PB94-964501
EPA/ROD/R09-94/105
July 1994
EPA Superfund
Record of Decision:
Indian Bend Wash Site,
Tempe, AZ
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o
tnvironrr
Protection
Agency
RECORD OF DECISION
Volume 1
Declaration, Decision Summary,
Response Summary
OPERABLE UNIT:
VOCs in Vadose Zone
Indian Bend Wash
Superfund Site, South Area
Tempe, Arizona
Plug-in and Presumptive
Remedy Approach
September 1993
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3EPA
RECORD OF DECISION
OPERABLE UNIT:
VOCs in Vadose Zone
Indian Bend Wash Superfund Site, South Area
Tempe, Arizona
Plug-in and Presumptive Remedy Approach
u.s. Environmental Protection Agency
Region IX
75 Hawthorne Street
San Francisco, California 94105
Volume 1 of 2
Declaration
Decision Summary .
Response Summary
September 1993
Uni1ed States
Envi ron mental
Protection
Agency
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CONTENTS-Volume 1 of 2
Section
Page
I
Declaration
. 1. Site Name and Location
2. Statement of Basis and Purpose
3. Assessment of the Site
4. Statement on Use of Innovative Approaches
5. Description of the Selected Remedy
6. Statutory Determinations
1-1
1-1
1-1
1-1
1-2
1-2
1-3
I
I
I
I
II Decision Summary .
1. Site Name, Location, History, and Description
1.1 Site Discovery and Listing
1.2 Land Use and Demographics
1. 3 Climate
1.4 Topography
1.5 Surface and Groundwater
1.6 Contaminants of Concern and Types of Sources
1.7 History of EPA Involvement
1. 8 Lead Agency
2. Statement on Innovative Approaches
3. Investigation Approach and Enforcement Activities
3.1 Investigation Approach
3.2 Enforcement Activities
4. Scope and Role of this Decision Document within the
Site Strategy .
5. Highlights of Community Participation
6. Summary of Site Characteristics
6.1 Fateffransport of Contaminants of Concern
6.2 Soils .
6.3 Groundwater and Hydrogeology
7. Justification for Presumptive Remedy
7.1 Presumptive Remedy Approach
7.2 Conditions at mw -South Amenable to SVE
7.3 SVE Remedy at mW-North Study Area
7.4 SVE Remedy at Phoenix-Goodyear Airport ("PGA")
Superfund Site
8. Description of Selected Remedy
8.1 The Plug-in Process: Basic Framework and
Requirements
II-I
II-I
II-I
II-4
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11-5
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CONTENTS-Volume 1 012 (Continued)
8. Description of Selected Remedy (continued)
8.1.1 Definition of "Subsite"
8.1.2 The Plug-in Approach in Concept
8.1.3 Plug-in vs. Traditional Superfund Remedy-
Justification for Using Plug-in at mW-South
8.1.4 . Plug-in Process Components and Terminology
The Selected Remedial Technology
8.2.1 Description of the Selected Soil Vapor
Extraction Alternative
Description of the No-Action Basis of
Comparison
Nine-Criteria Comparison with No-Action and SVE
Emission Control (Offgas Treatment) Design
Options and Requirements
SVE Enhancements-Design Options and
Perfonnance Standards
Plug-in Process Specification
8.3.1 Overview .
8.3.2 Options at the Plug-in Decision Point
8.3.3 How Plug-in of a Subsite will be Administered
8.3.4 Specification of the Remedy ProfIle
8.3.5 Specification of the Plug-in-Criteria
8.3.6 Specification of How Exceedance of the
Plug-in Criteria Will Be Evaluated
8.3.7 Specification of Cleanup Performance Standards
8.3.8 The Decision Tree
Integrated Risk Approach and Risk Templates for
Subsite Risk Characterization
8.4.1 Summary of Integrated Risk Approach
8.4.2 Specialized Strategy for Plug-in
8.4.3 Exposure Pathway Categories for IBW -South
8.4.4 Exposure Pathways Associated with VOCs in
Vadose Zone
Sumary of Chemicals of Concern and Toxicity
Assessment .
Summary of Basic Exposure Assumptions
Templates: Risk Characterization at Each
Subsite .
Evaluation of Environmental Risks
Section
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8.2.2
8.2.3
8.2.4
8.2.5
8.3
8.4
8.4.5
8.4.6
8.4.7
8.4.8
IV
Page
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CONTENTS-Volume 1 of 2 (Continued)
Section
8. Description of Selected Remedy (continued)
8.5 Clarifying Statement on Subsites Situated on Landfill
9 Statutory Detenninations
9.1 Protection of Human Health and the Environment
9.2 Compliance with ARARs
9.3 Cost-Effectiveness
9.4 Utilization of Permanent Solutions and Alternative
Treatment Technologies or Resource Recovery Technologies
to the Maximum Extent Practicable
9.5 Preference for Treatment as a Principal Element
lO Significant Changes
III , Response Summary
1. EP A Formal Comment Period and Public Meeting
2. Oral Comments Received at the Public Meeting
2.1 Question and Answer Session-Selected Questions
2.2 Oral Comments at Public Meeting
3. Comments Received at Public Meeting on Cards ,
4. Written Comments Received During Public Comment Period
4.1 Written Comments from Individuals
4.2 IMC Magnetics Corporation
4.3 Gateway Area Coalition
4.4 Arizona Department of Environmental Quality
4.5 Arizona Public Service Company,
5. 'Other Common Concerns and Questions
5.1 Health Concerns
5.2 Property Issues
5.2.1 Study Area Boundaries
5.2.2 Homeowner Liability
5.2.3 Lender Liability and Credit Risk
5.2.4 Property Values
5.3 Financial Impacts on Small Business
5.4 Other Common Questions
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Page
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III-49
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CONTENTS-Volume 1 of 2 (Continued)
Appendix
A
Applicable or Relevant and Appropriate Requirements
(ARARs) .
A.I Definition of ARARs and TBCs
A.2 Chemical-Specific ARARs and RCRA Threshold Values for
Treatment-Derived Water
A.3 Location-Specific ARARs
A.4 Action-Specific ARARs
A.4.1 "Contained in" Interpretation
A.4.2 Land Disposal Restrictions
A.4.3 Storage
. A.4.4 Treatment
A.4.5 Groundwater Monitoring and Groundwater Protection
Standards
A.4.6 Groundwater Use Requirements
A.4.7 Corrective Action.
A.4.8 Air Monitoring for Process Vents and Equipment Leaks
A.4.9 Air Emissions Requirements
A.5 Additional Legal Requirements'
A.5.1 The. Occupational Safety and Health Act
A.5.2 Standards for Transportation of Hazardous Waste and
U.S. DOT Hazardous Material Transportation Rules
Figure
II-I Site Location
II-2 Study Area
II-3 Structure of mw Project
II-4. Soil Sources and Groundwater Contamination
II-5 Source Investigation Screening
II -6 Remedial Investigation Process
II-7 Facilities Under Investigation
II-8 Distribution of VOCs in the Soil Matrix
II-9 Conceptual Geologic Cross Section
II-IO Contaminants Entering Groundwater as a Result of Changes
in Groundwater Level .
II-II Comparison of Traditional vs. Plug-in Approaches
II-12 Plug-in Process Components and Terminology
II -13 Existing Site Profile
II-14 Remedy Profile
II-15 Enhanced Remedy Profile
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Page
A-I
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A-2
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A-4
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A-7
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A-8
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A-8
. A-9
A-9
A-lO
Page
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II-IO
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II-12
II-15
. II-21
II-23
II-24 .
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II - 34
II-35
II-36
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CONTENTS-Volume 1 of 2 (Continued)
Figure (Continued)
II -16 Timing of Events within the Plug-in Process
11-17 Application of an SVE System to Remediate Vadose Zone
Contamination
11-18 Soil Vapor Extraction System Components
11-19 Components and Dimensions of a Typical SVE Well
11-20 Components and Dimensions of a Typical SVMW
11-21 Transfer of Contaminants between Different Phases in the
Soil Matrix
11-22 Overall Protection of Human Health and the Environment-
No-Action and the SVE Alternative
11-23 Reduction of Toxicity, Mobility, or Volume-the SVE
Alternative
11-24 Reduction of Contaminant Volume over Time-The SVE
Alternative
11-25 Annualized Costs for the SVE Alternative
II-26 Present Worth Costs for the SVE Alternative
II-27 Effectiveness of Offgas Treatment Options with Various
Concentrations of Extracted Vapor
11-28 Available SVE Enhancements at IBW-South
II-29 Events for a Typical Subsite
II-30 The Subsite Evaluation Approach within the Plug-in Process
II-31 Decision Tree-Specific
II-32 Risk Prism for IBW-South
II-33 Illustration of Potential Exposure Pathways at IBW-South
Table
II-I
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11-3
II-4
II-5
11-6
II-7
11-8
II-9
11-10
11-11
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Page
Unilateral Administrative Orders for Focused RI Work at
IBW-South (to date)
IBW-South Community Participation
Overall Protection of Human Health and the Environment-
Compliance with ARARs-Summary ,
Long-Term Effectiveness and Permanence-Summary
Reduction of Toxicity, Mobility, or Volume through
Treatment-Summary
Short-Term Effectiveness-Summary
Cost Estimate of Various SVE Enhancements
Description of Enhancements
Remedy Profile Parameters for Soil Vapor Extraction
The Plug-in Criteria
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II -44
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11-48
II-50
II-52
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II-63
II -64
VB
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CONTENTS-Volume 1 of 2 (Continued)
Table (Continued)
Page
II-12
II-13
II-14
II-15
II-16
Standards for Plug-in Criterion No.5: Federal MCLs
Threshold Values for RCRA Hazardous Waste Classification
at IBW-South
Oral/Inhalation Carcinogenic Classification and Critical
Toxicity Valu.es for Chemicals of Concern
Toxicity Summaries for Primary Chemicals of Concern
Assumed Transfer Efficiencies for Radon for Various
Water Uses in a Typical House
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II-74
II-82
II -85
II-87
, Risk Templates and Instructions
Page.
T-I
T-2
T-3
Cancer Risks from VOCs in Groundwater
Non-Cancer Effects of VOCs in Groundwater
Inhalation of VOCs Emitted from Soil
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II-97
III-l03
Located in Volume 2:
Administrative Record Index
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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 Superfund Site, South Area.
The Indian Bend Wash Superfund Site (IBW) is located in the cities of Scottsdale and
Tempe, Maricopa County, Arizona, and includes a portion of the Salt River Pima-Maricopa
Indian Community immediately east of Scottsdale and north of Tempe.
2.
Statement of Basis and Purpose
This ROD presents the selected remedial action for volatile organic compounds (VOCs) in
soils above the water table (the "vadose zone") at the Indian Bend Wash Superfund Site,
South Area (mW -South). VOCs in the vadose zone are an operable unit of mw -South.
The remedy is knownas the "VOCs-in-Vadose-Zone Remedy." This ROD selects a remedy
which includes both a remedial technology and a specialized process governing its applica-
tion. The VOCs-in-Vadose-Zone Operable Unit remedy will be consistent with all other
remedies to be selected for mw -South. This document also identifies applicable or rele-
vant and appropriate requirements (ARARs) and other criteria and requirements with which
this remedy shall comply. EPA has chosen this VOCs-in-Vadose-Zone Remedy for mw-
South in accordance with the Comprehensive Environmental Response, Compensation and
Liability Act, 42 U.S.c. ~9601 et seo. as amended by the Superfund Amendments and
Reauthorization Act of 1986, P.L. 99-499, 1QO Stat. 1613 (1986) (CERCLA) and, to the
extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan,
40 C.ER. Part 300 (NCP). Data at mw -South have been collected and analyzed in accor-
dance with EPA-approved sampling and quality assurance plans. EPA considers site data to
be of adequate quality to support the selection of the remedy presented in this ROD. The
decision in this ROD is based on the Administrative Record for the VOCs-in-Vadose-Zone
Remedy for mw -South, the index for which is included as Volume 2 of this document.
The State of Arizona, acting by and through its Department of Environmental Quality, con-
curs with the remedy selected in this document.
3. . Assessment of the Site
Releases of VOCs, common industrial solvents such as trichloroethylene (TCE), perchloro-
ethylene (PCE), and 1,1,1-trichloroethane (l,1,l-TCA), from several individual facilities
have contaminated the vadose zone and the groundwater at mw -South. Actual or
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threatened releases 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. .
4. Statement on Use 01
Innovative Approaches
IBW-South is complex and contains many subsites within the site. Based on the special
circumstances presented by IBW-South, EPA has determined that the use of tWo innovative
approaches to administering the site will greatly enhance the efficiency and effectiveness of
this remedy. These are the "Presumptive Remedy" and the "Plug-in Approach."
The Presumptive Remedy allows EP A to presume that a remedial technology is appropriate
in cases where voluminous treatability data indicate that it will be effective. Multiple alter-
natives are not evaluated specifically for this remedy, based on previous application of the
same remedial technology in other similar situations. .
The Plug-in Approach allows multiple, similar, but separate subsites (facilities or areas
within the larger site) to make use of the same remedy at different times. Under this
approach, EP A selects a standard remedy that applies to a given set of conditions rather
than to a specific subsite. At the same time, EP A selects a process and set of criteria for
determining where those conditions exist. Subsites are then fully characterized, at varying
times, after the ROD. Based on the process pre-established by the ROD, EPA then makes
subsite-specific determinations to "plug in" subsites to the remedy. The approach provides
flexibility to address unforeseen circumstances, while allowing EP A to address the majority
of similar sub sites without re-selecting the same remedy at each one.
EPA believes these approaches are consistent with CERCLA, the NCP, and the mandate to
protect human health and the environment.
5.
Description of the Selected Remedy
IBW-South contains multiple, distinct facilities that are releasing or have released VOCs
into soils. The releases from specific facilities (or small clusters of facilities) result in many
contiguous zones of soil contamination (subsites) separated by large gaps of uncontaminated
soils. Some of the released VOCs have passed through soils and have contaminated
groundwater. Other released VOCs are still in the vadose zone (the soils above the water
table) and can be sources of contamination to groundwater or ambient air in the future. The
purpose of this remedy is to control and remove future sources of groundwater and air
contamination by cleaning the vadose zone of VOCs at the multiple subsites where they
have been released. This action will minimize the extent and expense of groundwater
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'vI
cleanup that may be necessary for IBW-South. This remedy does not address VOC con-
tamination that has already reached the groundwater.
Based on site data and previous knowledge of SVE and this type of contamination, EPA has
detennined that Soil Vapor Extraction will be effective in removing VOCs from soils of
the type found at IBW-South and at facilities with characteristics seen to date. Significant
pre-existing treatability data support this conclusion, including data from mW-North, the
other study area of IBW. EPA has therefore selected Soil Vapor Extraction (SVE) as a
Presumptive Remedy. Remedial alternatives other than SVE and No Action have not been
evaluated. SVE, with air emissions treatment, will be applied to the soils at all subsites
detennined to have unacceptable levels of VOCs in the soils above the water table.
As stated in the last section, rather than study and select the same re~edy multiple times at
each facility, this remedy uses the Plug-in Approach. The remedy includes both the SVE
technology and a process for determining at which sub sites it must be applied. This process
includes methods for confmning that a sub site has conditions amenable to SVE, and also
for determining whether a sub site poses an unacceptable health risk. Subsites that have
completed RI work need not wait for all the other subsites to complete RI work.
This remedy provides for several options for emission controls and efficiency enhancements
to SVE, which can be selected as appropriate as each subsite plugs in to the remedy.
6.
Statutory Determinations
The selected remedy for VOCs-in-Vadose-Zone at mW-South:
.
Is protective of human health and the environment for the VOCs-in- Vadose-
Zone soils covered by this operable unit
.
Complies with federal and state requirements that are legally applicable or
relevant and appropriate to the remedial action
.
Is cost-effective
.
Utilizes permanent solutions and alternative treatment or resource recovery
technologies to the maximum extent practicable
.
Satisfies the statutory preference for remedies that employ treatment that
reduces the toxicity, mobility, or volume of contaminants as a principal
element
The remedy for this operable unit and other operable units at IBW -South will allow for
unlimited use and unrestricted exposure at the completion of all remedial actions. Accord-
ingly, the remedy is not subject to a statutory 5-year review. However, this is a long-term
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remedial action because complete cleanup will likely take more than five years to attain.
Accordingly, by policy, EPA shall perform a review not less than every five years after the
completion of the construction for all remedial actions at the site, and shall continue such
reviews until EP A detennines that hazardous substances have been reduced to levels protec-
tive of human health and the environment.
A remedial investigation/feasibility study is underway for the groundwater and a decision as
to whether further remedial action is necessary will be made upon its completion. ,EP A will
revisit the 5-year review status of the site when the groundwater remedy is selected, as
necessary.
JOh~ C. W '-<-L
Acting Regional Administrator
EP A Region IX
Q.17.ti3
Date
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II. DECISION SUMMARY
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II.
DECISION SUMMARY
The Decision Summary summarizes the information and approaches used which led to
EP A~ s decision on this remedy. It also establishes the remedy which EP A has selected.
This remedy incorporates two innovative approaches that cause the format of this Record of
Decision (ROD) to differ slightly from most RODs. The basis for using these approaches
and the differences they imply are explained within the Decision Summary.
1. Site Name, Location,
History, and Description
The Indian Bend Wash Superfund Site (IBW) consists of two study areas-Indian Bend
Wash North (IBW-North) and Indian Bend Wash South (IBW-South)-which lie within the
cities of Scottsdale and Tempe, Maricopa County, Arizona. See Figures TI-l and TI-2 for
the location of the site and the study area boundaries, respectively. This ROD addresses
remedial actions to be applied to the VOCs-in- Vadose-Zone Operable Unit of mw -South.
Other RODs address various operable units in mw -North (see Section 1.7, History of EP A
Involvement), and future RODs may address other operable units in mw -South as well.
1.1.
Site Discovery and Listing
The Indian Bend Wash Superfund Site was listed on the Superfund National Priorities List
(NPL) in September 1983. In October 1981, the City of Phoenix detected volatile organic
compounds (VOCs) , primarily trichloroethylene (TCE) and perchloroethylene (PCE) in
municipal groundwater production wells in the Scottsdaleffempe area. The Cities of
Scottsdale and Tempe and the Salt River Project, a local water purveyor, subsequently sam-
pled their groundwater production wells and also found VOCs. Affected wells were shut
down, and remain out of service to the present. One well, known as City of Scottsdale #6,
is an exception and is being operated with treatment at the wellhead. EP A listed mw as a
multiple-source Superfund site based on these fmdings.
At the time of the NPL listing, the extent of contamination was not known. However, EP A
established a study area as a frame of reference. This boundary covers 13 square miles, 10
square miles in Scottsdale and 3 square miles in Tempe. The study area boundaries are
Scottsdale Road (Scottsdale)/Rural Road (Tempe) on the west, Pima Road (Scottsdale)/Price
Road (Tempe) on the east, Apache Boulevard (Tempe) on the south, and Chaparral Road
(Scottsdale) on the north. Part of the mW-North study area lies within the Salt River
Pima-Maricopa Indian Community (SRPMIC). The SRPMIC lands do not lie within the
~' mw -South study area. .
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F~GURE 11-1
SITE LOCATION
INDIAN BEND WASH - SOUTH ROD
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SCOTTSDALE
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NTS
FIGURE 11-2
INDIAN BEND WASH - SOUTH
STUDY AREA
INDIAN BEND WASH - SOUTH ROD
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1.2.
Land Use and
Demographics
mW-South encompasses Sections 13 and 14
and the nonhern halves of Sections 23 and
24, Township 1 Nonh, Range 4 East.
Note on Boundaries
According to the NariOllal Oil arid Hazardous Substances
Contingency Plan (NCP), the SupeIfund definition of
"onsite" (i.e., the boundaries of a SupeIfund site) is "the
areal extent of coutamination and all suitable areas in very
close proximity to the coutamination necessary for imple-
mentation of the response action." TIris areal extent is
generally discovered in the course of the remedial investi-
gation. Therefore, the study area boundaries do not serve
as the legal definition of "onsite." Should EP A discover
contamination outside the study area bolDldaries, then the
site and the study, area would extend to incolpOrate it.
Conversely, areas that prove to be IDlcontamina1ed within ,
the study area are u:cImica1ly not within the site boun-
daries. The stUdy area bolDldaries and the site bOlDldaries
are not identical
North of University Avenue. Land use
nonh of University Avenue is primarily
industrial or commercial. The area west of
'Hayden Road is strictly industrial and has a
zero population. ,The area east of Hayden
Road has a population of 112, and most
residents live in mobile homes or trailers.
Roughly 66 percent of this population are betWeen the ages of 18 and 59. Nearly 24 per-
cent are under 17 years of age, and the remaining 10 percent are over 60 years of age.
Seven known active or inactive landfills exist east of Hayden Road along the Salt River.
Businesses unrelated to landfills have operated on top of landfill material in this area.
South of University Avenue. Land use south of University Avenue is more than 80 per-
cent residential, with the remaining land use for light industrial and commercial purposes,
such as restaurants, shops, and serviCe stations. The area east of McClintock Road is adja-
cent to Arizona State University and consists largely of the off-campus housing available to
students. Eighty-six percent of the population in this area are between 18 and 59 years of
age. Three percent are over 60 years of age, and the remaining 11 percent are under 18
years of age. Seventy-five percent of the residents live in apartments or condominiums.
The vacancy rate is 16 percent.
'In, the area north of McClintock Road, 76 percent of the population are between the ages of
18 and 59; 6 percent are over 60 years of age, and the remaining 18 percent are under 18
years of age. Sixty-three percent of the residents live in apartments or condominiums. The
vacancy rate is 15 percent
There is one public elementary school and one private "day'school" in mW-South. The
day school is in the southwest quadrant and has about 50 students, ages 1 to 10, enrolled
year-round. A senior center is located in the southeast quadrant, adjacent to the elementary
,school. No high schools, hospitals, or nursing homes are located within mW-South. More
detail on land use and demographics may be found in the Interim Remedial Investigation
Report, Admin. Rec. No. 1593. '
1.3.
Climate
The climate in the mW-South area is semiarid to arid, but is influenced by a high degree
of urban activity. The average daily maximum temperature is 85°F.' and the average daily
lOOI2ACA.WP5
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_J
"minimum temperature is 55°F. However, summer maximum temperatures routinely exceed
100 degrees, and occasionally exceed 110 degrees. The long-term average winds are from
the west at 6 miles per hour. Precipitation averages 7 inches of rain per year, more than
two-thirds of which falls in the summer and the winter. Winter rains are more gentle and
of longer duration than summer rains, which usually occur as short, intense, localized thun-
derstorms. Pan evaporation, measured at the nearby Mesa Experimental Farm, averaged
108.66 inches per year between 1972 and 1986.
1.4.
Topography
The surface topography of IBW-South is generally flat. The mW-South area is broken by
buttes of rock and surrounded by mountains at the edges of the valley. The surface ranges
from 1,150 to 1,200 feet above mean sea level. Slopes generally do not exceed about
2 percent. Slopes of over 100 percent exist only at the banks of the Salt River.
1.5.
Surface Water and Groundwater
The Salt River is the major surface-water body within mW-South. The Salt River flows
only about 10 percent of the time, but its flow is unpredictable in any given year. About 90
percent of the time the Salt River bed is dry within mW-South. This is because of the
impoundmen~ of water far upstream from mw -South. The Indian Bend Wash, a desert
wash that has been converted to a series of urban ponds linked by channels, meets the Salt
River at the northern boundary of the mW-South study area.
There are four main aquifers under mW-South: the upper, middle, and lower alluvial units,
and a fonnation called the "red unit." The alluvial units are mainly alluvial deposits laid
down by riverine action. Groundwater can usually be found at about 100 feet below land
surface (bls), although during heavy and sustained river flow the water table has been
observed to rise to about 55 feet bls. The bottom of the alluvial material in some areas of
mW-South is known to exceed 850 feet bls and may extend to more than 1,000 feet bls.
There is a definitive geologic connection among aquifers. The three alluvial units represent
an important aquifer resource to the people of Arizona, and wells within the mW-South
boundary likely would be used again if contamination were removed. More detail on sur-
face water and groundwater characteristics is provided in Section 6, Summary of Site
Characteristics.
1.6.
Contaminants of Concern
and Types of Sources
The contaminants of concern found in the affected wells in 1981 were volatile organic com-
pounds, or VQCs. These remain the primary contaminants of concern today. VOCs are a
type of solvent used by a variety of industries, especially electronics and circuitry manufac-
turing, to degrease and clean parts. They are also used heavily in dry cleaning.
lOO12ACA.WPS
ll-5
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mW-South contains a number of separate industrial and business properties that. have
. released contaminants into soils. These rel~ases have occurred by a variety of modes: dis-
charge of solvents or wastewater containing solvents through dry wells or into leach sys-
tems, direct discharge at land surface, leaking tanks or pipes, spills, and other means. VOC
contamination has moved downward. through the soils above the water table and reached
groundwater. Once in the groundwater, it has spread away from its sources as the ground-
water moves, and apparently has become a regional problem. In limited circumstances,
VOCs in the soil may also move upward and reach the ambient air, although EPA has not
observed such migration to date. .
Primary VOCs of interest at mW-South are trichloroethylene (TCE), 1,1,1-trichloroethane
(1,1,1-TCA), 1,1- and 1,2-dichloroethylene (DCE), and tetrachloroethylene (perchloroethy-
1ene, or PCE). EP A also is monitoring for vinyl chloride, which is a breakdown product of
the above compounds, and an array of non-VOC compounds.
The Salt River banks have been heavily mined and subsequently filled with landfill materi-
als. Most of these materials are inen debris and municipal solid waste. EP A has identified
some VOCs in landfill gas, however. The stabilization of the banks and the landfills, and
flood protection remain of concern to . local agencies.
EP A is also concerned about and is monitoring for heavy metals contamination, such as
. chromium or lead. These have not been detected at elevated levels in mW-South ground-
water, but the soils at some properties do contain metals, mostly from plating rinsate
wastes, and some of the landfills at mW-South have received metal foundry dusts. This
ROD selects a remedy for VOC contaminants only, but EPA will continue to monitor
metals contamination.
1.7.
History of EPAlnvolvement
As EP A began its mw investigation, .the highest levels of VOC contamination were found
in Scottsdale, and EP A initially focused resources there. EP A discovered that a facility
owned by Motorola Government Electronics Group was. a major source of this contamina-
tion. Subsequently, facilities owned by Seirnens Corporation, Beckman Instruments, and
other responsible parties also were identified as sources of the groundwater contamination in
Scottsdale. EP A issued enforcement actions against these parties requiring characterization.
of the groundwater and soils over a wide area.
At the end of 1987, EPA informally split the overallmW study area into two study areas
for more efficient management. The two areas are called Indian Bend Wash North (lBW-
North) and Indian Bend Wash South (mW-South). This divided the . original rectangular
IBW study area just north of the Salt River. Figure 11-3 shows the structure of the mw
project.
lOOI2ACA.WP5
11-6
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I(I\~~
...._....:..2~e~~~>.';:..............
'c~:.;:..~;\~.:~$~~~~¥~>.)\:.....
IBW-SOUTH .
STUDY AREA
(Tempe)
!
~
. .: ", .: :. '....~. ::'. '. ;:,":.::.:: ", "', . ::-.. ." '.~. 'n " .' .
.; :",:,:":,,;,::"':>:-::'.::.";":-:-:.::';:::.:. ,:~.:,,'-.;:.':::":
.I~.
,,".-",",.- .
Investigation
and Cleanup of
Groundwater
~.3
. ~ ",
...
.~. ,::,::-::,.'<:::,: ~.: .;.:..:. ~.:::
,-..',<-
- .. .,. -- -~"~. ... ~
FIGURE 11-3
STRUCTURE OF
IBW PROJECT
A partial remedy, called the "Scottsdale Operable Unit" has been selected for mW-North.
This remedy addressed the intennediate and deep groundwater of mW-North only. The
ROD for the Scottsdale operable Unit was signed in September 1988 and called for pump-
ing and treating the groundwater. EPA and responsible parties entered into a consent decree
on April 28, 1992, to implement the remedial design and action for the Scottsdale Operable
Unit This decree called for the City of Scottsdale to accept the water after it had been
fully treated to below health-based lev~ls. In September 1991, EPA signed another mw-
North ROD that addressed the shallow groundwater and the VOCs in mW-North soils.
