) Technologies For Treating MtBE
and Other Fuel Oxygenates
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May 2004
Technologies for Treating MtBE and Other Fuel Oxygenates
U.S. Environmental Protection Agency
Office of Solid Waste and Emergency Response
Office of Superfund Remediation and Technology Innovation
Washington, DC 20460
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Technologies for Treating MtBE and Other Fuel Oxygenates
TABLE OF CONTENTS
LIST OF ACRONYMS AND ABBREVIATIONS vi
FOREWORD vii
NOTICE AND DISCLAIMER viii
ACKNOWLEDGMENT viii
1.0 INTRODUCTION 1-1
1.1 What is the Purpose of This Report? 1-1
1.2 Who is the Intended Audience of This Report? 1-1
1.3 What Information Sources Were Used to Prepare This Report? 1-1
1.4 Considerations About the Performance and Cost Data Included in This Report 1-2
1.5 Report Organization 1-4
2.0 BACKGROUND 2-1
2.1 What are Fuel Oxygenates? 2-1
2.2 What Are the Sources of Oxygenates in the Environment? 2-2
2.3 What is the Prevalence of Contamination by Oxygenates in the Environment? 2-3
2.4 What are the Concerns About Contamination with Oxygenates? 2-4
2.5 How Are Oxygenates Assessed in the Environment? 2-5
2.6 How Do Oxygenates Migrate in the Environment? 2-6
2.7 How Do the Properties of Oxygenates Affect Treatment? 2-7
2.8 What Types of Technologies are Used in the Treatment of Soil, Groundwater, and
Drinking Water Contaminated with Oxygenates? 2-10
2.9 How Are Technologies Used to Treat Soil and Water Contaminated
with Oxygenates? 2-10
2.10 What Additional Technical Considerations are Associated with Remediating Sites
Contaminated with Oxygenates? 2-11
3.0 COMPARISON OF TREATMENT TECHNOLOGIES 3-1
3.1 What Types of Remediation Technology Projects were Considered
in this Comparison? 3-1
3.2 How Did These Remediation Technologies Perform? 3-2
3.3 What Did These Remediation Technologies Cost? 3-3
3.4 What Factors Should Be Considered When Identifying Technologies to Treat Fuel
Oxygenates? 3-5
4.0 TREATMENT TECHNOLOGIES 4-1
4.1 Air Sparging 4-2
4.
4.
4.
4.
4.
4.
.1 What is Air Sparging? 4-2
.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment? 4-2
.3 How is Air Sparging Applied to Treat Oxygenates? 4-3
.4 What Types of Projects Involve Air Sparging for Oxygenates? 4-4
.5 How Has Air Sparging Performed in Treating Oxygenates? 4-5
.6 What Costs Have Been Associated with Using Air Sparging
in Treating MtBE? 4-6
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.1.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment
Using Air Sparging? 4-7
4.1.8 Conclusions 4-8
4.1.9 Example Projects 4-9
4.2 Soil Vapor Extraction 4-9
4.2.1 What is Soil Vapor Extraction? 4-9
4.2.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?....4-10
4.2.3 How is Soil Vapor Extraction Applied to Treat Oxygenates? 4-10
4.2.4 What Types of Projects Involved Soil Vapor Extraction
to Treat Oxygenates? 4-13
4.2.5 How Has SVE Performed in Treating Oxygenates? 4-14
4.2.6 What Costs Have Been Associated with Using SVE in Treating MtBE? 4-15
4.2.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment
using SVE? 4-15
4.2.8 Conclusions 4-16
4.2.9 Example Projects 4-17
4.3 Multi-Phase Extraction 4-17
4.3.1 What is Multi-Phase Extraction? 4-17
4.3.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?....4-17
4.3.3 How is MPE Applied to Treat Oxygenates? 4-18
4.3.4 What Types of Projects Involve MPE for Treating Oxygenates? 4-19
4.3.5 How Has MPE Performed in Treating Oxygenates? 4-20
4.3.6 What Costs Have Been Associated with Using MPE in Treating MtBE? 4-21
4.3.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment
using MPE? 4-21
4.3.8 Conclusions 4-22
4.3.9 Example Projects 4-22
4.4 In Situ Bioremediation 4-23
4.4.1 What is Bioremediation? 4-23
4.4.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?....4-24
4.4.3 How is Bioremediation Applied to Treat Oxygenates? 4-26
4.4.4 What Types of Projects Involved Bioremediation to Treat Oxygenates? 4-28
4.4.5 How Has In Situ Bioremediation Performed in Treating Oxygenates? 4-29
4.4.6 What are the Costs of Using In Situ Bioremediation to Treat Oxygenates? 4-30
4.4.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment
using In Situ Bioremediation? 4-31
4.4.8 Conclusions 4-31
4.4.9 Example Projects 4-32
4.5 In Situ Chemical Oxidation 4-34
4.5.1 What is In Situ Chemical Oxidation? 4-34
4.5.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?....4-34
4.5.3 How is In Situ Chemical Oxidation Applied to Treat Oxygenates? 4-35
4.5.4 What Types of Projects Involve In Situ Chemical Oxidation
for Oxygenates? 4-37
4.5.5 How Has In Situ Chemical Oxidation Performed in Treating Oxygenates? 4-38
4.5.6 What Are the Costs of Using In Situ Chemical Oxidation to Treat MtBE? 4-39
4.5.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment
using In Situ Chemical Oxidation? 4-39
4.5.8 Conclusions 4-40
4.5.9 Example Projects 4-41
4.6 Groundwater Pump-and-Treat and Drinking Water Treatment 4-41
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.6.1 What is Groundwater Extraction for Pump-and-Treat and Drinking Water
Treatment? 4-41
4.6.2 How Do the Properties of MtBE and Other Oxygenates Affect Groundwater
Extraction? 4-42
4.6.3 How is Pump-and-Treat Applied to Treat Oxygenates? 4-42
4.6.4 What Projects Have Involved Pump-and-Treat for Treating Oxygenates? 4-43
4.6.5 How Has Pump-and-Treat Performed in Treating Oxygenates? 4-43
4.6.6 What Costs Have Been Associated with Using Pump-and-Treat in Treating
MtBE? 4-45
4.6.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment
Using Pump-and-Treat? 4-46
4.6.8 Conclusions 4-47
4.6.9 Example Projects 4-48
4.7 Treatment of Extracted Groundwater Used in Pump-and-Treat and Drinking Water
Treatment Systems 4-48
4.7.1 What is Above-Ground Treatment for Extracted Groundwater? 4-48
4.7.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?....4-49
4.7.3 How are Technologies Used for Above-Ground Treatment of Oxygenates? ...4-51
4.7.4 What Projects Have Been Used for Above-Ground Treatment of Extracted
Groundwater? 4-53
4.7.5 How Has Above-Ground Treatment Performed in Treating Oxygenates? 4-54
4.7.6 What Costs Have Been Associated with Using Pump-and-Treat in Treating
MtBE? 4-54
4.7.7 What Factors May Affect the Performance and Cost of Above-Ground Treatment
for Oxygenates? 4-55
4.7.8 Conclusions 4-55
4.7.9 Example Projects 4-56
4.8 Other Treatment Technologies: Phytoremediation, PRBs, and Thermal Treatment ....4-58
4.8.1 What Other Technologies are used to Treat MtBE and Other Oxygenates? ....4-58
4.8.2 How Is Phytoremediation Used in Treatment of Oxygenates? 4-58
4.8.3 How Are PRBs Used in Treatment of Oxygenates? 4-59
4.8.4 How Is In Situ Thermal Treatment Used for Remediation of Oxygenates? 4-60
4.8.5 What Factors may Affect the Performance and Cost of Phytoremediation, PRBs,
or Thermal Treatment? 4-61
4.8.6 Conclusions 4-61
5.0 NON-TREATMENT REMEDIES 5-1
5.1 Excavation 5-1
5.2 Free Product Recovery 5-2
5.3 Monitored Natural Attenuation 5-2
5.4 Institutional Controls 5-3
6.0 REFERENCES 6-1
in
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Technologies for Treating MtBE and Other Fuel Oxygenates
LIST OF TABLES
2-1 State Cleanup Levels for Fuel Oxygenates in Groundwater 2-5
2-2 Properties of Fuel Oxygenates and Other Fuel Constituents 2-8
3-1 Description of MtBE Remediation Technology Projects (323 Projects) 3-2
3-2 Performance Data for Completed MtBE Remediation Technology Applications (105
Applications1 Providing Data) 3-2
3-3 Duration of Completed MtBE Remediation Technology Applications (89 Applications
Providing Data) 3-3
3-4 Total Project Cost1 Data for MtBE Remediation Technology Applications (127
Applications Providing Data) 3-4
3-5 General Factors to Consider When Identifying a Remediation Technology for Sites
Contaminated with Fuel Oxygenates 3-5
3-6 General Factors to Consider When Selecting a Remediation Technology for Sites
Contaminated with Fuel Oxygenates 3-6
4-1 Types of Technologies Used to Treat MtBE and Other Fuel Oxygenates 4-1
4.1-1 General Information on 123 Air Sparging Projects 4-5
4.1-2 Completed Air Sparging Projects - Performance Summary for 19 Projects 4-6
4.1-3 Ongoing Air Sparging Projects - Performance Summary for 104 Sites 4-6
4.2-1 General Information on 138 SVE Projects* 4-13
4.2-2 Performance Summary for 19 Completed SVE Projects 4-14
4.2-3 Performance Summary for 119 Ongoing SVE Projects 4-15
4.3-1 Contaminant Properties Relevant to MPE 4-18
4.3-2 General Information on 13 MPE Projects 4-19
4.3-3 Completed MPE Projects - Performance Summary for 3 Projects 4-20
4.3-4 Ongoing MPE Projects - Performance Summary for 7 Sites 4-20
4.4-1 MtBE Biodegradation Mechanisms and Products 4-26
4.4-2 General Information from 73 Engineered Bioremediation Projects 4-28
4.4-3 Completed In Situ Bioremediation Projects Performance Summary for 31 Projects 4-29
4.4-4 Ongoing In Situ Bioremediation Projects Performance Summary for MtBE at 38 Sites 4-29
4.5-1 General Information on 21 In Situ Chemical Oxidation Projects 4-37
4.5-2 Completed In Situ Chemical Oxidation Projects - Performance Summary for 8 Projects 4-38
4.5-3 Ongoing In Situ Chemical Oxidation Projects - Performance Summary for 13 Sites 4-39
4.6-1 General Information about 100 Pump-and-Treat Projects 4-43
4.6-2 MtBE Performance Summary for 21 Completed Pump-and-Treat Proj ects 4-44
4.6-3 MtBE Performance Summary for 62 Ongoing Pump-and-Treat Proj ects 4-44
4.6-4 MtBE Performance Summary for 12 Ongoing Drinking Water Treatment Systems 4-45
4.6-5 TEA Performance Data for 9 Pump-and-Treat Projects 4-45
4.6-6 Cost Summary for 43 Pump-and-Treat and Drinking Water Treatment Proj ects 4-46
4.7-1 Above-Ground Treatment Technologies Used at 70 Groundwater Pump-and-Treat
Remediation and Drinking Water Treatment Projects 4-53
4.7-2 Cost Summary for Pump-and-Treat - By Aboveground Treatment Type 4-54
4.7-3 Estimated Range of Unit Costs for Above ground Treatment Technologies 4-55
4.8-1 General Information on 8 Projects Using Phytoremediation 4-59
IV
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Technologies for Treating MtBE and Other Fuel Oxygenates
LIST OF FIGURES
2-1 Molecular Structures of Common Fuel Oxygenates 2-2
2-2 Physical Properties of Fuel Oxygenates Relative to Benzene 2-9
2-3 Relative Solubility and Henry's Law Constants for Selected Fuel Oxygenates
(Henry's Law data for MtBE, TEA, and Benzene based onZogorski et. al., 1997) 2-9
4.1-1 Ranges of Henry s Law Constants (Dimensionless) for Common Fuel Oxygenates 4-3
4.2-1 Ranges of Vapor Pressures for Common Fuel Oxygenates 4-10
4.4-1 Proposed Degradation Pathway of MtBE and Other Oxygenates
(Church and Tratnyek, 2000) 4-25
4.4-2 Typical Zones Downgradient of Petroleum Contaminant Source 4-27
4.5-1 Stoichiometric Mineralization of Oxygenates Using Hydrogen Peroxide 4-34
4.7-1 Relative Ranges of Partition Coefficients for Fuels Oxygenates and BTEX 4-50
APPENDIX
MtBE Treatment Profile Data (see www.cluin.org/mtbe)
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Technologies for Treating MtBE and Other Fuel Oxygenates
LIST OF ACRONYMS AND ABBREVIATIONS
AST Aboveground storage tank
bgs Below ground surface
BTEX Benzene, toluene, ethylbenzene, and
xylenes
cfm Cubic feet per minute
C1O2" Chlorine dioxide
CLU-IN EPA's Hazardous Waste CLeanUp
INformation System
CO2 Carbon dioxide
COD Chemical oxygen demand
cy Cubic yard
DIPE Diisopropyl ether
DL Detection limit
DPE Dual-phase extraction
EPA United States Environmental
Protection Agency
EtBE Ethyl tert-butyl ether
FRTR Federal Remediation Technologies
Roundtable
Ft Feet/foot
GAC Granular activated carbon
gals Gallons
gpm Gallons per minute
H2O2 Hydrogen peroxide
HP Horse power
1C Institutional controls
K Hydraulic conductivity
LNAPL Light non-aqueous phase liquid
Ibs Pounds
MC Mixed culture
MCL Maximum Contaminant Level
mg/L Milligrams per liter
MNA Monitored natural attenuation
MnO4 Permanganate
mm Hg Millimeters of mercury
MPE Multi-phase extraction
MtBE Methyl tert-butyl ether
NAPL Non-aqueous phase liquid
ND Non detect
NEIWPCC New England Interstate Water
Pollution Control Commission
NO3" Nitrate
NOM Natural organic matter
NSCEP National Service Center for
Environmental Publications
O3 Ozone
OC1" Hypochlorite
O&M Operation and maintenance
Oxyfuel Oxygenated fuel
ppmv Parts per million by volume
PRB Permeable reactive barrier
psi Pounds per square inch
PVC Polyvinyl chloride
RCRA Resource Conservation and
Recovery Act
RFG Reformulated gasoline
RO Reverse osmosis
ROI Radius of influence
S2O8 Persulfate
SC Single culture
scfm Standard cubic feet per minute
SERDP Strategic Environmental Research
and Development Program
SO4"2 Sulfate
SSTL Site specific target level
SVE Soil vapor extraction
TAA Tert-amyl alcohol
TAEE Tert-amyl ethyl ether
TAME Tert-amyl methyl ether
TEA Tert-butyl alcohol
TBF Tert-butyl formate
TPE Two-phase extraction
TSP Trisodium phosphate dodecahydrate
USAGE United States Army Corps of
Engineers
UST Underground storage tank
UV Ultraviolet
VE/GE Vapor extraction/groundwater
extraction
VOC Volatile organic compound
ug/kg Microgram per kilogram
ug/L Microgram per liter
urn Micrometer
ZOI Zone of influence
VI
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Technologies for Treating MtBE and Other Fuel Oxygenates
FOREWORD
Fuel oxygenates, including methyl tert-butyl ether (MtBE), have been widely used in the United States for
the past several decades as an additive to gasoline intended to either boost octane ratings or to reduce air
pollution. The gasoline containing these oxygenates has been stored in aboveground and underground
storage tanks at a wide range of facilities, including refineries, terminals, service stations, and by end
users; and gasoline has been transported throughout the U.S. via pipeline, barge, rail, and truck. As a
result of leaks and spills, MtBE, other fuel oxygenates, and other gasoline components have been found in
soil and groundwater at these sites. Federal and state studies have found that these components, including
MtBE, have reached drinking water sources in many locations, including areas where the use of
oxygenated fuel has not been mandated.
The U.S. Environmental Protection Agency (EPA) has identified several hundred MtBE-contaminated
sites that have performed treatment of soil and groundwater to remove or destroy MtBE. Many of these
sites have also treated other fuel components, primarily benzene, toluene, ethylbenzene, and xylene
(BTEX), and some have treated fuel oxygenates other than MtBE. Although others have reported about
treatment technologies for MtBE cleanup, only limited information has been published about cleanup of
other oxygenates. These oxygenates include ether compounds, such as ethyl tert-butyl ether (ETBE), tert-
amyl methyl ether (TAME), diisopropyl ether (DIPE), and tert-amyl ethyl ether (TAEE), as well as
alcohol compounds, such as tert-butyl alcohol (TEA), tert-amyl alcohol (TAA), ethanol, and methanol.
This report provides an overview of the treatment technologies used to remediate groundwater, soil, and
drinking water contaminated with MtBE and other fuel oxygenates. The treatment methods discussed
include air sparging, soil vapor extraction, multi-phase extraction, in situ and ex situ bioremediation, in
situ chemical oxidation, pump-and-treat, and drinking water treatment. Information in the report can be
used to help evaluate those technologies based on their effectiveness at specific sites. The report
summarizes available performance and cost information for these technologies, examples of where each
has been used, and additional sources of information.
This report may be useful to cleanup professionals and researchers; federal, state, and local regulators;
remediation consultants; water treatment plant designers and operators; and other interested parties. The
report is intended to be a screening tool that can be used to identify treatment technologies for soil,
groundwater, and drinking water contaminated with MtBE and other fuel oxygenates. However, it should
be considered only as a starting point for such an analysis. The applicability of a particular treatment
technology is site specific, and depends heavily on factors such as site conditions and treatment goals.
Decisions about the use of a specific treatment approach will require further analysis, possibly including
treatability or pilot-scale studies. This report is not a guidance document and is not intended to prescribe
specific treatment technologies for certain types of applications. It was written assuming that readers
have a basic technical understanding of the treatment technologies and the chemistry discussed.
VII
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Technologies for Treating MtBE and Other Fuel Oxygenates
NOTICE AND DISCLAIMER
Preparation of this report has been funded wholly or in part by the U.S. Environmental Protection Agency
(EPA) under Contract Number 68-W-02-034. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use. A limited number of printed copies of Technologies
for Treating MtBE and Other Fuel Oxygenates is available free-of-charge by mail or by facsimile from:
U.S. EPA/National Service Center for Environmental Publications (NSCEP)
P.O. Box 42419
Cincinnati, OH 45242-2419
Telephone: (513) 489-8190 or (800) 490-9198
Fax: (513)489-8695
A PDF version of this report is available for viewing or downloading from the Hazardous Waste Cleanup
Information (CLU-IN) system web site at http: //www .cluin. org/mtbe. Printed copies of the report can
also be ordered through that web address, subject to availability. For more information regarding this
report, contact Linda Fiedler, EPA Office of Superfund Remediation and Technology Innovation, at
(703) 603-7194 or fiedler.linda@epa.gov.
ACKNOWLEDGMENT
Special acknowledgment is given to the federal and state staff and other remediation professionals for
providing information for this document. Their cooperation and willingness to share their expertise about
treatment technologies used to address MtBE and other oxygenates encourages their application at other
sites.
Vlll
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Technologies for Treating MtBE and Other Fuel Oxygenates
1.0 INTRODUCTION
1.1 What is the Purpose of This Report?
This report provides an overview of treatment technologies used to remediate groundwater, soil, and
drinking water contaminated with methyl tert-butyl ether (MtBE) and other fuel oxygenates. The purpose
of this report is to:
Identify technologies used to treat MtBE and other fuel oxygenates
Help screen those technologies based on their effectiveness in treating particular media and
contaminants under specific site conditions and application requirements
Provide available performance and cost information about the use of those technologies
Provide additional information relevant to the treatment of MtBE and other fuel oxygenates
Identify additional sources of information
This report is intended to be a screening tool that can be used to identify treatment technologies for
groundwater, soil, and drinking water contaminated with MtBE and other fuel oxygenates. However, it
should be considered only as a starting point for such an analysis. The applicability of a particular
treatment technology is site specific and depends heavily on factors such as site conditions and treatment
goals. Decisions about the use of a specific treatment technology will require further analysis, possibly
including treatability studies.
The performance and cost data in the report can help cleanup professionals, site managers, remediation
consultants, and others gain a broader understanding of the types of technologies that have been used to
treat MtBE and other fuel oxygenates, as well as the types of information available from sites that have
used those technologies. This report also provides information about the factors that potentially affect the
performance and cost of those technologies.
This report is not a guidance document and is not intended to prescribe specific treatment technologies for
certain types of applications. It was written assuming that readers have a basic technical understanding of
the treatment technologies and chemistry discussed. Readers requiring additional background
information on the treatment of MtBE and other oxygenates are referred to the information sources listed
in Section 6.0.
1.2 Who is the Intended Audience of This Report?
The information presented in this report may be useful to cleanup professionals and researchers; federal
(Superfund and Resource Conservation and Recovery Act (RCRA) remediation site managers), state, and
local regulators; remediation consultants; water treatment plant designers and operators; and other
interested parties.
1.3 What Information Sources Were Used to Prepare This Report?
The sources of information used to prepare this report include EPA's MtBE Treatment Profiles Website,
located at http://www.cluin.org/products/mtbe, technical publications, and other industry sources. As
discussed below and summarized in the text box on the following page, EPA's treatment profiles website
presents information about drinking water and remediation sites that treat soil and groundwater for MtBE.
Additional information sources used to prepare this report included EPA reports, other technical
publications, recent conference proceedings (such as from the National Ground Water Association and
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Technologies for Treating MtBE and Other Fuel Oxygenates
Battelle conferences), and contacts knowledgeable about projects involving remediation of MtBE,
including project managers and vendors. A list of these sources is included at the end of this report, with
specific sources cited throughout the body of the report. A complete summary of the project data
included in this report is contained in Appendix A. EPA has provided a contaminant focus area for MtBE
at www.cluin.org/mtbe.
EPA's MtBE Treatment Profiles Website
EPA's MtBE Treatment Profiles Website, available at www.cluin.org/products/mtbe. provides site-specific data
about the use of in situ and ex situ technologies that have been used to treat MtBE in groundwater, soil, and drinking
water. Profiles contain the following types of information, as available: project information, such as site
background and setting, contaminants and media treated, and area of contamination and quantity treated; technology
design and operation; cost and performance information, including cleanup goals; points of contacts; and references.
Profiles are available for nearly one dozen types of technologies, and are updated/expanded several times a year.
The profiles are based on information provided by site managers, regulatory officials, and technology providers, as
well as from published reports and conference proceedings. The website can be searched using pick lists for
selected parameters or by using a list of all available profiles. Each profile has a varying level of detail, depending
on the data and information that was available.
As of January 2003, the website contained information about 323 projects, including information about the
technology used, project scale, performance, and cost. Twenty-nine of these projects reported data on other fuel
oxygenates, including tert-butyl alcohol (TEA) for all 29 projects, tert-amyl methyl ether (TAME) for 3 projects,
ethanol for 3 projects, and diisopropyl ether (DIPE) for 1 project. This report discusses information available as of
January 2003; however, it should be noted that the web site since has been expanded to include information about
additional projects; as of April 2004, the web site included a total of 390 projects. A summary of information about
the 390 projects was presented at the National Ground Water Association conference on MtBE and Perchlorate, June
4, 2004, in a paper titled "Application and Performance of Technologies for Treatment of MtBE and Other
Oxygenates", available at www.cluin.org/mtbe.
The performance and cost data included in this report are primarily based on the database of information
from 323 site cleanups (projects) that involved treatment of MtBE and other fuel oxygenates. No
additional testing of technologies was performed during the preparation of this report, and no independent
review was performed for the data in the database. Generally, the available information included
information about technology design and operation, such as number and types of wells, additives, and
flow rates, as well as use of multiple technologies for a given project. In addition, project scale (full,
pilot, bench) and status (completed or ongoing) were typically identified. In some cases, only interim
data for ongoing projects are available.
1.4 Considerations About the Performance and Cost Data Included in This Report
The treatment performance and cost data presented in this report provide users with:
Data from actual field applications, focusing on full-scale and relatively large field
demonstrations, including design and operation information about use of treatment technologies
at more than 300 projects
Information about both conventional and innovative technologies that have been used to
successfully treat MtBE
Preliminary information about treatment of fuel oxygenates other than MtBE
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Technologies for Treating MtBE and Other Fuel Oxygenates
Lessons learned about the application of these technologies to cleanup media contaminated with
MtBE and other fuel oxygenates
The performance and cost data presented in this report are based on the data provided by project
managers and others in the source materials used to prepare the treatment profiles website. There was
variation among the profiles in the level of detail for performance and cost data by project. Many of the
treatment profiles contained only limited information about treatment performance and cost, generally
including a maximum concentration of MtBE for before-treatment and a maximum concentration after-
treatment. These concentrations often were limited to discussing how the treatment technology
performed relative to the cleanup goals for the site. Most treatment profiles did not provide detailed
performance data, such as MtBE concentration versus time over the duration of the project, or statistical
evaluations of performance data with confidence limits.
Treatment performance and cost are site specific and depend on many factors. These factors include site
conditions (such as soil types, permeability, conductivity, redox conditions, and degree of heterogeneity),
technology design and operation, and regulatory considerations such as cleanup levels. Additional factors
include duration of the release (such as a gasoline leak), presence of down-gradient water supply wells,
and distribution of contaminants in soil and groundwater.
While EPA has not promulgated a federal cleanup level for MtBE, some states have established cleanup
levels. However, as shown in Table 2-1, these vary by state, ranging from 5 to 202,000 ug/L, a difference
of more than three orders of magnitude. Because of the variation in MtBE cleanup levels, after-treatment
MtBE concentrations are reported based on information provided in the source documents, and are not
compared against a common cleanup level for all projects.
Projects generally reported concentrations of MtBE in groundwater or drinking water, with only limited
projects reporting MtBE concentrations in soil. As such, the technology performance information in this
report is presented primarily in terms of changes in concentration of MtBE in water. Performance data
are shown as the highest concentration reported prior to beginning treatment and the highest concentration
after treatment was completed (shown as "final concentration"). For projects that are ongoing, the final
concentration shown is the most current concentration reported in the source document. Final
concentrations identified in source documents as below a reported detection limit (DL), but which do not
provide a DL, are shown in this report as non-detect (ND).
For projects where more than one technology was used, such as a site that used air sparging, in situ
chemical oxidation, and SVE, performance information is presented under each of the technologies used
for that project.
With regard to treatment cost data, this report provides a summary of available data based on information
in the source materials. These cost data are intended to give a broad indication of the types of costs
associated with cleanup projects, and users should be cautious about drawing conclusions about the cost
of cleanup projects at specific sites based on these data. As discussed in more detail later in the report,
very few projects provided sufficient information to calculate a unit cost for treatment.
In addition, cost data are presented in terms of the total cost for cleaning up contaminated sites. In some
cases, the specific components that make up the total cost were not provided in the source materials, such
as for capital or operation and maintenance (O&M) activities. In other cases, the types of contaminants
present at the sites, other than MtBE, were not identified in the source materials. Sites may have been
contaminated with gasoline components such as petroleum hydrocarbons, as well as oxygenates, and the
treatment costs reported could be for cleanup of gasoline components as well as the oxygenates. For
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Technologies for Treating MtBE and Other Fuel Oxygenates
example, for a specific project, most of the cost for cleanup may be due to gasoline components other
than oxygenates.
EPA recently prepared a more detailed analysis of treatment cost for in situ treatment of fuel oxygenates.
The paper, "Cost of In Situ Treatment of Fuel Oxygenates", was presented at the National Ground Water
Association conference on Remediation: Site Closure and the Total Cost of Cleanup, New Orleans, held
November 13-14, 2003, and is available at www.cluin.org/mtbe.
1.5 Report Organization
The remainder of this report provides a summary of the information available about the treatment of
MtBE and other fuel oxygenates at the 323 projects reviewed and from other industry sources. Chapter 2
provides background information about fuel oxygenates, including information about their properties.
Chapter 3 provides a comparison of the treatment technologies used to treat oxygenates, while Chapter 4
includes technology-specific discussions for technologies used to treat soil, groundwater, and drinking
water. Chapter 5 provides information about non-treatment remedies. Chapter 6 contains a list of the
references used to prepare this report. A complete summary of the project data included in this report is
contained in Appendix A, available through www.cluin.org/mtbe. This appendix is organized by
treatment technology and contains a summary of key information for each project.
1-4
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Technologies for Treating MtBE and Other Fuel Oxygenates
2.0 BACKGROUND
2.1 What are Fuel Oxygenates?
Fuel oxygenates are oxygen-containing compounds used as gasoline additives to increase octane ratings
and produce cleaner burning fuel. The common oxygenates fall into two major chemical groups - ether
compounds, consisting of organic compounds characterized by an oxygen atom linking two hydrocarbon
groups; or alcohols, consisting of an alkyl group (such as methyl, ethyl, or isopropyl) bonded to a
hydroxyl (oxygen-hydrogen) group. In addition to MtBE and ethanol, other common oxygenates include
TEA, TAME, ethyl tert-butyl ether (EtBE), and DIPE. Tert-amyl ethyl ether (TAEE), tert-amyl alcohol
(TAA), and methanol have also been used to a lesser extent. Figure 2-1 shows the molecular structure of
commonly-used oxygenates. Some of these oxygenates could also be present in commercial formulations
of other oxygenates as by-products or degradation products. For example, TEA is often found in
commercial formulations of MtBE.
Oxygenates came into widespread use in the U.S. in the late 1970s as an octane booster, replacing alkyl
lead additives, which were being phased out in an effort to reduce lead emissions from vehicles. The use
of oxygenates in gasoline was increased after the passage of the 1990 Clean Air Act Amendments that
included requirements to increase the oxygen content of fuel to reduce air emissions. The amendments
required the use of oxygenated fuel (Oxyfuel) with a minimum of 2.7 percent by weight oxygen in 39
carbon monoxide non-attainment areas during wintertime and Reformulated Gasoline (RFG) with a
minimum of 2.0 percent by weight during the remainder of the year (Blue Ribbon Panel on Oxygenates in
Gasoline, 1999).
In 1998, approximately 30 percent of all gasoline in the U.S. contained oxygenates. At that time, MtBE
was the most common fuel oxygenate, present in more than 80 percent of oxygenated fuels. However,
due to increasing restrictions on the use of MtBE, this percentage has decreased over the past several
years. In 1998, ethanol was the second most common fuel oxygenate, present in about 15 percent of
oxygenated fuels. Other oxygenates were used in the remaining 5 percent of oxygenated fuels. As of
2002, 17 states and the District of Columbia were required to use gasoline that contains MtBE or other
oxygenates to reduce air pollution. Recent surveys have found that MtBE is present in states that did and
did not use RFG. MtBE has been found in gasoline, as well as heating oil and diesel fuel. Sources of
MtBE included areas used for storage, transportation, and use (McGarry, 2002).
