EPA542-6-97-Q1Q
May 1998
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THE WASTECH® MONOGRAPH SERIES (PHASE II) ON
INNOVATIVE SITE REMEDIATION TECHNOLOGY:
DESIGN AND APPLICATION
This seven-book series focusing on the design and application of innovative site remediation
technologies follows an earlier series (Phase I, 1994-1995) which cover the process descriptions,
evaluations, and limitations of these same technologies. The success of that series of publications
suggested that this Phase II series be developed for practitioners in need of design information
and applications, including case studies.
WASTECH® is a multiorganization effort which joins in partnership the Air and Waste Manage-
ment Association, the American Institute of Chemical Engineers, the American Society of Civil
Engineers, the American Society of Mechanical Engineers, the Hazardous Waste Action
Coalition, the Society for Industrial Microbiology, the Soil Science Society of America, and
the Water Environment Federation, together with the American Academy of Environmental
Engineers, the U.S. Environmental Protection Agency, the U.S. Department of Defense, and the
U.S. Department of Energy.
A Steering Committee composed of highly respected members of each participating organization
with expertise in remediation technology formulated and guided both phases, with project
management and support provided by the Academy. Each monograph was prepared by a Task
Group of recognized experts. The manuscripts were subjected to extensive peer reviews prior to
publication. This Design and Application Series includes:
Vol 1 - Bioremedlation
Principal authors: R. Ryan Dupont, Ph.D., Chair,
litah State University; Clifford J. Bruell, Ph.D.,
University of Massachusetts; Douglas C. Downey,
Parsons Engineering Science; Scott G. Huling, Ph.D.,
P.E., USEPA; Michael C. Marley, Ph.D., Environgen,
Inc.; Robert D. Norris, Ph.D., Eckenfelder, Inc.;
Bruce Pivetz, Ph.D., USEPA.
Vbl 2 - Chemical Treatment
Principal authors: Leo Weitzman, Ph.D., LVW
Associates, Chair, Irvin A. Jefcoat, Ph.D., University
of Alabama; Byung R. Kim, Ph.D., Ford Research
Laboratory.
Vol 3 - Liquid Extraction Technologies:
Soil Washing/Soil Flushing/Solvent Chemical
Principal authors: Michael J. Mann, P.E., DEE,
ARCADIS Geraghty & Miller, Inc., Chair; Richard
J. Ayen, Ph.D., Waste Management Inc.; Lome G.
Everett, Ph.D., Geraghty & Miller, Inc.; Dirk
Gombert II, P.E., LIFCO; Mark Meckes, USEPA;
Chester R. McKee, Ph.D., In-Situ, Inc.; Richard P.
Traver, P.E., Bergmann USA; Phillip D. Walling,
Jr., P.E.. E. I. DuPont Co. Inc.; Shao-Chih Way,
Ph.D., In-Situ, Inc.
Vol 4 - Stabilization/Solidification
Principal authors: Paul D. Kalb, Brookhaven National
Laboratory, Chair, Jesse R. Conner, Conner Technolo-
gies, foe.; John L. Mayberry, P.E., SAIC; Bhavesh R.
Patel, U.S. Department of Energy; Joseph M. Perez, Jr.,
Battelle Pacific Northwest; Russell L. Treat, MACTEC
Vol 5 - Thermal Desorption
Principal authors: William L. Troxler, P.E., Focus
Environmental Inc., Chair; Edward S. Alperin, IT
Corporation; Paul R. de Percin, USEPA; Joseph H.
Button, P.E., Canonic Environmental Services, Inc.;
JoAnn S. Lighty, Ph.D., University of Utah; Carl R.
Palmer, P.E., Rust Remedial Services, Inc.
Vol 6 - Thermal Destruction
Principal authors: Francis W. Holm, Ph.D., SAIC, Chair,
Carl R. Cooley, Department of Energy; James J.
Cudahy, P.E., Focus Environmental Inc.; Clyde R.
Dempsey, P.E.. USEPA; John P. Longwell, ScJX,
Massachusetts Institute of Technology; Richard S.
Magee, Sc.D., P.E., DEE, New Jersey Institute of
Technology; Walter G. May, Sc.D., University of Illinois.
Vol 7 - Vapor Extraction and Air Sparging
Principal authors: Timothy B. Holbrook, P.E., Camp
Dresser & McKee, Inc., Chair, David H. Bass, Sc.D.,
Groundwater Technology, Inc.; Paul M. Boersma,
CH2M Hill; Dominic C. DiGuilio, University of
Arizona; John J. Eisenbeis, Ph.D., Camp Dresser &
McKee, Inc.; Neil J. Hutzler, Ph.D., Michigan
Technological University; Eric P. Roberts, P.E., ICF
Kaiser Engineers, Inc.
The monographs for both the Phase I and Phase II
series may be purchased from the American Academy
of Environmental Engineers®, 130 Holiday Court, Suite
100, Annapolis, MD, 21401; Phone: 410-266-3390,
Fax: 410-266-7653, E-mail: aaee@ea.net
»U.S. GOVEESXESrr P-OTriNG OF7ICE: 1 998-621-059/93278
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INNOVATIVE SITE
REMEDIATION TECHNOLOGY:
DESIGN AND APPLICATION
VAPOR EXTRACTION
and AIR SPARGING
One of a Seven-Volume Series
Prepared by WASTECH®, a multiorganization cooperative project managed
by the American Academy of Environmental Engineers® with grant assistance
from the U.S. Environmental Protection Agency, the U.S. Department of
Defense, and the U.S. Department of Energy.
The following organizations participated in the preparation and review of
this volume:
Air & Waste Management
Association
P.O. Box 2861
Pittsburgh, PA 15230
American Academy of
Environmental Engineers®
130 Holiday Court, Suite 100
Annapolis, MD 21401
Hazardous Waste Action
Coalition
1015 15th Street, N.W., Suite 802
Washington, D.C. 20005
American Society of
Civil Engineers
345 East 47th Street
New York, NY 10017
Soil Science Society
of America
677 South Segoe Road
Madison, WI 53711
Water Environment
Federation
601 Wythe Street
Alexandria, VA 22314
Monograph Principal Authors:
Timothy B. Holbrook, P.E., DEE, Chair
David H. Bass, Sc.D. John J. Eisenbeis, Plti.D.
Paul M. Boersma Neil J. Hutzler, Ph.D., P.E.
Dominic C. DiGiulio Eric P. Roberts, P.E.
Series Editor
William C. Anderson, P.E., DEE
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Library of Congress Cataloging in Publication Data
Innovative site remediation technology: design and application.
p. cm.
"Principal authors: Leo Weitzman, Irvin A. Jefcoat, Byung R. Kim"--V.2, p. iii.
"Prepared by WASTECH."
Includes bibliographic references.
Contents: —[2] Chemical treatment
1. Soil remediation-Technological innovations. 2. Hazardous waste site remediation--
Technological innovations. I. Weitzman, Leo. II. Jefcoat, Irvin A. (Irvin Ally) III. Kim, B.R.
IV. WASTECH (Project)
TD878.I55 1997
628.5'5--dc21 97-14812
CIP
ISBN 1-883767-17-2 (v. 1) ISBN 1-883767-21-0 (v. 5)
ISBN 1-883767-18-0 (v. 2) ISBN 1-883767-22-9 (v. 6)
ISBN 1 -883767-19-9 (v. 3) ISBN 1 -883767-23-7 (v. 7)
ISBN 1-883767-20-2 (v. 4)
Copyright 1998 by American Academy of Environmental Engineers. All Flights Reserved.
Printed in the United States of America. Except as permitted under the United States
Copyright Act of 1976, no part of this publication may be reproduced or distributed in any
form or means, or stored in a database or retrieval system, without the prior written
permission of the American Academy of Environmental Engineers.
The material presented in this publication has been prepared in accordance with
generally recognized engineering principles and practices and is for general informa-
tion only. This information should not be used without first securing competent advice
with respect to its suitability for any general or specific application.
The contents of this publication are not intended to be and should not be construed as a
standard of the American Academy of Environmental Engineers or of any of the associated
organizations mentioned in this publication and are not intended for use as a reference in
purchase specifications, contracts, regulations, statutes, or any other legal document.
No reference made in this publication to any specific method, product, process, or
service constitutes or implies an endorsement, recommendation, or warranty thereof by the
American Academy of Environmental Engineers or any such associated organization.
Neither the American Academy of Environmental Engineers nor any of such associated
organizations or authors makes any representation or warranty of any kind, whether
express or implied, concerning the accuracy, suitability, or utility of any information
published herein and neither the American Academy of Environmental Engineers nor any
such associated organization or author shall be responsible for any.errors, omissions, or
damages arising out of use of this information.
Printed in the United States of America.
WASTECH and the American Academy of Environmental Engineers are trademarks of the American
Academy of Environmental Engineers registered with the U.S. Patent and Trademark Office.
Cover design by William C. Anderson. Cover photos depict remediation of the Scovill Brass Factory,
Waterbury, Connecticut, recipient of the 1997 Excellence in Environmental Engineering Grand Prize
award for Operations/Management.
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CONTRIBUTORS
PRINCIPAL AUTHORS
Timothy B. Holbrook, P.E., DEE, Task Group Chair
Camp Dresser & McKee Inc.
David H. Bass, Sc.D. John J. Eisenbeis, Ph.D.,
Fluor Daniel GTI Camp Dresser & McKee Inc.
Paul M. Boersma Neil J. Hutzler, Ph.D., P.E.
HNTB Michigan Technological University
Dominic C. DiGiulio Eric P. Roberts, P.E.
USEPA ICF Kaiser Engineers, Inc.
REVIEWERS
The panel that reviewed the monograph was reviewed by a panel comprised of
the Project Steering Committee, Chaired by Peter W. Tunnicliffe, P.E1., DEE,
Camp Dresser & McKee Inc.
i/iiL auu icmcuiauuu muuaujr.
HWAC's mission is to serve and
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CONTRIBUTORS
PRINCIPAL AUTHORS
Timothy B. Holbrook, P.E., DEE, Task Group Chair
Camp Dresser & McKee Inc.
David H. Bass, Sc.D.
Fluor Daniel GTI
Paul M. Boersma
HNTB
Dominic C. DiGiulio
USEPA
John J. Eisenbeis, Ph.D.
Camp Dresser & McKee Inc.
Neil J. Hutzler, Ph.D., P.E.
Michigan Technological University
Eric P. Roberts, P.E.
ICF Kaiser Engineers, Inc.
REVIEWERS
The panel that reviewed the monograph was reviewed by a panel comprised of
the Project Steering Committee, Chaired by Peter W. Tunnicliffe, P.E., DEE,
Camp Dresser & McKee Inc.
iii
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REVIEWING ORGANIZATIONS
The following organizations contributed to the monograph's review/ and acceptance
by the. professional community. The review process employed by each organiza-
tion is.described in its acceptance statement. Individual reviewers are, or are not,
listed according to the instructions of each organization.
Air & Waste Management
Association
The Air & Waste Management
Association is a nonprofit technical and
educational organization with more than
14,000 members in more than fifty
countries. Founded in 1907, the
Association provides a neutral forum
where all viewpoints of an environmen-
tal management issue (technical,
scientific, economic, social, political,
and public health) receive equal
consideration.
Qualified reviewers were recruited
from the Waste Group of the Technical
Council. It was determined that the
monograph is technically sound and
publication is endorsed.
The lead reviewer was:
Terry Alexander, Ph.D.
University of Michigan
American Society of Civil
Engineers
The American Society of Civil
Engineers, established in 1852, is the
premier civil engineering association in
the world with 124,000 members.
Qualified reviewers were recruited from
its Environmental Engineering Division.
ASCE has reviewed this manual and
believes that significant information of
value is provided. Many of the issues
addressed, and the'resulting conclu-
sions, have been evaluated based on
satisfying current regulatory require-
ments. However, the long-term stability
of solidified soils containing high levels
of organics, and potential limitations
and deficiencies of current testing
methods, must be evaluated in more
detail as these technologies are imple-
mented and monitored.
The reviewers included:
Richard Reis, P.E.
Fluor Daniel GTI
Seattle, WA
Hazardous Waste Action
Coalition
The Hazardous Waste Action
Coalition (HWAC) is the premier
business trade group serving and
representing the leading engineering
and science firms in the environmental
management and remediation industry.
HWAC's mission is to serve and
promote the interests of engineering and
science firms practicing in multi-media
environment management and
remediation. Qualified reviewers were
recruited from HWAC's Technical
Practices Committee. HWAC is
pleased to endorse the monograph as
technically sound.
The lead reviewer was:
James D. Knauss, Ph.D.
President, Shield Environmental
Lexington, KY
V
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t$5*
\ilV
V
Soil Science Society of ,
America
The Soil Science Society of
America, headquartered in Madison,
Wisconsin, is home to more than 5,300
professionals dedicated to the advance-
ment of soil science. Established in
1936, SSSA has members in more than
100 countries. The Society is composed
of eleven divisions, covering subjects
from the basic sciences of physics and
chemistry through soils in relation to
crop production, environmental quality,
ecosystem sustainability, waste
management and recycling,
bioremediation, and wise land use.
Members of SSSA have reviewed
the monograph and have determined
that it is acceptable for publication.
The lead reviewer was:
Mark Brusseau, Ph.D.
University of Arizona
Water Environment
Federation
The Water Environment Federa-
tion is a nonprofit, educational
organization composed, of member
and affiliated associations throughout
the world. Since 1928, the Federation
has represented water quality
specialists including engineers,
scientists, government officials,
industrial and municipal treatment
plant operators, chemists, students,
academic and equipment manufac-
turers, and distributors.
Qualified reviewers were
recruited from the Federation's
Hazardous Wastes Committee and
from the general membership. It has
been determined that the document is
technically sound and publication is
endorsed.
vi
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ACKNOWLEDGMENTS
The WASTECH® project was conducted under a cooperative agreement
between the American Academy of Environmental Engineers® and the Office
of Solid Waste and Emergency Response, U.S. Environmental Protection
Agency. The substantial assistance of the staff of the Technology Innovation
Office was invaluable.
Financial support was provided by the U.S. Environmental Protection
Agency, Department of Defense, Department of Energy, and the American
Academy of Environmental Engineers®.
This multiorganization effort involving a large number of diverse profes-
sionals and substantial effort in coordinating meetings, facilitating communica-
tions, and editing and preparing multiple drafts was made possible by a
dedicated staff provided by the American Academy of Environmental Engi-
neers® consisting of:
William C. Anderson, P.E., DEE
Project Manager & Editor
John M. Buterbaugh
Assistant Project Manager & Managing Editor
Robert Ryan
Editor
Catherine L. Schultz
Yolanda Y. Moulden
Project Staff Production
3. Sammi Olmo
I. Patricia Violette
Project Staff Assistants
vii
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TABLE OF CONTENTS
Contributors iii
Acknowledgments vii
List of Tables
List of Figures
1.0 INTRODUCTION 1.1
1.1 Vapor Extraction and Air Sparging 1.1
1.1.1 Vapor Extraction 1.1
1.1.2 Air Sparging 1.2
1.2 Development of the Monograph 1.2
1.2.1 Background 1.2
1.2.2 Process 1.4
1.3 Purpose 1.5
1.4 Objectives 1.5
1.5 Scope 1.5
1.6 Limitations 1.6
1.7 Organization 1.7
2.0 APPLICATION CONCEPTS 2.1
2.1 Scientific Principles 2.6
2.1.1 Chemical Equilibrium 2.6
2.1.2 Air Flow Principles 2.8
2.1.2.1 Air Flow in the Unsaturated Zone 2.9
2.1.2.2 Air Flow in the Saturated Zone 2.10
2.1.3 Mass Transfer Principles 2.11
2.1.4 Chemical Destruction Principles 2.15
2.2 Potential Applications 2.16
2.2.1 Vapor Extraction 2.16
ix
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Table of Contents
2.2.2 Air Sparging 2.17
i , " .I' ' ' ' " ,". ,.'•,, ! " '
2.2.2 Range of Applicability of Vapor Extraction/
Air Sparging Technology 2.17
2.2.3 Limitations of Technology 2.19
3.0 DESIGN DEVELOPMENT FOR VAPOR EXTRACTION 3.1
3.1 Soil Remediation Goals 3.2
3.1.1 Selecting Design Objectives 3.2
3.1.2 Establishing Soil Clean-up Criteria 3.3
3.1.3 Measuring Soil Clean-up Criteria 3.4
3.1.4 Achievable Soil Clean-up Concentrations 3.6
3.2 Design Basis 3.8
3.2.1 Site and Contaminant Characteristics 3.8
3.2.2 Pilot Testing 3.13
3.2.2.1 Conventional Vapor Extraction Pilot Tests 3.14
3.2.2.2 High-Vacuum Vapor Extraction, Dual-Phase
Vapor Extraction, and Bioslurping Pilot Tests 3.25
312.2.3 Bioventing Pilot Tests 3.27
3.2.3 Pilot Test Results Interpretation 3.28
3.2.3.1 Evaluating Air Permeabilities 3.29
3.2.3.2 Evaluating Other Parameters from Pilot Test Data 3.30
3.2.3.3 Evaluating High-Vacuum and Dual-Phase
Pilot Test Data 3.33
3.2.4 Preliminary Design Based on Full-Scale
Air Flow Analysis 3.34
,i , n i • ,•'"' ''I '",'', , " 'i
3.2.4.1 Evaluating Radius of Influence for a
Single Extraction Well 3.35
3.2.4.2 Evaluating Effective Radius of Influence Among
Extraction Wells 3.37
3.2.4.3 Air Injection 3.38
3.2.4.4 Horizontal Wells and Vented Trenches 3.39
1 ••• • .; . '•••' " :• . •• r '' • i
3.2.4.5 Thermal Enhancement 3.40
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Table of Contents
3.2.4.6 Pneumatic and Hydraulic Soil Fracturing for
Clay Soils 3.48
3.2.4.7 Dual-Phase Vapor Extraction 3.52
3.3 Equipment Selection 3.58
3.3.1 Pretreatment Equipment Selection 3.58
3.3.1.1 Air/Water Separators 3.58
3.3.1.2 Particle Removal 3.60
3.3.2 Well Construction and Field Piping Layout/Trenching 3.61
3.3.2.1 Well Screen Placement 3.61
3.3.2.2 Construction Considerations for Piping Layout 3.62
3.3.2.3 Pipe Material Selection and Sizing 3.62
3.3.3 Blowers (Vacuum Pump) Selection 3.65
33.3.1 System Curve Development 3.65
3.3.3.2 Blower Alternatives 3.66
3.3.3.3 Blower Selection 3.69
3.3.3.4 Blower Silencers and Acoustics 3.70
3.3.4 Tanks and Vessels 3.71
3.3.5 Structural Design Considerations 3.72
3.4 Process Modifications 3.73
3.4.1 Designing for Operational Flexibility and Expandability 3.73
3.4.2 Pulsing 3.76
3.4.3 Adapting to Nonideal Situations 3.77
3.4.3.1 Anisotropy 3.77
3.4.3.2 Short Circuiting 3.77
3.5 Posttreatment Processes (Offgas Handling) 3.78
3.5.1 Technology Descriptions 3.78
3.5.1.1 Vapor-Phase Carbon 3.79
3.5.1.2 Adsorption Resins 3.82
3.5.1.3 Catalytic Oxidation 3.82
3.5.1.4 Thermal Oxidation 3.83
XI
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Table of Contents
3.5.1.5 Internal Combustion Engines 3.85
3.5.1.6 Condensation 3.85
3.5.1.7 Biofilters 3.85
3.6 Process Instrumentation and Controls 3.86
3.6.1 Purpose 3.86
3.6.2 Instrumentation Selection 3.87
3.6.3 Controls and Alarms 3.88
3.6.4 Remote System Monitoring/Telemetry 3.89
3.7 Safety Requirements 3.89
3.7.1 Designing for Construction Safety 3.90
3.7.2 Building Code 3.91
3.7.3 Electrical Code 3.91
3.7.3.1 Area Classifications 3.92
3.7.3.2 Definition of Classified and Unclassified Areas 3.93
3.7.3.3 Application of Area Classification 3.95
3.7.3.4 Ventilation 3.96
3.7.4 Designing for Operational Safety 3.96
3.7.5 Fire Protection 3.97
3.8 Drawing and Specification Development 3.98
i
3,8.1 Purpose 3.99
3.8.2 Contractual, Financial, and Legal (Insurance)
Requirements 3.100
3.8.3 Wells, Vaults, Piping, and Equipment 3.100
3.8.3.1 Vertical Extraction Wells 3.100
- . . ' . ' |
3.8.3.2 Soil Gas/Vacuum Monitoring Points 3.108
|
3.8.3.3 Vapor Extraction Trenches 3.110
i
3.8.3.4 Piping 3.115
3.8.3.5 Valves 3.J17
3.8.3.6 Manifold Systems 3.118
3.8.4 Equipment Specifications 3.121
xii
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Table of Contents
3.8.5 Electrical 3.122
3.8.6 Equipment Buildings and Enclosures 3.122
3.9 Cost Estimating 3.122
3.9.1 Cost Estimating 3.123
3.9.2 Cost Estimating Procedures 3.124
3.9.3 Cost Estimating Approaches 3.126
3.9.4 Cost Estimating Checklist 3.126
3.10 Design Validation 3.130
3.11 Permitting Requirements 3.131
3.11.1 Air Permit Requirements 3.131
3.11.2 Surface Water Discharge Permit Requirements 3.133
3.11.3 Discharge Requirements to a POTW 3.134
3.12 Design Checklist 3.135
4.0 IMPLEMENTATION AND OPERATION OF
VAPOR EXTRACTION 4.1
4.1 Implementation 4.1
4.1.1 Contracting Strategies 4.1
4.1.2 Contracts 4.3
4.1.2.1 Lump-Sum 4.4
4.1.2.2 Cost-Plus-Fixed-Fee 4.5
4.1.2.3 Unit Price 4.5
4,1.2.4 Time and Materials 4.6
4.1.3 Role of the Engineer 4.7
4.1.3.1 Design Engineer 4.7
4.1.3.2 Construction Manager 4.9
4.1.3.3 Construction Overseer 4.13
4.1.3.4 Operator 4.15
4.1.4 Construction Activities 4.15
4.1.4.1 Drilling/Well Installation 4.15
4.1.4.2 Earthwork 4.15
xiii
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Table of Contents
4.1.4.3 Mechanical 4.16
4.1.4.4 Electrical 4.18
4.1.4.5 Concrete 4.18
4.1.4.6 Building 4.19
4.1.4.7 Equipment Assembly 4.19
4.1.4.8 Site Restoration 4.20
4.1.5 Construction Precommissioning Checklist 4.20
4.2 Start-up Procedures 4.21
4.2.1 Component Testing 4.22
4.2.1.1 Power Supply 4.22
4.2.1.2 Performance 4.23
4.2.2 System Testing 4.24
4.2.2.1 Instrument Calibration 4.24
4.2.2.2 Diagnostic Testing 4.24
4.2.3 Checklist for Startup 4.25
4.3 Maintenance 4.26
4.3.1 Extraction Systems 4.28
4.3.2 Vapor Treatment Systems 4.30
4.3.3 Wells, Trenches, and Well Points 4.30
4.3.4 Piping 4.30
4.3.5 Equipment Enclosure 4.31
4.3.6 Safety Considerations 4.31
4.3.6.1 Fire Safety 4.31
4.3.6.2 Air Quality 4.32
4.3.6.3 Physical Hazards 4.32
4.4 Performance Monitoring 4.33
4.4.1 Extracted Vapor Flow Measurement 4.34
4.4.2 Wellhead Pressure 4.35
4.4.3 Extracted Vapor Quality 4.35
4.4.4 Subsurface Vacuum Distribution 4.36
xiv
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Table of Contents
4.4.5 Condensate Production Rate Monitoring 4.36
4.4.6 Mass Removal Rate Calculations 4.37
4.4.7 Rebound Spike Concentration Monitoring 4.38
4.5 Operational Modifications 4.39
4.5.1 Balancing and Managing Air Flow 4.39
4.5.2 Targeting Residual Contaminants 4.39
4.6 Quality Control 4.40
5.0 DESIGN DEVELOPMENT FOR AIR SPARGING 5.1
5.1 Groundwater Remediation Goals 5.1
5.1.1 Selecting Design Objectives 5.1
5.1.2 Establishing Groundwater Clean-up Goals 5.3
5.1.3 Measuring Groundwater Clean-up Criteria 5.4
5.1.4 Achievable Groundwater Treatment Clean-up
Concentrations 5.7
5.2 Design Basis 5.9
5.2.1 Site and Contaminant Characteristics 5.9
5.2.2 Pilot Testing 5.13
5.2.2.1 Pilot Test Setup 5.15
5.2.2.2 Zone of Influence Monitoring 5.15
5.2.2.3 Step Test Procedures 5.21
5.2.3 Pilot Test Result Interpretation 5.23
5.2.3.1 Vertical Air Movement into the Vadose Zone 5.23
5.2.3.2 Lateral Air Movement into the Saturated Zone 5.24
5.2.3.3 Pressure/Flow Response 5.25
5.2.3.4 Biodegradation Rate 5.28
5.2.3.5 Rate of Contaminant Volatilization 5.29
5.2.3.6 Biofouling 5.29
5.2.4 Preliminary Design 5.30
5.3 Air Sparging and In Situ Equipment Selection 5.31
5.3.1 Air Sparging Well Location and Construction 5.31
xv
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Table of Contents
5.3.1.1 General 5.31
5.3.1.2 Vertical Wells 5.32
• • • >. ,, ' i ,
5.3.1.3 Horizontal Wells 5.33
5.3.2 Field and Manifold Piping 5.34
5.3.2.1 General 5.34
i :"
5.3.2.2 Design and Installation of the Manifold 5.34
5.3.3 Air Sparging Compressors 5.36
5.3.3.1 General 5.36
• • • j ,
5.3.3.2 Unit Selection 5.37
5.3.3.3 Air Filtering 5.38
5.3.3.4 Heat and Noise Control 5.39
5.4 Process Modifications 5.39
5.4.1 Additional Air Sparging Wells 5.40
5.4.2 Well Screen Placement 5.40
5.4.3 Sparging Curtains and Horizontal Air Sparging Wells 5.41
5.4.4 Heated Air Sparging 5.42
5.4.5 Ozone Sparging 5.42
5.4.6 Air and Methane Mixture 5.43
5.4.7 Pure Oxygen 5.44
i i • i , „ j
5.4.8 In-Well Aeration Systems 5.44
5.4.9 Nitrogen Sparging 5.49
5.5 Pretreatment Processes for Air Injection Systems 5.50
5.5.1 Temperature Reduction 550
5.5.2 Oil and Water Removal 5.50
! ' ij
5.6 Posttreatment Processes f>.51
5.7 Process Instrumentation and Controls 5.51
5.7.1 Air Sparging Instrumentation and Controls 5.51
5.7.2 Instrumentation Selection 5.52
5.7.3 Controls and Alarms 5.53
5.7.4 Remote System Monitoring/Telemetry 5.53
xvi
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Table of Contents
5.8 Safety Requirements 5.53
5.8.1 Building Code 5.54
5.8.2 Electrical Code 5.54
5.8.3 Designing for Operational Safety 5.54
5.9 Drawing and Specification Development ,5.55
5.9.1 Wells/Trenching/Field Piping 5.56
5.9.2 Equipment 5.56
5.9.3 Electrical 5.56
5.9.4 Mechanical 5.56
5.10 Cost Estimating 5.56
5.11 Design Validation 5.57
5.12 Permitting Requirements 5.58
5.13 Design Checklist 5.58
6.0 IMPLEMENTATION AND OPERATION OF AIR SPARGING 6.1
6.1 Implementation . 6.1
6.2 System Startup 6.1
6.2.1 Component Testing 6.2
6.2.1.1 Power Supply 6.2
6.2.1.2 Electrical Safety Checks 6.2
6.2.1.3 Shutdown Protocols 6.2
6.2.2 Leak Testing 6.4
6.2.3 System Shakedown 6.4
6.2.4 Pre-Startup Checklist 6.5
6.2.5 Startup Checklist 6.6
6.3 Operation and Maintenance 6.6
6.3.1 Performance Control Functions 6.7
6.3.2 Maintenance 6.9
6.3.2.1 Rotating Equipment 6.9
6.3.2.2 Wells, Trenches, and Well Points 6.9
6.3.3 Safety Considerations 6.10
xvii
-------
Table of Contents
6.3.3.1 Fire Safety 6.10
6.3.3.2 Air Quality 6.10
6.3.3.3 Physical Hazards 6.11
i
6.4 Performance Monitoring 6.11
6.4.1 Zone of Influence Monitoring 6.11
6.4.2 Injection Pressures and Flows 6.12
6.4.3 Downgradient Groundwater Quality Monitoring 6.12
6.4.4 Vadose Zone Monitoring 6.13
6.4.5 Pulsed Operation 6.14
6.4.6 Effectiveness and Rebound Monitoring 6.14
6.4.6.1 Petroleum-Contaminated Sites vs.
Chlorinated Sites 6.15
6.4.6.2 Factors Affecting Rebound 6.15
6.4.6.3 Dissolved-Phase Plumes vs. Source Areas 6.26
6.4.7 Health and Safety Monitoring 6.27
6.5 Operational Modifications to Enhance Performance 6.28
6.6 Quality Control 6.29
7.0 CASE HISTORIES 7.1
Appendices
A. Field-Scale Pneumatic Permeability Models A.1
B. Process Safety Review for VE/AS Systems B.I
C. Properties of Common Organic Pollutants C. 1
D. List of References D.I
xviii
-------
LIST OF TABLES
Table Title
2.1 Reported Air Sparging Field/Laboratory Applications 2.20
3.1 Pre- and Posttreatment Soil Sample Analysis Results for a
Superfund Site 3.7
3.2 Select Vendors of Horizontal Wells and Directional
Drilling Technology 3.41
3.3 Thermal Enhancement Performance Data 3.46
3.4 Select Examples of Remediation Technologies
Enhanced by Pneumatic and Hydraulic Fracturing 3.49
3.5 Select Vendors of Pneumatic and Hydraulic
Fracturing Technology 3.53
3.6 Offgas Control Technology Selection Issues 3.80
3.7 Extraction Well Materials 3.104
3.8 Types of Cost Estimates 3.123
3.9 Environmental Remediation Estimates: Characteristics 3.124
5.1 Sparging Pilot Test Objectives 5.14
5.2 Design System for Air Sparging Systems 5.32
6.1 Air Sparging Sites with Post-Closure Rebound 6.16
6.2 Air Sparging Sites without Post-Closure Rebound , 6.22
A.I Boundary Conditions for Governing Partial
Differential Equations A.23
A.2 Definition of Boundary Conditions A.24
C.I Selected Compounds and Their Chemical Properties C.4
C.2 Physicochemical Properties of PCE and
Associated Compounds C.5
XIX
-------
List of Tables
Table Tjtifi Page
C.3 Physicochemical Properties of TCA and
Associated Compounds C.6
C.4 Physical Properties of Fuel Components C.7
C.5 Selected Specification Properties of Aviation Gas
Turbine Fuels C.9
C.6 Detectable Hydrocarbons Found in U.S. Finished
Gasolines at a Concentration of 1 % or More C.10
C.7 Major Component Streams of European Automotive
Diesel Oil (Diesel Fuel No. 2) and Distillate Marine
Diesel Fuel (Diesel Fuel No. 4) C.ll
C.8 Henry's Law Constants for Selected Organic Compounds C.12
C.9 Chemical and Physical Properties of TPEf Components C. 14
C.10 Dimensionless Henry's Law Constants for Typical
Organic Compounds C.21
C.ll Chemical Properties of Hydrocarbon Constituents C.22
C.12 Composition of a Regular Gasoline C.23
C. 13 Composition of a Weathered Gasoline C.25
xx
-------
LIST OF FIGURES
Figure Title Page
2.1 Vapor Extraction System 2.2
2.2 Simplified Air Sparging/Vapor Extraction Schematic 2.3
2.3 Dual-Phase Extraction Schematic 2.4
2.4 Comparison of LNAPL Remediation Using Conventional
Two-Pump System (Left) and Bioslurper System (Right) 2.5
2.5 Two-Dimensional Analysis of Air Sparging 2.12
2.6 Prediction of Air Saturation in a Cylindrical
Laboratory Reactor 2.13
2.7 Technology Screening Decision Tree for
Vapor Extraction (VE) and Bioventing (BV) 2.18
3.1 Simplified Field Pilot Test Schematic for Vapor
Extraction-Based Technologies 3.16
3.2 Presentation of (a) Extraction and (b) Injection Test Data 3.17
3.3 Schematic of Apparatus for Sampling Vapors Under
Vacuum Conditions 3.21
3.4 Presentation of Extracted Vapor Analyses from Pilot Test 3.23
3.5 Tri-Level Pressure Monitoring Point Installation 3.24
3.6 Presentation of Subsurface Pressure Monitoring Results from
Pilot Test — (a) Transient Results, (b) Steady-State Results 3.26
3.7 Relationship Between Increasing Temperature and Vapor
Pressure for Several Chemicals 3.43
3.8 Schematic of a Dual-Phase Extraction System 3.54
3.9 Dual-Phase Drop-Tube Entrainment Extraction Well 3.55
3.10 Downhole-Pump Extraction Well 3.57
3.11 Friction Loss Chart 3.64
xxi
-------
List of Figures
Figure
3.12
3.13
3.14
3.15
3.16
3.17
3.18
3.19
5.1
5.2
5.3
5.4
5.5
5.6
5.7
6.1
6.2
6.3
6.4
7.1
A.I
v;?
Title
Blower Schematics
Schematic of Catalytic Oxidation Unit
Flaring Process
Schematic of Vapor Vacuum Extraction Offgas
Treatment with a Biofilter
Vertical Vapor Extraction Well/Monitoring Point
Construction Details
Typical Horizontal Vent Well Design
Valve Schematics
Typical Manifold System
Change in Dissolved-Phase PCE During/After Sparging
Change in Dissolved-Phase VOCs During/After Sparging
Overview of Sparging Evaluation and Implementation
Conceptual Sparging System
UVB System Combined with Vapor Collection
Density-Driven Convection System with Vapor Extraction
A No VOCs™ System
Impact of Pulsing on Performance
TDR Response to Pulsed Injection
Rebound as a Function of Flow and Well Spacing
Rebound as a Function of Flow and Number of Wells
Case Studies — Sparging System Layouts
Variables Used in Governing Equations for Vapor
Page
3.68
3.83
3.84
3.86
3.101
3.111
3.119
3.120
5.5
5.6
5.10
5.16
5.46
5.47
5.48
6.26
6.27
6.30
6.30
7.12
Extraction Water Table or an Impervious Unit
A.22
xxii
-------
Chapter 1
INTRODUCTION
This monograph, covering the design, applications, and implementation
of vapor extraction, bioventing, and air sparging, is one of a series of seven
on innovative site and waste remediation technologies. The series was pre-
ceded by eight volumes published in 1994 and 1995 to provide the descrip-
tions, discuss evaluations, and delineate limitations of the several remedia-
tion technologies, including vapor extraction. This book complements the
first book on vapor extraction by adding specific details on design, construc-
tion, and operation of such systems. In addition, this book addresses en-
hancements to the vapor extraction technology, including dual-phase vapor
extraction, bioventing, and air sparging.
This series of design and application monographs is being published as
part of the WASTECH® Project, a multiorganization effort involving more
than 100 experts. The series provides the experienced, practicing profes-
sional with guidance on innovative processes considered ready for full-scale
application. Other monographs in this design and application series and the
companion series address bioremediation; chemical treatment; liquid extrac-
tion; soil washing, soil flushing, and solvent/chemical extraction; stabiliza-
tion/solidification; thermal desorption; and thermal destruction.
7.7 Vapor Extraction and Air Sparging
1.1.1 Vapor Extraction
Vapor extraction, also known as soil vapor extraction, soil venting, and in
situ venting, involves the removal of contaminant-laden vapors from unsatur-
ated soil. A vacuum is applied by a pump or blower through a number of
extraction vent wells, vertical or horizontal, inducing gas flow through the
1.1
-------
Introduction
soil toward the vents. Certain chemicals volatilize into the clean air drawn
from the ground surface, passive vents, or air injection wells. The removed
vapors may require treatment before the air is discharged to the atmosphere.
The typical components of a vapor extraction system, such as shown in Fig-
ure 2.1, include vent wells, manifold piping, control valves to adjust flow,
vacuum blowers and controls, pressure gauges and flow meters, an air/water
separator, and a vapor treatment unit (Johnson et al. 1994). One of the major
advantages of vapor extraction is that most of the components are relatively
inexpensive and readily available.
:,,',' I ,i •'! i ,,;"
1.1.2 Air Sparging
The removal of volatile chemicals from the subsurface can be enhanced
by a number of ways including air sparging, air heating, and other air pre-
treatments. Air sparging involves the injection of air beneath the groundwa-
ter table. Air channels form as the air rises to the surface, and volatile
chemicals are removed from the contaminated groundwater. In addition, the
introduction of air into the subsurface in processes, such as bioventing and
biosparging greatly increases the oxygen concentration, thereby enhancing
biological degradation.
1.2 Development of the Monograph
1.2.1 Background
Acting upon its commitment to develop innovative treatment technologies
for the remediation of hazardous waste sites and contaminated soils and
groundwater, the U.S. Environmental Protection Agency (US EPA) estab-
lished the Technology Innovation Office (TIO) in the Office of Solid Waste
and Emergency Response in March, 1990. The mission assigned TIO was to
foster greater use of innovative technologies.
In October of that same year, TIO, in conjunction with the National
Advisory Council on Environmental Policy and Technology (NACEPT),
convened a workshop for representatives of consulting engineering
1.2
-------
Chapter 1
firms, professional societies, research organizations, and state agencies
involved in remediation. The workshop focused on defining the barriers
that were impeding the application of innovative technologies in site
remediation projects. One of the major impediments identified was the
lack of reliable data on the performance, design parameters, and costs of
innovative processes.
The need for reliable information led TIO to approach the American
Academy of Environmental Engineers®. The Academy is a long-standing,
multi-disciplinary environmental engineering professional society with
wide-ranging affiliations with the remediation and waste treatment profes-
sional communities. By June 1991, an agreement in principle (later formal-
ized as a Cooperative Agreement) was reached, providing for the Academy
to manage a project to develop monographs providing reliable data that
would be broadly recognized and accepted by the professional community,
thereby eliminating or at least minimizing this impediment to the use of
innovative technologies.
The Academy's strategy for achieving the goal was founded on a multi-
organization effort, WASTECH® (pronounced Waste Tech), which joined in
partnership the Air and Waste Management Association, the American Insti-
tute of Chemical Engineers, the American Society of Civil Engineers, the
American Society of Mechanical Engineers, the Hazardous Waste Action
Coalition, the Society for Industrial Microbiology, the Soil Science Society
of America, and the Water Environment Federation, together with the Acad-
emy, US EPA, DoD, and DOE. A Steering Committee composed of highly-
respected representatives of these organizations having expertise in
remediation technology formulated the specific project objectives and pro-
cess for developing the monographs (see page iv for a listing of Steering
Committee members).
By the end of 1991, the Steering Committee had organized the Project.
Preparation of the initial monographs began in earnest in January, 1992, and
the original eight monographs were published during the period of Novem-
ber, 1993, through April, 1995. In Spring of 1995, based upon the reception
by the industry and others to the original monographs, it was determined that
a companion set, emphasizing design and application of the technologies,
should be prepared as well. Task Groups were identified during the latter
months of 1995 and work commenced on this second series.
1.3
-------
Introduction
1.2.2 Process
For each of the series, the Steering Committee selected the technologies,
or technological areas, to be covered by each monograph, the monographs'
general scope, and the process for their development. The Steering Commit-
tee then appointed a task group composed of experts to write a manuscript
for each monograph. The task groups were appointed with a view to balanc-
ing the interests of the groups principally concerned with the application of
innovative site and waste remediation technologies — industry, consulting
engineers, research, academia, and government.
The Steering Committee called upon the task groups to examine and
analyze all pertinent information available within the Project's financial
and time constraints. This included, but was not limited to, the compre-
hensive data on remediation technologies compiled by US EPA, the
store of information possessed by the task groups' members, that of
other experts willing to voluntarily contribute their knowledge, and in-
formation supplied by process vendors.
To develop broad, consensus-based monographs, the Steering Committee
prescribed a twofold peer review of the first drafts. One review was con-
ducted by the Steering Committee itself, employing panels consisting of
members of the Committee supplemented by other experts (See Reviewers,
page iii, for the panel that reviewed this monograph). Simultaneous with the
Steering Committee's review, each of the professional and technical organi-
zations represented in the Project reviewed those monographs addressing
technologies in which it has substantial interest and competence.
Comments resulting from both reviews were considered by the task
group, appropriate adjustments were made, and a second draft published.
The second draft was accepted by the Steering Committee and participating
organizations. The statements of the organizations that formally reviewed
this monograph are presented under Reviewing Organizations on page v.
1.4
-------
Chapter 1
7.3 Purpose
The purpose of this monograph is to further the use of innovaitive vapor
extraction and air sparging site remediation technologies, that is, technolo-
gies not commonly applied; where their use can provide better, more cost-
effective performance than conventional methods. To this end, the mono-
graph documents the current state of vapor extraction, bioventing, and air
sparging practice.
7.4 Objectives
The monograph's principal objective is to furnish guidance for experienced,
practicing professionals and users' project managers. This monograph, and its
companion monograph (Johnson et al. 1994), are intended, therefore, not to be
prescriptive, but supportive. It is intended to aid experienced professionals in
applying their judgment in deciding whether and how to apply the technologies
addressed under the particular circumstances confronted.
In addition, the monograph is intended to inform regulatory agency per-
sonnel and the public about the conditions under which the processes are
potentially applicable.
7.5 Scope
The monograph addresses innovative vapor extraction, air sparging, and
bioventing technologies that have been sufficiently developed so that they
can be used in full-scale applications. It addresses all aspects of the tech-
nologies for which sufficient data were available to the task group to review
the technologies and discuss their design and applications. Actual case stud-
ies were reviewed and included, as appropriate.
The monograph's primary focus is site remediation. To the extent the
information provided can also be applied elsewhere, it will provide the pro-
fession and users this additional benefit.
1.5
-------
Introduction
Application of site remediation and waste treatment technology is site-
specific and involves consideration of a number of matters besides alterna-
tive technologies. Among them are the following that are addressed only to
the extent that they are essential to understand the applications and limita-
tions of the technologies described:
• site investigations and assessments;
• planning, management, and procurement;
• regulatory requirements; and
• community acceptance of the technology.
1.6 Limitations
The information presented in this monograph has been prepared in accor-
dance with generally recognized engineering principles and practices and is
for general information only. This information should not be used without
first securing competent advice with respect to its suitability for any general
or specific application.
Readers are cautioned that the information presented is that which was
generally available during the period when the monograph was prepared.
Development of innovative site remediation and waste treatment technolo-
gies is ongoing. Accordingly, post-publication information may amplify,
alter, or render obsolete the information about the processes addressed.
This monograph is not intended to be and should not be construed as a
standard of any of the organizations associated with the WASTECH® Project;
nor does reference in this publication to any specific method, product, pro-
cess, or service constitute or imply an endorsement, recommendation, or
warranty thereof.
1.6
-------
Chapter 1
7.7 Organization
This monograph is organized under a uniform outline and addresses the
design and application of two primary innovative treatment technologies —
vapor extraction and air sparging.
Chapter 2, Application Concepts summarizes the scientific principles and
potential applications of vapor extraction and air sparging. Design Develop-
ment for Vapor Extraction, Chapter 3, provides essential information for
those contemplating use of vapor extraction and Chapter 4 discusses its
implementation and operation. Chapter 5 discusses the development of de-
sign and its application for air sparging. The implementation and operation
of air sparging systems is discussed in Chapter 6. A series of Case Histories
are provided in Chapter 7 for each technology. The Appendices provides
details regarding applicable models, safety practices, relevant properties of
organic pollutants, and references.
1.7
-------
-------
Chapter 2
APPLICATION CONCEPTS
Vapor extraction, also known as soil vapor extraction, soil venting, and in
situ venting, involves the removal of contaminant-laden vapors from unsatur-
ated soil. A vacuum is applied by a pump or blower through a number of
extraction vent wells, vertical or horizontal, inducing gas flow through the
soil toward the vents. Certain chemicals volatilize into the clean air drawn
from the ground surface, passive vents, or air injection wells. The removed
vapors may require treatment before the air is discharged to the atmosphere.
The typical components of a vapor extraction system, such as shown in Fig-
ure 2.1, include vent wells, manifold piping, control valves to adjust flow,
vacuum blowers and controls, pressure gauges and flow meters, an air/water
separator, and a vapor treatment unit (Jphnson et al. 1994). One of the major
advantages of vapor extraction is that most of the components are relatively
inexpensive and readily available.
The removal of volatile chemicals from the subsurface cart be enhanced
by a number of ways including air sparging, air heating, and other air pre-
treatments. Air sparging involves the injection of air beneath the groundwa-
ter table. Air channels form as the air rises to the surface, and volatile
chemicals are removed from the contaminated groundwater. In addition, the
introduction of air into the subsurface in processes, such as bioventing and
biosparging greatly increases the oxygen concentration, thereby enhancing
biological degradation.
In bioventing, the air flow rate is usually reduced to decrease the fraction
of chemical removed by volatization and increase the amount biodegraded,
thereby reducing the volume of air requiring posttreatment. The same can
be said for biosparging.
Figure 2.2 illustrates a simplified air sparging/vapor extraction system. In
this system, an additional blower/compressor is added to inject air under
pressure below the groundwater table. Continuous air channels are formed
as the air rises to the surface (Ji et al. 1993; Johnson et al. 1993). The
2.1
-------
Application Concepts
channels branch to form more channels as the pressure decreases and the air
volume increases. The upward movement of air in the vicinity of the injec-
tion well induces some water movement that brings the contaminated
groundwater in closer contact with the air channels, thereby increasing the
rate at which the contaminants are removed from the water.
Figure 2.1
Vapor Extraction System
Bioventing
Air Injection Well
Ambient Air Blower
Vapor Extraction
Air/Water
Separator
Vapor
Treatment
2.2
-------
Chapter 2
Figure 2.2
Simplified Air Sparging/Vapor Extraction Schematic
Vapor
Treatment Unit
Blower/Compresser
i
Pressure Gauge
Source: Johnson etal. 1994
A variation of air sparging/vapor extraction, dual-phase extraction, in-
volves the dual extraction of air and water in an attempt to enlarge the unsat-
urated zone, thus exposing more soil to the vapor extraction process. Extrac-
tion of vapors and groundwater at the same time can be used as a means of
controlling groundwater mounding, dewatering soil to enhance vapor extrac-
tion or bioventing, and removing nonaqueous-phase liquids (NAPLs), if
present. To accomplish this, a separate groundwater pumping well can be
installed in the vicinity of the vapor extraction vent as shown in Figure 2.3.
In another variation, the liquids pump can be installed in the same casing
used for vapor extraction.
2.3
-------
Application Concepts
.o
"5
o
o
3|
O
O
D.
"o
Q
!
2.4
-------
Chapter 2
Figure 2.4 contrasts a conventional light nonaqueous-phase liquid
(LNAPL) recovery using a two-pump system with a bioslurper system. In
the conventional system, one pump produces a cone of groundwater depres-
sion while the other removes the LNAPL that flows toward the well. The
Figure 2.4
Comparison of LNAPL Remediation Using Conventional
Two-Pump System (Left) and Bioslurper System (Right)
Conventional
Bioslnrper
Air Treatment
or Discharge
Water Treatment/Discharge •*
Oil/Water Separator
Oil Smear Zone in Cone of Depression
How Due to
Pressure-Induced
Gradient
Flow Due to
Pressure-Induced
Gradient
Groundwater Depression Pump
Groundwater
Source: US ACE 1995
2.5
-------
Application Concepts
bioslurping system uses a suction tube placed at the NAPL/water inter-
face, producing a pressure (vacuum) gradient causing water, LNAPL,
and air to move to the tube without causing a cone of depression and a
resulting NAPL smear zone. When slurping is conducted to enhance
both free product recovery and biological degradation, the process is
called bioslurping (Kittel et al. 1994).
2.1 Scientific Principles
The rate of pollutant removal is affected by a number of mechanisms
including air flow rates and patterns, mass transport mechanisms, and chemi-
cal and biological degradation (Unger, Sudicky, and Forsyth 1995; Clayton
et al. 1996). In addition, partitioning dictates the state of chemicals during
the vapor extraction/air sparging process.
2.1.1 Chemical Equilibrium
The extent of partitioning of chemicals among the gas, liquid, solid, and
NAPL plays a significant role in performance of vapor extraction/air
sparging systems. One of the goals of evaluating system performance is to
predict the vapor concentrations of volatile compounds in the subsurface.
The following discussion assumes a homogeneous, isotropic aquifer matrix.
In general, the total volumetric concentration T^ (g-j/cm3-soil) of component
j is distributed in the subsurface among gas, water, soil, and NAPL as de-
scribed by the mass balance:
TJ = eacaj+ewcwj+p^+encnj (2.1)
where: 6a = air-filled porosity (cm3/cm3-soil);
9 = volumetric fraction of water (cm3/cm3-soil);
W
6 = volumetric content of NAPL (cm3/cm3-soil); and
p°b = bulk density of the soil (g/cm3 of soil).
The mass concentrations of j in air, water, and NAPL are Caj (g/cm3), Cwj,
and C ., respectively, and S. is the mass of j sorbed to the soil solids (g/g-
soil)(Johnson et al. 1994).
2.6
-------
Chapter 2
Raoult's Law is assumed to describe the relationship between the equilib-
rium concentrations in air and NAPL as follows:
C^X/T (2.2)
where: X. = the mole fraction of j in the NAPL; and
Csataj = the saturated vapor concentration of j (g of j/cm3-vapor)
and is defined as:
(2.3)
where: MW. = the molecular weight of j (g of j/mole);
Pvj = the vapor pressure of j at temperature T (arm);
R = the gas constant (82 cm3-atm/mole-(K); and
T = the absolute temperature (K).
The partitioning of j between NAPL and water can be described in a man-
ner similar to Equation 2.2:
C*-XjCj. (2.4)
where: Csatw. = the solubility of j in water (g of j/cm3-water).
The equilibrium between a chemical in the air and water phases is defined
by Henry's Law:
Crf-H^ (2.5)
where: H. = the Henry's Law partition coefficient for j.
To maintain consistency with Equations 2.2, 2.3, and 2.5, H. is defined as:
••H^cy/C* (2.6)
Equation 2.5 applies to areas of the unsaturated zone where NAPL is not
present.
The partitioning of chemicals to soil solids is described by sorption iso-
therms where the sorbed concentration is a function of the water-phase con-
centration:
) (2.7)
2.7
-------
Application Concepts
There are a number of relationships (Langmuir, Freundlich, and BET)
that provide a mathematical relationship between the mass sorbed and the
aqueous concentration. However, the most commonly used relationship for
soil is the partitioning equation:
S = KdCwj (2.8)
where: Kd = the partition or distribution coefficient.
By observation, Equation 2.8 is similar to Equation 2.5. Because sorption is
often considered to be partitioning of chemicals into the organic fraction of soil,
Kd is normalized by the fraction of organic carbon in the soil as follows:
Koc=Kd/foc (2.9)
where: K^, = the partition coefficient into organic carbon and f^, is the
fraction of soil that is organic carbon.
The utility of KM is that there are several correlations that relate K^ to
chemical properties, such as the octanol/water partition coefficient, Kow, or
the water solubility, Csatwj :
logKoc=alogKow+b or logKM ==clogC^ + d (2.10)
where: a, b, c, and d are empirical constants.
Fetter (1993) and Spitz and Moreno (1996) summarize the most com-
monly used correlations for K^,. The limitations of these correlations are
that they are generally developed for a specific class of chemicals and they
give a wide variation in the value for K^,, often as high as an order of magni-
tude. On the other hand, due to the general decrease in soil organic matter
with increasing depth, the relative importance of sorption decreases deeper
in the soil profile.
2.1.2 Air Flow Principles
Successful operation of in situ aeration systems requires that air flow be
established throughout the zone of contamination. The goal is to contact as
much of the zone of contamination as possible with air flow because such sys-
tems rely primarily on volatilization and subsequent advection of chemicals
2.8
-------
Chapter 2
from the soil and not on the slower process of diffusion to transfer chemicals to
the air stream. The air sparging enhancement requires injection of air below the
water table and establishment of air flow in the saturated zone. Again, the injec-
tion points should be placed close enough to one another to maximize contact
between the contamination and the moving air.
2. 1 .2. 1 Air Flow in the Unsaturated Zone
Equations describing air flow in unsaturated soil begin with a mathemati-
cal expression of mass conservation:
3>(P.q.> = 0 (2.11)
where: pa = the density of the vapor phase (g/cm3); and
qa = the specific discharge of the air (darcy velocity).
The first term in Equation 2.1 1 accounts for the accumulation of air in a
given volume of soil; the second term describes the mass flow rate of air
through it. The qa vector is related to the fluid potential <& (cm2/s2) through
the following form of Darcy's Law:
.(2.12)
where: jo, = the vapor-phase viscosity (g/cm-s); and
ka = air permeability (cm2).
For gases, is given by:
where: z = the elevation (cm);
g = the acceleration of gravity (981 cm/s2);
P = the gas-phase pressure (g/cm-s2); and
Po = a reference gas-phase pressure (g/cm-s2).
The relationship between the vapor-phase density and pressure is given by
the ideal gas law:
pa=MWaP/(RT) (2.14)
where: MW = the average molecular weight of the vapor phase.
2.9
-------
Application Concepts
By assuming that gz is negligible and that MWa is constant, Darcy's Law
simplifies to:
qa=-(ka/tO-VP (2.15)
This relationship demonstrates that air flow is clearly a function of pressure
gradient. The governing equation can be simplified to:
(20au.)3P / 3t = V • k • VP2 (2.16)
Appendix A presents a number of analytical solutions for linear and radial
flow for one- and two-dimensional scenarios. These are useful for prelimi-
nary calculations to estimate air flow as a function of soil permeability, ap-
plied vacuums, and radii of flow. Most problems, however, are three dimen-
sional. In this case, it is necessary to use numerical solutions for the govern-
ing flow Equation 2.16. Massmann (1989) determined that for extraction
vacuums less than about 0.2 atmospheres, air flow behaves as an incom-
pressible fluid and that conventional water flow models such as MODFLOW
can be used to simulate air flow. Hauge (1991) was able to simulate field
pressure and flow measurements by using a finite-element code developed
for groundwater flow by (1) using gas conductivity for hydraulic conductiv-
ity, (2) specifying the ground surface and a vertical boundary at an estimated
radius of influence, and (3) converting the output pressures interpreted as
head in units of air to conventional units of pressure. More recently, a num-
ber of numerical models specifically developed for soil vapor extraction have
become available. Section 3.2.3 describes several such models.
2.1.2.2 Air Flow in the Saturated Zone
When air is injected below the groundwater table during air sparging, the
injection pressure must be high enough to overcome the hydraulic head, the
soil air entry pressure, and the piping system pressure losses. In general, the
system pressure losses and the air entry pressure are negligible compared the
pressure required to overcome the hydraulic head above the injection point.
The minimum pressure required from the blower is given by:
Pbl=9800h (2.17)
where: Pb, = the blower pressure (N/m2); and
h = the depth in meters from the top of the injection well
screen to the groundwater table.
2.10
-------
Chapter 2
Air bubbles in most soils collapse on one another to form air channels.
The air channel diameters are of the scale of several grain sizes (Johnson et
al. 1993). As the air rises, the pressure decreases causing the air volume to
increase, and additional air channels form (Ji et al. 1993). Figure 2.5 shows
the branching of the air channels in a two-dimensional reactor and the effect
of soil layering on the zone of air influence.
Hein et al. (1997) used a numerical model to simulate air fluxes and water
saturation in the vicinity of air injection wells. Figure 2.6 depicts the air
saturation around a typical air injection well. The figure shows that the zone
of air flow is parabolic in shape, similar to that shown in Figure 2.5.
The mass flow rate of air leaving an injection well is constant for a given
blower, manifold, and valve arrangement and is given by:
G = paAacv (2-18)
where: G = the mass flow rate of air (g/s);
pa = the density of air (g/cm3);
A = the total area of the air channels (cm2); and
3C
v = the air velocity (cm/s).
Assuming that the velocity in the air channels is constant, Equation 2.18
can be rearranged to give air channel area as a function of air density:
Aac=G/(Pav) (2.19)
Since pa decreases with decreasing pressure (Equation 2.14), the total air
channel area must increase, which, in turn, means that the total number of air
channels must increase as the air approaches the groundwater table as is
shown in Figure 2.5.
As air rises, it induces water flow currents within the saturated zone, es-
pecially in course-grained soils. This has the effect of minimizing the dis-
tance that chemicals have to diffuse to move from the water to the air,
thereby decreasing the time to remove volatile chemicals from the water.
2.1.3 Mass Transfer Principles
Important mass transfer mechanisms for air sparging/vapor extraction are
advection with the air flow, dispersion/gas diffusion within the gas flow,
volatilization (which is generally fast relative to other mechanisms), and
2.11
-------
Application Concepts
a>
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2.12
-------
Chapter 2
Figure 2.6
Prediction of Air Saturation in a Cylindrical Laboratory Reactor
o.oo -
0.00 Q.20 0.40
Distance from Sparge Well (m)
I T
0.00 0.20 0.40- 0.60 0.80
Air Saturation
0.60
1.00
Source: Hein 1996
2.13
-------
Application Concepts
liquid diffusion out of the water. The mass flux due to molecular diffusion is
given by Pick's first law of diffusion:
(2.20)
where: F = the mass flux (g/cm2-s);
Dm = the molecular diffusion coefficient (crnVs); and
dC/dx. = the chemical concentration gradient.
If diffusion is one-dimensional, then Pick's second law of diffusion,
which is a mass balance, becomes:
(2.21)
Crank (1975) has compiled solutions to Equation 2.21 for numerous
boundary and initial conditions. For example, assuming that a chemical
diffuses into or out of a single layer of soil of infinite thickness, the concen-
tration at a given point and time is given by:
C(x,t) = C0erfc(x / (2(Dmt)"2)) (2.22)
where: Co = the initial concentration at the layer boundary; and
erfc = the complimentary error function.
The implication of Equation 2.22 is that diffusion through water, even a few
centimeters, is a relatively slow process. Thus, the removal of chemicals
from the subsurface is often diffusion-limited.
The general chemical transport equation for volatile organic chemicals in
a mobile fluid is given by:
aC/at + a-nXps/n)aS/at = -A(vC) + DA2C-^C-ZQcin (2.23)
where: n = the soil porosity;
ps = the density of soil solid (g/cm3);
A, = a decay constant (1/s); and
SOc. - = the sum of other source/sink terms such as the transfer
^- in
from one phase to another (Spitz and Moreno 1996).
The terms on the left side of Equation 2.23 represent the change over time in
mass of the chemical that is in the mobile fluid (water or air) and that is
sorbed on soil. The terms on the right side of Equation 2.23 represent the
2.14
-------
Chapter 2
rates of mass: (1) transferred by fluid flow, (2) transferred by diffusion and
dispersion, (3) loss to decay, and (4) in or out of the fluid to other sources or
sinks. Equation 2.23 can be applied to either water or air flow and generally
forms the basis for the development of numerical models for chemical trans-
port in general, and, more specifically, for vapor extraction/air sparging.
2.1.4 Chemical Destruction Principles
While abiotic processes, such as hydrolysis, dehalogenation, and chemical
oxidation may be responsible for the decay of volatile organic chemicals, bio-
logical degradation is the primary mechanism for the in situ destruction of
organic chemicals during vapor extraction/air sparging. The oxygen require-
ment can be approximated by stoichiometry. For example, complete, aerobic,
aliphatic hydrocarbon destruction is given by the following equation:
2CnH2n+2 + (3n + 1)O2 -> 2nCO2 + (2n + 2)H2O (2.24)
From this, the oxygen requirement is (24n + 8)/(7n +1) g-O2/g-hydrocarbon.
For octane (n = 8), the O2 required is 3.5 g/g-octane.
For aromatic hydrocarbons such as benzene, aerobic destruction is given by:
C6H6 + 7.5O2 -» 6CO2 + 3H2O (2.25)
The oxygen requirement is 3.1 g-O2/g-benzene. Since the mass fraction of
oxygen in air is 0.231 g-O2/g-air, there should be no trouble providing
enough oxygen to degrade hydrocarbons if air is supplied to the subsurface.
Biodegradation kinetics can be expressed mathematically as a hyperbolic
function, as given by the Michaelis-Menten equation:
R = _VC/(K + C) (2.26)
where: R = the reaction rate (1/s);
V = the maximum biodegradation rate (1/s); and
K = the half-saturation constant (mol/L).
The half-saturation constant is the contaminant concentration at which the
biodegradation rate is half that of the maximum biodegradation value (US
ACE 1995). C is the concentration of the chemical that limits the rate of
biodegradation. While this chemical is usually assumed to be the contami-
nant of interest, it also could be nitrogen or phosphorus. Although atypical,
2.15
-------
Application Concepts
nitrogen and/or phosphorus may need to be injected to achieve maximum
degradation rates.
From Equation 2.26, it can be seen that at high concentrations (C » K),
the reaction rate is independent of concentration:
R = -V (2-27)
At low concentrations (C « K), the reaction rate approaches a first-order rate:
R = -FV (2-28)
where the first-order rate constant F is approximated by V/K.
2.2 Potential Applications
Application of vapor extraction, air sparging, and associated variations
should be considered as a part of an overall site remediation strategy. For
example, it may be cost-effective to contain a contaminant plume using flow
barriers or pumping strategies. If free product exists as LNAPL, a free prod-
uct recovery system may be installed and operated before implementing
vapor extraction. Groundwater pumping may be used to lower the water
table, thereby increasing the volume of unsaturated soil to be treated by
vapor extraction. If emission rates are low, there are no receptors in the
area, and biological activity is the primary destruction mechanism or if there
is significant biodegradation in the vadose zone, vapor extraction may not be
needed as part of an air sparging system.
2.2.1 Vapor Extraction
Vapor extraction is now a well-established technology for the removal of
volatile organic chemicals from unsaturated soil (Hutzler, Murphy, and
Gierke 1990; Johnson et al. 1994). (Semivolatile compounds may be treated
by bioventing.) The technique works well in sandy soils with high
permeabilities, for chemicals with vapor pressures greater than 5 mm Hg,
and where site conditions are well defined. Conversely, vapor extraction is
usually not recommended for massive clays unless mechanical mixing is
used (Siegrist, West, and Gierke 1995). Sites with complicated geology and
2.16
-------
Chapter 2
underground structures and where the location of contamination is uncertain
require much more characterization and pilot testing. Figure 2.7 is a flow-
chart for evaluating the suitability of vapor extraction and bioventing. Most
of the steps listed in Figure 2.7 are discussed in this monograph.
2.2.2 Air Sparging
Air sparging is a newer technology. However, a growing body of litera-
ture indicates a broad applicability of the technique. Table 2.1 cites a num-
ber of cases where air sparging has been used to successfully remediate
groundwater. Soil types range from silty sand to sands and gravels. Cleanup
is usually completed within 24 months.
Most of the tests summarized in Table 2.1 were completed in relatively
shallow aquifers with a maximum injection depth of 30 ft. The range of
injection pressure for sparging ranged from approximately 2 to 60 psi, and
the flow rates ranged from 1 to 50 scfm. None of these tests exceeded 2
years. These site applications indicate that air sparging can accomplish
groundwater cleanup much more quickly than conventional pump-and-treat
operations. Because there is little site disturbance, the equipment can be
easily removed, and the site can be returned to its original appearance (Hein
1996). Sparging has been most successful with light hydrocarbons and chlo-
rinated solvents.
2.2.2 Range of Applicability of Vapor Extraction/Air Sparging
Technology
Vapor extraction, bioventing, and air sparging, along with their modifica-
tions, have been applied to a wide range of sites. At any given site, a number
of physical, chemical, and biological conditions, such as geologic structure
and soil properties (particle-size distribution, porosity, and moisture con-
tent), chemical properties, and biodegradability, have a significant impact on
the success of these technologies. Thus, the importance of site characteriza-
tion cannot be overemphasized.
Soil borings and geophysical techniques provide information on the na-
ture of soil horizons, moisture content, and texture. Subsurface features,
such as sandy or gravelly layers, promote preferential flow paths, while
finer-textured soils containing contamination indicate a system where con-
taminant removal will be limited by chemical diffusion. In industrial and
2.17
-------
Application Concepts
Figure 2.7
Technology Screening Decision Tree for
Vapor Extraction (VE) and Bioventing (BV)
Start
Relevant Information
Media Porosity
Air Permeability
High
Very Low
(<10-'°cm2)
Contaminant
Volatility
Low
(vapor pressure
<0.5 mm Hg at 20°)
Biodegradability
Low
High
Consider Possible
VE Phase Before BV
High
Biodegradability
Bioventing
Low
Evaluate Relative to a Variety of Site-Specific Factors,
Considering Experience at Other Sites
OK
Bench- and Pilot-Scale Testing
Not OK
Air permeability
Moisture content
Quit unless inclusion of porous
medium fracturing or water table
drawdown is warranted; also
may want to consider BV or VE
in aboveground piles
Vapor pressure
Henry's Law constant
Boiling point
Solubility
Biodegradation half-life
and other data
Initial and required contaminant
concentrations
Stratigraphy and heterogeneity
Depth to groundwater
Presence of NAPL
Moisture content/retention
Temperature
Organic carbon content
Bioventing only:
Toxic inhibitors
Nutrient concentrations
O2 and CO2 concentrations
Source: US ACE 1995
2.18
-------
Chapter 2
urban locations, the contrast between native soil and disturbed soil or fill
should be discerned. Vapor extraction, bioventing, and air sparging have
been applied over a wide range of soil permeabilities; the major difference is
the extraction/injection pressures and the time taken to complete
remediation. Soils with an intrinsic permeability less than 10'10 cm2 are not
likely candidates for vapor extraction/air sparging.
Chemicals most amenable to vapor extraction are volatile (vapor pressure
greater than about 5 mm Hg), have low Henry's Law constants, and include
gasoline, kerosene, diesel fuel constituents, and solvents, such as
tetrachloroethene, trichloroethene, and methylene chloride. Chemicals that
tend to be highly biodegradable include compounds with low Henry's Law
constants, such as gasoline, jet fuel, toluene, benzene, acetone, ketones, and
phenols. Fuel and lubricating oils, creosotes., and long-chain aliphatics are
moderately degradable, while chlorinated solvents and pesticides are diffi-
cult to degrade (Clayton et al. 1996).
2.2.3 Limitations of Technology
Vapor extraction, bioventing, and air sparging are usually not considered
for sites that do not meet the conditions outlined in Section 2,2.2. Nonethe-
less, research continues to extend the utility of this technology by use of
techniques, such as soil fracturing, soil mixing, and soil heating. Additional
limitations include the uncertainty in predicting time to cleanup or closure
since few predictive tools are presently available. Bench- and pilot-scale
testing as outlined in this monograph are still required to optimize design of
this technology. Several examples are given throughout this book on the
limitations of each approach. A more detailed coverage of the physical,
chemical, and biological factors that constrain the performance of these
technologies is beyond the scope of this monograph.
2.19
-------
Application Concepts
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2.20
-------
fo
Medium-grained sand — 25 ft deep, 3 ft Gasoline, Kerosine
of fine silty sand, 11 sparging wells inst.
approx. 28 ft below grade, pulsed oper.
Poorly-sorted medium sand, sparge well Syn. hydr. C5-C10
2.5 m below water table, laboratory test
(30 ft by 35 ft by 15 ft)
Paved region with 25 ft sand layer Gasoline
overlying a clay layer with a minimum
of 40 ft of sand below the clay,
unconfined water depth: 19 ft, confined
water depth: 40 ft, pilot test
Medium sand to a depth of 25 ft, fine Gasoline
silty sand to 28 ft, clay layer at 28 ft,
depth to water table is approx. 8 ft
14
Unknown
2.1,3.9,8.6,6.6,6.0
14
35
Approx. 1.5 m
17
35
25
2.1,4.0,
8.9,6.5,
6.1
30
decrease after Peterson, Alfonsi, and
3 months Livasy 1993
Johnson et al. 1992
70 min, 75 min, Brown, Payne, and
15 min, 100 min, Perlwitz 1993
135 min
3 months Peterson, Alfonsi, and
Livasy 1993
Hetero. porous media, 9 sparging wells
15 ft of clay and silty clay overlying 1-3
ft of more perm, clayey silts and silty
fine sands <
Acetone, TCE, 2, 3
DCE, DCA, PCE,
Petr. Hydro.
Gasoline 4.5
30 200 4 months Barrera 1993
(total)
15 8 33 Barrera 1993
"Unless specifically noied, the scale of application was field-scale.
o
ro
-------
-------
Chapter 3
DESIGN DEVELOPMENT
FOR VAPOR EXTRACTION
This chapter provides in-depth guidance for developing vapor extraction
and bioventing system designs. In general, the design process is comprised
of the following three steps:
1. Formulate Design Objectives, Design Constraints, and Clean-up
Concentrations and the Method(s) Used to Measure Them.
These parameters, plus a thorough understanding of site charac-
teristics, enable the engineer to complete a conceptual system
design. The importance and role of conceptual designs is dis-
cussed in Section 3.1.
2. Develop a Preliminary Design. Based on a quantitative evalua-
tion of the planned system that often includes pilot tests and air
flow modeling, the engineer develops a preliminary design. All
of the main system design parameters, such as well spacing and
configuration, flow rates, treatment equipment, and equipment
location are established. Most of the major decisions that will
determine the overall cost and eventual success of the design are
made during the preliminary design. Preliminary design is dis-
cussed in Section 3.2.
3. Complete the Final Design. For the final design, mechanical,
electrical, structural, and instrumentation and control plans and
specifications are developed to the extent required for construc-
tion. Details on the final design step are presented in Section 3.3.
3.1
-------
Design Development
3.7 Soil Remediation Goals
3.1.1 Selecting Design Objectives
The first step in the design process is to determine the overall design ob-
jectives and design constraints for the vapor extraction/bioventing system.
The design team needs to determine:
• if the contaminant mass removal mechanism is going to be pri-
marily physical removal (volatilization), biological degradation,
or some combination of both. This will determine if the system
is primarily a vapor extraction or biovenling system.
• if the vapor extraction/bioventing system is: (1) a soil clean-up
system, designed to achieve a targeted soil clean-up goal, or (2) a
long-term containment system. Most vapor extraction/bioventing
systems are for soil cleanup, but occasionally for sources that
cannot be removed (e.g., landfills) or that cannot cost-effectively
be removed, vapor extraction/bioventing may be used for long-
term vapor-phase contaminant control.
• the rate and duration of soil cleanup. For example, design objec-
tives may include extracting soil vapor so that offgas emissions
stay below concentrations requiring active treatment, injecting
only enough air into the soil to maintain aerobic conditions, or
maximizing the rate and minimizing the duration of vapor extrac-
tion/bioventing activities.
• site-specific constraints, such as buildings, roadways, under-
ground structures, and property limits that may affect where
wells are installed or influence well selection (i.e., vertical versus
horizontal wells).
• who is going to operate the system, the level of sophistication
required in the controls, and where the process equipment
will be housed.
• the integration of vapor extraction/bioventing equipment with
other groundwater clean-up equipment being used on the site.
Once these design objectives and constraints are determined and the target
zone is sufficiently delineated, the engineer can complete a conceptual
3.2
-------
Chapter 3
model of the vapor extraction/bioventing system. The conceptual model
shows the general placement of wells in relation to the zone or zones of
contamination and different soil types within the zone of contamination, an
initial screened interval of the wells, the use of vapor extraction and/or air
injection wells, the use of horizontal versus vertical wells, and the general
layout of the system within above- and belowground site constraints. A
proper conceptual understanding of what the system needs to accomplish
sets the framework for the more quantitative design evaluation. The engi-
neer, as discussed below, can then employ standard gas flow and contami-
nant partitioning equations to determine well spacing, flow rates, and mass
removal rates based on the site-specific contaminant concentrations and the
soil air permeability.
3.1.2 Establishing Soil Clean-up Criteria
Concurrent with establishing overall design objectives is the process of
identifying site-specific chemicals of concern and associated soil clean-up
criteria. The site-specific soil clean-up criteria are necessary to establish the
vertical and horizontal extent of the vapor extraction/bioventing target area.
Typically, the primary objective is to affect a percent removal of existing
contaminant concentrations that achieves risk-based clean-up criteria. This
target area is central to the overall design objectives regarding duration and
type of cleanup.
Increasingly, risk-based corrective action methods are being employed to
determine the level of site cleanup required. With such methods, the risk
posed by a site is determined from the location of potential receptors, the
possible exposure pathways, and the contaminant concentrations that may
reach the receptor. Exposure pathways can include direct contact with sur-
face or subsurface soil, windblown dust and vapor transport, subsurface soil
vapor transport, and dissolved-phase contaminant transport in groundwater.
Setting soil clean-up goals is complicated by the fact that geologic features
(soil type, relation of soil contamination to groundwater), receptor locations,
and chemical concentrations vary from site to site. In addition, the location
of points of compliance, exposure assumptions, and acceptable risk vary
from state to state. Regulatory programs also vary in relation to the applica-
tion of risk assessments. For example, for underground storage tank (UST)
related cleanups, there is a growing trend among many states to use the spe-
cific American Society for Testing and Materials (ASTM) standard for
3.3
-------
Design Development
risk-based corrective action (E-1739-95). Federal regulators have not
adopted the ASTM standard for programs such as CERCLA and RCRA, but
increasingly are considering the use of land restrictions to limit potential
receptors and to apply chemical fate and transport models to assess how
contaminants may migrate from a site.
The end result is that soil clean-up criteria can vary over several orders of
magnitude from site to site — there is no typical or universal soil clean-up
criteria. For example, soil clean-up concentrations for benzene in one state
range from 24 fJg/kg for sites where drinking water sources are being pro-
tected to 24 mg/kg for some types of commercial sites. Other petroleum
hydrocarbons and chlorinated solvents exhibit ranges from low part per bil-
lion concentrations for groundwater protection to the tens of parts per mil-
lion for direct contact on a commercial site.
While soil clean-up criteria are often established before the actual cleanup
is undertaken, at some sites the clean-up criteria are based on what is techni-
cally and, to a certain extent, economically feasible (referred to as technol-
ogy-based clean-up criteria). In such cases, rather than operating a system
until some specific concentration is met in the soil or offgas, a reasonably
designed system is operated until there is little additional mass removal.
