United States
Environmental Protection
Agency
Office of Emergency and
Remedial Response
Washington, DC 20460
EPA/540/2-91/019A
September 1991
Guide for Conducting
Treatability Studies
Under CERCLA:
Soil Vapor Extraction
Interim Guidance
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E PA/540/2-91/019A
September 1991
GUIDE FOR CONDUCTING
TREATABILITY STUDIES UNDER CERCLA:
SOIL VAPOR EXTRACTION
INTERIM GUIDANCE
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Office of Research and Development
Cincinnati, Ohio 45268
and
Office of Emergency and Remedial Response
Office of Solid Waste and Emergency Response
Washington, DC 20460
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DISCLAIMER
The information in this document has been Funded wholly or in part by
the U.S. Environmental Protection Agency (EPA) under contract No.
68-C8-0061, Work Assignment No. 2-10, to Science Applications
International Corporation (SAIC). It has been subjected to the Agency's
peer and administrative reviews, and it has been approved for publication
as an EPA document. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.
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FOREWORD
Today's rapidly developing and changing technologies and industrial
products and practices frequently carry with them the increased
generation of materials that, if improperly managed, can threaten both
public health and the environment. The U.S. Environmental Protection
Agency (EPA) is charged by Congress with protecting the Nation's land,
air, and water resources. Under a mandate of national environmental laws,
the Agency strives to formulate and implement actions leading to a
compatible balance between human activities and the ability of natural
systems to support and nurture life. These laws direct the EPA to perform
research to define our environmental problems, measure the impacts, and
search for solutions.
The Risk Reduction Engineering Laboratory (RREL) is responsible for
planning, implementing, and managing research, development, and
demonstration programs to provide an authoritative, defensible
engineering basis in support of the policies, programs, and regulations of
the EPA with respect to drinking water, wastewater, pesticides, toxic
substances, solid and hazardous wastes, and Superfund-related activities.
This publication is one of the products of that research and provides a
vital communication link between the researcher and the user community.
The purpose of this guide is to provide standard guidance for designing
and implementing a soil vapor extraction (SVE) treatability study in
support of remedy selection at Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA) sites. It uses a three tiered
approach to treatability testing that consists of 1) remedy screening, 2)
remedy selection, and 3) remedy design. It also presents guidance for
conducting treatability studies for remedy screening and remedy selection
in a systematic fashion to determine the effectiveness of SVE in
remediating a CERCLA site. The intended audience for this guide consists
of Remedial Project Managers (RPMs), On-Scene Coordinators (OSCs),
Potentially Responsible Parties (PRPs), consultants, contractors, and
technology vendors.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
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ABSTRACT
Systematically conducted, well-documented treatability studies are an
important component of the remedial investigation/feasibility study (RI/
FS) and the remedial design/remedial action (RD/RA) processes under the
Comprehensive EnvironmentalResponse, Compensation, andLiability Act
(CERCLA). These studies provide valuable site-specific data necessary to
aid in the selection and implementation of a remedy. This manual focuses
on soil vapor extraction (S VE) treatability studies conducted in support of
remedy selection that are conducted prior to developing the Record of
Decision (ROD).
This manual presents guidance for designing and implementing SVE
treatability studies for remedy screening and remedy selection. It
describes the SVE technology, discusses the applicability and limitations
of SVE, and defines the screening and field data needed to support
treatability testing. This manual presents an overview of the treatability
testing process. It also explains the applicability of tiered treatability
testing for evaluating SVE, and defines the specific goals and performance
levels that should be met at each tier before additional testing is
conducted. Finally, it covers the elements of a treatability study work plan
and discusses the design and execution of treatability tests for the remedy
screening and remedy selection tiers.
The manual is not intended to serve as a substitute for communication
with experts and regulators, nor as the sole basis for the selection of SVE
as a remediation technology at a particular site. SVE must be used in
conjunction with other treatment technologies since it generates
contaminated residuals that must be disposed of properly. In addition, this
manual is designed to be used in conjunction with the Guide for
Conducting Treatability Studies Under CERCLA (Interim Final ).(24) The
intended audience for this guide consists of Remedial Project Managers
(RPMs), On-Scene Coordinators (OSCs), Potentially Responsible Parties
(PRPs), consultants, contractors, and technology vendors.
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TABLE OF CONTENTS
Section Page
DISCLAIMER ii
FOREWORD 111
ABSTRACT iv
FIGURES vii
TABLES viii
ABBREVIATIONS, ACRONYMS, AND SYMBOLS ix
ACKNOWLEDGMENTS x
1. Introduction 1
1.1 Background 1
1.2 Purpose and Scope 1
1.3 Intended Audience 2
1.4 Use of This Guide 2
2. Technology Description and Preliminary Screening 5
2.1 Technology Description 5
2.2 Preliminary Screening and Technology Limitations 10
3. The Use of Treatability Tests in Remedy Evaluation 17
3.1 The Process of Treatability Testing in Evaluating a Remedy 17
3.2 Application of Treatability Tests to SVE 19
4. Treatability Study Work Plan 27
4.1 Test Goals 27
4.2 Experimental Design and Procedures 28
4.3 Equipment and Materials 33
4.4 Sampling and Analysis 33
4.5 Data Analysis and Interpretation 34
4.6 Reports 39
4.7 Schedule 39
4.8 Management and Staffing 40
4.9 Budget 41
5. Sampling and Analysis Plan 43
5.1 Field Sampling Plan 43
5.2 Quality Assurance Project Plan 44
6. Treatability Data Interpretation for Technology Selection 47
6.1 Technical Evaluation 47
6.2 Cost Estimation from Data 49
7. References 53
8. Glossary 56
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TABLE OF CONTENTS
(Continued)
Section Page
AppendixA GENERAL PROCEDURE FOR CONDUCTING COLUMN TESTS 59
Appendix B GENERAL PROCEDURE FOR CONDUCTING AIR PERMEABILITY TESTS 63
AppendixC GENERAL PROCEDURE FOR CONDUCTING FIELD VENT TESTS 65
Appendix D COST ESTIMATION DATA FOR IMPLEMENTING SVE TECHNOLOGY 67
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FIGURES
Number Page
2-1. SVE Technology Processes 6
2-2. Generic Soil Vapor Extraction System 7
3-1. Flow Diagram of the Tiered Approach 18
3-2. The Role of Treatability Studies in the RI/FS and RD/RA Process 19
3-3. General Sequence of Events During RI/FS for SVE 20
4-1. Diagram of Typical Laboratory Column Test Apparatus 30
4-2. Schematic for Typical Air Permeability Test 31
4-3. Extraction Well Construction Details 32
4-4. Hypothetical Column Test Data 35
4-5. Typical Field Air Permeability Test Data 36
4-6. Typical Mathematical Modeling Results 37
4-7. Typical Field Vent Test Data 38
4-8. Example Project Schedule For a Full-Tier SVE Treatability Study Program 40
4-9. Example Organization Chart 41
4-10. General Applicability of Cost Elements to SVE Remedy Selection Tests 42
6-1. Treatability Flowchart for Evaluating SVE 48
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TABLES
Number Page
2-1. SVE Technology - Contaminant, Soil, and Site Characteristics 12
2-2. Effectiveness of SVE on General Contaminant Groups for Soil 15
3-1. Column Test Advantages and Limitations 23
3-2. Field Air Permeability Test Advantages and Limitations 23
3-3. Mathematical Modeling Advantages and Limitations 24
4-1. Suggested Organization of SVE Treatability Study Work Plan 27
4-2. Testing Applications - Considerations for Composite and Undisturbed Samples 33
5-1. Suggested Organization of Sampling and Analysis Plan 44
6-1. Factors Affecting SVE Treatment Costs 50
A-l. General Procedure for Conducting Column Tests 60
B-l. General Procedure for Conducting Air Permeability Tests 64
C-l. General Procedure for Conducting Field Vent Tests 66
D-l. SVE Cost Estimation 68
D-2. SVE System Emission Control Costs 69
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ABBREVIATIONS, ACRONYMS, AND SYMBOLS
AAR Applications Analysis Report NPDES
ARAR applicable or relevant and appropriate requirement NPL
ARCS Alternative Remedial Contracts Strategy OERR
ASTM American Society for Testing and Materials ORD
ATTIC Alternative Treatment Technology Information OSC
Center OSW
BBS OSWER Electronic Bulletin Board System OSWER
BNA base, neutral, acid extractable PAH
BTEX benzene, toluene, ethylbenzene, xylene PCB
°C degrees Centigrade POTW
CERCLA Comprehensive Environmental Response, Com-
pensation, and Liability Act of 1980 (Superfund) PRP
cm centimeters PVC
cm2 square centimeters QAPjP
CFR Code of Federal Regulations QA/QC
COLIS Computerized On-Line Information System RCRA
d days RD/RA
DNAPL dense nonaqueous phase liquid REM
EPA U.S. Environmental Protection Agency RFP
°F degrees Fahrenheit RI/FS
FID flame ionization detector ROD
FR Federal Register RP
FSP Field Sampling Plan RPM
ft feet RREL
ft2 square feet RSKERL
F Y fiscal year
g grams S/C
gal gallons s
GC gas chromatography s2
GC/MS gas chromatography/mass spectrometry SAP
HSP Health and Safety Plan scfm
in inches SCH
inH2O inches of water SITE
in Hg inches of mercury SOP
k permeability given in darcies or cm2 SPDES
kg kilograms SVE
kg/d kilograms per day SVOC
L/min liters per minute TCE
Ib/d pound per day TCLP
LNAPL light nonaqueous phase liquid TPH
m meters TSDF
min minutes TSP
mmHg millimeters of mercury UST
MS mass spectrometry VOC
NAPL nonaqueous phase liquid VP
NIOSH National Institute for Occupational Safety WP
and Health
National Pollution Discharge Elimination System
National Priorities List
Office of Emergency and Remedial Response
Office of Research and Development
On-Scene Coordinator
Office of Solid Waste
Office of Solid Waste and Emergency Response
polynuclear aromatic hydrocarbon
polychlorinated biphenyl
publicly owned treatment works
(sewage treatment)
Potentially Responsible Party
polyvinyl chloride
Quality Assurance Project Plan
quality assurance/quality control
Resource Conservation and Recovery Act of 1976
remedial design/remedial action
Remedial Engineering Management
request for proposal
remedial investigation/feasibility study
Record of Decision
responsible party
Remedial Project Manager
Risk Reduction Engineering Laboratory
Robert S. Kerr Environmental Research
Laboratory
subcontractor
seconds
seconds squared
Sampling and Analysis Plan
standard cubic feet per minute
schedule
Superfund Innovative Technology Evaluation
standard operating procedure
State Pollution Discharge Elimination System
soil vapor extraction
semivolatile organic compound
trichloroethylene
toxicity characteristic leaching procedure
total petroleum hydrocarbons
treatment, storage, or disposal facility
Technical Support Project
underground storage tank
volatile organic compound
vapor pressure
work plan
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ACKNOWLEDGMENTS
This guide was prepared for the U.S. Environmental Protection Agency,
Office of Research and Development, Risk Reduction Engineering
Laboratory (RREL), Cincinnati, Ohio, by Science Applications
International Corporation (SAIC) and Foster WheelerEnviresponse, Inc.
(FWH) under Contract No. 68-C8-0061. Mr. David Smith served as the
EPA Technical Project Monitor. Mr. Jim Rawe and Mr. Seymour Rosenthal
were SAIC's Work Assignment Manager and FWEI's Subcontract
Manager, respectively. FWEI's Dr. James P. Stumbar and Mr. Jim Rawe
(SAIC) authored the document. Mr. Peter Michaels provided technical
advice forFWEI. Ms. Marilyn Avery served as Technical EditorforFWEI.
Mr. Clyde Dial and Mr. Thomas Wagner provided technical review for
SAIC. Dr. David Wilson of Vanderbilt University and Dr. Neil Hutzler of
Michigan Technological University served as scientific advisers.
Ms. Robin M. Anderson of the Office of Emergency and Remedial
Response (OERR) has been the inspiration and motivation for the
development of this document. Mr. Chi-Yuan Fan of RREL, Edison, New
Jersey, has provided much technical input on Soil Vapor Extraction (SVE)
technology and treatability studies. Ms. Dianne Walker of Region III has
provided comments which reflect her experience with SVE and present the
perspective of the Regional Remedial Project Managers.
The following other Agency, contractor, vendor, and user personnel have
contributed their time and comments by participating in the guide's
workshop and by peer reviewing the draft document:
Edward R. Bates
John Brugger
Miko Fay on
Bruce Bauman
Richard A. Brown
Ann N. Clarke
Russel Creange
David DePaoli
Brad G. Downing
Michael Finton
George E. Hoag
Paul C. Johnson
George Losonski
Paul Lurk
James Malot
Edward G. Marchand
Michael Marley
EPA, RREL
EPA, RREL
EPA, Region II
American Petroleum Institute
Groundwater Technology, Inc.
Eckenfelder, Inc.
Envirosafe Services, Inc.
Oak Ridge National Laboratory
MWR, Inc.
Foster Wheeler Enviresponse, Inc.
University of Connecticut
Shell Development Corporation
MWR, Inc.
U. S. Army Toxic and Hazardous Materials
Agency
TerraVac
U.S. Air Force
Vapex Environmental Technology
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George Mickelson State of Wisconsin Department of
Natural Resources
Donald Neeper Los Alamos National Laboratory
Emil Onuschak, Jr. State of Delaware Department of Natural
Resources & Environmental Control
Frederick C. Payne MWR, Inc.
Tom Pedersen Camp Dresser & McKee Inc.
Michael Peterson Terra Vac
Scott Richter Vapex Environmental Technology
Frank Rogers Terra Vac
John Schuring New Jersey Institute of Technology
David E. Speed IBM Corporation
Joe Tillman SAIC
James H. Wilson Martin Marietta
The document was also reviewed by EPA's Office of Waste Programs
Enforcement and the Technology Innovation Office. We sincerely hope
we have not overlooked anyone who participated in the review and
development of this guide.
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SECTION 1
INTRODUCTION
1.1 BACKGROUND
Section 121(b) of the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980
(CERCLA)mandates the U.S. Environmental Protection
Agency (EPA) to select remedies that "utilize permanent
solutions and alternative treatment technologies or
resource recovery technologies to the maximum extent
practicable" and to prefer remedial actions in which
treatment that "permanently and significantly reduces the
volume, toxicity, or mobility of hazardous substances,
pollutants, and contaminants is a principal element."
Treatability studies provide data to support remedy
selection and implementation. They should be performed
as soon as it becomes evident that the available
information is insufficient to ensure the quality of the
decision. Conducting treatability studies early in the
remedial investigation/feasibility study (RI/FS) process
should reduce uncertainties associated with selecting the
remedy and should provide a sound basis for the Record
of Decision (ROD).
Treatability studies conducted during the RI/FS phase
indicate whether a given technology can meet the
expected cleanup goals for the site. Treatability studies
conducted during the remedial design/remedial action
(RD/RA) phase establish the design and operating
parameters for optimization of technology performance.
Although the purpose and scope of these studies differ,
they complement one another (i.e., information obtained
in support of remedy selection may also be used to
support the remedy design)/36'
This document refers to three levels or tiers of treatability
studies: remedy screening, remedy selection, and remedy
design. Three tiers of treatability studies are also defined
in the Guide for Conducting Treatability Studies Under
CERCLA, Interim Final,(24) referred to as the "generic
guide" hereafter in this document. The generic guide
refers to the three treatability study tiers, based largely on
the scale of test equipment, as laboratory screening,
bench-scale testing and pilot-scale testing. Laboratory
screening is typically used to screen potential
remedial technologies and is equivalent to remedy
screening. Bench-scale testing is typically used for
remedy selection. Bench-scale studies can, in some cases,
provide enough information for full-scale design. Pilot-
scale studies are normally used for remedial design, but in
many cases may be required for remedy selection.
Because of the overlap between these tiers, and because
of differences in the applicability of each tier to different
technologies, the functional description of treatability
study tiers (i.e., remedy screening, remedy selection, and
remedy design) has been chosen for this document.
Some or all of the levels of treatability study testing may
be needed on a case-by-case basis. The need for and the
level of treatability testing required are management
decisions in which the time and cost necessary to perform
the testing are balanced against the risks inherent in the
decision (e.g., selection of an inappropriate treatment
alternative). These decisions are based on the quantity
and quality of data available and on other decision factors
(e.g., State and community acceptance of the remedy or
experience with the technology at other sites). The use of
treatability studies in remedy evaluation is discussed
further in Section 3 of this document. Section 6 provides
guidance on when various tiers of treatability tests should
be conducted; indicates the types of treatability tests that
are recommended; and gives recommendations for
interpreting the results.
1.2 PURPOSE AND SCOPE
This guide is designed to ensure that a credible approach
is taken to evaluate whether soil vapor extraction (SVE)
should be considered for site remediation. This guide
discusses all three levels of treatability studies but
focuses on the remedy screening and remedy selection
tiers.
SVE technologies have been used to remove vapor from
landfills since the 1970's.(27) Dunng the 1980's SVE was
applied extensively to remediating contaminated soil from
leaking underground storage tanks (USTs). Hence the
application of SVE to leaking UST problems is well
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understood. The application of SVE to remediate
Superfund sites has, until recently, been relatively limited.
As of fiscal year 1991 (FY 91), SVE has been selected as
the remedial technology, or a component thereof, for over
30 Superfund sites. Prior to 1988, SVE had been chosen as
a component of the ROD at only two sites. However, SVE
was chosen as a component of the ROD at 10 sites in 1988
and 17 sites in 1989.(28)(22) SVE has been used for the
remediation of at least four Superfund sites: Tyson's
Dump in Pennsylvania, Verona Well Field in Michigan,
Fairchild Semiconductor in California, and Upjohn in
Puerto Rico. Completion of fullscale systems at the
Groveland (Massachusetts) and Long Prarie (Minnesota)
sites is expected soon.1-22-1
There are significant differences between UST and
Superfund contamination problems. The dissimilarities
between UST and Superfund sites stem from the relative
complexity of the sites. The previous contents of USTs
are usually well-documented or can be fairly easily
identified. Therefore UST sites often have one type of
well-characterized contaminant. Conversely, contaminants
detected at Superfund sites commonly come from more
than one source. The contaminants are often found at
different locations on the site and in different geologic
structures, making these sites more complex. The
recommendations for treatability testing contained in this
document try to achieve a balance between limiting the
costs of treatability testing and reducing the risks of
selecting inappropriate cleanup remedies. This document
recognizes that deviations from these recommendations
may be justified as more experience is gained in
treatability testing of SVE for Superfund sites, or based
upon site-specific factors. Because of the evolving nature
of this technology, consultation with SVE experts is
especially critical.
Proper evaluation of the applicability of any technology
to site remediation requires a phased process of data
collection, testing, and evaluation. For SVE this process
starts with prescreening using available site
characterization data. Treatability testing may consist of
soil column tests for remedy screening; additional column
tests and field air permeability tests for remedy selection;
and pilot-scale tests for remedy selection and/or remedy
design. Mathematical modeling is frequently used to
obtain estimates of the required cleanup times and to
guide the designs of the pilot-scale and full-scale
systems.
1.3 INTENDED AUDIENCE
This document is intended for use by Remedial Project
Managers (RPMs), On-Scene Coordinators (OSCs),
Potentially Responsible Parties (PRPs), consultants,
contractors, and technology vendors. Each has a different
role in conducting treatability studies under CERCLA.
Specific responsibilities for each can be found in the
generic guide(24)
1.4 USE OF THIS GUIDE
This guide is organized into eight sections that discuss
the basic information required to perform treatability
studies during the RI/FS process. The guide is formatted
to permit the reader to refer to a particular section at a
specific time period during the execution of treatability
studies under CERCLA. Section 1 is an introduction
which provides background information on the role of
treatability studies in the RI/FS process, discusses the
purpose and scope of the guide; and outlines the
intended audience for the guide. Section 2 describes the
SVE process and discusses how to conduct preliminary
screening to determine if SVE treatment is a potentially
viable remediation technology. Section 3 provides an
overview of the different levels of treatability testing and
discusses how to determine the need for treatability
studies. Section 4 provides an overview of the treatability
study program; describes the contents of a typical Work
Plan; and discusses the major considerations for
conducting treatability studies. Section 5 discusses the
Sampling and Analysis Plan, including the Field Sampling
and the Quality Assurance Project Plans. Section 6
explains how to interpret the data produced from the
treatability tests and how to determine if further testing is
justified. Sections 7 and 8 are the references and glossary,
respectively.
This guide, along with guides being developed for other
technologies is intended to be used as a companion
documents to the generic guide.(24) In an effort to avoid
redundancy, supporting information in other readily
available guidance documents is not repeated in this
document.