The following documents contain additional information on the historic use of oxygenates:
Blue Ribbon Panel on Oxygenates in Gasoline. 1999. Achieving Clean Air and Clean Water:
The Report of the Blue Ribbon Panel on Oxygenates in Gasoline. EPA 420-R-99-021.
http://www.epa.gov/oms/consumer/fuels/oxvpanel/blueribb.htm
EPA. 1998. MtBE Fact Sheet #3: Use and Distribution of MtBE and Ethanol. EPA Office of
Underground Storage Tanks. EPA 625-K-98-001. September.
http://www.epa.gov/swerustl/mtbe/mtbefs3.pdf
2-1
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Technologies for Treating MtBE and Other Fuel Oxygenates
Figure 2-1. Molecular Structures of Common Fuel Oxygenates
Methyl tert-butyl ether
(MTBE)
Ethyl tert-butyl ether
(ETBE)
tert - Amyl methyl ether
(TAME)
Diisopropyl ether
(DIPE)
Ethanol
tert-Butyl alcohol
(TEA)
CH,
H3C- C- O- CH3
CH,
CH,
H3C-C-O-CH2-CH3
CH,
CH,
CH,
H3C- C- O- CH3
CH,
CH,
CH,
H3C-CH-0-CH-CH3
H3C -CH2OH
CH,
H3C-C-OH
CH-,
2.2 What Are the Sources of Oxygenates in the Environment?
As discussed above, oxygenates have been widely used in the U.S. for the past several decades as an
additive to gasoline intended to either boost octane ratings or to reduce air pollution. A significant
proportion of the more than 100 billion gallons of gasoline used in the U.S. annually has contained MtBE
2-2
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Technologies for Treating MtBE and Other Fuel Oxygenates
and other oxygenates at greater than 10 percent by volume. The volume of MtBE, ethanol, and other
oxygenates used in RFG and Oxyfuel in 1997 was estimated to be about 11 million, 2 million, and
700,000 gallons, respectively (White et al, 2002). The gasoline containing these oxygenates is stored in
aboveground storage tanks (ASTs) and underground storage tanks (USTs) at a wide range of facilities,
including refineries, terminals, service stations, and by end users; gasoline has been transported
throughout the U.S. via pipeline, barge, rail, and truck. There are an estimated 3.7 million USTs in the
U.S., including 700,000 regulated gasoline USTs at approximately 250,000 facilities and approximately 3
million underground fuel storage tanks that are exempt from federal regulations (for example, certain
farm and residential and home heating oil tanks) (Blue Ribbon Panel Report, 1999). Gasoline has been
released to the environment through spills and leaks from ASTs and USTs, as well as from
manufacturing, storage, and transport operations.
2.3 What is the Prevalence of Contamination by Oxygenates in the Environment?
MtBE has been detected nationwide in soil and groundwater. Federal and state studies have found that
MtBE contamination has reached drinking water sources in many locations, including areas where the use
of oxygenated fuel has not been mandated (GAO, 2002). This MtBE contamination has also been
documented in surface water bodies resulting from direct spills, storm water runoff, and emissions from
watercraft. The following federal and state studies contain additional information on the extent of
contamination by MtBE:
GAO. 2002. Testimony Before the Subcommittee on Environment and Hazardous Materials,
Committee on Energy and Commerce, House of Representatives, Environmental Protection,
MtBE Contamination from Underground Storage Tanks, Statement of John Stephenson, Director,
Natural Resources and Environment. GAO.02.753T. May 21. http://www.gao.gov/
New England Interstate Water Pollution Control Commission (NEPvVPCC). 2003. A Survey of
State Experience with MtBE Contamination at LUST Sites. August.
http://www.neiwpcc.org/mtbesum.pdf
Lawrence Livermore National Laboratory. 1998. An Evaluation of MtBE Impacts to California
Groundwater Resources. UCRL-AR-130897. July 11.
http://www-erd.llnl.gov/mtbe/pdf/mtbe.pdf
Maryland Department of the Environment. 2001. The Task Force on the Environmental Effects
of MtBE. Final Report. December.
http://www.mdarchives.state.md.us/msa/mdmanual/26excom/defunct/html/23mtbe.html
Of the 44 states that reported testing for MtBE at leaking tank sites, 35 states reported finding MtBE in
the groundwater at least 20 percent of the time they sampled for it. Twenty four states reported finding
MtBE at least 60 percent of the time (GAO, 2002).
Information about the prevalence of other oxygenates in the environment is limited. However, there is
evidence that other oxygenates may be found at sites contaminated with MtBE; non-MtBE oxygenates
were identified as a contaminant at 29 of the projects in the database. In addition, several surveys,
including those identified below, have assessed the nature and extent of contamination with other
oxygenates within the U.S.
U.S. Geological Survey. 2003. A National Assessment of Volatile Organic Compounds (VOCs)
in Water Resources of the U.S. Summer 2003. http://sd.water.usgs.gov/nawqa/vocns/
2-3
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Technologies for Treating MtBE and Other Fuel Oxygenates
American Water Works Research Foundation. 2003. Occurrence of MtBE and VOCs in
Drinking Water Sources of the U.S. http: //www. awwarf. or g
New England Interstate Water Pollution Control Commission (NEIWPCC). 2003. A Survey of
State Experience with MtBE Contamination at LUST Sites. August.
http://www.neiwpcc.org/mtbesum.pdf
2.4 What are the Concerns About Contamination with Oxygenates?
There have been several assessments of research concerning the health effects of MtBE and other
oxygenated fuels (National Science and Technology Council, 1997; California EPA, 1999). Recently,
results from research were published about a study of the movement of MtBE between tissues in human
volunteers (Prah, 2004). EPA is currently updating its assessment of the health effects of MtBE.
There is uncertainty as to what levels of MtBE in drinking water cause a risk to public health (GAO,
2002). EPA has issued an advisory suggesting that drinking water should not contain MtBE in
concentrations greater than 20 to 40 micrograms per liter (ug/L), based on taste and odor concerns, but
has not issued a federal maximum contaminant level (MCL) for MtBE, which will be based on the
ongoing EPA studies.
In addition, 31 states have established standards, guidelines, advisory levels, or action levels (some based
on the EPA advisory concentrations) for the maximum concentration of MtBE allowable in drinking
water. Forty two states have established cleanup levels or guidelines (some site-specific) for MtBE in soil
and groundwater, as shown at http://www.epa.gov/oust/mtbe/index.htm. MtBE drinking water standards
range from 5 to 240 ug/L, with 90 percent of state standards less than or equal to 100 ug/L. Soil cleanup
levels range from 5 to 280,000 ug/kg and groundwater cleanup levels range from 5 to 202,000 ug/L,
considering both potable and non-potable uses for groundwater (EPA, 2003a; Delta Environmental
Consultants, 2004; NEIWPCC, 2000). More than 75 percent of the states have groundwater cleanup
values less than 100 ug/L. Delta Environmental Consultants http://www.deltaenv.com/ compiled the
summary of state groundwater standards for EPA, and periodically updates their summary of the
standards.
Only limited information is available about the health risks of oxygenates other than MtBE. Fewer states
have established standards and cleanup levels for these contaminants than for MtBE. Currently, there are
no federal drinking water advisory or cleanup levels for these other fuel oxygenates. Several states have
established, and some states have plans to establish, cleanup levels for other oxygenates (Delta
Environmental Consultants, Inc., 2004). Table 2-1 summarizes the number of states that have cleanup
levels for fuel oxygenates along with the range of cleanup levels established for each.
2-4
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Technologies for Treating MtBE and Other Fuel Oxygenates
Table 2-1. State Cleanup Levels for Fuel Oxygenates in Groundwater
Fuel
Oxygenate
MtBE
TEA
DIPE
TAME
ETBE
Ethanol
Methanol
States with
Cleanup Level
(in 4/04)
42
11
7
6
5
6
11
Lowest Cleanup
Level (ng/L)
13
12
0.438
25
24
50
50
Highest Cleanup
Level (ng/L)
202,000
11,000
20,000
980
50
1,900,000
16,000
Note: Cleanup levels address both potable and non-potable sources of groundwater
Source: Delta Environmental Consultants, Inc., 2004
2.5 How Are Oxygenates Assessed in the Environment?
Analytical methods for petroleum hydrocarbons (usually benzene, toluene, ethylbenzene, and xylenes -
collectively BTEX) are well established and some of these protocols have been modified to include
oxygenates as individual target compounds. Until recently, validated EPA analytical methods existed for
only a few fuel oxygenates (specifically ethanol, methanol, and TEA). Methods that were developed for
analysis of petroleum hydrocarbons in water samples may not be appropriate for fuel oxygenates for
several reasons, such as analytical instruments may not routinely be calibrated for oxygenates,
inappropriate methods may be used for sample analysis, detection limits (particularly for alcohols) may
be higher than regulatory standards, or acid-catalyzed hydrolysis (breakdown) of ethers may occur during
sample processing and analysis. In April 2003, EPA published a Fact Sheet (EPA, 2003a) that specifies
the following steps that may be taken to address potential analytical problems with oxygenate analysis.
EPA has found that using this approach consistently results in detection limits of 5 ug/L or lower for
MtBE, TEA, ETBE, TAME, TAEE, TAA, DIPE, and acetone.
Routinely calibrate analytical methods for the suite of common fuel oxygenates
Use Method 8260 (GC/MS) or Method 8015 (GC/FID) for sample analysis
Modify sample preparation methods to increase sensitivity and decrease detection limits; in some
cases, samples should be heated during the preparative phase, especially when analyzing for
alcohols
Change the chemical preservation method to avoid the potential for ether hydrolysis; for example,
using base preservation to raise the pH to greater than 11 (including use of trisodium phosphate
dodecahydrate [TSP]), rather than acidification, would help avoid ether hydrolysis
Other researchers have provided additional information related to the methods used for the analysis for
fuel oxygenates. The following references provide more detailed information about this subject:
2-5
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Technologies for Treating MtBE and Other Fuel Oxygenates
White H., Lesnik B., Wilson J. 2002. Analytical Methods for Oxygenates. L.U.S.T.Line,
Bulletin 42, New England Interstate Water Pollution Control Commission, pp 1-8. October.
Discusses results from an EPA study to determine optimum conditions for purge-and-trap sample
preparation for MTBE and other fuel oxygenates.
http: //www. epa. gov/oust/mtbe/LL42 Analytical .pdf
Crumbling D.M., Lesnik B. 2000. Analytical Issues for MtBE and Related Oxygenate
Compounds. L.U.S.T.Line, Bulletin 36, New England Interstate Water Pollution Control
Commission, pp 16-18. Discusses relative appropriateness of using flame ionization detection
and mass spectrometry with proper preparation techniques.
http://www.epa.gov/oust/mtbe/LL36Methods.pdf
Halden, R. U., A. M. Happel, and S. R. Schoen. 2001. Evaluation of Standard Methods for the
Analysis of Methyl fert-Butyl Ether and Related Oxygenates in Gasoline-Contaminated
Groundwater. Environmental Science & Technology, Vol. 35, no. 7, pp. 1469-1474. (Additions
and Corrections, Vol. 35, no. 7, p. 1560.) Presents results from a formal method evaluation,
round-robin study, and a split-sample study (424 groundwater samples) that showed consistently
good results for mass spectrometry and flame ionization detection, but not for photoionization
detection, http://pubs.acs.org/
2.6 How Do Oxygenates Migrate in the Environment?
MtBE and other oxygenates typically enter the environment blended with gasoline or other refined fuel
products. However, these oxygenates migrate differently within the environment because of the
differences in physical properties between oxygenates and the other components of gasoline, such as
BTEX, of which benzene is typically the most common contaminant of concern. Table 2-2 contains a
summary of some properties that influence the migration of MtBE and other oxygenates in the
environment. As discussed later in this report, these physical properties also influence the treatability of
MtBE and other oxygenates.
Fuel oxygenates generally exhibit the following physical properties relative to benzene:
Greater tendency to partition into the vapor phase from the non-aqueous phase (vapor pressure)
(with the exception of TEA, ethanol, and TAME)
Greater solubility in water
Lesser tendency to partition to organic matter in soil (soil adsorption coefficient)
Lesser retardation factor (slowing of migration with groundwater due to sorption to aquifer
matrix)
Lesser tendency to partition into the vapor phase from the aqueous phase (Henry's Law Constant)
Because of their relatively higher vapor pressure, ether-based oxygenates in fuel will tend to volatilize
from releases (non-aqueous phase) exposed to the open air more rapidly than benzene. Alcohol-based
oxygenates will volatilize less rapidly than benzene. However, once fuel oxygenates enter the subsurface
and become dissolved in groundwater (aqueous phase), they are significantly less volatile (lower Henry's
Constant) than benzene. Oxygenates are many times more soluble than benzene; concentrations of MtBE
in groundwater as high as 1,000,000 ug/L are not uncommon. Also, because MtBE dissolved in
groundwater will partition (as a function of its soil adsorption coefficient) to the organic matter in
surrounding soil less readily than benzene, a dissolved MtBE plume typically migrates faster than a
dissolved benzene plume (lower retardation factor). As a result, MtBE contamination can result in a
2-6
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Technologies for Treating MtBE and Other Fuel Oxygenates
relatively larger groundwater plume, compared with plumes originating from gasoline constituents (EPA,
2001a;Kinner, 2001).
While all fuel oxygenates are more water soluble than other gasoline components (benzene), variations in
molecular structures result in a range of physical properties and affect the way that each of them migrate
in the environment. Figure 2-2 summarizes the physical properties discussed above for each of the
common fuel oxygenates relative to benzene, which is most often the chemical of concern in gasoline.
While the physical properties for each oxygenate is different, there are similarities among the alcohols
and the ethers. For example, as shown on Figure 2-3, alcohol-based oxygenates have a relatively greater
water solubility and much lower Henry's Constant than the ether-based oxygenates. Other properties
such as the soil partition coefficient, vapor pressure, and retardation factor do not adhere to these same
groupings.
2.7 How Do the Properties of Oxygenates Affect Treatment?
As discussed above, the properties of MtBE and other oxygenates, including water solubility, vapor
pressure, soil adsorption coefficient, retardation factor, and Henry's Law Constant, affect their fate and
transport in the environment relative to other contaminants. These same properties also affect the
selection and design of remediation technologies used to address soil and water contaminated with
oxygenates. In general, the same types of treatment technologies have been applied for treatment of
BTEX and MtBE, however design and operating conditions for MtBE may not be the same as for
treatment of BTEX. For example, carbon-based adsorption materials that work well for BTEX may not
be effective for removal of MtBE.
BTEX is most often the contaminant group targeted for treatment at gasoline spill sites, and in many cases
the treatment systems have been specifically designed to reduce concentrations of benzene. In some
cases, a treatment system designed to remove benzene can also remove the oxygenate contamination.
However, because of the differences in the physical properties of oxygenates relative to benzene, certain
oxygenates might not be effectively treated by a system designed to treat benzene. Also, because the
physical properties of individual oxygenates also differ from one another, a treatment system designed to
treat one oxygenate may not effectively treat another oxygenate. An overview of the effects of the
physical properties of oxygenates on the effectiveness of various remediation technologies is included in
Section 4. Primary considerations related to the treatment of oxygenates include:
The vapor pressures of most oxygenates, with the exception of ethanol, TEA, and TAME, can
result in them being more readily volatilized from soil using certain technologies, such as soil
vapor extraction (SVE) or multi-phase extraction (MPE) (EPA, 2001b; Kinner, 2001).
The relatively low Henry's Constants (the ratio of a compound's concentration in air relative to
its concentration in water) of oxygenates can result in them being more difficult to strip from
contaminated groundwater via air sparging or air stripping as part of a pump-and-treat remedy.
The presence of an ether bond or hydroxyl group in oxygenates results in these compounds being
significantly less likely to partition to organic matter (Koc), such as in use of granular activated
carbon (GAC) in pump-and-treat remedies.
Because they can be chemically oxidized or biologically degraded, chemical oxidation and
biodegradation technologies (both in situ and ex situ) can be effective in the treatment of
oxygenates.
2-7
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Technologies for Treating MtBE and Other Fuel Oxygenates
Figure 2-2. Physical Properties of Fuel Oxygenates Relative to Benzene
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2-9
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
2.8 What Types of Technologies are Used in the Treatment of Soil, Groundwater, and
Drinking Water Contaminated with Oxygenates?
Technologies that have been used to treat groundwater and soil contaminated with oxygenates include air
sparging, SVE, MPE, in situ bioremediation, in situ chemical oxidation (ISCO), groundwater extraction
and above-ground treatment (i.e., pump-and-treat or drinking water treatment), and phytoremediation.
Above-ground treatment for extracted groundwater includes technologies such as air stripping, activated
carbon, chemical oxidation, and bioremediation. Air sparging, SVE, and MPE rely generally on the use
of air flow to remove contaminants, and are discussed before the other technologies. Bioremediation and
ISCO rely on biological and chemical reactions to destroy MtBE and other oxygenates, while pump-and-
treat and drinking water treatment rely primarily on physical and chemical parameters to separate MtBE
and oxygenates from water. Other technologies discussed in this report, such as phytoremediation, in situ
thermal treatment, and permeable reactive barriers, have also been used at sites contaminated with
oxygenates, although less often at the sites in EPA's MtBE database. Non-treatment remedies that have
been used include excavation, free product recovery, monitored natural attenuation (MNA) and
institutional controls (1C). These technologies are discussed in more detail in Sections 4 and 5 of this
report.
Additional sources of information that discuss treatment of MtBE using multiple technologies include the
following:
Moyer, E.E. and Kostecki, P.T., Eds. 2003. MtBE Remediation Handbook. AEHS. Amherst
Scientific Publishers.
Evaluation of MTBE Remediation Options. 2004. The National Water Research Institute. April.
www.nwri-usa.org/.
2.9 How Are Technologies Used to Treat Soil and Water Contaminated with Oxygenates?
Remediation of a site contaminated with MtBE and other fuel oxygenates is often conducted using a
phased approach. Often, the first phase of remedial action at a site focuses on protecting receptors at the
site, such as nearby buildings or drinking water supplies. The second phase generally involves
controlling the source of the contamination, for example excavation of leaking underground storage tanks
(USTs) or contaminated soil, or free product removal. The next phase typically involves the active
cleanup of residual and dissolved contamination using one or more treatment technologies. Active
cleanup of residual and dissolved contamination often is followed by MNA (Jansen et. al., 2002).
Technologies might be applied sequentially or simultaneously in different parts of a contaminated site,
depending on the concentration of oxygenates and potential risks to receptors. For example, at a gasoline
service station site with a leaking UST, excavation, free product removal, or SVE might be performed at
the source area; air sparging, in situ chemical oxidation, or in situ bioremediation in the plume area (these
technologies could also be used for source area treatment at some sites); or pump-and-treat as the plume
gets closer to a receptor. If concentrations are sufficiently low, MNA might be used instead of an active
bioremediation technology or pump-and-treat for the residual plume. When considering MNA as a
potential remedy, remediation timeframe is an important factor to consider. Treatability studies (bench-
or pilot-scale) often are performed to evaluate how a technology would perform on the actual soil or
groundwater at a site. The results of these studies are used in preparing a design for full-scale
remediation (EPA, 1999b).
2-10
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Technologies for Treating MtBE and Other Fuel Oxygenates
2.10 What Additional Technical Considerations are Associated with Remediating Sites
Contaminated with Oxygenates?
Other technical considerations related to remediation of sites contaminated with MtBE and oxygenates
include contaminant concentration, cleanup goals, presence of other contaminants at the site, and site-
specific considerations that may affect the selection and design of treatment technologies. There tends to
be wide variability in the range of concentrations of MtBE or other oxygenates in soil and groundwater at
sites. The concentration of MtBE in contaminated groundwater and soil for the projects reviewed for this
report ranged from 5 to 1,000,000 ug/L. In addition, soil and groundwater treatment goals for MtBE-
contaminated sites are currently based on state-specific standards and risk-based levels that range from 5
to 280,000 ug/L in soil and from 5 to 200,000 ug/L in groundwater. State-established primary drinking
water limits for MtBE range from 5 to 240 ug/L (Delta Environmental Consultants, Inc., 2004). High
contaminant concentrations at sites with low cleanup goals can result in the need for treatment
technologies and system designs able to achieve higher removal efficiencies and more aggressive
remediation.
Many other factors can affect the performance and cost for implementing a technology at a given site,
including the nature and extent of contamination, depth of contamination, physical and chemical
characteristics of a site (such as dimensions and hydrogeology), design and operation of a treatment
system, regulatory requirements, and logistical issues. Typically, these factors are quantified before an
engineering level design is made for use of a technology at a given site.
In addition, it is important to recognize that sites with spilled or leaked gasoline contain 200-300 distinct
chemicals which can contaminate soil and groundwater; approximately 6-10% of the spilled/leaked
gasoline typically consist of fuel oxygenates such as MtBE (McGarry, 2002).
2-11
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
3.0 COMPARISON OF TREATMENT TECHNOLOGIES
This section contains a comparison of the following nine technologies that have been used to treat sites
contaminated with MtBE and other fuel oxygenates:
Air Sparging
Soil Vapor Extraction (SVE)
Multi-Phase Extraction (MPE)
In Situ Bioremediation
In Situ Chemical Oxidation (ISCO)
Pump-and-Treat
Other Treatment Technologies
o Phytoremediation
o Permeable Reactive Barriers
o In Situ Thermal Treatment
The information used for this comparison is based primarily upon information reported for 323 MtBE
remediation technology projects at EPA's MtBE Treatment Profile Website, available at
www.cluin.org/products/mtbe. as well as information available from published literature sources. This
section provides a summary overview of these technologies and Section 4 includes more detailed
information related to each individual technology, including a technology description, a discussion of
how the properties of fuel oxygenates affect treatment, and more detailed information summaries related
to the 323 projects in the dataset.
3.1 What Types of Remediation Technology Projects were Considered in this Comparison?
Information about 323 MtBE remediation technology projects was reviewed during the preparation of this
report. These projects employed primarily air sparging, SVE, MPE, bioremediation, ISCO, and pump-
and-treat to remediate MtBE and other oxygenates in groundwater and soil. Some sites also used
phytoremediation, PRBs, or in situ thermal treatment. Table 3-1 summarizes the number of projects that
used each of these technologies, as well as the scale (full-scale, pilot-scale, or bench-scale) and status
(completed or ongoing) of the projects reviewed, and the number of projects for which performance and
cost data were available. Among the six technologies, air sparging, SVE, bioremediation, and pump-and-
treat were used more frequently to remediate groundwater and soil contaminated with MtBE and other
oxygenates, and MPE, ISCO, phytoremediation, PRBs, and thermal treatment were used less frequently.
Nearly 25 percent of the projects have been completed, with the remaining 75 percent ongoing. Eighty
percent of the projects provided some type of performance data, and more than 30 percent provided cost
data. Performance and cost data were provided most often for projects using air sparging, bioremediation,
and pump-and-treat.
3-1
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
Table 3-1. Description of MtBE Remediation Technology Projects (323 Projects)
Technology
Air Sparging
Soil Vapor Extraction
Multi-Phase Extraction
Bioremediation
In situ Chemical Oxidation
Pump-and-treat
Phytoremediation
Permeable Reactive Barriers
Thermal Treatment
Number
of
Projects
123
138
13
73
21
100
8
6
1
Project
Scale
Bench
1
0
0
7
0
0
3
0
0
Pilot
2
1
4
13
4
16
4
2
0
Full
120
137
9
53
17
84
1
4
1
Project Status
Com-
pleted
19
19
4
35
8
22
5
4
1
On-
going
104
119
9
38
13
78
3
2
0
# of Projects
with
Performance
Data
113
129
10
68
20
76
1
4
1
# of Projects
with
Cost Data
39
24
2
28
2
43
0
0
0
Note: Each project may involve use of one or more than one specific technology.
Source: EPA, 2002a
3.2 How Did These Remediation Technologies Perform?
As shown on Table 3-1, performance data were available for all 323 of the MtBE remediation projects in
the dataset. However, most of these projects with performance data are ongoing. To evaluate
performance of specific technologies and projects, 105 completed projects with performance data were
identified, along with the minimum, median, and maximum of the highest concentration of MtBE
measured in the groundwater before treatment (initial) and after treatment (final), as shown in Table 3-2.
Limited performance data were available about the projects that employed phytoremediation, PRBs, and
thermal treatment, and are not presented in this table. A summary of the technology-specific data for
these technologies is included in Section 4, with project-specific data provided in Appendix A.
Table 3-2. Performance Data for Completed MtBE Remediation Technology Applications
(105 Applications1 Providing Data)
Technology
Air Sparging
Soil Vapor Extraction
Multi-Phase Extraction
Bioremediation
In situ Chemical Oxidation
Pump-and-Treat
#of
Completed
Projects with
Performance
Data
19
23
3
35
8
21
Initial MtBE Concentration 2 (ng/L)
in Groundwater
Minimum
5
5
11
5
55
3
Median
2,100
2,600
55
3,880
11,700
1,610
Maximum
62,000
44,400
6,140
100,000
475,000
475,000
Final MtBE Concentration 2 (ng/L)
in Groundwater
Minimum
2
2
79
<1
5
<1
Median
16
21
435
30
75
11
Maximum
2,070
3,200
791
33,000
68,400
68,400
Notes:
1 For projects where more than one technology was used, performance information is presented under each of the technologies used for the
project.
2 MtBE concentrations for all technologies are reported for groundwater. For technologies that affect soil (such as MPE and SVE), source
materials provided information on MtBE concentrations in groundwater. For all projects, the highest concentration reported prior to
beginning treatment (shown as "initial") and the highest concentration after treatment was completed (shown as "final") is provided.
Source: EPA, 2002a
3-2
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
As discussed in Section 1, these performance data are based on the data provided by project managers and
others in the source materials used to prepare the treatment profiles website. There was variation among
the profiles in the level of detail for performance data. Many of the treatment profiles contained only
limited information about treatment performance, generally including a maximum concentration of MtBE
before-treatment and a maximum concentration of MtBE after-treatment. Most treatment profiles did not
provide detailed performance data, such as MtBE concentration over the duration of the project, or
statistical evaluations of performance data with confidence limits.
As mentioned before, treatment performance is site-specific and dependent on many factors; thus it is
difficult to extrapolate from one site to another. The data are provided to give a general indication of
technology performance. These factors include site conditions (such as soil types, permeability,
conductivity, redox conditions, and degree of heterogeneity), technology design and operation, and
regulatory considerations, such as cleanup levels. Additional factors include duration of the release (such
as a gasoline leak), presence of down-gradient water supply wells, and distribution of contaminants in soil
and groundwater.
Table 3-3 summarizes the duration of 89 completed remediation projects. Although project duration is
dependent on a number of factors, such as extent of contamination and cleanup levels, the data from these
89 projects show a relatively shorter median duration for projects using bioremediation or ISCO,
compared with those using air sparging, SVE, pump-and-treat, or MPE.
Table 3-3. Duration of Completed MtBE Remediation Technology Applications
(89 Applications Providing Data)
Technology
Air Sparging
Soil Vapor Extraction
Multi-Phase Extraction
Bioremediation
In situ Chemical Oxidation
Pump-and-Treat
#of
Projects
18
22
1
24
7
17
Project Duration (months)
Minimum
3
3
Median
22
21
Maximum
75
66
45
<1
2
<1
6
12
31
60
18
75
Notes:
1 For projects where more than one technology was used, information is presented under each of the technologies used
for the project.
Source: EPA, 2002a
3.3 What Did These Remediation Technologies Cost?
Table 3-4 summarizes the cost information reported for 127 MtBE remediation technology applications.
Only costs reported as total project costs are summarized in this table. Note that these include both
completed and ongoing projects. Because of the wide variation in the components that were included in
the reported total project costs, these data should only be used as a general reference about costs and
should not be used as a sole basis to estimate costs for future MtBE remediation projects or to compare
the cost of technologies. Additional information about the costs reported for the remediation technologies
are provided in Section 4.
3-3
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Technologies for Treating MtBE and Other Fuel Oxygenates
Table 3-4. Total Project Cost1 Data for MtBE Remediation Technology Applications
(127 Applications Providing Data)
Technology
In situ Chemical Oxidation
Bioremediation
Soil Vapor Extraction
Air Sparging
Multi-Phase Extraction
Pump-and-Treat
# of Projects with
Cost Data
2
30
24
39
2
43
Total Project Costs Reported (S)
Minimum
$60,000
$4,000
$14,700
$13,700
$130,000
$65,000
Median
$103,000
$137,000
$206,000
$247,000
$257,000
$327,000
Maximum
$146,000
$5,200,000
$4,600,000
$1,050,000
$383,000
$4,000,000
Note:
1 For projects where more than one technology was used, cost information is presented under each of the technologies used for the project.
Table includes total costs for completed projects, and costs to date for ongoing projects. Projects were of varying sizes, concentrations, and
other site conditions. A summary of project-specific data for these technologies is provided in Appendix A.
2 Total project cost included more than just the treatment cost, such as cost for ancillary treatment processes, monitoring costs, or source
removal costs. The costs summarized in this table have not been normalized to account for the types of cost components included, locations
of the projects, or the time when the costs were incurred (inflation factors, see EPA 2001c). For a majority of the applications, reported
costs were based on actual incurred costs. However, for some applications, costs were estimated as projected full-scale costs based on a
scale up of pilot- or bench-scale projects.
Source: EPA, 2002a
In addition, EPA recently prepared a more detailed analysis of treatment cost for in situ treatment of fuel
oxygenates. The paper, "Cost of In Situ Treatment of Fuel Oxygenates", was presented at the National
Ground Water Association conference on Remediation: Site Closure and the Total Cost of Cleanup, New
Orleans, held November 13-14, 2003, and is available at www.cluin.org/mtbe.
As discussed earlier for performance data, the cost data are based on the data provided by project
managers and others in the source materials used to prepare the treatment profiles website. There was
variation among the profiles in the level of detail for cost data by project, with many of the treatment
profiles containing only limited information about treatment cost. Treatment cost is site specific and
depends on many of the same factors that also affect performance, such as site conditions, project scale,
technology design and operation, and regulatory considerations. Therefore, these cost data are intended
to give a broad indication of the types of costs associated with cleanup projects, and users should be
cautious about drawing conclusions about the cost of cleanup projects at specific sites based on these
data. As discussed later in the report, very few projects provided sufficient information to calculate a unit
cost for treatment.
For some of the treatment profiles, the specific components that make up the total cost were not provided
in the source materials, such as for capital or operation and maintenance [O&M] activities. In other cases,
the types of contaminants present at the sites, other than MtBE, were not identified in the source
materials. Sites may have been contaminated with gasoline components such as petroleum hydrocarbons,
as well as oxygenates, and the treatment costs reported are for cleanup of both the gasoline components as
well as the oxygenates. For example, for a specific project, most of the cost for cleanup may be due to
gasoline components other than oxygenates.