The soils remedy selected: for mW-North was soil vapor extraction (SVE). A consent
decree to implement this remedy was entered with the Federal District Court on August 11,
1993.
EPA began turning more resources to investigating mW-South in 1988. Available ground-
water VOC concentrations were much lower in mw -South, but these were still above
drinking water standards. Insufficient data existed to determine the maximum contaminant
concentrations in the study area.
Tempe currently receives its drinking water from the Salt River Project and not from wells
within the mW~South study area. Therefore, EPA does not believe that the public is cur-
rently exposed to the contaminated groundwater at mW-South. EPA's primary focus is to
protect the groundwater resource and to ensure that the contamination does not spread to
lOOI2ACA.WP5
TI-7
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I .;
I
drinking water wells outside mw -South, which could threaten public health in the future.
Those persons with concerns about possible past exposure to contaminated water should
contact the Agency for Toxic Substances and Disease Regisn-y (A TSDR); contacts are Bill
Nelson and Gwen Eng, who can be reached at 415n44-2194 and 415n44-2193, respec-
tively. ATSDR has staff available to answer health questions and in some cases may decide
to conduct formal health studies in a community. EP A's responsibility is to study the phys-
, ical problems and respond to present and future health risks.
As the site study has progressed, EP A has investigated approximately 70 facilities. Each
.facility may have several potentially responsible parties (PRPs) associated with it. EP A has
also established an expanding groundwater monitoring well network, which consists of
EPA-installed and PRP-installed monitoring wells, and production wells which existed prior
to EPA's investigation. More detail about the investigation approach is given in Section 3.
1.8.
,Lead Agency
EPA is the lead agency for the mW-South Superfund project. The principal coordinating
agency for the State is the Arizona Department of Environmental Quality (ADEQ). Fund-
ing is provided by a combination of sources, as PRPs are performing some work and the
Superfund is funding other work. EP A coordinates with many other agencies in addition to
AJ)EQ, including the Arizona Department of Water Resources, the City of Tempe, the U.S.
Fish & Wildlife Service, the U.S. Corps of Engineers, and the Flood Control District of
Maricopa County. .
.,
. 2. Statement on
Innovative Approaches
This VOCs-in-Vadose-Zone remedy utilizes two specialized and innovative approaches to
remedy selection at Superfund sites. The first is called the Presumptive Remedy Approach,
and the other is called the Plug-in Approach. EPA's Feasibility Study, the risk assessment,
and this ROD are all specially structured to interface with these approaches. EP A's
response under these approaches will comply with CERCLA and the NCP, and also will
allow EPA to address the complexity of mW-South more efficiently.
The Presumptive Remedy Approach allows EP A to presumptively make use of a technology
that has repeatedly been proven to be effective under identifIed site conditions. Description
of this approach and justlfication for its use at mW-South are given in Section 7,
JustifIcation for Presumptive Remedy, as well as in EPA's "Operable Unit Feasibility Study;
VOCs in Vadose Zone, Indian Bend Wash Superfund Site, South Area" [Admin. Rec. No.
1599]. .
The Plug-in Approach is designed to address a site that has many similar, smaller subsites
within it, by establishing a base remedy and then defining a process to allow the separate
subsites .to "plug in" to it. EPA has introduced the Plug-in Approach in order to more
IOOI2ACA.WP5
II-8
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effectively address the multirile contaminant sources in the mW-South study area. Because
of this approach, this ROD differs slightly from a ROD for a traditional Superfund site,
which often consists of only one contaminant source. For example, this Plug-in ROD calls
for a remedy to apply any time a predefined set of conditions occurs within IBW -South.
Therefore, the ROD does not discuss the remedy with respect to a single facility or location
within mW-South, as would a traditional ROD. Nonetheless, this ROD contains within it
the entire process by which the VOCs-in-Vadose-Zone cleanup will be completed within
mW-South. The Plug-in Approach is justified and explained in -detail in Section 8.
IBW-South covers a large area. Nationally, most Superfund sites are not this large. EPA
informally calls this type of site an areawide site. mW-South began merely as a zone
within which groundwater contamination was known or suspected. EP A calls this zone the
study area. There is no single locus of property serving as a source of all mw -South con-
tamination~ Rather, contamination is emanating or has emanated from many individual
facilities or properties over a wide area. Each small subsite is a separate source that must
be investigated and may need to be cleaned up in its own right. However, compared to the
total number of properties within mw -South, those actually serving as contaminant sources
are probably relatively few.
This adds a great deal of complexity to the way in which EP A must respond to the situation
presented by mW-South. For example, EPA's investigation of contamination has become
a number of smaller investigations within a regional investigation. Whereas EP A may
address a small Superfund site by means of steps taken in series, the process at mW-South
has been executed in several parallel phases. EP A's activities, including searching for
responsible parties, investigating the contamination, selecting and designing cleanup options,
and the use of the Presumptive Remedy and Plug-in Approaches, has been structured to
address this "smaller-sites-within-a-big-site" simation.
,3.
Investigation Approach and
Enforcement Activities
3.1.
-Investigation Approach
The Superfund process requires that the name and extent of contamination be investigated
sufficiently for a remedy to be selected. There are two sides to EPA's remedial investiga-
tion (RI) for IBW-South: a soil source investigation and a groundwater investigation.
Investigation work proceeds at the same time on both sides. - First, EP A investigates the
contamination residing in soils above the water table at individual facilities, or subsites.
This contaminated soil remains a source of future contamination of groundwater. The soil
source investigation is subsite-specific; the soil investigation at each facility is usually
undertaken separately. Figure 11-4 is a conceptual illustration of soil source and ground-
water contamination.
IOO12ACA.WP5
11-9
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FIGURE 11.4
SOIL SOURCES AND
GROUNDWATER
CO NT AMINAll0N
Source investigations of soils at individual facilities generally consist of two components.
First, EP A performs a Preliminary Property Investigation (pPI). The PPI allows EP A to
detennine that a facility warrants more investigation. If warranted, EP A issues an Adminis-
trative Order requiring PRPs to perform a Focused Remedial Investigation (Focused RI),
which is much more comprehensive than a PPI. Under the Plug-in Approach in this rem-
edy, these Focused Rls are completed after the ROD is in place.
The Focused RI is also designed to begin to gather information leading to eventual execu-
tion of the selected remedial alternative defined in Section 8.2 of this ROD. Each Focused
RI results in a Focused RI Report, which is specific to a particular facility or property
within mW-South. Focused RI Reports may be written by PRPs, with EPA oversight, or
EPA.
Focused Rls supply the information that allow the Plug-in Process in this ROD to determine
whether the selected remedy will apply to any particular subsite.
lOO12ACA.WP5
TI-lO
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Figure n-5 graphically depicts the screening of mW-South subsites through the source
investigation, resulting in a smaller number of subsite requiring Focused RIs.
1280_10
--.--.--.--.--.--.--.
.=-_=-_=-8=--=-_=-8=-
..............
.- .- .
8- --
. .
-.- .- . -.
- -
. ..
All Subsites within IBW-South
Identification for Preliminary Screening
Subsites Undergoing Preliminary Property
Investigation
Determination of Need for Focused Investigation
Subsites Undergoing Focused RI
FIGURE 11-5
SOURCE INVESTIGATION
SCREENING
While individual soil sources are being investigated, EP A is also investigating the regional
groundwater contamination. This investigation is not specific to a particular facility, but
covers all of mW-South. EPA is performing the groundwater investigation using data
acquired by sampling production and groundwater monitoring wells. Many monitoring
wells are being installed by EP A; others are being installed by PRPs under administrative
orders issued by EP A.
Typically, PRPs sample their own wells under EPA oversight and then transfer the ground-
water data to EP A. Information on contaminant sources derived from PPIs and Focused RIs
alsq guides EPA in its groundwater investigation. Currently, EPA regularly samples
roughly 30 wells and is installing 32 additional groundwater monitoring wells at varying
depths throughout mw -South. These wells are scheduled to be installed by November of
1993. . .
EP A is synthesizing all RI information into a "living document" called the "Interim RI
Report," or IRI Report. The IRI Report is updated periodically as EP A releases new RI
information. This approach allows certain elements of the RI work to be presented while
lOOI2ACA.WP5
11-11
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other RI work is still being completed. EP A released the first edition of the IRI in
September of 1991. The second edition was released in June of 1993.
Each edition of the IRI Report is a compendium of EP A's groundwater investigation data
and evaluation, all of the PPI Reports, and all of the Focused RI Reports, as of a cutoff date'
for that edition. The structure of the investigation and the resulting IRI Report contents are
shown in Figure TI-6.
Indian Bend Wash-South
, ",r Remediallnvestigation ~".,'
f',
I
I .
FIGURE 11-6
REMEDIAL
INVESTIGATION
PROCESS
3.2.
Enforcement Activities
EPA has information from its investigation for approximately 70 locations (each location
. supporting one or more facilities over time) as potential sources of VOC contamination.
There may be one or more PRPs associated with anyone facility. Only about 30 of these
locations are still considered by EP A to be possible or known sources, barring new
information. Some of the suspect facilities form contiguous clusters, but most of them are
physically distinct, separated by distances ranging from blocks to a mile or more. Because
most PRPs do not share a common zone of soil contamination for which they are
lOO12ACA.WP5
TI-12
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responsible, and because the point to which investigation has proceeded at any given facility
varies, a joint effort among PRPs for soils cleanup has not been forthcoming.
EP A has been performing the groundwater investigation. With regard to soils investigation,
EP A has been screening properties based on responses to requests for information under
CERCLA ~104(e), civil investigative information, review of agency files and aerial photog-
raphy, and in some but not all cases, screening samples for VOCs at individual properties.
These activities, taken together, comprise the PRP search for IBW-South. Most of this
information is contained within the PPI reports discussed above.
Once screening indicates a potential problem, a Focused RI is necessary (see Section 3.1).
Those facilities conducting Focused RIs are subject to the Plug-in Process embodied in this
ROD. The Focused RI provides the information required by the Plug-in Process embodied
in this ROD to determine whether the selected remedial action is required at a facility or set
of facilities (See Section 8).
EPA has issued Unilateral Administrative Orders under CERCLA ~106 to PRPs in order to
obtain Focused RIs. EP A chose not to use special notice. procedures under CERCLA
~122(e) because of the large number of individual actions required. So far, EPA has issued
five Unilateral Administrative Orders for Focused RI work. As more Focused RIs become
necessary, EPA may issue more orders, or may conduct work itself. The five orders issued
to date are shown in Table ll-l.
Table n-l
Unilateral Administrative Orders
for Focused RI Work aUBW-South (To Date)
Facility Respondent(s)
DeE Circuits (fonner V AFCO Trust (Rudy Vafadari, et al.); Arden Properties
operator)
IMC Magnetics IMC Magnetics, Arizona Division, Inc.
Unitog/Prestige Apparel Unitog Rental Services, Inc.
Prestige Drapery Prestige Cleaners, Inc.
Eldon Drapery Leibovitz Enterprises Limited Partnership; Y &S, Inc.
EP A has issued information request letters pursuant to CERCLA ~ 104( e) to more than 100
parties within IBW-South. These letters request information about practices of operation,
waste handling and disposal; spills; the presence of tanks, dry wells, drains, leach lines and
degreasers; and related matters.
lOO12ACA.WP5
ll-13
-------
In 1988 and 1990, EPA issued general notice letters to approximately 30 parties. In June
1993, just before this remedy was proposed, EPA issued a second general notice letter to
about 65 parties informing them not only of potential liability but of the Plug-in Process
and the importance of commenting on the remedy. EPA wanted to ensure that PRPs be
informed of their opportunity to comment on the ROD even if EP A had not yet investigated
their property. Some of the 65 parties who received this notice had also received the origi-
nal general notice in 1988 or 1990.
The level of information that EP A has. varies among the approximately 30 facility locations
and 65 parties still considered to be possible sources of VOC releases based on current
information. In some cases, EP A has definitive evidence indicating that a facility is a
source. In other cases, EP A has only limited information about solVent use. Therefore, it .
is important to note that not all of these facilities will ultimately be found to have
released VOCs to soils. - .
Figure TI-7 shows all of the approximately 70 facility locations about which EPA has
obtained information on and/or has investigated. As stated, only about 30 of these facilities
are still considered potential source areas. EP A intends to screen out as many facilities as
possible before subjecting the remainder to the Plug-in Process. The five facilities for
which Administrative Orders require FocusedRIs are marked in red on the figure. EP A
may consider ~ facilities for the Plug-in Process than are shown on this list, should
information indicate that they are a potential source of VOC contamination.
I '
4. Scope and Role of this Decision
Document within the Site Strategy
This remedy for mw -South is a portion of the remedy for the overall mw site, and
addresses the VOCs-in-Vadose-Zone operable unit ("OU").
The purpose of this remedy is to control and remove future sources of groundwater and air
contamination -by cleaning the vadose zone of VOCs at the multiple subsites where. they
have been released.
The remedial action selected by this document has the following specific response
objectives:
. Adequately protect human health from the ingestion or inhalation of VOCs that
migrate from the vadose zone to the groundwater -
. Adequately pro~t human health from the inhalation of VOCs that migrate from the
vadose zone to the atmosphere. .
lOOI2ACA.WP5
ll-14
-------
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r ('~L..
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.11
Q
..~ 0 400 --2J0 FEET
. FACIUTIES ORDERED BY EPA TO
CONDUCT FOCUSED REMEDIAl
,INVESTIGATIONS, TO DATE
FIGURE 11.7 .
FACIUTIES UNDER \
INVESTIGATION
INDIAN BEND WASH - SOUTH ROO
-------
. Conn-ol the sources of continuing groundwater contamination to minimize loss of the
groundwater resource and reduce the degree of groundwater cleanup that may be
required
While a major objective of this remedy is to prevent soil contamination from reaching
groundwater in the future, it does not address contamination that has already reached the
groundwater, nor ensure by itself that groundwater contaminant levels are protective of
human health. EP A will issue a separate ROD to address the final cleanup for the ground-
water for mw -South. This VOCs-in- Vadose-Zone remedy addresses a fmal cleanup for
the continuing sources of VOCs in soils, but is only an interim remedy for groundwater.
In conjunction with the groundwater remedy, this remedy will serve to address the principal
threats posed by contamination at mw-:south. It does not address non-VOC contaminants
that may be in soils, such as metals. Where necessary, EPA will use removal actions or
select other remedies for such contaminants, or modify this remedy to address them with an
amendment or an explanation of significant differences ("ESD"). This remedy will apply to
certain types of landfill materials. This is discussed in Section 8.5.
5. 'Highlights of
. Commununity Participation
Because the IBW-South and IBW-North study areas are part of one overall mw site, EPA
has joined community relations planning and execution for both areas. The Community
Relations Program therefore addresses the mWcommunity as a whole, although a given
factsheet or meeting usually pertains specifically to only one study area.
EPA currently maintains IBW~South information repositories at the EPA Region IX Office
in San Francisco, and at the Scottsdale, Tempe, and Phoenix Public Libraries. The EP A
Region IX Office and the Tempe and Scottsdale Public Libraries maintain copies of the
Adminisn-ative Record .file .on microfIlm, while the Phoenix Public Library maintains a
collection of selected key documents, including the Interim Remedial Investigation (IRI),
the Feasibility Study, the Proposed Plan, and this Record of Decision. In addition, the
Arizona Department of Environmental Quality maintains an information repository, with
various key documents, in its Phoenix Office. EP A 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, EP A sent a factsheet in
December of 1990 to approximately 35,000 addresses in the area of the Indian Bend Wash
Superfund site in an effort to expand the list This factsheet (and all EPA factsheets) pro-
vided a return coupon and telephone numbers that one could use to be placed on the mail-
ing list.
EPA also operates a toll-free information message line (800/231-3075) to enable interested
community members to call. EP A with questions or concerns about Indian Bend Wash
Superfund site activities. The message line is publicized through newspaper notices and the
lOO12ACA,WPS
II-17
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mailing list. EP A 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 Response Summary of
this Record of Decision.
Table II-2 presents a chronological list of other community relations activities that EPA has
conducted for IBW-South in order to comply with the public participation requirements of
CERCLA ~1l3(k)(2)(B) and CERCLA ~117. Activities that were specific to IBW-North
only are excluded from this list. .
Table 11-2
IBW -South Community Participation Highlights
, Page 1 of 2
September 1984 Released a community relations plan based upon interviews with Phoenix,
Scottsdale, and Tempe residents and State and local officials.
1984-1988 During this period. community relations activities addressed all interested persons
in the fBW community. buUnformation transfer centered on fBW -North.
December 1990 Distributed a factsheet to all persons on the mailing list providing infonnation on
IBW-South and groundwater monitoring and soils investigations.
.
Throughout 1991 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.
May 1991 Distributed a flyer and held a public meeting to update the community on the
findings of the remedial investigation, the type of contamination and movements
of groundwater, the potential sources, and EPA's remedial and enforcement strate-
gies; addressed community questions and concerns.
January 1992 Updated the 1984 community relations plan to reflect new site communication
strategies and infonnation from residents, officials, and other members of the
community.
September 1992 Distributed a factsheet providing infonnation about investigation activities and
Administrative Orders that had been issued, and. also announcing a public com-
ment period. on a Contingency Plan for Removal of Laridfill ~erials, which
ADOT was proposing as part of its work under its agreem~nt with EPA. Held a
30-day public comment period on this issue.
December 1992 Issued a flyer to residents in a surrounding neighborhood of. the fonner DCE
Circuits facility where EPA was beginning field work as part of a Focused Reme-
dial Investigation. Flyer explained the reason for, and nature and context of the
activities and gave contact names.
April 1993 Distributed a factsheet updating the community on activities at IBW-South,
including m.ore Administrative Orders, groundwater, and an initial description of
.. the Plug-in Approach to be used in the upcoming VOCs-in-Vadose-Zone remedy.
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11-18
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. Table ll-2
IBW -South Community Participation Highlights
Page 2 of 2
May 1993 Issued a flyer to residents affected by EPA's well drilling activities infonning
them of the reason for, and nature and context of the activities.
June 7, 1993 Distributed the Proposed Plan Factsheet 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, the comment period. the scheduled public meeting
and open house session, and the availability of the Administrative Record me.
June 7. 1993 Mailed Administrative Record file, on micromm, to Scottsdale and Tempe Public
Libraries. Hard copies of the IRI Report. the Feasibility Study, and the Proposed
Plan were sent to these libraries and the Phoenix Public Library.
June 9. 1993 Published a notice in the Tempe Tribune and the Arizona Republic announcing
the start of the public comment period. the scheduled public meeting and open
house session, and the availability of the Administrative Record me for the
VOCs-in-Vadose-Zone remedy.
June 9. 1993 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 me.
June 14. 1993 Began a 30-day public comment period on EPA's proposed remedy for VOCs in
the Vadose Zone at mW-South.
June 28, 1993 Held a meeting at the home of the leader of a Phoenix citizens group to which
several citizens groups were invited. to present EPA's proposal for VOCs-in-
Vadose-Zone remedy and to answer questions and concerns.
June 29, 1993 Held a meeting at the Holiday Inn in Tempe for all Potentially Responsible Par-
ties. to present EPA's proposal for VOCs-in-Vadose-Zone remedy and to answer
questions and concerns.
July 7. 1993 Held a fonnal public meeting at Gililland Jr. High 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.
July 8. 1993 Held an open house session at Gilliland Jr. High School in Tempe to present
EPA's proposed remedy for VOCs in the Vadose Zone. answer questions, and
receive wrinen comments; EPA was present between the hours of 1:00 to 5:00
p.m. and 7:00 to 9:00 p.m. to provide one-on-one responses to questions of the
, public.
July 26. 1993 Mailed a flyer to thy mailing list and published newspaper announcements in the
Tempe Tribune and the Arizona Republic extending the public comment period 31
days to August 14, 1993. in response to a wrinen request for an extension.
lOOI2ACA.WP5
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6. . Summary 01 Site
Characteristics
6.1.
FatelTransport 01 ,
Contaminants 01 Concern
Industrial facilities at IBW -South have used the VOCs trichloroethylene (TCE), perchloro-
ethylene (PCE), and l,l,l-trichloroethane (l,l,l-TCA), typically as solvents. These com-
pounds, along with l,l-dichloroethylene (1,I~DCE) and cis- and trans-I,2-dichloroethylene
(l,2-DCE), have been detected in groundwater from monitoring and supply wells. Vinyl
chloride has so far been detected only at relatively low levels in the landfIlls. DCE and
vinyl chloride may be present from direct release, and it is also possible that these
components are present as breakdown products of TCE or l,l,l-TCA. EPA is monitoring
for other VOCs that have been used at facilities within IBW-South, such as chlorobenzene,
ethylbenzene, benzene, toluene, xylene, and chloroform.
Heavy metals, including lead, chromium, nickel, copper, and cadmium, have been used by
many of the plating shops in the area and are present in some facility soils, as evidenced by
EPA's fIrst Focused RI. However, metals have not been found in groundwater at elevated
levels, based on wells installed to date. EP A will be installing more groundwater moni-
toring wells and will continue to monitor for metals.
. ,
VOCs in the soil matrix are distributed to the various phases in accordance with physical
properties of the ,contaminant (specifIcally vapor pressure, solubility, and Henry's Law con-
, stant), as well as properties of the soil (e.g., moisture content, clay mineral fraction, and
organic matter content). The VOCs rapidly achieve an equilibrium condition among these
various phases. Figure IT-8 is a graphic representation of soil particles with sorbed
contaminants surrounded by gaseous-phase and dissolved contaminants.
The following means may be influencing the transport of contaminants at IBW-South: .
. Leaching of contaminants from source areas by inflltrationand percolation of
precipitation, wastewater, or irrigation water to the water table
. Movement of relatively pure product (e.g., pure TCE) from a source to the water
table to form a dense non-aqueous phase liquid (DNAPL) source
.
Soil gas contamination of groundwater by infiltration of water, whiCh dissolves' the
gas phase contaminants, which percolate to the water table
. Soil gas migrating within the soil vapor and diffusing into the groundwater
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FIGURE 11-8
DISTRIBUTION OF VOCS
IN THE SOIL MATRIX
All of these mechanisms may exert some
influence on contaminants within mw-
South. Movement of relatively pure
product would result in the highest levels
and, potentially, long-term releases into
the groundwater as the pure VOC slowly
dissolves. Investigations to date have not
confirmed the presence of any DNAPL in
mw -South soils, but its presence is
possible. Available data indicate that a
significant fraction of the VOCs in the
vadose zone is present as soil vapor.
Because TCE can be used as an indicator
of the fate characteristics of most of the
VOCs of concern, it is further discussed
here.
With TCE's relatively high vapor
pressure, volatilization is the most signifi-
lOO12ACA.WP5
cant removal mechanism when TCE is
released into surface soils. When released
into the atmosphere, TCE is readily
photo-oxidized, ultimately to hydrochloric
acid (HCl), carbon dioxide (CO;>, and
carbon monoxide (CO). . While these
breakdown products are undesirable as
components of photochemical smog, the
long-distance transport and accumulation
of TCE itself in the atmosphere has
generally not been of concern because its
half-life in air is approximately 3.7 days.
Reported soil adsorption coefficients for
TCE indicate high mobility in soils and
low potential adsorption. Therefore, TCE
leaches readily to groundwater. Once
TCE reaches groundwater, volatilization
ceases to be a significant process, and
biodegradation is slow. Therefore; TCE is
expected to persist for many years in the
groundwater.
6.2.
Soils
Soil properties and conditions governing
the movement of air through soils and
subsequent volatilization of VOCs from
unsaturated soils include soil porosity,
temperature, convective currents, and
barometric changes.
mw -South lies in an arid climate. The
unsaturated soils in mw -South are
generally alluvial deposits with low clay
content, laid down by rivers and water
runoff over millions of years. There is
generally little organic matter in the soil.
These factors mean that VOCs do not
tend to adhere to the soil and therefore
migrate readily.
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I '
There is extreme difficulty ,in obtaining a representative soil sample (as opposed to a soil
gas sample) for VOC compounds in the mW-South environment, due to four primary
factors:
i ;
1. Aeration (and therefore loss) of VOCs from the sample during split-spoon retrieval
2. Aeration of VOCs from the sample during handling in the field
3. Aeration of VOCs from the sample during laboratory preparation
4. High variability in analyses at relatively low concentrations
For these reasons, soil gas samples for VOCs can show high levels of contaminant, while
soil samples for VOCs show little or no contaminant
At chemical equilibrium, a significant fraction of VOCs in mW-South soils is found in the
gas in the soil, the soil vapor phase. While there also may be. a significant fraction sorbed
to soil particles or dissolved in soil moisture, these oth<:fr fractions will readily move into
the vapor phase if the VOC vapor concentration is decreased. This makes the vapor phase
an efficient focus for evaluating and removing VOCs in the subsurface at mW-South.
Based on these facts, EPA's approach to characterizing and remediating soil at mW-South
relies heavily on soil gas sampling for VOCs, rather than soil sampling. In general, surface
soil gas sampling results in a contour map of VOC contaminants at about a 5-foot depth.
From this map, soil vapor monitoring wells are installed. These wells can be sampled at
multiple depths, allowing for a depth profIle of VOC contamination. Even low concentra-
tions at the surface can be indicative of high concentrations at depth.
VOC contaminants have been confirmed in mW-South soils at various individual facilities.
Surface soil gas samples. taken in 1988 and 1990 indicated concentrations up to 2,500
micrograms per liter (pg/l) of TCE and 1,500 pg/l of PCE, as well as concentrations of
1,1,I-TCA, benzene, ethylbenzene, 1,I-DCE, and 1,2-DCE at various facilities. As part of
recent Focused RIs, surface soil gas concentrations of over 12,000 pg/l of PCE have been
detected at the Unitog facility, and several hundred pg/l of TCE at the !MC Magnetics
facility. Even surface soil gas levels on the order of 10 pg/l may be indicative of much
higher concentrations at depth. Soil vapor monitoring wells at the former DCE Circuits
facility have now produced TCE concentrations in excess of 9,500 pg/l. The IRI Report
contains the results of soil gas data that EP A has used to initially evaluate subsites, as well
, as summaries of data from non-EPA investigations.
6.3.
Groundwater and Hydrogeology
While this is not a ROD for a groundwater remedy, a limited description of groundwater
characteristics is provided here to emphasize the migration that may occur if VOCs migrate
from the soils and enter groundwater, and the relation of groundwater to vadose zone soils.
lOO12ACA.WP5
ll-22
..
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At mw -South, VOCs that leave the vadose zone soils and enter groundwater have high
potential of migrating rapidly from their original source, both laterally and with depth and
in complex directions. Much more detail on groundwater can be found in the IRI Report
[Admin. Rec. No. 1597].
The hydrogeology and hydrodynamics at mW-South are extremely complex. Generally,
there are four major geologic units under the site, three of which are composed of alluvial
materials. These have been labeled the Upper Alluvial Unit (UAU), Middle Alluvial Unit
(MAU), and Lower Alluvial Unit (LAU). The LAU is not present at all locations under the
study area. The fourth major geologic unit under the site, labeled the Red Unit, underlies
all fonnations in the area.
Alluvial material extends to as much as 1,000 feet bls before bedrock is encountered; how-
ever, there are some areas under mw -South where bedrock is encountered within the first
300 feet bls. Figme II-9 illustrates the stratigraphy with approximate corresponding depths
at mw -South.
Tempe Buttes
(Rock Extrusion)
Ground Surface
Groundwater -
Monitoring Wells
.", ".
. . '. .. . . ..
.. . . - .
-.>.:'Upper Atiuvial Unit .
- .
- -
i:111111
FIGURE 11-9
CONCEPTUAL GEOLOGIC
CROSS SECTION
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While the stratigraphies of the three alluvial units are somewhat different, available data
indicate strong interconnection among the three units, with substantial vertical gradients.
No significant barrier to the vertical flow of water exists among the three units.
Transmissivities in IBW -South are extremely high, resulting in estimated groundwater par-
ticle velocities as high as 25 feet per day during high recharge (river flow). During low
recharge (dry river conditions) the particle velocities may still be as high as 2 to 5 feet per
day. It is therefore possible, though not confinned, that contaminants from IBW-South
sources have extended miles from their original point of entry to the groundwater.
The Salt River, which is ephemeral, is a powerful agent of.groundwater recharge in the
DAD. When the river is flowing heavily, EPA has recorded groundwater levels rising by as
much as 45 feet The river flows about 10 percent of the time' averaged over all time, but
may not flow at all in any given year.