Then it is shut down, and the cleanup is considered complete or other tech-
nologies/containment strategies are employed.
For additional information in determining site-specific clean-up concen-
trations, refer to:
• Standard Guide for Risk-Based Corrective Action Applied at
Petroleum Release Sites, ASTM E-1739-95;
• Interim-Final Risk Assessment Guidance for Superfund (Part A
and Supplemental Guidances) US EPA, December 1989; and
• State-specific clean-up guidance.
3.1.3 Measuring Soil Clean-up Criteria
Early in the design process, engineers need to account for how cleanup
will be assessed so that appropriate monitoring techniques can be imple-
mented with the design. This section discusses several methods that have
traditionally been used to assess the completeness of soil clean-up.
3.4
-------
Chapter 3
The easiest and least expensive method for tracking soil clean-up is to
monitor the contaminant concentrations in the offgas while the system is
operating. Offgas contaminant concentrations typically decline asymptoti-
cally, and when offgas concentrations reach a predetermined concentration
or rate of decline, the system can be shut off. However, there are several
drawbacks to this method. First, vapor-phase contaminant concentrations
may be diluted with vapor from clean soils and therefore are not representa-
tive of the target zone soil. Second, since most soil vapor flow comes from
soil near the vapor extraction wells, the offgas is not representative of all the
soil in the target zone. Third, the rate of contaminant desorption from the
soil is slow compared to the air flow through the soil. As a result, vapor-
phase contaminants are not in equilibrium with, and thus are not representa-
tive of, the adsorbed-phase contaminants. Fourth, changes in soil air perme-
ability will result in preferred air flow channels (either on a pore scale or
macro scale) and so the offgas contaminant concentrations are indicative of
only the more permeable soil zones.
An improvement to this method is to shut down the vapor extraction system
for a predetermined time period (days to weeks) and then restart the system. In
this case, the vapor-phase concentrations may be in equilibrium with, and there-
fore more representative of, the soil concentrations, but dilution of soil vapor
due to air permeability differences and other air dilution factors wilt still occur.
Still, this method of shutting down and subsequently restarting vapor extraction
systems is commonly used to assess system performance.
Another way to assess soil clean-up levels through vapor-phase analysis is
to collect vertically and horizontally discrete soil gas samples from the target
zone after the vapor extraction system has been shut off. The gas samples
are then analyzed for the site contaminants. This method is described in
detail in the first edition of the Innovative Site Remediation Technology:
Vacuum Vapor Extraction (Johnson et al. 1994). This method overcomes
some of the dilution and nonequilibrium limitations of the methods previ-
ously described. A similar technique can be used for assessing the progress
of bioventing systems. However, instead of collecting soil vapor samples for
analysis of vapor-phase contaminants, the change in oxygen content over
time is assessed through a respiration study. Such studies typically track the
oxygen demand of soils resulting from aerobic biodegradation over time.
Oxygen uptake rates may range from 1 to 20% per day. When no further
oxygen uptake is observed after shutdown of a bioventing system, the
3.5
-------
Design Development
biological activity in the soil is no longer oxygen limited and further active
bioventing may not be warranted.
Finally, soil cleanup can be assessed via collection and analysis of soil
samples — the most costly and time-consuming method. US EPA has provided
statistical methods of evaluating soil clean-up standards in its Methods for
Evaluating the Attainment of Cleanup Standards, Volume 1: Soil and Solid
Media (US EPA 1989). Such sampling involves careful planning regarding
acceptable levels of uncertainty in the decision process, development of a sam-
pling and analysis plan (random versus systematic sampling, simple versus
stratified sampling, sequential sampling), determining field sampling proce-
dures, and finally, statistical analysis. Often, project staff with backgrounds in
analytical chemistry and statistics are employed in setting up and executing
such sampling plans. The cost for such sampling even at a 1-acre site may be
tens of thousands of dollars. The advantage to this method is that soil sampling
provides the most rigorous documentation of soil cleanup achieved. A disad-
vantage of soil sampling is the assumption that the collected samples are repre-
sentative of the entire site, which may not always be true.
There is no universal method to measure the attainment of soil clean-up
criteria. The techniques discussed above should be considered a continuum
with the first ones being employed early in a project while the later ones are
employed only after more certainty exists that clean-up levels have been
achieved. Even then, the extent of soil sampling and the amount of statisti-
cal rigor will vary given the size of the site and the sensitivity of future re-
leases. Smaller UST releases may be closed with only a few soil samples,
while larger CERCLA and RCRA sites may require significant investment in
soil sampling and statistical interpretation.
3.1.4 Achievable Soil Clean-up Concentrations
Despite the thousands of vapor extraction projects completed in North
America, there are few published examples where a statistically significant
number of soil samples were collected in the treatment zone after
remediation to assess the final soil clean-up concentrations. In sites favor-
able for vapor extraction (uniform and coarse grain material), volatile or-
ganic compounds (VOCs) (contaminants with a Henry's constant greater
than 5 • 10'3 atm mVmole) can be treated to the part per billion range (and
often to the lower part of this range). For example, at one Superfund site
3.6
-------
Chapter 3
with a uniform sandy material, 106 samples were collected to document soil
cleanup over a less than 1-acre area. The results are shown in Table 3.1.
Table 3.1
Pre- and Posttreatment Soil Sample Analysis Results for a Superfund Site
Maximum Detected Maximum Detected
Pretreatment Soil Concentration Posttreatment Soil
VOC (Mg^g) Concentration (jig/kg)
Methylene Chloride
Acetone
1,1,1-Trichloroethane
Trichloroethene
Benzene
Tetrachloroethene
Xylene
Toluene
Ethylbenzene
4,390
1,166
500
2,470
17
23,600
35,000
19,000
7,420
2
180
4
47
1
54
4
73
4
Source: USEPA1995a
Sites with less favorable geology (clay soils, high moisture content, soil
heterogeneity) have more varied success in the VOC removals achieved. Part
of the variation is due to the intensity of soil treatment. Application of high
vacuums in conjunction with soil fracturing and hot air injection will yield
more mass removal than with low-to-moderate vacuum vapor extraction.
Many sites with unfavorable geologic conditions have still been remediated
with vapor extraction. The American Petroleum Institute has reported that
when vapor extraction was implemented in tight soils after controlled re-
leases of chlorinated solvents, less than 50% of the solvents were recovered.
Thus, there is no general guidance to achievable clean-up levels for either
less permeable soil or less volatile contaminants. Final contaminant
3.7
-------
Design Development
reduction can be as high as 90%, based on site characteristics and intensity
of treatment. Section 3.4 discusses process modifications that can be em-
ployed at difficult sites to improve the likelihood of success.
The U.S. Air Force has been studying the fate of benzene, toluene,
ethylbenzene, and xylenes (BTEX) and total petroleum hydrocarbons (TPH)
at more than 50 bioventing sites. The decreases in TPH concentrations at-
tributable to bioventing vary significantly. Even when very little actual
change in TPH is found, BTEX concentrations, which comprise only a por-
tion of the TPH measurement, typically are reduced to less than 1 mg/kg
after one year of bioventing.
3.2 Design Basis
The design for vapor extraction systems is usually based on the assump-
tion that air in the vadose zone moves under the influence of vapor extrac-
tion in a radially symmetric manner toward the extraction well. Although
symmetrical air flow rarely occurs in the subsurface, this assumption estab-
lishes a starting point for design. The fundamental design parameter is
therefore the radius of influence (ROI), which is determined from analysis of
pilot test data. The ROI is sometimes defined as the extent of measurable
vacuum hi the subsurface during vapor extraction. In more sophisticated
analyses where subsurface vacuum levels are evaluated in terms of the mag-
nitude of the induced air flow, the ROI can be defined as the distance from
the extraction well within which a target remediation can be achieved within
a desired time frame. In either case, the presumption is that air flows as a
continuous fluid throughout the entire unsaturated zone. Vapor extraction
system design should be based on providing adequate air flow to achieve
remediation goals over the entire treatment area, while providing sufficient
conservatism and flexibility to account for the deviations from perfect sym-
metry, which are inevitable in actual field conditions.
3.2.1 Site and Contaminant Characteristics
The success of vapor extraction is determined by the extent to which air
can be made to flow through contaminated soil and the response of the con-
taminant (i.e., volatilization and/or biodegradation) to air flow. However,
3.8
-------
Chapter 3
complete characterization of the contaminant distribution and the site param-
eters that determine air flow is rarely practical or cost-effective. A point of
diminishing returns occurs regarding the data needed for design and the cost
of data collection. Air flow during vapor extraction is likewise rarely uni-
form and follows preferential paths. Contaminants in high-permeability
paths are removed quickly, but remediation of lower permeability zones is
limited by diffusion. Despite these limitations, studies of site and contami-
nant characteristics can yield some general insights into the applicability and
potential effectiveness of vapor extraction, the nature of air flow through the
subsurface under vapor extraction conditions, and the initial offgas treatment
requirements. For a relatively small investment of time and resources in a
brief pilot test (often a half-day test is sufficient), a reasonable basis for va-
por extraction system design can be obtained. More elaborate testing may
be performed, depending on the scope of the envisioned full-scale system,
the regulatory requirements, and the complexity of the site. (Also, pilot tests
for high-vacuum and dual-phase extraction of low-permeability soils often
must be longer because the air permeability of the soil changes as moisture
is removed, and steady-state conditions may not be reached for weeks or
months.) The greater the investment in site soil and contaminant character-
ization, the greater the confidence with which the full-scale vapor extraction
system can be designed. However, regardless of level of site characteriza-
tion, vapor extraction system performance almost always deviates from ex-
pectations to some extent, and overdesigns, mid-course corrections, and
reassessment of remediation goals are common.
The site and soil parameters that are commonly measured and used as a basis
for design include background parameters, which are determined prior to any
pilot testing at the site and parameters that are assessed from observations dur-
ing or changes resulting from pilot testing. Background parameters include:
• Remedial Objectives. Clearly the first site parameter that should
be defined is the goal of the remediation. For example, designs
that employ vapor extraction to protect a building from vapors, to
evaporate a separate-phase hydrocarbon on the water table, or to
remediate adsorbed-phase contamination in unsaturated zone
soils would likely be very different from each other.
• Areal and Vertical Extent of Contamination. The better the ex-
tent of contamination is defined, the more efficient the vapor
extraction system will be at addressing the contamination.
3.9
-------
Design Development
Underestimating the extent will leave some area untreated, while
overestimating the extent will result in unnecessary expenditures
for equipment, operation, and offgas treatment. A soil gas survey
may help delineate the extent of the source zone, especially at
sites with relatively shallow groundwater. Samples from soil
borings should always be carefully monitored for organic vapors.
Soil Gas Analysis. Soil gas samples collected from water table
monitoring wells or vapor monitoring points prior to any
remediation activity can also provide information on the extent of
contamination. The analysis can be repeated during or after op-
eration of a pilot- or full-scale vapor extraction system to evalu-
ate the extent of impact of vapor extraction.
Activity at the Site. The requirements for remediation system instal-
lations at active and abandoned sites can vary substantially. For
example, vacuum lines must ordinarily be buried or carried over-
head at active sites, but can be placed at grade at abandoned sites.
Also, the degree of public access (for example, a retail site com-
pared with an industrial site) can dictate the ease of accessibility of
various system components in the vapor extraction design.
Accessibility. Constraints are often placed on vapor extraction
system designs by the presence of buildings in active use, storage
tanks, utilities and pipe trenches, pump islands, and property
boundaries. These constraints can affect the placement of vapor
extraction wells and their method of installation (e.g., angle
drilled, horizontal, etc.).
Nature of Ground Surface. A tight surface seal created by a con-
crete slab can dramatically affect air infiltration and hence the
design of multiple-well vapor extraction systems. In most cases,
asphalt does not create a tight surface seal. \
Stratigraphy. Low-permeability lenses increase the likeli-
hood that a significant portion of the remediation will be dif-
fusion-limited. Strata of substantial thickness must be ad-
dressed by separate remediation systems. Stratigraphy is
identified from soil borings and/or test pits. In addition, col-
umn tests on undisturbed samples can be used to estimate
how much contaminant can be removed from a small volume
of soil before diffusion limitations dominate.
3.10
-------
Chapter 3
• Soil Organic Carbon Fraction. This factor affects contaminant
partitioning. High levels of organic carbon, such as those typically
found in peat, can significantly compromise the effectiveness of
vapor extraction on contaminants that adsorb to organic matter.
• Depth to Groundwater and Thickness of Contaminated Vadose
Zone. The greater the thickness of the vented interval, the more
air flow is required. Seasonal water table variation must be taken
into account when selecting the screened interval for the extrac-
tion wells to ensure the wells are never fully submerged.
• Subsurface Vacuum. While this is one of the key parameters
during measured pilot test evaluations, it is essential to evaluate
the ambient subsurface vacuum levels as well to ensure that tid-
ally- and/or barometrically-induced fluctuations will not con-
found pilot test measurements.
The U.S. Army Corps of Engineers (US ACE) describes several additional
soil parameters that can be measured through laboratory analysis of soil
samples (US ACE 1995). Moisture content (measured in the field via neu-
tron probe or in the laboratory) and the soil moisture retention curve (from
an undisturbed soil sample) affect the relative air permeability (kr). Other
soil parameters sometimes measured include grain-size distribution, mois-
ture content, bulk density, and porosity. These parameters can enhance un-
derstanding of more complicated sites. However, the air permeability (ka), is
typically evaluated and used as a basis for design.
When use of bioremediatiqn is anticipated, soil nutrients (nitrogen and
phosphorous concentration and speciation and pH) are measured to ascertain
whether nutrient addition will be required. In addition, the soil bacteria
populations can be assessed in the laboratory to evaluate the viability of
bioventing, although this is commonly done through an in situ respirometry
test performed during pilot testing.
Parameters evaluated during pilot testing include:
• Air Permeability (ka). The single most important soil param-
eter is the flow achieved in response to an applied vacuum. It
determines how much air can be delivered to the subsurface
to effect remediation. Air flow response is typically mea-
sured directly in a field test and the air permeability is de-
rived from this measurement.
3.11
-------
Design Development
• Horizontal-to-Vertical Permeability Ratio (kh/k). This parameter
determines the distribution of air through the subsurface and the
infiltration of air from the ground surface. The ratio is based on
vacuum dissipation with depth and distance from the vapor ex-
traction well and the vadose zone thickness.
• Surface Permeability (k). Vapor extraction is often conducted
under an engineered surface seal, pavement, building, or natu-
rally-occurring low-permeability layer, any of which could have
a profound impact on surface air infiltration. Surface seals have
the greatest effect when vapor extraction Is applied to shallow,
porous soils (<5 ft). However, surface seals are not always as
tight as anticipated. Cracks in, and gravel bases for, pavement
and building foundations and vertical fractures in clays often
allow significant air infiltration. The effectiveness of a surface
seal can be assessed using the vacuum dissipation with distance
from the vapor extraction well and the vented interval thickness.
• Vapor Extraction Offgas Composition. The change in concentra-
tion of volatile contaminant vapors in the vapor extraction offgas
over the course of a pilot test lends insight into the location of the
vapor extraction well relative to the contaminant source and the
offgas technology required to treat the vapors. In extended pilot
tests, the rate of change in VOC concentrations can reflect on the
potential for mass removal before contaminant removal becomes
diffusion-controlled. Measurements of oxygen and carbon diox-
ide in vapor extraction offgas also reflect the extent of
bioremediation in the subsurface. Offgas analyses are typically
performed on-site with hand-held field screening instruments; it
is important to confirm these readings periodically with off-site
laboratory (TO-12/TO-14 or US EPA Method 18) analyses.
• In Situ Respirometry. To evaluate the viability of bioventing, an in
situ respirometry test is commonly performed in which biological
activity is determined from the change in oxygen and carbon diox-
ide immediately following termination of vapor extraction.
In addition to site and soil parameters, there are certain contaminant prop-
erties that affect ventability, including volatility, aqueous solubility, and
biodegradability (see Section 2.2). The first two of these determine the con-
taminant partitioning and hence the thermodynamic driving force for the
3.12
-------
Chapter 3
contaminant to enter the vapor-phase where vapor extraction can remove it.
For many contaminants of concern, these parameters are well known. How-
ever, petroleum products may consist of many components with a wide
range of physical properties. Laboratory analysis of soil or NAPL samples
is often used to determine the distribution of contaminants. A field pilot test
is performed to estimate vapor offgas concentration in the initial stages of
the remediation.
3.2.2 Pilot Testing
Pilot tests are commonly performed at sites where a large area is to be
treated or where the response to vapor extraction cannot be predicted with
confidence. In practice, most sites are subject to at least a short-term pilot
test, but systems for very small sites where the geology is known to be ame-
nable to vapor extraction are sometimes designed without a pilof: test.
Pilot testing is typically the first step in moving from a conceptual design
to a final design. A conceptual design is always developed prior to pilot
testing from an understanding of site conditions based on site investigation
results. The pilot test and site investigation are inextricably linked — the
pilot test is performed and interpreted in light of preceding site investiga-
tions, and the site investigation is reevaluated in light of the pilot: test results.
The results of the pilot test and site investigation lead to an understanding of
the site and the ultimate vapor extraction design concept. Evaluation of the
pilot test results then culminates in a preliminary design.
The primary objective of vapor extraction pilot testing is to provide infor-
mation on soil permeability and offgas contaminant loading so that effective
vapor extraction and offgas treatment systems can be properly sized. In
many cases, this information can be obtained from a short-term pilot test
requiring only a few hours and involving measurement of only the applied
and vadose zone vacuum, recovered soil gas flow rate, and composition of
the blower offgas. However, short-term pilot tests have their limitations and
may be incapable of achieving other objectives, such as those related to
bioremediation and dual-phase extraction. Therefore, longer term tests
should be considered for the following situations:
• The site has a deep vadose zone or a tight surface seal or is
highly stratified. In such cases, it may take more than a few
hours for the system to reach steady-state conditions.
3.13
-------
Design Development
• Contaminant fate information, typically in the form of soil or soil
gas samples collected before and after operation of vapor extrac-
tion is needed. Permanent substantial changes in these param-
eters can be expected only after weeks of operation.
• Detailed information on offgas composition is required. The initial
VOC, O2, and CO2 concentrations in the offgas usually change
gradually over time, so evaluation of long-term volatilization and
biodegradation rates for offgas treatment sizing and prediction of
remedial performance may require a longer pilot test.
• Treatment is to occur within a low-permeability, high residual
water saturation formation will a high vacuum, such as is typi-
cally done in dual-phase extraction. The relative air permeability
can change dramatically as soils are dewatered by the high
vacuum, resulting in significant changes in system performance
over the course of weeks or months.
The following sections discuss the setup, execution, and data acquisition
requirements for conventional vapor extraction pilot tests (Section 3.2.2.1);
high-vacuum, dual-phase, bioslurping pilot tests (Section 3.2.2.2); and
bioventing pilot tests (Section 3.2.2.3).
3.2.2.1 Conventional Vapor Extraction Pilot Tests
Pilot-scale activities for vapor extraction focus on in situ measurement of
parameters that facilitate the estimation of soil permeability to vapor flow,
volume of soil in which vapor extraction occurs, extracted vapor concentra-
tion and composition, aerobic biodegradation rates (if contaminants are aero-
bically biodegradable), and requirements for combination injection/extrac-
tion systems and flow balancing. Vapor extraction pilot testing requires a
minimum test system consisting of the following:
• test vapor extraction well screened within the contaminated soil;
• blower to induce air flow;
• vapor treatment system (if required);
• calibrated flow and vacuum measurement devices; and
• in situ vadose zone monitoring installations.
3.14
-------
Chapter 3
Depending on the information desired, additional characterization activi-
ties may also require the following:
• sampling ports in the process lines;
• gas sampling devices (sampling pumps, syringes, etc.);
• analytical instruments (hydrocarbon analyzer, gas chromato-
graph, respiration gas analyzer, etc.);
• tracer gas delivery system and monitoring system; and
• groundwater level monitoring device.
Pilot vapor extraction wells should be placed within the area to be treated
by the full-scale system. This typically means that extraction wells are
placed within the contaminated soil zone and screened so as to induce air
flow through or past (in the case of highly heterogeneous media) the zone
containing contaminants. At sites where a number of distinct zones are to
be treated and a full-scale system is likely to include wells screened in each
zone, more than one pilot test well is appropriate. In practice, existing
groundwater monitoring wells are often used for pilot-scale testing; how-
ever, this is appropriate only in cases where the capillary fringe area is the
zone of interest and only if the monitoring well is properly screened in the
contaminated portion of the vadose zone and within a single soil zone. Oth-
erwise, pilot tests conducted with these wells may not be representative of
full-scale operation.
Care should be taken in locating flow meters and pressure gauges with
relation to the blower. Since most blowers are driven by fixed-speed motors,
extraction flow rates are often controlled by installing gate, block, and/or
globe valves and an air inlet and outlet pipes on the manifold as shown in
Figure 3.1. Although a single in-line valve is sufficient to control the extrac-
tion flow rates, the air inlet and outlet pipes are typically included to allow
the same level of control, while also preventing the blower from overheating.
Flow meters and pressure/vacuum gauges should be placed between the
wellhead and the first encountered valve or piping junction, otherwise the
flow rate and applied vacuum at the wellhead cannot be measured accu-
rately. Unfortunately, these measuring devices are often incorrectly located
between the blower/vacuum pump and an air inlet/outlet valve resulting in
inaccurate data.
3.15
-------
Design Development
Figure 3.1
Simplified Field Pilot Test Schematic for Vapor
Extraction-Based Technologies
Air Outlet Pipe
Valves
Vapor-Liquid Air Inlet Pipe
Separator
Vapor
Treatment Unit
Blower
Pressure
Gauges
Row Meter / \ Meter
Source: Johnson et al. 1994
Vapor Flow vs. Applied Vacuum Test or "Step Test". To estimate air
permeability and select an appropriate vapor extraction blower/vacuum
pump for the full-scale system, extraction flow rates should be measured
during the pilot test as a function of applied vacuum for each test well. This
relationship can be established by conducting a "step test". For a pilot-test
system connected as shown in Figure 3.1, a step test is accomplished through
the following procedures:
1. Open the air inlet valve.
2. Close the valve leading to the wellhead.
3.16
-------
Chapter 3
3. Turn on the blower/vacuum pump so that air is drawn in through
the air inlet line only.
4. Fully open the valve leading to the wellhead.
5. In one step, or optionally in a series of increments, slowly close
the air inlet valve until fully closed.
6. For each increment, allow the flow rate to stabilize (this may take
several minutes or several hours, depending on soil permeability)
and record the wellhead vacuum and flow rate.
The extraction step test can usually be conducted within a few hours
since flow rates typically stabilize (for all practical purposes) fairly quickly.
Data from these tests are usually presented as shown in Figure 3.2. These
methods are recommended only; there are other acceptable methods of dis-
playing the data. Flow rates should be reported in "standard" flow rate
units, as discussed in Section 4.4.1.
Figure 3.2
Presentation of (a) Extraction and (b) Injection Test Data
(a) (b)
1 3°1
1 20-
f '
£ 10-
E
•a
5
dS °-
•
*
•
•
f
"c 40-
^
1 3°'
f" 20-
i
? 10-
1
.8
M o-
a
a
cP
a
•#•0
— IL^i — i I i I i | — i | i l — i —
0 100 200 300 400 0 400 800 1,200
\&cuum (in. H2O) A Pressure (in. H2O)
Source: Johnson et at. 1994
3.17
-------
Design Development
i
Extracted Vapor Characterization vs. Time. When evaluating vapor
extraction, air sparging, bioventing, or any other variation of the technology,
the extraction vapor concentrations and compositions observed during pilot
testing provide a basis for vapor treatment design. The pilot information,
along with knowledge of possible extraction well flow rates and regulatory
requirements, can be used to determine what process modifications (vapor
treatment units or lower flow rates) are necessary to comply with emission
requirements.
Extracted vapor quality data can be collected during or following the
extraction step test discussed above. There are three common methods of
measuring contaminant vapor concentrations as a function of time: (1) use
of a field total hydrocarbon analyzer (flame ionization detectors [FIDs] or
photoionization detectors [PIDs]; (2) use of an on-site portable gas chro-
matograph; or (3) collection of vapor samples in sampling bags or Summa
canisters with subsequent gas chromatographic analyses at an off-site labora-
tory. Regardless of the method chosen, at least a few samples should be sent
to an off-site laboratory for confirming analyses.
Typically, in-field screening is performed using a FID, a PID, or a combi-
nation PID/FID instrument. A PID will not detect methane and will respond
differently to various types of hydrocarbons (a FID will detect methane).
For this reason, at sites contaminated with mixtures of nonhalogenated or-
ganics, such as fuels, a combination PID/FID field instrument is the recom-
mended field screening device.
In the absence of chromatographic separation, the total PID or FID re-
sponse is used as a screening level indication of total contaminant concentra-
tion. For some organics, such as benzene, PID detectors are often used be-
cause of their high sensitivity; however, this sensitivity is compound-specific
and highly variable. Field-screening PIDs or FIDs are inexpensive and easy
to use, but no compound-specific data are available, and the sensitivity of
these instruments can change significantly for a particular compound de-
pending on such factors as vapor contaminant composition, temperature,
pressure, and water content of the vapor. Thus, the PID, and to a lesser ex-
tent the FID, is a poor indicator of total contaminant concentrations and
should not be used for this purpose unless it is known that a single compo-
nent dominates the vapor or that the instrument is equally responsive to all
compounds in the vapor stream. A PID or FID usually works best when a
single compound is present and its response is known. A "hot wire" detector
3.18
-------
Chapter 3
is used to monitor explosive vapors and is adequate for monitoring total
contaminant response at higher concentrations (above 100 ppmv).
It is important to recognize that expression of gas concentrations in vol-
ume/volume units is meaningless unless the calibration compound is also
specified. Thus, a total contaminant concentration of 100 ppmv measured on
a portable FID calibrated to methane must be expressed as 100 ppmv-meth-
ane to have meaning (e.g., a gasoline vapor stream reported to have a total
contaminant concentration of 100 ppmv-methane is not equivalent to a re-
ported total concentration of 100 ppmv-hexane).
On-site gas chromatographs (GCs) are valuable since compound-specific
composition of the vapor stream can be determined at the site in near real-
time. Even though the sample analysis process is simple, these instruments
should be only operated by knowledgeable personnel because troubleshoot-
ing and identifying erroneous results requires a thorough understanding of
the underlying principles of gas chromatography. It should be noted that
portable GCs typically cannot accurately quantify very volatile compounds
such as vinyl chloride and may not be able to separate all compounds of
concern, such as cis- and ?ra«j-l,2-dichloroethene.
Perhaps the most common approach to monitoring extracted vapor hydro-
carbon concentrations is to take readings with a PID/FID instrument in the
field at regular intervals throughout the pilot test and also to collect vapor
samples periodically for off-site GC analysis. This approach allows for
monitoring general trends in total contaminant concentrations while also
determining the individual compounds present in the vapor at select times
throughout the test.
For sites contaminated with fuels of unknown origin, it may be useful to
perform boiling point analyses. The results of these analyses show the com-
position of a vapor sample with regard to carbon chain length, which is re-
lated to the volatility of the vapor species. Conducting a boiling point analy-
sis on a sample of the fuel will provide an indication of the fraction of the
fuel that will volatilize under vapor extraction conditions. Boiling point
analyses conducted on a vapor sample during a pilot test will establish the
baseline with which samples collected during full-scale operation can be
compared. A comparison of the relative attenuation of various fractions over
the course of remediation lends insight into the fraction of material removed
by vapor extraction and can be used to extrapolate remediation time.
3.19
-------
Design Development
Although a particular vapor extraction system may not be intended to be a
bioventing system per se, respiration gas concentrations should be measured
in the extracted vapor stream if the site contaminants are aerobically biode-
gradable. In addition, in situ biorespiration tests (described in Section
3.2.2.3) should also be performed. Such tests should be conducted because
under conditions that are favorable to aerobic biodegradation, the amount of
contaminant mass removed by biodegradation resulting from soil aeration
induced by vapor extraction operation may easily surpass the mass removed
by physical processes, especially for heavier petroleum distillates and during
the later stages of remediation. Monitoring of respiration gases and perfor-
mance of in situ respiration tests provide data to estimate the mass removal
due to biodegradation.
Respiration gases are most effectively and simply measured by field infrared
gas analyzers equipped to measure oxygen, carbon dioxide, and methane.
These instruments provide simultaneous, real-time readings for all three gases.
Although collection and analysis of vapor samples is not complicated, the
following measures should be incorporated into any pilot test sampling plan:
: ' ' I
1. Samples should be collected between the extraction wellhead and
any air inlet line.
2. The test should be conducted for a long enough period to ensure
that vapor concentrations are representative of extended system
operation; vapor samples should be collected after extractions of
several pore volumes of soil gas.
3. Periodic monitoring of air treatment (e.g., carbon filter) exhaust
should be completed to ensure explosive conditions within any
air treatment equipment are noted and managed appropriately.
The first measure ensures that representative samples of the extracted
vapors are obtained. Sampling ports should not be placed within a few feet
of any air inlet junction as significant back-mixing may occur near the junc-
tion. Since vapor samples are being withdrawn from a system under
vacuum, this vacuum must be overcome to collect a sample. The recom-
mended sampling procedure is to drag the sample through on-line analyzers
or into sampling bags without having it pass through a pump. This is easier
to do with an on-line analyzer as a sampling pump can usually be installed
downstream of the detector. Bag samples can be obtained by pumping gas
directly from the wellhead into a sample bag using a manual or automated
3.20
-------
Chapter 3
sampling pump. However, a superior sampling method is depicted in Figure
3.3. The sampling bag is connected to a port within a chamber that can be
sealed and evacuated. The exterior port is then connected to the process
sampling location, and by evacuating the sealed chamber, a sample is drawn
into the sampling bag without passing through a sampling pump.
Figure 3.3
Schematic of Apparatus for Sampling Vapors Under Vacuum Conditions
From
Process
Evacuation Pump
Source: Johnson at at. 1994
The second measure is important because samples obtained at the start of
an vapor extraction pilot test are not representative of sustained full-scale
system operation. Typically, when flow is initiated in a pilot test, the rela-
tively high extracted vapor concentrations decrease rapidly over a period of a
few hours to a few days to some more stable level (at least, the rate of de-
cline in concentration is much slower than observed in the initial start-up
period). This is because the initiation of subsurface vapor flow draws vapors
from the contaminant source as well as from other areas to which contami-
nant vapors have migrated from the source over time. Until these vapors are
recovered by the extraction well, the measured extracted vapor concentration
is elevated above levels that will be observed during sustained operation of
the system. Consequently, it is useful to estimate how long a given test must
3.21
-------
Design Development
• i
be conducted. Johnson and Stabenau (1991) have presented the following
approach, which approximates this transient period Tstartup (in seconds) as the
time required to sweep one "pore volume" of vapors through the flow zone:
'startup f}
Vwell
where: eA = the air-filled void fraction in the subsurface (0.30 is a
good estimate for most unconsolidated soils);
O = the volumetric flow rate to the extraction well (cm3/s);
^well
and the flow zone has been approximated by a cylinder of radius Rp (cm)
and height Hp (cm). In the absence of any other information, Johnson and
Stabenau recommend that RF be estimated to be roughly equal to the depth
to the top of the screen for the well (HF). For an extraction well screened
from 3 to 4 m (10 to 15 ft) below ground surface (bgs) pulling 0.01 m3/s (20
standard fWmin), Equation 3.1 predicts the transient period to last approxi-
mately 50 minutes. Data collected during this test can be reduced and dis-
played as shown in Figure 3.4.
As mentioned in Section 3.2.1, when conducting vapor analyses in the
field, it is important to confirm and augment the field results with off-site
laboratory analyses using the TO-12 and/or TO-14 methods. Off-site analy-
sis, while more expensive and lacking the immediacy of field analysis, is
generally more accurate and can often better identify the individual sample
components.
Subsurface Vapor-Phase Pressure Distribution. The subsurface pressure
distribution in the vadose zone resulting from vapor extraction pilot test
operation should always be monitored. This information is used, along with
the vacuum/flow response information, to assess the air permeability andVor
the relative horizontal-to- vertical permeability ratio in the soil in the vicinity
of the test well. The zone of influence for the test well is determined from
this permeability information and can be used along with permeability distri-
bution data and vapor flow modeling results to gain a better understanding of
the subsurface vapor flow patterns. Pressure distribution is commonly mea-
sured only as a function of radial distance from the vapor extraction well.
This is usually adequate, but better results are obtained when the pressure
distribution evaluation also includes the vertical dimension, especially at
stratified sites where soil permeability varies substantially with depth.
3.22
-------
Chapter 3
Figure 3.4
Presentation of Extracted Vapor Analyses from Pilot Test
0. 0.03 0.08 0.16 0.24 0.4 1.2 2.1
Time Since Start-Up (d)
150
§ 100-
50-
II
0.0
Q= 12 standard ftVmin
0.5 1.0 1.5 2.0
Time Since Start-Up (d)
2.5
D BP Range 1: <28°C
H BP Range 2: 28-80°C
H BP Range 3: 80-111°C
• BPRange4:lll-144-C
• BP Range 5: >144°C
Adapted with permission from Johnson et ai., "Soil Venting at a California Site: Field Data Reconciled with Theory",
Hydrocarbon Contaminated Soils and Groundwater, Volume 1,1991, P.T. Kbstecki and E.J. Calabrese (eds.).
Copyright CRC Press, Inc., Boca Raton, FL.
Vertical changes in vacuum give an indication of the leakiness of the surface
and the vertical/horizontal air permeability ratio. The pressure distribution is
estimated by measuring the soil pressure at various distances from the test
well, preferably also at discrete depth intervals. Generally, the most cost-
effective method of installing pressure monitoring points is to use a direct-
push unit (i.e., Geoprobe). Direct-push installed vadose zone points consist
of small-diameter polyethylene tubing attached to a drive point that is driven
into the subsurface to the desired depth. Care should be taken during the
installation of shallow (less than 1.5 m [5 ft]) driven points as leakage or
short circuiting is possible. Direct-push vapor monitoring point installation
is best for applications involving shallow installation depths and granular
soils. Installation at depths greater than 15m (50 ft) can be problematic, and
direct-push probes can rarely penetrate cobble or cemented layers in soil.
3.23
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Design Development
Figure 3.5 depicts an example of a tri-level pressure monitoring point
installation. Existing groundwater monitoring wells can be used as pressure
monitoring points if the screened interval is at least partially exposed to the
vadose zone. However, this approach alone rarely provides a vertical profile
of pressures, which can be beneficial at sites with distinct strata of soils with
substantially differing permeabilities.
Figure 3.5
Tri-Level Pressure Monitoring Point Installation
Ground Surface
1/8" OD Teflon TUbing
Borehole
Box Containing \&por Sampling
Ports and Thermocouples
l"PVCPipe
Coarse Packing
ESI
Cement/Bentonite
Depth BGS
(ft) „
:0
10
--20
•30
•40
•50
Reprinted with permission from Johnson et al.. "Soil \fentlng at a California Site: Field Data Reooriciled with Theory",
Hyctiocaikon Contaminated Soils and Groundmter, Volume 1.1991, P.T. Kbsteoki and E.J. Calabrese (eds.).
Copyright CRC Press, Inc., Boca Raton, FL.
Vadose zone monitoring points should be placed over the full range of the
expected zone of extraction, with at least one well very close to the vapor
3.24
-------
. Chapter 3
extraction well. For example, monitoring points located at approximately 1.5,
3,7.5,15, and 23 m (5,10,25,50, and 75 ft) from the extraction well may be
needed depending on soil permeability and degree of heterogeneity. If vertical
profiling of soil pressures is also to be evaluated, three levels, or at least one
point in each distinct soil stratum, should be installed. In addition, in heteroge-
neous soils, monitoring points should be placed in at least three different direc-
tions from the test well to better define the soil pressure distribution and identify
regions that may not have significant vapor flow.
The step test described previously presents an opportunity for measuring
soil pressure distributions at a given extraction vapor flow rate. There are
two types of soil pressure data that can be collected during the pilot test:
transient data and steady-state data. Steady-state data are much easier to
acquire and, in most cases, are adequate to evaluate soil permeabilities and
the horizontal-to-vertical permeability ratio. In fact, it may not be practi-
cable to collect transient data in very permeable soils (medium to coarse
sands) without a robust and extensive surface seal, as the flow field is estab-
lished within a short period.
Transient data may be required in cases where the vadose zone is deep
(on the order of 30.5 m [100 ft] or more), where the vadose zone is highly
stratified, and/or where a robust and extensive surface seal exists (such as an
airport). Transient data are often presented as shown in Figure 3.6a. The
presentation of steady-state data varies, depending on the density of sam-
pling points. For sparse data, the presentation is usually similar to that of
Figure 3.6b.
3.2.2.2 High-Vacuum Vapor Extraction, Dual-Phase Vapor
Extraction, and Bioslurpjng Pilot Tests
The objectives for pilot testing of high-vacuum, dual-phase, and
bioslurping vapor extraction applications are dramatically different from
those described in Section 3.2.2.1 for conventional vapor extraction. The
high vacuum used in these applications often results in a gradual drying of
the vadose zone soil as pore water is mobilized by pressure gradients. The
vapor extraction well essentially acts as a large vacuum lysimeter, removing
soil moisture from the vadose zone. As the water saturation of the soil de-
creases, the air saturation increases, often resulting in a substantial increase
in air permeability of the soil after several weeks or months of operation.
3.25
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Design Development
Figure 3.6
Presentation of Subsurface'Pressure Monitoring tosujte from
Pilot Test — (a) Transient Results, (b) Steady-State Results
(a)
3-
c
•-s-
o
0-r
-2-
•
-4-
-6-
-8-
io-
° °0
<***\i>co
a
a
o
n
a
a
a HB-7D (r=3.4 m) n
A HB-6D (r=16m)
o HB-14D (n=9.8 m)
an
A
O
o
a a a
a
Depth = 40 ft
(b)
a
e
I
o
1UO,
0-
im
Depth = 40 ft
Q DO B
a Vacuum
• Injection
10 100
Time (min)
1,000
1 10
Distance from Well (ft)
100
?tt^^^
Copyright CRC Press, Inc., Boca Raton, FL.
Therefore, steady-state conditions are reached only after a long period of
operation — much longer than the duration of most high-vacuum pilot tests.
As an alternative to pilot testing for high-vacuum, dual-phase, and
bioslurping applications, phased implementation may be more appropriate.
At a large site with low-permeability soils where one of these approaches is
anticipated, several wells may be installed initially and operated for a period
of several months. Following review of the performance of these wells, the
full-scale system would then be installed. Obviously, at a small site, the
preliminary system would address the whole site, and adjustments (e.g.,
additional wells to provide tighter spacing, greater blower capacity, etc.)
would be made to the system after a few months of operation, rather than
expansion of the preliminary system into other areas.
Because of the time required to achieve steady-state conditions, and be-
cause high-vacuum, dual-phase, and bioslurping applications are generally
practiced at the highest vacuum attainable, testing of these applications is
3.26
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Chapter 3
generally performed at a single vacuum. This contrasts with conventional
vapor extraction tests, where step tests at several vacuum levels may be per-
formed. In addition, the pilot test equipment required for high-vacuum,
dual-phase, and bioslurping tests obviously will be different from that re-
quired for conventional vapor extraction tests since higher vacuums are ap-
plied and LNAPL and extracted groundwater must be separated from the
vapor stream and managed. In addition to the vapor extraction pilot param-
eters previously described, the following should also be collected during the
pilot test for high-vacuum, dual-phase, and bioslurping systems:
• water recovery rate vs. time;
• total mass removal vs. time;
• NAPL recovery rate vs. time;
• distribution of contaminant mass removed as aqueous product,
vapor, and NAPL; and
• recovered water quality and need for treatment.
3.2.2.3 Bioventing Pilot Tests
Each of the parameters described under vapor extraction pilot testing (soil
permeability, extraction/injection zone of influence, and step test results)
should also be measured for a bioventing pilot test. In addition, in situ respi-
ration tests must be performed to confirm that subsurface conditions are
favorable for biodegradation and to estimate the average biodegradation rates
that can be expected under full-scale operation.
Hinchee et al. (1992) have developed a detailed test protocol for in situ
respiration testing for the U.S. Air Force that has been used at many
bioventing sites in the Unites States. This protocol is available in a document
entitled, Test Plan and Technical Protocol for a Field Treatability Test for
Bioventing. In addition, the WASTECH® monograph, Bioremediation, gives
a detailed description of this testing (Dupont et al. 1998). A brief summary
is provided here.
After establishing baseline oxygen and carbon dioxide vapor concentra-
tions in the test wells, air is injected which contains an inert tracer gas (usu-
ally, 1-2 volume % helium) into the vadose zone. An area of highest VOC
contamination and an uncontaminated location having similar soil properties
are usually selected. The air provides oxygen to the soil and the helium
3.27
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Design Development
provides diffusivity data that can be used to estimate the diffusion of oxygen
from the ground surface. After some period of time, typically 24 hours, gas
injection is stopped, and concentrations of oxygen, carbon dioxide, and he-
lium are monitored periodically over several days. Alternatively, the soil gas
sampling for oxygen and carbon dioxide may be performed after an ex-
tended period of vapor extraction, such as at the end of a 24-hour pilot test.
The respiration gas concentrations should be monitored in several vadose
zone monitoring points like those used for soil pressure readings as de-
scribed in Section 3.2.2.1. It is imperative that the soils around the point
being monitored (1) are contaminated, and (2) have been adequately aerated
by operation of the air injection or by the vapor extraction system. Initial
oxygen concentrations in soil gas should be at least 15% (by volume) and
more desirably 19 to 21%. Respiration gas concentrations should be moni-
tored at appropriate time intervals to adequately define the oxygen utilization
rate until the oxygen concentration declines to about 2%.
At least one respiration test should also be conducted in a "background"
area to assess the rate of any "natural" subsurface oxygen-utilizing pro-
cesses. Ideally, the background area is similar with regard to geological and
microbial conditions and differs only in that no contaminants are present.
Interpretation of in situ respiration test data is discussed in Section 3.2.3.4.
'' : ••
3.2.3 Pilot Test Results Interpretation
' !
Interpretation of pilot test results usually involves extracting values for air
permeability (ka), the horizontal-to-vertical permeability ratio (kh/kv), and
sometimes the surface permeability (ks). These values are then input into an
air flow model to determine the spacing and operation of extraction (and
sometimes injection) wells such that the air flow provided throughout the
contaminated zone is adequate to effect the required remediation in the de-
sired time frame. The goal of interpretation of the pilot test results is the
evaluation of air flow paths, and the permeabilities are intermediate param-
eters calculated during this exercise. In fact, it is possible to evaluate air
flow paths directly without explicitly solving for the air permeabilities (Bass
1993a), but in practice, the intermediate step of solving for permeabilities is
usually taken.
3.28
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Chapter 3
3.2.3.1 Evaluating Air Permeabilities
A variety of models are available to determine ka from pilot test data.
Many of these models also can evaluate kh/kv and/or ks. All provide values
for ka that are averaged over the soil conditions in the immediate area of the
extraction well. Changes in location may result in different values for ka, as
will changes in soil water saturation over the course of remediation (of par-
ticular concern in high-vacuum and dual-phase applications).
One-Dimensional Radial Flow Solutions. One-dimensional radial flow
solutions have been developed by McWhorter (1990) and Johnson et al.
(1990), among others. McWhorter's solution consists of preparing a graph
of the square of the absolute pressure in the subsurface at distance (r) from
the extraction well, normalized to atmospheric pressure (P/Pa )2 versus the
log of the distance from the extraction well squared divided by the time
since the start of the test (InfrVt]) and using the slope of the resulting line in
the appropriate equation in Appendix A. Johnson's solutions can be evalu-
ated for ka by plotting gauge pressure in the subsurface at distance (r) from
the extraction well (P - Patra) vs. the log of the time since the start of the test
(ln{t}) and using the slope of the resulting line from the equation in Appen-
dix A. Johnson's approach has been implemented in the popular
"Hyperventilate" and "VENTING" design tools.
Because of the simplifying assumptions of one-dimensional radial flow
solutions, these methods should be used only for sites with an impermeable
surface seal where the entire vadose zone is to be addressed by vapor extrac-
tion. Few prospective vapor extraction sites meet these criteria (Beckett and
Huntley 1994), as surface infiltration of air is the rule, rather than the excep-
tion. For this reason, the subsurface vacuum field at most vapor extraction
sites rapidly achieves steady-state conditions, and the time-dependent sub-
surface pressure data necessary for McWhorter's and Johnson's analyses are
difficult to obtain.
Two-Dimensional Radial Flow Solutions. Models of this type, which
can account for surface infiltration and vertical anisotropy, have been devel-
oped by Shan, Falta, and Javandel (1992), Joss and Baehr (1995a), and Falta
(1996)(see Appendix A). There are no "cookbook" methods for regression
of pilot test data using this type of model to determine permeabilities. A
computer program must perform iterations until the permeabilities best fit
the field data. Unlike the one-dimensional radial flow solutions, the
3.29
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Design Development
two-dimensional solutions provide estimates of kh/kv in addition to ka. Fur-
thermore, Joss and Baehr's solution will also estimate ks. Joss and Baehr's
solution has been implemented in "AIR2D," a Fortran program available
from the U.S. Geological Service.
Two-dimensional radial flow solutions can be used for virtually any site
conditions. They assume steady-state operating conditions and therefore, do
not require time-dependent subsurface pressure data. At most sites, where
steady-state is reached rapidly, this makes pilot test data collection much
easier and less expensive. However, at the occasional site where a tight sur-
face seal does exist (e.g., beneath the hardstand. at an airport), steady-state
conditions may require days to establish. In such cases, pilot test duration
may be reduced by taking transient subsurface pressure data and using a
one-dimensional radial flow solution for the analysis. The disadvantage to
this approach is that vertical anisotropy cannot be evaluated.
To make optimum use of the capabilities of two-dimensional radial flow
models, subsurface vacuum should be measured at various depths within the
vadose zone, as well as at various distances from the vapor extraction well.
In many cases, this means that a substantial number of new vapor monitoring
points will have to be installed for the pilot test.
i : ' ' ' !
3.2.3.2 Evaluating Other Parameters from Pilot Test Data
The US ACE (1995) describes a number of additional analyses which can
be performed on pilot test data.
Vent Well Efficiency. Head losses between the vapor extraction well
and the subsurface soil can lead to underestimates of ka. When vent
efficiency (defined as the ratio of the vacuum just outside the test well to
the applied vacuum) is low, the conventional semilog plot of subsurface
pressure versus distance from the extraction well is shifted downward
(the applied vacuum appears to be lower than it actually is), although the
shape of the curve does not change. Therefore, estimates of ka (which is
intercept-dependent) are affected, although estimates of kh/kv (which is
slope dependent) are unaffected.
Vent efficiency can be estimated from direct measurements of vacuum
dissipation in the well annulus by installing a small-diameter piezometer in
the annulus of a vertical vent well or within a few centimeters of the vent
well borehole. Also, nesting a piezometer increases the risk of well seal
3.30
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Chapters
failure. Separate piezometer installations within a few centimeters of the
borehole are also problematic and carry additional expense.
A more practical method for estimating vent efficiencies is to compare the
applied vacuum in the test well to the theoretical vacuum predicted by steady-
state radial flow models. In most cases, a two-dimensional model will be nec-
essary for this comparison, and this will require computer iteration to find the
vent well efficiency that best fits the observed data. In rare cases where a sur-
face seal exists, a one-dimensional model can be used and simple, explicit equa-
tions for vent well efficiency can be applied (Appendix A).
In most cases, the variability in ka among vapor extraction wells will be
greater than the variation in well efficiency. The effect of well efficiency
will cancel out in any case, because the pilot test well will generally have a
well efficiency similar to the extraction wells in the full-scale system. Inves-
tigations of well efficiency would be necessary only if an existing monitor-
ing well of questionable construction was used for the pilot test and if the
results deviated significantly from what was expected. Typically, a semilog
plot of subsurface pressure versus distance from the extraction well will
intercept the y-axis at 10 to 30% of the applied vacuum, reflecting a well
efficiency of around 50%. If such a plot has a y-intercept of less than 10%
of applied vacuum, poor well efficiency may be suspected.
Air Saturation. US ACE (1995) cites the use of a one-dimensional radial
flow solution to estimate air-filled porosity. Air saturation can also be mea-
sured directly from laboratory analysis of an undisturbed soil sample. When
air saturation is low, air permeability is also low. Over the course of vapor
extraction operation, especially when high vacuum is employed, air satura-
tion may increase, leading to a dramatic increase in ka. Estimates of this
effect may be made using the soil moisture retention curve or a field method
such as a neutron probe. However, ka is so sensitive to small changes in air
saturation that precise estimates of the increase in permeability over the
course of vapor extraction operation are generally impractical.
Upwelling. Groundwater within the vapor extraction well is drawn up the
well by the applied vacuum. This has the effect of reducing the amount of
exposed well screen, and as the recovered soil gas is forced to pass through
smaller amounts of open area, the high velocity can entrain water into the air
stream and along the walls of the extraction well, resulting in water handling
problems at the surface. In some cases, upwelling leads to the paradoxical
result of an increase in applied vacuum, resulting in a lower rate of soil gas
3.31
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Design Development
recovery. Upwelling also reduces the magnitude of air flow in the lower
portions of the vadose zone, which is where the greatest contaminant con-
centrations are often found. Upwelling can be monitored by placing a pres-
sure transducer in the extraction well and comparing the head difference
when the vapor extraction system is on and off (Appendix A). Alternatively,
a bubbler tube can be installed in the vapor extraction well at a estimated
known elevation and sealed through the well cap. Water levels in the well
can be determined by measuring the pressure required to initiate a flow of air
through the bubbler tube.
The vacuum applied to the top of an extraction well is often the same as
the vacuum at the bottom of the well. Exceptions occur with high flow rates
in deep extraction wells, or in small-diameter (< 2 in.) extraction wells.
Pressure drop along the length of a vapor extraction well has been addressed
by Bass (1992), Skomsky and Fournier (1996), and McPhee, Bass, and
Mott-Smith (1997), among others. So long as these conditions do not occur,
it is a safe assumption that, at steady-state, the Upwelling within the vapor
extraction well will be nearly equal to the applied vacuum expressed in
height of water column, provided significant entrainment of groundwater
into the air stream is not occurring.
Field Criteria for Vapor Extraction Feasibility Screening. Peargin and
Mohr (1994) have developed pass/faii criteria for estimation of vapor extrac-
tion feasibility based on a comparison of field subsurface vacuum measure-
ments with the results of a numerical two-dimensional radial flow solution.
The solution is plotted using normalized variables with the log of subsurface
pressure (expressed as a percent of applied vacuum at the vapor extraction
well) on the vertical axis and distance from the extraction well (expressed as
multiples of vadose zone thickness) on the horizontal axis. Field data are
then superimposed on this plot. When the data fall largely below the nu-
merical solution with k,/kv = 1 (i.e., the horizontal permeability is apparently
less than the vertical permeability), then the site is probably unsuitable for
vapor extraction.
Peargin and Mohr's approach is simple yet elegant, and cookbook judg-
ments can be made quickly by junior staff using this approach. An apparent
kh/kv significantly less than one can often reflect conditions unsuitable for
vapor extraction, such as vertical fracturing of soil (common in clays) and
preferential pathways leading to short circuiting. However, some well con-
ditions, as well as site conditions, can also lead to negative results. A poor
3.32
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Chapter 3
well seal on the extraction well or monitoring points or poor extraction well
efficiency will lead to an apparently low kh/kv, and in high-vacuum applica-
tions, the response of the soil may change considerably with time as system
operation progresses. Therefore, an evaluation by experienced technical
personnel is advisable before a final judgement is reached.
3.2.3.3 Evaluating High-Vacuum and Dual-Phase Pilot Test Data
Pilot tests for high-vacuum and dual-phase extraction of low-permeability
soils often must be longer because the air permeability of the soil changes as
moisture is removed, and steady-state conditions may not be reached for
weeks or months. This effect can be estimated by measuring the soil mois-
ture retention curve from an undisturbed sample in the laboratory and inter-
preting short-term pilot test data in light of this measurement. However, ka is
so sensitive to small changes in air saturation that precise estimates of the
increase in permeability over the course of vapor extraction operation are
generally impractical. Therefore, from the standpoint of evaluating air flow,
it often makes the most sense not to perform a pilot test when the treatment
area is limited. Alternatively, a full-scale system can be installed and modi-
fied based on its performance over the first few months of operation. As
discussed in Section 3.2.2, long-term pilot tests or phased implementation is
still appropriate for large systems where cost considerations dictate that mid-
course corrections be minimized.
Short-term pilot tests for dual-phase applications may be useful for evalu-
ating groundwater recovery and drawdown parameters. Traditional methods
for evaluating hydrogeologic parameters are used, except the apparent draw-
down in the extraction well is the sum of the water table depression and the
applied vacuum expressed in height of water column.
Evaluating Bioventing Pilot Test Data. This section is adapted with
permission from Soil Vapor Extraction and Bioventing — Engineering and
Design (US ACE 1995). Additional information on bioventing pilot testing
and interpreting results can be found in the AFCEE document entitled Test
Plan and Technical Protocol for a Field Treatability Test for Bioventing
(Hinchee et al. 1992).
The concentrations of subsurface oxygen and carbon dioxide measured
during an in situ respirometry test are plotted against time, and the rate of
oxygen consumption (the initial slope) is expressed in terms of percent/day.
3.33
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Design Development
The biodegradation rate is usually calculated assuming hexane to be representa-
tive of hydrocarbons in the soil. The biodegradation rate is estimated as:
6.4)
K0=-0.01KnAD0C
I
where: KB = biodegradation rate (mg hexane/kg soil • day);
K = oxygen utilization rate (percent/day);
A = volume of air per mass of soil (L/lcg);
Do = density of oxygen gas (1,380 mg/L at 50°F and 1 atm); and
C = stoichiometric mass ratio of oxygen to hydrocarbon (3.53
for hexane).
I
3.2.4 Preliminary Design Based on Full-Scale Air Flow Analysis
i
Once the various permeabilities of the soil and ground surface have been
evaluated, these values can be input into a model to determine the number
and spacing of vapor extraction wells, the applied vacuum, and the antici-
pated soil gas extraction rate. These parameters are highly site-specific and
depend on depth of contamination, physical and chemical properties of con-
taminants, soil characteristics, and air permeability. These parameters are
also interrelated; as applied vacuum is varied, the flow and effective radius
of influence also change. Therefore, system design is an iterative process.
Typically, the engineer begins by selecting a set of operating conditions
that includes a high applied vacuum and soil gas extraction rate (for a single
well). At this stage, the diameter of the vapor extraction wells will typically
be assumed to be 2 inches in this initial design. At these conditions, the
effective radius of influence for remediation is then evaluated, and the num-
ber, spacing, and placement of wells on the site are determined accordingly.
The soil gas extraction rate for the entire system is then identified, and an
overall system cost is calculated.
In general, decreasing the applied vacuum will decrease the life cycle cost
for the final system since the reduced air handling and treatment costs will
outweigh the incremental drilling and piping costs for more wells. There-
fore, the next step in the design process is to reduce the applied vacuum and
repeat the evaluation of radius of influence and computation of system cost.
This process is repeated until the incremental cost savings from reduced air
handling reaches a point of diminishing return when compared with the
additional drilling and piping costs.
3.34
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Chapter 3
At this stage in the design process, the engineer may also wish to evaluate
variations of vapor extraction technology, such as air injection wells, hori-
zontal wells, vented trenches, thermal enhancement, or hydraulic fracturing.
3.2.4.1 Evaluating Radius of Influence for a Single Extraction Well
The primary goal of vapor extraction is to provide sufficient air flow
through contaminated soil to remediate the soil within a desired time frame.
For bioventing systems, the goal is to provide adequate air flow to prevent
oxygen deficiency from being a limiting factor in bioremediation. Well
spacing, based on an assumed radius of influence, is chosen with these goals
in mind.
Historically, radius of influence has been evaluated by plotting the log of
subsurface pressure (ln{P} or log10{P}) versus distance from the extraction
well (r), regressing, and extrapolating or interpolating the regression line to
an arbitrary pressure value, typically ranging from 0.025 to 2.54 cm (0.01 to
1 in.) water column (some practitioners have extrapolated to a percentage of
applied vacuum, typically 1%). The radius of influence evaluated in this
way is arbitrary since the vacuum cutoff level is arbitrary. Furthermore,
subsurface vacuum does not necessarily reflect subsurface air flow, and it is
the air flow that effects remediation. Focusing on vacuum rather than flow
gives a radius of influence that is insensitive to the volatility of the contami-
nant, the permeability of the soil, the required extent of remediation, and the
desired remedial time frame.
Many alternative approaches have been developed that focus on air flow.
All are more rigorous than the vacuum cutoff method and give more mean-
ingful results, but most are also more difficult to use. Flow-based models
determine how far from the extraction well sufficient air velocity can be
effected to achieve the required remediation within the desired time frame.
Flow velocity is generally expressed in terms of pore-volume exchanges.
The less volatile the contaminant, the greater the number of pore-volume
exchanges required, at least until the system becomes diffusion-limited. The
required air throughput is dependent on the initial soil concentrations (lower
concentrations require less air). Also, mass transfer kinetics can affect the
efficiency of the removal; the optimum well spacing may change over time,
since in the later stages of remediation, removal of the remaining contami-
nants from soil moisture and dead-end pores may be transport-limited.
3.35
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Design Development
The same model used to develop an effective radius of influence should
generally be used to determine permeabilities. All methods for estimating
permeability will incur some error due to modeling assumptions, but if the
same model is used to determine radius of influence, some of this error will
cancel out. In fact, it is theoretically possible to evaluate effective radius of
influence directly from pilot test data, without intermediate calculation of
permeabilities (Bass 1993a).
Estimating radius of influence using a one-dimensional radial flow solu-
tion is somewhat problematic because assuming a perfect seal both at the
surface and at groundwater means, mathematically, that there is no source
for air and steady-state can never be achieved. A radius of pressure influ-
ence must therefore be assumed, reflecting a phantom air source at some
distance from the extraction well. The air flux can then be calculated within
this distance from the well, and the distance at which sufficient air flow is
achieved can be determined. This approach works well when a good surface
seal exists and when air injection wells are used (approximating the phantom
air source). However, the approach will overestimate effective radius when
no surface seal is present since the model's presumption that all of the soil
gas recovered has passed through all of the contaminated soil is invalid.
Estimating radius of influence using a two-dimensional radial flow solu-
tion is complicated by the fact that the pore-volume exchange rate varies not
only by distance from the extraction well, but also by depth below ground
surface. AIR2D model can be used to identify the region in the subsurface
that has sufficient pore-volume exchange to achieve remediation goals, as
can the equations of Shan, Falta, and Javandel (1992). Peargin and Mohr
(1994) have plotted subsurface volumetric flow rates (normalized to the soil
gas extraction rate) versus distance from the extraction well (normalized to
the vadose zone thickness) based on a numerical two-dimensional radial
flow solution. For a given k^/k^ the area with a pore-volume exchange ex-
ceeding some threshold value is readily identifiable.
An approximate method for determining effective radius of influence,
developed by Bass (1993a), involves one-dimensional radial flow in which
the volume of gas decreases with distance from the extraction well, reflect-
ing infiltration of air from the ground surface. The surface flux is assumed
to be proportional to the subsurface vacuum which drives it, and hence at-
tenuates roughly exponentially with distance from the extraction well. This
approach has the simplicity of a one-dimensional radial flow solution but
3.36
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Chapter 3
does not overestimate radius of influence by ignoring surface infiltration.
Furthermore, effective radius of influence is calculated directly from field
data, rather than from intermediate permeability values.
3.2.4.2 Evaluating Effective Radius of Influence Among
Extraction Wells
When several vapor extraction wells are placed in close proximity, they
are affected by each other's vacuum and flow fields. In the region between
the wells, the wells essentially compete for the limited supply of air infiltrat-
ing the ground surface, an effect that is exacerbated by high kh/kv values and
low surface permeability. In the limiting case where the surface is com-
pletely sealed, air flow between wells becomes negligible, and all of the air
entering the vapor extraction system comes from outside the treatment zone
leading to poor remediation performance. Furthermore, the volumetric rate
of soil gas extraction is less than would be obtained by simply multiplying
the recovery rate for a single well by the number of extraction wells, so air
handling and treatment systems may be oversized.
Most analytical one-dimensional and two-dimensional flow solutions
offer little insight into this effect since they are inherently singles-well solu-
tions. However, the US ACE (1995) outlines how two-dimensional radial
flow solutions for several wells can be combined using the principle of su-
perposition to generate potential flow solutions for multiple-well systems.
Another approach is to use the calculated permeabilities as input parameters
for a three-dimensional numerical model, such as AIR3D — an adaptation of
MODFLOW for vapor extraction applications (Joss and Baehr 1995b), to
estimate flow fields for multiple-well systems. The model generally must be
calibrated so that its predictions conform to measured field parameters. This
method provides a rigorous analysis of the phenomenon and can be used to
evaluate well spacings in multiple-well systems, the potential need for injec-
tion wells, and strategies for operation of nearby wells sequentially or at
varying flow rates to move the stagnation point over time.
The approximate one-dimensional method for determining effective ra-
dius of influence developed by Bass can be modified to account for the inter-
action among wells in multiple-well systems (Bass, Lucas, and Kline 1993).
The decrease in the volume of gas with distance from each extraction well is
modified by the proximity of adjacent extraction wells. The surface flux,
which is the source of the air recovered by the extraction wells, is assumed
3.37
-------
Design Development
to be proportional to the subsurface vacuum that drives it, but is delivered
only to the closest extraction well. This results in a reduced air flow among
wells and, therefore, a reduced effective radius of influence and overall gas
recovery. This approach has the simplicity of a one-dimensional radial flow
solution and provides reasonable predictions of the flow response to an ap-
plied vacuum in a multiple-well vapor extraction system. Equations describ-
ing this approach are given in Appendix A.
The effective radius of influence is always greater for a single-well sys-
tem than that of a single well in a system with multiple wells. In a multiple-
well system, the single-well radius of influence should be used in determin-
ing how far from the edge of the treatment area the wells should be placed,
while the multiple-well radius of influence should be used for determining
distances between extraction wells. Therefore, ideal placement of vapor
extraction wells is slightly bunched in the middle of the treatment area,
rather than spread uniformly throughout.
3.2.4.3 Air Injection
When conditions are not favorable for air flow among extraction wells in
multiple-well systems due to high kh/kv or low ks/ka, air injection wells offer
a means of introducing air between extraction wells. Injection wells may
ultimately speed remediation on the most contaminated areas and allow
greater air flow rates than otherwise would be possible. However, such wells
entail additional well installation costs and additional energy costs for oper-
ating compressors or blowers, and, in some cases, may dilute vapor-phase
contaminant concentrations, thereby increasing offgas treatment costs.
I
Injection wells may be active or passive. Passive inlet wells are open to
the atmosphere, allowing air to be drawn into the soil from the lower atmo-
sphere. These wells are typically used to limit the radius of influence of a
particular well. An example would be the case where two adjacent proper-
ties have volatile contaminants in the subsurface. A passive inlet system
installed along the property boundary would allow vapor extraction/
bioventing to proceed at one of the properties without inducing migration of
contaminants from the other property (the inlet wells would probably need to
be quite closely spaced to create an effective boundary).
When passive injection wells are used to affect air flow paths within a
remediation system, there usually must be many more passive wells than
extraction wells. This is because they are usually of similar construction to
3.38
-------
Chapter 3
the extraction wells, but the driving force for air movement is lower (subsur-
face vacuum will have dissipated from the extraction wells to the passive
injection wells, often by more than 90%). This effect is mitigated somewhat
by the lower upwelling (hence more exposed screen) associated with lower
vacuum and the higher well efficiency associated with lower flows in the
injection well. Still, unless the subsurface vacuum in the vicinity of the
passive injection well is on the order of 10% or more of the applied vacuum,
air will be passively injected at only a small fraction of the extraction rate.
When venting is relatively shallow (<3 m [<10 ft]), an alternative to passive
injection wells is a gravel-filled trench, which has a much greater contact
area with the soil than a passive injection well, and thus is capable of provid-
ing much more air even at low subsurface vacuum levels.
Active injection wells use forced air from a blower or compressor to pro-
mote the movement of air through the soil. Active injection is typically used
to increase pressure gradients and thus induce higher flow rates in stagnant
areas near the fringe of a well's radius of influence. Injection wells should
be placed so that contamination is directed toward the extraction wells. Al-
though screened intervals vary in length, they should allow for uniform air-
flow from the injection to the extraction wells. Injection wells are usually
installed vertically outside the edge of the contaminated area. A well-de-
signed soil venting system allows vents to act interchangeably as extraction,
injection, and/or passive inlet wells.
The effects of active and passive injection wells can be modeled analyti-
cally by superimposing radial flow solutions or numerically using the
AIR3D model. Predicting air flow into an injection well is similar to pre-
dicting air flow out of an extraction well. However, extraction wells are
ordinarily under a substantial vacuum, while injection wells are under pres-
sure or, in the case of passive injection wells, much lower vacuum. The
amount of exposed screen is generally greater in the injection well than in
the extraction well because upwelling reduces the exposed screen to a much
greater extent in the extraction well.
3.2.4.4 Horizontal Wells and Vented Trenches
Increasingly, horizontally drilled wells and horizontal wells placed in
excavated trenches are used in vapor extraction applications. Horizontal
installations generally produce more air flow at lower applied vacuum and
influence at a greater distance than vertical wells. Vented trenches are
3.39
-------
Design Development
typically used in situations where groundwater is shallow and may provide
good areal influence with lower installation cost and less upwelling of
groundwater. Horizontally drilled wells, an offshoot of the oil and gas in-
dustry, are used especially where access is limited or where excavation of
trenches or installation of vertical wells could create^ safety hazard. US
EPA recently reviewed environmental applications of directional drilling and
a partial list is provided in Table 3.2 (US EPA 1997).
Effective operation of horizontal vapor extraction systems requires that air
flux from the formation be uniform over the length of the well. However,
frictional losses can result in the bulk pf the air being extracted at the end of
the well closest to the blower.
To obtain an even influx of air along the length of a horizontal vapor
extraction well, the percent open area, represented by the slot density or
the number and size of perforations, can be increased at greater distance
from the blower to compensate for the reduced vacuum due to frictional
losses. A computerized design tool has been developed (McPhee, Bass,
and Mott-Smith 1997) to predict how such a variation in open area can
be determined so as to ensure constant air flux along the length of the
well. This design tool describes air flow using the Manning equation for
flow through a circular pipe. The formation and slot resistance to air
flow is determined from a horizontal or vertical pilot test (vertical pilot
test results can be reduced using standard transport equations for buried
vertical rods and buried horizontal cables to represent vertical and hori-
zontal wells, respectively [Bass 1993b]). An iterative procedure is em-
ployed to converge on the slot density or hydraulic head profile required
to achieve uniform flux along the length of the well. Implementation
using standard spreadsheet programs (Lotus 1-2-3, Excel, etc.) produces
rapid convergence and ensures ease of use.
3.2.4.5 Thermal Enhancement
Soil heating has been demonstrated to improve the mass removal rate of
vapor extraction systems for VOCs and S VOCs. This approach may be par-
ticularly suited to lower permeability soils where volatile contaminants must
be removed. Raising the temperature of the subsurface increases the rates of
removal and transport mechanisms that typically control the rate at which a
site can be cleaned up using vapor extraction technology. The mechanisms
that are enhanced by heat include:
3.40
-------
Chapter 3
Table 3.2
Select Vendors of Horizontal Wells and Directional Drilling Technology0
Name of Vendor
Address
Contact/Phone
American Augers, Inc.
(Drill Rig Manufacturer)
Davis Horizontal Drilling, Inc.
Directed Technologies Drilling, Inc.
Directional Drilling, Inc.
Ditch Witch, Inc., The Charles
Machine Works, Inc.
(Drill Rig Manufacturer)
Drilex Inc.
P.O. Box 8 14
West Salem, OH 44287
7204 Timberlake
Mustang, OK 73064
1315 South Central Avenue, Suite G
Kent, WA 98032
P.O. Box 159
Oakwood, GA 30566
P.O. Box 66
Perry, OK 73077
15151 Sommermeyer
Houston, TX 77041
Gary Stewart
1-800-324-4930
Roland Davis
(405) 376-2702
Michael Lubrecht
1-800-239-5950
Jim McEntire
(770) 534-0083
Roger Layne
1-800-654-6481
David Bardsley
(713)957-5470
Fishbum Environmental Drilling
GTS Horizontal Drilling Co.
Horizontal Drilling Technologies
Horizontal Subsurface Technologies, Inc.
Horizontal Technologies, Inc.
KVA Slantwell Installations/
KVA Analytical Systems
Mears/HDD, Inc.
Michels Environmental Services
OHM Remediation Services Group
Pledger, Inc.
SCHEMASOIL®
Schumacher Filters America, Inc.
Stearns Drilling
Treachless Technology Center
Vermeer Manufacturing
(Drill Rig Manufacturer)
P.O. Box 278
Marengo, OH 43334
1231 B East Main Street, Suite 189
Meriden, CT 06450
2414 South Hoover Road
Wichita, KS 67215
634 West Clarks Landing Road
Egg Harbor, NJ 08215
P.O. Box 150820
Cape Coral, FL 33915
15 Carlson Lane
Falmouth, MA 02540
4500 North Mission Road
Rosebush, MI 48878-0055
817 West Main Street (main office)
Brownville, WI 53006
5731 West Las Positas Boulevard
Pleasanton, CA 94588
12848 S.E. Suzanne Drive
Kobe Sound, FL 33455
P.O. Box 8040
Asheville, NC28814
6974 Hammond S.E.
Dutton, MI 49316
Department of Civil Engineering
P.O. Box 10348
Louisiana Technical University
Ruston,LA71272
P.O. Box 200
Pella, IA 50219
Stuart Brown
Tom Bryant
1-800-239-8079
Mark Mesner
(316)942-3031
1-800-965-0024
Donald Justice
Steve or Pat
(508) 540-0561
Dick Gibbs
1-800-632-7727
Tim McGuire
(303) 423-5761
Robert Cox
(510)227-1105
Steve McLaughlin
(407) 546-4848
Anne Ogg
(704) 252-9000
Roland Clapp
(616) 698-7770
David Whampler
(515)628-3141
•This list is not inclusive of all vendors capable of providing horizontal wells and directional drilling technologies.
Source: US EPA 1997
3.41
-------
Design Development
• Gas Advection — the movement of air in response to density
gradients;
• Chemical Partitioning to the Vapor-Phase — the vapor pressure
of VOCs and SVOCs is increased significantly with increasing
temperature as Figure 3.7 illustrates;
• Chemical Partitioning to the Water Phase — the solubilities of
most VOCs and SVOCs are not dramatically affected by tem-
perature, but some increase or decrease substantially with in-
creasing temperatures;
• Gas-Phase Contaminant Diffusion — contaminant molecules
diffuse at a faster rate at higher temperatures;
1 . .
• Chemical or Biological Transformations — while chemical reac-
tions increase with temperature, biological degradation .rates
increase above ambient temperatures but fall off again at high
temperatures; and
'I |
• Soil Drying — the relative permeability to soil vapors increases
as the soil dries.
In a review article, US EPA (1997) described and evaluated five methods
of soil heating in conjunction with vapor extraction. The following ap-
proaches to thermal enhancement of vapor extraction were evaluated:
• steam injection/stripping,
• hot air injection,
• radio frequency heating,
. i .
• electrical resistance heating, and
• thermal conduction heating.
While each of these thermal enhancements has been demonstrated to
some extent, they all remain seldom-used niche technologies. The perfor-
mance and costs associated with each approach were presented along with
the limitations specific to each. In addition, case histories were presented for
steam injection and electrical resistance heating as well as a list of vendors
for each approach. The US EPA study concluded that thermal enhancement
technologies can improve mass removal rates and decrease treatment times if
certain site or contaminant characteristics constrain standard vapor extrac-
tion efficiency. Further details on these techniques follow.
3.42
-------
Chapter 3
Figure 3.7
Relationship Between increasing Temperature
and Vapor Pressure for Several Chemicals
1,000 -\
Methyl Isobutyl Ketone
Naphthalene
Adapted from Perry, Chilton, and Kirkpatrick 1963
Steam Injection/Stripping. Steam injection/stripping is an offshoot of
enhanced oil recovery technology and consists of injecting steam into the
contaminated soil mass in situ. This approach provides both heat and a sig-
nificant pressure differential in a formation to mobilize contaminants in the
vapor, aqueous, and NAPL phases. The heat increases chemical partitioning
into the vapor and water phases as contaminants are pushed ahead of the
condensing water vapor toward vapor extraction wells.
3.43
-------
Design Development
A steam-generating boiler, controls, fittings, valves, etc. for control of the
steam injection are required. Special attention must be paid to the high tem-
peratures anticipated in injection and extraction wells when specifying mate-
rials for piping, valves, check valves, and recovery pumps. Steam injection
wells are typically constructed of steel.
This approach is most suited to sites with moderate-to-high hydraulic
conductivities to allow the movement of the steam through the soil. In addi-
tion, the capture, control, and recovery of the condensate plume formed,
which can be difficult to predict in low-permeability formations, is crucial to
the effectiveness of the method. Therefore, this approach is not recom-
mended for sites with high clay or silt content. However, given proper site
conditions, the approach is more applicable to sites where NAPL is present
due to the condensate front that moves ahead of the steam and can displabe
and mobilize NAPL.
Hot Air Injection. Hot air injection can be used to increase the mass extrac-
tion flow rate by increasing the soil temperature through injection wells or in-
jection through a large mixing auger. This process can be less expensive than
using steam, especially if an inexpensive source of hot air, such as a thermal
oxidizer, is available immediately adjacent to the injection wells. However, the
process is much less efficient than steam, and costs for insulating hot air piping
are significant due to the relatively low heat capacity of air.
This process tends to dry the soil more than steam injection and can im-
prove mass removal from lower permeability soils. Drying lower permeabil-
ity soils can significantly increase the hydraulic and pneumatic permeability
and facilitate higher mass removal rates of volatile organic compounds.
However, drying does remove water from the soil, which will ultimately
hinder biodegradation, and drying may not be effective on SVOCs.
In addition, if exhaust from a thermal oxidizer or other combustion source
is used for the hot air, the oxygen concentration may be much lower than
heated ambient air. Furthermore, the output of a thermal oxidizer has sig-
nificant moisture content as a combustion product and therefore will not dry
the soil. If biological degradation is to be enhanced at the site or if drying of
the soil is desirable, an air-to-air heat exchanger may be needed to heat am-
bient air without contacting the oxygen-depleted combustion exhaust.