Costs for most of these projects were provided as a total remedial cost. Some projects also included the
cost for ancillary treatment processes, monitoring costs, or source removal costs in the total cost. For
most of the projects, reported costs were based on actual incurred costs. For other projects, costs were
estimated as projected full-scale costs based on a scale up of pilot-scale projects or on engineering
3-4
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Technologies for Treating MtBE and Other Fuel Oxygenates
estimates. Because most of the costs for use of the treatment technologies are related to system design,
installation, and startup, these partial or estimated costs may be relatively close to the eventual total
project cost. However, the reported project costs should still be considered estimates because the cost
components for each project are not consistent and it is possible that significant costs could be associated
with system operation, maintenance, monitoring, and decommissioning. In addition, these cost data were
not normalized to account for the project year or location. (Further information about normalizing cost
data is provided in EPA 200 Ic).
3.4 What Factors Should Be Considered When Identifying Technologies to Treat Fuel
Oxygenates?
Table 3-5 summarizes the general factors to be considered when identifying technologies to treat sites
contaminated with fuel oxygenates. These general factors were developed based on data from the 323
technology applications, as well as from the Remediation Technology Screening Matrix and Reference
Guide published by the Federal Remediation Technologies Roundtable (FRTR), and other industry
references. As shown in Table 3-5, these general factors include type of treatment, relative time to
complete, and relative cost.
Table 3-5. General Factors to Consider When Identifying a Remediation Technology for
Sites Contaminated with Fuel Oxygenates
Technology
Air Sparging
Soil Vapor Extraction
Multi-Phase Extraction
In situ Bioremediation
In situ Chemical Oxidation
Pump-and- Treat
Phytoremediation
Permeable Reactive Barriers
In situ Thermal Treatment
Type of Treatment
In situ/
Ex situ
In situ
In situ
In situ
In situ
In situ
Ex situ
In situ
In situ
In situ
Media
GW
Soil
Both
Both
Both
GW
Both
GW
Both
Source/
Plume
Plume
Source
Source
Plume
Source
Plume
Plume
Plume
Source
Relative Time to
Complete
Average
Average to Longer
Average
Average to Shorter
Shorter
Longer
Longer
Longer
Shorter
Relative Cost
Average to Lower
Lower
Average to Higher
Lower
Average to Lower
Higher
Lower
Lower
Average
Source: EPA 2002a and FRTR 2002
Table 3-6 summarizes some of the general factors that are often considered when selecting a remediation
technology for sites contaminated with fuel oxygenates. These include potential benefits (such as
minimal site disturbance, integration with other treatment technologies, or applicability to challenging site
conditions) and limitations (such as types of contamination not suited to treatment, undesired migration or
transformation of contamination, or health and safety considerations). A more detailed discussion of
specific factors for each technology is provided in Section 4.
3-5
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
Table 3-6. General Factors to Consider When Selecting a Remediation Technology for Sites
Contaminated with Fuel Oxygenates
Technology
Potential Benefits
Potential Limitations
Air Sparging
Causes minimal disturbance to site
operations
Addition of oxygen to the subsurface may
enhance aerobic biodegradation
Can be a cost-effective alternative for sites
with groundwater contamination
May cause a lateral spread of dissolved or
separate phase contaminant plume
Contamination may be transferred from
groundwater to the vadose zone
Has limited applicability at sites with confined
aquifers
SVE
Reduces the potential for migration of vapors
into buildings or leaching into groundwater
Causes minimal disturbance to site
operations
Can be a cost-effective alternative for sites
with soil contamination and, in some cases,
free product
Low soil permeability or other heterogeneous
conditions may reduce effectiveness
Shallow depths to groundwater or fluctuations
in groundwater table can cause upwelling and
interference with airflow
Off-gas typically requires treatment
MPE
May increase groundwater recovery rates,
compared to conventional pumping practices
in equivalent settings
Can be used to recover free product
May be used to remediate the capillary fringe
and smear zone
Can be a cost-effective alternative for sites
with contamination in both soil and shallow
groundwater
NAPL emulsions and VOC-laden vapors may
increase treatment requirements
Initial start-up and adjustment periods may be
relatively long
Some MPE configurations have depth
limitations
Off-gas typically requires treatment
In situ
Bioremediation
Causes minimal disturbance to site
operations
Often biodegradation can be enhanced by use
of other technologies, such as air sparging,
SVE, MPE, thermal, or ISCO
Can be a cost-effective alternative for sites
with contamination in both soil and
groundwater
Presence of other organic contaminants may
inhibit biodegradation
Degradation pathways for anaerobic processes
not as well understood as aerobic pathways;
anaerobic processes typically slower
High concentrations of contaminants may be
toxic and/or not bio-available
May be difficult to implement in low-
permeability aquifers
Re-injection wells or infiltration galleries may
require permits or may be prohibited
Biodegradation pathways may be site-specific,
potentially requiring pilot testing or
treatability studies
In situ Chemical
Oxidation
Can be a cost-effective alternative for hot
spots that may not be amenable to
bioremediation
Contaminants are treated rather than
transferred to a vapor phase
Causes minimal disturbance to site
operations
Relatively large amount of oxidant may be
needed for treatment of large contaminant
mass
May be low contact between oxidant and
contaminant in heterogeneous conditions or in
areas with low permeability
Special precautions may be needed to protect
worker health and safety during operation
Oxidation reactions may form toxic by-
products in the groundwater or in off-gases
and off-gas may require capture and treatment
3-6
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
Technology
Potential Benefits
Potential Limitations
Pump-and-Treat
Can be a cost-effective alternative to treat an
aquifer or to provide hydraulic containment
for sites contaminated with fuel oxygenates
May require an extended operation and
maintenance period
Cost of constructing, operating, and
maintaining treatment system can be relatively
high
Biofouling of extraction wells can reduce
system performance
The typical design of common above-ground
treatment systems may not be effective for
oxygenates
Phytoremediation
Can be a cost-effective alternative for
remediating or containing relatively low
concentration, shallow, and widespread soil
or groundwater plumes
Limited information available about the
specific processes used in phytoremediation
that reduce concentration of fuel oxygenates
Typically lengthy startup period
Phytoremediation generally less applicable to
higher concentrations or deeper groundwater
plumes
Permeable
Reactive Barriers
Can be a cost-effective alternative for
preventing the migration of contaminated
groundwater plumes
May affect natural groundwater flow gradients
at a site, potentially resulting in lateral or
vertical migration of the contaminant plume
Requires a high degree of engineering for
design and installation
In situ Thermal
Treatment
Can be a cost-effective alternative for
remediating source areas in soil or
groundwater
Tends to remove oxygenates when used to
treat other petroleum contaminants (such as
petroleum hydrocarbons)
May not be cost-effective for use at small sites
such as service stations
Requires a high degree of engineering for
design, installation, and operation
Sources: EPA 2002a and FRTR 2002
For practitioners of in situ technologies, note that EPA has issued a policy statement that reinjection of
contaminated groundwater is allowed under RCRA section 3020(b) as long as certain conditions are met.
This policy is intended to apply to remedies involving in situ bioremediation and other forms of in situ
treatment. Under this policy, groundwater may be reinjected if it is treated aboveground prior to
reinjection. Treatment may be by a "pump-and-treat" system or by the addition of amendments meant to
facilitate subsurface treatment. Also the treatment must be intended to substantially reduce hazardous
constituents in the groundwater (either before or after reinjection); the cleanup must be protective of
human health and the environment; and the injection must be part of a response action intended to clean
up the environment (EPA, 2000f).
3-7
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
4.0 TREATMENT TECHNOLOGIES
This section summarizes available information on nine treatment technologies that have been applied to
treat MtBE and other oxygenates in groundwater, soil, and drinking water. Table 4-1 provides a brief
description of these technologies, along with each technology's applicability to treat groundwater, soil, or
both to treat oxygenates either in situ or ex situ. Groundwater contaminated with MtBE has most often
been treated using air sparging, bioremediation, ISCO, pump-and-treat, and MPE. To date, soil
contaminated with MtBE has been treated primarily with SVE. Drinking water contaminated with MtBE
and other fuel oxygenates is typically treated using the same aboveground treatment technologies
associated with pump-and-treat, such as air stripping, adsorption, chemical oxidation, or bioremediation.
In addition to these treatment technologies, several non-treatment remedies (excavation, product recovery,
and monitored natural attenuation) have been used to enhance MtBE source removal or plume
management remedies and are discussed in Section 5. The remainder of this section provides information
summarized from 323 MtBE-remediation technology applications (based primarily on EPA MtBE
Treatment Profiles - see Section 1) that can assist in remedy selection at sites contaminated with MtBE
and other fuel oxygenates.
Table 4-1. Types of Technologies Used to Treat MtBE and Other Fuel Oxygenates
Section
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
Treatment
Technology
Air Sparging
SVE
MPE
In situ
Bioremediation
In situ Chemical
Oxidation
Groundwater
Extraction for
Pump-and-Treat
and Drinking
Water Treatment
Above-Ground
Treatment
Technologies for
Extracted
Groundwater
PRBs
Phytoremediation
In situ Thermal
Treatment
Ground
water
Soil
In Situ or
Ex situ
In situ
In situ
In situ
In situ
In situ
Ex situ
Ex situ
In situ
In situ
In situ
Description
Injection of air into the groundwater to strip
out VOCs
Application of a vacuum to the soil to
extract VOCs and treatment using
aboveground processes
Simultaneous extraction of VOCs from soil
and free product/groundwater and treatment
using aboveground processes
Addition of oxygen or other amendments to
stimulate and enhance biodegradation
Injection of chemicals such as ozone,
hydrogen peroxide, or permanganate into
the subsurface to oxidize contaminants
Extraction of contaminated groundwater for
treatment prior to use or disposal
Treatment of extracted groundwater using
ex situ processes such as air stripping,
adsorption, biological reactors, or oxidation
Placement of a reactive zone that treats
contaminants as groundwater flows through
the zone
Use of trees and other higher plants to
remove or destroy contaminants
Use of heat to mobilize or destroy
contaminants
4-1
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
4.1 Air Sparging
Overview
D Injection of air into the groundwater to strip out volatile contaminants
D EPA's MtBE Treatment Profiles dataset includes use at 123 sites to treat
MtBE, often in conjunction with SVE
D Some oxygenates may be less amenable to air sparging than other volatile
contaminants
4.1.1 What is Air Sparging?
Air sparging is an in situ technology that removes VOCs such as MtBE and other oxygenates from the
groundwater through the injection of air, which induces a phase transfer of VOCs from a dissolved state
to a vapor state that can be extracted from the subsurface or allowed to attenuate in the vadose zone.
During air sparging, biodegradation of contaminants (including MtBE and other oxygenates) can also be
promoted by the oxygen in the injected air. In some cases, pure oxygen or air amended with other gases,
such as triethylphosphate (a nutrient), or butane or propane (cometabolic substrates), are injected to
further promote biodegradation of contaminants. For the purpose of this report, technology applications
that rely on biodegradation as a primary pathway for contaminant remediation are considered to be
bioremediation projects, and are discussed in more detail in Section 4.4.
4.1.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?
In an air sparging system, the primary mechanism for contaminant removal is the transfer of contaminants
from the dissolved to the vapor phase. The extent to which this transfer can take place during air sparging
depends on the Henry's Law Constant, which is an indication of the extent to which each will partition
between the dissolved state and the vapor state under equilibrium conditions. A contaminant with a
greater Henry's Law Constant is more readily stripped from groundwater by air sparging than one with a
lower Henry's Law Constant.
Figure 4.1-1 shows the Henry's Law Constants for the common fuel oxygenates. The Henry's Law
Constants in this table are shown as dimensionless values representing the ratio of the concentration in the
vapor state compared to its concentration in the aqueous state at 25ฐC. As shown on the table, all of the
common oxygenates (with the possible exception of DIPE) have Henry's Law Constants that are lower
than those for benzene, toluene, ethylbenzene, and xylene (BTEX), which range from 0.22 for benzene to
more than 0.3 for xylene. Because of this, an air sparging system designed to remediate BTEX may not
adequately address oxygenates. Research has shown that the removal of MtBE requires 5 to 10 times
more airflow than would have been used for BTEX alone (Fields et al., 2001). In addition, the ether-
based oxygenates have Henry's Law Constants that are about two to three orders of magnitude greater
than those for alcohol-based oxygenates, suggesting that ether-based oxygenates, such as MtBE, can be
removed more readily using air sparging than alcohol-based oxygenates, such as TEA. However,
alcohol-based oxygenates may be more readily biodegraded (see Section 4.4) or may have less stringent
(higher concentration) cleanup goals at some sites than ether-based oxygenates. Thus, it is possible that
air sparging could be used to remediate sites contaminated with both alcohol-based and ether-based
oxygenates.
4-2
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
Figure 4.1-1. Ranges of Henry's Law Constants (Dimensionless) for Common Fuel Oxygenates
J
(0
(0
_o
c
o
'"> A 1
c 0.1 -
Q_
+ป
c
5 0.01 -
(0
c
o
O
<3 o.ooi -
(0
"ฃ
c
0)
n nnni
U.UUU 1
^
ETHER 041 BTEX
0.35 n 31
0 22 0.24
0.12 0.11 0.195
^H 0.052
0.023
ALCOHOL OXYGENATES
^^0.00059
0.00026
0.00021 0.00011
I I
^ 3) jfP '
Notes:
1. Henry's Law Constants shown as dimensionless values representing the ratio of the concentration in the vapor state compared to its
concentration in the aqueous state at 25ฐC.
2. Data from "Guidelines for Investigating and Cleanup of MtBE and Other Ether-Based Oxygenates", CalEPA, State Water Resources
Control Board, March 2000.
4.1.3 How is Air Sparging Applied to Treat Oxygenates?
During air sparging, compressed air is forced into the saturated zone through one or more injection points,
such as vertical or horizontal wells or engineered trenches, screened beneath the water table. The injected
air flows and rises through the saturated zone. As the injected air passes through groundwater containing
dissolved volatile contaminants, these contaminants partition to the injected air based on their individual
physical properties. In addition, oxygen present in the injected air will dissolve into the groundwater at
the gas-water interface and diffuse into the surrounding groundwater, potentially stimulating
biodegradation of contaminants. When the injected air reaches the vadose zone, it can be extracted using
SVE. Extracted vapors may be treated using aboveground technologies (Section 4.2 discusses SVE and
aboveground vapor treatment technologies) or is allowed to attenuate naturally in the vadose zone through
dispersion and biodegradation. Air sparging has been used without SVE when contaminant
concentrations are relatively low or potentially affected receptors are far from the area being treated
(Symons and Greene, 2003).
The design and configuration of air sparging systems to treat oxygenates varies widely based on site-
specific conditions and is typically established through pilot-scale testing to determine the radius of
influence (ROI) or zone of influence (ZOI) of an air sparging well under site conditions. The ROI or ZOI
is the area around an injection well where there is adequate sparge pressure and airflow to enhance the
transfer of contaminants from the dissolved phase to the vapor phase. Spacing between air sparging wells
typically ranges from 5 to 40 feet (ft), depending on the surrounding soil characteristics, and airflow rates
commonly range from 1 to more than 40 standard cubic ft per minute (scfm). Pilot testing is typically
4-3
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
employed to determine an appropriate airflow rate (maximizing the ROI/ZOI while limiting the potential
for unintended subsurface fracturing and over-mobilization of the contamination) for a given site. The
flow of air through the sparging wells can be continuous or pulsed. Pulsed systems have been shown to
increase mass transfer removal in some instances (EPA, 1995; FRTR, 2002; USAGE, 1997).
More detailed information relevant to the application of air sparging at sites in general or those
contaminated with MtBE and other fuel oxygenates is available in the following documents:
Symons, Brian D., and J. Greene. 2003. "Soil Vapor Extraction, Bioventing, and Air Sparging".
In Moyer and Kostecki, Eds. 2003. MtBE Remediation Handbook. Amherst Scientific
Publishers.
Naval Facilities Engineering Service Center. 2001. Final Air Sparging Guidance Document.
NFESC Technical Report TR-2193 -ENV. August 31.
U. S. Environmental Protection Agency. 2001. Development of Recommendations and Methods
to Support Assessment of Soil Venting Performance and Closure. EPA 600-R-01 -070.
U.S Army Corps of Engineers. 1997. USAGE Engineering Manual: In Situ Air Sparging.
EM 1110-1-4005. September 15.
American Petroleum Institute. 1995. InSitu Air Sparging: Evaluation of Petroleum Industry
Sites and Considerations for Applicability, Design and Operation. Product Number 146090.
May.
4.1.4 What Types of Projects Involve Air Sparging for Oxygenates?
From the 323 projects in EPA's MtBE Treatment Profiles dataset, 123 projects were identified where
MtBE was treated using air sparging alone or in conjunction with another technology. Information on the
treatment of other fuel oxygenates during these 123 projects is limited; one project also reported TEA as a
co-contaminant and another project reported TEA and ethanol as co-contaminants.
Table 4.1-1 summarizes the scale and operational status for the 123 air sparging projects. The data used
to compile this information was current at the time the profile for each project was compiled. It is
possible that some projects shown as ongoing may now be completed. Short summaries for two projects,
Air Sparging at Exxon and Mobil Service Stations in Smithtown, NY and Air Sparging at Eaddy Brothers
Service Station in Hemingway, SC, are included at the end of this section, with additional information
about all 123 projects provided in Appendix A.
4-4
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
Table 4.1-1. General Information on 123 Air Sparging Projects
Technology (ies)
Air Sparging Only
Air Sparging with SVE
Air Sparging with Pump-and-
Treat
Air Sparging with SVE and
Pump-and-treat
Air Sparging with Multiple
Technologies
TOTAL
# of Projects
13
74
4
19
13
123
Operational Status
Completed
3
2
2
5
7
19
Ongoing
10
72
2
14
6
104
Scale
Bench
0
0
0
0
1
1
Pilot
1
0
0
0
1
2
Full
12
74
4
19
11
120
As shown in Table 4.1-1, most of the 123 air sparging projects were conducted at full scale (120 projects)
and were ongoing (104 projects) at the time the profile was prepared. In addition, while most (87) of the
projects used air sparging alone or in conjunction with SVE, 36 projects supplemented air sparging
treatment with pump-and-treat or other technologies, such as MPE, bioremediation, free product recovery,
and ISCO.
The 123 air sparging projects primarily used vertical wells; three projects reported use of horizontal wells.
For 69 projects for which information about the number of air sparging wells was available, 48 used 2 to
8 wells per project, with a range of 1 to 30 wells. One project identified an ROI (27 ft). Three projects
reported continuous airflow, two reported pulsed flow, and the remainder provided no information on the
type of airflow. For the 74 projects that used air sparging with SVE, the number of SVE wells used
ranged from 1 to 23 wells per project, with 30 projects in the range of 2 to 5 wells per project. Four of
these 74 projects reported the type of air emission treatment used, with two reporting use of GAC, one of
catalytic oxidation, and one of thermal oxidation.
4.1.5 How Has Air Sparging Performed in Treating Oxygenates?
The treatment performance data for 123 projects presented in Tables 4.1-2 and 4.1-3 show that air
sparging (either alone or in combination with other technologies) has been used to reduce MtBE in
groundwater from concentrations greater than 1,000,000 ug/L to less than 50 ug/L. The median project
duration for the 19 completed sites ranged from 1 to 5 years. Although 2 of the 123 projects listed TEA
as a co-contaminant, neither of these projects reported TEA concentrations before or after treatment; no
data for other fuel oxygenates was reported.
4-5
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
Table 4.1-2. Completed Air Sparging Projects - Performance Summary for 19 Projects
Technology(ies)
Air Sparging Only
Air Sparging with
SVE
Air Sparging with
Pump-and-Treat
Air Sparging with
SVE and Pump-and-
Treat
Air Sparging with
Multiple Technologies
#of
Projects
3
2
2
5
7
Initial MtBE Concentration 1
(Hg/L)
Minimum
230
99
1,200
5
55
Median
1,600
218
6,100
203
7,940
Maximum
62,000
337
11,000
2,600
44,400
Final MtBE Concentration 1
(Hg/L)
Minimum
5
Median
27
Maximum
980
NR
16
2
79
1,040
3
79
2,070
5
79
Median
Project
Duration
(months)
18
57
43
50
18
Notes:
NR Information not provided
1 Treatment performance data are based on the data provided by project managers and others in the source materials used to prepare the
treatment profiles website, as shown in cluin.org/products/mtbe. and summarized in Appendix A. Appendix A shows the specific sites that
are summarized here, along with technology design, operation, and performance data for each of the projects.
2 Performance data are shown in terms of changes in concentration of MtBE in the groundwater, as provided in the reference materials and
from the project contacts, except as noted. MtBE concentrations prior to beginning treatment (shown as "initial concentration") and after
treatment was completed (shown as "final concentration") are provided. For projects where more than one technology was used,
performance data are presented under each of the technologies used for the project.
Table 4.1-3. Ongoing Air Sparging Projects -[Performance Summary for 104 Sites
MtBE Concentration Range
Greater than 100,000 ng/L
Greater than or equal to 10,000 ng/L but
less than 1 00,000 ng/L
Greater than or equal to 1 ,000 |ig/L but
less than 10,000 (ig/L
Greater than or equal to 100 (xg/L but
less than 1, 000 ng/L
Greater than or equal to 50 |ig/L but
less than 100 (xg/L
Less than 50 (ig/L
# of Projects
Reporting Initial
MtBE
Concentrations
4
16
24
25
4
18
# of Projects with
Last Reported
MtBE
Concentrations
1
3
10
20
5
15
4.1.6 What Costs Have Been Associated with Using Air Sparging in Treating MtBE?
Project cost data were reported for 39 of the 123 air sparging projects in the dataset; these include data for
both ongoing and completed projects. In most cases, the components that make up the project costs were
not reported. However, other components, such as treatment, monitoring, design, oversight, and health &
safety, may be included in the cost. Most (38 projects) of the reported costs were for ongoing projects
and represent either a partial actual cost as of the time that the report was made or an estimated total
project cost.
4-6
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
The median reported total cost for all air sparging projects was approximately $250,000, with most
projects having a total cost between $100,000 and $350,000. For 7 of these projects that used air sparging
alone, the total cost ranged from $20,000 to $345,000 per project. For the 17 projects that used air
sparging with SVE, the total cost ranged from $27,000 to $1,051,000 per project. The total cost for 15 of
the projects ranged from $96,000 to $672,000 per project.
Because the area, volume, or mass treated was not consistently available for the 39 air sparging projects,
no unit costs were calculated. The cost per volume of groundwater treated (identified as tons of saturated
soil) was reported in one literature source as ranging from $20 to $50 per ton of saturated soil for air
sparging in general (EPA, 1995). Another source identified the unit cost as $371,000 to $865,000 per
hectare ($150,000 to $350,000 per acre) of groundwater plume treated for air sparging in general (FRTR,
2002). The cost of air sparging generally is considered to be better than average, among the costs for
remediation technologies, for treatment of contaminated groundwater (FRTR, 2002). Because of the
relative airflow requirements necessitated by the lower Henry's Law Constants of MtBE and other
oxygenates, the unit costs for the remediation of sites contaminated with MtBE and other oxygenates
could be at the upper end of these ranges.
4.1.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment Using Air
Sparging?
Because ether- and alcohol-based oxygenates exhibit different properties (specifically, Henry's Law
Constant) than other common fuel contaminants such as BTEX, their presence may affect the size and
design of the air sparging system required to remediate the site and, as a result, the cost of remediation.
Research has shown that the removal of MtBE (ether-based) requires 5 to 10 times more airflow than
used for BTEX alone (Fields, et al., 2001). The other common ether-based oxygenates have higher
Henry's Law Constants than MtBE and are theoretically more amenable to treatment via air sparging
(although still less amenable than BTEX components). The common alcohol-based oxygenates have
Henry's Law Constants two to three orders of magnitude lower than those of the ether-based oxygenates,
and may theoretically require 100 to 1,000 times greater airflow. In practice, air sparging may not be
feasible if high enough airflow rates cannot be achieved without causing unwanted subsurface fracturing
or contaminant mobilization. However, the biodegradation potential of both ether- and alcohol-based
oxygenates will also influence system design and may reduce the airflow and time required for
remediation.
In addition to the oxygenate-specific factors described above, additional variables may also affect the
performance and cost of an air sparging system. These factors include the concentration, mass, and
distribution of contaminants in the groundwater; subsurface geology and hydrogeology; cleanup goals;
and requirements for site cleanup. For example, heterogeneity within the subsurface may result in
preferential pathways that prevent injected air from contacting contaminated areas. These factors affect
the number and spacing of air sparging wells, flow rates, and the length of time required for treatment,
which typically will be determined during pilot testing. Air sparging also has potential to cause a lateral
spread of dissolved or separate phase contaminant plumes. For example, in formations with laterally-
oriented clays interbedded with sand, there is a possibility of spreading the contamination when using air
sparging.
4-7
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
4.1.8 Conclusions
Based on the information available from the air sparging MtBE treatment profiles, and other information
contained in the reference documents reviewed in preparation of this report, the following conclusions
may be made regarding the use of air sparging to remediate sites contaminated with MtBE and other
oxygenates:
Data from Air Sparging MtBE Treatment Profiles
Widely used to remediate groundwater contaminated with MtBE - it was employed at 123 of 323
(38%) of projects in the dataset
Most often used alone or in conjunction with SVE (71% of air sparging profiles in dataset); to a
lesser extent has been employed with pump-and-treat or other technologies
Employed to remediate MtBE in groundwater from concentrations greater than 1,000,000 ug/L to
concentrations of less than 50 ug/L and has achieved MtBE concentration reductions greater than
99 percent
Median project duration for different types of air sparging projects (including air sparging alone
or in conjunction with SVE) ranged from 1 to 5 years
Median reported total cost was approximately $250,000, with most projects having a total cost
between $100,000 and $350,000
Treatability of MtBE and Other Oxygenates Using Air Sparging
Increased airflow (compared to a system employed to treat only BTEX) is required to physically
strip common oxygenates using air sparging; based on their Henry's Law Constants; ether-based
oxygenates would require up to 10 times greater airflow and alcohol-based oxygenates would
require 100 to 1,000 times greater airflow than the airflow required to physically strip the same
mass of BTEX components
Air sparging often will promote further removal of oxygenates through biodegradation
mechanisms (Refer to Section 4.4 - Bioremediation for more information)
The varied treatability of oxygenates in extracted vapors using off gas treatment technologies is
an important design consideration if SVE is employed (Refer to Section 4.2 - Soil Vapor
Extraction for more information)
Other Potential Advantages of Applying Air Sparging (EPA, 1995; FRTR, 2002)
Generally considered to be easy to construct, operate, and maintain
Configurations can be designed to cause minimal disturbance to site operations
In some cases, such as areas of lower contaminant concentrations or in remote locations,
contaminants stripped from the groundwater may be allowed to attenuate naturally in the vadose
zone
Other Potential Limitations to Applying Air Sparging (EPA, 1995; FRTR, 2002)
Often contaminants stripped from the groundwater must be extracted and treated aboveground
using SVE
High airflow rates may result in unintended fracturing leading to non-uniform flow or short-
circuiting of injected air in the subsurface, or may result in unintended mobilization of
contaminants as non-aqueous phase liquids (NAPL), dissolved in groundwater, or in soil gas
Has limited applicability at sites with confined aquifers and stratified layers; soil heterogeneities
may limit effectiveness
Has potential to cause a lateral spread of dissolved or separate phase contaminant plumes
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
4.1.9 Example Projects
Air Sparging at Exxon and Mobil Service Stations, Smithtown, NY
A full-scale cleanup is being performed using air sparging, SVE, and groundwater pump-and-treat to prevent
further off-site migration of MtBE, TEA, and BTEX in groundwater originating from two service stations in
Smithtown, New York. The lithology of the site consists of fine to course grained sands with varying amounts
of silt and fine gravel. At the Exxon service station, a 300-scfm air sparging system in conjunction with SVE
was used to replace pump-and-treat remediation. Operation of the air sparging system began in April 2001, and
was continuing to operate at the time when the profile for the project was updated (June 2003). Initial MtBE
concentrations were 15,600 ug/L and initial TEA concentrations were 365 ug/L. The cleanup goal for MtBE is
1,000 ug/L; progress toward meeting the cleanup goal was not reported (EPA, 2003).
Air Sparging at Eaddy Brothers Service Station, Hemingway, SC
A full-scale cleanup is being performed using air sparging and SVE to treat MtBE and other contaminants at a
service station in Hemingway, South Carolina. Soil at the site consists of silty clays with clayey sand lenses.
The SVE system consisted of 230 ft of horizontal SVE piping installed immediately below the asphalt parking
lot surface of the site. Extracted vapors were treated using a thermal oxidizer. The air sparging system, which
began operating two weeks after the SVE system was activated, consisted of 10 vertical sparging wells, each
installed at a depth of 26 ft with 5 ft well screens. The wells were connected to an air sparge compressor
operating at 68 to 70 pounds per square inch (psi). Site specific target levels (SSTLs) for this site ranged from
5 to 80 ug/L per contaminant. As of June 2003, the maximum concentrations of MtBE and BTEX in the
groundwater decreased, with the SSTLs being met for toluene, ethylbenzene, and xylenes. Maximum MtBE
concentrations were reduced from more than 1,000,000 ug/L to 568 ug/L (a 99.99 % reduction), and maximum
BTEX concentrations reduced to 9,690 ug/L. The cost for this application was $195,515 (EPA, 2003b).
4.2 Soil Vapor Extraction
D
D
Overview
Application of a vacuum to soil to extract contaminated vapors
EPA's MtBE Treatment Profiles dataset includes use during 138 projects to
treat MtBE or other oxygenates (used during additional projects as a
component of SVE)
Used to reduce concentration and mass of MtBE and other oxygenates in soil
that may be a source of groundwater contamination
Subsurface air flow may promote biodegradation of contaminants
4.2.1 What is Soil Vapor Extraction?
SVE is an in situ technology in which VOCs such as MtBE and other oxygenates are removed with soil
vapor from the vadose zone. It involves the application of a vacuum to the soil to create a negative
pressure gradient that induces subsurface vapor flow toward one or more extraction points. Soil vapors
are collected from the extraction points and generally are captured and then treated with one or more
aboveground treatment technologies prior to being discharged to the atmosphere.
SVE is used to reduce the concentration and mass of MtBE and other oxygenates in the vadose zone,
which reduces its potential to migrate as vapors into buildings or to act as a continuing source of
groundwater contamination. SVE may also reduce groundwater contaminants through the enhanced
evaporation of NAPL, volatilization of contaminants dissolved in pore water, and stimulation of
biodegradation. SVE also is used as a component of air sparging or other systems to collect injected
4-9
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
gases that have stripped contaminants from groundwater. This section discusses SVE used for treatment
of the vadose zone only. SVE used as a component of air sparging is discussed in Section 4.1.