Because the water table rises and falls dramatically with temporal variations in river flow,
contamination in the vadose zone at depth can enter groundwater when the water table rises
to meet it, as shown in Figure II-lO. When the water table falls again, some of the VOCs
will have dissolved and will recede with the groundwater. Groundwater concentrations also
tend to fluctuate as the thickness, and therefore the volume of the DAD changes.. '
Groundwater flow direction in the DAD is
extremely complex, varying both tempo-
rally and laterally. During no river flow,
the DAD gradient varies from south-
southeast to south-southwest depending on
one's location. With river flow episodes,
all gradients shift eastward by IO to 25
degrees, and then slowly return to normal.
The flow direction in the MAD is less
well-characterized, but appears to be to
the northeast This is virtually anti-
inclined to the gradients in the DAD.
Thus, contamination may start out in the
soils at a subsite, enter the DAD moving
in one direction, gradually sink to the
MAD, and return at greater depth in the
direction from which it originally came.
These factors imply that a particle of
contamination, once reaching ground-
water, follows a tortuous path that is
dependent on changes in recharge rates.
FIGURE 11-10
CONTAMINANTS ENTERING
GROUNDWATER AS A RESULT
OF CHANGES IN GROUND-
WATER LEVEL
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7. Justification for
Presumptive Remedy
As stated, EP A is using two innovative approaches in tandem in this remedy, the Presump-
tive Remedy Approach and the Plug-in Approach. These two concepts work well together
at IBW-South, but are nonetheless independent. This section justifies the Presumptive Rem-
edy Approach for VOCs in the Vadose Zone at IBW -South.
7.1.
Presumptive Remedy Approach
When EP A began administering the Superfund program in 1980, very few technologies
were available for cleaning up unconttolled releases of hazardous substances, and little data
were available on their effectiveness. With the passage of time,. an industt'y was spawned
to develop, test, and implement these technologies, and as more sites were addressed, a
much wider range of technologies has become available. Additionally, there are now data,
called treatability data, indicating conditions under which different technologies are
effective.
Even with this new information and capability, it remains necessary at most sites nationwide
to consider a full range of technical options in an FS Report, before selecting one of them
in the ROD. However, EPA has recognized that there are certain situations in which the
conditions at a site are so well suited to a particular technology that the use of that technol-
.ogy can be presumed to work (the Presumed Remedy). The Presumptive Remedy Approach
is considered when there is a remedial technology or process option that has repeatedlv
been shown to work in the range of conditions present at a site; and there are no apparent
. conditions at the site that are markedly different from the conditions under which the tech-
nology has previously been tested or used. When the Presumptive Remedy Approach is
used by EP A, the FS Report and the ROD do .!!Q! evaluate a full range of varied options.
Rather, only the Presumed Remedy and the No-Action Alternative are evaluated and com-
pared. The FS and ROD describe why it is appropriate to presume that the alternative will
be effective. .
By presuming one alternative, EPA does not imply that there are no other alternatives that
might be effective in cleaning up the contamination at IBW -South. Rather, EP A con-
cludes that the effectiveness of the Presumed Remedial Alternative will be fully acceptable
without making a comparison to other alternatives.
Soil vapor extraction (SVE) is the technology presumed to be effective for VOCs in the
IBW-South soils. In this ROD, SVE will sometimes' be referred to as the Presumed Reme-
dial Alternative.
SVE is presumed, in part, because it. has been selected as the remedial action for similar
sites with similar contamination problems. In Maricopa County alone, there are approxi-
mately 70 SVE projects either in the process of being permitted or currently operating.
lOOI2ACA.WP5
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Two remedial investigation/feasibility study (RIIFS) programs previously have been com-
pleted by.EPA for sites located near the mW-South study area. Both FSs evaluated several
remedial alternatives; they did 'not use a Presumptive Remedy Approach. These sites have
vadose zone soil conditions and contamination problems similar to those observed at IBW-
South. EP A therefore did not believe that it would be necessary or cqst-effective to
re-analyze the same alternatives at IBW-South. A brief description of these sites follows in
paragraphs 7.3 and 7.4.
7.2.
Conditions at IBW-South
Amenable to SVE
I ;
Soils in the vadose zone at IBW -South typically consist of moderately permeable sands,
silts, and gravels, with cobbles and thin clay beds. The vadose zone consists especially of
loose alluvial deposits with a large cobble fraction. The soils typically have low organic
carbon content Significant clay layers, as well as other phases such as oil, have not been
observed. These soil types, in general, are conducive to effective SVE removal of VOCs.
Shallow soil gas sampling at a variety of locations at IBW-South has indicated that soil gas
contaminants at most subsites are the type that can be remediated by SVE.
Excavation and removal of contaminated soils at IBW-South are restricted because many
contaminated areas are located under buildings and roadways. Capping the contaminated
areas decreases upward migration to limit exposure risks; however, it does not remove the
potential for migration of VOCs from the unsaturated zone to groundwater. In addition,
because some VOCs have been found at IBW-South at depths of up to 100 feet, the avail-
ability of many other treatment remedies, especially ex situ ones, is limited. While EP A
has not thoroughly evaluated these other remedies, these factors lend further support for
EP A's decision to presume a technique that has been proven effective in all these
conditions.
SVE can remove VOC contaminants from beneath buildings and roadways with minimal
disturbance to structures and is proven to be effective with a minimum of disruption to
urban environments. The SVE remedy removes the VOCs from the vadose zone, thereby'
reducing their potential threat to groundwater and public health. Also, SVE can effectively
treat VOCs at the depths to groundwater expected at IBW-South.
SVE has been proven as an inexpensive technology relative to excavating soil or treating
soil by chemical or thermal means. It is therefore appropriate to presume that SVE will be
cost-effective as well as technically effective. This should be true even after accounting for
the potential use of SVE enhancements.
SVE is particularly suited to IBW-South not only because it is effective in removing and
treating VOCs in soils of the type at IBW-South, but also because its capabilities are quite
broad. Under the Plug-in Approach, EPA must select a technology to address many distinct
lOO12ACA.wP5
II-26
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subsites, which are not yet fully characterized. Therefore, it makes sense to select a versa-
tile (robust) technology that is relatively insensitive to unexpected variations from one sub-
site to the next. This is true of SVE.
7.3.
SVE Remedy at IBW-North
Study Area
The IBW-North study area is part of the same Superfund site as IBW-South. The study
area is located immediately adjacent to IBW-South, north of the Salt River, and has vadose
zone characteristics similar to those observed at IBW-South. In September 1991, EPA
issued a ROD for IBW-North that selected SVE as the remedial action to remediate VOC-
contaminated soils [IBW-North Admin. Rec. Nos. 2055 through 2057J.
The primary contaminants of concern for the IBW-North Superfund site are similar to those
in the IBW-South site, as many of the same types of industries are located in both areas.
Primary contaminants requiring removal by the SVE treatment selected for IBW-North
included TCE, PCE, l,l,l-TCA, DCE, 1,2,-DCE, cis- and trans- isomers, and chloroform.
Similar to conditions at IBW -South, a large fraction of VOCs in the vadose zone in IBW-
North was found to be present as soil vapor with high mobility in soils and low potential
adsorption. Because of the close proximity of IBW-North to IBW-South, the climate,
topography, urban setting, soil, groundwater characteristics, and stratigraphy are very
similar.
EPA selected SVE to remediate the VOCs in the vadose zone at IBW-North after complete
analysis and comparisons with other remedial technologies such as excavation, soil washing,
and capping. EP A's fun analysis was performed in accordance with the nine evaluation
criteria set forth in EPA's Guidance for Conducting Remedial Investigations and Feasibility
Studies under CERCLA, 1988, as cited in the Feasibility Study, Admin. Rec. No. 1599.
7.4.
SVE Remedy at Phoenix-Goodyear
Airport (npGAn) Superfund Site
The PGA site is located approximately 20 miles to the west of IBW -South, within the Salt
River Valley. The vadose zone lithology at PGA is similar to that observed at IBW-South.
A pilot study was conducted at PGA in 1988 using an SVE system. Results of this pilot
study demonstrated that SVE would be an effective solution for removing VOCs from
vadose zone soils that have lithology similar to IBW-South. In September 1989, EPA
signed a ROD for PGA selecting SVE as the remedial action [Admin. Rec. No. 1603J.
The primary VOC contaminants of concern for the PGA vadose zone included TCE, PCE,
l,l,-DCE, chlorofonn, and carbon tetrachloride, which are the same or similar contaminants
to those at IBW-South.
. lOOI2ACA.WPS
II-27
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The climate and soil sttatigraphy at PGA are also similar to those of IBW-South, with long,
hot summers, and short, mild winters. The alluvial deposits of the western Salt River
Valley consist of an Upper Alluvial Unit, Middle Fine-Grained Unit, and a Lower Conglom~
erate Unit, whose sttatigraphy and water migration are similar to IBW-South.
The remedy selection process for PGA soils, like that for IBW-North, also evaluated a full
suite of remedial action alternatives using the nine standard criteria for Superfund remedy
comparison.
8. Description of.
Selected Remedy
The remedy selected for VOCs in the vadose zone at IBW-South is to use SVE to remove
and tteat VOCs in soils at those sub sites that "plug in" to the remedy. The process for
4etermining which subsites must plug in to the remedy is called the "Plug-in Process," and
is hereby incorporated as part of the remedy. The Plug-in Process shall be applied once for
each subsite at which a Focused Rl is perfonned. The tenn "subsite" and the details of the
Plug-in Process are defined below.
For all SVE systems that are required, air emission conttol (offgas tteatment) shall be
included. One of three types of emission conttols defined below shall be applied at any
subsite which plugs in. EP A shall identify which of the three emission conttols will be
used at any particular subsite as part of the remedial design for that subsite. All conttols
shall meet the Applicable or Relevant and Appropriate Requirements ("ARARs") or other
requirements specified in this document.
For any SVE system, certain SVE enhancements shall be considered available as part of this
remedy. Decisions on the use of and choice among these enhancements shall be part of the
remedial design of each SVE system. The available enhancements are specified and
described below.
8.1.
The Plug-in Process: Basic
Fram,ework and Requi~ements
This section discusses the concept, justification, and terminology of the Plug-in Approach.
The detailed specification of the process is provided in Section 8.3, after discussion of the
selected remedial technology in Section 8.2.
8.1.1.
Definition of "Subsite"
IBW -South contains zones of VOCs in soils separated by large, zones of uncontaminated
soil. Generally speaking, VOC-contaminated soil zones correspond to facility locations:
certain facilities have released VOCs into soils. However, VOCs may have sttayed from
. lOO12ACA.WP5
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one facility onto neighboring facilities, or several adjoining facilities may have released
contamination so that a single zone of VOC-contaminated soils spans a cluster of facilities.
EP A shall consider one contiguous zone of VOC soil contamination, and the associated
facilities and properties, as a "subsite." A subsite is a candidate for plug-in, the unit on
which EPA will apply the Plug-in Process to determine whether a cleanup is necessary. A
subsite defines one VOC contamination problem to which one SVE cleanup system would
be applied, where determined necessary.
8. 1.2.
The Plug-In Approach in Concept
The Plug-in Approach is a way of structuring a remedy for complex Superfund sites such as
mW-South. The approach can be used when a Superfund site contains multiple areas or
"subsites" that are similar physically and share similar contaminants. Each subsite has con-
tamination that must be addressed.
This Plug-in Remedy identifies SVE as a standard remedial action, and then defmes a pro-
cess that will be used to determine where the remedial action shall be applied. The ROD
does not select a remedial action for a specific subsite. Rather, it selects a remedial action
to apply to any subsite exhIbiting certain conditions. The ROD defmes what these condi-
tions are and selects a process for determining whether they exist.
The Plug-in Remedy is selected prior to fully characterizing the subsites. Subsites will be
characterized concurrently or at different times. If the conditions at a sub site match pre-
defined conditions, the subsite will "plug in" to the remedial action and be subject to its
requirements. Each sub site has a separate Plug-in Decision. This ROD fully contains the
basis and process to be used for all Plug-in Decisions. Therefore, following the prescribed
process in the ROD completes the remedy for any particular subsite. The Plug-in Remedy
contains a "blueprint" directing decisions as to its own application.
By separating selection of SVE, the cleanup technology, from a decision about its applica-
tion at a particular subsite, EP A can verify that the cleanup technology is appropriate for a
sub site after all sampling data about it have been collected. At the same time, EP A does
not have to evaluate and select a separate remedy for each subsite.. .
After plugging in to the remedy, remedial design and action can begin at a subsite. Sub-
sites not matching the conditions and criteria are not plugged in, but still can be addressed,
if necessary, by other remedies, removal actions, or through modifications to the remedy.
Because unexpected conditions or situations may occur during Focused RI work at a sub-
site, the Plug-in Approach is designed to be flexible enough to adjust to these conditions.
VOCs in soils at all subsites will be addressed by this single Operable Unit ROD. Reme-
dial action will occur at some subsites while investigation work continues at other subsites.
Thus, sitewide, remedial investigation and remedial action actually occur concurrently (see
Figure ll-16). .
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8. 1.3.
Plug-In vs. Traditional Superfund'
Remedy-:Justification "or Using
Plug-In at IBW-South .
Traditionally, the Superfund remedy selection process is site-specific. Each site is consid-
ered a unique problem that is fIrst investigated. and a remedy selected after considering a
range of potential solutions. Usually, EPA characterizes the nature and extent of contami-
nation with a remedial investigation (RI), then evaluates and compares several remedial
alternatives in a Feasibility Study (FS), proposes one of those alternatives to the public in a
Proposed Plan, receives public comment on that alternative, and then selects an alternative
in a ROD. After the ROD, the exact technical specifications and construction detail of the
remedy are developed during remedial design, and fInally, the cleanup takes place in a
remedial action phase. The part of this process starting with the FS and ending with the
ROD is called remedy selection.
In traditional remedy selection, several alternatives are matched, or evaluated, for a single
site. Site characterization is usually substantially complete before any fInal decision is
made on remedy selection. This is important because, should a remedy be based on inade-
quate data, unknown characteristics of the site may render a selected remedy ineffective.
Multiple-source sites, such as IB\y--South, present a number of challenges with regard to
remedy selection. In the case of VOCs in soils at mW-South, the problem is not in find-
ing a technical alternative to treat VOCs; as discussed, SVE has been demonstrated to work
at similar sites. Rather, the difficulty lies in administering many similar, yet distinct
subsites. The soils at IBW -South are very similar from one .location to the next, being laid
down by the same alluvial activity and existing in the same arid environment. The VOC
contaminants are generally chlorinated solvents, the behavior of which is fairly predictable
in these soils. EP A expects that VOCs in this type of soil would tend to move readily into
the soil vapor. There are proven remedial technologies, broadly suited to a wide range of
conditions (i.e., robust), which remove the VOC vapor from soils.
Until Focused RI work is completed at a subsite, EPA cannot know whether that subsite
even needs a remedy. However, as more has become known about mW-South, it has
become apparent that wherever a remedy is necessary, it is likely to be the ~remedy.
Therefore, before Focused RI work is completed at subsites, the remedial action for VOCs
in soils can be presumed at most subsites.
Therefore, the traditional approach makes little sense in the case of mW-South. The tradi-
tional approach would select a separate remedy for each particular subsite. If EP A per-
formed a separate remedy selection for each subsite, the likely result would be a large num-
ber of virtually identical FS. Reports and RODs. This would be an inefficient. use of
resour~es.
In contrast, the Plug-in Approach selects a remedy for a given range of conditions. Assum-
ing these conditions will exist most of the time, one needs only assess whether a particular
l0012ACE.WP5
II-3D
-------
Traditional Superfund Approach
Matching Alternative to a Site
Plug-in Approach
Matching Subsites to an Alternative
128('-14
FIGURE 11-11
COMPARISON OF TRADITIONAL VS
PLUG-IN APPROACHES
INDIAN BEND WASH - SOUTH STUDY AREA
-------
sub site meets these conditions. Provided it does, it can "plug in," and there is no need to
perform a separate remedy selection. Instead of matching several remedies to a single
subsite, the Plug-in Approach matches several subsites to a single remedy. Figure II-ll
illustrates this. concept.
I:
I
The Plug-in Approach retains all the basic components of the traditional Superfund process,
but rearranges and optimizes the order in which they are executed to minimize redundancy.
Just as in the traditional Superfund process, a final decision on remedy selection for any ~
subsite is not in place until after Focused RI work is complete at that subsite.
The Plug-in Approach carries many benefits. First, it allows remedial action to begin with-
out redundant remedy selection processes. Taken over all subsites at mw -South, this is
expected to save a significant amount of time and resources, both for EP A and for
PRPs. Second, it allows focused investigation at each subsite to occur at its own pace. The
Plug-in Remedy is available as soon as each subsite's investigation is completed. Because
Focused RI work and remedial action can occur at the same time, subsites that have com-
pleted Focused RI work and have plugged in can begin remedial design and remedial action
immediately, and are not held back by other subsites that are still performing a Focused RI.
Third, rather than treating each subsite in a vacuum, the Plug-in Approach focuses the col-
lection of data at subsites on the most-likely remedial alternative. Thus, there are less data
to collect in remedial design, and actual remedial action (cleanup itself) can begm sooner.
In all, the Plug-in Approach minimizes waste, time, and resource use, and begins remedial
action sooner. .
8. 1.4.
Plug-In Process Components
and Terminology
The Plug-in Process is fully detailed in Section 8.3. However, its terms and components are
first defined in this section. Figure II-12 identifies elements established by this ROD, in
conjunction with the Feasibility Study and the IRI Report. The figure also graphically
depicts how these components, once in place, serve to ensure that only appropriate subsites
are plugged-in to the remedy. .
The Existing Site Profile
The selected remedial action in a Plug-in
Remedy must be able to address the vast
. majority of subsites if the Plug-in
Approach is to be efficient. The range of common conditions among subsites that has been
observed at IBW-South is collectively called the existing site profile.
The observed "similar conditions" that
SVE, the Presumed Remedial Alterna-
tive, will have to address. .
lOOI2ACE.WP5
II-31
-------
Existing site
profile
Presumed
Remedial
Alternative
Remedy
Profile
Enhancements
to the remedial
alternative
Plug-In
Criteria
Plug-In
Decision Point
Those conditions
seen to exist so far
A robust technology
that can address
the existing site
profile
''';'''\I!: ..
1280_04
Technological
supplements that
enhance, or widen
the remedy profile
Plug-In
determination for
each sub site based
on criteria and
process contained
In ROD
."".,...,.,. -'," .."...'." ~-"'......,.......
",,,,,"""''''''''''''''''''''''
" -..).-.."- ,~,,'" """" "".. ".., .
...........
..""",,,"""'"
. ""'"~''''''' . .'..
FIGURE 11-12
PLUG-IN PROCESS COMPONENTS AND
TERMINOLOGY
INDIAN BEND WASH - SOUTH ROD
-------
; .
The existing site profile is defined in tenns of various physical and contaminant parameters
that might have an impact on the effectiveness of a remedial alternative. For example, for
SVE, the air permeability of the soil and the volatility of the contaminants strongly impact
its effectiveness. The existing site profile for. mw -South is defined by the IRI Report
{Admin. Rec. No. 1597] and Chapter 1 and 2 of the Feasibility Study [Admin. Rec. No;
1599]. It is also summarized in this document under Section 6, Summary of Site
Characteristics. Figure 11-13 shows a conceptual illustration of the existing site profIle.
FIGURE 11-13
EXISTING SITE PROFILE
The Presumed Remedial
Alternative
The remedial action to be taken for
VOCs in the vadose zone if a subsite is
plugged in.
The Presumed Remedial Alternative is the
action that will be taken at all subsites that
meet the Remedy Profile and the Plug-in Criteria (defined below). The Presumed Remedial
Alternative is selected to meet all identifIed applicable or relevant and appropriate require-
ments (ARARs). SVE is the Presumed Remedial Alternative for this remedy. SVE is
described and its applicable specifications are stated in Section 8.2.
The Remedy Profile
The range of conditions that the Presumed
Remedial Alternative can address is called
the Remedy Profile. Mter a subsite com-
pletes its Focused RI, the fIrst test of whether it can be plugged in to the remedy is whether
it exhibits conditions within the Remedy Profile. Like the existing site profile, the Remedy
Profile is defined in terms of physical and contaminant parameters that may have an impact
on the effectiveness of the Presumed Remedial Alternative.
The range of conditions that SVE, the
Presumed Remedial Alternative, is able
to address.
I .
I
i
Figure 11-14 shows a conceptual illustration of the Remedy Profile. The context of the
Remedy Profile in the Plug-in Remedy is shown in Figure II-12. SVE is selected as the
. Presumed Remedial Alternative because it can be expected to address those conditions seen
. to date. (the existing site profile). SVE may be capable of addressing conditions even
beyond those seen to date. Therefore, this ROD establishes reasonable boundaries on what
lOO12ACE.WP5
TI-34
-------
SVE can address. This is important because, should a subsite exhibit characteristics outside
these boundaries, SVE may not be effective at that subsite, and that subsite should not be
plugged in.
This subsite can
plug in to the
remedy directly
. Remedy Profile
The r2'lOS cj CC'ldl[jons
[hat SVE ca~l a~jdress
FIGURE 11-14
REMEDY PROFILE
If a sub site exhibits conditions outside the Remedy Profile, EP A will assess whether the
Remedy Profile can be enlarged by use of a teclmical enhancement Certain teclmical
enhancement options are incorporated in this remedy and are discussed below. If a subsite
cannot be brought within the Remedy Profile by use of an enhancement, that subsite cannot
directly plug in. In such a case, there are several possibilities which are discussed in Sec-
tion 8.3.2.
As an example, the SVE remedial alternative addresses VOCs because they move easily
into the soil vapor phase and can be subsequently removed by the SVE system. Should a
subsite contain only metals in the soil, however, SVE would be useless as a remedy to
address those metals. Metals are not volatile and would be unaffected by the removal of
soil gas. The Remedy Profile is defined by certain parameters such that a subsite with
metals only would fall outside the Remedy Profile. The Remedy Profile is specified in
Section 8.3.4.
lOOI2ACE. WP5
ll-35
-------
Enhancements to the Pre-
sumed Remedial Alternative
Technological enhancements to SVE
that may be necessary to widen the
Remedy Profile or allow SVE to operate
more efficiently.
I ;
Certain technical enhancements shall be
considered available as pan of this rem-
edy. The available enhancements are listed
in Section 8.2.5. At some subsites, it is conceivable that some of these enhancements may
be necessary in one of three situations: (1) to widen the enhanced Remedy Profile so that
SVE will apply, (2) to make SVE more efficient even if it would otherwise apply, or (3) to
meet an ARAR. Situation (2) is considered the most likely at mW-South. In such a
situation, SVE would be effective in cleaning the vadose zone, but it may take a longer
time due to an unforeseen condition, such as an unusual soil type. In such a case, the use
of the enhancement may substantially reduce the treatment time and increase its efficiency.
Decisions on the use of enhancements shall be made as pan of remedial design after a
sub site is plugged in.
Figure ll-15 is a conceptual illustration of an enhanced Remedy Profile where the Remedy
Profile has been widened by the addition of technical enhancements.
This subsite can
plug in to the
remedy directly
This subsite can plug
in, but it is best if an
enhancement is used
FIGURE 11-15
ENHANCED REMEDY
PROFILE
lOO12ACE.WPS
ll-36
-------
-- ---- -- ----------- - - --
,,'
The E1.Y.g-ln Cdteria '
Even if conditions at a particular sub site
are amenable to SVE (within the Remedy
Profile), there still may not be enough con-
tamination there to make SVE necessarv. ,
There must therefore be criteria based on potential health threats that serve as the standard
for EPA to determine whether an action is necessary. EPA can plug in those subsites that
exceed any of the Plug-in Criteria. Those not exceeding the Plug-in Criteria do not need a
VOCs-in-Vadose-Zone remedy and EPA will not plug in such subsites to the remedy.
The criteria determining whether con-
tamination is serious enough to require
that a cleanup for VOCs in soils be
implemented.
Most of the IBW -South Plug-in Criteria are specific to the various pathways by which
persons may be exposed to VOC contaminants in the soils from a sub site, either currently
or in the future. These pathways are identified and evaluated in the Risk Assessment in
Appendix A of the Feasibility Study, and are discussed in this document in Section 8.4.
The Plug-in Process and risk assessment for mW-South allow EPA to compare the risk
from VOCs in soils at any given sub site against this fixed set of Plug-in Criteria. The Plug-
in Criteria and the process for using them are established by Section 8.3 and are also
,discussed by Chapter 5 and Appendix A of the Feasibility Study [Admin. Rec. No. 1599].
As an example, VOCs may leak downward and enter groundwater, which may then be
withdrawn and consumed. Or, VOCs may volatilize upward and be inhaled near the ground
surface. The Plug-in Crit~ria, in effect, set separate limits on the levels of VOCs that may
reach the groundwater and levels of VOCs that may volatilize upward into the air, due to
any single subsite. If either of these types of limits is exceeded, a remedial action is nec-
essary, and EP A would plug in the subsite and require the Presumed Remedial Alternative,
SVE. If neither of the limits is exceeded, there is no unacceptable health threat posed by
the VOCs in the soil, and implementation of the Presumed Remedial Alternative is not
necessary .
The Plu -in Decision Point
This remedy selects a remedial action that
will apply whenever certain conditions
exist at mW-South. There are two condi-
tions that a subsite must meet before being
plugged in (See Figure TI-16). First, the sub site must exhibit conditions falling within the
Remedy Profile, and second, the subsite must exhibit contamination exceeding one or more
of the Plug-in Criteria. At the Plug-in Decision Point, a determination is made as to
whether to plug in one subsite and require the selected SVEaction. This decision is made
according to the process set in advance by this ROD. There will be one Plug-in Decision
Point for each facility that proceeds through the Plug-in Process. It is a Plug-m Decision as
sanctioned by this ROD that causes SVE to be reqillred at any particular sub site. Note that
the Plug-in Decision Point occurs at different times for different subsites. See Figure II-16.
After the ROD, when sampling work is
completed at a single subsite, a decision
is made whether to plug in the subsite
(reqillre the remedial action).
l0012ACE.WP5
II-37
-------
1 I I
1 11 1 " 1
1 1 1 11 11 21 21
Z 21 2 2! 21 71 21
21 31
;i}~~A:0jl;J(t'iAi~:;;tb;i,>'l;LL/i1:f:,a")iM;'05.r
,jJijX{{;J1J;kD'3i:iI!.~;,ak;'V} ,<',,;;;2>
. - , . ,', ... ',,' -", . --"-, -,
;">-,:":,'-<,-. ',""""-. -..--:,-, ::.' '- --_:.;:_~-,>:': .-: -. ,'-':--:'----~..-- '~"'< -'.;
. . .',' . ',' - ','. " .' " '-' -. ~
r\~;'/.\: ::--~:",,: :-'.~ :;:\"'./. :'~;:" .:-.:::".?:: ;':.jt,.::,.;.:':.:::~' ";<:..:( :-'.>...: ::::~~:;;
PLUG-IN
Decision
fJi~fl;;i;i;uj0:i!i{fljli:jL;!iJ.i;i}Ji.Ji;lfiSjf;~;;'
It'~~\1~~;}~:~~,;~jJ~ifi~~t}11j~}~ff9,!ijf£~)j~ii;;~';0'jfi
PLUG-IN
Decision
Feasibility Study
PLUG-IN ROD
. .... .," ~.'''' .." "...... "."' .','.',' ,,',' .~~. .., . ,". "'~'." . '." ,,,,..",',\ .'," '~"'."',"".'..~,.....'.... '"." ."." ,','... .",' .',',,~,', ,,' ,'. "','~',""',". .vA',',"""' ,.;,:,'~ ,'.',' "',,:.., ,',',' ','''''' '''."..~'", ' '.',' ""........, ,'",~"...~,.~ ".'.',""""'.. -.'".-;,'.......... ','.',,:,',,''''.' """;""':';""";'-'';''''''''.'''''' """""''''''..''''''' "" .
1245_05
FIGURE 11-16
TIMING OF EVENTS WITHIN THE
PLUG-IN PROCESS
INDIAN BEND WASH - SOUTH P'
-------
8.2.