3.44
-------
Chapter 3
Radio Frequency Heating. Radio frequency (RF) soil heating uses elec-
trodes or antennae powered by a radio-frequency generator that operates in
the industrial, medical, and scientific band (1 to 10 megahertz). The elec-
trodes are either placed on the surface or in boreholes drilled into the con-
taminated area. Vapor extraction is used to collect the resulting vapors.
RF heating can be used to increase soil temperatures above those attain-
able by steam injection or hot air injection. During treatment, RF heating
dries the soil, which results in decreased thermal conductivity. This has
caused uneven and slow heating at some sites (US EPA 1997). At the same
time, the pneumatic conductivity is increased by the removal of water in soil
pores. Therefore, the net effect is to increase the mass removal rate in the
vicinity of the electrodes, and if the electrodes are properly spaced, the con-
taminated soil mass can be treated.
If this approach is used, selection of construction materials for the wells
and the vapor extraction system must account for the highest temperatures
anticipated in the soil, typically 150 to 200°C (302 to 392°F)(US EPA 1997).
Performance data for four sites where RF heating was used to enhance a
vapor extraction system are presented in Table 3.3 (US EPA 1997).
Electrical Resistance Heating. Electrical resistance (ER) heating is com-
parable to RF heating except it is slightly less efficient in heating the soil.
Typically, an array of metal pipes is inserted vertically into the contaminated
soil area. By applying an electrical current, a voltage differential is created
between electrodes placed in two different boreholes, which causes resis-
tance heating to occur between them. As in RF heating, the soil is dried and
VOCs are removed via a vapor extraction system. The same limitations of
uneven soil heating and slow heating that occur in RF heating are exagger-
ated with ER heating because the electrical conductivity of soil decreases
dramatically when moisture is removed. For this reason, the attainable tem-
perature using ER heating cannot practically exceed 100°C (212°F), but
temperatures high enough to oxidize residual VOCs that are not removed by
standard vapor extraction can still be created.
ER heating was applied on a pilot scale at the Savannah River Site in
Aiken, South Carolina, to assess the technique's effectiveness in removing
VOCs from a 3 m (10 ft) thick clay layer at a depth of approximately 12 m
(40 ft) below ground surface in the vadose zone (US EPA 1997). A high-
voltage power source (750 kva) was used to supply 480-volt three-phase
power to a six-phase power transformer that in turn was connected to a series
3.45
-------
Design Development
Table 3.3
Thermal Enhancement Performance Data
i • i
Vendor
Battelle Pacific Northwest
Laboratories
Geo-Con, Inc.
Flour-Daniel GTI (FD GTI)
FDGTI
FDGTI
Hrubetz Environmental
Services, Inc. (Hrubetz)
Hrubetz
Hughes Environmental
Systems, Inc.
HT Research Institute
HT Research Institute
HT Research Institute
KAI Technologies, Inc.
Lawrence Livermore
National Laboratory
Novaterra, Inc.
Praxis Environmental
Technologies, Inc.
R.E. Wright
Environmental, Inc.
SIVE Services
Thermal
Enhancement
Six-Phase Soil
Heating
Hot Air Injection
Steam Sparging
Hot Air Sparging
Electrokinetic
Heating
Hot Air Injection
Hot Air Injection
Steam Recovery
Radio-Frequency
Heating
Radio-Frequency
Heating
Radio-Frequency
Heating
Radio-Frequency
Heating
Steam Stripping and
Electrical Heating
Steam Stripping
Steam Extraction
Steam Stripping
Steam Injection
Date of
Scale Demonstration Location
Field
Demonstration
Full
Full
Full
Full
Full
US EPA
Demonstration
Full
US EPA
Demonstration
Pilot
Pilot
US EPA
Demonstration
Full
Full
Pilot
Pilot
Full
'
NA
NA
1995
1993
1994
1990
NA
1991
1994
1992
1989
1994
1993
1988
1988
NA
1989
Aiken, SC
Piketon, OH
Bremerton, WA
Union, MA
Netherlands
Ottawa, Ontario
Canada
Kelly Air Force
Base, TX
Huntington
Beach, CA
Kelly Air Force
Base, TX
Rocky Mountain
Arsenal, CA
Volk Air National
Guard Base, WI
Kelly Air Force
Base, TX
Lawrence Livermore
National Laboratory
San Pedro, CA
McCIellan Air
Force Base, CA
Bradford, PA
San Jose, CA
gw Groundwatar NA Not applicable PCE Tetrachloroethene
TCE Trichloroethene ND Non-detect TPH Total petroleum hydrocarbons
DCE Dichloroethena OCA Dichloroethance BTEX Benzene, toluene, ethylene, and total xylenes
Source: US EPA 1997
3.46
-------
Chapter 3
Table 3.3 (cont.)
Thermal Enhancement Performance Data
Target Contaminant
PCE
TCE
TCE
No. 6 Fuel Oil
Diesel Fuel
Chlorinated Solvents
BTEX
Diesel Fuel
Jet Fuel
Jet Fuel (JP-4)
TPH (diesel fuel)
Aromatics
Nonaromatics
Aldrin
Dieldrin
Endrin
Isodrin
Aromatic VOCs
Aliphatic VOCs
Aromatic SVOCs
Aliphatic SVOCs
Hexadecane
Total Recoverable
Petroleum
Hydrocarbons
BTEX
TPH (gasoline)
DCA
DCE
Bis(2-
ethylhexyOphthalate
Aromatics
Butyl Carbitol
TCE
TPH
VOCs
Concentration Before
Treatment
ND to 500 mg/kg
ND to 200 mg/kg
1 to 100 mg/kg
88,000 mg/kg TPH
100 mg/kg soil
10 mg/L (gw)
BTEX (gw):
13,400 Ug/L
Diesel (gw):
7,300 jig/L
TPH (soil):
9,000 mg/L
21,000 mg/L
NA
3,790 mg/kg
40 mg/kg
200 mg/kg
1,100 mg/kg
490 mg/kg
630 mg/kg
2,000 mg/kg
212 mg/kg
4,189 mg/kg
252 mg/kg
1,663 mg/kg
3 1.5 mg/kg
1,238 mg/kg
4,800 mg/kg
8,600 gal
10 to 200 mg/kg
20 to 100 mg/kg
100 to 80,000 mg/kg
1,200 mg/kg
6,000 mg/kg
ND to 40 mg/L
50,000 to
100,000 mg/kg
NA
Concentration After
Treatment
ND to 0.5 mg/kg
ND to 0.5 mg/kg
10 mg/kg
Ongoing
Ongoing
BTEX (gw): ND
Diesel (gw):
<50ng/L
TPH (soil):
9 to 220 mg/L
ND to 215 mg/L
12,799 Ib removed
2,290 mg/kg
2.84 mg/kg
7.2 mg/kg
11 mg/kg
3.2 mg/kg
2.8 mg/kg
2.8 mg/kg
0.88 mg/kg
28 mg/kg
2.3 mg/kg
95 mg/kg
5.4 mg/fcg
636.9 mg/kg
140 mg/kg
1,000 gal
0.47 to 0.82 mg/kg
0.23 to 2.41 mg/kg
52.67 mg/kg
10.77 mg/kg
4.20 mg/kg
ND to 0.05 mg/L
4,500 mg/kg
70,000 Ib removed
Volume
Treated
1,100yd3
20,000yd3
25,000yd3
30,000yd3
10,500yd3
300yd3
890yd3
150,000yd3
44yd3
30yd3
19yd3
56yd3
100,000 yd3
30,000yd3
5,000 yd3
330yd3
30,000yd3
SoilType
Clayey Soil
Clayey Soil
Sandy Till
Glacial Till
Sandy Clay
NA
NA
Layered
Sand/Clay
Silt, Clay,
and Cobbles
Sandy Clays
and Clayey
Sands
Sandy Soil
Sandy Soil
Alluvial Soil
with Silt
Clay and
Gravel
NA
NA
NA
NA
Treatment
Time
18 days
NA
Ongoing
Ongoing
24 weeks
90 days
18 days
730 days
60 days
35 days
13 days
45 days
145 days
Late 1989
to Early
1990
NA
45 days
400 days
3.47
-------
Design Development
of electrodes placed in boreholes in a 9 m (30 ft) wide hexagonal pattern
within the impacted area. Vapors, including steam, were captured, con-
densed, and treated by electrical catalytic oxidation.
The results indicated the range of removal of TCE and PCE from soil to be
93 to 99.7%. The mass removal rate of PCE increased threefold after the treat-
ment zone was heated and dried. Approximately 17,000 L (4,486 gal) of water
were removed as steam from the pilot test site due to drying of the soil.
Thermal Conduction Heating. Thermal conduction heating uses electri-
cal heating elements placed on the surface of the soil or in boreholes to heat
and volatilize VOCs in the soil above the water table. This method is slow
and inefficient in comparison to the other soil heating methods, but it can be
less expensive. The approach would be most applicable to sites with shallow
contamination, low-permeability soils, and VOCs with low boiling points.
Clearly, if a heating element is placed in a potentially explosive atmosphere,
the element must be explosion-proof, and the atmosphere above the soil
must be monitored to ensure safe working conditions. Little documentation
of applications of this technique are currently available.
3.2.4.6 Pneumatic and Hydraulic Soil Fracturing for Clay Soils
Pneumatic and hydraulic fracturing of fine-grained and consolidated sedi-
ments is an offshoot of the oil field production industry where it has been
used successfully to enhance the production of oil extraction or injection
wells. This technique involves the injection of air or liquids (water or slur-
ries) into a formation to create fractures and increase the permeability of the
area surrounding a recovery well. When applied to vapor extraction, this
technique can improve the pneumatic and hydraulic conductivity of sites
where residual VOCs are present in tight clay or silt soils. In some cases, it
may make vapor extraction possible where it otherwise would be ruled out.
!
Compressed air injection requires a sudden, massive volume of air which
is normally supplied by gas cylinders. The gas cylinders are charged by
compressors and can deliver 800 to 1,800 ft3/min at pressures of 500 to
2,000 kPa (approx. 70 to 300 psi). Pneumatic fracturing also requires the
use of open boreholes which later can be completed as extraction wells.
Pneumatic fracturing is a developing technology for enhancing vapor extrac-
tion and, as such, limited performance or cost information is available.
Table 3.4 summarizes the results obtained to date at several sites where
pneumatic fracturing has been applied.
3.48
-------
Table 3.4
Select Examples of Remediation Technologies Enhanced by Pneumatic and Hydraulic Fracturing
Technology
. Pneumatic Fracturing and
SVE with Hot Gas Injection
Pneumatic Fracturing
M and SVE
£>.
O
Pneumatic Fracturing
and DVB
Pneumatic Fractuing
and Fuel Recovery
Pneumatic Fracturing and
In Situ Bioremediation
Pneumatic Fracturing and
In Situ Bioremediation
Pneumatic Fracturing
and SVE
Pneumatic Fracturing
and DVB
Developer or Vendor
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Accutech Remedial
Systems, Inc.
Terra Vac, Inc.
Site Location
Somerville, NJ
Santa Clara, CA
Highland Park, NJ
Oklahoma City, OK
Oklahoma City, OK
Remington, NJ
Coffeyville, KS
New York, NY
Geologic Formation
Type
Shale
Silty clay, sandy
silts, and clays
Shale
Shale and sandstone
Sandy, silty shale,
and clay stone
Shale
Silty clay
Clay soils
Wastes Treated
VOCs, primarily TCE
VOCs, primarily TCE
VOCs, primarily TCE
No. 2 Fuel Oil as
free product
VOCs, primarily
BTEX and TCE
VOCs, primarily TCE
VOCs, primarily TCE
TCE, PCE, BTEX,
and other VOCs
Technology Performance
After Fracturing
• Rate of air flow increased by more
than 600%.
• Rate of TCE mass removal increased
by approximately 675%.
• Rate of air flow increased 3.5 times.
Permeability increased as much as
510 times.
• Rate of TCE mass removal in clay
zones increased as much as
46,000 times.
• TCE mass removal increased
times.
• Rate of recovery of free product
increased by approximately 1,600%.
• Transmissivity increased by
approximately 400%.
• Transmissivity increased by 85%.
• Rate of air flow increased more than
5 times.
• Rate of air flow did not increase
appreciably.
Concentration of VOCs in the
extracted air stream increased
10 times.
§
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Design Development
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fe
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_g
IS
_o
"o
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>, 1
t3 O
0 "S
.5 B
o
3 'O
53 2 TJ
•8{S|
•S«-8i
43 O _,
a s s §
«vo«5
PCE, BTEX,
therVOCs
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'X
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jf
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^
!f
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txo
•§
3
y
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'§w
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« s B s g s s
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primarily
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•a
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•is3
3.50
-------
Hydraulic Fracturing
andSVE
Hydraulic Fracturing
andSVE
Hydraulic Fracturing and
In Situ Bioremediation
Hydraulic Fracturing
j «\rrj
andSVE
Hydraulic Fracturing
j OX 7C
andSVE
Hydraulic Fracturing
and Electroosmosis
Hydraulic Fracturing
andDVE
Hydraulic Fracturing
andDVE
Hydraulic Fracturing
andSVE
University of
Cincinnati
Fuss and O'Neill, Inc.
and FRX Inc.
FRXInc.
FRXInc.
FRXInc.
FRXInc.
Colder Applied
Technologies, Inc.
Frac Rite
Environmental, Ltd.
and Echo-Scan
Corporation
Remediation
Technologies, Inc.
Beaumont, TX
Woodstock, CT
Denver, CO
Lima, OH
Oakfield, ME
Columbus, OH
Atlanta, GA
Alberta, Canada
Bristol, TN
•Clay
Silty clay
Shale and clay
Clay and silty clay
Clay and silty clay
Clay and silty clay
Clay
Clayey silt, silty
sands
Bedrock
Gasoline and
cyclohexane
VOCs, primarily
paint thinner
TPH
Gasoline
Gasoline and
diesel fuel
Unspecified water-
soluble contaminants
Chlorinated solvents
Hydrocarbon
condensate and free-
phase hydrocarbons
TCE
• Rate of recovery of LNAPL
increased 10 times.
• Rate of fluid flow increased as much
as 6 times.
• Reduction of concentrations of TPH
in. soils was approximately 90% in
5 months.
• Rate of fluid flow increased more
than 10 times.
• Rate of fluid flow increased as much
as 10 times.
• Graphite-filled fractures created an
electrical field required to induce
electroosmotic migration of water
and contaminants.
• Average product recovery rate
increased 4 times.
• Hydraulic conductivity increased 10
times and the ROI increased 4 times.
• Volumetric rate of recovery of
condensate increased approximately
7 times.
• Rate of extraction increased by as
much as 6 times.
• Rate of TCE extraction increased by
as much 70 L/min.
Source: US EPA 1997
o
a
1
CO
-------
Design Development
Hydraulic fracturing consists of injecting water or a slurry into a borehole
to create and maintain fractures for air and water movement. The slurry may
consist of sand, guar gum gel, or other materials that can prop open the frac-
ture after it is formed (US EPA 1997). The borehole is constructed with a
hollow-stem auger fitted with a fracturing lance designed especially for this
purpose and is terminated just above the target zone. The fracturing lance
creates a space below the auger casing within which high-pressure water is
injected to form the fracture. Once the fractures are created, a sand slurry
can be injected to create secondary permeability from fissures that form
preferential migration channels.
; i
Fracturing is not recommended for sites where buildings are nearby. The
fracturing pressure must be carefully calculated and controlled to induce
fractures useful to vapor extraction. Therefore, detailed borehole logs that
are representative of the soil column are critical in planning for, and success-
fully executing, a fracturing project. Table 3.4 lists the results obtained at
sites where hydraulic fracturing has been applied to date, and Table 3.5 lists
vendors of this technology (US EPA 1997).
i
i i • •
3.2.4.7 Dual-Phase Vapor Extraction
Modifications to a dual-phase vapor extraction system that can increase
the mass removal rate include drop-tube entrainment, well screen entrain-
ment, and down hole pumping.
j • • i
Drop-Tube Adjustments and Air Bleed Valves. The simplest form of
dual-phase vapor extraction consists of a vertical well screened across the
water table with a drop tube for collection of fluids (Figures 3.8 and 3.9).
Practical experience has shown that entrainment of water in the drop tube
can be sporadic and has been described as a slurping sound, similar to that
created by sucking a cold drink though a straw at the bottom of a glass. In
fact, the term "slurping" has been coined to indicate the process of collecting
liquid and air at the water table interface through a drop tube (US ACE
1995). When NAPL is also collected and the intent is to also provide oxy-
gen for biodegradation, the term bioslurping is applied.
The most common modification to dual-phase systems is adjustment in
the depth of the drop tube. Assuming the applied vacuum and air flow rate is
sufficient to entrain liquids and air, the depth of the drop tube will determine
the relative amounts of liquid and air removed. Depending upon the soil
3,52
-------
Chapter 3
type, the working water table level within the well will typically reach equi-
librium quickly after lowering the drop tube. The working water table can
be maintained at the LNAPL/water interface to minimize formation of a
smear zone, which is typically formed by conventional water table depres-
sion and LNAPL collection systems.
Table 3.5
Select Vendors of Pneumatic and Hydraulic Fracturing Technology0
Name of Vendor
Address
Contact/Phone
Pneumatic Fracturers
Accutech Remedial Systems, Inc.
First Environmental, Inc.
McLaren/Hart Environmental
Engineers, Inc.
Terra Vac, Inc.
Cass Street and Highway 35
Keyport, NJ 07735
90 Riverdale Road
Riverdale, NJ 07457
25 Independence Boulevard
Warren, NJ 07059
92 North Main Street
Windsor, NJ 08561
John Liskowitz
(908) 739-6444
Richard Dorrler
(201) 616-9700
James Mack
(908)647-8111
Loren Martin
(609)371-0070
Hydraulic Fracturers
EMCON
ERM-Southwest, Inc.
Frac Right Environmental, Ltd.
FRXInc.
Fuss and O'Neill, Inc.
Colder Applied Technologies. Inc.
Gregg Drilling and Testing, Inc.
Remediation Technologies, Inc.
3300 North San Fernando Boulevard
Burbank, CA 91504
16300 Katy Freeway, Suite 300
Houston, TX 77094-1609
6 Stanley Place S.W.
Calgary, Alberta
Canada T2S 1B2
P.O. Box 37945
Cincinnati, OH 45222
146 Hartford Road
Manchester, CT 06040
3730 Chamblee Tucker Road
Atlanta, GA 30340
2475 Cerritos Avenue
Signal Hill, CA 90806
23 Old Town Square, Suite 250
Fort Collins, CO 80524
Donald L. Marcus
(818)841-1160
H. Reiff'ert Hedgcoxe
(713) 579-8999
Gordon H. Bures
(403) 620-5533
William W. Slack, Ph.D.
(513)556-2526
David L. Bramley
(203) 646-2469
Grant Hocking
(770) 496-1893
John Gregg
(310)427-6899
Ann Colpitts
(970) 493-3700
"This list is not inclusive of all vendors capable of providing pneumatic and hydraulic fracturing technologies.
Source: US EPA 1997
3.53
-------
Figure 3.8
Schematic of a Dual-Phase Extraction System
Discharge
ps
fc
From Other
Dual-Phase
Extraction Wells
Extracted Vapor
and Groundwater
D
-------
Chapter 3
Figure 3.9
Dual-Phase Drop-Tube Entralnment Extraction Well
Extracted Soil Vapor
and Groundwater to
Extraction Pump and
Air/Water Separator
NAPL
Residual VOC
Contamination
Soil Vapor and Entrained Groundwater
In soil with high hydraulic conductivities, it may be necessary to use a
bleed air line to introduce air at the bottom of the drop tube to initiate air and
liquid flow up the tube. This approach consists of a small-diameter tube,
typically 1.25 cm (1/2 in.) diameter or less, installed along the side of the
3.55
-------
Design Development
drop tube. One end extends to the bottom of the drop tube and the other
exits the top of the wellhead through a sealed opening and is connected to a
valve to the atmosphere. If the bottom end of the drop tube is submerged
and no water is forthcoming with the applied vacuum, the air bleed valve at
the top of the wellhead can be opened, allowing a small amount of air to
enter the well at the bottom of the drop tube. Another method of initiating
air and liquid flow is to raise the drop tube and lower it slowly until flow is
initiated. In some cases, compressed air may be needed to feed the air bleed
valve. This creates an air lift effect and will result in rapid withdrawal of
liquids and lowering of the working water level to the bottom of the drop
tube. After dual-phase flow is initiated and the working water level is near
the bottom of the drop tube, the bleed air valve can usually be closed.
Well Screen Entrainment. In applications of dual-phase extraction to shal-
low soils (less than 7.5 m [25 ft]), drop tubes may not be necessary to achieve
collection of liquids and vapors (US EPA 1997). If smaller diameter wells are
used (5 cm [2 in.] or less) and the air flow rate and vacuum is sufficient, liquids
can be effectively entrained into the air stream for collection and treatment at
the ground surface. This results in a less expensive system and may allow the
use of existing monitoring wells as extraction wells. However, the approach
provides less flexibility and control over air and water recovery rates than the
other methods in this section and so is not a particularly robust design. Cer-
tainly, this approach is not applicable to deeper wells.
To effectively dewater dual-phase extraction wells without drop tubes, it
may be necessary to install an air bleed tube in the well as described in Sec-
tion 3.2.4.7. In this case, the air bleed tube is simply a small-diameter poly-
ethylene tube (1.25 cm [1/2 in.]) with a weight on the end to ensure one end
sinks to the bottom of the well bore. The other end extends to the wellhead
through a sealed hole and into a control valve that can allow entry of ambi-
ent air. To prevent accumulated solids at the bottom of the well bore from
clogging the tube, the tube can be tied onto the top of a piece of steel pipe,
approximately 30 to 60 cm (1 to 2 ft) long, which is capped at the bottom
end and lowered to the bottom of the well bore.
. i | ,
Downhole-Pump Extraction. This modification adds a submersible
pump to the typical vapor extraction well as shown in Figure 3.10. The sub-
mersible pump operates to maintain the water level in the well at a predeter-
mined depth. This depth normally exposes a smear zone to air flow due to
the vacuum applied to the well casing.
3.56
-------
Chapter 3
Figure 3.10
Downhole-Pump Extraction Well
Extracted Groundwater to
Groundwater Treatment
Soil Vapor
-A--
Pump
Extracted Soil
- Vapor to Vapor
Treatment
• Screen
Residual VOC
Contamination
3.57
-------
Design Development
This technique is especially useful at depths exceeding 7.5 m (25 ft),
where the yield of a well exceeds 56.78 L/min (15 gal/min), or where a
smear zone must be exposed to circulating air. As with conventional extrac-
tion wells, the submersible pump must have a separate discharge line and be
placed and controlled such that it will turn off when the water in the well
reaches the working level. The pumping rate and vacuum applied to the
extraction well are adjusted to maximize mass removal in both the liqmd-
and vapor-phase. Variable-speed pumps can be used to match the water
yield of the well. Downhole pumping systems do not result in the rapid
mixing of air and water typical of other dual-phase extraction systems and
they may produce much greater quantities of water than drop-tube systems,
but for high-permeability soils, such systems may be the only way to expose
contaminated soils to vapor extraction air movement.
3.3 Equipment Selection
This section addresses the design of vapor extraction and bioventing wells
and piping. In addition, guidance is provided for selection of the major
pieces of equipment necessary for a successful vapor extraction, dual-phase,
or bioventing project. Refer to Sections 3.9.3 for specifications for wells and
piping systems and to Sections 3.3.1 and 3.5 for information on pre- and
posttreatment equipment, respectively.
•' I .
i • '
3.3.1 Pretreatment Equipment Selection
i ' !
There is relatively little pretreatment equipment required for vapor
extraction/bioventing applications! Required equipment usually in-
cludes air/water separators and particulate filters, each of which is dis-
cussed in this section.
3.3.1.1 Air/Water Separators
Extraction of soil vapor includes both the unintentional and intentional
removal of soil moisture. The soil moisture needs to be removed from the
offgas to (1) protect the blower and (2) facilitate treatment for both
3.58
-------
Chapter 3
vapor- and dissolved-phase contaminants. Regenerative and positive dis-
placement blowers are sensitive to water going through them since water
will result in internal corrosion and affect the seals.
While liquid-ring blowers require water to form a seal, air/water separa-
tion is still required after the blower to treat each medium. In addition, water
recovered from the subsurface may not be suitable for seal formation in a
liquid-ring blower so air/water separation may be required before the blower
in this case.
For many applications, soil moisture is removed unintentionally through
offgas condensation and entrainment of soil moisture. The relative humidity
of soil gas is typically 100%, at least initially in the project. In addition, the
soil gas temperature remains relatively constant if it is being extracted at
least 1.5 m (5 ft) below the ground surface. When the soil gas enters pipes
above ground or near the surface below ground, the temperature may be
colder, and in these cases, moisture condenses from the soil gas. Such con-
densation can be particularly heavy in winter conditions. The amount of
condensation can be estimated through the use of psychometric charts. Typi-
cally, a vapor extraction system may generate as much as tens of gallons per
day of moisture through condensation depending on the initial soil moisture
content, rainfall events, total air flow, and temperature changes.
A vapor extraction system may also intentionally or unintentionally en-
train water if the vapor extraction wells intersect perched water or the water
table. In these instances, the source of the water is not condensation, but
rather soil water pulled into the extraction well screen under the influence of
the system vacuum. At sites with tight soils and high moisture content, it
may be a design objective to apply sufficiently high vacuum that will result
in the removal of soil pore water and even the "slurping" of groundwater to
aid in the recovery of NAPL and to increase the air-filled pore space of the
soil. Whether intentional or unintentional, removing entrained water from
soil can produce a substantial volume of water that needs to be removed with
an air/water separator.
Almost all air/water separators used on vapor extraction/bioventing appli-
cations are centrifugal separators. The air/water enters a tank through a
tangential inlet to create a vortex, and the gas stream is expelled through the
top of the cylinder. This vortex forces water particles to the outside wall
where they settle to the bottom by gravity (US ACE 1995).
3.59
-------
Design Development
1
Design considerations include:
• Amount of Storage Volume Required in the Air/Water Separator—
For separators without automatic liquid removal, the tanks should
be sized to hold the amount of water accumlated over several weeks
to minimize system maintenance requirements.
• Vessel Vacuum Rating — The vessels need to be rated at a
vacuum commensurate with the applied vacuum. In some cases,
vacuum relief valves are installed on the vessels for protection.
• Heat Tracing — Many air/water separators are located outside or
in unheated areas; heat tracing is required to prevent freezing of
the separator water.
• Water Removal Systems—Water removal may be as simple as
shutting down the system and opening a drain to remove water or as
complex as an automatic pumping system that gauges and removes
water from the separator. More complex pumping systems are
typically used for those applications where removal rates may ex-
ceed a hundred gallons per day. When designing automatic pump-
ing systems, engineers need to account for the vacuum in the sepa-
rators against which the pumps will need to work.
• High-level Shutoff— Almost all air/water separators include
high-level alarms that automatically shut off the blower. These
protect the blower from pulling water through them.
• Head Loss Through the Separator.
\
3.3.1.2 Particle Removal
Particulate filters are typically installed between the air/water separator
and the blower inlet. Although the condensate removal system will decrease
the concentrations of airborne paniculate, the removal efficiency may not be
sufficient. High particulate levels may cause operational problems with the
blower, downstream piping, or offgas treatment equipment. Particulate air
filters should be employed to remove airborne particles down to the 1 to 10-
micron range.
Cartridge filters are often used for this application. Filter elements are
manufactured from a wide variety of materials, including pleated paper, felt,
or wire mesh. Felt and wire mesh filters may be washed. The filter is
3.60
-------
Chapter 3
selected based on air flow rate, desired removal efficiency, and pressure
drop. Pressure gauges or a single differential pressure gauge should be in-
. stalled upstream and downstream of the filter. Filters should be changed
when indicated by the pressure differences across the filter.
3.3.2 Well Construction and Field Piping Layout/Trenching
Section 3.8 provides construction details and specifications for vertical
and horizontal vacuum extraction wells, monitoring points, and piping.
3.3.2.1 Well Screen Placement
The main objective in extraction well placement is to induce air to flow
through the zone of contamination. Well screen placements range from
screening the entire unsarurated zone to screening a short interval corre-
sponding to the thickness of a highly contaminated zone. In general, extrac-
tion wells should be screened only within the impacted zone.
If groundwater has been impacted, the greatest concentrations of vapors
will often be found immediately above the water table, especially when free-
floating product is encountered. In this case, the screened sections of the
wells should be placed in proximity to the water table for optimal removal
efficiency (but with some portion of the vent screen extending far enough
above the water table to prevent upwelling or seasonal variations in water
level from occluding the screen). Additionally, the placement of the well
screen deeper in the soil column has been shown, both analytically and em-
pirically, to maximize the radius of influence of a given extraction well
(Shan, Falta, and Javandel 1992). Flow models, such as AIRFLOW,
AIRTEST, or MODFLOW may be used to optimize screen depths.
Passive/active injection wells are similar in construction to extraction
wells (e.g., diameters typically 5 to 10 cm [2 to 4 in.]), but they sometimes
have longer screened intervals. Injection wells should generally be piped so
that they can be used as extraction wells and vice-versa.
Monitoring wells screened in more than one soil stratum may not provide
an accurate indication of the specific soil strata where the contamination is
present. In most cases, vapor monitoring wells can be simple and inexpen-
sive (e.g., 2.5 cm [1 in.] diameter, driven well points). To accurately repre-
sent the VOC concentration in or near the vadose zone impacted area,
3.61
-------
Design Development
monitoring wells with short screened intervals are recommended (e.g., less
than 60 cm [2 ft]). Nested vapor monitoring wells can be effective only if
the annular seal can be proven to be intact.
3.3.2.2 Construction Considerations for Piping Layout
Many site-specific factors need to be considered in designing the location
of the remediation system equipment and the layout of the piping network.
These factors primarily relate to the activities occurring on the property and
the existing structures and features in the vicinity of the area to be
remediated. Within these site-specific constraints, the overall objective of
the layout is to minimize construction costs.
Specific factors that should be considered while designing the placement
of the remediation equipment and piping include:
• location of existing buried and overhead utilities and the electri-
cal power source for the remediation system;
• current plant operations and levels of activity;
• future plant construction plans;
• building lines/right-of-way/zoning requirements;
• proximity to residential areas;
• existing facility structures (buildings, ASTs/USTs, storage
yards, etc.);
i '' ' i '
• aesthetics (e.g., straight paving cuts and patching);
• proximity to sewers, if applicable;
• available pipe fittings (e.g., 12.5-, 45- and 90-degree elbows); and
• surface cover in the area to be remediated (e.g., locating piping in
I '
grassed areas versus paved areas).
Once these factors have been considered, an optimal equipment location
and piping scheme will become apparent.
! :,. I, ,.
3.3.2.3 Pipe Material Selection and Sizing
Selection of an appropriate piping material is an essential design step.
The key considerations include (1) costs, (2) process conditions
3.62
-------
Chapter 3
(e.g., temperature, pressure, freeze/thaw, expected condensate, etc.), (3)
compatibility with process chemicals, and (4) environment in which the
piping will be placed. For vapor extraction systems, polyvinyl chloride
(PVC) is commonly the most economical and effective piping material, ex-
cept where elevated temperatures are expected, such as near the exhaust port
of a vacuum blower.
Once the piping material has been selected and the piping layout has been
identified, it is possible to identify the appropriate piping diameter. Of
course, to complete the pipe sizing analysis, the design flow rates and tem-
perature/pressure conditions through the piping network must also be estab-
lished. Pipe sizes are selected by evaluating friction losses for various pipe
diameters and selecting a pipe diameter that offers an acceptable head loss.
For a system that is to include an individual vapor extraction pipe extending
to each extraction well, a conservatively estimated common diameter can be
established by investigating the frictional losses that occur in the longest
vapor extraction piping run. This simplified approach is as follows:
1. Select the longest piping run (e.g., pipe from furthest extraction
well to the remediation equipment);
2. Calculate the total length of the pipe (horizontal and vertical);
3. Estimate the number of valves and fittings and translate these
numbers to equivalent pipe lengths using various published
tables;
4. Add the equivalent pipe lengths to the total pipe length;
5. If pipe is to process air, convert the design scfm flow rate to acfm
under the design operating temperatures and pressures;
6. Given the total pipe length and the design flow rate, determine
frictional head loss for several pipe diameters by consulting pub-
lished friction loss charts (Figure 3.11) or by direct calculation
(e.g., using the Darcy-Weisback equation);
7. Compare the magnitude of the calculated friction loss for each
pipe diameter to the magnitude of the design vacuum or pressure
condition to be exerted on the subsurface; and
8. Select a pipe diameter that results in frictional losses less than
5% of the design vacuum/pressure.
3.63
-------
Design Development
10,000
9,000
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
900
800
700
600
500
400
Figure 3.11
Friction Loss Chart
(not to scale)
.01 .02.03.04.05 .06.07.08.09.1 .2 .3.4.5.6.7.8.91 2 45678910
Friction Loss (in. of Hg per 100 ft of line with inlet air at 70*F and 14.7 PSIA
A chart like this, drawn to scale, can be used to compute friction losses in a piping system. For example, determine the
friction loss incurred when 70 fP/min flows through a 2 in. pipe, 50 ft long.
Stepl: Intersect 70 fP/min and the sloping line for 2 in. pipe.
Step 2: Drop a vertical from this point of Intersection and read the toss, 100 ft of line. If this chart were to scale, the loss
would be 60 Hg/100 ft.
Step 3: Multiply the loss/100 ft of line by the length of run/160 ft. The loss tor 50 ft, then is:
'„„ /length of run \
601 100ft '-
0.30 in. Hg
Also: Velocity in the line may be read from the negatively sloping lines on the graph, to get 70 ft3/mln through a
2 in. line, the air must travel at a velocity of approximately 3,000 ft/min.
Reproduced courtesy of Spencer Turbine Company (1987)
3,64
-------
Chapter 3
This simplified approach is best applied when piping segments to the
extraction wells do not vary significantly in length and the velocity does not
change significantly between piping segments. If significant variations in
pipe length and/or flow rates are expected between piping segments or where
manifolding of piping of various diameters is involved, the calculation of
friction losses for each individual pipe segment may be necessary.
3.3.3 Blowers (Vacuum Pump) Selection
The blower is a crucial component of a vapor extraction system and its
selection, therefore, must be made after carefully considering the system
requirements. One of the most basic requirements that a blower must meet
is to provide the design system air flow and vacuum while accommodating
frictional losses through piping and other equipment components (e.g., air/
water separator, filters, offgas treatment system, etc.). Other blower consid-
erations include power use, maintenance requirements, flexibility, noise, and
potential as an ignition source. This section identifies a method for deter-
mining the blower system design requirements and various types of blowers
that have been employed.
3.3.3.1 System Curve Development
A blower may only be properly specified for a system once the system
flow and vacuum requirements have been defined. These flow and vacuum
requirements are established during the design based on soil permeability,
extraction configuration, and frictional losses through system components.
The established relationship between applied vacuum and extracted soil
vapor air flow, accounting for all frictional losses, is referred to as the system
curve. A suggested approach to defining these requirements and developing
a system curve that has largely been adapted, with permission, from US ACE
1995, is provided in this section.
The first step in developing the system curve is to define the relationship
between applied vacuum to the soil and the resulting soil vapor yield. This
is commonly determined from a single well during a pilot study by varying
the magnitude of the applied vacuum and measuring the corresponding soil
vapor yield from the well. The single well vacuum/flow relationship is often
directly extrapolated to the number of wells that are to be included in the
extraction system to obtain total system flow at various applied vacuums (the
baseline curve). It should also be noted that the soil vapor yield estimated
3.65
-------
Design Development
with this extrapolation is conservative (high) because it does not account for
the competing effects of multiple wells. Various models have been used to
better predict the soil vapor yield in a multiwell system.
As discussed above, the system curve accounts for all friction losses.
Therefore, during the development of ttie system curve, friction losses in
piping and system components are calculated for a range of flow rates.
These calculated frictional losses are added to the baseline curve in order to
obtain the system curve.
t
The friction losses in the piping are most readily calculated by looking up
unit head losses for various flow rates (in acfm) in published charts as dis-
cussed in Section 3.3.2.3. Equipment iosses are generally obtained from
manufacturers' literature. Components often included in vapor extraction
systems for which head loss estimates for various flow rates would need to
be determined include:
i, • I '•
• particulate filter,
• moisture separator,
i i
i • . i i
• silencer, and
i j
• granular activated carbon.
! ",;'', I i.
The engineer must verify that the flow rates and pressures are within the
operating range of the blower.
I i . . • .. .
Where there are several geological units on-site with air permeabilities
that differ greatly, it may be difficult or inefficient to attempt to balance the
flows to a single blower. It may be worthwhile to design multiple blowers,
configured in parallel. Each blower would have a blower curve that would
match the associated geological unit.
3.3.3.2 Blower Alternatives
The type and size of blower selected for a vapor extraction system should
be based on both the vacuum required to achieve the design vacuum at the
extraction wellheads (including upstream and downstream piping and equip-
ment losses) and the total design flow rate. Five types of blowers are com-
monly considered for vapor extraction/bioventing systems: regenerative
blowers, rotary-lobe blowers, liquid-ring vacuum pumps, centrifugal ex-
hausters, and centrifugal fans.Where the system vacuum requirement is low
but the flow requirement is relatively high, the engineer should investigate
! ' j
! , ' ! ...
3.66
-------
Chapter 3
the use of a centrifugal fan. Centrifugal exhausters are potentially applicable
where the system requires a moderate vacuum coupled with relatively high
air flow rates. Finally, rotary-lobe blowers should be considered for moder-
ate-to-high vacuum/low-to-moderate flow applications, and regenerative
blowers should be evaluated for moderate-to-low vacuum/moderate flow
applications. Schematics of these blowers are presented in Figure 3.12.
Although detailed descriptions of these blower systems are readily avail-
able from manufacturers and suppliers of the equipment, a brief discussion
of the blowers and how they function is provided here (US ACE 1995).
Regenerative Blowers. These blowers are typically employed for vapor
extraction/bioventing applications requiring less than 203 cm (80 in.) of
water vacuum. Regenerative blowers are compact and produce an oil-free
air flow. The principle of operation is as follows: (1) a multistage impeller
creates pressure through the use of centrifugal force, (2) a unit of air enters
the impeller and fills the space between two of the rotating vanes, and (3) the
air is thrust outward toward the casing but then is turned back to another area
of the rotating impeller. This process continues regenerating the pressure
many times until the air reaches the outlet.
Rotary-Lobe Blowers. These blowers are typically used for a medium
range of vacuum levels (roughly 50 to 406 cm [20 to 160 in.] of water).
During operation of these blowers, a pair of matched impellers which rotate
in opposite directions trap a volume of gas at the inlet, and move the gas
around the perimeter to the outlet. Rotation of the impellers is synchronized
by timing gears that are keyed into the shaft. Oil seals are required to avoid
contaminating the air stream with lubricating oil. These seals must be
chemically compatible with site contaminants. When a belt drive is em-
ployed, blower speed may be regulated by changing the diameter of one or
both sheaves or by using a variable-speed motor.
Liquid-Ring Vacuum Pumps. A liquid-ring vacuum pump transfers both
liquid and gas through the pump casing. Centrifugal force acting on the
liquid within the pump causes the liquid to form a ring around the inside of
the casing. Gas is trapped between rotating blades, compressed by the liquid
ring, and forced radially inward toward a central discharge port. After each
revolution, the compressed gas and accompanying liquid are discharged.
Vacuum levels close to absolute vacuum (i.e., absolute pressure equals zero)
can be generated in this manner. These pumps generate a waste stream of liquid
that must be disposed properly. The waste stream can be reduced by recycling
3.67
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Chapter 3
the liquid; however, a cooling system for the liquid stream or adequate volume
of seal water is typically required to avoid overheating the pump.
Centrifugal Fan. A centrifugal fan (such as a squirrel-cage fan) should
be used for relatively high air flow and low-vacuum (less than 76 cm [30 in.]
of water) applications. The impellers of a centrifugal fan are typically
straight and it is the rotation of these blades that thrusts the air to the outside
of the fan casing that allows relatively high volume of air to be processed by
this type of blower.
Centrifugal Exhauster. The centrifugal exhauster is constructed with a
slight curvature to the blower vanes that enables additional pressure to be
developed relative to the centrifugal fan. Its relatively high flow capacity
stems from the high rotation speed of the exhauster impeller.
3.3.3.3 Blower Selection
The blower is selected by comparing candidate blower curves to the sys-
tem curve and the design operating flow/vacuum condition. Where the sys-
tem curve (in light of the design operating condition) consistently falls be-
neath a candidate blower curve, the blower is generally considered adequate
for the application. To ensure that the blower is not significantly oversized
for the system, the design system operating vacuum/flow point should be
below, but close to the blower curve.
Discriminating factors in the selection of a blower include:
• Capital Cost. The engineer should investigate not only the pur-
chase price of a blower system but other important factors includ-
ing the degree of complexity required to integrate such a system
into the design, added equipment or instrumentation require-
ments, and space requirements.
• Operating Cost. The engineer should consider the costs associ-
ated with operating the blower system. Factors to consider in-
clude power consumption, reliability of the blower, and mainte-
nance requirements (e.g., oil changes, belt tensioning,
manufacturer's parts replacement schedule, etc.).
3.69
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Design Development
• Noise. The engineer should consider the possible nuisance
caused by excessive blower noise (see Section 3.3.3.4). Some
blowers require that operators use hearing protection regardless
of whether the blower is equipped with silencers.
„„ r i , • i • / iir
• Flexibility. At the beginning of system operation, higher flows
may be needed, requiring greater blower capacity. But as the
project progresses, the flow rates may decrease as wells are
closed off or as bioventing replaces vapor extraction. For flex-
ibility, the engineer may consider employing a single variable-
speed blower or multiple blowers with good turn-down capabili-
ties. However, the range of speeds on some variable-speed
blowers may be inadequate^ For example, the efficiency of ro-
tary-lobe blowers decreases with changes in speed. Vapor ex-
traction/bioventing systems should also have ambient air intake
valves that (among other things) can regulate flow from the sub-
surface by adjusting the ratio of ambient air to soil vapor while
keeping total flow to the blower relatively constant. This type of
flow adjustment avoids overheating and maintains the blower
within the proper operating range. However, the power require-
ments are not reduced as soil vapor flow rate and contaminant
concentrations in the offgas are reduced, decreasing offgas treat-
ment efficiency.
i
• Potential as an Ignition Source. When there is a possibility that
the extracted soil gas may contain concentrations of vapors ap-
proaching the lower explosive limit, the blower housing, at a
minimum, must be constructed of a nonsparking material. De-
pending on how the blower is coupled to the motor and the loca-
tion of the blower, the engineer may also need to specify that the
motor meet NEMA 7 requirements (approved for operation in a
potentially-explosive atmosphere).
i •
3.3.3.4 Blower Silencers and Acoustics
"
Depending on the size of the blower and the location of the vapor extrac-
tion/bioventing system, inlet and outlet silencers may be necessary to reduce
blower noise. Blowers present two noise problems: (1) pulsation within the
piping system and (2) noise radiation from the blower itself. Pulsation noise
3.70
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Chapter 3
peaks can be severe for large blowers and can result in noise discharges in
the high-decibel range.
Silencers are selected based on flow capacities and noise attenuation
properties. These devices typically contain chambers with noise absorptive
elements. Silencer manufacturers should provide the engineer with an at-
tenuation curve, which is a plot of noise attenuation (decibels) versus fre-
quency (hertz). The objective is to obtain the greatest noise reduction in the
range of sound frequencies emitted by the blower.
Also, if the vapor extraction/bioventing system is located within a build-
ing, shed, or trailer, the acoustical properties of the wall material should be
considered. Tables of absorption coefficients of various building materials
versus frequency are published in architectural acoustics references.
Hearing protection must be addressed in the Site Safety and Health Plan.
Occupational Health and Safety Administration (OSHA) regulations are
applicable to occupational noise exposure. The 8-hour time-weighted aver-
age (TWA) sound level is 85 decibels. The TWA represents an action level
for requiring that workers be provided with hearing protection.
3.3.4 Tanks and Vessels
Pressure vessels and storage tanks must be designed, constructed, tested,
certified, and inspected as noted below (US ACE 1995):
• Atmospheric tanks (0-3.5 kPa [0-0.5 psi]) must be designed to
operate at pressures from atmospheric to 3.5 kPa (0.5 psi).
• As part of implementation of a vapor extraction/bioventing
system, petroleum, hydrocarbon, or flammable product tanks
may be needed to store flammable products. There are some
systems, such as those with liquid-phase carbon and on-site
carbon regeneration, that recover pure product from the vapor
stream. The thermal treatment of offgases often uses a fuel
source, such as propane, which must be stored on-site. Also,
some vapor extraction/bioventing projects may have an asso-
ciated groundwater and/or free-product extraction compo-
nent; thus, free product would be recovered directly from the
subsurface.
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Design Development
• The tanks for storage of hydrocarbon products, especially
flammable products, must be designed, installed, and speci-
fied in accordance with NFPA standards and US EPA reguia-
I j ' i
tions governing UST (underground storage tanks) and AGT
(aboveground storage tanks). In accordance with federal and
local fire codes, tanks containing flammable products must be
located at prescribed distances from buildings, property lines,
and ignition sources.
I
• Storage tanks for vapor extraction/bioventing systems are most
frequently aboveground. If belowground tanks are employed,
they must be double-walled and include leak detection. These
tanks must be designed and constructed in accordance with the
following standards:
UL-142 Shop Fabricated Aboveground Tanks
UL-58 Underground Tanks
UL-80 Oil Burner Fuel Tanks
,j • ;
API-650 Field Erected Tanks
.•
• Tanks storing in excess of 11,000 L (2,900 gal) of VOCs are not
recommended, but if necessary, must be designed in accordance
with 40 CFR Part 60.
j - '
• Low-pressure tanks (3.5-103.5 kPa [0.5-15 psi]) are designed to
operate at pressures above 3.5 kPa (0.5 psi) but not less than
pressures specified in the ASME Boiler and Pressure Code, Sec-
tion Vin, Division 1.
i | . {
3.3.5 Structural Design Considerations
j ,..',•
When determining the design load for a foundation for tanks and vessels,
the stability factor and the results of the soil report should be considered in
the analysis. Uplift, dead loads, live loads, wind, seismic, snow, thermal,
crane, hoist, vehicle, and operating loads should be evaluated as well. Foun-
dation design requires the consideration of underlying soil stability consider-
ations. Some specific guidance is as follows:
• Wind Load. Apply to full projection of all equipment, tanks,
skids, and platforms in accordance with ANSI Standard A58.1 or
local building code if more stringent.
i
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Chapter 3
Seismic Load. Estimate in accordance with ANSI Standard
A58.1 or local building code if more stringent.
Live Load. Consider the combined total weights of all equipment
when full.
Anchorage. Design to resist lateral and uplift forces.
Foundations. Use allowable bearing pressure on concrete of
8,000 kPa (1,200 psi) for design.
3.4 Process Modifications
The vapor extraction and bioventing process can be, and in most cases,
must be modified to accommodate initial system performance. Typical
modifications to the initial design include installation of additional vapor
extraction wells to reflect the distribution of volatile or biodegradable con-
taminant mass determined to be present at the site. As discussed previously,
the number of extraction wells required to be effective on a specific target
area is based initially on pilot test results. However, as the vapor extraction
or bioventing system operates, contaminant mass distribution, soil moisture
content, and biological activity will vary substantially. This necessitates that
the engineer provide for future modifications to the design that may be re-
quired to maintain a maximum mass removal rate over the entire affected
area during the life of the remedial project.
This section focuses on modifications that can be made during the design
phase and improvements to existing systems.
3.4.1 Designing for Operational Flexibility and Expandability
In many cases, minor modifications to a simple vapor extraction system
can have significant impacts on the mass removal rate. If the engineer keeps
this in mind during the design process, then minor process modifications can
be made at minimum cost.
Wells should be designed for maximum flexibility. Providing each well-
head with separate flow measurement and control capabilities facilitates flow
balancing and variation. For sites with large vented intervals, designing
3.73
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Design Development
wells with two or more discrete screened sections allows flow to be targeted
as a function of depth.
In many cases, vapor extraction systems do not perform as expected with
respect to mass removal rate or time to closure. To have a significant impact
on these parameters, additional vapor extraction wells could be required.
After trying variable flow rates, zone operation, etc. without significant in-
1 ,°!l , '' i ' '!„ ' i ',!.„! i1' if! II! i • ' I • »
creases in the mass removal rate, and if a mass of volatile soil contamination
. . :l I .., ' • I" , ''! ' , ; . ) •«».'
is known to still exist (by virtue of soil sampling, consistently high concen-
trations of VOCs in certain wells, or other means), additional wells may be
required to achieve closure goals in a reasonable time frame. Accommodat-
ing additional wells requires that the piping, manifolding, vacuum blower,
and air emissions equipment be specified such that additional air flow and
contaminant vapors can be properly handled by the system. In the case of
dual-phase vapor extraction, additional water piping, manifolding, and
vacuum pump capacity may be needed.
For example, designing a pipe manifold to accommodate additional vapor
extraction wells may add little, if any, additional cost, but would be critical
in allowing the additional air flow should additional wells be needed to ac-
celerate the remediation. Additional "T" fittings and valves (routed to blank
pipe ends) could be added to the main manifold near the vapor extraction
blower intake for additional wells should they be needed in the future.
Additional buried piping will be required to connect new wells to the
vapor extraction system. Labor and equipment for excavation and resurfac-
ing typically comprise the majority of the costs for installing buried piping.
Materials are a relatively minor cost. Therefore, if the engineer specifies
additional (initially unused) buried transmission piping in piping trenches,
the cost of tying into those pipes with additional wells will be minimized.
Typically, additional buried piping is only placed when routing the transmis-
sion piping through zones of significant contaminant mass, not in peripheral
areas. However, if site logistics dictate few transmission routes or if only
limited site characterization data are available to define the contaminant
1 i' ' , , ,1 ' i '' ! , ,,'"',•• "I '; 'i"., i „ .. ii I ' *! •
mass location, then additional buried piping may be an inexpensive insur-
ance policy in the event that additional wells are needed at a later date to
f ! I I- 'I ,'! , „ I ,
achieve closure goals. When power supply and electrical control wiring is
placed in the same trench, separate conduits for power and control wiring are
necessary and the conduits should not be placed less than 12 inches apart.
3.74
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Chapter 3
This approach is particularly applicable to piping beneath buildings, into
remediation equipment buildings, or through existing structures at the site.
For example, the placement of sleeves and pipe stubs in concrete slabs to
accommodate future needs will add little cost during construction compared
to excavation and coring at a later date. This same concept is applicable to
electrical and control wiring conduits, in the event additional power or con-
trol wiring is needed in the future. Whenever empty conduits are installed,
care must be taken to ensure they are sealed to prevent soil, debris, or water
from accumulating in them prior to future use.
Vacuum blower characteristics, (pump vacuum or air flow capacity) may
limit the effectiveness and potential expansion of an existing vapor extrac-
tion system. In this case, the available capacity may be focused on fewer
wells at higher vacuums and lower total flow rates. This may increase the
mass removal rate. If these inexpensive modifications are not successful in
increasing the mass removal rate, additional vacuum or air handling capacity
may be needed. The engineer must consider the blower curve (which relates
the induced vacuum versus the air flow rate) for the existing blower to evalu-
ate the capacity for more air or a higher vacuum condition. The existing
blower or blowers may be able to perform at the flow rate and vacuum con-
dition required for maximum mass removal. If not, a different blower will
be required. For larger systems, several small blowers instead of one very
large blower may provide more operating flexibility.
Clearly, if the air flow rate and quality of vapors changes significantly, the
capacity and adequacy of the existing vapor treatment system must be evalu-
ated and modified to accommodate the changing process flow. In some
cases, the vapor treatment equipment may be eliminated or downsized as the
remedial project progresses, depending upon the air discharge permitting
requirements applicable to the site. However, when evaluating a change in
air treatment capacity, VOC contaminant spike concentrations occurring
after a period of inactivity (1 week to 1 month depending upon the ambient
temperature and the volatility of the contaminant) for each well must be used
to ensure maximum concentrations will be adequately treated.
The use of control valves and the design and placement of manifolds must
accommodate the need to target residual hot spots as the project progresses.
This is particularly important on larger sites where there is a temptation to
manifold several wells into one vapor extraction pipe. With this
3.75
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Design Development
configuration, balancing the air flow among the wells is difficult even with
control valves at each wellhead. This is because each well will produce a
different vapor flow rate at a given valve setting and the flow rate from each
well is also affected by the valve setting at another well on the same mani-
fold. Therefore, the initial design needs to consider how each area of the site
could be targeted at future stages of the project. Where practical, individual
pipes for each vapor extraction well are recommended. Individual pipes also
simplify operations since all the pressure and flow monitoring and gas sam-
pling can be performed in one location.
3.4.2 Pulsing
i ,
Pulsing of vapor extraction wells is another modification that can be used
in the later stages of remediation to reduce offgas treatment costs. Pulsing
involves the periodic application of vacuum to each vapor extraction well.
This may be accomplished by pulsing the entire system with on/off cycles or
by manually or automatically operating control valves for each well or
manifolded-well network. In the late stages of remediation, where diffusion
limits mass removal, pulsing can maximize the contaminant concentration
within the offgas and minimize the duty cycle of the offgas treatment sys-
tem. However, the overall mass removal will always be less in pulsed opera-
"• i " ' ''•;!' '!l , "!:• » ',' I • ,,,i , i •
tion than with a corresponding continuous-flow operation.
On/off pulsing of the entire system creates stress on the motor starter for
the vacuum blower. If this approach is chosen, the motor starter must be
designed for this purpose and be capable of handling high-voltage switching
on a continual basis .
; i
, • » , i ., i
Pulsing may allow the initial selection of a smaller vacuum blower in
terms of air-handling capacity. For example, if a total of 50 vapor extraction
wells comprise the system, but only 5 are pulsed at a time, the blower may
be sized to accommodate up to 5 wells at a time If the necessary automatic
valving is provided for each 5-well group. More importantly, the blower
may be selected for a wider vacuum range than may be needed initially. The
additional cost of valving, especially automatically-operated valves, must be
considered in the decision to include pulsing to improve the overall mass
removal rate.
i
i
Finally, piping, valves, and other components will be exposed to the
stresses of pulsing from a high vacuum to atmospheric pressure multiple
3.76
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Chapter 3
times over the course of the project. Therefore, these components must be
constructed of materials capable of withstanding the stress of pulsing.
3.4.3 Adapting to Nonideal Situations
3.4.3.1 Anisotropy
Anisotropy refers to a difference in hydraulic or pneumatic conductivity
with a change in direction within the subsurface. For example, stratified
clay soils may be present above and below a sandy layer. In this case, air or
water flow would be favored in the horizontal direction (in the sand layer)
and limited in the vertical direction. In such cases, the process of vapor
extraction can be modified to focus on the soil type containing residual con-
taminants in excess of the closure goal. This is effected by adjusting the
screened interval of the extraction wells to intercept only one type of soil or
by using multiple screened intervals in one well that focus vapor extraction
air movement on zones with comparable conductivities.
Where sand or clay lenses are abundant, careful evaluation of the location
of the contamination is needed to account for preferential flow layers. Site
hydrogeology can be used to advantage in some cases. For instance, when
contamination is perched atop a clay lens in a perched water table, dual-
phase vapor extraction may be used in that area to remove a continuing
source of groundwater contamination.
3.4,3.2 Short Circuiting
Short circuiting of air flow patterns around contaminated zones can limit
the effectiveness and lengthen the time to achieve closure goals,, Short cir-
cuiting is caused by anisotropic conditions which are either natural or man
made. Classic examples of man-made anisotropic conditions are buried
utilities, such as storm or sanitary sewers; petroleum, natural gas, or water
pipelines; or cable television, telephone, or electrical wiring. Considering
that the backfill for these buried utilities is typically sand and that compac-
tion of native fill may not be extensive after construction, almost all
remediation sites will have such man-made potential short circuit pathways.
The first step in understanding the potential for, and guarding against,
short circuiting is to prepare several detailed cross sections of the site show-
ing the soil types, buried utilities, and contaminant distribution. Planning for
3.77
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Design Development
vapor extraction well locations and depths must account for the most likely
air flow patterns in response to applied vacuums, or in the case of dual-phase
extraction, the most probable air and water flow patterns.
When a vapor extraction system is designed to effect mass removal in a
shallow soil (less than 3 m [10 ft] deep), short circuiting to the surface may
occur. In this case, a surface cover may enhance vapor penetration into con-
taminated zones and limit short circuiting; to the soil surface. One simple
way to provide a surface cover is to apply 12 to 24 mil polyethylene plastic
sheet covered with a thin layer of sand (less than 10.25 cm [4 in.]); however,
unless the edges of the polyethylene cover are keyed into the soil, the cover
will have little effect on the underlying air flow pathways. Paved areas may
limit short circuiting to the surface, but unless the concrete or asphalt is rela-
tively new and devoid of cracks and other penetrations, significant short
circuiting may still occur.
To confirm short circuiting is not occurring, a gas tracer test can be com-
pleted (US EPA 1996). A conservative (nonreactive) tracer gas, such as
argon or helium is injected at a known rate in one well or drive point within
the contaminant mass (unused vapor extraction or monitoring well) and the
concentration of the tracer gas is measured at a series of points as it moves
through the contaminated area and into a vapor recovery well. If no tracer
gas can be recovered, it is likely that the majority of the air coming into the
recovery well is not coming from the contaminated zone and short circuiting
is occurring. To remedy this situation, new well points (to let in air at strate-
gic points) or new vapor extraction wells (to collect vapors at different
points) may be necessary.
3.5 Posttreatment Processes (Offgas
Handling)
.. i, i , .
3.5.1 Technology Descriptions
As discussed in Section 3.12, the need for offgas treatment and the associ-
ated regulatory requirements vary greatly among sites. Yet, offgas treatment
can account for half of the overall system construction and operation costs.
3.78
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Chapter 3
A vapor extraction/bioventing system engineer can choose from among a
wide variety of offgas treatment technologies. Complicating selection of the
most cost-effective treatment technology is the fact that offgas treatment
concentrations and composition change with time. During the initial period
of remediation offgas concentrations are highest; midway in the remediation
offgas concentrations tend to decrease exponentially; and in the final stage
offgas concentrations are relatively steady. Therefore, a cost-effective tech-
nology for initial conditions may not remain so throughout.
In general, offgas treatment technologies can be classified as one of three
types: physical, thermal, and biological. Physical offgas treatment tech-
nologies are typically based on the adsorption of vapor-phase contaminants
onto a medium or resin. Contaminants are not destroyed (until the adsorp-
tion medium is regenerated) but only transfer phase. Vapor-phase carbon is
the most common of these technologies. Thermal treatment technologies
rely on the thermal oxidation of vapor-phase contaminants. Thermal oxida-
tion (flares), catalytic oxidation, and internal combustion engines are all
variations of basic thermal treatment processes. In direct thermal oxidation,
contaminants are heated until they oxidize. Biological treatment is based on
the biological oxidation of vapor-phase contaminants. Equipment used to
biologically treat vapor-phase contaminants is typically termed a "biofilter".
Transfer of contaminants from one media to another must be considered to
minimize impacts to human health and the environment during remediation.
Cross-media transfer issues have been elaborately covered in a recent US EPA
publication, Best Management Practices (BMPs)for Soil Treatment Technolo-
gies, EPA 530-R-97-007, May 1997.
Table 3.6 presents a comparative summary for various offgas control tech-
nologies. The following paragraphs give a detailed explanation for each of
these treatment technologies (US ACE 1995).
3.5.1.1 Vapor-Phase Carbon
Vapor-phase carbon can remove many classes of organic compounds
including aromatics, aliphatics, and halogenated hydrocarbons. Some VOCs
(such as vinyl chloride) cannot be removed by carbon so the applicability of
3.79
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Design Development
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Chapter 3
carbon should be checked prior to selecting it as a vapor treatment method.
Many vapor extraction systems utilize granular activated carbon in flow-
through reactors. When properly designed, these systems are relatively
simple to operate. Adsorption is due to chemical and physical attractive
forces between liquid or gas-phase molecules and the molecules of the solid
adsorbent. Activated carbon is commonly manufactured from raw materials,
such as wood, coal, coke, peat, and nut shells.
A carbon adsorption design usually includes multiple adsorbers, in which
case the columns are operated either in series or in parallel. The series ar-
rangement is generally operated so that the secondary acts as a backup when
breakthrough occurs on the primary column. When the first column is re-
moved from service, the second column is moved up to the first position, and
the new column (or regenerated column) is installed in the second position.
Carbon vessels must be capable of withstanding the temperatures/pressures
needed to mobilize site contaminants.
Adsorption is normally a reversible process. That is, under suitable con-
ditions, materials that have accumulated in the carbon can be driven off, and
the carbon can be reused. Thermal reactivation is the most widely used re-
generation technique. In vapor extraction systems where carbon usage is
low, on-site regeneration will not be cost-effective, and the spent carbon
should be either disposed or regenerated off-site. For larger, long-term vapor
extraction systems, on-site regeneration should be considered. The decision
to regenerate on-site would be based on a complete life-cycle cost analysis.
The concentration threshold for considering on-site regeneration is typically
between 50 and 500 ppm for a project duration of several years. If possible,
the engineer should estimate the total carbon usage for the life of the project
and compare the carbon cost with the capital and operation and maintenance
cost of the regeneration system. A similar economic analysis could be per-
formed for comparison with catalytic and thermal oxidation.
Carbon becomes less efficient with high relative humidity. Activated
carbon relies on an extensive network of internal pores to provide surface
area for adsorption. Although there is not direct surface attraction, the water
vapor occupies internal pore space due to capillary condensation. A rela-
tively small increase in temperature will improve carbon efficiency by reduc-
ing the relative humidity (as a rule of thumb, a 10°C [18°F] increase in tem-
perature will reduce relative humidity from 100% to below 50%), but a large
3.81
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Design Development
i
detrimental to the carbon efficiency. A heat
lower the temperature.
to
temperature increase would be
exchanger or chiller could be used
3.5.1.2 Adsorption Resins
Adsorption resins are commercially available for use in collection of po-
lar hydrocarbons and solvents that are difficult to collect on granular acti-
vated carbon. While these materials are traditionally used in wastewater
applications, they may be adapted to use on vapor streams. The initial resin
expense can be high, but they are usually regenerated to recover solvents or
other materials, providing an offsetting return and saving on disposal costs.
One advantage of resins over activated carbon is that they can safely handle
acetone ancl other ketones, that decompose exothermically on granular acti-
vated carbon and can ignite the vapor stream.
3.5.1.3 Catalytic Oxidation
Catalytic oxidation is a common means of offgas treatment in vapor ex-
traction systems. The catalyst, often platinum, lowers the activation energy
of the oxidation reaction allowing it to proceed at a lower temperature, usu-
ally between 288 and 371°C (550 and 700"F). The lower combustion tem-
perature results in significant energy savings. Catalyst manufacturers typi-
cally claim 95% conversion of non-methane hydrocarbons. A complete
catalytic oxidation system may include a burner, a heat exchanger, the cata-
lytic reactor, and a stack (see Figure :3.13).
Catalytic oxidation is subject to several limitations. The following con-
taminants are known catalyst deactivators and contribute to shortened cata-
lyst life: lead, mercury, zinc, arsenic, antimony, copper, tin, iron, nickel,
chromium, sulfur, silicone, and phosphorus. Catalytic oxidizers will over-
heat if the fuel content of the vapor extraction air stream is too high. This
should be considered at sites where the vapor levels exceed 10% of the lower
explosive limit. Under favorable conditions, catalysts need to be replaced
approximately every three years.
Recent advances in catalyst technology have resulted in catalysts that are
resistant to halogenated compounds. However, catalytic oxidation of haloge-
nated hydrocarbons generates acidic vapors that require treatment. Conse-
quently, scrubbers are typically installed in such systems. Scrubbers can add
significant capital and operating costs.
3.82
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Chapter 3
Figure 3.13
Schematic of Catalytic Oxidation Unit
Feed
Feed Stream
From Air
Stripper
r
Condensate
Drain
Stack _
Effluent
Fluidized
Catalyst Bed
Preheater
Effluent
Open-Flame
Preheater Fueled
by Natural Gas
3.5.1.4 Thermal Oxidation
Thermal oxidation involves heating the air stream to a temperature high
enough for combustion (Figure 3.14). Thermal oxidizers typically operate
between 900 and 1,600°K. They are generally simpler and more versatile
than catalytic systems because there is no need to be concerned with com-
patibility of the compounds with the catalyst. Thermal units could be used
initially and as long as concentrations remain high. However, they are much
less efficient after concentrations decline because supplemental fuel is re-
quired at low concentrations to maintain the relatively high operating tem-
perature. Thus, in most vapor extraction applications, thermal oxidation is
not economical over the entire life cycle of remediation. Combined thermal/
catalytic oxidation units are available to accommodate changing concentra-
tions in the vapor extraction offgas.
Significant cost savings can be realized by utilizing heat recovery tech-
niques. Primary heat recovery exchanges heat from the air exiting the com-
bustion chamber with the air entering the combustion chamber. Secondary
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Design Development
Figure 3.14
Flaring Process
Exhaust
Waste Gas from
Soil Vapor Extraction
Blower Unit
— >. 1 —
, " - r5"
Igniter v^
-1 ?*"
,
<<{— UV Flame Sensor
1 x
=^~ i 4 o v-
t
Flame
Arrestor
Combustion
Air Blower
Natural Gas
Supplement Fuel
heat recovery uses the heated exhaust to preheat plant air or produce steam. As
with all heat exchange systems, there is a trade-off between heat recovery effi-
ciency and the size, or more precisely the surface area, of the heat exchanger.
A scrubber could be used in a vapor extraction system to control acid gases
generated by thermal or catalytic oxidation. Scrubbers reduce acid gases and
particulate in an ah- steam by transferring these compounds to a circulating
liquid stream. For acid gas control, the pH of the liquid would subsequently be
neutralized. Scrubbers are available in various configurations including venturi,
'• I' !" • I
spray tower, packed-bed, fluidized-bed, and sieve tray.
, : i , : i ,i, . i
A flare unit or even an internal combustion engine are modified forms of
furnace-style oxidation units. Both of these forms of oxidation can process
very rich hydrocarbon streams; they are intended to operate in the explosive
range, although fuel still may be added. Flares are rarely used in vapor ex-
traction/bioventing offgas treatment because the fixed installation costs are
usually high and the influent hydrocarbon concentration is rarely high
enough to justify the fixed installation cost.
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3.5.1.5 Internal Combustion Engines
Internal combustion engines (specifically diesel-fuel-driven engines) have
been marketed to perform both the vacuum pump function and the offgas
treatment. The well(s) is connected to the air inlet of the engine, which op-
erates on a test stand to combust the hydrocarbons from the well. Diesel
engines are used because they are better able to operate on a continuous
basis. This approach offers competitive installation costs but is usually more
difficult to permit and operate because emissions from the engine exhaust
must be monitored, and the engine can be sensitive to abrupt changes in soil
conditions (especially moisture).
3.5.1.6 Condensation
Condensation can sometimes be considered for use if the hydrocarbons
are (1) sufficiently high-boiling to be readily condensable and (2) present in
high concentrations. While some product recovery is possible with this
approach, materials that are readily condensable do not usually volatilize
well at typical soil temperatures. This technology is better suited to applica-
tions where heating is used to increase the hydrocarbon removal rate from
the subsurface.
3.5.1.7 Biofilters
Biofilters have been used for odor control for industrial processes since
1953. An estimated 500 biofilters are currently in service in Europe, and 100
are in service in the United States, mainly for odor abatement. Biofiltration to
reduce hazardous air pollutant emissions is a more recent development of the
1980s (Severin, Shi, and Hayes 1994). Use of biofilters to treat contaminated
air streams, such as vapor extraction offgas, is expanding due to its low cost
relative to other alternatives, such as thermal incineration and carbon adsorption
(Govind et al. 1994; Severin, Shi, and Hayes 1994; Kosky and Neff 1988). A
typical biofilter process is shown in Figure 3.15.
A variety of support media have been used in biofilters including soil,
peat, compost, oyster shells, and pelletized activated carbon. A limitation of
biofilters using these materials is the inability to control biomass buildup
without periodically replacing the filter media. Improved support media are
currently being developed such as ceramic filter material with straight
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Design Development
Figure 3.15
Schematic of Vapor Extraction Offgas Treatment with a Biofilter
passages. Biomass periodically sloughs off from the straight passages, re-
sulting in a self-cleaning medium.
The straight passages within the support medium can also have a car-
bon coating. This helps protect the microorganisms from shock loadings
because high contaminant concentrations will initially adsorb to the
carbon and later desorb when air-phase contaminant concentrations are
low (Govind et al. 1994).
3.6 Process Instrumentation and Controls
3.6.1 Purpose
The most important purpose of instrumentation and controls is safety.
Instrumentation can detect unsafe conditions, shut the system down safely,
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and notify the operator. The health and safety of personnel operating the
system or those nearby is of primary importance. Therefore, the minor cost
of safety monitoring and shutdown alarm devices is mandatory. Emergency
shutdown switches should be easy to find and operate. The engineer must
specify these components and ensure they are installed and function properly
at startup and conduct periodic tests to ensure continued functionality.
Other purposes of instrumentation and controls are to monitor the perfor-
mance of the vapor extraction or bioventing system and to minimize operator
labor and costs. The engineer must ensure that safe operating conditions are
maintained and that the design conditions for each system component (vapor
extraction, bioventing, air treatment or air/water separators, and water treat-
ment equipment) are maintained. Ultimately, the level of instrument sophis-
tication depends on complexity of the process, remoteness of the site, and
how long the system is expected to operate.
3.6.2 Instrumentation Selection
Instrumentation refers to the sensors used to detect a change in conditions
in the field, along piping runs, or at the collection and treatment equipment.
Sensors are categorized as responding to either physical, chemical, biologi-
cal, or thermal inputs.
For a typical vapor extraction or bioventing system, the following sensors
are permanently affixed to the system:
• Physical — air flow sensors, air flow meters, high-level switches
on air/water separator tanks, vacuum gauges, pressure gauges,
vacuum switches, pressure switches, etc.; and
• Thermal — thermistors inside rotating motors or control panels
that shut down motors when thermal overloads occur.
Portable instruments that are typically used to monitor a vapor extraction
or bioventing system are:
• Chemical — portable PIDs, FIDs, lower explosive limit (LEL)
meters, explosimeters, oxygen sensors; and
• Biological — portable oxygen, carbon dioxide sensors, in situ
respirometry equipment.
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Instrument selection must based on the anticipated operating conditions
and ranges (e.g., physical limits for float switches, chemical concentrations,
temperature ranges, etc.) that could exist during operations, available power,
weather conditions (if outside), exposure to water (weather or other pro-
cesses in the equipment room or compound), compatibility with remote
control systems, telemetry systems, etc.
3.6.3 Controls and Alarms
: i i', '" ' I; 'i" • • •
Sensors provide a signal to a control system or directly initiate other ac-
tions. In a simple vapor extraction or bioventiog system, controls will con-
sist of relays that turn equipment, such as blower motors, on or off in re-
sponse to certain conditions. Conditions that should result in system shut-
down include LEL conditions, high water in the air/water separator tank,
vacuum exceeding design conditions, or temperature overload of the blower
motor. System shutdown can also be tied to unauthorized entry into an
equipment enclosure or building.
More sophisticated systems use programmable logic controllers (PLCs)
that replace relay switches and perform the same function, but can be pro-
grammed to provide a wide variety of control functions in response to sensor
input. PLCs are typically more cost-effective than relays when more than 20
relays are needed. Recent advances in PLC technology now enable cost
savings even on simple systems.
If VOC concentrations measured during site characterization, soil
sampling, or pilot testing indicate the potential for VOCs to be present
in excess of the LEL or OSHA threshold limit values (TLV), an LEL
alarm (audible and flashing light) should be installed and tested periodi-
cally to ensure functionality.
• i • i ' • " i •
Another useful alarm function is to monitor for high temperatures in the
' . ;|
exhaust stack, indicating the blower is operating beyond the design range or
rapid vacuum losses, which could indicate a broken pipe. Finally, a simple
and inexpensive smoke detector is recommended for all enclosed equipment
buildings or equipment containers. Containers may create confined spaces
as defined by OSHA, and special portable monitoring or permanent detec-
tors and alarms may be needed to meet OSHA entry requirements.
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Chapter 3
Control functions are related to the system piping and other components
on the piping and instrumentation (P&I) diagram. The P&I diagram is a
crucial part of the design drawing package and shows the interrelationships
and control features of the entire system. Instrumentation is also shown as
well as how the output of the various sensors is used to control equipment,
switches, valves, and other equipment.
3.6.4 Remote System Monitoring/Telemetry
Remote monitoring has been used in industrial settings for years to con-
trol complicated automated processes (i.e., robotics). Recently, several re-
mote system monitoring devices have been developed and used effectively to
monitor remediation system performance from a remote location. Each
device requires a telephone line or cellular phone to advise a remote operator
of a system malfunction. The simplest device can call a pre-programmed
telephone number (or pager number) if a system alarm occurs. Another
simple device can send a fax to a pre-programmed fax number with daily
operational data or immediately in the case of an alarm. The most sophisti-
cated devices can send current sensor data to a remote computer which,
when fitted with the proper software, can provide a visual representation of
system performance. Many of these software-driven systems can also be
used to troubleshoot the system from a remote location. If selected and
installed properly, most of these systems can minimize the day-to-day atten-
tion necessary for safe system operation.
3.7 Safety Requirements
This section presents the basic safety requirements of a vapor extraction
or bioventing system. The requirements presented here are not exhaustive;
they are intended only to provide the engineer with a list of minimum safety
requirements. A process safety review is recommended and may be required
if the system emissions are permitted as stipulated by the Clean Air Act. To
this end, Appendix B includes an example process hazard review form and a
list of guide words to be used to identify possible safety hazards under con-
ceivable operating and nonstandard conditions.
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3.7.1 Designing for Construction Safety
' :; v . • i: , .• , • L- .r . . . -1 ' iv •••;'
The vapor extraction/bioventing system engineer can minimize hazardous
conditions during the construction phase by evaluating the steps necessary
for construction and associated potential hazards. Through good design, the
engineer can eliminate potentially unsafe or difficult assembly procedures
and reduce (1) the time required for construction and (2) the risk of injury to
site workers.