4.2.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?
In an SVE system, the primary mechanism for contaminant removal from the soil to the vadose zone is
the volatilization of contaminants present in the pure or adsorbed phase onto soil into the vapor phase, as
the vapor phase is continually extracted. The property that shows the extent to which this transfer can
take place during SVE is vapor pressure, which provides an indication of the extent to which each
contaminant will partition between the liquid phase and the vapor state at equilibrium conditions.
Generally, a contaminant with a greater vapor pressure more readily volatilizes than one with a lesser
vapor pressure.
Figure 4.2-1 shows the vapor pressures, in units of millimeters of mercury (mm Hg), for the common fuel
oxygenates as compared to BTEX. Generally, contaminants with vapor pressures greater than 10 mm Hg
are considered to be amenable to treatment using SVE. As shown on the table, each of the common
oxygenates have vapor pressures greater than 10 mm Hg, with ether-based oxygenates generally having
greater vapor pressures than alcohol-based oxygenates. In addition, most of the common oxygenates
(with the exceptions of TEA, TAME, and ethanol) have greater vapor pressures than BTEX, suggesting
that they are more readily extracted using SVE than BTEX, which are commonly addressed with SVE.
Figure 4.2-1. Ranges of Vapor Pressures for Common Fuel Oxygenates
300
250-
200-
X
E
E_
ฃ
i 15ฐ"
ฃ
Q.
5
Q.
100-
50-
0-
ETHER OXYGENATES
256
- ^J
240
152 151
^^~
149
130
75
^^g
68.3
MtBE ETBE TAME DIPE
ALCOHOL OXYGENATES
4-21.6
56.5
42 ^f
40 44
TBA Ethanol Methanol
BTEX
95.2
76
28.4
9.5 8.3
Benzene Toluene Ethylbenzene Xylenes
4.2.3 How is Soil Vapor Extraction Applied to Treat Oxygenates?
During SVE, contaminated soil vapors are extracted by inducing a vacuum at one or more extraction
points that are typically constructed as vertical vapor extraction wells. Horizontal extraction wells or
trenches have also been employed as extraction points. In general, SVE is applied at depths ranging from
10 to 50 ft bgs, but has been applied as deep as 300 ft bgs (EPA, 1995). Shallower applications typically
4-10
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
employ some manner of a surface seal to minimize short-circuiting of the system by ambient air. Typical
flow rates for extracted soil vapors range from 60 to 700 cubic feet per minute (cfm). The vacuum
pressures required at the top of the vapor extraction well (wellhead vacuum) to produce the desired vapor
extraction rate typically range from 3 to 100 inches of water, and vary depending on soil permeability
(FRTR, 2002; EPA, 1995). The ROI of an extraction well is used to determine the number and spacing of
extraction wells. The ROI is the distance from an extraction well to the point at which a vacuum can be
induced to enhance volatilization and extraction of contaminants from the soil.
SVE is considered to be most effective in more homogeneous and higher permeability geologies because
subsurface preferential pathways may result in short circuiting and tighter formations may minimize the
radius of influence of extraction points. In general, vapor extraction points are designed and spaced to
provide for a reduced pressure gradient throughout the contaminated zone. Remediation of MtBE and
other oxygenates using SVE may also potentially benefit from aerobic conditions generated by subsurface
air flow that may result in conditions that are amenable to in situ biodegradation of contaminants. At
some sites, groundwater or free product extraction equipment may be incorporated into vapor extraction
points. Extraction systems that incorporate the recovery of multiple phases are discussed in Section 4.3
about multi-phase extraction and separate systems to recover these other phases are discussed in Section
4.6 about groundwater pump-and-treat and Section 5.2 about product recovery.
Extracted soil vapors, containing volatilized contaminants, are routed to an aboveground treatment system
prior to being discharged to the atmosphere. The types of aboveground vapor treatment technologies that
have been used for treating MtBE and other fuel oxygenates include the following (Symons and Greene,
2003):
Adsorption - Processes in which vapor phase contaminants are adsorbed onto a medium, such as
GAC or resin, as driven by equilibrium forces
Thermal Treatment - Processes in which vapor-phase contaminants are destroyed via high-
temperature oxidation; primary categories of thermal treatment used to treat MtBE and other
oxygenates include thermal oxidation, which employs a flame to generate the high temperatures
needed to oxidize contaminants, and catalytic oxidation, which employs lower temperatures in the
presence of a catalyst (typically platinum, palladium, or other metal oxide) to destroy
contaminants
Biofilters - Processes in which contaminants are biodegraded in a fixed-film bioreactor, typically
consisting of a bed of high surface area filter media, such as GAC, that acts as a support matrix
for a thin film consisting of microbes that are acclimated to the biodegradation of MtBE or other
contaminants
The type of vapor treatment that is used will depend on factors such as the contaminant concentrations in
the extracted vapors and the air emission discharge limitations for the site. Highly contaminated vapors at
a site with stringent air emissions limitations may require a multi-step vapor treatment train, such as
thermal oxidation followed by carbon adsorption. Less contaminated vapors at a site with less stringent
air emissions limitation may require minimal or no vapor treatment. A significant amount of literature
(some of which is listed as references at the end of this report) has been dedicated to the design of vapor
treatment systems. Some of the key considerations for relevant to the treatment of MtBE and other
oxygenates in extracted vapors are summarized below.
4-11
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
Adsorption
Because of their equilibrium properties, MtBE and other oxygenates have a relatively low
breakthrough concentration with bituminous coal-based GAC. Other, more preferentially
adsorbed, contaminants in extracted vapor may reduce the capacity of GAC to remove MtBE and
other oxygenates. In some cases, more absorbable contaminants may displace MtBE or other
oxygenates that are already adsorbed.
Certain types of adsorption media have been shown to preferentially adsorb certain contaminants.
For example, current research shows that, in some cases, coconut shell based GAC removes
MtBE better than other GAC varieties (California MtBE Research Partnership, 1999). In
addition, synthetic resins have been developed to preferentially adsorb some oxygenates, such as
TEA, that are less absorbable by GAC.
Thermal Treatment
As with the treatment of other contaminants, the presence of catalyst poisons, such as metals and
other inorganics, in the vapor stream can reduce the effectiveness of catalytic oxidation.
Biofilters
Biofiltration is a newer technology that has seen less frequent use, but becoming more popular for
treating soil gas contaminated with MtBE and other oxygenates; currently they are used to treat
relatively low concentrations of these contaminants
One reference described the following rules of thumb for selecting vapor treatment (Fields and others,
2001):
Thermal oxidation for VOC concentrations greater than about 2,000 parts per million by volume
(ppmv)
Catalytic oxidation for VOC concentrations between about 100 and 2,000 ppmv
GAC treatment for VOC concentrations between about 35 and 100 ppmv
Direct discharge for VOC concentrations less than 35 ppmv
More detailed information on the application of SVE at sites contaminated with MtBE and other
oxygenates and in general is available in the following documents:
EPA. 2001. Development of Recommendations and Methods to Support Assessment of Soil
Venting Performance and Closure. EPA 600-R-01 -070.
Symons, Brian D., and J. Greene. 2003. Soil Vapor Extraction, Bioventing, and Air Sparging.
In Moyer and Kostecki, Eds. 2003. MtBE Remediation Handbook. Amherst Scientific
Publishers.
U. S. Army Corps of Engineers (USAGE). 1995. USAGE Engineering Manual: SVE and
Bioventing. EM 1110-1 -4001.
4-12
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
4.2.4 What Types of Projects Involved Soil Vapor Extraction to Treat Oxygenates?
From the 323 projects listed in EPA's MtBE Treatment Profiles dataset, 138 projects were identified
where MtBE was treated using soil vapor extraction. Information on the treatment of oxygenates other
than MtBE during these 138 projects is limited. Two projects reported treating these other oxygenates;
one project reported TEA and one reported ethanol.
Table 4.2-1 summarizes the scale and operational status for the 138 SVE projects. The data used to
compile this information was current at the time the profile for each project was completed. Short
summaries for two projects, SVE at Kansas Site U6-077-231, Atwood, KS and SVE at Creek & Davidson
Site G: Service Station, CA, are included at the end of this section, with additional information about all
138 projects provided in Appendix A.
Table 4.2-1. General Information on 138 SVE Projects*
Technology (ies)
Soil Vapor Extraction Only
Soil Vapor Extraction with Air
Sparging
Soil Vapor Extraction with Air
Sparging and Pump-and- Treat
Soil Vapor Extraction with
Bioremediation
Soil Vapor Extraction with In
Situ Chemical Oxidation
Soil Vapor Extraction with
Multiple Technologies
TOTAL
# of Projects
20
74
19
1
2
22
138
Operational Status
Completed
4
2
5
0
1
7
19
Ongoing
16
72
14
1
1
15
119
Scale
Bench
0
0
0
0
0
0
0
Pilot
0
0
0
0
0
1
1
Full
20
74
19
1
2
21
137
* Information about projects that used SVE with air sparging are discussed in Section 4.1.
As shown in Table 4.2-1, most of the 138 SVE projects were full scale (137 projects) and were ongoing
(119 projects) at the time that its profile was published. In addition, most of the projects used SVE in
conjunction with air sparging (74), or SVE alone (20); the remaining projects supplemented SVE
treatment with bioremediation, ISCO, pump-and-treat, or multiple technologies.
The 138 SVE projects primarily used vertical wells; three projects used horizontal wells. For 23 projects
for which information about the number of SVE wells was available, 20 used 2 to 8 wells per project,
with an overall range of 1 to 16 wells. For the 74 projects that used air sparging with SVE, the number of
SVE wells used ranged from 1 to 23 wells per project, with 30 projects in the range of 2 to 5 wells per
project. Four of these 74 projects reported the type of air emission treatment used, with two reporting use
of GAC, one of catalytic oxidation, and one of thermal oxidation. Eight of the SVE projects reported the
types of aboveground treatment technologies that were employed to treat off gas containing MtBE and
other oxygenates. For seven of these eight projects, thermal treatment was employed; six projects used
catalytic oxidation and one project used thermal oxidation. One of the projects that used catalytic
oxidation and one other project also used GAC adsorption to treat the SVE off gas.
4-13
-------
Technologies for Treating MtBE and Other Fuel Oxygenates
4.2.5 How Has SVE Performed in Treating Oxygenates?
Several approaches have been used to evaluate SVE performance for MtBE treatment, including
analyzing the changes in MtBE concentrations in soil, soil vapor, or groundwater, or estimating the mass
of contaminant removed. SVE is used to reduce the mass of contaminants that may leach or otherwise
migrate from the vadose zone to the groundwater. This reduced leaching rate may result in lower
concentrations of contaminants in groundwater, and the performance data provided here are for MtBE
concentrations in groundwater (EPA, 200Ib).
The treatment performance data for 138 projects presented in Tables 4.2-2 and 4.2-3 show that SVE
(either alone or in combination with other technologies) has been used to remediate MtBE in groundwater
from concentrations greater than 100,000 [^g/L to less than 50 [^g/L and has achieved MtBE concentration
reductions greater than 99 percent. The median project duration for the 19 completed sites ranged from 3
months to 5 years. Table 4.2-2 provides a summary of specific projects with performance data for one or
more projects. SVE with pump-and-treat had one completed project, however, no performance data was
reported and therefore was not included in the table below.
Table 4.2-2. Performance Summary for 19 Completed SVE Projects
Technology (ies)
Soil Vapor
Extraction Only
Soil Vapor
Extraction with Air
Sparging
Soil Vapor
Extraction with Air
Sparging and Pump-
and- Treat
Soil Vapor
Extraction with In
Situ Chemical
Oxidation
Soil Vapor
Extraction with
Multiple
Technologies
#of
Projects
4
2
5
1
7
Initial MtBE Concentration 1
Minimum
48
99
5
Median
6,900
218
203
Maximum
8,900
337
2,600
17,000
4,151
10,800
44,400
Final MtBE Concentration 1
Minimum
21
Median
1,800
Maximum
3,200
NR
2
3
5
31
NR
Median
Project
Duration
(months)
24
57
22
9
12
Notes:
NR Information not provided
1 Treatment performance data are based on the data provided by project managers and others in the source materials used to prepare the
treatment profiles website, as shown in cluin.org/products/mtbe. and summarized in Appendix A. Appendix A shows the specific sites that
are summarized here, along with technology design, operation, and performance data for each of the projects.
2 Performance data are shown in terms of changes in concentration of MtBE in the groundwater, as provided in the reference materials and
from the project contacts, except as noted. MtBE concentrations prior to beginning treatment (shown as "initial concentration") and after
treatment was completed (shown as "final concentration") are provided. For projects where more than one technology was used,
performance data are presented under each of the technologies used for the project.
4-14
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Technologies for Treating MtBE and Other Fuel Oxygenates
Table 4.2-3. Performance Summary for 119 Ongoing SVE Projects
MtBE Concentration Range
Greater than 100,000 ng/L
Greater than or equal to 10,000 (ig/L but
less than 1 00,000 ng/L
Greater than or equal to 1 ,000 |ig/L but
less than 10,000 (ig/L
Greater than or equal to 100 (xg/L but
less than 1, 000 ng/L
Greater than or equal to 50 |ig/L but
less than 100 (xg/L
Less than 50 (ig/L
# of Projects
Reporting Initial
MtBE
Concentrations
7
18
26
29
6
20
# of Projects with
Last Reported
MtBE
Concentrations
1
4
10
21
7
22
4.2.6 What Costs Have Been Associated with Using SVE in Treating MtBE?
Project cost data were reported for 24 of the 138 SVE projects in the dataset; these include data for both
ongoing and completed projects. In most cases, the components that make up the project costs were not
reported. However, it is likely that these incorporate different components, such as treatment, monitoring,
design, oversight, and health & safety. Twenty two of these projects reported were ongoing; therefore
costs represent either a partial actual cost as of the time that the report was made or an estimated total
project cost.
The median reported total cost for all SVE projects was approximately $206,000, with most projects
having a total cost between $100,000 and $400,000.
The unit cost of SVE was reported in one literature source as ranging from $ 10 to $40 per cubic yard of
soil treated. This source identified the cost of SVE as generally better than average among the costs for
remediation technologies for treatment of contaminated soil (FRTR, 2002).
In another source, the unit cost of SVE ranged from $60 to nearly $350 per cubic yard of soil for projects
treating less than 10,000 cubic yards of soil, to less than $5 per cubic yards for projects treating more than
10,000 cubic yards of soil. This source also identified the unit cost as ranging from $300 to more than
$10,000 per pound of contaminant removed for projects where up to 3,000 pounds of contaminant mass
were removed, to less than $15 per pound removed for projects where larger quantities were removed
(EPA, 200 Ic). These unit cost ranges represent treatment costs for use of SVE in general, and are not
specific to its use for treatment of MtBE.
4.2.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment using SVE?
Key factors that affect the performance and cost of a SVE system include: the concentration, mass, and
distribution of contaminants in the soil; geology and heterogeneity of the subsurface; cleanup goals; and
requirements for discharging emissions to the atmosphere. These factors affect the number of vapor
extraction wells, vacuum level required, type of off-gas treatment, and length of time required for
treatment (FRTR, 2002).
4-15
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.2.8 Conclusions
Based on the information available from the SVE project MtBE treatment profiles and other information
contained in the reference documents reviewed in preparation of this report, the following conclusions
were identified regarding the use of SVE to remediate sites contaminated with MtBE and other
oxygenates.
Data from SVE MtBE Treatment Profiles
Has been used to remediate soil and groundwater contaminated with MtBE - it was employed at
138 of 323 (38%) of projects in the dataset; of these, SVE was used at 74 projects in conjunction
with air sparging
For projects without air sparging, has been used to remediate MtBE in groundwater from
concentrations greater than 100,000 ug/L to less than 50 ug/L and has achieved MtBE
concentration reductions greater than 99 percent
Median project duration for different categories of projects (for example, SVE alone, SVE with
pump-and-treat, etc.) ranged from 3 months to 5 years
Median reported total cost was approximately $206,000, with most projects having a total cost
between $100,000 and $400,000
Treatability of MtBE and Other Oxygenates Using SVE
All of the common oxygenates have vapor pressures that are greater than 10 mm Hg and are
amenable to treatment using SVE, with ether-based oxygenates generally having greater vapor
pressures than alcohol-based oxygenates
GAC adsorption may be less effective than other thermal treatment in removing alcohol-based
oxygenates from SVE off gas
Other Potential Advantages of Applying SVE (EPA, 1995; FRTR, 2002)
Removal of MtBE from soil generally is considered to be more cost-effective than removal of
MtBE that has dissolved in the groundwater (EPA, 1995; FRTR, 2002).
Reduces the potential for MtBE to migrate as vapors into buildings or leach to the groundwater
Is relatively low cost compared with other remediation technologies
Causes minimal disturbance to site operations
Other Potential Limitations to Applying SVE (EPA, 1995; FRTR, 2002)
Low soil permeability may limit vapor movement through the soil, reducing SVE effectiveness
At heterogeneous sites, contaminants may be difficult to extract from low permeability layers
(soil vapors may be collected mainly from higher permeability layers, while contaminants may be
present in lower permeability layers)
Shallow depths to groundwater or fluctuations in the groundwater table can cause upwelling and
interference with airflow
May not be capable of reaching very stringent soil cleanup levels (soil concentrations may reach
an asymptotic level that is higher than the cleanup level)
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.2.9 Example Projects
SVE at Kansas Site U6-077-231, Atwood, KS
A full scale cleanup was performed using SVE to treat MtBE from a UST site in Atwood, Kansas. Soil at the
site consists of 1 to 18 ft of silt and clay overlying 18 to 50 ft of sand and gravel. The SVE system consisted of
8 vapor extraction wells, installed to a depth of 12 ftbgs. Operation of the SVE system began in February 1994
and the system is currently operational. As of June 2003, the concentration of MtBE in the groundwater has
been reduced from 480 g/L to 93 g/L (an 80% reduction). The most recent cost data available depicts a total
remediation cost of $298,040 (EPA. 2002a).
SVE at Creek & Davidson Site G: Service Station, CA
A full-scale cleanup was performed using SVE to treat MtBE and benzene from a UST leak at a service station
in California. Soil at the site consists of 10 ft of clay overlying sand and gravel. The SVE system consisted of
5 vapor extraction wells and a 700 cfm vacuum system. Thermal oxidation was used for off-gas treatment.
After 2.2 years of SVE operation, the concentration of MtBE in the groundwater (measured in 11 monitoring
wells) was reduced from as high as 8,900 g/L to 21 g/L and the concentration of benzene was reduced from
670 g/L to 0.5 g/L (both more than 99% reductions). The thermal oxidizer destroyed greater than 95% of the
VOCs in the off gases, and remediation at the site is reported to be complete. As of June 2003, the cost data
available depicts a total remediation cost $140,000 (EPA. 2002a).
4.3 Multi-Phase Extraction
Overview
Uses a combination of SVE and groundwater pump-and-treat to extract
MtBE in soil vapor and groundwater, simultaneously
EPA's MtBE Treatment Profiles dataset included use at 13 sites to treat
MtBE
Is most applicable to fine-grained formations in the fine sand to silty sand
range
4.3.1 What is Multi-Phase Extraction?
MPE is a generic term for technologies that extract VOCs such as MtBE and other fuel oxygenates from
the subsurface in soil vapor and groundwater, simultaneously. In addition, it can be used to remove free
product or other NAPLs. MPE is referred to by several other names in the technical literature. Examples
of terms referring to MPE and its configurations are dual-phase extraction (DPE), two-phase extraction
(TPE), and vapor extraction/groundwater extraction (VE/GE). In general, all of these configurations
couple SVE with groundwater (and in some cases NAPL) extraction and employ some form of
aboveground water and vapor treatment technologies (EPA, 1999a; FRTR, 2002). Groundwater pump-
and-treat and aboveground water treatment technologies are discussed in more detail in Section 4.6 and
SVE and aboveground vapor treatment are discussed in more detail in Section 4.2.
4.3.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?
The primary removal mechanisms for MPE are volatilization with subsequent air advection for the vapor
phase and dissolution and aqueous advection in groundwater. Vapor pressure, solubility, and
organic/water partition coefficient are the primary properties of MtBE and other oxygenates that
correspond to these removal mechanisms. In general, contaminants with higher solubility and vapor
pressure and lower partition coefficients, such as fuel oxygenates, are more appropriate for removal using
MPE than BTEX. As shown on Table 4.3-1, the properties of both ether- and alcohol-based oxygenates
suggest that they may be more favorably removed from the subsurface by the vapor and groundwater
4-17
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Technologies for Treating MtBE and Other Fuel Oxygenates
extraction components of MPE than BTEX constituents. One exception to this generalization is that
certain alcohol-based oxygenates, specifically TEA and ethanol, may be less readily removed in the vapor
phase because of their relatively low vapor pressures.
MPE provides several advantages when compared with use of SVE or pump-and-treat alone. MPE
provides for an increase in groundwater recovery rates, an increase in radius of influence in individual
groundwater recovery wells, and recovery of shallow free product. By depressing the groundwater table
in the vicinity of the extraction wells, MPE provides for remediation of the capillary fringe and smear
zone, and remediation of volatile, residual contaminants located above and below the water table (EPA,
1999a).
However, while the contaminant properties are important considerations in the selection and design of an
MPE system for a given site, the applicability of MPE is more dependent on media properties, primarily
hydraulic conductivity (K), transmissivity, depth to water table, and soil moisture (EPA, 1999a).
Table 4.3-1. Contaminant Properties Relevant to MPE
Contaminant Category
BTEX Constituents
Ether-Based Oxygenates
(such as MtBE)
Alcohol-Based Oxygenates
(such as TEA)
Solubility into H2O from
Gasoline Range (mg/L)
3-100
750 - 5,500
> 25,000
Vapor Pressure Range
(mmHg)
8-95
68-250
40 - 120
Partition Coefficient
(log I/kg)
1.5-3.2
1.0-2.2
0.2-1.6
Source: Based on information in Table 2-2.
4.3.3 How is MPE Applied to Treat Oxygenates?
MPE can be implemented in a variety of configurations, including single pump, two pump, and
bioslurping. In the single pump configuration, a single drop tube is employed to extract both liquid and
vapor from a single well. The vacuum and liquid suction lift is achieved by one vacuum pump (liquid-
ring pumps, jet pumps, and blowers are typical). In the two-pump configuration, a submersible pump is
used for groundwater recovery in conjunction with a separate vacuum applied at the sealed wellhead. In
this configuration, liquid and vapor streams are separate from one another. Depending on application,
two-pump systems can use electric or pneumatic submersible pumps for groundwater recovery and liquid
ring pumps or blowers to induce vacuum. Applications that recover free product or LNAPL typically use
pneumatic submersible pumps for liquid recovery. Bioslurping uses the same configuration as for a
single pump system, however the drop tube is set at, or just below, the liquid-air interface. The extraction
point alternates from recovering liquid to air, emanating a slurping sound. This configuration has been
effective in free product recovery, and also enhances in situ aerobic bioremediation, due to the increased
airflow.
In some configurations, the vacuum used in MPE increases the effective drawdown of groundwater (i.e.,
increase or lower the depth to groundwater table) locally near the pumped well. This has the affect of
increasing exposed soil in the saturated zone and the removal of volatile contaminants located above and
below the original water table.
Extracted vapors and liquids commonly are treated aboveground. The types of technologies used for
aboveground treatment are similar to those used for SVE and groundwater pump-and-treat, respectively,
and are discussed further under those technologies.
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Technologies for Treating MtBE and Other Fuel Oxygenates
More detailed information relevant to the application of MPE at sites in general or contaminated with
MtBE and other oxygenates is available in the following documents:
U.S. Army Corps of Engineers. 1999. Engineering and Design: Multi-Phase Extraction (EM
1110-1-4010). June 1. http://www.usace.army.mil/inet/usace-docs/eng-manuals/emlllO-l-4010/
U.S. Environmental Protection Agency. 1999. Multi-Phase Extraction:
Office of Solid Waste and Emergency Response. June.
http://cluin.org/download/remed/mpe2.pdf
State of the Practice.
U.S. Environmental Protection Agency. 1997. Presumptive Remedy: Supplemental Bulletin,
Multi-Phase Extraction Technology for VOCs in Soil and Groundwater. Office of Solid Waste
and Emergency Response. April, http://clu-in.org/download/toolkit/finalapr.pdf
4.3.4 What Types of Projects Involve MPE for Treating Oxygenates?
From the 323 projects in EPA's MtBE Treatment Profiles dataset, 13 projects were identified where
MtBE was treated using MPE. Information on the treatment of other oxygenates during these 13 projects
is limited; no projects reported treating other oxygenates. Table 4.3-2 summarizes the scale and
operational status for the 13 MPE projects. The data used to compile this information was current at the
time the profile for each project was completed. Short summaries for two projects, MPE at Service
Station A, MD, and MPE at Sparks Solvent/Fuel Site, Sparks, NV, are included at the end of this section,
with additional information about all 13 projects provided in Appendix A.
Table 4.3-2. General Information on 13 MPE Projects
Technology (ies)
Multi-Phase Extraction Only
Multi-Phase Extraction with
Air Sparging
Multiple Phase Extraction with
In situ Chemical Oxidation
TOTAL
# of Projects
9
2
2
13
Operational Status
Completed
3
1
0
4
Ongoing
6
1
2
9
Scale
Bench
0
0
0
0
Pilot
4
0
0
4
Full
5
2
2
9
As shown in Table 4.3-2, most of the 13 MPE projects were full-scale (9 projects) and were on-going (9
projects) at the time that its profile was published. Most of the projects (9) used multi-phase extraction
only; the remaining 4 projects supplemented MPE with air sparging (2 projects) and ISCO (2 projects).
Five of the projects (4 pilot scale and 1 full scale) used the Bubblex system, a patented method that
simultaneously extracts vapor and water using a high vacuum. One full-scale project used a VE/GE
system (used at 8 sites), and 1 full-scale project used total fluid extraction with advanced oxidation
technology. The VE/GE systems used 4 to 17 VE wells, with average airflow rates ranging from 4.6 to
18.5 scfm, and 2 to 8 GE wells, with pumping rates ranging from 0.11 to 0.67 gpm.
As another example, a site in Fountain Valley, CA had an air sparge/SVE system installed which
appeared to remediating a BTEX plume with the exception of one recalcitrant area. However, an
MTBE/TBA plume developed which did not appear to be affected by the operation of the air sparge/SVE
system. MTBE was reduced but the TEA concentration was found to be increasing. After conducting
feasibility tests, a dual-phase extraction (MPE) system to remove and treat ground is being installed
(O'Connell, 2004).
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.3.5 How Has MPE Performed in Treating Oxygenates?
For the 13 projects identified from 323 MtBE treatment profiles, MPE treated MtBE with concentrations
as high as 100,000 [^g/L (JFK International Airport, Jamaica City, NY) and achieved as low as 50 |lg/L in
groundwater after treatment. None of the 13 projects listed TEA as a contaminant. Therefore, this
section only highlights performance for MtBE.
Tables 4.3-3 and 4.3-4 summarize performance data for 3 completed and 7 ongoing MPE projects.
Because the dataset included relatively few completed projects with performance data, Table 4.3-3
provides a summary of specific projects instead of a summary of minimum, median, and maximum
concentrations. The reason for the increase in the MtBE concentration at the Tahoe Boat Company, CA
site was not specified.
Table 4.3-3. Completed MPE Projects - Performance Summary for 3 Projects
Technology (ies)
Multi-Phase
Extraction Only
Multi-Phase
Extraction Only
Multi-Phase
Extraction with Air
Sparging
Site Name and Location
Site CA - X, Lawndale, CA
Eight Service Stations MD - A,
MD
Tahoe Boat Company, Lake
Tahoe, CA
Scale
Pilot
Full
Full
Initial MtBE
Concentration 1
(Hg/L)
11
6,140
55
Final MtBE
Concentration 1
(Hg/L)
NR
791
79
Median
Project
Duration
(months)
NR
NR
45
Notes:
NR Information not provided
1 Treatment performance data are based on the data provided by project managers and others in the source materials used to prepare the
treatment profiles website, as shown in cluin.org/products/mtbe. and summarized in Appendix A. Appendix A shows the specific sites that
are summarized here, along with technology design, operation, and performance data for each of the projects.
2 Performance data are shown in terms of changes in concentration of MtBE in the groundwater, as provided in the reference materials and
from the project contacts, except as noted. MtBE concentrations prior to beginning treatment (shown as "initial concentration") and after
treatment was completed (shown as "final concentration") are provided. For projects where more than one technology was used,
performance data are presented under each of the technologies used for the project.
Table 4.3-4. Ongoing MPE Projects - Performance Summary for 7 Sites
MtBE Concentration Range
Greater than or equal to 10,000 p.g/L but
less than 1 00,000 (ig/L
Greater than or equal to 1 ,000 |ig/L but
less than 10,000 jig/L
Greater than or equal to 100 (ig/L but
less than 1, 000 ng/L
Greater than or equal to 50 ng/L but less
than 100 ng/L
Less than 50 (ig/L
# of Projects
Reporting Initial
MtBE
Concentrations
1
1
2
0
0
# of Projects with
Last Reported
MtBE
Concentrations
0
2
0
1
1
Note:
Performance data were not available for some sites
4-20
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.3.6 What Costs Have Been Associated with Using MPE in Treating MtBE?
The total project cost was reported for 2 of the 13 MPE projects identified above. The completed Kings
Beach Swiss Mart, CA project, which employed MPE alone, reported a total project cost of $130,000 and
the completed Tahoe Boat Company, CA project, which employed MPE with air sparging, reported a
total project cost of $383,000. Both of these total costs were the amounts reported by the state cleanup
fund. Because the area, volume, or mass treated was not available for this project, a unit cost was not
calculated.
Little additional information was identified in the literature about the costs of using MPE for the treatment
of MtBE and other oxygenates, or for other contaminants. The cost per volume of subsurface treated
(identified as cubic yards of subsurface) was reported in one literature source as ranging from $36 to $170
per cubic yard for sites contaminated with chlorinated solvents (EPA, 1999a). The cost of MPE generally
is considered to be average, among the costs for remediation technologies, for treatment of contaminated
groundwater (FRTR, 2002). However, project costs will likely be driven primarily by the aboveground
treatment required. The cost of aboveground water treatment technologies is discussed in Section 4.6; the
cost for aboveground vapor treatment is discussed in Section 4.2.
4.3.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment using
MPE?
When MtBE or other oxygenates are present and must be remediated at a site, MPE, either alone or in
combination with other technologies, may be a suitable remediation approach. MPE affects mass removal
by volatilization, dissolution, and advective transport. In general, if both SVE and groundwater pump-
and-treat are potentially applicable technologies, then MPE may be considered as a remedial alternative.