The Selected Remedial Technology
Because this is a Presumptive Remedy, the Feasibility Study only compared SVE with the
No-Action Alternative. Comparison with No-Action is required by the NCP, and the No-
Action Alternative provides a basis of comparison for SVE. EP A has determined that SVE
is preferable to No Action as a remedy for VOCs in the vadose zone at IBW-South. This
section provides a description of the SVE alternative, a summary of the comparison with the
No-Action Alternative under the nine standard criteria, and a description of available
emission control (air treatment) options, SVE enhancement options, and Performance
Standards for their use. The nine criteria serve as a basis for defining why SVE should be
an effective remedy at IBW-South. The Feasibility Study analysis compared the conse-
quences of taking no action versus using SVE at subsites that have been determined to meet
the Plug-in Criteria and therefore pose an acceptable health threat. ' Subsites .!!Q1 meeting
the Plug-in Criteria are, in effect, screened out by the Plug-in Process, and therefore, no
remedial action is necessary at those subsites, by definition.
8.2. 1.
Description of the Selected Soil
Vapor Extraction Alternative
SVE is a means of physically removing VOCs from contaminated soil. This is accomp-
lished by inducing airflow through soils containing VOCs and collecting the contaminated
soil gas through an extraction well. The withdrawn contaminated soil gas can be treated at
the ground surface, after which the treated air is released to the atmosphere. Conceptually,
an SVE system is analogous to vacuuming the subsurface soil.
A typical SVE system consists of one or
more extraction wells, connected by
manifold to a vacuum blower and other
associated air-processing equipment.
This equipment would include valves
for flow control, an air-water separator
to remove excess moisture, monitoring
gauges (e.g., flow meters, pressure
meters, temperature probes), a mech-
anical blower (such as a regenerative or
positive displacement type) and an air
treatment system (such as carbon
adsorption, catalytic oxidation, thermal
destruction, or regenerative sorbent).
A typical SVE system is shown in
Figure TI-17, and SVE components are
shown in Figure TI-18.
FIGURE 11-17
APPLICATION OF AN SVE
SYSTEM TO REMEDIATE
VADOSE ZONE CONTAMINATION
lOO12ACE.WP5
TI-39
-------
FIGURE 11-18
SOIL VAPOR EXTRACTION
SYSTEM COMPONENTS
The fundamental subsurface component
of S VE consists of one or more extrac-
tion wells placed in the contamination
zone. A consistent vacuum is pulled on
these wells in order to remove VOC
contaminants. These wells need to be
placed to effectively induce subsurface
airflow through zones of VOC contami-
nation; the optimum placement and dis-
tribution of a multiple well system is
typically designed using a predictive
flow model. Figure IT-19 shows the
various components and dimensions of a
typical SVE well.
The other primary subsurface compo-
nent of SVE systems is the network of
soil vapor monitoring wells (SVMWs)
that is used to evaluate the SVE system
performance. SVMWs are used to mea-
sure and verify propagation of vacuum
in the subsurface. This information is
then used to estimate or predict the zone
through which airflow is occurring.
lOO12ACE. WP5
. fICH FUlL PORT PVC VALve
<-INCH PVCTHREAOED TEE
TEMPORARY PWG
o
z
Q::;
~~
:11-
~ 0
:z:
o
"'~
zii:
o
"'to.
zo
W:z:
~S
o
~
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g
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z!Z
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zl\!
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IJ4.4NCH PEAGRAva
4-IoiCH SCHEDU\.E <0
SlOTTED PVC CASING
SVE Well Construction
DIMENSION AAPPAOXIMATeLY80 FEET
DIMENSION BAPPROXIMATEIY IS FEET
DIMENSION CAPPROXIMATEIY 2S FEET
DIMENSION 0 AI'I'RCIXIIoW'EY IS FEET
OIMEHSION EAPPROXIMATEIY S FEET
FIGURE 11-19
COMPONENTS AND DIMENSIONS
OF A TYPICAL SVE WELL
SVMWs are also used to collect periodic
soil gas samples, which are used as proxies
for soil concentration data samples to assess
the rate at which soil decontamination is
occurring.
These data, together with the monitoring of
the concentrations of contaminants in the
blower discharge, are commonly used to
predict the remaining time necessary for
SVE system operation.
IT-40
-------
Both extraction wells and SVMWs can
be completed below grade or slightly
above grade. Piping connecting
extraction wells to the "plant" (pumps,
blowers, valves, water separator, and
treatment system) can then be installed
either above or below grade. The
amount of space required for the SVE
system is minimal, although the plant
may occupy it for an extended period of
time.
SVE usually can be installed with only
minor disruption to urban buildings or
facilities, as compared to other measures
such as soil washing or excavation of
contaminated soil. Figure II-20 shows
the various components and dimensions
of a typical SVMW.
SVE decontaminates soil by extracting
the contaminated soil gas, which is at
equilibrium with the other contaminated
phases (See Figure II-8), resulting in its
replacement with uncontaminated
air. This shifts the equilibrium and
causes the contamination in sorbed, dis-
solved, and free phases to tend to move
into the vapor phase. In this way,
VOCs are transferred from the other
phases into the vapor phase and are
progressively removed by the SVE
system. The paths that contaminants
follow during transfer from one phase to
another are analogized in Figure II-21.
Chapter 3, Section 3.1.2.2, of the
Feasibility Study [Admin. Rec. No.
1599] provides a detailed discussion of
the various parameters that affect SVE
efficiency, the amount of air that must
be withdrawn to achieve cleanups, and
the conditions under which enhance-
ments to SVE may be necessary.
lOOI2ACE.WP5
NO.' MOHTaIEY
SNIO. TYP
1lENT0Mre. TYP
I'. PEA GRAVa.. TYP
:~~
SCREEN. TYP
111m
.u. srAM.ess ST'EEI.
(SST) IS TYPf ,,,
FIGURE 11-20
COMPONENTS AND DIMENSIONS
OF A TYPICAL SVMW
Also included is a discussion of typical
values of the parameters at mW-South.
These data in the Feasibility Study support
EPA's decision to use SVE under the
conditions observed at mw -South.
Air flow rates ranging from 1 to 100
standard cubic feet per minute (cfm) per
foot of well screen are expected from SVE
systems operating at mW-South. A
minimum of 500 to 1,000 pore volume
exchanges of air is assumed to be needed,
II-41
-------
"",,@"""It"""
'(W ~ .. .. .. .. .. .. .. "
:'i~ -~ .~
" -:.., .:~
''', .,.
....,.,. .,.~..
".." ,. " ~..
"..".. ~..
- - ."''''J:8f''lal-
FIGURE 11-21
TRANSFER OF CONTAMINANTS
BETWEEN DIFFERENT PHASES
IN THE SOil MATRIX
and cleanup times are expected to take an average of I to 2 years and as many as 5 years.
In cases where a period of more than 5 years is projected to be required for cleanup, EP A
will consider the use of enhancements to the SVE remedy to increase its effectiveness.
8.2.2.
Description of the No-Action
Basis of Comparison
Selecting the No-Action Alternative would mean that nothing would be done to address the
current VOC contamination in the vadose zone at mW-South. Under the No-Action Alter-
native, any VOC contaminants in the vadose zone would remain in place and would be
allowed to continue to migrate in the subsurface. '
Specifically, the contaminants might become entrained in infiltrating rainwater and percolate
downward to groundwater, or groundwater may rise to meet the contaminants; vapor phase
contaminants in the vadose zone would also tend to migrate in all directions in response to
a concentration gradient.
These VOC contaminants' would also pose a potential exposure risk in excess of the risk-
based Plug-in Criteria (see Section 8.3.5) should future excavation activity penetrate the
VOC-contaminated areas.
lOO12ACE. WP5
II-42
-------
Nine-Criteria Comparison with No-Action and SVE
Overall Protection of Human Health and the Environment
8.2.3.
The No-Action Alternative would not be protective of human health and the environment
By definition, subsites exceeding Plug-in Criteria for which no action was taken would pose
a cancer and non-cancer risk to human health in excess of levels in the Plug-in Criteria
(specified in Section 8.3.5) and therefore pose an unacceptable threat to human health and
. the environment Under the No-Action Alternative, contaminated soil and soil gas would be
left in place with continued groundwater impacts caused by the downward migration of
VOCs and the potential for human exposures should excavation into contaminated soil
occur. The presence of these soils as continuing sources of potential groundwater contami-
nation could also compromise any groundwater remedy that EP A might propose in the
future.
Figure II-22 graphically compares threats to human health and the environment under both
the No-Action Alternative and the SVE Alternative.
IID-Action
SVE Actian
FIGURE 11-22
OVERALL PROTECTION OF HUMAN
HEALTH AND THE ENVIRONMENT-
NO-ACTION AND THE SVE ALTERNATIVE
The SVE Alternative will offer overall protection of human health and the environment
because the threatening contaminants will be removed from the vadose zone and either
destroyed or captured onto sorbents. Some low-level VOC emissions could occur during
remediation; therefore, onsite monitoring will be conducted to check for unacceptable VOC
emission levels.
l0012ACE. WP5
II-43
-------
By reducing the amount of VOCs remaining
in the vadose zone, SVE will reduce signifi-
cantly the cancer and non-cancer risk to
human health and also the potential for
future negative impacts to groundwater and
ambient air. During oper~tion, an SVE sys-
tem will overcome the natural migration
mechanisms that lead to groundwater and
ambient air contamination, lending additional
protection to human health and the environ-
ment during operation. .
Com~ce with ARARs
Table 0.3
OveraU Protection of Human Health
and the Environment-Summary
Soil Vapor No
Extraction Action
Alternative protects "
human health
Alternative protects the "
environment
Because the ARARs for this remedy are primarily action-specific, rather than chemical-
specific (see Appendix A), the No-Action Alternative may not violate ARARs directly.
However, the No-Action Alternative might render a potential groundwater remedy unable to
meet ARARs, as VOC contamination sources would continue. The SVE alternative will
meet chemical-, action-, and location-specific ARARs. SVE systems for mW-South will be
designed to comply with all ARARs identified by EP A. Appendix A discusses ARARs for
this operable unit.
I Table D-4 I
Compliance with ARARs-Summary
SVE No Action
Alternative can comply with chemical-specific ARARs ./
Alternative can comply with action-specific ARARs ./ Not Applicable
Alternative can comply with location-specific ARARs wi Not Applicable
Alternative can comply with other regulatory criteria ./
Lon -Term Effectiveness and Permanence
The No-Action Alternative would not alter the human health risks posed by contamination
at a particular source area. No controls would be used on the contamination residing in the
. vadose zone. While dispersion and degradation of contaminants would occur naturally, the
ability to accurately estimate these mechanisms is weak, and it cannot be assumed that deg-
radation would take place before the contaminants reached groundwater wells or before
humans were exposed to them;." ..,
lOO12ACE.WP5
TI-44
-------
The SVE system will remove the contaminants from. the vadose zone to levels that comply
with ARARs and health-based criteria. SVMWs will be used to monitor the amount of
VOCs remaining in the vadose zone during treatment.
The SVE system will continue to operate until the mass of VOCs in the vadose zone has
been reduced below the Performance Standards in this ROD. The SVE technology will be
able to meet these standards for subsites that match the Remedy Profile. SVE enhance-
ments such as steam or hot air injection may be required for subsite conditions outside the
Remedy ProfIle. Onsite monitoring will be conducted to check for. low-level VOC
emissions.
Pilot-study data from the PGA Superfund site indicate that SVE will adequately remove
VOCs from vadose zone soils similar to those at mW-South. SVMWs will be required to
monitor effectiveness of SVE during remediation.
When the SVE action. is completed, any remaining soil contaminants should be at levels that
no longer pose a threat to human health or the environment. The removal of VOCs will be
permanent. .
O&M activities required for the SVE
Alternative include:
.
Monitoring of the offgas for low-level
VOC emissions
.
Monitoring of SVMW s
.
Monitoring system components to
check for failures and to identify the
need for replacement equipment
(components of this system are
readily replaceable if necessary)
Table n.s
Long-Term Effectiveness and Permanence-Summary
Soil Vapor
Extraction No Action
Treatment residuals will be ren- "
dered harmless
Long -tenn controls are adequate "
and reliable to monitor residual
untrealed VOCs in the vadose
zone
In situ residual contamination will "
be reduced to levels protective of
human health and the environment
Reduction of Toxicity.
Mobility. or Volume through TreaTIlliml
The No-Action Alternative would not reduce toxicity, mobility, or volume through treat-
ment. No treatment activities are associated with the No-Action Alternative.
Reduction .of toxicity, mobility, and volume of contaminants by use of an SVE system is
graphically depicted in Figure 11-23.
lOOI2ACE.WP5
11-45
-------
I .
FIGURE 11-23
REDUCTION OF TOXICITY,
MOBILITY, OR VOLUME-
THE SVE ALTERNATIVE
I :
SVE will physically remove the VOCs
from the vadose zone. A variety of
different offgas treatment options could
be used to remove the VOCs from the
airstream. Offgas treatment options
specified in Section 8.2.4 include
adsorptive treatment (such as vapor-
phase activated carbon), thermal
destruction, and catalytic oxidation. The
selection of an appropriate offgas treat-
ment method occurs in remedial design
and will be based on data from specific
subsites (see Section 8.2.4).
The Reduction of Toxicity, Mobility, or
V olume criterion must be evaluated for
two separate questions: First, are there
reductions with respect to the
contaminant that actually remains in the
ground? Second, are there reductions
with respect to the contaminant that has
been removed from the ground and is
now present in some form at the ground
surface?
l0012ACE.WPS
Toxicity
Toxicity of any VOCs left in the ground
after SVE would be the same, strictly
speaking. However, there would no longer
be exposure pathways to humans due to
groundwater or soil gas itself. Therefore,
the potential for toxic effects is reduced.
The toxicity of the VOCs after removal
would depend on the offgas treatment
selected. Where adsorption-based systems
are used, the toxicity of the adsorbed VOCs
is not reduced,' should anyone be directly
exposed to the adsorbent. Such exposure is
unlikely, and because the adsorbent would
be removed from the site, the only humans
at risk would be workers handling the
adsorbent, and they would have received
training to handle it safely.
Where catalytic oxidation or thermal
destruction is used, the toxicity of the
VOCs is removed permanently, as they are
destroyed by the process.
The type of treatment residuals generated
by an SVE system depends on the selected
offgas treatment method. Vapor-phase
activated carbon offgas treatment would
generate spent carbon, requiring either
regeneration or disposal. A method such as
thermal destruction or catalytic oxidation
that included a scrubber unit to neutralize
HCI would produce scrubber water with
high total dissolVed solids and pH. These
residuals are far less toxic than the original
VOCs. The air-water separator may also
produce wastewater containing VOCs. The
quantity of treatment residuals would be
assessed for each subsite after sufficient RI
data have been obtained to estimate the
quantities of VOCs in the vadose zone.
EP A has selected Performance Standards
for treatment-derived wastewater in Section
8.3.7.
II -46
-------
The statutory preference for treatment at Superfund sites is best met by the catalytic oxida~
tion and thermal destruction offgas treatment options, as these permanently destroy the
waste. However, the preference is also significantly served by SVE with an adsorption off-
gas treatment system, such as vapor-phase activated carbon.
Mobility
SVE will strongly reduce contaminant mobility in the ground by containing the spread of
. the contaminant both vertically and laterally, and eventually removing it altogether. This
will prevent most of the VOCs from reaching the water table. Groundwater moves very
quickly at mw -South, and VOCs become much more mobile after reaching the water table.
The mobility of the contaminants after removal will also be reduced with the SVE Alterna-
tive. All offgas treatments will either trap or destroy the VOC contaminants, rendering
them immobile. The small percentage of VOC contaminants that pass emission controls,
which are 95 percent or more effective will become more mobile in the atmosphere.
Volume (and Mass)
By physically removing contaminants from the ground, SVE will significantly reduce the
mass and volume of overall contaminants remaining in the ground at mW-South. The mass
and volume of VOCs that will be removed depends on the areal and vertical extent of con-
tamination at the subsite in question. Information from Focused RIs at individual subsites
can be used to estimate the amounts of material that will be treated by SVE at each subsite
that meets the Plug-in Criteria.
Figure 11-24 graphically depicts the reduction of volume of contaminants by SVE systems
over time.
FIGURE 11-24
REDUCTION OF CONTAMINANT
VOLUME OVER TIME-
THE SVE ALTERNATIVE
The actual fmal volume of the contaminants themselves, after removal from the ground, will
depend on the offgas treatment used. This remedy contains use of offgas treatment in all
cases. With offgas treatment systems based on adsorption, such as vapor-phase carbon, the
l0012ACE.WP5
II-47
-------
contaminant on the adsorbent still retains its original mass and has a certain volume. How-
ever, this volume is dramatically reduced because the contaminants have been concentrated
onto the adsorbent. This makes the contaminants more manageable and, potentially, more
reusable. . .
With catalytic oxidation or thermal treatment, the contaminants are destroyed, so the mass
and volume are virtually eliminated. Destruction efficiencies of 95 to 99 percent can be
achieved by these offgas treatment options.
Table ll-6
Reduction of Toxicity, Mobility, or Volume through Treatment-Summary
SVE with
SVE with Carbon Thermally
or Regenerative Destructive
Sorbent Offgas Offgas
Treatment Treatment No Action
Toxicity of VOCs above ./
ground is reduced
Toxicity of VOCs below ./ ./
ground is reduced
Mobility of VOCs above ./ ./
ground is reduced
Mobility of VOCs below ./ ./
ground is reduced
Volume of VOCs above ./ ./
ground is reduced
Volume of VOCs below ./ ./
ground is reduced
Treatment process is irrever- " Not Applicable
sible
Short-Term Effectiveness
Since no remedial action occurs for the No-Action Alternative, no short-term effects would
occur that differ from the current condition. No-Action would provide no disruption to the
community or to property owners, and in the short-term, public exposures to VOCs would
be minimal.
Implementation of the SVE Alternative will entail construction-related risks during drilling
of vapor extraction and monitoring wells. However, with appropriate and readily available
monitoring and protective equipment, safety risks associated with installation and operation
of SVE systems at IBW-South should not be any greater than those associated with similar
.drilling activities at uncontaminated sites. The ground is not opened to the atmosphere with
lO012ACE.WP5
II-48
-------
I~~---- .- -..
an SVE system, other than to drill boreholes for monitoring wells. There is little potential
for public exposure to the contaminants in the short-term. Standard worker safety plans, in
accordance with Occupational Safety and Health Act ("OSHA") regulations at 29 CFR
Section 1910.120, shall be followed for all drilling activities.
Some environmental impact may occur during construction activities for the SVE Alterna-
tive, including noise and vibrations during drilling and disruptions of streets and sidewalks
during the laying of manifold piping. Some noise may also be generated during SVE sys-
tem operation, but should be sufficiently muffled to avoid becoming a public nuisance.
It is difficult to predict the time required to meet remedial response objectives with the SVE
Alternative for any particular subsite. Extraction rate is a function of site-specific character-
istics such as quantity and nature of VOC contamination, air pel11)eability, and depth to
groundwater. On the basis of extraction rates cited by other SVE remediation projects, the
SVE Alternative at IBW-South is expected to remove the bulk of the vadose zone contami-
nant mass in a time frame on the order of several years. VOCs begin to be removed as
soon as pumping begins.
There are potential short-term risks associated with the various offgas treatment options.
With catalytic oxidation and thermal destruction, there is a small chance that these systems
would fail, resulting in an untreated discharge of soil gas to the atmosphere. . However, the
risk associated with this is small for three reasons. First, at any given time there is only a
small mass of soil gas in the system, so there is no potential for a large, uncontrolled
release of VOCs. Second, any such discharge would be of short duration, as the system
would be shut down. Third, the contaminant concentration in the airstream is relatively low
to begin with; it would likely meet air quality regulations even without treatment.
The other short-term risk from these offgas treatment systems is the very small amount of
VOCs that are not treated. This amount is not expected to exceed 5 percent of the influent
concentration and should average less than 1 percent. EP A does not believe this will cause
any adverse health effects. All discharges will meet ARARs and Performance Standards
selected in this ROD to ensure protectiveness during remedial implementation.
With adsorption offgas systems, there is essentially no short-term risk associated with han-
dling the spent carbon and, potentially, no short-term risk with the VOCs at their fmal desti-
nation (a RCRA landfill, regeneration facility, or in the case of an accident, on the ground).
About 40 gallons per week of wastewater may be generated from the air/water separator
during SVE system operation. This wastewater will be tested, and if found to be hazardous,
will be handled in a manner compliant with all ARARs. Section 8.3.7 specifies concentra-
tion levels at which water from the air/water separator must be handled as a hazardous
waste.
If a scrubber is necessary to neutralize excess hydrochloric acid with an offgas treatment
using catalytic or thermal oxidation, then water with high total dissolved solids and high pH
may result. Such water would be handled in accordance with all ARARs. If found to be a
1 OOl2ACE. WPS
ll-49
-------
RCRA characteristic waste, the water would be treated to remove the characteristics, or
properly removed from the site as a hazardous waste.
If water from either process is sampled and found to . be non-hazardous, it may be dis-
charged to the ground surface or evaporated, as appropriate. No such water will be injected
into the ground via wells or discharged into surface waters.
Table ll-'
Sbort- Term Effectiveness-Summary
SVE with Offgas
Treatment No Action
Protection of communio/ during implementation of "
Remedial Action
Protection of workers during implementation of Reme- "
dial Action
Ability to comply with air quality standards "
Environmental impacts during construction in compli- " Not Applicable
ance with regulations
Remedial response objectives achievable within an "
aCCeptable timeframe
lmplementability
The No-Action Alternative implies no action is implemented.
The activities required for installing an SVE remediation system include drilling the nec-
essary extraction and monitoring wells, laying out the manifold piping, and plumbing the
piping into the selected off gas treatment unit. Construction and operation of an SVE system
are readily achievable in the IBW-South environment The Arizona Department of Environ-
mental Quality ("ADEQ") estimates that approximately 70 SVE projects in Maricopa
County are currently in the process of being permitted or are operating. Nationwide, EP A
has selected 83 SVE remedial actions for Superfund sites that are in the pre-design, design,
or operational phase. In some instances, problems siting equipment in optimal locations are
likely and expected; however, equipment placement should generally be possible and in
most cases; be implementable with a minimum of disruption to surrounding activities.
'SVE has proven to be effective at remediating VOC-contaminated soils at many other sites
[Hutzler, N. J., et aI., 1991, as cited in the FS, Admin. Rec. No. 1599]. The equipment
required for an SVE system is well-proven and reliable. It is also replaceable should a
failure occur.
lOO12ACE.WPS
II-50
-------
Additional remediation may be required at subsites that have metals or other non- VOC con-
taminants in the vadose zone. Additional remediation may also be necessary at subsites
where the underlying groundwater is highly contaminated with VOCs. If VOC levels in
groundwater are high. the VOCs can migrate upward from the water table and recontami-
nate the vadose zone. The SVE system, once having achieved cleanup standards and the
other requirements of this ROD for VOCs in the vadose zone, may be dismantled and
removed from the site so that it will not interfere with other potential remedial actions.
Monitoring can be used to measure the effectiveness of the SVE remedy through two
mechanisms:
.
Monitoring of SVMWs to provide an estimate of the amount of residual mass of
VOCs remaining in the vadose zone
.
Monitoring of the offgas to provide a measure of the mass of VOCs that have been
removed from the vadose zone
Pertinent regulatory interests outside of EP A include air discharge (Maricopa County and
ADEQ), installation of extraction and monitoring wells (Arizona Department of Water
Resources), and right-of-way and traffic (City of Tempe). Onsite remedial actions are
exempt from administrative permit requirements by CERCLA ~121(e).
Offsite treatment is not required for the SVE remedial action since treatment occurs onsite.
Facilities with adequate storage I capacity and necessary disposal services are available to
support the implementation of SVE at IBW-South.
Cost
There would be no direct cost associated with the No-Action Alternative.
ever, be indirect costs associated with loss of the groundwater resource.
not quantified by the Feasibility Study for this Operable Unit.
There may, how-
These costs were
Feasibility cost estimates are projected on the basis of the total costs of a remedial alterna-
tive for the duration of the alternative. These estimates have an expected accuracy of
approximately +50 to -30 percent.
Catalytic oxidation was selected as the representative offgas treatment option for performing
the cost estimate because reasonable cost estimates can be provided, calculated from an
assumed extraction flow rate and time of operation.
In contrast, reasonable cost estimating for a vapor-phase activated carbon offgas treatment
system requires subsite-specific remedial investigation data on the types and total mass of
VOCs in the vadose zone. RI data are currently inadequate to provide accurate cost esti-
.mates for vapor-phase activated carbon offgas treatment at any particular subsite. However,
an estimate using vapor-phase carbon to treat chlorinated solvents in soils at IBW-North
IOOI2ACE.wP5
II-51
-------
was prepared in 1991 [U.S. EPA, 1991, Public Comment Draft North Indian Bend Wash
RIfFS Report, mW-North Admin. Rec. Nos. 1874 to 1878]. For a two-well SVE system
operated for 2 full years, the estimated 1993 present worth cost was approximately
$720,000, assuming a 5 percent discount rate for the years 1991 to 1993.
. ,
Subsites with relatively low extracted vapor concentrations that can economically use vapor-
phase activated carbon may have substantially lower remediation costs than those presented
below. Figures IT-25 and IT-26 represent present-worth and annualized cost estimates,
respectively, for a single SVE system with one, three, or five extraction wells. The effect
of adding enhancements is shown in the Table TI-8. Use of enhancements is described in
Section 8.2.5, and more detail on cost is presented in the Feasibility Study.
$1 ,600,000 ..... ..-......",,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,-, .........,..... .-.... ........... .......... ,,,"'''''''''''''''' ... ..._...._..._.................._..........._.......~_........._..
. 1 SVE Well
- -0. -...-...... -",'0"--'--'-"""--"" _.....o_._,""'''''''''''''U' "-...........
. 3 SVE Wells
.......,............................... ...................,.. ''''.....,..... ....... II 5 SVE Wells
$400,000 .......-
$200,000 -.. ""
'..._..0_.- ....o..-'-""'-""'--""""""'O_'U"'''''-'''''O...-"""-".""-,,,,,,'--"""""'- """"""""""""'" ................"--
$1,400,000 .,.. .............._u.
1:"
II $1,200,000 """"--'"
.~
! $1,000,000......m........
en
o
(,)
"C
j
as
:s
c
c
CC
$800,000 .... ....
$600,000'" .m
.'.'h................-..."-'-"'" ......,.-.o.-....-u....""""''''''''--'''''-'''''''''''--"""h""""'"
$0
2
3
4 5
FIGURE 11-25 '
ANNUALIZED COSTS FOR
THE SVE ALTERNATIVE
Years of Implementation
Table n-8
Cost Estimate of Various SVE Enhancements
Enhancement Cost of Enhancement
Hot air injection 1.5 to 2.5 times non-enhanced SVE system cost
Steam injection 1.5 to 2.5 times non-enhanced SVE system cost
High vacuum SVE system 1 to 1.5 times non-enhanced SVE system cost
Horizontal extraction wells 1 to 1.5 times non-enhanced SVE system cost
SVE system with ground surface sealing 1 to 1.5 times non-enhanced SVE system cost
Bioventing 0.5 to 1 times non-enhanced SVE system cost
1001 2ACE. WP5
IT-52
-------
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$1,3oo,000.:y'iIO'- ,.'''''''''''''1.''.'.''..''''''+'''.'''.''''''':''.'.'''''; i .'''''.'''''.'r'''''''''.''''r.'''''''''''.''i''''''''''''''''"J".
':::f--!----":~=-=T:::-=E:::-=-==:T-:=::l::---::~:~:~-::_~----~
$500,000 .. ."".."".""'j.................t................1................t..,.............-/.................[.................~.......... == ::: ::::s
$300,000 ... .................t""""'."""r""'"''.'''r'''''''''....-[-..............."!-...............t................;.......... GII!OID 5 SVE Wells
$100,000 ;; :;
o
2
3
4.5
5
3.5
4
0.5
1.5
2.5
Years of Implementation
FIGURE 11-26
PRESENT WORTH COSTS FOR
THE SVE ALTERNATIVE
~e Acceptance
The State of Arizona concurs with the use of the SVE alternative for VOCs in the vadose
zone at mW-South above health-based limits, and with the use of the Plug-in Approach, as
selected by this ROD. The State prefers the use of SVE over the No-Action Alternative.