This document was reviewed by representatives from
EPA's Office of Emergency and Remedial Response
(OERR). Office of Research and Development (ORD), and
the Regional offices, as well as by a number of contractors
and academic personnel. The constructive comments
received from this peer review process have been
integrated and/or addressed throughout this guide.
Treatability studies for SVE are in their infancy.
Procedures for conducting column, air permeability,
and pilot-scale tests, and for performing
mathematical modeling have not been standardized
or validated. There are disagreements among experts
concerning the relative utility of the above tools for
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evaluating the applicability of the technology. The lack of Mr. David Smith
consensus stems from the uncertainties associated with U.S. Environmental Protection Agency
the use of in situ technologies (See subsection 2.2.4). Office of Research and Development
Risk Reduction Engineering Laboratory
As we gain treatability study experience, EPA anticipates 26 W. Martin Luther King Drive
further comment and possible future revisions to this Cincinnati, OH 45268
document. For this reason, EPA encourages further (513) 569-7957
constructive comments. Comments should be directed to:
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SECTION 2
TECHNOLOGY DESCRIPTION AND
PRELIMINARY SCREENING
This section presents an overall description of the full-
scale SVE technology and a discussion of the necessary
information for prescreening the technology prior to
commitment to a treatability test program. Subsection 2.1
gives a short explanation of the physical principles and
theory on which the technology is based and describes a
typical SVE system. Subsection 2.2 discusses the field
data and literature and data base searches used to
prescreen SVE as a potential candidate for cleanup at a
specific site. This subsection also discusses the technical
assistance available at the prescreening stage and the
technology limitations.
2.1 TECHNOLOGY DESCRIPTION
The SVE process is a technique for the removal of volatile
organic compounds (VOCs), and some semivolatile
organic compounds (SVOCs), from the vadose zone. The
vadose zone is the subsurface soil zone located between
the land surface and the top of the water table. SVE is
used with other technologies in a treatment train since it
transfers contaminants from soil and interstitial water (see
Figure 2-1) to air and the entrained and condensed water
wastestreams. These streams require further treatment.
Information on the technology applicability, the latest
performance data, the status of the technology, and
sources for further information are provided in one of a
series of engineering bulletins being published by the
EPA Risk Reduction Engineering Laboratory in Cincinnati,
Ohio.(22)
2.1.1 SVE Technology Theory
In order to better understand the process, the applicability
and limitations of SVE technology, and other topics
discussed in this document, an overview of SVE
technology theory is presented in this subsection. Figure
2-1 illustrates the processes that occur in soil
contaminated by VOCs and the mechanisms of
contaminant removal.
Contaminants exist in the soil in one or more of the
following forms: nonaqueous phase liquids (NAPLs),
solutions of organics in water, material adsorbed to the
soil, and mixtures of free vapor. (7-)(-29-) Under static
conditions, these phases are in equilibrium. The
distribution between phases is determined by various
physical phenomena controlling the equilibrium.
NAPLs can occur in the soil as pools of contaminants or
as residual liquids trapped between soil particles. In the
vicinity of the NAPLs, the equilibrium between vapor and
liquid phases is governed by Raoult's Law.1-10-"-32-1 NAPLs
consist of light nonaqueous phase liquids (LNAPLs) and
dense nonaqueous phase liquids (DNAPLs). LNAPLs,
which include hydrocarbons, ketones, etc., are less dense
than water. DNAPLs, which include chlorinated
hydrocarbons, are more dense than water.
In many instances the contaminants are dissolved in the
pore water that fills the interstices between soil particles.
Equilibrium between the contaminant in the aqueous
solution and that in the associated vapor is then
governed by Henry's Law.(7)(29)(31)(32)(34)
If the contaminant is strongly adsorbed to solid material,
the equilibrium between vapor and adsorbed contaminant
is likely to be controlled by adsorption isotherm
parametersPX29X32) Adsorption control may be operative
for low contaminant concentrations, clayey soils, soils
containing large amounts of humus, and soils containing
large amounts of solid organic matter that can adsorb the
contaminant phase of interest. Soil moisture conditions
also affect contaminant adsorption since water molecules
compete for the soil adsorption sites. The amount of time
that contaminants have been in the soil may affect the
amount of material that is adsorbed, especially when the
adsorption processes are slow.
Several factors affect the movement of contaminants in
soil and groundwater. Soluble compounds tend to travel
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farther in soils where the water infiltration rate is high.
Chemicals with affinity for soil organic material or mineral
adsorption sites will move slowly. Contaminant density
and, to a lesser extent, viscosity have an impact on
organic liquid movement and the location of the
contaminants. LNAPLs will sink through the soil until
they reach the capillary fringe where they tend to form
pools. DNAPLs will continue to sink below the water table
until they encounter an impermeable layer.
The dynamic process of SVE is characterized as follows.
When air is drawn through the soil, it passes through a
series of pores, most readily following the paths of low
resistance (through zones of high air permeability). Air
that is drawn through pores that contain contaminated
vapor and liquids will carry the vapor away (advect the
vapors). Contaminants will vaporize from one or more of
the condensed phases (organic, aqueous, adsorbed),
replacing the vapors that were carried away in the air
stream. The vaporization tends to maintain the
vapor-condensed phase equilibrium that was established
prior to removal of the contaminants. This process will
continue until all of the condensed-phase organics are
removed from the regions of higher permeability soil.
Contaminants in lower permeability zones will not be
removed by advection since the air stream will flow
through higher permeability zones. If the contamination is
located in a stagnant region some distance from the air
flow, the vapor must diffuse to the air stream before it can
be carried away. This diffusion process would then limit
the rate of contaminant removal by the SVE process. If the
rate of diffusion is very slow, it can limit the ability of SVE
to remove contaminants in an acceptable time frame.
2.1.2 Process Description
Vapor extraction wells and air vents or injection wells are
installed in the contaminated zone. As air is removed from
the soil, ambient air is injected, or is drawn into the
subsurface at locations around the contaminated site.
When ambient air passes through the soil, contaminants
are volatilized and removed as discussed in the previous
section.
A schematic of a generic SVE system is shown in Figure
2-2. It consists of the following: (1) one or more vapor
extraction wells, (2) one or more air inlet or injection wells
I
Extraction
Well
(1)
Air Vent or
Injection Well
(
*-
^~~
i
J
Clean Air
1
Vacuum 1 ^ Vapor I
^ Blower I ~T Treatment I
, L (4) ^i
Extracted U-MU, ^ f Process Residual ^
V8P°r .fc 1 imiiH I
i (M | Separator |
f . .. <> Liquid 1 Clrtnn Water
,g. Treatment 1 ^
V Process Residual
Injection Well
ImpflnrwflMft Cnp (7) Gr°und Snrf«c*»
~~ Contaminated
^ Zone
1 1' V
Water Table =
Figure 2-2. Generic soil vapor extraction system.
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(optional), (3) vapor/liquid separator (optional), (4)
vacuum pumps or air blowers, (5) vapor treatment (per
regulations), (6) liquid treatment (per regulations), and (7)
an impermeable cap (optional).1-11-"-22-"-31-1
Vapor extraction wells are typically designed to penetrate
the lower portion of the vadose zone to the capillary
fringe. If the groundwater is at a shallow depth, or if the
contamination is confined to near-surface soils, the vapor
extraction wells may be placed horizontally.1-7-"-29-"-31-1
Vapor extraction wells usually consist of slotted pipe
placed in permeable packing. For long-term applications,
the well casing material should be selected to be
compatible with the contaminants of concern. The
permeable packing consists of coarse sand or gravel. The
top few feet of the augered column for vertical wells, or
the trench for horizontal wells, is grouted to prevent the
direct inflow of air from the surface (short circuiting) along
the well casing or through the trench.
In some cases, it may also be desirable to install air inlets
or inj ection wells to enhance and control air flow through
zones of maximum contamination. These wells are
constructed similarly to the vapor extraction wells. Inlet
wells or vents are passive and allow air to be drawn into
the ground. Air inj ection wells force air into the ground.1-18-1
In general, more air is withdrawn than injected.However,
if too much air is injected, contaminant laden air can be
forced out of the soils through the ground surface.
Piping material connecting the wells to headers is selected
based on contaminant compatibility. The headers are
connected to the blowers or pumps. Pipes and headers
may be wrapped with heat tape and insulated in northern
climates to reduce condensation and to prevent freezing
of any condensate.
The vacuum pumps or blowers reduce gas pressure in the
extraction wells and induce subsurface air flow to the
wells. Ball or butterfly valves are used to adjust flow from
or into individual wells. The pressure fromthe outlet side
of the pumps or blowers can be used to push the exit gas
through a treatment system and back into the ground (if
air injection wells are used). The induced vacuum causes
a negative pressure gradient in the surrounding soils. The
projected area of soil affected by this pressure gradient is
called the zone of influence. The radius of influence is the
radial distance from the vapor extraction well that has
adequate air flow for effective removal of contaminants
when a vacuum is applied to the vapor extraction well.
Hence, the radius of influence and the extent of
contamination determine the number of extraction wells
required on the site. Site characteristics such as
stratigraphy, the presence of an impermeable surface or
subsurface barrier, and soil properties such as porosity
and permeability affect the radius of influence. The use of
air vents or air injection wells and increases in the
strength of the applied vacuum can be used to maximize
the radius of influence. l-12-)(-29-) Reported radius of influence
values for permeable soils (sandy soils) range from 30 to
120 feet. Good surface seals are required, especially for
shallow wells (screened less than 20 feet below surface),
to prevent short circuiting of air flow to the surface. For
less permeable soils (silts, clays) or for shallow wells, the
radius of influence is usually less.1-12-1 The radius of
influence in fractured bedrock or in other non-
homogeneous stratigraphies will not be symmetrical (i.e.,
the radius of influence may extend 200 feet along a
fracture but be only 2 or 3 feet wide).
An "impermeable" cap over the treatment site (optional)
serves several purposes. First, it minimizes infiltration of
water from the surface. Infiltration water can fill soil pore
spaces and reduce airflows. A cap may also increase the
system's radius of influence by preventing short
circuiting. Finally, it may also help to control the
horizontal movement of inlet air, which can bypass
contaminants. Plastic membranes, existing buildings and
parking lots, and natural soil layers of low permeability
may serve this purpose.(31)
The following instruments monitor process conditions.
Gas flow meters measure the volume of extracted air.
Pressures in the overall system are measured with vacuum
gauges. Temperatures are measured by thermometers or
other devices. Sampling ports may be installed in the
system at each well head, at the blower, and after vapor
treatment. In addition, monitoring probes may be placed
to measure soil vapor concentrations, temperatures, and
the radius of influence of the vacuum from the vapor
extraction wells.
A vapor/liquid separator is installed on some systems to
protect the blowers and to increase the efficiency of vapor
treatment systems. The entrained groundwater and
condensate brought up through the system may then
have to be treated as a hazardous waste, depending on
the types and concentrations of contaminants.
Vapors extracted by the S VE process are typically treated
using carbon adsorption, thermal destruction by
incineration or catalytic oxidation, or
condensation.^-"-12-"-31-1 Other methods, such as biological
treatment, ultraviolet oxidation, and dispersion also have
been applied in SVE systems. The type of treatment
chosen depends on the composition and concentration of
contaminants. Methods that destroy or recover
contaminant vapors for reuse are preferable.
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Carbon adsorption is the most commonly employed vapor
treatment process and is adaptable to a wide range of
VOC concentrations and flowrates.1-29-1 Skid-mounted,
offsite-regenerated,carbon-canistersy stems are generally
employed for low gas volumes and onsite-regenerated
bed systems are employed for high gas volumes and
cleanups of extended duration.
Thermal destruction of contaminant vapors by
incineration or catalytic oxidation is quite effective for a
wide range of compounds. Catalytic oxidation is effective
on hydrocarbon vapors. Recently developed catalysts
permit the efficient destruction of halogenated
compounds (bromides, chlorides, or fluorides) also.1-19-1
Condensation can be used to separate the effluent VOCs
from the carrier air. This is usually accomplished by
refrigeration1-30'. The efficiency of this technique is
determined by the effect of temperature on the vapor
pressure (VP) of the VOCs present. Condensation is most
efficient for high concentrations of vapors. The
technology becomes less efficient as the cleanup
progresses and vapor concentrations drop. It may be
ineffective during the last stages of the cleanup. Since
vapors are not completely condensed, a carbon
adsorption or other additional treatment step may be
required to remove residual vapors from the effluent
stream.
Dispersion of the effluent vapors has been used during
the application of the technology to cleanups of
contaminants from leaking USTs, but it is not
recommended by the EPA. Dispersion is not a treatment
technology; it releases contaminants into the air.
Dispersion of some contaminants is prohibited in non-
attainment areas and in many states.
Many states require an air permit. Since SVE is an in situ
process, the land ban restrictions apply only to treatment
residues such as spent activated carbon and recovered
organic liquids. Individual states may, however, have
rules or regulations affecting cleanup levels for a
particular VOC contaminant in the soil. Cleanup levels
must be established on a site-specific basis.
When properly designed and operated, SVE is a safe
process. Potentially explosive mixtures of the extracted
gas may be encountered on some sites, such as landfills
or gasoline spill sites. Among the 25 most common
substances identified at Superfund sites,(14) benzene,
ethylbenzene, toluene, 1,1-dichloroethane, 1,2-
dichloroethane, chlorobenzene, 1,2-dichloroethylene, and
methylene chloride are all capable of forming explosive
mixtures at ambient conditions. For these situations,
explosion-proof equipment should be utilized. This
includes explosion-proof blowers and motors, flame
arresters, instrumentation to minimize the probability of an
explosion, equipment interlocks to prevent potentially
dangerous conditions, and special procedures.
EXPLOSION-PROOF EQUIPMENT SHOULD BE USED
unless it can be demonstrated that there is no potential
explosive hazard. The probability of encountering
explosive mixtures can be very high at complex CERCLA
sites.
Contaminated residuals are produced from the application
of this technology. These may include recovered
condensate (contaminated water and possibly
supernatant organics), spent activated carbon from off gas
treatment, nonrecovered contaminant in the soil, soil
tailings from drilling, and air emissions after treatment.
Contaminated water requires treatment in accordance with
the State/National Pollution Discharge Elimination System
(SPDES/ NPDES) permit levels prior to surface water
discharge, or in accordance with pretreatment
requirements prior to discharge to a publicly owned
treatment works (POTW). When contaminated water is
recovered by the SVE process, it can usually be treated
with carbon adsorption or air stripping followed by
discharge to surface waters, POTW, or by onsite
reinjection. If this is not feasible, the contaminated water
can be pumped into a holding tank. This holding tank can
be emptied by a tank truck that periodically hauls the
contaminated water to an appropriate treatment and
disposal facility. Soil tailings from the drilling operation
may be contaminated. They can be placed in covered piles
and treated onsite by adding vent connections to the SVE
system. The soil tailings can also be collected in drums or
dumpsters and sent for offsite treatment.1-28-1 Any spent
activated carbon should be disposed of in accordance
with regulations and policy.
Equipment used in the SVE process can be either mobile
or field-constructed. Mobilization of portable equipment
can usually be accomplished within one week, with
startup and full-scale operations in about two weeks. The
construction of the vapor extraction and monitoring wells
requires the mobilization of a portable drill rig. When
activated carbon canisters are used for offgas treatment,
they are skid-mounted so that they can be moved with a
forklift truck. Operation and maintenance requirements are
low. Systems have demonstrated their ability for safe,
continuous operation with a minimum of attention.
Note that several United States patents may be applicable
to the employment of the technology. This should be
discussed with appropriate SVE vendors.
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2.2 PRELIMINARY SCREENING AND
TECHNOLOGY LIMITATIONS
The determination of the need for and the appropriate tier
of treatability study required is dependent on the
literature available on the technology, expert technical
judgment, and site-specific factors. The first two
elements- the literature search and expert consultation-
are critical factors of the prescreening phase in
determining whether adequate data are available, or
whether a treatability study is needed.
2.2.1 Literature/Data Base Review/
Information Sources
Several reports and electronic data bases exist that should
be consulted for prescreening technologies and for
planning and conducting SVE treatability studies. Existing
reports include:
Soil Vapor Extraction: Reference Handbook.
U.S. Environmental Protection Agency, Office of
Research and Development and Office of
Emergency and Remedial Response, Washington,
D.C. EPA/540/2-91/003,1991.
Guide for Conducting Treatability Studies Under
CERCLA, Interim Final. U.S. Environmental
Protection Agency, Office of Research and
Development and Office of Emergency and
Remedial Response, Washington, D.C. EPA/540/
2-89/058, December 1989.
Guidance for Conducting Remedial Investigations
and Feasibility Studies Under CERCLA, Interim
Final. U. S. Environmental Protection Agency,
Office of Emergency and Remedial Response,
Washington, D.C. EPA/540/G-89/004, October
1988.
Superfund Treatability Clearinghouse Abstracts.
U.S. Environmental Protection Agency, Office of
Emergency and Remedial Response, Washington,
D.C. EPA/540/2-89/001, August 1989.
The Superfund Innovative Technology Evaluation
Program: Technology Profiles. U.S. Environ-
mental Protection Agency, Office of Solid Waste
and Emergency Response and Office of Research
and Development, Washington, D.C. EPA/540-5
90/006, November 1990.
Summary of Treatment Technology Effectiveness
for Contaminated Soil. U.S. Environmental
Protection Agency, Office of Emergency and
Remedial Response, Washington, D.C. 1989 (in
press).
Technology Screening Guide for Treatment of
CERCLA Soils and Sludges. U.S. EPA/540/2-88/
004, September 1988.
Currently, the Risk Reduction Engineering Laboratory
(RREL) in Cincinnati is expanding the RREL Treatability
Data Base. This expanded data base will contain data from
soil treatability studies. A repository for the treatability
study reports will be maintained at the RREL in Cincinnati.
The contact forthis data base is Glenn Shaul at (513) 569-
7408.
The Office of Solid Waste and Emergency Response
(OSWER) maintains an Electronic Bulletin Board System
(BBS) for communicating ideas, disseminating
information, and serving as a gateway for other OSW
electronic data bases. Currently, the BBS has eight
different components, including news and mail services,
and conferences and publications on specific technical
areas. The contact is James Cummings at (202) 382-4686.
RREL in Edison, New Jersey, maintains a Computerized
On-Line Information System (COLIS), which consolidates
several RREL computerized data bases in Cincinnati and
Edison. COLIS contains three files, consisting of Case
Histories, Library Search, and Superfund Innovative
Technology Evaluation (SITE) Applications Analyses
Reports (AARs). The Case Histories file contains
historical information obtained from corrective actions
implemented at Superfund sites. The Library Search
system provides access to special collections and
research information on many RREL programs, including
SVE. The SITE AARs file supplies actual cost and
performance information. The contact is Pacita Tibay at
(201) 906-6871.
ORD headquarters maintains the Alternative Treatment
Technology Information Center (ATTIC), which is a
compendium of information from many available data
bases. Data relevant to the use of treatment technologies
in Superfund actions are collected and stored in ATTIC.
ATTIC searches other information systems and data
bases and integrates the information into a response. It
also includes a pointer system that refers the user to
individual experts in EPA. The system currently
encompasses technical summaries from SITE program
abstracts, treatment technology demonstration projects,
industrial project results, and international program data.
Contact the ATTIC System Operator at (301) 816-9153.
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2.2.2 Technical Assistance
The Technical Support Project (TSP) is made up of six
Technical Support Centers and two Technical Support
Forums. It is a joint service of OSWER, ORD, and the
Regions. The TSP offers direct site-specific technical
assistance to EPA's On-Scene Coordinators (OSCs) and
RPMs, and develops technology workshops, issue
p apers, and other information for Regional staff. The T SP:
Reviews contractor work plans, evaluates
remedial alternatives, reviews RI/FS, assists in
selection and design of final remedy
Offers modeling assistance and data analysis and
interpretation
Assists in developing and evaluating sampling
plans
Conducts field studies (soil gas, hydrogeology,
site characterization)
Develops technical workshops and training,issue
papers on groundwater topics, generic protocols
Assists in performance of treatability studies.
The following support centers provide technical
information and advice related to SVE and treatability
studies:
1. Groundwater Fate and Transport Technical
Support Center
Robert S. Kerr Environmental Research Laboratory
(RSKERL), Ada, OK
Contact: Don Draper
FTS 743-2202 or (405) 332-8800
RSKERL, Ada, Oklahoma, is EPA's center for fate
and transport research, focusing its efforts on
transport and fate of contaminants in the vadose and
saturated zones of the subsurface, methodologies
relevant to protection and restoration of groundwater
quality, and evaluation of subsurface processes for
the treatment of hazardous waste. The Center
provides technical assistance such as evaluating
remedial alternatives; reviewing RI/FS and RD/RA
Work Plans; and providing technical information and
advice.
