAU aquifer. The Proposed Plan stated that the exact end use for the treated groundwater
would be determined during remedial design for the remedy.
Routine monitoring of the groundwater before and after treatment would be conducted to
assess operational conditions and ensure cleanup goals are met. The portion of the UAU that is
not actively pumped and treated, and the MAU aquifer, would migrate a short distance and
naturally attenuate to MCLs within a reasonable time frame. EPA had conducted modeling to
determine how far portions of the VOC-contaminated areas not treated by air stripping could
migrate before reaching cleanup goals through natural attenuation processes. The results, as
presented in the FS, were as follows:
• Western UAU contaminated area-The entire contaminated area is hydraulically contained,
and therefore does not migrate;
• Central UAU contaminated area-Migrates less than 2,000 feet before meeting MCLs
throughout the contaminated area in less than approximately 30 years;
• Eastern UAU contaminated area-Migrates approximately 2,000 feet before meeting MCLs
throughout the contaminated area in less than approximately 30 years;
• MAU contaminated area (Subunits B and C)-Migrates less than 2,000 feet before meeting
MCLs throughout the contaminated area in less than approximately 30 years.
Newly installed wells, in addition to existing monitoring wells, are sampled to monitor the
progress of the decreases in VOC concentrations during the natural attenuation process to
ensure that cleanup levels are met.
RDO-SFOJ982450006.DOC (CLB263.00C) (97) 11-47
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II DECISION SUMMAflY
In situ cleanup ARARs would be met within the portions of the contaminated areas that would
be hydraulically contained. Chemical-specific discharge requirements, presented in Table 12,
will be met prior to discharge to any one of the three potential end uses. Location-specific
ARARs, air quality standards, and waste management ARARs can be met.
Using the validated data through July 1994, ARARs could be met only if a portion of each of the
three contaminated areas in the UAU were extracted. However, as described in the following
section, extraction is not needed in all three areas when the more recent data are evaluated. The
following section describes the selected remedy.
Selected Remedy-Partial Containment: Extraction Wells/Treatment Plant
Air Stripping/Discharge to Town Lake, SRP Tempe Canal No. 6, or
Aquifer Reinjection/Monitored Natural Attenuation
A brief description of the selected remedy is provided here. Additional information is provided
in Sections 9.0,10.0, and 11.0. As described in those sections, the selected remedy is Alterna-
tive 4, as modified on the basis of public comments on the Proposed Plan and results of the
groundwater evaluation using data collected through October 1997. Major components of the
selected remedy are described in Table 8. Contaminated groundwater will be extracted only
from the western contaminated area in the UAU. MNA will be used to meet the RAOs in the
remaining portions of the central and eastern contaminated areas in the UAU, and for the entire
contaminated area within the MAU.
The exact location of the treatment plant, and the exact end use for extracted groundwater will
be determined during remedial design.
All ARARs are expected to be met. The contaminated areas that will not be hydraulically
contained are expected to migrate less than 2,000 feet before reaching MCLs, and all
groundwater concentrations are expected to reach MCLs within approximately 30 years.
Contingency Remedy-Additional Groundwater Extraction and Treatment
As described in Section 11.0, a contingency remedy exists for the situation in which the MNA
portion of the selected remedy does not perform as expected. This contingency remedy will be
activated according to the criteria presented in Section 11.0. A brief description of the contin-
gency remedy is provided here. Additional information is provided in Sections 9.0,10.0, and
11.0. As described in those sections, public comments on the Proposed Plan and the results of
the groundwater evaluation using data collected through October 1997 provided the basis for
the contingency remedy. Major components of the contingency remedy are described in
Table 8.
In addition to the contaminated groundwater that will be extracted from the western
contaminated area in the UAU, groundwater will also be extracted from portions of the eastern
contaminant area of the UAU or MAU. The area and volume of additional groundwater to be
extracted will depend on which of the trigger criteria are exceeded. For costing purposes, it was
assumed that a portion of the eastern contaminated area would be extracted and treated.
Additional assumptions regarding the cost estimate for the contingency remedy are provided
in Appendix A of this ROD. MNA may still be used to meet the RAOs in some portions of the
contaminated areas.
11.46 RDD-SFO/982450006.DOC (CLR263.00C) (97)
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n DECISION SUMMARY
The exact location of any additional treatment plant(s), and the exact end use of the additional
groundwater that will be extracted, will be determined during remedial design for the
contingency remedy.
All ARARs are expected to be met for the contingency remedy. Table 9 lists the estimated
cleanup times and migration distances for the contingency remedy.
8.5 Alternative 5—Regional Containment: Extraction Wells/
Treatment Plant Air Stripping/Discharge to SRP Tempe Canal No. 6
The objective of this alternative was to reach aquifer cleanup goals by extraction and treatment
of all of the groundwater contaminated above MCLs in each contaminated area. This
alternative incorporates discharge of treated water to the SRP Tempe Canal No. 6.
The major components of Alternative 5 are described in Table 8. The conceptual design for
Alternative 5 includes eight extraction wells in the UAU and four in the MAU. Similar to
Alternative 4, contaminated groundwater would be conveyed by pipeline to a centralized air
stripping treatment plant and offgas would be treated using VGAC. The treated groundwater
would be conveyed by pipeline to the SRP Tempe Canal No. 6 for discharge. Routine moni-
toring of the groundwater before and after treatment would be conducted to assess operational
conditions, to ensure that discharge criteria were achieved, and to monitor progress of
remediation.
As indicated in Table 9, contaminated groundwater within the areas of contamination is
expected to meet cleanup standards within a reasonable time frame of less than approximately
30 years. Groundwater that is extracted will be treated to chemical-specific discharge
requirements prior to discharge to SRP Tempe Canal No. 6. The alternative is protective of
human health and the environment because the areas of contamination are hydraulically
contained and do not migrate. Location-specific ARARs, air quality standards, and waste
management ARARs can be met.
8.6 Alternative 6-Regional Containment: Extraction Wells/
Treatment Plant Air Stripping/Aquifer Reinjection
Alternative 6 is similar to Alternative 5, except that the end use of treated groundwater would
be reinjection into the MAU. The major components of Alternative 6 are listed in Table 8. Eight
reinjection wells would inject the treated groundwater into the MAU. As in Alternative 5, the
contaminated groundwater would be conveyed via a new pipeline to a centralized air stripping
treatment plant. The offgas would be treated using VGAC. Routine monitoring of the ground-
water before and after treatment would be conducted to assess operational conditions and to
ensure that cleanup goals were achieved.
As in Alternative 5, all ARARs would be met.
RDD-SFCV982450006.DOC (CIH263.DOC) (97) IM9
-------
I1DECISWN SUMMARY
9.0 Comparative Analysis of Alternatives
The Groundwater FS presented the detailed evaluation of each alternative using the nine
evaluation criteria listed below. Each of the three potential end-use options was evaluated and
included in the selected remedy presented in Section 8 of the Groundwater FS (EPA, 1997c).
This section compares the remedial alternatives described in Section 8.0 of this ROD. The
comparative analysis provides the basis for determining which alternative presents the best
balance among EPA's nine evaluation criteria listed below. The first two cleanup evaluation
criteria are considered threshold criteria that must be met by the selected remedial action. The
next five criteria are balanced to achieve the best overall solution. The final two modifying
criteria that are considered in remedy selection are state acceptance and community acceptance.
• Threshold Criteria
1. Overall Protection of Human Health and the Environment addresses whether a remedy pro-
vides adequate protection and describes how risks posed through each pathway are
eliminated, reduced, or controlled.
2. Compliance with Applicable or Relevant and Appropriate Requirements addresses whether a
remedy will meet all federal and state environmental laws and/or provide grounds for
a waiver.
• Primary Balancing Criteria
3. Long-Term Effectiveness and Permanence refers to the ability of a remedy to provide reli-
able protection of human health and the environment over rime.
4. Reduction ofToxicity, Mobility, or Volume through Treatment refers to the preference for a
remedy that reduces health hazards of contaminants, the movement of contaminants, or
the quantity of contaminants through treatment.
5. Short-Term Effectiveness addresses the period of time needed to complete the remedy,
and any adverse effects to human health and the environment that may be caused dur-
ing the construction and implementation of the remedy.
6. Implementability refers to the technical and administrative feasibility of an alternative or
a remedy. This includes the availability of materials and services needed to carry out a
remedy. It also includes coordination of federal, state, and local government efforts.
1. Cost evaluates the estimated capital and O&M costs of each alternative in comparison to
other equally protective alternatives.
• Modifying Criteria
8. State Acceptance indicates whether the state agrees with, opposes, or has no comment on
the preferred alternative.
9. Community Acceptance includes determining which components of the alternatives
interested persons in the community support, have reservations about, or oppose.
H-SO RDD-SFCV982450006.DOC (OR263.DOC) (97)
-------
I DECISION SUMMARY
The strengths and weaknesses of the alternatives and the contingency remedy were weighed to
identify the alternative providing the best balance among the nine evaluation criteria. The
comparative analysis of the alternatives is provided in the following discussion.
A summary of the results of the comparative analysis of the alternatives and the contingency
remedy is provided in Table 10. The comparative cost of each alternative is also depicted
graphically in Figure 9. The comparative analysis discussions are organized from the best
performing alternatives to the worst performing alternatives within each criterion. Only those
factors where there are substantial differences among the alternatives are discussed.
9.1 Threshold Criteria
Overall Protection of Human Health and the Environment
Overall protection of human health and the environment addresses whether each alternative
and the contingency remedy provides adequate protection of human health and the
environment and describes how risks posed through each exposure pathway are eliminated,
reduced, or controlled through treatment, engineering controls, and /or institutional controls.
Table 10 presented the estimated distances each contaminated area would migrate for each
alternative. The table also indicated whether the aquifer could be restored to the MCLs for TCE
and PCE, the two main COCs, within a reasonable time frame of approximately 30 years.
Alternatives 5 and 6 are marginally more protective of human health and the environment (i.e.,
the groundwater resource). Under these alternatives, all groundwater contamination exceeding
aquifer cleanup standards, the majority of which are MCLs, is hydraulically contained by
pumping from extraction wells, and groundwater is restored within a reasonable time frame
and more rapidly than other alternatives. No new areas of groundwater would be impacted.
Alternative 4, the selected remedy, is also protective of human health and the environment.
Contamination in the western area will be remediated by extraction and treatment within a
reasonable time frame. Some portions of groundwater contaminated areas that exceed aquifer
cleanup standards will migrate downgradient. However, MNA is expected to reduce
contaminant concentrations in those portions of the groundwater so that the groundwater is
restored and site risks are reduced within a reasonable time frame. Groundwater monitoring
and institutional controls will provide protection of human health and the environment. No
currently used groundwater wells are impaired, and aquifer cleanup standards will be reached
in approximately 30 years sitewide.
Alternative 2 is less protective than the active remediation actions taken under Alternatives 4, 5,
and 6. Alternative 2 relies entirely on MNA and institutional controls to achieve protection of
human health and the environment. Under this alternative, more extensive migration into
currently uncontaminated areas of the aquifer would occur, and the aquifer would not be
restored within a reasonable time frame. Institutional controls would be required over a larger
area than in Alternative 4. Alternative 3 provides a very similar level of protection as
Alternative 2. The primary difference is the lack of monitoring for Alternative 3.
The No-Action Alternative provides no overall protection to human health or the environment
because no monitoring is performed and no institutional controls are put in place to protect the
public from exposure to contaminated groundwater.
ROD-SFO/982450006.DOC (CLR263.DOC) (97) 11-51
-------
R DECISION SUMMARY
The contingency remedy is also protective of human health and the environment. It will ensure
that migration of contaminants in natural attenuation areas is limited, if necessary, and that
aquifer cleanup levels are achieved in a reasonable time frame.
Compliance with ARARs
Section 121(d) of CERCLA requires that remedial actions at CERCLA sites attain legally
applicable or relevant and appropriate federal and state requirements, standards, criteria, and
limitations which are collectively referred to as "ARARs," unless such ARARs are waived
under CERCLA Section 121(d)(4).
Applicable requirements are those substantive environmental protection requirements, criteria, or
limitations promulgated under federal or state law that specifically address hazardous sub-
stances, the remedial action to be implemented at the site, the location of the site, or other
circumstances present at the site. Relevant and appropriate requirements are those substantive
environmental protection requirements, criteria, or limitations promulgated under federal or
state law which, while not applicable to the hazardous materials found at the site, the remedial
action itself, the site location or other circumstances at the site, nevertheless address problems
or situations sufficiently similar to those encountered at the site that their use is well-suited to
the site.
As indicated in Table 10, Alternatives 4 (selected remedy), 5, and 6, and the contingency
remedy would fully comply with all ARARs (chemical-, location-, and action-specific).
Chemical-specific ARARs for aquifer remediation would be achieved within a reasonable time
for each of these alternatives.
Aquifer cleanup standards would not be met in a reasonable time for Alternative 2 in the
western contaminated area. Modeling indicates that MCLs would be met within a reasonable
time frame for the central and eastern areas of UAU contamination and in the MAU. The
majority of aquifer cleanup standards are MCLs for the COCs. Alternative 3 is similar to
Alternative 2 in its level of compliance with ARARs.
The No-Action Alternative is similar in performance to Alternatives 2 and 3 and would not
comply with ARARs. The No-Action Alternative provides the least compliance with ARARs
because no institutional controls would be in place to protect the public from ground water
contaminated above regulatory limits, and no monitoring is performed, so the areas of
contamination would migrate unchecked. Each of the three potential groundwater end uses
and each of the three potential treatment process options would meet ARARs.
Each of the three potential groundwater end uses and each of the potential treatment process
options would meet ARARs. The contingency remedy would also comply with ARARs.
9.2 Primary Balancing Criteria
Long-Term Effectiveness and Permanence
Long-term effectiveness and permanence refers to expected residual risk and the ability of a
remedy to maintain reliable protection of human health and the environment over time, once
cleanup levels have been met. This criterion includes the consideration of residual risk and the
adequacy and reliability of controls.
11-52 RDD-SFO/982450006.DOC (CLR263DOC) (97)
-------
Vltematives with EPA's Nine Evaluation Criteria
Irlteria
ption
i of Human
ivironment
VRARs
veness
aty.
a through
iveness
331
it Worth
Alternative 1
No-Action
No
No
No, does not reduce long-
term risk
None
Not applicable
Not applicable
SO
SO
SO
Alternative 2
Natural Attenuation: Well
Permit Requirements/
Groundwater Use
Restrictions/ Groundwater
and Verification Monitoring
No; aquifer cleanup
standards will not be met in
the UAU in a reasonable
time frame.
No; aquifer cleanup
standards will not be met in
the UAU In a reasonable
time frame.
No; same as Alternative 1
None
Construction-related risks
can be minimized.
Yes; equipment and
services are readily
available.
$890.000
$110.000
$13,950.000
Alternative 3
Limited Action: Weihead
Treatment at COT No. 71
COT Potable Water Wen
Permit Requirements/
Groundwater Use
Restrictions/Groundwater
Monitoring
No; treated drinking water
from COT No. 7 would pose
no risks, but contaminated
arsas will migrate a/id will
not be monitored.
No; same as Alternative 2.
No; same as Alternative 1 .
Very little reduction of
toxicrty, mobility, or volume
when treatment occurs at
COT No. 7.