* ''' | ! ' ' ' ., • " *'. ! | - jjn »"'
For example, OSHA regulations stipulate that a poorly-ventilated enclo-
sure, where ingress and egress is limited due to small openings or obstruc-
tions, be considered a "confined space" (40 CFR, Part 129). Confined
spaces can be quite hazardous and require specific permits, and strict, time-
consuming procedures. Therefore, if an engineer increases the size of access
doors, makes below-grade vaults no deeper than 46.75 cm (18 in.), and relo-
cates obstructions to ingress and egress, a confined space will not be created
and a safer system will result.
Trenching for vapor extraction and bioventing systems need not be in-
stalled below the frost line if piping is sloped back toward extraction wells to
facilitate back flushing and gravity drainage of condensate. In extreme cold
conditions, the lines may need to be insulated. Shallower trenches can mini-
mize the potential for caving. Providing sufficient working room in well
vaults to allow access to vapor and flow monitoring points can minimize the
potential for back and hand injuries.
Most regenerative blowers used for vapor extraction generate significant
noise levels. The engineer must consider the decibel rating of each blower
(or other piece of equipment) and persons who may be exposed to the noise.
For example, technicians adjusting the system while it is operating will need
hearing protection, especially when the blower is located inside a contain-
ment building or enclosure. Of particular concern is the noise level of vapor
extraction systems in residential neighborhoods. In some cases, sound insu-
lation may be required to minimize noise pollution.
1 • '•., ' , . i !: ' 11, • I 'i ,(,•• ,, ,. ' 'i ' ;,„,„ • •. '•, , • ", ' ,( ••' ;.,;:';„ , ', ih. ,; \ •"'" * ll'ii'
Planning the sequence of construction and specifying it in the plans and
specifications can minimize site disturbance and, for active sites where other
activities are ongoing, minimize the potential for injuries to site personnel
who are unassociated with the remediation project. Specifying material
storage locations, no smoking areas, and temporary fencing around the con-
struction area will also lessen the potential for injuries.
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j ' ,;;,•" • ' " '•' !, '„,
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3.7.2 Building Code
The Uniform Building Code (UBC) has been developed to regulate the con-
struction of structures in the United States. Many regions, states, counties, and
cities have additions or modifications to the UBC that regulate the construction
of buildings, buried piping, sewer discharge lines, etc. These codes must be
adhered to, as applicable, for vapor extraction and bioventing systems. In fact,
in most locations in the United States, a building permit must be obtained from
the local regulatory authority prior to initiating construction.
With few exceptions, design drawings and supporting structural calcula-
tions must be submitted to the proper building officials for review as part of
the permitting process. Such submittals are in addition to those required by
the environmental regulatory agency. All state laws and most regulatory
authorities require that the design be completed and certified by a profes-
sional engineer, licensed in the state where the project is located and com-
petent in the specific area(s) of expertise of the work shown on the plans
and specifications.
With the increase in number of remediation projects in all parts of the
country, some local building officials have developed regulations and codes
specific to this type of activity. Contacting the local building department
prior to design will save a significant amount of time and money compared
to the seemingly endless iterative process of revisions that may be required if
this simple step is ignored.
3.7.3 Electrical Code
This section has been duplicated from a guide published by US ACE
(1995). The guide establishes the basic requirements of materials, equip-
ment, and installation for electrical systems.
Like all systems included in the design, the basic electrical-related con-
siderations that will affect the overall design must be reviewed at the begin-
ning of the design phase. Electrical system planning should include any
power needs that can be anticipated. In addition to technical arid statutory
needs, the design philosophy must emphasize the following:
• safety of personnel and equipment,
• flexibility for expansion, and
• accessibility for operational and maintenance needs.
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Design Development
The following electrical-related topics should be covered by the design
plans and/or specifications:
• electrical conduits,
• electrical duct runs,
• buried ducts,
• trenching and backfilling procedures,
• overhead power lines,
• lighting fixtures,
• emergency lighting,
• motors,
• system voltage,
• package equipment, and
• electrical heat tracing.
A list of applicable reference codes, standards, and specifications for
electrical systems is included in Appendix B.
3.7.3.1 Area Classifications
The National Eleptrical Code (NEC) stipulates area classifications that are
a crucial part of the electrical design for all vapor extraction, dual-phase, and
bioventing systems. All electrical equipment involved in the vapor extrac-
tion/bioventing system must be selected and installed in accordance with the
requirements of the classifications of the various areas. Depending primarily
on the expected presence of explosive vapors, the areas to be categorized fall
into one of the following NEC classifications:
• Class I, Group D, Division 1;
• Class I, Group D, Division 2; or
• Unclassified.
! 'I I
,,!,,'!, "
All area classifications should consider long-term needs, such as future
changes/modifications that may be made to the system.
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3.7.3.2 Definition of Classified and Unclassified Areas
All control rooms, battery rooms, and switch houses shall be designed as
unclassified areas. Where these rooms are located within, or adjacent to, a
hazardous area, the rooms shall be pressurized in accordance with NFPA
496. All such pressurized rooms shall be provided with means of egress
directly to the outside without passing through the hazardous area. Where
this is not practicable, a suitable single-door system shall be installed. In-
stallation of double airlock-type door systems is discouraged.
Areas shall be physically separated from each other, and classified as Class I,
Division 1; Class I, Division 2; or Unclassified. These classifications are as
defined in the NEC. Unclassified zones shall be maintained at a higher pressure
than Division 2 zones, and Division 2 zones higher than Division 1 zones in
order to prevent hydrocarbon vapors from migrating into areas containing igni-
tion sources. Differential pressure switches with alarms shall be installed be-
tween adjacent fire zones where assurance of a positive differential pressure
between fire zones with different classifications is required.
Classification of an area as Division 1 or Division 2 requires careful con-
sideration of the process equipment in that area, the physical characteristics
of hazardous liquids/gases, the amount of ventilation provided to the area,
and the presence of various equipment, such as piping with valves, fittings,
flanges, and meters. The volume and pressure of the gases or liquids in-
volved in the process should also be considered.
The classification of Class I hazardous locations as Division 1 or Division 2
is not a straightforward task. NFPA has developed a recommended practice
(NFPA 497) that should be followed.
In summary, the distinguishing features of Divisions 1 and 2 and Unclas-
sified areas are as follows:
Class I, Division 1 locations may be distinguished by an affirma-
tive answer to any one of the following questions:
• Is a flammable mixture likely to exist under normal operat-
ing conditions?
• Is a flammable mixture likely to exist frequently because of
maintenance, repairs, or leakage?
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Design Development
• Would a failure of process, storage, or other equipment be
likely to cause an electrical failure simultaneously with the
release of flammable gas or liquid?
• Is the flammable liquid or vapor piping system in an inad-
equately ventilated location, and does the piping system
contain valves, meters, seals, and screwed or flanged fit-
tings that are likely to leak significant volumes in propor-
tion to the enclosed space volume?
• Is the zone below the surrounding elevation or grade such
that flammable liquids or vapors may accumulate?
"' I . ' '" !'"
Class I, Division 2 locations may be distinguished by an affirma-
tive answer to any one of the following questions:
' . i • ' .' .!| i •' i I, ""' ' ,.','. , ', .. .,j :,: '; ,, t " ,'.",,
• Is the flammable liquid or vapor piping system in an inad-
equately ventilated location, and is the piping system (con-
taining valves, meters, seals, and screwed or flanged fit-
tings) not likely to leak?
.| , , , , t i. • ••
• Is the flammable liquid or vapor being handled in an ad-
equately ventilated location, and can liquid or vapor escape
only during abnormal conditions such as failure or rupture
of a gasket or packing?
J "• I. •: '. ; I".. ",
• Is the location adjacent to a Division 1 location, or can
vapor be conducted to the location as through trenches,
pipes, or ducts?
• If positive mechanical ventilation is used, could failure or
abnormal operation of ventilating equipment permit mix-
tures to build up to flammable concentrations?
Outdoor installations, usually consisting of open pipeways, are
adequately ventilated and do not justify a Class I, Division 2 classi-
fication because only a catastrophic failure would result in an explo-
sive concentration of gas or vapor. Jrlowever, each specific case
must be reviewed carefully before a classification is assigned.
; • :.[j, ;;, :; -1 •] •,:'"., • • • , ;
Unclassified locations are defined as follows:
a. Locations that are adequately ventilated (including most
outdoor installations) where flammable substances are
contained in suitable, well-maintained closed piping
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Chapter 3
systems which include only pipe, valves, fittings, and
flanges are considered nonhazardous. Most outdoor open
pipeways are considered nonhazardous. Areas that are not
ventilated, provided the piping system is without valves,
fittings, flanges, or similar appurtenances, are also consid-
ered nonhazardous.
b. Locations containing permanent sources of ignition, such as
fired boilers, pilot lights, equipment with extremely high
surface temperatures (above the ignition point of the gases
in the area) are not deemed hazardous when considering
electrical installations because the electrical equipment
would not be the primary source of ignition.
3.7.3.3 Application of Area Classification
Hazardous locations exist in many areas of a facility where flammable
liquids or gases are processed. All of these locations should be identified
and equipped with appropriate electrical equipment to ensure safety of per-
sonnel and facilities. There are three basic questions to be answered in clas-
sifying a location:
1. Will there be flammable gases or liquids stored, handled, or pro-
cessed within or adjacent to the location?
2. What is the likelihood that a flammable concentration of gases or
vapors will collect in the atmosphere of the location?
3. Once determined to be hazardous, how far could the hazard pos-
sibly extend?
In discussing flammable gas/air mixtures, a knowledge of vapor densities
and liquid volatility is important. Vapor density indicates whether a gas is
heavier or lighter than air. Lighter-than-air gases released in an open area
will often dissipate rapidly because of their low relative density. Classifica-
tion based on heavier-than-air flammable gases is normally conservative
when compared to lighter-than-air gases or vapors.
The likelihood of a release of a sufficient quantity of flammable sub-
stances to form an explosive mixture depends upon the equipment, contain-
ers, and/or piping system containing the gas or liquids. If valves, compres-
sors, pumps, or meters are present, they could leak. The likelihood also
depends upon whether ventilation is available to dissipate the gas or vapors.
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Design Development
j , ;;, , | '. , . | :
The extent of the hazardous area is determined by the presence of walls or
barriers and air currents that may carry the gas or vapors away from the
1, " 'i i
point of release.
•i . . • •
111
3.7.3.4 Ventilation
!" , • j,i ' ' I ,; , I : .
For the purposes of area classification as outlined in this section, the defi-
nition of adequate ventilation is as follows:
a. Open Structures. An adequately-ventilated location is any build-
ing, room, or space that is substantially open and free from ob-
struction to the natural passage of air through it, vertically or
horizontally. Such locations may be roofed over with no walls or
may be closed on one side (Basis: NFPA 497).
b. Enclosed/Partially Enclosed Structures. Adequate ventilation, as
defined in NFPA 30, is that which is sufficient to prevent accu-
mulation of significant quantities of vapor-air mixtures in con-
centrations over one-fourth of the lower flammable limit (LFL).
3.7.4 Designing for Operational Safety
The following process controls and alarms are recommended for all vapor
extraction and bioventing systems. -At'a minimum, the following process
control components are required:
• Pressure/vacuum and flow indicators for each well, of the appro-
priate range for anticipated conditions
• Blower motor thermal overload protection
• Vacuum relief valve or vacuum switch to effect blower shutdown
• Sampling ports before and after air treatment and at each wellhead
, • I: ,„ • -, [ , • , • • , ..
• Pressure and temperature indicators, as well as flow control
valves and pressure relief valves at blower inlet and outlet
• High level switch/alarm for condensate collection system
• Explosimeter — for sites with recently measured LEL levels
greater than 10%
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Chapter 3
• For catalytic or thermal oxidizers:
• automatic burner shutoff
• temperature monitoring and control
• interlock with vapor extraction control system
• UL listed burners and fuel train.
3.7.5 Fire Protection
Fire detection and protection requirements will be dictated by local build-
ing and electrical codes and, if not otherwise stipulated by the NEC. The
engineer must consider the need for, and appropriate placement and
placarding of, fire extinguishers, smoke detectors, sprinkler systems (espe-
cially above or near activated carbon vessels), thermal overload switches for
motors, and other alarms to minimize the risk of fire.
The engineer needs to delineate and classify each area within the equip-
ment building or fenced compound according to NEC provisions.
Following are key topics that the electrical plan and specifications need to
address:
• Fire detection
• A hydrocarbon gas detection system employing primary gas
detectors calibrated for methane and supplemental detectors cali-
brated for propane and heavier gases
• A fire detection system employing thermal, ionization, and ultra-
violet detectors
• Ventilation systems to maintain the specified number of air ex-
changes per hour to prevent buildup of explosive vapors
• Independently-controlled ventilation system and independently-
controlled fire extinguishing system approved for the specific
application. The fire extinguishing system should be designed to
operate both automatically and manually
• All installations should comply with SAPC Design Guide Z501.
Piping components that may eventually leak should not be installed
above electrical equipment. Such components include screwed
fittings (not seal welded), flanged joints, and any type of valve
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Design Development
i; ,!,,„,,,, , ;;,;,
raction treatment systems have sprin-
kler heads inside the carbon vessels for fire protection. A heat
detector may be included to activate the fire suppression system.
Otherwise, a fire department connection may be sufficient to
! ' ' " | i , !: " I , , I ' '" i
allow spraying of water on the carbon
3.8 Drawing and Specification
Development
1 '
" ' '•' • ' '. ••" •:• ' ':' , '' ;,'-' '
The level of detail for design documentation for vapor extraction/
bioventing systems varies widely depending upon contractual arrangements,
site size and complexity, and whether prefabricated systems are used. Given
this wide range of variability, it is the responsibility of the engineer in re-
sponsible charge to ensure that safety and human health precautions are
adequate and that remedial goals can be attained in a cost-efficient manner.
In the past few years, package-type vapor extraction/bioventing systems have
proliferated. The engineer must realize that the design criteria for a package
or skid/containerized vapor extraction system may not be appropriate for a
specific site. It is therefore imperative that the engineer gather and review
the information and data in a set of drawings and specifications as described
in this section.
A complete design package for a vapor extraction or bioventing system
will consist of a drawing set, specifications, vendor cut sheets (for key pieces
of equipment showing blower and/or pump curves), design calculations
(head loss in piping, tank sizing, etc.), pilot test results, and documents
describing current site conditions. An operation, maintenance, and monitor-
ing plan may also be required. The following list of drawings is recom-
mended for all such design projects:
1. Site Plan — shows current site conditions, property boundaries,
ownership, buried utilities, structures, canopies, driveways, sur-
face cover (e.g., concrete, gravel, or asphalt), and all existing
structures. Existing and proposed piping and well locations must
be clearly differentiated. A well schedule, listing all wells on-
site, their current and proposed use, size, materials of
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Chapter 3
construction, depth, screened interval, etc. can eliminate confu-
sion during construction and operation.
2. Well and Piping Construction Details — provides a detailed
cross section of each well with materials and dimensions speci-
fied, well vault details, trench cross sections, piping connections,
other yard details, fencing details, etc.
3. Process and Instrumentation Diagram — presents a schematic
view of the entire process from the wells to the final treated sys-
tem exhaust, including water collection, storage, treatment, and
discharge; valves; instruments; electrical interlocks; alarms; and
switches (level, pressure, vacuum, vacuum relief, etc.).
4. Mechanical Details — includes dimensional details of pipe
manifolds, attachment of vacuum gauges and other instrumenta-
tion, valves, well vaults, monitoring points, and equipment.
5. Electrical Plans — detail the location of the power source, wir-
ing routes, lighting, alarms, outlets, and heaters; and provides
NEC classifications of each area of the equipment enclosure,
ladder logic diagrams for PLC, control panel layout, motor con-
trol panel layout, existing and proposed electrical panels, etc.
6. Building or Equipment Enclosure Plan and Equipment Layout
Plans — show excavation plan, footings, foundation details, slab
details, slab drainage (sump) details, dimensions of building or
enclosure, locations of each piece of equipment, electrical panels,
penetrations (for containers, specify vendor-supplied or field-
built), elevations of outside and inside equipment enclosure,
exhaust stack location, pipe manifolds, interior walls,, etc.
3.8.1 Purpose
Design drawings and specifications are necessary to communicate the
layout, operation, and construction details to a number of people with a wide
degree of knowledge and concerns about the proposed project. These docu-
ments provide the owner with the layout of the system so that local facility
personnel can be prepared for the construction and operational procedures.
The construction contractor needs enough detail to safely build the system as
designed and estimate construction costs. For simple systems, sufficient
specifications may be provided directly on the design drawings. However, a
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Design Development
separate specifications document may be needed for more complex systems.
This ensures that the engineer has considered and included all necessary
components.
Standard specifications have been developed that may be applicable to a
specific site or project. These sets of standard specifications have been created
(and are updated periodically) by various trade and professional organizations
and, in some cases, the federal government. Such specifications include:
1. Construction Specifications Institute — publishes standardized
specifications for all construction trades.
2. Naval Facilities Engineering Command (NAVFAC) and National
Defense Center for Environmental Excellence (NDCEE) Pro-
gram — are developing criteria for the engineering design of
remediation technologies.
3. National Institute of Building Sciences — publishes Construction
Criteria Data Base.
•, , i .
Many times, a vapor extraction or bioventing construction project is di-
vided into several tasks based on the various trades that will be necessary to
complete the project. Similarly, specifications are often organized based on
construction segment as indicated in the following sections.
•• .; v • •':•''•' ; .•. v: ;"i-1'; ; • j ;j;: ':";" \ '„.'••" .' -i'^:;v:'\, '"' , •• >;
3.8.2 Contractual, Financial, and Legal (Insurance)
Requirements ' ' ' '"' ^ ' ' """'^ ' \" ' " ' ' ' " ' '
The design specifications also identify the owner of the facility being
built, in other words, the party ultimately responsible for the health and wel-
fare of the people working in or near the system. The specifications also
must identify the engineer of record (who has supervised the design) and
who will be responsible for the actual construction of the system.
.. • !.-. ;; ':. " -:".!:•;:;' i,' '• •':;' , • " :. i;
3.8.3 Wells, Vaults, Piping, and Equipment
3.8.3.1 Vertical Extraction Wells (US ACE 1995)
Vertical extraction wells can be used for passive or active air injection,
including bioventing vents (Figure 3.16).
5.100
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Chapter 3
Figure 3.16
Vertical Vapor Extraction Well/Monitoring Point Construction Details
(not to scale)
' Airtight Well Cap With
Barbed/Valved Fitting!
Fittings
Surface Completion Varies
1.9-5.1 cm PVC
Casing Flush Threaded
, • -*-
1 Minimum 0.9 1m
Minimum 0.3 m f
1.9-5.1 cm
PVC Well Screen,
10-20 Slot or
Continuous Wrap
(Length Varies)
1\
' -*
Typi
Moni
X
•"„•
A
—
.
IT1M,
L
\
'.'•
.•.
',*
r777. \
*- Cement —
Bentonite Grout
t Bentonite Seal
Filter Pack , 1
0.91-
4 1.52cm
0.61-0.91 cmt
T"
^ Threaded End Plug
Minimum
12.1 cmh-
cal Vacuum
Maximum 30.3 cm
vV
85
'•*•/
•"•*".*•'
'"•".""•"•
i
"•*."•*"
••"."•"••
i
^aLis;
=t=
m
:
=
1 Ground Suiface
i&
S
J^-
.'•'/•'
"•"'••"."•
.**•''•*.'
••$
fAvvVV:'-;-'/-:
t ^1 Minimum
~*l 20.3 cm
Typical SVEW
y 'J?J?T.J.
— 10.2 cm Nominal or Larger
PVC Riser, Schedule 40
*- Cement — Bcntonite Grout
'
«— Bentonite Seal
.^ 10.2 cm Nominal or Larger
PVC Well Screen, 5 20 Slot —
Continuous Wrap (Length Varies)
— Filter Pack
— Threaded End Plug
«— Total Depth (Varies)
K-
ell
Source: US ACE 1995
3.101
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Design Development
1. Standards. Standards for thei materials and installation of extrac-
tion wells have been developed by such organizations as the
ASTM, the American Water Works Association (AWWA), the
American National Standards Institute (ANSI), the National
Sanitation Foundation (NSF), and US EPA. A listing of the perti-
nent standards is provided below:
Well Construction and Materials
ASTM F480
ASTM D1785
ASTM D2241
ASTM D 5092
AWWA A100
NSF 'Standard 14""
US EPA 570/9-75-001
Cement Specifications
ASTM
ASTM
ASTM
C150
D2487
D2488
Thermoplastic Well Casing Pipe
Couplings Made in Standard
Dimension Ratios (SDR),
Schedule 40/80, specification.
Specification for Poly vinyl Chloride
(PVC) Plastic Pipe, Schedules
40, 80, and 120.
I • , . .•.• j .,, .
Specifications for PVC Pressure-Rated
^ipe (SDR-Series).
Practice for Design and Installation of
Ground Water Monitoring Wells in
Aquifers.
| I ;! ;.' ' t, , ;,. ••.'... ' • j
Water wells.
,i) • 1 . • , | , ;; | ;:[||i;. ' ; ( ^,.1, ,. I' .;
Plastics, Piping Components and
Related Materials.
'.
,
Manual of Water Well Construction
I ; • ' ' i
Practices.
Specifications for Portland Cement.
Soil Classification
11 i . i
Classification of Soils for Engineering
Purposes.
Practice foi; Description and
Identification of Soils (Visual-Manual
" I'1! " I " ' i' '•
Procedure).
3.102
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Chapter 3
2. Materials.
a. Casings. New PVC pipe, 100 to 150 mm (4 to 6 in.) in diam-
eter, is normally used for vapor extraction well casing. A
reference to ASTM D 1785 or ASTM F 480 is appropriate.
Larger diameters are preferred to increase flow capacity, but
require larger boreholes. Assess the vacuum drop inside the
well casing and screen diameters based on the pneumatic
analysis procedures used for piping. Casing and screen diam-
eters of 100 mm (4 in.) are adequate for most applications
unless the formation has a high air permeability, and indi-
vidual well extraction rates are high (say 400 scfm or higher),
in which case larger diameters may be appropriate. Other
materials may be specified if contaminants, at expected con-
centrations, are likely to damage PVC. Materials with appro-
priate physical properties and chemical resistance may be
used in place of PVC where economical. Heat-resistant mate-
rials should be used if thermal enhancements to vapor extrac-
tion are applied at the site. PVC casing exposed to sunlight
should be protected or treated to withstand ultraviolet radia-
tion without becoming brittle. The casing must be strong
enough to resist collapse at the expected vacuum levels and
grout pressures. The specifications should require casing with
flush-threaded and O-ring seals. Table 3.7 indicates a range
of acceptable sizes for extraction well materials including
casing.
b. Screen. The well screen is usually PVC with slotted or
continuous-wrap openings. Continuous-wrap screen is
strongly preferred because the increased open area reduces
the pressure drop across the screen and therefore reduces
blower energy costs. Slot size is generally 0.5 mm (0.02
in.) but should be as large as possible to reduce the pres-
sure/vacuum drop across the screen. Slot sizes of 1.01 mm
(0.04 in.) or larger may be used. Larger slots sizes may, in
a few cases, lead to increased entrainment of abrasive par-
ticles in the air flow. If the well will be used to recover
groundwater or other liquids, the slot size must be chosen
based on formation gradations. Screen with flush-threaded
joints and O-ring seals is preferred.
3.103
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Design Development
Table 3.7
Extraction Well Materials
Components
Casting
Screen
Operating Size Ra
Metric
50mm
100mm
ISO mm
SO mm
100mm
150 mm
npe
English
1 ' ,»''' ill'1 ''" 1., V1 !!'.i!: ':i' !'' ,1:1
Comments
'i1'1 / :• Ji1
. ; •„. .' -j .•• ,, ,. ,. . • ,; ' ,
2 in. Sch 40
4 in. Larger diameters should be used
6 in. where vacuum losses inside well
may be high
2 in. Sch 40
4 in. 0.5 mm or larger slots
6 in.
Filter Pack
C,,<;2.5
Refer to Section 3.8.3.1-(2)(c)
t Filter Pack
Piping
Valves (Ball)
Joints (Elbow)
... ,
SO mm
100 mm
150mm
200mm
50mm
100mm
150mm
200mm
50 mm
100mm
150mm
200mm
2 in. Sch 40
4 in.
6 in.
8 in.
2 in. Sch 40
4 in.
6 in.
8 in.
2 in. Sch 40
4 in.
6 in.
Sin.
Source: US ACE 1995
c. Filter Pack. Pack material should be a commercially avail-
able, higher uniform gradation of siliceous sand or gravel
•• '„ " . .( r I
with no contaminants (chemical or physical). A uniformity
coefficient (Cu) of 2.5 or less is recommended. The actual
gradation should generally be based on the formation grain
size and the screen slot size. Coarser material may be used;
hovveyer, coarser gradations may, in a.few cases, lead to
increased entrainment of abrasive, particles in the air flow.
If the well is to be used to recover liquids as well as air, the
filter pack must be sized appropriately.
.,-.'. i ! • , , , • :. .i •>' • • • '|: > . ' .-. • I
d. Seal and Grout. A well seal is necessary to prevent entry of
grout into the filter pack and well screen. Unamended
sodium bentonite, as pellets, granules, or a high-solids
3.1
-------
Chapter 3
bentonite grout, is normally specified for the seal material.
The seal is placed above the water table and thus pellets
and granules must be hydrated. A cement grout is preferred
to fill the annulus above the seal to the ground surface be-
cause it resists desiccation cracking. The mixture of the
grout should be specified and is normally one 42.6 kg (94
Ib) bag of cement (optionally with up to 2.25 kg [5 Ib] of
bentonite powder to further resist cracking), with less than
18 L.(4.75 gal) of clean water. Reference should be made
to ASTM C 150 in the specifications as appropriate.
e. End Caps and Centralizers. Flush-threaded end caps, consis-
tent with the casing and screen in size and material, should be
specified. Centralizers center the well in the borehole and
must be sized appropriately for the casing and borehole. Cen-
tralizers should be made of material that will not lead to gal-
vanic corrosion of the casing. Stainless-steel centralizers are
recommended with PVC or stainless-steel casings.
3. Installation.
a. Drilling Methods. There are many methods for drilling.
Some methods would, however, be less desirable because
of the potential to smear the borehole and plug the unsatur-
ated soils. For example, use of drilling mud should be
prohibited. Hollow-stem auger drilling is most common
and is preferred.
b. Soil Sampling and Logging. Sampling of soils encountered
during drilling increases understanding of the subsurface
and allows better decisions to be made about well construc-
tion including screen placement. Sampling of soils at regu-
lar intervals, at least every 1.5 m (5 ft) is recommended;
sometimes, continuous sampling is appropriate. Samples
should be obtained by an appropriate method, such as split-
spoon sampler or thin-walled tube according to ASTM D
1586 or D 1587, respectively. Sample volume requirements
should be considered when specifying the sampling
method. The sampling for chemical and physical analyses
should be done according to an approved sampling and
analysis plan. It is strongly recommended that a drilling
3.105
-------
Design Development
11 „ • j " | i . .»i , r 'i , /ii : i i> : i1 1.1
log be prepared by a geologist or geotechnical engineer.
Materials encountered should be described according to a"
standard such as ASTM D 2488. In particular, features
relevant to air transmission, such as shrinkage cracks, root
holes, thin sand layers, and moisture content should be
i i
identified.
c. Borehole Diameter and Depth. Normally, the diameter is at
least 101 mm (4 in.) greater than the diameter of the casing
and screen to allow placement of the filter pack. The depth
of the borehole should be based on the screen depth. The
borehole should only extend to 0.3 m (1 ft) below the pro-
jected bottom of the screen.
d. Screen and Casing Placement. Screen and casing should
be joined by flush-threaded joints and suspended in the
center of the borehole. Centralizers should be placed on
|. .' • • ' : ' -.:'• •",; .M '•! • i ' : , „ , :;I,V "M,, ,•, 'i , .1 : . \ . • i,!; I-.,-
the casing at regular intervals if the depth of the well ex-
ceeds some minimum value such as 6 m (20 ft).
e. Filter Pack Placement. The filter pack should be placed
around the screen to some level above the top of the screen,
.. ! I... „. 'I : | . i i I. .. . i
normally about 1 m (3 ft). Filter pack is normally placed
'I i ,' ,.H ] |, h ""l , , ' I'ii >' l!i< ' |,"I IIM ,1 . ''hi '' '' ! ,' I ' ii '' I '
dry by pouring down a tremie pipe. The pipe is used to
prevent bridging of grains in the annulus and is kept near
the top of the pack material during placement. The pack
material should be carefully stored and handled to avoid
contamination from undesirable materials.
!V '• :.; • .j'^'v •.)•••. • ', ' •• • 'jr...
f. Seal and Grout Placement. The grouting of the well is
critical to preventing short circuiting. Normally 1 to 2 m (3
to 6.5 ft) of a bentonite well seal are placed above the filter
pack. The specification should include a requirement for
hydrating the bentonite before placement of the grout. The
specification should require the addition of a volume of
distilled or potable water for every 150 mm (6 in.) lift of
bentonite pellets or granules. The bentonite should hydrate
for at least 1 to 2 hours before placing the grout. This can
be avoided by using a bentonite high-solids grout as the
seal. The high-solids bentonite grout should be placed by
3.106
-------
Chapter 3
tremie pipe. Cement grout should also be pumped into
the annular space via a side-discharge tremie pipe, and
the pipe should be kept submerged in the grout during
grout placement. If the grout is to be placed to a depth
of less than 4.5 m (15 ft), the grout may be poured into
place directly from the surface.
g. Surface Completion. The completion of the wellhead
will depend on the other features of the design, such as
the piping and instrumentation requirements. An appro-
priate "tee" may be placed below or at grade to establish
a connection with buried or aboveground piping, respec-
tively. A vertical extension from the tee to a specified
level will allow attachment of appropriate instrumenta-
tion. If finished above grade, the well may require suit-
able protection, such as bollards, to avoid damage to the
well from traffic, etc. A well vault may be required. If
a surface cover is used, the cover must be sealed around
the well. In colder climates, where frost is a factor,
subsurface vaults and wellheads must be protected from
freezing. For this purpose, electric heat tape is fre-
quently used for wrapping pipes and fittings. In regions
of extreme cold where electric heating is economically
infeasible, extruded styrofoam insulation (which has a
low moisture absorptivity) is placed over the vault.
Frost will not readily penetrate directly below the insu-
lation. Wellhead security is provided by installing
vaults with padlocks. Aboveground wellheads can be
enclosed within steel casings with steel caps, which can
then be locked. In addition to sampling ports in the
extraction manifold, ports should also be located on
individual wellheads in order to differentiate between
various extraction locations. Also, each wellhead
should be fitted with both a vacuum gauge and a shutoff
valve, and possibly, a flow-measuring device if indi-
vidual wellhead flow rates are desired.
h. Surveys. The horizontal coordinates of each well should be
established by survey. The elevation of the top of the cas-
ing, if the well intercepts groundwater, and the water
3.107
-------
Design Development
elevation are of interest. The accuracy of the surveys de-
pends on the project needs, but, generally, it should be to
the nearest 0.3 m (1 ft) for the horizontal coordinates and
the nearest 0.003 m (0.01 ft) for elevation.
•i '•.•.• : .f1:' | ;
Dual Recovery. If groundwater has been impacted, the
same well may be used for vapor and groundwater extrac-
tion. The screened interval should intercept the groundwa-
ter zone as well as the contaminated vadose zone. Ground-
water pumps can be installed to remove the impacted
gfoundwater and also serve to depress the water table. This
will counteract the tendency for groundwater to upwell and
will expose more soil to air wliile a vacuum is being ap-
plied within the well.
3.8.3.2 Soil Gas/Vacuum Monitoring Points
This section provides guidance for design and specification of soil gas/
vacuum monitoring points.
1. Materials. Generally, the same materials can be used for the
monitoring points as for the extraction wells; however, there are
differences in size.
a. Casing. Generally, 20 to 50 mm (3/4 to 2 in.) diameter
PVC pipe is used. Flush-threaded pipe is preferred, but for
smaller diameters, couplings may be needed. Smaller di-
ameter metallic or plastic rigid piping may also be used.
Smaller diameters require less purging prior to sampling.
Flexible tubing can be used as well, but it is not recom-
mended for long-term use.
; . j , „•; . . 1
b. Screen. Either slotted or continuous-wrap screen can be
specified. Slotted pipe is adequate for monitoring ports.
Continuous-wrap screen is not commonly available at the
smaller diameters (less than nominal 50 mm [2 in.] diam-
eter) but can be ordered. Slot sizes smaller than those typi-
cally used for extraction wells may be appropriate for
monitoring points (i.e., 0.25 to 6.50 mm or 0.01 to 0.02 in.
slots). Other "screen" types caiii be used. Options include
3.108
I i';
-------
Chapter 3
slotted drive points, porous points, or, for short-term use,
even open-ended pipe.
c. Filter Pack. Filter pack material should be appropriately
sized for the screen slot width. The pack simply provides
support for the screen and is not critical to monitoring point
function. In some cases, no filter pack will be necessary.
2. Installation.
a. Drilling Methods. Although a hollow-stem auger is still the
primary means of installing monitoring points, direct-push
methods can also be used to place slotted drive points or
other vacuum/soil gas probes at specific depths. Again,
mud or fluid-based drilling methods are not appropriate for
this work.
b. Soil Sampling and Logging. As with vapor extraction/
bioventing wells, it is appropriate to adequately sample the
materials encountered for logging purposes and physical
and chemical testing.
c. Borehole Diameter and Depth. The borehole diameter
should be approximately 101 mm (4 in.) larger than the
screen/casing to allow placement of the filter pack. This
would not apply to points placed by direct-push methods.
Adequate room for proper installation should be allowed if
multiport monitoring systems are to be used. Multiport
monitoring systems are difficult to place and it is often
more time-efficient to drill separate holes for the points at
different depths in a cluster. Monitoring point depth selec-
tion is entirely site dependent, but monitoring of multiple
depths within the vadose zone is recommended. It may be
appropriate to extend the monitoring point into the water
table to monitor water table fluctuations due to seasonal
change or in response to the vapor extraction/bioventing
system or other remedial actions.
d. Screen and Casing Placement. Casing and screen is nor-
mally placed by methods similar to those used to install
vapor extraction/bioventing extraction wells; however,
direct-push techniques are alternatives for quickly placing
3.109
-------
Design Development
monitoring points to the desired depths. The actual means
of placement is dependent on the system, materials used,
and site geology.
e. Filter Pack, Seal, and Grout Placement. The procedures
I | .;..,., , * , . , ..
for sealing the well would generally be the same as those
used for vapor extraction/bioventing wells. Points placed
by direct-push methods may depend on a tight seal with
native soil to prevent leaks. Multiport monitoring systems
require careful placement of seals between the monitored
intervals to prevent "short-circuiting" between the various
; . l • ::, .' • I I' . -;r i, ;• . .... i . • i • ,••:" n; ••• ,i i
intervals.
f. Surface Completion. The monitoring points should be
completed with a suitable barbed/valved sampling port or
septum attached by threaded connection to an appropriate
end cap. The cap should be attached to the top of the cas-
ing by an airtight connection. The points can be set above
grade with suitable protection or below grade, typically in a
flush-mount valve box.
' i . , i .,, ,
i •.'','. r i .•' ,;.. •„• , •• ••• i •. • •• i
g. Surveys. Horizontal coordinates are necessary for each
point, and vertical coordinates to the nearest 0.003 m (0.01
ft) are necessary if monitoring the water levels.
3.8.3.3 Vapor Extraction Trenches
I ' i '• "
Vapor extraction trenches are often used at sites with shallow groundwater or
, ' ' , ! , , , | " ,'" ' ,- | : " • ' .. I1 :•" :: - , - i
near-surface contamination; thus, the depth of excavation is often modest.
Placement of multiple pipes in the same trench, each with a separate screen
interval should be considered if selective extraction from various portions of the
trench is required. The placement of a horizontal recovery system can be ac-
complished by several methods, including normal excavation, trenching ma-
chines (which excavate and place pipe and filter pack in one pass), and horizon-
tal well drilling. Figure 3.17 illustrates a typical horizontal vent well design.
1. Materials. Materials specified for extraction trench construction
, ,„ | i , ' '! „ , | „
are often similar to those specified for vertical wells. Different
materials may be needed if specialized trenching (or drilling/
jacking) methods or machines are used. Differences between
horizontal and vertical applications aire discussed below.
.3.110.
-------
Chapter 3
Figure 3.17
Typical Horizontal Vent Well Design
Protective Soil Cover
Over Geomembrane
Ground Surface
Geotextile
(Optional*)
Geomembrane Surface Cover
(Optional, Extent Varies)
Filter Pack
Bedding Material
Trench
"61 cm (typical) width"
Tie Edge of
Geomembrane to
Clay Filled Trench
Backfill (clay or native soil)
Compacted to * 90%
Optimum Density in 15.2-203 cm lifts
Bentonite Seal
(Optional*)
Screen — PVC, 10.2 cm
Diameter or Larger, 20-40
Slot — Continuous Wrap or Slotted
10.2-20.3 cm — Depth Varies (maintain
sufficient vertical
spacing above water
table to prevent
inundation)
NOT TO SCALE
•Geotextile and behtonite seal may be replaced with geomambrane
Source: US ACE 1995
a. Casing. Although PVC casing is commonly used, flexible
or rigid polyethylene pipe may be more efficient for certain
excavation methods such as trenching machines. The pipe
must resist the crushing pressures of the backfill and com-
paction equipment. Reference should be made to the
3.111
-------
Design Development
where required. PVC pipe is not appropriate for uses involving
high pressures (i.e., many atmospheres) because it cannot safely
withstand the stresses that are imposed. However, since less than
one atmosphere of vacuum or pressure should ever be exerted
with vapor extraction/bioventing, PVC can be used provided
there are appropriate pressure/vacuum relief valves. When using
flexible hpse lines on the vacuum side of the system, the engineer
should be aware that vacuum limits may be far less than pressure
limits.
, : '• . .• , ]: :.':., v| . •'• . , .. \
2. Temperature Limitations. Plastic piping, such as PVC, chlorinated
polyvinyl chloride (CPVC), polypropylene (PPE), or
polyvinylidene fluoride (PVDF), is commonly used for vapor ex-
traction/bioventing systems. Temperature limitations of the material
must not be exceeded. Plastic piping should not be used on the
blower discharge; if the blower overheats, the piping may melt.
. ,; •• i ,j h , , ' •'",,»: .•' «;,- Si.,' >"> - j • , v ' v • . I .>* ;
. ij. , •.!!'.,•• ' , I.. Ill' •• I '.!!• 3 , ' ', • ' ' 1 1 • .' , ..I ' ',' ' 11 I •,
3. Insulation. Insulation and heat tracing can be used to prevent
1 ";, ' ' \- , , ' '.'1 i ••„:, ' - . r ' , "' . i .;:
unwanted condensation in the piping. High-temperature incin-
erator components should be installed to prevent burn hazards.
4. Mechanical Stress. Supports for all piping should have a
nominal diameter of at least 5 cm (2 in.). The supports
should be designed and spaced in accordance with ANSI/MSS
SP-58, -69,-89, and -90.
: ' . i
5. Pneumatics and Hydraulics. The piping system must be sized to
be compatible with the overall pneumatic scheme. In addition to
considering frictional losses, it may be necessary to size the pip-
ing small enough to achieve sufficient velocity to prevent solids
from settling. Velocities greater than 18 m (6 ft) per second are
recommended for pumped condensate lines.
6. Chemical Compatibility. A list of acceptable materials is provided
m Table 126 1 of ANSI B311 Specifically, chlorinated solvents
. '. '-,, II . .|T . . ,M; . ',; ]'• '.It. 7 " ll| . II* , . " ',• , I; I.;
may degrade plastic piping. Piping that will be exposed to sunlight
must be UV resistant or have a UV-protective coating applied.
f. Pipe Slope. All piping shoulcl be sloped to promote drainage of
11 I i" 'i '|i; ' '" • i» IT ' .,. . H | "';'| i • ' n i' , ' . ' I1 ' . i . "
condensate back toward the we,l|l|eaci or to cqndensate collection
points. Low spots are to be avoided in piping runs.
3.T
-------
Chapter 3
3.8.3.5 Valves
In vapor extraction/bioventing systems, valving is used for flow rate and
on/off control. A typical system will have a flow control valve on each ex-
traction or injection line.
1. The valves may be manually controlled or automatically actuated
by an electric or pneumatic power source. Pneumatic actuators tend
to be simpler and less costly than electric actuators, particularly for
explosion-proof applications. However, if a pneumatic power source
is not readily available, an air compressor must be procured, oper-
ated, and maintained. Since vapor extraction/bioventing systems do
not typically have a large number of automated control valves and
electric power is necessary for other components, electrically-actu-
ated valves are frequently employed.
2. Most of the above considerations that apply to piping also apply
to valves. The valves must be chemically compatible with the
liquid or air stream; they must operate safely in the temperature
and pressure range of the system; they must not create excessive
frictional loss when fully opened; and in some situations, they
must be insulated and/or heated to prevent condensation. Also,
the operating range of a control valve must match the flow con-
trol requirements of the application.
3. The control valves must be properly sized. A flow control valve
functions by creating a pressure drop from the valve inlet to outlet.
If the valve is too large, the valve will operate mostly In the almost-
closed position, giving poor sensitivity and control action. If the
valve is sized too small, the upper range of the valve will limit flow.
Formulas and sizing procedures vary with valve manufacturer.
Computations typically involve calculating a capacity factor (Cv),
which depends on the flow rate, specific gravity of the fluid, and
pressure drop. The engineer calculates Cv at the maximum and
minimum required flow rates. The calculated range of Cv values
must fall within the range for the valve selected.
4. During the mechanical layout of the system, care needs to be
taken to ensure that the valves are accessible. They should be
numbered and tagged and referred to by number in the design
and in the operation and maintenance manual.
3.117
-------
Design Development
5. The following is a brief description of several valves commonly
employed for vapor extraction/bioventing systems (Figure 3.18):
! ' ' ! ,'" • ,' I
a. Ball Valve. Used primarily for on/off control and some
throttling applications, the ball valve uses a rotating ball
with a hole through the center to control flow.
I ! |
b. Butterfly Valve. Used for both on/off and throttling applica-
tions, the butterfly valve controls flow with a rotating disk
or vane. This valve has relatively low friction loss in the
fully open position.
I i • ...:•' : . v
c. Diaphragm Valve. A multiturn valve used to control flow in
both clean and dirty services. The diaphragm valve con-
! ,| ",',„ '. / "" | i .,,'• ,i . ' J ' ,], • ,|i,; : ", ' , • ' r. • , .1 ,, • ,M | ,„ i|ir '
trols flow with a flexible diaphragm attached to a compres-
sor and valve stem.
d. Needle Valve. A multiturn valve used for precise flow con-
trol applications in clean services, typically on smaller
diameter piping. Needle valves have relatively high fric-
tional losses in the fully open position.
,1 ,; ;
e. Globe Valve. Used for on/off service and clean throttling
| i • i • ... .•]• j -i •• ,• , il ,• . 'i • • , : ( ff-, ,
applications, this valve controls flow with a convex plug
lowered onto a horizontal seat. Raising the plug off the seat
allows for fluids to flow through.
3.8.3.6 Manifold Systems
A manifold system interconnects the injection or extraction wells into a
single flow network prior to being connected to the remainder of the vapor
extractipn/bioventing system (Figure 3.19). A manifold system will include
a series of flow-control valves, pressure and air flow meters, and VOC sam-
pling ports at each wellhead These devices may be grouped in one central
location for convenience. The manifold system is typically constructed of
PVC, high-density polyethylene (HOPE), or stainless steel.
The manifold system should have a manual air control valve to bleed
fresh air into the vapor extraction/bioventing pump system or reduce vacuum
levels and temperatures within the motor/blower. Air control valves control
the applied vacuum in the subsurface and are used to start the vacuum sys-
tem from a condition of zero applied vacuum. 'fhese valves should be olf a
3.118
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Chapter 3
Figure 3.18
Valve Schematics
Flow
Flow
(a) Ball Valve
(b) Butterfly Valve
Flow
Flow
(c) Diaphragm Valve
(d) Needle Valve
Flow
(e) Globe Valve
Source: US ACE 1995
3.119
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Design Development
performance curves, and design vacuum or pressure and flow rate. Key
pieces of equipment include blowers, vacuum pumps, water pumps, air
filters, control or automatic valves, pressure/vacuum relief valves, silencers,
air and water treatment equipment, and condensate accumulation tanks.
For dual-phase systems, the pump vacuum curve and temperature curve
are critical in planning for adequate seal water flow to prevent overheating.
3.8.5 Electrical
The design of any vapor extraction or bioventing system must comply
with local, state and national electrical codes. Most important in design-
ing a system is the compatibility of the equipment with a potentially
explosive atmosphere created from extracting VOCs from soil as de-
scribed in Section 3.7.3.
3.8.6 Equipment Buildings and Enclosures
Specifications for buildings must include excavation sequence; fate of all
removed materials; responsibility for management of removed materials;
concrete specifications; and foundation and footing design loadings for
wind, snow, weight of equipment or vehicles inside building, etc. Equip-
ment enclosure specifications need to address weight, dimensions, loading
lugs, structural anchoring, penetrations (vendor-supplied or field-built), size
of all openings, locking mechanisms, ventilation openings and blowers (if
package unit), electrical requirements, and controls provided.
3.9 Cost Estimating
This section discusses considerations in
tion/bioventing systems. The strategy and
ing for vapor extraction/bioventing remediation
ACE 1995).
estimating costs of vapor extrac-
general approach to cost estimat-
are presented below (US
3.122
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Chapter 3
3.9.1 Cost Estimating
The four basic levels of cost estimates that can be developed for environ-
mental remediation projects, from least accurate to most accurate, are: (1)
planning, (2) feasibility, (3) preliminary, and (4) detailed. These four esti-
mates are normally completed in sequence as a remediation project
progresses. The level of detail, accuracy, and reliability of the cost estimate
increases as the project life cycle increases from the planning stage to the
design stage. The time and effort to prepare each level of cost estimate also
increases with the level of accuracy desired.
As shown in Table 3.8, the nomenclature for these four remediation cost
estimates parallels the construction and waste management operations indus-
tries. For instance, the detail and reliability of the remediation planning
estimate is roughly equivalent to that of a magnitude estimate in waste man-
agement operations. Similarly, a remediation feasibility cost estimate is
similar to a budget estimate in the construction field.
Table 3.8
Types of Cost Estimates
Level of detail,
accuracy, and
reliability increases
Construction
Planning/Feasibility Study
Budget/Conceptual Design
Preliminary Design
Detailed Design
Environmental Remediation
Planning
Feasibility
Preliminary
Detailed
Waste Management Operations
Magnitude
Preliminary
Performance
Source: DOE 1994
Table 3.9 summarizes the level of accuracy associated with each of the
four basic forms of environmental remediation cost estimates. The planning
estimate is often completed when there are a large number of unknowns and,
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Design Development
therefore, has a relatively low accuracy ranging from -50% to +100%. In
contrast, a detailed estimate is completed once the complete scope of the
remediation work has been identified and the remediation details and com-
plexities are well known and quantified. A detailed estimate provides a
much higher degree of accuracy, normally within +/-25%. Along with each
of these cost estimates, the engineer must document assumptions used in
preparing the estimate, include an assessment of the accuracy of the costs,
arid provide a statement of limitations.
Level o
accura
reliability
>
Env
f detail,
cy, and
increases
(
' «
11 • :; ' '.:, "1 ' • - ' •. • ';> . 'i
Table 3,9
ronmental Remediation Estimates: Characteristics
' • ; I. , .. ' i
,i
Type
Planning
Feasibility
Preliminary
Detailed
Accuracy
-50% to +100%
-30% to +80%
-30% to +70%
+/-25%
Source: DOE 1994
3.9.2 Cost Estimating Procedi
The following steps are typically i
[:, In ."III, ':"" mi 'i |l .1. '' ,l|M ," ,,' Hi i 1 " n "„.' i '" 1, ' . ',l|!l' i,, t
Characteristics
• Large amount of unknowns
• Analogy or parametic method typically used
• Low level of detail
• Takeoffs as basis
• After preliminary assessment is complete
• Site inspection complete
• Unit costs applied to some categories
• Final estimate for assessment and cleanup phase
• All scoping complete
• Details/complexities well known
f '. '"
• j ; !• • •
' ijj'l,
. .*' i, "::,"'" n
i ' i||ii
, '• ' . ;j :„ '• „ . , ,
jres
bllowed when estimating costs.
. , , ,: ,,| , ;
Step 1. Separate Estimate into Categories. Categories of costs in esti-
mates include site work, capital, nonconstruction, operation, maintenance,
and shutdown costs. Proper categorization is essential when using cost ra-
tios; for example, process equipment replacement is often estimated as a
percentage of capital equipment costs, particularly in early stage cost
3.124
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Chapter 3
estimates. The capital equipment cost should not include items such as
earthwork that require little or no equipment replacement.
Step 2. List Cost Components. A list of cost components is prepared
for each category. Components common to vapor extraction/bioventing
remediation are discussed throughout this manual and are listed in Sec-
tion 3.9.4.
Step 3. Obtain Cost Information. Cost information can be obtained from
various cost data sources, including vendor quotes, cost estimating manuals,
previous remediation projects, and literature searches. Experienced cost
engineers maintain files on former price quotes for common components.
Whenever possible, prices should be obtained from several sources. The
engineer must be aware of exactly what is included in unit prices and docu-
ment this information in the estimate.
Step 4. Analyze Cost Data. Cost information is often used to decide
among remediation alternatives. It is also used to make financial decisions
such as whether to lease or purchase equipment. The goal of the estimate
affects the method and level of detail of analysis. A detailed discussion of
finance is beyond the scope of this monograph; however, the engineer should
be familiar with the following terms and concepts:
• net present worth analysis,
• rate of return method,
• capitalized cost method, and
• depreciation methods.
These financial analysis tools should be used for appropriate decision
making. More detailed financial and economic considerations, such as
taxes, future interest rates, and future inflation rates, are typically not consid-
ered in engineering cost estimates for analysis of remediation alternatives.
Step 5. Prepare Assumptions and Limitations. Often, the assumptions
and limitations are as important as the estimate itself. Examples of limita-
tions include:
• estimates based on limited data, such as limited characterization
or design information;
• assumptions regarding the means and method of construction
have been made;
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Design Development
• price fluctuation for materials and abor; and
• unpredictable regulatory decisions,
i ' ' , M | ,fi j .fr"; • ,',,,' : :• I ' "M
A typical list of assumptions will contain information regarding analysis
of site conditions, quantities, project duration, and equipment. Sources of
cost information, such as vendors and cost guides, should be referenced.
3,9.3 Cost Estimating Approaches
'•..,• ', 'i \' •• ..•• (•; • • '. rft11!.. ';..» ] i , '• , •' •• * J • •
The cost engineer must ensure that costs are based on the appropriate
operating vapor extraction/bioventing system. Operating costs can vary
depending on the type and/or configuration of the system. Likewise, the
operating approach to remediation can change the operating cost. If cleanup
is scheduled for a shorter period of time, the system may be larger, with a
higher cost. If cleanup is allowed to take longer, a smaller system that may
operate more efficiently could be used.
: ','" -.,„ '•' i,!, , ,•;, |. iij1 .' , - [ , [ ••• i ',:
11 : ' " : '.'' ""• ' ''"ii- " i :;- f * ' i,1"" ,": ''• '' ' ' ! ..
3.9.4 Cost Estimating dheck isf
A suggested cost estimating checklist is provided below (US ACE 1995).
This list includes most major vapor extraction system cost components and
has been divided into the following six categories: (1) pilot studies, (2) site
work, (3) treatment system capital components, (4) nonconstruction, (5)
annual operation and maintenance, and (6) shutdown. This is a typical list of
cost components for preparing cost estimates for a feasibility study. Esti-
mates for later design stages would likely be more detailed.
PUot Studies
' !
• Equipment rental or lease
• Equipment purchase
• " • j ' | • j
• Equipment assembly
L .' . J 1 I •' '
• Extraction well and piezometer installation
• Drilling
• Materials
• Supervision
• Impermeable liner construction
• Materials
kl26
-------
Chapter 3
• Labor
• Construction equipment and operator
• Mobilization and transportation of equipment
• On-site labor to conduct the pilot study
• Laboratory analysis
• Data validation and interpretation
• Report writing
• Quality assurance project plan
• Health and safety plan
• Contingency plan
• Air monitoring plan
• Groundwater monitoring plan
Site Work
• SVE/bioventing well and piezometer installation
• Drilling
• Materials
• SVE/bioventing trench installation
• Earthmoving equipment and operator
• Sand, gravel, and clean fill
• Geotextile fabric
• Soil disposal
• Site cleaning
• Foundation or pad
• Manholes
• Belowground piping
• Belowground electrical
• Surface cover
• Building construction
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Design Development
3.10 Design Validation
, :'.'.;; • , ,. .-,..•.:;• j ..:} /.':. &,-• ,„, " •...;,|,::" i:
Design validation refers to the ongoing process of checks and improve-
ments that are carried out in the planning, design, construction, startup, and
operational phases. There is inherent uncertainty associated with any sub-
surface design since engineers must interpolate and extrapolate subsurface
site conditions from a very small percentage of "the soil actually observed
and tested during a typical site investigation. The uncertainty for vapor ex-
traction design is compounded because small changes in soil permeability
can dramatically affect system performance. While engineers cannot over-
come the uncertainty, they can incorporate contingencies into the design and
implementation process.
During the conceptual design phase, engineers need to ask what may go
wrong and how site conditions may vary from assumed conditions. During
the preliminary design phase, engineers should develop strategies for assess-
ing changing geologic or contaminant distribution conditions. These strate-
gies may include layout of the monitoring system (piezometers, monitoring
wells, offgas monitoring points) and system flexibility (additional smaller
blowers instead of fewer larger ones, expandable manifolds, easily change-
able offgas treatment options, extra pipes in'trenches, etc.)] Decision trees
should be developed during the preliminary design phase to show how sys-
tem layout or operating parameters can be varied for changing site condi-
tions or if cleanup criteria are not met at compliance points.
During construction, further site knowledge is typically gained through
the installation of additional wells or excavations. Processes need to be in
place enabling (1) additional site information to be collected during con-
struction by the field staff and (2) the engineers to capture that knowledge
and make field changes as needed. For instance, the depth of contamination
may be deeper than first estimated and so the depth of the vapor extraction
wells would need to be modified. Finally, during system operation, the
monitoring plans need to be implemented based" on observed operating data,
with changes in layout or operation as appropriate.
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Chapter 3
3.77 Permitting Requirements
3.11.1 Air Permit Requirements
Most vapor extraction/bioventing systems that discharge contaminants to
the air need an air discharge permit or at least a formal variance from the air
discharge permit requirements. The Clean Air Act, with associated amend-
ments, provides the overall framework for U.S. air regulations. The Clean
Air Act is the basis for National Ambient Air Quality Standards (NAAQS)
and delineation of nonattainment zones where the NAAQS are not being
met. However, at a practical level for vapor extraction/bioventing implemen-
tation, air discharges are regulated at the state level. State laws vary greatly
concerning when permits are required, how they need to be obtained, and
type of compliance monitoring required. Some states may require a formal
air discharge permit for a system, while others may require only a formal
registration of discharge if the discharge levels are below certain thresholds.
A number of states also have streamlined processes for obtaining air dis-
charge permits in conjunction with soil and groundwater remedial activities
and do not require a permit if the engineer agrees to use some type of stan-
dard offgas treatment device (vapor-phase carbon, thermal treatment). Other
states have permit exemptions for limited-duration pilot tests. Finally, coun-
ties or regions within states may also have regulations governing the type of
treatment required, particularly, if such areas happen to be NAAQS
nonattainment areas.
Although states vary as to when permits are required, information com-
monly requested in permit applications is described below. Generally, engi-
neers have most of this information by the time a design is complete.
• Application Forms. Basic information on the site address, per-
mittee information, and dates of installation and operation.
• Process Information. Discussion and depiction of the system pro-
cess, including the offgas treatment system. A piping and instru-
mentation diagram and mechanical drawings are often sufficient.
• Regulatory Discussion. Summary of statutes and regulations
under which the process is to be regulated.
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Design Development
• Control Technology Analysis. Description of how the offgas
control device will control contaminants, if required.
• Emission Summary. Summary of the expected contaminants and
actual and potential emission rates. Actual and potential emission
fates can be difficult to predict if a pilot test has not been completed.
In these cases, the engineer may need to estimate rates based on the
approximate amount of contaminated mass in the soil and provide
some basic site characterization information. Material safety data
sheets may be required for each contaminant.
• Stack Parameters. Discussion of the discharge location and
height. Catalog cuts of the treatment system can provide this
information. The discharge flow rate, temperature, and gas sam-
pling locations may also be required.
! ' . . | | I
• Site Information. U.S. Geological Survey (U.S.G.S) map show-
ing the site and a site plan showing discharge location, property
boundaries, and surrounding off-site buildings and land use.
'' ", '; : " "['I J; ;:"; ' ' ,'| ' ' ' ; ; _ ' , • l! """: "
• Operation and Maintenance Information. Discussion of how the
system is to be operated and maintained.
:"'" ' ' ;' :••. ' ' , ••'"" "••••H'-[:-"' 1 '•'••' :: '• • :[•• ''"
• Receptor Information. Names, addresses, and phone numbers of
adjacent property owners/residents may be required.
Also, some states will require that this infoirmation be submitted by a
professional engineer licensed in the state.
Compliance monitoring requirements for air discharge permits also vary
widely among states. Most states require laboratory analysis of offgas con-
centrations at some specified interval (monthly or quarterly). A common
offgas sampling technique is use of SUMMA canisters — evacuated canis-
ters supplied by a laboratory with one atmosphere of vacuum in the canister.
The vacuum in the canister enables me canister to withdraw its own sample
when the sampling valve is opened. Tlie valve can be adjusted to collect
either an instantaneous or time-weighted sample for analysis. The analysis
Can be a TO-12 method, which analyzes non-methane hydrocarbons to a 1-
ppb detection limit, or a TO-14 analysis, which measures individual VOC
concentrations to a 0.1- to 0.5-ppb detection limit. Other common sampling
methods include TQ-1 and TO-2. In either method, an air sampling gump is
used to draw a predetermined volume of air across an absorbent cartridge
3.132
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Chapter 3
(Tenax for TO-1 and Carbon Molecular Sieve for TO-2). US EPA Method
18 can also be used.
For thermal treatment systems, states may also specify process controls as
part of compliance. For example, a specific residence time and combustion
temperature may be required with routine monitoring of these parameters.
3.11.2 Surface Water Discharge Permit Requirements
Vapor extraction/bioventing systems may generate up to thousands of gal-
lons of wastewater per day. Generation rates depend on the soil geology and
whether active soil water removal is an intentional part of remediation or an
unintended byproduct of soil vapor extraction. For systems generating little
water (tens of gallons per day), the simplest method of water disposal may be
containerization followed by batch discharge into a private or publicly-owned
wastewater treatment plant. In such cases, appropriate authorizations are re-
quired from the owners/operators of the treatment systems. In cases where
hundreds to thousands of gallons of water per day are being generated, the engi-
neer needs to include a continuous method of water disposal. Unless the water
can be continuously discharged to a private wastewater treatment plant, the two
common discharge options are discharge to a surface water body or discharge to
a publicly-owned treatment works (POTW).
The Clean Water Act established a national permit system for wastewater
discharges directly to surface water bodies or indirectly into surface water
bodies via a POTW. Direct discharges to surface water bodies are regulated
by Section 402 of the Clean Water Act, which established the National Pol-
lutant Discharge Elimination System (NPDES). NPDES permits are admin-
istered by US EPA or authorized states. In general, an NPDES permit will:
• provide effluent limitations;
• establish monitoring and reporting requirements;
• establish a compliance schedule; and
• provide other general conditions.
Effluent limits may be based on water quality criteria, which consider the
specific discharge characteristics (flow and quality of discharge, discharge
loading rates, receiving stream flow and quality). The intent is to maintain
national water quality criteria within the receiving stream. Effluent limits
may also be based on technology considerations, .such as what limits a
3.133
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Design Development
liquid-phase carbon or air stripping treatment technology should achieve.
Some states will grant general wastewater treatment permits for discharges
of groundwater that have been contaminated with only petroleum products
and are being treated with a multi-stage liquid phase carbon treatment sys-
tem. The presumption is that the discharge levels of petroleum hydrocarbons
will be below normal analytical detection limits.
Monitoring and reporting requirements will determine the frequency and
type of sampling. For example, weekly sampling during the first several
weeks of discharge may be required, with a shift to monthly effluent sam-
pling after system performance has been established. Monthly discharge
monitoring reports on the results of effluent sampling generally must be
submitted to the regulatory agency.
General conditions of the permit may establish other criteria. For ex-
ample, periodic inspections of the outfall may be required. Some states may
require that the system be maintained by an operator with certification for
the specific treatment technologies being employed at the site. In addition,
the state's prerogative regarding site access, re-opening the permit, require-
ments for other submittals, such as operation and maintenance plans, and
sampling and record keeping requirements are in the general conditions of
the permit.
To obtain an NPDES permit, the engineer needs to submit to the primary
regulatory agency (state or US EPA) the following information:
• information on the owner of the facility and site location;
• a description of the process, including any water treatment pro-
i cesses; i i ' i i '
• a site location map (USGS) and site plan;
• information on the flow rates, contaminant concentrations, and
• . I1 ' • : "t • • !••
receiving water; and
• names and addresses of surrounding property owners/residents.
3.11.3 Discharge Requirements to a POTW
The Clean Water Act also requires that POTWs establish their own pre-
•f •' '' ' ' '• ' "'"* .'i''!fHl'V' "'"' '','( «-* i ,( , ;., ...;,.„ . , ,.,,., .\ ,
treatment requirements for discharge into the wastewater treatment plant.
Most of these prefreatment standards apply to specific industrial activities.
However, some pretreatment standards apply to the discharge of
3.134
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Chapter 3
groundwater, and are based on the discretion of the local POTW ordinances.
Pretreatment standards are designed to protect against the generation of un-
safe vapors in sewers or wastewater treatment plants, protect the basic treat-
ment processes employed by the plant, and help ensure that the plants, in
turn, do not generate sludges or other wastes that cannot be disposed. Pre-
treatment requirements may vary widely depending on the size and type of
POTW. In'addition, depending on the POTW design capacity, some discour-
age the discharge of groundwater into sanitary sewers. If they do accept the
discharge, discharge costs may be in the range of $1 to $2 per thousand gal-
lons, which can add considerable operational cost to a system.
Monitoring parameters for discharges typically include total organics,
specific organic contaminants found at the site, some metals (depending on
the plant), total suspended solids, pH, and flow. Monthly reports with ana-
lytical results may also be required.
3.72 Design Checklist
This section summarizes the activities and considerations discussed in this
chapter in checklist form. While not all activities may relate to a particular
project, the checklist should provide the engineer with an overall list of con-
cerns/activities that should be considered.
Site Investigation/Regulatory Review
• Develop target zones from site investigation report
• Construct cross-sections from soil borings showing target
cleanup zones
• Develop list of potential environmental permits
• Develop preliminary soil cleanup concentrations
• Determine list of chemicals of concern
Design Planning
• Develop overall design objectives, including desired time
frame for remediation
3.135
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Design Development
• Complete conceptual design of treatment system on-site
cross-sections and plan views
• Estimate contaminant mass to be removed/contained
• Identify need for pilot testing based on size and complexity
1:' 'ofsite " '. ".. '
•••• •: ' •••"-!:• •••• •••-.•• "•'•' -i *>.:..• :••! .'-•.- •:•• - • . :! I ;
• Identify pilot test data objectives
!• • • • !••••.. •! ' • I
• Assess need for pilot test and full-scale offgas treatment
' : : ; , • . • !;,:-,:•. • • J ,, • . • ;.. : , • , i
• Identify other factors that will affect design, such as space,
proximity to electrical power source, noise, facility opera-
tions, property, and access constraints
• Determine how the system will be built and relationship
between desinger/contractor/operator
Preliminary Design
!".. ' < • ; |, , I ',! .•(."; | . ' I •:. !
• Complete pilot test work plan
•I1 ' • •.• "• •• ]" V'!"1' ; " 1 •• .•..: "' • •'' ': I ;-.: '•.
• Undertake pilot test
• Interpret pilot test results in terms of initial conceptual
' i.. I1: I " 'ininJ
design; modify conceptual approach as required
• Complete air flow modeling as appropriate to design the
rest of the treatment system (injection/extraction wells)
• Layout aboveground aspects of system — piping runs,
equipment locations, discharge; points
• Estimate total flow and mass removal rate; determine need
for offgas treatment
i, i! • i"1'!' I1 ' •! •,"' •, 11" I' 'i'1'!!1'1:!!" ,v" 1||l|if, • J '•„ '"' '• ' '•'•[. -T
• Evajluate and select appropriate offgas treatment technology
• Begin application for air and water discharge permits
.'. •/ •!!•- • '• "' ...••:-.; - :•". :;*'.. .•: I .', <:.; .-.. ' ...: . •••.:: ! , •.
• Develop a listing of major equipment items and preliminary
sizing of those items
• Complete a piping and instrumentation diagram showing
controls and interconnects
• Consider future modifications that may be required for
the system
3.136
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Chapter 3
• Determine how discharge compliance and eventual soil
cleanup will be demonstrated
• Determine electrical classifications
• Determine how subsurface air flow will be assessed during
full-scale operations
Final Design Activities
• Complete analysis of system vacuum/pressure requirements
with head loss assumptions
• Finalize sizes of blower(s) and other major equipment
• Complete civil construction details and specifications (well,
trench, building foundation details)
• Complete final electrical and instrumentation and control
drawings and specifications
• Complete final architectural drawings for buildings
• Develop construction quality assurance plan, including
system functional and performance testing
• Develop a start-up plan, including samples to be collected
and analyzed
• Develop an operations and maintenance plan for long-term
system operation, including contingency plan for system
modifications as required, reporting requirements, safety,
compliance
• Develop a construction and operation safety plan
• Develop a final cost estimate for construction and operation
• Obtain final air and water discharge permits
3.137
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Chapter 4
IMPLEMENTATION AND OPERATION
OF VAPOR EXTRACTION
The initial phases of implementation include development of a procure-
ment strategy and contract negotiation. Later phases include design, con-
struction, startup, operation, and monitoring of the vapor extraction system.
This chapter discusses these basic project components in the sequence in
which they generally occur.
4.1 Implementation
The key initial activities include identifying the resources needed to
implement the technology, the contracting strategies to be used to secure the
resources, and the form(s) of contracts to be employed. Resources typically
required include engineers and a variety of construction contractors within
multiple specialty and trade disciplines. More information is presented be-
low on the preferred procurement strategies and contracting methods, espe-
cially as they relate to the role of the engineer. Also provided in this section
is a brief overview of the construction of a typical vapor extraction system
and the more common specialty construction disciplines that may be re-
quired to install and operate it.
4.1.1 Contracting Strategies
(,
Two common approaches used to contract the resources to install vapor
extraction systems are (1) the design-build or "turnkey" approach in which a
single contractor designs, builds, constructs (and possibly operates, under a
separate contract) the system; and (2) the conventional phased, design-bid-
construct-operate approach which can involve multiple contractors and engi-
neering firms (Fulton 1995). During the 1980s and early 1990s when fewer
4.1
-------
Implementation and Operation of Vapor Extraction
i ! , ' . I
vendors had experience with vapor extraction, designing and installing such
systems typically followed the conventional phased, design-bid-construct-
operate approach. More recently, with the dramatic increase in the number
of engineering and construction firms with direct experience with the tech-.
nology, there is a growing interest in and use of the turnkey implementation
philosophy and process (Schriener 1995).
Turnkey contractors are generally selected based upon bids received in
response to the owner's preliminary design and performance specifications
package. The turnkey team that is awarded the project is subsequently re-
sponsible for final design, construction, startup and, potentially, operation of
the vapor extraction system. The level of system design and specification
does not need to be nearly as detailed when using the turnkey approach
where a single entity is responsible for both design and construction as com-
pared to that required using the phased implementation approach. In fact,
the design and construction specifications for turnkey projects can almost be
entirely performance-based.
- , • ,...:. i , .1 , . , , ' ),. .
The continuity provided by this contracting strategy can also optimize
project efficiency largely due to the construction manager's involvement in
the project from the start through construction. The other key advantages of
the turnkey approach are that it often shortens the project schedule and
thereby possibly decreases overall project costs. The turnkey approach can
help transfer many of the project risks and much of the management respon-
sibility from the owner to the engineer/builder. This is, in part, due to the
.', HI,
-------
Chapter 4
4.1.2 Contracts
Firms hired to implement vapor extraction systems typically enter into
one or a combination of four basic types of legal contracts with the buyer of
the services. These forms of contracts include:
• lump sum, in which a single payment is provided for the defined
scope of work;
• cost-plus-fixed fee, in which the direct costs of the services pro-
vided are reimbursed and an agreed-upon fee is paid for comple-
tion of the work;
• unit price, in which compensation is based upon agreed-upon
unit costs and the number of units provided;
• time-and-materials, in which compensation is provided based
upon agreed-upon labor rates, the estimated maximum number of
man-hours worked, an project expenses incurred, agreed-upon
handling charges for subcontractors and other direct costs; and
• some combination of various components of one or more of the
four contract forms.
The four contracting options offer a range of tradeoffs between potential
risks and rewards to the seller and the buyer. A buyer generally decides
which type of contract will be employed to govern the installation of the
vapor extraction system and selects the form of contract that provides the
balance of risks and rewards consistent with the project objectives. Nor-
mally, the seller is only in a position to either accept or reject the terms.
However, in many circumstances, particularly during the final stages of pro-
curement, the seller may be successful in proposing an alternate form of
contract that is attractive to both parties in order to close the deal. For ex-
ample, a project may be bid as a time-and-materials, not-to-exceed contract.
During contract negotiations, however, a contractor may offer to perform the
work under a lump-sum arrangement that minimizes the financial risk to the
buyer of the services while increasing the potential reward to the contractor.
Theoretically, the design and specifications for the vapor extraction sys-
tem to be constructed should be sufficiently comprehensive to ensure that the
work would be completed at roughly equivalent costs regardless of the form
of contract employed. However, in reality, as discussed below, the inherent
characteristics of each of the four types of contracts can influence the
4.3
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Implementation and Operation of Vapor Extraction
quality, schedule, and cost of a vapor extraction system installation. This is
particularly true when the installation specifications are more performance-
based than design-based.
4.1.2.1 Lump-Sum
Lump-sum contracts are typically employed when the plans and specifica-
tions for the installation work are sufficiently detailed to allow the prospec-
tive construction firms to precisely project the manpower and materials re-
quired to complete the job. A lump-sum contract requires that, upon satis-
factory completion of an identified scope of work, the contractor be compen-
sated for the fixed dollar amount identified in the contract. The contractor is
awarded the fixed dollar amount regardless of whether more or less money is
expended than originally budgeted for construction. However, the contractor
may be given less than the fixed dollar amount if any set-offs, liquidated
damages, or other penalties are provided for in the contract documents and
assessed. Conversely, the contractor may be awarded more than the fixed
dollar amount if owner-approved work is completed that was not included in
the original scope of work for the lump sum contract. The contractor may
also be compensated for more than the lump-sum figure if the contract con-
tains a financial incentive clause that rewards the contractor for successful
performance.
Lump-sum contracts generally present both a greater financial risk and
potential reward to construction contractors compared with other forms of
contracts. The contractors have little recourse fqr recovery of funds if their
budget estimate is too low or if they forget to include some element of work.
The many unknowns involved with working in the subsurface during the
installation of a vapor extraction system make this type of contract even
riskier to the contractor. For example, a contractor may develop a lump-sum
cost estimate assuming that the pipe trench excavations would proceed rela-
tively quickly through the near-surface soils. However, in reality, the trench-
ing may take twice as long due to the presence of unanticipated boulders,
inclement weather, or other variables not addressed in the contract terms and
conditions.
As a result of the high level of risk to the contractor associated with this
type of contract, risks are typically addressed through contingency factors
added into the project budget. If the work proceeds better than anticipated,
the contractor may benefit by avoiding use of the built-in contingency fund.
4.4
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Chapter 4
While this may result in an inflated price for the work, the owner benefits
from the profit considerations motivating the contractor to complete the
work in the least practicable time.
4.1.2.2 Cost-Plus-Fixed-Fee
The cost-plus-fixed-fee contract is typically employed where the pre-
cise scope of work has yet to be defined. Such could be the case if the
vapor extraction system needs to be installed in an emergency situation
and prior to completion of a formal design. Another example where a
cost-plus-fixed-fee contract may be appropriate is where an experimen-
tal variation of vapor extraction is to be applied and many unknowns are
associated with construction activities. Finally, this contract vehicle
may be appropriate if the vapor extraction system is to be constructed in
a relatively inaccessible area, and the costs for conducting work in such
areas are unknown.
Under the terms of a cost-plus-fixed-fee contract, the owner agrees to
reimburse the contractor for all costs associated with the installation
work and to pay the contractor an agreed-upon fee for the work. How-
ever, the fixed fee afforded to the contractor often does not increase even
if the original work scope is expanded. With this form of contract, the
owner assumes a greater degree of financial risk because no limits on
costs are set. In addition, all scope changes and unknowns are the re-
sponsibility of the owner. Conversely, the contractor has no risk and
little incentive to complete the installation work in a timely manner or at
least cost. However, the contractor may provide a lower bid with this
form of contract due to the reduced risk.
4.1.2.3 Unit Price
A unit-price contract may be used to facilitate construction if the
volume of work cannot be established in advance of construction and
where large quantities of few types of construction are involved. Under
a unit-price contract, the contractor is compensated at an agreed-upon
unit price for the number of specific units delivered. The agreed-upon
unit costs include all of the contractor's labor, equipment, material, sub-
contractor, and overhead costs as well as desired profit. Examples of
construction tasks associated with a vapor extraction system installation
that could be included in a unit-price contracts include vapor extraction
4.5
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Implementation and Operation of
Vapor Extraction
Wells ($/liner foot), trenching ($/linear foot), piping ($/linear foot), soil
disposal ($/ton), paving ($/square foot), and saw cutting ($/linear foot).
The principal advantage to the buyer in a unit-price contract is an in-
creased ability to control and forecast costs. This is due in part because the
number of variables that define the total project cost reduces to one: the
number of units required to complete the work. While unit costs may sim-
plify project cost controls, without a contract ceiling, the financial risk iies
' ," * I j 'j, :, , , in MM ,',', . in ',,-I- i •• in •' ' , . . .••',. ,
mainly with the owner.