2. Engineering Technical Support Center
Risk Reduction Engineering Laboratory (RREL),
Cincinnati, OH
Contact: Ben Blaney
FTS 648-7406 or (513) 569-7406
The Engineering Technical Support Center (ETSC) is
sponsored by OSWER but operated by RREL. The
Center handles site-specific remediation engineering
problems. Access to this support Center must be
obtained through the EPA Remedial Proj ect Manager.
RREL offers expertise in contaminant source control
structures; materials handling and decontamination;
treatment of soils, sludges and sediments; and
treatment of aqueous and organic liquids. The
following are examples of the technical assistance
that can be obtained through the ETSC:
Screening of treatment alternatives
Review of the treatability aspects of RI/F S
Review of RI/FS treatability study Work Plans
and final reports
Oversight of RI/FS treatability studies
Evaluation of alternative remedies
Assistance with studies of innovative
technologies
Assistance in full-scale design and startup.
2.2.3 Prescreening Characteristics
Several variables determine the potential of SVE as a
candidate for site remediation and provide information
required for the prescreening phase of the site remedial
investigation. These variables are summarized in Table 2-1
and discussed below. These contaminant, soil, and site
characteristics were compiled from literature, data base
sources, and site characterizations. They represent the
data collected during site scoping and prescreening of the
SVE technology.
In conjunction with the site conditions and soil
properties, contaminant properties will dictate whether
SVE is feasible. SVE is most effective at removing
compounds which have high vapor pressure and which
exhibit significant volatility at ambient temperatures in
contaminated soil. Low molecular weight, volatile
compounds are most easily removed by SVE. Compounds
exhibiting vaporpressures over 0.5 millimeters of mercury
(mm Hg) can most readily be extracted using SVE/4-1
Trichloroethene, trichloroethane, tetrachloroethene, and
many gasoline constituents have been effectively
removed by SVE. Compounds which are less suitable for
removal include trichlorobenzene, acetone, and other
extremely water soluble volatiles, and heavier petroleum
fuels.
Table 2-1 presents a number of contaminant/
site characteristics that should be considered
when evaluating the applicability of SVE. This table
also identifies when those characteristics
should be considered in the evaluation pro-
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TABLE 2-1. SVE Technology - Contaminant, Soil, and Site Characteristics
Characteristics
Impacting Process
Feasibility
CONTAMINANT
Type
Low volatility
(vapor pressure)
High density,
High water solubility
SOIL
Low air permeability
High humic content
High moisture content
Low temperature
High clay content
PH
Low porosity
SITE
Distribution and quantity of
contaminants
Reason for
Potential Impact
SVE suitability
SVE system design
Indicative of low potential for contaminant
volatilization
Tendency to migrate to less SVE efficient
saturated zone
Hinders movement of air through soil matrix
Inhibition of volatilization, high sorption of
VOCs, need for column test verification
Hinders movement of air through soil and
is a sink for dissolved VOCs. May require
consideration of water table depression
Lowers contaminants' vapor pressures
Loss of structural support through the
drying of clay. Hinders movement of air
through soil. Need for field air permeability
tests.
Materials selection
Hinders movement of air through soil.
Need for field air permeability test
May not be cost effective. Will require
overall definition of contamination and
Data
Collection
Requirements
Contaminant
identification
Contaminant
Identification
Contaminant
Identification
Field air
permeability test
Analysis for
organic matter
Analysis of soil
moisture content
Soil temperature
Shrinkage limit tests
Field air permeability
moisture content, grain
size tests
Porosity (calculated
specific gravity bulk
density
Soil mapping, soil gas
survey, site
characterization
Application
of
Data
All Phases
Remedy
Screening
Remedy
Screening
Remedy selection
(See Section 3)
Remedy
Screening
All Phases
All Phases
Remedy
Screening
Remedy Selection
Remedy Selection
and Remedy
Design
All Phases
Remedy Selection
Standard
Analytical
Method
Methods 8010,
8015, 9071. 8040,8120,8240,
3810, 8020, 8270, 9071, 9310,
9315, 9060, 1311
Literature
Literature
None
None (Humic Acid Titrimetric)
ASTM D 2216, (drying oven) ASTM D
3017 (in situ)
None (Thermometer)
ASTM D422, 1140, 2419
ASTM D 4546
None (See above)
Method 9045
ASTM 854
ASTM D 2937
1556,29,2167
Method 3810, 8240
Reference
35
42
12
1
2
2
12
2
12
35
2
35
Variable soil
conditions/characteristics
Lithology,
heterogeneity
Buried debris
potential NAPL pools. Need pilot scale
verification.
Inconsistent removal rates "short circuiting"
or bypassing or contaminated zones
Affects well design and placement and
SVE system design. Need field air
permeability tests and/or pilot-scale
verification
Inconsistent removal rates. Need field air
permeability and/or pilot-scale verification
Soil mapping and
characterization (type,
particle, size, porosity)
Field air, permeability
(distribution) test
Site history,
geophysical testing
Remedy Selection
Remedy Selection
Remedy
Screening
ASTM D 2487, 2488
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cess (i.e., during screening, selection, or design). It is not
necessary that knowledge of all these characteristics be
obtained before deciding to proceed with treatability tests
forSVE.
Methods for detecting and analyzing soil gas are
important during the site characterization for assessing
the potential of SVE for site remediation. Analysis of
contaminants in the soil gas can provide critical data
regarding contaminants and their distribution at the site.
Identification of the contaminants may help to pinpoint
the source of contamination a leaking UST, past spills,
or an offsite source. Identifying the source may enable
quicker characterization of any remaining contamination.
Soil gas samples should be taken to indicate areas of
potential contamination. Soil borings can then be made in
those areas to delineate the amount, the location, and the
extent of the contamination.
It is important to identify geologic structures which may
be situated between the surface and the lower limit of the
contamination. These structures (i.e., large clay lenses,
large rocks and boulders, and large cavities) can
significantly impede vapor extraction. The most reliable
way to identify these structures is to evaluate the
lithologic descriptions of soil boring logs (either existing
or those conducted as part of the evaluation). Blow
counts recorded from drilling operations can indicate
densely compacted layers that may impede vapor
extraction. Geophysical surveys, such as electrical
resistivity, can also be conducted at the surface to
delineate in general terms the existance of subsurface
geologic structures.
Afterthe contaminants and geologic structures have been
identified, their occurrences should be mapped in relation
to each other. By doing this, it can be determined where
the SVE system should be placed (i.e., where the
contaminants are of highest concentration) and if any
geologic structures will interfere. To evaluate this
relationship, both plan view and cross-sectional maps
should be generated; or, if available, a 3D
computer-generated map would serve this purpose.
Typically, soils and groundwater are analyzed for VOCs,
base, neutral, and acid extractables (BNAs), and total
petroleum hydrocarbons (TPH). For complex mixtures
such as gasoline, diesel fuel, and solvent mixtures, it is
more economical to measure indicator compounds such as
benzene, toluene, ethylbenzene, and xylenes (BTEX) or
trichloroethylene (TCE) rather than each compound
present. Biodegradation products should be considered
as possible target compounds because they are often
more toxic than the parent compound (e.g., TCE may be
converted to vinyl chloride). Since SVE may not remove
all contaminants, soils should be analyzed for less volatile
or nonvolatile contaminants (BNAs and TPH) to assess
the need to remediate by other methods (excavation,
biotreatment, soil washing, etc.). Contaminants in the
groundwater indicate a potential for high mobility and
increased health risks. The contaminants may be
dissolved in the groundwater or may be moving
downward as free organics through the saturated soil.
Since insoluble contaminants tend to concentrate at
impermeable or semipermeable interfaces, LNAPL may be
present as free product at the capillary fringe and DNAPL
may occur as free product at the bottom of the aquifer.
Determination of the extent of groundwater contamination
aids in assessing the need for remediation by pump and
treat technology.
The soil characteristics of the site have a significant effect
on the applicability of SVE. The air permeability of the
contaminated soils controls the rate at which air can be
drawn through the soil by the applied vacuum. The soil
moisture content or degree of saturation is also important.
It is usually easier to extract VOCs from drier soils due to
the greater availability of pore area, which permits higher
air flowrates. Operation of an SVE system can dry the soil
by entrainment of water droplets (32)(34) and, to a lesser
extent, by evaporation. However, extremely dry soils may
tenaciously hold VOCs, which are more easily desorbed
when water competes with them for adsorption sites.1-6-"-38-1
This phenomenon, which may occur more frequently in
the southwestern states, favors a certain quantity of
moisture to be present in the soil to prevent sorption of
contaminants.
Soils with high clay or humic content generally provide
high adsorption potential for VOCs, thus inhibiting the
volatilization of contaminants. However, the high
adsorption potential of clayey soils does not necessarily
make SVE inapplicable to these soils. Clayey or silty soils
may be effectively treated by SVE.1-32-"-34-1 The success of
SVE in these soils may depend on the presence of more
permeable zones (as would be expected in alluvial
settings) that permit air flow close to the less permeable
material (i.e., clay).
Soil and ambient temperatures affect the performance of
an SVE system primarily because they influence
contaminant vapor pressure. At lower temperatures, the
potential for contaminant volatilization decreases.
Most site conditions cannot be changed. The extent to
which VOCs are vertically and horizontally dispersed in
the soil is an important consideration in deciding whether
SVE is preferable to other methods. Soil excavation and
treatment are probably more cost effective when only a
few hundred cubic yards (yd3) of near-surface soils are
contaminated. If the spill has penetrated more than 20 or
30 feet (ft), has spread through an area of several hundred
square feet (ft2) at a particular depth, or has contaminated
a soil volume of 500 yd3, excavation costs begin to exceed
those associated with an SVE system.(18:>(37)
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The depth to groundwater is also important because SVE
is applicable only to the vadose zone (area above the
water table). If contaminated soil is below the top of the
watertable, the level of the water table may be lowered, in
some cases, to increase the volume of the unsaturated
zone that can be treated.
Water infiltration decreases the air-filled porosity and
increases the amount of water entrained by the SVE
system. This reduces the rate of contaminant removal and
increases residual treatment costs. The water infiltration
rate can be controlled by placing an "impermeable" cap
over the site. Such a cap can also increase the system's
radius of influence. If used, a cap must be specifically
designed for the site. For instance, if a thick layer of
gravel exists below an asphalt or concrete cap, there can
be significant short circuiting through the gravel.
Heterogeneities, such as debris, fill material, and
geological anomalies, influence air movement as well as
the location of contaminants. The uncertainty in the
location of heterogeneities makes it more difficult to
position vapor extraction and inlet wells. There generally
will be significant differences in die air permeability of the
various soil strata.
SVE may be favorable for a horizontally stratified soil
because the relatively impervious layers will limit the rate
of vertical inflow of air from the surface and tend to extend
the applied vacuum's influence from the point of
extraction.
Buried debris can affect the application of many
remediation technologies. SVE may also be a
cost-effective alternative at such sites or when
contamination extends across property lines, beneath
buildings, or under extensive utility trench networks.
Prescreening of SVE examines the field data for the types
and concentrations of contaminant present, and for soil
temperature to determine contaminant vapor pressure. If
the vapor pressure of the contaminants of concern is
below 0.5 mm Hg, SVE is considered to be generally
unsuitable. Soil characteristics, site geology and
hydrogeology, and the elevation of the water table
relative to contamination zones are also considered during
prescreening. If the site conditions are favorable and if the
vapor pressure at the temperature of the soil is above 0.5
mm Hg, treatability testing should be conducted (see
Section 6.1). Example 1 illustrates the use of existing site
data in making a decision on the need for treatability
studies.
Example 1. Prescreening Initial Data
Background
A former 4-acre industrial site in the southeastern United States was used for manufacturing and
chemical storage over the last 25 years. During that time, waste and chemical spills from various
chemical handling, storage, and transfer activities had contaminated the site.
Use of the Data to Prescreen SVE
The site manager performed the prescreening by conducting a literature survey, reviewing existing data,
and obtaining expert opinion. Preliminary site characterization data indicate the contaminants of concern
are trichloroethane, benzene, 1,2-dichlorobenzene, and styrene. Soil concentrations of all these
contaminants are above 1000 ppm. Previous soil borings had shown that most of the contamination was
located 20-30 feet below grade. The zone of contamination covers 3 acres. Groundwater occurs at 50
feet below grade, 20 feet above the bedrock surface; it is not contaminated. The soils at the site are
sandy clay and fairly homogeneous. The literature survey showed the following:
All contaminant vapor pressures exceed 0.5 mm Hg.
SVE has been demonstrated in sandy clay soils.
Styrene and 1,2-dichlorobenzene have the lowest vapor pressures
The experts recommended SVE for further consideration as a site remedy. They recommended
treatability tests starting with column tests for remedy screening to demonstrate the effectiveness of
SVE on styrene and 1,2-dichlorobenzene. If these tests demonstrated the potential applicability of SVE,
they would be followed by more detailed column tests for remedy selection and then field air permeability
tests.
Decision
Based upon the above factors, the RPM retained SVE for the Remedy Screening Phase.
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2.2.4 Technology Applicability
The applicability of SVE for general contaminant
groups in soil is shown in Table 2-2.(22) SVE has been
successfully implemented under buildings, industrial
tank farms, gas stations, and beneath large diameter (
150 ft) above-ground storage tanks.(-5><-34> SVE has also
been applied in fractured bedrock. However, data for
evaluating its performance and effectiveness in this
medium are lacking. If the contaminant has reached the
bedrock, the installation of SVE wells into the bedrock
(even if air flowrates are low) may reduce or eliminate
the spread of contamination to underlying
groundwater.
SVE often provides effective source control of
contaminants in soils. It is often a safer and
more cost-effective alternative than excavation
and disposal. Soil excavation can release
significant amounts of volatile contaminants
Table 2-2.
Effectiveness of SVE on General
Contaminant Groups for Soil
Contaminant Croups
1
I
Halogenated volatiles
Halogenated semivolatiles*
Nonhalogenated volatiles
Nonhalogenated semivolatiles*
PCBs
Pesticides
Dioxins/Furans
Organic cyanides
Organic corrosives
Volatile metals
Nonvolatile metals
Asbestos
Radioactive materials
Inorganic corrosives
Inorganic cyanides
Oxidizers
Reducers
Effectiveness
m
V
a
a
a
Q
a
a
a
Q
Q
a
a
Q
V
Demonstrated Effectiveness: Successful treatability test at some
scale completed
T Potential Effectiveness: Expert opinion that technology will work
Q No Expected Effectiveness: Expert opinion that technology will
not work
* Demonstrated effectiveness on some compounds in the
containment group.
into the atmosphere, even where engineering controls
are in place. Release of such volatiles could violate air
emissions regulations, cause unnecessary health risks
to workers and to people in nearby residences, and
causenuisance odors. One significant advantage of the
SVE process is that sites are treated in situ, without
excavation.1-34'
When volatile and nonvolatile contaminants such as
pesticides, polychlorinated biphenyls (PCBs),
polynuclear aromatic hydrocarbons (PAHs), or metals
are present simultaneously at a site, the applicability of
SVE must be carefully assessed. In some cases, SVE will
not be applicable (e.g., concentrations of volatiles are
low but concentrations of metals are high). In other
cases, SVE could be applied to the volatiles prior to
excavation of the soil and use of another technology,
such as incineration, to remediate the other
contaminants. For example, SVE could be applied to
remove tetrachloroethylene. The soil could be
excavated and incineration could be applied to remove
PCBs. The incinerated soil could then be stabilized to
reduce the mobility of lead. Finally, SVE could be
applied as a sole remedy to prevent migration of mobile
materials, such as chloroform, to the groundwater, and
the other contaminants could be left in place after
capping of the site because of low mobility. The
presence of both volatile and nonvolatile contaminants
often occurs at CERCLA sites, and one or more of the
above strategies may have to be applied to different
parts of a complex site.
SVE may be enhanced by the use of heated air and
increased natural biological activity,(-sW><-17'1 but these
topics are beyond the scope of this guide.
2.2.5 Technology Limitations
Limitations of the SVE technology are those
characteristics of the contaminants, soil, and site that
hinder the extraction of the contaminants from the
unsaturated soil. Table 2-1 summarizes the
characteristics that impact SVE feasibility, gives reasons
for the potential impact, and presents the data
collection requirements that identify these technology
constraints.
A number of uncertainties appear to limit the
application of SVE and other in situ technologies.
Areas of uncertainty include: lack of precise information
on site heterogeneities and contaminant location;
inability to accurately predict cleanup times, doubt in
some cases whether cleanup goals can be achieved at
sites with very low cleanup targets or at those in
fractured bedrock. These uncertainties must be
recognized when conducting treatability studies, when
performing the detailed analysis of alternatives, and
when applying the technology for site remediation.
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Some of the data collection requirements outlined in potential remediation technology. It also discussed the
Table 2-1 should be satisfied before the prescreening need for further evaluation through a tiered treatability
phase. These consist of the compilation of data from study program. Where data collection requirements are
literature and data base sources, and from site-specific satisfied during the treatability tests, it is so noted
assessments, investigations, and characterizations. under the column labeled "Application of Data" in the
Subsection 2.2.3 discussed these existing data and their table.
applicability in determining the viability of SVE as a
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SECTION 3
THE USE OF TREATABILITY STUDIES
IN REMEDY EVALUATION
This section presents an overview of the use of
treatability tests in confirming the selection of S VE as the
remedial technology under CERCLA. It also provides a
decision tree (Figure 3-1) that defines the tiered approach
to the overall treatability study program. Examples
illustrate the application of treatability studies to the
RI/FS and remedy evaluation process. Subsection 3.1
briefly reviews the process of conducting treatability
tests. Subsection 3.2 explains the tiered approach to
conducting treatability studies. It shows how to apply
each tier of testing, based on the information previously
obtained, to assess and evaluate SVE technology during
the remedy screening and remedy selection phases of the
site remediation process.
3.1 THE PROCESS OF TREATABILITY
TESTING IN EVALUATING A
REMEDY
Treatability studies should be performed in a systematic
fashion to ensure that the data generated can support the
remedy evaluation process. The results of these studies
must be combined with other data to fully evaluate the
technology. This section describes a general approach
that should be followed by RPMs, PRPs, and contractors
throughout the investigation. This approach includes:
Establishing data quality objectives
Selecting a contracting mechanism
Issuing a Work Assignment
Preparing the Work Plan
Preparing the Sampling and Analysis Plan
Preparing the Health and Safety Plan
Conducting community relations activities
Complying with regulatory requirements
Executing the study
Analyzing and interpreting the data
Reporting the results.
These elements are described in detail in the generic
guide.(24) General information applicable to all treatability
studies is presented first, followed by information specific
to the testing of SVE.
Treatability studies for a particular site often entail
multiple tiers of testing. Duplication of effort can be
avoided by recognizing this possibility in the early
planning of the project. The Work Assignment, Work
Plan, and other supporting documents should specify all
anticipated activities to reduce duplication of efforts and
provide for the full data needs as the project moves from
one tier to another.
There are three levels or tiers of treatability studies:
remedy screening, remedy selection, and remedy design.
Some or all of the levels may be needed on a case-by-case
basis. The need for and the level of treatability testing are
management-based decisions in which the time and cost
of testing are balanced against the risks inherent in the
decision (e.g., selection of an inappropriate treatment
alternative). These decisions are based on the quantity
and quality of data available and on other decision factors
(e.g., State and community acceptance of the remedy, or
new site data). The flow diagram in Figure 3-1 shows the
decision points and factors to be considered in following
the tiered approach to treatability studies.
Technologies generally are evaluated first at the
remedy screening level, and progress through the
remedy selection to the remedy design level.
A technology may enter, however, at whatever
level is appropriate, based on available data on the
technology and site-specific factors. For example, a
technology that has been studied extensively may
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i
s
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Remedial Investigation/
Feasibility Study (RI/FS)
Identification
of Alternatives
Record of
Decision
(ROD)
Remedy
Selection
Remedial Design/
Remedial Action -
(RD/RA)
Scoping
- the -
RI/FS
Literature
Screening
and
Treatability
Study Scoping
Site
Characterization
and Technology
Screening
REMEDY
SCREENING
to Determine
Technology Feasibility
Evaluation
of Alternatives
REMEDY SELECTION
to Develop Performance
and Cost Data
Implementation
of Remedy
REMEDY DESIGN
to Develop Scale-Up, Design,
and Detailed Cost Data
Figure 3-2. The role of treatability studies in the RI/FS and RD/RA process.
not need remedy screening studies to determine whether
it has the potential to work. Rather, it may go directly to
remedy selection to verify that performance standards can
be met.
Figure 3-2 shows the relationship of three levels of
treatability study to one another and to the RI/FS and
RD/RA processes. Remedy screening tests are designed
to occur early in the RI/FS process when a minimum of
site characterization data is available. Remedy screening
is used to identify alternatives for consideration in remedy
selection. Later in the RI/FS, remedy selection is used to
develop cost and performance data for the evaluation of
alternatives prior to the record of decision (ROD). During
the remedy implementation phase (afterthe ROD), remedy
design studies provide detailed cost and design
information for full-scale implementation.