Same as Alternative 2.
Yes; the treatment
technology is proven,
reliable, and readily
available.
$1,240.000
$440,000
$8,000.000
Alternative 4 (EPA's
Selected Remedy)
Partial Containment/
Treatment/COT Storm Drain
leading to Town Lake/
Natural Attenuation Well
Permit Requirements/
Groundwater Use
Restrictions/Groundwater
Monitoring
Yes; groundwater extraction
and MNA will limit migration,
and aquifer cleanup
standards will be met in a
reasonable time frame.
Yes.
Yes; long-term risks are
greatly reduced.
Yes; toxicity and volume are
greatly reduced throughout
the contaminated area.
Mobility is greatly reduced in
the area of highest
contamination.
Additional short-term risks
from construction of
treatment plant and piping.
Yes; the treatment
technology is proven.
reliable, and readily
available. Installation of
pipeline may be difficult
because of existing
conditions.
$6.170,000
$1.060,000
$22.460,000
Contingency Remedy
Additional extraction and
treatment
Same as Alternative 4.
Yes
Same as Alternative 4.
Yes; toxicity and volume are
greatly reduced throughout
the contaminated area.
Mobility is greatly reduced in
the area of highest
contamination.
Slightly more construction
than Alternative 4, but less
than Alternatives 5 and 6.
Same as Alternative 4.
$2.410.000 (additional)1
$10.000 (additional)*
$2.570,000 (additional)*
Alternative '.
Regional Containme
Treatment/Tempo C
No. 6 Well Permit
Requirements/ Grou
Usf Restrictions/
Groundwater Monito
Sarhe as Alternative
Yea
Same as Alternative
Yes; toxicity, mobility
volume throughout
contaminated area ai
reduced.
Short-term risks grea
Alternative 4 resulting
largtr treatment plant
more piping.
Yes; Same as Alterru
except that the Pipelii
mor» extensive and w
result in greater const
mpacts than Alternati
and ihe contingency
remtdy.
$12.600.000
Sl,5ftO,000
$36.^70.000
HI of Alternative 4, ihe selected remedy.
-------
30,000,000
3 25,000,000
H 20,000,000
O
j 15,000,000
10,000,000
5,000,000
^ 4,000,000
(O
K
O
U
S
4
O
3,000,000
2,000,000
1,000,000
0
X
£
u
at
R
70,000,000
60,000,000
50,000,000
40,000,000 - —
30,000,000
20,000,000 4
10,000,000 -[
3
f
«
Selected Contingency
Remedy Remedy*
n
Selected Contingency
Remedy Remedy*
• 5-YEAR
D 30-YEAR
Selected Contingency
Remedy Remedy*
ALTERNATIVES
Note: 'Costs presented fo the Contingency Remedy represent
the total combined costs for Alternative 4 (Selected Remedy) and
the additional costs for the Contingency Remedy
FIGURE 9
COMPARATIVE COST
OF ALTERNATIVES
INDIAN BEND WASH-SOUTH
GROUNDWATER OU ROD
ROO\ODIN\PRCU\147921VflOO SUPPORT\Costf2.xls\FIGURE 9
-------
UOfOSIONSUMMRY
Magnitude of Residual Risk—Alternatives 4,5, and 6, and the contingency remedy have the
lowest magnitude of residual risk. Under these alternatives, extraction and treatment and MNA
of contaminated groundwater exceeding aquifer cleanup standards will reduce residual risk to
acceptable levels within a reasonable time of approximately 30 years. Untreated residual
contamination in groundwater will not pose a risk to human health.
Alternative 2 is higher than Alternative 4 in the magnitude of residual risk during the life of the
remedy because no contaminated groundwater is extracted and treated. Alternative 2 relies
entirely on natural attenuation to reduce contaminant concentrations, and they will not be met
in the western area of contamination within a reasonable time frame. Similar to the other
alternatives, the untreated residual contamination will not pose a risk to human health because
monitoring and institutional controls will be implemented.
Alternative 3 is similar to Alternative 2 in the magnitude of residual risk.
The magnitude of residual risk under the No-Action Alternative is higher than for the other
alternatives because no actions are taken to remediate contamination, and no monitoring or
institutional controls would be in place to protect the public from exposure to contaminated
groundwater.
Adequacy and Reliability of Controls-Alternatives 4,5, and 6, and the contingency remedy
use pump and treat processes that are well-established, reliable, and capable of meeting
performance requirements. No difficulties associated with the long-term operation of these
alternatives are anticipated. VGAC carbon replacement and routine maintenance of air
stripping towers, UV/Ox systems, and extraction wells will be required, but these are standard
operating procedures. Long-term monitoring will assess and ensure the adequacy of the
alternatives at meeting cleanup objectives. The long-term reliability of institutional controls is
somewhat less certain. Institutional controls are subject to changes in political jurisdiction, legal
interpretation, and enforcement.
Under Alternatives 2 and 4, the adequacy and reliability of the MNA portion of each alternative
to meet cleanup goals is somewhat less certain than the pump and treat actions taken under
Alternatives 5 and 6, but MNA is expected to reach cleanup levels in a reasonable time frame in
the central and eastern contaminated areas. However, by setting the contingency criteria to
activate pump and treat. Alternative 4 is more reliable in meeting cleanup goals if MNA fails.
Alternative 2 is less reliable because, unlike Alternative 4, it does not include extraction in the
western contaminated area.
Alternative 3 is similar to Alternatives 4,5, and 6 with respect to the pump and treat aspect of
the alternative. Wellhead air stripping and VGAC treatment of offgas are well-established and
reliable processes. However, Alternative 3 only addresses contaminated groundwater at COT
No. 7 (a much smaller volume) and not overall groundwater contamination at IBW-South, and
would be operated only sporadically.
The No-Action Alternative is inadequate and not reliable because no actions are taken, and no
monitoring is conducted.
Reduction of Toxicity, Mobility, or Volume through Treatment
Reduction of toxicity, mobility, or volume through treatment refers to the anticipated per-
formance of the treatment technologies that may be included as part of a remedy.
11-56 RDO-SfO«82450006.DOC (Ofl263.DOC) (97)
-------
I DECISION SUMUflY
Treatment Processes Used and Materials Treated-Alternatives 4,5, and 6 and the contingency
remedy would use treatment trains which may consist of air stripping with VGAC, LGAC, or
UV/Ox. Alternative 3 would use a treatment train assumed to consist of air stripping and
VGAC treatment of offgas to treat VOC-contaminated groundwater.
Under the No-Action Alternative and Alternative 2, no treatment processes are used.
Degree of Expected Reductions in Toxicity, Mobility, or Volume-Under Alternatives 4,5,
and 6, and the contingency remedy, air stripping, LGAC, or UV/Ox will remove 99.9 percent of
the VOCs in the groundwater extracted from the aquifer. The volume of contaminated ground-
water at concentrations exceeding aquifer cleanup standards is hydraulically contained and
gradually reduced through groundwater pumping.
Alternative 3 is a limited action that will not provide significant reductions in the toxicity,
mobility, or volume of groundwater contamination at IBW-South. This alternative will provide
some minor reduction in the volume of contaminants through occasional pumping of COT
No. 7 and operation of the treatment system, but this is considered insignificant. Alternative 3
is similar to Alternative 2, in that the majority of reductions in contaminant toxicity in the
aquifer will only occur as the result of naturally occurring processes. Migration of contaminated
groundwater will be similar to Alternative 2.
The No-Action Alternative does not provide any reduction in toxicity, mobility, or volume
through active treatment.
Degree to Which Treatment is Irreversible-Under Alternative 3, air stripping with VGAC, and
under Alternatives 4,5, and 6, air stripping with VGAC adsorption of contaminants in the
offgas, LGAC treatment are inherently irreversible treatment processes as long as the spent
carbon is properly disposed of offsite.
Type and Quantity of Treatment Residual-Under Alternatives 3,4,5, and 6, it is assumed that
air stripping treatment would transfer VOCs to air, and this offgas generated from the air
stripping would be treated using VGAC. It is possible that LGAC, UV/Ox may be used as the
treatment option for the selected alternative. However, the calculations of spent carbon for the
alternatives is based on use of air stripping with VGAC offgas treatment. The quantity of spent
carbon under each alternative is as follows, in declining order:
• Alternative 6-160,000 pounds per year
• Alternative 5-150,000 pounds per year
• Contingency remedy-67,000 pounds per year
• Alternative 4 (selected remedy)-44,000 pounds per year
• Alternative 3-unknown, because the amount of intermittent pumping at COT No. 7 cannot
be estimated (but it is much less than the quantity generated under Alternative 4)
• No treatment residuals are generated under the No-Action Alternative and Alternative 2.
RDO-SFCV982450006.DOC (Ofl263.DOC) (97) U-57
-------
II DECISION SUMMARY
Short-Term Effectiveness
Short-term effectiveness addresses the period of time needed to implement the remedy and any
adverse impacts that may be posed to workers and the community during construction and
operation of the remedy until cleanup goals are achieved.
Protection of Community and Workers During Remedial Action—Alternative 2 poses only
minimal risks to the community and workers associated with the installation of natural
attenuation monitoring wells.
Alternative 3 involves construction of a wellhead treatment unit, consisting of an air stripper
and VGAC adsorption vessels, at the COT No. 7. The minimal risk posed to the community is
similar to that posed by Alternative 2. Discharges from the treatment unit will meet local air
district emissions requirements..
Because of the additional construction activities under Alternatives 4,5, and 6, slightly higher
risks are posed than under Alternatives 2 and 3. However, the risks to the community are still
fairly minimal if proper health and safety procedures are followed. Alternative 4 and the
contingency remedy pose less risk than Alternatives 5 and 6 because there is less construction.
Environmental Impacts—Alternatives 2 and 3 pose only minimal risks to the environment
associated with the installation of natural attenuation monitoring wells. Good work practices
will provide environmental protection during remedial action activities. Discharges from the
treatment unit installed for Alternative 3 will meet local air district emissions requirements that
are set to be protective of the environment.
Alternatives 4,5, and 6, and the contingency remedy all involve construction of a treatment
plant(s) using air stripping/VGAC, LGAC, or UV/Ox treatment, installation of conveyance
pipeline, and installation of extraction and monitoring wells. Because of the additional
complexity and scope of these alternatives, slightly higher environmental risks are posed than
under the simpler actions taken under Alternatives 2 and 3. However, similar to Alternatives 2
and 3, the risks to the environment are still expected to be minimal. Risks posed by
Alternative 4 would be slightly less than Alternatives 5 and 6 because there is less construction.
Alternative 6 may pose more risks than Alternative 5 because it requires construction of an
injection well. Discharges from the treatment unit will meet local air district emissions require-
ments that are set to be protective of the environment. Similarly, discharge of treated ground-
water will comply with appropriate regulations for discharge to surface water or aquifer
reinjection.
Alternative 4 has fewer short-term environmental impacts because a considerably smaller
volume of groundwater is extracted, treated, and disposed of. Therefore, less groundwater is
disturbed, less energy is used in treating it, fewer treatment residuals are created, and less
disposal capacity is used.
Time Until Remedial Objectives are Achieved-The estimated times until cleanup goals will be
achieved under each alternative were presented in Table 10 and are as follows:
• Alternatives 4, 5, and 6-less than approximately 30 years for UAU and MAU
• Alternative 2-The western area of contamination UAU will require more than 100 years to
meet MCLs; MCLs will be met in the MAU within approximately 30 years.
11-58 RDD-SFCV982450006.DOC (CUC63.00C) (97)
-------
I DECISION SUMMRV
• Alternative 3 and the No-Action Alternative-similar to Alternative 2, except no monitoring
is conducted to assess progress towards cleanup.
Implementability
Implementability addresses the technical and administrative feasibility of a remedy from
design through construction and operation. Factors such as availability of services and
materials, administrative feasibility, and coordination with other governmental entities are also
considered.
Ability to Construct and Operate the Technology and Reliability of the Technology-All of
the alternatives are expected to be readily constructed and operated using reliable technologies.
Although the natural attenuation technology is less proven than the pump and treat technolo-
gies, it is expected to be reliable.
Alternatives 4,5, and 6, and the contingency remedy all involve construction of air stripping/
VGAC, LGAC, or UV/Ox treatment plant, installation of conveyance pipelines, and installation
of extraction and monitoring wells. Alternative 6 also involves installation of ground water
injection wells. Because of the additional complexity and scope of these alternatives, more
difficulties during construction will likely be encountered than under the simpler actions taken
under Alternatives 2 and 3. Alternative 4 presents fewer implementation problems than
Alternatives 5 and 6 because considerably less construction is necessary in MNA areas. How-
ever, the active treatment components of Alternatives 4,5, and 6 are commonly employed and
not exceptionally difficult to construct or operate. Because IBW-South is in a developed
industrial /commercial area, difficulties may arise associated with the installation of convey-
ance pipelines. Complications caused by obtaining required utility clearances, implementing
traffic controls, and obtaining easements may also be encountered. Such implementability
difficulties are likely to be somewhat more significant for Alternatives 5 and 6 than Alternative
4 because active measures and pipeline cover greater area.
Pilot testing of the groundwater injection wells installed under Alternative 6 may be required.
Operation of the extraction/treatment/aquifer reinjection system under Alternative 6 makes
this alternative the most difficult to construct and operate.
Ability to Monitor Effectiveness of Remedy-No difficulties in the ability to monitor the effec-
tiveness of the remedy are anticipated under Alternatives 2,4,5, and 6, and the contingency
remedy. Groundwater monitoring will be conducted to monitor the effectiveness of the remedy
at reducing contaminant concentrations. For Alternatives 3,4, 5, and 6, treatment plant air and
water effluent monitoring will be conducted without significant difficulty to ensure that
discharge requirements are met. For Alternative 6, water level measurements will also be
routinely collected to evaluate the extent of groundwater mounding near injection wells.
Alternative 3 is a limited action with limited monitoring compared with that conducted under
Alternatives 2,4,5, and 6, and the contingency remedy. No difficulties are anticipated in con-
ducting this monitoring. Wellhead treatment plant air and water effluent monitoring will be
conducted to ensure that discharge requirements are met.
Coordination with Other Agencies-Under each of the other alternatives, considerable coordi-
nation between EPA, ADEQ, ADWR, City of Tempe, and SRP will be required. The level of
effort required to accomplish this coordination for each alternative is uncertain. The inter-
agency coordination issues include the following.
RDO-SFO982450006.DOC (CU363.00C) (97) 11-59
-------
Under Alternative 2, EPA will need to coordinate with state and local agencies including
ADWR, ADEQ, and the City of Tempe (e.g., to obtain necessary substantive permit require-
ments). Natural attenuation engineering evaluations will be performed and provided to
agencies to ensure that future institutional controls are considered and implemented by state
and local authorities to protect the public from VOC-contaminated groundwater.
Under Alternative 3, EPA will need to coordinate with state and local agencies including
ADWR, ADEQ/ and City of Tempe with regard to the community water supply that may be
provided from COT No. 7 in the event of an emergency.