The unit-cost contract also inherently provides financial incentive to the
contractor to complete the work as quickly and efficiently as possible. How-
ever, the contractor does not have any incentive to find ways to use fewer
units during construction.
,'" , „ : •. . ii :':: v:,' '. , '.',' I'! ':::,','"''r !; •:•;-, ":,;:, '•• ;:;' • \.. v1''; I;"";:1 /'":"'
Because the volume of work assopiated with the installation of vapor
extraction systems can generally be well defined and because certain ele-
ments of the installation dpnot lend themselves'to the: unit-price concept
(e.g., the purchase and installation of extraction blowers, instrumentation,
controls, and treatment equipment), the unit-price contract is rarely used by
itself in contracts for, these installations. Unit costs are, however, frequently
and effectively incorporated into lump-sum contracts for vapor extraction
construction work. In such a contract, the installation of the extraction and
treatment equipment inside an equipment building may be covered under the
lump-sum portion of the contract, white well installation, trenching, and
piping is addressed by unit costs.
; ,. , ,' j • " ! •.
4.1.2.4 Time and Materials
-i. i ; i i • " it ' "" . M,I!I,!'|II :! vi,1!1 ' •!'-,'I' j •• j; ;,[ • " i V i •, . ., ,: ' | ;,- i
Similar to a cqst-plus-fixed-fee contract, a time-and-materials con-
tract may be employed to govern the installation of a vapor extraction
system if the precise scope of work is poorly defined. Under a time-
and-materials contract,, the contractor is compensated for the labor hours
expended, the materials used, and the subcontractors employed to ac-
, , 1 i , i , * •' ,,
complish a scope of work. Agreed-upon labor rates and handling charges
for subcontractors and other direct costs are employed to determine the
compensation due the contractor.
Time-and-materials contracting is often employed where implementation of
vapor extraction is being completed using the turnkey approach. For example,
an architectural/engineering firm may be hired on a time-and-materials basis to
4.6
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Chapter 4
design and manage the construction, startup, and operation of a vapor extraction
system.
The advantage of this form of contracting to the buyer and the supplier of
the services is the relative flexibility in modifying the scope of work to be
performed. Generally, this form of contract does put the buyer of the ser-
vices at greater financial risk; however, the contract typically includes a not-
to-exceed stipulation that is specifically intended to reduce this risk. The
not-to-exceed condition in time-and-materials contracts can also provide
incentive to the contractor to complete the work in a timely manner.
4.1.3 Role of the Engineer
The level of engineering needed to install and operate a vapor extrac-
tion system can vary significantly, depending on the construction ap-
proach taken (i.e., turnkey or design-bid-construct-operate). Typically,
the engineer's involvement is greatest with the turnkey approach where
the engineer is normally involved with the project from design through
construction and operation. In contrast, where the conventional phased
implementation strategy is employed, the engineer may be involved with
only select project phases. For example, in cases where the system is
designed by the owner, the engineer may only be hired specifically for
construction management.
The possible extent of engineering involvement in a turnkey project is
discussed in this section. Given that engineers can also be retained un-
der the conventional phased scenario to perform one or more of these
services, emphasis has been placed on four of these component engi-
neering roles, namely, design engineer, construction manager, construc-
tion overseer, and operator.
4.1.3.1 Design Engineer
The design engineer is typically tasked with taking the preliminary vapor
extraction system design provided by the owner to the final design stage to
enable full-scale construction. Usually, this entails going from the 30%
design level to 100% (Middleton 1995). While the hand-off of the project to
the turnkey team at the 30% design level is typical, it is not uncommon for
the hand-off to occur with a preliminary design package significantly less
4.7
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Implementation and Operation of Vapor Extraction
complete, for example, the owner may supply only site assessment data,
vapor extraction pilot study data, and basic remedial objectives.
, i - I' •„ « „,, . , '':,, i, ...
The preliminary design provided to the turnkey engineer usually includes
information on the number, location, and constructipn specifications of ex-
traction wells/trenches. It also includes data on vapor extraction rates and
applied vacuums designed for each well. Estimates of expected VOC con-
centrations in extracted soil gas and data on vapor treatment efficiency re-
quirements are provided. A preliminary piping and instrumentation diagram
is usually provided to schematically illustrate the process flow and basic
control logic. Finally, a site layout showing the proposed location of the
vapor extraction system equipment relative to boundaries, buildings, and
other key features will normally be included.
! ' \ "{
One of the foremost design tasks of the turnkey engineer is to work with
vendors and suppliers to translate the performance specifications provided into
specific equipment requirements. This work element encompasses the full
range of equipment requirements for the system from identifying the make,
materials, electrical rating, and model number of the vapor extraction blower(s)
to determining the actual flow sensors and associated soil gas sampling ports of
the equipment to be ordered. On-site availability of electrical service and other
utility availability (e.g., natural gas for thermal oxidation), as well as material
compatibility analysis, electrical classification, equipment lead-time estimates,
value engineering, and other factors all play an important part in the final selec-
tion of performance-based equipment. Once the electrical system components
are identified, the engineer typically develops the electrical schematics that
illustrate the system power requirements and control system enabling the sys-
tem to be safely operated and maintained.
The design engineer is also tasked with translating the performance-
based specifications into site-specific construction plans and specifica-
tions. These details are developed by the engineer with the active in-
volvement of construction personnel or contractor members of the turn-
key team and through owner and tenant interviews, utility mark-outs,
reviews of facility layout and grade, identification of health and safety
issues, and constructability analysis.
,,• Si"'
4.8
: 'C, ;:
IM «
I: • v
i' " Hi'1 1 I''*1" I"!
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Chapter 4
Plans and specifications developed by the design engineer for a typical
system include the optimum routing of piping from:
• each of the extraction wellheads to the building or structure
where the major equipment components will be housed; and
• the equipment building to the nearest electrical power source and
other necessary utilities (e.g., telephone, natural gas, storm/sani-
tary sewer, etc.).
Wellhead and trenching completion details are also typically developed
by the design engineer with feedback from the construction manager to en-
sure access to the wells while protecting the piping from surface loads (i.e.,
vehicle traffic). Finally, the design engineer typically provides plans for any
equipment buildings and foundations. The design and specification package
is subsequently employed by the engineer to competitively procure the ser-
vices of the constructor(s).
Once the extraction system design has been peer reviewed, reaches the 100%
level, and has been successfully employed to develop construction specifica-
tions to contract the constructor(s), the design engineer's role changes from
engineer to construction manager. The responsibilities of the design engineer in
this capacity are similar, if not identical, to those described below for the engi-
neer hired for the specific task of construction management under the design-
bid-construct-operate approach.
4.1.3.2 Construction Manager
Construction management is an essential task in most construction
projects. While this work element may be one of many that the turnkey
engineer is tasked to perform, an engineer may specifically be contracted to
perform construction management services under the design-bicl-construct-
operate approach. However, regardless of whether construction management
is included in a larger scope of work (turnkey) or whether construction man-
agement is the engineer's only assignment, responsibilities of the engineer as
a construction manager are essentially the same.
General activities associated with the installation of a vapor extraction
system for which the construction manager may be responsible include:
• project management;
• health and safety;
4.9
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1. •
Implementation and Operation of Vapor Extraction
• partitioning of work into subcontract specialties;
. ' • ' ' ' ""-:":;; • •''•" '• '••• ' :' ' M : "i"'- '• '"' \ • • ':'•' ' •••
• permit acquisition;
• subcontractor procurement/management;
• equipment procurement;
• construction quality assurance;
• , i • „ ' • !
• as-built documentation;
:" /' .':"" " .' i1:.":':: r:".. ' ', " i1 i
• field design change authorization;
• field testing (slump, compaction, hydraulic/pneumatic, equip-
ment assembly, start-up diagnostics, etc.);
• documentation (manpower, materials, etc);
• regulator, client, and tenant liaison; and
; ' . l> ' ' I - i' . • . ," .' L i. ,',;>' " . ' i ' ' " • I "
• communication with the owner.
. • • ," • :, J..J '.:, . •:, . , "' ' A *>.! : !':''.,;!""' : ": r" ." , .. •", : •;»!-•• .'.•
Under the design-bid-operate-build approach, the engineer ordinarily
assists the owner in bidding and selection of the constructor(s) in addition to
developing the specifications. With this approach, the construction manager
may or may not be picked by the owner prior to selection of construction
firms. The procurement of the construction manager following contracting
the constructors can result in a loss of continuity and efficiency, as the con-
struction manager delays commencement of construction to study and digest
the design and specifications.
In the turnkey approach, the construction manager, rather than the engi-
neer, may partition the construction work into the specialty trades. Once
partitioned, the construction manager identifies and isolates design elements
and specifications that pertain to the particular construction or equipment
specialty and distributes these specific portions of the design and specifica-
tions to qualified specialty contractors or vendors for bids. The construction
manager subsequently selects the best specialty contractors or vendors on
the basis of cost, experience, and other factors critical to the particular instal-
lation work. Subcontract agreements in the turnkey approach are subse-
quently signed between the construction manager and the specialty trade
firms to perform the specified work. Finally, the construction manager over-
sees the performance of the subcontractors to ensure that the specifications
are met. 1
4.10
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Chapter 4
Where the construction management firm has some capacity to perform
construction work, a fewer number of subcontracts may be required. On the
other hand, an engineering consulting firm with few, if any, in-house con-
struction capabilities, may require subcontracting of all construction work
elements. Listed below are some of the more common specialty service areas
associated with the installation of vapor extraction systems:
• drilling/well installation;
• waste management, characterization, and hauling;
• laboratory services;
• utility locators;
• surveyors;
• permitting services;
• excavation/trenching/grading/restoration;
• mechanical/plumbing;
• electrical;
• building construction;
• foundation construction;
• saw cutting;
• concrete/asphalt paving;
• equipment and controls (including package vapor extraction
systems);
• specialty fabrication;
• security; and
• dewatering/water management/storage.
In addition to the verification of subcontractor conformance to construc-
tion specifications, the construction manager is responsible for ensuring that
the construction work force complies with the facility's specific health and
safety requirements as well as any local, state, and federal requirements. For
example, the construction manager must ensure that construction workers
who are likely to come into contact with hazardous constituents have the
necessary training and be involved with a medical surveillance program
4.11
-------
'"Ill ":' ""V-'!!
''•'If'l, lip,,,:: jj!,:,1: j'
Implementation and Operation of Vapor Extraction
' , ,' I "i ,i , I i ,i ,; r ,,., , . . , ,,.' .
ii1 >w"*"i I1 '•• wii.'5"i!!'»! 5"': *' ifI'iiiiiiF"'J5fi»ii;'"Iff 'iJSi iji|
1 • „„ f:1, -',: r , '
*•'•• ..•
consistent with the federal regulations (e.g., OSHA 1910.120). Electrical
installation/troubleshooting work should be monitored by the construction
manager to ensure that proper lock-out tag-out procedures are used. Where
the potential exists for accumulation of explosive vapors in a work area (e.g.,
NEMA 7-rated areas including wellheads and piping trenches), the construc-
tion manager should enforce continuous vapor monitoring, especially when
sparking or abrasion tools are being used in the area. Another health and
safety consideration for which the construction manager is responsible in-
volves ensuring that confined space work is completed by trained personnel
in accordance with appropriate methods.
Under the design-bid-construct-operate approach, the project schedule is
often developed by the constructor. In contrast, under the turnkey approach,
the engineer or the construction manager may develop the construction
schedule. In either case, schedule maintenance is an additional important
•I • . ' .1 r ,M i • • , .| i" .• • '
responsibility of the construction manager. The efficiency and overall cost
of vapor extraction implementation projects is often determined by the suc-
cessful sequencing of individual construction components around site- and
project-specific constraints. The duration of each work step in the critical
path of the project must be accurately forecasted to avoid costly standby
time and scheduling conflicts with the subcontractors. Where the project
schedule has not appropriately forecasted the duration of a construction
event, the construction manager must evaluate the impact of the change on
the overall project schedule and identify cost-effective means of getting trie
project back on schedule. There are two basic methods that the construction
manager can employ for schedule development and maintenance: (1) critical
path method (CPM) and (2) program evaluation and review technique
(PERT). However, CPM is the most widely used and preferred scheduling
method as the size and complexity of vapor extraction implementation
projects do not generally warrant the use of probabilistic models.
In the construction management role, the engineer is also responsible for
verifying and documenting that the installation is consistent with the design
„ ' ^"11 ', .!, | J'illlmil'l!' Ili II ,4,1 Wllll ,' . II "til ,1 'I I M||, ,,11111 '!,! .i,""i|'N' „ " ,||,, „ ,.',J, ,,K
specifications. Consequently, the engineer is responsible for conducting or
overseeing and documenting the independent verification tests. For ex-
ample, the vapor extraction system specifications maycall for a minimum
' | ' I'l ,, f H, "• '!, ||< , ' h i, ! ,:
degree of piping slope from the equipment building to the extraction wells.
To ensure that this specification is met, the construction manager may survey
a number of the piping legs before the subcontractor is authorized to backfill
the trenches. Other examples of the many tests or observations that can be
4.
12
-------
Chapter 4
performed by the engineer to verify conformance to the design and specifi-
cations include:
• concrete slump test;
• concrete compression test;
• soil compaction tests;
• trenching backfill sieve analysis; and
• pneumatic/hydraulic piping leak detection.
Typically, the construction manager does not have the authority to alter
the design of the vapor extraction system due to unforeseen field conditions
or construction circumstances (unless the construction management is being
performed under a turnkey contract). The engineer is typically made avail-
able by the owner to provide input on design changes based upon the input
from the construction company and the construction manager. However, if
construction management is awarded to the owner's consulting engineer, the
owner may defer field design changes to the engineer. It is the responsibility
of the construction manager to document field design changes regardless of
their origin.
An important element of the engineer's role in construction management is
construction monitoring. Diligent construction monitoring and documentation
is key to a project's success as this activity provides the first link in the commu-
nication chain that allows for informed decisions. A separate discussion of
construction monitoring/oversight responsibilities of the construction manager
is provided below to emphasize the importance of this engineering role.
4.1.3.3 Construction Overseer
A primary role of the engineer responsible for construction monitoring is
to oversee the construction activities and to report progress and problems to
the construction manager, the owner, or both. If the overseer finds that work
is being performed outside of the specifications, the deficiencies are docu-
mented, and the contractor is notified of the findings by the engineer if the
work is being completed under the design-bid-construct-operate approach,
the problems are promptly shared with the owner. Contractors that do not
take corrective action on their own will normally be directed to do so by the
construction manager, owner, or both. If the constructor(s) are directly
4.13
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Implementation and Operation of Vapor Extraction
contracted by the owner, the overseer is typically not in a contractual posi-
tion to directly instruct the contractors.
. , , .> u, -, „; r,| r ,, , ; I ., • .... . .... j .;•
The overseer is also responsible for maintaining documentation and report-
ing field observations. These observations may include a daily record of:
' ' i ;
• construction firms present;
• manpower by firm;
• machinery by firm;
• materials/quantity imported/exported by firm;
• work completed;
, , ; ... , , , , „ , ,, . , ; ,
• problems encountered;
• solutions implemented;
• -ivl: '.,:,:. ' :.; ..i:.:. , J , , „ : : ! ;: :;,„
• out-of-scope work;
• compliance with health and safety requirements; and
; i -I i
• quality assurance testing (i.e., pipe integrity, concrete specifica-
tion, and equipment operation, etc.).
The recording of these and other site observations is a primary function of
the overseer, and the value of such information should not be underesti-
• . i . |. ., , . ... i ..i , . .. i
mated. This information may be employed by the construction manager and/
or owner to validate:
" ' '":: • :.:!U :.-.;,. •>"•[ ' j, 'i::,; •••'••.'• :1- •-.- :,' :'..*.; . .^.':..! ;:
• contractor invoices;
* change order requests;
• standby time cost repercussions;
„ : . i i *:-,, •' i .•
• uncontrollable costs associated with a. force mqjeure;
; • • i i v i - ;, !
• contractor safety procedures; and
•'• •' ' ! : : i " i
• corifbrmance to installation design specifications.
,•:• iji ,.•''.' !,' ., -... ' ' :•'• ,;,, i i, .
-------
Chapter 4
4.1.3.4 Operator
As the operator of the remediation system, the engineer has several
key responsibilities. First, the engineer must ensure that the system is
operating safely at all times. The engineer must also ensure that the
system continuously meets its permit requirements and, where neces-
sary, take proactive steps to avoid any potential permit excursions. Sys-
tem data need to be reviewed and evaluated by the engineer to ensure
that the equipment is operating within design limits and that the system
is operating as efficiently as possible.
4.1.4 Construction Activities
4.1.4.1 Drilling/Well Installation
Vapor extraction system wells are often installed by drilling into the soils
to a predetermined depth and then installing a well that is screened over a
particular interval. Particular care must be taken during the installation to
ensure that the well screen is placed at the appropriate depth, that a clean,
granular sand pack is placed in the annular space between the well screen
and the boring wall, and that an adequate bentonite seal is placed in the bor-
ing above the well screen to prevent the short circuiting of air flow during
system operation. It is imperative that the well construction details devel-
oped during the design are implemented as intended.
4.1.4.2 Earthwork
Earthwork for vapor extraction system installations typically involves
excavation and relocation of pavement and/or soil. These activities often
begin following the installation of the remediation system wells. Initially,
pavement is cut along the planned piping runs, and pavement and soils are
excavated to form the piping trenches. The base of the trench is normally
excavated to provide a uniform slope toward the vapor extraction wells from
the equipment compound. Typically, piping placed within the trenches is
bedded in an imported self-compacting granular material (e.g., pea gravel or
washed crushed stone) prior to backfilling and trench completion with addi-
tional imported material or compacted native soil. Excavation of the equip-
ment building foundation footings and any associated grading often occurs
concurrently with the excavation of the piping trenches. The trenches are
4.15
-------
Implementation and Operation of Vapor Extraction
I,
verified and the appropriate
paved once the backfill compaction has been
specified standards have been met.
41.4.3 Mechanical
The primary mechanical tasks required for an installation consists of the
construction of the vapor extraction piping network. One of the first me-
chanical activities is constructing piping from the vapor extraction system
wellheads to the equipment compound. This activity may involve the
plumbing of individual piping spans from the equipment compound to the
vapor extraction wells, manifolded piping, or some combination of the two.
Mechanical work also typically includes the manifolding of vapor extraction
piping entering the equipment building, which allows for adjustment of the
vapor extraction system operation from the equipment building. The mani-
fold installation completed by the mechanical contractor typically includes
instrumentation (e.g., vacuum gauges, switches, transmitters, etc.), control
valving (e.g., isolation, balancing, etc.), and sample ports. Manifold piping
is connected directly to the vapor extraction blower system.
| !
The basic mechanical components of the vapor extraction blower system
can consist of intejrconnected piping, valving and instrumentation associated
with a moisture separator, particulate filter, blower silencer(s), blow-back
:' • , , li / ... • , • „ .I',. ; ulii ,.- ,. . ,i. .••• • .1 -::, IT
loop, and discharge stack. Aqueous process piping that may be included in a
vapor extraction blower system includes that interconnecting the moisture
separator to the condensate holding tank, a transfer pump, and the discharge
outfall. Should emission control equipment be required, relatively minor
additional piping (as required for granular activated carbon adsorbers) to
significant supplementary mechanical work (as required for a gas-fired ther-
mal oxidizer with wet scrubber) may be necessary.
111 • ,: : ' '•• ','• :' : • •• >• t ; • •''[-"•• -.•
Prior to backfilling the piping trenches, the mechanical contractor typi-
cally must demonstrate proper workmanship liy leak testing the piping!
Such testing is evaluated for several reasons. First, leaks in piping can lead
to reduced system performance and effectiveness (e.g., where blower flow
capacity is partially absorbed by ambient air entering through vacuum piping
leaks). Second, leaks found during installation or start-up activities can
identify areas where a greater potential for future integrity problems may
.exist (e.g., a PVC slip coupling where a contractor has failed to use glue)
that could result in future catastrophic piping failure. Third, leaks may result
i
!4.16
t, „•
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Chapter 4
in hazardous vapors entering unexpected areas. Lastly, the leaks may result
in fugitive emissions and/or surface water discharges that are not permitted.
Pipe testing associated with vapor extraction system installation is gener-
ally completed in at least two phases. The first phase often occurs during
trenching and prior to pipe burial. Once the remediation equipment has been
secured inside the equipment building and mechanically and electrically
interconnected, the abovegrade piping is tested.
The most common method of piping leak detection is the hydrostatic test
(Nayyar 1992). In this method, a segment of piping is filled with water at
ambient temperatures and pressurized to between 1.25 and 1.5 times the
design operating pressure of the piping before being isolated from the pres-
surization pump. The pressure in the piping is subsequently monitored using
pressure gauges located at both ends of the piping segment over a specified
period of time. Often, the required period of time for monitoring the pres-
sure condition in the pipe is specified to be a minimum of one hour. The
piping segment passes the tightness test if the pressure in the pipe does not
increase or decrease above or below a tolerance interval during the specified
period. A commonly used tolerance interval is 2% of the applied pressure.
Piping systems may also be tested pneumatically. For this method, piping
is typically pressurized using clean, oil-free air or nitrogen gas to a pressure
equal to 110% of the design operating pressure. Similarly, a vacuum 10%
greater than the design vacuum can also be used. Similar to hydrostatic
testing methods, the piping segment is isolated once pressurized and the
pressure is monitored at both ends of the segment over a period of time.
Typically, the pressure within the piping must remain within 2% of the ap-
plied pressure over a minimum of one hour for the segment to pass the integ-
rity test. During pneumatic pressure testing, soapy water is applied to the
outside of the piping to locate small piping or fitting leaks so that they may
be quickly repaired.
These descriptions of hydrostatic and pneumatic pipe testing procedures
explain the typical methods used during vapor extraction system installations.
However, specific testing requirements and criteria for passing an integrity test
vary based on the construction standards specified by the engineer.
Regardless of test method (hydrostatic or pneumatic) and specifications,
the contractor should know the pressure rating of each piping segment being
tested. In addition, on each of the piping systems being tested, the
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••; '"ii r
Implementation and Operation of Vapor Extraction
contractor should place a relief valve that is set to release the pressure if (1)
the pressure exceeds the test pressure by a predesignated percentage or (2)
the pressure approaches the piping pressure rating. Typically, the pressure
relief valve is set to open if the pressure in the pipe exceeds the test pressure
by 10% while remaining at least 109^ below the pressure rating of the pipe.
' i 'i
4.1.4.4 Electrical
,, :.• , ;' " .. ' '••[.: ;:;;, .: • 'i. : , , • . I,;::"
A separate electrical service from the utility may be brought to the
remediation site or electrical power may be tied into the existing power grid
at the facility. In either case, the power is typically brought to a pole adja-
cent to the equipment compound where a disconnect switch and service
meter may be Installed! A circuit-breaker panel is fed by the service to con-
trol the distributionof power to the individual electrical components of the
system (e.g., motors, lighting^ heating, ventilation, receptacles, instrumenta-
tion, telemetry, etc.). For relatively simple systems (i.e., minimal controls
and automation), the power distribution panel may feed electrical power
directly to the vapor extraction system blower(s) and puinp(s). However, for
more complex systems where a greater number of controls govern operation,
the power distribution system may feed directly into a PLC. that distributes
the power to the pumps and blowers when the Instruments indicate that the
appropriate motor should be energized.
'..! ;| : .:', ,:. i: ' ' i : :
Conditions that can be monitored to control vapor extraction system op-
eration and, that require installation of electrical wiring to the sensor/trans-
mitter include gas composition, explosive vapor concentration, vacuum,
pressure, temperature, air flow, and water level.
4.1.4.5 Concrete
; : ., vp.i,: • . ,' . .. .. ,:
The concrete work required for the installation of vapor extraction sys-
tems is typically minimal. It has two primary uses: (1) repaying areas that
were excavated to install the piping grid, and (i) construction of the equip-
ment building foundation. Concrete is often employed to cap piping
trenches where the trenches cross driveways and other vehicle traffic areas.
In such cases, concrete provides a monolithic bridge across the piping trench
to evenly distribute traffic loads and to compensate for areas where the back-
fill in the piping trenches has settled. It has advantages over an asphalt cap
because'the asphalt surface is much less rigid and is prone to sagging. If an
equipment building is to be constructed to house the vapor extraction
4.18
Ill
ri|
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4
• "iPil'1'
.iijii
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«:, ''* '.'.V ill !••<••'' "• ''' '•"'•
("1 1 1
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1
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Chapter 4
equipment, a foundation is excavated and forms are constructed in prepara-
tion for pouring of the concrete footings and pad. Concrete pad construction
ranges in complexity from a simple slab-on-grade to a heavily reinforced
structure, depending on the system needs and local building codes. The
concrete specifications and testing requirements (e.g., slump, compression
strength, etc.) are normally developed with the design, and the installation is
completed in conformance with the developed requirements.
4.1.4.6 Building
Depending on the design specifications and local building code require-
ments, buildings constructed to house vapor extraction equipment may be
preconstructed, prefabricated, preengineered, and/or constructed on-site.
Building materials can include wood, concrete blocks, or sheet metal. For
smaller systems, it is common to have the vapor extraction equipment
preassembled and shipped within an equipment enclosure. Larger systems
that require more interior space often require the on-site erection of
preengineered sheet metal buildings. Regardless of the specific type of
building constructed, it should be adequately anchored to its foundation and
connected to the electrical grounding system. Specifications for building
construction are typically included with the system design.
4.1.4.7 Equipment Assembly
During the 1980s when the first vapor extraction systems were first in-
stalled, it was common for the system components to be assembled at the
installation site. Blowers were secured to the equipment pad and mechani-
cally and electrically interconnected with moisture separators, holding tanks,
vapor treatment equipment, and instrumentation and controls. Since the
1980s, with recognized need to increase construction efficiencies and lower
installation costs, the practice of assembling system components on-site has
fallen from favor. Now, equipment manufacturers are often tasked with
preassembly of equipment onto skids and pretesting the equipment assem-
blies at the factory prior to shipment to the site. Once the equipment arrives
on-site, it is typically ready for operation after a few relatively minor me-
chanical and electrical connections are made. Since the prefabrication of the
equipment in such cases involves both mechanical and electrical work, the
design construction specifications developed in these areas apply equally to
the off-site work as well as the on-site construction activities. Care must be
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Implementation and Operation of Vapor Extraction
taken to inspect the prefabrication work to verify conformance with specifi-
cations prior to shipment to the site.
4.1.4.8 Site Restoration
Following construction, a short period is typically allotted for returning
the work area to as close to its preconstruction condition as possible. During
this period, property damaged or destroyed by the contractor during system
installation is fixed or replaced by the responsible contractor. Reparations
often include replacement of paving that was damaged by the contractor's
heavy equipment. Additionally, where use of heavy equipment on unpaved
surfaces during earth moving activities has resulted in the formation of ruts,
the restoration work includes grading and revegetating these areas. The
contractor is typically required to replace all landscaped vegetation that was
destroyed during construction with equivalent varieties and sizes. Finally, all
contractor equipment, materials, and construction debris are removed from
the site during this phase.
4.1.5 Construction Precommissioning Checklist
The following construction precommissioning checklist is adapted in
large part from the US ACE (1995).
Subsurface
• Wells/trenches installed to specifications
• Wells purged/cleaned
• As-built elevations of well screens field-checked
• Monitoring points installed
• Instrumentation installed on wellheads
• " ! ;: ' "', "•' ' ' | • ; , " ;" •' ' ' . "• i "
• Underground piping to wells installed/tested
'• • 1< ' • • '! '"' ' -I1 •' """ •• •• I-
• Piping flushed/cleaned
• ' •' • " '!" • " • • • "" -• -1 • •-•• -• «••• •••'• •••••••••• <' <• ' " '!•'
• Strainers/filters installed/cleaned
• Valves installed and operation verified
• Pressure test complete
li'ir'ilj* li'i'lrt'll, ',
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Chapter 4
Housing, Blowers, and Pumps
• Foundations complete
• Blowers, pumps, and motors bolted in place
• Vibration dampers installed
• Coupling alignment/level to specifications
• Pipe connections installed/tested.
• Seals intact (no leaks)
Electrical
• Grounding installed/checked
• Lighting/HVAC functional
• Lockouts/covers/panels in place
• Blower rotation verified
• Disconnects in sight of unit being controlled
• Controls/alarms and interlocks functional
• Power connected to monitoring instruments
Mechanical Units
• Instruments calibrated
• Air treatment system installed/functional
• Auxiliary fuel (if needed) operational
• Aftercooler system functional (if needed)
4.2 Start-up Procedures
Once a vapor extraction system has been installed, it is prudent to follow
a carefully planned and orchestrated start-up procedure. Following a devel-
oped start-up protocol will not only minimize the potential health and safety
hazards that exist with initial operation of such equipment, but also reduce
the potential of incurring additional costs and extending the implementation
schedule by operating equipment outside of manufacturer specifications.
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Implementation and Operation of Vapor Extraction
While the variability in site settings, contamination, system designs, and
equipment specifications suggest that a customized start-up plan be devel-
oped for a particular installation, many of the start-up procedures are com-
mon to all installations. The focus of this section is on procedures that are
likely to be common to a wide variety of vapor extraction systems. First, a
discussion is provided on methods to test individual components of a system.
This is followed by testing procedures for the system as a whole, and a gen-
eral start-up checklist.
4.2.1 Component Testing
One of the most important start-up tasks is component testing. Comple-
tion of this testing ensures that the system components are being operated in
accordance with manufacturer recommendations, the system will operate
safely, and the control logic programmed into the system is consistent with
the design. Minimizing the importance of component testing during the
start-up phase can lead to several undesirable consequences including pre-
mature equipment failure, voided warrantees, contractor stand-by time,
costly system troubleshooting, delayed system startup, misdiagnosis of per-
formance variances, permit violations, and personnel injury. A discussion of
prudent system diagnostic testing is provided in the following sections.
4.2.1.1 Power Supply
A number of precautions need to be taken early in the startup in connec-
tion with the power supply to individual system components. These precau-
tions need to be taken to protect operators of the system as well as to ensure
that the equipment is adequately protected. The precautions include:
• verifying the proper grounding of equipment;
• cross-checking the supply voltage with motor name-plate voltage;
• confirming sizing of thermal magnetic circuit breaker ratings for
each motor; and
• testing ground-fault circuits.
In addition, it is essential that three-phase motors be checked for proper
rotation prior to operating the motors for any extended period of time. Mo-
tors generally operate more efficiently from three-phase power sources than
a single-phase supply. For this reason, design specifications for the blowers,
4.22
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Chapter 4
pumps, and fans of vapor extraction systems typically call for motors that
can accommodate three-phase power if it is available. While the three-
phase motors provide increased efficiency, they can be inappropriately wired
because two of the wiring legs can be connected interchangeably, resulting
in an opposite rotational direction from that intended.
improper rotation of an impeller will, at a minimum, result in poor
blower, fan, or pump performance. Specifically, the improperly rotating
equipment will be unable to achieve the design pressure and flow conditions.
In the worst case, the impeller may be designed to rotate in only one direc-
tion, and prolonged rotation in the opposite direction could cause serious
damage to the equipment.
Testing for rotation during startup consists of "bumping" or energizing
the motor for a fraction of a second while monitoring the equipment impel-
ler. The perceived direction of rotation of the impeller is compared to the
rotation specified by the manufacturer. Typically, the design rotation of the
impeller is imprinted on, or cast into, the housing of the equipment. If re-
wiring is necessary, the procedure is repeated to verify that the appropriate
action was taken.
4.2.1.2 Performance
Once the basic electrical testing has been completed, the performance of
individual system components should be checked against manufacturers'
specifications. For vapor extraction blowers, performance testing includes
measurement of the initial running amperage and comparison of the mea-
sured value to the manufacturer's tolerances. The initial running amperage
of the vapor extraction blower and other motors should be recorded as
baseline conditions from which future operating conditions can be com-
pared. The vapor extraction blower performance testing should also include
measurement of air flow rates under various simulated vacuum/pressure
conditions to establish the field blower performance curve. This curve
should closely resemble the manufacturer's performance curve for the
blower. Significant deviations between the field blower curve and the
manufacturer's curve warrant further investigation prior to placing the sys-
tem in operation.
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Implementation and Operation of Vapor Extraction
4.2.2 System Testing
Following the successful testing of individual components, the vapor
extraction system is tested as a unit. Such testing entails verification that the
multiple components of the system will operate simultaneously, that commu-
nication between instruments and the controller is accurate and functional,
and that the control logic conforms to the design. The following discussion
covers instrument calibration and diagnostic testing.
'i ! ' • ! , , ' ''.,'•
4.2.2.1 Instrument Calibration
For economic reasons, vapor extraction systems are typically designed to
operate unattended over extended periods. The automated operation of va-
por extraction systems is facilitated by use of electronics to monitor critical
system conditions and to control the operation of system components. Suc-
cessful use of electronics in a design yields a system that operates safely yet
does not strain the system, causing frequent automated system shutdowns.
Reliable automated operation also requires that electronics be thoroughly
calibrated and tested during system startup and at regular intervals during
operation.
Calibration of the in-line mechanical and electrical monitoring and con-
trol instruments during the start-up period is critical to successful operation.
Mechanical gauges (e.g., vacuum/pressure) are zeroed while the system is at
idle and cross-checked with an independent gauge once the system has been
activated. The linear voltage/current output of system transmitters (e.g.,
flow, pressure, level) is calibrated to expected ranges of conditions using
independently-calibrated field instruments. Finally, the set-points on instru-
mentation switches are checked to verify that the switches activate at the
design low and/or high parameter condition(si).
4.2.2.2 Diagnostic Testing
After initial calibration of instruments, the control logic programmed into
the system can be checked to verify the shutdown protocols of the design.
This check is generally performed during the start-up activities by simulating
an operating condition that is critical to a control sensor and observing the
subsequent automated response. For example, an in-line LEL meter is to
terminate operation of the vapor extraction blower(s) but allow continued
operation of a ventilation blower if vapor concentrations of 10% LEL are
detected. A local alarm is to be displayed while a remote operator is to be
4.24
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Chapter 4
notified via telephone of the alarm condition. To test the control logic, the
LEL sensor is exposed to a 10% LEL calibration gas while the system is
fully operating and the sequence of programmed responses is confirmed.
During the start-up phase, the alarm conditions associated with each
switch and transmitter in the control loop are simulated, and the system's
automated response is monitored and compared to design protocols. The
system should be started and stopped over a dozen times to ensure that the
system shutdown protocols have been thoroughly checked. After these
simulations of alarm conditions have been performed and the system re-
sponses found to be as designed, the vapor extraction system is ready for
operation.
4.2.3 Checklist for Startup
The following checklist is typical for startup of a vapor extraction system.
• Remove debris from piping interior (PVC shavings, soil, etc.)
• Complete pipe integrity testing
• Eliminate piping blockages
• Appropriately position all system valves
• Orient valving on blower piping in start-up configuration for least
flow resistance
• Cross check motor supply voltages with motor plate voltages
• Cross check thermal magnetic circuit breaker ratings with motor
amperage specifications
• Verify that motors and hand switches are properly grounded
• Collect background data (e.g., static soil pressure, VOC concen-
trations, depth to water, etc.)
• Secure and post requisite discharge permits
• Check equipment lubricating fluid levels
• Verify proper rotation of motors
• Record initial running amperage of motors
• Recalibrate all in-line instruments
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Implementation and Operation of Vapor Extraction
• Check switch set-points
• Compare and adjust sensor transmitter spans relative to actual
conditions
• Simulate alarm conditions; verify automated operations
• Confirm remote access to telemetric data
• Reconfigure valving to achieve design vacuum/flow
• Compare blower/pump performance to manufacturer's perfor-
mance curves
• Check vacuum at wellheads to confirm minimal piping headless
• Record influence vacuums at influence monitoring wells
• Collect influent and effluent vapor samples for baseline field and
laboratory analysis
4.3 Maintenance
A successful vapor extraction system design and installation does not
directly translate into a successful remediation. Without the development
and full implementation of an appropriate operations and maintenance
(O&M) plan, even the best system design could result in a faculty
remediation program. An O&M plan is typically developed following the
system design.
O&M plans vary in content and complexity depending on the specifics of
a particular installation. Factors that contribute to the customization of
O&M plans include a variety of site conditions (setting, contaminants, site
use, geology, hydrogeology, etc.), scale of the remediation system, and type
of remediation equipment employed.
A generic table of contents for an O&M manual is presented below to
help in identifying the main issues. The items listed are by no means ex-
haustive for any particular system, the table is simply provided as an aid in
developing an O&M manual that provides the information required by a
qualified operator to operate a system and meet the overall remedial objec-
tives for a site.
4.26
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Chapter 4
O&M Manual Sample Table of Contents
1.0 Introduction
1.1 Purpose of the O&M Manual
1.2 O&M Manual User's Guide
1.3 Remedial System Overview
2.0 Remedial Objectives
2.1 Short Term
2.1.1 Operate Using Design Parameter Values
2.1.2 Modify Operational Parameters to Maximize Mass
Removal
2.1.3 Maximize Cost-Effectiveness of Operation
2.2 Long Term
2.2.1 Attain Clean-up Goals
2.2.2 Minimize Time of Remediation
3.0 Remedial System Description
3.1 Facility Layout
3.2 Remedial System Instrumentation
3.3 System Component Descriptions
4.0 System Operations
4.1 Operator Duties
4.1.1 Daily Responsibilities
4.1.2 Periodic Maintenance
4.1.3 Certification
4.2 Start-up/Shutdown Procedures
4.3 Routine Operation and Operational Control
4.4 Troubleshooting
5.0 Sampling and Monitoring
5.1 Types of Samples
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Implementation and Operation of Vapor Extraction
5.2 Sampling Locations
5.3 Sampling Frequency
5.4 Sample Tracking and Handling
5.5 Monitoring Procedures
5.5.1 Overview of Standard Operating Procedures
i • :<
6.0 Record Keeping and Reporting
6.1 Operation Forms
6.2 Monitoring Forms
6.3 Quality Assurance/Quality Control Procedures
7.0 Alarm Response Procedures
8.0 Safety
8.1 Contents of Health and Safety Plan
8.2 Injury Response
Possible Appendices
List of Manufacturers'Literature
Health and Safety Plan
Spill Prevention, Control, and Couintermeasure (SPCC) Plan
Operation Logs and Inspection Forms
Standard Operating Procedures
As-Built Drawings
Although an O&M plan is typically unique to the particular remediation
system for which it is developed, there are fundamental operation, mainte-
nance, and safety elements that are common to all forms of vapor extraction
systems. These common elements are discussed in the following sections.
4.3.1 Extraction Systems
Although a vapor extraction system may be ideally designed, flawlessly
installed, and have the best O&M plan, success of the remediation relies
heavily on maintenance of the system. Typically, a relatively large capital
investment is made for the design, purchase, and installation of remediation
4.28
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Chapter 4
equipment. The return on this investment can be measured by the percent-
age of time that the system is operable and progress is made in remediating
the site. Equipment that is frequently idle due to poor maintenance results in
a low return on the investment and increased project costs!
Maintenance requirements for vapor extraction systems vary according to
the specific design and equipment employed in the system. Many of the
maintenance procedures that must be followed are those that are specifically
required by the equipment manufacturer. However, maintenance require-
ments that are typical of these types of remediation systems include:
• cleaning/replacing particulate filters;
• cleaning/testing level switches;
• changing oil/cooling fluids;
• changing/tensioning belts;
• disposing of accumulated condensate;
• blowing back accumulated condensate in system piping to the
wells;
• visually inspecting of equipment, valves, piping, etc. for leaks,
cracks, and wear;
• testing pressure/vacuum switches;
• replacing spent granular activated carbon adsorbers;
• replacing poisoned/spent catalysts;
• cleaning heat exchanger cooling fins;
• measuring motor amperage draw;
• inspecting/testing of pressure/vacuum relief valves;
• calibrating instruments; and
• inspecting/testing alarms/controls.
Special maintenance procedures for select system components are dis-
cussed below.
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Implementation and Operation of Vapor Extraction
4.3.2 Vapor Treatment Systems
Vapor treatment systems should be operated and maintained in strict ad-
herence to manufacturer's recommendations. Generally, monitoring the
efficiency of a vapor treatment system over time provides a good indication
of the success of a maintenance program. A measured reduction in adsorp-
tion capacity in a granular activated carbon treatment system could signal
that excessive moisture is being permitted to enter the carbon vessels to
compete with the constituents of concern. Reduced treatment efficiencies in
catalytic oxidation systems could signal the premature poisoning of a cata-
lyst or simply that one or more of the catalyst beds requires regeneneration.
The manufacturer of the treatment equipment should be contacted to see if
additional maintenance activities are warranted if approved maintenance
procedures do not provide the anticipated treatment efficiency results.
4.3.3 Wells, Trenches, and Well Points
Generally, the maintenance requirements associated with the wells,
trenches, and well points of a vapor extraction system are minimal. How-
ever, inspection of these components should be completed on a regular basis,
especially when they are located in roadways. Truck traffic, deicing chemi-
cals, and snow removal equipment can damage surface expressions of each
of these components. Specific maintenance tasks related to these compo-
nents that should be completed on a routine basis include:
• extraction of accumulated water in wellhead vaults;
• removal of accumulated sediment in wellhead vaults;
• inspection/replacement of well seals/locks;
! ' •' • "'„:'' v' , ' if :
• inspection of wellheads for frost heave and grout integrity;
• inspection of pavement for loss of integrity — patch/seal where
required; and
• inspection of pavement over trenches for settlement.
4.3.4 Piping
Above-grade piping should be regularly inspected for corrosion, heat
damage, stress cracks, sunlight (UV radiation) damage, and leakage. Piping
damaged during system operation should be replaced, and corrective
4.30
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Chapter 4
measures should be taken to prevent repeated piping failures. Typical cor-
rective measures include adding pipe bracing/support, installing piping insu-
lation, changing piping material, and replacing "sticky" valves.
4.3.5 Equipment Enclosure
The equipment building should be regularly inspected for leaks and struc-
tural damage and repaired, as needed, to help ensure the continuous safe
operation of the vapor extraction system equipment.
4.3.6 Safety Considerations
Operation of vapor extraction systems presents a number of health and
safety hazards to the operator and the surrounding population. Procedures
must be in place to address these potential hazards during system operation.
The most basic health and safety consideration for the operator is that the
system is likely processing hazardous chemicals, and therefore, the operator
should complete training and participate in a medical monitoring program in
accordance with OSHA 1910.120. Other operational hazards that need to be
considered during system operation.are discussed below.
4.3.6.1 Fire Safety
Fire safety is an important consideration during the operation of any
remediation system and it is of particular importance when the installation is
at an active facility where flammable and/or toxic chemicals are present.
The moderate level of risk of fire presented by the electrical equipment asso-
ciated with an enclosed vapor extraction system is significantly increased by
the operation of the equipment and the processing of combustible VOCs.
Equipment and piping must be carefully monitored and maintained to guard
against the accumulation of hazardous, if not potentially explosive levels, of
VOCs anywhere in the system or equipment building.
Prudent measures that should be followed during operation of a vapor
extraction system include the following:
• placement of fire extinguishers both inside and outside the equip-
ment building and routine inspection of the extinguishers;
• enforcement of a no-smoking policy in and around the equipment
building; and
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Implementation and Operation of Vapor Extraction
• implementation of a formal "hot-work" permitting program that
requires that a permit be obtained prior to using any sparking or
abrasive/friction-generating equipment or electrical hand tools.
(The permit should require results of vapor monitoring prior to
approval.)
4.3.6.2 Air Quality '
The extraction of soil gas containing hazardous chemicals presents addi-
tional operational safety hazards. First, fugitive vapors from the extraction
system have the potential to accumulate in the equipment area and could
result in operator exposure to the toxic chemicals. Second, extracted vapors
may become more concentrated than the system was designed to accommo-
date, resulting in excessive VOC emissions to the atmosphere.
Prudent measures that can be taken by the operator to reduce the risk of
exposure to extracted VOCs include the following:
• monitor the concentrations of VQCs in the equipment building
prior to entering and while inside;
• wear a protective respirator when sampling soil gas piping that is
under pressure; and
• reduce soil gas extraction rates when concentrations of VOCs in
the vapor stream approach the treatment limits and/or permitted
levels and increase the effluent monitoring frequency until the
concentrations plateau.
4.3:6.3 Physical Hazards
Equipment for vapor extraction systems can present many potential physi-
cal hazards to the operator of the system and to others. Potential hazards
include those associated with tripping and falling, impacting, entrapment,
entanglement, exposure to hot equipment, and excessive noise.
i , „ i, • „ • i i , '.'I;-1
Blowers used in vapor extraction systems are often decoupled from their
motors and belt-driven. Normally, a protective cage is provided with these
systems to prevent entanglement during system operation. To ensure safe
operation of this equipment, the operator should routinely inspect the protec-
tive cage to verify that it is secure. Following belt tensioning or any other
maintenance task that requires removal of the cage, the operator should re-
quire that the cage be resecured before the system is restarted.
4.32
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Chapter 4
Piping exiting blower systems can hot enough to burn skin. Where the
operator observes such a condition and where there is a reasonable potential
that maintenance or monitoring personnel could contact the piping, the op-
erator should insulate the piping and periodically inspect and maintain the
insulation for the duration of the project.
Extraction wellheads also require periodic inspection and maintenance. For
wellheads that are flush with the ground surface, inspection and maintenance
can typically be performed only following removal of vault lids. Left unat-
tended for any period of time, these open wellhead vaults present a serious trip
hazard to anyone with access to the area. At a minimum, the operator should
employ traffic cones or barricades around any open wellhead.
Equipment used in a vapor extraction system is generally secured to the
floor or building walls during installation. However, the operator should
regularly inspect the bracing of such equipment to verify that vibrations have
not jarred the equipment loose, creating a potential fall/impact/entrapment
hazard.
Blower systems that are frequently employed in vapor extraction sys-
tems generate a significant level of noise. Even when equipped with
silencing equipment, these blower systems can generate enough noise to
be damaging to human ears in a relatively short period. In such in-
stances, the operator should require that all entrants to the equipment
building wear hearing protection.
4.4 Performance Monitoring
Design of vapor extraction systems is, for all practical purposes, a con-
tinuous process that begins with the initial conceptual design and continues
after the system is installed and operating. Monitoring data are a key basis
for assessing system performance, calibrating models, and making necessary
operational changes and equipment modifications. This section discusses
data presentation options for full-scale continuously operating systems.
There are a wide range of monitoring options and it is up to the practitioner
to select monitoring requirements based on the particular need for informa-
tion. For example, there are typically three types of system monitoring that
are performed for vapor extraction systems: (1) process monitoring, in
4.33
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Implementation and Operation of Vapor Extraction
which data are collected to evaluate whether the vapor extraction equipment
continues to operate within manufacturers' recommended tolerances;
(2) compliance monitoring, in which data are obtained to document compli-
ance with air and water discharge permit conditions; and (3) performance
monitoring, in which data are collected to evaluate the effectiveness of the
system in remediating the site. Depending on the level of complexity of a
system, the practitioner may elect to emphasize one form of monitoring over
another in order to best meet the intended objective. This chapter focuses on
performance monitoring.
The following requirements are presented in relative order of importance
hi assessing system performance. While there is flexibility in choosing
monitoring strategies, there is a minimum level of information that must be
gathered in order to make basic performance evaluation decisions.
j" ' • ! i
4.4.1 Extracted Vapor Flow Measurement
The most straightforward means of assessing vapor extraction process
performance is to monitor the flow and composition of the extracted gases.
This is the minimum monitoring required and is conducted to track mass
removal rates, compositional changes, and mass and vapor flow rates. Soil
gas extraction rate measurements and soil gas analyses need to be completed
for each of the extraction wells to assess the effectiveness of each and make
adjustments accordingly. Interpretation of the data can lead to identification
of permeability changes and mass-transfer limitations.
The actual flow rate (Q) may be measured by a number of means. It
should be corrected to some standard volume per unit of time; i.e., (Q*) at a
standard pressure and temperature:
Q* = Q(P /1 atm)(293°K / T)
(4.1)
where: P (atm) = absolute pressure measured at the flow rate measuring
device
T (°K) = absolute temperature measured at the flow rate
measuring device.
Examples of the most widely used expressions of flow rate units are scfm
(this implies flow rates corrected to 1 atmosphere and 20°C). The use of stan-
dard units is especially important, as most gas analyses are expressed on similar
bases, and these two values are multiplied to assess mass removal rates.
4.34
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Chapter 4
A variety of methods are available for measuring gas flow rates. Pilot
tubes or orifice plates combined with an inclined manometer or a differential
pressure gauge are acceptable for measuring flow velocities of at least 400
m/min (1,300 ft/min). For lower flow rates, a rotometer will typically pro-
vide a more accurate measurement. To be able to express the measured flow
rate on a standard basis (1 atm, 20°C), the pressure and temperature at the
point of flow measurement must be known. Mass flow meters automatically
correct for changes in temperature and pressure and typically are coupled
with a flow totalizer, which provides valuable data for performing mass
removal calculations. All extraction flow meters and pressure garages must
be placed between the wellhead and first downstream junction or valve (or
upstream in the case of air injection wells). There are also other guidelines
for flow meter placement that are specific to different types of flow meters
(e.g., placement of at least 10 pipe diameters away from constrictions);
manufacturer guidelines should be followed closely.
4.4.2 Wellhead Pressure
Vacuum should be monitored at the extraction wellhead, typically with a
permanently installed pressure gauge or a "quick-release" connection that
facilitates measurement. The pressure measurements required for flow rate
measurement are also useful in interpreting system operation and perfor-
mance. Pressure changes at the wellhead over time (at constant flow rate)
indicate soil-gas permeability changes and usually are the result of soil mois-
ture changes (due to upwelling, infiltration, or drying). Figure 3.6a presents
pressure and flow rate data for a vapor extraction system. The figure indi-
cates that a permeability reduction occurred with time, as the flow rate de-
creased with time and the applied vacuum remained constant. In this case,
the reduction was attributed to groundwater elevation changes (Johnson et al.
1991). Similar injection pressure versus flow rate plots should be made for
bioventing systems that use air injection wells.
4.4.3 Extracted Vapor Quality
Extracted vapor quality is monitored to determine contaminant removal
rates and assess mass-transfer limitations. At a minimum, composition mea-
surements should include some measure of the target contaminant concentra-
tion. Respiratory gas measurements (oxygen and carbon dioxide) can pro-
vide an indicator of biological degradation activity when the contaminants
4.35
-------
Implementation and Operation of Vapor Extraction
are aerobically biodegradable. As discussed in Section 3.2.2.1, a variety of
techniques are available for measuring contaminant concentration in the
extracted vapors; the choice in a given situation may be dictated by regula-
tions or permitting procedures.
For sites contaminated with mixtures of hydrocarbons such as fuels,
time trends in boiling point distribution are valuable in monitoring the
progress of a particular system. Near the end of remediation, it is ex-
pected that the majority of compounds in the C1-C8 range (the lightest,
most volatile compounds) will be seen in limited concentrations in the
extracted vapors, and the C8 -C12 compounds should dominate the boil-
ing point distribution. Once the volatile and semivolatile compounds
have been removed by vapor extraction, the remaining less volatile com-
pounds (if they need to be removed) can be remediated by
bioremediation. At that point in operation, depending on the cleanup
levels for site soils, operation of the system may be switched to focus on
bioventing (i.e., lower flow rates and/or pulsed operation).
i '
4.4.4 Subsurface Vacuum Distribution
The vadose zone monitoring points should be periodically measured for
soil pressure to ensure that the design zone of influence is maintained. As
full-scale operation proceeds, soil permeability may be modified for the
reasons discussed in Section 4.4.1. If "dead zones" (i.e., zones of soil that
do not have significant air flow) develop, it is necessary to modify the
vacuum applied to nearby wells to change the vapor flow pattern. The ap-
plied vacuum should be increased until pressure readings at the pressure
monitoring points indicate that soil gas flow has been re-established.
4.4.5 Condensate Production Rate Monitoring
The air/water separator water level should periodically be monitored to
determine the condensation production rate and how this rate changes under
different environmental conditions. Condensation production will peak
during cold weather as the moisture in the relatively warm soil gas con-
denses in manifolding. Correspondingly, drains in the manifolding should
be checked more frequently during cold weather and after heavy precipita-
tion events, as these are the periods when condensate is expected to accumu-
late in the largest volumes.
4.36
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Chapter 4
4.4.6 Mass Removal Rate Calculations
Concentrations of contaminants in vapor samples are most often reported
by laboratories as parts per million by volume (ppmy) (sometimes called (oL/
L). This is a measure of the partial pressure of the gas and should not be
confused with parts per million by mass or mass per volume (i.e., mg/kg or
mg/L). Concentrations may also be expressed as mass per unit volume of
vapor, such as Jjg/m3 or mg/L. The basic relationship between partial pres-
sure and mass per unit volume is:
^ , , 3s ^ , ,10"6MW
Cv.por.CMfi / m ) = Cvapor(pprnv)———
where: MW (jjg/mole) = molecular weight of the contaminant used to
calibrate the detector (may not be the actual
contaminant being monitored)
R = gas constant (8.2° 10'5 m3-atm/mole-K), and
T = 293°K(20°C).
This equation is essentially the Ideal Gas Law where Cvapor (ppmv) 10'6
represents the partial pressure of the gas being monitored. As previously
mentioned, it is important to recognize that expression of gas concentrations
in volume/volume units is meaningless unless the calibration compound is
also specified. Thus, a total contaminant concentration of 100 ppmv mea-
sured on a portable FID calibrated to methane must be expressed as 100
ppmv-methane to have meaning. For example, a gasoline vapor stream re-
ported to have a total contaminant concentration of 100 ppmv-methane
(0.067 |Jg/m3) is not equivalent to a reported total concentration of 100 ppmv-
hexane (0.358 ug/m3).
For performance monitoring, vapor concentrations should be reported and
recorded in mass/volume units, as this facilitates the calculation of removal
rates (Rv, mass/time) and confusion is minimized. Rv is the product of the
flow rate (volume/time) and vapor concentration (Cvapor, mass/volume):
Rv=Q*Cvapor (4.3)
Here, the flow rate is expressed in standard units (Q*) as most gas samples
are analyzed from sample containers maintained at 1 atm pressure. To calcu-
late contaminant removal rate over a given time interval, the concentration of
target contaminant is assumed to be constant over that time interval. A
4.37
-------
Implementation and Operation of Vapor Extraction
cumulative contaminant mass recovered by volatilization (Tv, mass) can be
computed by integrating the recovery curve over time:
I ,! | I: I, .....
- t
Tv= fRvdt
,=o (4.4)
4.4.7 Rebound Spike Concentration Monitoring
Several studies have indicated that when contaminant mass removal by
vapor extraction becomes diffusion-limited, pulsed operation from individual
wells is more efficient than continuous operation on a mass extracted per
unit of energy expended basis (Hutzler, Murphy, and Gierke 1989; Crow et
al. 1987). Pulsed operation of a vapor extraction well allows soil vapor to
equilibrate with the surrounding soils via diffusion from solid phase to the
soil pore space when extraction stops. When a vacuum is again applied to
the well, the soil vapor extracted will contain higher concentrations of VOCs
to the extent to which diffusion has occurred and has limited mass transfer
during continuous operation.
To investigate the extent to which diffusion-limited transport is occurring
at soils surrounding a particular well, a "rebound spike test" can be per-
formed. In this test, the extracted vapor VOC concentration is first measured
at the test extraction well during continuous operation. The vacuum at the
test well is then shut off for a period of at least one week. The vacuum is
then reapplied to the test well, and the VOC concentration in the vapors of
the extraction well is immediately measured. The difference in vapor VOC
concentrations during continuous operation and after restart is referred to as
the rebound spike. The magnitude and duration of this spike can be used to
determine the relative extent to which diffusipn is limiting mass removal
from soils within the zone of influence of the Jest well,
A series of rebound spike test results is often needed to provide evidence
to support site closure. Favorable results will show a declining rebound
spike (both in terms of extent and duration) in a series of rebound spike tests.
4.38
-------
Chapter 4
4.5 Operational Modifications
Modifications that can be made during the design stage to enhance the
mass extraction rate are explained in Section 3.4. Once a vapor extraction or
bioventing system is built, modifications may be made by adjusting the sys-
tem operational controls in response to performance monitoring data.
Over time, the mass extraction rate from a well is expected to change in
response to drying, wetting conditions (water table fluctuations), and re-
moval of VOCs. Many practitioners refer to two distinct stages, the advec-
tion-controlled and the diffusion-controlled stages. The advection-controlled
stage is indicated by sustained, high concentrations of VOCs in the extracted
air from a vapor extraction well. In this case, the rate of volatilization of
VOCs to the air stream in the subsurface is not limited. As the remediation
progresses and the mass is removed, the rate of volatilization decreases,
leaving diffusion as the primary controlling process. Under diffusion-con-
trolled conditions, air flow may not be limiting the overall system mass re-
moval rate at all locations at the site. When air flow is not limiting, alternate
operational modes can be effective hi maximizing mass extraction rates and
reducing operational costs.
4.5.1 Balancing and Managing Air Flow
Control valves on the vapor extraction manifold can be adjusted while
measuring the air flow from each well. During initial stages of a project, a
balanced flow rate among all of the vapor extraction wells is typically de-
sired. As the project progresses, wells yielding little or no VOCs can be
turned off or flow rates can be minimized for diffusion-controlled wells and
increased from extraction wells with the highest VOC concentrations (advec-
tion-controlled wells).
4.5.2 Targeting Residual Contaminants
Typically, a few vapor extraction wells in the most contaminated area will
be the slowest to clean up. By adjusting the air flow and vacuum to concen-
trate on the remaining "hot spots," the cleanup process may be accelerated in
these areas. Another approach is to use vapor extraction or monitoring wells
near the residual mass to inject ah* while extracting vapor in say, one well, to
create different ah* flow patterns in the subsurface. Installation of additional
4.39
-------
Implementation and Operation of Vapor Extraction
air infiltration wells in the residual mass may also increase mass removal. Fi-
nally, increasing the vacuum in a vapor extraction well may also be effective.
I , . I ill. , , „ '' . . » ', , i I I! 'I
4.6 Quality Control
Prior to using analytical data for decision-making purposes, some data
validation should be performed. In most cases, full validation in accordance
with formal US EPA protocols is not required for site characterization or
pilot test data. However, if comparisons to clean-up criteria are intended,
full validation may be justified. At a minimum, data received from an ana-
lytical laboratory should be qualitatively assessed. A review of compounds
detected in duplicates and blanks as well as the percentage of surrogate re-
coveries in matrix spike samples provides an indication of the quality of
analytical data. The sampling and analysis plan must include appropriate
quality control samples, such as duplicates, matrix spikes, and field and trip
blanks at specified frequencies, usually as a percentage of the total number
of samples collected.
The topics and issues that need to be addressed with regard to quality
control during operation of a vapor extraction system are typically covered
in the O&M manual.
4.40
-------
Chapter 5
DESIGN DEVELOPMENT
FOR AIR SPARGING
5.7 Groundwater Remediation Goals
5.1.1 Selecting Design Objectives
As with vapor extraction/bioventing, engineers need to clearly delineate the
design objectives for a sparging system. Identifying design objectives and con-
straints is the first step in the design process. The considerations include:
• Primary Mass Removal Mechanisms (volatilization or biodegra-
dation). However, unlike vapor extraction systems, it is difficult
to selectively increase either mechanism. Conditions favorable
for volatilization of dissolved-phase contaminants out of ground-
water are also favorable for partitioning of oxygen into ground-
water. Still, a design objective may be to maintain aerobic condi-
tions in the treatment zone.
• Purpose of the Sparging System. Some sparging systems are
designed as dissolved-phase plume cutoff walls. These may
consist of a line of sparging wells, a sparging trench, or a funnel-
and-gate type array. Either way, they .are intended to be a long-
term containment approach to reduce dissolved-phase VOCs to
some concentration before they reach a point of compliance.
Other sparging systems are designed to address an entire dis-
solved-phase plume through a series of vertical or horizontal
5.1
-------
Design Development for Air Sparging
sparging wells in close proximity. Treatment systems designed
for cleanup have an operating life of months to a few years, but
ultimately need to achieve some clean-up criteria for dissolved-
phase contaminants throughout the treatment zone. Finally, a
system may be designed to help address an LNAPL source zone.
Such systems intensively aerate smear zone contaminants to
attack the source of contamination. The success of such systems
is evaluated by both dissolved-phase contaminants in the ground-
water and residual soil concentrations in the smear zone and even
in the vadose zone. Sparging systems are almost never employed
to reduce mobile DNAPLs since there is little documentation to
support such applications.
• Type and Complexity of Operations. The expected duration of
treatment, size of the system, and identification of probable treat-
ment operators may dictate the level of automation and sophisti-
cation required in the design and controls.
....." ";„; • , [ , . ; . i . . | if.'
When implemented for groundwater treatment, sparging involves the
volatilization of at least some of the dissolved-phase contaminants into the
vadose zone. Many times, the aeration of the vadose zone that is associated
with groundwater sparging can be an oxygen source for vadose zone con-
taminant biodegradation. This is especially important at most fuel release
sites where vadose zone biodegradation is a major part of cleanups. Thus,
the layout and operation of such sparging systems needs to satisfy the objec-
tives of both groundwater and vadose zone aeration. In most cases, a vapor
extraction system will need to be designed to capture volatilized contami-
nants. In other cases, engineers may rely on natural vadose zone biodegra-
dation to treat the volatilized contaminants. Such an approach requires that
the natural attenuation of the vapor-phase contaminants in the vadose zone
be monitored. In addition, operation of the sparging system may be limited
by the assimilative capacity of the vadose zone for the volatilized contami-
nants. In either case, the effect of sparging on the vadose zone and overall
site closure issues must be considered.
Conceptual site models that show contaminant distribution, aeration from
the sparging system, and effects of aeration on contaminant volatilization
and biodegradation are key to final project success. Specific site features
that may affect implementation, such as building constraints, changes in soil
5.2
-------
Chapter 5
types, subsurface structures, and access constraints, also need to be shown
on conceptual models. The conceptual model provides the means on which
to base the more quantitative evaluation of sparging system flow rates, well
sparging, and mass removal.
5.1.2 Establishing Groundwater Clean-up Goals
Traditionally, groundwater clean-up goals have been the maximum con-
taminant levels (MCLs) established under the Safe Drinking Water Act. For
most common contaminants treated with sparging (BTEX and chlorinated
solvents), the MCLs range from five to tens of parts per billion. Today,
MCLs remain clean-up goals at many sites, particularly those with ground-
water that may be used for human consumption. However, as discussed in
Section 3.1.2, the risk-based corrective action model can also be applied to
groundwater concentrations. Actual groundwater clean-up criteria vary
widely depending on the end use of the site, the point of compliance, and the
location of potential receptors. For example, the benzene MCL is 5 JJg/L.
An allowable concentration for benzene in groundwater at a nonresidential
site may be tens of parts per billion. Allowable benzene concentrations in a
groundwater discharge to surface water may be hundreds of parts per billion.
Through the use of more sophisticated fate and transport models that account
for biodegradation before the point of compliance, benzene clean-up criteria
significantly higher than these values may be acceptable. As with soil con-
centrations, a comprehensive approach to establishing groundwater clean-up
concentrations is beyond the scope of this monograph, but an adequate un-
derstanding of clean-up criteria is critical to the design of a sparging system.
The following sources can be consulted for further guidance:
• Standard Guide for Risk-Based Corrective Action Applied at
Petroleum Release Sites by the ASTM (E-1739-95);
• The Interim-Final Risk Assessment Guidance for Superfund (Part
A and Supplemental Guidances) US EPA, December 1989; and
• State-specific clean-up guidance.
Groundwater clean-up criteria need to be determined when design objec-
tives are set. For many sites, groundwater clean-up levels may be technol-
ogy-based instead of performance-based (i.e., clean-up criteria are set de-
pending on what the system can achieve).
5.3
-------
Design Development for Air Sparging
5.1.3 Measuring Groundwater Clean-up Criteria
Measuring changes in dissolved-phase groundwater concentrations with time
and comparing these concentrations to clean-up criteria is a simpler task with
groundwater sparging than assessing changes in soil concentrations during
vapor extraction In general, groundwater samples are collected from a series of
monitoring wells and piezometers (small diameter well, e.g., 1 in.). For sys-
tems designed for long-term plume containment, groundwater monitoring wells
downgradient from the sparging system and outside of the direct influence of
the sparging system are used to monitor for compliance. Wells on either edge
of the line of sparging wells should be monitored for plume displacement.
Typically, monitoring wells screened over the entire impacted depth of the aqui-
fer are typically used to assess groundwater quality.
For systems designed to address an entire plume or source area, ground-
water monitoring is best conducted at vertically and horizontally discrete
areas through the plume. There can be great variation in treatment effective-
ness over relatively short horizontal and vertical distances. For example,
Figure 5.1 shows the changes in four groundwater monitoring piezometers at
various vertical and horizontal distances from a sparging well. All four pi-
ezometers were within 6 m (20 ft) of the sparging well, yet show different
concentration fluctuations. Collection of such data indicates where the sys-
tem is less effective and consequently where operational or design changes
are required. Typically, a combination of monitoring wells around the
sparging target zone and monitoring piezometers within the sparging zone is
appropriate for system monitoring. At a minimum within the treatment
zone, two separate monitoring piezometers, each with at least two vertically
discrete sampling intervals, should be used to assess system performance.
More monitoring peizometers may be required for larger sites. Using solely
traditional monitoring wells does not provide adequate data to assess system
performance.
When assessing cleanup, it is necessary to distinguish between dissolved-
phase VOC concentrations that may be observed during sparging and con-
centrations that may be observed weeks or months after groundwater
sparging. Groundwater samples should never be collected during active
sparging since air bubbling up through monitoring wells or piezometers will
volatilize VOCs and provide low results compared to actual VOC concentra-
tions in the formation. In addition, rebound of dissolved-phase VOCs after
termination of groundwater sparging is well documented (see Figure 5.2).
5.4
-------
g-g
it? °«O»
•o •DTJT3TJ
3. NINNN
. S roro-L-i
1 ocooco
a.™
Concentration ((ig/L)
O
Q
(Q
0
O
<§
Q.
8?
-------
Design Development for Air Sparging
s
o>
I
I
I
Q
CIS
10 n
3
0
6
s
S
I
§
8
(T/Sil) ipM uopoBjjxg ui uopcnusouoj OQA
cti
<{
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-------
Chapter 5
Rebound is generally from residual NAPL or adsorbed-phase VOCs that con-
tinue to partition to the groundwater after sparging is stopped. This phenomena
is further documented in studies by Bass and Brown (1997). Ideally, monitor-
ing of sparging system performance should continue for at least four quarters
after termination of groundwater sparging. Section 6.4 presents a more inclu-
sive overview on monitoring groundwater sparging systems.
5.1.4 Achievable Groundwater Treatment Clean-up
Concentrations
There is little consensus on what concentrations are achievable with
groundwater sparging. However, the following serve as general guidelines:
• For favorable sparging sites (uniform sandy material) with only dis-
solved-phase plumes, reductions in dissolved-phase VOC concentrations
from the low ppm to the low ppb range are realistic.
• Sparging systems have been successfully used as cut-off wells at
many sites.
• For dissolved-phase plumes in more geologically conijplex sites,
it is possible to reduce concentrations from the low ppm range to
the low ppb range, but the chances of success are considerably
less, and there is a high likelihood that operational and design
changes will be required during the project. There are few, reli-
able predictive tools that suggest when to expect failure and
when to expect success.
• For sites with residual LNAPL, there are few data available to
suggest that MCL drinking water levels can be met. Sparging is
effective at removing some residual NAPL and even reducing the
amount of continuous (floating) LNAPL. As a result, sparging
can shrink some plumes and reduce overall concentrations.
However, there has not been sufficient soil and groundwater sam-
pling at these sites throughout the groundwater and smear zone
with the statistical rigor required to prove that MCL-level con-
centrations can be achieved.
At this time, it is impractical to predict with certainty whether a particular
sparging system will be successful and how long it will take for such a sys-
tem to achieve success. Much of the research into air sparging, both in the
5.7
-------
Design Development for Air Sparging
laboratory and in the field, suggests that sparging should rarely work be-
cause air flow is channeled along preferential pathways. On the other hand,
examples of full-scale sparging systems that have achieved significant and
permanent reductions in groundwater concentrations abound. It is likely that
hundreds of sparging sites have achieved closure at this time.
Some success and failures of air sparging systems have been documented
by Bass and Brown (1997) who compiled a database of about 40 completed
in-situ air sparging sites where groundwater contaminant concentrations
were compared before sparging was initiated, just before sparging was termi-
nated, and in the months following shutdown of the system. The case stud-
ies included both chlorinated solvent and petroleum hydrocarbon contamina-
tion and covered a wide range of soil conditions and sparging system param-
eters. No absolute predictive indicators for sparging success were obvious
from review of this database, but some general trends were evident. Air
sparging systems achieved a substantial and permanent decrease in ground-
water concentrations at sites with both chlorinated and petroleum contamina-
tion, both sandy and silty soils, and both continuous- and pulsed-flow
sparging. However, in other cases, particularly at sites contaminated with
petroleum hydrocarbons, groundwater concentrations either did not decrease
during sparging or rebounded significantly after the sparging system was
terminated. When sparging was successful at petroleum sites, the permanent
reductions in groundwater concentrations were much greater than at chlori-
nated sites. Poor sparging performance at petroleum-contaminated sites was
more likely when high initial groundwater contamination levels suggested a
substantial smear zone of residual NAPL. The best sparging performance at
petroleum sites was generally associated with a high density of sparging
wells addressing the entire source area, a high sparging air injection rate, and
a stable water table.
It is necessary to balance these observations with the site clean-up goals.
For example, a required 99% reduction of dissolved-phase VOCs at a site
with favorable sparging conditions may have the same chance for success as
a required 50% reduction in concentrations at a site with less favorable con-
ditions. Sparging at a site with some residual LNAPL may not achieve
MCLs in the groundwater, but may result in significant mass reduction and
meet a requirement to address LNAPL. Sparging needs to be evaluated at
each site in the context of regulatory requirements, site-specific features, and
implications for partial or total failure.
5.8
-------
Chapter 5
5.2 Design Basis
The design basis for sparging systems is fundamentally different than that
for vapor extraction/bioventing. There is no practical method by which field
measurements can be incorporated into standard gas flow equations for po-
rous media to predict system performance as with vapor extraction/
bioventing. Actual air distribution is dictated by pore-scale variations in soil
particle size, packing, and permeability that cannot be practically modeled
from site information; the design process needs to account for these inherent
uncertainties. Therefore, it is necessary to rely on a more observational
approach, where systems are installed, operated, and modified as required.
This section presents site data required for full-scale design. Figure 5.3
presents an overview of the sparging design/implementation process.
5.2.1 Site and Contaminant Characteristics
Evaluation of the following site parameters is necessary for system design.
• Soil Characteristics and Stratigraphy. Low-permeability soils
(hydraulic conductivities less than 10'5 cm/s) are often unsuitable
for air sparging since the pressures required to force sparging air
into the formation generally will fracture the soil, producing
preferential pathways. Continuous,, low-permeability lenses (of
even modest thickness) within higher permeability formations,
can result in lateral diversion of sparging air. This can leave
some areas of the site unaffected by sparging. Continuous strata
of substantial thickness within the saturated zone are a significant
limitation for air sparging. Consequently, adequate delineation
of soil stratigraphy via continuous logging of multiple soil
borings is critical to the design process.
• Depth to Groundwater and Range of Fluctuation. In most cases,
sufficient vadose zone thickness (at least 1 m [3 ft]) must be
present to allow for operation of vapor extraction to recover the
sparged air, or for biodegradation of volatilized contaminants to
be essentially complete before the sparging air exits to the
ground surface. Water table variations, both seasonal and during
sparging transients, affect not only the design of the vapor extrac-
tion wells but also the thickness of the smear zone that forms
when the contaminant reaches the water table as a separate phase.
5.9 ;
-------
Design Development for Air Sparging
Figure 5.3
Overview of Sparging Evaluation and Implementation
Complete Site Investigation
Evaluating Sparging Feasibilit;
Is Regulatory
Environment Favorable
for Sparging?
Is Physical
Environment
Favorable for
in
Conducted Limited
Combine
with Other
Technologies?
. Complete Design
(May Include More Detailed Pilot Test)
Drop from
Further Consideration
Start-Up System
Are
Required
Responses
Observed?
Source: Boersma, Newman, and Plontek 1994
5.10
-------
Chapter 5
• Saturated Zone Thickness. The extent of lateral movement of
sparging air is determined in part by the depth of the well seal (or
of the top of the well screen if the well is driven) below the water
table surface. If the saturated zone is significantly less than 2 m
(6.5 ft) thick, it may be difficult for a sparging well to attain sig-
nificant lateral influence.
• Pressure/Flow Response. The flow achieved in response to an
applied pressure determines how much air can be delivered to the
subsurface to effect remediation and hence places constraints on
the sparging compressor sizing. The sparging pressure must not
exceed the soil column pressure or fracturing of the soil may
occur. Excessive pressure may also result in upwelling during
startup, which can render the vapor extraction system temporarily
inoperable.
• Evidence of Vertical Air Movement into the Vadose Zone. Deter-
mined by a pilot test, this is by far the most important informa-
tion for air sparging that can be gained from site investigation.
• Evidence of Lateral Air Movement into the Saturated Zone. The
lateral influence of sparging is difficult to measure, and is rarely
radially symmetric. Therefore, the term "radius of influence" can
be misleading. However, it is important to identify and measure
some lateral effect during pilot testing to ensure that the move-
ment of air into the vadose zone is not the result of a poor
sparging well seal.
A pilot test providing the above information need not require more than a
day in the field to perform. For most smaller sites, this will be sufficient, but
extended testing, spanning a few months, may be considered if the size of
the envisioned full-scale system is very large. In this case, it is advisable to
operate a few sparging wells for an extended period to ensure that substantial
and permanent reduction in groundwater concentrations can, in fact, be ef-
fected before a large investment is made in an extensive sparging system.
The contaminant properties that most affect sparging feasibility include
volatility, aqueous solubility, and biodegradabilify. The first two determine
the contaminant partitioning and hence the thermodynamic driving force for
the contaminant to enter the sparged air. For many contaminants of concern
these parameters are well known. However, many petroleum products and
5.11
-------
Design Development for Air Sparging
mixed organic wastes consist of components with a wide range of physical
properties. Laboratory analysis of soil or NAPL samples is often used deter-
mine the distribution of physical properties.