3.2 APPLICATION OF TREATABILITY
TESTS TO SVE
The determination of the appropriate level of a treatability
study is dependent on the literature available on the
applicability of SVE to the contaminants of interest, the
judgment of technical experts, and site-specific factors.
The first two elements-the literature search and expert
consultation-are critical factors in determining whether
additional data or a treatability study are needed. Previous
studies or actual implementation at essentially identical
site conditions may preclude the need for additional
studies. The basis for such a decision should be well
documented.
Treatability testing for SVE may involve column tests,
field air permeability measurements, mathematical
modeling, and pilot testing. It will generally not be
possible to conduct all of these tests during the 24-month
RI/FS timeframe. It is therefore important to anticipate the
degree of treatability testing early in the RI/FS time frame
so that ROD target dates can then be adjusted
accordingly. Figure 3-3 shows the general sequence of
treatability studies for SVE in the RI/FS process. SVE can
be eliminated from furtherconsideration at any one of the
steps shown. Certain steps can be skipped if the
information available at the previous step indicates the
success of SVE is very likely and the proposed step will
provide little additional information.
SVE treatability study objectives must meet the specific
needs of the RI/FS. There are nine evaluation criteria
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specified in the EPA's RI/FS Interim Final Guidance
Document (OSWER-9335:301).(23) Treatability studies can
provide data by which seven of these criteria may be
evaluated. These seven criteria are as follows:
Overall protection of human health and
environment
Compliance with applicable or relevant and
appropriate requirements (ARARs)
Long-term effectiveness and permanence
Reduction of toxicity, mobility, or volume
through treatment
Short-term effectiveness
Implementability
Cost.
check on the implementability of the technology at the
specific site. Even after these steps are taken, there may
be a high degree of uncertainty as to the ability of the
technology to reach the contaminant target levels in a
reasonable time.
Long-term effectiveness indicates how effective a
treatment will be in maintaining protection of human
health and the environment after the response objectives
have been met. Basically, the RPM must evaluate the
magnitude of any residual risk as well as the adequacy of
controls. The residual risk factor, as applied to SVE,
reflects the risks remaining from residual contaminants in
the soil, and possibly in the groundwater, after treatment.
The reliability of controls factor assesses the adequacy
and suitability of any controls that are necessary to
manage treatment residuals at the site (e.g., soil from well
borings). Such assessments are usually beyond the scope
of the column and air permeability tests of the treatability
study, but may be addressed conceptually based on their
results.
The first four criteria deal with the degree of contaminant
reduction achieved by the SVE process. How "clean" will
the treated soil be? Will the residual contaminant levels be
sufficiently low to meet the risk-based maximum
contaminant levels established to ensure protection of
human health and the environment? Have contaminant
toxicity, mobility, or volume been reduced through
treatment? Column tests for remedy selection show the
technology's MAXIMUM POTENTIAL to meet the first
four criteria. A successful column test for remedy
selection only shows that SVE will meet the required
target concentrations under idealized conditions. The
results of successful column tests must be combined
with air permeability data and mathematical modeling to
The fifth criterion short-term effectiveness addresses
the effects of the treatment technology during the time
span from remedy construction and implementation
through completion of the response objectives. The
estimates of cleanup times related to the concentration of
contaminants remaining in the soil, which are obtained
through mathematical modeling and testing, provide
information on SVE's short-term effectiveness.
The implementability criterion evaluates the
technical and administrative feasibility of an
alternative. This relates to the availability of
required goods and services as well as the technical
feasibility of SVE at the site. The key to assessing
Perform
Remedy
Screening
Column
TMta
Rwrwdy
Selection
Pilot
TMt
Figure 3-3. General sequence of events during RI/FS for SVE.
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SVE under this criterion is whetherthe contaminated soil
has chemical and physical characteristics that are
amenable to SVE treatment. The folio wing questions must
be answered in order to address the implementability of
SVE:
What are the pneumatic permeabilities of the
site soils?
Are there any soil heterogeneities that would
cause air flows to bypass portions of the
contaminated zone?
To what depth does the vadose zone extend?
What is the water infiltration rate? (A thin
vadose zone and a high water infiltration rate
may adversely affect implementability.)
What are the characteristics and quantities of
contaminants that will not be removed by
SVE?
The seventh EPA evaluation criterion is cost. Column
tests for remedy selection, air permeability tests, and
mathematical modeling can provide data to estimate the
following initial cost factors:
Design of the full-scale unit, including vapor
and contaminated water treatment systems
Estimated operating costs
Estimated time required to achieve target
concentrations
Additionally, they provide cost and design
estimates for the pilot-scale unit which may be
needed for remedy selection or remedy design.
Pilot-scale treatability studies provide additional data to
refine these estimates. In many cases, pilot-scale studies
will be required due to the uncertainties of contaminant
distribution and site geology.
Treatability tests do not directly relate to the final two
criteria, State and community acceptance, because these
criteria reflect the apparent preferences or concerns about
alternative technologies of the State and the community.
A viable remediation technology may be eliminated from
consideration if the State or community objects to its use.
However, treatability studies may provide data that can
address State and community concerns and, in some
cases, change their preferences.
3.2.1 Remedy Screening
Remedy screening is the first tier of testing. It is used to
screen the ability of a technology to treat a waste. These
studies are generally low total cost (e.g., $10,000 to
$50,000). The column tests require weeks to plan, obtain
samples, and execute. A test run usually requires days to
complete. Test runs yield data that can be used as
indicators of a technology's potential to meet
performance goals, and can identify operating standards
for investigation during remedy selection. They generate
little, if any, design or cost data, and should not form the
sole basis for selection of a remedy. It is recommended
that the remedy screening tier be skipped for evaluation
of SVE technology when the vapor pressure of the target
contaminants equals orexceeds 10mmHg. Whenremedy
screening is performed, a column test is operated until
2,000 pore volumes of air are passed through the column
(about 6 days of operation). An air-filled pore volume is
the total soil volume available for air (i.e., pore volume =
total volume minus volume occupied by solids and
liquids) in the soil sample being tested in the column. The
passage of 2,000 pore volumes of air through a column is
comparable to the volumetric throughput of air during
approximately 3 to 6 years of SVE operation in the field.
Column tests for remedy screening answer the question:
Is SVE apotentially viable remediation technology? These
tests pro vide qualitative information for the evaluation of
SVE performance on a particular contaminant. The tests
focus on whether SVE removes contaminants of interest
without regard to reaching an endpoint. They may give a
crude estimate of the time required to meet an endpoint
during a column test for remedy selection. Normally the
soil gas concentration of the target contaminants would
be monitored during the test. A reduction of 80 percent or
more of the soil gas concentration of the target
contaminants shows that SVE is potentially viable and
that column tests for remedy selection should be
conducted as shown in Figure 6-1. If a substantial
reduction (>95 percent) in the soil gas concentration of
the target contaminants has occurred, the RPM may
choose to have the residual soil ftorn the column test
analyzed. In this case, removal of the target contaminants
to below the anticipated target level in the soil shows that
column tests forremedy selection may be skipped, and air
permeability tests should be conducted. The evaluation
of treatablility test results is discussed further in
subsection 6.1. Example 2 illustrates the use of column
tests for remedy screening of SVE.
3.2.2 Remedy Selection
Remedy selection testing is the second tier of testing. It
is used to evaluate the technology's performance on a
contaminant-specific basis for an operable unit. These
studies generally have moderate total costs (e.g., $30,000
to $100,000 for SVE). These tests require months to plan,
obtain samples, and execute. Column tests for remedy
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selection require weeks of actual testing time. Air
permeability tests require hours to days for each field test,
depending on site conditions. Pilot-scale testing, if
required, increases remedy selection testing time to weeks
or months (planning and execution require months) to
complete, with much higher costs (e.g., $50,000 to
$250,000). They yield data that verify the technology's
ability to meet expected cleanup goals and provide
information in support of the detailed analysis of the
alternative (i.e., seven of the nine evaluation criteria).(3)
Column tests for remedy selection are run until an
endpoint is achieved. Since SVE is an in situ technology,
the laboratory treatability studies are supplemented with
field air permeability tests and mathematical modeling
during the remedy selection phase. The combination of
column tests, field air permeability tests, and mathematical
modeling provide quantitative and qualitative
performance information for the evaluation of SVE, as well
as cost and design information. However, due to the high
degree of uncertainty associated with implementation of
SVE, pilot-scale testing is often performed to support the
remedy selection phase. SVE is evaluated during the
remedy selection phase as follows:
Bench-scale column tests are performed to
establish whether SVE can meet the site
performance goals.
Following successful column tests for remedy
selection, field air permeability tests are
conducted to check SVE implementability.
Column tests for remedy selection and field air
permeability tests are supplemented with
mathematical modeling.
If warranted, pilot-scale testing for remedy
selection is performed.
Column tests for remedy selection establish whether SVE
can potentially meet expected target concentrations fora
given site. They can also provide information on the
contaminant distribution functions (partition functions)
for use with certain mathematical models. These column
tests do not, however, give reliable air permeability data.
They do not permit the determination of whether mass
transfer limitations will occur in the field application of
SVE. Table 3-1 presents the advantages and limitations of
column tests.
Column tests for remedy selection are not generally neces-
ary for several site conditions. Column tests may not be
required for very volatile compounds, such as those with
a vapor pressure > 10 mm Hg. If column tests for remedy
screening show that contaminant target levels can be
achieved, column tests for remedy selection may be
skipped.
Example 2. Remedy Screening
Background
In Example 1, recommendations were made to proceed with remedy selection treatability tests to check
the potential feasibility of SVE. Styrene and 1,2-dichlorobenzene were chosen as indicator
contaminants.
Results of Testing
Column tests for remedy screening were conducted by a contractor in accordance with the procedures,
equipment, and test designs presented in Section 4.2 of this document. After 2,000 air-filled pore
volumes had passed through the column, the soil gas concentration of styrene and 1,2-dichlorobenzene
had been reduced by about 82 percent and 84 percent, respectively.
Decision
Since the tests indicated that SVE could potentially remove the contaminants, the RPM decided to
conduct remedy selection treatability tests. If the test had shown a greater reduction in the soil gas
concentration (e.g., 95 percent), the RPM could decide to have the soil from the completed column test
analyzed for the indicator compounds. Then the residual concentrations could be compared to
anticipated cleanup targets. If the residual concentrations were less than the cleanup targets, column
tests for remedy selection could be skipped as shown in Figure 6-1.
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Table 3-1. Column Test Advantages and Limitations
ADVANTAGES
LIMITATIONS
1. Accelerates the SVE process to permit evaluation of
maximum contaminant removal potential.
2. Gives order of magnitude information on the partition
coefficients needed for mathematical modeling.
3. Order of magnitude air permeability measurements may be
obtained with "undisturbed" samples.
1. Stripping air always has good access to the
contaminants throughout the column. Air flow to
different zones varies widely in the field.
2. Diffusional processes are not properly modeled.
3. More accurate air permeability results must be
obtained through field air permeability measurements.
4. Standard procedures must be formulated and
validated.
Column tests are not practical for sites with fractured
bedrock and for sites containing very heterogeneous fill
consisting of large pieces of debris. Pilot tests to measure
the contaminant removal rate from the contaminated
bedrock are needed to evaluate the feasibility of SVE.
Column tests require a discrete sample. From 2 to 8
kilograms (kg) of contaminated soil are needed to perform
a column test. The duration and cost of column testing for
remedy selection of SVE depend primarily on the soil
characteristics, the contaminants, the analyses being
performed, and the number of replicates required for
adequate testing. The laboratory portion of remedy
selection column testing can normally be performed within
3 to 7 weeks. Total costs, including planning, sampling,
execution, and report, range between $30,000 and $50,000.
Air permeability tests should be conducted at the site
after the column tests show that SVE can meet the
expected target concentrations. Air permeability tests
provide information on the air permeability of the different
geological soil formations in the vadose zone at the site.
Typically, results are expressed as k with dimensions in
length squared. The customary unit of k is the darcy (1
darcy = 0.987xlO"8, cm2). The data canbeusedto estimate
onsite air flow patterns and to determine if the slow
process of diffusion will limit the application of SVE as a
remediation process. Air permeability tests may not be
necessary for remedy selection when the estimated air
permeability of site soils is high (k > 10"6 cm2). Table 3-2
presents the advantages and limitations of field air
permeability tests.
Air permeability data can also be used during the initial
design to determine the radius of influence of vapor
extraction wells, expected air-flow rates, moisture removal
rates, and initial contaminant mass removal rates (when
the effluent gas is analyzed). The air pertneability tests
cost about $1,500 to $2,500 per well. Total costs may run
from $10,000 to $50,000. They are normally performed
within a time range of 2 to 5 days.
Table 3-2. Field Air Permeability Test Advantages and Limitations
ADVANTAGES
LIMITATIONS
1. Provides the most accurate air permeability
measurements.
2. Permits measurements of the air permeability of
several geological strata.
3. Measures the radius of influence in the vicinity of
the testing point.
4. When coupled with analytical measurements, gives
information about initial contaminant removal rates.
1. May give low air permeability measurements in soil
zones where significant water removal may later take
place during the operation of the SVE system.
2. Does not show the location of NAPL pools.
3. Requires a health and safety plan and may require special
protective equipment.
4. May require an air permit on Superfund sites.
5. Provides information for designing a pilot-scale test. 5.
Cannot be used to measure air permeabilities in a
saturated zone that will be dewatered prior to application
of the technology.
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Mathematicalmodelmg(3)(8X12)(13X15X16X39)(40X41)canbeused
to provide rough estimates of the cleanup times required
to achieve contaminant reductions to the target goals.
These predictions are needed to evaluate health risks
associated with short-term effectiveness and to estimate
the total cost of the remediation. Mathematical modeling
can also provide sensitivity analyses for critical variables,
such as air permeability, radius of influence, and vacuum
applied!1-8"-41' To be most effective, the modeling should
use field-measured data on contaminant concentrations,
air permeability, location of contaminants, soil porosity,
soil moisture content, and soil temperature. Partition
coefficients are obtained from measurements taken during
column tests for remedy selection. Field and column test
data are the input variables to the model. Table 3-3
presents advantages and limitations of mathematical
modeling.
For complete characterization of the SVE process, the
mathematical model must simulate both the flow field in
the soil and the behavior of the contaminants within the
soil matrix. There are three major classes of models:
Models that simulate air flow patterns
Models that simulate contaminant behavior in a
simplified air-flow pattern
Models that couple air-flow patterns and
contaminant behavior.
Models that simulate air-flow patterns are useful for
designing the SVE system but they are not used for
cleanup time predictions. These models, when used with
site geologic data, can be important for assessing the
potential for difflusion control to be operative at a site.
Models that couple air-flow patterns and contaminant
behavior have been used to predict remediation
conditions where the vapor phase is in local equilibrium
with a liquid.1-3"12"13"40' This applies to regimes where
Raoult's Law or Henry's Law control contaminant
behavior. In these regimes contaminant removal is
relatively rapid.
Newly available models simulate SVE in soil matrices
where mass transfer limitations from diffusion are
important in limiting the rate of VOC removal.1-16"-39' SVE
from such matrices is impeded because the VOCs must
diffuse through regions of low permeability (such as clay
lenses) to reach the advective soil gas stream. If such
processes are rate-limiting, the latter portion of the
cleanup shows a slow reduction (tailing) of the soil gas
concentrations as aresult of diffusion control. Desorption
from the soil may control contaminant removal from
clayey soils and from soils rich in humic content.
Mathematical models for the SVE process that include
diffusion control can also include desorption control if
suitable data are available/40'
In general, mathematical models using the local
equilibriumassumption provide a lower bound estimate of
the time required to remediate a site using SVE. This
means that actual remediation times will be greater than
thosepredictedby such mathematical modeling. The local
equilibrium assumption posits that the contaminants in
the vapor phase remain in equilibrium with the
contaminants in the liquid and solid phases as
contaminant vapors are carried away by the air.1-3'1-40' If
diffusion is limiting the SVE process, these cleanup time
estimates may be low by as much as two orders of
magnitude. Also die presence of hidden pockets of heavy
contamination, unidentified soil heterogeneities, and
debris may extend remediation times beyond those
predicted by the mathematical models by as much as two
orders of magnitude. Therefore, lengthy cleanup time
predictions from a modelmustbe seriously considered as
an indicator for discontinuing treatability assessments of
SVE.
Pilot-scale testing for remedy selection is recommended
for sites that have contamination in the bedrock, and
Table 3-3.Mathematical Modeling
ADVANTAGES
Advantages and Limitations
LIMITATIONS
1. Provides order of magnitude estimates of SVE cleanup
times.
2. A prediction of a lengthy cleanup time based on
mathematical modeling is Indicative that the SVE process
is not applicable.
3. Provides sensitivity analyses for critical variables such as
air permeability, radius of influence, partition coefficients,
and vacuum applied.
1. Most models underestimate the time required for
cleanup. Prediction of a short cleanup time does not
indicate that SVE will be successful.
2. Different modules must be used to simulate vadous
field conditions. These models must be applied
carefully.
3. There are limited field data available for validation of
the mathematical models.
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complex sites that are very heterogeneous. Sites that
contain pools of NAPL may also require pilot-scale
testing. Pilot-scale tests determine whether sufficient air
flow can be achieved in the zones of contamination to
produce adequate cleanup rates. Pilot-scale data can also
be used to determine the radius of influence of the vapor
extraction wells, moisture removal rates, and contaminant
flowrates.
Example 3 illustrates how column tests, air permeability
tests, and mathematical modeling results are applied in the
decision-making process. Example 4 shows how a pilot-
scale test can verify the results of remedy selection
treatability testing. Example 5 presents a case where
prescreening indicates that column and air permeability
tests are impractical. The contaminant data obtained
during remedy prescreening, however, indicates that S VE
may be a viable remedial technology. Pilot-scale tests for
remedy selection verified SVE as a potential remediation
technology.
3.2.3 Remedy Design
Remedy design testing is the third tier of testing and is
normally performed after the ROD. It is used to provide
quantitative performance, cost, and design information for
remediating an operable unit. This level of testing also can
produce data required to optimize performance. These
studies are of moderate to high cost (e.g., $50,000 to
$250,000 for SVE) and may require months to complete.
They yield data that verify performance to a higher degree
than remedy selection tests and provide detailed design
information.
In addition to being used for remedy selection tests at
complex sites, pilot-scale field tests are normally required
for remedy design. Pilot-scale testing may help identify
contaminants or other characteristics that affect the SVE
implementability. Physical characteristics ofthe contami-
nants may increase maintenance due to blocked wells.
Bacterial formation, hardness of the site water, and the
Example 3. Remedy Selection Treatability Studies Using
Column Tests and Air Permeability Tests
Background
In Example 2, recommendations were made to proceed to remedy selection treatability tests to further
define the feasibility of SVE. Styrene and 1,2-dichlorobenzene were chosen as the indicator
contaminants.
Results of testing
Column tests for remedy selection were conducted by an SVE contractor/vendor in accordance with the
procedures, equipment, and test designs presented in Section 4.2. Data from these tests showed that
both 1,2-dichlorobenzene and styrene could be removed from the soil to below the target clean up goals.
Air permeability tests were conducted in accordance with the procedures, equipment, and test designs
presented in Section 4.2. Soil permeability to air flow in the contaminated soil was calculated to be
greater than 10~10 square centimeters (cm2).
Mathematical models were based on field air permeability and column test results, as well as the
prescreening site, soil, and contaminant data. They indicated that a 90 percent cleanup (removal ofthe
contaminants) could be accomplished in 1 to 4 years, depending on the input variables employed in the
modeling runs.
Decision
Since the tests and mathematical modeling indicated that a relatively short cleanup time was possible,
the RPM decided that SVE was a promising technology for site remediation. However, because ofthe
uncertainties of modeling in situ technologies, the RPM decided that an onsite pilot test for remedy
selection was needed to confirm this conclusion.
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Example 4. Remedy Selection Treatability Studies Using Pilot-Scale Tests
Background
Pilot-scale tests were conducted at the site, described in Example 1, using a commercial-size mobile
test rig. The procedures, equipment, and test designs were in accordance with those discussed in
Section 4.2.
Results of Pilot-Scale Test for Remedy Selection
The pilot-scale tests had excellent results. The contaminant removal rates were in excess of 200 pounds
per day (Ib/d). The measured 45 feet (ft) radius of influence was reasonable, indicating that only 20 wells
would be required for the 3-acre site. Based on these tests and the additional modeling studies that were
conducted, remediation of the site to cleanup levels was predicted in 5 to 7 years.
Decision
The pilot-scale tests showed that the technology was likely to be implementable and cost effective at
the site. The RPM decided that SVE was a viable remedial technology for the site.