Under Alternatives 4,5,6, arid the contingency remedy, the above coordination as described in
Alternative 2 is required. In addition, if groundwater is extracted from within the SRP service
area and used outside the service area (i.e., Town Lake), discussions will be held with SRP to
consider water quality issues, water rights, water accounting, cost, liability, and operational
concerns. These water rights issues will not affect implementation of the alternative, but could
affect budget and schedule. Coordination between EPA and ADEQ will be required concerning
substantive water quality requirements for discharge to Town Lake, if this is the end use deter-
mined during remedial design. Coordination between SRP and EPA will be required
concerning substantive water quality requirements for discharge of treated groundwater to SRP
Tempe Canal No. 6. Coordination between SRP and EPA will be required if treated ground-
water is injected within the SRP service area. Additional coordination with ADEQ and DWR
may be required on groundwater resource protection issues.
Availability of Offsite Treatment, Storage, and Disposal Services and Capaciry-Under Alter-
natives 2, 4,5, and 6, and the contingency remedy, contaminated groundwater that is purged
from monitoring wells during verification sampling will be disposed of in the City of Tempe
sanitary sewer system if the discharge requirements are met.
For Alternatives 3,4,5, and 6, a vendor will be used to remove, transport, and dispose of spent
carbon from VGAC or LGAC units. These types of vendors are readily available and have
sufficient capacity to handle the volume of carbon to be used at IBW-South.
The amount of treated groundwater to be discharged under Alternative 4 and the contingency
remedy is potentially less than that for Alternatives 5 and 6. The discharge end-use options
under consideration will be able to accommodate the maximum estimated flow rate from the
treatment plant(s) under normal conditions. However, if Town Lake is selected as the end use
of Alternative 4 (selected remedy), the capacity of the existing storm sewer system to convey
treated groundwater to Town Lake may be reduced during storm events, potentially affecting
full flow capacity for storm runoff.
Cost
Table 11 lists the capital, annual O&M, and present worth costs for each alternative. The esti-
mated 30-year present worth for the alternatives, not including the No-Action Alternative,
ranges from $2.6 million for Alternative 2 to $48.9 million for Alternative 6.
RDD-SRy982450006.DOC (CLR2M.OOC) (97)
-------
I DECISION SUMMARY
TABLE 11
Cost
Alternative 1
Alternative 2
Alternative 3
Alternative 4 (Selected Remedy)
Alternative 5
Alternative 6
Contingency Remedy*
Capital Cost
($)
0
890,000
1,240,000
6.170.000
12,600,000
21,260,000
2,410.000
Annual O&M
Cost
($)
0
100,000
440,000
1.060,000
1,540,000
1,600,000
10.000
30-Year Total
Present Worth
($)
0
2,580,000
8,000,000
22,460,000
36.270.000
48,930,000
2,570,000
5-year Total
Present Worth
(S)
0
1,370,000
3,140.000
10.760.000
19.270.000
29,050,000
2.450,000
* The cost of the components that would be in addrtion to the cost of Alternative 4. the selected remedy.
The cost of each alternative increases as the volume of groundwater to be extracted and treated
increases. Alternatives 5 and 6 do not provide a significant increase in protectiveness over
Alternative 4; the portions of contaminated groundwater that will not be extracted with the
selected remedy will be remediated using MNA. The MNA in central and eastern areas will
meet the same RAOs in the same time period, and will be equally protective, as Alternatives 5
and 6, but at a greatly reduced cost. The selected alternative costs approximately $14 million
less than Alternative 5.
9.3 Modifying Criteria
State Acceptance-The State of Arizona prefers Alternative 4 (selected remedy) with the option
to employ the contingency remedy, as needed, over the remaining alternatives because this
alternative restores the groundwater resource without extracting large quantities of ground-
water and because it is more cost-effective than Alternatives 5 and 6, while still being protective
of human health and the environment and meeting ARARs within a reasonable time frame of
approximately 30 years.
Community Acceptance-The community has expressed concern about using the SRP Tempe
Canal No. 6 as an end use for treated groundwater. The community generally supports
Alternative 4 more than Alternatives 5 and 6 because it is more cost-effective, and it extracts a
smaller volume of groundwater while still meeting aquifer cleanup goals within a reasonable
time frame of approximately 30 years and at a reduced cost.
RDD-SFCV962450006.DOC (CLR263JXX) (97)
H-61
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I DECISION SUMMHY
10.0 Explanation of Significant Differences
10.1 Difference in Selected Remedy
The selected remedy is Alternative 4 (presented in the FS) with minor modifications. The sel-
ected remedy differs from Alternative 4 with adjustments in the volume and area of the partial
target volume to be extracted and treated, the addition of a contingency remedy, the revision of
the time period in which EPA expects the groundwater to meet aquifer cleanup goals, and a
lower cost. EPA's modeling has shown that it is no longer necessary to include portions of the
central and eastern areas of contamination in the partial target volume for extraction and
treatment. MNA alone should be sufficient to meet EPA cleanup objectives in these areas.
In the groundwater FS, EPA estimated partial and regional target volumes to evaluate a range
of alternatives that might achieve EPA's remedial action objectives. The regional target volume
represents the volume of groundwater in the UAU and MAU areas of contamination estimated
to be above MCL concentrations. The partial target volume represented a volume that would be
necessary to extract and treat, when combined with MNA of lesser contaminated areas of
groundwater, that would meet MCLs within a reasonable time frame of 30 to 50 years with
limited migration to 2,000 feet beyond the estimated extent of the central and eastern areas of
contamination.
The preferred remedy of Alternative 4 in the Proposed Plan specified extraction and treatment
of the partial target volume that included all of the western area of contamination above 5 ppb,
the MCLs for TCE and PCE, and extraction and treatment of only the most highly VOC-
contaminated portions of the central and eastern areas of contamination. The partial target
volumes presented in the Proposed Plan were based on groundwater data collected through
July 1994. EPA stated in the Proposed Plan that the target volumes were based on modeling
performed in the FS and that additional work would be necessary during remedial design to
further refine the target volumes.
EPA received several comments on the Proposed Plan centered around the use of older data
(data collected through July 1994) to model target volumes of VOC-contaminated groundwater
for extraction and treatment and areas for MNA. EPA anticipated the need to modify the partial
target volumes during remedial design, but because of the lapse of time between release of the
FS and the issuance of this ROD, EPA performed modeling to evaluate more recent data. EPA
has presented these results here in this ROD and in the Technical Memorandum Documentation
of the Indian Bend Wash-South Groundwater Flow and Solute Transport Models, dated August 12,
1998, which is available in the site Administrative Record.
The results of the updated modeling effort show that extraction and treatment are still neces-
sary for all of the western area of contamination. However, MNA of the central and eastern
areas of contamination in the UAU will be sufficient to meet MCLs within a reasonable time
frame of approximately 30 years and will allow only limited migration of contaminated
groundwater to approximately 2,000 feet.
As a result of this review and modeling of more current data, EPA therefore has modified
Alternative 4 by changing the volume of contaminated groundwater that will be extracted and
1142 flDD-SFCV982450006.DOC (CUC63.00C) (97)
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II DECISION SUMMARY
treated. The selected remedy eliminates the extraction of groundwater from the central and
eastern areas of contamination. Those areas will be remediated by MNA.
EPA has revised the time period to meet cleanup objectives to approximately 30 years based on
comments submitted during the public comment period, because all modeling evidence
indicates that cleanup levels can be met within this time frame. EPA believes this is a
reasonable time given the current contaminant concentrations and other circumstances at the
site in which to expect aquifer cleanup goals to be met.
Another change to the preferred remedy set forth in the Proposed Plan is the addition of a
contingency remedy to ensure that cleanup goals are met within the central and eastern UAU
areas of contamination and the MAU, where MNA is the remedy. EPA has developed a contin-
gency remedy and specific criteria which, if exceeded, will activate the contingency remedy of
extraction and treatment of partial target volumes of the central and/or eastern UAU areas of
contamination and/or the MAU areas of contamination to meet the performance standards.
Contingency Remedy
A contingency remedy of extraction and treatment of appropriate target volumes of
contaminated groundwater in MNA areas will be triggered to satisfy the following two criteria:
(1) attaining aquifer cleanup standards within a reasonable time frame of approximately
30 years, and (2) preventing migration of groundwater contaminated above the aquifer cleanup
standards to and beyond the compliance boundaries. The appropriate "target volume" of
contaminated groundwater to be extracted and treated will be determined to ensure that these
two criteria are met.
The compliance boundary for the central and eastern UAU areas of contamination is located
approximately 2,000 feet south of Broadway Road, bounded by Price Road to the east and
Dorsey Lane to the west. Sentinel wells will be located in the UAU upgradient of the UAU
compliance boundary in an area bounded by Broadway Road to the north, approximately 1,000
feet south of Broadway Road to the south, approximately 1,000 feet east of Price Road to the
east, and Dorsey Lane to the west. The compliance boundaries are shown on Figure 10.
The compliance boundary for the MAU areas of contamination is located approximately 2,000
feet east of the current extent of VOC contamination and is bounded by Rio Salado Parkway to
the north and Apache Boulevard to the south. Sentinel wells will be located approximately
1,000 feet upgradient of the MAU compliance boundary, as shown on Figure 10. The sentinel
wells will be monitored at least quarterly.
For the UAU or MAU, the contingency remedy will be triggered if either one of the following
situations occurs:
(a) If verification sampling at the sentinel wells confirms that data collected during quarterly
sampling exceed the aquifer cleanup standards, and if the average contaminant
concentration collected from the next two consecutive quarterly sampling rounds from this
well exceeds the aquifer cleanup standards, then the contingency remedy will be activated.
The contingency remedy may be implemented sooner, if needed.
(b) EPA-approved flow and transport modeling will be conducted using data collected during
each EPA 5-year review period. If the modeling evaluation indicates that the MNA remedy
ROD-SFOfl82450006.DOC (CUC63.DOC) (97) 11-63
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R DECISION SUUMOr
will not attain aquifer cleanup standards within a reasonable time frame of approximately
30 years from the start of remedial action, then the contingency remedy will be activated.
10.2 Differences in Cost
Modifying the remedy presented in the Proposed Plan with a potential contingency remedy to
allow for MNA in the central and eastern UAU areas of contamination has allowed the costs for
the selected remedy to be reduced as follows.
The capital cost of the selected remedy decreased by $2.15 million (from $8.32 million to
$6.17 million) because of the reduction in the number of extraction wells, the length of
conveyance piping, and the changes in the treatment requirements. The annual O&M cost
decreased by $240,000 (from $1.3 million to $1.06 million) because of lower power requirements
and less O&M required for the extraction wells. The 30-year total present worth cost decreased
by more than 20 percent, from $28.3 million to $22.46 million.
The costs for the contingency remedy were not presented in the FS. These costs are discussed in
Chapters 9.0 and 11.0 of this ROD.
10.3 Potential Differences in End Use of Treated Water
In the Alternative 4 presented in the Proposed Plan, the name of the alternative included Town
Lake as the discharge location. The Proposed Plan did state that the exact end use would be
determined during remedial design. EPA has proposed in the selected remedy to discharge
extracted groundwater, once it has been treated to health-based levels, to one of the following
three places: City of Tempe Town Lake, groundwater reinjection to the MAU, and the SRP
Tempe Canal No. 6.
Several comments were received during the comment period concerning discharge of the
treated groundwater to the SRP Tempe Canal No. 6 because of the potential for water from this
canal to be used as a source of drinking water. Groundwater would be treated to meet the
standards for protection of drinking water sources as specified in Section 12 before it enters the
canal. EPA will consider eliminating this discharge option from the list of possible end-use
options when the end-use determination is made during the remedial design phase. EPA
intends to keep the community involved during the selection of end use of treated
groundwater.
11-64 RDD-SFCV982450006.DOC (cm263DOC) (97)
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COMPLIANCE BOUNDARY
FOR MNA IN MAU
•24.5.2.5
MAU AREA
OF SENTINEL WELLS
COMPLIANCE BOUNDARY FOR
MIGRATION OF MNA AREAS IN UAU
LEGEND:
o
ESTIM/
AREA;
GROW
-\ ESTIM/
/ AREA;
' GROUh
• WATER
• MONITC
• MONITC
•24.4.1.5
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I DECISION SUMMRY
11.0 Selected Remedy
After considering CERCLA's statutory requirements, the detailed analysis of alternatives for
IBW-South, and the public comments on the Proposed Plan, EPA, in consultation with the State
of Arizona, has determined that the most appropriate remedy for VOCs in groundwater at
IBW-South includes the following:
• Extraction of the western UAU area of VOC-contaminated groundwater to attain aquifer
cleanup standards and hydraulic containment of the contaminated areas to inhibit both
lateral and vertical migration
• Treatment of extracted water to performance standards using liquid granular activated
carbon (LGAC), air stripping with vapor granular activated carbon (VGAC), or ultraviolet
light oxidation (UV/Ox)
• Discharge of treated groundwater to the City of Tempe storm drain system leading to Town
Lake, the SRP Tempe Canal No. 6, or reinjection.
• MNA of the central and eastern UAU areas of VOC-contaminated groundwater and the
MAU areas of VOC-contaminated groundwater to attain aquifer cleanup standards within
those areas, and to prevent migration of groundwater contaminated above the aquifer
cleanup standards to and beyond the compliance boundaries established in this ROD.
• The establishment of compliance boundaries for those areas where the MNA remedy is
selected. The compliance boundaries represent borders beyond which VOC-contaminated
groundwater above aquifer cleanup standards will not be allowed to migrate. The
compliance boundary for the central and eastern UAU areas of contamination is located
approximately 2,000 feet south of Broadway Road, bounded by Price Road to the east and
Dorsey Lane to the west. Sentinel wells will be located in the UAU upgradient of the UAU
compliance boundary in an area bounded by Broadway Road to the north, approximately
1,000 feet south of Broadway Road to the south, approximately 1,000 feet east of Price Road
to the east, and Dorsey Lane to the west. The location of the compliance boundaries and
areas for sentinel wells are shown in Figure 10 in Section 10.0. The sentinel wells will be
monitored at least quarterly for the hazardous substances for which aquifer cleanup
standards are established (see Section 12.0), and for other substances as appropriate.
The compliance boundary for the MAU areas of contamination is located approximately
2,000 feet east of the current extent of VOC contamination and is bounded by Rio Salado
Parkway to the north and Apache Boulevard to the south. Sentinel wells will be located
approximately 1,000 feet upgradient of the MAU compliance boundary, as shown in Figure
10 in Section 10.0. The sentinel wells will be monitored at least quarterly for the chemicals
for which aquifer cleanup standards are established (see Section 12.0), and for other
substances as appropriate.
• Continued monitoring of groundwater to verify the effectiveness of the extraction and
treatment and MNA remedies and to ensure that aquifer cleanup goals are met throughout
the areas of VOC contamination.
• Institutional controls to protect the public from exposure to contaminated groundwater
exceeding aquifer cleanup levels until cleanup levels are met. Institutional controls will
RDD-SFO9e2450006.DOC (CW263.00C) (97) W7
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lOECSMNSUMUflr
include various Arizona well siting, permitting, and construction restrictions, and notices
distributed by the ADWR, Arizona Department of Health Services, or EPA concerning risks
from exposure to contaminated groundwater. Additional institutional controls to prevent
interference with EPA's remedial efforts also may be established.
• Sealing or abandonment of Well SRP23E, 2.9N to eliminate this potential path of VOC
contaminant migration from the UAU to the MAU. This well is located in an area of
shallow contamination and represents a potential conduit for downward contaminant
migration. Other monitoring wells that will not be included in the long-term monitoring
network will be abandoned as appropriate.