Community Acceptance
The community's response to EPA's proposed remedy, and EPA's response to public com-
ments and concerns, are in the Response Summary, in Part ill of this ROD. Those
responding to EPA's proposal and attending public meetings accepted the Plug-in Concept
and the use of the SVE technology, in general. Concerns centered on who will be held
liable for contamination and the amounts of liability. Also of concern was the indirect
effect of the Superfund site on financing and real estate. These issues are addressed in the
Response Summary. EPA received no comments requesting that EPA select the No-Action
Alternative.
8.2.4.
Emission .Control (Offgas Treatment)
Design Options and Requirements
The "offgas" is the air that is removed from the ground by an SVE system. During reme-
dial action, this air contains the VOCs extracted from the soil, the subject of this Operable
Unit. EPA's proposed remedy included three options for emission controls, or treatment of
this offgas, and stipulated that any of the options may be used at any particular facility.
IOOI2ACE.WP5
IT-53
-------
. All SVE systems operated as part of this remedy will contain continuous emission controls.
EP A has selected use of emission controls for several reasons:
.
The greater Phoenix area is a non-attainment area for ozone under the Clean Air
Act, and several of the VOCs in question are precursors to ozone in the atmosphere,
thus adding to photochemical smog problems.
.
Because a Plug-in Approach is being used, there could be several SVE systems
operating concurrently, thus raising the issue of cumulative impacts if the VOCs
were directly discharged without treatment.
.
The SVE systems will be operating in an area with relatively high VOC solvent use.
Offgas treatment selection. for any given subsite shall be made during remedial design for
that subsite, but shall be chosen from among three available options. Offgas treatments
among these options shall be considered part of this selected remedy. If offgas treatments
other than those specified by this ROD are necessary, then EP A will amend the ROD or
issue an explanation of significant differences ("ESD"), as appropriate. EP A will declare
the likely offgas treatment for a given subsite at the time that the subsite plugs in to the
remedial action.
The selection of an appropriate offgas treatment method at any particular subsite will be
made on the basis of subsite-specific remedial design data. The specific offgas treatments
discussed in Chapter 3, Section 3.1.3, of the Feasibility Study [Admin. Rec. No. 1599] are
hereby selected as the available offgas treatment design options for this remedy. These
include:
.
Adsorptive Treatment. This treatment option includes the use of vapor-phase
activated carbon or other sorbents. Offgas treatment by vapor-phase activated
carbon is well-proven for VOC-contaminated air. Carbon treatment is accomplished
by placing vessels containing activated carbon in the vented airstream. Other proven
methods of adsorptive offgas treatment include the use of proprietary sorbents that
are regenerated on site. .
These treatments work by adsorbing the VOCs from the offgas. Organic molecules
are selectively adsorbed to the surface pores of the carbon or sorbent granules, and
contaminant is transferred from the air to the sorbent. This technique is commonly
used to remove organic vapors from air.
Carbon treatment requires periodic carbon replacement as the carbon surfaces
become saturated with VOCs. The saturated or II spent II carbon then requires trans-
port to a licensed regeneration facility or to a treatment, storage, or disposal facility
approved by RCRA (meets the requirements of the Resource Conservation and
Recovery Act). Operation and maintenance ("O&M") costs for carbon treatment can
become prohibitive for soil gas concentrations in excess of I part per million by
I0012ACE.WP5
II-54
-------
volume (ppmv). Some non-carbon regenerable sorbents can be regenerated without
disposal, leaving pure VOCs only for recycling and disposal.
.
Catalytic Oxidation and Thermal Oxidation. Thermal treatment and catalytic
oxidation are alternative methods that destroy the VOCs in the offgas. The two
methods are similar in that heat is used to reduce VOCs to complete products of
combustion. However, in catalytic oxidation, a catalyst causes VOC destruction to
occur 10 times more quickly and at temperatures approximately 50 percent lower
than required for thermal destruction. These technologies will reduce chlorinated
VOCs to carbon dioxide, water, and hydrochloric acid (HCI). A caustic scrubber
would.be required at the outlet of the treatment unit to neutralize the HCl.
Unlike adsorbent systems, thermal treatment and catalytic oxidation literally destroy
the VOC contaminants. Such systems would produce offgas of essentially carbon
dioxide and water vapor. VOC contaminants that may remain in the of (gas would
be below standard air discharge limits for facilities. Such offgas may have lower
VOC levels than the surrounding ambient air.
Thermal destruction may be the most economical for extracted vapor concentrations
in excess of 2,500 ppmv. Catalytic oxidation may be the most economical for
extracted vapor concentrations ranging from 600 to 2,500 ppmv. Proprietary sor-
bents and on site regeneration may be economically feasible at any conc~ntration
encountered in SVE and should be considered on a case-by-case basis for specific
subsites.
Any of these offgas treatments can be designed for a minimum 95 percent removal effi-
ciency, and can be safely and economically implemented and operated.
Figure n-27 shows the concentration levels at which the various treatments would be con-
sidered most effective and economical. This is intended as a guideline only. EPA will
decide which option to use in a given case based on the rate of extraction required, the
location of buildings and other constraints, and other design considerations and data.
Performance Standards for Emissions Controls
As described in Appendix A (ARARs), EP A has considered the following Maricopa County
Air Pollution Control Division rules in establishing performance standards for emission
controls. These rules are not ARARs for this remedy. However, these rules were used in
setting air emission Perfonnance Standards for the mw -South site based on the potential
impacts of the soil vapor extraction systems that likely will be in operation at the site.
. Rule 21O-Lists requirements for major sources of air emissions, defined by Rule 210,
~212 as capable of emitting 100 tons per year or more of any air pollutant subject to
regulation under the Clean Air Act.
IOOI2ACE.WPS
II-55
-------
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..........-..................
....... ..... ........ .......... ..........-.. ........ ......0. - ..-.--
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.-[[[
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..................... "n""~"~'.~'.~_.~..~U~'. ~.."""n_"~ .......'u~..
Legend
-
Cost-effective range
1280_03
FIGURE 11-27
EFFECTIVENESS OF OFFGAS
TREATMENT OPTIONS WITH V AR'IOUS
CONCENTRATIONS OF EXTRACTED VAPOR'
Rille 210, ~304 requires a new stationary source which emits up to 150 pounds/day or
25 tons/year of VOCs to apply reasonably available control technology ("RACT").
RACT is defined in ~220 as the lowest emission limitation that a particillar source is
capable of achieving by the application of control technology that is reasonably avail-
able considering technological and economic feasibility.
. Rille 210, ~303 provides that sources emitting more than 150 pounds per day are
required to use best available control technology ("BACT").
-------
. . .
. Rule 330, ~301-Prohibits discharge of more than 15 pounds of VOCs into the atmos-
phere in anyone day from any device involving heat
. Rule 330, ~302-If heat is not involved, VOC emissions are limited to no more than 40
pounds per day.
. Rule 330, ~304-If either of the limitations set forth in ~30l or ~302 is exceeded, the
emissions must be reduced by incineration with a 90 percent oxidation rate to carbon
dioxide, adsorption with an 85 percent capture rate, or other similarly effective process.
This section also states efficiency requirements for the emissions reduction process.
EP A believes that the emission control options for this remedy would meet both RACT and
BACT requirements (although emissions from SVE systems are not expected ever to exceed
the l50-pounds-per-day threshold for BACT). As stated above, emissions controls will be
applied to all SVE systems. The following additional performance standards shall apply to
emission controls: .
. Emission controls for offgas treatment shall attain a minimum 90 percent efficiency
rate (either by removal or oxidation to CO2 and H20)
. Routine monitoring of the offgas shall be performed during the remedial action, to
ensure that no ARARs or performance standards are being violated.
. If the emission controls should fail, the SVE system will be shut down until the
emission controls are again effective.
8.2.5.
SVE Enhancements-Design Options
and Performance Standards
SVE enhancements are specific technological supplements that allow SVE to' remove con-
taminants more efficiently. Enhancements are not separate remedies, but design options for
the SVE remedy. Based on data seen to date, EPA does not believe that enhancements will
be necessary for most subsites at mW-South. However, this remedy contains a list of
seven enhancement options that shall be available as part of this remedy. If an
enhancement is to be used at a particular subsite, it shall be determined as part of the
remedial design of the SVE system for that subsite. At the time of plug-in, EP A will
declare in the public notice of the plug-in (see Section 8.3.3) whether enhancements are
expected, and which enhailcements are most likely. If enhancements or modifications other
than the seven options listed in this section are necessary, EPA will amend the ROD or
issue an explanation of significant differences ("ESD") to address such changes.
SVE enhancements may be required for specific subsites at mW-South to accomplish either
of two objectives:
lOO12ACE.WP5
IT-57
-------
1. To expand the range of conditions over which SVE is effective (Le., expansion of
. the SVE Remedy Profile) at subsites that exhibit conditions near, but not within the
Remedy Profile. This may allow a larger variety of subsites to plug in and allow
SVE to be implemented where it would otherwise not be possible. For example,
part of a subsite may contain a significant layer of clay with low air permeability.
An SVE enhancement could be used to bring the VOCs out of the clay more
efficiently.
2. To optimize SVE system operation (improve the efficiency and performance) of
SVE systems at subsites exhibiting conditions that do fall within the Remedy Pro-
file. While SVE can remediate such subsites, it may take too long to do so. Perfor-
mance improvements would provide increased rate. of contaminant removal or
decreased remediation cost.
EP A will consider the use of. an enhancement as part of a subsite remedial design plan
when: .
1. EP A projects that the cleanup time for a subsite or part of a subsite will be greater
than 5 years, or . .
2. One or more of the following physical conditions. are present:
.
Contaminants are present with vapor pressures less than 1 mm Hg at 20° C.
.
Contaminants are present with Henry's Law constants less than 100 atmosphere
per mole-fraction. .
.
Soil intrinsic perqleability is less than 1 x 10-3 darcies, either over all depth, or
in any significant stratigraphic layer which holds VOCs.
.
Soil water saturation exceeds 60 percent.
~
Depth to groundwater is less than 5 feet.
3. The use of an enhancement is necessary in order to meet an ARAR or other require-
ment specified by this ROD. .
However, where use of an enhancement would lessen the cost of overall remediation, then
even where the above conditions do not exist, an enhancement may be considered. EP A
does not anticipate that SVE enhancements will be necessary in most cases at mW-South.
. When. they are used, it is expected that in most cases it will be with the objective of
increasing the rate of VOC withdrawal, thereby shortening overall cleanup times. In such
cases, SVE may be effective with or \\jthout the enhancement, but it is more economically
and environmentally feasible to run the enhanced SVE system for a shorter time, rather than
unenhanced SVE for aJonger time.
lOOl2ACEWPS
IT-58
-------
At a limited number of subsites, enhancements may be needed to allow SVE to work at all;
these subsites would fall outside the Remedy Profile without an enhancement
Most SVE enhancements will have an effect on the projected cost of an SVE system. This
effect is generalized in Section 8.2.3 and in Chapter 3 of the Feasibility Study. The thermal
enhancements are most e~pensive, while the physical and operational enhancements are the
least expensive. Ground surface sealing, for instance, may add little cost compared to the
cost of a basic SVE system, if the sub site is small. The degree to which an enhancement
will affect cost will depend on whether the enhancement is part of the original design of the
SVE system, or is added after the system
is in place; also whether it effects
operation and maintenance costs, or only
implies an initial capital outlay. Costs
,may be offset by savings derived from a
shorter cleanup timeframe that is achieved
with the enhancement EP A believes that
it is appropriate to presume SVE is a
cost-effective remedy at mW-South, even,
after accounting for the potential use of
enhancements.
Figure 11-28 lists available SVE enhance-
ments for mW~South. Table 11-9 summa-
rizes the description of the enhancements
and general guidelines for which enhance-
ments are indicated under which condi-
tions. The conditions used are Remedy
Profile parameters and limits. A more
detailed discussion of enhancements and
the technical situations for their use is
presented in Chapt~ 4 of the Feasibility
Study.
SVE Enhancements
:.;?~i~t~,:;:..~-:;:,%.~:-'./;:::HA/':}.'+ei.Y,:,.....,;,",,:>X'::i;
, ~ High Vacuum SVE ,
, :;':I-/-~~~~g~J~~~~:~~':':~~'-H{t;..."".'" ',,":/:-.,
~ Ground Surface Sealing
m Hot Air Injection
[i;'~I;~/.Y:~~I;t~~~~:;'./,;':}f'M\.@1i~}~i'~+(s":;.'/i~J'';!;~,i
Biological
'~~If.f:;;{Ii~~~:h~,6.~,;~'\~~':U.~;~.:h:;:}i:;~J,~.:<;.~.:~~N'{:x'.)~k~[
Operational
'}~,I~~m~~r$~~'~~~~~~i~J~ij::F;;,''.2i~;?'::':::);:'(:';;::
FIGURE 11-28
AV AILABLE SVE ENHANCEMENTS
AT IBW-SOUTH
8.3.
Plug-In, Process Specification
8.3.1.
Overview
As previously discussed, this remedy contains both a remedial technology, selected in
Section 8.2, and a process for determining whether a subsite must execute it This section
defmes the process that shall be used to determine which subsites shall plug in to the SVE
remedy. This section also specifies the cleanup performance standards for subsites that are
plugged in.
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H
H
I
0'1
o
I Table 11.9 I
Description of Enhancements
Enhancement Description Indications
Hot air injection Hot air injection wells are used in tandem with extraction wells to increase the tendency of VOC vapor pressure < I mm Hg @ 20° C, or VOC Henry's
(TIIERMAL) ~uhsurface VOCs 10 volatilize into the vapor phase. Increases vapor pressure and Henry's I JlW Conslanl < 100 aim/mole-fraction, or soil intriluic per-
constant of vue contaminant, and therefore rale of removal of VOCs. Removes excess soil meability < Ix 10') darcies, percent soil water saluration >
moisture, increases rate of VOC diffusion. 60%.
Steam injeclion Hot air injection \\Iells are used in tandem with extraction wells to increase the tendency of VOC vapor pressure < I mm Hg @ 200 C, or VOC Henry's
(TIIERMAL) suhsurfaee VUCs 10 volatilize into the vapor phase. Increa.ses vapor pressure and Henry's Law Constant < 100 alm/mole-fractioil, or soil intrinsic per-
constant of vue contaminant, and therefore rate of removal of VUCs. Increases rate of meability < Ix 10') darcies.
VOl: diffusiun.
lIigh vaeuulII SV E lIigh vacuums are applied through zones of low air penneahility to increase the removal of Percenl soil water saturation> 60%, depth 10 groundwater
system contaminants. Increases air permeabiliiy of the soil. less than 5 feet, soil intrinsic permeability < xlO') dareies.
(pHYSICAL)
l1ori1',onlall"xlmdion I\ori;wnlal wells arc inslalledlo IICel'SS l,oncs of snhsnrfaec l'onillminniion nol IIcn'ssihk hy Ikpth 10 groul1llwllter les~ 1111111 .S reel, low-pennenhilily
wells conventional SVE I'.!ells. zones IUIIning laterally, zones ina~'Cessible to normal SVE
(pHYSICAL) wells.
SVE system with GroWtd surface is sealed to increase the lateral influence of SVE wells and to prevent exces. Depth to groundwater less than 5 feet.
ground surface sealing sive air leakage from the atmosphere which reduces SVE efficiency.
(pHYSICAL)
Bioventing SVE wells are operated at low flow that allows biological activity to break down biade- VOC vapor pressure < I mm Hg @ 200 e, or VOC Henry's
(BIOLOGICAL) gradable contaminants. Increases oxygen content of soils. Law Constant < 100 aim/mole-fraction,
Pulsed System SVE wells are operated intermittently in accordance with a schedule. Shifts partitioning VOC vapor pressure < I mm Hg @ 20° C, optimization of
Operation equilibriwn. Allows more VOC to diffuse out of zones of lower permeability. Minimizes SVE system needed.
(OPERATIONAL) "rebound" at end of cleanup. Increases total voe recovery.
IOOI2AOI.WPS. I
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Those subsites that EP A screens from further consideration prior to requiring a Focused RI
are not considered to be subject to a Plug-in Detennination. The specific sampling, model-
ing efforts, and risk estimations described in Section 8.3 of this ROD will not be performed
for such subsites. Therefore, no determination will be made as to whether such subsites
exceed the Plug-in Criteria. However, by screening out such subsites without requiring a
Focused RI, EP A will have detennined that insufficient evidence exists to consider them as
contaminant sources.
The decision tree (Section 8.3.8) is the blueprint for Plug-in Decisions. The tree incorpo-
rates the elements of the process specified in Section 8.3.
8.3.2.
Options at the Plug-In Decision Point
The possible options at the Plug-in Decision Point are shown in Figure II-29. Most cases
are expected to move through the "plug-in directly" route.
Remedial
design
Other ROD or
removal
FIGURE 11.29
EVENTS FOR A TYPICAL SUBSITE
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"
The Presumed Remedial Alternative is designed so that it will apply to a majority of sub-
sites. Nonetheless, EP A has several options to address subsites that exceed the Plug-in
Criteria, but have contaminants other than VOCs, or exhibit other characteristics outside the
Remedy ProfIle. In such a case, the subsite cannot be plugged in to the remedy directly,
because the Presumed Remedial Alternative, SVE, will be at least partially inappropriate.
In such instances, EP A may decide to select a remedy for that subsite by another means.
Options would include taking removal actions in conjunction with plugging the sub site into
the remedy, amending or' otherwise modifying the remedy to address special situations at
the subsite, or selecting an entirely separate remedy. Such remedies would be subject to all
requirements of CERCLA and the NCP.
8.3.3.
How,Plug-in of a Subsite.
Will Be Administered
For any subsite passing through a Focused RI, EP A will make the results of the Focused RI
available to the public. BPA will prepare a document showing the results of the Plug-in
Process specified in this section for the subsite. This will include the comparison of the
data from the sub site with the Remedy ProfIle and Plug-in Criteria. In this document, EP A
will make a determination as to whether the subsite plugs in. The determination will be
published regardless of whether the subsite plugs in.
EP A will summarize, and give notice of the availability of the Focused RI and EP A's Plug-
in Determination in a factsheet, which will be distributed to EP A's Community Relations
mailing list and to the local libraries. For each subsite that EP A determines will plug in to
the remedy, EPA will hold a 30-day public comment period. Prior notice of the comment
period will be given in the factsheet. During this comment period, EP A will onLy address
comments on: (1) whether the Plug-in Process as determined by this ROD was followed in
making the Plug-in Determination, and (2) whether subsite-specific data were used in an
appropriate fashion. Neither the Plug-in Process itself, nor the use of the SVE technology,
will be re-opened for public comment during such periods.
It is this ROD in coni unction with a subsite-specific Plug-in Decision made in accordance
with the process in this ROD, that constitutes a fmal decision for VOCs in soils at a partic-
ular subsite.
8.3.4.
Specification of the Remedy Profile
Table n-lO specifies the unenhanced Remedy Profile for mW.;...South.
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Table 11-10
Remedy ProfIle Parameters for Soil Vapor Extraction
Remedy ProfIle Boundaries
Remedy ProfIle Parameter and Range of Inclusion
Soil Permeability of the Vadose Zone Greater than 1 x 10-3 darcies
Percent Saturation Less than 60 percent
Depth to Groundwater Greater than 5 feet
Henry's Law Constant of Contaminant Greater than 100 ann/mole fraction
Vapor Pressure of Contaminant Greater than 1.0 mm Hg @ 20°C
8.3.5.
Specification of the Plug-in Criteria
This remedy addresses VOCs in soils as future sources of groundwater and air contamina-
tion. The amount that the concentration of VOCs in groundwater or air would increase due
solely to VOCs in a subsite's soils is referred to as the incremental concentration, and the
risk to public health posed by the incremental concentration of VOCs is referred to as the
incremental risk from that subsite. For mW-South, the Plug-in Criteria are limits on the
incremental risk and incremental concentrations of VOCs from a subsite.
The Plug-in Criteria for mW-South are not point-specific concentration limits for the soil
medium itself. Rather, they apply to the effect of soil VOCs on other media. This effect is
estimated by the process put forth in Section 8.3.6. For mw -South, EP A has defmed four
of the five Plug-in Criteria in terms of incremental risk by three pathways of exposure for
VOCs in soil identified in the risk assessment (Appendix A of the Feasibility Study; also
summarized below in Section 8.4).
The reasoning for risk pathways assigned to each criterion was discussed in the Feasibility
Study ("FS"), Chapter 5, and the Risk Assessment, Appendix A of the FS.
The cancer risk Plug-in Criteria, based on I in 1 million, or 10-6 excess cancer risk, may be
considered conservative (erring on the side of greater safety). However, in this case, EPA
believes that reasonably protective levels are appropriate for several reasons. First, there are
as yet unquantified risks, such as groundwater risks, that may apply to mw -South. EP A
must allow for all risks at the site. Second, the proximity of the contaminated sub sites to
each other cannot be fully determined initially, introducing some uncertainty as to the
cumulative effects of the risks posed by the subsites. Third, it is important to ensure that
the future threat to groundwater is reduced sufficiently so no subsite could by itself produce
enough groundwater contamination to make a groun<;twater remedy necessary in areas where
it is not otherwise needed today. Finally, the Arizona drinking water classification for
mW-South aquifers, which is an ARAR, requires that stringent source control be imple-
mented with the objective of keeping or restoring the aquifer to drinking water standards.
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In shon, there is sufficient uncertainty and cause to select Plug-in Criteria for VOCs in soils
that are near the more protective end of EPA's risk range of 10-4 to 10-6.
The Plug-in Criteria for this remedy are shown in the Table II-II. Execution of SVE will
be required if the VOCs present in the soils at a subsite would, as calculated by the risk
assessment, exceed any of the five criteria listed.
I Table U-ll I
The Plug-in Criteria
1 Present a cancer risk (incremental risk) of more than 1 in 1 million to a person from both ingestion
of VOCs in groundwater and inhalation of VOCs during other household uses of groundwater, such
as showering, over a lifetime.
2 Present a cancer risk to a person of more than 1 in 1 million from inhalation of air above the soils at
the subsite itself, over a lifetime.
3 Present a hazard index for non-cancer effects of more than 1 to a person from both ingestion of
VOCs in groundwater and inhalation of VOCs during household uses of groundwater, over a life-
time.
4 Present a hazard index for non-cancer effects of more than 1 to a person from inhalation of air above
the soils at the subsite itself, over a lifetime.
5 Increase the concentration of VOCs in groundwater (incremental concentration) by an amount greater
than the federal Maximum Contaminant Level (MCL) under the Safe Drinking Water Act.
There is one Plug-in Criterion (No.5) that is not based directly on risk, but rather on
federal drinking water standards. Note that this Plug-in Criterion does not set a limit on the
allowable total concentration of VOCs in' groundwater. . Rather, it limits that part of the
groundwater concentration due solely to the incremental (extra) VOCs from soils at a
subsite that would reach the groundwater over time. Therefore, by this criterion, a subsite
would not be allowed to increase the existing groundwater concentration by more than one
"MCL's worth" of any VOc.
This standard is purposely designed so that, where there is no groundwater contamination
today, a single subsite would not be able to raise the groundwater concentration above the
MCL in the future. However, where there is groundwater contamination today, a separate
groundwater cleanup may be necessary to ensure protective groundwater, levels.
Table ll-12 presents a list of the MCL standards that will be used as the basis for Plug-in
Criterion No.5. This criterion (No.5) shall not be in effect for compounds which have no
MCL (shown in Table n-12 as "--"). Adequate human health protection from such com-
pounds will be provided by the other four Plug-in Criteria. In fact, in the majority of cases,
the risk-based Plug~in Criteria (Nos. 1 through 4) will be more stringent than Criterion
No.5. Note that the MCLs are not ARARs for this remedy (See Appendix A) because this
remedy does not directly address groundwater. Rather, EPA has chosen MCLs as one basis
for selecting Plug-in Criteria.
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Table 11-12
Standards for Plug-in Criterion No. S:
Federal MCLs (Concentrations in pg/I)
Acetone -- trans-l,2-Dichloroethylene 100
Benzene 5 1,2- Dichloropropane 5
Benzyl Chloride -- 1,3- Dichloropropene --
Bromodichloromethane 100 Dichlorotetrafluoroethane --
Bromoform 100 Ethylbenzene 700
Bromomethane -- Hexachlorobutadiene --
Carbon Tetrachloride 5 Methylene chloride --
Chlorobenzene 100 Methyl Ethyl Ketone --
Chloroform 100 Styrene 100
Chloromethane -- 1,2,2,2- Tetrachloroethane --
Dibromochloromethane 100 Tetrachloroethylene 5
1,2-Dibromoethane 0.05 Toluene 1,000
1,2- Dichlorobenzene 600 1,2,4- Trichlorobenzene 70
1,3- Dichlorobenzene 600 1,1, I-Trichloroethane 200
1,4- Dichlorobenzene 75 1,1,2- Trichloroethane 5
Dichlorodifluoromethane -- Trichloroethylene 5
1,1-Dichloroethane -- Trichlorofluoromethane --
1,2- Dichloroethane 5 1,1,2- Trichloro-2,2,I- --
Trifluoroethane
cis-l ,2- Dichloroethane 70 Vinyl Chloride 2
1,I-Dichloroethylene 7 Xylenes (Total) 10,000
The risk assessment presents a complete sttategy for integrated risk management so that it
can be verified-that all remedies for IBW-South, operating together, are protective of human
health. The Plug-in Criteria are based only on those exposure pathways pertinent to the
contaminants in this Operable Unit, the VOCs-in-Vadose-Zone soils. The Plug-in Criteria
are not intended to have any bearing on whether a groundwater remedy may be necessary at
a later date for contaminants already in the groundwater.
8.3.6.
Specification of How Exceedance of the
Plug-In Criteria Will be Evaluated
The process described in this section is depicted in Figure II-30.
VOCs in the vadose zone at a sub site may pose a threat if they migrate from soils to
groundwater or to ambient air. The purpose of the soil remedy is to limit the amount of
VOCs that can enter the groundwater or the air, due to any particular subsite. Evaluating
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the threat of a subsite must depend, therefore, on making an estimate of the incremental
VOCs that will enter the groundwater (or the atmosphere) over time due to anyone suh-
site. The process in this section will be used to estimate the maximum effect that the VOC
mass distribution at a subsite will have on groundwater or ambient air in the future. This
estimated effect will then be compared with the Plug-in Criteria.
Focused RI Data Collection
Data will be obtained from Focused RIs for each subsite subject to the Plug-in Process.
Information obtained during the Focused RI at each subsite shall include, at a minimum:
.
Subsurface lithology from soil borings
.
Identification and vertical distribution of non- VOC contaminants in the vadose zone
from soil samples obtained from soil borings .
.
Vertical distribution and type of VOC contaminants in the vadose zone ~om soil gas
samples obtained from SVMWs
.
Sufficient numbers of SVMWs and shallow soil gas samples to provide a mass
estimate of vadose zone contamination at the subsite
.
Groundwater quality information obtained by sampling monitoring wells installed at
the subsite
.
Any additional information or activities determined necessary by EP A pursuant to
regulation, statute, or EP A guidance.
A Focused RI may obtain data on contaminants other than VOCs. It is not necessary for a
subsite to be fully characterized for these non- VOC contaminants prior to beginning the
Plug-in Process.
Performance of vac Mass Estimates wi,h, Deglli
For sub sites with VOCs in the vadose zone, the total contaminant mass and the horizontal
and vertical distribution of mass shall be estimated for each VOc. The sources of data that
will be available to estimate the horizontal and vertical mass distribution are shallow soil
. gas surveys and depth-specific soil gas samples collected from SVMWs during the Focused
.RI. The measured soil gas. concentrations shall be convened. to total contaminant mass
estimates.
The horizontal distribution of 'near-surface contamination will be estimated from shallow
soil gas survey data. The mass of contaminant represented by each measured soil gas con-
centration can be estimated by assuming that each soil gas data point is representative of a
given area of soil surrounding the sampling location.