Example 5. Treatability Study Using Fractured Bedrock
Background
A former 2-acre disposal site in the northeastern United States was used to dispose of a number of
solvents, including trichloroethylene, 1,1,1-trichloroethane, and carbon tetrachloride, in a shallow
impoundment over the last 25 years. During that time, the chemicals seeped into cracks in the bedrock
that formed the floor of the impoundment.
Decision Based on Remedy Screening
Column tests cannot be performed on bedrock. However, all of the listed compounds are highly volatile
with vapor pressures exceeding 120 mm Hg. Because of the complex site geology, the RPM decided
that pilot-scale testing should be conducted for remedy selection. The purpose of the pilot-test was to
determine whether SVE could remove significant quantities of the contaminants from the bedrock to
mitigate further migration.
Pilot-Scale Result
The pilot-scale tests showed that an airflow of 15 standard cubic feet per minute (scfm) could be
sustained and that contaminants were removed at a rate of 20 Ib/d. This was considered to be an
adequate removal rate. SVE was retained for further consideration as a remedial technology during the
evaluation of alternatives because it was the only viable treatment option for the bedrock.
presence of viscous organics have caused blockages in estimates of sidestream and residuals generation.
vapor extraction wells. Remedy design studies yield Pilot-scale SVE systems can be mobile or constructed at
information on process upsets and recovery. They are the site. The vapor extraction wells installed for a
used to improve cleanup time estimates and indicate the successful pilot-scale test are often incorporated in the
need for additional wells. These studies can also provide full-scale system.
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SECTION 4
TREATABILITY STUDY WORK PLAN
Section 4 of this document is written assuming that a
Remedial Project Manager is requesting treatability
studies through a work assignment/work plan mechanism.
Although the discussion focuses on this mechanism, it
would also apply to situations where other contracting
mechanisms are used.
This chapter focuses on specific elements of the
Treatability Study Work PI an that relate to SVE treatability
studies. These elements require detailed discussions that
are not presented in other sections of this document.
These elements include test objectives, experimental
design and procedures, equipment and materials, reports,
schedule, management and staffing, and budget. These
elements are described in Sections 4.1 - 4.9.
Complementing these subsections are Section 5 (Sampling
and Analysis Plan, which includes a Quality Assurance
Project Plan) and Section 6 (Treatability Data
Interpretation). The Work Plan elements for an SVE
Treatability Study are listed in Table 4- 1.
Table 4-1. Suggested Organization of SVE
Treatability Study Work Plan
1. Project Description
2. Remedial Technology Description
3. Test Objectives (Section 4.1)
4. Experimental Design and Procedures (Section 4.2)
5. Equipment and Materials (Section 4.3)
6. Sampling and Analysis (Section 4.4)
7. Data Management
8. Data Analysis and Interpretation (Section 4.5)
9. Health and Safety
10. Residuals Management
11. Community Relations
12. Reports (Section 4.6)
13. Schedule (Section 4.7)
14. Management and Staffing (Section 4.8)
15. Budget (Section 4.9)
Carefully planned treatability studies are necessary to
ensure that the data generated are useful for evaluating
the validity or performance of the technology. The Work
Plan sets forth the contractor's proposed technical
approach to the tasks outlined in the RPM's Work
Assignment. It also assigns responsibilities, establishes
the project schedule, and estimates costs. The Work Plan
must be approved by the RPM before work begins. The
generic guide(24) presents additional detail on these
procedures.
4.1. TEST GOALS
Setting goals for the treatability study is critical to the
ultimate usefulness of its results. Goals must be well
defined before the study is performed. Each tier or phase
of the treatability study program requires performance
goals appropriate to it. For example, column tests for
remedy selection could answer the question, "Will SVE
reduce contaminants to the required concentrations?"
The remedy selection column tests measure whether the
process could reduce contamination to below the
anticipated performance criteria to be specified in the
ROD. This indicates whether the process has potential
applicability at the site and further testing is warranted.
The ideal performance goals are the cleanup criteria for
the operable unit. For several reasons, such as continuing
waste analysis, applicable or relevant and appropriate
requirement (ARAR) determinations, and risk assessment
preparations, some cleanup requirements am not finalized
until the ROD is signed. Nevertheless, definite treatability
study goals must be established as a measuring stick
before the study is performed. In many instances, this
may entail an educated guess about projected cleanup
levels by the RPM. Estimated cleanup levels should
consider these objectives:
Provide long-term effectiveness
Comply with land disposal restrictions
Make the waste acceptable for delisting
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Achieve State or Regional standards for a
similarly contaminated site.
Cleanup criteria directly relate to the final management of
the material. They may dictate the need for complementary
treatment processes to remediate the entire wastestream
(i.e.,treatmenttrains). For example, SVE can treat volatiles;
a follow-on technology may be needed to treat metals and
nonvolatiles, depending on site characteristics. Such
combinations must be considered during the planning of
the treatability studies and in the overall remedy
evaluation phase.
The development of graduated goals for contaminant
reduction may fully address these complex needs. For
example, if SVE can reduce soil contaminant levels to 50
parts per billion (ppb), no further treatment may be
necessary. If, however, SVE technology can only reduce
the contaminant level to 5 ppm, treatment with another
technology may be mandated. If both residual volatile
organics and nonvolatile contaminants are at
concentrations that require further treatment, the
reduction of soil gas levels to minimize fugitive emissions
(e.g., during excavation) may govern the cleanup criteria
for SVE as one stage in a treatment train.
4.1.1 Remedy Screening Goals
Bench-scale column tests are used for remedy screening.
Remedy screening goals should simply require that the
contaminant of interest shows a greater than 80 percent
reduction in soil gas concentration. The goal is to show
SVE has the potential to work at the site. Frequently,
sufficient information exists about soil conditions and
contaminant volatility so that remedy screening tests will
not be necessary.
4.1.2 Remedy Selection Goals
Column tests for remedy selection can determine if SVE
has the potential to meet ultimate cleanup levels at a site.
When SVE is the primary treatment technology, the
suggested cleanup goals are set by the ARARs. If no
ARARs have been established for the site, a conservative
goal must be selected. Such a conservative goal would be
to show removal to below drinking water standards. This
goal would require that the leachate from Toxicity
Characteristic Leaching Procedure (TCLP) analysis of soil
treated in the completed column tests meet the drinking
water standards for the contaminants of interest. The
rationale for recommending this conservative goal is as
follows:
Site cleanup goals are often aimed at protecting
drinking water aquifers
Soil gas concentrations that are measured at the
column outlet may not guarantee adequate
cleanup
Measurement of total concentrations in the
treated soil is too conservative because it
measures both leachable and nonleachable
components
TCLP is a standard procedure for characterizing
hazardous wastes for regulatory purposes.
If the particular site does not require cleanup to drinking
water standards, the RPM may specify a less stringent
preliminary or target cleanup goal for treatability tests.
Field air permeability tests are conducted during remedy
selection. A field air permeability of greater than 10"10 cm2
for all soil types and geological formations appears to be
the lower feasibility limit for site air permeability. If the
permeability is lower, the technology may not be feasible.
However, as was discussed in subsection 2.2.3, a low
permeability layer may sometimes be used as an
advantage in applying SVE technology.
Pilot-scale testing frequently is used during remedy
selection, Pilot-scale tests usually encompass the
operation of a mobile SVE treatment unit onsite for a
period of 1 to 2 months. For more complex sites (e.g., sites
with different types of contaminants in separate areas or
with varying geological structures), the test rig may need
to be moved around the site, and much longer overall
testing periods may be required.
The goal of pilot-scale testing for remedy selection is to
confirm that the cleanup levels and treatment times
estimated in Section 4.1.1 are achievable. This goal is
accomplished by checking for diffusion control or
problems due to the site conditions.
4.2 EXPERIMENTAL DESIGN AND
PROCEDURES
Section 4.2 discusses the experimental designs and
procedures required in the Work Plan for die remedy
selection phase. Careful planning of experimental design
and procedures is required to produce adequate
treatability study data. The experimental design must
identify the critical parameters and determine the number
of replicate tests necessary.
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System design, test procedures, and test equipment will
vary among vendors. For this reason, this manual will not
strictly define test procedures. The information presented
in this section provides an overview of the test equipment
and procedures as these relate to each type of test.
4.2.1 Remedy Screening
Column tests performed during the remedy screening
phase of the treatability study are short-term tests (6-day
testing period) that provide qualitative information for the
evaluation of SVE performance on a particular
contaminant. These tests use column test procedures for
remedy selection similar to those presented in Appendix
A. After 2,000 air-filled pore volumes have passed
through the column, the test is completed and the
recommended analyses are performed. This typically
simulates the total air-filled pore volume throughput for
several years of field operation. The number of replicate
tests and the quality assurance/quality control (QA/QC)
levels are minimal in remedy screening studies.
4.2.2 Remedy Selection
Remedy selection testing is conducted both in the
laboratory and in the field. Each test has a specific
purpose and critical variables. These variables influence
the required number of tests and the QA/QC levels.
Mathematical modeling also has distinct requirements.
Column Tests
Properly designed column tests determine the practical
cleanup level limits of the contaminated soil and the
partition coefficient for use with mathematical modeling.
The key design variables for SVE column tests are
contaminant concentrations and air-flow rates.(3)(12)(40)
Contaminant levels of samples used for the column tests
should reflect the maximum concentrations of the
indicator contaminants at the site. If an anomalously high
maximum concentration exists at the site, professional
judgment should be used to select the samples for the
column tests.
The flowing air acts as a carrier for contaminants. Since
air-flow rates vary within the zone of influence of a vapor
extraction well, column tests should be run at a minimum
of two air-flow rates. Separate tests should be performed
at air-flow rates ranging from 0.01 liters per minute (L/min)
to 0.05 L/min and at 0.5 L/min to 1.0 L/min to check
sensitivity to air-flow. These rates correspond to a 2.5
inch diameter column. For larger diameters, the flow
should be adjusted in proportion to the increased area.
Since the air flow through the column depends on
pressure drop, vacuum levels for each air-flow sensitivity
test should be recorded.
Four column tests should be performed to evaluate data
repeatability and to determine the end-point. Three
columns should be run at the higher air-flow rates to
determine the achievable end-point for comparison with
the target concentration goals. A fourth (duplicate)
column test should be conducted at the higher air-flow
rates to check on the repeatability of the test. Use of these
additional columns to determine the end-point is explained
in greater detail below.
The following procedure for determining the target end-
point is recommended:
1. Take composite or core samples in the field (see
section 4.4.1). Analyze them for soil gas and total
contaminant levels. If ARARs or soil cleanup
levels have not been established, perform the
TCLP procedure, and analyze the leachate for
contaminants of interest.
2. Run four columns simultaneously under identical
conditions. Using a simple mathematical model and
the first day's operating data, estimate the time to
reach the required cleanup level or target
end-point. After running the test for 1/2 of the
estimated time to reach the target end-point, stop
testing one column. Repeat the analyses specified
in step 1 on the soil from the column.
3. Use the data collected during step 2 to refine the
endpoint prediction with a mathematical model for
column operation.1-3-"-40-1
4. At the end of the time predicted to reach the
end-point predicted by the model, stop testing a
second column. Repeat the analyses specified in
step 1.
5. If the soil contaminant levels are above the target
cleanup levels, or if ARARs have not been
established, and TCLP shows contaminant levels
in the leachate to be above drinking water
standards, continue the test with the other
columns as discussed in steps 7 and 8.
6. If the contaminant levels are below the target
cleanup levels, stop the test and analyze the third
column for repeatability.
7. Use the soil gas data, total contaminant levels, and
TCLP (if necessary) collected from the preceding
steps to further refine the mathematical model.
Predict the end point of the third column.
8. When the third column reaches the time predicted
for the end-point, stop both the third and fourth
columns and analyze them for repeatability.
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A fifth column may be run concurrently at low air-flow
rates to verify partition function data.
Measurements taken prior to the column tests consist of
analyses of contaminant concentrations in the soil matrix,
in TCLP leachate, and in the head space. Soil porosity,
bulk density, and moisture content are also measured.
Measurements taken during the tests are column
pressures, contaminant concentrations in the offgas,
air-flow rates, and ambient air dry-bulb and wet-bulb
temperatures. After the test, contaminant concentrations
in the soil matrix and in TCLP leachate are measured for
comparison with the target concentrations of the
treatability study.
Figure 4-1 shows an example column test apparatus. It
consists of a stainless steel or glass column with a 2.5-in
minimum diameter (4-in diameter columns are commonly
used) and a 12-in minimum filled length (filled lengths of
2-ft are not uncommon). This is connected with glass or
stainless steel tubing to a vacuum pump which pulls air
through the column. Plastic tubing is not recommended
because it may react with some contaminants. A
humidifier should be placed upstream of the column to
ensure that air with a constant humidity is supplied
throughout the test. A pollution control device
appropriate to the types and concentrations of the
contaminants should be located downstream of the
column to protect the laboratory personnel. Instruments
for measuring air-flow rate, air temperature, and air
pressure should be included. Pressure measurements
should be taken in the vicinity of the gas sampling ports.
These are located immediately upstream and downstream
of the column and downstream of the carbon bed. A gas
chromatograph is recommended to measure contaminant
concentrations. Appendix A presents a general procedure
for running a column test.
Air Permeability Tests
Air permeability tests determine whether sufficient airflow
can be attained in the zones of contamination to permit
adequate cleanup rates, Air permeability should be
measured for each geological unit at the site. These
measurements should be repeated on a grid pattern of
appropriate area in zones of known contamination. The
size of the selected pattern will depend on the complexity
of the site. Extraction probes are used fordepths up to 20
ft. Vapor extraction wells are used for depths in excess of
20ft.
The key control variable for air permeability testing is the
air-flow rate through the vapor extraction probe or well.
The key measured variables are vacuum levels, air-
flow rates and soil gas pressure or vacuum levels at
monitoring probes or wells. Measurements of effluent
Vwit
Vacuum
Pump
(ff) Ftowmeter/lndlcator
Sample Probe/Connector
(Q Pressure Gauge
M Valve to Control Flow
QAC Granulated Activated Carbon Bad
Soil Vapor/Liquid
Column Separator
Figure 4-1. Diagram of typical column test apparatus.
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30
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contaminant concentrations and moisture levels in the
offgas are recommended.
Figure 4-2 shows a typical air permeability test.(12) A vapor
extraction probe or extraction well is connected to a
vacuum pump. Piezometric probes measure soil pressure
levels at various horizontal and vertical distances from the
extraction point. This apparatus also contains a vapor
treatment unit. Instrumentation includes a flowmeter,
pressure or vacuum gauges, and a vapor sampling port.
Contaminant concentrations may be measured with a
portable gas chromatograph (GC), or gas samples may be
collected for laboratory analysis. Appendix B presents a
general procedure for running an air permeability test.
An air injection well may be used instead of a vapor
extraction well. If air injection is used, at least one air
permeability measurement should be made using a
paired-well system consisting of an injection and a vapor
extraction well. The use of an injection well may cause
uncontrolled venting of VOCs to the atmosphere.
Mathematical Modeling
Since mathematical modeling of SVE requires special
expertise, the OSWER Technical Support Project (see
Section 2.2.2) should be consulted for technical
assistance in applying mathematical models. Improper use
of mathematicalmodels can lead to incorrect conclusions.
Requests for assistance from the EPA TSP must be
directed through the RPM. Section 3.2.2 presents an
overview of the modeling process.
Vacuum Pump
Soil Gas
Sampling/
Pressure
Monitoring
Probes
Vapor
Treatment
Unit
Vapor Extraction Well
Soil Gas
Sampling/
Pressure -
Monitoring
Probes
Vapor
Flow
Flowmeter/lndicator
Sample Probe/Connector
Pressure Gauge
Temperature Indicator
X Valve to Control How
GAG Granulated Activated Carbon Bed
< Vapor Flow
Figure 4-2. Schematic for typical air permeability test.
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Pilot-Scale Tests
Pilot-scale or field venting tests determine whether
sufficient air flow can be attained in selected zones of
contamination to produce adequate cleanup rates. The
design should incorporate the available field data,
including air permeability measurements and the locations
and concentrations of contaminants. Mathematical
modeling may supplement the above data.
The key control variable for field vent tests is vacuum
level at the extraction well. The key measured variables are
the vacuum levels (at various locations to establish the
radius of influence), air-flow rates, soil gas pressure
levels, and soil and gas temperatures. Measurements of
effluent contaminant concentrations and moisture levels
from the extension well am also very important. These
provide contaminant and moisture-removal rates when
they are combined with the air-flow rates. The amount and
composition of liquids collected by the vapor/liquid
separator should also be measured.
A pilot-scale field vent test system consists of the same
elements identified for a typical air permeability test rig, as
presented in Figure 4-2. The above-ground portion of the
pilot-scale SVE system is usually mounted on a mobile
unit. The below-grade portion normally consists of one or
more extraction wells, and three or more probes or
monitoring wells to measure soil pressure levels at various
depths and distances from the extraction point. Air
injection wells may also be used to examine the effect of
air injection.
The extraction wells are connected in a manifold
arrangement. The wells encompass a specified sector of
the overall site. Although the well arrangement is site-
specific, the pilot-scale tests commonly cover an area
ranging from several hundred to several thousand ft2.
An extraction well, as shown in Figure 4-3, consists of a
slotted plastic pipe.1-31-1 The slots form a well screen. They
are positioned according to the location of the
contaminants and the underlying impermeable layer.
However, stainless steel or another material may be
required if the plastic is not compatible with the
contaminants.
The plastic or stainless steel manifold is connected to the
auxiliary equipment mounted on the mobile unit. The
auxiliary equipment consists of a blower or vacuum pump,
air-flow meters, pressure gauges, vacuum gauges,
thermometers or temperature indicators, an air-water
separator, post-treatment equipment, and a power supply.
Sampling ports should be installed at the exit of the
extraction well, in the piezometric probes, and at the outlet
of the post-treatment equipment. An impermeable
Vatv«
2"-4-Plastic Pip*.
10-Aug*rl
Slotted PVC-
Scr«*n
Cwiwnt Bwrtonlt* Grout
B«ntonlt« P«ll«ts
Co* re* Send
Figure 4-3. Extraction well construction details.
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cap may be installed to prevent water infiltration and to
increase the radius of influence. If pilot studies were
used for remedy selection, the same system may be used
for remedy design studies.
If the results from the field vent tests verify site remedy
objectives, the pilot-test system can be expanded to the
entire site by replacing the vacuum pump and vapor
treatment unit with commercial-scale site-specific
equipment connected to an expanded manifold of
extraction wells. Monitoring wells would also be added.
Multiple systems, similar in capacity to the pilot-scale
system, can also be employed to treat the overall site.
Post-treatment equipment usually consists of carbon
adsorbers for both off gas and water treatment. However,
incineration, catalytic oxidation, and condensation may
also be used for offgas treatment. Air stripping with a
carbon adsorber polishing step or biological treatment
may also be used for water treatment. Appendix C
presents a general procedure for running a field vent test.
4.3 EQUIPMENT AND MATERIALS
This part of the Work Plan should list the equipment and
materials required for each type of remedy selection test.
Section 4.2 addresses specific equipment and materials,
while describing the designs and procedures for the tests.
4.4 SAMPLING AND ANALYSIS
The Work Plan should address the tests needs for
sampling and analysis work, as well as quality assurance
support, in the Sampling and Analysis Plan (SAP). The
SAP, which will be prepared after Work Plan approval,
helps to ensure that the samples are representative and
that the quality of the analytical data generated is
generally known. The SAP addresses field sampling,
waste characterization, and the sampling and analysis
during treatability testing. It consists of two parts: the
Field Sampling Plan (FSP) and the Quality Assurance
Project Plan (QAPjP). Further discussion of the FSP and
QAPjP and specific sampling and analytical tests and
protocols are presented below, in Section 5, and in the
generic guide.(24)
4.4.1 Field Sampling
This subsection discusses sampling activities associated
with SVE testing for remedy selection. Composite samples
of soil should be prepared for the column tests.
Compositing reduces the variability in contaminant
concentration, and provides more accurate soil
concentration data before and after the column testing.
Some volatiles will be lost during compositing. Typically,
the volatile contaminants lost to any significant extent
would be those that are easily removed in the column
tests. However, because the goal of column tests is to
establish the potential of SVE to meet
Table 4-2. Testing Applications - Considerations for Composite and Undisturbed Samples
COMPOSITE
UNDISTURBED
1. Permits testing of a more uniform matrix. Useful 1.
for running column tests to ascertain if target
concentration goals can be met.
2. Permits better determination of reproducibility. 2.
3. Does not destroy adsorption/desorption 3.
properties.
4. Increased air permeability permits better access
to air flow and accelerates the SVE process.
5. Lose greater amounts of the more volatile
components.
Required to measure bulk density and calculate
porosity.
Air permeability is closer to field conditions.
Access to air flow is still excellent because of the
small cross section of the equipment.
Does not destroy adsorption/desorption
properties.