Contingency Remedy
A contingency remedy of extraction and treatment of appropriate target volumes of
contaminated groundwater in MNA areas may be triggered to satisfy the following two criteria:
(1) attaining aquifer cleanup standards within a reasonable time frame of approximately 30
years, and (2) preventing migration of groundwater contaminated above the aquifer cleanup
standards to and beyond the compliance boundaries. The appropriate "target volume" of
contaminated groundwater to be extracted and treated will be determined to ensure that these
two criteria are met.
For the UAU or MAU, the contingency remedy will be triggered if either one of the following
situations occurs:
(a) If verification sampling at the sentinel wells confirms that data collected during quarterly
sampling exceed the aquifer cleanup standards, and if the average contaminant
concentration collected from the next two consecutive quarterly sampling rounds from this
well exceeds the aquifer cleanup standards, then the contingency remedy will be activated.
The contingency remedy may be implemented sooner, if needed.
(b) EPA-approved flow and transport modeling will be conducted using data collected during
each EPA 5-year review period. If the modeling evaluation indicates that the MNA remedy
will not attain aquifer cleanup standards within a reasonable time frame of approximately
30 years from the start of remedial action, then the contingency remedy will be activated.
Both the selected groundwater remedy and the contingency remedy meet the two NCP
threshold evaluation criteria of overall protection of human health and the environment and
compliance with ARARs, provide the best balance of tradeoffs based on the primary balancing
criteria, and are acceptable to the State of Arizona and the community.
The groundwater cleanup (including groundwater extraction and MNA), treatment and
discharge, and additional components of the selected remedy and the contingency remedy are
described in the following subsections. The ARARs for the selected remedy are described in
Section 12.
D-68 RDO-SFO/M2450006.DOC (CUC63JX3C) (97)
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I DECISION SUMMARY
11.1 Groundwater Restoration Component
This section describes the groundwater restoration components of the selected remedy. Both
groundwater extraction and MNA are described in this section, along with associated
performance standards and contingency actions.
Groundwater Extraction
The groundwater extraction component of the selected remedy addresses containment and
cleanup of VOC-contaminated groundwater in the western area of the UAU. Groundwater
extraction will be used to remediate groundwater that is contaminated in excess of ground-
water cleanup standards. It will also prevent migration of the contaminated area. Approxi-
mately three wells will be installed and screened in the UAU to extract contaminated
groundwater. Modeling reported in the FS and more recent modeling show that without
extraction and treatment, PCE and TCE, the main COCs, would migrate 7,000 feet.
Performance Standards and Compliance Monitoring
The groundwater extraction component of the groundwater remedy will be operated until
groundwater no longer exceeds the aquifer cleanup standards throughout the contaminated
area. Groundwatr extraction will also contain the plume, and the compliance boundary for this
portion of the remedy is the extent of contaminated groundwater above the aquifer cleanup
standards throughout the western UAU contaminated area.
Water levels will be monitored in monitoring wells to show that the groundwater extraction
system is controlling the horizontal and vertical migration of groundwater contaminated above
aquifer cleanup levels. If the groundwater extraction containment system is not effective in the
western UAU, additional measures will be implemented to ensure that performance standards
are met. Examples of such measures may include, but are not limited to, any of the following:
more closely spaced extraction wells to facilitate containment or higher extraction rates to
increase hydraulic control and expedite restoration. EPA may also determine that more
extensive groundwater monitoring is required to ensure that downgradient VOC
concentrations in currently clean areas are not increasing.
Monitored Natural Attenuation
As described in Section 10.0, EPA's modeling has shown that MNA alone should be sufficient
to meet EPA cleanup objectives in the central and eastern UAU and MAU areas of
contamination.
The objective of the MNA component of the remedy is to allow contaminant concentrations in
groundwater in the eastern and central UAU and the MAU areas of contamination to be
reduced to groundwater cleanup standards within all contaminated areas above aquifer
cleanup standards and within a reasonable time frame of approximately 30 years. Natural
attenuation reduces contaminant concentrations by dispersion, dilution, biodegradation, and
related natural processes. As discussed below, it is anticipated that MNA will accomplish these
goals before contaminated groundwater above aquifer cleanup standards reaches the
compliance boundaries. The compliance boundaries represent borders beyond which VOC-
contaminated groundwater above aquifer cleanup standards will not be allowed to migrate.
The compliance boundary for the central and eastern UAU areas of contamination is located
RDD-SFO982450006.DOC (CU1263.DOC) (97)
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I DECISION SUMMARY
approximately 2,000 feet south of Broadway Road, bounded by Price Road to the east and
Dorsey Lane to the west. The compliance boundary for the MAU areas of contamination is
located approximately 2,000 feet east from the current downgradient extent of VOC contami-
nation at the MCLs and is bounded by Rio Salado Parkway to the north and Apache Boulevard
to the south. These boundaries are depicted in Figure 10 in Section 10.
For the contaminated areas where MNA will be implemented, the following are estimates
based on EPA modeling presented in this ROD of how far the contamination may migrate
beyond its current extent and when the groundwater will meet MCLs for TCE and PCE, the
two main COCs:
• Central UAU area of contamination-Recent data indicate that groundwater concentrations
do not exceed MCLs.
• Eastern UAU area of contamination-Migrates approximately 2,000 feet before meeting
MCLs throughout the area in less than approximately 30 years
• MAU area of contamination (Subunits B and C)-Migrates less than 2,000 feet before
meeting MCLs throughout the area in less than approximately 30 years.
New and existing monitoring wells will be sampled to monitor the progress of the decreases in
VOC concentrations during the natural attenuation process to ensure that cleanup levels are
met and to determine if the contingency remedy trigger criteria (described below) have been
exceeded.
MNA will encompass EPA's guidelines on Use of Monitored Attenuation at Superfund, RCRA
Corrective Action and Underground Storage Tank Sites (OSWER Directive 9200.4-18 Interim Final
as published in the Federal Register December 8,1997.
Performance Standards and Compliance Monitoring
For the MNA component of the remedy to meet the performance requirements, VOC concen-
trations in groundwater must be reduced to aquifer cleanup standards in approximately
30 years or less and groundwater exceeding cleanup standards must not reach the compliance
boundaries established for the central and eastern UAU and MAU. Specific trigger criteria have
been developed to determine if natural attenuation is progressing as expected and will meet the
cleanup objectives. These are described below.
Contingency Trigger Criteria for UAU
Sentinel wells will be located in the UAU upgradient of the UAU compliance boundary in an
area bounded by Broadway Road to the north, approximately 1,000 feet south of Broadway
Road to the south, approximately 1,000 feet east of Price Road to the East, and Dorsey Lane to
the west. For the UAU, the contingency remedy will be triggered if either one of the following
situations occurs:
(a) If verification sampling at the sentinel wells confirms that data collected during quarterly
sampling exceed the aquifer cleanup standards, and if the average contaminant
concentration collected from the next two consecutive sampling rounds from this well
exceeds the aquifer cleanup standards, then the contingency remedy will be activated. The
contingency remedy may be implemented sooner, if needed.
H-70 ROD-SKV962450006.DOC (OR263JXX) (97)
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IDCCeiON SUMMARY
(b) EPA-approved flow and transport modeling will be conducted vising data collected during
each EPA 5-year review period. If the modeling evaluation indicates that the MNA remedy
will not attain aquifer cleanup standards within a reasonable time frame of approximately
30 years from the start of remedial action, then the contingency remedy will be activated.
Contingency Trigger Criteria for MAU
Sentinel wells will be located approximately 1,000 feet upgradient of the MAU compliance
boundary. For the MAU, the contingency remedy will be triggered if either one of the following
situations occurs:
(a) If verification sampling of the sentinel wells confirms that data collected during quarterly
sampling exceed the aquifer cleanup standards, and if the average contaminant
concentration collected from the next two consecutive sampling rounds from this well
exceeds the aquifer cleanup standards, then the contingency remedy will be activated. The
contingency remedy may be implemented sooner, if needed.
(b) EPA-approved flow and transport modeling will be conducted using data collected during
each EPA 5-year review period. If the modeling evaluation indicates that the MNA remedy
will not attain aquifer cleanup standards within a reasonable time frame of approximately
30 years from the start of remedial action, then the contingency remedy will be activated.
Contingency Remedy - Additional Extraction and Treatment
If the MNA does not perform as expected and the trigger criteria described above are exceeded,
the contingency remedy will be implemented. The contingency remedy will include ground-
water extraction in the central and/or eastern UAU or the MAU of a target volume of
contaminated groundwater, followed by groundwater treatment, and treated water discharge.
The location and magnitude of groundwater extraction for the target volume required will be
determined on the basis of groundwater conditions at the time the trigger criteria are exceeded.
The groundwater extraction of the target volume implemented as part of the contingency action
must be sufficient to ensure that groundwater cleanup standards are not exceeded at the com-
pliance boundary and that the time to meet aquifer cleanup standards is not exceeded. If appro-
priate, the monitored natural attenuation remedy may still be in use in portions of the central
and/or eastern UAU and the MAU even as active extraction is occurring in other portions of
these areas.
Groundwater treatment and treated water discharge under the contingency remedy would
have the same components, performance standards and monitoring requirements as described
below in Section 11.2 for the western area of contamination in the selected remedy. The location
of any additional treatment plant(s) and the end use of the additional treated water will be
determined during the remedial design phase of the contingency action.
11.2 Groundwater Treatment and Discharge Component
This section describes the treatment of the contaminated groundwater and discharge of the
treated water. This includes the treatment of the western UAU area of contamination, as well as
any target volume of the central and/or eastern UAU and MAU areas of contamination treated
because of activation of the contingency remedy.
RDO-SFCV982450006.DOC (CU363.DOC) (97) 11-71
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I DECISION SUMMARY
The groundwater extracted as part of any groundwater remedial action will be piped to a
treatment system for VOC removal. It is expected that the VOCs will be removed from the
groundwater by air stripping with offgas treatment using VGAC vessels. However, the LGAC
or UV/Ox treatment processes may also be used if more cost-effective. A more detailed
description of these three groundwater treatment processes is provided in Section 8 of this ROD
and in the FS (EPA, 1997). The appropriate treatment process will be selected during remedial
design when more is known about the anticipated influent flow rates and contaminant
concentrations of the target volumes to be extracted.
The treated water will be discharged to either the City of Tempe storm drain system leading to
Town Lake, the SRP Tempe Canal No. 6, or to the MAU aquifer through reinjection. EPA will
determine the selected end-use option for the treated groundwater during remedial design and
will consider the input provided by the community during the public comment period.
Performance Standards
The treatment plant discharge performance standards will vary with the different discharge
options considered for the treated groundwater, as further defined in the ARARs section of this
ROD (Section 12.0). The treatment plant(s) will be capable of meeting the effluent discharge
standards. If discharge of the treated groundwater is to Town Lake, then aquatic and wildlife
standards for a warm water fishery would be met. If discharge is to Tempe Canal or reinjection
to the MAU, then the MCL or human health-based guidance level (HBGL) listed in Table 12 of
the ARARs section (Section 12) would be met.
11.3 Additional Components
This section describes additional components of the selected remedy, including well abandon-
ment, institutional controls, and groundwater monitoring.
Well Sealing or Abandonment
The selected remedy includes sealing or abandonment of Well SRP23E, 2.9N to eliminate this
potential path of VOC contaminant migration from the UAU to the MAU. This well is located
in an area of shallow contamination and represents a potential conduit for downward
contaminant migration. The sealing or abandonment will be done in accordance with appro-
priate State of Arizona guidelines. In addition, other monitoring wells that will not be included
in the long-term monitoring network will be abandoned, as appropriate, in accordance with
State of Arizona guidelines.
Institutional Controls
Institutional controls will be established to protect the public from exposure to contaminated
groundwater exceeding aquifer cleanup levels until aquifer cleanup goals are met. Institutional
controls will include various Arizona well siting, permitting/ and construction restrictions, and
notices distributed by the ADWR, Arizona Department of Health Services, or EPA concerning
risks from exposure to contaminated groundwater. Additional institutional controls to prevent
interference with EPA's remedial efforts also may be established.
U.72 RDO-SKV9e2450006.DOC (Ofl263.00C) (97)
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I DECISION SUMMARY
Groundwater Monitoring
Continued monitoring of groundwater will be performed to verify the effectiveness of the
extraction and treatment and MNA remedies and to ensure that aquifer cleanup goals are met
throughout the areas of VOC contamination. A long-term monitoring program will be designed
and implemented during the RD/RA and will continue as long as contamination remains
above cleanup standards. The monitoring program will assess performance of the groundwater
containment system or systems, monitor the progress of natural attenuation in areas without
active groundwater extraction, monitor to determine if the contingency remedy trigger criteria
are exceeded, and monitor effluent chemical concentrations from the treatment system.
11.4 5-Year Review
This remedial action is expected to take more than 5 years to achieve aquifer cleanup levels.
Accordingly, by policy, EPA will perform a review of the selected remedy no less than 5 years
after completion of the construction for all remedial actions at the site. This review will ensure
that the remedy is operating and functioning as designed, that institutional controls are in place
and are protective, and that natural attenuation is progressing as expected. An additional
purpose for the review is to evaluate whether the performance standards specified in this ROD
remain protective of human health and the environment. EPA will continue the reviews until
no hazardous substances, pollutants, or contaminants remain at IBW-South above levels that
allow for unrestricted use and unlimited exposure to groundwater.
11.5 Conceptual Design
The conceptual design for the extraction and treatment components of the selected remedy is
shown in Figure 11.
The extent of UAU contamination at the western area would be contained and restored using
three extraction wells positioned approximately along the downgradient edge of the area
contaminated above aquifer cleanup standards.
The well locations shown on Figure 11 were selected during the FS and are based on the extent
of contamination using data through February 1995. The revised extent of contamination using
data through April 1998 is also shown on Figure 11. The well locations and pipe routing were
not revised to prepare the cost estimate because further modifications will be required based on
the location of the highest contaminated area during remedial design.
The extracted groundwater is piped to a centralized treatment system and the VOCs are
removed from the groundwater by air stripping (or other treatment). VOC-contaminated offgas
from air stripping is treated by using VGAC vessels. The treated water would then be delivered
to the City of Tempe storm drain system leading to Town Lake, the SRP Tempe Canal No. 6, or
reinjected to the MAU aquifer. The Proposed Plan stated that the exact end use for the treated
groundwater will be determined after EPA considered all comments received on the Proposed
Plan and performed remedial design work for the remedy.
Groundwater contamination in the MAU and those portions of the central and eastern areas of
the UAU that are not contained by the extraction wells would be allowed to naturally atten-
RDCVSFO/982450006.DOC(CU«63.DOC){97) 11-73
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IDECNONSIMUHY
uate. Additional monitoring wells and verification monitoring will be performed to verify the
natural attenuation process.
The costs for the selected remedy were estimated assuming the following components and are
discussed in Appendix A.
• Three extraction wells installed in the UAU
- Total depth = 170 feet
- Screened Interval = 46 to 126 feet bgs
- Total flow rate = 2,940 gallons per minute (gpm)
- Three telemetry systems (one per extraction well)
- Three electrical hookups (one per extraction well)
• Treatment plant
- One air stripping tower (height = 28 feet)
- Two VGAC offgas treatment units (capacity of each = 9,830 standard cubic feet per
minute (scfmj)
• Number of samples
- 106 bi-monthly VOC air samples
- 53 bi-monthly VOC water samples
- 14 annual genera] chemistry water samples.