The performance of MPE is governed, primarily, by media properties and, to a lesser extent, by
contaminant properties. MPE is most applicable to fine-grained formations in the fine sand to silty sand
range (K = 10"3 to 10"5 centimeters per second) with low transmissivity (less than 200 gallons per day per
foot).
A typical result of conventional pumping in low conductivity and transmissivity formations is increased,
and sometimes rapid, drawdown with steep gradients, with corresponding low recovery rates. This
condition limits the influence of the conventional pumping well. MPE overcomes this limiting factor
with the application of a vacuum. The vacuum enhancement of MPE also can overcome the capillary
forces that can trap contaminants within the capillary zone. This allows better recovery of LNAPL, which
tends to accumulate in the capillary zone at the air-water interface.
In addition to the technology-specific factors described above, additional factors may also affect the
performance and cost of any MPE system. These factors include:
The concentration, mass, and distribution of contaminants in the soil and groundwater
Geology, hydrogeology, and heterogeneity of the subsurface; cleanup goals
Requirements for air emissions and water discharges
These factors affect the number and type of extraction wells, vacuum level, pumping rate, type of
aboveground water and off-gas treatments, and length of time required for treatment (FRTR, 2002). More
information about the factors that influence the performance and cost of air sparging systems in general is
available in the references listed in this report.
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.3.8 Conclusions
Based on the information available from the MPE project MtBE treatment profiles and other information
contained in the reference documents reviewed in preparation of this report, the following conclusions
were identified regarding the use of MPE to remediate sites contaminated with MtBE and other
oxygenates.
Data from MPE MtBE Treatment Profiles
Has been used to remediate groundwater contaminated with MtBE, but less frequently than some
other technologies, such as air sparging and bioremediation - it was employed at 13 of the 323
(4%) of the projects in the dataset
Most often used without in situ technologies (70% of projects in dataset); to a lesser extent has
been employed in conjunction with air sparging or ISCO
Has been used to remediate MtBE in groundwater from concentrations greater than 100,000 ug/L
to less than 50 ug/L and has achieved MtBE concentration reductions greater than 99 percent
Cost information is limited - total costs for two project in dataset were $130,000 and $383,000
Treatability of MtBE and Other Oxygenates Using MPE
While the contaminant properties are important considerations in the selection and design of an
MPE system for a given site, the applicability of MPE is more dependent on media properties,
primarily hydraulic conductivity and transmissivity (EPA, 1999a).
Other Potential Advantages of Applying MPE (EPA, 1999a)
Has potential for increase in groundwater recovery rates, compared to conventional pumping
practices in equivalent settings
Has potential for increase in radius of influence of individual groundwater recovery wells
Has potential for recovery of free product or other LNAPL
Has potential for remediation of the capillary fringe and smear zone
Simultaneous remediation of soil vapors and groundwater
Effective on lower permeability soil sites
Other Potential Limitations of Applying MPE (EPA, 1999 a)
Potentially greater aboveground treatment requirements as a result of NAPL emulsions and VOC-
laden vapors
Initial start-up methods and adjustment period may be longer, compared to conventional practices
Potentially higher capital costs compared to conventional pumping approaches
Depth limitations to some MPE configurations
4.3.9 Example Projects
MPE at a Service Station MD-A, MD
At a service station in Maryland, MPE was conducted using a VE/GE system that consisted of 10 VE wells and
6 GE wells. The sites were located on coastal plain, and the soil consisted of sandy silts and clays. The average
flow rates were 9.8 scfm in the VE wells and 0.24 gpm for the GE wells. The concentration of MtBE in
groundwater was reduced from 27,027 jig/L to 32 jig/L over 3.5 years of system operation. The cleanup was
reported as completed, however a cleanup goal was not provided (EPA, 2000c).
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Technologies for Treating MtBE and Other Fuel Oxygenates
MPE at Sparks Solvent/Fuel Site, Sparks NV
Since 1995, the Sparks Solvent/Fuel Site located in Sparks, Nevada, a remediation system consisting of MPE,
air sparging, and SVE has been operational. The treatment system consists of 29 MPE wells, an oil-water
separator, and a fluidized bed bioreactor, with an influent flow rate of 370 gpm and a retention time of 8
minutes. Vapors are sent through a condenser, followed by a thermal oxidizer, before release to the
atmosphere. Condensate is sent back through the oil-water separator. Performance data, available for the first
650 days of site operation, showed a reduction in MtBE concentration across the bioreactor from 2,400 to 55
ug/L. No data was provided for reduction of MtBE concentrations in the aquifer (EPA, 2000b).
4.4 In Situ Bioremediation
Overview
Enhances the mechanisms that biologically degrade MtBE and other
oxygenates in contaminated soil and groundwater
EPA's MtBE Treatment Profiles dataset includes use at 73 sites to treat
MtBE; 12 of these sites also reported treating TEA
Typically used to treat residual soil and groundwater contamination after
contaminant source has been removed
4.4.1 What is Bioremediation?
Bioremediation is a process by which microorganisms, fungi, and plants metabolize pollutant chemicals.
It has been used to treat oxygenates in soil and groundwater both in situ and ex situ. Generally, an
engineered bioremediation system stimulates the biodegradation of contaminants through the introduction
of electron acceptors (typically oxygen), electron donors (substrates or food sources), nutrients, or
microbes that are acclimated to the contaminated soil or groundwater. These amendments are either
introduced to the subsurface in situ or are added to extracted groundwater or excavated soil. A
description of the various types of amendments is provided below (Wilson, 2003c).
Amendments
Electron Acceptors - Oxygen is the most common electron acceptor used to promote
biodegradation and is added in different ways including: in sparged air, through injection of a
solid or liquid that generates oxygen, or through in situ electrochemical generation. Other
electron acceptors, including nitrate, sulfate, and iron (III) compounds, may be added to support
anaerobic biodegradation.
Electron Donors - In direct biodegradation pathways, the contaminant acts as the electron donor
or substrate. However, during cometabolic degradation, a different electron donor is metabolized,
resulting in the consequential oxidation of the contaminant. In some contaminated plumes, other
electron donors, such as other constituents of gasoline, may also be present. In cases where they
are not, and cometabolic degradation pathways are desired, electron donors may be added.
Nutrients - Nutrients, such as nitrogen and phosphorus and other trace elements, are necessary
for cell growth because they are key biological building blocks. Addition of nutrients as a
supplement helps ensure that concentrations of nutrients do not become a limiting factor for
bioremediation.
Bioaugmentation - involves the addition of supplemental microbes to the subsurface where
organisms able to degrade specific contaminants are deficient. Microbes may be grown from
populations already present at a site or "seeded" from cultures grown in aboveground reactors or
available commercially as cultivated strains of bacteria known to degrade specific contaminants.
The application of bioaugmentation technology is highly site-specific and dependent on the
microbial ecology and physiology of the subsurface (EPA, 1998b).
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Technologies for Treating MtBE and Other Fuel Oxygenates
This section focuses on engineered in situ remediation technologies that use microorganisms to
biodegrade pollutant chemicals. In situ bioremediation technologies are configured to either directly
inject supplements into the contaminated media; to place the supplements in the pathway of groundwater
flow; or to extract contaminated groundwater, amend it with supplements, and recirculate the amended
groundwater through the contaminated zone (further information about groundwater extraction is
provided in Section 4.6 about pump-and-treat). EPA policy regarding injection of supplements is
discussed in Section 3.4. Some of the key considerations for various types of engineered in situ
remediation systems are summarized below (EPA, 1998b). A discussion of ex situ applications of
bioremediation, which focuses on biological treatment of extracted groundwater, is included in Section
4.7 about treatment of extracted groundwater.
Engineered Systems
Direct Injection Wells/Trenches - In a direct injection system, degradation is enhanced through
the addition of microbes, nutrients, electron acceptors, or electron donors directly into the aquifer
at injection points or directly into the soil. Direct injection technologies include those that
employ injection wells or trenches through which supplements are introduced. Some common
direct injection technologies use chemical or electrochemical means to increase the level of
oxygen in the groundwater, or inject microorganisms that are specifically conditioned to
degrading the contaminants of concern. The natural flow of the groundwater generally is not
impeded, but is monitored to determine that the degradation of the contaminants and their
daughter products is completed within an acceptable distance from the source.
Recirculation Systems - A recirculation system extracts contaminated groundwater from the
site, adds to or amends the extracted water ex situ, and reinjects the "activated" water to the
subsurface, generally upgradient of the contaminated zone. As an alternative, extraction and
injection are performed at different elevations in a single well, creating vertical circulation. A
groundwater recirculation configuration may be used to provide containment of a plume or to
allow the addition of amendments in a more controlled environment.
Permeable Reactive Barriers - The placement of supplements in the pathway of groundwater
flow constitutes a PRB, sometimes referred to as a treatment zone or "bio-barrier". With a PRB
approach, an active bioremediation zone is created by such methods as backfilling a trench with
nutrient-, oxidant-, or reductant-rich materials, or by creating a curtain of active bioremediation
zone through direct injection or groundwater recirculation at the toe of a plume. PRBs contain a
contaminant plume by treating only groundwater that passes through it.
The design and configuration of in situ bioremediation systems varies widely based on site-specific
conditions. A treatability study or pilot-scale testing is often performed to determine the type and amount
of amendments required to create and maintain the conditions optimal for biodegradation as well as to
select the type of engineered system that is most suitable to introduce the amendments to the subsurface
(EPA, 2000a).
4.4.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?
Early studies on MtBE contamination of groundwater concluded that the compound was either non-
biodegradable or very resistant to biodegradation. However, more recent research has shown that MtBE
can be degraded both aerobically and anaerobically, although anaerobic intrinsic degradation rates are
relatively slow. The research has found that there are naturally occurring microbes capable of using
MtBE as their sole carbon and energy source. Such microorganisms seem to be widespread, but are
present natively in low numbers and take time to reach a sufficiently dense population to sustain MtBE
degradation. As a result, cometabolic approaches are often considered for MtBE bioremediation, wherein
an organic substrate (electron donor) that is readily degraded is added to the subsurface, resulting in the
4-24
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Technologies for Treating MtBE and Other Fuel Oxygenates
consequential oxidation of MtBE. Because the ability of microorganisms to cometabolically degrade
MtBE is consistently found in strains that are predisposed to catabolize structural analogs of MtBE,
suitable co-substrates include simple branched and even non-branched alkanes such as propane and
butane (Wilson, 2003a; Bradley, 2001; Vance, 2003; Hyman, 2000; Steffan et al, 1997).
Although detailed comparative evaluations of the aerobic degradation rates of other fuel oxygenates have
not been performed to date, the aerobic biodegradation rates of TAME, EtBE, DIPE, TEA, and TAA
were observed to be of the same order of magnitude as the aerobic degradation rate of MtBE in one
research study using a mixed culture (Church and Tratnyek, 2000). Together with the similarity of
product chemical structure, these results suggest that the same or similar enzyme systems and pathways
are responsible for the biodegradation of these oxygenates (see Figure 4.4-1 below) and that the
bioremediation of fuel oxygenates other than MtBE therefore has similar constraints (EPA 200 la).
Figure 4.4-1. Proposed Degradation Pathway of MtBE and Other Oxygenates
(Church and Tratnyek, 2000)
O%
HgjCHaC-C-QH *-
CHa
OH3
H3CH2C-O-O-CH3
CHj
CH3
CH3 H
HjC-C-O-C-CHa
H CH3
IP
T,
HjC-C-OH
H
etc.
Successful field-scale applications of engineered bioremediation systems have been limited to the aerobic
pathway, as opposed to the anaerobic pathway. The advantages of the aerobic pathway include:
More energy is derived by microorganisms from the aerobic metabolism of MtBE and other fuel
oxygenates; consequently, MtBE degrading cultures grow more quickly under aerobic conditions
There are a number of aerobes that are known to use MtBE as a sole carbon and energy source;
anaerobic pathways and the types of microorganisms involved are less well documented
Where the terminal electron acceptor is not present initially in sufficient quantity, addition of
oxygen for aerobic bioremediation can be as simple as bubbling air into the aquifer; addition of
electron acceptors for anaerobic bioremediation is more complex and can foster concerns
regarding the toxicity and fate of the added material
Laboratory studies have provided inconsistent results regarding the degree to which MtBE is
biodegraded anaerobically to end products and the extent to which other oxygenates are
biodegraded under anaerobic conditions
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Technologies for Treating MtBE and Other Fuel Oxygenates
However, the many pathways by which MtBE and other oxygenates may be biodegraded anaerobically
have been the subject of recent research and ongoing studies. Table 4.4-1 highlights the various electron
acceptors that are used in anaerobic bioremediation studies and contrasts the products of complete
anaerobic degradation with those for aerobic metabolism.
Table 4.4-1. MtBE Biodegradation Mechanisms and Products
Zone
Aerobic
Anaerobic
Nitrate Reducing
Iron Reducing
Sulfate Reducing
Methanogenic
Electron
Donor
MtBE
MtBE
MtBE
MtBE
MtBE
Electron
Acceptor
02
NCV
Fe+3
so4-2
CO2
Products of Complete
Degradation
CO2 and H2O
N2, NH3, CO2, and H2O
Fe+2,CO2, andH2O
H2S, CO2, and H2O
CH4, CO2, and H2O
While Table 4.4-1 lists the products of complete degradation of MtBE, incomplete degradation of MtBE
and other oxygenates may also occur under certain conditions. Of specific note, TEA has been shown to
be a degradation intermediate that may persist under anaerobic conditions (Vance et al, 2003). In some
cases, this can result in MtBE plumes having a concentration of TEA in excess of the concentration of
MtBE (Wilson, 2003a). A paper published as this report went to print (Schmidt, 2004) provides further
information about the role of TEA in microbial biodegradation. Therefore, application of bioremediation
approaches to MtBE and other oxygenates often have considered the complete pathway to end products
and the possible stall of the bioremediation process at intermediates along that pathway.
4.4.3 How is Bioremediation Applied to Treat Oxygenates?
Bioremediation is applied to MtBE and other oxygenates in systems that range in complexity from not
being engineered at all (natural biodegradation) to systems that are completely engineered, including the
addition of conditioned microorganisms (bioaugmentation) and of nutrients as well as co-substrates and
electron acceptors (biostimulation). Further, these systems can be based on aerobic or anaerobic
pathways, or a sequential combination of these pathways.
The rate at which natural biodegradation of MtBE and other oxygenates will occur at a site is affected by
a number of site conditions, including groundwater chemistry, presence of other contaminants, and
number of native microbes capable of degrading MtBE or other oxygenates. Whether the contaminated
zone is aerobic or anaerobic (nitrate reducing, iron reducing, sulfate reducing, or methanogenic), and
other chemical parameters (for example, pH, alkalinity, and inorganic content) will determine what types
of microbes may be able to grow and what type of biodegradation pathway may be followed. Figure 4.4-
2 depicts the oxidative zones which may be present in a plume at a petroleum-contaminated site and
illustrates how each of the anaerobic and aerobic pathways listed in Table 4.4-2 may be part of the natural
biodegradation process.
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Technologies for Treating MtBE and Other Fuel Oxygenates
Figure 4.4-2. Typical Zones Downgradient of Petroleum Contaminant Source
: Source Zone : : :
' Carbon Dioxide (CO2) Reducing (Methanogenic) Zone
Sulfate (SO4) Reducing Zone :
Iron (III) Reducing Zone :
1 Nitrate (NO3) Reducing Zone
Oxygen Reducing Zone
Source: Modified from Anderson, R.T. and D.R. Lovley 1997
Multiple microbes that are capable of biodegrading oxygenates have been identified at sites contaminated
with MtBE and other oxygenates. Whether such microbes are present at a specific site will affect the
viability of natural biodegradation without the need for bioaugmentation. Where these microbes are
present, natural biodegradation or limited biostimulation, such as air sparging to increase oxygen levels,
may be effective in reducing the concentrations of MtBE and other oxygenates. However, other
conditions must be conducive to support significant natural biodegradation. Typically, only those sites
that have aerobic conditions in the contaminated zone because of shallow water tables and high rates of
groundwater recharge have achieved significant natural biodegradation of MtBE and other oxygenates
(Stocking et al., 2000).
In some cases, the presence of other contaminants, such as benzene, has been shown to facilitate the
natural biodegradation of MtBE and other oxygenates through co-metabolism. However, contaminants
such as BTEX also may inhibit the biodegradation of oxygenates through the depletion of electron
acceptors or nutrients, or may be preferentially used because of the relatively slow growth of oxygenate-
degrading microorganisms (EPA, 200la; Deeb and Kavanaugh, 2002).
In addition, sites contaminated with alcohols such as ethanol also may inhibit the biodegradation of ether-
based oxygenates such as MtBE through the depletion of electron acceptors or nutrients (da Silva, 2003).
Fully-engineered systems for the bioremediation of oxygenates typically incorporate both biostimulation
and bioaugmentation to accelerate the biodegradation process. Most commonly, these systems are based
on the aerobic pathway so that the biostimulation component includes the addition of oxygen, through
air/oxygen sparging or addition of oxygen releasing chemicals, as well as the addition of nutrients. The
addition of oxygen through one of these means can be used to make the entire contaminant zone aerobic
and thereby provide more uniform conditions for accelerated biodegradation. Maintaining high oxygen
levels is especially important to effective aerobic biodegradation in that oxygenate-degrading organisms
have been shown in research studies to require a higher concentration of oxygen. The bioaugmentation
component is achieved by adding microbial cultures that are conditioned to degrade oxygenates either by
being grown on these contaminants or by culturing isolated species that have the required enzymes.
Bioaugmentation is often critical to the success of an engineered bioremediation system in that
microorganisms capable of degrading oxygenates may not be present natively and are slow growers
(Rittman, 2003, Wilson, 2003b).
The use of anaerobic pathways may have engineering advantages under certain conditions, such as in
treating oxygenate contamination in deep aquifers or source zones. Recent research and field studies have
focused on the various anaerobic pathways for biodegradation of MtBE and other fuel oxygenates (Vance
et al, 2003). However, the results of these studies in terms of oxygenate degradation efficiency have been
4-27
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Technologies for Treating MtBE and Other Fuel Oxygenates
variable and no single anaerobic pathway has demonstrated consistent success for degrading oxygenates
to end products, even in the laboratory environment (Finneran and Lovely, 2003e). Therefore, site-
specific treatability studies and pilot testing are generally performed if bioremediation using anaerobic
pathways is to be considered at a site.
Engineered systems may also incorporate the addition of a co-substrate to help establish an active
microbial community and thereby accelerate the biodegradation of oxygenates. Hydrocarbon gases, such
as propane and butane are one type of co-substrates that has been used in field applications due to the
simplicity of injecting and diffusing a hydrocarbon gas (Steffan et al, 2003). Some proprietary
technologies are based on the use of specific co-substrates and strains of microbes.
4.4.4 What Types of Projects Involved Bioremediation to Treat Oxygenates?
From the 323 MtBE projects in EPA's MtBE Treatment Profiles dataset, 73 projects were identified
where MtBE was treated using engineered bioremediation systems, either alone or in conjunction with
another technology. Information on the treatment of other oxygenates during these 73 projects is limited,
with a total of 12 of the 73 projects reporting TEA as a co-contaminant.
Table 4.4-2 summarizes the scale and operational status for the 73 bioremediation projects. These
projects include only engineered bioremediation systems and exclude projects that used natural
biodegradation as part of a monitored natural attenuation approach (see Section 5.3 for a discussion of
monitored natural attenuation).
Table 4.4-2. General Information from 73 Engineered Bioremediation Projects
Technology (ies)
# of Projects
Operational Status
Completed
Ongoing
Scale
Bench
Pilot
Full
IN SHU PROJECTS
Bioremediation Only
Bioremediation with Air Sparging
Bioremediation with Pump-and-
Treat
Bioremediation with SVE
Bioremediation with Air Sparging
and SVE
Bioremediation with Multiple
Technologies
55
2
1
1
6
1
25
0
0
0
6
0
30
2
1
1
0
1
2
0
0
0
0
0
12
1
0
0
0
0
41
1
1
1
6
1
EX SITU PROJECTS
Bioremediation Only
TOTAL
7
73
4
35
3
38
5
7
0
13
2
53
As shown in Table 4.4-2, 62 of the 73 bioremediation projects employed either in situ or ex situ
bioremediation alone. However, 11 of the projects supplemented bioremediation treatment with air
sparging, SVE, or pump-and-treat. Most of the bioremediation projects in the dataset were full scale (53
projects) and were ongoing (38 projects) at the time that its profile was published. For the 40 projects
specifying the type of MtBE biodegradation mechanism employed, 37 reported using the aerobic
pathway, 1 project reported using cometabolic pathways, 1 project reported using a combination of
aerobic and anaerobic pathways, and 1 project reported using a combination of aerobic and cometabolic
pathways. Short summaries for two of these projects, In Situ Bioremediation at Port Hueneme - D,
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Technologies for Treating MtBE and Other Fuel Oxygenates
Oxnard, CA, In Situ Bioremediation at Sunoco Service Station, MA, and In Situ Bioremediation at South
Beach Marina, Hilton Head, South Carolina, are included at the end of this section, with additional
information about all 73 projects provided in Appendix A.
4.4.5 How Has In Situ Bioremediation Performed in Treating Oxygenates?
Tables 4.4-3 and 4.4-4 summarize performance data for the 35 completed and 38 ongoing in situ
bioremediation projects that reported this information. The concentration of MtBE in groundwater prior
to treatment was as high as 870,000 ug/L (ongoing project at Site NY - F), and as low as 10 ug/L (Main
Street Shell Conway, SC and Speedway #226, North Charleston, SC).
Table 4.4-3. Completed In Situ Bioremediation Projects
Performance Summary for 31 Projects
Technology(ies)
In situ Bioremediation
Only
In situ Bioremediation
with Air Sparging and
SVE
#of
Projects
25
6
Initial MtBE Concentration 1
(Hg/L)
Minimum
5
4,151
Median
2,800
10,800
Maximum
100,000
44,400
Final MtBE Concentration 1
(Hg/L)
Minimum
1
NR
Median
35
NR
Maximum
33,000
NR
Median
Project
Duration
(months)
6
12
Notes:
NR Information not provided
1 Treatment performance data are based on the data provided by project managers and others in the source materials used to prepare the
treatment profiles website, as shown in cluin.org/products/mtbe. and summarized in Appendix A. Appendix A shows the specific sites that
are summarized here, along with technology design, operation, and performance data for each of the projects.
2 Performance data are shown in terms of changes in concentration of MtBE in the groundwater, as provided in the reference materials and
from the project contacts, except as noted. MtBE concentrations prior to beginning treatment (shown as "initial concentration") and after
treatment was completed (shown as "final concentration") are provided. For projects where more than one technology was used,
performance data are presented under each of the technologies used for the project.
Table 4.4-4. Ongoing In Situ Bioremediation Projects Performance Summary for MtBE at 38 Sites
MtBE Concentration Range
Greater than 100,000 (ig/L
Greater than or equal to 10,000 |ig/L but
less than 100,000 ug/L
Greater than or equal to 1 ,000 |ig/L but
less than 10,000 ng/L
Greater than or equal to 100 (ig/L but
less than 1,000 ug/L
Greater than or equal to 50 p.g/L but
less than 100 |ig/L
Less than 50 |ig/L
# of Projects
Reporting Initial
MtBE
Concentrations
1
12
11
4
0
5
# of Projects
Reporting Post-
treatment MtBE
Concentrations
0
1
3
3
1
5
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Technologies for Treating MtBE and Other Fuel Oxygenates
The data presented in Table 4.4-3 and Table 4.4-4 shows that bioremediation (either alone or in
combination with other technologies) has been employed to remediate MtBE in groundwater and soil to
concentrations less than 50 ug/L and has achieved MtBE concentration reductions greater than 99
percent. The median project duration for the 20 completed sites ranged from 6 months to 1 year.
In addition to the performance data reported for MtBE, 8 of the 12 projects in the dataset that reported
treating TEA using bioremediation also provided performance data. All 8 of these sites provided TEA
concentration prior to bioremediation treatment (the highest initial concentration was 90,000 ug/L) and 2
provided TEA concentrations following treatment (both achieved less than 5 ug/L).
Because of the heightened interest in bioremediation of TEA, additional information was obtained about
several of these sites. These data, provided in the online database, show that several sites were able to
reduce the concentration of TEA, sometimes to less than its site-specific cleanup level. For example, at
several sites in Texas, including Turtle Bayou Easement Area and Rural Area Disposal Area, in situ
bioremediation was used in conjunction with other technologies such as SVE and in situ thermal
desorption. At these sites, the concentrations of TEA were reduced to less than its cleanup goal, with
concentrations after treatment ranging from 100 - 1,000 ug/L. At the Naval Base Ventura County, Port
Hueneme, CA, in situ bioremediation was used in a biobarrier configuration, and the concentration of
TEA was reduced from > 1,000 to <5 ug/L (information about required cleanup levels was not provided).
4.4.6 What are the Costs of Using In Situ Bioremediation to Treat Oxygenates?
Project cost data were reported for 28 of the 73 bioremediation projects in the dataset; these include data
for both ongoing and completed projects. In most cases, the components that make up the project costs
were not reported. However, it is likely that the reported costs incorporate different components, such as
treatment, monitoring, design, oversight, and health & safety. Most (21 projects) of the reported costs
were for ongoing projects and represent either a partial actual cost as of the time that the report was made
or an estimated total project cost.
The median reported total cost for all bioremediation projects was approximately $125,000, with most
projects having a total cost between $50,000 and $350,000. The total cost for all 28 projects reporting
this information ranged from $4,000 to $5,200,000 per project, depending on scale, type of engineered
application, and site conditions. For example, as shown in Section 4.4.8, at the Port Hueneme site, a 500-
ft wide biobarrier was constructed in a shallow sand aquifer and had an installation cost of $435,000, with
first year O&M costs of $75,000. At a site in South Carolina, 3,000 gallons of a liquid microbial solution
were injected through 40 monitoring and 15 injection points, for a total cost of $63,500.
Because the area, volume, or mass treated was not consistently available for the 28 bioremediation
projects, no unit costs were estimated. The cost per volume of subsurface treated (identified as cubic
yards of subsurface) was reported in one literature source as ranging from approximately $170 to $330
per cubic yard for in situ bioremediation in general. This source also reported unit costs for ex situ
bioremediation ranging from $12 to more than $1,000 per cubic yard treated (EPA, 200 Ic). These results
suggest that the cost for bioremediation is highly variable and depends on site-specific conditions and
remedial goals. Overall, the cost of bioremediation generally is considered to be better than the average
for applicable groundwater remediation technologies (FRTR, 2002).
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.4.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment using In
Situ Bioremediation?
When oxygenates are present and must be remediated at a site, bioremediation, either alone or in
combination with other technologies, may be a suitable remediation approach. Although both ether- and
alcohol-based oxygenates are susceptible to biodegradation, the site conditions will determine whether
bioremediation is an appropriate technology for a given site. Key factors that affect the performance and
cost of bioremediation include: the concentration, mass, and distribution of VOCs in the soil and
groundwater; geology, moisture content, mineral content, pH, temperature, the concentrations of terminal
electron receptors and nutrients, as well as the presence of appropriate microbes, in the subsurface;
cleanup goals; and requirements for site cleanup. These factors affect the design of bioremediation
system, the biodegradation pathways that can be employed, and the amendments that must be added to
enhance bioremediation (EPA, 1995; FRTR, 2002).
Bioremediation generally is considered to be more suitable for the dissolved phase in groundwater plumes
or low concentrations in soil rather than grossly contaminated source areas where free product may be
present. Other technologies that incorporate free product removal, such as MPE and pump-and-treat, are
generally considered more applicable to source areas. Therefore, source areas are typically treated
through removal or another technology prior to application of bioremediation. Research is ongoing into
the potential use of bioremediation near source areas.
Because of the above factors, the design of a bioremediation system is typically based on significant site
analysis and bench- and pilot-scale testing rather than the application of packaged treatment systems.
More information about the factors that influence the performance and cost of bioremediation systems is
available in the references listed in this report.
4.4.8 Conclusions
Based on the information available from the bioremediation project, MtBE treatment profiles, and other
information contained in the reference documents reviewed in preparation of this report, the following
conclusions may be made regarding the use of bioremediation to remediate sites contaminated with MtBE
and other oxygenates:
Data from Bioremediation MtBE Treatment Profiles
Used to remediate groundwater contaminated with oxygenates - it was employed at 73 of the 323
of the projects in the dataset, primarily in the in situ mode
Most often used alone (92% of projects in dataset); to a lesser extent has been employed in
conjunction with air sparging, pump-and-treat, or SVE
Employed to remediate MtBE in groundwater from concentrations greater than 100,000 ug/L to
less than 50 ug/L and has achieved MtBE concentration reductions greater than 99 percent
Median project duration is approximately 1 year
Median reported total cost for all bioremediation projects in the dataset was approximately
$125,000, with most projects having atotal cost between $50,000 and $350,000
Treatability of Oxygenates Using Bioremediation
Most research has focused on bioremediation of MtBE and TEA; information on biodegradation
of other oxygenates is limited, but similar degradation pathways are employed for many
oxygenates
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Technologies for Treating MtBE and Other Fuel Oxygenates
Presence of ethanol may affect the aerobic biodegradation of MtBE and lead to longer MtBE
plumes. Recent research has indicated that ethanol can deplete available electron acceptors and
stimulate methanogenesis.
Effective biodegradation of MtBE and other oxygenates has been reported in a variety of
applications of the aerobic pathway; results for anaerobic pathways have been confined to
laboratory studies and have not been consistent
Intermediate degradation products of MtBE and other oxygenates, such as TEA, may remain in
the subsurface under natural conditions or when using anaerobic pathways
Oxygenate-degrading microorganisms are typically very slow growing; bench- and pilot-studies
may be needed to confirm the applicability of bioremediation and to select an appropriate design
Other Potential Advantages of Applying Bioremediation (EPA, 1995; EPA, 2000a)
Application involves equipment that is widely available and relatively easy to install
In situ systems create minimal disruption and/or disturbance to ongoing site activities
Time required for subsurface remediation using aerobic bioremediation may be shorter than time
required for pump-and-treat
Is generally recognized as being less costly than other remedial options (for example, pump-and-
treat or chemical oxidation)
Can be combined with other technologies (for example, bioventing, soil vapor extraction) to
enhance site remediation
In many cases, does not produce waste products that require disposal
Other Potential Limitations to Applying Bioremediation (EPA, 1995; EPA, 2000a):
Injection wells and/or infiltration galleries may become plugged by microbial growth or mineral
precipitation.