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cleanup targets for those compounds that have marginal
volatility in the matrix tested, loss of some of the more
volatile contaminants and changes in soil structure are
not critical.
The natural structure of the soil will also be destroyed by
compositing. Column tests may also be used for
estimating air permeability and measurements of the soil
bulk density for calculating the air-filled porosity at field
conditions. Composite samples are not recommended for
such studies. "Undisturbed" or intact samples must be
used for these purposes. Table 4-2 shows the testing
applications and considerations for composite and
"undisturbed" samples.
Samples should be collected from the zone of maximum
contaminant concentrations. They should also be
collected from areas of the site that have different types
of VOCs or semivolatiles. Forthese purposes, a sufficient
number of split spoon samples should be taken from each
area of concern to provide enough material for five
column tests and for analytical testing for the
contaminants of interest. The soil from the split spoons
should be mixed and composited and placed in large glass
containers with teflon-lined lids. The containers should be
sealed and cooled to 4 ° C. All samples should be recorded
in a permanent logbook. Sample containers should be
shipped using chain-of-custody procedures. Also, Shelby
tube samples should be taken for moisture, density, and
porosity measurements of each contaminated soil type or
geological structure. Shelby tubes can be used for
undisturbed samples.
Onsite air permeability tests should obtain the air
permeability of each geological formation identified during
the site characterization. The tests should be performed in
areas of high contaminant concentrations and in areas of
lower contamination where contaminant compounds with
different properties (volatility, solubility) have been
found. A sampling grid should be established for these
tests. Advice from experts should be sought for
establishing the sampling grid. The dimensions of each
sampling zone are site specific. Complex sites require more
sampling points.
4.4.2 Contaminated Soil Analysis
The contaminated matrix analysis characterizes the
physical and chemical properties of the contaminants and
the soil in which they reside. Analyses conducted during
the site investigation were discussed in Section 2.2.2.
Analyses recommended during the treatability study are
discussed below.
Analysis of the composited soil samples should be made
prior to and after the column tests. The analysis should
cover only those contaminants that are of interest for the
treatability tests (e.g., contaminants that may be difficult
to remove by the SVE technology and contaminants
occurring at high concentrations). The effluent gas
should be analyzed during the tests for a few of the above
"indicator" contaminants. Several analytical methods for
the column tests are listed in Table 2-2. When combined
with the airflow rates, the initial contaminant removal rates
can be estimated for full-scale SVE.
During the air permeability and pilot-scale tests, the
effluent concentration in the soil gas should be measured.
Use of an instrument that directly measures total organic
concentrations (e.g., a portable GC/FID) is preferable.
Alternatively, samples may be collected in gas collection
bombs, sorbent tubes, or other suitable sample collection
devices, and analyzed using the applicable methods.
4.4.3 Process Control Measurements
Process control and monitoring measurements are
essential for air permeability test column tests, and field
vent tests. The most important variables are vacuum
measurements and vapor flow rates. Ambient air
temperatures and soil temperatures should be measured
during the air permeability and field venting tests.
Water-removal rates and water table level should be
measured during the field venting tests.
4.4.4 Residuals Sampling and Analysis
The normal residuals from SVE are effluent gas from
extraction wells, contaminated water removed in the
air/water separator and, in many cases, spent activated
carbon from the treatment of the effluent gas and water.
Residual contaminants may be in the soil. Analysis of the
effluent gas was discussed in section 4.4.2. A
representative sample of the contaminated water should
be collected after the pilot-scale tests are completed. The
sample should be analyzed for the "indicator"
contaminants to supplement contaminant removal data. It
should also be analyzed for the entire list of site
contaminants given in Table 2-1 to determine disposal
requirements.
4.5 DATA ANALYSIS AND
INTERPRETATION
The Work Plan should describe the data
reduction procedures to be used. Upon
completion of each tier of SVE treatability tests,
the data must be summarized, interpreted,
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34
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and evaluated to assess SVE performance and the
advisability of proceeding to the next tier. Data reduction
is discussed below; data interpretation is discussed in
Section 6.
4.5.1 Data Reduction
The raw data will be obtained in the form of charts and
data logs. These data should be reduced to summary
figures and tables to facilitate interpretation and
evaluation.
Tabulated data from column tests will include analytical,
test variable, and soil characteristic data as follows:
Analytical data for each indicator compound
concentration in the off gas for the length of the
run
the initial and final concentration in the
headspace, in the TCLP leachate from the
column, and in the column soil
moisture content
Test variable data
pressure levels
temperature levels
air-flow rates
Soil properties
soil porosity
bulk density and true specific gravity
Plots of the soil gas concentration and the number of air
pore-volume changes as a function of time should be
presented. Figure 4-4 illustrates the suggested format for
presenting effluent gas concentrations.^2' After the data
are reduced, the final contaminant concentrations should
be compared to the target level concentrations. The
partition functions for mathematical modeling are obtained
by calculating the contaminant mass removed in the
column as a function of time and changing the partition
function until the predictions of the mathematical model
match the column data.
5000
- 4000
- 3000
- 2000
r 1000
Time
Where:
C (t) »Indicator contaminant concentration at time = "t"
C (o) = Indicator contaminant concentration after 1 pore turnaround.
A pore volume air change (turnaround) la a calculated value for the
volume of air required to displace the air that f Ilia the entire pore space
of the soil in the column.
(Pore Volume = column volume x air-filled porosity)
Figure 4-4. Hypothetical column test data.
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35
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a) Air Extraction Test
o-
-2-
Pressure
Decrease -4-
6-
9-
-10
JtA
D HB-7D (r * 3.4m)
A HB-6D (r = 16.m)
O HB-14D(r = 9.8m)
a a
a D
10\ 100
Tim* (min)
1000
b) Air Injection Test
50-
40-
Pressure
Increase 30
(In Hp>
20-
10-
mm
/
Well Notation and Location
/ r radial distance from \
\ injection/extraction point /
D HB-7D (r « 3.4m)
A HB-6D(r = 16.m)
O HB-14D(r = 9.8m)
+ HB-10 (r * 7.6m)
T^^TT"^^^^^^~^^^^ i i i i I I |
i i i i i i i i
1 10 100 1000
Tim* (mln)
Note: Inches of water (In. HaO) denote vacuums expressed as equivalent
water column heights. The ordinate Is the difference between the
pressure/vacuum at time (t) and the Initial pressure/vacuum.
Figure 4-5. Typical field air permeability test data.
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Tabulated data from air permeability tests will include the
following: vacuum applied, air-flow rate, pressure
distribution, and total contaminant concentrations in the
offgas. The location of the extraction point should be
given. If a well is used, the well design data (e.g., depth,
length of screened section, diameter of coarse sand or
gravel packing) are also needed. Pressure changes are
plotted as a function of time. Figure 4-5 illustrates the
suggested format for displaying field air permeability
results.1-12-1 The soil permeability to air flow may be
calculated from the slope and intercept of the data
obtained from plots similar to Figure 4-51-12-1 as follows:
k = 10«r'eu exp(_B + Q5772)
4P
WHERE:
= air permeability (cnf)
= radial distance from extraction well (m)
= air-filled soil porosity (void fraction)
= viscosity of air (1.8x10~4g/cm-s)
= ambient atmospheric pressure (1
atm = 1.013x106g/cm-s2)
= y-intercept (g/cm-s) (see Figure 4-5)
= slope (g/cm-s2) (see Figure 4-5)
After the data are reduced, the calculated air
permeabilities should be compared to the criteria for
adequate permeability in Figure 6-1. If the air
permeabilities are less than 10"10 cm2, SVE may not be
feasible. If the air permeabilities are greater than 10"6 cm2,
then the site has adequate air permeability.
If the air permeabilities are intermediate, mathematical
modeling should be performed to give a cleanup time
estimate.
100
10
1
0.1
ID"2
10*
so
100
Time (days)
150
Output from mathematical modeling will listthe predicted
concentration of the indicator contaminant remaining in
soil as a function of cleanup time. SVE modeling variables
that affect this prediction, including variations in
permeability, vacuum applied, radius of influence of the
extraction well, and partition functions, will also be
tabulated. A plot of predicted residual mass as a function
of operation time is the suggested method for presenting
the data (Figure 4-6).
Tabulated data from pilot-scale tests will include applied
vacuum, air-flow rates, offgas moisture levels, amount of
moisture removed, soil pressures, and effluent
contaminant concentrations. Cumulative contaminant
mass removed should be calculated or measured.
Variables that determine efficiency of the treatment
technologies for the effluent gas and water (e.g., carbon
loading factor) should also be tabulated. Operating
conditions of any auxiliary equipment should be listed.
Plots of contaminant removal rates, flow rates, and applied
vacuums as functions of time are acceptable methods of
presenting pilot-scale data. Figure 4-7 shows examples of
these plots.(12(32)(34) Afterthe data are reduced, the results
should be compared with the predictions of mathematical
modeling. If the modeling predictions and pilot-scale test
results differ significantly, the data should be reconciled,
and the model assumptions should be checked for
validity. The modeling should be repeated using the
parameters obtained from the pilot-scale test. The
estimated cleanup time predictions from the revised
modeling should be compared to the site cleanup goals.
Engineering modifications to the pilot-scale unit should
be pursued before abandoningthe technology. Modeling
can be helpful in identifying potential modifications.
4.5.2 Assessment of Data Quality
A secondary goal of data analysis is to determine the
quality of the data collected. Field data should be checked
for adequate instrument calibrations. All data should be
checked to assess precision (relative percent difference
for duplicate matrix spikes), accuracy (percent recovery of
matrix spikes), and completeness (percentage of data that
are valid). If the QA objectives specified in the QAPjP
have not been met, the RPM and the EPA management
must determine the appropriate corrective action. The data
that must be obtained for each tier are discussed in
Sections 2, 3, and 4.2.
Figure 4-6. Typical mathematical modeling results.
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A. Vacuum/Flowrate Data
in
CM
140
120
100
80
60
40
20
-
-
-
A
»*;*
Vacuum
>- Howrmtt
. A
\J\ .
» ; \ ?, f*,
*« V
*
» *
\j
t
t <
W »t »
/
15
10
B. Removal Rate/Cumulative
Recovered
0
20 40 60 80 100 120
Time (days)
o
0 20 40 60 80 100 120
Time (days)
C. Wellhead Vapor/Concentration Data
1000
100
10
0.1
0.01
« * *OVt '
20 40 60 80 100
Day of Active Treatment
Figure 4-7. Typical field vent test data.
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4.6 REPORTS
The Work Plan should discuss the organization and
content of interim and final reports. Once the data have
been gathered, interpreted, and analyzed, they must be
incorporated into a report. Section 4.12 of the generic
guide1-24-1 provides the suggested organization for the
treatability study report and a generic discussion of the
report's contents.
If the SVE technology is to be tested in multiple tiers, a
formal report for each tier of the testing is not required.
Interim reports and project briefings should be prepared
at the completion of each tier for the interested parties to
present the study findings and to determine the need for
additional testing. A final treatability study report that
encompasses the results of the entire study should be
developed after testing is complete.
4.6.1 General Results Reported
For each tier of testing, all data collected should be
presented and discussed. Raw data and charts should be
included in appendices. In general, significant results from
the remedy selection tests should be presented in the
formats of Figures 4-4,4-5, and 4-6 for column tests, field
air permeability tests, and mathematical modeling,
respectively.
The pilot-scale field vent tests that precede full-scale
remediation will provide actual field-log remediation data
(associated with equipment and system operations) and
effluent contaminant concentrations. These data will
include vacuum levels, vapor-flow rates, and
vapor-contaminant concentrations versus operating time.
Typical field vent test data should be formatted like the
plots in Figure 4-7.
4.6.2 Mathematical Modeling
A mathematical modeling report should include:
A physical-chemical description of the model
The rationale for input parameter selection
Plots of log 10 residual contaminant mass versus
time for each run (See Figure 4-6.)
Times required to achieve specified cleanup levels
(such as 90 percent, 99.9 percent, etc.)
Tables showing the sensitivity to key variables
(e.g., air permeability, partition functions, radius of
influence, etc.)
Representative contaminant distributions as
cleanup progresses (optional)
The report may also address randomly generated
permeability functions and diffusion/desorption kinetics.
4.6.3 Treatability Data Base
As an aid in the remedy selection and the planning of
future treatability studies, the Office of Emergency and
Remedial Response requires that the contractor send a
copy of all treatability study reports to the Agency's
Superfund Treatability Data Base repository. The Work
Assignment must stipulate this requirement. This data
base is being developed by the Office of Research and
Development. A copy must be sent to:
Mr. Glenn Shaul
Superfund Treatability Data Base
U.S. Environmental Protection Agency
Office of Research and Development
Risk Reduction Engineering Laboratory
26 W. Martin Luther King Drive
Cincinnati, Ohio 45268
4.7 SCHEDULE
The Work Plan should discuss the schedule for
completing the treatability studies. The schedule lists the
anticipated starting and ending dates for each task
described in the Work Plan. It also shows how the various
tasks interface. The time span for each task should take
additional factors into account: the time span required to
prepare the Work Plan, to hire subcontractors, and to
obtain other formal approvals (e.g., disposal approval
from a commercial treatment, storage, or disposal facility
(TSDF)); the duration of test operations; the analytical
turnaround time; and the review and comment periods for
reports and other project deliverables. Some slack time
should be built into the schedule to accommodate
unexpected delays (e.g., bad weather, equipment
downtime) without delaying the project completion date.
The schedule is usually displayed in the form of a bar
chart. If the study involves multiple tiers of testing, all
tiers should be shown on one schedule. Careful pretest
planning is essential. Depending on the length of the
review and approval process, planning can take several
months. Figure 4-8 presents a modified bar chart that
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39
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Months From Project Start
Activity Description
Data Review
SIC, SAP, HSP, CRP Prep
Bench Scale
Column Test(s)
Data Analysis
Field Air Perm
Data Analysis
Math Model
Data Analysis
Final Report
Remedy
Screening
Site Remediation
and RI/FS
Schedule Overview
Remedy Selection
I I I
Remedial Investigation - SVE
I I 1 I
Feasibility Study -
Other Technologies and
Not*: Abbreviations defined In Abbreviations, Acronyms, and Symbols (p. Ix)
Figure 4-8. Example project schedule for a full-tier SVE treatability study program.
identifies the key activities associated with the multiple
tiers of SVE technology evaluation and treatability
testing. Estimates are shown for each activity's time
span. It may take a year to complete the treatability
testing and results reporting.
4.8 MANAGEMENT AND STAFFING
The Work Plan should discuss the management
and staffing for treatability studies. The Work
Plan identifies key management and technical personnel
and defines specific project roles and responsibilities.
The line of authority is usually presented in an
organization chart, as in Figure 4-9. The RPM oversees
the project, including the establishment of
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LAB TECHNICIANS
> Execute treatability studies
> Execute sample collection
and analysis
CONTRACT WORK
ASSIGNMENT MANAGER
Report to EPA Remedial
Project Manager
Supervise overall project
GEOLOGIST
Oversee treatability study
execution
Oversee sample collection
> Prepare applicable sections
of report and Work Plan
QA MANAGER
> Oversee Quality
Assurance Program
> Prepare applicable
sections of report and
Work Plan
CHEMIST
> Oversee sample collection
procedures and analysis
> Prepare applicable section
of report and Work Plan
Figure 4-9. Example organization chart.
data quality objectives, selection of vendors and
subcontractors, the implementation of contracts, and
issuance of the Work Assignment. At Federal- and
State-lead sites, the remedial contractor directs the
treatability study. This contractor oversees the execution
of the tasks shown in Figure 4-8. At private-lead sites, the
PRP performs this function and bears responsibility for
the contracting mechanism and the Work Assignment.
The RPM may subcontract the treatability study in whole
or in part to a vendor, laboratory, or testing facility with
expertise in the subject technology.
Once the decision to conduct a treatability study has
been made and its scope defined, the RPM must engage
a contractor or vendor with the requisite technical
capabilities and experience. In support of the Superfund
Program, ORD has compiled a list of treatability study
vendors and contractors entitled: "Inventory of
Treatability Study Vendors," EPA/540/2-90/003a.(26)
In general, there are three methods of obtaining
treatability study services. Remedial Engineering
Management (REM) and Alternative Remedial
Contractors Strategy (ARCS) contracts obtain
management and technical services in support of remedial
response activities at CERCLA sites. A specific waste
may require specialized expertise that is not available from
firms accessible through existing REM or ARCS contracts.
The RPM may then need to investigate firms that have
this unique capability and implement other contracting
mechanisms, such as a Request for Proposal (RFP).
4.9 BUDGET
The Work Plan should discuss the budget for conducting
treatability tests. Figure 4-10 illustrates the major cost
elements associated with each tier.
Analytical costs significantly impact project costs during
all treatability testing tiers. Data analysis and quality
assurance activities can represent 50 percent or more of
the total test cost. Several factors affect the expense of an
analytical program, including: the laboratory performing
the analyses, the analytical target list, the number of
samples, the required turnaround time, QA/QC level, and
reporting requirements. Analytical costs vary
substantially from laboratory to laboratory. However,
before prices are compared, the subject laboratories
should be properly investigated. What methods will be
used for sample preparation and analysis? What detection
limits are needed? Does each laboratory fully understand
the matrix that will be received (e.g., sludge, oily soil,
slag)? Are they aware of interfering compounds that may
be in the sample (e.g., sulfide)? If all laboratories are using
the same methods and equipment, and understand the
objectives of the analytical program, their charges can be
validly compared.
The number and the types of analytes can also affect
analytical costs. Analysis of a few "indicator" contami-
nants may greatly reduce costs compared to analyzing for
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Cost Element
WP, S/C, SAP, HSP Preparation
Mobilization/Demobilization
SVE Vendor Equipment
Materials
Utilities
Sampling, Monitoring
Analytical
Residuals Management
Data Analysis, Report Preparation
Estimated total cost
Field Air
Permeability
Test
0
0
A
0
o
o
0
0
o
$10,000-
$50,000
Bench-Scale
Column
Test(s)
O
o
A
O
O
O
o
o
o
$30,000-
$70,000
Computer
Model
A
A
O
A
A
A
A
A
O
$10,000-
$20,000
Pilot-Scale
Reid Test
0
o
$100,000+
Not Applicable and/or No $n
Cost Incurred:
o
$1.000 -$10,000
Figure 4-10. General applicability of cost elements to SVE remedy selection tests.
all contaminants. Also, analyses of some analytes cost
more than others. Often, there are analytes that provide
information, but are not critical to the study. The selection
of analytes for analysis could be more cost effective if the
parameter-specific costs were known.
The number of samples, turnaround time, QA/QC
procedures, and reporting requirements also affect
analytical costs. Often, laboratories discount on sample
quantities greater than 5, greater than 10, and greater than
20 when the samples arrive at the same time. They also
apply premiums of 25, 50, 100, and 200 percent when
analytical results are requested in a faster turnaround
time, less than 15 to 25 working days. If matrix spike and
matrixspike duplicates are required, the analytical cost will
increase due to those QA/QC samples.
Section 2 discusses typical analytical tests for an SVE
treatability study program. Vendor equipment is a key
cost element in pilot-scale testing. Vendors often provide
operators, personal protective equipment, chemicals, and
decontamination supplies during pilot-scale tests.
Treatment system capital costs may range from $50,000 for
transportable units to extensive site-installed facilities
costing $500,000. Operation, maintenance, andmonitoring
may cost $10,000 to $100,000 per month of operation.
Pilot-scale tests may total $20 to $80 per ton of treated
soils. The pilot-scale equipment can be used as part of a
full-scale remedial installation to significantly reduce
overall costs. Vendor equipment is usually full-scale
capacity. The actual remedial action may require only the
addition of extraction wells.
Residuals management costs may include offgas
treatment and wastewater disposal costs (depending on
local, State and Federal regulations). These can range
from$ 10 to $30 per ton of treated soil. Site-specific criteria
will affect actual costs.
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SECTION 5
SAMPLING AND ANALYSIS PLAN
The Sampling and Analysis Plan (SAP) consists of two
partsthe Field Sampling Plan (FSP) and the Quality
Assurance Project Plan (QAPjP). The purpose of this
section is to identify the contents of and aid in the
preparation of these plans. The RI/FS requires a SAP for
all field activities. The SAP ensures that samples obtained
for characterization and testing are representative, and
that the quality of the analytical data generated is known
and appropriate. The SAP addresses field sampling, waste
characterization, and sampling and analysis of the treated
wastes and residuals from the testing apparatus or
treatment unit. The SAP is usually prepared after Work
Plan approval.
5.1 FIELD SAMPLING PLAN
The FSP component of the SAP describes the sampling
objectives; the type, location, and number of samples to
be collected; the sample numbering system; the
equipment and procedures for collecting the samples; the
sample chain-of-custody procedures; and the required
packaging, labeling, and shipping procedures.