The number of samples also includes quality control samples at 10 percent frequency.
• Conveyance pipeline, between extraction wells and treatment plant, made of high-density
polyethylene (HDPE) dual-cast (DC) pipe
- 4,400 linear feet of 10-inch-diameter
- 1,000 linear feet of 12-inch-diameter
- 5,500 linear feet of 14-inch-diameter
• Distribution pipeline, between treatment plant and Town Lake, made of HDPE DC pipe
- 50 linear feet of 16-inch-diameter (connection to COT storm drain)
• One distribution pump station (60 hp) located within the treatment plant boundary
• One outfall structure
11.74 RDD-SFO/9824S0006.DOC (OA263.DOC) (97)
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I DECISION SUMMARY
• Ten new monitoring wells (total depth 170 feet each)
• 176 VOC monitoring samples per year
• 53 general chemistry monitoring samples per year
• Annual sampling for general chemistry
- 43 existing monitoring wells
- 10 new monitoring wells
• Sampling for VOCs
- Quarterly at 26 existing and 10 new monitoring wells
- Semi-annually at 3 existing monitoring wells
- Annually at 22 existing monitoring wells
- Every other year at 8 existing monitoring wells
The number of samples also includes quality control samples at 10 percent frequency.
• Sealing of screen interval at Well SRP23E,2.9N in the UAU.
Contingency Remedy
The costs for the contingency remedy were estimated assuming the components in the list
below were added to the selected remedy. Details of the cost estimate for the contingency
remedy are provided in Appendix A of this ROD.
• Three additional extraction wells installed in the UAU
- Total depth = 170 feet
- Screened Interval = 46 to 126 feet bgs
- Total flow rate = 2,940 gpm
- Three telemetry systems (one per extraction well)
- Three electrical hookups (one per extraction well)
• Treatment plant
- One additional air stripping tower (height = 28 feet)
- Two additional VGAC offgas treatment units (capacity of each = 7,420 scfm)
• Number of additional samples
- 106 bi-monthly VOC air samples
- 53 bi-monthly VOC water samples
- 14 annual general chemistry water samples.
The number of samples also includes quality control samples at 10 percent frequency.
RDD-SFO/982450006.DOC (CLR263.DOC) (97) 11-77
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II DECISION SUMMARY
• Additional conveyance pipeline, between extraction wells in eastern contaminated area and
conveyance pipeline included in selected remedy, made of HOPE DC pipe
- 8,200 linear feet of 12-inch-diameter
- 3,100 linear feet of 8-inch-diameter
11.6 Cost of the Selected Remedy and Contingency Remedy
The approach used to estimate costs for the alternatives in the FS and the selected and
contingency remedies were presented in Section 8.0 and Appendix A of this ROD and in
Appendix D of the FS.
Selected Remedy
Estimated costs of the selected remedy are:
• Capital Costs $ 6,170,000
• Annual O&M Costs $ 1,060,000
• Present Worth Cost (30 years) $22,460,000
These costs are based on the conceptual design for this remedy as described above.
Contingency Remedy
The estimated increase in cost if the contingency remedy is implemented is:
• Capital costs $2,410,000
• Annual O&M costs $10,000
• Present worth cost (30 years) $2,570,000
U-78 RDD-SFO/962450006.DOC (Clfl263.DOC) (97)
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I DECISION SUMMARY
12.0 ARARs for Indian Bend Wash-South
Section 121 (d) of CERCLA requires that remedial actions at CERCLA sites must attain (or
justify the waiver of) any federal or more stringent state environmental standards, criteria, or
limitations that are determined to be ARARs. Applicable requirements are those cleanup
standards, criteria, or limitations promulgated under federal or state law that specifically
address the situation at a CERCLA site. A requirement is applicable if the jurisdictional
prerequisites of the environmental standard show a direct correspondence when objectively
compared with the conditions at the site.
If a requirement is not legally applicable, the requirement is evaluated to determine whether it
is relevant and appropriate. Relevant and appropriate requirements are those cleanup stan-
dards, standards of control, and other substantive environmental protection requirements,
criteria, or limitations promulgated under federal or state law that, while not applicable,
address problems or situations sufficiently similar to the circumstances of the proposed
response action and are well-suited to the conditions of the site. The criteria for determining
relevance and appropriateness are listed in Title 40, Code of Federal Regulations (CFR),
Section 300.400(g)(2) (40 CFR 300.400[g][2]). If no specific ARAR exists, then other guidelines or
criteria "to be considered" (TBC) may be identified and used to ensure protection of human
health and the environment.
ARARs are divided into three categories: chemical-specific, location-specific, and action-
specific requirements. The chemical-specific ARARs are health- or risk-based concentration
limits, numerical values, and methodologies for contaminant media. The chemical-specific
ARARs for the IBW-South remedial actions define the concentration levels for contaminants in
the groundwater that determine whether a problem exists at the site and the subsequent
cleanup criteria. Chemical-specific ARARs also define the concentration levels required for
satisfactory groundwater treatment and implementation of the end-use alternatives for the
treated groundwater. Location-specific ARARs relate to the geographical or physical location of
the site, and may limit what actions can be taken, given the specific geographic characteristics
of the site. Action-specific ARARs are technology- or activity-based requirements triggered by
the type of remedial activity being conducted. Examples are requirements that define accept-
able treatment and disposal procedures for hazardous substances. A detailed discussion of the
potential ARARs identified for the IBW-South site is provided in the IBW-South 1997 FS.
The ARARs for the IBW-South site have been identified in a sequential manner. First, the
ARARs that impact remedial goals, independent of the remedial alternatives, were identified.
These are the chemical- and location-specific regulations and objectives that govern the release
and need for remediation of specific hazardous substances and present how the physical
location of the site can determine where and how facilities can be constructed and operated.
Next, the action-specific ARARs are identified for each alternative. These define the perfor-
mance requirements of the system and may impact cost and implementability of the alternative.
The State of Arizona identified proposed ARARs to EPA.
ARARs include only the substantive, not the administrative, requirements of a statute or
regulation. The substantive portions of the regulation are those requirements that pertain
directly to actions or conditions in the environment. Examples of substantive requirements
include quantitative health- or risk-based restrictions upon exposure to types of hazardous
substances. Administrative requirements are the mechanisms that facilitate implementation of
ROD-SFO/982450006.DOC (CLR263.DOC) (97] 11-79
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II DECISION SUMMARY
the substantive requirements. Administrative requirements include issuance of permits, docu-
mentation, reporting, recordkeeping, and enforcement. Thus, in determining the extent to
which onsite CERCLA response actions must comply with environmental laws, a distinction
must be made between substantive requirements, which may be ARARs, and administrative
requirements, which are not.
The ARARs provision in CERCLA applies only to onsite actions. "Onsite" is defined as the areal
extent of contamination and areas in proximity to it necessary for the implementation of the
remedy. According to CERCLA §121(e), a remedial response action that takes place entirely
onsite is exempt from administrative portions of ARARs and may proceed without obtaining
permits.
A requirement may not meet the definition of an ARAR as defined above, but may still be use-
ful in determining whether to take action at a site and/or to what degree action is necessary.
This can be particularly true when there are no ARARs for a site or a particular contaminant.
Such requirements are TBC requirements. TBC materials are nonpromulgated advisories or
guidance documents issued by federal or state government that are not legally binding, but that
may provide useful information or recommended procedures for remedial action. Although
TBCs do not have the status of ARARs, they may be considered together with ARARs to
establish the required level of cleanup for protection of human health and the environment.
The federal and state statutes and requirements examined for EPA's ARARs analysis for IBW-
South are identified in Appendix B to the IBW-South 1997 Feasibility Study.
12.1 Chemical-Specific ARARs
The chemical-specific ARARs that have been identified for IBW-South are those that: (1) affect
groundwater remedial goals, and (2) determine to what degree groundwater should be treated
prior to discharge. The major statutes and regulations that contribute to the list of potential
chemical-specific ARARs are the Clean Water Act (CWA), the Safe Drinking Water Act
(SDWA), Arizona Water Quality Standards for Navigable Waters, and Arizona Aquifer
Protection Standards. The chemical-specific TBCs for the IBW-South site consider the ADHS
HBGLs for Contaminants in Drinking Water. Chemical-specific ARARs for the more commonly
detected organic compounds at IBW-South are summarized in Table 12. SDWA MCLs and
nonzero MCLGs are the standards for aquifer cleanup, unless otherwise noted. Inorganic com-
pounds are not considered COCs for IBW-South groundwater; however, they are included in
Table 12 because inorganics will need to be considered in treating groundwater for discharge.
Chemical-Specific ARARs for Groundwater Remedial Goals
This section addresses the chemical-specific ARARs for aquifer remediation. The presence of
contaminants above SDWA MCLs has degraded the beneficial uses of the groundwater at
IBW-South; therefore, remedial actions will need to restore the contaminated groundwater and
protect groundwater outside of the area of contamination.
The numerical values in the SDWA MCL standards are enforceable, health-based concentration
limits formulated to protect water for human consumption for drinking, cooking, bathing, and
other water-contact activities. MCLs are applicable to the quality of drinking water at the tap
pursuant to the SDWA. Pursuant to 40 CFR Section 300.430(e)(2)(i)(B), MCLs and non-zero
Maximum Contaminant Level Goals (MCLGs) may be relevant and appropriate as in situ
11-80 RDO-SFO/982450006.00C (CUC63.00C) (97)
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D DECISION StMMflY
TABLE 12
Chemical-Specific ARARs for the IBW-South Site (concentrations in uo/l)
Aquifer Cleanup
Standard
Discharge Limits for
Tempe Canal and
Re-injection
Discharge Limits for
Town Lake
Parameter
Organics
Benzene
Bromodichloromethane
Chloromethane
Chloroform
1,2-Dibromoelhane
1,2-Dichloroethane
1,1-Dichloroethene
1,2-Dichloropropane
Methylene Chloride
1 . 1 ,2,2-Tetrachloroethane
Tetrachloroethene (PCE)
Trichloroethene (TCE)
Inorganics
Antimony
Arsenic
Barium
Beryllium
Cadmium
Chromium (total)
Copper
Cyanide
Lead
Mercury
Nickel
Selenium
Thallium
Zinc
(MCL or HBGL)
5"
lOO"'0
2.7d
IOC"'0
0.05b
5"
76.6
5"
5b
0.1 8d
5b
5"
(MCL or HBGL)
5"
ICO6-0
2.7*
100"-c
0.05b
5b
7b..
5b
5b
0.17*
5b
5b
6b
50'
2,000"
4b
5b
100"
1.300" 9
200"
15b-o
2"
100'
50"
2b
2,100*
(A&Wwa
Acute)
2.700
-
270,000
14,000
-
59,000
15.000
26,000
97,000
4.700
6,500
20,000
88
360
-
65
_h
-
_h
41'
.h
2.4
.h
20
700
.g
(AAWwa
Chronic)
180
-
15,000
900
-
41.000
950
9.200
5,500
3.200
680
1.300
30
190
-
5.3
.h
-
.0
9.7'
.9
0.01
.g
2.0
150
.9
a Aquatic and Wildlife (warm water fishery).
"Maximum Contaminant Level (MCL).
cFor total Irihalomethanes.
dHuman Health-Based Guidance Level (HBGL) for drinking water (December 1997 Update).
•Maximum Contaminant Level Goal is identical to the MCL.
'Arizona state MCL.
SAction level, not to be exceeded in more than 10 percent of samples.
"Concentrations vary depending on the hardness of the receiving water body.
'Arizona water quality standard for drinking water sources.
Note: The Arizona Aquifer Water Quality Standards for benzene, 1-2 dichloroelhane, 1,1-dichloroethene,
1,2-dichloropropane, PCE, total trihalomethanes, TCE, antimony, barium, beryllium, cadmium, chromium,
cyanide, selenium, and thallium are identical to the federal MCLs; identical to the state MCL for nickel; and
50 pg/L for lead.
RDOSFO/9824S0006.DOC (Clfl263.DOC) (97)
11-61
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II DECISION SUMMARY
aquifer cleanup standards for groundwater that is or may be used for drinking water. The
MCLs and non-zero MCLGs are relevant and appropriate standards for the groundwater
restoration at IBW-South because the beneficial uses of the groundwater aquifers include being
potential drinking water supplies under ARS §49-224 and AAC §R18-11-407. The MCLs and
non-zero MCLGs for the most common VOCs at IBW-South are presented in Table 12 under the
aquifer cleanup standards heading. The state MCLs, found in AAC §R18-4-205 and 211 are
listed in Table 12 only if they are more stringent than the federal MCLs or non-zero MCLGs.
For the main COCs, TCE and PCE, the MCL and the aquifer cleanup standard are 5 ug/L. The
aquifer cleanup standards for the other most commonly detected VOCs, including PCE and
TCE, are shown in Table 12.
The Arizona Aquifer Water Quality Standards (AAC §R18-11-406) are standards developed to
protect groundwater by preventing discharges of pollutants that are above certain concentra-
tions to aquifers, that endanger human health, or that impair the uses of the aquifer. In Arizona,
all aquifers are identified as drinking water source aquifers unless specifically exempt (ARS
§49-224). The Aquifer Water Quality Standards that are applied to aquifers classified as sources
of drinking water are currently identical to the federal SOW A MCLs. The federal MCLs or the
federal non-zero MCLGs for some hazardous substances are selected as ARARs because the
state standards are not more stringent than the federal MCLs.
TBCs that have been evaluated for some substances at the IBW-South site include the ADEQ
HBGLs which are health-based levels for drinking water. These levels, although set forth in
Arizona regulations, are not "promulgated" in the sense of being legally enforceable and
generally applicable. They are useful, however, for determining potential cleanup levels for
groundwater at IBW-South for compounds that do not have federal or state MCLs.
EPA has not selected HBGLs as cleanup standards for any hazardous substance for which there
is an MCL or non-zero MCLG because MCLs and MCLGs are health-based standards and are
thus adequately protective. Moreover, the Arizona Aquifer Water Quality Standards are gen-
erally identical to the MCLs and they, rather than the HBGLs, are the state's promulgated
aquifer standards. The HBGLs to be considered for the groundwater remedy pertain only to
those hazardous substances for which no MCL or MCLG has been established: chloromethane,
1,1,2,2-tetrachloroethane, and zinc. These HBGLs are also included in Table 12.
The following chemicals have been detected more than three times at IBW-South but only at
concentrations significantly less than the MCL (or HBGL for chemicals without an MCL):
acetone, 2-butanone, carbon disulfide, cis-l,2,-dichloroethene; rrans-l,2-dichloroethene, 1,1,1-
trichloroethane, and vinyl chloride. Accordingly, EPA has not included these substances in
Table 12. Additionally, ethyl benzene, toluene, styrene, and total xylenes have been detected
above MCLs at wells installed as part of State Leaking Underground Storage Tank (LUST)
investigations (e.g., MOBIL2-1). Although initially detected at concentrations higher than the
corresponding MCL, none of these chemicals has been detected above the MCL since 1996.
Therefore, EPA has not included these substances in Table 12.