I 00 I 2ACF.WP5
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RiskTemplate
Calculations
Focused
Investigation Data
Reduction
VLEACH and Mixing
Zone Modeling and
Analysis
COMPARISON WITH PLUG-IN CRITERIA
1280_11
RGURE 11-30
THE SUBSITE EVALUATION APPROACH
WITHIN THE PLUG-IN PROCESS
INDIAN BEND WASH - SOUTH ROD
-------
The estimation of the vertical distribution of VOC mass in the vadose zone may be more
uncertain due to a lower density of data points available to characterize the distribution. H
the data collected from SVMWs indicate a consistent contaminant distribution with depth
across the subsite, the results from the sh3.now soil gas survey can be applied to a normal-
. ized depth distribution to obtain the vertical contaminant distribution at each sampling loca-
tion. H the vertical contaminant distributions vary across the subsite, the subsite will be
divided into regions. The vertical contaminant distribution in each region shall be defined
separately by the data collected from the SVMWs. Subsequent calculations, determinations,
and completion of cleanup for each area shall then be accomplished and verified for each
area separately. .
VLEACH Vadose Zone Trans ortModel
EP A will estimate the maximum future incremental concentrations from the VOCs in soils
at anyone subsite by using a computer model. The model to be used shall be the EP A
computer model VLEACH, or an equivalent model approved by EPA for mW-South.
VLEACH is a one-dimensional, computer-based finite difference model. The mass distri-
bution of VOCs with depth in soils is input to VLEACH. The model then simulates the
movements of VOCs in the vadose zone and predicts the mass loading (flux, or rate of
leaching) of volatile contaminants to groundwater and ambient air over time. A separate
VLEACH analysis is required for each VOC identified in the vadose zone.
VLEACH shall be applied in accordance with Appendix C of the Feasibility Study, which
is incorporated by reference into this ROD. That appendix presents a more detailed model
description, the VLEACH user's guide, a listing of the VLEACH FORTRAN code, a sam-
ple input file, and an application case study. VLEACH shall be applied in accordance with
the example given in the case study (unless otherwise approved by EPA) and with all other
requirements in this ROD. EP A shall approve the design of the model application. Should
a later version of VLEACH be approved by EPA, the later version, and its user's guide,
shall replace the version and user's gUide presented in Appendix C of the Feasibility Study
and shall become applicable to the Plug-in Process under this remedy.
In cases where EP A determines that the outcome of VLEACH is mathematically certain
without running the model, EP A may approve that the conclusion be accepted without I11n-
ning the model. For exarriple, one could make the extreme assumption that the entire VOC
mass in the vadose zone instantly arrived in groundwater. An estimate of the effect of
VOCs on groundwater under such an assumption would be much greater than a correspond-
ing VLEACH estimate, as VLEACH computes the gradual arrival of VOCs over many
years. If even under this assumption, the Plug-in Criteria would not .be exceeded, then'
actually running VLEACH may not be necessary. EPA will have sole discretion to make.
such determinations. .
It should be noted the VLEACH model simulates the movement of VOCs in the vadose
zone. If other contaminants, such as semi-volatiles or heavy metals, are detected during a
Focused RI, the subsite cannot directly plug in to the VOCs-in-Vadose-Zone remedy. Other
1 OO12ACF. WP5
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means will then be required to assess contaminant transport to groundwater, and these
would be developed by a separate or modified remedial action.
Mixing Zone Model Calculations
The flux (output) from VLEACH is then input into a "Mixing Zone ModeL" There is one
mixing zone model for groundwater and one for ambient air. EPA will use the maximum
flux over time, as estimated by VLEACH, in the mixing zone model. The model calculates
an incremental concentration in groundwater or air due to VOCs in the vadose zone at one
subsite.
Estimating Incremental Groundwater Concentrations: The
Groundwater Mixing Zone
For groundwater, a simple mixing zone model shall be used to convert the maximum mass
fluxes of VOCs over time predicted by VLEACH into concentration levels. The simple
mixing zone approach calculates groundwater concentrations on the basis of an assumed
mixing depth in the aquifer beneath the subsite and an estimated flow of clean groundwater
originating from upgradieitt sources.
The saturated thickness of the UAU beneath the IBW-South site has been observed to vary
dramatically with recharge from the Salt River. In the simple mixing cell model, EP A
proposes to use a mixing depth of 50 feet:, or the saturated thickness of the UAU, whichever
is less. This scheme is proposed for several reasons.
First:, 50 feet is a reasonable estimate of the recent thickness of the UAD during dry (non-
river flow) conditions. It is not reasonable to use the current saturated thickness of the
DAD (about 80 to 90 feet) because wet (river flow) conditions currently exist, and the
thickness of the DAD in the short term is therefore increased compared to its long-term
average. The leaching of the contaminants will occur over a long time frame in the future,
during which dry conditions are more likely to prevail, especially after the planned raising
of the upstream dams on the Salt River. .
Second, 50 feet is a reasonably conservative estimate for the length of a well screen that
might be used on a drinking water well.
Third, if the mixing zone depth is much more than 50 feet:, the assumption of uniform
mixing departs too far from the realm of plausibility.
EPA may change the mixing cell model procedure if necessary to address technical condi-
tions. As an example, if the DAU were to dewater entirely, the model would have to
address the MAU rather than the DAU, and different parameters may be indicated.
Note that clean water flow-though is assumed in the mixing cell model, even though the
current groundwater may. be already contaminated. This is because the Plug-in Criteria
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address the incremental VOCs resulting from leaching from soils only. Existing ground-
water contamination will be addressed by a separate remedy, as necessary. EPA's overall
integrated risk strategy does allow for existing groundwater contamination.
Alternate methods to estimate incremental groundwater concentrations may be considered if
EP A believes they are better suited for the individual subsite being evaluated.
Estimating Incremental Ambient Air Concentrations:
The Air Mixing Zone
A box modeling technique shall be used to convert the maximum mass fluxes of VOCs
predicted by VLEACH into air concentrations. The formulation of the model is based on
guidance presented in EPA's Assessing Potential Indoor Air Impacts for Superfund Sites,
1992, as cited in the Feasibility Study, Admin. Rec. No. 1599. While an indoor air model
is used, the parameters are formulated to address both indoor and outdoor conditions at the
subsite. Estimation of air concentrations is based generally on the following:
C=E
Q
[1]
Where:
C = Air concentration (glm3)
E = Contaminant infIltration rate into the structure (gls)
Q = Structure ventilation flow rate (m3fs)
Assuming that soil gas enters a structure only by diffusion, contaminant infiltration into
the building can be estimated as:
E=JxAxF
[2]
Where:
J = Contaminant flux estimated from VLEACH (glm2-s)
A . = Floor area of the structure (m2)
F = Fraction of floor area through which soil gas can enter. F - 0.7 to 1.0 for
buildings with ventilated crawl spaces
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The structure ventilation flow rate can be estimated as follows:
Q = ACH x V
36f1Jslhr
[3]
Where:
ACH = Building air changes per hour (1/hr), typical ranges from 0.5 to 1.5
V
= Building volume (m3)
The incremental air concentration is then calculated by dividing the contaminant inf1ltration
rate (E) by the ventilation flow rate (Q).
Other similar modeling methods may be used with EPA's approval, depending on subsite-
specific conditions.
Risk . Templates
Once the model has estimated the incremental concentrations, the risk templates in the Risk
Assessment (Appendix A of the Feasibility Study, and also included in this document at the
end of Part TI) can be used to estimate the incremental risk (the risk due to the incremental
concentration). The risk templates are simple spreadsheets which act as a "fill in the
blanks" baseline risk assessment into which the toxicological profiles and scenarios of the
Risk Assessment are already installed. Incremental concentrations are entered on the left,
the prescribed calculations are run, and the estimated incremental risk emerges on the right.
The calculated risks then will be compared to the risk-based Plug-in Criteria. If the Plug-in
Criteria are exceeded, then a remedial action is required.
Virtually any VOC that may be present in the vadose zone at mW-South will be represen-
ted on the templates; nonetheless, if a VOC is found at a subsite that does not appear on the
template, the templates for that subsite may be revised by EPA to incorporate that VOC.
(
Figure TI-30, presented earlier, illustrates the concepts just described. These procedures are
referenced by the Decision Tree in Section 8.3.8.
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8.3.7.
Specification of Cleanup Performance Standards
The SVE system at each subsite that plugs in to the remedy will operate continuously until
the VOCs in soils have been reduced such that Plug-in Criteria selected in Section 8.3.5 are
no longer exceeded. Evaluation of whether Plug-in Criteria are still exceeded as cleanup
nears completion shall be accomplished by the same process and methods used to determine.
that the Plug-in Criteria were exceeded originally; through sampling of soil vapor, use of
the VLEACH and mixing zone models, and the risk templates. .'
The party responsible for remediating the subsite will be required to submit a monitoring
plan along with the remedial design to EP A for approval. This monitoring plan shall
include provisions to meet all requirements in this ROD, monitoring methods, schedules,
documentation and ttacking, methods of analysis, a time frame for continued monitoring
after cleanup performance requirements have been met, and a provision for resuming
remedial action if post-cleanup monitoring reveals exceedance of cleanup standards as
defined in this ROD. The monitoring plan shall also include a reponmg procedure to notify
EP A when cleanup performance requirements have been met, with allowance for EP A to
verify analysis. Monitoring plans and programs may be subject to other requirements based
on EP A regulations or guidance.
Each subsite's monitoring program will audit the progress of the subsite's remedial action.
SVMWs will be sampled periodically, according to an EPA-approved plan, to estimate the
mass of contamination remaining in the vadose zone after a period of implementation. In
addition, the contaminated offgas will be sampled periodically before and after tteatment to
assess the mass of contamination removed and the quality of the air discharge, in accor-
dance with Section 8.2.4.
The remedial action plan shall identify additional requirements that shall apply to an SVE
system before it is determined that the SVE system can be shut down. These requirements
shall include: .
1. A minimum number of samplings spaced evenly over a specified period of time that
must show contamination not exceeding the Performance Standards before the SVE
system can be shut down'
2. Mter SVE system .shutdown, a minimum number of samplings spaced evenly over a
specified time period that must show contamination below the cleanup standards in
this ROD, proving that contamination is not returning, before the SVE system is
made no longer immediately available
3. A provision for using the pulsed pumping enhancement in the event that contami-
nant levels rebound
If a system is shut down after reaching cleanup standards, and VOC levels rebound to levels
above the cleanup standards, then the above requirements shall apply anew.
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i--
Each subsite monitoring plan approved by EP A shall include a schedule of frequency and
duration of long-term monitoring of the remedial action, and compliance with the 5-year
review requirement in accordance with CERCLA ~121(c).
Treatment-Derived Wastewater
An air/water separator may be required on SVE systems to remove soil vapor from the air
stream prior to treatment EP A will address this treatment-derived water in accordance with
all identified ARARs. Among the options available would be to discharge this water to the
sewer under a pretreatment permit, treat the water to health-based levels onsite, and to
discharge the water to the ground surface if it is sampled and found not to be a hazardous
waste.
,In accordance with the policy stated in the memo from Sylvia Lowrance, Director of EP A
Office of Solid Waste, to Jeff Zelikson, Director of EPA Region IX Toxics and Waste
Management Division, dated January 24, 1989, groundwater from CERCLA actions may be
considered to be not a RCRA waste if it contains chemicals in concentrations below health-
based levels selected by EPA Region IX. Table TI-13 shows these levels for the mW-South
site. If treatment-derived water is to be discharged to the land, the water will first be
treated to these health-based levels.
In addition, if a scrubber is necessary to neutralize excess hydrochloric acid with an offgas
treatment using catalytic or thermal oxidation, then water with high total dissolved solids
and high pH may result. Such water would be handled in accordance with ARARs. If
found to be a RCRA characteristic waste, the water will be treated to remove the hazardous
characteristics before being discharged, or properly removed from the site as a hazardous
waste.
8.3.8.
The Decision Tree
Figure ll-31 shows graphically the decision tree' for the Plug-in Process that will be used for
this remedy. The details of tile process displayed by the decision tree are specified in the
foregoing sections.
There are three major blocks on the detailed decision tree in Figure TI-31. These corres-
pond to the three fundamental questions:
A. Does the subsite fall within the Remedy ProfIle?
B. Is remedial action necessary for VOCs in soils (Le., does the subsite exceed Plug-in
Criteria)?
C. Have cleanup perfonnance requirements been achieved at the' subsite?
lOO12ACF.WP5
ll-73
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Table n-13
Threshold Values For
RCRA Hazardous Waste Classification at IBW-South
(Concentrations in JIg/I)
Acetone 700' trans-l,2-dichloroethylene 100
Benzene 5 1.2- Dichloropropane 5
Benzyl Chloride 140' 1.3-Dichloropropene 0.19'
Bromodichloromethane 100 Dichlorotetrafluoroethane 100"
Bromofonn 100 Ethylbenzene 700
Bromomethane 9.8" Hexachlorobutadiene 1.4"
Carbon Tetrachloride 5 Methylene chloride 5<
Chlorobenzene 100 Methy1ethylketone 350"
Chlorofonn 100 Styrene 100
Chloromethane 2.8" 1.2.2,2- Tetrachloroethane O.08d
Dibromochloromethane . 100 Tetrachloroethylene 5
l,2-Dibromoethane 0.05 Toluene 1.000
1,2- Dichlorobenzene 600 1,2,4- Trichlorobenzene 70
1.3- Dichlorobenzene 600 1.1.1- Trichloroethane 200
1,4- Dichlorobenzene 75 1.1.2- Trichloroethane 5
Dichlorodifluoromethane 1,400' Trichloroethylene 5
1.1- Dichloroethane 1,OW Trichlorofluoromethane 2.100"
1,2- Dichloroethane 5 1.1.2- Trichloro- 2,2.1- Trifluoro- 210,000'
ethane
cis-l ,2- Dichloroethane 70 Vinyl Chloride 2
1,1-Dichloroethylene 7 Xylenes (Total) 10.000
"Level based on Arizona Health~Based Guidance Level for water. -
~o fonnal toxicity standards exist for this compound. which isaiso known as FREON 114. Level is
based on a limited no-observed-adverse-effect-Ievel as detennined by data from the Hazardous S ub-
stance Database, with an uncertainty factor of 10. The study used as the basis was Campbell DD et al;
Br J lnd Med 43:107-/1 (1986).
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1.UII
B. DOES THE SUBSI1E
MEET PLUG.IN
CRITERIA?
,"""".J',
~~~p;
I
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I,
C. HAVE CLEANUP STANDARDS
BEEN ACHIEVED AT THE
SUBSI1E?
r'-'-'-'~'-'-'-'-' .-.-.-.-.-.-.-.-
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RGURE 11.31
DECISION TREE - S~ECIRC
VOCe IN YADOSE ZONE FS
INDIAN BEND WASH - SOUTH ROD
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8.4.
Integrated Risk Approach and Risk
. Templates for Subsite Risk
Characterization
8.4. 1.
Summary of Integrated Risk Approach
BPA's Interim Risk Assessment for mW-South currently appears as Appendix A to the
Feasibility Study. This section provides a summary of risk assessment for mW-South.
Because of the Plug-in Approach, a specialized approach is being used for site risks. The
risk assessment with risk templates for completing risk characterization is hereby incorpora-
ted into the remedy by reference. The following is only a summary.
While the interim risk assessment identifies and considers risks to ensure protection of
human health and the environment, risks must also be evaluated at different stages, timed
with this and other Operable Unit remedies for mw:-south. The risk assessment presented
in Appendix A of the Feasibility Study is' therefore "interim" until all risks have been
evaluated.
The current version of the interim risk assessment develops the framework for considering
risks at all Operable Units of mW-South, including future Operable Units not addressed by
the VOCs-in-Vadose-Zone remedy. It then characterizes risks addressed by the VOCs-in-
Vadose Zone remedy. When the FS and ROD for the groundwater remedy (and other rem-
edies if needed) is completed, this risk assessment will be amended to evaluate groundwater
risks and integrate them with the VOCs-in-Vadose-Zone risks. By considering all risks at
the beginning, BPA will select interim risk goals for the Operable Unit remedies along the
way so that the total risk after cleanup will not exceed EPA's acceptable risk range.
8.4.2.
Specialized Strategy for Plug-in
The Plug-in Approach requires a specialized strategy for risk assessment for the VOCs in
the vadose zone because the selection of the remedy occurs prior to completion of Focused
RIs at each subsite. As of this date, the subsite-specific data are not available to determine
the risk at any given sub site. Therefore, the risk assessment becomes a component within
the context of the Plug-in Process.
In this. strategy, the current risk assessment does not calculate the baseline risk for any
given subsite. Rather, it performs all but the final calculations for a standardized subsite.
Subsite data then "fIll in" a risk template to arrive at the baseline risk. A separate baseline
risk assessment for VOCs in'soils is, in effect, complete each time the Plug-in Process is
executed. Just as this ROD provides a standard remedy which becomes the remedy for a
particular subsite when connected with a Plug-in Determination, so also the risk assessment
and template become a baseline risk assessment for a particular subsite once subsite-specific
lOOI2ACF.WP5
II-77
-------
data are available. Based on the resulting baseline risk, EP A can compare the subsite with
the risk-based Plug-in Criteria.
The risk assessment supports setting the Plug-in Criteria, using the Plug-in Criteria to make
a Plug-in Determination, and setting the cleanup standards for this remedy. The risk
template serves as the standardized means for determining whether Plug-in Criteria have
been exceeded.
8.4.3
Exposure. Pathway Categories For IBW-South
Potential exposure pathways at mw -South have been classified into three different cate-
gories. Each of the exposure pathway categories, or "compartments," can be conceptualized
as one section of a risk prism (see Figure TI-32). This risk prism is a geometric
representation of the total risk that exists at mw -South.
The three compartments are (1) potential exposure pathways associated with VOCs in the
vadose zone (VOCs-in-Vadose-Zone Compartment), (2) potential exposure pathways
associated with contamination in the groundwater (Groundwater Compartment), and
(3) potential exposure pathways associated with metals or other non- VOCs in the vadose
zone (Non- VOCs Compartment).
The pathways in the VOCs-in-Vadose\.
Zone Compamnent are different in that
they imply potential fut:nre rather than
current exposures due to the VOCS
migrating from the soils to the other
media. Unless the VOCs are removed
from the soil, these future risks will
become current risks. Figure TI-33
provides an illustration of the potential'
exposure pathways at the mW-South
site. The VOCs-in-Vadose-Zone remedy
will address risks resulting from the
pathways in the VOCs-in-Vadose-Zone
Compartment. The groundwater remedy,
if necessary, will address risks resulting
from the pathways in the Groundwater
Compartment.
Other Operable Units, removal actions, or
even modifications to the VOCs-in-
Vadose-Zone remedy may address risks
resulting from the pathways in the Non-
VOCs Compartment, if necessary.
lOO12ACF.WP5
Y~~:~~t!~;~;~~~~f~~~E~~;~;;
FIGURE 11.32
RISK PRISM FOR IBW-SOUTH
TI-78
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Disclaimer: The Inlenl 01 this figure Is 10
lIIustmle possible exposure routes at
IBW-Soulh. The exposure scenarios shown
may nol exist aIIBW.South.
1280_08
FIGURE 11-33
IllUSTRATION OF POTENTIAL
EXPOSURE PATHWAYS AT IBW-SOUTH
INDIAN BEND WASH. SOUTH ROD
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Because VOCscan migrate from soils to the groundwater, the pathways associated with the
VOCs-in-Vadose-Zone Compartment nonetheless include exposure routes that involve
groundwater. The Groundwater Compartment covers risks from contamination currently
existing in the groundwater. In contrast, the VOCs-in- Vadose-Zone Compartment covers
risks solely attributable to the potential for VOCs in soils today to enter the groundwater or
the air in the future. The VOCs-in-Vadose-Zone Compartment addresses how much of an
incremental risk is posed by the fact that VOCs currently reside in soils at a particular
subsite.
8.4.4.
Exposure Pathways Associated
with VOCs in Vadose Zone
The pathways associated with the VOCs in Vadose Zone Compartment are those associated
with the future migration of VOCs from the soils to other media, namely groundwater and
ambient air. Where VOCs reside in the soils at depths beyond likely excavation, a direct
exposure pathway does not exist. However, when the VOCs migrate, a potential pathway
from VOCs in soil to a receptor is completed, through the other media. These pathways are
called "future potential exposure pathways." .
The future potential pathways for VOCs in soil, which the VOCs-in-Vadose-Zone Remedy
must address, are:
1. Ingestion of VOCs that migrate from the vadose zone to the groundwater. An
example of this would be a person in the future drinking domestic groundwater that
was contaminated by VOCs observed today in the vadose zone.
2. Inhalation of VOCs that migrate from the vadose zone to the groundwater. An
example of this would be a person in the future using domestic groundwater for
shower water that was contaminated by VOCs observed today in the vadose zone.
3. Inhalation of VOCs, by a person in the future, that have migrated from the vadose
zone through the ground surface to the ambient air at the subsite itself.
EP A expects that the third pathway is insignificant unless the concentration of VOCs at a
subsite is fairly high and the VOCs are at a shallow depth. Nonetheless, to be protective,
Plug-in Criteria will be based on this exposure pathway.
Plug-in Criteria for cancer and non-cancer contaminants have been developed for the sum of
the risk from the fIrst two pathways, and separately for the risk from the third pathway.
This is based on the assumption that exposure by all three pathways at once is unlikely.
lOOI2ACF.WP5
II-80
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8.4.5.
Summary of Chemicals of Concern
and Toxicity Assessment
For the purposes of the risk assessment, "chemicals of concern" were taken to be the
majority of chemicals on the EP A Method TO-14 list of volatile organics plus methylethyl-
ketone. Although not all of these chemicals have been detected at IBW-South, EPA
developed the risk template using all the chemicals, so that if new VOC chemicals were
discovered at subsites in the future, the risk templates would still serve as a standardized
means of determining whether Plug-in Criteria were exceeded. These chemicals of concern
, and their corresponding toxicity values and characteristics, are presented in Tables II-14
and II-IS. These tables discuss the primary chemicals of concern, those that have actually
been commonly detected at IBW-South. These include l,l-dichloroethylene (l,l-DCE),
cis- and trans-l,2-dichloroethylene (1,2-DCE), tetrachloroethylene (perchloroethylene, PCE),
trichloroethylene (TCE), and vinyl chloride.
8.4.6.
Summary of Basic Exposure Assumptions
For the ingestion of groundwater pathway, EPA assumed a residential scenario. The
assumed exposed individual had a mass of 70 kg, and the exposure averaging time. was 70
years for carcinogens, 30 years for non-carcinogens. Exposure duration was assumed to be
for 30 years, 350 days per year. Ingestion rate was assumed to be 2 liters of water per day.
For the inhalation of VOCs during domestic use of groundwater pathway, the same assump-
tions were used, except the daily inhalation rate was assumed to be 15 cubic meters of air
per day. Table 1I-16 on page II-87 shows the assumed efficiencies with which various
household water uses would transfer VOCs to the air.
For the pathway involving inhalation of VOCs due to volatilization from soils at the subsite,
the same assumptions were used, except that the inhalation rate was assumed to be 20 cubic
meters of air per day, because the exposed individuals would likely be workers at IBW-
South facilities. A residential scenario was imposed, nonetheless, because the future uses of
the IBW-South area are uncertain. There are some mobile homes in the area, and resi-
dences border the study area on three sides. Once bank protection is provided to the Salt
River banks, there is no guarantee that residential development will not occur. Therefore, to
be protective of human health, a residential scenario has been used.
8.4.7.
Templates: Risk Characterization
at Each Subsite
As discussed previously, the incremental risk due to VOCs in soils at each subsite will be
estimated and compared with the Plug-in Criteria, which place a limit on that risk. The
Plug-in Criteria for the incremental risk due to VOCs in soils at each subsite are specified
in Section 8.3.5 of this ROD.
lOO12ACF.WPS
II-81
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Table 0-14
. Oral/Inhalation Carcinogenic Classification and
Critical Toxicity Values for Chemicals of Concern
lOW-South Interim Risk Assessment
, Page 1 of 3
Carcinogenic Noncarcinogenic
, (oral/inhalation) (oral/inhalation)
Slope Factor Weight 'of RID
Chemicals. (mg/kg-day)-l Evidence Source (mg/kg-day) Source
Benzene 0.029/0.029 NA IRISIHEAST -/- IRIS/-
Benzyl Chloride 0.17/- B2/- IRIS/- -/- -/-
Bromomethane -/- DID IRIS/IRIS 0.00 14/0.
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Table 0-14
Oral/Inhalation Carcinogenic Classification and
Critical Toxicity Values for Chemicals of Concern
IBW-South Interim Risk Assessment
Page 2 of 3
Carcinogenic Noncarcinogenic
(oral/inhalation ) (oral/inhalation)
Slope Factor Weight of RID
Chemicals' (mg/kg-day)'l Evidence Source (mg/kg-day) Source
1,2- Dichloropropane 0.068/- 82/B2 HEAST/- -/- OOS/-
cis-l,3-Dichloropropene O.l8f/O.13f 82f/B2f HEAST/" 0.00031/0.0057f OOS/"
trans-l,3-Dichloropropene 0.18f/- 82f/- HEAST/- O.oooY/- OOS/-
Ethylbenzene -1- DID OOS/lRIS 0.1/0.286 IRIS/''
4-Ethyltoluene -/~ -/- -1- -/- -1-
Freon 11 (Trichlorofluoromethane) -1- -/- -/- 0.3/0.2 OOSIHEAST
Freon 12 (Dichlorodifluoromethane) -1- -/- -1- 0.2/0.05 OOS/HEAST
Freon 113 -1- -/- -/- -/- -1-
Freon 114 (Dichlorotetrafluoroethane) -1- -/- -1- 30/8.6 OOS/"
Hexachlorobutadiene 0.078/0.078 C/C OOSIHEAST 0.0021- OOSI-
Methyl Ethyl Ketone -1- DID HEASTIHEAST 0.05/0.1 HEASTIHEAST
Styrene -1- 82/B2 OOS/lRIS 0.2/0.29 OOS/"
1,1,1,2- Tetrachloroethane 0.026/0.026 C/C IRISIHEAST 0.03/- IRIS/-
Tetrachloroethylene (PeE) 0.051/0.0018 82/B2 HEAST/HEAST 0.01/- OOSI-
Toluene -1- DID OOS/lRIS 0.2/0.114 OOS/"
1 ,2,4- Trichlorobenzene -1- DID IRIS/lRIS 0.0110.003 OOS/HEAST
1,1,1- Trichloroethane -1- DID -/lRlS 0.09/0.03 HEAST/"
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Table 0-14
Oral/Iobalation Carcinogenic Classification and
Critical Toxicity Values for Cbemicals of Concern
IBW-Soutb Interim Risk Assessment
Page 3 of 3
Carcinogenic Noncarcinogenic
(oral/inbalation) (oral/inbalation)
Slope Factor Weigbt of RID
Cbemicals' (mg/kg-day)"l Evidence Source (mg/kg-day) Source
1,1,2- Trichloroethane 0.057/0.057 C/C IRISIHEAST 0.004/- IRIS/-
Trichloroethylene (TCE) 0.01 1/0.006 B2/B2 HEASTIHEAST -/- IRIS/-
Vinyl Chloride. 1.9/0.29 AlA HEASTIHEAST . -/- HEAST/-
Total Xylenes -/- DID IRIS/IRIS 2.0/0.09 HEASTI'
aBased on analytes from U.S. EPA Method TO-14.
"'This value is calculated from the Unit Risk Factor or Reference Concentration.
"'This value is for subchronic; no chronic value is given.
dEPA Region IX recommends characterizing health risks using a modified RID value of 0.0009 mg/kg/day (Exposure FaclOrs Handbook, U.S. EPA,
1990, as cited in Appendix A of the Feasibility Study, Admin. Rec. No. 1599.
"'This value is based on 1,2-Dichloroethylene mixture.
This value is based on 1,3-Dichloropropene mixture.
Notes:
- = No date/data not available/inadequate data.
* = pending
IOOI294A.RDD-3
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Cbemlcal
1,l-Dichloroethylene
(Vinylidene chloride;
1,I-DCE)
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cis- and trans-I ,2- Dichloro-
ethylene
(l,2-DCE)
Tetrachloroethylene
(Perchloroethylene, PCE)
IOOI2ADI.WP5-2
Table 11-15
Toxldty Summaries for Primary Cbemlcals of Concern -
VOCs.ln-Vadose-Zooe .
Acute Toxicity Summary
Exposures to high levels can produce central ner-
vous system (CNS) depressiqn. The liquid is mod-
erately irritating to the skin and eyes (Siegel et aI.,
1971; Hathaway et aI., 1991).
Exposures .10 high levels can produce CNS depres-
sion and pathological changes in the heart. Vapor
or aerosols are mildly irritating to the eyes. 1,2-
DCE in combination with ether has been used in
the past as a general anesthetic (Hathaway et aI.,
1991).