Field samples are taken to provide baseline contaminant
concentrations and soil for treatability studies. The
sampling objectives must be consistent with the
treatability test objectives.
The primary objective of remedy selection treatability
studies is to evaluate the extent to which specific
chemicals are removed from the soil. The primary sampling
objectives include:
Acquisition of samples representative of
conditions typical of the entire site or defined
areas within the site. Because a mass balance
is required for this evaluation, statistically
designed field sampling plans may be required.
However, professional judgment regarding the
sampling locations may be exercised to select
sampling sites that are typical of the area (pit,
lagoon, etc.) or appear above the average
concentration of contaminants in the area
being considered for the treatability test.
This may be difficult because reliable site
characterization data may not be available early
in the remedial investigation.
Acquisition of sufficient sample volume
necessary for testing, analysis, and quality
assurance and quality control.
From these two primary objectives, more specific
objectives/goals are developed. When developing the
more detailed objectives, consider the following types of
questions:
How many samples should be composited to
provide better reproducibility for the
treatability test? This question, including the
type of compositing, is addressed in section
4.4.1.
Are there adequate data to determine sampling
locations indicative of the more contaminated
areas of the site? Have soil gas surveys been
conducted? Contaminants may be widespread
or isolated in small areas (hot spots).
Contaminants may be mixed with other
contaminants in one location and appear alone
in others. Concentration profiles may vary
significantly with depth.
Are the soils homogeneous or heterogeneous?
Soil types can vary across a site and with
depth. Depending on professional judgment,
contaminated samples from various soil types
may have to be taken to conduct treatability
tests. Changes in soil composition can affect
the effectiveness of SVE.
Is sampling of a "worst-case" scenario
warranted? Assessment of this question must
be made on a site-by-site basis. Hot spots and
areas with soils which may be difficult to treat
should be factored into the test plan if they
represent a significant portion of the waste
site. Thick lenses of clay may be especially
difficult to treat with SVE.
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After identifying the sampling objectives, an appropriate
sampling strategy is described. Specific items that should
be briefly discussed in the FSP are listed in Table 5- 1.
Table 5-1. Suggested Organization of
Sampling and Analysis Plan
Field Sampling Plan
1. Site Background
2. Sampling Objectives
3. Sample Location and Frequency
- Selection
- Media Type
- Sampling Strategy
- Location Map
4. Sample Designation
- Recording Procedures
5. Sample Equipment and Procedures
- Equipment
- Calibration
- Sampling Procedures
6. Sample Handling and Analysis
- Preservation and Holding Times
- Chain-of-Custody
- Transportation
Quality Assurance Project Plan
1. Project Description
- Test Goals
- Critical Variables
- Test Matrix
2. Project Organization and Responsibilities
3. QA Objectives
- Precision, Accuracy, Completeness
- Representativeness and Comparability
- Method Detection Limits
4. Sampling Procedures
5. Sample Custody
6. Calibration Procedures and Frequency
7. Analytical Procedures
8. Data Reduction, Validation, and Reporting
9. Internal QC Checks
10. Performance and System Audits
11. Preventive Maintenance
12. Calculation of Data Quality Indicators
13. Corrective Action
14. QC Reports to Management
15. References
16. Other Items
5.2 QUALITY ASSURANCE PROJECT
PLAN
The QAPjP consists of sixteen sections. Since many of
these sections are generic and applicable to any QAPjP
and are covered in available documents^23-"-24-1 this guide
will discuss only those aspects of the QAPjP that are
affected by the treatability testing of SVE technology.
5.2.1 Project Description
Section 1 of the QAPjP must include an experimental
project description that clearly defines the experimental
design, the experimental sequence of events, each type of
critical measurement to be made, each type of matrix
(experimental setup) to be sampled, and each type of
system to be monitored. This section may reference
Section 4 of the Work Plan. All details of the experimental
design not finalized in the Work Plan should be defined in
this section.
Items to be included, but not limited to, are:
Number of samples (areas) to be studied
Identification of treatment conditions
(variables) to be studied for each sample
Target compounds for each sample
Number of replicates per treatment condition
Criteria for technology retention or rej ection
for each type of remedy selection test.
The project description clearly defines and distinguishes
the critical measurements from other observations made
and system conditions (e.g., process controls, operating
parameters, etc.) routinely monitored. Critical
measurements are those measurements, data gathering, or
data generating activities that directly impact the technical
objectives of a project. At a minimum, the determination
of the target compounds (identified above) in the initial
and treated soil samples will be critical measurements for
column tests. Air permeability measurement and radius of
influence will be critical for air permeability tests. Airflow
rates, concentration of target compounds, radius of
influence, and vacuum applied will be critical
measurements for pilot-scale tests.
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5.2.2 Quality Assurance Objectives
Section 3 lists the QA objectives for each critical
measurement and sample matrix defined in Section 1.
These objectives are presented in terms of the six data
quality indicators: precision, accuracy, completeness,
representativeness, comparability, and, where applicable,
method detection limit.
5.2.3 Sampling Procedures
The procedures used to obtain field samples for the
treatability study are described in the FSP. They need not
be repeated in this section, but should be incorporated by
reference.
Section 4 of the QAPjP contains a description of a
credible plan for subsampling the material delivered to the
laboratory for the treatability study. The methods for
allocating the material for determination of chemical and
physical characteristics such as bulk density, true specific
gravity, moisture content, contaminant concentrations,
etc., must be described.
5.2.4 Analytical Procedures and Cali-
bration
Sections 5, 6, and 7 describe or reference appropriate
analytical methods and standard operating procedures for
the analytical method for each critical measurement made.
In addition, the calibration procedures and frequency of
calibration are discussed or referenced for each analytical
system, instrument, device, or technique for each critical
measurement. The procedures presented in Appendices
A, B, and C list some of the calibrations that should be
performed for SVE remedy selection tests.
The methods for analyzing the treatability study samples
are the same as those for chemical characterization of field
samples. Table 2-1 presents suitable analytical methods.
Preference is given to methods in "Test Methods for
Evaluating Solid Waste, SW-846, 3rd. Ed., November
1986.(35) Other standard methods may be used, as
appropriate.<-l~><-2'1 Methods other than gas
chromatography/mass spectrometry (GC/MS) techniques
are recommended to conserve costs when possible.
5.2.5 Data Reduction, Validation, and
Reporting
Section 8 includes, for each critical measurement and each
sample matrix, a specific presentation of the requirements
for data reduction, validation, and reporting. Aspects of
these requirements are covered in Sections 4.5, 4.6, and
6.1 of this guide.
5.2.6 Quality Control Reports
Section 14 describes the QA/QC information that will be
included in the final project report. As a minimum, reports
include:
Changes to the QA Project Plan
Limitations or constraints on the applicability
of the data
The status of QA/QC programs,
accomplishments, and corrective actions
Results of technical systems and performance
evaluation QC audits
Assessments of data quality in terms of
precision, accuracy, completeness, method
detection limit, representativeness, and
comparability.
The final report contains all the QA/QC information to
support the credibility of the data and the validity of the
conclusions. This information may be presented in an
appendix to the report. Additional information on data
quality objectives1-21-1 and preparation of QAPjPs(25:i is
available in EPA guidance documents.
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SECTION 6
TREATABILITY DATA INTERPRETATION FOR
TECHNOLOGY SELECTION
6.1 TECHNICAL EVALUATION
To properly evaluate S VE as a remediation alternative, the
data collected during remedy screening and remedy
selection phases must be compared to the test objectives
and other criteria that were established before the tests
were conducted. Figure 6-1 is a flowchart for evaluating
SVE as a potential remedy. It presents a framework of the
decision-making process that is based on the comparison
between the treatability test objectives and test results. It
also includes considerations of contaminant volatility,
ability to get air flow to the contaminant, and predicted
cleanup times. The flowchart discussed below presents a
recommended approach and may be modified based on
site-specific conditions. Consultation with experts is
recommended.
6.1.1 Remedy Screening Phase
The most important data for decision making during
remedy screening are the vapor pressures of the
contaminants of concern at the measured soil temperature.
Based upon the literature, SVE is not generally feasible for
contaminants that have a vapor pressure of less than or
equal to 0.5 mm Hg. If the vapor pressure exceeds 0.5 mm
Hg, column tests should be executed. If the column test
shows 80 percent or more reduction in the soil gas
concentration of the contaminant of interest, column tests
for remedy selection should be carried out. If the remedy
screening tests show that the concentration of the
contaminant of interest is below any set target level, field
air permeability tests should be conducted for soils with
estimated air permeabilities less than or equal to 10"6 cm2.
If the vapor pressure of the contaminant equals or
exceeds 10 mm Hg, column testing is not required due to
the high volatility. However, air permeability tests may be
required.
The soil characteristics are also important because these
determine the air permeability. If the soil is sandy and the
vapor pressure of the contaminant of concern is equal to
or above 10 mm Hg, there is historical evidence that SVE
is applicable and remedy selection treatability testing may
be skipped.
6.1.2. Remedy Selection Phase
The data considered in the work sheet for the remedy
selection phase of testing consist of air permeability data,
the column test results (for screening and end-point
determination), cleanup time predictions based upon
mathematical modeling and pilot-scale tests, if necessary.
The column tests require that target concentration levels
be set in advance for the contaminants of concern. If after
completion of the test, these concentrations exceed the
target levels, SVE should be considered infeasible. If the
column test shows that the contaminants of concern can
be reduced to below the target level, and all other criteria
are met, the air permeability tests should be executed.
These may be skipped if the estimated air permeabilities
are greater than or equal to 10"6 cm2. If the air permeability
test results are also favorable as discussed below,
pilot-scale testing for remedy selection is recommended.
Pilot-scale tests may also be warranted if mixed results are
obtained (i.e., air permeability in some strata is less than
10"10 cm2). Decisions for further testing when mixed results
are obtained should be based on expert opinion. Further
remedy selection testing is not recommended if air
permeability tests indicate that SVE is not likely to
succeed.
The permeability data measure the ability to
achieve adequate air-flow rates at the site.
If the permeability is less than or equal to 10"10 cm2,
SVE is not feasible. If the permeability is greater than 10"10
cm2, the pilot-scale remedy selection treatability study
should be executed provided that the results of
mathematical modeling are encouraging. If the
permeability exceeds or equals 10"6 cm2, and the
vapor pressure of the contaminant of concern is
equal to or greater than 10 mm Hg, SVE should be
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considered in the evaluation of alternatives. After
selection, remedy design/implementation at the pilot-scale
may be required.
Mathematical modeling can be used to predict lower
bound (i.e., quickest) cleanup times. If mathematical
modeling, based on field measurements of permeability
and distribution coefficient data from the column tests,
predicts that cleanup to the target level will be greater
than the period set by the RPM, SVE should be
considered to be infeasible. If mathematical modeling
predicts that the cleanup target level can be achieved in
less than the period set by the RPM, the pilot-scale
treatability tests should be conducted for remedy
selection. If mathematical modeling predicts that cleanup
to the target level can be achieved in 2 years or less and
site characterization data show no great potential for
diffusion control, SVE should be considered for remedy
design/implementation at the pilot scale.
If the data interpretation provided by Figure 6-1 indicates
that SVE should be retained for further evaluation, a pilot
test should be run for remedy selection purposes. Based
upon the results of the pilot test, the cleanup should be
mathematically modeled. During the cleanup, contaminant
concentrations in the offgas should be measured
periodically, and these should be compared to the
predictions from the mathematical model. If after a
reasonable period of operation (1 to 2 months), the rate of
cleanup is much lower than that predicted by the model,
the cause should be investigated. This may be due to
short circuiting, improper well placement, unexpected
concentration of free NAPL, or unexpected diffusion
control. If the problems cannot be resolved, the use of the
technology should be reevaluated. If the rate of cleanup
is reasonably consistent with the predictions, SVE should
be retained for evaluation in the FS.
6.2 COST ESTIMATION FROM DATA
Treatability data for evaluating SVE are very useful in
generating cost estimates. These estimates will be most
precise when they are based on pilot-scale data. Table 6-1
relates data collected during the treatability studies to the
major components affecting the SVE costs. The cost of
piping, which is associated with the number and depth of
wells, can be significant. Instrumentation and analytical
costs for monitoring the process will also affect system
costs. Further cost information is presented in Appendix
D.
6.2.1 Well Design
The number and depth of wells are major cost
considerations. The number of vapor extraction wells is
determined by their radius of influence and the extent of
contamination. The radius of influence can be determined
during air permeability or pilot-scale tests. Sensitivity
studies using mathematical models can optimize the
installation of wells. The extent of contamination is
determined by the site investigation, using soil gas
concentrations and soil borings. The depth to the
impermeable layer and the location of contaminants
determine the depth of the wells. The number of
monitoring wells is related to the number of extraction
wells.
Site soil characterization, air permeability tests, pilot-scale
tests, and mathematical modeling aid in determining
whether air inj ection wells or passive vents are warranted
and, if so, in locating them.
6.2.2 Vacuum Pump or Blower
The vacuum pump or blower size is determined by the
required air-flowrate and vacuum level. These parameters
can be determined from the air permeability or pilot-scale
tests results, and the number of extraction wells. If site
conditions warrant air injection wells, the required blower
size can be determined from the air permeability and pilot-
scale test data.
6.2.3 Vapor/Liquid Separator
The vapor/liquid separator size is based upon vapor-flow
rates and the moisture content in the offgas. Since
moisture infiltration rates may vary considerably and
measured rates may underestimate maximum liquid
loading, it is advisable to provide excess separator
capacity. Also, if carbon is being used to treat the offgas,
use of a mist eliminator prior to the carbon beds is
recommended to remove the greatest amount of water
possible. Use of a mist eliminator should reduce carbon
usage significantly.
6.2.4 Surface Seals
The need for surface seals is determined by the air-flow
distributions and the potential for surface water
infiltration from rainfall or snow. Data from the air
permeability or pilot-scale tests, and mathematical
modeling of air-flow patterns are useful for determining
the need for surface seals to provide adequate subsurface
air distribution. Surface water infiltration may be estimated
based on rainfall records and the permeability of the
surface soils.
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Table 6-1. Factors Affecting SVE Treatment Costs
Component Affected
Factors Governing
Component Selection
Data Required
Well design
Number of wells
Depth of wells
Passive wells (inlet) and air
injection wells
Vacuum pump or blower
Vapor/liquid separator
Surface seals
Water table depression pumps
Offgas treatment
Liquid (water) treatment
Operating costs
Radius of influence
Extent of contamination
Depth to impermeable layer
Location of contaminants
Air flow distributions
Vacuum level and air flow
rate
Liquid (water) removal rates
Air-flow distributions
Surface water infiltration
Depth to water table
Depth of contaminants
Water infiltration rates
Contaminant removal rates,
Contaminant identities,
Moisture content after vapor/
liquid separator
Site water removal rates
treatability factors
Size of SVE system, cleanup
time, analytical costs, and
residual disposal costs
Pressure profiles from air permeability
and pilot tests, mathematical
modeling to optimize selection(1).
Contaminant distributions.
Depth to bedrock'2', depth to water
table.
Contaminant distributions.
Air permeability tests, pilot tests,
mathematical modeling.
Air permeability tests, pilot tests,
number of vapor extraction wells.
Moisture content, vapor flowrates
(better oversized; mist eliminator
recommended).
Air permeability tests, pilot tests,
mathematical modeling, or air-flow
patterns.
Rainfall, permeability of surface soils.
Depth to water table. Site
hydrological behavior.
Air permeability tests, pilot tests.
Moisture content during pilot tests.
Site hydrological behavior, moisture
content in offgas, contaminant
concentrations in water. Inorganic
chemistry tests.
All of the above, plus cleanup time
predictions based upon mathematical
modeling and prior experience.
<1> In general, specify more wells than predicted by mathematical modeling as optimum because of
uncertainties in the contaminant location and subsurface conditions.
<2> On some sites, SVE may be the only available technology to apply to fractured bedrock. These wells
will be much more costly than wells bored into soil.
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6.2.5 Water Table Depression Pumps
The need for water table depression pumps is
determined by the depth to the water table relative to
the location of the contaminated zone. The pump sizes
are determined by the water infiltration rates obtained
from the hydrological behavior of the site.
6.2.6 Offgas Treatment
The need for offgas treatment is determined by
contaminant type and concentration, results of the
health risk assessment for contaminant releases, and
localregulations. If offgas treatment is required, its cost
is related to the type of treatment, the contaminant
removal rates, and the moisture content downstream of
the vapor/liquid separator. The contaminant removal
rates and moisture content can be determined during
the air permeability or pilot-scale tests.
6.2.7 Liquid (Water) Treatment
The need for water treatment is based on the
contaminant concentrations in water removed from the
subsurface environment. The equipment size is
determined by the amount of water and the contaminant
type concentrations in the water. The amount of water
is a result of the site hydrological behavior and the
moisture content in the SVE offgas.
6.2.8 Operating Costs
The operating costs of the SVE system are related to
the size of the system, the power requirements, the
amount of residues treated, the analytical costs for
monitoring the operation, maintenance costs, and the
cleanup time required to remediate the site. The
approximate cleanup time predictions obtained from
mathematical modeling and prior experience can be
used to estimate the total operating cost.
6.2.9 Total Cost Estimate
The total cost of SVE includes capital, and operating
and maintenance costs. Capital costs may be roughly
estimated by determining the system size (using the
considerations from the preceding sections) and
multiplying unit size estimates by the values given in
Appendix D.
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SECTION 7
REFERENCES
1. American Society for Testing and Materials. Annual Book
of ASTM Standards, 1987.
2. American Society of Agronomy, Inc. Methods of Soil
Analysis, Part 2, Chemical and Microbiological Properties.
2nd Ed., 1982.
3. Baehr, A.L., G.E. Hoag, and M.C. Marley. Removing
Volatile Contaminants from the Unsaturated Zone by
Inducing Advective Air Phase Transport. Journal of
Contaminant Hydrology, Vol. 4, 1989.
4. Bennedsen, M.B., J.D. Hartley, and J.P. Scott. Use of
Vapor Extraction Systems for In Situ Removal of Volatile
Organic Compounds from Soil. Presented at Hazardous
Controls Research Institute Conference, 1987.
5. Danko, J. Applicability and Limitations of Soil Vapor
Extraction for Sites Contaminated with Volatile Organic
Compounds. Presented at the Soil Vapor Extraction
Technology Workshop on Soil Vacuum Extraction, U.S.
Environmental Protection Agency, Risk Reduction
Engineering Laboratory, Edison, New Jersey, June 28-29,
1989.
9. Hinchee,R.E., B.C. Downey, andE. J. Coleman. Enhanced
Bioreclamation Soil Venting and Groundwater Extraction:
A Cost-Effectiveness and Feasibility Comparison.
Proceedings of Petroleum Hydrocarbons and Organic
Chemicals in Groundwater: Prevention, Detection, and
Restoration. Houston, Texas, 1987.
10. Hoag, G.E. Soil Vapor Extraction Research Developments.
Presented at the Soil Vapor Extraction Technology
Workshop on Soil Vacuum Extraction, U.S. Environmental
Protection Agency, Risk Reduction Engineering
Laboratory, Edison, New Jersey, June 28-29,1989.
11. Hutzler, N.J., J.S. Gierke, and B.E. Murphy. Vaporizing
VOCs. Civil Engineering, 60(4): 57-60,1990.
12. Johnson, P.C., M.W. Kemblowski, J.D. Colthart, D.L.
Byers, and C.C. Stanley. A Practical Approach to Design,
Operation, and Monitoring of In Situ Soil Venting
Systems. Presented at the Soil Vapor Extraction
Technology Workshop on Soil Vacuum Extraction, U.S.
Environmental Protection Agency, Risk Reduction
Engineering Laboratory, Edison, New Jersey, June 28-29,
1989.
6. DePaoli, D.W., S.E. Herbes, M.G. Elliot, Capt. USAF.
Performance of In Situ Soil Venting System at Jet Fuel
Spill Site. Presented at the Soil Vapor Extraction
Technology Workshop on Soil Vacuum Extraction, U.S.
Environmental Protection Agency, Risk Reduction,
Engineering Laboratory, Edison, New Jersey, June
28-29,1989.
7. DiGiulio, D.C., J.S. Cho, R.R. DuPont, and M.W.
Kemblowski. Conducting Field Tests for Evaluation of Soil
Vacuum Extraction Application. Proceedings of Fourth
National Outdoor Action Conference on Aquifer
Restoration, Groundwater Monitoring, and Geophysical
Methods. NWWA, Las Vegas, Nevada, 1990.
8. Gannon, K., D.J. Wilson, A.N. Clarke, R.D. Mutch, Jr.,
and J.H. Clarke. Soil Cleanup by In Situ Aeration. II.
Effects of Impermeable Caps, Soil Permeability, and
Evaporative Cooling. Separation Science and Technology,
24(11): 831-862,1989.