This ROD does not address either the remediation approach or cleanup standards for methyl
tertiary butyl ether (MTBE). Only recently has MTBE been detected at IBW-South at levels
significantly above the Arizona HBGL of 35 ug/L and EPA's health advisory range of 20 to 40
Mg/L for taste and odor. Given the recent detection of significant levels of MTBE, limited
toxicity data available, and other factors, MTBE was not determined to be a chemical of concern
11-82 RDD-SFO982450006.DOC (OH2W DOC) (97)
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I DECISION SUMMARY
in EPA's 1997 Risk Assessment. The elevated levels of MTBE are located in a small part of the
central contaminated area, which is covered by a corrective action plan issued by the ADEQ
Leaking Underground Storage Tank (LJST) program. If it becomes apparent that ADEQ's UST
efforts will not result in the cleanup of MTBE in the aquifer, EPA will evaluate the necessity
and appropriateness of remedial action for MTBE. Additionally, if the contingency remedy is
activated for the VOCs where MTBE is found, and if MTBE thus would be present in extracted
groundwater, EPA would evaluate treatment systems and seek to treat the extracted
groundwater to the appropriate discharge level considering the end use of the treated
groundwater and other relevant circumstances.
Other chemicals have been detected but are not expected to be present in extracted ground-
water for a variety of reasons, including infrequent detections or detections at very low con-
centrations. Such chemicals have not been identified as chemicals of potential concern (COPCs)
or COCs because of their infrequent detection and low levels; thus, EPA need not establish
aquifer cleanup standards for these chemicals and has not included them in Table 12.
ARARs Regulating Groundwater Discharge Concentrations
This section addresses chemical-specific ARARs for the onsite treatment of extracted
groundwater.
Section 304 of the CWA requires EPA to publish water quality criteria for specific pollutants or
their by-products. The Federal Clean Water Act, 33 U.S.C. § 1251, et seq., and its implementing
regulations, the National Pollutant Discharge Elimination System (NPDES), 40 CFR Parts 122-
125, require direct discharges from CERCLA sites to surface waters to meet substantive Clean
Water Act limitations. EPA develops two kinds of water quality criteria: one for the protection
of human health and another for the protection of aquatic life. Federal water quality criteria are
non-enforceable guidelines used by the states to set water quality standards for surface water.
The states develop water quality standards to protect existing and attainable uses of the
receiving water.
The limits for extracted groundwater quality will vary with the end use, which is to be finalized
during Remedial Design. If discharge is to surface waters, state water quality standards will
generally be ARARs; if discharge is to groundwaters, other standards are triggered. The
possible end-use ARARs are discussed below.
Discharge to Tempe Canal No. 6
In Arizona, the narrative and numerical water quality standards promulgated pursuant to the
Clean Water Act discussed above, found in ARS §49 - 222 and AAC §R18-11-108 and 109, are
applicable to discharges to surface waters to protect the beneficial uses of the water. These
standards vary with the designated beneficial use of the receiving water, pursuant to
AAC R18-11-104. The beneficial uses may include domestic water source, full body contact,
partial body contact, fish consumption, use by aquatic organisms and wildlife, agriculture
irrigation, and agriculture livestock watering. If treated groundwater is discharged to SRP
Tempe Canal No. 6, then it must meet the standards for the protection of domestic water
sources because the water in the canal is used as a source of drinking water. The drinking water
source numeric water quality standards are identical to the federal SDWA MCLs for the
following substances: benzene, 1,2-dibromoethane, 1,2-dichloroethane, 1,1-dichloroethene,
1,2-dichloropropane, TCE, bromodichloromethane, and chloroform (AAC Title 18, Chapter 11,
Section R18-11-109 and Appendix A). For 1,1,2,2-tetrachloroethane, the Arizona Standard is
RDD-SFO/982450006.0OC
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BKCISION SUMMARY
0.17 ug/L. Because state limits are not more stringent, the federal MCLs will be applicable,
unless otherwise indicated in Table 12. The MCLs and other standards are presented in Table
12. The water quality standards that the treated groundwater would have to meet prior to
discharge to Tempe Canal No. 6 would typically be presented in the NPDES substantive
requirements.
Arizona's antidegradation policy for navigable waters is applicable to the discharge of treated
groundwater to navigable water (AAC §R18-11-107). This regulation states that where existing
water quality in a navigable water does not meet applicable water quality standards, degrada-
tion of the water is not allowed. Where the existing water quality exceeds applicable standards,
the existing quality will be maintained and protected. According to SRP personnel, Tempe
Canal No. 6 is considered a navigable water; therefore, the antidegradation policy applies to
discharges of treated groundwater to the canal.
Discharge to Town Lake
If treated groundwater is discharged to Town Lake, then the numerical water quality stan-
dards, both acute and chronic, for Aquatic and Wildlife (warm water fishery) (A&Ww) would
be applicable to protect the beneficial uses of Town Lake. These beneficial uses include use of
the surface-water body by animals, plants, or other organisms (excluding salmonids) for
habitation, growth, or propagation. According to COT and ADEQ personnel, the beneficial uses
of Town Lake do not include domestic water supply or swimming; therefore, the water quality
standards for full or partial body contact and drinking water do not apply. These A&Ww
standards are presented in Table 12. Although not an ARAR, NPDES requirements would
apply to the offsite discharge of treated groundwater to Town Lake.
Reinfection
As discussed above, the Arizona Aquifer Water Quality Standards (AAC §R18-11-401 et seq.)
are standards developed to protect human health and the uses of the aquifer by preventing
discharges, including treated groundwater that is reinjected to groundwater above certain
concentrations. These standards are currently identical to the SDWA MCLs and state MCLs;
thus, federal MCLs (and more stringent state MCLs) are the relevant and appropriate ARARs
for reinjection. If treated groundwater is reinjected into a contaminated aquifer, then the
reinjection cannot cause additional degradation of the aquifer.
12.2 Location-Specific ARARs
Location-specific ARARs differ from chemical-specific or action-specific ARARs in that they are
not closely related to the characteristics of the wastes at the site or to the specific remedial
action being taken. Location-specific ARARs are concerned with the area in which the site is
located. Actions may be required to preserve or protect aspects of the environment or cultural
resources of the area that may be threatened by the existence of the site or by the remedial
actions to be undertaken at the site. Location-specific ARARs for the IBW-South site are listed
in Table 13.
Extraction of contaminated groundwater at the IBW-South site may occur within the SRP
service area as part of the remedial action. If groundwater is extracted from within the SRP
service area, substantive requirements will be obtained from SRP as necessary. In addition, if
groundwater is extracted from within the SRP service area and used outside the service area
11-84 ROD-SFO982450006.DOC (CU363.00C) (97)
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II DECISION SUMUARY
(i.e., Town Lake), discussions with SRP will be conducted to consider such issues as water
quality, water rights, water accounting, cost, liability, and operational concerns.
12.3 Action-Specific ARARs
Action-specific ARARs have been identified for the implementation of the remedial action. A
description of the requirements associated with some of the significant ARARs and a discussion
of the conditions under which the ARAR is applicable or relevant and appropriate is included
below. The actions addressed include components of the extraction, treatment, and
groundwater end-use options for the remedial action. Action-specific ARARs for the IBW-South
site are presented in Table 13.
Hazardous Waste Management ARARs Under RCRA
The Resources Conservation and Recovery Act (RCRA), as amended, regulates the
management, treatment, storage, and disposal of solid and hazardous wastes. The RCRA
program is a delegable program: the states may manage the program in lieu of EPA if the state
statutes and regulations are equivalent to or more stringent than the federal statutes and
regulations. EPA authorized Arizona to run the RCRA hazardous waste program; therefore, the
relevant provisions of the state statutes and regulations are treated as the federal requirements,
in lieu of the federal statutes and regulations. Arizona requirements that exceed the scope of the
federal requirements for these programs are treated as state requirements. Therefore, in some
cases the applicable or relevant and appropriate RCRA requirement will be cited as state law
and in other cases as federal law.
At the IBW-South site, the contaminated groundwater is not a listed RCRA hazardous waste
because insufficient information exists at this time on the genesis of the groundwater
contamination to determine whether the groundwater could be listed. The groundwater is not a
characteristic hazardous waste because the contaminants in the groundwater are below the
levels established for the characteristic of toxicity. Consequently, the RCRA requirements that
are triggered by the hazardous nature of waste are not applicable to the untreated ground-
water, but are relevant and appropriate. For these same reasons and because of EPA's exception
for contaminated media (e.g., memorandum from Silvia K. Lowrance to Jeff Zelikson, January
24,1989), the groundwater that has been treated to health-based standard (i.e., MCLs) would
not be a RCRA hazardous waste, and the RCRA requirements would not be triggered. Some
RCRA requirements are applicable or relevant and appropriate to excavated soils, spent carbon,
or other wastes resulting from the remedial efforts (if such materials are characterized as
hazardous waste) and are discussed below.
Storage and Handling
The substantive requirements for storage of hazardous waste of RCRA's regulations found in
40 CFR 264, as incorporated into or modified by AAC R18-8-264, are applicable to the storage of
hazardous wastes generated onsite, such as contaminated carbon. These include requirements
for container storage, management, and secondary containment; they are summarized in
RDD-SFO/982450006. DOC (UR263.00C) (97) 11-85
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TABLE 13
LocalJon-Specific and Acton-Specific ARARs tor the IBW-Soutti Site
Location
Requirement
Prerequlslte(s)
Citation
Classification
Comments
Location - Specific ARARt
Within 100-year
lloodplain
Facility must be designed,
constructed, operated, and
maintained to avoid washout.
RCRA hazardous waste;
treatment, storage, or
disposal.
40 Code ol Federal
Regulation (CFR) §264.18
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TABLE 13
Location-Specific and Aden-Specific ARARs tor foe IBW-South Site
Location
Requirement
Prerequlsite(s)
Citation
Classification
Comments
location - Specific ARAB*
Within area where
action may cause
irreparable harm. loss.
or destruction of
significant artifacts
Place where artifacts.
human remains, or
funerary objects are
discovered.
Historic project owned
or controlled by federal
agency
Critical habitat upon
which endangered
species or threatened
species depend
Action to recover and preserve
artifacts.
Requirements for archedogical
discovery and preservation.
Action to preserve historic
properties; planning of action to
minimize harm to National Historic
Landmarks.
Action to conserve endangered
species or threatened species,
including consultation with the
Department of the Interior. Lists
species ol birds protected by four
treaties between the U.S., Canada.
Mexico, Japan, and Russia.
Alteration of terrain that
threatens significant scientific.
prehistoric, historic, or
archaeological data.
Discovery of artifacts, human
remains, or funerary objects.
Property included in or eligible
for the National Register of
Historic Places.
Potential presence of
endangered species or
threatened species or
migratory birds.
National Archaeological and Applicable
Historical Preservation Act
(16 USC Section 469); 36
CFR Part 65
ARS Section 41 -84 1 through Applicable
41-844
National Historic Applicable
Preservation Act Section 106
(16USC4700fseq.);36
CFR Part 800. 40 CFR
§6301
Endangered Species Act of Potentially
1973 (16 USC 1531 el seq.). applicable
50 CFH Part 200. 50 CFR
Part 402. Migratory Bird
Treaty Act (16 USC 703-712)
The IBW-South site Is essentially completely
developed. However, artifacts have been located In
areas near IBW-South. The potential for impacts to
artifacts will need to be considered and addressed
during the design and Implementation of the remedial
action.
Archaeological objects have been discovered.
according to the State of Arizona, near the site.
The DCE Circuits Building is included in the National
Register of Historic Places (Inventory No. 151). The
groundwater remedy will not impact this building.
Applicable if critical habitats are discovered. No
endangered species are currently known to exist on
the IBW-South site. Migratory birds must be pro-
tected from poisoning at hazardous waste sites. Trie
remedy will not expose migratory birds to hazardous
materials.
ROD SFO/982460003.0OC-3 (CAH349 OOC)
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TABLE 13
Location-Specific and Action-Specific ARARs (or the IBW-South Site
Action
Requirements
Pr«requlsite(s)
Citation
Classification
Comments
Action-Specific ARAR»
Container storage (onsite)
Container ol hazardous waste
must be: maintained in good
condition; compatible with
hazardous waste to be stored:
and dosed during storage
(except to add or remove
waste).
Place containers on a stepsd.
sufficiently impervious crack-
free base, and protect from
contact with an accumulated
liquid. Provide containment
system with a minimum capa-
city of 24-hour. 25-year storm
plus 10 percent of the volume ol
containers ol tree liquids or the
volume of the largest container.
whichever is greater.
Remove spilled or leaked waste
in a timely manner to prevent
overflow of the containment
system.
At closure, remove all hazard-
ous waste and residues from
the containment system, and
decontaminate or remove all
containers and liners.
RCRA hazardous waste held
for a temporary period before
treatment, disposal, or storage
elsewhere, in a container (i.e..
any portable device in which a
material is stored, transported,
disposed ol. or handled).
Containers used tor storage
ol hazardous waste onsite tor
more than 90 days must be:
• Maintained in good
condition (R18-8-264.171)
• Compatible with other
stored wastes (R18-8-
264.172)
• Closed during storage
(R18-8-264.173)
• Placed on a sloped, crack-
tree base with containment
system in place capable of
handling 10 percent ol the
Iree liquids stored (R1B-B-
264.175)
• At closure, all hazardous
wastes and residues from
containment system must
be removed (R18-8-
264.178)
• Secondary containment is
required lor storage ol
hazardous wastes over
90 days (R18-8-264 175).
• Prior to transportation,
containers should be
packaged, labeled,
marked, and placarded in
accordance with RCRA
and DOT requirements
(R 18-8-262.30 through
H 18-8-262.33).
Applicable to These requirements are applicable or relevant and
hazardous waste appropriate lor untreated soil, groundwater. or
treatment system residuals (e.g., contaminated
carbon) that is a RCRA characteristic hazardous
waste that might be containerized and stored onsite
prior to treatment or final disposal. Currently, the
untreated groundwater is not a RCRA hazardous
waste, but these RCRA requirements are relevant
and appropriate to it.
RDD-SFO/982460003.DOC-4 (CAH349 DOC)
-------
TABLE 13
Location-Specitic and Action-Specific ARARs lor the IBW-South Site
Action
Requirements
Prerequisites)
Citation
Classification
Comments
Action-Specific ARAR»
Storage of hazardous wastes
subject to land disposal
restrictions
Control ol fugitive dust
Processing, storing, using, or
transporting of solvents or
volatile compounds: activities
that can emit odors or other
gaseous air contaminants.
Air Stripping
Treatment (miscellaneous)
Restrictions on storage, and
requirements tor marking and
dating drums, tanks, etc.
Decrease emissions of fugitive
dust from construction
activities.
To adopt available means to
effectively reduce the
contribution to air pollution (torn
evaporation, leakage, discharge
or materials.
Control of air emissions of
volatile organics and gaseous
contaminants.
Control of air emissions from air
strippers at Superfund sites.
Standards for miscellaneous
units require new units to satisfy
environmental performance
standards tor protection of
groundwater, surface water,
and air quality, and by limiting
surface and subsurface
migration.
Wastes subject to land
disposal restrictions (LOR)
that do not meet the treatment
standards.
Construction activities that
generate dust.
Construction or other activities
that could emit odors or other
gaseous contaminants.
Emissions of VOCs or
gaseous air contaminants.
Groundwater remedial actions.