Oxygenate-degrading microorganisms are typically slow growing and may not be present
natively at all sites; pilot or treatability studies may be needed to confirm the applicability of
bioremediation at a specific site
Bioremediation of source zones may take substantial time due to the presence of free product and
lack of immediate bioavailability
Difficult to implement in low-permeability aquifers (hydraulic conductivity less than 10~4
centimeters per second)
Re-injection wells or infiltration galleries may require permits or may be prohibited. Some states
require permits for air injection
May require long-term monitoring and maintenance for bio-barrier type applications
Effective remediation may only occur in more permeable layers or channels within an aquifer
4.4.9 Example Projects
In Situ Bioremediation at Port Hueneme - D, Oxnard, CA
A full-scale cleanup has been ongoing using in situ bioremediation to treat MtBE, BTEX, and TEA in
groundwater at the Naval Base Ventura County, Port Hueneme in Oxnard, California. Geology at the site
consists of a shallow sand aquifer bounded on the bottom by a clay aquitard, through which ground water flows
at an average velocity of 1 ft/day. At a depth of 10-20 ft below ground surface (bgs), the 5,000- by 500-ft
dissolved MtBE plume mixes with a smaller BTEX plume that originates from sands contaminated with
residual nonaqueous phase liquid (NAPL).
The in situ bioremediation system consists of a 500-foot-wide "bio-barrief', which acts as a passive flow-
through system and was installed just downgradient of the NAPL plume. Contaminated groundwater
containing dissolved MtBE, TEA, and BTEX travels through the bio-barrier and is injected with various
combinations of oxygen, air, and conditioned microorganisms. Oxygen gas and bioaugmented sections are
4-32
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Technologies for Treating MtBE and Other Fuel Oxygenates
located in the central core of the dissolved contaminant plume and air injections are used on the edge of the
plume. Operation of the system began in the Fall of 2000. Initial MtBE, BTEX, and TEA concentrations in the
groundwater plume were greater than 10,000 |ig/L in the center of the plume.
After 18 months, contaminant concentrations were reduced to less than 5 |j,g/L in monitoring wells
downgradient of the bio-barrier and extending across the length of the bio-barrier. No significant differences in
performance were observed for the differently operated sections of the barrier. Dissolved oxygen increased
from a pre-injection concentration below 1 mg/L to 10-35 mg/L throughout the treatment zone, thereby
increasing the potential for aerobic biodegradation to occur. In addition, increased dissolved oxygen levels
upgradient of the treatment zone due to dispersion of the injected gas appear to cause upgradient reductions in
MtBE and benzene concentrations. Peripheral monitoring wells have not shown an increase in contaminant
concentrations, indicating that groundwater is flowing through and not around the bio-barrier.
The biobarrier system includes 252 gas injection wells, 174 monitoring wells, 25 satellite gas storage tanks, 154
solenoid valves, a 240 ft3/hr-capacity oxygen generator, automated timer circuits, and associated piping and
electrical lines. The total installation cost of this equipment was $435,000; initial year (FY 01) O&M costs
were $75,000 and are expected to continue for a service life of 40 years. A preliminary cost comparison with
an existing pump-and-treat system at this site suggests savings of more than $34 million over the project life.
The state regulatory agency recently approved continued use of this biobarrier and installation of a second
biobarrier (at the toe of the plume) as the final remedy for the MtBE plume (Miller 2002, ESTCP, 2003).
In Situ Bioremediation at Sunoco Service Station, MA
A full-scale cleanup was performed using in situ bioremediation to treat MtBE and BTEX at a service station in
Massachusetts. Soil at the site consists of a layer of sand and gravel underlain by peat, silt, and clay. The in
situ bioremediation system consisted of 12 injection wells and two butane injection panels used to stimulate
cometabolic aerobic biodegradation of the contaminants in groundwater. The system was operated between
October 2000 and January 2001. MtBE concentrations were reduced from 370 to 12 jig/L and BTEX
contamination in groundwater was reduced by approximately two orders of magnitude during the 4 month
period (Global BioSciences, Inc., 2001).
In Situ Bioremediation at South Beach Marina, Hilton Head, South Carolina
A full-scale cleanup was performed using in situ bioremediation to treat MtBE, BTEX, and naphthalene in
groundwater at a service station with leaking underground fuel storage tanks. At this site, groundwater is 4.32
to 6.92 feet bgs, with an average hydraulic gradient of 0.078 feet/feet and with a calculated velocity of 6.42 feet
per year. No confining units were identified at the site.
The in situ bioremediation application at this site included injection of a liquid microbial solution into the
subsurface through monitoring and injection wells. This solution includes microbes (Pseudomonas, Bacillus,
and Corynebacterium), oxygen, emulsifier, surfactant, and nutrients. Five injections were conducted. Over
3000 gallons was injected from February 1999 through September 2000 into approximately 40 wells and 15
Geoprobeฎ injection points. As of September 2000, MTBE levels decreased by 96% (from 3,310 to 146 ug/L),
while benzene decreased by 83% (2,571 ug/L to 435 ug/L); toluene by 66% (24,330 ug/L to 8,300 ug/L), and
naphthalene by 84% (5,377 ug/L to 853 ug/L); xylene levels increased and were above pre-operational level as
of September 2000. The system will continue to be operated until all target levels have been met. The total
cost for the cleanup of this site is $63,500; no additional information on cost breakdown was available (FRTR
2001).
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.5 In Situ Chemical Oxidation
Overview
Injection of an oxidant and other amendments to convert site
contaminants into innocuous products such as carbon dioxide and water
EPA's MtBE Treatment Profiles Website dataset included use at 21 sites
to treat MtBE
Successful application depends on matching oxidant and delivery system
to contaminants and site conditions
4.5.1 What is In Situ Chemical Oxidation?
In situ chemical oxidation (ISCO) is a technology in which an oxidant, and other amendments as
necessary, is introduced into contaminated media to react with site contaminants such as MtBE, other fuel
oxygenates, and other organic compounds, converting them to innocuous products, such as carbon
dioxide and water. Typically, hydrogen peroxide (H2O2), ozone (O3), or permanganate (MnO4~) oxidants
have been used to treat MtBE in soil and groundwater. Persulfate (S2O8~) compounds have also been used
as chemical oxidants for treating MtBE. All of these chemicals react, either directly or through the
generation of highly-reactive free radicals, such as OHซ, and Hซ, or SO4 with organic compounds such as
MtBE to break hydrocarbon bonds and form degradation products such as alcohols, carbon dioxide, and
water. In some applications, different oxidants may be used in combination, such as H2O2/O3, or in
conjunction with catalysts, such as H2O2 in the presence of ferrous iron (Fenton's chemistry or reagent), to
enhance oxidation through the generation of free radicals. Depending on site conditions, oxidants may be
introduced to the contaminated area using a variety of engineered approaches, including groundwater well
injection, groundwater well recirculation, lance injection (jetting), PRBs, deep soil mixing, or soil
fracturing (GWRTAC, 1999).
4.5.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?
As with other organic and some inorganic contaminants, MtBE and other oxygenates are susceptible to
degradation through oxidations reactions. If a sufficient amount and strength of oxidant and enough time
are provided, all of the ether- and alcohol-based fuel oxygenates can be mineralized to carbon dioxide and
water. For example, Figure 4.5-1 shows the equations for the stoichiometric mineralization of some of
the common oxygenates through oxidation using hydrogen peroxide.
Figure 4.5-1. Stoichiometric Mineralization of Oxygenates Using Hydrogen Peroxide
ETBE, TAME, DIPE:
MtBE:
TEA:
Ethanol:
Methanol:
C6H140+18H202 -
C5H120+15H202
C4H100 + 12 H202
C2H6O + 6 H2O2
CH30 + 5/2 H202
> 6 CO2 + 25 H20
> 5 C02 + 21 H20
> 4 C02 + 17 H20
> 2 CO2 + 9 H20
> C02 + 4 H20
Analogous equations can be derived for mineralization using other oxidants. However, the oxidation of
MtBE or other oxygenates to carbon and water is a multi-step, multi-path process in which each step has
different equilibrium and kinetic factors that govern the extent and rate that each reaction can take place.
Not all oxidants have proven successful in mineralization of MtBE, leaving by-products such as tert-butyl
formate (TBF) and TEA. The full spectrum of possible reaction intermediates and governing criteria
4-34
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Technologies for Treating MtBE and Other Fuel Oxygenates
have not been determined for MtBE and the other oxygenates. However, in general, the greater number
of carbon atoms in the oxygenate, the greater stoichiometric proportion of oxidant that will be required
(under the same conditions) to fully oxidize it. For example, based on the equations in Figure 4.3-1, the
complete mineralization of one pound of ETBE, MtBE, TEA, ethanol, and methanol would require 6.0,
5.7, 5.5, 4.4, and 2.7 pounds of hydrogen peroxide, respectively (Kelley, Marley, and Sperry, 2002).
While the above comparison (or similar comparisons for other oxidants) of the amount of oxidant
required for different oxidants may hold under controlled laboratory conditions, the actual amount and
type of oxidant that is necessary for the treatment of MtBE or other oxygenates at a given site will depend
on numerous factors beyond the amount of contaminant present, including:
The amount and types of other contaminants (such as other petroleum constituents) that will also
consume oxidant
The chemical composition of the soil and groundwater, specifically the amount of natural organic
matter (NOM) and other reduced species, such as iron (II) or manganese (II); often analyzed as
the chemical oxygen demand (COD) of the soil, or soil oxidant demand
The pH, alkalinity, and temperature of the treatment area; these conditions will affect equilibrium
and kinetic constants defining the extent and rate that each oxidation step can take place
The potential for biodegradation of site contaminants or oxidation products
Hydraulic and geologic parameters, such as hydraulic conductivity, hydraulic gradient, and
permeability, that will affect the migration and dissolution of the oxidant once it is introduced to
the subsurface
Because these factors can vary from site to site, typically field analyses of these parameters and bench-
and pilot-scale studies are conducted to determine the type and amount of oxidant required for a specific
application.
4.5.3 How is In Situ Chemical Oxidation Applied to Treat Oxygenates?
During ISCO, oxidants and any necessary amendments are introduced to the treatment area with one or
more of the available delivery approaches. Pilot-scale testing is often used to determine the type of
amendment and delivery system used at a given site. EPA policy regarding injection of supplements is
discussed in Section 3.4. Some of the key considerations for the common oxidants and delivery
approaches are summarized below.
Oxidants/Amendments
Hydrogen Peroxide (H2O2) - Hydrogen peroxide has been used alone or in combination with
other chemicals (such as using ferrous iron as a catalyst to generate free radicals through Fenton's
chemistry) or with ultraviolet (UV) light. When used alone, hydrogen peroxide is typically
injected as a concentrated solution (35-50%), which decomposes violently when contacting
groundwater, generating heat and high volumes of gas. When using Fenton's chemistry, the pH
of the treatment area is typically maintained at acidic (pH < 4) conditions and a more dilute
hydrogen peroxide solution is used. Hydrogen peroxide and iron catalysts are typically injected
separately, such as through specific ports in an injection lance, or through injection wells, because
free radicals tend to react rapidly and can dissociate if generated prior to injection. Excess
4-35
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Technologies for Treating MtBE and Other Fuel Oxygenates
hydrogen peroxide that is not used in degrading organic compounds will rapidly degrade to water
and oxygen (Leethem, 2001).
Ozone (O3) - Ozone is a highly reactive chemical that has been used to treat organic compounds
in ex situ groundwater and drinking water treatment systems. It can also be used to treat MtBE in
an ozone-air sparging system. This system injects ozone through tubing to a microporous sparge
point designed to generate very small bubbles ("microbubbles", approximately 50 micrometers
(|im) in diameter), which have a high surface-to-volume ratio. Organic contaminants in
groundwater, such as MtBE, volatilize into the ozone bubbles and are oxidized. Ozone that is not
consumed degrades to oxygen. Ozone is often used in combination with other oxidants, such as
hydrogen peroxide, to enhance oxidation through the generation of free radicals. If bromine is
present in the treatment area, bromate generation, which can occur during ozonation, is typically
monitored during treatment.
Permanganate (MnO4~) - Permanganate is often employed in the form of solid or a solution of
potassium or sodium permanganate for groundwater treatment. It has a smaller oxidizing
potential than ozone and hydrogen peroxide using Fenton's chemistry, resulting in the relatively
slower oxidation of MtBE and other oxygenates. However, permanganate has a longer half-life
compared to the stronger oxidants, and persists in the environment for a longer time. The end
product of permanganate oxidation is manganese dioxide, which, depending on the groundwater
pH, can precipitate into the formation. Excessive precipitation may reduce soil permeability.
Other Oxidants - Combinations of the above oxidants and other oxidants such as persulfate
compounds are also being used to treat MtBE and other oxygenates. These and other
combinations and other oxidants are being developed to maximize the generation of highly-
oxidizing free radicals, increase oxidant persistence, or otherwise enhance in situ oxidation.
Delivery Approaches
Groundwater Well Injection - Oxidants may be introduced to the treatment zone through
existing or new groundwater monitoring wells either as a liquid, gas, or solid. This method relies
on the natural migration of oxidants from the well into the formation. Injection wells need to be
adequately spaced to allow for oxidant delivery to the entire treatment area.
Groundwater Recirculation - A groundwater recirculation system may be used to extract
groundwater from within or at the downgradient edge of the contaminated area, introduce
oxidants and amendments aboveground, and reinjectthe groundwater upgradient of the treatment
area. This approach can be used to increase the flow-through of oxidant through the treatment
area, as well as to achieve downgradient containment of a contaminated groundwater plume.
Lance Injection, Jetting, Fracturing - Use of a high-pressure lance can create micro-fractures
in soils that increase soil permeability and allow for direct injection of oxidants and amendments
into a desired treatment area without the need for an existing or new groundwater well.
Soil Mixing - For lower permeability soils, soil mixing using tilling for shallow soil or an auger
for deeper soil can be used to introduce oxidants to a treatment area.
PRB - Oxidants can be injected into the treatment zone of a PRB to oxidize the groundwater that
flows through it. This approach can be used as a containment approach for a contaminated
groundwater plume. Also, a PRB could be placed upgradient or within a treatment area allowing
the oxidized groundwater leaving the PRB to flow through the treatment area.
There are also technologies that use electrical or other forms of energy to generate oxidizing and reducing
radicals in aqueous solution and thereby destroy contaminants such as MtBE and other oxygenates.
These technologies include ultrasound and electron beam treatment, and are primarily used in ex-situ
applications (see Section 4.6). Recently, however, ultrasound treatment has been proposed as a potential
in-situ application by incorporating ultrasonic transducers into a robotic self-powered mining head
(Chang and Yen 2000).
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Technologies for Treating MtBE and Other Fuel Oxygenates
Additional information relevant to the application of ISCO at sites in general or contaminated with MtBE
and other oxygenates is available in the following documents:
Kelley, Marley, and Sperry, 2003. In Moyer and Kostecki, Eds. 2003. MtBE Remediation
Handbook. Amherst Scientific Publishers.
Ground-Water Remediation Technologies Analysis Center. 1999. Technology Evaluation
Report, In Situ Chemical Treatment (TE-99-01). Prepared by Yin, Y. and Allen, H.E. July.
http: //www. gwrtac. org/pdf/inchem .pdf
Interstate Technology and Regulatory Cooperation Work Group. 2001. Technical and
Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater.
June. http://www.itrcweb.org/ISCO-l.pdf
Naval Facilities Engineering Service Center. Chemical Oxidation, In-Situ Technology Web
Page, http://enviro.nfesc.navv.mil/erb/restoration/technologies/remed/phys chem/phc-43.asp
Strategic Environmental Research and Development Program (SERDP). 2003. In Situ Chemical
Oxidation Initiative. http://www.serdp-estcp.org/ISCO.cfm
4.5.4 What Types of Projects Involve In Situ Chemical Oxidation for Oxygenates?
From the 323 MtBE projects in EPA's MtBE Treatment Profiles dataset, 21 projects were identified
where MtBE was treated using in situ chemical oxidation. No ISCO projects reported treating other
oxygenates. Four of the projects used ozone and 17 used hydrogen peroxide either alone or with Fenton's
chemistry.
Table 4.5-1 summarizes the scale and operational status for the 21 ISCO projects. The data used to
compile this information was current at the time the profile for each project was completed. Short
summaries for two projects, Ozone Sparging at Former Service Station, Bucks County, PA and Fenton 's
Chemistry at a Warehousing Facility, Union, NJ, are included at the end of this section, with additional
information about all 21 projects provided in Appendix A.
Table 4.5-1. General Information on 21 In Situ Chemical Oxidation Projects
Technology(ies)
In situ Chemical Oxidation Only
In situ Chemical Oxidation with
Air Sparging
In situ Chemical Oxidation with
Pump-and- Treat
In situ Chemical Oxidation with
SVE
In situ Chemical Oxidation with
Multiple Phase Extraction
TOTAL
#of
Projects
14
2
1
2
2
21
Operational Status
Completed
6
0
1
1
0
8
Ongoing
8
2
0
1
2
13
Scale
Bench
0
0
0
0
0
0
Pilot
4
0
0
0
0
4
Full
10
2
1
2
2
17
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Technologies for Treating MtBE and Other Fuel Oxygenates
As shown in Table 4.5-1, most of the 21ISCO projects were performed at full scale (17 projects) at the
time that their profiles were compiled. Eight of the 21 projects were identified as completed, and the
remaining 13 as ongoing. In addition, while most (14) of the projects used ISCO alone, 7 projects
supplemented ISCO with air sparging, pump-and-treat, SVE, or MPE.
4.5.5 How Has In Situ Chemical Oxidation Performed in Treating Oxygenates?
Tables 4.5-2 and 4.5-3 summarize performance data for the 8 completed and 13 ongoing ISCO projects.
The data presented in these tables show that ISCO (either alone or in combination with other
technologies) has been used to remediate MtBE in groundwater from concentrations greater than
10,000 ug/L to less than 50 ug/L and has achieved MtBE concentration reductions greater than 99
percent. Because the dataset included relatively few completed projects with performance data, Table
4.5-2 provides a summary of specific projects instead of a summary of minimum, median, and maximum
concentrations. The median project duration for the 19 completed sites ranged from 9 to 18 months.
None of the projects reported performance data for other oxygenates.
Table 4.5-2. Completed In Situ Chemical Oxidation Projects - Performance Summary for 8
Projects
Technology(ies)
In situ Chemical
Oxidation Only
In situ Chemical
Oxidation Only
In situ Chemical
Oxidation Only
In situ Chemical
Oxidation Only
In situ Chemical
Oxidation Only
In situ Chemical
Oxidation Only
In situ Chemical
Oxidation with SVE
In situ Chemical
Oxidation with
Pump-and-Treat
Site Name and Location
Former Maintenance and Repair
Garage, NY - H, West Chester,
NY
Spill Site (Long Island, New
York), Long Island, NY
Service Station, PA - D,
Warminster, PA
Service Station, NJ - E, North
Halden, NJ
Garage, NJ - F, Island Heights, NJ
Warehousing Facility in Union
County New Jersey, NJ
Former Service Station, PA - A,
Bucks County, PA
North Texas Service Station, TX
Scale
Pilot
Pilot
Full
Full
Full
Full
Full
Full
Initial MtBE
Concentration 1
(Hg/L)
451
6,300
50,000
403,000
55
6,400
475,000
17,000
Final MtBE
Concentration 1
(Hg/L)
171
79
6.6
1,430
4
70
68,400
31
Median
Project
Duration
(months)
12
2
14
2
14
NR
18
9
Notes:
NR Information not provided
1 Treatment performance data are based on the data provided by project managers and others in the source materials used to prepare the
treatment profiles website, as shown in cluin.org/products/mtbe. and summarized in Appendix A. Appendix A shows the specific sites that
are summarized here, along with technology design, operation, and performance data for each of the projects.
2 Performance data are shown in terms of changes in concentration of MtBE in the groundwater, as provided in the reference materials and
from the project contacts, except as noted. MtBE concentrations prior to beginning treatment (shown as "initial concentration") and after
treatment was completed (shown as "final concentration") are provided. For projects where more than one technology was used,
performance data are presented under each of the technologies used for the project.
4-38
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Technologies for Treating MtBE and Other Fuel Oxygenates
Table 4.5-3. Ongoing In Situ Chemical Oxidation Projects - Performance Summary for 13 Sites
MtBE Concentration Range
Greater than 100,000 ng/L
Greater than or equal to 10,000 (ig/L but
less than 1 00,000 ng/L
Greater than or equal to 1 ,000 |ig/L but
less than 10,000 (ig/L
Greater than or equal to 100 |ig/L but
less than 1,000 (ig/L
Greater than or equal to 50 |ig/L but less
than 100 ng/L
Less than 50 (xg/L
# of Projects
Reporting Initial
MtBE
Concentrations
0
1
3
6
0
2
# of Projects with
Last Reported
MtBE
Concentrations
0
0
2
2
1
6
4.5.6 What Are the Costs of Using In Situ Chemical Oxidation to Treat MtBE?
The total project cost was reported for 1 of the 21ISCO projects identified above. The completed Former
Service Station, PA - A project, which employed used ISCO with SVE, reported a total project cost of
$146,000. This cost was broken down further into $90,000 of capital cost and $56,000 of operation and
maintenance cost. Because the area, volume, or mass treated was not available for this project, no unit
cost was calculated.
There is little additional information in the literature about the costs of using ISCO for the treatment of
MtBE and other oxygenates, or for other contaminants. The cost per volume of subsurface treated
(identified as cubic yards of subsurface) was reported in one literature source as ranging from $52 to $310
per cubic yard in general (GWRTAC, 1999). The cost of ISCO generally is considered to be average,
among the costs for remediation technologies, for treatment of contaminated groundwater (FRTR, 2002).
4.5.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment using In
Situ Chemical Oxidation?
When MtBE or other oxygenates are present and must be remediated at a site, ISCO, either alone or in
combination with other technologies, may be a suitable remediation approach. Although both ether- and
alcohol-based oxygenates are susceptible to chemical oxidation, the chemical, hydraulic, and geologic
conditions of a given site will determine whether ISCO is a feasible option for treatment. For example,
ISCO may not be economically feasible for sites with high concentrations of NOM or other constituents
that may consume large amounts of oxidant. In addition, sites with low subsurface permeability may
require more complex approaches, such as fracturing or soil mixing, to deliver the necessary oxidant to
the treatment zone, potentially increasing costs. Other site characteristics, such as pH, alkalinity, and
temperature will also affect system design and impact cost and performance. For example, for oxidants
that have specific pH requirements, pretreatment of the aquifer with an acid solution to lower the pH is
typically considered. In addition, off-gas generated by the chemical reactions in ISCO may require
capture and treatment (Kelley, Marley, and Sperry, 2002).
In addition to the technology-specific factors described above, additional factors may also affect the
performance and cost of an ISCO system. These factors include: the concentration, mass, and distribution
of contaminants in the groundwater; subsurface geology and hydrogeology; cleanup goals; and
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Technologies for Treating MtBE and Other Fuel Oxygenates
requirements for site cleanup. For example, heterogeneity within the subsurface may result in preferential
pathways that prevent injected oxidant from reaching the entire treatment area.
Because of the above factors, the design of an ISCO system is typically based on pilot-scale testing rather
than generic design equations. More information about the factors that influence the performance and
cost of ISCO systems in general is available in the references listed in this report.
4.5.8 Conclusions
Data from In Situ Chemical Oxidation MtBE Treatment Profiles
Used to remediate groundwater contaminated with MtBE, but less frequently than some other
technologies, such as air sparging and bioremediation - it was employed at 21 of the 323 (6.5%)
of the projects in the dataset
Most often used alone (67% of projects in dataset); to a lesser extent has been employed in
conjunction with pump-and-treat or other technologies
The cost common oxidant applied was hydrogen peroxide with ferrous iron (Fenton's chemistry)
Used to remediate MtBE in groundwater from concentrations greater than 10,000 ug/L to less
than 50 ug/L and has achieved MtBE concentration reductions greater than 99 percent
Median project duration is approximately 1 year
Cost information is limited - one project reported total project cost of $ 146,000
Treatability of MtBE and Other Oxygenates Using In Situ Chemical Oxidation
All ether- and alcohol-based oxygenates susceptible to chemical oxidation
In general, the greater number of carbon atoms in the oxygenate, the greater stoichiometric
proportion of oxidant will be required (under the same conditions) to fully oxidize
Applicability to given site based primarily on factors not related to type of oxygenate (that is, all
oxygenates can be treated using chemical oxidation, but certain other site conditions, like high
concentrations of native organic matter or low permeability, may make other treatment
technologies more attractive)
Other Potential Advantages of Applying In Situ Chemical Oxidation (EPA, 1995; FRTR, 2002)
Has potential to be used to target hot spots that may not be amenable to bioremediation
Has potential to achieve cleanup goals in relatively short amount of time (several months to a
year)
Depth of application is only limited to the delivery approach used
Other Potential Limitations to Applying In Situ Chemical Oxidation (EPA, 1995; FRTR, 2002)
Relatively large amount of oxidant may be needed for treatment of large masses of contaminant
(oxidant does not target only the contaminants of concern)
May have low contact between oxidant and contaminant in heterogeneous media or in areas with
low permeability
Special precautions may need to be taken to protect worker health and safety during operation
(because of use of strongly oxidizing chemicals); also concentrated oxidant injection can result in
violent subsurface reactions
Chemical reactions may form toxic by-products (such as bromate during ozone oxidation) in the
groundwater
Off-gas may require capture and treatment
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.5.9 Example Projects
Ozone Sparging at Former Service Station, Bucks County, PA
At a former service station located in Bucks County, PA, remediation needed to be completed within nine
months to facilitate the sale of the property. The cleanup approach used ozone sparging, pump-and-treat, MPE,
and SVE to treat MtBE. Free product was removed prior to performing ozone sparging. The sparging system
consisted of multiple, nested sparge wells in a treatment area of 180 ft by 150 ft, and used an ozone dosage of
2.5 Ibs/day at 2 scfm over a 4 month period. MtBE concentrations in groundwater were reduced from 17,000
ug/L to 31 ug/L, which was below the cleanup level of 2,900 ug/L. The total cost reported for treatment was
$146,000, consisting of $90,000 for capital and $56,000 for O&M (EPA, 2002a).
Fenton's Chemistry at Warehousing Facility in Union County New Jersey, Union City, NJ
Groundwater at an operating warehousing facility in Union, NJ was contaminated with MtBE (concentrations
up to 6,400 ug/L), TEA, and BTEX. Soil at the site consists of soft red shales interbedded with harder
sandstones and minor amounts of conglomerate. After completing a pilot study, hydrogen peroxide and
catalysts were injected at six points during three treatment cycles over a three-month period in mid-1996 (each
cycle consisted of 15 days injection followed by 15 days without injection). MtBE concentrations in
groundwater were reduced to less than 5 ug/L, which was below the cleanup level of 70 ug/L. Rebound was
evaluated four months after treatment was complete; results remained below the cleanup level. There was no
current cost data provided for this site (EPA, 2002a).
4.6 Groundwater Pump-and-Treat and Drinking Water Treatment
Overview
Extraction of contaminated groundwater from the subsurface and treatment
using one or more ex situ technologies
EPA's MtBE Treatment Profiles Website dataset includes use during 100
projects to treat MtBE or other oxygenates
o 85 pump-and-treat projects
o 15 drinking water treatment projects
Used to reduce the concentration and mass of MtBE or other oxygenates from
groundwater or for hydraulic containment
4.6.1 What is Groundwater Extraction for Pump-and-Treat and Drinking Water Treatment?
Groundwater pump-and-treat involves the extraction of groundwater from a contaminant plume and the
treatment of extracted water using one or more aboveground technologies. Drinking water treatment
systems where the extracted water is contaminated with fuel oxygenates involves many of the same
activities as groundwater pump-and-treat. In general, the methods for extraction of the groundwater are
not linked to or limited by the aboveground (ex situ) treatment technologies. This section focuses on
groundwater extraction, while the following section (Section 4.7) focuses on above-ground treatment of
extracted groundwater, for both pump-and-treat and for drinking water treatment.
The groundwater extraction component typically consists of multiple wells and/or trenches for extraction
of groundwater and includes differential control of extraction rates from individual wells to optimize
operation. Most groundwater extraction systems incorporate extraction wells that are installed within the
contaminant plume downgradient from the source. These extraction wells are designed and controlled to
act as a barrier to additional downgradient movement of the contaminant plume and, over a long period of
time, to extract contaminant mass. Due to the water solubility of MtBE and other oxygenates, and the
associated occurrence of significant quantities of contaminant mass in the dissolved phase, such
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Technologies for Treating MtBE and Other Fuel Oxygenates
groundwater extraction systems have specific application to the remediation of plumes incorporating
oxygenate contamination.
4.6.2 How Do the Properties of MtBE and Other Oxygenates Affect Groundwater Extraction?
The properties of MtBE and other oxygenates are relevant to both the extraction and treatment
components of pump-and-treat. As discussed in Section 2.6, the properties of fuel oxygenates,
specifically their relatively high aqueous solubility and low tendency to partition to organic matter, affect
how they migrate with groundwater. As a result, oxygenates tend to become dissolved in and migrate
with groundwater more readily than other petroleum contaminants such as BTEX. One consequence of
this tendency that is beneficial to pump-and-treat remediation is that oxygenates are also more readily
extracted with groundwater than other contaminants.
4.6.3 How is Pump-and-Treat Applied to Treat Oxygenates?
A pump-and-treat system consists of an extraction and a treatment component. Groundwater is typically
extracted through vertical groundwater recovery wells although, in the last decade or so, horizontal wells
and trenches have also been employed. Variables in the design of a typical system include (EPA, 200 Id):
Types of extraction systems to be used
Number and location of extraction points
Design of extraction points (for example, diameter, depth and well screen interval)
Type of pumping apparatus to employ (for example, aboveground vacuum, submersible,
pneumatic)
Design of a distribution system to transport extracted groundwater to the aboveground treatment
system (for example, aboveground vs. underground piping or possible need for double-walled
piping at RCRA-regulated sites)
For the most part, the above considerations are not affected by the specific contaminants present at the
site, but by site characteristics, such as plume distribution, hydrogeologic characteristics, and above-
ground obstacles (such as buildings or active roadways). Typical extraction system construction
materials, such as polyvinyl chloride (PVC) piping and stainless steel pumps, are appropriate for fuel
oxygenates at typical contaminated groundwater concentrations. Groundwater extraction system
optimization approaches at sites contaminated with MtBE and other oxygenates are similar to those used
at other sites, such as use of phased construction, adaptive management of pumping rates, periodic
modeling of the well arrays, and pulsed pumping (Li etal, 2003).
A conventional pump-and-treat extraction system is typically designed to recover only groundwater.
Integrated or separate systems have also been used to capture free product or contaminated vapor
concurrently with groundwater. Extraction systems that incorporate the integrated recovery of multiple
phases are discussed in Section 4.3 (MPE) and separate systems to recover these other phases are
discussed in Section 4.2 about SVE and Section 5.2 about free product recovery.