The concentration of contaminants in the soil and the total mass of con-
taminants released can also have a profound impact on the effectiveness of
air sparging. Dissolved plumes are remediated much more quickly and with
wider well spacing than source areas with extensive residual NAPL in a
smear zone. Unfortunately, the precise location and total mass of residual
NAPL is never known and cannot be reliably estimated from site soil, soil
gas, or groundwater analytical data. One approach to dealing with this un-
certainty is to install a sparging system initially with wider well spacings,
then fill in where groundwater concentrations do not show adequate re-
sponse. In this approach, the sparging system is used as both a remediation
system and a diagnostic tool to find areas of high residual NAPL.
Several additional parameters are sometimes measured through laboratory
analysis of soil samples. (If soils samples are collected, each major strati-
graphic unit between the seasonal high water table elevation and the eleva-
tion of the sparging screen should be sampled.) Organic carbon content
affects contaminant partitioning and high levels, such as those typically
found in peat, can significantly compromise the effectiveness of vapor ex-
traction on contaminants that adsorb to organic matter. Moisture content
(measured in the field via neutron probe or in the laboratory) and the soil
moisture retention curve (from an undisturbed soil sample) may be useful in
determining the dynamics of air entry into the soil. Other soil parameters
sometimes measured include pneumatic and hydraulic conductivity, grain
size distribution, bulk density, and porosity. While all of these parameters
are often of scientific interest and enhance understanding of the site, at this
time they are rarely considered for the initial design basis, but can be used in
modeling efforts to track the progress of remedial efforts.
When bioremediation is anticipated to be a significant contributor to
remediation, nutrients in soil and groundwater (nitrogen and phosphorous
concentrations and speciation and pH) can be measured to ascertain whether
nutrient addition will be required. Biological and chemical oxygen demand
(BOD and COD, respectively), sulfur and iron concentrations and speciation,
dissolved oxygen, and redox potential also can be measured to shed light on
the oxygen requirements for bioremediation. In addition, soil bacteria popu-
lations can be assessed in the laboratory to evaluate the viability of
5.12
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Chapter 5
bioventing, although they are more commonly evaluated through an in situ
respirometry test in which biological activity is determined from changes in
dissolved oxygen or subsurface temperature during and following sparging
system operation.
5.2.2 Pilot Testing
Currently, since there is no known reliably consistent relationship be-
tween the transport of injected air into saturated porous media and the result-
ing air flow distribution and contaminant mass transfer, pilot testing is
needed to assess the feasibility of using air sparging at a site. Thus, the pri-
mary objective for pilot testing is to assess the basic feasibility of sparging at
a site by looking for failures. The most common of these is when air does
not exit the saturated zone in the vicinity of the sparging well. Another com-
mon failure at low-permeability sites is the inability to induce air flow with-
out fracturing the soil.
A common objective of pilot tests is to assess the zone of influence
around a sparging well. Zone of influence can be defined as a volume of
saturated soil around a sparging well where air flow can be detected or
where the effects of air contact, groundwater mixing, or groundwater oxy-
genation are detectable. This zone is usually estimated by one or more mea-
surements during pilot testing. It should be noted that given, the variation in
treatment effectiveness within a region influenced by sparging, the term
"radius of influence" (ROI) is misleading, and that the term zone of influ-
ence represents a better conceptual understanding of this design parameter.
As discussed later in this chapter, the ability to measure the zone of influ-
ence with commonly employed field observation methods is limited.
Sufficient time is typically unavailable to evaluate fate and transport re-
moval rates during pilot tests. Pilot tests of air sparging technology reported
in an American Petroleum Institute database (American Petroleum Institute
1995) were usually less than one day in duration. In that time period, sig-
nificant improvements in groundwater quality were not observed. In addi-
tion, the database indicated that due to the limitations of the monitoring
techniques most frequently used in pilot testing, the outcome of pilot-scale
evaluations with regard to well spacing was an estimate of ROI rather than
zone of influence. Unfortunately, this provides the engineer with only the
most simplistic understanding of ah" flow.
5.13
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1 I Ml '"'
Design Development for Air Sparging
In addition to zone of influence monitoring, the other objectives of pilot
testing are to determine the optimal injection pressures and flow rates and to
evaluate offgas handling options, contaminant volatilization to the vadose
zone, need for offgas treatment, amount of groundwater mounding, and
amount of induced vadose zone biodegradation. These criterian are dis-
cussed in the following sections. Table 5.1 summarizes pilot test objectives
and the relative certainty that a pilot test will meet the objectives.
Table 5.1
Sparging Pilot Test Objectives
Pilot Test Objective
Data Required to Meet
Objective
Relative Certainty that Pilot
Test Will Meet Objective
Air entry pressure
Duration of groundwater
mounding
Optimal flow rates
Decrease in dissolved-phase
contaminants
Need for SVE system to control
vapor-phase contaminants in
vadose zone
Amount of induced vadose zone
biodegradation
Flow/pressure relationship at
sparging well
Frequent groundwater level
measurements around sparging
well
Relationship of flow to dissolved
oxygen and dissolved
contaminant concentration
changes
Analysis of groundwater samples
Contaminant concentrations in
soil gas, soil gas pressure
resulting from sparging, receptor
locations
Oxygen uptake studies before
and after sparging
Optimal sparging well spacing All of the above
High
High
Low — little rational basis to
determine optimum flows. Upper
limit on flow is point where
matrix fracturing takes place.
Moderate/High —several-week
pilot test duration required.
Moderate/High
Moderate
Low — difficult to determine
actual vertical/horizontal air
distribution. May vary
significantly among sparge
wells at some sites.
Source: Boersma, Newman, and Piontek 1994
5.14
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Chapter 5
5.2.2.1 Pilot Test Setup
This section provides general guidance for the basic equipment that is
typically used in air sparging pilot tests. For additional information, refer to
American Petroleum Institute (1995) and Wisconsin Department of Natural
Resources (1993).
The typical pilot test setup includes one or more injection wells, at least
two monitoring piezometers, an injection pump, blower or compressor, and
ancillary equipment that may include a pressure relief valve, an inlet filter, a
flow control valve, and flow meter(s)(Figure 5.4). Provisions must be made
for monitoring the pressure, flow rate, and temperature at the wellhead of
each injection well. The ultimate fate of the pilot test components should be
considered during the selection process, including whether the main compo-
nents could potentially be used in the full-scale system.
Section 5.3 presents information concerning selection of air sparging
equipment for full-scale systems; however, this information is also pertinent
to choosing pilot system equipment.
5.2.2.2 Zone of Influence Monitoring
This section discusses available methods for estimating the zone of influ-
ence of an air sparging well(s) during pilot testing.
Dissolved Oxygen Measurement. Increased dissolved oxygen (DO) con-
centrations are often observed in monitoring wells and piezometers during
sparging. American Petroleum Institute (1995) indicates that DO monitoring
is the most common method of determining the zone of influence of a
sparging application. In addition, monitoring of DO during biosparging is
critical to understanding the rate of aerobic biodegradation that occurs as
remediation proceeds.
Johnson et al. (1995) and Boersma, Piontek, and Newman (1995) demon-
strated that the interpretation of sparging effectiveness is dependent on the
monitoring strategy employed, especially with regard to the length of
screened intervals. Johnson et al. (1995) reported that during short-term
pilot testing, DO and the tracer gas helium concentrations in conventional
monitoring wells rose, suggesting a broad, and fairly uniform, saturated zone
air distribution profile with evidence of injected air having traveled substan-
tial distances (18m [60 ft]) from the sparging well. However, discrete im-
plants (15 cm [6 in.]) indicated little oxygen and helium transfer in the
5.15 ;
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Design Development for Air Sparging
to
D)
«t £
co
o
o
O
1
J
5.16
-------
Chapter 5
saturated zone, suggesting at best sporadic saturated zone air distribution and
limited usefulness of sparging at that particular site. It is likely that wells
with long screened intervals had a greater probability of intersecting air
channels, and lack of an increase in DO and helium in implants Indicated
that air channels were not homogeneously distributed. Helium was detected
in only two vadose zone implants, again suggesting that air channel forma-
tion was erratic. Also, even when a vapor extraction rate was greater than
the air injection rate by a factor of 5, only about 50% of the injected helium
was recovered by the vapor extraction system, yet again suggesting lack of
control in air channel propagation. A monitoring strategy using conventional
monitoring wells is much more common and thus likely gives an overly
optimistic picture of sparging effectiveness at many sites.
Within a monitoring well, obtaining reliable DO measurements of
groundwater that are representative of the aquifer DO concentrations can be
a difficult task. Often the very act of collecting a sample can result in aera-
tion and an overestimation of DO. For this reason, it is recommended that at
least two methods of DO measurement be used when possible.
The most common methods available for determination of DO in the field
are (1) use of a down-hole oxygen probe/oxygen meter, (2) use of an oxygen
probe/meter to analyze a sample that has been bailed or pumped from a well,
and (3) titration of a sample that has been pumped or bailed. Down-hole
probes are easy to use provided the target measurement depth is reachable
with the probe connection. Care should be taken to purge the well'before
taking a down-hole DO reading. In addition, it is common to see significant
drift in readings as the probe is moved (even slightly) within the well or even
when the probe remains stationary. A standard measurement procedure
should be used at each well so that all readings will be comparable. Also, it
is important to calibrate the probe/meter often and within the expected tem-
perature range of the aquifer.
When collecting a groundwater sample for analysis, aeration of the
sample should be minimized. A peristaltic pump can be used if the sample
depth is shallow and use of the pump will not introduce oxygen to the
sample. Use of bailers should be avoided if possible.
Titration of a sample using the Winkler method can produce repeatable
DO results. The titration process can be greatly simplified by using a field
titration method such as the one manufactured by Hach.
5.17
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Design Development for Air Sparging
Monitoring Well Bubbling. Monitoring wells located near sparging wells
often experience bubbling. Bubble formation in monitoring wells is likely
caused by air channels intercepting the well bore, allowing air to rise verti-
cally through the well. If the monitoring well is sealed, local transient
mounding and subsequent propagation of air channels should occur. There-
fore, a well with air flow or bubbling should be sealed. Also, samples do not
provide useful information when collected from wells experiencing bubbling
for DO and VOC analysis — the wells are effectively operating as an air
stripper and there are not representative of the groundwater in the formation.
Neutron Moisture/Density Probes. A neutron moisture probe is a field
instrument that can be used to estimate changes in soil water saturation due
to the effects of air sparging. The probe contains a "fast" radioactive neutron
source and a "slow" neutron detector (Acomb et al. 1996). The probe is
typically lowered down an access pipe and a cloud of fast neutrons is re-
leased into the surrounding soils. The neutrons collide with hydrogen atoms,
thereby slowing or thermalizing the neutrons. The slow neutrons are then
counted by the neutron detector, and the results are converted to an estimate
of soil saturation based on baseline measurements for 100% and 0% satura-
tion. Unfortunately, the probe measures hydrogen, which can be found in
either water or contaminants. Therefore, it is (difficult to differentiate water
saturation from contaminant saturation.
Neutron probes have been used for over 50 years and have been commer-
cially available for more than 35 years. The technology is well established
in the agricultural, environmental, and petroleum and gas industries. Neu-
tron probes offer a precise, inexpensive (about $5,000), nondestructive, and
real-time method of monitoring relative saturation. The probes are also
fairly easy to use. Newer designs are highly automated with computer con-
trol of measurements and data collection.
Acomb et al. (1996) recently published neutron probe results from an air
sparging site characterized by uniform "beach sand" and contaminated with
gasoline and diesel range hydrocarbons. They found measurable air distribu-
tion in previously water-saturated soil at 3.5 m (12 ft) from the air sparging
well. The air distribution was found to stabilize within 12 hours of sparging
startup. Further, the results indicated that frequent pulsing is needed to opti-
mize air transport with subsequent groundwater mixing.
5.18
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Chapter 5
Time Domain Reflectometry (TDR). TDR measures soil moisture con-
tent by propagation of electromagnetic pulses along a pair of transmission
waveguides in direct contact with the soil. TDR offers precise measurement
of soil moisture content because the dielectric constant for dry soil particles
differs so much from that of water (Topp, Zegelin, and White 1994). TDR
systems have been used to monitor air sparging systems by Clayton, Brown,
and Bass (1995) by pushing a pair of waveguides (a probe) into the bottom
of a soil boring to a known depth and backfilling above the probe with grout.
TDR is a well-established technology that provides real-time moisture and
time series measurements that can be procured commercially.
Electrical Resistivity Tomography (ERT). ERT is a technique for survey-
ing the two-dimensional electrical conductivity of the subsurface between
wells spaced 1.5 to 7.5 m (5 to 25 ft) apart (Lundegard, Chaffee, and
LeBrecque 1996). Conductivity is directly related to water saturation.
Therefore, this technology can be used to determine the percent air satura-
tion extending outward from an injection well. The method has been used in
air sparging research but has had little use in pilot tests to date.
Tracer Gas Tests. Tracer gas tests use gases not naturally occurring in the
subsurface of a site, such as sulfur hexafluoride or helium, to indicate rates and/
or patterns of injected air flow. The advantage of using tracer gases is that,
unlike oxygen, they are conservative and not depleted by geochemical or bio-
logical reactions. During the pilot test, the tracer gas is injected directly into the
injection airstream. Required equipment includes a tracer gas cylinder, pressure
regulator, flow meter, piping to the injection point, a sample pump, and a tracer
gas detector. Soil gas and groundwater is monitored for the tracer gas at dis-
crete saturated zone monitoring points to define the distribution at various times
during sparging. Tracer tests can be valuable in clarifying uncertainty about
uncontrolled VOC emissions to exposure points.
Groundwater Mounding. Mounding, simply defined, is the observation
of elevated water levels in monitoring wells and piezometers during
sparging. If the water table is close to the surface, water level rise can be-
come fairly dramatic as some wells may become "artesian" (i.e., water flows
freely from wells). Mounding can be described as a multistage process. The
first stage is characterized by a period of vertical and radial displacement of
groundwater with pressurized air. During this time, the rate of air injection
into the saturated zone exceeds the rate of air flow out of the saturated zone
resulting in pressure buildup and thus elevated water levels in piezometers
5.19
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Design Development for Air Sparging
and monitoring wells. Elevated pressure during this stage allows initial for-
mation of air channels or zones of desaturation. Numerical, multiphased
modeling by Lundegard and Andersen (1996) indicates that in relatively
homogeneous media, formation of air channels away from the sparging
wells should result in a region of desaturation resembling a teardrop- or bell-
shaped geometry. Because the compressibility of water is very low, pressure
buildup (mounding) propagates a far greater distance than the region of air
flow. Thus, the use of mounding as an indicator of the zone of influence
typically results in an overestimation of the region of air flow. In an uncon-
fined aquifer, some portion of mounding manifested by water level rise in
piezometers is likely due to actual physical elevation in the water table in
addition to a pressure response.
When the significant air flow finally breaks through to the vadose zone,
pressure is released since the air flux out of the saturated zone is greater than
the air flux into the saturated zone and mounding dissipates. Decrease in
pressure results in collapse of air channels more radially distant from the
sparging well, and air flow is confined to regions of higher permeability near
the sparging well. During this period, grqundwater flow back toward the
sparging well would be expected. Thus, the radial extent of air flow actually
decreases as steady-state conditions are approached. Lundegard and
Andersen's (1993) numerical simulations indicate that when air breaks
through to the vadose zone, the region of desaturation resembles a conical
shape. When steady-stage conditions are reached, little or no mounding
exists. Thus, the importance of achieving steady-state conditions during
sparging testing becomes apparent in that transient or short-term testing will
likely result in overestimation of the region of air flow. After achievement of
steady-state conditions, a persistent water level elevation may be observed
hydraulically upgradient of sparging wells due to diversion of groundwater
flow. Displacement of groundwater and creation of a zone of desaturation
during sparging may create a region of limited lateral groundwater flow due
to lowered conductivity.
The relationship between groundwater mounding and displacement of the
dissolved-phase plume or displacement of continuous NAPL has been the
subject of much debate. It is unlikely that continuous NAPL is displaced by
temporary groundwater mounding. The NAPL may be submerged during
the groundwater mounding, and there may be some mixing of the NAPL as
the groundwater subsides, but there does not appear to be significant hori-
zontal displacement of continuous NAPL. Fears that continuous NAPL may
5.20
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Chapter 5
"slide down" the groundwater mound are unfounded. There is some dis-
placement of the groundwater and hence the dissolved-phase plume. Simple
groundwater flow calculations of the magnitude of temporary horizontal and
vertical gradients induced by sparging and the duration of those gradients
suggest that groundwater displacement is on the order of millimeters to
inches, but not several feet per sparging cycle (Boersma, Piontek, and
Newman 1995). While the displacement would not be sufficient to result in
large-scale plume displacement, the groundwater movement may result in
added mass removal since each sparging cycle results in varied groundwater
distribution in relation to the air channels, which remain fixed. In this way,
sparging is more effective in dissolved-phase plumes than residual NAPL
since dissolved-phase contaminants may eventually come in contact with an
air channel due to displacement, while residual NAPL is fixed in the soil
pore and may not be removed if it is not directly contacted by an air channel
(Boersma, Piontek, and Newman 1995).
Given this description of the dynamics of groundwater mounding during
air sparging, the importance of monitoring water table elevations during
sparging pilot testing should be apparent. In most cases, simple groundwater
level probes are sufficient. For more complex sites or where more accurate
readings are needed, or in wells where bubbling (from nearby sparge wells)
is expected, pressure transducers with data loggers can be used.
5.2.2.3 Step Test Procedures
An air injection step test may be conducted during the pilot testing using
a procedure similar to the vapor extraction step test described in Section
3.2.2.1. The recommended sequence is:
1. Open the air outlet valve, which discharges compressed air to the
atmosphere.
2. Close the valve leading to the wellhead.
3. Turn on the blower so that air is being forced out through only
the air outlet valve.
4. Fully open the valve leading to the wellhead.
5. In a series of increments, slowly close the air outlet valve.
6. For each increment, allow the flow rate to stabilize and record
the wellhead pressure and flow rate into the sparging well.
5.21
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Design Development for Air Sparging
No flow v/ill be measured until the minimum pressure required to
initiate flow is exceeded. Record the; pressure at which flow is
first initialed.
7. Continue closing the outlet valve until the desired flow rate is
achieved.
Step test results generally fall under one of the following three scenarios
with regard to how injected air is transported in the formation (Baker,
Pemmireddy, and McKay 1996):
,|, , , , ,
1. Air flow commences at, or very close to, the hydrostatic pressure
(the pressure required to push the water within the well down to
the top of the screen interval). This suggests that the air entry
pressure (the pressure required to force air into the formation) is
small and that air flow is occurring primarily within large pores.
Air flow may be well distributed in this case if uniform sands are
present; however, if the soils are heterogeneous, preferential flow
via the most permeable pathways is likely.
2. Air flow does not occur until a pressure greater than the hydro-
static pressure is applied, indicating that the well screen did not
intersect macropores or high-permeability lenses. Air flow in
this case may be well distributed if the formation consists of
uniform fine sands or silts.
3. No significant air flow is measured even when the injection
pressure is increased to 0.8 of the overburden pressure (the
pressure due to the weight of the soil and groundwater above
the top of the screen). In this case, the sparging screen is
located within a low-permeability zone of soil and the well
should be depressurized since there is a risk of pneumatically
fracturing the formation.
When conducting sparging pilot tests, both pressure and flow rate
need to be monitored and controlled. Varying pressure, so that it is the
independent variable, will allow the operator to achieve the desired flow
rate. However, it is ultimately flow that needs to be controlled in a pi-
lot- or full-scale application.
5.22
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Chapters
5.2.3 Pilot Test Result Interpretation
5.2.3.1 Vertical Air Movement into the Vadose Zone
The principal function of a sparging pilot test is to ascertain if sparging is
feasible, i.e., whether sparged air is reaching the vadose zone. The surest
way to determine vertical air movement is to inject a tracer into the sparging
air during pilot testing and analyze the vapor extraction offgas for the tracer.
Helium (He) and sulfur hexafluoride (SF6) are the most commonly used
tracers. Helium is inexpensive and easy to identify using a field thermal
conductivity detector, but the detector is not very sensitive (detection limits
for helium using a typical field helium detector are 0.01% to 0.1% by vol-
ume). Hydrogen, which can be present in highly-reducing environments due
to microbial activity, can interfere with helium detection. For these reasons,
SF6 is usually a better choice as a tracer. A field gas chromatograph
equipped with an electron capture detector can accurately detect SF6 at levels
less than 1 ppbv.
The tracer gas can be either injected all at once or continuously bled into
the sparging air. Monitoring offgas or soil vapor after injection of a slug of
tracer provides the impulse response of the system. If the tracer gas is ob-
served in the vapor extraction offgas within a few minutes, the sparging air
has moved vertically unimpeded into the vadose zone. If the time until
tracer is first detected is on the order of an hour or more, the sparging air has
traveled largely laterally for some distance before finding a path to the va-
dose zone. Radial air flow models can be used to estimate transit time to the
vapor extraction well as a function of distance from the well; this would
represent the upper bound of the distance the air from the sparging air would
have had to travel before reaching the vadose zone. If a monitoring well
penetrating deep into the saturated zone is present within this distance, it
may be that the monitoring well is providing a preferential pathway through
an impermeable barrier, and the results of the test should not be viewed as
unequivocally positive. .
Tracer slug tests can also be used to perform a mass balance between
tracer injection in the sparging air and tracer recovery in the vapor extraction
offgas. However, there is always some retardation of tracer in the saturated
zone through sorption and retention of air. For mass balance calculations, it
is usually better to bleed tracer into the sparging ah" continuously at a known
mass rate. The sparging system is then operated continuously and the vapor
5.23
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Design Development for Air Sparging
extraction offgas monitored for tracer gas until steady-state conditions are
reached. A mass balance is performed by comparing the rate of tracer flow
into and out of the subsurface.
For any mass balance calculation, it is crucial that the vapor extraction
system is recovering all soil gas within the anticipated zone of sparging in-
fluence. This may mean operating the vapor extraction system at a flow rate
much higher than the air sparging rate, sealing the ground surface to mini-
mize air infiltration, and/or operating more than one vapor extraction well
during the test.
When a tracer test cannot be performed, evidence of sparging air reaching
the vadpse zone can be' found from monitoring the vapor extraction offgas
for volatile contaminant vapors. Typically, the VOC concentrations in vapor
extraction offgas will reach a steady-state value after a few pore volume
exchanges in the vadose zone. If a sparging system is turned on after these
steady-state conditions have been established, then the VOC concentrations
in the vapor extraction offgas will suddenly increase provided the sparged air
is reaching the vadose zone. This is a less definitive determination than a
tracer test, but it is also less susceptible to false positive results when there is
a poor seal on the sparging well. In this case, tracers would readily enter the
vadose zone through the failed well seal, but the vadose zone VOC levels
would not be significantly affected since the sparging air would be passing
through clean well gravel.
Evidence can also be found for sparging air reaching the vadose zone
when doing pilot tests without vapor extraction. Observation of positive
pressure in the vadose zone is evidence that sparging air is entering the va-
dose zone, especially if the positive pressure dissipates with distance from
the sparging well. It is necessary to perform background vadose zone pres-
sure measurements when applying this technique, especially when the depth
to groundwater is large, to ensure that barometric pressure fluctuations are
not producing false positives.
5.2.3.2 Lateral Air Movement into the Sqturated Zone
It is important to identify some lateral effect during pilot testing to ensure
that the movement of air into the vadose zone is not the result of a bad
5.24
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Chapter 5
sparging well seal. If a tracer gas has been injected with the sparging air, the
observation of the tracer in groundwater in a monitoring well or piezometer
is unequivocal evidence that the sparged air has moved laterally through the
saturated zone.
The observation of bubbling in a monitoring well obviously means
sparged air has reached the monitoring well through the saturated zone.
High pressure in a monitoring well is also strong evidence that sparging air
is reaching the well through the saturated zone. This is particularly true if
the monitoring point is occluded, i.e., screened exclusively below the water
table. When this is the case, there are no plausible means by which air could
enter the well except through the saturated zone. When measuring pressures
on an occluded monitoring well, it is always necessary to vent the well
briefly before applying the pressure measurement device so that a water
table rise is not misinterpreted as pressurization of the monitoring well by
sparged air.
Large increases in VOC concentrations in the headspace of a monitoring
well screened across the water table are sometimes taken as evidence that
sparged air has reached the monitoring well through the saturated zone. In-
creases in dissolved oxygen levels in the monitoring wells often are inter-
preted in this way as well. However, dissolved oxygen can be difficult to
measure reliably using a field probe since disturbing the monitoring well can
change the apparent dissolved oxygen level. Various methods to obtain more
reliable dissolved oxygen information have been explored, including (1)
continuous pumping of the well; (2) installation of galvanic oxygen monitors
directly in the saturated zone; and (3) lowering evacuated ampules contain-
ing a reagent into a well, breaking the ampule tip remotely, and analyzing
the recovered water standards colorimetrically.
5.2.3.3 Pressure/Flow Response
The flow achieved in response to an applied pressure is a key parameter in
sparging system design as it determines the appropriate sparging compressor
or blower sizing. The pressure/flow response also lends insight into the
nature of sparging air movement through the subsurface and may be useful
in assessing the potential efficacy of a sparging system.
5.25
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Design Development for Air Sparging
Sparging air flow does not commence until sparging pressure exceeds a
threshold pressure, consisting of the sum of the hydrostatic pressure and the
air entry pressure through the filter pack (if present) and the formation. Hy-
drostatic pressure is expressed as
Ph=PwgAz (5.1)
where: Ph = hydrostatic pressure;
pw = density of water;
g = acceleration of gravity (9.81 m/s2 or 32.17 ft/s2at mean
Sea level); and
z = distance from static groundwater surface to top of the
sparging well screen!""
Air entry pressures, which can range from a few centimeters water col-
umn or less in coarse sands and gravels to more than a meter water column
in silts, are represented by:
where: Pe = air entry pressure;
a = surface tension of water in air; and
d = diameter of constrictions along the largest pores of entry.
• • i
Sustained air flow requires that air not only enter individual pores but also
form continuous channels through the entire formation. This occurs at the
inflection point of a Van Genuchten curve fitted to the soil moisture retention
data. The inflation pressure (P.nfl) is a slightly higher pressure than Pe. Once
sustained flow is achieved, friction in the sparging well casing will contrib-
ute to pressure loss. The Manning (or Darcy) equation for head loss due to
friction of a fluid moving through a cylindrical pipe is generally used, pro-
vided the density of the sparging air does not change substantially (due to
pressure and temperature changes) within the sparging well riser. The diam-
eter of the sparging well should always be sufficient to ensure that, at the
flow rate and sparging depth required, the frictional losses are negligible.
As sparging pressure increases above that necessary to sustain air
flow, more and more air will flow through the formation creating chan-
nels through smaller and smaller pores. Hov/ever, at the point where the
applied pressure exceeds the weight of the soil column above it, the soil
may fracture, and the resulting large channels will serve as preferential
5.26
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Chapter 5
pathways for sparging air. Optimum sparging pressure is therefore the
highest pressure achievable without risking soil fracturing (Wisconsin
Department of Natural Resources 1993).
To estimate the maximum operating pressure (i.e., a function of the
weight of the soil and water column above the top of screen), the following
simplistic example is provided (Wisconsin Department of Natural Resources
1993) which assumes a:
• soil specific gravity of 2.7;
• water table depth of 5.5 m (18 ft);
• sparging well screened from 9.1 to 10.7 m (30 to 35 feet);
• porosity of 30%; and
• homogeneous, isotropic, and unconsolidated soils.
Using English-system units for illustration, the overlying pressure exerted
by the weight of the soil column:
Weight of soil per square foot = 30 ft • 2.7 • (1 - 0.3) • 62.4 Ibs / ft3 = 3,538 Ibs / ft2
Weight of water per square foot = (30 - 18)ft • 0.3 • 62.4 Ibs / ft3 = 224 Ibs / ft2
Total = 3,538 + 224 = 3,762 Ibs / ft2 • 1 ft2 /144 in2 = 26 psig at 30 feet of depth
In this example, injection pressures greater than 179 kPa (26 psig) could
cause system problems and secondary permeability channels to develop.
Therefore, as with all designs, a factor of safety should be used equivalent to
60-80% of the overlying pressure (i.e., 107-143 kPa or [15.6-20.8 psig] for
this example). Engineers must remember that each site has specific condi-
tions and requirements and should use all available information when per-
forming these calculations.
Using the calculated pressure data along with pilot test data, the pressure
necessary to deliver the desired air flow rate under all seasonal operating
conditions can be calculated. Professional judgment is required to determine
design pressures and flow rates for each sparging well. If an air flow rate of
0.5 scfm per well cannot be maintained at the site, the soil permeability may
be too low and air sparging may not be appropriate for the site.
In some cases, the apparent rise in groundwater table that occurs when
sparging is initiated may limit sparging air pressure to levels below the rec-
ommended maximum based on soil fracturing considerations. In situations
5.27
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ft 7,, V. in:"! »'!! ill "". J _'', ,T» ' '."[ , J1 '. : ' ?! :', 1:Hfe 1fe .'
' . | , "Illi; i , . II .„ i , ' !! '"i!!,ii|, ' "i"1,
Design Development for Air Sparging
where the depth to groundwater is relatively shallow (less than 3 m [10 ft]),
and especially where the soil permeability is fairly low, upwelling in moni-
toring wells during startup due to excessive sparging air pressure may be
problematic. If the upwelling approaches or exceeds the top of the vapor
extraction well screens, the vapor extraction system will be rendered tempo-
rarily inoperable due to excessive water entrainment or deadheading of the
extraction wells.
5.2.3.4 Biodegradation Rate
Saturated zone in situ respirometry methods have recently been tested at
an air sparging site in Ft. Wainwright, Alaska (Gould and Sexton 1996).
Microbial uptake of dissolved oxygen in the saturated zone was measured
quarterly, and the decrease in dissolved oxygen concentration was attributed
to biodegradation of hydrocarbons based on certain assumptions, including
soil porosity and zone of influence. Accounting for advective and dispersive
fluxes of dissolved oxygen away from the zone of influence following shut-
down of the sparging system, as well as the effects of nontarget inorganics
such as ferrous ion on oxygen uptake, are limitations of such methods.
An alternative approach to assessing biodegradation rates from sparging
operation is to assign temperature rise in the saturated zone to biological
activity (Acomb et al. 1996; Veenis, Bass and Bartholomae 1997). Tempera-
ture increases in groundwater during air sparging may be as much as 30°C,
although they are more commonly in the range of 5 to 10°C. A steady-state
heat balance explaining this temperature change is complex. Energy inputs
include the heat of biological activity (the variable for which the equation is
solved), sensible heat of injected air, latent heat of moisture condensation in
injected air, plus various other convective and conductive terms. Energy
losses include sensible heat leaving with sparging air and latent heat of
evaporation, as well as other convective and conductive terms. The biodeg-
radation rate is calculated from the heat of biological activity, assuming the
hydrocarbon is degraded to some proportion of cell mass and carbon diox-
ide/water. Although many estimations and assumptions are required in the
computation of biodegradation rate, the input data (i.e., temperatures in the
subsurface as a function of depth) are easy to measure accurately. This ap-
proach has been used to provide estimates of bioremediation rates which
generally agree with the results of other methods.
5.28
,!|! ' in ' 'fir'", "' • I'i'l !i! „ , '"|!i''i: ,• i";., ' ;',;' .: ,| , ,!', „ li!":!!1
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Chapter 5
5.2.3.5 Rate of Contaminant Volatilization
A final key parameter to monitor during a sparging pilot test is the rate of
contaminant volatilization from the groundwater and smear zone. When
sparging in only dissolved-phase plumes, the rate of. contaminant volatiliza-
tion is typically low. Vapor-phase contaminant concentrations may remain at
only the low ppm or even ppb levels. During the design phase, the mass flux
of contaminants being transported into the treatment zone can be estimated
from dissolved-phase concentrations and the groundwater flow velocity.
Assuming that all of the dissolved-phase VOCs are volatilized,, the maximum
concentration of vapor-phase contaminants can be estimated. These esti-
mates, can be coupled with vapor-phase transport models to assess if active
soil gas collection is needed. If the natural attenuation of contaminants oc-
curs at a rate faster than the advective transport of contaminants to some
compliance point, active soil gas collection and treatment may not be re-
quired. Such estimates and models are useful during pilot test planning and
design stages of the project. There is a growing body of literature that sug-
gests significant retardation and biodegradation of vapor-phase contaminants
in the root zone of the soil column (Kampbell, Wilson, and Griffin 1992).
When sparging through residual NAPL from petroleum product releases,
it is common to observe in situ vapor-phase hydrocarbon concentrations in
the percent range (greater than 10,000 ppm); these concentrations are in the
explosive range as well. In such cases, soil vapor collection arid treatment is
almost always required. It is also necessary to consider the risks associated
with the uncontrolled migration of potentially explosive vapors to sewers,
basements, and other subsurface structures.
5.2.3.6 Biofouling
There has been much speculation about the potential for fouling of the
aquifer due to iron precipitation as a result of sparging. The anearobic activ-
ity at many sites results in high dissolved-phase iron concentrations in the
groundwater. The iron can quickly become oxidized in the presence of air
introduced via a sparging system and precipitate out of solution. The
sparging guidance published by the Wisconsin Department of Natural Re-
sources in 1993 suggested that iron precipitation may be a problem at iron
concentrations greater than 10 mg/L, but also acknowledged some uncer-
tainty with regard to the accuracy of the number. Many more sparging
5.29
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Design Development for Air Sparging
projects have been undertaken since that time, and there is little evidence to
suggest that iron precipitation is a concern at most sites.
5.2.4 Preliminary Design
During preliminary design, the final well spacing and layout based on
pilot test results or past experience is to be established. As previously dis-
cussed, determining the radius of sparging influence for most applications
using conventional field measurements is difficult. Arguably, the concept of
a radius of influence does not even apply to sparging since sparged air often
moves outward from the sparging well in radially asymmetric patterns. Fur-
thermore, it is the density of air fingers and channels that determine the ef-
fectiveness of air sparging, not the mere presence of sparged air in the
saturated zone. A few channels of air may move a considerable distance in
the saturated zone from the injection point, but the region of effective
remediation would be considerably smaller.
Rather than basing sparging system design on an elusive radius of influ-
ence, a more realistic approach may be to rely on past experience. Bass and
Brown (1997) found that, in general, source areas with extensive residual
NAPL present in a smear zone responded better to sparging systems with
closer well spacings (less than 6 m [20 ft]) ami higher sparging air flow rates
(greater than 5 scfm). Dissolved plumes responded much more quickly and
with much wider well spacings than source zones. Since the precise location
and total mass of residual NAPL is never known and cannot be reliably esti-
mated from site soil, soil gas, or groundwater analytical data, it is advisable
to install a sparging system initially with wider well spacings, then fill in
where groundwater concentrations do not show adequate response.
When the sparging system is used in this way as both a remediation system
and as a diagnostic tool to find areas of high residual NAPL, the initial sparging
system design will require modification or upgrading after several months to a
year of operation. Appropriate flexibility in both design and budgeting are
required to ensure the effectiveness of an air sparging application.
5.30
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Chapter 5
5.3 Air Sparging and In Situ Equipment
Selection
This section has been adapted with permission from Dupont et al. (1998)
and US ACE (1996).
5.3.1 Air Sparging Well Location and Construction
5.3.1.1 General
As discussed at the beginning of this chapter, well system configurations
can be designed to accomplish different strategies and may consist of a lin-
ear orientation perpendicular to groundwater flow direction (sparging cur-
tain), nested wells (air sparging and vapor extraction from different depths of
the same or nearby boreholes), encapsulation of the contaminant plume (sur-
rounding the plume with air sparging wells), and horizontal air sparging
wells. When using sparging curtains, care must be taken in both the design
and operation to ensure that sufficient contact is achieved between the
sparged air and the contaminated groundwater plume passing through the
curtain. Additionally, the use of a sparging curtain may result in contami-
nated groundwater migration around the curtain due to a likely decrease in
hydraulic conductivity and increase in upgradient head. Likewise, nested
wells and plume encapsulation approaches require care in design and opera-
tion. Nested wells have a primarily vertical pressure gradient that can reduce
the zone of influence and require special operating schemes. Encapsulation
systems must be designed and operated to account for transient groundwater
mounding that will occur with the injection of sparging air.
If the selected configuration addresses only a portion of the plume,
groundwater extraction is likely to be required to control potential lat-
eral migration. Conversely, if sparging wells extend to the perimeter of
the contaminant plume, groundwater extraction wells may not be neces-
sary. A complete understanding of site conditions is required so a con-
figuration can be chosen that will effectively remediate the affected
aquifer and fringe areas.
During air sparging system operation, lateral distribution of contaminants
in the saturated zone may increase due to new induced groundwater flow
patterns. Additional monitoring wells and air sparging wells should be
5.31
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Design Development for Air Sparging
considered for placement near the perimeter of the contaminated zones.
Prior to finalizing the well layout, existing utilities must be located, with
relocation of air sparging wells or utilities ancl service requirements for new
equipment taken into account as appropriate. Site access, including consid-
erations for support facilities, storage areas, and parking, should also be
identified to prevent the potential release or migration of contaminants by
installation equipment during construction.
5.3.1.2 Vertical Wells
Most groundwater sparging systems are installed with vertical
sparging wells. Typical design parameters are shown in Table 5.2.
Sparging wells are typically constructed of PVC or galvanized steel and
can be installed through drilling with a hollow-stem auger or driven with
a geoprobe. For most applications, it is important to develop the
sparging wells before sparging, since fines can accumulate in the bottom
of the wells and block the relatively short well screens. When installing
wells in varied stratigraphy, conventional drilling and soil logging tech-
niques should be used so there is a record of the geology in the immedi-
ate vicinity of the sparging well; this information will help with final
screen placement as well as future data interpretation.
Tqble 5.2
Design Parameters for Air Sparging Systems
Parameter Typical Range
Well Diameter 2.5 to 10 cm (1 to 4 in.)
Well Screen Length "'l5 to 300 cm (6.5 to 10 ft)
Well Screen Depth Below Water Table 0.6 to 15 m"(2.0 to 50 ft)
Air Sparging Flow Rate 6.08 to0.5m3/min(3 to 20 scfm)
Air Sparging Injection Overpressure* 7 to 70 kPa (1 to 10 psig)
Air Sparging Zone of Influence 1.5 to 7.5m (5 to 25 ft)
•Overpressure is Injection pressure in excess of hydrostatic pressure
Source: US ACE 1996
5.32
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Chapter 5
5.3.1.3 Horizontal Wells
Increasingly, horizontally-drilled wells are used in sparging applications,
and horizontal wells placed in excavated trenches are used for sparging bar-
riers. Effective operation of such horizontal vapor extraction systems re-
quires that air flux to the formation be unifoim over the length of the well.
However, frictional losses can result in the bulk of the air exiting the well at
the end nearer the sparging blower.
Several approaches to obtain a constant flux along the length of a hori-
zontal sparging well have been explored. A diffuser pipe with a large pres-
sure drop can be placed within the sparging well along its entire length
(Wade 1996). In this case, the pressure drop is so great for air exiting the
diffuser pipe that a very high applied pressure is required. The pressure drop
along the length of the pipe is therefore negligible in comparison. This ap-
proach carries additional expenses for the coaxial diffuser pipes as well as
greater blower requirements to deliver air at higher pressures.
Another approach is to vary the depth of the horizontal well installation
below the top of groundwater such that the hydraulic head decreases at
greater distance from the blower to compensate for the reduced pressure due
to frictional losses. Computerized design tools have been developed to pre-
dict how the sparging well can be pitched so as to ensure constant air flux
along the length of the well (Fournier and Skomsky 1996; McPhee, Bass,
and Smith 1997).
While both of these approaches are appealing in theory, long, horizon-
tally-drilled sparging wells are likely to find and inject air preferentially into
the most permeable areas of the soil. Reducing the length of the horizon-
tally-drilled wells will reduce the disproportion of air flow, but will also
increase installation costs. Therefore, horizontally-drilled wells should be
used only to treat source areas and downgradient plumes with soils display-
ing a high degree of uniformity. Placing horizontal sparging wells in
trenches, where the uniformity of the backfill can be ensured, will circum-
vent this problem, but this approach can only be used in sparging barrier
applications.
5.33
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Design Development for Air Sparging
5.3.2 Field and Manifold Piping
5.3.2.1 General
Figure 5.4, presented earlier, is a schematic diagram that includes a typi-
cal air sparging manifold design. The construction of an air sparging mani-
fold generally includes the following components:
• pressure and temperature gauges;
< i ., . . , i .. « . ,i
• air flow meters;
• pressure relief valve or bypass line;
• throttle valves;
• manifold piping or hose;
. ' Iilf " ' • I ' • ' H •• • „." . i
• check valves; and
• optionally, solenoid valves and sample ports.
Each of these components is discussed below. The piping system can be
designed for installation either above or below the ground surface depending on
the traffic requirements of the area and the need for protection against frost.
5.3.2.2 Design and Installation of the Manifold
Beginning at the outlet of the air supply source (typically a compressor,
blower, or gas cylinder), compatible materials are connected to supply head-
ers for the air sparging wells. Typical manifold construction materials in-
clude metal piping, rubber hose, or ABS pipe. PVC pipe, although in com-
mon use, is not recommended by manufacturers for air pressure service.
Prior to routing to individual air sparging wells, permanent pressure and
temperature gauges and switches along with an air flow meter are installed
for quick visual measurements during routine system checks. The measure-
ment devices are also connected to the electrical supply system in case of
system nonconformances to specified operating conditions. These perma-
nent measurement devices should be installed in accordance with the manu-
facturers' recommendations for length of unobstructed flow, etc. A pressure
relief valve (manual or automatic) or system by;pass line should be installed
to exhaust excess pressure from the manifold. This will prevent excessive
pressure, which could cause damage to the manifold or aquifer. Exhaust air
5.34
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Chapter 5
can be directed to the atmosphere or to the air source intake. A silencer for
exhaust air should be considered based on site conditions and air velocities.
A header from the manifold to each well must be designed. Reasonable
construction options for piping materials and associated costs must be evalu-
ated to determine the most effective air delivery system to each sparging
well. Once the piping materials are selected, each well should have a
throttle valve; check valve; temporary ports for flow, pressure, and tempera-
ture measurements; and, optionally, a solenoid valve and sampling port. The
throttle valve is used for air flow adjustment or well isolation from the mani-
fold system. Typical throttle valves used are gate, globe, butterfly, or ball
valves. Check valves are installed on each well to prevent temporary back
pressure in the screened interval of the aquifer from forcing air and water up
into the manifold system during system shutdowns. If a check valve is not
installed on each well, a single check valve must be located on the manifold
line between the permanent instrumentation and the gas pressure source.
One or more ports that can be used for temporary measurements of air
flow, pressure, and temperature are recommended to perform sjrstem optimi-
zation adjustments during operations. Solenoid valves are optional features
and their use is dictated by the system operating strategy. If pulsed operation
of the system is anticipated for more effective remediation or reduced energy
consumption (discussed in detail in 6.4), solenoid valves must be installed
for ease of individual well activation and deactivation. Simple analog or
PLC timers can be used to actuate the solenoid valves based on specified
time intervals. It should be noted that check and solenoid valves may sig-
nificantly restrict air flow or generate significant line pressure drops. The
pressure drop across these appurtenances, if they are used, must be ac-
counted for when sizing manifold piping. Also, all manifold instrumentation
should be constructed with quick-connect couplings for ease of maintenance
and removal.
The manifold that delivers supplied air to each air sparging well is typi-
cally installed underground below the site-specific frost line. If piping is
installed in the frost line or aboveground, it may need to be protected from
freezing with insulation and/or heat tape. Aboveground installation designs
should be reviewed for items such as shock load, photo-oxidation, and po-
tential vehicular damage. All construction including excavation, trench bot-
tom preparation, and backfilling/compaction should be performed in accor-
dance with industry-accepted standards. The manifold sizing is site-specific
5.35
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Design Development for Air Sparging
and dependent on factors, such as air flow rate, pressure losses, material
costs, and line distribution patterns. As stated above, although convenient
for short-term tests, PVC is not recommended for air pressure service. All
piping should be installed in accordance with the manufacturer's recommen-
dations. If rubber hose or AI3S pipe is used, the installation should include
tracing tape or other appropriate material that can be located with a metal
detector, if necessary, after completion of the installation (except at sites
where surface or subsurface conditions would prohibit locating efforts, such
as reinforced concrete paving or underground lightning grids). Once the
manifold has been completed to each well, high-pressure air hose or hard
pipe, accompanied with couplings and plugs, can be used to secure the mani-
fold to the well header.
5.3.3 Air Sparging Compressors
5.3.3.1 General
Air delivery sources are designed on (1) design calculations of required
minimum pressures due to hydrostatic head, air-entry pressure, and manifold
losses and (2) system requirements developed from pilot tests. Upon
completion of the total system design calculations and review of pilot test
data, the optimum pressure and flow for each well is determined for the site-
specific geologic and physical domain. Typically, the air supply is provided
by either an air compressor or blower.
Air compressors are typically quite noisy, and if they are to be near resi-
dential areas, they should be located in enclosures outfitted with noise abate-
ment equipment and insulation. Air compressors can also generate signifi-
cant heat; therefore, piping material should be compatible with expected
discharge pressures and temperatures. This is often accomplished by using
several lengths of metal piping to allow for heat transfer and system cooling
before coupling to piping made of polymeric materials.
Air compression leads to the precipitation of water in the compressor
receiver tank and manifold lines. Therefore, air tanks should be drained
regularly to prevent condensate buildup. It may be necessary to winterize
the compressor system and heat trace exposed piping to avoid system icing
and blockage.
5.36
,!?!., i
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Chapter 5
Continuous-duty, oil-less air compressors are typically used to avoid in-
troducing hydrocarbons to the aquifer. An alternative to oil-less compressors
is use of oil filters to remove hydrocarbons from the air stream before it
enters the groundwater.
Rotary-vane pumps or regenerative blowers can be used only when low
air pressures (i.e., up to 69 kPa [10 psig]) are required. Rotary-lobe blowers
can be used for sparging sites when air pressures do not exceed 103.5 kPa
(15 psig). Reciprocating compressors are generally required for pressures in
excess of 103.5 kPa (15 psig). Reciprocating compressors can generally
achieve over 621 kPa (90 psig) pressures and often use Teflon® cbmponents
to avoid the use of lubricants. Other types of compressors (i.e., rotary screw)
can potentially be used if provisions are made to keep hydrocarbon lubri-
cants from entering the air stream.
In all cases, compressor air inlets should be located to avoid the introduc-
tion of airborne contaminants. Therefore, inlets should not be located within
service garages or in close proximity to vapor extraction stacks.
5.3.3.2 Unit Selection
The first consideration when beginning calculations for operating pres-
sures is to avoid excessive pressures that could cause system malfunctions
and/or the creation of secondary permeability in the aquifer. The estimation
of minimum and maximum air pressures required for operation begins with
the assumption that the pressure must at least equal the pressure head at the
top of the well screen plus the air-entry pressure required to overcome capil-
lary forces. For calculating the minimum required system operating pres-
sure, use the common conversion that each foot below the water table equals
2.97 kPa (0.43 psig), and add the estimated air-entry pressure, yielding the
minimum required operational pressures (see Section 5.2.3.3). Water table
fluctuations must be considered when estimating the top of screen depth
below the water table.
The selected air delivery equipment must be capable of producing pres-
sures sufficient to depress the water table below the screen in all air sparging
wells and delivering the required air flow to each well. Common air delivery
sources, along with a brief explanation of mechanical and operational con-
siderations and the interrelationship with the design variables, are provided
in the following paragraphs. Additional considerations, such as
5.37
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Design Development for Air Sparging
explosion-proof equipment, silencers, dryers, filters, and air coolers are also
discussed. As with any equipment specification, the manufacturer's perfor-
mance Curves should be review
rated for continuous duty.
Reciprocating Air Compressors. These units are used when high pres-
sure is required and a low flow rate is acceptable. Only oil-less units should
be used to eliminate the potential to inject oils into the subsurface if me-
chanical failure occurs. These units are capable of producing substantial
pressures that could cause manifbic! "problems.' Therefore, an automatic pres-
sure relief valve on the air compressor outlet should be specified for this type
of unit.
Rotary Screw Air Compressors. While possessing a wider range of capa-
bility for air sparging service, these units typically contain oil that could
accidentally be discharged into the subsurface. Therefore, a filter is needed
to ensure removal of any oil in the air compressor outlet. These units are
acceptable for air sparging service, but may require more maintenance than
reciprocating compressor units.
Regenerative Blowers. This type of blower is typically used for applica-
tions of up to 69 kPa (10 psig), i.e., sites conducive to air flow at low pres-
sures. There are several advantages associated with using these units, in-
cluding low capital cost, low maintenance, and oil-free air delivery. If higher
pressures are required, a multistage blower system may be used.
Rotary Lobe Blowers. These units are generally capable of producing up
to 103.5 kPa (15 psig). The units may have an oil-filled gear case, and a
filter should be used for oil removal as necessary. If higher pressures are
required, a multistage blower system may be used. Advantages of rotary
lobe blowers include low maintenance and flexibility of operating pressure
range by adjustment of belt drives to modify the blower speed.
5.3.3.3 Air Filtering
Air is usually supplied to the specified compressor or blower unit from an
ambient air intake. Based on the location of the intake, it may be necessary
to install an inlet filter to remove particle matter. If possible, the unit should
be installed a minimum of 3 m (10 ft) away from possible contaminant
sources (including soil venting systems). Non-explosion-proof equipment
may be used if the unit and appurtenances are located in a safe environment.
§.38
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Chapter 5
It is the responsibility of the engineer to verify the safety of non-explosion-
proof equipment and to specify use of explosion-proof equipment as neces- .
sary. Local electrical and building inspectors may require'the use of explo-
sion-proof equipment on a site-specific basis.
5.3.3.4 Heat and Noise Control
Compression of air can generate a significant amount of noise and heat.
A silencer or appropriate noise controls should be considered for all applica-
tions, especially in noise-sensitive areas. Excess noise can typically be re-
duced to acceptable levels through the proper application of standard noise
reduction materials in the equipment housing.
Additionally, as part of the system design, calculations should be made to
determine anticipated system exhaust temperatures. Discharge piping must be
able to withstand the compression discharge temperature and pressures. All
discharge piping should be properly anchored to overcome pressure forces
generated from the unit. The air injection discharge should have temperature
and pressure sensors and switches that are interlocked into the electrical control
panel for automatic shutdown when the pressure and/or temperature exceeds
safe operating criteria. An aftercooler can be used to reduce the discharge tem-
perature to acceptable levels prior to entry into manifold systems. Aftercoolers
are designed to facilitate processing of condensate water that is generated due to
temperature drops. If an aftercooler is not used, provisions must be made to
remove moisture condensation caused by the compression of air in the supply
unit or manifold piping. A receiver tank with a manual or automatic drain to
remove condensate is suggested either between the air inlet and the air supply
unit (for larger systems) or on the unit discharge manifold. A dryer can also be
used to remove generated condensate.
5.4 Process Modifications
The air sparging systems as originally designed and installed are often
modified to fit specific site conditions. Most importantly, the engineer must
acknowledge that air movement patterns in the subsurface are not well un-
derstood. Therefore, the design must be adaptable to rapidly changing or
unexpected conditions. Pilot test results will provide an expected range of
5.39
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Design Development for Air Sparging
air injection pressure, for initial starting conditions. However, all areas of the
site may not behave similarly with respect to air movement, and during the
life of the remedial project, subsurface conditions will likely change. As a
result, the original design must allow the operator to modify several param-
eters and be flexible in the application of sparging air. This built-in flex-
ibility will provide the most effective system. System changes that may
be required are discussed in this section.
5.4.1 Additional Air Sparging Wells
The cost of installing and piping an air sparging well is relatively low
(less than 1% of the total project cost). Therefore, the price of a few addi-
tional air sparging wells to ensure overlap of the zone of influence from each
air sparging well is minimal compared to the cost of having to operate the
system for an additional period of time while all areas are remediated.
Therefore, the design needs to allow for additional air sparging wells, espe-
cially if data collected during installation of the minimum amount of wells
indicates more complicated anisotropic conditions or a different mass distri-
bution pattern than originally anticipated. A pulsing approach may be used
to supply air to all air sparging wells periodically rather than increasing the
size of the air compressor due to the additional wells. Sparging wells that
are not being used can serve as monitoring points when they are not in the
pulsing rotation.
As with vapor extraction and bioventing systems, the ability to accommo-
date additional wells or different size compressors should be incorporated in
manifolding and piping systems. However, unlike vapor extraction systems,
additional air treatment capacity is not likely to be needed.
5.4.2 Weil Screen Placement
Placing sparging points at different depths rather than only one depth may
be appropriate to ensure effective distribution of air in the subsurface or to
accommodate fluctuations in the water table. Separate wells are recom-
mended for sparging at different depths in the same area. Nested sparging
wells have been used for this purpose but problems may develop because the
constant pressure, settling of well packings, and drying of bentonite or other
seals between the screens may cause short circuiting between or among
screened intervals in the nested well. Uneven hydration of bentonite pellets
has also contributed to failure of nested sparging wells.
5,40
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Chapter 5
5.4.3 Sparging Curtains and Horizontal Air Sparging Wells
Sparging curtains are a series of vertical air injection wells located along
a line and spaced to ensure that adequate aeration occurs between each well.
This forms a zone of aeration comparable to a curtain so that any mobile
contaminants in the groundwater moving through the curtain are exposed to
a highly-aerated, highly-bioreactive zone. Any volatile contaminants are,
therefore, subjected to conditions favoring rapid volatilization and biodegra-
dation. For low-concentration, dilute plumes with known groundwater ve-
locities, this approach may be successfully used to create a treatment zone
downgradient from a migrating plume. Groundwater monitoring wells and
piezometers up- and downgradient of the sparging curtain are used to ensure
the hydraulic gradient is maintained through the curtain and that treatment is
effective in removing contaminants. In this application, a high air flow rate,
which favors more dense channel formation, is critical to success. Higher air
flow rates may displace sufficient water such that soil pores are filled with
air — a condition which inhibits and can even prevent groundwater move-
ment through the sparging curtain. Because of this, sparging curtains are
usually operated in a pulse mode* with the "on" cycle correlated to the rate
of groundwater flow through the curtain.
Section 3.2.4.4 describes how horizontal wells are installed and used for
vapor extraction. Air sparging horizontal wells are installed in the same
fashion but below the water table. Special provisions for handling drilling
liquids, especially if NAPL may be encountered, during installation. If the
potential target for injected air and the extent or shape of the impacted area
lends itself to a linear, horizontal injection system and other site conditions
favor horizontal installation methods, then a horizontal air sparging well can
be most effective and least costly. However, due to the relative low cost of
vertical, driven well points that are typically used for air sparging, the added
cost of a horizontal well may not be justified unless access for vertical wells
is not possible.
The same limitations of horizontal vapor extraction in a horizontal well
apply to air sparging in terms of air flow through the screened interval. To
minimize the possibility of injected air being concentrated in one area of the
screen, the screen slot size or openings can be varied along the length of the
screen with smaller openings near the air source and larger openings at the
farthest point from the air source.
5.41
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Design Development for Air Sparging
An alternative and potentially more effective method is to install sections
of blank pipe between small screened sections to ensure even air distribution
during air sparging. Finally, for longer horizontal sparging wells (more than
15 m [50 ft]), provisions must be included for monitoring the air flow, pres-
sure, or dissolved oxygen (within 1.5 m [5 ft] of the well) at intervals along
the screened interval to ensure that the entire length of screen is delivering
1 ' '•" , : ' ' •' ••.'• l"1" '•'•'• 'I ' ' ' ''"'I :l
air evenly.
• • , . • " - : . v .. ] l • , li'4 . t
5.4.4 Heated Air Sparging
In some cases, injected air has been heated to improve VOC stripping and
recovery and to enhance biodegradation. However, the heat capacity of air
compared to soil and groundwater is very low. Consequently, the ability to
heat groundwater with sparged air is limited and would normally take weeks
to months This approach is attempted only with" stagnate groundwater such
as in perched groundwater zones. Air-to-air heat exchangers or the exhaust
from a catalytic oxidizer are used to heat air prior to injection. If exhaust air
from a thermal oxidizer unit is used, the oxygen content may be substantially
decreased, especially if the VOC loading in the feed air to the oxidizer is
heavy. This can slow biodegradation effects considerably, and in such cases,
an air-to-air heat exchanger is recommended to facilitate both diffusion/
transport and biodegradation benefits from air injection. When using heated
air, all materials delivering such air must be capable of withstanding the
maximum operating temperatures. '.
5.4.5 Ozone Sparging
A recent development in air sparging technology has been the use of
ozone gas mixed with injected air. Ozone is a chemical oxidizer which,
upon contact with VOCs, can break down chlorinated and nonchlorinated
VOCs to simpler molecules that are more readily biodegraded. In addition,
ozone? upon contact with organic matter, liberates oxygen which enhances
biodegradation of residual organics. Another benefit of ozone is that the
injected concentration is very low (less than 3% by volume) thus reducing
the hazard of exposure to the injected air. There are few data available
showing that ozone is more effective than air for common VOCs. Ozone
may be more effective for contaminants with low volatility or high solubility,
which would not generally be removed with traditional sparging. Ozone is
5.42
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Chapter 5
not stable in groundwater and can quickly dissipate. Therefore, pilot testing
is recommended for this approach.
5.4.6 Air and Methane Mixture
Indigenous methanatropic organisms can be biostimulated with the addi-
tion of methane as an electron donor and oxygen as an electron acceptor.
Methanotrophs produce the enzyme methane monooxygenase (MMO),
which initiates the first step of methane oxidation when methane is used as
the sole carbon source for energy and growth (Semprini et al. 1990). Under
aerobic conditions, MMO can epoxidize alkenes. Aerobic TCE oxidation
can be accomplished by mixed cultures of methanotropic and heterotrophic
organisms. TCE oxidation first involves the epoxidation of TCE by
methanotrophs, an abiotic hydrolysis of the epoxide to nonvolatile products,
followed by heterotrophic degradation of the products to CO2, chloride, and
water (Semprini et al. 1990).
Laboratory studies have shown that this process can be conducted aerobi-
cally with an air phase that contains as little as 0,6% natural gas (i.e., meth-
ane) by volume (Wilson and Wilson 1985). In microcosms, optimum gas-
phase oxygen and methane content to promote TCE degradation were deter-
mined to be between levels of 7.7 to 8.7% and 1.7 to 2.7%, respectively,
which correspond to aqueous concentrations of 3.2 to 3.7 mg/L and 0.4 to
0.6 mg/L, respectively (Kane, Fischer, and Wilson 1996).
A comprehensive investigation of the addition of methane to sparging air to
enhance the biodegradation of TCE is planned at the USGS field research site
located at the Picatinny Arsenal, New Jersey (Fischer, Wilson, and Kane 1995).
Methane can be added to sparging air by piping a methane line equipped
with a check valve, isolation valves, and flow meter to a sparging well. The
methane supply must produce sufficient line pressure to overcome pressure
resulting from the air sparging compressor or blower. Methane content of
sparging air should be maintained below the LEL of 5% to prevent explosive
conditions. The methane addition must occur only when a sparging blower
is operating; this can be accomplished with an interlocked valve rated for
natural gas service.
Methane injection via sparging continues to be the focus of research.
Currently, little is known about when and how to apply methane injection.
5.43
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Design Development for Air Sparging
Consequently, methane injection is still considered a research modification
of groundwater sparging.
5.4.7 Pure Oxygen
Delivery of oxygen is often the rate-limiting step controlling biodegrada-
tion. Air contains approximately 20% oxygen, by volume. When using air as
a sparging gas, the maximum DO concentration that may be obtained within
an aquifer is 8 mg/L, based on partitioning described by Henry's Law at
typical groundwater temperatures. Soils with low permeabilities may se-
verely restrict the rate at which sparging gas, and therefore oxygen, can be
introduced into an aquifer formation. When sparging gas flows are restricted
to less than 2 scfm, the use of pure oxygen as a sparging gas should be con-
sidered. With 100% oxygen as a sparging gas, the resulting DO level is 40
mg/L. Therefore, the amount of DO delivered and rate of biodegradation
can be as much as five times faster than air when using pure oxygen as a
sparging gas. This benefit may offset the lower sparging gas flow rates.
Additionally, higher DO concentrations result in greater concentration gradi-
ents and higher rates of mass transfer to areas not directly contacted by
sparging gas. Furthermore, in biosparging applications, the injection of pure
oxygen can provide a means of effective sparging in geologic conditions not
suited to traditional air sparging.
As an example, a biosparging pilot study was conducted for groundwater
and soils contaminated with semivolatile organic compounds at a facility in
Texas used to store wastes and waste waters containing elevated levels of
nitroaromatic and aromatic compounds. Site operations led to release of
these compounds into the groundwater, whicli was located in a confined
sandy aquifer underlying a clay aquiclude. These site conditions prevented
implementation of a cost-effective vapor extraction system for sparging gas
capture. The pilot study demonstrated the successful application of pure
oxygen into the aquifer. At an oxygen flow rate of less than 1 scfm, a zone
of influence in excess of 9.1 m (30 ft) was observed.
5.48 In-Well Aeration Systems
In-well aeration (also called groundwater circulation and air lifting pump-
ing) uses specially designed multiple screened wells in which a pressure
gradient is established between the isolated screen intervals. This pressure
5.44
n n
I-
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Chapter 5
gradient results in groundwater recirculation within the aquifer in the vicin-
ity of the well. As contaminated groundwater is brought into the well it is
treated via in-well air stripping. The injection of air into the well performs
two purposes: (1) it establishes a pressure gradient via air lift pumping; and
(2) it air strips VOCs from groundwater within the well. The vapor phase
VOCs are collected either from within the well or via a S VE well located
near the recirculation well. Figures 5.5 through 5.7 depict three patented
approaches to in-well aeration. The primary differences in the three ap-
proaches involve the manner in which a pressure gradient is established and
the location of the upper screened interval with respect to the water table.
The recirculation well is typically installed to a point near the bottom
of the groundwater plume such that the full depth of the plume is within
the capture zone when air is fed through. The inner well casing is typi-
cally perforated at two depths: (1) within the saturated zone where the
casing is in contact with the contaminant plume, and (2) within the va-
dose zone at a selected height above the water table. Air is injected by
means of a compressor and interior pipe so that a continuous stream of
bubbles is formed in the casing starting just above the lower perforated
section. The gas may be air, oxygen, or nitrogen depending upon
geochemical considerations. Air is the least expensive alternative, but
may cause biofouling or oxide precipitation.
Oxygen can enhance bioremediation in the formation, but is more expen-
sive. Nitrogen is used to prevent oxidation-related fouling. Regsirdless of
the gas selected, its introduction constitutes an air lift pump (i.e., the pres-
ence of the bubbles in the casing causes the column of water in the casing to
have a lower density than the water outside the casing and, as a result, water
flows into the well in response to the pressure differential). The inflowing
groundwater carries dissolved VOC contamination with it.
A packer or solid deflector plate is installed at the top of the casing just
above the upper perforated zone. The packer prevents the combined flow of
water and vapor from rising any higher in the casing, thereby forcing it to
pass out through the perforations into the vadose zone. A second outer well
casing of larger diameter than the inner well is positioned around the inner
well from the packer to the ground surface. The annular space between the
inner and outer casings is maintained under vacuum by means of a blower or
ventilator whose exhaust is directed to an offgas treatment unit.
5,45
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Design Development for Air Sparging
Figure 5.5
UVB System Combined with Vapor Collection
Vacuum
Gauge
Compressor
•ffi.Gnrot'sedfo^
z^S&w£^#w$%K
fffffJfffiJ'fJ'rf'J'iJ'i'f?*:'^!***
^^•^'^ Aeration Chamber / v'Wx'VWs
Reproduced courtesy of SBP Technologies, Inc.
5.46
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Chapter 5
Figure 5.6
Density-Driven Convection System with Vapor Extraction
Pressurized
Blower Motor or
Compressor
Vacuum Vacuum
Gauge Pump
fffffffifffffffff
ffftffff
ssssssss
fffffftt
SSSSSSSS
ftfftftf
SSSSSSSS
ffffffff
sssssssss
s's's's's's'sVs'
fffff-fff
v:" Oxygenated .
.'-:-: Water Outflow
\s\sss
f f f f f t t
kSSSSSSSS,
ffffffftf**
s s s s s s s
SfftSfff
s s s s s s s
ssssssssssss s s
fSS
ssssssssssss
Contaminated
Water Inflow
11 Screen V-yV*
Reproduced courtesy of Wasatch Environmental. Inc. (U.S. Patent Number 5,425,598)
5.47
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Design Development for Air Sparging
Figure 5.7
A NoVOCs™ System
Vapor Treatment
Injection
Blower
Groundwater
Recirculation
Zone
VOC-Contaminated Water
Reproduced courtesy of MACTEC, Inc.
5.48
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Chapter 5
When operated, the air lift pump draws contaminated water into the inner
well where volatile contaminants vaporize as they are transferred into the
bubbles in the water column. The transfer continues until equilibrium is
reached as defined by Henry's Law. At the packer, the bubbles break and
coalesce. The water percolates downward through the vadose zone, while
the contaminant vapors are drawn off by the vacuum in the outer well. Since
the Henry's Law constant for most contaminants is insufficient to produce
drinking water quality on a single pass, the pumping rates and well place-
ment are selected to accommodate multiple cycles for each unit of water.
The optimum number of cycles is dependent on the starting concentration
and the flow rate of the ground water. Some additional removal occurs in
the vadose zone where the soil particles act like packing in an air stripper.
The degree of additional removal achieved will depend on the size of the soil
particles, the amount of flow induced by the vacuum, and the degree of satu-
ration produced by the infiltrating water.
Even though in situ air stripping is commonly discussed in conjunction
with groundwater sparging, it is really more similar to a groundwater extrac-
tion treatment method, subject to many of the same limitations of groundwa-
ter pump-and-treat technology. There is no sparging of air through saturated
zone soil.
5.4.9 Nitrogen Sparging
Nitrogen has been used on only a few occasions, and these were usually
at sites where high iron concentrations occurred in the groundwater. Nitro-
gen was used in an effort to prevent oxidation of the iron and potential clog-
ging of the aquifer. The most economical way to generate nitrogen on-site is
with use of a pressure-swing adsorption unit. These units use adsoiption
resins to separate nitrogen from oxygen in atmospheric air. While skid-
mounted units are available, energy requirements are substantial. For ex-
ample, a pressure-swing adsorption unit that can produce a 40 scfm flow of
nitrogen may require a 60 to 70 hp motor. The energy cost of these units
along with the inconclusive data regarding iron clogging have resulted in
infrequent use of nitrogen sparging.
5.49
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Design Development for Air Sparging
5.5 Pretreatment Processes for Air
Injection Systems
Little pretreatment is required for injection of air into the groundwater.
Some treatment of the compressed air may be required to (1) reduce the
temperature and/or (2) to reduce the oil and water. At other times, injecting
a gas other than air may be required for a site.
5.5.1 Temperature Reduction
Positive displacement blowers are often employed when sparging pres-
sures are less than 103.5 kPa (15 psi). The temperature increase resulting
from air compression may be significant. Temperature increases for a given
blower can be obtained from the blower manufacturer's literature. Many
types of flow meters, as well as PVC piping, are designed for temperatures
less than 60°C (146°F). Compressing ambient air to 69 kPa (10 psi) can
increase the blower exhaust air temperatures to exceed material temperature
ratings for some piping and meters.
Consequently, some sparging designs need to include heat exchangers. In
some cases, the required heat exchange can be conducted through passive
techniques, such as running extra steel piping on the roof or below the
blower building. This allows the piping to dissipate the heat in the com-
pressed air to acceptable temperatures. The success of such passive systems
may depend on the climate and amount of heat reduction required. Passive
techniques are particularly effective in northern climates.
A more robust heat reduction system includes the use of an air-to-air heat
exchanger. In these heat exchangers, a fan blows ambient air across metal
pipes carrying the compressed gas, and in the process, cools the compressed
gas to within a few degrees of ambient temperature. Heat exchangers can be
controlled so they come on and off with the blower. They are relatively low
cost and provide protection of other equipment as well.
5.5.2 Oil and Water Removal
For larger sparging systems requiring more than 103.5 kPa (15 psi) for
injection, rotary-screw compressors are often used. Such compressors are
normally fitted with receivers to hold the compressed air. Since air from
these compressors is not oil free, oil filters (centrifugal and/or coalescing)
5.60
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Chapter 5
need to be fitted on the discharge from the compressor. An oil filter can
remove more than 99.99% of the oil carried over from the compressor. Wa-
ter can also condense in the receiving tank; thus, these tanks need to be
equipped with a discharge line to remove waiter.
5.6 Posttreatment Processes
For groundwater sparging, posttreatment processes are those which treat
contaminants volatilized into the vadose zone. Volatilized contaminants
need to be treated further through either natural biodegradation in the vadose
zone or active collection with a soil vapor collection system. These concepts
are discussed further in Section 3.5.1.
5.7 Process Instrumentation and Controls
Refer to Section 3.6 for a discussion of instrumentation and controls ap-
plicable to vapor extraction and bioventing, much of which is also applicable
to air sparging systems. This section highlights aspects of instrumentation
and controls that are unique to an air sparging system.
5.7.1 Air Sparging Instrumentation and Controls
Due to the presence of pressurized air, several sensors, relief valves,
and controls are necessary to ensure a safe and functional system. The
following sensors, switches, and controls are recommended for all air
sparging systems:
• pressure gauges at each wellhead, manifold, and compressor air
storage tank;
• pressure relief valves,at the compressor and for the sparging air
piping system — all set to release pressure at an adjustable set
point, but no greater than the maximum design pressure;
• pressure regulator between the compressed air source (air com-
pressor) and the air sparging well field;
5.51
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Design Development for Air Sparging
• temperature sensor and switch on the outlet side of the air com-
pressor to protect the piping;
:. ;;,:• •, ,|..; •.,: -.. _ •,,: i
• electrical interlock to allow air sparging operation only in con-
junction with concurrent vapor extraction;
• control valves on each line to each sparging well and at each
wellhead;
• check valves at each sparging well to prevent the backflow of air
toward the blower when it is shut down;
• Pressure/vacuum and flow indicators for each well, of the appro-
priate range for anticipated conditions;
• Air compressor motor thermal overload protection;
• Pressure relief valve or vacuum switch to effect blower shut-
down; and
• Explosimeter within enclosed spaces at sites with recently mea-
sured LEL levels greater than 10%.
5.7.2 Instrumentation Selection
As with vapor extraction and bioventing systems, all materials used for
delivering air to the subsurface (well materials, diffusers, etc.) must be com-
patible with the concentration of contaminants present. Although the instru-
ments installed will contact moisture-laden air and possibly water in injec-
tion lines due to condensation, the compressed air system and delivery pip-
ing will not normally come in contact with the contaminants. Therefore,
function, serviceability, and cost factors will drive the selection of instru-
ments in the equipment building.
Instruments located in well vaults and air injection lines will be subject to
high humidity and wet conditions and must be corrosion resistant. Air flow
sensors and differential pressure sensors must be able to function in high
humidity conditions (inside the piping) and withstand weather extremes
outside in well vaults or unheated spaces.
5.52
II, ,111,11' lini; nil, • ','| ........ ij ..... 'KilJIlill nnlllun ....... Illliill III ,' i'n ,"'! ....... .'("i""' 11 Hll ' ». il" lllli
^ '.iVI'i-'1 Ill ["ill
-------
Chapter 5
5.7.3 Controls and Alarms
The primary control elements in an air sparging system are the pressure
and temperature of the injected air. Overpressuring can lead to low channel
density due to soil fracturing. Most air compressors are sold with internal
pressure-regulating devices that allow the delivery of air within a specified
pressure range. Typically, this range is much higher than the pressure neces-
sary for ah" sparging, and therefore, a pressure regulator is required down-
stream of the compressor.
A pressure relief valve is also mandatory on the piping side of the com-
pressor to prohibit pressures above the design maximum from developing in
the air sparging piping network. Each air sparging well must have a flow
control valve that allows the operator to adjust the air flow throughout the
anticipated design range at each wellhead. Air flow monitoring ports are
needed at each wellhead or at each manifold to ensure air flow is occurring
in all wells.
5.7.4 Remote System Monitoring/Telemetry
An introduction to remote monitoring and telemetry devices is presented
in Section 3.6.4. For air sparging systems, remote monitoring parameters to
be tracked by will include sparging manifold pressure, compressor motor
operation, and vapor extraction blower function. These parameters will
verify that the-system is operating within the design range and that the vapor
extraction system is operating if the air sparging system is operating. More
advanced telemetry units, when combined with on-line instrumentation for
air flow and VOC concentration, can track and transmit mass removal infor-
mation continually. Such controls are installed only in more complex and
long-term operating systems.
5.8 Safety Requirements
Section 3.7 discusses safety requirements that are also applicable to air
sparging. This section highlights the special safety requirements of an air
sparging system.
5.53
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Design Development for Air Sparging
Air sparging typically generates higher air pressures than bioventing. In
both cases, compressed air can create a serious hazard. To provide for
safety, pressure relief valves are mandatory on all air sparging piping and
wells as previously discussed.
Air compressors have their own set of safety precautions. Any moving
parts Such as flywheels or belts must be enclosed to prevent entanglement of
clothing or limbs. When compressor air storage tanks are emptied periodi-
cally to remove accumulated condensatej the rush of compressed air from
the drain valve can project liquid and air a significant distance; gradual bleed
ing of the accumulated pressure and eye protection are two recommended
precautions.
i ::'
5.S.1 Building Code
' j -. >"; "-
The same recommendations for building code compliance for vapor ex-
traction and bioventing, presented in Section 3.7.2, apply to air sparging.
5.8.2 Electrical Code
° • i, ' . '
The same recommendations for electrical code compliance for vapor
extraction and bioventing, presented in Section 3.7.3, apply to air sparging.
5.8.3 Designing for Operational Safety
Several design factors that contribute to the safety of a vapor extraction or
bioventing system are presented in Section 3.7 and are directly applicable to
air sparging systems. One notable addition to these safety considerations is
that air sparging is commonly conducted concurrent with vapor extraction.
Therefore, electrical interlocks are required to allow the operation of the air
sparging air compressor or the air sparging piping control valve only when
the vapor extraction blower is activated. In addition, flammable gas detec-
tors or explosimeters should be placed in enclosed buildings within VOC
impacted areas where air sparging will be performed. These detectors
should be interlocked to shutdown the air sparge system when they detect
explosive or hazardous conditions.