Treatment of hazardous
wastes in units not regulated
elsewhere under RCRA (e.g.,
air stoppers).
40 CFR Section 268 50
Maricopa County
Rule 310
Maricopa County Rule 320
Maricopa County Rules 200.
270. and 330
OSWER Directive
No. 9355 0-28
40 CFR §264.601
Applicable it any
hazardous wastes
are subject to LDRs
Applicable
Applicable
Applicable
TBC
Relevant and
Appropriate
Limits fugitive dust emissions during construction
Where means are available to reduce air pollution
from leaks, discharge, or evaporation, the use of
such controls is mandatory.
Rules to control air emissions for the air stripping and
vapor-phase activated carbon offgas treatment option
for the remedial action.
The substantive portions of these requirements may
be relevant and appropriate lo the construction,
operation, maintenance, and closure of any
miscellaneous treatment unit (a treatment unit fiat Is
not elsewhere regulated) constructed on the IBW-
South site for treatment of groundwater.
RDD-Sf0/982460003.DOC 5(CAH349 DOC)
-------
TABLE 13
Location-Specific and Action-Specttc ARARs lor the IBW-South Site
Action
Requirement*
Prerequltlteft)
Citation
Classification
Comments
Action-Specific ARARs
Underground injection of
wastes and treated
groundwater
Underground Injection Control
(UIC) program prohibits:
• Injection activities that
allow the movement ot
contaminants into under-
ground sources of drinking
water (USDW) and result
in violation of MCLs or
adversely affect health.
Underground Injection of
treated hazardous waste.
40 CFR §144.12- 16
Substantive requirements of
th» Aquifer Protection Permit
Program, including AAC
§R18-9-106, -11 Land-112..
Applicable or Certain substantive requirements of the UIC program
Relevant and will not apply to onsite relnjection of treated
Appropriate if groundwater. Including those governing Class IV
reinfection is wells (wells used for the reinfection of extracted and
selected as treated groundwater) because both extracted and
discharge option. treated groundwater at the site are not considered
RCRA hazardous wastes. Such requirements are
relevant and appropriate If reinfection is selected as
the end use for treated groundwater.
Construction of new Class
IV weds and operation and
maintenance o< existing
wefts except weto used to
retnject treated ground-
water as part ot a
CERCIA action.
Substantive requirements of the Arizona Aquifer
Protection Permit Program, including recharge, poor
quality groundwater withdrawal, and wed installation
requirements are applicable.
Injection pressure may not
exceed a maximum level
designed to ensure that Injec-
tion does not Initiate new
fractures or propagate existing
ones and cause the movement
of fluids Into a USDW.
Continued monitoring of
injection pressure, flow rate.
and volume is required.
Relnjection with Class V wells
shafl not cause a violation of
primary MCLs in the receiving
aquifer.
Continued monitoring of Injec-
tion pressure. Now rate, and
volume is required.
RDD-SFO/9B2460003 DOC-6 (CAH349 DOC)
-------
TABLE 13
Location-Specific and Acton-Specific ARARs lor the IBW-South Site
Action
Requirements
Prerequisites)
Citation
Classification
Comments
Action-Specific ARARs
New well construction and
withdrawal, treatment, and
reinjection ol extracted
groundwaler occurring as part
ol a CERCLA remedial action.
Specific requirements for wells.
groundwater withdrawal,
treatment, and reinjection.
CERCLA remedial action
ARS §45-454 01
Applicable Exempts new well construction, withdrawal.
treatment, and relnjectton Into the aquifar ol
groundwater that occur as part ol a CERCLA
remedial action from requirements of Arizona
Groundwater Code, except that they must comply
with the substantive requiremens of:
• ARS 45-594 (well construction standards)
• ARS 45-595 (well construction requirements)
• ARS 45-596 (notice of intenton to drill well)
• ARS 45-600 (filing ol log by driller of well)
In addition, this statute requires that uses of
extracted groundwater be consistent with various
articles ol Chapter 2 of the Groundwater Code, which
are discussed In the text.
RDO SFO/982460003.DOC-7 (CAH349.DOC)
-------
II DECISION SUMMARY
Table 13. In addition, some requirements pertaining to the handling of hazardous wastes in
R18-8-262.30 through R18-8-262.33 are applicable to any hazardous wastes generated onsite.
Treatment
The substantive requirements for miscellaneous RCRA units may be considered relevant and
appropriate to air stripping towers and offgas treatment units managing or treating hazardous
wastes even though the site and remedial efforts are not a treatment, storage, or disposal
facility. These include the substantive requirements of 40 CFR 264.601, which regulate the
design, operation, and maintenance of miscellaneous units.
Reinfection ARARs
If reinjection to the aquifer of extracted, treated groundwater is selected as the end use for the
treated groundwater, certain additional action-specific ARARs will be implemented. (The
chemical-specific ARARs are discussed above, under Reinjection.)
Federal regulations that govern underground injection programs are found in 40 CFR 144.12
and 144.13. According to these regulations, the injection of treated ground water cannot allow
movement of contaminants into underground sources of drinking water which may result in
violations of MCLs or adversely affect health. Reinjection of treated groundwater into the same
formation it was withdrawn from is allowed as part of a CERCLA action.
If treated groundwater is reinjected into an aquifer, substantive requirements concerning
recharge, poor quality groundwater withdrawal, and well installation will be applicable
(Arizona Aquifer Protection Permit program [AAC §R18-9-108, -111, and -112J).
Groundwater Remediation Action-Specific ARARs
Arizona's state Superfund program, known as the Water Quality Assurance Revolving Fund
(WQARF), provides for cleanup of hazardous substances in groundwater (ARS § 49-281 et seq.).
Section 49-282.06 of WQARF, as recently amended, requires groundwater remedial actions to
ensure the protection of public health, welfare, and the environment; to manage and cleanup
hazardous substances, to the extent practicable, so as to allow for the maximum beneficial uses
of the waters of the state; and to be reasonable, necessary, cost-effective, and technically fea-
sible. These criteria are very similar to criteria applicable to response actions under CERCLA
and the NCP. Those authorities require that remediations be protective of human health and
the environment, meet ARARs, and consider advancing numerous other factors, including
long-term permanence, the reduction of toxicity, mobility or volume; implementability, and
cost-effectiveness. In addition, the NCP requires that groundwater remedial actions generally
attain federal MCLs and non-zero MGCLs, where relevant and appropriate; the NCP also
requires remedial alternatives developed to take into account the expectation that the remedial
action will return groundwater to beneficial uses wherever practicable within a reasonable time
frame for the site circumstances.
The WQARF provision does not appear to be more stringent than those in the NCP and there-
fore its requirements are not ARARs. Nonetheless, any remedy EPA selects will meet the
WQARF statutory criteria by meeting the NCP requirements.
A WQARF regulation, Section R18-7-109, addresses remedial action requirements. That
regulation incorporates many of the requirements of WQARF Section 49-282.06 discussed
11-92 BDD-SFO/982450006.DOC (CiR263.DOC) (97)
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II DECISION SUMMARY
above, and incorporates by reference provisions of state law establishing that all definable
aquifers are drinking water aquifers unless they qualify for an exemption, and that establish
water quality standards for discharges to aquifers. Section R18-7-109 is not more stringent than
the requirements in the NCP and is therefore not an ARAR. However, the regulation requires
remedies to be consistent with provisions of the Arizona Groundwater Code. Section 45-454.01
of the Arizona Groundwater Code, the substantive requirements of which would apply to the
site, exempts from the Groundwater Code's requirements onsite construction of wells, and the
withdrawal, reinjection, and treatment of groundwater occurring as part of and on the site of
CERCLA remedial actions, with few exceptions. These exceptions include the substantive
provisions of the following Arizona statutes, the substantive requirements of which are
applicable to the installation of groundwater extraction or reinjection wells.
• ARS § 45-594 (well construction standards)
• ARS § 45-595 (well construction requirements)
• ARS § 45-596 (notice of intention to drill well)
• ARS § 45-600 (filing of log by driller of well)
In addition, ARS Section 45-454.01 requires that the uses of extracted groundwater at the site be
consistent with the following articles of the Arizona Groundwater Code, Title 45, Chapter 2:
• Article 5 (grandfathered groundwater rights)
• Article 6 (groundwater rights)
• Article 7 (groundwater withdrawal permits)
• Article 8 (transportation of groundwater)
• Article 8.1 (withdrawal of groundwater for transportation for active management area)
• Article 9 (groundwater management)
• Article 10 (wells)
Air Emissions Requirements
The federal Clean Air Act (CAA), 40 CFR 7401, et seq., implemented through its regulations at
40 CFR Parts 50-99, establish National Ambient Air Quality Standards (NAAQS). The Clean Air
Act's NAAQS are not ARARs because they are not enforceable as applied to individual sources.
Rather, the NAAQS are implemented through State Implementation Plans (SIPs).
Maricopa County has issued air pollution control rules, the substantive requirements of which
apply to the air stripper that may be used to treat extracted groundwater at IBW-South, and are
discussed below:
1. Maricopa County Rule 200, Permit Requirements—Specifies general requirements for major
sources of air emissions. Major sources are defined as those sources capable of emitting
100 tons per year or more of any regulated air pollutant. Rule 200 exempts sources where
total uncontrolled VOC air emission would be less than 3 pounds per day. The IBW-South
groundwater treatment site is not expected to be a major source of VOC emissions;
however, the pretreated airstream from the air stripping tower may require treatment or
control of the offgas if found to exceed 3 pounds of VOC emissions per day.
2. Rule 270, Performance Tests—Establishes performance testing requirements for owners and
operators of stationary sources to determine compliance with emission standards.
RDD-SFO/982450006.00C (CLR263.DOC) (97) 11-93
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II DECISION SUMMAflY
3. Rule 310, Open Fugitive Dust Emissions—This regulation will apply to construction of the
treatment system. It imposes limits on the emission of particulate matter for any action,
including construction activities, that can cause open fugitive dust emissions.
4. Rule 330, Volatile Organic Compounds—VOC emissions are limited to no more than
40 pounds per day. If this limitation is exceeded, emission of VOCs to the atmosphere must
be reduced by specified methods including incineration, adsorption, or other processes not
less effective than incineration or adsorption. Rule 330 includes efficiency requirements for
the reduction process, and monitoring and testing requirements for VOC emissions.
Additional performance standards are addressed in Table 12.
11-94 RDD-SFO962450006.DOC (CLR263.DOC) (97)
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HDEO90N SUMMARY
13.0 Statutory Determinations
Under CERCLA Section 121, EPA must select remedies that are protective of human health and
the environment, comply with ARARs, are cost-effective, and utilize permanent solutions and
alternative treatment technologies or resource recovery technologies to the maximum extent
practicable. In addition, CERCLA includes a preference for remedies that employ treatment
that permanently and significantly reduces the volume, toxicity, or mobility of hazardous
wastes as a principal element. The following sections discuss how the selected remedy and the
contingency remedy meet these statutory requirements.
13.1 Protection of Human Health and the Environment
The selected remedy and contingency remedy will protect human health and the environment
by extracting and treating VOC-contaminated groundwater and MNA to ensure that the
existing contamination does not migrate to groundwater users and that VOC contamination is
reduced to groundwater cleanup standards in a reasonable time frame of approximately 30
years. Institutional controls will be enforced to protect the public from exposure to
contaminated groundwater in the IBW-South area until cleanup standards are achieved.
The combination of groundwater extraction and natural attenuation will reduce the VOC con-
centrations in groundwater at the IBW-South site. Groundwater at the IBW-South site is
currently used for industrial supply. Inactive municipal wells are also present. PCE and TCE
were detected most frequently in the UAU and the MAU/LAU wells.
The selected remedy and contingency remedy will reduce the VOC contaminant levels to
protective ARAR levels to restore groundwater to its beneficial use. The selected and
contingency remedies will protect the groundwater resource by ensuring that VOC
contamination in excess of aquifer cleanup standards does not migrate beyond compliance
boundaries established in this ROD.
No short-term threats are associated with the selected remedy and contingency remedy that
cannot be readily controlled. In addition, no adverse cross-media impacts are expected from the
selected and contingency remedies.
13.2 Compliance With Applicable or Relevant and Appropriate
Requirements
The selected remedy and contingency remedy of groundwater extraction and treatment and
MNA will comply with all ARARs identified for this action at the IBW-South site. The
groundwater extraction, treatment, and MNA in selected areas will reduce the groundwater
concentrations to chemical-specific ARARs within a reasonable time frame and ensure that
additional migration of contaminated groundwater is limited. The ARARs for the selected
remedy and contingency remedy are presented in detail in Section 12.0.
RDD-SFO/982450006.DOC (CLR263 DOC) (97) 11-95
-------
nOCOSION SUMMARY
13.3 Cost-Effectiveness
The selected remedy and contingency remedy are cost-effective for mitigating the risks posed
by VOC-contaminated groundwater at the IBW-South site. Section 300.430(f)(l)(ii)(D) of the
NCP requires EPA to determine cost-effectiveness by evaluating the cost of an alternative
relative to its overall effectiveness. Effectiveness is defined by three of the five balancing
criteria: long-term effectiveness, short-term effectiveness, and reduction of toxicity, mobility,
and volume of the contamination through treatment. The overall effectiveness is then
compared to cost to ensure that the selected remedy is cost-effective.
The selected remedy will have long-term effectiveness because, by extraction and MNA, it will
reduce contaminant levels to aquifer cleanup standards and maintain them. The selected
remedy will have short-term effectiveness because there are minimal adverse impacts to the
community, workers, and the environment during the implementation of the remedial action.
The selected remedy will achieve a reduction in toxicity, mobility, and volume through
treatment where treatment is warranted. Relative to the cost of the remedy, these results will
provide a good value and will be cost-effective.
The estimated present worth cost of the selected remedy is $22,460,000. Although lower cost
alternatives were evaluated (Alternatives 1 through 3), these alternatives are not effective and
do not adequately meet EPA's threshold criteria of overall protection of human health and the
environment and compliance with ARARs, nor do they ensure as much short-term effective-
ness or reduction of toxicity, mobility, and volume of contamination through treatment.
Alternatives 5 and 6 may somewhat speed the groundwater restoration, but these alternatives
cost approximately $14 million and $26 million more than the selected remedy, respectively,
and pose greater implementability difficulties than does Alternative 4. The costs represent
increases of 64 percent and 115 percent, respectively. The selected remedy (Alternative 4) is the
lowest cost remedy that is also effective and achieves EPA's remediation goals within a
reasonable time frame. Therefore, the selected remedy is the most cost-effective remedy for
remediation of VOC-contaminated groundwater at the IBW-South site.
The additional cost of the contingency remedy of extraction and treatment in MNA areas is
estimated at $2,570,000. The contingency remedy will have the same effectiveness as the
extraction component of the selected remedy, and is thus cost-effective.
13.4 Utilization of Permanent Solutions and Alternative Treatment
Technologies to the Maximum Extent Practicable
EPA has determined that the selected remedy and the contingency remedy represent the
maximum extent to which permanent solutions and treatment technologies can be used in a
practicable manner at the IBW-South site. Of those alternatives that are protective of human
health and the environment and comply with ARARs (Alternatives 4,5, and 6), EPA has
determined that the selected remedy and contingency remedy provide the best balance of
tradeoffs in terms of the five balancing criteria, while also considering the statutory preference
for treatment as a principal element and considering State and community acceptance.