More detailed information re levant to the application of pump-and-treat at sites contaminated with MtBE
and other oxygenates and in general is available in the following documents:
Cohen, R.M., J.W. Mercer, and R.M. Greenwald. 1998. EPA Groundwater Issue, Design
Guidelines for Conventional Pump-and-Treat Systems. EPA 540/S-97/504. September.
http://www.epa.gov/ada/issue.html.
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Technologies for Treating MtBE and Other Fuel Oxygenates
Li, Tie, U. Raaj, P.G. Patel, D.K. Ramsden, and J. Greene. 2003. "Groundwater Recovery and
Treatment". In Moyer and Kostecki, Eds. MtBE Remediation Handbook. Amherst Scientific
Publishers.
California MtBE Research Partnership. 2000. Treatment Technologies for Removal of Methyl
Tertiary Butyl Ether (MtBE) from Drinking Water, Second Edition. February.
4.6.4 What Projects Have Involved Pump-and-Treat for Treating Oxygenates?
From the 323 projects in EPA's MtBE Treatment Profiles dataset, 85 projects were identified where
MtBE in groundwater was remediated using pump-and-treat along with 15 additional projects that treated
MtBE in drinking water (collectively referred to as pump-and-treat projects). Information on the
treatment of other oxygenates was reported for 20 of these 100 projects: 16 projects reported TEA, 6
projects reported TAME, 2 projects reported ethanol, and 1 project reported DIPE as a contaminant in
addition to MtBE.
Table 4.6-1 summarizes the scale and operational status for the 100 pump-and-treat projects. Short
summaries for two complete pump-and-treat projects, Pump-and-treat at Christy Station, North
Windham, ME and Pump-and-treat and SVE at Service Station NH-B, NH, are included at the end of this
section.
Table 4.6-1. General Information about 100 Pump-and-Treat Projects
Technology (ies)
Pump-and-Treat Only
Pump-and-Treat with Air
Sparging and SVE
Pump-and-Treat with SVE
Pump-and-Treat with Air
Sparging
Pump-and-Treat with Other
Technologies
Drinking Water Treatment
TOTAL
# of Projects
45
18
14
4
4
15
100
Operational Status
Completed
12
5
1
2
1
1
22
Ongoing
33
13
13
2
3
14
78
Scale
Bench
0
0
0
0
0
0
0
Pilot
13
0
1
0
1
1
16
Full
32
18
13
4
3
14
84
Note: Fifteen (15) drinking water treatment projects are included
As shown in Table 4.6-1, most of the 100 pump-and-treat projects were full scale (84 projects) and were
ongoing (78 projects) at the time that its profile was published. In addition, while most (54%) of the
projects used pump-and-treat alone, almost half supplemented pump-and-treat with air sparging, SVE or
other technologies, such as phytoremediation, bioremediation, or ISCO.
4.6.5 How Has Pump-and-Treat Performed in Treating Oxygenates?
For the 100 pump-and-treat projects in the dataset, initial concentrations in groundwater were as high as
475,000 ug/L (North Texas Service Station, TX). Concentrations after treatment were as low as non-
detectable (the typical reporting limit for MtBE is 5 ug/L). Tables 4.6-2 through 4.6-5 summarize
available MtBE and TEA performance data for pump-and-treat projects.
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Technologies for Treating MtBE and Other Fuel Oxygenates
The data presented in Table 4.6-2 for 21 completed pump-and-treat projects (either alone or in
combination with other technologies) shows that MtBE concentration reductions in groundwater of
greater than 99 percent have been achieved in several projects. The median project duration for the 21
completed sites ranged from 1.5 to 5.5 years.
Table 4.6-2. MtBE Performance Summary for 21 Completed Pump-and-Treat Projects
Technology (ies)
Pump-and-Treat Only
(groundwater)
Pump-and-Treat with
Air Sparging and SVE
Pump-and-Treat with
Other Technologies
#of
Projects
8
5
4
Initial MtBE Concentration 1
(Hg/L)
Minimum
96
3
1,200
Median
1,800
10
11,000
Maximum
8,000
390
475,000
Final MtBE Concentration 1
(Hg/L)
Minimum
2
2
18
Median
24
3
2,070
Maximum
68
4.8
68,400
Median
Project
Duration
(months)
27
50
40
Notes:
Treatment performance data are based on the data provided by project managers and others in the source materials used to prepare the
treatment profiles website, as shown in cluin.org/products/mtbe. and summarized in Appendix A. Appendix A shows the specific sites that
are summarized here, along with technology design, operation, and performance data for each of the projects.
Performance data are shown in terms of changes in concentration of MtBE in the groundwater, as provided in the reference materials and
from the project contacts, except as noted. MtBE concentrations prior to beginning treatment (shown as "initial concentration") and after
treatment was completed (shown as "final concentration") are provided. For projects where more than one technology was used,
performance data are presented under each of the technologies used for the project.
Treatment performance data for ongoing projects are shown on Tables 4.6-3 and 4.6-4, for pump-and-
treat and drinking water treatment projects, respectively. Both types of projects treated groundwater with
relatively high initial MtBE concentrations (greater than 100,000 (^g/L). The available data show that 10
of 11 drinking water treatment projects achieved treated MtBE concentrations of less than 50 (^g/L, while
the results for pump-and-treat were more widely distributed.
Table 4.6-3. MtBE Performance Summary for 62 Ongoing Pump-and-Treat Projects
MtBE Concentration Range
Greater than 100,000 ng/L
Greater than or equal to 10,000 |ig/L but
less than 1 00,000 (ig/L
Greater than or equal to 1 ,000 (ig/L but
less than 10,000 ng/L
Greater than or equal to 100 |ig/L but
less than 1,000 (ig/L
Greater than or equal to 50 (ig/L but
less than 100 (ig/L
Less than 50 |ig/L
# of Projects
Reporting Initial
MtBE
Concentrations
4
11
14
11
3
10
# of Projects with
Last Reported
MtBE
Concentrations
1
2
5
3
2
13
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Technologies for Treating MtBE and Other Fuel Oxygenates
Table 4.6-4. MtBE Performance Summary for 12 Ongoing Drinking Water Treatment Systems
MtBE Concentration Range
Greater than 100,000 ng/L
Greater than or equal to 10,000 p.g/L but
less than 1 00,000 (ig/L
Greater than or equal to 1 ,000 (xg/L but
less than 10,000 ng/L
Greater than or equal to 100 |ig/L but
less than 1,000 (ig/L
Greater than or equal to 50 (xg/L but
less than 100 (ig/L
Less than 50 |ig/L
# of Projects
Reporting Initial
MtBE
Concentrations
3
2
5
1
0
1
# of Projects with
Last Reported
MtBE
Concentrations
0
0
0
1
0
10
Table 4.6-5 provides a summary of treatment performance data for 9 pump-and-treat projects that
provided performance data for TEA. Initial TEA concentrations were as high as 17,000 [^g/L, with most
after-treatment concentrations less than 50 [^g/L. Due to the additional interest in TEA, a review of data
for the 390 projects in the database as of April 2004 showed a total of 15 pump-and-treat projects
reporting performance data for TEA. Most of these projects reported using the HiPOx process for
treatment of extracted groundwater, with additional projects using GAC treatment.
Table 4.6-5. TEA Performance Data for 9 Pump-and-Treat Projects
Concentration Range
Greater than 100,000 (ig/L
Greater than or equal to 10,000 (ig/L but
less than 1 00,000 ng/L
Greater than or equal to 1 ,000 |ig/L but
less than 10,000 (ig/L
Greater than or equal to 100 (xg/L but
less than 1, 000 |ig/L
Greater than or equal to 50 |ig/L but
less than 100 (ig/L
Less than 50 (ig/L
# of Projects
Reporting Initial
Concentrations
0
1
4
4
0
1
# of Projects with
Last Reported
Concentrations
0
0
1
0
0
7
4.6.6 What Costs Have Been Associated with Using Pump-and-Treat in Treating MtBE?
Project cost data were reported for 43 of the 100 pump-and-treat projects in the dataset; these include data
for both ongoing and completed projects. In most cases, the components that make up the project costs
were not reported. However, it is likely that these costs incorporate different components, such as
treatment, monitoring, design, oversight, and health & safety. Most (40 projects) of the reported costs
were for ongoing projects and represent either a partial actual cost as of the time that the report was made
or an estimated total project cost.
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Technologies for Treating MtBE and Other Fuel Oxygenates
Tables 4.6-6 summarize the cost information from these 43 projects, broken down by type of other
technologies used in conjunction with pump-and-treat.
Table 4.6-6. Cost Summary for 43 Pump-and-Treat and Drinking Water Treatment Projects
Technology(ies)
Pump-and-Treat Only
Pump-and-Treat with Air Sparging and SVE
Pump-and-Treat with Air Sparging
Pump-and-Treat with SVE
Pump-and-Treat with Other Technologies
Drinking Water Treatment
#of
Projects
15
9
1
7
1
10
Total Cost Range (S)
Minimum
71,900
96,400
672,000
160,000
65,000
119,000
Maximum
1,120,000
567,000
672,000
624,000
65,000
4,000,000
Median Total
Reported Cost
(S)
500,000
327,000
672,000
339,000
65,000
245,000
Another source reported the unit costs of pump-and-treat (based only on capital cost) as less than $20 per
1,000 gallons per year for projects treating more than 20 million gallons of groundwater per year, and unit
costs (based on O&M cost) as less than $5 per 1,000 gallons per year for projects treating more than 20
million gallons of groundwater per year (EPA, 200 Id). These unit costs represent treatment costs for use
of pump-and-treat in general, and are not specific to the treatment of MtBE and other oxygenates. In
another source, the cost of pump-and-treat generally is considered to be worse than average, among the
costs for remediation technologies, for treatment of contaminated groundwater (FRTR, 2002).
4.6.7 What Factors May Affect the Performance and Cost of Oxygenate Treatment Using
Pump-and-Treat?
Because of the high water solubility of oxygenates, groundwater extraction may be effective in removing
a significant mass of these contaminants. Key factors that affect the performance and cost of the
extraction component of a pump-and-treat system include:
The depth and accessibility of the plume; site hydrogeologic characteristics, such as aquifer
permeability
The hydraulic conductivity, and flow gradient
Remedial goals for the site
The presence or prior removal of the contaminant source
If groundwater contamination is deep or beneath areas (such as buildings and rail lines) where
conventional vertical wells cannot be placed, innovative drilling techniques or more powerful extraction
pumps may be required. Alternatively, shallow and accessible groundwater may be easily extracted using
simple collection trenches. Hydrogeologic characteristics will define the number, design, and spacing of
extraction points, with tighter formations typically requiring more extraction points for a given area.
Groundwater flow characteristics and the number and spacing of wells will be the basis for determining
the flow rate of groundwater that needs to be extracted to achieve the desired capture zone. Cleanup
goals are also a factor. On-site containment goals may require only pumping from the downgradient edge
of a plume, whereas a goal of complete aquifer restoration may require more well points pumping at a
higher extraction rates.
One of the most significant factors that affect cost and performance is whether the contaminant source
area at a site is present. If a contaminant source area is allowed to continue to contribute to the
groundwater plume, groundwater extraction may be required for much longer periods of time than if the
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Technologies for Treating MtBE and Other Fuel Oxygenates
contaminant source is removed or treated prior to beginning groundwater pump-and-treat. Because they
are relatively water soluble, oxygenates tend to dissolve in groundwater rather than form NAPL. When
they do form NAPL, they float rather than sink, and thus form an LNAPL. Thus, removal or treatment of
MtBE and other oxygenate source areas can be more straightforward than for other contaminants such as
chlorinated solvents.
4.6.8 Conclusions
Based on the information available from the pump-and-treat projects listed in the MtBE Treatment
Profiles Website dataset and other information contained in the reference documents reviewed in
preparation of this report, the following conclusions were identified regarding the use of pump-and-treat
to remediate sites contaminated with MtBE and other oxygenates.
Data from Pump-and-Treat MtBE Treatment Profiles
Has commonly been used to remediate groundwater contaminated with MtBE and other
oxygenates - it was employed at 85 of the 323 (26%) of the projects in the dataset (drinking water
treatment projects represented an additional 15 projects in the dataset)
Most often used alone or in conjunction with air sparging and SVE; to a lesser extent, has been
employed in conjunction with other technologies
Has achieved MtBE concentration reductions greater than 99 percent in several projects
Median project duration ranged from 1.5 to 5.5 years
Median reported total cost was approximately $500,000 for pump-and-treat alone
Treatability of MtBE and Other Oxygenates Using Pump-and-Treat
Groundwater Extraction - Fuel oxygenates are relatively well suited to removal with extracted
groundwater
Other Potential Advantages of Applying Pump-and-Treat (EPA, 1995; FRTR, 2002)
Properties of MtBE (high water solubility and low organic/water partition coefficient) make it
amenable to groundwater extraction
Can be used to remediate an aquifer or to provide for hydraulic containment
Other Potential Limitations to Applying Pump-and-Treat (EPA, 1995; FRTR, 2002)
Long-term operation may be required to achieve remediation goals for large plumes, complex
hydrogeologies, or if an active source remains in place
The cost of constructing, operating, and maintaining treatment systems is considered to be
relatively high
Biofouling or mineral precipitation in extraction wells or treatment processes can reduce system
performance
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.6.9 Example Projects
The following two project descriptions incorporate examples of completed, full-scale applications of
pump-and-treat technology to MtBE-contaminated sites:
Pump-and-Treat at Christy Station, North Windham, ME
MtBE was detected in groundwater at Christy Station, located in North Windham, Maine, soon after the fuel
station was constructed in 1997. Between May and June 1998, a full-scale cleanup was performed using a
pump-and-treat system that consisted of two extraction wells operating at a combined 3 gpm. Extracted
groundwater was treated using shallow tray aeration followed by GAC, and the treated groundwater was
disposed off site. Initial concentrations of MtBE in groundwater were as high as 6,000 ug/L, but MtBE
concentrations stabilized at 300 ug/L with the operation of the pump-and-treat system. The goal was to reduce
MtBE in the aquifer to concentrations less than 500 ug/L. Following aeration, MtBE in extracted groundwater
was reduced to concentrations ranging from 10 to 30 ug/L and following GAC adsorption, MtBE was reduced
to concentrations of less than 2 ug/L. A performance standard for extracted groundwater was not identified.
The cost assessment for the remediation was $200,000, the capital cost for the pump-and-treat system was
$60,000 and the O&M cost was $11,000 for 1 month of operation (Eremita, 2000).
Pump-and-Treat and SVE at Service Station NH-B, Somersworth, NH
During inventory measurements in September 1996, a gasoline station in New Hampshire, referred to as
Service Station NH-B, detected a release of 2,100 gallons of gasoline. Soil at the site consists of 4 to 8 ft of
sandy fill overlying 2 to 13 ft of glacial till, with bedrock occurring at 10 to 15 ft below ground surface (bgs).
The depth to groundwater ranges from is 5 to 15 ft bgs. The site is characterized by fractured bedrock and a
hydraulic gradient of 30 ft/1,000 ft. Remedial activities included the removal of 3 USTs, 860 tons of
contaminated soil, 27,000 gals of groundwater containing 158 Ibs of hydrocarbons, and 120 gals of light non-
aqueous phase liquids (LNAPL). A pump-and-treat system consisting of 7 recovery wells screened to bedrock
and operating at a total flow rate of 7.5 gpm was implemented. Extracted groundwater was treated using
oil/water separation, filtration, and air stripping. The air stripper contained a 7 horse power (HP) blower which
operated at 1,000 scfm. Maximum concentrations in the influent to the air stripper were 1,670,000 ug/L of
MtBE and 439,000 ug/L of BTEX. SVE was conducted using 11 vertical wells and 4 horizontal wells, and a 15
HP blower operated at 300 scfm and 3.5 to 5 inches of mercury. No vapor treatment was performed. As of
January 2000, pump-and-treat system had removed 4,300 Ibs of hydrocarbons and SVE had removed 2,976 Ibs
of hydrocarbons. They currently use performing enhanced bioremediation at the site. The current total
remediation cost for this site is $590,000 (EPA, 2002a).
4.7 Treatment of Extracted Groundwater Used in Pump-and-Treat and Drinking Water
Treatment Systems
EPA's MtBE Treatment Profiles Website dataset includes use at 70 projects to treat MtBE or
other fuel oxygenates
Common processes such as air stripping and adsorption may not be as effective for oxygenates
as for common fuel components such as BTEX
4.7.1 What is Above-Ground Treatment for Extracted Groundwater?
The above-ground (ex situ) treatment technologies used for extracted groundwater are applied both in
pump-and-treat systems and drinking water treatment systems. In general, the methods for extraction of
groundwater are not linked to or limited by the type of above-ground treatment technologies. This section
focuses on above-ground treatment of extracted groundwater, for both pump-and-treat and drinking water
treatment, while the previous section (Section 4.6) focuses on groundwater extraction. This section also
includes specific examples of treatment applications used in pump-and-treat and drinking water treatment
systems.
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Technologies for Treating MtBE and Other Fuel Oxygenates
The general types of aboveground technologies that have been used for treating extracted groundwater
that is contaminated with MtBE and other oxygenates include the following (California MtBE Research
Partnership, 2000):
Air Stripping - Processes in which contaminants are volatilized from water to air in an
engineered system, such as a packed tower; treatment of the resulting contaminated vapor phase
may also be required
Adsorption - Processes in which contaminants are adsorbed from water onto a medium, such as
granular activated carbon (GAC) or resin, as driven by equilibrium forces
Chemical Oxidation - Processes in which contaminants are sequentially oxidized to less toxic
products through the introduction of chemical oxidants or the creation of oxidizing conditions
through other means, such as using ultraviolet (UV) radiation, electrical stimulation, or cavitation
Biotreatment - Processes in which contaminants are biodegraded in an engineered system, such
as an attached growth or activated-sludge bioreactor
4.7.2 How Do the Properties of MtBE and Other Oxygenates Affect Treatment?
The properties of MtBE and other oxygenates affect their relative treatability in extracted water using
different technologies. Air stripping, adsorption, oxidation, and biotreatment technologies are technically
capable of and have been used to treat water contaminated with some or all of the fuel oxygenates.
However, the properties of oxygenates versus other fuel contaminants such as BTEX, and the different
properties of ether-based versus alcohol-based oxygenates, are important to consider when selecting and
designing an above-ground treatment system. The effect of fuel oxygenate' properties on treatment using
each of the commonly used technologies is briefly discussed below.
Air Stripping
Similar to air sparging, air stripping relies on the volatilization of contaminants from the aqueous to the
vapor phase. The property that shows the extent to which this transfer can take place during air sparging
is the Henry's Law Constant, which represents the extent to which a contaminant will partition between
the dissolved state and the vapor state under equilibrium conditions. A contaminant with a greater
Henry's Law Constant is more readily stripped from water during air stripping than one with a lesser
Henry's Law Constant. The discussion in Section 4.1.2 related to the affect of the properties of fuel
oxygenates on air sparging is also applicable to air stripping. As discussed in that section, all common
fuel oxygenates (with the possible exception of DIPE) are less readily stripped than BTEX (based on their
Henry's Law Constants). Because of this, air stripping systems designed to treat oxygenates often are
designed to allow for more air/water contact time than a system designed to treat BTEX constituents at
the same concentrations. This is typically accomplished by use of a larger stripping tower or packing
material with a higher specific surface area. As an illustration, based on their ranges of Henry's Law
Constants, ether-based oxygenates would require 5 to 10 times more air contact than BTEX to volatilize
the same concentration of contaminant. Because of this, an air stripping system designed to treat BTEX
may not be capable of adequately addressing ether-based oxygenates. Alcohol-based oxygenates are even
more difficult, and in some cases impractical, to strip from groundwater.
The properties of oxygenates may also affect the applicability and design of a system to treat the
contaminated vapor effluent resulting from air stripping, if one is required. These affects are discussed in
Section 4.2 about SVE.
Adsorption
In adsorption processes, contaminated water is contacted with a solid adsorption media, such as GAC or
resin. Based on their equilibrium properties relative to the specific adsorption media, contaminants will
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Technologies for Treating MtBE and Other Fuel Oxygenates
partition from the water to the solid until the system has reached equilibrium. The maximum
concentration of a given contaminant that can be adsorbed is dependent on the type of adsorption media
used, the specific contaminant and its concentration, concentrations of other substances in the water that
may competitively adsorb, as well as other parameters such as temperature. Although the actual
treatability of a contaminated water stream is dependent on all of these parameters, the relative treatability
of MtBE and other oxygenates can be estimated based on their relative tendency to partition from water to
an organic matrix. One common measure of this tendency is the organic carbon-based partition
coefficient. Generally, contaminants with lower partition coefficients are less amenable to treatment
using GAC or resin adsorption. Figure 4.7-1 shows the ranges of partition coefficients for ether- and
alcohol based coefficients and BTEX.
Figure 4.7-1. Relative Ranges of Partition Coefficients for Fuels Oxygenates and BTEX
3.5-
j? 2.5-
0.5-'
ETHER OXYGENATES
2.2 2.2
1.1
1.0
1.5
ALCOHOL OXYGENATES
-1.6
0.9
BTEX
2.3
2.2 _
II
1.5
MtBE ETBE TAME DIPE
TBA Ethanol Methanol Benzene Toluene Ethyl- Xylenes
benzene
As shown in Figure 4.7-1, the average partition coefficients for ether- and alcohol-based oxygenates are
much lower than for BTEX. Based on this, it would be expected that adsorption systems designed only to
treat BTEX may not be able to effectively address ether-based oxygenates, and that the lower molecular
weight alcohol-based oxygenates would not be amenable to adsorption.
Chemical Oxidation
As discussed in Section 4.5 about in situ chemical oxidation, MtBE and other oxygenates are susceptible
to degradation through oxidation reactions. If a sufficient amount and strength of oxidant and enough
time are provided, all ether- and alcohol-based fuel oxygenates can be destroyed via chemical oxidation.
However, the amount and type of oxidant that is necessary for the treatment of MtBE or other oxygenates
at a given site will depend on numerous factors beyond the amount of contaminant present. These factors
are discussed further in Section 4.5.
There are also technologies that use electrical or other forms of energy to generate oxidizing and reducing
radicals in aqueous solution and thereby destroy contaminants such as MtBE and other oxygenates.
These technologies include electron beams and ultrasound. High-energy electron beams (E-beams)
induce radiolysis (radiation driven splitting) of water to form oxidizing hydroxyl radicals (OHซ) as well as
reducing hydrated electrons (eaq-) and hydrogen (Hซ). Ultrasound technology relies on the breakdown of
water molecules into oxidizing and reducing free radicals (OHซ and Hซ) under the intense heat and
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Technologies for Treating MtBE and Other Fuel Oxygenates
pressures generated during ultrasound-induced cavitation. Both of these technologies have been
demonstrated on the pilot scale in application to groundwater contaminated with MtBE (Kelley, Marley,
and Sperry, 2003).
Biotreatment
As discussed in Section 4.4 about bioremediation, MtBE and other oxygenates are susceptible to
biodegradation. For in situ biological treatment, the primary focus is on creating conditions that are
conducive (sufficient electron acceptors, nutrients, microbes, and co-metabolite) to stimulate
biodegradation. With aboveground biotreatment, the creation of these conditions is simpler because the
treatment is occurring in a defined, controlled, and accessible system. However, the relative
biodegradability of different contaminants, such as ether- and alcohol-based oxygenates, is an important
consideration in the selection and design of a biotreatment component for a pump-and-treat system.
These factors are discussed further in Section 4.4.
4.7.3 How are Technologies Used for Above-Ground Treatment of Oxygenates?
One or more above-ground technologies are typically used to treat extracted groundwater before
reinjection or discharge to surface water or the sewer. Multiple technologies, or treatment trains, are
commonly used at sites contaminated with MtBE and other oxygenates (for example, air stripping
followed by GAC polishing). A significant amount of literature (some of which is referenced at the end
of this report) has been dedicated to the design of above-ground treatment systems. Some of the key
considerations relevant to treatment of MtBE and other oxygenates in extracted groundwater are
summarized below (California MtBE Research Partnership, 2000).
Air Stripping
A typical volumetric ratio of air to water for effective treatment of MtBE is at least 150 to 200
parts air to 1 part water, greater than that required to solely remove BTEX.
Most states require the capture and treatment of air stripper off gas. Typical off-gas treatment
technologies that are applicable to MtBE and other oxygenates are adsorption, thermal treatment,
and biotreatment. These technologies are discussed in more detail in Section 4.2 about SVE.
Adsorption
Because of their water solubility and low partition coefficients, MtBE and other oxygenates are
difficult to adsorb on GAC. Other, more preferentially adsorbed, contaminants in groundwater
may also reduce the capacity of GAC to remove MtBE and other oxygenates. In some cases, the
more absorbable contaminants may even displace MtBE or other oxygenates that are already
adsorbed. In addition, natural groundwater constituents, such as iron, manganese, or organic
carbon may also consume adsorption capacity. Because of this, two or more GAC beds are often
used in series so that contaminant breakthrough can be monitored in the first bed without risking
the discharge of contaminants into the effluent.
Certain types of adsorption media have been shown to preferentially adsorb certain contaminants.
For example, research has shown that, in some cases, coconut shell based GAC removes MtBE
better than typical coal-based GAC. In addition, synthetic resins have been developed to
preferentially adsorb some oxygenates, such as TEA, that are less absorbable by GAC. Often,
adsorption processes also take advantage of the biodegradability of MtBE and other oxygenates
by promoting bacterial growth on the adsorption media (refer to Section 4.4.3 about use of
combined treatment technologies that employ adsorption and biological treatment).
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Technologies for Treating MtBE and Other Fuel Oxygenates
Chemical Oxidation
For the ex situ treatment of groundwater contaminated with MtBE or other oxygenates using
chemical oxidation, most systems rely on processes that generate hydroxyl radicals, which are
capable of completely oxidizing organic material to primarily carbon dioxide and water.
Approaches that have been used to generate hydroxyl radicals for the oxidation of MtBE and
other oxygenates include the following. In some cases, the treatment system has been tailored for
aboveground application. In other cases (for example, ultrasonic cavitation and electron beam),
the technologies have only been used in aboveground treatment systems.
o Combination of hydrogen peroxide and UV light
o Combination of hydrogen peroxide and ferrous iron (Fenton's chemistry)
o Combination of ozone and UV light
o Combination of ozone and hydrogen peroxide (such as in the HiPOx system)
o Ultrasonic Cavitation (using high-energy ultrasonic vibrations to generate high temperatures
and pressures)
o Electron Beam (using high energy electrons to split water molecules into free radicals)
The incomplete oxidation of MtBE and other oxygenates may result in the generation of
undesirable intermediate products, such as TBF, TEA, and acetone. The design (oxidant dosage
and contact time) should be adequate to achieve complete oxidation or additional treatment
processes, such as GAC, may be used to address residual contamination.
The presence of other oxidant-consuming constituents in the feed water, such as iron, natural
organic carbon, carbonates, bromide, and other contaminants, may require pretreatment of the
feed stream, additional oxidant dosage, or more contact time to adequately destroy the MtBE and
other oxygenates.
Biotreatment
Biological treatment systems that incorporate mechanisms to retain sufficient biomass generally
are applicable to groundwater containing lower concentrations of contaminants. These systems
typically consider the limited supply of carbonaceous material (food) to sustain a viable
population of degrading microbes. Attached growth bioreactors, and suspended growth
bioreactors that incorporate membrane-based biomass separation systems, generally are
appropriate for these applications.
Because the biological degradation rate of MtBE has been observed to be slower than for other
common contaminants, such as BTEX, MtBE will typically be the rate-limiting contaminant that
determines the necessary hydraulic retention time for a mixed contaminant system, since it will
typically be the slowest to degrade (see additional discussion in Section 4.4 about relative rates of
biodegradation among oxygenates).
Due to the difficulties involved in maintaining an adequate microbial mass in application to low
concentrations of MtBE or other oxygenates in groundwater, treatability studies are often
performed to confirm that extracted groundwater can be adequately treated in a bioreactor.
Recently, some efforts have been made to combine treatment technologies that employ adsorption and
biological treatment. Biological treatment technologies that use naturally occurring microorganisms have
successfully treated MtBE-contaminated groundwater. However, these microorganisms do not grow
efficiently on MtBE, and thus require a microbial retention mechanism. Granular activated carbon (GAC)
serves as an attachment media that immobilizes microbes. Other retention mechanisms include
permeable barrier membranes and reactive barriers. GAC is often promoted for its adsorption capability
of environmental pollutants. However, in the presence of BTEX, the affinity of MtBE and TEA to adsorb
to carbon is lowered. Consequently, GAC may not offer substantial adsorption capacity for MTBE or
TEA.
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Technologies for Treating MtBE and Other Fuel Oxygenates
More detailed information relevant to the application of above-ground treatment at sites contaminated
with fuel oxygenates and in general is available in the following documents:
Cohen, R.M., J.W. Mercer, and R.M. Greenwald. 1998. EPA Groundwater Issue, Design
Guidelines for Conventional Pump-and-Tr eat Systems. EPA 540/S-97/504. September.
http://www.epa.gov/ada/issue.html.
Li, Tie, U. Raaj, P.O. Patel, D.K. Ramsden, and J. Greene. 2003. "Groundwater Recovery and
Treatment". In Moyer and Kostecki, Eds. MtBE Remediation Handbook. Amherst Scientific
Publishers.
California MtBE Research Partnership. 2000. Treatment Technologies for Removal of Methyl
Tertiary Butyl Ether (MtBE) from Drinking Water, Second Edition. February.
4.7.4 What Projects Have Been Used for Above-Ground Treatment of Extracted
Groundwater?
From the 323 projects in the MtBE Treatment Profiles Website dataset, 85 projects were identified where
MtBE in groundwater was remediated using pump-and-treat along with 15 additional projects that treated
MtBE in drinking water (collectively referred to as pump-and-treat projects). 70 of these projects
reported the type of above-ground treatment used, as shown in Table 4.7-1. Short summaries for three
demonstration-scale projects of above-ground treatment technologies, High Biomass Retention Reactor,
HiPOx Advanced Oxidation Technology, and High Energy Electron Beam, are included at the end of this
section.
Table 4.7-1. Above-Ground Treatment Technologies Used at 70 Groundwater
Pump-and-Treat Remediation and Drinking Water Treatment Projects
Aboveground Treatment
Technology Employed
Air Stripping Only
Air Stripping with Adsorption
Adsorption Only
Adsorption with Oxidation
Oxidation Only
Biotreatment Only
TOTAL
# of Pump-and-
Treat Projects
8
9
18
1
19
1
56
# of Drinking
Water Treatment
Projects
3
1
8
2
0
0
14
To tal# of Projects
11
10
26
3
19
1
70
Notes:
Based on the data provided by project managers and others in the source materials used to prepare the treatment profiles website,
as shown in cluin.org/products/mtbe. and summarized in Appendix A. Appendix A shows the specific sites that are summarized
here, along with technology design, operation, and performance data for each of the projects.