Occupational exposure to high levels in air has
produces CNS depressiQn with symplQms including
dizziness, light-headedness, and difficulty in walk-
ing. The liquid is moderately irritating tQ the skin
and eyes. Liver injury fQllQwing acute occupa-
. tional exposures has been reported (NlOSH, 1976;
Stewart, 1969; Hathaway et aI., 1991).
Cbronlc Toxicity Summary
1,1- DCE administered in drinking water to rats
for tWQ years produced dQse-related fatly
changes and swelling in the liver. The IQwest
Qbserved adverse effect level (LOAEL) was
calculated tQ be 9 mg/kg-day (Quast et aI.,
1983). Fatty changes in the liver have alSQ
been produced in rats by chronic inhalatiQn
exposure (QuasI et aI., 1986).
trans-I,2-DCE administered in drinking waler
to rats for 90 days produced dose-related
. increases in kidney weights (Hayes et aI.,
1987).
ProlQnged QccupatiQnal exposure has produced
symptQms including memQry impairment,
numbness Qf the extremities and visual impair-
ment (NIOSH, 1976), and clinical detectable
neurQlogical impairment (WHO, 1984).
Studies Qf reproductive tQxicity in wQrkers are
incQnclusive (Hathaway et aI., 1991). Sub-
chrQnic exposures tQ rats and mice (both by
oral and inhalatiQn routes) have prQduced liver
tQxicity, with mice shQwing greater sensitivity
than rats (Buban and O'Flaherty, 1985;
Schumann et aI., 1980; Kjellstrand et aI.,
1984). The nQ Qbserved adverse effect level
(NOAEL) for liver tQxicity is estimated to be
14 mg/kg-day (Buban and O'Flaherty, 1985).
Page 1 of 2
Cancer Potential
1,I-DCE is classified as a PQssible human
carcinQgen (CategQry C), based Qn tumQrs
Qbserved in one inhalatiQn mQuse bioassay
(Maltoni et aI., 1985). Several Qther animal
biQassays are negative fQr carcinogenicity.
1,I-DCE is mutagenic in several bacterial
test strains, but nQt in mammalian cells.
I,I-DCE is strUcturally .related to vinyl
chlQride, a knQwn human carcinQgen (U.S.
EPA, IRIS, 1992).
Has nQI exhibited mutagenicity in bacterial
Qr mammalian cell assays. As with Qther
chlorinated hydrocarbons, 1,2-DCE has
promoted unscheduled DNA synthesis. No
animal biQassay or human epidemioIQgical...
data available. Regarded as not classifiable
as to human carcinogenicity (Category D)~.
(U.S. EPA, IRIS, 1992).
PCE is judged to be a probable human
carcinogen based Qn increased incidence of
liver tumors in mice (Category B2).
Weight-of-evidence classification is cur-
rently under review by EPA. Evidence of
carcinogenicity based on epidemiQlogical
data or mutagenicity testing is inconclusive
(U.S. EPA, IRIS, 1992).
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Table 11-15
ToxIcity Summaries for PrImary Chemicals of Concern -
VOCs.ln- Vadose-Zone
Chemical
Acute ToxIcIty Summary
Trichloroethene
(TCE)
Occupational exposure to high levels has produced
CNS depression and intolerance to alcohol
(Udegreaser's" flush), the laller presenting as a
tiansient redness to the face and neck. TCE is a
mild skin and eye irritant (NIOSH, 1976;
Hathaway et aI., 1991).
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Vinyl chloride
Exposures to very high levels in air produce central
nervous system depression. Skin and eye contact
with the liquified gas can produce frostbite (Siegel
et aI., 1971; Hathaway et aI., 1991).
ChronIc ToxIcity Summary
Long-term occupational exposure has produced
CNS effects, with symptoms including fatigue,
vertigo, dizziness, headaches, and memory
impairment. Some evidence of mild liver
dysfunction has been observed in workers
exposed to levels sufficient to produce marked
CNS effects (Hathaway et aI., 1991). Fatty
liver and hepatotoxicity have been observed in
mice exposed by ingestion (Stott et aI., 1982).
Worker exposure studies have not indicated a
. potential for adverse reproductive effects
(Hathaway et aI., 1991). Adverse reproductive
effects also have not been reported in studies
with laboratory animals (Schwetz et aI., 1975;
Taylor et aI., 1985).
Long-term occupational exposure has produced
effects including impaired liver function,
Raynaud's syndrome, hematological effects,
and acroosteolysis (degeneration of tissue in
the fmgers) (Hathaway et aI., 1991).
Page 2 of 2
Cancer Potential
Qassified as a probable human carcinogen
based on hepatocellular tumors observed in
mice (Category B2). Classification is cur-
rently under review (U.S. EPA, IRIS,
1992). Recent epidemiological studies have
not shown significant or persuasive
association between TCE exposure and
excess of cancer (Spirtas et aI., 1991).
. The principal adverse effect of vinyl chlor-
ide exposure in humans is an increased
incidence of cancer of the liver. Carcino-
genicity of vinyl chloride in the liver has
been confirmed in studies with laboratory
. animals, and the EPA has identified vinyl
chloride as a known human carcinogen
(Category A) (U.S. EPA, IRIS, 1992).
NOTE: References listed in this table include the following: Ruben, 1. A., and E. I. O'FIaherty, 1985; Hathaway, G. 1., et aI., 1991; Hayes, 1. R., ~t aI., 1987; Kjellstrand, P., et aI.,
1984; Maltoni, C., et aI., 1985; NlOSH (National Institute for Occupational Safety and Health), 1976; Quast, I. F., et aI., 1986; Schumann, A. M., et aI., 1980; Schwetz, B. A., et aI.,
1975; Siegel, 1., et aI., 1971; Spirtas, R., et aI., 1991; Stewart, R. D., 1969; Stott, W. T.;et aI., 1982; Taylor, D. H., et aI., 1985; U.S. EPA, IRIS (Integrated Risk Information System
Data Base), 1992; and WHO (World Health Organization), 1984. All of these references are as cited in Appendix A of the Feasibility Study [Admin. Rec. No. 1599].
IOOI2ADI.WP5-3
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Table 11-16
Assumed Transfer Efficiencies for
Various Water Uses in a Typical House
Daily Transfer Weighted
Water Use Quantity (I) Efficiency (%) Value
Showers 150 63 9,450
Tub baths 150 47 7.050
Toilet 365 30 10.950
Laundry 130 90 11.700
Dishwasher 55 90 4.950
Drinking and kitchen use 30 30 900
Oeaning
10 90 '900
Total Water Use
890
Weighted Sum 45.900
Use volume-weighted mean 51.6
(Source: Prichard and Gesell. 1982. "An Estimate of Population Exposures Due to Radon in Public Water
Supplies in the Area of Houston. Texas." Health Pbys. 41:599-606. as cited in Appendix A of the Feasibility
Study. Admin. Rec. No. 1599.)
The risk estimates for each subsite will be carried out using the calculations in the risk
templates. These templates are used to perform the risk estimates for each subsite. There
are three templates that address the following:
.
Cancer risks from VOCs in Groundwater-Template T-I I
Non-cancer effects from VOCs in Groundwater-Template T-2
Inhalation of VOCs Volatilized from Soil-Template T-3
.
.
Each template provides a location for entering information identifying the sub site, locations
for entering incremental concentrations in groundwater or air (which have been estimated by
VLEACH modeling), and step-by-step instructions for calculating chemical intake rates and
health risk estimates and comparing the risk estimates to the Plug-in Criteria. Chemical
intake rates (in mg/kg-day) for each exposure pathway can be related to the exposure con-
centrations by simple relationships, shown in Table A-6 of the Risk Assessment.
Health risks for each subsite are calculated in a two-step process: (1) calculate risks (either
lifetime cancer risks or hazard quotients) from the modeled exposure concentrations for
, each VOC, and (2) add the risk estimates from all VOCs to estimate the total lifetime can-
cer risk or the hazard index for the subsite. The multiplicative factors in the templates
already take into account all of the exposure assumptions and toxicity values.
The templates shall be used as the basis for determining whether a sub site has exceeded the
Plug-in Criteria. The basis and assumptions for establishing the relationships between expo-
sure and risk, and a sample calculation, are included in the Risk Assessment, Appendix A to
the Feasibility Study. Virtually any VOC that may be present in the vadose zone at IBW-
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11-87
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South will be represented on the templates; nonetheless, if a VOC is found at a subsite that
does not appear on the template, the templates for that subsite may be revised by EP A to
incorporate that VOC. . The templates are located at the back of Part II.
8.4.8.
Evaluation of Environmental Risks
No endangered species or critical habitats have been identified at IBW-South. There are no
wetland habitats. The one exception to this may be at the Salt River itself, which is ephem-
eral. The U.S. Fish & Wildlife Service has not identified wetlands in this area to EPA.
The VOCs are underground, and the mW-South area is heavily urbanized and largely
paved. There are no identifiable populations, nor modes for surface wildlife to be exposed
to VOCs in soils or the groundwater.
8.5.
Clarifying Statement on Subsites
Situated on Landfill
As stated above, the mw site includes areas which contain landfill material. There are
generally two types of such material: inert and municipal solid waste ("MSW"). Inert
materials do not release methane or other gases and typically include construction debris
such as bricks, mortal, cement, and similar wastes. MSW supports a wide range of micro-
organisms and typically produces copious amounts of methane as it degrades. At IBW-
South, there are some locations where a layer of normal soil fill is packed on top of landfill
material, and a facility is sitting on top of the soil fill.
The following addresses the issue of the applicability of this remedy in the event that such
a facility has contaminated the soil and/or landfill material beneath it with VOCs.
EPA and the State of Arizona are exploring various regulatory options for addressing
cleanup, stabilization, and closure of the landfills. Therefore, while Focused RIs may be
conducted for subsites on fill material, EPA and the State may addrC?ss the subsites under
another regulatory program.
Even if EPA decides to address subsites situated on the landfills with this remedy, there are
certain situations in which the SVE Alternative selected by this document may not apply to
. landfill materials or to soil fill above landfill materials. These situations are discussed
below.
In the event that landfill material is inen (see above), SVE would be effective for removing
VOCs with no significant changes to the remedy proposed in this document. However,
where there is MSW with significant methane gas production, or anaerobic conditions,
fundamental or significant modifications may be necessary to the selected remedy. For
example, special changes may be necessary to address methane production. Also, anaerobic
(no oxygen) microorganisms feeding on MSW usually produce heat. Suddenly adding
oxygen to these landfills, by SVE wells or otherwise, may cause landfill fires. These
.
lOOI2ACF.WP5
II-88
-------
conditions were not evaluated or contemplated by the remedy selection process leading to
this ROD. .
Accordingly, at subsites situated on or above landfills, EPA will evaluate the soil and fill
material prior to plugging in such subsites. If insignificant methane and relatively normal
soil oxygen levels are present (indicating the absence of anaerobic MSW breakdown) and
. the material in the landfill in question is expected to be inert, then such subsites may be
plugged in directly.
If there is an absence of oxygen or high levels of methane are present in landfills known or
expected to have received MSW, then such subsites will be considered outside the scope of
this remedy. In instances where EP A decides to make a fundamental or significant change
to the remedy in order to address landfill materials, EP A would amend the remedy or issue
an ESD, as appropriate, to incorporate these differences and would follow all public partici-
pation and other CERCLA requirements prior to implementing a remedy at the location.
9.1.
9. Statutory Determinations
Protection 01 Human Health
and the Environment
This Operable Unit remedy (including modifications, as necessary) is protective of human
health and the environment with respect to VOCs in the vadose zone. This remedy must
operate in conjunction with other Operable Units to ensure protectiveness of human health
and the environment from all contaminants at the site.
At mw -South, the principal risk to human health is through inhalation and ingestion of
VOCs that volatilize from contaminated groundwater. By removing from the vadose zone
VOCs that could threaten groundwater quality, the selected remedy will assist in ensuring
that the groundwater underlying mW-South is returned to levels acceptable 'for drinking
water use in a reasonable timeframe. In addition, in areas where there is no groundwater
contamination, the selected remedy will reduce levels of VOCs in soils above the water
table such that the soils could not, by themselves, cause the groundwater to be contaminated
above health-based levels. . .
This remedy places the continuing soil sources of VOCs under tight control. It therefore
limits the extent to which existing groundwater contamination will spread.
This remedy removes VOCs to levels such that any threat from direct inhalation of VOCs
from soils above health-based levels is eliminated.
The requirements of this remedy were designed in response to an integrated risk assessment
that accounts for all eventual. Operable Units, so that the risks to anyone reasonably
exposed individual from carcinogenic contaminants will ultimately be reduced to within the
lOOI2ACF.WP5
II-89
-------
EP A risk range of 10-6 to 10-4. Likewise, the hazard index due to exposure to non-carcino-
genic contaminants for any reasonably exposed individual will be reduced below a value
of 1.
9.2.
Compliance with ARARs
Appendix A identifies the ARARs for mW-South. The selected remedy shall comply with
all ARARs identified in Appendix A.
9.3.
Cost-Effectiveness
The remedial actions selected in this remedy are cost-effective. Because it requires much
more time and money to remove VOCs from groundwater than to remove VOCs from soil
gas, this remedy is a good investment against the prospect of a greatly worsened future
groundwater problem. Groundwater. problems typically require extensive monitoring and
many costly groundwater wells, and can require as much as 100 years to clean up. In addi-
tion, the cost of the loss of the groundwater resource in the mw arid environment during a
groundwater cleanup would be substantial.
SVE involves minimal disruption to urban soils and environment, thereby reducing costs
from lost business and use of property. Because only air is extracted from the soil, the
costs of disposal are also minimized. SVE is easily amenable to modular enhancements that
allow for incremental outlay of capital costs. SVE is less expensive, or at worst, equal in
cost to most VOC remedies for soils, especially ex situ remedies such as soil washing or
incineration. .
At the same time, SVE will reduce the primary risks from the VOCs in soils to the cleanup
standards within a reasonable time. .
In addition, using the Plug-in Process will ensure that a protective cleanup is achieved,
while saving EP A and PRPs both the time and the money required to evaluate and select
separate remedies on every sub site within mW-South.
9.4.
Utilization of Permanent Solutions and
Alternative Treatment Technologies or
Resource Recovery Technologies to
the Maximum Extent Practicable
The remedy selected by this ROD utilizes permanent solutions and alternative technologies
or resource recovery technologies to the maximum extent practicable. EP A has determined
that the selected SVE alternative provides long-tenn effectiveness and pennanence; reduc-
tion in toxicity, mobility, and volume of contaminants through treatment; short-tenn
lOO12ACF.WP5
11-90
-------
effectiveness; implementability; and cost-effectiveness, considering both state and
community acceptance.
The State of Arizona has concurred with this remedy; the coinmunity has expressed very
few concerns related to the SVE remedy itself or the Plug-in Approach.
The SVE Alternative will reduce both the mobility and volume of VOCs, permanently elim-
inating a long-term threat to groundwater and an immediate threat to ambient air without
unreasonable costs or significant short-term impacts. SVE was chosen presumptively as the
remedy, so no comparison of treatment alternatives was made. However, the substantial
period of time over which groundwater quality would be impaired with the No-Action
Alternative was a significant factor in choosing SVE.
VOCs can be recovered from SVE for reuse. SVE, in removing a source of contaminants
to groundwater, assists in recovery of the groundwater resource.
9.5.
Preference for Treatment
as a Principal Element
The SVE systems selected in this remedy, which cause removal of.VOCs followed by emis-
sions treatment, satisfy the statutory preference for the use of remedies that include treat-
ment as a principal element. .
10m
Significant Changes
1. EP A has selected remedy Performance Standards that comply with certain Maricopa
County Air Pollution Control Division Rules and Guidelines for Remediation of
Contaminated Soil, even though these guidelines are not ARARs. This is discussed in
Section 8.2.4 and in Appendix A, ARARs. The effect of this decision is that emission
control (offgas treatment) systems must be at least 90 percent effective.
2. EP A has reconsidered Plug-in Criterion No.5 as it appeared in the Feasibility Study and
the Proposed Plan Factsheet and has chosen to modify it. Criterion No.5 (the fifth of
five), as originally proposed by EPA, would have required that a subsite plug-in to the
remedy if subsite VOCs would cause groundwater concentrations to increase by more
than the more stringent of the federal MCL or the Arizona Health-Based Guidance
Level for water (HBGL). EPA has decided to remove the HBGL from the criterion,
which is now based solely on the federal MCL.
Upon reconsideration, EP A decided that HBGLs were not appropriate for this use. The
principal goal of Criterion No.5, as a standard-based criterion, is to provide an added
assurance that no single sub site is able to cause clean groundwater to become
contaminated above groundwater standards in the future. HBGLs are not promulgated
and are not intended to be used as in situ groundwater standards. EP A is confident that
lOO12ACF.WPS
ll-91
-------
[
the four risk~based Plug-in Criteria (Nos. 1 through 4) will be sufficient to protect
human health and will in most cases be more stringent than either the original or
modified Criterion No.5.
3. EPA has clarified that this remedy may be used to address subsites situated on landfIll
materials under certain circumstances. This is discussed in Section 8.5 of this Decision
Summary.
4. EPA has clarified that when a subsite is plugged in, EPA will document the plug-in and
also provide public notice of the plug-in determination. This determination will contain
a declaration of the most-likely off gas treatment and enhancement options that will be
used. Mter a determination is made to plug in a subsite to the remedy, there will be a
30-day public comment period. During such comment periods, the selection of the SVE
technology and the Plug-in Process itself shall not be subject to comment Details are
provided in Section 8.3.3.
5. In response to a public comment, EPA has modified the risk templates to allow for
segregating the effect of non-cancer toxicity by target organ. In instances where non-
cancer risk is the sole Plug-in Criterion which is exceeded, the effect of non-cancer risk
will be evaluated for each target organ separately, rather than as a sum over all com-
pounds. This approach is supported by EP A's Risk Assessment Guidance for Superfund.
6. The ROD, in Section 8.3.7, provides levels at which treatment-derived wastewater (such
as water from the air/water separator component of SVE systems) will be treated as a
RCRA hazardous waste. The FS did not provide as much detail about EP A's intentions
with regard to this water.
7. Appendix B of the FS inadvenently stated that certain requirements were ARARs. The
FS identifies only potential ARARs; the ROD (Appendix A) solely identifies actUal
ARARs for this remedy. .
8. Figure 1-3 in the Feasibility Study was incorrectly labeled. This figure appears again in
the ROD with the correct label. The figure shows about 70 facilities which represent
the universe of facilities for which EP A has gathered investigation data. However, not
all of these facilities will undergo focused RIs, as indicated by the label in the FS.
lOOIZACF.WP5
ll-92
-------
Figure T-1
Risk Assessment Template for:
Cancer Risks from VOCs In Groundwater
Indian Bend Wash. South
See Instructions following this template.
Chemical
Subsite Information:
Line 1
Concentration
In Groundwater
m
......
"""......".......","..'
,-""-,,,,,-,,,,,,,
.......".. "." ...
.".'..
.n' un
0.057
0.057
Prepared By:
Date:
Line 6
Estimated
Cancer
Risk -
In estion
::.'/'
Line 8
Estimated
Cancer
Risk -
Inhalation
...
.........
.::~::.
-'"'"."
-------
Figure T-1
Risk Assessment Template for:
Cancer Risks from VOCs In Groundwater
Indian Bend Wash - South
See Instructions following this template.
Chemical
Subslte Information:
Prepared By:
Date:
Line 1
Line 3
Chemical
Intake.
Inhalation
-da
Concentration
In Groundwater
Line 11: Estimated lifetime Cancer Risk Exceeds Plug-In Criteria
Line 12: Estimated lifetime Cancer Risk Does Not Exceed Plug-in Crileria
Be sure to atso compare concentrations In groundwater with MCL values.
Line 5
Inhalation
Slope
Factor
m -da-1
0.006
0.29
Line 6
Estimated
Cancer
Risk-
~
~
Line 71
Total
Ingestion
Risk
Line 10
Total Subslte Risk
CJ
CJ.
Line 8
Estimated
Cancer
Risk -
~
ILind I
Tolal .
. Inhalation
Risk
-------
------;-;----- -
Template T-l
Cancer Risks from VOCs in Groundwater
Instructions for Risk Assessment Template Preparation
Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
Step 7:
Step 8:
Step 9:
Step 10:
lOO1296C.WPS
Enter concentration in groundwater of each individual VOC in Line 1
(concentrations are obtained from modeling performed prior to preparing this
template). Groundwater concentrations must be in units of mg/l (1 mg/l =
1,000 pg/l). If a VOC has not been modeled or detected at the subsite, enter
zero for that VOC.
Multiply the value for each VOC in Line 1 by 0.01174. Enter the result in
Line 2. Skip this step if the line is filled for that VOC.
Multiply the value for each VOC in Line 1 by 0.044. Enter the result in
Line 3. Skip this step if the line is filled for that VOc.
Multiply the value for each VOC in Line 2 by the corresponding value in
Line 4. Enter the result in Line 6. Skip this step if the line is filled for that
VOc.
Add the values for all of the VOCs in Line 6 and enter the sum in Line 7.
Multiply the value for each VOC on Line 3 by the corresponding value in
Line 5. Ente~ the result in Line 8. Skip this step if the line is filled for that
VOC. .
Add the values in Line 8 and enter them in Line 9.
Add the values in Lines 7 and 9 and enter the sum in Line 10. Round the
value in Line 10 to one significant figure (for example, 1.17 x 10'6 is
rounded to 1 x 10'6).
If the value in Line 10 exceeds 1 x 10.6 or 0.000001 ,enter a check in
Line 11; otherwise enter a check in Line 12.
Be sure to also compare the concentrations in groundwater (Line 1) with
MCL values.
TI-95
-------
Figure T-2
Risk Assessment Template lor:
Noncancer Effects from VOCs In Groundwater
Indian Bend Wash - South
See instructions following this template.
Chemical
Benzene
Benzvl chloride
Bromomethane
Carbon Tetrachloride
Chlorobenzene
Chloroform
Chloromethane
1 2-Dibromoethane
1.2-Dlchlorobenzene
1.3-Dlchlorobenzene
1.4-Dlchlorobenzene
1.1-Dlchloroethane
1.2-Dichloroethane
1.1-Dlchloroethvlene
cls-1 2-Dlchloroethvlene
trans-1 2-Dichloroethvlene
Dichloromethane
1 2-DichloroDroDane
cis-1 3-DichloroDroDene
trans-1 3-DichloroDroDene
Ethvlbenzene
4-Ethvltoluene
Trlchlorofluoromethane (Freon 11)
Dichlorodifluoromethane (Freon 12)
1 1 2-trichloro-1 2 2-trifluoroethane (Freon 113)
Dlchlorotetrafluotoethane (Freon 114)
Hexachlorobutadiene
Methvlethvlketone (MEK)
Styrene
1 1 1 2- Tetrachloroethane
Tetrachloroethvlene (PCE)
Toluene
1 2 4-Trlchlorobenzene
1,1 1- Trichloroethane
1 1 2-Trlchloroethane
Line 1
Concentration
In Groundwatel
(mail)
Subslte Information:
Line 2
Chemical
Intake -
Ingestion
Line 3
Chemical
Intake -
Inhalation
Line 4
Oral
Reference
Dose
Line 5
Inhalation
Relerence
Dose
Noncancer
Target Organ!
Critical Toxic
Effect -
Inaestlon
-
(malka-dav) (malka-dav) (malka-dav) malka-dav)
~
0.0014
0.0007
0.02
0.01
GI
LIVER
LIVER
LIVER
Prepared by:
Date:
Line 6
Noncancer
Hazard
Quotients -
Noncancer
Target Organ!
Critical Toxic
Effect -
Line 8
Noncancer
Hazard
Quotients -
'~
URT
LIVER
LIVER
LIVER
Inhalation
-
~=09 O~~VER ~ ~~
- 0.1 0.2 LIVER LIVER
~ 0.1 0.1 LIVER JJ:~
.. 0.0009 _0.0009 LIVER LIVER
0.009 LIVER ~
0.009'):;':;'" LIVER ~
~~ ~: ~~
~ 0.006 LIVER
0.0003 0.006 LIVER
I 0.1 0.29 LIVER
0.001
0.005
0.3 0.2 BW
0.2 0.05 BW
~~~~BW
~ 0.002 ~ LIVER
0.05 0.1 CNS
0.2 0.3 LIVER
0.03 .., " LIVER
0.01"'''''m LIVER
0.2 0.1 I LIVER
0.01 0.003 I LIVER
~ 0.09 0.3 I LIVER
~ 0.004 LIVER
LIVER
URT
URT
URT
DEV
URT
LIVER
~..
DEV
LIVER
. "
.... ........."........-....
...............-............
~~..
CNS
LIVER
DR
...,'
. ",'
, ,
,.
. P'
-------
Figure T.2
Risk Assessment Template lor:
Noncancer Effects from VOCs In Groundwater
Indian Bend Wash - South
See Instructions following this template.
Chemical
Subslte Information:
Line 2
Chemical
Concentration Intake -
in Groundwatel Ingestion
m m k-da
Line 1
Line 4
Oral
Reference
Dose
-da
Line 23: Estimated Hazard Index Exceeds Plug-in Criteria
Line 5
Inhalation
Reference
Dose
-da
Llne11a
Line 12a
Llne13a
LIne 14a
Line 15a
Llne16a
Line 24: Estimated Hazard Index Does Not Exceed Plug-in Criteria
8e sure to also compare concentrations In groundwater with MCL value..
LIne 7
Total
Ingestion HO .
Line 10
Hazard Index
Prepared by:
Date:
Noncancer
Target Organ!
Critical Toxic
Effect -
Inhalation
I Line 9
Total
Inhalation HO
Segregated Hazard Quotients'
Ingestion
11b
12b
13b
14b
15b
16b
Segregated Hazard fndlces
Line 17
Line 18
Line 19
Line 20
Line 21
Line 22
I
I
I
Critical effect!
Target organ
GI
URT
LIVER
DEV
BW
CNS
GI
URT
LIVER
OEV
BW
CNS
-------
1---.--
Template T-2
Non-Cancer Effects of VOCs in Groundwater
Instructions for Risk Assessment Template Preparation
Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
Step 7:
Step 8:
Step 9:
Step 9a.
lOO1296E.WP5
Enter concentration in groundwater of each individual VOC in Line 1
(concentrations are obtained from modeling performed prior to preparing this
template). Groundwater concentrations must be in units of mg/l (1 mg/l =
1,00011g/l). IT a VOC has not been modeled or detected at the subsite, enter
zero for that VOc.
Multiply the value for each VOC in Line 1 by 0.0274: Enter the result in
Line 2. Skip this step if the line is filled for that VOC.
Multiply the value for each VOC in Line 1 by 0.0001. Enter the result in
Line 3. Skip this step if the line is filled for that VOC.
Divide the value for each VOC in Line 2 by the corresponding value in
Line 4. Enter the result in Line 6. Skip this step if. the line is filled for that
VOC.
Add the values for all of the VOCs in Line 6 and enter the' sum in Line 7.
Divide the value for each VOC in Line 3 by the corresponding value in Line
5. Enter the result for that VOC in Line 8. Skip this step if the line is filled
for that VOC.
Add the values for all of the VOCs in Line 8 and enter the sum in Line 9.
Add the values in Lines 7 and 9 and enter the sum in Line 10. Round the
value in Line 10 to two significant figures (for example, 1.2731 is rounded to
1.27). .
If the value in Line 10 exceeds 1.0, hazard indices need to be segregated by
target organ/critical effect; proceed to Step 9a. If the value in Line 10 is less
than 1.0, go to Step 12.
Sum ingestion hazard quotients (HQs) in Line 6 for all chemicals with GI
(gastrointestinal) target organ/critical toxic effect Enter the result in Line
lla.
11-99
-------
Step 9b.
Step 9c.
Step 9d.
Step ge.
Step 9f.
Step lOa.
Step lOb.
Step lOc.
Step lOd.
Step We.
lOO12%E.WPS
Sum inhalation HQs in Line 8 for all chemicals with GI target organ/critical
toxic effect. Enter the result in Line 11 b.
Sum ingestion hazard quotients (HQs) in Line 6 for all chemicals with URT
(upper respiratory tract) target organ/critical toxic effect Enter the result in
Line 12a. .