The selected remedy and contingency remedy treat the threats posed by the site, achieving
significant reductions in VOC concentrations in groundwater. The selected remedy and
II-96 RDD-SFO/982450006.DOC (CLR263.00C) (97)
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n DECISION SUMMARY
contingency remedy satisfy the criteria for long-term effectiveness by reducing VOC
contamination in groundwater through extraction and MNA and destroying the VOCs during
regeneration of the offgas system carbon or other treatment residual. Groundwater
containment will effectively reduce the mobility of the VOCs in groundwater; extraction,
natural attenuation, and treatment will reduce the toxicity and volume of VOC-contaminated
groundwater. The selected remedy and contingency remedy do not present short-term risks
different from other alternatives that incorporate treatment. No special implementability issues
set the selected and contingency remedies apart from the other alternatives evaluated.
13.5 Preference for Treatment as a Principal Element
The selected remedy includes extraction and treatment of the contaminated groundwater in the
western UAU area of contamination (and potentially other areas if the contingency remedy is
implemented) through air stripping and carbon adsorption, or an alternate treatment option to
be selected during remedial design. In combination with the remedy selected in the Vadose
Zone OU ROD, the selected remedy and contingency remedy address the principal threats
posed by the IBW-South site through the use of treatment technologies. By using treatment as a
significant portion of the remedy, the statutory preference for remedies that employ treatment
as a principal element is satisfied.
13.6 Five-Year Review Requirements
This remedial action is expected to take more than 5 years to achieve aquifer cleanup levels to
allow for unlimited use and unrestricted exposure. Accordingly, by policy, EPA will perform a
review not less than 5 years after completion of the construction for all remedial actions at the
site, and may continue such reviews until EPA determines that hazardous substances have
been reduced to levels protective of human health and the environment.
13.7 Implementability
The selected remedy is considered to be administratively and technically implementable. The
services and materials required to implement this remedy are readily available and use current
technologies.
13.8 Cost
The selected remedy is not the least costly of the alternatives considered, but it has significant
advantages over less costly alternatives. In particular, unlike those alternatives that are less
expensive, the selected remedy will result in cleanup levels being met within a reasonable time
frame of approximately 30 years through active extracting and treating of groundwater and
through MNA processes.
13.9 State Acceptance
The State of Arizona concurs with the selected remedy for IBW-South.
RDO-SFO/982450006.00C (Clfl263.00C) (97) "-97
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I DECISION SUMU/Wr
13.10 Community Acceptance
In general, comments on the Proposed Plan for IBW-South have indicated that the community
supports the selected remedy for VOCs in ground water.
Comments from some PRPs opposed EPA's preferred alternative for groundwater because they
felt that MNA could be implemented without any groundwater extraction and treatment. In
response to these concerns, EPA performed additional groundwater modeling but still finds
that ARARs cannot be achieved within a reasonable time frame without active treatment in the
western contaminated area. Extraction and treatment are therefore required, and the specific
target volume of groundwater to be extracted will be determined during remedial design.
The community has expressed concern about the SRP Tempe Canal No. 6 as an end use. The
community and some government agencies generally support Alternative 4 more than
Alternatives 5 and 6 because it is more cost-effective and it extracts a smaller volume of
groundwater.
H-98 RDD-SFO/982450006.DOC (Cl.R263.DOC) (97)
-------
Appendix A
Cost Evaluation
-------
APPENDIX A
Cost Evaluation
A.1 Introduction
The purpose of this appendix is to document the estimated capital, annual operation and
maintenance (O&M), and present worth (PW) costs associated with the selected remedy and
contingency remedy for the Indian Bend Wash- South Superfund Site. These cost estimates
are order-of-magnitude estimates and are expected to be accurate within +50 to -30 percent.
The summary of the costs for the selected and contingency remedy is presented in Table
A-l.
TABLE A-1
Costs for the Selected Remedy and the Contingency Remedy
Cost
Capital
Annual O&M
30- Year Present Worth
5- Year Present Worth
Selected
Remedy
6,170.000
1.060,000
22,460,000
10,760,000
Contingency
Remedy
8,580,000
1,070,000
25.030.000
13.210.000
The components for each remedy consist of containment, treatment, end use, and
monitoring. The selected remedy consists of partial containment with three new UAU
extraction wells and a total flow of 2,940 gallons per minute (gpm). The contingency
remedy consists of partial containment with three additional new UAU extraction wells, as
well as those used in the selected remedy, and a total flow of 4,440 gpm. Appendix D of the
FS contains all the detailed information regarding the cost estimating procedures and
assumptions. Table A-2 in this Appendix shows the detailed parts for the components for
each remedy.
For cost comparison, a PW cost was calculated. The PW is the present value of the remedy
at some defined period in the future. Because the length of time to achieve remediation of
ground water is undefined, the PW is calculated for a 5-year and a 30-year time period, both
at an interest rate of 5 percent. The analysis of each remedy's power requirements and costs
are provided in Attachment A-l. Attachment A-2 summarizes the capital and O&M costs
for the treatment component of each remedy. The detailed capital and O&M costs for each
remedy are presented in Attachment A-3.
RDQOOMPflOJ/U792t/APP£NDIXA.DOC
-------
Table A-2
Component Details for the Selected Remedy and Contingency Remedy
Alternative
Flow (gpm]
Components
Selected Remedy
2,940
Contingency Remedy
4,440
Containment
Number of UAU Extactton Weds
Number of MAU Extraction Weds
Number of Existing COT Municipal Wells
Number of Additional Monitoring Wells
Number of Tetemeky Systems for each Extraction &
Rehjection Wefl
Number of Site Electricity Setups for each Extraction
WeB
3
0
0
10
3
3
Treatment
Treatment Plant
Number of Air Stripping Towers
Number of VGAC Units
Linear Feet of Conveyance Pipeline:
6" Diameter
8' Diameter
10' Diameter
12" Diameter
14' Diameter
16* Diameter
18" Diameter
20* Diameter
24* Diameter
28* Diameter
30* Diameter
1
2
0
0
4,400
1.000
5.500
0
0
0
0
0
0
6
0
0
10
6
6
2
4
0
0
7.400
9.500
5.500
0
0
0
0
0
0
End Use
Linear Feel of Distribution Pipeline:
6* Diameter
8* Diameter
10* Diameter
12* Diameter
14* Diameter
16* Diameter
18* Diameter
20* Diameter
24* Diameter
28* Diameter
30* Diameter
Distribution Pump Station (HP)
Number of Outfal Structures
Number ot UAU Reinfection Wells
Number of MAU Reinjecbon Wells
0
0
0
0
0
50
0
0
0
0
0
60
1
0
0
0
0
0
0
0
50
0
0
0
0
0
60
1
0
0
Monitoring
Monitoring Samples per Year
252 252
RDD/ODIN/PROJ/SIBW/Fina! Rerwdy
Pag* 1 of 1
-------
Attachment A-1
Pump Station and Power Cost Calculations
Parameter
Assumed Value
Power Cost
(S/Mi)
0.09
Pump/Motor
Efficiency
1
Treatnenl Plant
Residual Head
(ft)
30
End Use
Residual Head
(ft)
10
Elevation Head
(H)
20
Selected Remedy
End Use—Town Lake
Conveyance Pipeline and Pumping
Extraction Well
Extraction Well
EWA-1
EWA-2
EWA-3
Pumping
Rate (gpm)
990
870
1.080
Static Lift
(«)
75
75
75
Pipeline
Length (ft)
9,600
6,600
5.200
Friction
Loss («)
86
59
47
Extraction Well Pump
TDH(ft)
211
184
172
Calculated
HP
76
58
67
Installed HP
80
60
75
Total Flow
2.940
Distribution Pipeline and Pum
Pumping
Rate (gpm)
2.940
Static Uft
(«t)
0
Length (ft)
50
Friction
Loss (ft)
0
ping
TDH (ft)
50
Calculated
HP
54
Installed HP
60
Total HP Required =
Annual kWh =
Annual Power Cost =
254
1,660.469
149,442
Contingency Remedy
End Use—Town Lake
Conveyance Pipeline and Pumping
Extraction Well
Extraction Well
EWA-1
EWA-2
EWA-3
EWA-4a
EWA-Sa
EWA-6a
Pumping
Rate (gpm)
990
870
1.080
500
500
500
Static Lift
(«)
75
75
75
75
75
75
Pipeline
Length (ft)
9,600
6.600
5,200
9,300
9.700
9,700
Friction
Loss (ft)
86
59
47
84
87
87
Extraction Well Pump
TDH (ft)
211
184
172
209
212
212
Calculated
HP
76
58
67
38
38
38
Installed HP
80
60
75
80
60
75
Total Flow
4.440
Distribution Pipeline and Pum
Pumping
Rate (gpm)
4,440
Static Lift
(ft)
0
Length (ft)
50
Friction
Loss (ft)
0
ping
TDH (ft)
SO
Calculated
HP
81
Installed HP
60
Total HP Required =
Annual kWh =
Annual Power Cost =
281
1,839.064
165.516
RDOADDIN/PROJ/StBW/Final RorrxxJy
Page 1 oft
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Attachment A-2
Summary of Treatment Costs
Alternative
Sebctod ffomtdy
Contingtrcy Remedy
Treatment
Plant
1
1
Flow
(gpm)
2.940
4,440
Flow-walghtad
Concentration*
TCE
(ngrt-)
17
15
PCE
(P9/L)
0
0
Capital
Co«t($)
1,089.606
1,279.536
Annual
0AM ($)
773.737
774.951
RDD/ODIWPROVSIBW/Final Rem«}y
Pagei oil
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AttachmtntA-3
Estimated Capital and O&M Costs for the Selected Remedy and Contingency Remedy
Assumptions
1. Convsyancs Pjps Cost
2. Distribution Pj»s Cost
3. Pipeline Appurtsflancm
4. ExpSClsdfibof
Pipelne
Pimps
Wells
Traatmeni Plaits
Telemetry
SD« Electric
Ouftall Structure
s. OAM costs
Extraction Wells
Ppetne & Appurt.
Distribution Pumps
RanJKtnn Wels
Outtal Structure
Telemetry
Sle Electrical
6. Purwp Station Cost*
7. Lump Sam* lor fofcwing capital costs:
Telemetry tor Ex & Reinj. Weds
Sue Elect nc. tof Ex. Weils
Discharge Structure
MAU Reiriection Wells
UAU Extraction Wells
MAU Extraction Wells
Ad*onal UAU Monitoring Weds
Cement liner (of SRP23E. 2.9N
aVOCAiiMleslCosto
1 Physical Prapsdiss Aiulyticji Costs
tO.QA/QCFrs9Mney
1 1 . Constnidton Alswsncs
12. Bid Contingency
13. Seeps Continosncy
14. Lsgsl Fsss, PsrmMng Fss*. etc.
1 S. Ssrvicss during conttructio*
16. Engisssring Ossign
S per dam-nlP
5 perdiam-r^F
15% ol pipe capital cost subtotal
40 years
IS years
30 years
30 yean
X years
30 years
40 years
1% ol capital
0.5% ol capital
5%ot capital
2% of capital
3% ot capital
2% fl» capital
2% ol capjUl
1.200 per motor HP
20.000 perwel
30.000 perweH
50.000 each
210.000 each
76.000 each
170.000 each
76.000 each
1SO.OOO each
300 per sample
135 per sample
10% ol total number ol samples
12%
20%
20% Extraction. Rehjactkm. Conveyance
2%
6%
15%
17. Extndioa and isinjcdkm wsV costs Inelsds driHing, dsvstopmsnt. pump, and motor costs.
RDO/ODIN'PROJ/SIBW/Rnal Remedy
Page 1 oi 3
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Attachment A-3
Estimated Capital and O&M Costs for the Selected Remedy and Contingency Remedy
Alternative
End Use
Containment Scenario
Number of Treatment Plant*
Selected Remedy
Discharge to Town Lake
Partial
One
Facilities
UAU Extraction Web
MAU Extraction Wefc
A&ttoeal UAU MoMtorinf Welt
CeMMt Uner for SHPBE. M N
Trwtawn* Plait 1
No. Towers
No. VGACUMs
TreatMiitPlantl
Comeysnce Pe?eSn» (da-fo)
i
8
10
12
14
16
18
20
24
28
30
Subtotal
Appurtenances
Distribution P«Mfee
6
e
10
12
14
16
18
20
24
28
30
Subtota
AppUrtSMncaa
Power
Distrbtition Pump SUtioa (TP 1)
(HstrfertiM Pwnp Station (TP 2)
Tabmetry for EK. • rtowj. Wells
SteEbdric.forEi.Wtft>
CMtiHStrudur*
UAU Reinjsction Wets
Monftorino.
Annual nspoitinaOata Evaluation
Subtotal Capital Coot
Constructor) Allowance
8d Contingency
Scope Contingency
Total CoMtractmiCott
Legal Fees. Penrottjng Fees. etc.
Services During Construction
Total bnplemMtation Cost
Engineering Oeson Costs
Altornalivo Total Cost
Estimated
Quantity
to
;
NA
0
0
4,400
t.OOO
5.500
0
0
0
0
0
0
10,900
0
0
0
0
0
so
0
0
0
0
0
so
60
0
3
3
t
0
194
58
Unit
Each
Each
Each
IS
LS
LF
IF
LF
LF
IF
IF
LF
LF
LF
LF
LF
LS
LF
LF
LF
LF
LF
LF
LF
LF
LF
F
F
S
HP
HP
Each
Each
Each
Each
VOC samples per year
Property samples pat year
Unit Price (S)
$76.000
$170.000
$76,000
$150.000
X
40
50
60
70
80
90
100
120
140
150
30
40
50
60
70
80
90
100
120
140
150
1200
1200
20.000
30.000
50.000
210.000
300
135
Extended Capital
Cost ($)
228.000
760.000
150,000
1.089.606
i
220.000
60.000
385.000
(
0
0
0
0
0
665.000
99.750
0
0
0
0
0
4.000
0
0
0
0
0
4,000
600
72.000
0
60.000
90,000
50.000
0
3.268.956
392.275
653.791
653.791
4.968.813
99.376
298.129
5.366.318
804.948
$6.170.000
oaiiCost(S)
2.280
0
7.600
0
773.737
0
0
1.100
300
1.925
0
0
0
0
0
0
3.325
499
0
0
0
0
0
20
0
0
0
0
0
20
3
149.442
3.600
0
1,200
1.800
1.500
0
58.200
7.830
50.000
$1. 060.000
RDD/ODIM^PROJ/SIBW/Rnal Remedy
Page 2 of 3
-------
Attachment A-3
Estimated Capital and O&M Costs for the Selected Remedy and Contingency Remedy
Alternative
EndUae
Containment Scenario
Number of Treatment Plants
Contingency Remedy
Oltcharga to Town Lake
Partial
One
Facilities
UAU Extraction We*
MAU Extraction Wei»
Addkonal UAU aVutoring Well*
Cement liner lot SRP23E, 2.9 N
Treatment Plant 1
No. Towers
No. VGAC Urals
Treatment Plaat 2
Conveyance Pipeline (db«)
6
8
10
12
14
16
18
20
24
28
30
Subtotal
Appurtenance*
Distribution Pipeline
6
8
10
12
14
16
IB
20
24
28
30
SvMoti
Appurtenance*
Power
Distribution Pump 9
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