5.54
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Chapter 5
5.9 Drawing and Specification
Development
A discussion of drawings and specifications for vapor extraction and
bioventing systems is presented in Section 3.8. This section focuses on addi-
tional drawings or specifications that are necessary for an air sparging system.
Additional Drawings:
1. Site Plan. The site plan and layout must show air sparging wells
and piping locations. As with vapor extraction and bioventing
systems, a schedule of wells to be used for air sparging and
monitoring air sparging effectiveness provides an efficient way to
identify which wells are existing, those that will be converted to
sparging or monitoring use, and those that will be drilled; the
well screen intervals; etc.
2. Well and Piping Construction Details. Cross sections of each
different sparging well are needed to illustrate depth of screen
placement, construction materials, wellhead details, valves,
monitoring access points, etc.
3. Process and Instrumentation Diagram. A separate P&I diagram
for the air sparging system is recommended. This diagram must
show the pressure regulation, pressure relief, and control valves
necessary for a safe air sparging system. Electrical interlocks to
the vapor extraction or bioventing system must also be shown.
4. Mechanical Details. The mechanical drawing(s) should illustrate
details of sparging pipe manifolds, attachment of pressure and air
flow measurement devices, etc.
5. Electrical Plans. In addition to the items listed in Section 3.8,
the electrical plan must show the air compressor, power source,
power for instrumentation, interlocks or logic for concurrent
vapor extraction and air sparging operation, etc.
6. Building or Equipment Enclosure. This drawing must show the
air compressor or the source of compressed air, manifolds for the
sparging system, etc.
5.55
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; if , ''.I- i ••; •." ,;.'• '•,,!,;,",." S"
Design Development for Air Sparging
5.9.1 Wells/Trenching/Field Piping
Well packing must be compatible with the geologic formation to prevent
short circuiting to the surface. Section 3.8.3 provides detailed information on
wells, piping, valves, etc. that is directly applicable to air sparging.
5.9.2 Equipment
" „ , , , , , ;i ,| „,
Equipment, in addition to that described in Section 3.8.4, includes the
sparging air compressor. At a minimum, compressor specifications include
the volumetric flow rate of air under various pressure conditions, pressure
range, temperature rise at compressor discharge point, recommended lubri-
cation requirements, oil type, electrical requirements, motor starter, and
thermal overload for motor (may or may not be included in vendor package).
, „ , ,, , , ,,,,,|, ,
5,9.3 Electrical
Electrical specifications must include the power requirements of the air
compressor and related control and instrumentation.
5.9.4 Mechanical
—' ..',:• , . . ,> . :: : '. ] :,' , . '. , . '• ' i '':,
Mechanical specifications for an air sparging system will include the
operating range of the air compressor, pressure relief valve specifications,
piping specifications, wellhead detail, check valves (at each wellhead), and
sampling points.
5.70 Cost Estimating
Refer to Section 3.9 for a breakdown of costs applicable to vapor extrac-
tion and bioventing systems. In addition, the costs of the air sparging com-
pressor, air drying unit (if needed), piping (to the extent that vapor extraction
trenching cannot be used), instrumentation and controls for the air sparging
system, well vaults, well drilling, etc. must be considered.
5.56
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Chapter 5
5.77 Design Validation
Design validation refers to the ongoing process of checks and improvements
carried out in the design planning, construction, startup, and operational phases.
Since interpolation and extrapolation of subsurface site conditions from a small
percentage of the soil actually observed and tested during a typical site investi-
gation is necessary, there is inherent uncertainty associated with any subsurface
design. The uncertainty for sparging design is compounded since small
changes in soil permeability can dramatically affect system performance.
While uncertainty cannot be overcome, provision for contingencies can be
incorporated into the design and implementation process.
During the conceptual design phase, the engineer must identify what may
go wrong and how site conditions may vary from assumed. During the pre-
liminary design phase, strategies for assessing changing geologic or con-
taminant distribution conditions must be developed. These strategies may
include layout of the monitoring system (piezometers, monitoring wells,
offgas monitoring points) and system flexibility (additional smaller blowers
instead of fewer larger ones, expandable manifolds, easily changeable offgas
treatment options, burying extra pipes in trenches, etc.). Decision trees
should be developed during the preliminary design phase to show how sys-
tem layout or operating parameters can be varied for changing site condi-
tions or if cleanup criteria are not met at compliance points.
During construction, further site knowledge is typically gained through
the installation of additional wells or excavations. Processes need to be in
place so that (1) additional site information is collected during construction
by the field staff and (2) this knowledge is conveyed to the engiineer so that
field changes can be made as needed. For instance, the depth of contamina-
tion may be deeper than first estimated and therefore, the depth of the
sparging wells must be modified. Finally, during system operation, the
monitoring plans need to be implemented based on observed operating data
with changes in layout or operation as appropriate.
5.57
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Design Development for Air Sparging
5.12 Permitting Requirements
Air and water discharge permitting requirements are covered in Section
3.11. Generally, states do not require a specific permit to conduct an air
sparging test beyond the requirements for air and water discharge permits.
Depending on the regulatory program and degree of state involvement,
various levels of monitoring requirements may be implemented. Some states
may also have design guidance regarding the amount of air injected in a
sparging system versus the amount of air removed with an vapor extraction
system, monitoring programs, and minimum provisions for pilot- and full-
scale operational reports. However^ these should be considered requirements
to assess and document the overall performance of the pilot test or full-scale
system, rather than compliance requirements.
Also, there may be related provisions regarding well construction or aban-
donment, well identification, investigative waste disposal, and electrical
safety that must be followed. For an example of more detailed state guid-
ance for sparging systems, refer to the Wisconsin Department of Natural
Resources' Guidance for Design, Installation, and Operation of In Situ Air
Sparging Systems (1993).
When a gas other than air is being sparged, states typically require a
groundwater injection permit. In such cases, the gas to be used, its intended
effect on contaminants in the groundwater, and how uncontrolled migration
of the injected gas will be monitored must be documented.
5.73 Design Checklist
This section summarizes the activities to be considered during design of
an air sparging system in checklist form. While not all items may be needed
for a particular project, the checklist provides an overall list of concerns/
activities that should be considered.
5.58
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Chapter 5
Site Investigation/Regulatory Review
• Develop target zones from site investigation report
• Construct cross-sections from soil borings showing target
cleanup zones
• Develop list of potential environmental permits
• Develop preliminary soil and groundwater clean-up concentrations
• Determine list of chemicals of concern
Design Planning
• Develop overall design objectives, including desired timeframe
for remediation
• Complete conceptual design of treatment system for the site in-
cluding cross-sections and plan views
• Estimate contaminant mass to be removed/contained
• Identify need for pilot test based on size and complexity of site
• Identify data objectives of pilot test
• Assess need for pilot test and full-scale offgas treatment
• Identify other factors that will affect design such as space, prox-
imity to electrical power source, noise, facility operations, prop-
erty, and access constraints
• Determine how the system will be built and relationship between
designer/contractor/operator
Preliminary Design
• Complete pilot test work plan
• Undertake pilot test
• Interpret pilot test results in terms of initial conceptual design;
modify conceptual approach as required
• Layout, aboveground aspects of system, including piping runs,
equipment locations, discharge points
• Estimate total flow and mass removal rate; determine need for
soil vapor extraction
5.59
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Design Development for Air Sparging
• Begin application for air and water discharge permits
• Develop a list of major equipment items and their preliminary
sizing
• Complete a piping and instrumental on diagram showing controls
and interconnects
• ' ' ,1'' II ' ', " "„„ ••' ill ,' ' „ . _ ' i '' ,'li' '•":! „ |l ' ,i|:'''" ' |h "
• Consider future modifications that may be required for the system
• Determine how discharge compliance and eventual soil cleanup
will be demonstrated
• Determine electrical classifications
• Determine how subsurface air flow will be assessed during full-
scale operations
Final Design Activities
• Complete analysis of system pressure requirements with head
loss assumptions
n1 " , 'Si!1',!!," : • „• '•, "' •!•,, i, 11, :, Vli'i:1'! "•:,'' |»i',,, •'ill niM1!1. .'"i1 • • : ;,,, '•, , „ Ji, "!',i"'i; ;,!' .'.i1''1'1"1, «. || w,!1 ', ,'"»:;!!
I ,„ • ,'"|., ". ii1' !,,i i, ;,n 'liP'ii iN'i.ii, ''fi'j,,',,; j,,,, ji" j|i.|,|, i,'1!,!!,!!,..1',!..!,!.1!' • "if,,:,,," ':, \ s®f ; i,;:»," niii',,1 ,."' " ill • i1'1'1 :, i •"•" ' ' ii": "
• Finalize blower sizing as well as other major equipment
• Complete civil construction details and specifications (well,
trench, building foundation details)
• Complete final mechanical drawings and specifications of piping
and equipment
'• ' " " '!»„ »| ' ,i V , »• • ""j1,!,, ""ii11 , h1 „„,," i:l "MS::, "I'* ' [". , j'i « • , , ",• ,1 ill" ",,iii, .',.,, . „„ , I, .i|,ii
• Complete final electrical and instrumentation and control draw-
ings and specifications
• Complete final architectural drawings for buildings as needed
• Develop construction quality assurance plan, including functional
and performance checking of the system
• Develop a start-up plan, including samples to be collected and
analyzed
• Develop an operations and maintenance plan for long-term sys-
tem operation; include contingency plan for system modifications
as required, reporting requirements, safety, compliance
• Develop a construction and operation safety plan
• Develop a final cost estimate for construction and operation
5.60
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Chapter 6
IMPLEMENTATION AND OPERATION
OF AIR SPARGING
6.1 Implementation
Implementation of an air sparging system follows essentially the same
procedures as those described for a vapor extraction system as described in
Section 4.1.
6.2 System Startup
While carefully following a detailed start-up plan is important with any
system involving multiple motors, blowers, pumps, and piping systems, it is
especially important for air sparging systems. This is primarily because air
sparging systems present potential hazards above and beyond those of other
systems. These supplementary hazards include:
• conveyance of compressed air that, if suddenly released, could
present a health and safety hazard; and
• the generation of hazardous vapors in the subsurface that could
migrate to sensitive receptors.
This section discusses prudent activities that can be taken to minimize the
hazards associated with startup of air sparging systems. A general start-up
checklist is also provided.
6.1
-------
Ill II ill
Implementation and Operation of Air Sparging
": , • '"I!
1R '':;;""
"lillill „..'!' "
6.2.1 Component Testing
As discussed in Section 4.2.1, component and system diagnostic testing
may be the most important of the start-up tasks. Such testing:
• ensures that equipment has been installed to operate in accor-
dance with manufacturer's specifications;
• verifies that the system has been installed to operate safely; and
'• confirms that the automated safety control logic was pro-
grammed into the system in accordance with the design.
Specific component diagnostic testing that should be included in system
Start-up activities include rotating of equipment, electrical safety checks, and
testing of automated shutdown protocols.
6.2.1.1 Power Supply
The direction of rotation of pumps, blowers, compressors, and other
equipment is often established by the electrician when connecting the unit to
the power supply. Because an incorrect direction of rotation can adversely
affect the performance and possibly damage the equipment, the rotational
direction of rotating equipment needs to be checked prior to continuous
operation. A general discussion of the necessity for, and methods of, verify-
ing the proper rotation of remediation equipment is provided in Section
4.2.1.1. .The guidance in that section also applies to air sparging systems.
6.2.1.2 Electrical Safety Checks
Electrical safety precautions and inspections prior to air sparging system
startup are comparable to those applicable to vapor extraction system opera-
tion. These recommended safety measures are discussed in Section 4.2.1.2.
.. I:' lii ',: .' ' ' J," • • ' / . , , .
6.2.1.3 Shutdown Protocols
1 • - ' , •„ ,! , " 'iVi''1' , ' ' • ' i •••:,'!I • i1 'in, ''" ',• ,i, "'„'! ii "• • :" ,'"• • „ ' ',',,• I *
i i,, 11 "I1 i,,1 •• , i ," ,,il' i .' ..i, ii I Hr, '!,!i":!.,iii.. I,1 |, ;!• ! '. , ' .. ' i'" I ,:";."' • , •:•, i| ', "'lii, Lin.1:
Air sparging systems, like vapor extraction systems, are typically de-
signed to be fully automated, requiring only periodic operator involvement.
With this degree of automation, calibration of control instrumentation and
testing of automated system shutdown protocols during system startup is
essential to ensure that equipment is adequately protected and mat system
operation will not present a health and safety hazard. The calibration and
shutdown simulation procedures described in Section 4.2.2 for vapor
6.2
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Chapter 6
extraction systems are directly applicable to air sparging systems. However,
typical shutdown protocols that are specific to air sparging systems warrant
further discussion here.
One of the chief operating concerns for air sparging systems is the pro-
duction of hazardous vapors in the subsurface and the possibility that these
hazardous vapors could escape the confines of the system and enter and
accumulate in one or more locations where sensitive receptors may be
present (e.g., residential basements, utilities, buildings, etc.). The accumula-
tion of vapors may present not only an exposure hazard to inhabitants or
workers, but also, in the worst case, an explosion hazard. To minimize these
potential hazards, air sparging systems typically have instrumentation and
control devices that are designed to detect possible loss of subsurface vapor
flow control and to terminate the sparging component of the system if this
event arises.
A frequently employed instrumentation/control logic to alleviate the con-
cerns surrounding fugitive vapors ties the supply of sparging air to the
sparging wells with a measure of adequate vacuum applied to surrounding
vapor extraction wells. In this safety system's simplest form, a pressure
switch that is mounted on the vapor extraction system manifold piping de-
energizes a solenoid valve on the air sparging compressed air manifold to cut
off sparging air flow in the event that an insufficient vacuum is detected at
the vapor extraction system manifold. A more complex safety net may link
the supply of compressed air to the sparging wells to soil pressures detected
at strategic influence monitoring wells.
Where there is an even greater threat of hazardous vapors entering and
accumulating in structures, added safety measures are typically taken with
respect to instrumentation and controls. One of the methods that is em-
ployed is the installation of vapor monitoring probes within likely accumula-
tion areas of the structures. The control logic Is typically programmed such
that if the vapor monitoring probe(s) detect any hazardous vapor concentra-
tion above background, the compressed air supply to the sparging wells is
terminated.
Should these instruments and controls be included in a system design,
they represent the most important and critical part of the system. As such,
particular care must be taken at startup to calibrate the instruments, verify
the alarm set points, and simulate the alarm condition to confirm that the
design shutdown sequence occurs. Subsequent to the start-up phase, these
6.3
-------
Implementation and Operation of Air Sparging
IS'
procedures should be repeated on a regular basis to ensure operation of these
critical functions.
6.2.2 Leak Testing
Leak testing of air sparging system piping during startup is typically per-
formed for the following reasons:
• an undiscovered leak can lead to reduced system performance
and effectiveness (e.g., if the air compressor cannot supply a
sufficient volume of air to the sparging wells due to excessive air
(>, 1|! -loss); _ ' '_' ^ "(_" ' ' ; '" ^ "_
; *V !1 • "" a detected leak may be indicative of a larger instillation proW^
that if uncorrected could lead to a catastrophic pipe failure; arid
• a subsurface air leak could result in a localized pressure build-up
",'";: :', in the soif that could" deflect" "Hazardous" vapors '"away JrOm"vapor
,1,1! I »''„ " ,11 i iir ,j.! r '.i ,,.. , 'i • . ,„ ',11, ,1,1 • vi,, j,| ,;,i,;,i|,,, ivir „• m, • Mini'ij j1 <, "H \.rt &, , : P< !r,, , .ii'V1' | " i !"! '
recovery wells.
1 , ;" 1 , ' : ' : .1, "!\'
Pipe leak testing is typically completed using either hydrostatic or pneu-
matic testing methods. A basic description of both' testing methods is pro-
vided in Section 4.1.4.3.
6.2.3 System Shakedown
• An important step in the startup of an air sparging project is a full-system'
shakedown. Each mechanical and electrical component of the system is
checked for functionality over an operating range that spans the design oper-
ating conditions. The system is operated in bothmanual and automated
modes under a rarige of operating scenarios. In the automatic mode, the
alarm conditions that precipitate automated equipment shutdown are once
again simulated to verify final set points and shutdown protocols.
During the system shakedown, pressure and vacuum relief valves are
tested to ensure that the valves are set to open at the appropriate
vacuum. The air sparging system is typically ready for continuous operation
once the system shakedown has been successfully completed.
"" "li1"!'" I1 I ,„"[. ' .. ' t ,' ! i, ,'. . i •',.'. ," , 1 . .'• i / '•:(>'' !';, si : I'L ''.•'• , ' ''''. • '. ni ' it, !•?• , '*,i it "i ':''' .•!'!«. •' >: '•If.&.ti -'I1 i ":"" III l| 111 I
I ,if-
' [ r'l '•'
6.4
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Chapter 6
6.2.4 Pro-Startup Checklist
The following checklist is typical for the pre-startup phase of air sparging
implementation.
• Remove debris from piping interior (PVC shavings, soil, etc.)
• Complete pipe integrity testing
• Eliminate piping blockages
• Appropriately position all system valves
• Orient valving on blower piping in start-up configuration for least
flow resistance
• Cross check that motor supply voltages match motor plate voltages
• Cross check thermal magnetic circuit breaker ratings with motor
amperage specifications
• Verify that motors and hand switches are properly grounded
• Collect background data (e.g., static soil pressure, VOC concen-
trations, depth to water, etc.)
• Secure and post requisite discharge permits
• Check equipment lubricating fluid levels, if applicable
• Verify proper rotation of motors
• Record initial running amperage of motors
• Recalibrate all in-line instruments
• Check switch set-points
• Compare and adjust sensor transmitter spans relative to actual
conditions
• Simulate alarm conditions and verify automatic operations
• Confirm remote access to telemetric data
• Reconfigure valving to achieve design vacuum/flow
• Compare blower/pump performance to manufacturer's perfor-
mance curves
• Check vacuum at wellheads to confirm minimal piping head loss .
6.5
-------
"111'" n IT ftMI \ ir~n\ \ I lyI | linnlliliiilii'
-f '.III! ", •' 1 ! • . .'i. I "MM . •( ,
Implementation and Operation of Air Sparging
• Record influence vacuums at influence monitoring wells
• Collect influent and effluent vapor samples for baseline field and
laboratory analysis
6.2.5 Startup Checklist
Typical procedures for the startup of an air sparging system are as follows.
1. With the vapor extraction blower operating, activate the com-
pressed air source, and using a pressure regulator, gradually in-
crease the supply pressure until the design air flow rate for the
i chosen well group or the entire system is attained. (Set measure
vapor extraction system emissions to verify compliance with
permit conditions.).
, , ,,, , , ; ,j , , ,
2. Balance the air flow to each air sparge well.
"''.• '••" ;. I. t " ' ," l|,:1'1 1,',l|:l!i"ll;l":i:it! '""'ilF!,!!1,; f ,-:. ,|ji- (•';,!„! ;• , . • . | ,(.H i:.,.1
3. Establish the applied pressure and compressed air flow relation-
ship for each well.
4. Following flow balancing, check for agreement between flow
meters to verify that total air supply equates to the sum of the
supply to the individual wells.
5. Periodically collect water level measurements, soil pressure/
vacuum measurements, and soil gas VOC concentrations.
6. Adjust system pressures/flows if unsafe conditions are observed
from the vadose zone monitoring data.
,, , ., .. ,. , •. ' ,,- ....•:,: ;;„;,; , 1 ;.,.., , ; , ,: , , • ;!'.:; .:...
7. Repeat for each of the air sparging well groups.
6.3 Operation and Maintenance
The success of a remediation project can depend heavily on the manner in
which the system is operated and maintained. Carefully operated systems
generally result in a reduced clean-up" time" while minimizing safety hazards.
Well-maintained remediation systems tend to operate with an increased level
of efficiency and with less downtime. This section discusses a number of
6.6
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Chapter 6
key operation and maintenance procedures for air sparging systems that can
optimize performance.
For most air sparging systems, the primary objectives of a system opera-
tion and maintenance program are to:
• achieve the remedial objectives at the earliest date;
• prevent further environmental impact via waste streams or con-
taminant mobilization;
• maximize the lifetime of the equipment;
• collect sufficient data to help realize these objectives;
• achieve project objectives while keeping present-value project
costs to a minimum; and
• ensure safety of operation.
Controls that can be employed to optimize system operations and help
achieve these objectives are discussed in subsequent sections.
6.3.1 Performance Control Functions
To optimize system performance, the operation of air sparging systems
may be controlled in three basic ways. System adjustments may be made to
modify: ;
• magnitude of applied vacuums to the soil and air sparging pres-
sures (extracted/injected air flow rates);
• configuration of wells to which the vacuums/pressures (extracted
soil gas/injected sparging air flow) are applied; and
• duration of applied vacuums/sparging pressures (extracted/in-
jected sparging air flow).
Performance optimization is achieved when these adjustable parameters
are regularly reconfigured to achieve the system's performance objectives at
the least present-value cost. For air sparging systems, optimized perfor-
mance typically means that VOC mass recovery rates are maximized over
the period of system operation, while ensuring that the system is operated
safely. For biosparging systems, this typically means the uniform and consis-
tent delivery of oxygen to the entire treatment area to safely maximize the
biodegradation of organic contaminants.
6.7
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Implementation and Operation of Air Sparging
Routine collection and evaluation of system operating data provides the
information that is needed to make the regular system adjustments to opti-
mize performance. By adjusting these three basic control functions, subsur-
face air flow patterns may be modified"'to' direct air toward"(1) pockets of
dissolved- and adsorbed-phase VOC contamination, (2) areas where oxygen
levels are depressed, or (3) center of me treatment area to reduce the poten-
tial of fugitive vapors in the subsurface. These routine adjustments can also
be made to eliminate no-flow zones where competition for air results in
, ,, I „'„:•,, | , ,,•'.',„: „ !| « i",N|. ,'i i ,|i|i, ..,||< '•' ,,'»" Ill ,,,!'' V: ,,!i II111 •', , ' , !| • li,,''l
relatively static (flat pressure gradient) conditions that, if not addressed, can
undermine the performance of the remediation system.
,,; „• • ; ,", •-,,;,,, ;i;J • : .;•.' ,:: , • i '/ •
Routine system optimization adjustments are made while an air sparging
system operates in either the continuous or pulsed modes: Selection of the
appropriate operational mode for a given site can further optimize the perfor-
mance of an air sparging system.
An air sparging system designed for continuous operation will include
sparging, vapor extraction, and treatment equipment that are sized to accom-
modate flow to and from all wells in the system. Such systems allow for
subsurface air flow to be adjusted to optimize system performance. This
flexibility is important because VOC recovery rates and distribution of dis-
solved oxygen rapidly decrease shortly after commencing operation under a
single configuration/flow regime.
, :;, • , .:•. - : . ,;, ,h, :,. , .. : •• •. : i :;; :
One method that can be employed to reduce the degree to which
channelization occurs and/or to induce air flow channel to cycle or change
course during continuous operation is to routinely modify applied sparging
pressure/air flows and applied vacuums. Careful evaluation of system moni-
toring data can reveal how the system configuration should be modified to
enhance performance and the interval of time that the system should be per-
mitted to operate prior to reconfiguration.
Air sparging systems designed to operate in a pulsed mode may have
air injection and extraction/treatment capacities sufficient to employ
only a fraction of the remediation system wells at one time. In such a
configuration,subsets of the wells are alternately operated to optimize
system performance. Where an air sparging system has been designed
to accommodate the simultaneous use of all remediation system wells,
i • , i< -i t - " - :5: iti iff ., V '• 'i1' t; ,: 11 i ! i a : nil;!:.,!,,»', iSfe • j: MiiJ! • i "I«!'i!) »i >' • *>.' Ji» '# • . ,• , •: .,•-, ,,i- »,» ,,
pulsed operation may consist of alternately activating and terminating
operation of the entire system.
6,8
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Chapter 6
The duration of a pulsing event to optimize system performance can vary.
Temporary groundwater mounding during sparging may suggest what the
optimum pulsing period should be for a given site. During the initial intro-
duction of air into the saturated zone, the air displaces some of the water,
creating a temporary groundwater mound. However, once stable air flow
patterns in the saturated zone have developed or channelization of the air
flow has occurred, the mound .typically collapses as the initially dewatered
zone resaturates. It has been suggested that if the duration of the transient
mounding period can be determined, this period may provide a design dura-
tion and pulsing frequency for maximized groundwater mixing (US ACE
1997). However, pulsing frequency and duration should ultimately be deter-
mined based on monitoring data. Specifically, the pulse that results in the
highest mass removal rate (as measured by vapor extraction mass removal
rates during sparging or by declines in contaminant concentrations at com-
pliance points) should be used.
6.3.2 Maintenance
The maintenance requirements of an air sparging system are slightly in-
creased relative to those required to operate a vapor extraction system as dis-
cussed in Section 4.3. The increased maintenance requirements stem mainly
from the addition of an air compressor and its peripherals (e.g., receiving tank,
filters, dryers, etc.), the associated instrumentation and controls, and the addi-
tion of air sparging wells screened in the saturated zone. The effect of these
additions on maintenance requirements is discussed below.
6.3.2.1 Rotating Equipment
Equipment rotation as described in Section 4.3.2 for vapor extraction
maintenance is equally valid for air sparging systems and the reader is di-
rected to that section for further information on the subject.
6.3.2.2 Wells Jrenches,and Well Points
The maintenance requirements for wells, trenches, and well points that
were identified in Section 4.3.2 are equally valid for the operation and main-
tenance of air sparging systems. In addition, air sparging well screens may
periodically need to be cleaned to remove accumulated fines carried into the
well by water entering between pulses. Air lift pumping can remove accumu-
lated solids within the well.
6.9
-------
I'lNINJ INIPIjlll
Implementation and Operation of Air Sparging
Sparge well screens may also be impacted by inorganic precipitation (pri-
marily iron) and/or biofouling. This potential is not clearly established, and
could be a function of the redox potentialof the injectant, the aquifer alka-
linity, the frequency of pulsing, and the type and abundance of organic
complexing compounds.
A number of different methods for cleaning air sparging wells may be
employed If chemical or biological fouling is present, physical agitation, or
chemical treatment can be effective In extreme cases, mineral deposits on
well screens can be removed using low-pH solutions such as hydrochloric or
sulfuric acid. Iron bacteria can be removed by introducing bactericides (e.g.,
Chlorine dioxide) followed by low-pH treatment after the chlorine is re-
moved from the well. Recommended procedures for chlorine control of iron
bacteria are detailed in Driscqll (1975).
6.3.3 Safety Considerations
Air sparging systems present operator and public safety concerns beyond
those discussed in Section 4.3.6 for vapor extraction systems. These addi-
tional hazards arise from the use of compressed air for air sparging and the
inherent potential for air sparging to generate fugitive hazardous vapors in
the subsurface.
6.3.3.1 Fire Safety
Fire safety considerations during operation and maintenance of air
sparging systems are similar to those associated with vapor extraction sys-
tem operation. These considerations are discussed in Section 4.3.6.1.
6.3.3.2 Air Quality
Air quality concerns during operation and maintenance of an air sparging
system overlap greatly with those identified in Section 4.3.6.2 for vapor
extraction systems. However, an additional air quality concern that is spe-
cific to air sparging operation warrants further discussion.
The sparging of air into contaminated groundwater generates hazardous
vapors in the subsurface. During sparging, these vapors could etude capture
and enter into nearby structures. If potential receptors are in the vicinity of
air sparging activities, vapor monitoring within associated structures should
6.10
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Chapter 6
be considered as part of the routine operation and maintenance procedures to
reduce the risk of exposure to the hazardous constituents.
6.3.3.3 Physical Hazards
The physical hazards that exist with the operation of an air sparging sys-
tem are similar to those discussed in Section 4,3.6.3 for operation of vapor
extraction systems. However, the compressed air used in an air sparging
system adds a significant physical hazard which the operator should be
aware. The hazard is related to the energy that can be released during;the
sudden decompression of air. A sudden release of pressure due to broken
piping or the decoupling of a compressed air hose can cause serious and
permanent injury. Maintenance of piping protectors and safety pins in com-
pressed air hosing connections should be mandatory, and the operator should
be aware of the potential hazards of compressed air.
6.4 Performance Monitoring
The main goals of a performance monitoring program for an air sparging
system should include:
• tracking the progress of remediation toward remedial goals;
• achieving the required level of remediation as quickly as possible;
• preventing further environmental impacts from waste streams or
contaminant mobilization;
• collecting defensible data to support site closure;
• minimizing the costs needed to achieve the above consider-
ations; and .
• safety monitoring.
6.4.1 Zone of Influence Monitoring
The zone of influence that has been assumed during full-scale design
should be confirmed once operations begin to identify any injection wells
that may have zones of influence significantly different from design values.
6.11
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Implementation and Operation of Air Sparging
Zones of influence should be monitored using a combination of those meth-
ods described in Section 5.2.2. If a particular well is shown to have a small
zone of influence due to the screen interval being completed within a lower
permeability soil zone, the applied pressure can be increased. In addition,
pulsed operation in the vicinity of this "dead zone" will increase mass re-
moval from the area.
:• ' ;; | •:
In some cases, zone of influence monitoring data will indicate that
the system is operating as designed, but contaminant concentrations at
compliance monitoring points exceed acceptable levels. Although not
indicated by the employed zone of influence monitoring methods, this
may be due to uneven aeration of the contaminated portion of the aqui-
fer. In these cases, the system modifications discussed in Sections 6.3.1
and 6.5 should be considered.
6,4.2 Injection Pressures and Flows
• •• : • ' •-./*"..• •• -' ••' • . f- ! ..'.,•. , • A. 1 ;,:;,!„::„,,
The injection flows at individual wells should be regularly monitored, and
necessary valve adjustments should be made to ensure that the system flow
is balanced as designed. As operational data are collected for a given sys-
tem, it is common for different injection flows to be used at various wells
due to water table fluctuations or heterogeneities in the aquifer or targeting
of "hot spots."
A major concern with air sparging system operation is well screen and/or
aquifer fouling by precipitate buildup or microbial growth. Fouling of the
well or aquifer may be indicated by a reduction in injection flow rate at a
given pressure over time. Therefore, it is important to regularly monitor the
injection flows and pressures at individual injection wells to determine the
week-to-week variability in these parameters and to identify any evidence
that a loss of permeability may be occurring due to fouling and/or scaling.
6.4.3 Downgrcidient Groundwater Quality Monitoring
Downgradient ground water quality is usually used as the ultimate perfor-
mance monitoring measure of an air sparging system. For this reason, the
groundwater quality in both up- and downgradient wells should be docu-
mented at regular intervals during system operation. These records are nec-
essary to define:
6.12
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Chapter 6
• characteristics of contaminant source material;
• water flow velocity or direction on a seasonal basis; and
• operational changes.
Care should be taken to ensure that uniform and acceptable methods of
sample collection and analysis are used during the entire monitoring period
and at all wells. In this way, time trend analysis of the data can be per-
formed without having to consider changes in sampling and/or analytical
methods.
6.4.4 Vddose Zone Monitoring
As previously discussed, the vadose zone surrounding an air sparging
system needs to be monitored for pressure to ensure that the injected air is
collected by the vapor extraction system, if one is used. If a vapor extraction
system is not used due to reliance on the vadose zone soils to act as a
biofilter to the contaminants in vapors released from the aquifer, then addi-
tional vadose zone monitoring is needed.
To define the extent to which contaminants, are removed from vapors
traveling through the vadose zone, the vapor quality should be monitored at
discrete points throughout the affected vadose zone. Direct push probes,
such as described in Section 3.2.2.1, can be used to collect subsurface pres-
sure data and monitor the soil gas quality during sparging. In situ respiration
tests are typically performed to estimate the extent of biodegradation within
the vadose zone. In addition, while sparging is occurring, it is useful to
monitor the oxygen and carbon dioxide concentrations at the vadose zone
monitoring points to:
• ensure that sufficient oxygen (greater than approximately 5%) is
present in the soil gas for biodegradation; and
• determine if carbon dioxide is present.
If less than 5% oxygen is present in the soil gas, it may be necessary to
increase the sparging flow rates to supply more air to the subsurface for
biodegradation. If, on the other hand, little (<1%) or no carbon dioxide is
measured in the soil gas, the sparging flow may be too high, resulting in too
short of a residence time in the vadose zone for biodegradation of the vapor
contaminants.
6.13
-------
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Implementation and Operation of Air Sparging
6.4.5 PuJsed Operation
The theory and benefits of pulsed operation of an air sparging system are
discussed in previous sections. With regard to performance monitoring of
pulsed systems, the pulse duration and interval should be periodically moni-
tored for effectiveness by measuring the contaminant concentration in the
vapor extraction effluent (if such a system is used) or in the soil gas col-
lected from vadbsezone monitoring points (if a vapor extraction system is
not used) at regular intervals during the pulse cycle. The objective is to esti-
mate the amount of contaminants being removed from groundwater and into
soil gas due to the sparging pulse.
If the soil gas or vapor extraction effluent contaminant concentrations
remain high at the end of a pulse cycle, this may be an indication that a
longer pulse would be more effective. This approach is only valid if no sub-
stantial vadose zone contamination remains, since the soil gas quality needs
to be indicative of the contaminant mass being transported/ram the aquifer.
',„,!! "iiil'U, '!'i il'i" ' , |" '! ii» ' 'lii'in'l,!;, ! f ,'"!' '"i 1' , ii'ii'W jiilErllillllli '«!„ "„,!•',!' f:,1,iri1ll'i!!v4'lli*iP!,,!i'- ' •• li,:1' "ii i in*1*:' • ' ' .I1'!!,,!,!* !'•,' •'« _ ' 'I1'1"1'!1
If vadose zone soils are contaminated, the pulse duration and interval may
be evaluated by monitoring the transient mounding mat occurs upon com-
mencement of a pulse. ''ffi'l^T'ca®e',1J8Eie objective would be to modify the
pulse cycle to coincide with the time to Fbrm'arTd then collapse the ground-
water mound around a particular sparging well.
6.4.6 Effectiveness and Rebound Monitoring
. ,',ii '*•., ' " •;, '• ",',„!'iff,in, :," .'i, ,',,ii *''iRsJi1"1:: '","+*' .li f! ", i1 i" •,»»! •,:, JiiJ iiir'i'r i-'i .I'lii ,1 'i,i "A.i!1"1. ",i|i|:i. '.. •..' li'mi,:,"!" . ,,i 'V^1 m ",!:,:ii,''il i :'i:* '! ;|..;
Bass (1998) presented a review of case studies to shed light on how
well air sparging achieves permanent reduction in groundwater contami-
nant concentrations^ They also compiled basic design features that were
used iii the case studies. Tables 6.1 and 6.2 summarize 21 sparging sites
(6 chlorinated solvents, 15 petroleum hydrocarbons). Soils ranged from
silt to coarse sand and gravel, with both native and backfilled material as
the sparged matrix. Sparging well spacing ranged from 3.5 to 24 m (12
to 80 ft), and flow rate per sparging well from 3 to 35 scfm. Some of
the systems injected sparging air continuously, others used pulsed opera-
tion. Well systems ranged from 1 to 16 wells and included both hori-
zontal and vertical types. Durations of sparging system operation
ranged from a few months to more than four years.
6.14
-------
Chapter 6
In each case study, groundwater concentrations were compared before
sparging was initiated, just before sparging was terminated, and in the
months following shutdown of the sparging system. Post shutdown monitor-
ing data are available for only a few months in most cases, but at some sites
more than a year of post shutdown data have been collected. While this is a
limited database, examination of the characteristics and behavior of thfe
sparging study sites in Tables 6.1 and 6.2 lead to the following insights pre-
sented by Bass (1998).
6.4.6.1 Petroleum-Contaminated Sites vs. Chlorinated Sites
Only 30% of the chlorinated sites rebounded, while about 50% of the
petroleum sites rebounded. The magnitude of the rebound at the chlorinated
sites was also considerably smaller than at the petroleum sites. Groundwater
contaminant concentrations initially decreased during sparging by 1 to 4
orders of magnitude, but when rebound occurred (especially at the petroleum
sites), contaminant concentrations increased several orders of magnitude
again after sparging was terminated so that the overall reduction was less
than an order of magnitude.
6.4.6.2 Factors Affecting Rebound
In general, the more successful sparging systems had air flow rates
greater than 10 scfm/well, and well spacings less than 6 m (20 ft). The suc-
cessful systems addressed the entire source area. Sparging systems that
achieved a significant reduction in groundwater concentrations, bet re-
bounded when the system was shut off, were characterized by a low sparging
air flow rate, a low sparging well density, and/or a failure to address the
entire source area.
As shown in Figure 6.1, low flow and large v/ell spacing were generally
associated with more rebound. The greater the spacing, the greater the ;air
flow required to achieve a permanent reduction in groundwater contaminant
levels. An interesting exception to this trend was the behavior of several
chlorinated sites. These sites had well spacing on the order of 24 m (80 ft)
but showed no rebound. The possible explanation is that these sites had only
dissolved contaminants.
6.15
-------
Implementation and Operation of Air Sparging
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6.16
-------
O
Site #3 (CT)
Service station
4 sparge wells
= 50 ft spacing
5 scftn/well
Continuous flow
• Total BTEX 17,000
68
1,800
31,000
21 10 Gasoline,
diesel
• Benzene SPHC
SPHC
SPHC
380
• Total BTEX SPHC
SFHC
SPHC
SPHC
400
3,300
• TPH SPHC
SPHC
SPHC
SPHC
592
6
346
2,610
94
930
3,700
830
1,376
2,365
7,310
376
8
1,773
32,000
7,100
28,000
15,800
23,590
147
1,617
21,190
78
810
1,400
510
325
1,508
9,470
9
23
1,961
7,000
560
20,000
2,310
3,930 ftg/L 4 months after sparge
system shutdown'
27 \Lg/L 4 months after sparge
system shutdown
77 fig/L 4 months after sparge
system shutdown
1,900 ng/L 4 months after sparge
system shutdown
Fine sand; shut down when
system struck by car
Source area monitoring well
Source area monitoring well
Source area monitoring well
Downgradient monitoring well
Source area monitoring well
Source area monitoring well
Source area monitoring well
Source area monitoring well
Upgradient area monitoring well
Downgradient area
monitoring well
Source area monitoring we"
Source area monitoring well
Source area monitoring well
Source area monitoring well
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Site #5 (CT) 17
Service station
2 sparge wells
= 40 ft spacing
3.5 scfm/well
Pulsed (daily cycle)
Site #6 (WA) 21
Service station
3 sparge wells
30 ft spacing
4 scfm/well
Pulsed (= 4 week cycle)
4 Weathered gas
• Benzene 2,000
9,400
7
27
5
• Total BTEX 76,000
119,000
68
200
660
2 Fresh gasoline
• Benzene 11,000
2,200
22
• Total BTEX 37,800
12,170
114
• TPH 82,000
52,000
1,000
2,000
32
160
17
2
3
2,300
11,000
300
11
84
<0.3
<0.3
<0.3
6
4
<2
87
60
<10
<10
120
-
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4
22
26,000
-
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5
2,400
6
71
<0.3
1,054
1,566
<2
10,000
21,000
<10
<10
Tight soil; pilot system only
Source area monitoring well
Source area monitoring well
Source area monitoring well
Crossgradient monitoring well
Downgradient monitoring well
Source area monitoring well
Source area monitoring well
Source area monitoring well
Crossgradient monitoring well
Downgradient monitoring well
Sparged in tank pit surrounded by
tight soil
Within tank pit
Within tank pit
Outside tank pit
Within tank pit
Within tank pit
Outside tank pit
Within tank pit
Within tank pit
Outside tank pit
Outside tank pit
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Implementation and Operation of Air Sparging
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Site #9 (CA) a 1
Service station
9 sparge wells
= 20 ft spacing
Pulsed (12 hr cycle)
Initiated 7/93
.
•Initial analysis date was about 5 months after the start of sparging.
Permission to reproduce granted by David H. Bass (1998)
• Total BTEX 964
2,575
3,270
65
2,906
102
Weathered gas
• Benzene 1,000
680
• Total BTEX 2,760
1,081
• TPH as 9,400
gasoline
3,400
1,779
4
1,920
35
<5
549
34
53
425
102
510
130
622
4
11,900
70
<5
12,434
210
14
245
263
2,500
120
Source area monitoring well >
Source area monitoring well
Source area monitoring well
Source area monitoring well
Downgradient monitoring well
Downgradient monitoring well
Sand; some of source plume may
be under building
Source area monitoring well
Source area monitoring well
Source area monitoring well
Source area monitoring well
Source area monitoring well
Source area monitoring well
O
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-------
a : -I "i j - -, i - i= i
IO
Table 6.2
Air Sparging Sites without Post-Closure Rebound
Duration (months) Contaminant Concentration (ue/L)
Site Specifics
Site #1 (WI)
Industrial
3 sparge wells
= 80 ft spacing
10 scfm/well
Pulsed (4 hr cycle)
Site #2 (WI)
Industrial
5 sparge well
= 80 ft spacing
10 scfm/well
Pulsed (4 hr cycle)
Site #3 ON)
Industrial
1 1 sparge wells
•* 50 ft spacing
15 scfm/well
Continuous flow
Sparging Post-Closure Contaminant @ Start
14 4 Solvents
• TCE 670
17
10 4 Solvents
• TCE 32
99
83
160
18 4 Solvents
« 1,1,1-TCA 4,000
260
• DCE.DCA 720
134
@ Shutdown Post-Closure
9.9
0.95
32
12
0.66
25
24
12
13
12
5.7
16
IS
3.7
052
W
15
3
12
7
Comments
Addresses source area; began
pulsing after 7 months
Source area monitoring well
Downgradient monitoring well
Addresses downgradient plume;
began pulsing after 3 months
Sand and gravel
Source area monitoring well
Downgradient monitoring well
Source area monitoring well
Downgradient monitoring well
a>
-------
Site #4 (MA)
Industrial
3 sparge wells
80-150 ft spacing
18 scfin/well
Continuous flow
Site #5 (NY)
Service station
7 sparge wells
= 12 ft spacing
13 scfm/well
Continuous flow
O
Fo
CO
Site #6 (MA)
Service station
1 sparge well
35 scfm
Continuous flow
7 1.5 Solvents
• 1,1,1-TCA 200
M
• 1,1-DCE 27
• PCE 85
15 1 Gasoline
• Total BTEX 18,500 <5
• TPH 32,000 <100
5,600 < 100
11 2 Fresh gasoline
• Total BTEX 4,000 8
1,000 1,2500
5.300 1,770
190 474
640 436
770 <5
93
5.8
2.0
6.0
<5
<100
<100
26
331
117
38
106
<5
Sand; wells placed in non-
contiguous pockets of
contamination; crossgradient well
operated only 2 months
Downgradient monitoring well
Crossgradient monitoring well
Downgradient monitoring well
Crossgradient monitoring well
Source area monitoring well
Source area monitoring well
Downgradient monitoring well
Uniform sand
Source area monitoring well
Source area monitoring well
Source area monitoring we!!
Downgradient monitoring well
Downgradient monitoring well
Source area bedrock monitoring
well
O
Q
-------
o
Table 6.2 (cont.)
Air Sparging Sites without Post-Closure Rebound
Site Specifics
Site #7 (NY)
Service station
Horizontal wells
90 scfrn total
Continuous flow
Site #8 (NH)
Service station
8 sparge wells
i= 20 ft spacing
3 scfm/well
Pulsed (daily cycle)
Site #9 (MA)
Service station
5 sparge wells
~ 13 ft spacing
2.5 scrm/well
Duration (months') Contaminant Concentration (ue/U
Sparging Post-Closure Contaminant @ Start @ Shutdown Post-Closure
17 10 Gasoline
• Total BTEX 14,000 480 8
93 330 290
24 1 1
49 8 Weathered gas
• Benzene 70 <0.4 70
1,400 500
79 35 160
SPHC <2
SPHC < 1
• Total BTEX 5,470 3,260 3,651
1,269 13,300 3,380
19 10 Gasoline
• Total BTEX 480 BDL BDL
Comments
Nutrients added to fine sands,
returned to tank pit
Source area monitoring well
Source area monitoring well
Crossgradient monitoring well
Medium sand; 5 wells installed
after 11 months to address
upgradient source (which
continues)
Source area monitoring well
Source area monitoring well
Downgradient well (=* 75 ft from
sparge system)
Crossgradient monitoring well;
near off-site source
Upgradient monitoring well; near
off-site source
Source area monitoring well
Downgradient well (= 75 ft from
sparge system)
Some excavation of source area
123 ng/L 5 months after
shutdown; downgradient well
I
Q.
O
i; ,t:- H -;j*
-------
Site #10 (FL) 3
Service station
6 sparge wells
6 scfm/well
= 45 ft spacing
Continuous flow
Initiated 1/95
Site#ll(NH) a
Fueling station
7 sparge wells
5 scfm/well
= 20 ft spacing
Pulsed (12 hr cycle)
O>. Initiated 7/93
fo
Oi
Site #12 (FL) 2
Gas/diesel USTs
1 sparge well
10 scfm/well
Pulsed (1-2 hr cycle)
Initiated 3/95
1 Weathered gas
• Benzene 2,175
183
481
• Total BTEX 13,068
788
1 Gasoline
« Benzene 510 5.0
11A 1/\
1 1U 117
420 <2.5
28 3.0
• Total BTEX 37,110 4,355
36,410 13,910
9,948 1,524
0.75 GasGiific/diese!
• Total BTEX 5,322 110
60 ft depth to water; sandy; no
product reached water table, so
plume is purely dissolved phase
<0.5
-------
Implementation and Operation of Air Sparging
I,,1 '••i f:';!- ;; . '- . "-' '^. ;i
There was a 70% rebound rate in systems treating the source area as com-
pared to only a 28% rebound rate in systems treating a dissolved groundwa-
ter plume. The dissoived-phase plumes that did rebound were generally
associated. wi^h sitesTjiavingI'a'large'or'highly-coritarninated source area that
was not fully removed prior to sparging. When the released petroleum did
6.26
-------
Chapter 6
not contact the groundwater to create a smear zone of adsorbed product,
remediation by sparging was more effective even with less aggressive
sparging systems. For example, in Site 9 (Table 6.2), where the source area
had been excavated, no rebound was observed even though the flow^ rate per
sparging well was only 2.5 scfm. In Site 10 (Table 6.2), where the released
product did not extend downward through the entire 18 m (60 ft) deep va-
dose zone, remediation was rapid despite a 1.4 m (45 ft) well spacing.
Figure 6.2
TDR Response to Pulsed Injection
(3 m radius @ injection depth)
35.2
03:14PM
03:21 PM
03 57 PM
Time
Time series moisture content data collected during pulsed sparging shows a distinct response to each air injection pulse,
increasing the displacement of groundwater and improving mixing.
Reprinted from In Situ Aeration: Air Sparging, Bioventlng, and Related Remediation Processes, WS. Clayton, R.A. Brown,
and D.H. Bass, "Air sparging and bioremediation: the case for in situ mixing", 1995 with permission of Battelle Press.
6.4.7 Health and Safety Monitoring
An industrial hygienist should be responsible for reviewing compliance
with health and safety requirements during operation of the air sparging
system. The site should have a health and safety plan prepared in
6.27
-------
Implementation and Operation of Air Sparging
accordance with OSHA and all other applicable standards. At a minimum,
the plan should address the following.
• Contaminant characterization
• Hazard/risk analysis
• Staff organization and qualifications
• Training
• Personal protective equipment
• Medical surveillance
• Exposure monitoring
i : 'i
• Heat/cold stress monitoring
1 I
• Standard operating safety procedures
• Site control measures
:: :' i i "
• Personal hygiene and decontamination
. ; i •,.
• Emergency equipment and first aid requirements
• Emergency response and contingency procedures
• Accident prevention
• Logs
•'," ',•']•'. , .
• Reports
• Record keeping
6.5 Operational Modifications to
Enhance Performance
• i • i
Section 5.4 presents the modifications that can be made during the design
stage to enhance the mass extraction rate of an air sparging system. If an
operating system does not produce acceptable contaminant concentrations at
6.28
-------
Chapter 6
compliance monitoring points, the following operational controls can be
adjusted as necessary:
• air sparging wells-on/off, air injection pressure, air flow, pulsing,
balancing with other wells in network; :
• air compressor-pressure setting, manifold pressure setting, main
air flow control valve to manifold;
• manifold-total air flow to well network, operating pressure, well
selection (partial on, on/off), backflushing of air lines to remove
condensation; and
• monitoring points-monitor impact of any change made in operat-
ing scheme and record influence and result in log book. ;
By adjusting these parameters, the operator can create conditions that
favor an even distribution of air to the impacted zone. The ultimate criteria
for assessing the effectiveness of any system modifications are typically
attainment of acceptable contaminant concentrations at the compliance
monitoring points and achieving an acceptable mass removal rate. Further
operational changes and adjustments are discussed in Section 6.3.1.
6.6 Quality Control
The general quality control issues that pertain to operation of an air
sparging system are very similar to those described for vapor extraction
systems in Section 4.6 (see Figures 6.3 and 6.4).
6.29
-------
Implementation and Operation of Air Sparging
Figure 6.3
Rebound as a Function of Flow and Well Spacing
40
30
I
20
E
10
NR,
•PH
10
20
30 40 50
Well Spacing (ft)
NR No Rebound
R Rebound
PH Petroleum Hydrocarbon
Cl Chlorinated
Permission to reproduce granted by David H. Bass (1998)
Figure 6.4
Rebound as a Function of Flow and Number of Wells
E
40
30
20
10
-NRpH
NR,
pH
RPH NRPH
-NRPH NRC1 NRa j.
r, u j
Rebound
12 16 20
Number of Wells
24
28
32
NR No Rebound
R Rebound
PH Petroleum Hydrocarbon
Cl Chlorinated
Permission to reproduce granted by David H. Bass (1998)
6.30
-------
Chapter 7
CASE HISTORIES
Case 7 — Petroleum Distribution Facility in
Sparks, Nevada
General Site Information
Name: Petroleum Distribution Facility
Location: Sparks, Nevada
Remediation Contractor: Camp, Dresser & McKee, Inc., Reno/Denver
Regulatory Factors
Authority
Nevada Division of Environmental Protection, US EPA
Requirements/Cleanup Goals
Control contaminant sources; recover free product; no further degradation
of groundwater '
Results
After one year of operation, the remediation system had removed approxi-
mately 1.27 million kg (2.8 million Ib) of contaminants as follows: ;
• 256,000 kg (564,000 Ib) removed via vapor extraction;
• 1,013,000 kg (2,233,000 Ib) removed via aerobic biodegradation
enhanced by vapor extraction;
7.1 !
-------
Case Histories
• 480 kg (1,055 Ib) removed via groundwater extraction/treatment;
and
• 545 (1,200 Ib) removed as free product.
Remediation is ongoing.
Operation
Type
" ! I ',
Full-scale remediation
1 • ' " I ,!iir
Period
November 1995 - ongoing
Waste Characteristics
1i i »,,, i ii'ii'i'
Source
Leaking aboveground and underground storage tanks and surface spillage
Contaminants
Gasoline, diesel fuel, aviation fuel, and lesser amounts of chlorinated
ethenes and ethanes
Type of Media Treated
Sandy soils and groundwater
Quantity of Media Treated
Approximately 0.91 million m3 (1 million yd3) of soil over 127 acres.
Approximately 757 million L (200 million gal) of groundwater.
7.2
-------
Chapter 7
Technology
Description
The remedial system is comprised of:
• 30 combination groundwater and vapor extraction wells;
• two thermal oxidation units with a combined capacity of 9,000
fWmin;
• fluidized bed biological reactors;
• oil-water separator; and
• mobile free product recovery trailer.
Cost Data
Remediation is still in progress.
7.3
-------
Case Histories
Case 2 — NYSDEC, Bioventing of
Chlorinated VOCs in Sweden, NY
General Site Information
Name: Sweden-3 Chapman Site
Location: Sweden, New York
Owner: Confidential
Owner Contact:
Nick Kolak, Ph.D.
New York State Department of Environmental Conservation
Albany, NY
(518). 475-3372
Remediation Contractor:
Peter J. Cagnetta, CPSSc
R. E. Wright Environmental, Inc.
3240 Schoolhouse Road
Middletown, PA 17057
Project Description
As part of the US EPA Superfund Innovative Technology Evaluation pro-
gram, R. E. Wright constructed a bioventing system to decontaminate glacial
till soil containing trichloroethene (TCE) and 1,2-dichloroethene (DCE).
The system consisted of 30 soil gas extraction wells manifolded to the
vacuum port of a 5-horsepower positive displacement blower and 30 gas-
phase amendment injection wells manifolded to the discharge port of the,
blower unit. A timer controlled the periodic extraction of soil gas from the
soil. When operating in the injection mode, anhydrous ammonia and meth-
ane were injected into the injection air stream and into the subsurface.
Within five months of treatment, the concentrations of TCE and 1,2-DCE
have declined significantly below the cleanup goals. Mass balance calcula-
tions indicated that 80% of the initial mass of TCE had been biodegraded,
and 12% had been vapor extracted. 914.4 m3 (1,000 yd3)of soil was treated
using this process. The use of this technology for site-wide remediation of
9,144 m3 (10,000 yd3) of soil is pending.
7.4
-------
Chapter 7
Regulatory Factors
Authority
New York State Department of Environmental Conservation (NYSDEC)
Requirements/Cleanup Goals
TCE 1,500 micrograms per kilogram Qog/kg)
1,2-DCE 600ng/kg
Results
• NYSDEC soil cleanup goals achieved for TCE arid 1,2-DCE
within five months. .
• 92% reduction in TCE mass (80% biodegraded and 12% vapor
extracted).
• Mean TCE soil concentration declined from 4,900 JJg/kg to 56
JJg/kg. ;
Operation
Type
Large-scale demonstration pilot
Period
July 1994 to December 1994
Waste Characteristics
Source
Improper disposal of drums containing industrial solvents
Contaminants
TCE 4,960 milligrams per kilogram (mg/kg)
1,2-DCE 610 mg/kg
7.5
-------
Case Histories
Type of Media Treated
USDA texture — loam, glacial till
Quantity of Media Treated
914.4m3 (1,000 yd3)
Technology
Description
In situ bioventing consisting of soil gas extraction wells and gas-phase
amendment injection wells. Methane, oxygen, and anhydrous ammonia
injected to stimulate indigenous microorganisms. Blower unit operated in
timed extraction/injection cycle.
Significance
Remediated chlorinated solvent-impacted soil using indigenous microor-
ganisms and conventional vapor extraction equipment and wells. Rigorous
US EPA quality assurance/quality control oversight independently confirmed
successful results.
Cost Data
Total project cost of $136,900 included design, construction, operation,
and closure. A comprehensive sampling and analysis program was imple-
mented throughout the project to quantify the decreases of TCE and 1,2-
DCE in soil and identify the primary removal mechanism (bioremediation).
7.6
-------
Chapter 7
Case 3 — PECO Energy Company,
Bioventing of Diesel-Range Hydrocarbons
and 111-TCA in Philadelphia,
Pennsylvania
General Site Information
Name: PECO Energy Company — Oregon Maintenance Shop
Location: Philadelphia, Pennsylvania
Owner: PECO Energy Company
Owner Contact:
Mr. Fred Gloeckler, P.E.
PECO Energy Company
Philadelphia, PA
(215)841-4660
Remediation Contractor:
Gregory J. Burgdorf, P.O.
R. E. Wright Environmental, Inc,
3240 Schoolhouse Road
Middletown, PA 17057
Project Description
Approximately 7,711 tonne (8,500 ton) of in-place soil were impacted by
predominantly diesel-range hydrocarbons and a smaller quantity of 1,1,1-
trichloroethane (TCA). The impacted soil was located within the facility
storage area and was caused by accidental releases from aboveground stor-
age vessels. After pilot testing and system design, remediation activities
were initiated in June 1994. 1,1,1-TCA and the volatile hydrocarbons were
removed from the ground via vapor extraction. At system start-up and peri-
odically throughout treatment, the subsurface was amended with nutrients
essential for bacterial growth and a surfactant to enhance the biodegradation
of the less volatile hydrocarbons. Formal state-approved closure was
granted in October 1996.
7.7
-------
Case Histories
Regulatory Factors
Authority
Pennsylvania Department of Environmental Protection
Requirements/Cleanup Goals
Total Petroleum Hydrocarbons (TPH) 1,000 mg/kg
1,1,1-TCA 1 mg/kg
! ,
Results
• Treatment of Area 1 (5,897 tonne [6,500 ton]) completed in
6 months of operation.
• Treatment of Area 2 (1,814 tonne [2,000 ton]) completed in 12
months of operation.
• Treatment of all soil completed for approximately $30/ton.
Operation
Type
Full-scale site-wide system
Period
June 1995 to May 1996
Waste Characteristics
j ,i !
Source
Accidental releases from aboveground storage vessels
Contaminants
TPH 25,000 mg/kg
' ! !
1,1,1-TCA 1,500 mg/kg
7.8
-------
Chapter 7
Type of Media Treated
USDA texture — sandy loam
Quantity of Media Treated
7,711 tonne (8,500 ton) i
Technology
Description i
In situ bioventing consisting of nine vapor extraction wells manifolded to
a 5 hp 500 ftVmin regenerative blower and three vapor extraction wells
manifolded to a 3 hp 200 ftVmin regenerative blower. Each skid-mounted
blower unit was equipped with a moisture knockout tank and vapor-phase
granular-activated carbon unit.
Significance
Remediated soil in-place so that daily activities at the site could continue.
Significant cost savings were realized by in situ treatment versus excavation
and off-site treatment/disposal.
Cost Data
The total bioventing project cost of $275,0(30 included pilot testing, de-
sign, construction, operation, and closure.
7.9
-------
Case Histories
Case 4 — Two Air Sparging Case Studies
This section presents observations by the monograph Task Group from
two sparging case studies. While similar results have been observed at other
sparging sites, these two were selected as representative.
Case Study 4A
In Case Study 4A, a release of perchlorethylene (PCE) through floor
drains underneath building resulted in vadose zone contamination and devel-
opment of a dissolved-phase plume.
During the site investigation, the soil was logged by a geologist on 0.6 m
(2 ft) intervals and classified as a clean, fine- to medium-grained sand with
depth to water at about 10.6 m (35 ft) below ground surface. A sieve analy-
sis on selected samples confirmed the field description. Based on pump
tests, the soil hydraulic conductivity was 1 • 10'2 cm/sec. During the site
investigation, there was no indication of field-scale heterogeneity.
Vapor extraction was implemented for several months to remove PCE
from the vadose zone soil underneath the building and to prevent further
contaminant loading to the groundwater. A 30-day groundwater sparging
pilot test was then conducted.
One groundwater sparging well was installed through the building floor
and screened from 7.6 to 8.2 m (25 to 27 ft) below the water table. Two
monitoring piezometer nests were installed at horizontal distances of 3 to 6
m (10 to 20 ft) from the sparging well. Within each nest, one piezometer
was screened from 2.4 to 3 m (8 to 10 ft) below the water table, and the other
from 5.5 to 6 m (18 to 20 ft) below the water table. Figure 7.1 shows the
system layout.
For most of the sparging pilot test, the system was operated for 4 hours
per day at a 10 scfm flow rate. Groundwater samples collected from each
piezometer about every 5 days were analyzed for PCE. The piezometers
were also monitored for pressure buildup or bubbling, either of which might
have suggested that injected air was short-circuiting through the piezom-
eters. Pressure buildup or bubbling was not detected. The changes in dis-
solved-phase PCE concentrations during and after the pilot test are shown in
Figure 5.1.
7.10
-------
Chapter 7
In Case Study 4B, a large release of petroleum solvents resulted in both
vadose zone and groundwater contamination. The ground water was about
4.6 m (15 ft) below ground surface. After 555 L (150 gal) of floating NAPL
were recovered, contamination in the source area still included NAPL at
residual saturation 1 m (3.28 ft) above and below the groundwater table. An
analysis of the NAPL showed it occupied about 20% of the saturated zone
pore space in the affected area and consisted of mostly nonpriority pollutants
such as hexane and mineral spirits. PCE, trichlorethylene (TCE), and other
chlorinated solvents made up 1 to 2% of the NAPL. The NAPL was a con-
tinual source of VOC contamination in the groundwater.
The soil at the site was logged at numerous borings on 0.6 m (2 ft) inter-
vals by a geologist and classified as a uniform, clean, fine- to medium-
grained sand. The field analysis was confirmed by sieve analysis of selected
samples. Based on slug test results, a 1 • 10T* cm/sec hydraulic conductivity
was estimated.
A groundwater extraction and vapor extraction system was installed at the
site. After 700 operating days, average VOC concentrations in the soil were
less than 14 ug/kg (based on more than 100 soil samples collected vertically
and horizontally throughout the target zone). After 4 years of operation, the
groundwater extraction system had reached an asymptote of about 1,500 jug/
L of total dissolved-phase VOCs in the groundwater discharge. Continual
release of VOCs from the residual NAPL to the groundwater prevented fur-
ther reduction in dissolved-phase concentrations.
A sparging system was then employed to directly contact the residual
NAPL with a gas to better volatize the VOCs. Three sparging wells were
installed in the source area around an operating groundwater extraction well.
The sparging system was continuously operated for 5 months, during which
time groundwater samples from the extraction well were analyzed monthly.
Samples from the well were also analyzed bimonthly for several months
before and after the sparging pilot test. The sparging system layout is shown
in Figure 7.1, and the changes in the dissolved-phase VOC concentrations in
water from the extraction well are shown in Figure 5.2.
7.11
-------
Case Histories
Figure 7.1
Case Studies — Sparging System Layouts
CASE STUDY 4A
Plan View
Monitoring
piezometers
Cross Section
O1
10
20
30 „
•••*•
40
SO
66
1 '1
s.
\
"
r
q
11
\
""]
r
1
\
y*t
?2
1 \
I-1S
,-ID
[
r
*-*
1
\
r
f
\
K
Pi
1
I
Z-2S
!i-2D
,1
Rtproducad courtesy of CH2M HHI
7.12
-------
: Chapter/
Figure 7.1 (cont.)
Case Studies — Sparging System Layouts
Plan View
) Sparge Well
Extraction Well
CASE STUDY 4B
Sparge Well
Sparge Well
Cross Section
0 -
10
20
30
40
50
66
SP-1 U
SP-2 SP-3
Residual NAPL
EW-8:
Reproduced courtesy of CH2M Hill
7.13
-------
Case Histories
Discussion
Monitoring Well Network Design and Reliability
Sparging-induced changes in dissolved-phase contaminants can be moni-
tored with monitoring wells screened over 3 to 6 m (10 to 20 ft) of the aqui-
fer, discrete piezometers screened over 0.3 to 0.6 m (1 to 2 ft) of the aquifer,
and/or multilevel monitoring points installed with a geoprobe and each
screened over a few inches.
The data from Case Study 4A (presented in Figure 5.1) suggest that the
interpretation of sparging effectiveness may vary significantly depending on
the type of monitoring system employed. The data from this site suggest
removal efficiencies of 85% in the lower 4.6 to 7.6 m (15 to 25 ft) sparging
zone and 15% in the upper 4.6 m (15 ft) sparging zone after 30 days of
sparging.
It is believed that the building previously discussed (which prevents infiltra-
tion through the soil) and the degree of treatment achieved with the vapor ex-
traction system immediately above the sparging system prevented continued
contamination of the shallow groundwater. The lower treatment efficiency in
the shallow groundwater is not attributed to new contamination in the shallow
zone, but appears to be due to anisotrbphy, and possibly pore-scale heterogene-
ity, which altered air flow pathways through this zone. Field-scale soil hetero-
geneity was not detected during continuous logging of the soil. Analysis based
solely on monitoring wells screened over the upper 4.6 m (15 ft) of the aquifer
would have resulted in an incomplete and inaccurate assessment of the sparging
effectiveness at the site. Likewise, more vertically and horizontally spaced
monitoring points might have resulted in a still more complex and varied pic-
ture of treatment effectiveness. In summary, vertical variations in treatment
effectiveness were observed even through there were no observable changes in
soil type or grain-size distribution.
Some data from monitoring wells and piezometers are suspect because of
the potential for the wells or piezometers to become preferred-flow pathways
for the sparged air (Johnson et al. 1993). The authors have observed this at
some sites when injected air bubbles up through a monitoring point. In such
cases, fairly rapid decline of dissolved-phase VOC concentrations would be
expected since the VOCs in the wells would be quickly stripped. In these
cases, a pressure of 1 to several centimeters of water can also be measured in
the wells. The gradual decline of dissolved-phase VOC concentration
7.14
-------
Chapter 7
presented in Figure 5.1, and the lack of detectable pressure in the wellhead,
suggest that air flow is not short-circuiting through the piezometers at this
site. Thus, these wells probably serve as good indicators of what is happen-
ing in the aquifer in their immediate vicinity.
Sparging in Residual NAPL vs. Dissolved-Phased Plumes
A main difference between Case Study 4A and Case Study 4B is that, at
the former site, sparging was implemented in a dissolved-phase plume, while
at the latter, sparging was implemented in an airea of nonmobile, residual
NAPL. Theoretical considerations and the post-sparging monitoring results
at the two sites suggest that there may be significant differences in treatment
potential and required duration for residual NAPL sites compared to those
for dissolved-phase plume sites.
Within the dissolved-phase plume at Site 4A, a 50% overall reduction of
dissolved-phase PCE was observed after 30 days of sparging. In the area of
residual NAPL at Site 4B, there was a 50% reduction after 60 days of
sparging and a 90% reduction in dissolved-phase VOCs after 150 days (as
measured in samples collected from an operating groundwater extraction
well within the sparging zone).
In the Site 4A dissolved-phase plume, post-sparging monitoring data
indicated that dissolved-phase PCE concentrations were similar to those at
the end of the sparging period (Figure 5.1). In the area of residual NAPL at
Site 4B, post-sparging monitoring data indicated that dissolved-phase VOC
concentrations increased to nearly the same level as before the test (Figure
5.2). After 5 months of sparging, the NAPL still provided further VOC load-
ings to the dissolved-phase plume.
The data suggest that sparging at residual NAPL sites may exhibit limita-
tions similar to those observed with the groundwater extraction at residual
NAPL sites (e.g., preferential fluid flow channels and contaminants needing
to diffuse to those preferential flow channels). When air directly contacts a
NAPL, the partitioning of VOCs into the air is relatively fast (as in the soil
immediately adjacent to a sparging well). The rate-limiting step is likely
VOC diffusion within the NAPL. However, with sparging, some or much of
the NAPL more than 1.5 to 2 m (5 to 7 ft) from the sparging well may not
directly contact the air. Thus, the VOCs still must diffuse into and through
the water to an air channel. While a sparging system may be effective at
treating the NAPL in the area where much of the water-filled porosity is
7.15
-------
Case Histories
converted to air-filled porosity, in areas farther from the sparging well where
air channel density is lower, it will take much longer to treat residual NAPL.
The above discussion focuses primarily on contaminant volatilization.
With time, it may be possible to biodegrade the residual NAPL as a result of
oxygen transfer from the vapor phase into the dissolved phase. However,
some of the same diffusion limitations for VOC mass transfer apply for oxy-
gen mass transfer. There have been no conclusive estimates of oxygen trans-
fer efficiency in sparging systems, but estimates have ranged from 0.05 to
0.5% (Boersma et al. 1993). In a conceptual cylinder 9 m (30 ft) in diam-
eter, 4.6 m (15 ft) in length, with an average total petroleum hydrocarbon
contamination of 2,000 mg/kg, and a sparging flow rate of 20 scfm, it would
take 5 to 50 years to provide the stoichiometric requirements of oxygen for
hydrocarbon biodegradation.
Recommendations
Based on these two case studies, the following recommendations are
made for implementing sparging systems.
• First, given the typical anisotropy of even apparently uniform
soil, vertically discrete groundwater monitoring points should be
used with data from traditional monitoring wells to assess the
performance of groundwater sparging systems. Anisotropy and
pore-scale heterogeneities will cause vertical variation in treat-
ment effectiveness.
• Second, spatial variations in treatment effectiveness around a
groundwater sparging well suggest that the term "radius of influ-
ence" is misleading. A term such as "zone of sparging influence"
is more accurate, and its use is recommended.
• Third, at most NAPL sites, a sparging system will probably have
to operate for several years to volatilize and/or biodegrade the
NAPL that is beyond the zone where 20-40% air saturation is
achieved.
7.16
-------
Appendix A
FIELD-SCALE PNEUMATIC
PERMEABILITY MODELS
The purpose of this Appendix is to provide the reader with a comprehen-
sive summary of existing analytical solutions for field scale determination of
pneumatic permeability. This will assist in selection of an appropriate model
for site-specific testing. The solutions are summarized in consistent nomen-
clature and variables to avoid confusion when comparing various solutions.
Field scale gas permeability testing originated in the petroleum industry
for use in gas reservoir evaluation (Muskat and Botset 1931). However, over
the past thirty or forty years soil scientists have conducted field scale air
permeability tests to evaluate gas exchange betv/een soils and the atmo-
sphere, soil structure, and the movement of subsurface water as affected by
simultaneous air movement. The advent of soil venting to remove or en-
hance biodegradation of hazardous organic compounds has hastened the
development of analytical solutions for field scale gas permeability testing in
the field of subsurface hydrology field over the past 10 years. Most of these
solutions have been based on methods used in groundwater well hydraulics.
Air or pneumatic permeability tests typically involve the measurement of
air flow in vapor extraction or air injection wells with concurrent measure-
ment of pressure differential in surrounding vapor probes. Pneumatic per-
meability is then calculated using analytical solutions to selected governing
partial differential equations. One approach to determine air permeability is
to simply modify existing analytical groundwater solutions (Johnson, :
Kemblowski, and Colthart 1988, Johnson et al. 1990; Massman and Madden
1994; Beckett and Huntley 1994). Another example is the use of the ground-
water hydraulics programs to analyze transient and steady-state pump test
data. This approach is useful when there is a low pressure differential be-
tween the pumped well and the surrounding formation and an analytical gas
permeability solution is not yet available for the Iboundary conditions incor-
porated in the groundwater solution. The error involved in this method
A.1
-------
• .T: '.'ii1 • • '• "•' " : v 'f:V,->t r"1' i1 "t* I1"-: ',•:••'
Field-Scale Pneumatic Permeability Models
should be small as long as pressure differentia! remains small. Falta (1996)
points out that a drawback of this approach is that for some gas permeability
problems there are no analogous groundwater solutions available. An ex-
ample, which is quite common, is a gas permeability test performed in a
formation open to the atmosphere. In this case, the atmosphere acts as a
constant head boundary. Falta (1996) also states that there are basic differ-
ences in the nature of the test data collected during gas pump tests compared
to groundwater tests. Groundwater test data often consist of transient draw-
down data from a single observation well while gas pump test data often
consist of steady-state pressure data from several observation locations.
Measuring transient pressure in a gas pump test can be difficult in high per-
meability sands or gravels due to the rapidity (seconds) of establishment of
steady-state gas flow conditions in media of high permeability. Considering
that analytical solutions and software packages now exist which incorporate
compressibility, partial penetration, constant pressure boundary conditions
(atmospheric pressure) and flux boundary conditions (leakage through a
confining layer), the use of groundwater flow equations to estimate pneu-
matic permeability is often not justified. AIR2D, a public domain model
developed by Joss and Baehr (1995a), provides solutions for steady-state
conditions and is available through the USGS. GASSOLVE developed by
Falta (1996) provides solutions for transient conditions and is available from
the developer upon request. When practical, transient tests are preferred
over steady-state tests because numerous measurements can be collected at
each vapor probe within the time frame of transient testing as opposed to just
one measurement at each probe during steady-state testing. For media of
high permeability such as sands, steady-state occurs under many circum-
stances (e.g., depth to well less than 15 ft) within seconds. For low perme-
ability soils, however, such as clays and glacial till, steady-state may not
occur for minutes or hours.
Another approach to pneumatic permeability determination is the use of
numerical models. Numerical models, especially those specifically for gas
flow such as AIR3D, which is a public domain modification of MODFLOW
(finite-difference) developed by Joss and Baehr (1995b) for the USGS, are
undoubtedly the most flexible methods of analyzing the gas punip test re-
sults. Initial and boundary conditions can be incorporated for problems
which can not be solved analytically. Analytical methods are not suitable for
analyzing numerous soil layers of various permeabilities, spatial variability
within discrete layers, and site-specific anomalies (underground trenches for
A.2
-------
Appendix A
piping, etc.). Edwards and Jones (1994) provide an example of the use of
finite-element numerical modeling to determine pneumatic permeability.
Numerical models, however, should be used with caution. They are usually
more computationally intensive than analytical solutions and are prone to
truncation error in the hands of inexperienced users. However, the greatest
limitation in using numerical models for gas pump test analysis is that ad-
equate field data are rarely available to justify their use. The problem is
inherently ill-posed. Falta (1996) states that unless a large amount of field
data are available, the analysis of pump test data by fitting a numerical
model is more likely to suffer from problems of nonuniqueness than the
analysis of the data by fitting an analytical model. The problem of '•
nonuniqueness means that a large number of data variations may produce a
response similar to that observed in the field. This is due to the large num-
ber of unknown parameters (i.e., the permeability of each gridblock).
It is important for the reader to be aware of the numerous assumptions
necessary to enable formulation of analytical solutions. Often, practitioners
use gas permeability solutions without appreciation of these assumptions
and, hence, do not realize the limitations and errors inherent in testing.
Sometimes pneumatic permeability tests can be conducted to purposely
minimize these errors. Identification and discussion of assumptions will be
presented in the context of derivation of the governing partial differential
equations for single-phase gas flow. The derivation starts with a discussion
of basic fluid mechanics principles. This background is necessary to under-
stand gas flow in porous media.
Quantitative evaluation of gas flow in porous media starts with develop-
ment of a mass balance or continuity equation. The total mass m of a gas in
a closed soil region is given by:
m = JJJep(x,y,z,t)dV (A.I)
where: p = density of gas (M/L3)
9 = volumetric gas content (L3/L3)
The rate at which mass increases is given by:
A.3
-------
f '
Field-Scale Pneumatic Permeability Models
If change in mass is due only to flow in and out of a closed soil region,
then an alternative expression for (A.2) is:
^f = -JJ(P2'a)d . (A.3)
where: a = the darcy discharge vector (L/t),
n = normal vector.