13. Marley, M.C., S.D. Richter, B.L. Cliff, and P.E.
Nangeroni. Design of Soil Vapor Extraction Systems -A
Scientific Approach. Presented at the Soil Vapor Extraction
Technology Workshop on Soil Vacuum Extraction. U.S.
Environmental Protection Agency, Risk Reduction
Engineering Laboratory, Edison, New Jersey, June 28-29,
1989.
14. McCoy & Associates. Hazardous Waste Consultant. 3(2),
1985.
15. Mutch, R.D., and D.J. Wilson. Soil Cleanup by In Situ
Aeration. IV. Anisotropic Permeabilites. Separation
Science and Technology, 25(1): 1-29, 1990.
16. Oma, K.H., D.J. Wilson, and R.D. Mutch, Jr. In Situ
Vapor Stripping: The Importance of Nonequilibrium
Effects in Predicting Cleanup Time and Cost. Eckenfelder,
Inc., Nashville, Tennessee, 1990.
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17. Ostendorf, D.W., and D.H. Kampbell. Biodegradation of
Hydrocarbon Vapors in the Unsaturated Zone. Presented
at the Workshop on Soil Vacuum Extraction. Robert S.
Kerr Environmental Research Laboratory, Ada, Oklahoma,
April 27-28, 1989.
18. Payne, F.C., C.P. Cubbage, G.L. Kilmer, andL.H. Fish. In
Situ Removal of Purgeable Organic Compounds from
VadoseZone Soils. In: Proceedings of the 41st Purdue
University Industrial Waste Conference, West Lafayette,
Indiana, pp. 365-369,1986.
19. Trowbridge, B.E. and R.E. Malot. Soil Remediation and
Free Product Removal Using In Situ Vacuum Extraction
with Catalytic Oxidation. In: Proceedings, 4th National
Outdoor Action Conference of Aquifer Restoration,
Groundwater Monitoring and Geophysical Methods, Las
Vegas, Nevada, May 11-17, p. 559, 1990.
20. U.S. Environmental Protection Agency. Assessing UST
Corrective Action Technologies: Site Assessment and
Selection of Unsaturated Zone Treatment Technologies.
Risk Reduction Engineering Laboratory, Cincinnati, Ohio.
EPA/600/2-90/011,1990.
21. U.S. Environmental Protection Agency. Data Quality
Objectives for Remedial Response Activities. OSWER
Directive 9355.0-7B. Office of Emergency and Remedial
Response and Office of Waste Programs Enforcement,
Washington, D.C. EPA/540/G-87/003, 1987.
22. U.S. Environmental Protection Agency. Engineering
Bulletin: In Situ Soil Vapor Extraction Treatment. Risk
Reduction Engineering Laboratory, Cincinnati, Ohio.
EPA/540/2-91/006,1991.
23. U.S. Environmental Protection Agency. Guidance for
Conducting Remedial Investigations and Feasibility Studies
Under CERCLA. Office of Emergency and Remedial
Response, Washington, D.C. EPA/540/G-89/004, 1988.
24. U.S. Environmental Protection Agency. Guide for
Conducting Treatability Studies Under CERCLA, Interim
Final. Office of Emergency and Remedial Response,
Washington, D.C. EPA/540/2-89/058, 1989.
25. U.S. Environmental Protection Agency. Interim Guidelines
and Specifications for Preparing Quality Assurance Project
Plans. Office of Monitoring Systems and Quality
Assurance, Office of Research and Development,
Cincinnati, Ohio. QAMS-005/80, 1980.
26. U.S. Environmental Protection Agency. Inventory of
Treatability Study Vendors. EPA Risk Reduction
Engineering Laboratory, Cincinnati, Ohio.
EPA/540/2-90/003a, 1990.
27. U.S. Environmental Protection Agency. Recovery of
Landfill Gas at Mountain View. Engineering Site Study.
Solid Waste Management Office, Cincinnati, Ohio.
EPA/530/SW-587d orNTIS PB-267 373, 1977.
28. U.S. Environmental Protection Agency. ROD Annual
Report: FY 1989. Office of Emergency and Remedial
Response, Washington, D.C. EPA/540/8-90/006,1990.
29. U.S. Environmental Protection Agency. Soil Vapor
Extraction Technology: Reference Handbook. Risk
Reduction Engineering Laboratory, Cincinnati, Ohio.
EPA/540/2-91/003,1991.
30. U.S. Environmental Protection Agency. Soil Vapor
Extraction VOC Control Technology Assessment. Office
of Air Quality Planning and Standards, Research Triangle
Park, North Carolina. EPA/450/4-89-017, 1989.
31. U.S. Environmental Protection Agency. State of
Technology Review: Soil Vapor Extraction System
Technology. Hazardous Waste Engineering Research
Laboratory, Cincinnati, Ohio. EPA/600/2-89-024, 1990.
32. U.S. Environmental Protection Agency. Technology
Evaluation Report: SITE Program Demonstration Test,
Terra Vac In Situ Vacuum Extraction System, Groveland,
Massachusetts, Volume I. U.S. Environmental Protection
Agency, Risk Reduction Engineering Laboratory,
Cincinnati, Ohio. EPA/540/5-89/ 003a, 1989.
33. U.S. Environmental Protection Agency. Technology
Screening Guide for Treatment of CERCLA Soils and
Sludges. Office of Emergency and Remedial Response,
Washington, D.C. EPA/540/2-88/004,1988.
34. U.S. Environmental Protection Agency. Terra Vac In Situ
Vacuum Extraction System, Applications Analysis Report.
Risk Reduction Engineering Laboratory, Cincinnati, Ohio.
EPA/540/A5-89/003, 1989.
35. U.S. Environmental Protection Agency. Test Methods for
Evaluating Solid Waste. 3rd Ed., Office of Solid Waste and
Emergency Response, Washington, D.C. SW-846, 1986.
36. U.S. Environmental Protection Agency. Treatability
Studies Under CERCLA: An Overview. Office of Solid
Waste and Emergency Response, Washington, D.C.
OSWER Directive 9380.3-02FS.il, 1989.
37. U.S. Environmental Protection Agency. Verona Well
Field - Thomas Solvent Company, Battle Creek, Michigan,
Operable Unit Feasibility Study. Region V. 1985.
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38. Valsaraj,K.T.,LJ. Thibodeaux. Equilibrium Adsorption of 41. Wilson, D.J., A.N. Clarke, and R.D. Mutch, Jr. Soil
Chemical Vapors on Surface Soils, Landfills, and Cleanup by In Situ Aeration. III. Passive Vent Wells,
Landfarms - A Review. Journal of Hazardous Materials, Recontamination, and Removal of Underlying Nonaqueous
19: 79-99, 1988. PhaseLiquid. Separation Science and Technology, 24 (12):
939-979, 1989.
39. Wilson, D.J. Soil Cleanup by In Situ Aeration. V. Vapor
Stripping from Fractured Bedrock. Separation Science and 42. 40 CFR 286; Appendix I; 51 FR 40643, November 1986.
Technology, 25(3): 243-262, 1990.
40. Wilson, D.J., A.N. Clarke, and J.H. Clarke. Soil Cleanup
by In Situ Aeration. I. Mathematical Modeling. Separation
Science and Technology, 23(10 & 11): 991-1037,1988.
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SECTION 8
GLOSSARY
This glossary defines terms used in this guide. The
definitions apply specifically to the treatability study
process. They may have other meanings when used in
different contexts.
adsorption - The process by which a contaminant
molecule or other type of molecule is attracted and
held on a solid surface.
advection The process of transfer of fluids (vapors
or liquids) through a geologic formation in
response to a pressure gradient that may be
caused by changes in water table levels, rainfall
percolation, or induced lows (pressurized air or
vacuum).
air permeability A measure of the ability of a soil to
transmit gases. This property relates the pressure
gradient to the flow. Air permeability can be
measured in darcies, which are expressed in cm2.
aquifer A porous, underground geological
formation-often composed of limestone, sand,
or gravel-bounded by impervious rock or clay
and able to store water and transmit economic
quantities of water to wells and springs.
bentonite An expanding colloidal clay, largely made
up of the mineral sodium montmorillonite,
anhydrated aluminum silicate.
bulk density The amount of mass of a soil per unit
volume of soil; where mass is measured after all
waterhas been extracted and total volume includes
the volume of the soil itself and the volume of air
space between the soil grains.
capillary fringe The zone of a soil (porous medium)
above the water table within which water is drawn
by capillary action. The capillary fringe is usually
saturated and it is considered to be pat of the
vadose zone.
dense nonaqueous phase liquid (DNAPL) A liquid
consisting of a solution of free organic compounds
which is more dense than water. These liquids will
sink until they reach an impermeable geological
layer such as clay. DNAPL pools can be found
below the water table. DNAPLs are often
composed of chlorinated hydrocarbons.
Henry's Law The relationship between the partial
pressure of a compound and its equilibrium
concentration in a dilute aqueous solution through
a constant of proportionality known as the Henry' s
Law Constant. The compound is the solute portion
of the solution.
impermeable cap A ground covering (synthetic or
natural) that prevents the passage of air or water
into the ground. These are used to increase the
radius of influence of extraction wells and reduce
the infiltration of soil water.
injection well A well that serves as a conduit for
atmospheric air to strata below the surface of the
ground. Pressurized air is injected into the injection
well.
inlet well A well used during soil vapor extraction
through which air enters the soil under the
influence of the vacuum from the extraction well.
in situ treatment The process of treating a
contaminated matrix (soil, sludge, or ground water)
in place without excavation. In situ processes may
use physical, chemical, thermal, or biological
technologies to treat the site.
lead agency The Federal or State agency having
primary responsibility and authority for planning
and executing remediation at a CERCLA site.
light nonaqueous phase liquid (LNAPL) A liquid
consisting of a solution of free organic compounds
which is less dense than water. LNAPL will move
downward until it reaches the water table. LNAPL
pools can be found floating on the water table.
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mobility The ability of a contaminant to migrate from
its source.
molecular diffusion The process where molecules
tend to migrate from areas of high concentration to
areas of low concentration.
nonaqueous phase liquid (NAPL) A liquid
consisting of a solution of organic compounds.
partial pressure The portion of total vapor pressure
due to one or more constituents in a vapor mixture.
permeability A measure of a soil's ability to permit
fluid flow. Permeability, along with fluid viscosity
and density, are used to determine fluid
conductivity.
piezometerAn instrument used to measure pressure
head. Often used in reference to tubes inserted into
the soil for measuring water level in soil.
porosity The volume fraction of a rock, soil, or
unconsolid ated sediment not occupied by solid
material but usually occupied by water and/or air.
pressure gradient A pressure differential in a given
medium, such as water or air, which tends to
induce movement from areas of higher pressure to
areas of lower pressure.
pulsed venting A method of operation in which the
system vacuum, or vacuum to an individual
extraction well, is operated intermittently. During
periods when the vacuum is off, the contaminant
vapors re-equilibrate with contaminant in the
stationary phases. When the system is turned back
on, extracted vapors have higher concentrations.
Pulsed venting may be less expensive than
continuous operation due to lower power
consumption.
radius of influence The radial distance from an
extraction well that has adequate air flow for
effective removal of contaminants when a vacuum
is applied to the extraction well.
Raoult's Law A physical law which describes the
relationship between the vapor pressure of a
component over a solution, the vapor pressure of
the same component over pure liquid, and the mole
fraction of the component in the solution. The
component is the solvent portion of the solution.
For an ideal solution: P = (X)(P°)
Where:
P = vapor pressure of the component over the solution.
X = mole fraction of the component in the solution.
P° = vapor pressure of the pure component.
Resource Conservation and Recovery Act (RCRA)
A 1976 Federal law that established a regulatory
system to track hazardous substances from the
time of generation to disposal. Designed to prevent
new CERCLA sites from ever being created, RCRA
requires the use of safe and secure procedures in
the treatment, transport, storage, and disposal of
hazardous wastes. RCRA was amended in 1984 by
the Hazardous and Solid Waste Amendments
(HSWA).
Toxic Characteristic Leaching Procedure (TCLP)
The method for determining one of the four
hazardous waste characteristics defined under
RCRA (40 CFR 261.24). A waste is toxic if the TCLP
extract is found to contain concentrations of
certain metals, organic compounds, and pesticides
in excess of those listed in RCRA.
soil gas surveyInvestigation of the distribution of
soil gas concentrations in three dimensions. The
term may apply to the map or to data documenting
the soil gas concentrations.
vadose zone A subsurface zone containing water
below atmospheric pressure and gases at
atmospheric pressure (typically unsaturated).
vapor extraction well A well to which a vacuum is
applied. The applied vacuum provides a motive
force to remove contaminated vapors using
atmospheric air as a carrier gas.
vapor/liquidseparatorA device to separate, through
additional retention time, physical means, or
cooling, entrained liquids from a vapor stream.
vapor pressure The equilibrium pressure exerted on
the atmosphere by a liquid or solid at a given
temperature. Also a measure of a substance's
propensity to evaporate or give off vapors. The
higher the vapor pressure, the more volatile the
substance.
volatilization The process of transfer of a chemical
from the water or liquid or adsorbed phase to the
air or vapor phase. Solubility, molecular weight,
and vapor pressure of the liquid, and the nature of
the air-liquid/water interface, affect the rate of
volatilization.
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water table The water surface in an unconfined well screen The segment of well casing which has
aquiferat which the fluid pressure in the voids is at slots to permit the flow of liquid or air but prevent
atmospheric pressure. the passage of soil or backfill particles.
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APPENDIX A
GENERAL PROCEDURE FOR CONDUCTING
COLUMN TESTS
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Table A-1. General Procedure for Conducting Column Tests
Preparation
1. Calibrate vacuum/pressure sensors.
2. Calibrate air-flow meter.
3. Calibrate contaminant measuring device.
4. Check vacuum pump and perform any required maintenance.
5. Leak check equipment.
Field
1. Select sampling areas.
2. Collect sufficient sample material for analysis and to run a minimum of five tests.
3. Composite the sample material.
4. Seal sample containers and cool them to prevent loss of
volatiles.
Laboratory
1. Analyze composited samples for soil gas concentrations, contaminant concentration in the soil,
contaminant concentrations in TCLP leachate, moisture, density, and porosity.
2. Prepare five columns for testing.
Fill five columns with composited sample material. The material should be compacted to simulate
field densities.
3. Allow the columns to equilibrate to the temperature of the test.
4. Start the column testing under the following conditions (See section 4.2.2.)
Column 1 - Base test conditions; sacrifice at 1/2 estimated end-point
Column 2 - End-point determination (Use base test conditions.)
Column 3 - End-point determination (Use base test conditions.)
Column 4 - Duplicate of base test conditions
Column 5 - Low air-flow rate test
5. Collect the following data on a bi-hourly basis during the day:
Vacuum level
Ambient temperature
Air-flow rate
Humidifier liquid level
6. Collect the following effluent gas data twice daily for the base column and daily for the other columns
at the beginning of the run. When contaminant concentrations are not changing rapidly, the analyses
can be collected once every 2 to 3 days:
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Contaminant concentrations
Moisture content
Note that an on-line instrument also could be used to give continuous measurements.
7. Calibrate analytical instruments on the days used, or check calibration and recalibrate as needed.
8. Use porosity measurements to calculate air-flow volume required for one pore-volume exchange.
9. Plot the contaminant removal data versus time and versus the pore-volumes of air passed through
the column.
10. Determine end-point as discussed in section 4.2.2 of the text.
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APPENDIX B
GENERAL PROCEDURE FOR CONDUCTING
AIR PERMEABILITY TESTS
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Table B-1. General Procedure for Conducting Air Permeability Tests
Preparation
1. Calibrate vacuum/pressure sensors.
2. Calibrate air-flow meter.
3. Calibrate contaminant measuring device.
4. Check vacuum pump and perform any required maintenance.
5. Leak check equipment.
Field
1. Select areas for taking measurements.
2. Insert extraction and/or injection wells, and pressure probes.
3. Check for leaks and adequate sealing.
4. Establish an air flow. (Corresponding to 1 to 4 in Hg vacuum or pressure).
Measure pressure profiles and air-flow rate as functions of time.
Allow vacuum and air flow to stabilize.
Measure ambient or background contaminant concentrations in the surrounding air.
Measure contaminant concentrations and moisture level at the beginning and end of each run.
Plot the pressure profiles versus the log of time, and calculate the air permeability per
Johnson(12)or an equivalent method.
5. Increase air flow. (Increase vacuum by 2 in Hg if possible.)
Repeat above measurements.
6. Move probes to next position and repeat the above steps.
NOTE:
Different vacuums or pressures may be required for the testing, depending on local conditions. For
example, high vacuums may be required when testing the air permeability of bedrock.
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APPENDIX C
GENERAL PROCEDURE FOR CONDUCTING
FIELD VENT TESTS
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Table C-1. General Procedure for Conducting Field Vent Test
Preparation
1. Calibrate vacuum/pressure sensors.
2. Calibrate air-flow meter.
3. Calibrate contaminant measuring device.
4. Check vacuum pump and perform any required maintenance.
5. Leak check equipment.
Field
1. Select areas for taking measurements.
2. Drill vapor extraction well and air injection well (if applicable).
3. Insert pressure probes.
4. Check for leaks and adequate sealing of the well and probes.
5. Establish extraction flow.
Measure pressure profiles and air-flow rate as functions of time.
Allow vacuum and air flow to stabilize.
Measure contaminant concentrations before and after treatment system, carbon dioxide
(optional), moisture level in the effluent gas twice daily, and water level in the vapor-liquid
separator.
Measure ambient or background contaminant concentrations in the surrounding air.
Note any weather extremes (e.g., heavy rains, snow, etc.).
6. Determine screen placement, radius of influence, any need for an impermeable cap.
7. Measure contaminant concentrations in water collected at the end of the test.
8. Move to other areas of the site and repeat the test if site characteristics warrant further testing.
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APPENDIX D
COST-ESTIMATION DATA FOR IMPLEMENTING
SVE TECHNOLOGY
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Table D-1. SVE Cost Estimation
Components
Extraction Well
Construction
Casing
Screen
Sand or Gravel
Piping
Valves (Ball)
Joints (Elbow)
Water Table
Depression Pumps
Surface Seals
Bentonite
Polyethylene
HOPE
Asphalt
Blower (Rotary or
Ring)
Vapor/Liquid
Separators
Operating Flow range
size range (scfm)
2 inch
4 inch
6 inch
2 inch
4 inch
6 inch
2 inch
4 inch
6 inch
8 inch
2 inch
4 inch
6 inch
8 inch
2 inch
4 inch
6 inch
8 inch
45-95 gpm
0-1000 scfm
300-500 scfm
60hp 1,000 scfm
1,000- $3,500-
2, 000 gal 17,500
Cost
Capital
$2,000-5,000/well
PVC
$2-3/ft
$3-5/ft
$7-12/ft
$2-4/ft
$5-7/ft
$10-15/ft
$15-20/yd3
$1-2/ft
$2-4/ft
$6-10/ft
$12-16/ft
$60
$150
$700
$1,300
$11
$50
$100
$460
$3,700
$9.2/ft2
$0.25/ft2
$5/yd2
$5/yd2
$5,000-25,000
$13,000
$40,000
O&M
304 SS
$12-14fr
$23-25/ft
$36-40/ft
$15-17/ft
$27-31 /ft
$41-46/ft
$9. 5-11 /ft
$22-25/ft
$34-38/ft
$52-55/ft
$1,000
$2,000-
2,200
$3,200
$5,000
$20
$52
$300
$560
0.75xhp/hr
Notes
SCH. 40
SCH. 40
Any slot
Size
SCH 40
SCH 40
SCH 40
SCH 40
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Table D-1. SVE Cost Estimation (continued)
Components
Operating Flow range
size range (scfm)
Cost
Capital
O&M
Notes
Instrumentation
Vacuum Gauge
Flow (Annular)
Sampling Port
Gas Chromotography/
Photoionization Detector
$50-75
$300
$20-30
$20,000
Usually rented
Table D-2. SVE System Emission Control Costs
Treatment
Flow (scfm)
Rental
Capital
Operation
Notes
Carbon
Adsorption
Thermal
Incineration
Catalytic
Oxidation
100-500 $650/200 Ib can
$5,600/1 ,800 Ib
can
$1 9,500/5,700 Ib
can
50-570 $1 1 ,500-23,000
200 - 500 $65,000-80,000
500 -1 ,000 $50,000-90,000
1 ,000-5,000 $85,000-200,000
Carbon can be
reactivated.
Recovery and
disposal of
contaminant
is required.
Fuel Cost Natural gas
Propane
Fuel Cost May be
susceptible to
poisoning and
fouling.
U.S. Government Printing Office: 1991548-187/40630
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United States Center for Environmental Research BULK RATE
Environmental Protection Information POSTAGE & FEES PAID
Agency Cincinnati OH 45268 EPA
PERMIT No. G-35
Official Business
Penalty for Private Use, $300
EPA/540/2-91/019A
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