Sum inhalation HQs in Line 8 for all chemicals with URT target
organ/critical toxic effect. Enter the result in Line 12b.
Sum ingestion hazard quotients (HQs) in Line 6. for all chemicals with
LIVER target organ/critical toxic ef(ect. Enter the result in Line 13a. .
Sum inhalation HQs in Line 8 for all chemicals with LIVER target
organ/critical toxic effect. Enter the result in Line 13b.
Sum ingestion hazard quotients (HQs) in Line 6 for all chemicals with DEV
(developmental toxicity) target organ/critical toxic effect. Enter the result in
Line 14a.
Sum inhalation HQs in Line 8 for all chemicals with DEV target
organ/cri~cal toxic effect. Enter the result in Line 14b.
Sum ingestion hazard quotients (HQs) in Line 6 for all chemicals with BW
(reduced body weight) target organ/critical toxic effect. Enter the result in
Line 15a. .
. Sum inhalation HQs in Line 8 for all chemicals with BW target organ/critical
toxic effect. Enter the result in Line l~b.
Sum ingestion hazard quotients (HQs) in Line 6 for all chemicals with CNS
(central nervous system) target organ/critical toxic effect. Enter the result in
Line I6a. .
Sum inhalation HQs in Line 8 for. all chemicals with CNS target.
organ/critical toxic effect. Enter the result in Line I6b.
Sum Lines lla and llb and enter the result in Line 17.
Sum Lines 12a and 12b and enter the result in Line 18.
Sum Lines 13a and 13b and enter the result in Line 19.
Sum Lines 14a and I4b and enter the result in Line 20.
Sum Lines 15a and I5b and enter the result in Line 2L
II -100
-------
Step lOf.
Step 11.
Step 12.
Step 13:
1001 296E.WP5
Sum Lines 16a and 16b and enter the result in Line 22.
If any of the values in Lines 17 through 22 are greater than 1.0, enter a
check in Line 23.
Enter a check in Line 24 (value in Line 10 is less than 1.0).
Be sure to compare the concentrations in groundwater (Line 1) with MCL
values.
IT-lOl
-------
Figure T -3 .
Risk Assessment Template for:
Inhalation of VOCs Emitted from Soli
Indian Bend Wash - South
Subsite Information:
See instructions following this template.
line 1
Chemical
".',."."
0.026
0.0016
",""" .
...~.. .
......
'.':::,::.':,'.1
0.1
0.003
0.3
:"""":::"".""::"'""";,'.'''."
,'::,!,-'::',';.::;'l;,,';';';"';~':':';'
Prepared by:
Date:
line 6
Estimated
lifetime
Cancer
Risk
Noncancer
Target Organ!
Critical Toxic
Effects
""",'
.".............
DEV
LIVER
......
......,
..
CNS
LIVER
LIVER
line 8
Noncancer
Hazard
Quotients
.......
-------
Figure T,3
Risk Assessment Template for:
Inhalation of VOCs Emitted from Soil
Indian Bend Wash - South
See Instructions following this template.
Chemical
Subsite Information:
Line 1
Line 15: Estimated Lifetime Cancer Risk Exceeds Plug-In Criteria
Line 16: Estimated Lifetime Cancer Risk Does Not Exceed Plug-In Criteria
Line 17: Estlmaled Hazard Index Exceeds Plug-In Criteria
Line 18: Estimated Hazard Index Does Not Exceed Plug-In Criteria
Line 5
Inhalation
Reference
Dose
m -da
Prepared by:
Date:
Line 6
Estimated Noncancer
Lifetime Target Organ! Noncancer
Cancer Critical Toxic Hazard
1",,::':::~rmi~W:1
Line 7 I
Total
Cancer
Risk
Line 8
I Llne9
Hazard
Index
Segregated Hazard Indices
r=J
r=J
c=J
r=J
Line 10
Line 11
Line 12
Line 13
Line 14
Target Organ!
~crltl~~;OXIC Effect
LIVER
DEV
BW
CNS
-------
Template T-3
Inhalation of VOCs Emitted from Soil
Instructions for Risk Assessment Template Preparation
.Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
Step 7:
Step 8:
Step 9:
1001 296F.RDD
Enter concentration in air of each individual VOC in Line 1 (concentrations
are obtained from modeling performed prior to preparing this template).
Concentrations in air must be in units of mg/m3 (1 mg/m3 = 1,000 pg/m3). If
a VOC has not been modeled or detected at the subsite, enter zero for that
VOC.
Multiply the value for each VOC in Line 1 by 0.1174. Enter the result in
Line 2. Skip this step if the line is fIlled for that VOC.
Multiply the value for each VOC in Line 1 by 0.274. Enter the result in
Line 3. Skip this step if the line is filled for that VOC.
Multiply the value for each VOC in Line 2 by the corresponding value in
Line 4. Enter the result in Line 6. Skip this step if the line is filled for that
VOC.
Add the values for all of the VOCs in Line 6 and enter the sum in Line 7.
Round the value in Line 7 to one significant figure (for example, 1.17 x 10-6
is rounded to 1 x 10-6).
Divide the value for each VOC in Line 3 by the corresponding value in Line
5. Enter the result for that VO~ in Line 8. Skip this step if the line is filled
for that VOC.
Add the values for all of the VOCs in Line 8 and enter the sum in Line 9.
Round the value in Line 9 to two significant figures (for example, 1.2713 is
rounded to 1.27).
If the value in Line 7 exceeds 1 x 10-6 or 0.000001, enter a check on Line
15, otherwise enter a check on Line 16.
If the value in Line 9 exceeds 1.0, calculate segregated hazard indices in
Step 10, otherwise enter a check on Line 18.
II-105
-------
Step lOa.
Step lOb.
Step lOc.
Step lOd.
Step lOe.
Step 1 L
1 001 296F.RDD
Sum hazard quotients (HQs) in Line 6 for all chemicals with URT (upper
respiratory tract) target organ/critical toxic effect. Enter the result in Line
10. .
Sum hazard quotients (HQs) in Line 6 for all chemicals with LIVER target
organ/critical toxic effect. Enter the result in Line 11.
Sum hazard quotients (HQs) in Line 6 for all chemicals with DEV.
(developmental toxicity) target organ/critical toxic effect. Enter the result in
Line 12.
Sum hazard quotients (HQs) in Line 6 for all chemicals with BW (reduced
body weight) target organ/critical toxic effect. Enter the result in Line 13.
Sum hazard quotients (HQs) in Line 6 for all chemicals with CNS (central
nervous system) target organ/critical toxic effect. Enter the result in Line 14.
If any of the values in Lines 10 through 14 are greater than 1.0, enter a
check in Line 17.
II -106
-------
Appendix A
APPLICABLE OR RELEVANT
AND APPROPRIATE'
REQUIREMENTS (A'RARs)
-------
Appendix A
APPLICABLE OR RELEVANT
AND APPROPRIATE
REQUIREMENTS (ARARs)
A.1.
Definition of ARARs and TBCs
Congress mandated in Section l2l(d) of the 1986 Superfund Amendments and Reauthoriza-
tion Act (SARA) that remedial actions conducted under the Comprehensive Environmental
Response, Compensation, and Liability Act (CERCLA or Superfund) must attain a degree of
cleanup which assures protection of human health and the environment. Additionally, reme-
dial actions conducted entirely onsite must comply with the applicable or relevant and
appropriate requirements ("ARARS") of federal and state environmental laws.
Identification of ARARs must be made on a site-specific basis and involves a two-part
analysis: fIrst, a determination of whether a given requirement is applicable; then if it is
not applicable, a determination of whether it is both relevant and appropriate.
Applicable requirements are those cleanup. standards, standards of controJ, and other sub-
stantive environmental protection requirements, criteria, or limitations promulgated under
federal or state law that directly apply and specifically address a hazardous substance, pol-
lutant, contaminant, remedial action, location, or other circumstance at a CERCLA site.
Relevant and appropriate requirements are those cleanup standards, standards of control, and
other substantive environmental protection requirements, criteria, or limitations promulgated
under federal or state law that, while not specifically" applicable" to a hazardous substance,
pollutant, contaminant, remedial action, location, or other circumstance at a CERCLA site,
address 'problems or situations sufficiently similar to those encountered at the CERCLA site
that their use is well-suited to the particular site. If no ARAR addresses a particular situa-
tion, or if an ARAR is insufficient to protect human health or the. environment, then non-
promulgated standards, criteria, guidances, and advisories (referred to as liTo Be Consid-
ered", or "TBCS") can be selected as requirements in order to provide a protective remedy.
ARARs by definition include only substantive requirements, and not administrative require-
ments. If an environmental law imposes a certain liinit that is an ARAR while also requir-
ing that one obtain a permit, EPA need meet only the limit (substantive), and would not
have to obtain the permit (administrative) before taking the remedial action. However,
response actions which take place offsite must comply with both administrative and sub-
stantive requirements of all laws applicable at the time the offsite activity occurs.
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Five criteria must be met for a state requirement to be considered an ARAR:
1. It must be a promulgated standard, requirement, criterion, or limitation.
2. It must be more stringent than parallel federal standards, requirements, criteria, or
limitations.
3. It must be identified to EP A by the State in a timely manner.
4. It must be structured so it does not result in a statewide prohibition on land disposal.
5. It must be consistently applied statewide.
If a state standard is detennined to be "applicable" while a more stringent federal standard.
is "relevant and appropriate," the more stringent federal standard will govern.
A.2. Chemical-Specific ARARs and
RCRA Threshold Values for
Treatment-Derived Water
Neither EP A nor the State of Arizona have promulgated chemical-specific cleanup criteria
for soils. Therefore, there are !J:Q chemical-specific ARARs for this remedy with regard to
the degree of soil cleanup. Maximum Contaminant Levels under the Safe Drinking Water
Act ("MCLs") are used in developing one basis for the Plug-in Criteria and Performance
Standards under this remedy. Nonetheless, MCLs, as applied in situ to groundwater in the
aquifer, are not ARARs, because this remedy applies to soils and does not directly address
groundwater. The same is true of other chemical-specific standards that apply in situ to
groundwater. .
SVE systems at IBW-South may utilize an air/water separator, which removes water vapor
from the soil gas before it is treated. This treatment-derived water may be subject to other
requirements in this appendix, depending on whether it is a RCRA waste.
In accordance with the policy stated in the memo from Sylvia Lowrance, Director of EP A
Office of Solid Waste, to Jeff Zelikson, Director of EPA Region IX Toxics and Waste Man-
agement Division, dated January 24, 1989, groundwater from CERCLA actions may be
considered to be not a RCRA hazardous waste if it contains chemicals in concentrations
below health-based levels selected by EP A Region IX. The health-based RCRA threshold
values selected for this remedy at IBW -South are specified with the Performance Standards
in Section 8.3.7 of this ROD.
Table A-I lists compounds which, if present in concentrations .above the health-based levels
specified in Section 8.3.7, are:
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1) RCRA listed wastes (the RCRA requirements listed in this section will be applicable to
treatment-derived wastewater), or
2) Not known to be RCRA listed wastes (RCRA requirements in this section will be con-
sidered to be relevant and appropriate for the treatment-derived wastewater).
I Table A-I I
Acetone trans-l,2- Dichloroethylene
Benzene 1,2- Dichloropropane
Benzyl Chloride 1,3- Dichloropropene
Bromodichloromethane Dichlorotetrafluoroethane
Bromoform Ethylbenzene
Bromomethane Hexachlorobutadiene
Carbon Tetrachl9ride Methylene chloride
Chlorobenzene Methylethylketone
Chloroform Styrene
Chloromethane 1,2,2,2- Tetrachloroethane
Dibromochloromethane Tetrachloroethylene
1,2- Dibromoethane Toluene
1,2- Dichlorobenzene 1,2,4- Trichlorobenzene
1,3- Dichlorobenzene 1,1,1- Trichloroethane
1,4- Dichlorobenzene 1,1,2- Trichloroethane
Dichlorodifluoromethane Trichloroethylene
1,1- Dichloroethane Trichlorofluoromethane
1,2- Dichloroethane 1,1,2- Trichloro- 2,2,1- Trifluoroethane
cis-l ,2-Dichloroethane Vinyl Chloride
1,l-Dichloroethylene Xylenes (Total)
A.3.
Location-Specific ARARs
Location-specific ARARs for this remedy appear in Table A-2.
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Table A-2
Location-Specific ARARs for IBW-South
Location Requirement PrerequlsUe(s) Citation comments
\. Within 100-year flood plain Facility must be designed, con- RCRA hazardous waste; 40 CFR 264.l8(b) Ponions of the IBW-Soulh site are located within a 100-
structed, operated, and main- treatment, storage, or (R I 8-8-264) year flood plain. A RCRA facility located in a 100-year
!ained to avoid washout. disposal. flood plain must be designed, constructed, operated, and
maintained to prevent washout of any hazardous waste by a
IOO-year flood.
2. Wi,hin flood plain Action to avoid adverse effects, AClion that will occur in a Execulive Order Federal agencies are directed 10 ensure Ihal planning
minimize potential harm, restore flood plain, i.e., lowlands, 11988, Protection of programs and budget requests reflect consideration of flood
and preserve natural and and relatively flat areas Hood plains (40 CFR plain management, including the restoration and
beneficial values. adjoining inland and coastal 6, Appendix A) preservation of such land as natural undeveloped flood
waters and other flood- plains. If newly constructed facilities are to be located in a
prone areas. flood plain, accepted floodproofing and olher flood control
measures shaU be undenaken to achieve flood protection.
Whenever practical, structures shall be elevated above the
base flood level rather than fiUing land. As pan of any
federal plan or action, the potential for restoring and
preserving flood plains so their natural beneficial values can
be realized must be considered.
Crossing of the IBW-South site with piping or location of
we Us in the 100-year flood plain will be designed to result
in no impact to flood surface profiles. Any potential pipe
or well breakage due to flooding wilJ likely not introduce
new contamination because of the regional nature of the
DAD contamination.
3. Within area where action Action to recover and preserve Alteration of terrain tllat National Archaeologi- The IBW-South site is essentially completely developed.
may cause irreparable harm, anifacts. threatens significant scien- cal and Historical
loss, or destruction of signif- tific, prehistoric, historic, or Preservation Act (16 Anifacts have been located in areas near IBW -South.
icant anifacts archaeological data. USC Section 469); 36
CFR Pan 65
4. Historic project owned or Aclion to preserve historic Propeny included in or National Historic The DCE Circuits Building is included in the National
controUed by federal agency propenies; planning of action to eligible for the National Pre.servation Act Register of Historic Places (Inventory No. 151).
minimize harm to National Register of Historic Places Section 106 (16 USC
Historic Landmatks. 470 et seq.); 36 CFR
Pan 800
5. Critical habitat upon which Action to conserve endangered Determination of endan- Endangered Species No endangered species are known 10 exist on the
endangered species or species or threatened species, gered species or threatened Act of 1973 (16 USC IBW -Soulh site.
threatened species depends including consultation with Ihe species 1531 et seq.); 50 CFR
Depanment of the Interior. Pan 200, 50 CFR Part
402
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A.4.
Action-Speci'fic ARARs
Action-specific ARARs for IBW -South that are derived from the Resource, Conservation
and Recovery Act ("RCRA") are presented in Table A-3. These RCRA ARARs, and
action-specific ARARs derived from other laws, are discussed in the following subsections.
A.4.1.
"Contained in" Interpretation
The EPA's "contained in" interpretation provides that an environmental medium (e.g., soil,
groundwater, debris, surface water, sediment) that has been contaminated by a listed hazar-
dous waste above a risk-based level or a level of concern must be managed as if it were a
hazardous waste. Therefore, the RCRA regulations are relevant and appropriate to the
management of contaminated environmental medium, if, at the IBW-South site, it is tem-
porarily stored prior to treatment, disposed of, or stored elsewhere.
A.4.2.
Land Disposal Restrictions
The land disposal restrictions (LDRs), 40 CFR Part 268, and the general land disposal pro-
hibition in absence of a pennit (Ariz. Admin. Code ~RI8-8-270.1) will be applicable to
discharges of RCRA wastes to land. Water removed by SVE may be disposed of within the
site through discharge to soil. . Treatment of the water may be necessary before land dispo-
sal is allowed. Where treatment is necessary, treatment levels required are set forth in
Section 8.3.7 of this ROD as Performance Standards. For treatment-derived water that is a
characteristic waste, the water will be treated to remove the hazardous characteristic before
any discharge to soil will be allowed.
The remedial action at the IBW-South site includes removal of soil gas from the vadose
zone, separation of water, treatment to reduce VOC content, then discharge to soil or to the
sewer. This will trigger LDRs as ARARs if discharge is to the soil.
A.4.3.
Storage
The RCRA substantive storage requirements, Ariz. Admin. Code ~~RI8-8-264.170 to
254.1.18, will be relevant and appropriate to the storage of contaminated treatment-derived
wastewater for more than 90 days.
A.4.4.
. Treatment
Soil vapor extraction units and offgas thermal treatment units are miscellaneous RCRA
units. Therefore, the substantive requirements of 40 CFR Subpart X, including any closure
and postclosure care, will be relevant and appropriate. The remedy selected will be per-
formed entirely onsite and will not require compliance with administrative requirements.
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Table A-3
Action-Specific ARARs for IBW.South
From Resource, Conservation and Recovery Act (RCRA)
Page 1 of 2
Action Requirements Prerequisites Citation Comments
Container Storage Containers of hazardous waste must be: RCRA hazardous waste (listed or These requirements are applicable or relevant and
(Onsite) characteristic) held for a temporal)' appropriate for any contaminated soil or ground-
. Maintained in good condition period before treatment, disposal, or 40 CFR 264-171 (R18- water or treatment system waste that might be con-
slorage elsewhere, (40 CFR 264.lOnn 18-264.170, el seq.) tainerized and stored onsite prior 10 treatment or
a container (i.e., any portable device final disposal.
. Compatible with hazardous waste to be stored in which a material is stored, trans- 40 CPR .264.172
ported, disposed of, or handled). Groundwater or soil or soil gas coolaining a lisled
. Closed during storage (except to add or remove 40 CPR 264.173 waste must he managed as if it were a hazardous
waste) waste so long as it contains the listed waste. (See
"Contained-in" policy.)
Inspect container storage areas weekly for deteri - 40 CFR 264.174
oration.
Place containers on a sloped, sufficiently impervious 40 CFR 264.175
'. crack-free base, and protect from contact with an
accumulated liquid. Provide containment system with
a minimum capacity of 24-hour, 25-year storm plus
10 percent of the volume of containers of free liquids
or the volume of the largest container, whichever is
grealer.
Remove spilled or leaked waste in a timely manner to 40 CPR 264. 176
prevent overflow of the containmenl system.
Keep containers of ignitable or reactive waste at least 40 CFR 264.177
50 feet from th.e facility's property line.
Keep incompatible materials separate. Separate
incompatible materials stored near each other by a
dike or other barrier.
At closure, remove all hazardous waste and residues 40 CFR 264.178
from the contailUnent system, and decontaminate or
remove aU containers, liners.
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Table A.3
Actlon.Speclnc ARARs for IBW.South
From Resource, Conservation and Recovery Act (RCRA)
Page 2 of 2
Acllon Requirements Prerequisites Cltallon Comments
Soil Vapor Treat- RCRA standards for control of emissions of volatile RCRA hazardous waste. 40 CFR 264 The proposed standard requires reduclion of VOC
menl organics Subpart AA & BB emissions from "product accumulator vessels," and
leak detection and repair programs.
Control of air emissions of volatile organics and Emissions of VOCs or gaseous air 40 CFR 61
gaseous contaminants contaminants.
Treatment Standards for miscellaneous units {long-tenn retriev- Trealment of hazardous wastes in 40 CFR 264 (Sub- The substantive portions of these requirements will
(Miscellaneous) able storage, thennal treatment other than incinerators, units not regulated elsewhere under part X) be applicable or relevant and appropriate to the con-
open burning, open detonation, chemical, physical, and RCRA (e.g., air strippers). struction, operation, maintenance, and closure of .
biological treatment unils using olher than tanks, any miscellaneous trealment unil (a Ireatment unit
surface impoundments, or land trealment units) require that is not elsewhere regulated) constructed on the
new miscellaneous units to satisfy environmental IBW -South site for treatmenl and or disposal of
performance standards by protection of ground water, hazardous site wastes.
surface water, and air quality, and by limiting surface
and subsurface migration.
Treatment of wastes subject 10 ban on land disposal Trealment of LOR wasle. 40 CFR 268 (Subpart The substantive ponions of these requiremenls are
must attain levels achievable by besl demonstrated 0) applicable 10 the disposal of any IBW -South sile
available trealment technologies (BOAT) for each. wastes that can be defined as restricted hazardous
hazardous conslituent in each lisled waste. wastes.
BOAT standards are based on one of four technologies The substantive ponions of these requirements are
or combinations: for waslewaters (I) steam stripping; relevant and appropriate to the Irealment prior to
(2) biological treatment; or (3) carbon adsorption and disposal of any JBW -South site wastes .hat
(alone or in combination with (I) or (2); and for all con lain components of restricted wastes in con-
other wastes (4) incineration. Any technology may be ccntralions that make Ihe site wastes sufficienlly
used, however, if it will achieve the concentration similar 10 Ihe regulated wasles. The requiremenls
levels specified. specify levels of trealment Ihat musl be atlained
prior to land disposal.
Regulalions for land-based correclive actions at RCRA Land-based remedial action. 40 CFR Subpans
facililies. (Revised)
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A.4.5.
Groundwater Monitoring and Ground-
water Protection Standards
EP A does not expect that creation of RCRA disposal units will be necessary as part of this
remedy. However, groundwater monitoring requirements set forth at 40 CFR Part 264,
Subpart F, are applicable if the CERCLA remedial action involves creation of a new dispo-
sal unit when remedial actions are undertaken at existing RCRA units, or where disposal of
RCRA hazardous wastes occurs as part of the remedial action~ Treatment and disposal of
water removed during the SVE process is an element of the remedy; therefore, the ground-
water monitoring requirements are applicable if the water is a RCRA waste and it is dis-
posed of onsite.
In the above situation, the requirements of 40 CFR ~264.94 establish three categories of
groundwater protection standards that are relevant and appropriate: background concentra-
tions, RCRA MCLs, and Alternative. Concentration Limits (ACLs). The MCLs under the
SDW A are relevant and appropriate for the site. In complying with SOW A MCLs, cleanup
will also be consistent with RCRA MCLs. When no MCL has been established, a remedia-
tion level that is the equivalent of a health-based ACL under RCRA will be relevant and
appropriate. ..
A.4.6.
Groundwater Use Requirements
Portions of the Arizona Revised Statutes for cleanup of hazardous substances related to
contaminated groundwater ("Arizona Superfund," Ariz. Rev. Statute Section 49-282, et seq.)
and implementing regulations (Ariz. Admin. Code ~R 18-7 -109, et seq.) are applicable or
relevant and appropriate for the mW-South site. The implementing regulations incorporate
by reference state law provisions that (1) establish that all definable aquifers are drinking
water aquifers unless they qualify for an aquifer exemption, and (2) establish water quality.
standards for these aquifers. Finally, the Arizona Superfund statute and regulations require
that, to the extent practicable, mW~South remedial actions provide for the control or
cleanup of hazardous substances so as to allow the maximum beneficial use of the waters of
the State. '
The State aquifer classification system. identifying all aquifers as drinking water aquifers
unless specifically exempt.. is more stringent than the federal aquifer classification scheme,
and therefore is relevant and appropriate. Federal and State MCLs. applied in situ to
groundwater in the aquifer, are not ARARs for this remedy, because this remedy addresses
soils and not contamination already in groundwater. However, because the State drinking
water aquifer classification is an ARAR, an objective of this source-control remedy, in
conjunction with a future groundwater remedy as determined necessary, is to return
groundwater to health-based levels. Accordingly, EPA has used the MCLs as one basis for
its Plug-in Criteria and has set other Plug-in Criteria so as to meet this goal.
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A.4.7.
Corrective Action
The proposed 40 CFR Part 264, Subpart S, corrective action regulations are ARARs for
land-based remedial actions undertaken at the IBW-South site.
A.4.8.
Air Monitoring for Process
Vents and Equipment Leaks
The substantive requirements of 40 CFR Part 264, Subparts AA and BB, are applicable.
Operation and maintenance of the SVE units will be conducted entirely onsite. Therefore,
permit applications, recordkeeping requirements, and other administrative procedures are not
required. However, the design, performance, and operation and maintenance of the unit
must fully comply with the substantive requirements of these ARARs, which include 40
CFR ~~264.1030 - 264.1034 and 40 CFR ~~264.1050-264.1O63.
A.4.9.
Air Emissions Requirements
The Clean Air Act ("CAA") has been implemented through a series of regulations
(40 CFR Parts 50-99) that define the air quality management programs used to achieve the
CAA goals. CERCLA remedial actions conducted entirely onsite must comply with the
substantive requirements of the CAA and its related programs. Under the CAA, the State
of Arizona is responsible for preparation of a State Implementation Plan ("SIP"), which
describes how the air quality programs will be implemented to achieve compliance with
. primary air standards. Once EP A approves the SIP (and subsequent changes to it), the,
requirements in the SIP become potential federal ARARs. .
The following Maricopa County Air Pollution Control Division ("MCAPCD") rules are
applicable to this remedy because they are included in the State of .Arizona approved SIP:
Regulation III, Rule 21
Regulation III, Rule 30
Regulation III, Rule 31
Regulation III, Rule 32
Regulation III, Rule 34(f)-(k)
Regulation III, Rule 3S
Source Air Emissions
Visible Emissions
Particulate Matter
Odors and Gaseous Emissions
Organic Solvents
Incinerators
MCAPCD now has established new rules which supercede the rules listed above. However,
the new rules have not yet been incorporated into the approved SIP. Therefore, the new
rules are not ARARs. Nonetheless, EPA has used most of the new rules as "To-Be-Consid-
ered Criteria" and has selected Performance Standards in this ROD which comply with
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them. A discussion of these rules, and the selected Performance Standards, is set forth in
Section 8.2.4 of this ROD.
I ,
National Primary and Secondary Ambient Air Quality Standards (NAAQS) (40 CFR 50) are
established for criteria pollutants. The current list of NAAQS includes sulfur oxides (S02)'
nitrogen dioxide (NOJ, ozone (reactive organic gases (ROG) and NOx are precursors to
ozone formation), carbon monoxide (CO), lead, and particulate matter less than 10 microns
in diameter (PMlO). Primary standards for these pollutants have been established by the
SIP at levels necessary to protect human health with an "adequate margin of safety."
NAAQS are not ARARs. However, the Arizona SIP establishes the primary standards
based on the NAAQS, and provides for how the standards will be attained. Under the
CAA, upon meeting the primary standards, an Air Quality Control Region (AQCR) would
be classified as "in attainment." If an area fails to meet any of the primary standards, it is
classified as a "nonattainment area." Currently, the IBW-South site is located in a non-
attainment area due to noncompliance with CO, ozone, and PM 10 primary standards.
MCAPCD rules require that Reasonably Available Control Technology ("RACT") be
applied in non-attainment areas. While this requirement is not an ARAR, EP A believes that
the emission control (offgas treatment) methods incorporated in this remedy nonetheless
meet the RACT definition. "
A.5.
Additional Legal Requirements
Additional legal requirements are applicable to the IBW -South site, although they are not
environmental protection standards and therefore are not ARARs.
A.5.1.
The Occupational Safety and Health
Act (29 U.S.C. fi651 et seq., 29 CFR
fi1910.120)
The Occupational Safety and Health Act (OSHA) requirements for worker protection, train-
ing, and monitoring are applic~ble to remedial actions at the IBW-South site, and will also
be applicable to the operation and maintenance of any treatment facilities, containment
structures, or disposal facilities remaining onsite after the remedial action is completed.
OSHA regulates exposure of workers to a vari~ty of " chemicals in the workplace, and speci-
fies "training programs, health and environmental monitoring, and emergency procedures to
be implemented at facilities dealing with hazardous waste and hazardous substances.
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A.5.2.
Standards for Transportation 01 Haz-
ardous Waste -(40 CFR ~263, 49 CFR)
and U.S. DOT Hazardous Material
Transportation Rules
These standards are applicable to wastes that are tninsported offsite. The transportation
standards define the types of containers, labeling, and handling required for shipment of
hazardous wastes or regulated materials over public roads or by common carriers. Any
action or waste management occurring offsite is subject to full regulation under federal,
state, an~ local law.
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