As shown in the table, the projects in the dataset used adsorption most frequently, either alone or in
combination with other technologies. Nine of the 39 projects that used adsorption reported information
about the type of adsorption media that was used in the treatment system. Bituminous carbon was used
for 4 projects; coconut shell carbon for 2 projects; and, organoclay carbon, resin, or biologically-enhanced
GAC were used for one project each. Air stripping (21 projects) and oxidation (22 projects) were also
used frequently. Three of the air stripping projects reported that catalytic oxidation was used for off-gas
treatment. No other projects reported information about off-gas treatment. Two of the air stripping
projects reported air-to-water ratios; they were 150:1 and 200:1. Most (21) of the oxidation projects
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Technologies for Treating MtBE and Other Fuel Oxygenates
reported the type of oxidation that was employed. Hydrogen peroxide/ozone was used for 16 projects;
hydrogen peroxide/UV was used for 3 projects; hydrogen peroxide alone and ultrasonic cavitation were
used for one project each.
As an example of above-ground treatment, a site in Mission Viejo, CA had an operating dual-phase
extraction system withdrawing soil vapor and groundwater for treatment with oxidation and bioreaction,
respectively. Initially, the major contaminant was TEA, with a lesser concern about MtBE. However, as
the formation dried out and more porosity developed, the concentrations of BTEX were found to be
climbing. Site consultants considered that if the BTEX exceeded the TBA/MTBE concentration for a
long time period, then the bio-mass would prefer the BTEX and would lose its ability to consume
TBA/MTBE. To address this concern, a "sacrificial" carbon canister containing 200 pounds of coconut
carbon was installed ahead of the bio-reactor to remove the BTEX while allowing the TBA/MTBE to pass
through and be remediated in the bio-reactor. While feeding approximately 1.5 gpm of a stream
containing approximately equal concentrations of TBA/MTBE and BTEX, the stream exiting the carbon
canister showed breakthrough for TEA in two days, the first time a sample was taken. The TEA entering
and leaving the carbon canister showed no decrease in concentration after the first week. The BTEX took
about 45 days to break through (O'Connell, 2004).
4.7.5 How Has Above-Ground Treatment Performed in Treating Oxygenates?
Of the projects in the database, four completed projects using pump-and-treat provided performance data
for initial and final MtBE concentrations. Median concentrations were 27,000 ug/L for before treatment,
and less than lug/L for after treatment. The median project duration for these projects was 14 months.
Note that these treatment performance data are based on the data provided by project managers and others
in the source materials used to prepare the treatment profiles website, as summarized in Appendix A.
Appendix A shows the specific sites that are summarized here, along with technology design, operation,
and performance data for each of the projects. For projects where more than one technology was used,
performance data are presented under each of the technologies used for the project.
4.7.6 What Costs Have Been Associated with Using Pump-and-Treat in Treating MtBE?
Project cost data were reported for 12 pump-and-treat projects in the dataset based on type of above-
ground treatment used; these include data for both ongoing and completed projects. In most cases, the
components that make up the project costs were not reported. However, it is likely that these costs
incorporate different components, such as treatment, monitoring, design, oversight, and health & safety.
Most of the reported costs were for ongoing projects and represent either a partial actual cost as of the
time that the report was made or an estimated total project cost.
Table 4.7-2 summarizes the cost information from these 12 projects, broken down the type of above-
ground treatment technologies used.
Table 4.7-2. Cost Summary for Pump-and-Treat - By Aboveground Treatment Type
Aboveground Treatment
Technology(ies)
Air Stripping Only
Air Stripping with Adsorption
Adsorption Only
TOTAL
#of
Projects
6
3
3
12
Total Cost Range
Minimum
74,000
216,000
160,000
450,000
Maximum
1,200,000
1,180,000
624,000
3,000,000
Median Total
Reported Cost ($)
545,000
339,000
180,000
1,060,000
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Technologies for Treating MtBE and Other Fuel Oxygenates
Table 4.7-3 summarizes ranges of projected unit costs estimated by the California MtBE Research
Partnership for the treatment of different flow rates (60, 600, and 6,000 gallons per minute (gpm) of
MtBE-contaminated water using air stripping, oxidation, and adsorption technologies. These results show
that air stripping is less costly than either adsorption or oxidation, and that there are economies of scale
with treatment of relatively larger quantities of water.
Table 4.7-3. Estimated Range of Unit Costs for Above ground Treatment Technologies
Technology Category
Air Stripping
Adsorption
Oxidation
S/1,000 Gallons Treated
(60 gpm system)
Minimum
1.66
2.30
2.18
Maximum
3.20
4.61
4.11
S/1,000 Gallons Treated
(600 gpm system)
Minimum
0.30
0.77
0.57
Maximum
1.09
2.37
2.08
S/1,000 Gallons Treated
(6,000 gpm system)
Minimum
0.13
0.30
0.32
Maximum
0.64
2.22
1.59
Source: The California MtBE Research Partnership, 2000
4.7.7 What Factors May Affect the Performance and Cost of Above-Ground Treatment for
Oxygenates?
Once water contaminated with MtBE or other oxygenates has been extracted, the relative tendency to
remain in the aqueous phase can make above-ground treatment more complicated than the treatment of
other contaminants, such as BTEX. Key factors that may affect the cost and performance of above-
ground treatment include:
The concentrations of oxygenates and other contaminants
Extracted groundwater flow rates
Other groundwater chemistry parameters that may interfere with treatment, such as natural
organic carbon, iron, manganese, hardness, alkalinity, pH; effluent water and off-gas discharge
standards
These factors may influence the specific above-ground treatment technology that is selected, the possible
need for multiple above-ground treatment processes (treatment trains), and the need for pre-treatment of
groundwater or post-treatment of off-gas. Also, as with the extraction component, the presence of an
active source area may result in the need for long-term operation of above-ground treatment systems.
4.7.8 Conclusions
Based on the information available from the projects listed in the MtBE Treatment Profiles Website
dataset and other information contained in the reference documents reviewed in preparation of this report,
the following conclusions were identified regarding the use of above-ground treatment for sites
contaminated with MtBE and other oxygenates.
Treatability of MtBE and Other Oxygenates Using Above-Ground Treatment
Air Stripping - Treatment of ether-based oxygenates may require greater air to water ratios than
treating only BTEX; treatment of alcohol-based oxygenates may be impractical
Adsorption - Ether-based oxygenates are less readily removed than BTEX using GAC and some
alcohol-based oxygenates may not be adsorbable at all; synthetic resins that more selectively
remove fuel oxygenates are available
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Technologies for Treating MtBE and Other Fuel Oxygenates
Chemical Oxidation - Fuel oxygenates can be destroyed using hydroxyl radical oxidation;
oxidant dosage and contact time based more on overall oxidant demand of extracted groundwater
than types of oxygenate contaminants
Biotreatment - Fuel oxygenates can be biodegraded given adequate retention time in a
bioreactor with a sufficient mass of conditioned microbes
In general, above-ground treatment systems can be more readily controlled and monitored to
optimize the removal of MtBE and other oxygenates than in situ treatment systems
Other Potential Limitations to Applying Above-Ground Treatment (EPA, 1995; FRTR, 2002)
The cost of constructing, operating, and maintaining treatment systems is considered to be
relatively high
Biofouling or mineral precipitation in extraction wells or treatment processes can reduce system
performance
4.7.9 Example Projects
The following two project descriptions relate to demonstrations of innovative ex situ treatment systems
for groundwater contaminated with MtBE and other oxygenates:
Biodegradation of MtBE in a High Biomass Retention Reactor: Demonstration Study at Pascoag, RI
A pilot-scale specialized Biomass Concentrator Reactor (BCR), an activated sludge type bioreactor that uses a
membrane-based biomass separation system, was tested for the aerobic biodegradation of MtBE. The BCR
design encompasses an aeration chamber housing a high surface area porous polyethylene membrane system
that retains all of the biomass within the aeration chamber. Its simple operation and low maintenance
requirements may render it economically more feasible than other water treatment technologies. The water flux
through the membrane relies completely on gravity. The system includes 30 membrane compartments, with
each one removable for cleaning.
The BCR was used in a demonstration at a Pascoag, RI abandoned gasoline station where substantial amounts
of gasoline have leaked into the groundwater, contaminating it with MtBE, TEA, TAME, TAA, DIPE, TBF,
acetone, methanol, ethanol, and BTEX. The objective of the study was to demonstrate the effectiveness of the
BCR in treating MtBE, other oxygenates, and BTEX to near or below detectable limits. The BCR was operated
at the Pascoag site for nearly 6.5 months at up to 5 gpm. Average influent concentrations of volatile organic
compounds were: MtBE, 6,500 ug/L; TEA, 69 ug/L; TAME, 1,130 ug/L; TAA, 130 ug/L; DIPE, 36 ug/L;
TBF, 29 ug/L; acetone, 480 ug/L; methanol, 300 mg/L; and the sum of BTEX, 3,700 mg/L. Effluent
concentrations were very low despite continual flow interruptions from the source wells. Over the entire
project, including flow interruptions and non-steady-state flow conditions, MtBE in the effluent averaged near 9
Ug/L (< 5 p,g/L during 5 gpm steady state flow conditions without flow interruptions), TEA, 0.5 ug/L; TAME,
1.4 ug/L; TAA, -0.06 ug/L; DIPE, 0.05 ug/L; TBF, 0.02 ug/L; acetone, 6.6 ug/L; methanol, 2 ug/L; and sum of
BTEX, 1.3 ug/L. Non-purgeable organic carbon (NPOC) was reduced by close to 50%. A detailed cost
analysis has not yet been conducted (Venosa 2003).
Demonstration of the HiPOx Advanced Oxidation Technology for the Treatment of
MTBE-Contaminated Groundwater at Port Hueneme, CA
The HiPOx technology is an advanced oxidation process that incorporates high-precision delivery of ozone and
hydrogen peroxide to chemically destroy organic contaminants while minimizing bromate formation. A MtBE-
contaminated groundwater (initial MtBE concentration of 748 ug/L) from the Ventura County Naval Base in
Port Hueneme, CA was used to evaluate this technology. Due to extremely high concentrations of bromide in
the feed water (1.3 mg/L) and the desire to limit bromate formation, a pilot-scale system was operated with 630
ozone injector ports in series, as part of EPA's SITE program.
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Technologies for Treating MtBE and Other Fuel Oxygenates
The HiPOx process achieved greater than a 99.87 percent reduction in MTBE concentration and easily met the
treatment goal of reducing the concentration of MtBE to below 5 ug/L. However, significant concentrations of
MtBE degradation intermediates and oxidation by-products were present in the final effluent. TEA was
produced early during the chemical oxidation process. Its concentration was diminished by further oxidation,
reaching below its regulatory limit of 12 ug/L in two of the three runs. Acetone was generated and a sizable
percentage was left unoxidized in the final effluent (>100 ug/L). Bromate concentrations in the effluent
exceeded the drinking water standard of 10 ug/L for all three runs.
A model calculation showed that the HiPOx system may have been fully successful in limiting bromate
formation under the chosen oxidant doses if the influent bromide concentration was 0.56 mg/L, or less. Since a
bromide concentration of 0.56 mg/L is still extremely high for a drinking water source, the HiPOx system
appears to hold promise for destroying MTBE and its oxidative byproduct TEA while controlling bromate
formation, even in waters that have high bromide concentrations (Speth and Swanson 2002).
Application of High Energy Electron Beam (E-Beam) to the Treatment of MtBE-contaminated Groundwater
at Port Hueneme, CA
A demonstration of the high-energy electron injection (E-Beam) technology in application to groundwater
contaminated with MtBE and with BTEX was conducted at the Naval Base Ventura County, Port Hueneme,
CA, as part of EPA's SITE program. The E-beam technology destroys organic contaminants in groundwater
through irradiation with a beam of high-energy electrons; the oxidizing radicals that are generated by the E-
beam react with and destroy organic contaminants, including MtBE and its breakdown products.
Results of two weeks of steady state operation at an E-beam dose of 1,200 kilorads (krads) indicated that MtBE
and BTEX concentrations in the effluent were reduced by greater than 99.9 percent from influent concentrations
that averaged over 1,700 ug/L MtBE and 2,800 ug/L BTEX. Further, the treatment goals for the demonstration,
which were based on drinking water regulatory criteria, were met for all contaminants except for TEA, a
degradation product of MtBE. Dose experiments indicated that TEA was not consistently reduced to below the
treatment goal of 12 ug/L although the results indicated that tBA by-product formation decreased as dose
increased. Acetone and formaldehyde were the two most prevalent organic by-products that were formed by E-
beam treatment, with mean effluent concentrations during the two-week steady state testing of 160 and 125
ug/L, respectively. Bromate was not formed during E-beam treatment.
An economic analysis of the E-beam treatment system indicated that the primary costs are for the E-beam
equipment and for electrical energy. The estimated cost ranged from over $40 per 1000 gallons for a small-scale
remedial application to about $1.00 per 1000 gallons for a larger-scale drinking water application (Venosa and
Swanson 2002).
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Technologies for Treating MtBE and Other Fuel Oxygenates
4.8 Other Treatment Technologies: Phytoremediation, PRBs, and Thermal Treatment
Overview
Other technologies that have been used to treat MtBE and other
oxygenates include:
o Phytoremediation (8 projects in dataset)
o Permeable Reactive Barriers
o Thermal Treatment
4.8.1 What Other Technologies are used to Treat MtBE and Other Oxygenates?
In addition to the technologies discussed earlier in this chapter, three additional technologies
(phytoremediation, PRBs, and thermal treatment) have also been used to treat MtBE and other oxygenates
in soil and groundwater. Phytoremediation is a category of treatment technologies that employ plants (or
in some cases fungi) to conduct remediation. Treatment during phytoremediation can be accomplished
through one or more natural processes, including enhanced bioremediation in the rhizosphere (plant root
zone), phyto-stabilization of contaminants by organic plant material, plant uptake, plant metabolism, and
phytovolatilization (volatilization through plant leaves) (EPA, 2000g). PRBs are subsurface barriers that
remediate groundwater as it passes through an engineered treatment zone. For the treatment of MtBE and
other oxygenates, treatment zones that use bioremediation processes are most common (EPA, 2002e).
Thermal treatment is a generic term that applies to technologies that use heat to mobilize, extract, or
destroy contaminants either in situ or ex situ. While these technologies were applied less frequently, they
may represent viable treatment options at some sites contaminated with MtBE and other oxygenates.
4.8.2 How Is Phytoremediation Used in Treatment of Oxygenates?
Properties
Phytoremediation, as it applies to MtBE and other oxygenates, is a relatively new remedial approach and
many of the removal and degradation pathways are currently being studied. However, it is known that
phytoremediation relies on multiple processes to accomplish the removal of contaminants from shallow
groundwater. Each of these processes is affected by different chemical properties as well as site-specific
conditions. The biodegradability of oxygenates affects their treatment in the rhizosphere, where the
conditions support an abundance of metabolically-active bacteria and fungi that may enhance contaminant
degradation. The relatively high solubility and low organic partition coefficients (discussed earlier in this
section) of oxygenates generally limits significant removal through phyto-stabilization, but facilitates
removal through root uptake. In addition, volatility and Henry's Constants may affect the removal
through phytovolatilization (Chard and others, 2001).
Application -
The manner that phytoremediation can be applied to treat MtBE and other fuel oxygenates is highly
variable, based on the site conditions, specific contaminants to be treated, cleanup goals, and other
factors. Information relevant to the application of phytoremediation at sites contaminated with MtBE and
other oxygenates is available in the documents:
EPA. 2000. Introduction to Phytoremediation. Office of Research and Development. EPA 600-
R-99-107. February.
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Technologies for Treating MtBE and Other Fuel Oxygenates
Chard, J., A.M. Ferro, and J. Greene. 2001. "Recent Advances in Phytoremediation of MtBE
Groundwater Plumes". Contaminated Soil, Sediment, and Water. Spring.
Landmeyer, J. E., D. A. Vrblosky and P. M. Bradley. 2000. "MtBE and BTEX in Trees above
Contaminated Groundwater". Battelle International Conference on Remediation of Chlorinated
and Recalcitrant Compounds, Monterey, CA.
Newman, Lee and Charles Arnold. 2003. "Phytoremediation of MTBE- A Review of the State
of the Technology". In Moyer and Kostecki, Eds. MtBE Remediation Handbook. Amherst
Scientific Publishers.
Rubin, E. and A. Ramaswami. 2001. "The Potential for Phytoremediation of MtBE". Water
Res. 35(5): 1348-1353.
Projects -
From the 323 MtBE treatment profiles, 8 projects were identified where MtBE was treated using
phytoremediation. These projects used various approaches, including hybrid poplar trees, Monterey pine,
oak, eucalyptus, and engineered wetlands.
Table 4.8-1 summarizes the scale and operational status for the 8 projects in the datasetthat used
phytoremediation. The data used to compile this information was current at the time the profile for each
project was completed. Further information about these projects is provided in Appendix A, including
available performance data.
Table 4.8-1. General Information on 8 Projects Using Phytoremediation
Technology
Phytoremediation
# of Projects
8
Operational Status
Completed
5
Ongoing
3
Scale
Bench
3
Pilot
4
Full
1
Costs -
No total project cost data were reported for any of the projects in the dataset that employed
phytoremediation technology.
4.8.3 How Are PRBs Used in Treatment of Oxygenates?
Properties
A PRB is a treatment system configuration with treatment zones that can employ any of a number of
treatment technologies, such as in situ bioremediation or in situ chemical oxidation. Depending on which
treatment technology is employed, the properties of MtBE and other oxygenates as they apply to that
specific technology (as discussed earlier in this section) will affect treatment differently.
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Application -
Information relevant to the application of PRBs at sites contaminated with MtBE and other oxygenates is
available in the documents:
Gavaskar, A., N. Gupta, B. Sass, R. Janosy, and J. Hicks. 2000. Design Guidance for
Application of Permeable Reactive Barriers for Groundwater Remediation. Prepared for U.S.
Air Force, Air Force Research Laboratory. March.
ITRC. 1999. Regulatory Guidance for Permeable Reactive Barriers Designed to Remediate
Chlorinated Solvents. December.
EPA. 1998. Permeable Reactive Barrier Technologies for Contaminant Remediation.
EPA/600/R-98/125. Office of Research and Development. September.
EPA. 2002. Field Applications of In Situ Remediation Technologies: Permeable Reactive
Barriers. Office of Solid Waste and Emergency Response. January.
EPA. 2002. Economic Analysis of the Implementation of Permeable Reactive Barriers for
Remediation of Contaminated Ground Water. EPA/600/R-02/034. National Risk Management
Research Laboratory, Ada, Oklahoma. June.
Projects -
While no projects in the dataset were identified explicitly as using PRBs, several projects discussed under
other technologies involved these types of components. For example, several bioremediation projects,
such as at Port Hueneme, were performed using a PRB configuration; these are discussed further in
Section 4.4.
Costs -
No total project cost data were reported for any of the projects in the dataset that employed in situ thermal
treatment technology. However, additional information in the literature includes information about the
application of PRBs for the treatment of other contaminants. One reference showed a range of total costs
for 16 PRB projects ranging from $43,000 to $1,900,000 with a median total cost of $680,000 (EPA,
2000c).
4.8.4 How Is In Situ Thermal Treatment Used for Remediation of Oxygenates?
Properties
Thermal treatment can be used to mobilize or destroy MtBE and other oxygenates from soil either in situ
or ex situ, similar to other petroleum contaminants. Projects in the dataset applied in situ thermal
treatment. Volatilization from soil is affected by vapor pressure, with a higher vapor pressure making
volatilization occur more readily. In general, alcohol-based oxygenates have lower vapor pressures than
ether-based oxygenates, but the vapor pressures of both are comparable to or greater than other petroleum
contaminants such as benzene. Similar to other organic contaminants, MtBE and other oxygenates may
also be susceptible to thermal destruction at high temperatures.
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Application -
Information relevant to the application of in situ thermal treatment at sites contaminated with MtBE and
other oxygenates is available in the following document:
EPA. 2004. In Situ Thermal Treatment of Chlorinated Solvents: Fundamentals and Field
Applications. EPA 542-R-04-010. Office of Solid Waste and Emergency Response. March.
Projects -
While no projects in the dataset were identified explicitly as using in situ thermal treatment, several
projects discussed under other technologies involved these types of components. For example, one site in
Texas also discussed under bioremediation (Rural Area Disposal Area, Liberty, TX) used a combination
of technologies that included an in situ thermal treatment component.
Costs -
No total project cost data were reported for any of the projects in the dataset that employed in situ thermal
treatment technology.
4.8.5 What Factors may Affect the Performance and Cost of Phytoremediation, PRBs, or
Thermal Treatment?
When MtBE or other oxygenates are present and must be remediated at a site, phytoremediation, PRBs,
or in situ thermal treatment, may be part of a suitable remediation approach. Information about the
factors that influence the performance and cost of these systems in general is available in the references
listed in this report.
4.8.6 Conclusions
Data from MtBE Treatment Profiles Reporting About Other Treatment Technologies
Phytoremediation, PRBs, and thermal treatment have been used to remediate groundwater
contaminated with MtBE, but less frequently than some other technologies such as air sparging
and bioremediation; phytoremediation has been used at 8 sites for MtBE
All PRB projects in the dataset have treatment zones that employed bioremediation technology
The thermal treatment projects in the dataset used thermal desorption in conjunction with other
technologies, such as in situ bioremediation
No information on total project cost was reported for projects using phytoremediation, PRBs, or
thermal treatment
Treatability of MtBE and Other Oxygenates Using Other Treatment Technologies
Treatability during phytoremediation based on multiple contaminant properties, including
biodegradability, solubility, partition coefficient, vapor pressure, and Henry's Constant
Treatability using PRBs dependant on reactive treatment zone employed
Vapor pressure from soil affects volatilization during thermal treatment; generally oxygenates
have comparable or higher (more favorable for volatilization) vapor pressures than other
petroleum contaminants
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Technologies for Treating MtBE and Other Fuel Oxygenates
Other Potential Advantages of Applying Other Treatment Technologies
Phytoremediation or PRBs may be a cost-effective alternative for remediating or containing
relatively low concentration, shallow, and widespread groundwater plumes
Thermal treatment technologies tend to remove oxygenates along with other petroleum
contaminants (such as petroleum hydrocarbons) that are more typically treated using this
technology
Other Potential Limitations to Applying Other Treatment Technologies
The processes that effectively treat MtBE and other oxygenates during phytoremediation are still
being studied
Phytoremediation may be less applicable to higher concentration or deeper groundwater plumes
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Technologies for Treating MtBE and Other Fuel Oxygenates
5.0 NON-TREATMENT REMEDIES
Overview
Non-treatment remedies that address oxygenates include excavation, free
product recovery, MNA, and institutional controls
Non-treatment remedies may be appropriate for use either alone or in
conjunction with one or more of the other remedies discussed in this report
Containment (caps or vertical barrier walls) typically have not been used at
sites contaminated with MtBE, and is not discussed further
While this report focuses on treatment technologies that have been used for MtBE and other fuel
oxygenates, many sites are being remedied using non-treatment options that include excavation, free
product recovery, MNA, and institutional controls. In addition, these remedies sometimes are used in
conjunction with one or more of the treatment technologies discussed in Section 4.
5.1
Excavation
Excavation is the removal of contaminated soil or sludge from a site by use of mechanical equipment. It
often is used at sites where significant volumes of petroleum products are present in the soils located near
the surface, and which are likely to be a continuing source of contaminant migration. Commonly,
excavation is performed prior to or while implementing other remedies such as groundwater treatment
technologies. Similar to free product recovery, excavation is used to remove/control the source of
contamination, so that MtBE will not continue to migrate to the vadose zone and groundwater (FRTR,
2002).
Site-specific characteristics, such as the presence of aboveground and below ground obstructions, largely
dictate the implementation of excavation. Locations where underground utilities or storage facilities exist
may require extensive and time-consuming exploratory excavation and hand-digging. Excavation around
or near buildings may require the use of underpinning or sheet piling to stabilize the structure and
rerouting of utility lines. Shoring or sloping may be required in sandy soil to maintain trench wall
stability. Monitoring for air quality may be required during excavation. When fugitive air emissions
exceed air quality standards, there may be limitations imposed on the quantity of soil that can be
excavated per day.
Excavation equipment ranges from hand tools, such as pick axes and shovels, to backhoes, front-end
loaders, clamshells, and draglines, depending on the amount of soil to be excavated, the total depth of the
excavation, moisture content of the soil, and the space allowed at the site for staging of excavated
material. Backhoes and front-end loaders are the most commonly used equipment for excavation of
relatively shallow (less than 15 ft bgs) soils. Excavation rates for these types of units with 1 cubic yard
bucket capacities are typically 75 cubic yards per hour. Larger bucket capacities can increase this rate to
up to 160 cubic yards per hour (ECHOS, 2002). The maximum excavation rate using hand tools is
approximately 1 cubic yard per hour /laborer.
Factors that affect the costs for excavation include the depth of contamination, depth of groundwater
(requiring dewatering), and extent of underground infrastructure and/or nearby structures that require
shoring. The cost for excavation tends to be higher for areas with deeper contamination, shallower
groundwater, and more infrastructure and nearby structures.
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Technologies for Treating MtBE and Other Fuel Oxygenates
5.2 Free Product Recovery
Free product recovery is the extraction of separate phase material (primarily petroleum liquids) that is
located in the subsurface (in the case of petroleum liquids, at the top of the water table). It is often used at
sites where significant volumes of petroleum products have reached the water table, and which are likely
to be a continuing source of contaminants migrating to the vadose zone or dissolving in groundwater.
Commonly, free product recovery is performed prior to or during implementation of remedies such as
groundwater treatment. Similar to excavation, free product recovery is used to remove/control the source
of contamination, so that the source will not continue to migrate to the vadose zone or the groundwater.
Note that free product removal is a Federal regulatory requirement, under 40 CFR Section 280.64. This
section requires owners and operators to remove free product to the maximum extent practicable, while
continuing other remedial actions, as discussed in that section.
Technologies typically used to recover free product include skimming equipment in wells, trenches, or
excavation pits, and pumping of free product. These approaches have been used with and without
depressing the water table to enhance migration of free product to a well or drain. The design of a free
product recovery system requires an understanding of the site hydrogeology and characteristics, the types,
extent, and distribution of free product in the subsurface, and the engineering aspects of the equipment
and installation. Free product recovery sometimes is combined with other technologies to enhance
removal of contaminants from the vadose zone or that are dissolved in the groundwater.
EPA published a guide for state regulators about how to effectively recover free product at leaking USTs,
How to Effectively Recover Free Product at Leaking Underground Storage Tank Sites; A Guide for State
Regulators (EPA, 1996). In that guide, EPA provided scientific and engineering considerations for
evaluating technologies for the recovery of free product from the subsurface. The guide discussed the
behavior of hydrocarbons in the subsurface, methods for evaluating recoverability of subsurface
hydrocarbons, and recovery systems and equipment.
5.3 Monitored Natural Attenuation
EPA defines MNA as "the reliance on natural processes, within the context of a carefully controlled and
monitored site cleanup approach, to achieve site-specific remediation objectives within a time frame that
is reasonable compared to that offered by other more active methods. The natural processes include
biodegradation, dispersion, dilution, sorption, volatilization, stabilization, and transformation. These
processes reduce site risk by transforming contaminants to less toxic forms, reducing contaminant
concentrations, and reducing contaminant mobility and bioavailability". Other terms for natural
attenuation in the literature include "intrinsic remediation", "intrinsic bioremediation", "passive
bioremediation", "natural recovery", and "natural assimilation" (EPA, 1999b).
While offering the potential to cleanup sites at lower cost, MNA typically would require a longer period
of time to achieve remediation objectives, compared to active remediation measures. In addition, it
generally requires extensive long-term monitoring data. Other potential limitations of MNA include the
potential that the toxicity and/or mobility of transformation products may be greater than for the parent
compound (e.g., TEA as a degradation product of MtBE); hydrologic and geochemical conditions
amenable to natural attenuation may change over time and could result in renewed mobility of previously-
stabilized contaminants; and more extensive education and outreach efforts may be required to gain
public acceptance of MNA. Information about research into field use of MNA is provided in Schirmer
1999.
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Technologies for Treating MtBE and Other Fuel Oxygenates
EPA published a guide about the steps needed to understand the rate and extent to which natural
processes are reducing contaminant concentrations, Technical Protocol for Evaluating Natural
Attenuation of Chlorinated Solvents in Ground Water (EPA, 1998b). While this guide is directed at sites
contaminated by chlorinated solvents, some of the steps would also have relevance for sites contaminated
by oxygenates like MtBE. The guide identifies parameters that are useful in the evaluation of natural
attenuation and provides recommendations on how to analyze and interpret the data collected from the
site characterization process. It also provides suggestions for integrating MNA into an integrated
approach to remediation that includes an active remedy.
Recently, EPA published a report titled "Performance Monitoring of MNA Remedies for VOCs in
Ground Water" (EPA, 2004a) that provides guidance about types of monitoring used during MNA
remedies.
5.4 Institutional Controls
ICs are non-engineered instruments such as administrative and/or legal controls that minimize the
potential for human exposure to contamination by limiting land or resource use, and generally are used in
conjunction with engineering measures such as treatment or containment. ICs are used during all stages
of a cleanup and often involve multiple activities ("layered 1C") implemented in parallel or in series.
Examples of ICs are easements, covenants, well drilling prohibitions, zoning restrictions, and special
building permit requirements (sometimes referred to as deed restrictions) (EPA, 2000d).
Often, ICs are considered within the context of long-term plume management and MNA. Typically, after
the source of contamination has been addressed (such as through removal or destruction), ICs are used to
limit the long-term use of a site and the potential for exposure of residual contaminants to human or
environmental receptors. When deciding about appropriate types of ICs, site managers look at the life-
cycle strengths, weaknesses, and costs for implementation, monitoring, and enforcement, and
coordination with state and local governments that have responsibilities for ICs. Additional information
about ICs is available in Institutional Controls: A Site Manager's Guide to Identifying, Evaluating, and
Selecting Institutional Controls at Superfund and RCRA Corrective Action Clean-ups (EPA, 2000d).
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Technologies for Treating MtBE and Other Fuel Oxygenates
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Technologies for Treating MtBE and Other Fuel Oxygenates
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Technologies for Treating MtBE and Other Fuel Oxygenates
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6-7
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APPENDIX A
MtBE TREATMENT PROFILE DATA
(see www.cluin.org/tntbe)
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ซa
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