By the divergence theorem, (A.3) is the same as:
-JJ/V.(Pq)dV (A.4)
Equating (A.2) and (A.4) yields:
f f f o ^P vy / \ (A 5)
Thus, the continuity equation for single phase gas flow is:
1 • ' ' ! I • i •
3(p6) rr f \ r\ f A f\\
4~ V * vPQ/ ~~ ^ \-^v*u/
3t -
The continuity equation can be used with Darcy's Law, Bernoulli's Equa-
tion, and the Ideal Gas Law to formulate an equation for single-phase gas
flow in porous media. If Darcy's Law is assumed valid for gas flow in a
homogeneous, anisotropic media, then:
1 O Q / JL- *7\
q = -^kVH . (A./)
where: g = acceleration due to gravity [L/t2]
k = gas permeability tensor [L2]
H = total head [L]
(0, = dynamic viscosity of gas [M/Lt].
Darcy's law is widely accepted as a valid approximation to the conserva-
tion of momentum principle for airflow in porous media at low Reynolds
Number (Re) as defined by: . ,
A.4
-------
Appendix A
^e (A.8)
where: d = representative pore-space diameter [L]
qm = specific mass flux [M/L2-tj.
Yu (1985) conducted column experiments to test the validity of Darcy's
law for air flow through various-sized sands and showed that Darcy's Law
was valid for Re <6.
One important assumption that is made in the use of Darcy's Law to de-
scribe airflow is that gas slippage or the Klinkenberg effect (Klinkehberg
1941) is negligible. The Klinkenberg effect is an enhancement of air phase
permeability through slippage of air molecules along the boundaries of air-
filled pores. Air flow along a pore wall is not zero as is assumed for laminar
liquid flow. This occurs when the mean free path (distance between Consecu-
tive collisions or between the last collision and the pore wall) of air mol-
ecules approaches the dimensions of the pores (Dullien 1992). Thus, it oc-
curs in small pores under low pressure or high vacuum. Therefore, the
Klinkenberg effect is important when a vacuum is applied to soils having
small, desaturated pores. Klinkenberg (1941) expressed this effect by:
where: k^ = a soil's "intrinsic" permeability [L2]
b = a parameter of the porous medium [M/Lt2],
Pm = mean pressure [M/Lt2].
In this context, intrinsic permeability refers to the soil's permeability
without consideration of the Klinkenberg effect. It includes consideration of
relative permeability to air in the presence of soil-water. Thus, it is not an
independent soil property as usually expressed in groundwater literature.
The intrinsic permeability is obtained by plotting (1/PJ versus k and ex-
trapolating data to infinite pressure. The parameter b can be obtained by the
slope of this straight line. Baehr and Hult (1991) demonstrate through calcu-
lations how omission of the Klinkenberg effect can result in errors >10% for
soils having intrinsic permeabilities of less than 10'9 cm2. Massmanri (1989)
related the relative importance of slip flow to viscous flow for low pressure
A.5
-------
Field-Scale Pneumatic Permeability Models
systems. He calculated that materials with pore radii greater that 0.001 mm
would exhibit minimal effects of slip flow relative to Darcy flow. Silt and
clay materials often demonstrate pore radii of this magnitude. Incorporation
of Equation A.9 introduces nonlinear terms that preclude the development of
analytical solutions. Thus, it is typically ignored during pneumatic perme-
ability testing.
Darcy's Law requires knowledge of the total head gradient. Bernoulli's
Equation for a compressible fluid can be used to express the components of
energy of head
.
2g
where: z = a vertical distance above an arbitrary datum [L]
v = velocity [L/T]
P = air pressure [M/LT2]
P = a reference air pressure [M/LT2].
If both the velocity and elevation contributions to total head are assumed
negligible, total head can now be expressed as:
" I" •• • ..... ! .......... -. ........
where: R = universal gas constant [M-L2/T2-mol-T]
T = temperature [K]
co = molecular weight of air [M/rnole].
..... I :| 'i1 , , , i!,,, "' ij • ', •
The assumption of a negligible component of velocity head may not be
accurate near an extraction or injection well. The assumption of negligible
elevation head may not be accurate for chlorinated contaminant laden air
present at many hazardous waste sites under low gradient conditions. In
Bernoulli's Equation, head is expressed as energy per unit weight. Terms on
the right hand side of the equation represent the contribution of elevation,
velocity, and pressure head respectively to total head. If it is assumed that
the Ideal Gas Law is valid for gas flow under pressures typical of pneumatic
permeability determination, gas density can be related to air pressure, tem-
perature, and molecular weight by:
A.6
-------
Appendix A
P =
0)P
RT
(A. 12)
Darcy's law given in terms of its gas permeability tensor is:
k k k
*-xx *-xy ^x
If k V
NX *-yy ^-y
k k k
*- ^ *-
(A.13)
where: k „ =
XY
yz
- k
~ Kz
= k
zy
In analytical gas permeability testing, it is assumed that site-specific coor-
dinates are aligned with the principal axes of gas permeability. However, it
must realized that this is done for mathematical convenience, specifically to
allow development of analytical solutions, and that the actual principal direc-
tions of gas permeability may be quite different than that used for the model.
This would become readily apparent if one injected a gas tracer and noted
movement in a direction inconsistent with the head gradient. Analytical
expressions for gas permeability are typically expressed in radial or cylindri-
cal coordinates. If symmetry around a well is assumed, then
3r'
'(A. 14)
If alignment along the principal axes is assumed, then Darcy's Law for
gas flow can be expressed as
OT-3H/3r'
0 k7J-3H/3Z
(A.15)
Like alignment with the principal directions of permeability, symmetry is
assumed for mathematical convenience. However, observation of asymmet-
ric pressure or head distribution in the field is common especially in highly
heterogeneous media such as glacial till.
A.7
-------
Field-Scale Pneumatic Permeability Models
Baehr and Hult (1991) substituted Equations A.7, A.ll, A.12, and A.15
into A.6 and let P2 = <|> to yield:
(A.16)
In this derivation, they assumed that the molecular weight of air is con-
stant and that:
S=0 M-o £-0
3t 3t 3r
which, in words, means a steady temperature distribution, steady-state air-
water distribution, and no variation in temperature with radial distance.
Baehr and Hult (1991) state that natural areal temperature variations can be
neglected over the scale of a pneumatic test. Also, temperature variations
due to energy transport associated with induced air movement will be negli-
gible as a result of the high thermal capacity of natural sediments and low-
energy content of air. The assumption of constant volumetric air content,
however, may impart a major error under aggressive operating conditions
(e.g. high vacuum or pressure) in soils having a high moisture content. This
is not a problem in well-drained soils such as coarse sands, but will likely be
important in less permeable, more water saturated soils such as silts, clays,
and glacial till. Redistribution of air and water during pneumatic testing can
change the original spatial distribution of gas permeability. Vapor extraction
will cause water to move towards the well while air injection will cause
water to move away from the well. Thus, air extraction and air injection
pneumatic tests may provide different estimates of pneumatic permeability.
Another indicator of fluid redistribution during pneumatic testing is a no-
table change in air pressure and mass flow rate at the wellhead during test-
ing. For instance, during sparging, where water is aggressively displaced
A.8
-------
Appendix A
from the vicinity of the well, a significant increase in the mass flow rate of
air and decrease in applied air pressure is often observed. When conducting
pneumatic permeability tests in soils having a high moisture content, it is
recommended that in-situ moisture monitoring (e.g., neutron probe) be used
to determine whether moisture redistribution is occurring.
Derivation of analytical solutions requires! additional assumptions
3r 3z 9z 3z
which state that there is no spatial variation of radial and vertical permeabil-
ity and that temperature and viscosity do not vary with depth. This allows
expression of the air flow equation in a compact form:
V4> 3t (A. 17)
This equation, however, is nonlinear, thus some form of linearization of the
V equal to a constant. Baehr and
Hult (1991) and Falta (1996) explicitly let V$ = Patm. Falta (1996) states that
with this approximation, the gas is assumed to be compressible with a con-
stant compressibility factor of l/Patm. According to Massmann (1989), for a
pressure differential of less than 0.5 atmospheres, this linearization results in
an error within a few percent of exact solutions. A second approach is to
replace V<|> with a prescribed time-varying function which in some manner
reflects the rate of change of the initial pressure distribution (Drake 1997).
Drake (1997) attempted linearization through, the method of perturbation or
successive approximations where each step involves the solution of a linear
system. He concluded, however, that at least in his efforts, this approach had
not been useful. Johnson, Kemblowski, and Colthart let P2 = P » Paim and the
P term in the denominator of the left hand side of the equation equal to Patm.
With the exception of Johnson, Kemblowski, and Colthart's (1988) solution,
all analytical solutions given in this paper involved linearization by letting
V = Patm. With the use of appropriate boundary conditions, Equation A. 17
can then be used to develop analytical solutions for air flow in one-dimen-
sional, radial and cylindrical domains.
A.9
-------
Field-Scale Pneumatic Permeability Models
One-Dimensional, Transient Flow Testing
On a field-scale, one-dimensional, transient flow testing is useful in deter-
mining in situ vertical pneumatic permeability due to variation in barometric
pressure. The method is based upon the observation that when atmospheric
pressure changes at the land surface, air moves to or from the vadose zone to
maintain a pressure balance between air in the soil and the atmosphere. The
rate of air movement and the resultant rate of pressure change at depth are
affected by both the pneumatic permeability and air-filled porosity of materi-
als in the vadose zone (Weeks 1978). Movement of air to and from the va-
dose zone due to variation in barometric pressure was first analyzed by
Buckingham (1904). He presented an equation for the attenuation of the
amplitude and phase lag of a periodic atmospheric pressure wave at any
depth in a homogeneous layer bounded below by an impermeable boundary
(e.g., water table). Later (much later), Stallman (1967) and Stallman and
Weeks (1969) measured variation in barometric pressure and pressure varia-
tion at depth to determine in situ vertical pneumatic permeability. Their
method was based on the assumption that the unsaturated materials com-
prised a single homogeneous layer. Using the same assumptions, Rosza,
Shoeberger, and Baker (1975) used an analytical solution and the principle
of superposition to determine pneumatic permeability of material comprising
several nuclear chimneys (vertical sections of bedrock containing rubble
caused by subsurface nuclear explosions) at the Nevada Test Site. The
nuclear chimney rubble was assumed to consist of a homogeneous unit ex-
tending to infinity below land surface. Although the assumption that air
movement can occur to infinite depth did not accurately represent actual
boundary conditions, computed pneumatic permeabilities compared well
with those determined by numerical analysis of air injection data. Weeks
(1978) used the methods of Stallman (1967) and Stallman and Weeks (1969)
to estimate the pneumatic permeability of discrete layers using a numerical
one-dimensional program, AIRK. The pneumatic permeability of each layer
was determined through trial and error. Air compressibility was ignored,
assuming that it would result in insignificant error due to the relatively small
magnitude of barometric pressure variations.
A.10
-------
Appendix A
Weeks (1978) found it convenient to obtain pressure data during a normal
afternoon barometric decline which was equivalent to a pressure drop of 3 to
4 millbars in 4 to 5 hours. Data was collected at 15 minute intervals. Read-
ing continued until 6 or 7 p.m. when a diurnal barometric rise normally oc-
curs. "Chasing fronts" should be resisted as major atmospheric pressure
changes occur in a few minutes to an hour and are difficult predict. Weeks
(1978) found that pneumatic pressure differences occurring during the nor-
mal afternoon diurnal barometric change were large enough to be detected
and analyzed at sites where the unsaturated zone was more than 20 meters
thick and there was at least one layer with a permeability of no more than 2
to 3 darcies. At other sites, where the unsaturated zone was thinner and the
layers more permeable, pressure differences during diurnal change were too
small to be accurately measured. Also, short-term atmospheric pressure
changes tended to mask longer term trends.
Shan (1995) used a solution containing time-dependent boundary condi-
tions from Carslaw and Jaeger's (1959) classic text on "Conduction of Heat
in Solids" to develop a strategy for one-dimensional, transient, pneumatic
permeability testing. The governing equation is given as:
Two scenarios for testing are presented: (1) a domain consisting of. a re-
gion between the water table and the soil surface or at some depth in soil,
and (2) a domain between any two points within the soil. The latter scenario
provides a method to evaluate pneumatic permeability in discrete layers.
Both methods require a minimum of three measurement points; one on each
boundary and one between boundaries. For the case of a single layer soil
bounded below by the groundwater table, he sets the origin (z==0) at the wa-
ter table and time variation of pressure at some distance (L) above the water
table. Thus the initial and boundary conditions are:
(z,0) = f(z)
= 0
-------
Field-Scale Pneumatic Permeability Models
The solution is given as:
Iu=JoLf(z*)sin(anz*)dz
Iw = J0'exp(a2nat *)[f ,(t*)dt
(2n
kP
(t*)]dt *
(A. 19)
where:
Iu=JoLf(z*)cos(anz*)dz Iw
(2n + l)7t
2L
oc==
)f(t*)dt!
Pa is the mean pressure during testing, and z* and t* are integral variables.
These integral variables could have been expressed as any letter but are ex-
pressed here with the original variable and an asterisk to remind us that we
are solving for z and t. The initial and boundary conditions for the second
scenario are:
(z,0) f(z) (0,t)
, .. ,.
The solution is given as:
where:
(0,t) f2(t)
(z,t) = -JTexp(-afct)sin(a*z)[lu + ocanlw] (A.20)
i.. i .•!,•••
Iu = J f(z*)sin(anz*)dz
Iw = Jotexp(a2nat *)[f ,(t*)dt - (-I)"f2(t*)]dt *
_ (2n + l)?t _ kPa
a" ~ 2L "= 6u
A.12
-------
Appendix A
Integration of functions f (z) and f (t) achieved by the use of tabulated
data and linear interpolation. This approximation allows piecewise integra-
tion of Iu and Iw. Results from 2 test sites are given (27.5 m and 26.5 m).
Comparison of simulated versus actual data is generally excellent.
One-Dimensional Steady-State Flow
One-dimensional, steady-state flow is typically used in laboratory column
studies and is described by:
dz2 (A.21)
The boundary conditions used to solve this equation are:
-2QraRT|i
= 0) = (!>0or(|>atra
Z=L coAkz
The solution to the one-dimensional, steady-state flow equations with these
boundary conditions is easily obtained through integration:
•TX' TU ^ Akzo> ; (A.22)
where A is the cross-sectional area of the column and Qm is the mass flow
rate. In the literature, flow rates are sometimes expressed in terms of volume
and sometime in terms of mass. The mixing of units often causes confusion
among practitioners. In this Appendix, all flow units are expressed in terms
of mass to maintain consistency and to emphasize the point that all analyti-
cal solutions given here demand a constant mass flux of air into or out of the
formation or column.
The relationship between volumetric flow (Qv) and mass flow is given by:
Qv=~Pro~ (A.23)
A.13
-------
Field-Scale Pneumatic Permeability Models
Radial, Transient, Confined Flow
Without doubt, the equations used most by practitioners in the subsurface
remediation field are solutions to the transient and "steady-state" radial flow
equation. The transient, radial flow equation is expressed as:
(A.24)
with boundary conditions:
The solution given by Johnson et al. (1988, 1990) is:
(A.25)
11 ' ' : , i,
where:
r26Li
u = - E— -
4kPt
atm
P' is a gauge pressure. The solution is obtained in P instead of P2 because
Johnson et al. (1988, 1990) linearized the radial, transient equation by letting
p2_ p*pa)m instead of explicitly solving for P2. A solution to transient, radial
flow equation using these boundary conditions, Laplace Transforms and the
assumption that V<|) = Patm gives:
(A.26)
where:
u =
4krtPatm
A. 14
-------
Appendix A
The integral on the right-hand-side of the equation is the well known
exponential integral. When u < 0.01, it can be approximated by:
r
Ju
>e~T
« -0.57721-In u (A.27)
Radial, Pseudo-Steady-State, Confined Flow
The equation describing radial, pseudo-steady-state, confined flow is
expressed as:
dr r dr
with boundary conditions:
(A.28)
= ::QJRTii
, d<{>
l dr
- w •
If air is extracted from soil, Qm is negative and the solution for the
pseudo-steady-statQ flow equation is given by: :
ln (A>29)
C07tbkr r
which is a modified form of the well known Thiem Equation. The term
pseudo steady-state is emphasized because in reality there is no steady-state
solution to the radial flow equation unless a constant head boundary is en-
countered at some radial distance. Otherwise, vacuum or pressure will
propagate indefinitely. Inserting <=<> for r in the equation above or (°P) re-
sults in infinite pressure squared at infinite distance, which obviously is not
realistic. Johnson et al. (1990) used this equation by letting , =
-------
Field-Scale Pneumatic Permeability Models
and as expressed in the rest of this Appendix. The ROI is often determined
by measuring the radius at which some small subjectively determined
vacuum extends from an air extraction well or by extrapolating measure-
ments to zero by transforming radial distance on a logarithmic scale. As can
been seen, however, from the general form of the equation, the use of a ROI
is unnecessary. One simply needs a vacuum or pressure measurement at two
points or at the well and another point. This simple observation is unfortu-
nately missed by many practitioners, since the vacuum measurements in
vapor probes around extraction wells are typically used for ROI extrapola-
tion instead of direct pneumatic permeability measurement. Perhaps more
importantly though, strictly radial flow rarely occurs in soils during pneu-
matic permeability testing because of partial penetration of the screened
interval and a constant pressure (atmospheric) boundary at the soil surface.
Even when a lower permeability lens separates the modeled domain from the
atmosphere, there is almost always a strong vertical component of flow be-
cause of significant leakage. Soil venting practitioners typically use this
equation to estimate pneumatic permeability regardless of applicable bound-
ary conditions. The use of the radial transient, and pseudo-steady-state
equations are strongly discouraged in favor of solutions derived from cylin-
drical coordinates which provide more realistic boundary conditions. It is
argued by some that "reasonable" results are obtained with radial flow equa-
tions even though the boundary conditions are grossly violated. While riot as
notorious as numerical methods for giving non-unique estimates of perme-
ability, it should be remembered mat analytical solutions also can provide
incorrect answers while still appearing to "reasonably" fit field data.
Axisymmetric, Cylindrical, Transient,
Unconfined, Flow
The previous discussion on the limitations of radial flow modeling pro-
vides an introduction on the need to consider the use of axisyrnmetric, cylin-
., ' '" i , i '"II"" , •! ii""!. If" .i'l| " .' ' " ', , ', . i ...
drical equations for determination of pneumatic permeability. The govern-
ing equation for unconfined (open to the atmosphere), transient cylindrical
flow is:
A.16
-------
Appendix A
28z2
with the initial condition:
and boundary conditions:
(A.30)
())(r, 0, t) = <|>atm lim(r -» °o)<|>(r, z, t) = (|>at
3z
= 0
z=b
or
l
-------
Field-Scale Pneumatic Permeability Models
(A.35)
Axisymmetric, Cylindrical, Steady-State,
Leaky-Confined Flow
The equation for cylindrical, leaky, leaky-confined, steady-state flow is:
z
Vr2 rorj z oz2 (A.36)
with boundary conditions:
- = 0 at r = rw 1 < z < b
or
-1 = 0 at r = rw 0
-------
Appendix A
approximation of specific discharge across the; thickness of the layer of
lower permeability and equating the resultant expression to the vertical com-
ponent of mass flow defined in the domain as z approaches zero. Baehr and
Joss (1995) state that this is a more rigorous ajpproach than adding a
leakance term to the governing partial differential equation. Unfortunately,
they did not provide an analysis of error incurred by using the stated less
rigorous approach.
The solution provided by Baehr and Joss (1995) for axisymmetric, cylin-
drical, steady-state, leaky confined flow is given by:
where:
h = (k^)/(kz
!/2
a = (kr/kz)!
= gjn[q.(b-d)/b]-«in[q.(b-l)/b]
'
q n are positive solutions (n = 1, 2, 3, . . . ) to
tan(qn) = h/qn (A.37)
It is important to note that none of the equations for transient testing given
here consider the effects of a finite radius well with wellbore storage. , Ravi
and DiGiulio (1997), however, recently considered these effects for cylindri-
cal transient flow open to the atmosphere, cylindrical, transient flow in a
domain separated from the atmosphere by a leaky confining unit, and for
radial, transient flow in a perfectly confined system.
For easy reference, Figure A.I illustrates the variables used in the govern-
ing equations for cylindrical coordinates. Tables A.I and A.2 contain the
boundary conditions for all radial and cylindrical coordinates.
A.21
-------
••• r
Field-Scale Pneumatic Permeability Models
Figure A. 1
Variables Used in Governing Equations for Vapor
Extraction Water Table or an Impervious Unit
z = 0-
z = b-
• Water Table or an Impervious Unit
= b-
.\
V
;-X"x": ;*: xi-eaky Layer = k'
I*',**'*•'*<*•.-j*f--«%***'*****"-"-^
2 = 0-
= b-
• Water Table or an Impervious Unit
Lii^:
• Water Table or an Impervious Unit
A.22
-------
Appendix A
Table A.1
Boundary Conditions for Governing Partial Differential Equations
One-Dimensional
Steady-State
Radial
Pseudo-Steady-State
Transient
Cylindrical-Unconfined
Steady-State
Transient
Cylindrical-Leaky Confined
Steady-State
Transient
Inner
NV
d
f
g
h
g
h
Outer (ir > rw)
NV
c
e
e
e
e
e
Upper (z = 0)
a
k«
k*
a
a
i
k
Lower (z = b)
b
j*
; J'
j
j
; j
• J
'These boundary conditions are not necessary to solve equations, but are assumed present in radial (low problems.
CONCLUSION
The analytical equations used for pneumatic permeability testing have
been derived from basic principles of fluid mechanics. During this deriva-
tion process, all the assumptions necessary for analytical model development
were identified and most were discussed. The primary assumptions used
during pneumatic permeability testing are;
• Darcy's Law is valid for air flow;
• Klinkenberg effect is negligible;
• velocity and gravitational head is negligible;
• ideal gas law correctly defines air density;
• alignment of permeability tensor is in principal direction of verti-
cal and radial permeability;
• temperature gradients in vertical arid radial direction are negligible;
A.23
-------
Field-Scale Pneumatic Permeability Models
Table A-2
Definition of Boundary Conditions
a: (z = 0) = oOratn)
b: "A
dz
. d* -Qn.RTu.
f: rlhn-
r-»0 i
-^- = 0 at r = rw l(l-d)
rr- = 0 at r = rw l
-------
Appendix A
volumetric water and air contents do not change in space or time;
air viscosity does not change in space or time;
vertical and radial permeabilities are constant in space in the
simulated domain;
the air flow equation can be linearized by letting P2 = <(> and
• capillary fringe no flow boundary remains flat (no upwelling).
Most of these assumptions are reasonable, however, several stand out as
being primary causes of error. These are: alignment of permeability tensor
in principal direction vertical and radial permeability (anisotropy), constant
radial and vertical permeabilities in space, constant volumetric water and air
content in time and space, and constant flat lower no flow boundary. Nu-
merical modeling can be used to simulate these effects, however, the prob-
lem of nonuniqueness in parameter determination limits the usefulness of
this approach. Given these problems, it is wise for the field practitioner to
attempt to conduct pneumatic permeability testing in a manner which mini-
mizes deviation from these assumptions, such as low pressure gradient test-
ing in soils having a high water content and to view results in the context of
the limitations of analytical modeling.
Analytical solutions from various authors have been summarized. With
the exception of solutions developed by Johnson, Kemblowski, and Colthart
(1988) and Johnson et al. (1990), all transient solutions employ the lineariza-
tion of P2 = and assumption that V(|> = Patm. Air flow was expressed in terms
of mass versus volume to ensure consistency in the variables used in the
equations and to emphasize that for radial and cylindrical coordinate solu-
tions, that constant mass flux is necessary for testing.
A.25
-------
I
-------
Appendix B
PROCESS SAFETY REVIEW
FOR VE/AS SYSTEMS
This appendix has been adapted from US ACE (1995).
a. Process Safety Review/HAZOP Review. A formal hazard and
operability (HAZOP) review of the system and its integration
with other systems (designed and supplied by others) may be
required. The review shall consider operation of each unit, pos-
sible hazards, and operation and maintenance difficulties that
might occur. All findings shall be recorded, and a formal re-
sponse shall be prepared. The review should be held no later
than 30 calendar days before the stairt of the vapor extraction/
bioventing system operation, and all deficiencies should be cor-
rected prior to system startup.
b. HAZOP Study. A HAZOP study is a formal, systematic., and de-
tailed examination of the process and engineering intent of new or
existing facilities to assess the hazard potential of operation outside
the design intent or malfunction of individual equipment items and
the consequential effects on the facility as a whole.
c. Guide Words. During examination sessions, the study team tries
to visualize all possible deviations from every design and operat-
ing intent. These deviations can each be associated with a word
or phrase, called "guide words." When used in association with a
design and operating intent, such words guide and stimulate cre-
ative thinking toward appropriate deviations. The following is a
list of example deviations and associated guide words:
NO FLOW: Wrong routing - blockage - incorrect slip blind - incorrectly
installed check valve - burst pipe - large leak - equipment failure (control
valve, isolation valve, pump, vessel, etc.) - incorrect pressure differential -
isolation in error.
B.I
-------
Process Safely Review for VE/AS Systems
REVERSE FLOW: Defective check valve - siphon effective - incorrect
differential pressure - two-way flow - emergency venting - incorrect opera-
tion - in-line spare equipment.
American Petroleum Institute (API)
• • • " . "" • • »: • "i i • i -I.
RP500 A Recommended Practice for Classification of Areas for
Electrical Installations in Petroleum Refineries
RP500B Recommended Practice for Classification of Areas for
Electrical Installations at Drilling Rigs and Production
Facilities on Land and on Fixed and Marine Platforms
RP500C Electrical Installations at Petroleum and Gas Pipeline
Transportation Facilities
" :-. - " , ' ' • • "• • I'.' .' • .^(^•'•f'|:v , v - .. • \l- f;
American National Standards Institute (ANSI)
C80.1 National Electrical Safety Code Specification for Rigid
Steel Conduit, Zinc Coated
C80.5 Specifications for Rigid Aluminum Conduit
'••:•'.:.' lj.,° 'I ' '
National Fire Protection Association (NFPA)
30 Flammable and Combustible Liquids Code
70 National Electrical Code
" ,: "' , ', : " ' ' '',;,!, ' ' ! i " ' i '
496 Purged and Pressurized Enclosures for Electrical Equip-
ment in Hazardous Locations
497 Class I Hazardous Locations for Electrical Installations
in Chemical Plants
Institute of Electrical and Electronics
141
Recommended Practice
for Industrial Plants
Engineers (IEEE)
for Electrical Power Distribution
518
The
trical Noise Inputs to
B.2
Installation of Electrical Equipment to Minimize Elec-
Controllers from External Sources
-------
Appendix C
PROPERTIES OF COMMON
ORGANIC POLLUTANTS
This appendix has been adapted from US ACE (1995).
C.J Introduction
Appendix C consists of 13 tables, each presenting physical and/or chemical
properties of compounds and fuel products. This information, including, for
example, molecular weights, boiling points, Henry's Law Constants, vapor
pressures, and vapor densities may prove helpful in evaluating whether a given
site with its contaminants of concern is amenable to Soil Vapor Extraction/
Bioventing. In addition, this information may be needed in calculating various
operating parameters or outcomes of an Soil Vapor Extraction/Bioventing'sys-'
tem at a given site with a given suite of contaminants of concern. :
C.2 List of Tables
C.I Selected Compounds and Their Chemical Properties. Lists
molecular weight, compound boiling point, vapor pressure,
and equilibrium vapor concentration.
C.2 Physicochemical Properties ofPCE and Associated Com-
pounds. Lists molecular weight, liquid density, melting point,
boiling point, vapor pressure, water solubility, log octanol-
water coefficient, soil sorption coefficient, and Henry's Law
constant for PCE; TCE; 1,1-DCE; 1,2-DCE; and vinyl chloride.
C.I
-------
" T HI
Properties of Common Organic Pollutants
C.3 Physicochemical Properties of TCA and Associated Com-
pounds. Lists same properties as Table C.I for 1,1,1 -TCA;
1,1-DCA; and CA.
C.4 Physical Properties of Fuel Components. Lists molecular
weight, solubility, soil sorption coefficient, log octanol-water
cofficient, and vapor pressure for n-alkanes, isoalkanes,
cycloalkanes, alkenes, aromatics, and PAHs.
:'' ,,',! ,• ••Jl! ,1 ,'! ' '' ' ' '' ' 'f ' ' '"''i11 :' ! ! ',ii ' "1|!h!1""
C.5 Selected Specification Properties of Aviation Gas Turbine
Fuels. Lists data on composition, volatility, fluidity and
combustion for Jet Fuels A and B and JP-4, -5, -7, and -8.
C.6 Detectable Hydrocarbons Found in U.S. Finished Gasolines
at a Concentration of 1% or More. Lists constituents and
estimated ranges of weight percentages of each.
C.7 Major Component Streams of European Automotive Diesel
Oil (Diesel Fuel No. 2) and Distillate Marine Diesel Fuel
(Diesel Fuel No. 4). Lists nonspecific components by Toxic
Substances Control Act (TSCA) inventory name and identifi-
cation number, as well as volumetric percentages of each in
both automative diesel oil and distillate marine diesel fuel.
C.8 Henry's Law Constants for Selected Organic Compounds.
Lists values of H at 20-25°C for chlorinated nonarematics,
chlorinated ethers, monocyclic aromatics, pesticides, PCBs,
and polycyclic aromatics.
C.9 Chemical and Physical Properties of TPH Components.
Lists molecular weight, water solubility, specific gravity,
vapor pressure, Henry's Law constant, diffusivity, Koc, log
Kow, Fish Bioconcentration Factor (BCF), and Surface-
Water T1/2, for alcohols, cycloalkenes, cycloalkanes, chlori-
nated aliphatics, ethers, ketones^ methyl alkanes, methyl
alkenes, mono- and polycyclic aromatic hydrocarbons,
simple alkanes, and simple alkenes.
» ' i ',•".„" N • 'i'lift,,,1":1 .»!," • 'I1'. 1 « " , "',, ,»,il,.i • ' I'l,,,1, ,'?,'• l "•
C. 10 Dimensionless Henry's Law Constants for Typical Organic
Compounds. Lists values of H for various compounds at
different temperatures.
C.2
-------
Appendix C
C.ll Chemical Properties of Hydrocarbon Constituents. Lists
liquid density, Henr's Law Constant, water solubility, vapor
pressure, vapor density, and Koc for n-alkanes, mono-aro-
matics, phenols, and diaromatics.
C.I 2 Composition of Regular Gasoline. Lists chemical formula,
molecular weight, mass fraction, and mole fraction of 58
components of regular gasoline.
C.I 3 Composition of a Weathered Gasoline. Lists same properties
as Table C.12 for 58 components of weathered gasoline.
C.3
-------
Properties of Common Organic Pollutants
Table C.1
Selected Compounds and Their Chemical Properties
Compound
n-Pentane
n-Hexane
Trichloroethane
Benzene
Cyclohexane
Trichloroethylene
n-Heptane
Toluene
Tetrachloroethylene
n-Octane
Chlorobenzene
p-Xylene
Ethylbenzene
m-Xylene
o-Xylene
Styrene
n-Nonane
n-Propylbenzene
1 ,2,4-Trimethylbenzene
n-Dccane
Dibrompchloropropane
n-Undecane
n-Dqdecane
Naphthalene
Tetraethyl Lead
(g/mole)
722
862
133.4
78.1
84.2
131.5
100.2
92.1
166
114.2
113
106.2
106.2
106.2
106.2
104.1
128.3
120.2
120.2
142.3
263
156.3
170.3
128.2
323
fb(l atm)
(K)
309
'" Sti'"
348
353
„, :: *•'.'. ' , 1
354
360
371
384
394
399
405
411
411
'."' 4l2
417
418
424
432
442
446
469
469
489
il
489
decomposes @ 473K
Pv° (K)
(atm)
051
0.16
0.132
0.10
0.10
0.026
0.046
0.029
0.018
0.014
0.012
0.0086
0.0092
0.0080
0.0066
0.0066
0.0042
0.0033
0.0019
0.0013
0.0011
0.0006
0.00015
0.00014
0.0002
(mgflL)
1,700
560
720
320
"340' " '"" '
140
190
110
130
65
55
37
40
' 35
29
28
22.0
16
9.3
7.6
11
'•' 3.8
1.1
0.73
2.6
N^ molecular weight
Tb(1 atm) compound boiling point at 1 atm absolute pressure
Pv° (293 K) vapor pressure measured at 293 K
C^, equilibrium vapor concentration
Johnson. Kemblowski, and Colthart (1988). "Practical screening models for soil venting applications." In: Proceedings
ofNWWA/API; Conference on Petroleum Hydrocarbons and Organic Chemicals in Groundwater. Houston, TX.
Reprinted by permission o< Ground Water Publishing Company ©1988.
C.4
-------
p
bi
Physipchemical
Formula pc EC f\4
Molecular weight (g/mol) 165.85
Liquid density (g/cm3) 1.625
Melting point (K) 250.6
Boiling point (K) 394
Vapor pressure (mmHg) 14
Water solubility (mg/L) 150
Log octanol - water coefficient 3.14
Soil sorption coefficient (L/kg) 665
Henry's Law constant (atm. m3/mol) 0.023
*A1I values are at 293 K, unless otherwise indicated.
SValue is a specific gravity measurement.
'At 298 K.
NA = information not available.
Table C.2
Properties of PCE and Associated Compounds*
TCBCJHCI, 1.1
131.40
1.46
200
360 '
69°'
1,100"
2.42
NV
.0103'
Arthur D. Little. Inc. (1987). TTie Installation Restoration Program Toxicology Guide, Volume 1.
- "if x_C A-- jtlj vJ 2
96.95
1.214
150.4
304.6
500
400
213
65
0.154
Seeiion 2:1-16.
96.95
1.257
223.6
320.7
JO
6,300
209
59
0.0066'
-------
Properties of Common Organic Pollutants
''•III1 ."il'IIPitllHIli"''1 , '' 11111'!!"! ,lL
*
t/5
T3
a
o
o
TJ
0)
1
O
S
O
D
(D
a
g
a.
1
o
a.
6
_A*
a-
e g
lef
€
AII value
At 273 K
A1298K
Arthur D.
d.6
-------
Appendix C
Table C.4
Physical Properties of Fuel Components
Component
n-Alkanes
n-Butane
n-Decane
n-Dodecane
n-Hexane
n-Heptane
n-Nonane
n-Octane
n-Pentane
n-Tridecane
n-Undecane
Isoalkanes
2-Methyldecane
2-Methylhexane
2-Methylpentane
2,4-Di methylhexane
2,5-Dimethylhexane
2,2,3-Trimethylpentane
2,2,4-Trimethylpentane
3-Methylhexane
3-MethyIpentane
3,4-DimethyIoctane
4-MethyIheptane
Isobutane
Isododecane
Isopentane
Isoundecane
Cycloalkanes
1 ,3,5-TrimethylcycIohexane
Cyclohexane
Methylcyclohexane
Melhylcyclopentane
MW
58.12
142.28
17033
86.18
100.20
128.25
114.23
72.15
184.35
156.31
156.31
100.20
86.18
114.23
114.23
114.23
114.23
100.20
86.18
142.28
114.23
58.12
170.33
72.15
156.31
126.24
84.16
98.19
83.15
Solubility KM LogKow Vapor Pressure
61 1,555.33
0.009 <20) 2.7
0.0037 5,500,000 7.06 0.3
9-5 3,830 3.9 121.24
2.4 (20) 35.55
0.07 (20) 3.22
0.0657 73,000 4.00 ' 10.46
38-5 424.38
0.013
1(32.7)
51.9
13-8 171.5
23.32
36,000 4.87 :
056 36,000 5.02
3,830 3.9
48.9 2,252.75
47.7 900 23 574.89
50,500 5.02
55.6 1,330 3.44 77.55
14(20) 6,070 4.1 144
42.7 1,400 2.35 :
C.7
-------
Properties of Common Organic Pollutants
Table C.4 (cpnt.)
Physical Properties of Fuel Components
Component
Alkenes
Trans-2-Butene
2-Methyl-2-butene
Aromatics
l-Methyl-3-ethylbenzene
1 -Methyl-3-n-propylbenzene
1,2,3-Trimethylbenzene
1 ,2,4-Trimethylbenzene
1 ,3,5-Trimethylbenzene
1,2,3,4-Tetramethylbenzene
Benzene
Ethylbenzene
Isopropylbenzene
Toluene
Xylenes
PAHs
1-Methylnaphthalene
2-Methylnaphthalene
Acenaphthene
Acenaphthylene
Anthracene
Chrysene
Naphthalene
Phenanthrene
Pyrene
MW
56.11
70.13
120.19
134.22
120.19
120.19
120.19
134.22
78.11
106.17
120.19
92.14
106.17
14250
142.20
154.21
152.20
178.23
228.20
128.16
17852
202.24
Solubility
i, i, i|
57.6
1,760
152
50.1
515
175
27
4.09
3.93
129
0.006
31.7
154
0.15
KM
''
,
2,150
2,150
2.15Q
65
1,200
240
700
3,570
3,570
5,250
2,890
13,500
220,000
962' "'
16,000
44,000
LogKow
4.65
3.65
3.65
Z13
334
3.43
269
3.16
3.87
3.87
3.98
3.72
4.45
5.61
33
4.45
4.88
Vapor Pressure
760 (0.9)
1.73
755
7S&
21.84
6/16
0.0016(25)
0.03
0.00024 (25)
6.3E-09 (25)
0.09 (25)
9.4E-04 (25)
2.5E-06 (25)
Solubility In mg/L water at 198 K. unless otherwise noted In parentheses. or.nll,aMa
Vapor Pressure of pure compound in mm Hg at 20 'C, unless otherwise noted in parentheses.
ABB Environmental Services, Inc. (1990). -Compilation of datapn the «mpi»««V#£**"?'££ %&?$'
solubility of fuel products.' Prepared for. Massachusetts Department ol Environmental Protection. Job No. 6042-04.
pp1-3.
C.8
-------
Table C.5
Selected Specification Properties of Aviation Gas Turbine Fuels
p
<>
Civil ASTM D 1655
Characteristic
Composition
aromatics, % by volume maximum
sulfur, % by weight maximum
Volatility
distillation-10% received
temperature-50% received
maximum k-endpoint
vapor pressure at 311 K kPa maximum (psi)
density at 288 K, kg/m3
Fluidity
freezing-point, k maximum
viscosity at 253 K, mm3/s maximum (=cSt)
Combustion
heat content, MJ/kg, minimum
smoke point, mm, minimum
H2 content, % by weight minimum
Jet A kerosene
20<=
03
204
573
775-840
233
-------
Properties of Common Organic Pollutants
Table C.6
Detectable Hydrocarbons Found in U.S. Finished
Gasolines at a Concentration of 1% or More0
Chemical
Toluene
2-Methylpentane
+ 4-Methyl-cis-2-pentene
+ 3-Methyl-cis-2-pentenec
n-Butane
iso-Pentane
n-Pentane
Xylene (three isomers)
2,2.4-Trimethylpentane
n-Hexane
n-Heptane
2,3,3-TrimethyIpentane
2,3,4-Trimethylpentane
3-Methylpentane
Methylcyclohexane
+ l-cis-2-Dimethylcyclopentane
+ 3-Methylhexanec
Benzene
2,2,3-Trimethylpentane
Methyl tertiary butyl ether
Methylcyclopentane
2,4-Dimethylpentane
Cyclohexane
1,2,4-Triniethylbenzene
2-Methyl-2-butene
2,3-Dimethylbutane
trans-2-Pentene
Methylcyclohexane
3-Ethyltoluene
2,3-Dimethylpentane
2,5-Dimethylpentane
2-Methyl-l-butene
Ethyl benzene
Weight %
Estimated Range
5-22
4-14
3-12
5-10
1-9
1-10
-------
Table C.7
Major Component Streams of European Automotive Diesel Oil (Diesel Fuel No 2)
and Distillate Marine Diesel Fuel (Diesel Fuel No. 4)
Toxic Substances Control Act (TSCA) Inventory
Name and Identification Number
Refinery Process Stream
(nomenclature used in Europe)
Automotive Diesel Oil
(% by volume)
Distillate Marine Diesel Fuel
(% by volume)
O Straight-run (atmospheric) gas oil
—i Straight-run middle distillate
Straight-run gas oil
Light vacuum distillate
Light thermally cracked distillate
Light catalytically cracked distillate
light
heavy
Vacuum WQs ^*i
Thermally cracked gas oil
Light catalytically cracked gas oil (cycle oil)
40-100
40-100
0-iO
0-20
0-25
0-3
0-50
0-20
0-30
040
°" «" —« °< -"*"•-« - * *""• - o-P" exposures in
T3
T>
(D
Q.
X'
O
-------
Properties of Common Organic Pollutants
Table C.8
Henry's Law Constants (H, atm-m3/mol)
for Selected Organic Compounds
Compound
Chlorinated Nonaromatics
Benzene
Chlorobenzene
o-Dichlprobenzene
m-Dichlorobenzene
p-Dichlorobenzcne
1 ,2.4-TrichIorobenzene
Methyl chloride
Methyl bromide
Methylene chloride
Chlorofonn
Bromodichloromethane
Dibromochlorpmethane
Bromoform
Dichlorodifluoromethane
Trichlorofluoromethane
Carbon tetrachloride
Chloroethane
,1-Dichloroethane
,2-Dichloroe thane
,1,1 -Trichloroethane
,1,2-Trichloroethane
,1,2,2-TetrachIoroethane
lexachloroethane
Vinyl chloride
,1-DichIoroethene
,2-trans-Dichloroethene
Trichloroethene
Tetrachloroethene
1,2-Dichloropropane
trans- 1 ,3-Dichloropropene
Hexachlorocyclopentadiene
Hexachlorobutadiene
Chlorinated Ethers
Bis(chioromethyi)ether
Bis(2-chloroisopropyljelher
4-Chlorophenyiphenylether
4-Bromophenylphenylether
Monocyclic Aromatics
Naphthalene
Acenaphthene
Acenaphthylene
Anthracene
Phenanthrene
H
0.0055
0.0036
0.0019
0.0036
0.0031
0.0023
0.0+
020
0.0020
0.0029
0.0024
0.00099
0.00056
3.0
O.U
0.023
0.15
0.0043
0.00091
0.03
0.00074
0.00038
0.0025
0.081
0.19
0.067
0.0091
QMS!
0.0023
0.0013
0.016
0.026
... , .. -
0.00021
0.00011
0.00022
0.00010
0.00046
0.000091
0.001S
0.000086
0.00023
t(K)»
298
293/298
293
298
298
298
293
293
293/298
293
293/295
293/295
293
298
293
293
293
293
293
298
293
293
293/295
298
298/293
293
293
%293
293
293/298
298
293
293/298
293
293
293/298
298
298
293/298
298
298
C.12
-------
Appendix C
Table C.8 (cont.)
Henry's Law Constants (H, atm-m3/mol)
for Selected Organic Compounds
Compound
H
t(K)»
Polycyclic Aromatics
Hexachlorobenzene
Toluene
Ethylbenzene
o-Xylene
m-Xylene
p-Xylene
1 ,2,3-Trimethylbenzene
1 ,2,4-Trimethylbenzene
1 ,3.5-Trimelhy Ibenzene
Propylbenzene
Isopropylbenzene
1 -Ethyl-2-methy Ibenzene
1 -Ethyl-4-methylbenzene
n-Buty Ibenzene
Isobutylbenzene
sec-Butylbenzene
tert-Buty Ibenzene
1 ,2,4,5-Tetramethylbenzene
l-Isopropyl-4-methylbenzene
n-Pentylbenzene
Pesticide and Related Compounds, and PCBs
Ethylene dibromide (EDB)
trans-Chlordane
Heptachlor
Heptachlor epoxide
2,3,7,8-TCDD
Aroclor 1016b
Aroclorl221b
Aroclor 1242 b
Aroclor 1248b
Aroclor 1254b
0.00068
0.0067
0.0066
0.0050
0.0070
0.0071
0.0032
0.0059
0.0060
0.0070
0.0013
0.0043
0.0050
0.013
0.033
0.014
0.012
0.025
0.0080
0.0060
0.00082
0.000094
0.0040
0.00039
0.0021
0.00033
0.00017
0.0020
0.0036
0.0026
293/298
293
293
298
298
298
298
298
298
298
298
298
298
298
298
298
298
298
298
298
298
298
298
298
-
298
298
298
298
-
•Where two temperatures are given, the first is the temperature at which the vapor pressure was measured, and the
second is the tern pera ture at which the solubility was measured.
"Mixture-average value.
Pankow, J.F., Johnson, R.L, and Cherry, J.A. (1993). Air sparging in gate wells in cutoff walls and trenches for
control of volatile organics, Ground Water 31(4):654-63. Reprinted by permission of Ground Water Publishing
Company O1993.
C.13
-------
-iiii^.-:- -::;;
Constituents
Alcohols
Ethyl alcohol
Methyl alcohol
t-Butyl alcohol
Cycloalkanes
Cyclopentane
Methyl cyclohexane
Cycloalkenes
Cyclohexene
Cyclopentene
Chlorinated Aliphatics
1 ,2-Dichloroethane
Dibromoethane
1,1-Dichloroethane
Ether
Methyl-t-butyl ether
Molecular
Weight
46.07
32
74.1
70.14
98.19
84.16
68.12
99
187.88
99
88
Chemical
Water
Solubility
mg/L298K
280,000
300,000
160
14
55 (20'C)
7,986-8,650
4.32 (30'C)
5,060
4,800
Table C.9
and Physical Properties of TPH Components
Specific
Gravity
0.789
0.788
0.751
0.77
0.779
0.77
1.23
2.701
1.1757
0.74
Vapor
Pressure
nunHg
298 K
59
130
42
42.4
6.18
77 (20"C)
87
17 (30'C)
182.1
250
Surface-
Henry's Law Water T1/2
Constant atm- Diffusivity K,,,. Fish BCF (days)
m3/mol298K cm2 /sec mL/g LogKow L&S Low-High
1.2&05 0.12368 03 3.1 034
2.0E05 0.16211 0.1 1.5 23
0.09752 037
1.9E+Q1
43E+01
13E-03 0.09451 65 1.48-113 5.6 28-180 - - = ,
5.9E-03 00959 3Q2 1.79
5.9E-03 0.10172 . 41 12 15 28-180
Ketone " " -:
Properties of Commor
O
a
o
Q
- — — -
9.4E-05
0.07588 19 to 106 1.19
-------
Methyl Alkanes
2,3-Dimethylbutane
2,3-Dimethylpentane
2,4-DimethyIpentane
3,3-Dimethylpentane
2-Methylheptane
3-Methylheptane
4-Methylheptane
2-Methylhexane
3-Methylhexane
4-Methyloctane
2-MethyIpentane
•_] 3-Methylpentane
01 2,2,4-Trimethylhexane
2,2,5-Trimethylhexane
2.3,3-Trimethylhexane
2,3,5-Trimethylhexane
2,4,4-Trimethylhexane
2,2,3-Trimethylpentane
2,2,4-Trimethylpentane
2,3,3-Trimethylpentane
2,3,4-TrimethyIpentane
Methyl Alkenes
2-MethyI-l-butene
2-Methyl-2-butene
86.7
10051
10051
10051
11453
11453
11453
10051
10051
128.26
86.17
86.17
12856
128.26
128.26
128.26
12856
114.23
11453
11453
11453
70.14
70.14
19.1
555
55
5.94
0.792
254
4.95
0.115
13
13.1
1.15
2.44
23
313
9.18
13.1
11
2.6
8.78
851
0.903
0.654 285
0.6645 253
251
656
_ 3.6
0.65
0.668
1.3Ef02
1.8E+02
3.0E+02
1.9Bt02
3.8E+02
3.5E+02
2.4E-KJ2
l.OE+03
1.7E-H)2
1.7E+02
3.5E402
3.3E-f02
1.9E+02 . . . .
T3
®
Q.
x"
O
-------
Constituents
Methyl Alkencs
3-Methyl-l-butene
2-Methyl-l-pentene
2-Methyl-2-pentene
3-Methyl-cis-2-pentene
o
'. . 3-Methyi-irans-2-penicne
O»
4-Methyl-cis-2-pentene
4-Methy]-trans-2-pentene
Molecular
Weight
70.14
86.16
86.16
86.16
86.16
86.16
86.16
Chemical
Water
Solubility
mg/L298K
130
78
Table C.9 (cont.)
and Physical Properties of TPH Components
Specific
Gravity
0.648
0.6817
Vapor Surface-
Pressure Henry's Law Water T1/2
mmHg Constant aim- Diffusivity Koc FishBCF (days)
298 K m3/mo!298K cra2/sec rnL/g LogKow ^^S Low-High
120 5.5E+01
0.67
067 ,
monocyeJie Aromaiie Hydrocarbons . :
Benzene
Butylbenzene
n-Butylbenzene
sec-Butylbcnzene
t-Butylbenzene
1,2-Diethylbenzene
1,3-Diethylbenzene
Ethylbenzene
78
134
134
134
134
136
136
106
1.780
50
30.9
34
152 to 208
0*8
0X6
0.86
0.87
0.862
0.87
95 5.5E-03 9.30E-02 49 to 100 136 to 52 5
Z1S
1(23*C) 1,500
1(23'C) 1.3E-tOO
1.5(20'C) 1.4E-KX)
1.1 (20'C) 1^E^«)
1,500
1,500
95 8.7E-03 6.70E-02 95 to 260 3.05 to 37.5 3 ; ^
3.15
TJ
S
T5
m
\v
in ;
O"=
o
3 ;
O !
D
O
Q
0
I
&--
Q ' ; i
h£
55"
!-i "- -
: - =- - / t-t I
ra j
-------
O
Isobutylbenzene
eip-lsopropylbenzene
n-Pentylbenzene
Propylbenzene
n-Propylbenzcne
1.2,3,4-
Tetrameihylbenzene
1.2,3,5-
Tetramethylbenzene
1,2,4,5-
Tetramethylbenzene
Toluene
1,2,3-Trimethylbenzene
1,2,4-Trimethylbenzene
1,3,5-Trimethylbenzene
m-Xylene
o-Xylene
p-Xylene
Xylenes
134.2
120
149
1202
120
215.9
215.9
1342
92
120
120
120
106
106
106
106
10.1
50 (20'C>
60
60(15Q
431
35
3.48
490 to 627
57 (20'C)
61
173
204
200
162 to 200
0.862
0.862
0.87
088
0.865
0.8684
0.87596
0.85665
0.87
0248
3.2 (20*C)
0.449
2,5 (20'Q
0.00876
0.0186
0.0659
28
1.4
J,4
10
10
10
6.6 to 8.8
3.3E+00
l.OE-02
7-OE-l
5.6E-03 (15'C)
2.6E-01
5.9E-01
25E+00
6.7E-03
3.9E-01 (20'C)
3.7E-01
6.3E-03
5.4E-03
6.3E-03
6.3E-03
2,520
1,500
1500
1.500
7.80E-02 115 to
150
884
1,600
1.6QE-KS2 3.4
1,585
129
204
7.20E-02 128 to
1,580
3.66 2
357to
2.11 to 10.7 4
2.8
3.4 230 7
ion
32
2.77to
3.16
3.15
2.77 to 132 7
32
Polycyciic Aromatic Hydrocarbons
Anthracene
Benzo(a)pyrene
Benzo(b)fluoranthene
178
252
252
0.030 to
0.1125
0.0038 to
0.004
0.0012
124
135
ND
1.7E-05 to
1.95E-4
5.5E-09
5.0E-07
6.5E-05
pendix C
-------
Constituents
Molecular
Weight
Chemical
Water
Solubility
mg/L298K
Table C.9
(cont.)
and Physical Properties of TPH
Vapor
Pressure
Specific mm Hg
Gravity 298 K
Henry's Law
Constant atm-
m3/mol 298 K
Components
Diffusivity
cm2/sec
K_
mL/g LogK,,,,
Surface-
WaterT1/2
Fish BCF (days)
L/kg Low-High
Polycyclic Aromatic Hydrocarbons
Benzo(e)pyrene
1,2-
, Dimethylnaphtbalene
O 1-3-
'_, Dimethylnaphthalene
00 :
Fluoranthene
Fluorene
Methylnaphthalene
1-Methylnaphthalene
2-Methylnaphthalene
Naphthalene
Phenanthrene
Pyrene
252
158
158
202
166
142
142
142
128
178
202
0.206 to
0.373
1.66 to 1.98
27
28
25
30 to 34
0.71 to 129
0.013 to
0.171
125 0.000005
12 lE-3to
1E-2
1.025 ND
1.001 0.045
1.16 23E-1 to
8.7E-1
1.18 0.00068
127 6.85E-07 to
2.5E-06
1.7E-02
2.1&04
ND
3.4E-04
4.6E-04
2.6E-05
1.1E05
4.70&02
42E-02
5.70E-02
ND
6.20E-02
8.20E-02
5.40E-02
5.00E-02
4,230
4,230
522 1,150
5,000 4.12 to
438
ND ND
7,400 to 3.86 to
8,500 4.11
550 to 3.2 to 4.7
3,160
5,250 to 4.2 to 4.6
38,900
46,000 to 4.88 to
135,000 532
- 3 =:
0.875 Z6
30 32
129 ND
190 ND
105 0.5
30 0.125/1.04
30 0.028/0.085
* s "-
-a
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Simple Alkanes
n-Butane
Decane
n-Decane
Dodecane
n-Dodecane
n-Eicosane
n-Heptane
n-Hexadecane
n-Hexane
Isobutane
- Isopentane
n-Nonane
n-Octadecane
n-Octane
n-Pentane
Propane
n-Tetradecane
Undecane
n-Undecane
58.13
14858
148.28
170.33
170.33
2816
100.21
226.44
86
58.13
72.15
128.26
254.4
114.23
72.15
44.09
190.38
156.32
156.32
61 0.6
0.008
0.052
0.0037
0.0019
3
0.00628
18 (20°C) 0.66
48.19
48
0.07
0.0021
0.66
35
63 0.58
. 0.00696
0.044
1.82E+03
131
0.0118
2.67B-06
0.515
0.00917
1.2E-2
(20'C)
2,678
695
4.281
2.50E-05
14
513
64
0.0095
039
9.6E01
7.0E-KX)
7.5E+00
2.9E-01
2.3E+00
ISE-tQl
7.7E-01 7.50E-02 890 177 ND ND
1.2E+00
1.4E-fOO
5.0E+00
2.9E+00
3.0E+00
1.3E+00
1.1E+00
1.9E401
CD
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Constituents
Simple Alkenes
2-Butene
cis-2-Butene
trans-2-Butene
cis-3-Heptene
trans-3-Heptene
cis-2-Hexene
trans-2-Hexene
cis-3-Hexene
trans-3-Hexene
1-Pentene
2-Pentene
cis-2-Pentene
trans-2-Peniene
Molecular
Weight
56.1
56.1
98
98
84
84
84
84
70.14
70.14
70.14
70.14
Table C.9 (cont.)
Chemical and Physical Properties of TPH Components
Vapor Surface-
Water Pressure Henry's Law Water T,n
Solubility Specific mmHg Constant atm- Diffusivity K.- Fish BCF (davsl
mg/L298K Gravity 298 K mVmol298K cm2/sec mL/g LogK^, LAg Low-High
210
0.6
0,64
9
30 0.86
3D 0.86
- -: = -
150 85 4.0E401
203 66 2.3E+01
BCF bioconcentration factor
Tw half life
ND not detected
Heath, J.S., Koblis, K., Sager, S.L, and Day, C.
Volume III . Lewis Publishers, Chelsea, Ml. pp.
_..,.. _
(1993). Risk assessment for total petroleum hydrocarbons. Calabrese, EJ., and Kostecki, P.T. (eds.). Hydrocarbon Contaminated Soils •
267-301. Reprinted by permission of Lewis Publishers, an imprint of CRC Press. Boca Raton, FL
I
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-------
Appendix C
Table C.1D
Dimensionless Henry's Law Constants for Typical Organic Compounds
Component
Nonane
n-Hexane
2-Methylpentane
Cyclohexane
Chlorobenzene
1 ,2-Dichlorobenzene
1 ,3-Dichlorobenzene
1 ,4-Dichlorobenzene
o-Xylene
p-Xylene
m-Xylene
Propylbenzene
Ethylbenzene
Toluene
Benzene
Methylethylbenzene
1 , 1 -Dichloroethane
1,2-DichIoroethane
1,1,1-Trichloroethane
1 , 1 ,2-Trichloroethane
cis- 1 ,2-DichloroethyIene
trans- 1 ,2-Dichloroethylene
Tetrachloroethylene
Trichloroethylene
Tetralin
Decalin
Vinyl chloride
Chloroe thane
Hexachloroethane
Carbon tetrachloride
1 ,3,5-Trimethy Ibenzene
Ethylene dibromide
1,1-Dichloroethylene
Methylene chloride
Chlorofonn
1 , 1 ,2,2-TetrachIoroethane
1 ,2-Dichloropropane
Dibromochlnromethane
1 ,2,4-Trichlorobenzene
2,4-Dimethylphenol
1 , 1 ,2-Trichlorotrifluoroethane
Methyl ethyl ketone
Methyl isobutyl ketone
Methyl cellosolve
Trichlorofluoromethane
283 K
17.21519
10.24304
29.99747
4.43291
0.10501
0.07015
0.09511
0.09124
0.12266
0.18076
0.17689
0.24446
0.14030
0.16397
0.14203
0.15106
0.15838
0.05035
0.41532
0.01678
0.11620
0.25390
0.36410
0.23154
0.03228
3.01266
0.64557
0.32666
0.25522
0.63696
0.17344
0.01291
0.66278
0.06025
0.07403
0.01420
0.05251
0.01635
0.05552
0.35678
6.62785
0.01205
0.02841
1.89798
2.30684
289 K
20.97643
17.46626
29.35008
5.32869
0.11884
0.06048
0.09769
0.09177
0.15267
0.20427
0.20976
0.30915
0.19073
0.20807
0.16409
0.17762
0.19200
0.05498
0.48635
0.02664
0.13787
0.29815
0.46943
0.28208
0.04441
3.53977
0.71049
0.40515
0.23641
0.80776
0.19454
0.02030
0.85851
0.07147
0.09854
0.00846
0.05329
0.01903
0.04441
0.28504
9.09260
0.01649
0.01565
1.53517
2.87580
293 K
13.80119
36.70619
26.31372
5.81978
0.14175
0.06984
0.12222
0.10767
0.19704
0.26813
0.24859
0.36623
0.24983
0.23071
0.18790
0.20910
0.23404
0.06111
0.60692
0.03076
0.14965
0.35625
0.58614
0.35002
0.05654
4.40641
0.90207
0.45727
0.24568
0.96442
0.23736
0.02536
0.90622
0.10143
0.13801
0.03035
0.07898
0.04282
0.07607
0.41986
10.18462
0.00790
0.01206
4.82210
3.34222
298 K
16.92131
31.39026
33.72000
7.23447
0.14714
0.06417
0.11649
0.12957
0.19905
0.30409
0.30409
0.44343
0.32208
0.26240
0.21581
0.22807
0.25S45
0.05763
0.71119
0.03719
0.18556
0.38625
0.69892
0.41690
0.07643
4.78211
1.08313
0.49456
0.34129
1.20575
0.27507
0.02657
1.05860
0.12098
0.17207
0.01022
0.14592
0.04823
0.07848
0.20150
13.03840
0.00531
0.01594
1.26297
4.12815
303.K
18.69235
: 62.70981
34.08841
8.96429
0.19014
0.09527
0.16964
0.15637
0.25164
0.37988
0.35656
0.55072
0.42209
0.32480
0.28943
0.30953
0.31194
0.06995
0.84819
0.05346
0.23114
0.48640
: 0.98487
0.51454
0.10773
7.99952
1.12556
0.57484
0.41405
1.51951
0.3871 1
' 0.03216
1.27832
0.14512
0.22270
0.02814
0.11497
0.06110
0.11939
0.15074
' 12.90375
0.00442
0.02734
1.53277
4.90423
Source: US EPA
C.21
-------
I :-
O
to
ro
Table C. 11
Chemical Properties of Hydrocarbon Constituents
Chemical Class
n-Alkanes
C4
C5
C6
C7
C8
C9
CIO
Mono-aromatics
C6
C7"
C8
C8
C9
CIO
Phenols
Phenol
Cl-Phenols
C2-Phenols
C3-Phenols
C4-Phsnols
Indanol
Di-aromatics
MA not available
Source: US EPA
Representative Liquid Density
Chemical (g/cm3)@293 K
n-Butane
n-Pentane
n-Hexane
n-Heptane
n-Octane
n-Nonane
n-Decane
Benzene
Toluene
m-Xylene
Ethylbenzene
1 ,3,5-Trimethylbenzene
1 ,4-Diethylbenzene
Phenol
m-Cresol
2,4-Dimethylphenol
2,4,6-Trimethylphenol
m-EthylphenoI
Indanol
Naphthalene
0.579
0.626
0.659
0.684
0.703
0.718
0.730
0.885
0.867
0.864
0.867
0.865
0.862
1.058
1.027
0565
NA
1.037
NA
1.025
Henry's Law Constant Water Solubility
(dimensionless) (mg/L)@298 K
25.22
29.77
36.61
44.60
52.00
NA
NA
0.11
0.13
0.12
0.14
OXB
0.19
0.038
0.044
0.048
NA
NA
NA
NA
61.1
412
125
268
0.66
0.122
0.022
1,780
515
162
167
7Z6
15
82,000
23,500
1,600
NA
NA
NA
30
Pure Vapor
Pressure Vapor Density
(mm Hg)@293 K (g/rn3)@293 K
1,560
424
121
35.6
105
3.2
0.95
752
21.8
6.16
7.08
1.73
0.697
0529
0.15
0.058
0.012
0.08
0.014
0.053
4,960
1,670
570
195
65.6
224
7.4
321
110
355
41.1
11.4
5.12
272
0.89
039
0.09
053
0.1
037
Soil Sorption
Constant (K,,,.)
(L/kg)@298 K
250
320
600
UOO
2,600
5,800
13,000
38
90
220
210
390
1,100
110
8.4
NA
NA
NA
-NA
690
O
T5
-------
Table C.I2
Composition of a Regular Gasoline
p
N>
Co
Initial
Component Number
Propane
Isobutane
n-Butane
trans-2-Butene ,
cis-2-Butene
3-Methyl-l-butene
Isopentane
1-Pentene
2-Methyl-l-butene
2-Methyl-l,3-butadiene
n-Pentane
trans-2-Pentene
2-Methyl-2-butene
3-Methyl-l ,2-butadiene
3,3-Dimethyl-l-butene
Cyclopentane
3-Methyl-l -pentene
2,3-Dimemylbutane
2-Methylpentane
3-Methylpentane
n-Hexane
Methylcyclopeatane
2,2-Dimethylpentane
Benzene
Cyclohexane
2,3-DimethyIpentane
3-MethyIhexane
3-EthyIpentane
Chemical Formula
C3H8
C4H10
C4H10
C4H10
C4H10
C5H10
C5H12
C5H10
C5H10
C5H8
C5H12
C5H10
C5H10
C5H8
C6H12
C5H10
C6H12
C6H14
C6H14
C6H14
C6H14
C6H12
C7H16
C6H6
C6H12
C7H16
C7H16
C7H16
Mw4(g)
44.1
58.1
58.1
56.1
56.1
70.1
712
70.1
70.1
68.1
722
70.1
70.1
68.1
842
70.1
842
862
862
862
862
842
100.2
78.1
842
100.2
100.2
1002
Mass Fraction
0.0001
0.0122
0.0629
0.0007
0.0000
0.0006
0.1049
0.0000
0.0000
0.0000
0.0586
0.0000
0.0044
0.0000
0.0049
0.0000
0.0000
0.0730
0.0273
0.0000
0.0283
0.0000
0.0076
0.0076 . .
0.0000
0.0390
0.0000
0.0000
Mole Fraction
0.0002
0.1999
0.1031
0.0012
0.0000
0.0008
0.1384
0.0000
0.0000
0.0000
0.0773
0.0000
0.0060
0.0000
0.0055
0.0000
0.0000
0.0807
0.0302
0.0000
0.0313
0.0000
0.0093
0.0093
0.0000
0.0371
0.0000
0.0000
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II1'"1 "I" I 'I Hi 'I'*'
Properties of Common Organic Pollutants
i11", 1111"", , ''iSiiir'ihi'ii!,! i »ii .iH
hiiii
0)
8
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,
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a!
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C.24
-------
Table C.I3
Composition of a Weathered Gasoline
p
N>
Cn
Component Number
Propane
Isobutane
n-Butane
trans-2-Butene
cis-2-Butene
3-MethyI-l-butene
Isopentane
1-Pentene
2-Methyl-l-butene
2-Methyl-l,3-butadiene
n-Pentane
trans-2-Pentene
2-Methyl-2-butene
3-Methyl-l ,2-butadiene
3,3-Dimethyl-l-butene
Cyclopentane
3-Methyl-l-pentene
2,3-Dimethylbutane
2-Methylpentane
3-Methylpentane
n-Hexane
Methylcyclopentane
2,2-Dimethylpentane
Benzene
Cyclohexane
2,3-Dimethylpentane
3-Methylhexane
3-Ethylpentane
Initial
Chemical Formula
C3H8
C4H10
C4H10
C4H8
C4H8
C5H10
C5H12
C5H10
C5H10
C5H8
C5H12
C5H10
C5H10
C5H8
C6H12
C5H10
C6H12
C6H14
C6H14
C6H14
C6H14
C6H12
C7H16
C6H6
C6H12
C7H16
C7H16
C7H16
Mw,i (g)
44.1
58.1
58.1
56.1
56.1
70.1
722
70.1
70.1
68.1
722
70.1
70.1
68.1
842
70.1
842
862
862
862
862
842
100.2
78.1
842
1002
100.2
100.2
Mass Fraction
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0200
0.0000
0.0000
0.0000
0.0114
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0600
0.0000
0.0000
0.0370
0.0000
0.0000
0.0100
0.0000
0.1020
0.0000
0.0000
Mole Fraction
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0290
0.0000
0.0000
0.0000
0.0169
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0744
0.0000
0.0000
0.0459
0.0000
0.0000
0.0137..
0.0000
0.1088
0.0000
0.0000
TJ
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Table C.13 (cont.)
Composition of a Weathered Gasoline
Initial
Component Number
2,2,4-TrimethyIpentane
n-Heptane
Methylcyclohexane
2,2-Dimethylhexane
Toluene
2,3,4-Trimethylpentane
2-MethyIheptane
3-Methylheptane
n-Octane
2,4,4-Trimethylhexane
2,2-Dimethylheptane
p-Xylene
m-Xylene
3,3,4-Trimethylhexane
o-Xylene
2,2,4-Trimethylheptane
3,3,5-Trimethylheptane
n-Propylbenzene
2,3,4-Trimethylheptane
1,3,5-Trimethylbenzene
12,4-TrimethyIbenzene
Methylpropylbenzene
Dimethylethylbenzene
1 ,2,4,5-Tetramethy Ibenzene
! ,2,3,4-Tstrainethylbenzene
1 ,2,4-Trimethy 1-5-ethylbenzene
n-Dodecane
Naphthalene
n-Hexylbenzene
Methylnaphthalene
Total
Chemical Formula
C8H18
C7H16
C7H14
C8H18
C7H8
C8H18
C8H18
C8H18
C8H18
C9H20
C9H20
C8H10
C8H10
C9H20
C8H10
C10H22
C10H22
C9H12
C10H22
C9H12
C9H12
C10H14
C10H14
C10H14
C10H14
C11H16
C12H26
C10H8
C12H20
C11H10
MW.J (g)
114.2
100.2
982
114.2
911
114.2
114.2
114.2
114.2
128.3
128.3
1062
1062
1283
1062
1413
142.3
120.2
1413
120.2
120.2
134.2
1342
1342
134.2
1482
170.3
128.2
162.3
1422
Mass Fraction
0.0000
0.0800
0.0000
0.0000
0.1048
0.0000
0.0500
0.0000
0.0500
0.0000
0.0000
0.1239
0.0000
0,0250
0.0000
0.0000
0.0250
0.0829
0.0000
0.0250
0.0250
0.0373
0.0400
0.0400
0.0000
0.0000
0.0288
0.0100
0.0119
0.0000
1.0000
Mole Fraction
0.0000
0.0853
0.0000
0.0000
0.1216
0.0000
0.0468
0.0000
0.0468
0.0000
0,0000
0.1247
aoooo
0.0208
0.0000
0.0000
0.0188
0.0737
aoooo
0.0222
0.0222
0.0297
0.0319
0.0319
aoooo
0.0000
0.0181
0.0083
0.0078
aoooo
1.0000
6
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JS
Johnson. P.O., Kemblowski, M.W., and Colthart, J.D. (1990b). "Quantitative analysis for the cleanup of hydrocarbon-contaminated soils by in-situ venting," Ground Water 28(3):413-29.
-------
Appendix D
Y
LIST OF REFERENCES
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Bass, David H. 1993a. Estimation of effective cleanup radius for soil vapor extraction systems.
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D.I
-------
List of References
Bass, David H. 1998. Personal communication from David H. Bass of FDGTI to Tim Holbrook.
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case studies. Fourth Internatioi
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Bass, David H. and Richard A. Brown. 1997. Performance of air sparging systems — a review of
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I1,,;1
Bass, David H, Natalie A. Lucas, and Barry A. Kline. 1993. Scaling up single-well vapor extraction
pilot tests to multiple-well systems. HMCRUSuperfimd XIV Conference Proceedings. Rockville,
)^: HMCRI. ' , ', ,' ' . '"„. " , , \", ". ' . ,.'
Bausmith et al. 1996. In situ air stripping. Water Environment & Technology. February.
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-------
Appendix D
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DA
-------
Appendix D
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D,5
-------
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D.8
-------
THE WASTECH® MONOGRAPH SERIES (PHASE II) ON
INNOVATIVE SITE REMEDIATION TECHNOLOGY:
DESIGN AND APPLICATION
rhis seven-book series focusing on the design and application of innovative site remediation
technologies follows an earlier series (Phase 1,1994-1995) which cover the process descriptions,
jvaluations, and limitations of these same technologies. The success of that series of publications
suggested that this Phase II series be developed for practitioners in need of design information
and applications, including case studies.
•VASTECH® is a multiorganization effort which joins in partnership the Air and Waste Manage-
ment Association, the American Institute of Chemical Engineers, the American Society of Civil
'ngineers, the American Society of Mechanical Engineers, the Hazardous Waste Action
Coalition, the Society for Industrial Microbiology, the Soil Science Society of America, and
he Water Environment Federation, together with the American Academy of Environmental
ingineers, the U.S. Environmental Protection Agency, the U.S. Department of Defense, and the
J.S. Department of Energy.
^. Steering Committee composed of highly respected members of each participating organization
vith expertise in remediation technology formulated and guided both phases, with project
nanagement and support provided by the Academy. Each monograph was prepared by a Task
3roup of recognized experts. The manuscripts were subjected to extensive peer reviews prior to
mblication. This Design and Application Series includes:
r'ol 1 - Bioremediation
••'ncipal authors: R. Ryan Dupont, Ph.D., Chair,
tah State University; Clifford J. Bruell, Ph.D.,
Jniversity of Massachusetts; Douglas C. Downey,
'arsons Engineering Science; Scott G. Huling, Ph.D.,
'.E., USEPA; Michael C. Marley, Ph.D., Environgen.
nc.; Robert D. Norris, Ph.D., Eckenfelder, Inc.;
iruce Pivetz, Ph.D., USEPA.
'ol 2 - Chemical Treatment
rincipal authors: Leo Weitzman, Ph.D., LVW
ussociates, Chair; Irvin A. Jefcoat, Ph.D., University
f Alabama; Byung R. Kim, Ph.D., Ford Research
aboratory.
rol 3 - Liquid Extraction Technologies:
oil Washing/Soil Flushing/Solvent Chemical
rincipal authors: Michael J. Mann, P.E., DEE,
.RCADIS Geraghty & Miller, Inc., Chair; Richard
. Ayen, Ph.D., Waste Management Inc.; Lome G.
Iverett, Ph.D., Geraghty & Miller, Inc.; Dirk
lombert II, P.E., LIFCO; Mark Meckes, USEPA;
hester R. McKee, Ph.D., In-Situ, Inc.; Richard P.
raver, P.E., Bergmann USA; Phillip D. Walling,
r., P.E., E. I. DuPont Co. Inc.; Shao-Chih Way,
h.D., In-Situ, Inc.
ol 4 - Stabilization/Solidification
rincipal authors: Paul D. Kalb, Brookhaven National
aboratory, Chair, Jesse R. Conner, Conner Technolo-
es, Inc.; John L. Mayberry, P.E., SAIC; Bhavesh R.
atel, U.S. Department of Energy; Joseph M. Perez, Jr.,
attelle Pacific Northwest; Russell L. Treat, MACTEC
Vol 5 - Thermal Desorption
Principal authors: William L. Troxler, P.E., Focus
Environmental Inc., Chair; Edward S. Alperin, IT
Corporation; Paul R. de Percin, USEPA; Joseph H.
Huttoni, P.E., Canonie Environmental Services, Inc.;
JoAnn S. Lighty, Ph.D., University of Utah; Carl R.
Palmer, P.E., Rust Remedial Services, Inc.
Vol 6 •• Thermal Destruction
Principal authors: Francis W. Holm, Ph.D., SAIC, Chair,
Carl R. Cooley, Department of Energy; James J.
Cudahy, P.E., Focus Environmental Inc.; Clyde R.
Dempscy, P.E., USEPA; John P. Longwell, Sc.D.,
Massachusetts Institute of Technology; Richard S.
Magee, Sc.D., P.E., DEE, New Jersey Institute of
Technology; Walter G. May, ScJD., University of Illinois.
Vol 7 • Vapor Extraction and Air Sparging
Principal authors: Timothy B. Holbropk, P.E., Camp
Dresser & McKee, Inc., Chair, David H. Bass, Sc.D.,
Groundwater Technology, Inc.; Paul M. Boersma,
CH2M Hill; Dominic C. DiGuilio, University of
Arizona; John J. Eisenbeis, Ph.D., Camp Dresser &
McKee, Inc.; Neil J. Hutzler, Ph.D., Michigan
Technollogical University; Eric P. Roberts, P.E., ICF
Kaiser Engineers, Inc.
The monographs for both the Phase I and Phase II
series may be purchased from the American Academy
of Environmental Engineers'", 130 Holiday Conn, Suite
100, Annapolis, MD, 21401; Phone: 410-266-3390,
Fax: 4110-266-7653, E-mail: aaee@ea.net
»U.3. GOVETSJJEST P-C3TING OFTICE: 1998-621 -059/93278 !
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